Friday, January 07, 2011

SIB332 Sensor Interface Board for Hamamatsu S8550 32 Element APD Array

Vertilon Corporation
66 Tadmuck Road
Westford
MA
01886-3135
United States

Tel: 978-692-7070

The SIB332 sensor interface board provides the electrical and mechanical connectivity between a Hamamatsu S8550 4 x 8 element APD array and a Vertilon PhotoniQ multi-channel data acquisition system.

The SIB332 sensor interface board provides the electrical and mechanical connectivity between a Hamamatsu S8550 series 4 x 8 element APD array and a Vertilon PhotoniQ multi-channel DAQ system. The S8550 mounts directly to the SIB332 where electrical connections to the 32 APD anodes are routed to a micro-coaxial cable assembly that connects the APD outputs to the PhotoniQ. The negative high voltage bias to the APD array is made through a separate dedicated connector that connects to the high voltage output from the PhotoniQ. Also available on the SIB332 are two outputs that are used in conjunction with the APD array’s common cathode current signal — an amplified version of the signal and a pulse discriminator trigger output.

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Thermally Conductive Epoxy Delivers Heat Resistance & Electrical Insulation

Master Bond Inc.
154 Hobart St
Hackensack
NJ
07601
United States

Tel: 201-343-8983
Fax: 201-343-2132

Master Bond has developed a thermally conductive epoxy system that is specially designed to help mitigate the issues associated with tightly packed components and miniaturized electronic circuits.

With a thermal conductivity over 22 BTU•in/ft2•hr•ºF and serviceability from -60 to 400°F, Master Bond EP21ANHT delivers outstanding performance in the most demanding microelectronic applications. The cured adhesive is also a superior electrical insulator, further expanding its usefulness.

This two component adhesive, sealant, and coating has a convenient 1 to 1 mix ratio by weight or volume and offers room temperature and faster elevated temperature cures. EP21ANHT has a low coefficient of thermal expansion of 18-20 in/in x 10-6/ºC, a dielectric strength of >400 volts/mil, and a tensile shear strength greater than 1,000 psi. It resists a wide range of chemicals and adheres well to a variety of substrates.

Cryogenically Serviceable Epoxy Meets NASA Low-Outgassing Specifications Sep 13, 2010Thermally Resistant Epoxy Features Glass Transition Temperature Exceeding 220ºC Jul 9, 2010UV Curable Adhesive/Sealant Meets NASA Low Outgassing Requirements Jul 8, 2010Epoxy Meets NASA Low Outgassing Specifications and is Cryogenically Serviceable Nov 12, 2010Ultra-Fast Curing, Thermally Stable Epoxy Meets NASA Low Outgassing Requirements Oct 1, 2010Flexibilized Epoxy Combines High Strength and Toughness with Chemical Resistance Sep 9, 2010Thermally Conductive, Low Viscosity Epoxy Features Cryogenic Serviceability Sep 8, 2010Reinforced Epoxy Adhesive Improves Structural Bonding Jan 18, 2010Non Yellowing Permanent/ Temporary Adhesive Cures Rapidly Jan 14, 2010

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Italy approves SuperB particle collider

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Jan 6, 2011

The Italian government has given final approval for building a new €500m collider that will investigate the small but significant differences between matter and antimatter. The SuperB facility will smash electrons and positrons together to produce particle/antiparticle pairs of B-mesons, D-mesons and tau-leptons. Measuring the subtle differences in how these particles and their antiparticles decay could help shed light on the mystery of why there is so much more matter than antimatter in the universe.

The SuperB facility will be built by Italy's national institute for nuclear and particle-physics research (INFN). It will consist of a 2 km circumference ring with two accelerators – one for electrons and the other for positrons. Collisions will occur within a large detector that will track the decay products and measure their energy.

The facility is expected to produce B-mesons at a rate 50–100 times greater than existing and previous "B factories" such as BaBar in the US and Belle in Japan. Marcello Giorgi from the INFN's lab in Pisa, who is director of the SuperB project board, says that the experiment could begin taking data by 2016.

SuperB will also produce synchrotron radiation, which will be used in a wide range of experiments in condensed-matter physics, chemistry, biology and materials science. The synchrotron facility will have six beamlines – three extracting light from the electron beam and three from the positron beam. Although this is a small number of beamlines compared with other synchrotron facilities, Giorgi told physicsworld.com that "the brilliance of the light will be greater than any existing synchrotron".

The SuperB synchrotron, plans for which were finalized in February 2010, will be run by the Italian Institute of Technology (ITT). Once particle-physics experiments are finished at SuperB, the facility will eventually be devoted solely to synchrotron-radiation research. However, Giorgi, stresses that particle physics is the priority and he does not expect the matter/antimatter studies to be adversely affected by the synchrotron research.

Although the funding announcement has been delayed by a year – due in part to the global financial crisis – Giorgi expects work to begin on the facility later this year. Commissioning of the accelerator is scheduled for late 2015 and the first data should emerge in 2016. Physicists should be able to keep to this tight schedule because many of the accelerator components will be reused from the defunct PEP-II electron–positron collider at SLAC National Accelerator Laboratory in the US, which hosted the BaBar experiment until 2008.

Despite this tight schedule, the INFN has still not decided where to build the facility. The leading candidate is INFN's Frascati lab just outside Rome. Frascati is already home to the DAFNE electron–positron collider, which is used to study CP violation in K-mesons. Although the INFN site is not large enough to hold the entire ring, it could be shared with the adjoining Frascati campus of Italy's national energy research lab ENEA. According to Giorgi, the INFN is in the final stages of negotiating this plan, which includes building tunnels under a main road.

If the Frascati plan falls through, the alternative site is Rome's University of Tor Vergata, which is about 2.4 km from the Frascati lab. According to Giorgi, a site will be chosen by the end of January.

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Ultra Fast Camera Enhances Understanding of High Explosive Detonation...

Specialised Imaging Ltd.
Unit 1 Silk Mill Industrial Estate
Tring
Herts
HP23 5EF
United Kingdom

Tel: +44-1442-827728

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Specialised Imaging has released a new application note that describes how its SIM8 ultra fast camera offers the capability to capture and diagnose the process of detonation of high explosive driven liner.

Application note 14 describes how a SIM8 Ultra Fast Camera running at 1 million frames per second (1360 x 1040 pixels per frame) with 500ns exposures and front lighting was used to record the detonation of high explosive driven liner using a EBW detonator. Initial timing for the detonator and camera were generated using timing from digital delay generators. Additional synchronization of precise delays to start of frames and flashes were achieved using internal camera timing generators with nanosecond accuracy.

Imaging Phenomena On The Picosecond Timescale Oct 7, 2010High Speed Imaging News & Events Sep 8, 2010Developments in Ultra High-Speed Imaging Camera Technology Jul 21, 2010Ultra Fast Framing Cameras for Scientific Research Jul 20, 2010Compact, High Performance Ballistic Range Camera Jun 18, 2010Accurate Modelling Ensures Precise Projectile Tracking May 26, 2010Specialised Imaging Ltd Announces New Website May 6, 2010High-Speed Imaging Applications Bibliography Mar 23, 2010Specialised Imaging Ltd Announces US Office... Feb 2, 2010

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Startupsadviser.com

Startupsadviser.com is a leading strategic consulting firm specializing in meeting the business development, marketing and sales needs of emerging and start-up technology organizations.

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Professional Guide to Infrared Gas Detection

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FLIR Advanced Thermal Solutions (ATS) has announced a new revised version of its popular publication - 'Gas Detection - the Professional Guide'.

Infrared cameras have revolutionised maintenance in many industries, proving to be the most superior technology for finding hidden mechanical and electrical faults as well as locating invisible gas leaks. Not only do industrial gas leaks potentially harm the environment and be pinpoints of potential danger but they can also cost companies substantial amounts of money.

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Chell Instruments Ltd

Chell Instruments Ltd
Folgate House
Folgate Road
North Walsham
Norfolk
NR28 0AJ
United Kingdom

Tel: 01692 500555
Fax: 01692 500088

Specialising in the fabrication and intrumentating of medium and UHV vacuum systems for over 30 years, Chell also manufacture miniature K-Cells and needle valves. Our UKAS calibration lab. has the lowest uncertainties for vacuum in the UK.

Chell's convenient & fast UKAS Calibration Service:-

Chell’s BS/EN/ISO/IEC 17025 accredited Calibration Laboratory provides a comprehensive service for Vacuum, Pressure and Gas Flow measuring, controlling and generating instrumentation
Our calibration standards have been developed to provide a service having some of the lowest uncertainties in their fields, providing our customers with the greatest confidence in their “bought-in” uncertainties.
Requirements for reduced operational uncertainties in industries such as pharmaceuticals, power generation and aerospace are best achieved by using the Chell Calibration Laboratory for periodic calibration of your Standards.
Chell also offers a UKAS accredited on-site gas flow calibration service with similarly low uncertainties, allowing in-situ calibration of line or production flowmeters with the minimum of disturbance to workflow.
Flow Rate – gas: Flows from 0.001 to 3600 litre/min with traceability to National standards in the EU.
Typical instruments calibrated are:-
Thermal Mass Flow Meters
Variable area meters (Rotameters)
Coriolis flow meters
Turbine flow meters
Orifice plate / venturi flow meters
Piston provers / bubble-meters

Vacuum: This is amongst the most difficult pressure measurements to undertake.
Chell is accredited to perform vacuum calibrations down to 1.3x10-4 Pa (1x10-6 Torr), employing a range of fundamental and Transfer Standards.
Typical gauges calibrated are:-
Pirani & thermocouple gauges
Capacitance Manometers
Cold Cathode & Ion gauges
Vacuum transducers & transmitters
Vacuum switches
Spinning rotor gauges

Gas Pressure – Absolute: Chell currently has the lowest commercially available uncertainties for barometric region pressure calibration in Europe, achieved through the use of our accredited Schwien mercury manometers.

We are able to both generate and measure pneumatic pressures over the barometric range with a measurement uncertainty of ±0.0020% + 0.25 Pa.
Typical sensors calibrated are:-
Resonant and quartz bourdon type transducers
Vibrating element transducers
Precision pressure generators & transfer standards
Air Data Test Sets
Pitot Static Test Sets
Pressure Scanners, both high & medium density
High accuracy capacitance manometers
Precision aneroid barometers
Standard test gauges
Digital pressure indicators, calibrators & controllers
Gas Pressure – Gauge: We are able to both generate and measure pneumatic gauge pressures over the range 0 kPa to 7MPa with the lowest measurement uncertainties available outside National Standards.

Our gauge pressure facility uses standards having three fundamentally different principles which provides us with excellent cross-comparison opportunities to reduce our uncertainties yet further.
Typical gauge devices calibrated are:-
Pressure transducers & transmitters
Micro-manometers
Inclined manometers
Capacitance manometers
Gauge pressure switches
Gas Pressure – True Differential: Chell are, we believe, the only calibration laboratory in the World to have two accredited Schwien Merco-Master manometers working side-by-side. This facility affords us the ability to both measure and generate differential pressures over the range +/- 190 kPa with uncertainties well below 30ppm.
These safety critical instruments are routinely calibrated:-
Airspeed indicators
Altimeters
Rate of Climb (or Vertical Speed) Indicators
Ps channels of Air Data Test Sets and Pitot Static Testers

… .. as well as differential pressure transducers, transmitters and dp cells
(Link to Cal page: www.chell.co.uk/lab/callab.htm)
For more information on Chell's calibration services, please contact Jamie Shanahan or Paul Marks.

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Piezo Motors and Microdispensers for Medical Design & Biotech

Piezo & Motion Control Specialist PI has published a brochure on advanced motion control solutions for medical design

Piezo Mechanics Catalog: Piezo Motors, Piezo Systems, Piezo Actuators Nov 5, 2010New Website on Piezo Technology, Piezo Components and Piezo Actuators Aug 5, 2010Miniature 6-Axis Robot / Parallel Kinematics Hexapod for Precision Alignment Apr 1, 2010Paper on Imaging Resolution Enhancement / Pixel-Sub-Stepping / with Piezo Apr 1, 2010New Piezo Controllers feature fast USB interface with 24-Bit Resolution Apr 1, 2010PI News: 2009 Nanopositioning & Piezo Technology Book: Tools for Physicists Apr 1, 2010Non Magnetic Low Profile, High Speed Piezomotor Rotary Stage @ Photonics West Feb 17, 2010New Controller for Optical Path Control, Beam Steering & Image Stabilization Feb 17, 2010Super Resolution Microscopy Stage / PI nano™ P-545 Piezo Stage & Controller Feb 17, 2010

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SuperPower Inc.

SuperPower Inc.
450 Duane Ave
Schenectady
NY
12304
United States

Tel: 518.346.1414
Fax: 518.346.6080

SuperPower Inc. develops & manufactures long lengths of high-performance second-generation high temperature superconductor wire in application-specific configurations. Offering design, fabrication, and testing of 2G HTS coils & engineering services.

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Versatile Camera for Furnace, Boiler and Electrical Inspections

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The FLIR GF309 is a new infrared camera from FLIR Advanced Thermal Solutions (ATS) specially designed for high temperature inspection of industrial furnaces, heaters and boilers.

Custom-built to see through flames, the GF309 also features a detachable heat shield designed to reflect heat away from the camera and camera operator, providing increased protection. The camera is equipped with a special mid wave "flame filter" that is specifically engineered for high temperature operation (up to 1500°).

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Physicists find new clue in coronal heating mystery

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Jan 6, 2011

The latest research from a team of international astronomers could help to explain the long-standing mystery of why the Sun's outer atmosphere – or corona – is so much hotter than its surroundings.

The corona, the vast gossamer atmosphere of plasma visible from Earth during a total solar eclipse, can notch up temperatures in excess of one million degrees Kelvin (MK). Several rival explanations have jostled to account for why the corona is unexpectedly over 200 times hotter than the visible surface, or photosphere, of the Sun. However, in recent years one theory has charged from the back of the pack to become a frontrunner in the race to solve the mystery: spicules – or fountain-like jets of plasma. These emanate from the chromosphere, a relatively thin layer separating the photosphere and corona.

Previously, the spicule theory was largely discredited due to an absence of correlating phenomena in the corona itself. Then, in 2007, researchers led by Bart De Pontieu at the Lockheed Martin Solar and Astrophysics Laboratory in California, US, found a new breed of spicule, which they dubbed "Type II"; Type II spicules are shorter-lived but faster moving than their Type I cousins. In his latest research, published in Science, De Pontieu and colleagues now believe they have found evidence implicating Type II spicules in the heating of the corona.

"Spicules play a significant role in coronal heating, which doesn't fit any of the current theories. This also suggests that there is significant heating going on in the first few thousands of kilometres [of the corona], which is very different from what people have assumed before," De Pontieu told physicsworld.com. When the spicule jets occur on the solar disc they leave a tell-tale signature in the spectral lines observed in the chromosphere: fast-occurring blue-shifts, known as rapid blue-shift events (RBEs). De Pontieu used data from the Solar Optical Telescope (SOT), aboard the Sun-orbiting Hinode spacecraft, to build up a catalogue of RBEs, which he then compared to coronal data from NASA's Solar Dynamics Observatory.

We haven't completely solved the problem, but we've certainly added a significant new wrinkle to it Scott McIntosh, NCAR

"The high temporal and spatial resolution of this generation of solar observatories allowed us to discover that spicule events in the chromosphere are correlated to brightenings in the corona," De Pontieu explained. The team found that the vast majority of the spicule plasma is only heated to between 0.02–0.1 MK and sinks back down into the chromosphere. However, the key finding is that a small but significant portion of the plasma is heated beyond 1 MK and uplifted into the corona. The researchers found this process to be ubiquitous across the Sun.

However, the search for a definitive answer to the coronal heating mystery isn't over. "We haven't completely solved the problem, but we've certainly added a significant new wrinkle to it," second author Scott McIntosh, at the National Center for Atmospheric Research (NCAR) in Colorado, explained.

Lucie Green of the Mullard Space Science Laboratory at University College London, who was not involved in the research, agrees: "My hunch is that the solution to the [coronal heating] problem is a mix of answers, a combination of different mechanisms. We shouldn't be looking for just one 'golden' answer," she said. "However, this research is something new and it will definitely sit alongside the other explanations," she added.

Whatever mechanism, or mix of mechanisms, is responsible for the soaring temperatures of the corona, finding an answer is important. "Heating causes the corona to expand outwards, forming the solar wind. This is ultimately what drives lots of processes throughout the solar system, so it would be great to better understand how that heat is being put into the solar atmosphere," said Green.

In order to pinpoint the exact role of spicules in coronal heating and to understand what drives and heats them in the first place, De Pontieu hopes to exploit an upcoming NASA mission. "Fundamentally we need new instrumentation. The Interface Region Imaging Spectrograph (IRIS), is due to launch in December 2012 and it is really focused on the physics of the region between the solar surface and corona," De Pontieu explained. "That would really help us to follow up this research," he added.

The research is described in Science.

Colin Stuart is a science writer and astronomer based in London

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Photomultipliers and associated operating and signal processing hardware

ET Enterprises Ltd
45 Riverside Way
Uxbridge
Middlesex
UB8 2YF
United Kingdom

Tel: 01895200880
Fax: 01895270973

The photomultiplier is a very sensitive light detector providing a current output proportional to light intensity. Main benefits are large detection area, high gain and single photon capability.

The photomultiplier detects light at the photocathode (k) which emits electrons by the photoelectric effect. These photoelectrons are electrostatically accelerated and focused onto the first dynode (d1) of an electron multiplier. On impact each electron liberates a number of secondary electrons which are in turn, electrostatically accelerated and focused onto the next dynode (d2). The process is repeated at each subsequent dynode and the secondary electrons from the last dynode are collected at the anode (a). The ratio of secondary to primary electrons emitted at each dynode depends on the energy of the incident electrons and is controlled by the inter-electrode potentials. By using a variable high voltage supply, the amplitude of photomultiplier output can cover a wide dynamic range.

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Gravcore

R & D for Inverse Square Energy. We are building a machine to mechanically combine RCF and MMF in an attempt to electrically export the unified sum.

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The Capital Spillway Trust

Concept created in 1994 while in direct correspondence with Mr. Eddie George, Governor The Bank of England in a debate about how to capitalise new inventions. Now presented to the UK government at the suggestion of Mervyn King, present Governor BoE.

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SIB1256 Sensor Interface Board for SensL SPMArray4

Vertilon Corporation
66 Tadmuck Road
Westford
MA
01886-3135
United States

Tel: 978-692-7070

The SIB1256 sensor interface board allows up to four SensL SPMArray4 silicon photomultiplier arrays (SiPM) to easily interface to a Vertilon PhotoniQ multichannel data acquisition system.

The SIB1256 allows up to four SensL SPMArray4 SiPM devices to interface to a Vertilon PhotoniQ multichannel data acquisition system. The devices are inserted into the board where their anode signals are routed to cable assemblies that connect the 64 device outputs to the PhotoniQ. Bias to SiPM arrays is provided by four on-board adjustable high voltage bias supplies that include a voltage trimming function for gain matching between the arrays. A special current-sense output from each bias supply is summed together to represent the total AC charge signal measured by all four SiPM arrays. This signal is fed into a user-programmable leading edge discriminator that generates a trigger signal when an event exceeding a preset energy threshold is detected on any of the SPMArray4 devices.

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Thursday, January 06, 2011

SPIE Security+Defence 2011

The optics and photonics conferences in SPIE Security+Defence cross the divide between fundamental optical science and the application of the underpinning technologies in advanced defence and security systems. This is a unique symposium that will offer many opportunities to network with colleagues from a variety of disciplines in academia, industry, and government from all over the World, while addressing the new challenges that continue to emerge: network-enabled capability/network-centric warfare evolve; asymmetric warfare: military operations in the urban theatre; and peace-keeping.
SPIE Security and Defence will consider how the fundamental and emerging technology base is likely to be exploited in the future will be changing:
+ Unmanned/Unattended Sensors and Sensor Networks
+ Electro-Optical and Infrared Systems: Technology and Applications
+ Electro-Optical Remote Sensing
+ Technologies for Optical Countermeasures
+ Military Applications in Hyperspectral Imaging and High Spatial Resolution Sensing
+ Advanced Free-Space Optical Communication Techniques and Applications
+ Photonic Components and Architectures in Defence Systems
+ Millimetre Wave and Terahertz Sensors and Technology
+ Optical Materials in Defence Systems Technology
+ Optics and Photonics for Counterterrorism and Crime Fighting
+ Optically Based Biological and Chemical Detection for Defence
+ Quantum Information Security
With a European focus, this event attracts more than 400 attendees in the security and defense sector, and is collocated with the SPIE Europe Remote Sensing meeting, allowing you to also take advantage of the cross section of 600 attendees working in a technical area rich in solutions for the security and defence community. Explore new opportunities to collaborate with colleagues and potential new partners in industry, academia, and government from around the world.
Co-located Symposium – SPIE Remote Sensing
Two great meetings in one great location! Your registration fee gains you access to all the conferences in both Security+Defence 2011 and Remote Sensing 2011.

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The Scholar and the Caliph

N.B. This is a fictionalized account – see author's note below

An illustration of Ibn al-Haytham

In the hush just before fajr, before the devout gather to greet the sunrise with prayers towards Mecca, the Scholar emerges from a fitful sleep and confronts the darkness. He remembers, as consciousness returns, that he is a prisoner in his own home. There is nothing to alleviate the mind-numbing sameness of days, no friendly voice or warm touch to keep the suffocating isolation at bay – not even the musty comfort of his books. Truly, I am cursed among men.

This is not how he envisioned his future as an ambitious young man back in Basra. There, he devoured the works of Aristotle and dreamed of scientific pursuits. "The ink of the scholar is more holy than the blood of the martyrs," the Koran says, and he believed it. So he followed the throngs of Basran fortune-seekers to Cairo, home to the Dar al-'llm ("House of Knowledge"), and found lodgings near the Azhar Mosque. He taught in the mosque's school, and worked as a scribe in the Dar al-'llm, copying Arabic translations of Euclid, Ptolemy and his beloved Aristotle, being careful not to smudge the pages with ink-stained fingers. All the knowledge in the world was at his fingertips. Yet the wisdom of the Ancients could not help him to foresee the ill fortune about to befall him.

One day he received a summons from Cairo's reigning Caliph, al-Hakim bi-Amr Allah – a tremendous honour for a humble scribe. The Scholar felt small and insignificant as he passed through the palace gates into a large courtyard ringed by stone archways; twin minarets cast their shadows over a reflecting pool. He was even more cowed by the majesty of the blue-domed throne room – its stucco walls dotted with bright mosaic tiles. Even the Caliph seemed dwarfed by the setting, despite his robes of state and jewelled turban.

The Caliph was most eager to find a man who could solve a perplexing problem, he explained, and the Scholar came highly recommended. Every year, the flooding of the Nile served as a harbinger for the end of summer, and an omen for that year's harvest. Too much flooding, and the crops would be destroyed; too little, and drought and famine would ravage the land. His people were utterly dependent on the fickle whims of the great river for their survival. Man's ingenuity had already produced watermills to grind grain, and water-raising machines. If men could control water in this way, could they not also build a dam to control the flooding and bend the Nile to the Caliph's will?

The Scholar was flattered by the Caliph's attentions, and tempted by the promise of riches and fame should he succeed. Silencing the doubt in his mind, he told al-Hakim "It can be done." And the Caliph appointed him head engineer of the project. But when the Scholar arrived at the proposed site, a cold dread ran through him, despite the dry heat of the desert: the sheer scale of the river and valley were beyond imagination. How could anything control such a force of nature? With a sick feeling he drew up detailed plans for the dam's construction, made measurements, devised various schemes and tested inventions. But the scale of the engineering needed was beyond even the vast resources of the Caliph. In the end, he realized that it could not be done. He had failed.

The prospect of facing the Caliph with this news filled the Scholar with dread. People whispered that al-Hakim had once disembowelled a horseman in his service with a spear just outside the gates of the mosque. An abusive grocer turned muhtasib had his tongue and hands cut off before being summarily executed, and a corrupt judge was beheaded and burned for illegally seizing 20,000 dinars from a young man's inheritance. Even minor infractions were met with arrests, stiff fines or beatings, if not death. Yet al-Hakim was not without compassion: once, after brutally beheading a man, he relented a few days later and ordered the body to be exhumed for proper burial and funeral rites.

The Scholar had heard the stories, and he feared the worst.

An illustration of Ibn al-Haytham

As he made his way back to his lodgings along the narrow winding streets of Cairo, he had a heavy heart, anxiety building with every step. He passed a beggar, noting the torn garments, tangled hair smeared with faeces, the jerky motions and staccato outbursts – all the hallmarks of a confused mind. He paused to drink from a public fountain and caught a glimpse of his own reflection in the water. He looked very much like that lunatic beggar: bedraggled, smelly, with unkempt hair and an unruly beard from his months camped out in the field, haunted eyes set deep in a face drawn taut with worry.

And then the Scholar had an epiphany. Would not the Caliph show mercy to a madman?

His fellow scribes at the Dar al-'llm thought it might just work when he told them of his plan, and they agreed to help. He locked himself in his home and resisted the urge to bathe, while they spread rumours that his mind had snapped under the strain of trying to tame the mighty Nile. The gossip soon reached the Caliph, and he summoned the Scholar to gauge for himself the mental state of his engineer.

Heart pounding, the Scholar shambled into the throne room, doing his best to mimic the beggar's behaviour – rocking and muttering to himself, even pulling out tufts of hair in only half-feigned agitation. His friends swore that he had been in this state for weeks, and they feared he would not recover. If the Caliph's physicians who examined him suspected the pretence, they did not betray him. They told al-Hakim his engineer had, indeed, gone mad, and recommended confining the stricken Scholar to his home.

Mercurial he may have been, but the Caliph was no fool. "I see," he murmured when his physicians gave their verdict. Eyes narrowed, hands clasped behind his back, he slowly circled the Scholar, coldly assessing the man with the supposed broken mind cringing on the ground before him. He wrinkled his nose at the stench.

"Very well," he said at last. "He shall be placed under house arrest until further notice. But his worldly goods shall be forfeited."

"Yes, yes, of course, a small price to pay." The Scholar's friends kissed the hem of the Caliph's robes in relief, bowing repeatedly as they backed towards the door with the newly diagnosed lunatic between them.

"Wait." Al-Hakim held up a hand, and guards promptly blocked their exit. "Confiscate his books, too." He smiled slyly. "After all, what use does a madman have for reading?"

And so the Scholar escaped with his life, but not his freedom – a forgotten man leading a solitary life. No books, no visitors – no distractions to fill the hours. Al-Hakim chose the punishment well; it could drive a sane man mad. Each day, the Scholar counts the hours until night, when he can lose himself in slumber. He always awakens too soon.

Now, many moons later, as the merchants noisily make their way to the marketplace to set up their wares, he watches the first light of dawn stream through the bedchamber door and finds himself wondering how that light can reach him in the darkness. If only I had my books. The Scholar sighs, itching to feel the crisp pages between his fingers. He ponders what he recalls from the Ancients. Aristotle wrote of mysterious "forms" travelling from objects into the eye, while Euclid and Ptolemy proclaimed that the eye emits rays of light that strike and illuminate surrounding objects.

Yet when lying alone in his darkened room, no light shines forth from the Scholar's eyes to illuminate the bare walls before him. He sees nothing until sunrise. There is a window high above the archway to his bedchamber, on the eastern wall. The sunlight streams through the window and reflects off the western wall directly across from the archway, sending that reflected light back through the opening to provide faint illumination in his bedchamber. As the morning light grows stronger, so does the light reflecting into his bedchamber.

Is it possible that the Ancients were mistaken? This is an audacious thought – who is he to question Aristotle? But then he conceives an alternative explanation. Perhaps light radiates in many different straight lines, from every point of a luminous object, travelling in every direction at once. We only "see" objects that reflect those rays of light that enter the eye.

The Scholar decides to put his theory to the test. He lacks his books, but he has lamps and candles; screens and wooden blocks; tubes and makeshift rulers, and a sheet of thin copper. He has paper and ink. And not even al-Hakim has the power to take away his senses, or his mind. I can still be a Scholar.

First, he gazes through a tube at objects in the room, using a ruler to measure the line of sight. He can only "see" an object when it stands directly in front of the tube's opening. Then he covers part of the opening. Now, he can only see that part of the object that is opposite the uncovered part of the tube.

His excitement mounting, the Scholar next punches a large round hole in a sheet of copper and inserts a tube that is open at one end and closed at the other, save for a pinhole the width of a needle. He holds a candle flame to the open end and places an urn in front of the pinhole at the other. Only a little light from the flame travels through the pinhole to the urn; the copper sheet blocks the rest. Then he moves the candle, and the light cast upon the urn looks different. When just the tip of the flame is in front of the pinhole, only a little light falls on the urn; when the centre of the flame is in front of the pinhole, more light falls on the urn. But there is always some light that reaches the urn; it must radiate from each point of the fire.

There is no mysterious "form" that all objects emit, nor do our eyes emit rays of light so we can see. Instead, there are sources of primary light – the Sun or a candle's flame – and this light is reflected from other objects (secondary light) and passes into our eyes so that we can perceive them. So Aristotle was wrong about light and vision. So were Euclid and Ptolemy. And if such great minds could be wrong about this, they might be wrong about other supposed "truths" as well!

Never again will the Scholar blindly accept assertions made by the Ancients, however revered; he vows to test and question everything. I will make myself the enemy of all I have read, attack the old ideas from every angle and dismantle all that do not pass my tests until only the truth remains.

An illustration of Ibn al-Haytham

Now the Scholar's days and nights are filled with activity. He studies how curved mirrors and glass bend and warp the light. He places lamps at different points around his bedchamber, all facing a single pinhole in the wall, and observes how the light from each lamp appears as a distinct spot on the far wall in the darkened room next door. He screens one lamp, then another, and notes how just the spot from the screened lamp disappears from the wall next door when he does so.

The outside world fades as he works with increasingly feverish intensity, oblivious to the sounds of city life echoing in the streets beyond his stone walls. Days turn into weeks, then months, then years, as he painstakingly records the details of all he discovers. There are seven volumes by the time he is done – a unified theory of light and vision that cites not a single ancient authority. He calls his manuscript Kitab al-Manazir (Book of Optics).

A decade has passed. One morning the Scholar hears a knock on his door. No-one knocks at his door – the guards leave food, water and other necessities, but have never interacted with him. He opens the door to al-Hakim's vizier, a servant by his side. The three men stand in awkward silence, the servant shifting nervously from one foot to the other, eyes fixed resolutely on the ground. The vizier clears his throat.

"Our Caliph is missing," he says. Lately, he explained, al-Hakim had taken to riding out into the al-Muqattam hills at night to fast and meditate. "Alas – this time, he has not returned."

Only his bloodstained robes and donkey had been found. There are whispers of foul play, of assassins hired by al-Hakim's half-sister, Sitt al-Mulk, so that she can rule as regent until the Caliph's young son comes of age. But there is no proof of such a plot, and little choice but to declare al-Hakim dead.

The vizier studies the Scholar for a moment, then pulls a scroll from his robes. "This is a decree by the court physicians that the curse of madness is no longer upon you. Your house arrest is lifted. You are free to go."

He snaps his fingers and turns to leave with his servant, pausing at the door to glance back at the Scholar. "May Allah smile upon you," the vizier murmurs. And he is gone.

The Scholar stands trembling in the cool shadows. Could it be true? He takes a shuffling step towards the door, then another. No guard tries to stop him. In the bright bustle of dhuhr, as the Sun reaches its zenith and the devout kneel for their noontime prayers, he emerges from his prison, blinking in the sudden glare, as if awakening from an unpleasant dream. He tilts his head back, raises his palms, and embraces the light.

This is a work of fiction – a fanciful re-imagining of a 10-year period in the life of the medieval Muslim polymath Ibn al-Haytham (AD 965–1040) considered by many historians to be the father of modern optics. Living at the height of the golden age of Arabic science, al-Haytham developed an early version of the scientific method 200 years before scholars in Western Europe, and is most celebrated for the seven-volume Kitab al-Manazir (Book of Optics). The first three books deal with visual perception and psychology, while the remaining volumes focus on physical optics. It is frequently ranked alongside Newton's Principia as one of the most influential books in physics.

Very little is known about al-Haytham, other than what is contained in his written works – those that survived the pillaging of the Crusades in the 11th century and the sacking of Baghdad in the mid-13th century, which effectively ended the golden age. This story is inspired by historical accounts, but I have taken some liberties for the sake of the narrative. For instance, accounts differ as to whether al-Haytham was placed under house arrest or imprisoned in an asylum; I have opted for the former.

It is likely that al-Haytham did fail to build a dam to regulate the flooding of the Nile, at a site near the modern Aswan Dam, and feigned madness to escape execution by the Caliph al-Hakim of the Fatimid dynasty. He wrote the Book of Optics during this period, although details of the exact conditions under which he worked are lacking. There really was a House of Knowledge, and visitors to Cairo can still visit the Azhur Mosque where he taught. Al-Haytham went on to make contributions to astronomy, mathematics, engineering, medicine and physics. The year 2011 marks the millennial celebration of the Book of Optics.

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CasaXPS software training for XPS/ESCA

The course will include an overview of the features in CasaXPS, converting data in different file formats (such as from Kratos, Physical Electronics, and Thermo Fisher Scientific [formerly VG]) into the ISO standard format, different display modes, different peak identification and labeling methods, different background subtraction methods (linear, Shirley, Tougaard,…), peak areas, sensitivity factors and their linked databases, quantitative analysis using default transitions and user-selected transitions, adding peaks, curve fitting, selection of lineshapes and backgrounds, curve fitting using reference spectra, combining curve fit data into quantitative analysis tables, correcting energy scale for sample charging, propagating processed data to other data, depth profile data, least squares fitting, annotation relative to peaks or to the display box, spectrum zoom, inserting additional spectra within a window, copying spectra into reports, changing aspect ratios, changing fonts, changing line colors, batch processing, customizing CasaXPS, creating and saving versions with special databases, and its use in data processing with other techniques such as AES and SIMS.

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3D magnetic domains imaged for the first time

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Jan 5, 2011

Physicists in Europe are the first to obtain 3D images of magnetic domains – regions within a material in which all the magnetic moments point in the same direction. While 2D magnetic domains on surfaces can be imaged using several different techniques, 3D images have eluded scientists since such magnetic domains were first proposed over 100 years ago. As well as providing better insight into how domains form and evolve, the technique could also help to improve hard disks – which store data in magnetic domains.

Below a critical temperature the magnetic moments in a ferromagnetic material such as iron tend to point in the same direction as their neighbours. In the absence of an applied magnetic field, however, all the moments in an iron sample will not always point in the same direction. Instead microscopic regions – called domains – can form whereby all the moments of one domain will point in one direction, while all the moments of a neighbouring domain may point in a different direction.

While physicists have been able to study the effect of domains on the magnetic properties of materials, they had not been able to make 3D images of domains deep within the bulk of a material. Instead they had to settle on destructive techniques such as imaging domains near the surface of the sample and then shaving off a thin layer and repeating the measurement.

But now Ingo Manke and Nikolay Kardjilov of the Helmholtz Centre Berlin and colleagues in Germany, Switzerland and the UK have created the first 3D images using a new technique called Talbot-Lau neutron tomography. They did this by firing a coherent beam of low-energy neutrons at a sample of an iron-silicon alloy. A small number of the neutrons are deflected slightly when they cross a boundary between two domains. This deflection occurs because the index of refraction of the material changes abruptly at the boundary. A diffraction grating with a detector behind it is scanned across the beam of deflected neutrons to determine the angle of deflection.

This measurement is repeated many times as the sample is rotated through 360°. The data are then fed into a computer program developed by the team, which produces a 3D image of the domains. The images have a spatial resolution of about 35 µm, which Manke and Kardjilov say could be improved to about 1 µm by using a neutron detector with a better spatial resolution and a higher neutron flux.

Bruce Gaulin of McMaster University in Canada told physicsworld.com, "I am very impressed with the quality of the 3D visualization of the magnetic domains and the quantitative analysis that this quality of data enables." Gaulin, who was not involved in the research, added that the work represents "a significant advance and I would expect it to allow much more detailed understanding of domain structures in materials of practical interest".

As well as improving their experimental set-up, the team is also developing better ways to interpret the data. The team also plans to use the technique to put magnetic-domain theories to the test and to make measurements in strong magnetic fields.

The work is describe in Nature Communications DOI:10.1038/ncomms1125.

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Chaos, Complexity and Transport (CCT11)

The main goal of the CCT11 conference is to discuss shared phenomena in nonlinear dynamics related to chaos, transport and complexity. A strong emphasis will be put on the interdisciplinary character of the conference. In the spirit of its interdisciplinary character, CCT11 will contain theoretical, numerical and experimental contributions (as lectures, oral communications and posters). The committees will encourage the interactions between experimentalists and theoreticians in the same fields but also cross-disciplinary contributions.

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Model 24C Cryogenic Temperature Controller

The Model 24C is a four-input, four control loop cryogenic temperature controller designed for general purpose laboratory and industrial use.

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Highlights of the Model 24C:

*Four multipurpose input channels support Diode, Platinum RTD and most cryogenic NTC resistive temperature sensors. Thermocouple inputs are optional.

*Operation from 250mK to over 1500K with an appropriate sensor. Constant-Voltage, AC excitation of resistive sensors minimizes errors and extends their useful temperature range.

*Four control loops: Loop #1: 50-Watt, three range, Loop #2: 10-Watt, Loops #3 and #4: non-powered.

*Large, bright and highly configurable display.

*Synchronous input filter improves control accuracy and stability in cryocooler based systems.

*Two dry-contact relay outputs.

*Data logging to internal Non-Volatile memory.

*Fail-safe cryostat protection features protect user equipment from damage.
Table mode control automatically switches the loop input sensor to allow smooth, continuous control over a wide range of temperature.

*Remote interfaces include 100/10 Ethernet and RS-232. IEEE-488.2 (GPIB) and USB are optional.

*Remote command language is IEEE SCPI compliant.

*National Instruments, Inc. LabVIEW™ drivers are available for all interfaces.

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SPIE Remote Sensing 2011

Remote sensing is a fast-growing technology using highly sophisticated sensors on satellites and other elevated platforms as well as on the ground, together with adapted signal and image processing, to deliver many practical applications hardly to be conceived of a few decades ago. The SPIE Remote Sensing Symposium has become the largest and most prestigious annual international meeting on this subject in Europe with more than 600 attendees and each year sees comprehensive coverage of scientific topics, applications, sensors, systems, and satellite platforms and more than 25 countries are represented.
+ Remote Sensing for Agriculture, Ecosystems, and Hydrology
+ Remote Sensing of the Ocean, Sea Ice, Coastal Waters, and Large Water Regions
+ Sensors, Systems, and Next-generation Satellites
+ Remote Sensing of Clouds and the Atmosphere
+ Optics in Atmospheric Propagation and Adaptive Systems
+ Remote Sensing for Environmental Monitoring, GIS Applications, and Geology
+ Lidar Technologies, Techniques, and Measurements for Atmospheric Remote Sensing
+ Addressing Natural Disasters and Sustainable Resources Using Satellite Data
+ High-Performance Computing in Applied Remote Sensing
+ Special Joint Session on Airborne Remote Sensing
Co-located with the SPIE European Symposium on Defence & Security, this event will provide an excellent opportunity to explore new opportunities to collaborate with new partners from other related fields of activity.
Co-located Symposium – SPIE Security+Defence
Two great meetings in one great location! Your registration fee gains you access to all the conferences in both Remote Sensing 2011 and Security+Defence 2011.

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Pyramid metrologists

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Jan 5, 2011

Robert P Crease finds echoes of modern anti-reform movements in a bizarre 19th-century anti-metric effort that sought to base a measurement system on Egypt's Great Pyramid of Giza

The only surviving member of the Seven Wonders of the Ancient World, the Great Pyramid of Giza has captivated the imaginations of visitors for thousands of years. Alexander the Great visited it, as did Napoleon. In the late 19th century, however, the Great Pyramid took on a new role as a prop in an anti-metric movement. In doing so, this ancient Egyptian edifice became possibly the most bizarre example ever of an object proposed as a metrological standard.

Truth be told, the pyramid's solidity and permanence are properties one desires in a standard. Among the early "pyramid metrologists" was John Taylor, a partner in a London publishing firm, who (despite never having seen the Pyramid) believed its dimensions encoded secret knowledge, including the magnitudes of ancient units. In Taylor's view, the pyramid's mathematical relationships were simply too sophisticated for the ancient Egyptians to have devised – he claimed, for example, that the ratio of two sides of its base to its height is p, which is an irrational number that was unknown when the pyramid was built.

Taylor therefore asserted that the pyramid's architect must have been an Israelite obeying divine instructions. In the pyramid's dimensions, we can find God's own units of length, such as the "sacred cubit" (about 25 inches), and weight and capacity (from the coffer in the King's Chamber). The pyramid, in other words, revealed the true sizes of things both ancient and modern. For Taylor, the ancient, sacred, natural measurement system was superior to the modern, artificial, metric system – a point he voiced in his 1864 book The Battle of the Standards.

Taylor's book in turn inspired Charles Piazzi Smyth, the Astronomer Royal of Scotland and an amateur Egyptologist. Smyth became convinced that "the Great Pyramid, besides its tombic use, might have been originally invented and designed to be appropriate for no less than a primitive Metrological Monument". Smyth wrote a 664-page book, Our Inheritance in the Great Pyramid, that included other numerological claims.

The fundamental pyramid unit was not the cubit but its 25th part – the "pyramid inch" – which Smyth said was exactly 1/500,000,000th of the Earth's axis of rotation. It, rather than the metre, was the genuine natural standard. Smyth said that pyramid measurements were "true cosmical relations in their original units", and that the pyramid was "a Bible in stone, a monument of science and religion never to be divorced".

Smyth scorned the metric system, its inventors and its champions. For him, Anglo-Saxon peoples had wisely hewed to the pyramid-inch measure, from which the imperial inch differed only by a negligible fraction. "Simultaneously with the elevation of the metrical system in Paris," he thundered, "the French nation did for themselves formally abolish Christianity, burn the Bible, declare God to be a non-existence, a mere invention of the priests, and institute a worship of humanity, or of themselves."

In late 1864 Smyth set off for Egypt to investigate first-hand the metrological wonders encoded in the pyramid's dimensions: the distance of the Earth to the Sun; the length of the year; and the diameter and density of the Earth. He even found a temperature scale, with a zero point that was the freezing point of water and its 50 degree mark as the temperature of the King's Chamber.

When Smyth returned, his Royal Society colleagues were unimpressed and demolished his numerology, finding errors in his work that included the fact that the famous ratio of twice one side to height was not p but the more mundane ratio 22/7. (Martin Gardiner, that great exposer of pseudoscience, analyses Smyth's errors in his book Fads and Fallacies in the Name of Science.) As the controversy heated up, so did Smyth's confidence, to the point where he began making absurd comparisons: himself to Kepler, and opponents to the know-nothings who ridiculed him. In a fit of rage following a tangle with James Clerk Maxwell, Smyth resigned from the Royal Society in 1874.

A few years later, however, Smyth found enthusiastic followers in the US among its extreme anti-metric movement: members of the International Institute for Preserving and Perfecting Weights and Measures. This campaign exhibited the classic signs of US anti-reform movements then and now: rabid rhetoric, fabrication of "facts", reimagining history, conspiracy theories and appeals to preserve the purity of race, nature and nation. The enemy was the "other": subversives, socialists, foreigners, atheism and artifice. The good guys were patriots, capitalists, Christians and adherents to God, country and nature.

US anti-reformists often trace their cause back to divine commandments and they love wacky props. The anti-metricists adopted the Great Pyramid as theirs, interpreting it as the same as the one in the Great Seal of the United States, which appears on the reverse of every dollar bill. The literary organ of the movement was the International Standard, whose issues contained numerological studies of the Great Pyramid, rants against the metric system, poems and even anti-metric songs.

Smyth wrote frequently for the Standard, and tried to enlist the movement's members in projects such as sending him back to Egypt for further measurements, and having the pyramid declared an international metrological park to protect it from war: "neutral ground under the guardianship of all English-speaking people, or of all Christian nations". Were he and the institute members drawn together more by the anti-metric cause or the pyramidology? This is unclear and does not matter; the two interests fed each other. At last Smyth found in them a receptive audience, at least for as long as the organization lasted, until 1888. When he died in 1900, Smyth's tombstone was formed from a stone pyramid topped by a cross.

The history of metrology contains numerous efforts to tether units to artefacts, natural phenomena and physical constants, but this is one of the few attempts to secure units by divine revelation. The Great Pyramid episode is fascinating in the way that it exhibits the passions that tend to crystallize around the quest for metrological finality.

Robert P Crease is chairman of the Department of Philosophy, Stony Brook University, and historian at the Brookhaven National Laboratory, US

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The Scholar and the Caliph

N.B. This is a fictionalized account – see author's note below

An illustration of Ibn al-Haytham

In the hush just before fajr, before the devout gather to greet the sunrise with prayers towards Mecca, the Scholar emerges from a fitful sleep and confronts the darkness. He remembers, as consciousness returns, that he is a prisoner in his own home. There is nothing to alleviate the mind-numbing sameness of days, no friendly voice or warm touch to keep the suffocating isolation at bay – not even the musty comfort of his books. Truly, I am cursed among men.

This is not how he envisioned his future as an ambitious young man back in Basra. There, he devoured the works of Aristotle and dreamed of scientific pursuits. "The ink of the scholar is more holy than the blood of the martyrs," the Koran says, and he believed it. So he followed the throngs of Basran fortune-seekers to Cairo, home to the Dar al-'llm ("House of Knowledge"), and found lodgings near the Azhar Mosque. He taught in the mosque's school, and worked as a scribe in the Dar al-'llm, copying Arabic translations of Euclid, Ptolemy and his beloved Aristotle, being careful not to smudge the pages with ink-stained fingers. All the knowledge in the world was at his fingertips. Yet the wisdom of the Ancients could not help him to foresee the ill fortune about to befall him.

One day he received a summons from Cairo's reigning Caliph, al-Hakim bi-Amr Allah – a tremendous honour for a humble scribe. The Scholar felt small and insignificant as he passed through the palace gates into a large courtyard ringed by stone archways; twin minarets cast their shadows over a reflecting pool. He was even more cowed by the majesty of the blue-domed throne room – its stucco walls dotted with bright mosaic tiles. Even the Caliph seemed dwarfed by the setting, despite his robes of state and jewelled turban.

The Caliph was most eager to find a man who could solve a perplexing problem, he explained, and the Scholar came highly recommended. Every year, the flooding of the Nile served as a harbinger for the end of summer, and an omen for that year's harvest. Too much flooding, and the crops would be destroyed; too little, and drought and famine would ravage the land. His people were utterly dependent on the fickle whims of the great river for their survival. Man's ingenuity had already produced watermills to grind grain, and water-raising machines. If men could control water in this way, could they not also build a dam to control the flooding and bend the Nile to the Caliph's will?

The Scholar was flattered by the Caliph's attentions, and tempted by the promise of riches and fame should he succeed. Silencing the doubt in his mind, he told al-Hakim "It can be done." And the Caliph appointed him head engineer of the project. But when the Scholar arrived at the proposed site, a cold dread ran through him, despite the dry heat of the desert: the sheer scale of the river and valley were beyond imagination. How could anything control such a force of nature? With a sick feeling he drew up detailed plans for the dam's construction, made measurements, devised various schemes and tested inventions. But the scale of the engineering needed was beyond even the vast resources of the Caliph. In the end, he realized that it could not be done. He had failed.

The prospect of facing the Caliph with this news filled the Scholar with dread. People whispered that al-Hakim had once disembowelled a horseman in his service with a spear just outside the gates of the mosque. An abusive grocer turned muhtasib had his tongue and hands cut off before being summarily executed, and a corrupt judge was beheaded and burned for illegally seizing 20,000 dinars from a young man's inheritance. Even minor infractions were met with arrests, stiff fines or beatings, if not death. Yet al-Hakim was not without compassion: once, after brutally beheading a man, he relented a few days later and ordered the body to be exhumed for proper burial and funeral rites.

The Scholar had heard the stories, and he feared the worst.

An illustration of Ibn al-Haytham

As he made his way back to his lodgings along the narrow winding streets of Cairo, he had a heavy heart, anxiety building with every step. He passed a beggar, noting the torn garments, tangled hair smeared with faeces, the jerky motions and staccato outbursts – all the hallmarks of a confused mind. He paused to drink from a public fountain and caught a glimpse of his own reflection in the water. He looked very much like that lunatic beggar: bedraggled, smelly, with unkempt hair and an unruly beard from his months camped out in the field, haunted eyes set deep in a face drawn taut with worry.

And then the Scholar had an epiphany. Would not the Caliph show mercy to a madman?

His fellow scribes at the Dar al-'llm thought it might just work when he told them of his plan, and they agreed to help. He locked himself in his home and resisted the urge to bathe, while they spread rumours that his mind had snapped under the strain of trying to tame the mighty Nile. The gossip soon reached the Caliph, and he summoned the Scholar to gauge for himself the mental state of his engineer.

Heart pounding, the Scholar shambled into the throne room, doing his best to mimic the beggar's behaviour – rocking and muttering to himself, even pulling out tufts of hair in only half-feigned agitation. His friends swore that he had been in this state for weeks, and they feared he would not recover. If the Caliph's physicians who examined him suspected the pretence, they did not betray him. They told al-Hakim his engineer had, indeed, gone mad, and recommended confining the stricken Scholar to his home.

Mercurial he may have been, but the Caliph was no fool. "I see," he murmured when his physicians gave their verdict. Eyes narrowed, hands clasped behind his back, he slowly circled the Scholar, coldly assessing the man with the supposed broken mind cringing on the ground before him. He wrinkled his nose at the stench.

"Very well," he said at last. "He shall be placed under house arrest until further notice. But his worldly goods shall be forfeited."

"Yes, yes, of course, a small price to pay." The Scholar's friends kissed the hem of the Caliph's robes in relief, bowing repeatedly as they backed towards the door with the newly diagnosed lunatic between them.

"Wait." Al-Hakim held up a hand, and guards promptly blocked their exit. "Confiscate his books, too." He smiled slyly. "After all, what use does a madman have for reading?"

And so the Scholar escaped with his life, but not his freedom – a forgotten man leading a solitary life. No books, no visitors – no distractions to fill the hours. Al-Hakim chose the punishment well; it could drive a sane man mad. Each day, the Scholar counts the hours until night, when he can lose himself in slumber. He always awakens too soon.

Now, many moons later, as the merchants noisily make their way to the marketplace to set up their wares, he watches the first light of dawn stream through the bedchamber door and finds himself wondering how that light can reach him in the darkness. If only I had my books. The Scholar sighs, itching to feel the crisp pages between his fingers. He ponders what he recalls from the Ancients. Aristotle wrote of mysterious "forms" travelling from objects into the eye, while Euclid and Ptolemy proclaimed that the eye emits rays of light that strike and illuminate surrounding objects.

Yet when lying alone in his darkened room, no light shines forth from the Scholar's eyes to illuminate the bare walls before him. He sees nothing until sunrise. There is a window high above the archway to his bedchamber, on the eastern wall. The sunlight streams through the window and reflects off the western wall directly across from the archway, sending that reflected light back through the opening to provide faint illumination in his bedchamber. As the morning light grows stronger, so does the light reflecting into his bedchamber.

Is it possible that the Ancients were mistaken? This is an audacious thought – who is he to question Aristotle? But then he conceives an alternative explanation. Perhaps light radiates in many different straight lines, from every point of a luminous object, travelling in every direction at once. We only "see" objects that reflect those rays of light that enter the eye.

The Scholar decides to put his theory to the test. He lacks his books, but he has lamps and candles; screens and wooden blocks; tubes and makeshift rulers, and a sheet of thin copper. He has paper and ink. And not even al-Hakim has the power to take away his senses, or his mind. I can still be a Scholar.

First, he gazes through a tube at objects in the room, using a ruler to measure the line of sight. He can only "see" an object when it stands directly in front of the tube's opening. Then he covers part of the opening. Now, he can only see that part of the object that is opposite the uncovered part of the tube.

His excitement mounting, the Scholar next punches a large round hole in a sheet of copper and inserts a tube that is open at one end and closed at the other, save for a pinhole the width of a needle. He holds a candle flame to the open end and places an urn in front of the pinhole at the other. Only a little light from the flame travels through the pinhole to the urn; the copper sheet blocks the rest. Then he moves the candle, and the light cast upon the urn looks different. When just the tip of the flame is in front of the pinhole, only a little light falls on the urn; when the centre of the flame is in front of the pinhole, more light falls on the urn. But there is always some light that reaches the urn; it must radiate from each point of the fire.

There is no mysterious "form" that all objects emit, nor do our eyes emit rays of light so we can see. Instead, there are sources of primary light – the Sun or a candle's flame – and this light is reflected from other objects (secondary light) and passes into our eyes so that we can perceive them. So Aristotle was wrong about light and vision. So were Euclid and Ptolemy. And if such great minds could be wrong about this, they might be wrong about other supposed "truths" as well!

Never again will the Scholar blindly accept assertions made by the Ancients, however revered; he vows to test and question everything. I will make myself the enemy of all I have read, attack the old ideas from every angle and dismantle all that do not pass my tests until only the truth remains.

An illustration of Ibn al-Haytham

Now the Scholar's days and nights are filled with activity. He studies how curved mirrors and glass bend and warp the light. He places lamps at different points around his bedchamber, all facing a single pinhole in the wall, and observes how the light from each lamp appears as a distinct spot on the far wall in the darkened room next door. He screens one lamp, then another, and notes how just the spot from the screened lamp disappears from the wall next door when he does so.

The outside world fades as he works with increasingly feverish intensity, oblivious to the sounds of city life echoing in the streets beyond his stone walls. Days turn into weeks, then months, then years, as he painstakingly records the details of all he discovers. There are seven volumes by the time he is done – a unified theory of light and vision that cites not a single ancient authority. He calls his manuscript Kitab al-Manazir (Book of Optics).

A decade has passed. One morning the Scholar hears a knock on his door. No-one knocks at his door – the guards leave food, water and other necessities, but have never interacted with him. He opens the door to al-Hakim's vizier, a servant by his side. The three men stand in awkward silence, the servant shifting nervously from one foot to the other, eyes fixed resolutely on the ground. The vizier clears his throat.

"Our Caliph is missing," he says. Lately, he explained, al-Hakim had taken to riding out into the al-Muqattam hills at night to fast and meditate. "Alas – this time, he has not returned."

Only his bloodstained robes and donkey had been found. There are whispers of foul play, of assassins hired by al-Hakim's half-sister, Sitt al-Mulk, so that she can rule as regent until the Caliph's young son comes of age. But there is no proof of such a plot, and little choice but to declare al-Hakim dead.

The vizier studies the Scholar for a moment, then pulls a scroll from his robes. "This is a decree by the court physicians that the curse of madness is no longer upon you. Your house arrest is lifted. You are free to go."

He snaps his fingers and turns to leave with his servant, pausing at the door to glance back at the Scholar. "May Allah smile upon you," the vizier murmurs. And he is gone.

The Scholar stands trembling in the cool shadows. Could it be true? He takes a shuffling step towards the door, then another. No guard tries to stop him. In the bright bustle of dhuhr, as the Sun reaches its zenith and the devout kneel for their noontime prayers, he emerges from his prison, blinking in the sudden glare, as if awakening from an unpleasant dream. He tilts his head back, raises his palms, and embraces the light.

This is a work of fiction – a fanciful re-imagining of a 10-year period in the life of the medieval Muslim polymath Ibn al-Haytham (AD 965–1040) considered by many historians to be the father of modern optics. Living at the height of the golden age of Arabic science, al-Haytham developed an early version of the scientific method 200 years before scholars in Western Europe, and is most celebrated for the seven-volume Kitab al-Manazir (Book of Optics). The first three books deal with visual perception and psychology, while the remaining volumes focus on physical optics. It is frequently ranked alongside Newton's Principia as one of the most influential books in physics.

Very little is known about al-Haytham, other than what is contained in his written works – those that survived the pillaging of the Crusades in the 11th century and the sacking of Baghdad in the mid-13th century, which effectively ended the golden age. This story is inspired by historical accounts, but I have taken some liberties for the sake of the narrative. For instance, accounts differ as to whether al-Haytham was placed under house arrest or imprisoned in an asylum; I have opted for the former.

It is likely that al-Haytham did fail to build a dam to regulate the flooding of the Nile, at a site near the modern Aswan Dam, and feigned madness to escape execution by the Caliph al-Hakim of the Fatimid dynasty. He wrote the Book of Optics during this period, although details of the exact conditions under which he worked are lacking. There really was a House of Knowledge, and visitors to Cairo can still visit the Azhur Mosque where he taught. Al-Haytham went on to make contributions to astronomy, mathematics, engineering, medicine and physics. The year 2011 marks the millennial celebration of the Book of Optics.

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Monday, January 03, 2011

Invisibility cloaks shield the large and visible

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Jan 1, 2011

Two independent groups of physicists have built invisibility cloaks that can shield large objects lying on a plane. These "carpet cloaks" are far closer to the intuitive idea of an invisibility cloak than devices previously built, they argue, because they hide objects that can be seen with the naked eye and do so at visible wavelengths. The cloaks are also relatively cheap and easy to make, being constructed from the natural material calcite.

Carpet cloaks were proposed in 2008 by John Pendry of Imperial College, London as a way of extending the operating range of invisibility cloaks, which were mostly limited to microwave wavelengths. These devices are placed over an object sitting on a reflective plane and alter the path of light bouncing off the object in such a way that the light appears to have bounced straight off the plane.

However, all visible-light carpet cloaks built so far were demonstrated under a microscope, hiding objects no larger than 100 wavelengths across (about 50 µm). In addition, these cloaks were difficult to make, since they consisted of complex, artificially engineered materials. And they were not portable because the cloak, object and surrounding medium all tended to be made from a single structure.

The latest devices follow on from the work of Yu Luo of Zhejiang University in China and colleagues who realized last year that carpet cloaks can be built from homogeneous – rather than more complex inhomogeneous – materials, as long as those materials are anisotropic. Both devices in fact are built from the naturally occurring crystalline material calcite, the refractive index of which depends on the relative orientation of an incoming light wave’s polarization axis and the calcite’s optical axis.

George Barbastathis and co-workers at the Singapore-MIT Alliance for Research and Technology (SMART) in Singapore made their cloak by gluing together two pieces of calcite with differently oriented optical axes. These orientations were fixed such that light waves with a given polarization that bounce off a wedge-shaped object placed underneath the cloak emerge travelling in the same direction and at the same height that they would have done had they bounced straight off the mirror beneath the object. The wedge, having a base length, width and height of 38 mm, 10 mm and 2 mm respectively, can easily be seen with the naked eye.

The team used a technique known as transformation optics to design their cloak. They calculated the optical parameters that were needed to transform the space between a small and a large triangle, such that light passing through this space would do so as if it were passing through all of the larger triangle, thereby effectively rendering the smaller triangle – the wedge – invisible. Having calculated these parameters the researchers were able to construct their cloak using conventional lens fabrication, with the cross section of the cloak being equal to the space between the two triangles, minus the top of the larger triangle.

The researchers then tested the cloak by directing a polarized laser beam so that the beam passed through a stencil, and then part of the emerging beam entered the cloak and bounced off the wedge while the remainder of the beam bounced directly off a reflective surface beneath the wedge. By detecting the different parts of the beam with a CCD camera they were able to show that the cloak worked. The team optimized the cloak so that it worked best at green wavelengths, which is where the eye is most sensitive, but showed that, some aberration aside, it also worked at red and blue wavelengths (arXiv:1012.2238).

Both the device and the experiment used to test it bear a striking resemblance to those of the second group, which includes John Pendry. This team published its research at arXiv:1012.2783 but is unable to discuss its work while the paper is being reviewed for acceptance in a scientific journal.

Pendry’s group tested its device in air, while Barbastathis and team immersed their cloak and wedge in a tank of colourless laser oil. They did this in order to simulate the environment in which the device would be used – in the sea around Singapore. Light tends to have a particular polarization in water and so the device can be tuned to that polarization. According to SMART’s Baile Zhang, the cloak could be used by engineers to hide cables along the seabed or to help biologists image the behaviour of fish and other sea creatures unobtrusively.

Tomas Tyc of Masaryk University in the Czech Republic, who was not a member of either group, thinks that the papers "describe important achievements in the area of experimental cloaking." But he maintains that a carpet cloak is quite different to a fully fledged Harry Potter-style invisibility cloak. He points out that a carpet cloak only really works when viewing an object – be it a rucksack or a sword on someone's back, for example – side on. Otherwise the object will appear flat but still be visible.

Zhang acknowledges this. Making free-standing cloaks, he says, "is the direction we need to move in". But doing so, he adds, will be very difficult since it will require the fabrication of materials with "extreme parameters".

Edwin Cartlidge is a science writer based in Rome

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