Multiplication by Infinity

Friday, July 22, 2011

Cat Burglar Identified Using Modern Technology

Night vision video surveillance is a great boon to police work. Using this wonderful modern technology a thief has been caught:

Much thanks to U. Kansas Physics Grad Student J.L. Nielsen for alerting the community to this video.

Night vision is the ability to see in low light conditions. Whether by biological or technological means, night vision is made possible by a combination of two approaches: sufficient spectral range, and sufficient intensity range. Humans have poor night vision compared to many animals, in part because the human eye lacks a tapetum lucidum.^[1]

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Types of ranges

Spectral range

Night-useful spectral range techniques can sense radiation that is invisible to a human observer. Human vision is confined to a small portion of the electromagnetic spectrum called visible light. Enhanced spectral range allows the viewer to take advantage of non-visible sources of electromagnetic radiation (such as near-infrared or ultraviolet radiation). Some animals can see using much more of the infrared and/or ultraviolet spectrum than humans.

Intensity range

Sufficient intensity range is simply the ability to see with very small quantities of light. Although the human visual system can, in theory, detect single photons under ideal conditions, the neurological noise filters limit sensitivity to a few tens of photons, even in ideal conditions.^[2]

Many animals have better night vision than humans do, the result of one or more differences in the morphology and anatomy of their eyes. These include having a larger eyeball, a larger lens, a larger opticalaperture (the pupils may expand to the physical limit of the eyelids), more rods than cones (or rods exclusively) in the retina, a tapetum lucidum.

Enhanced intensity range is achieved via technological means through the use of an image intensifier, gain multiplication CCD, or other very low-noise and high-sensitivity array of photodetectors.

Biological night vision

For more details on this topic, see Adaptation (eye).

In biological night vision, molecules of rhodopsin in the rods of the eye undergo a change in shape as they absorb light. Rhodopsin is the chemical that allows night-vision, and is extremely sensitive to light. Exposed to a spectrum of light, the pigment immediately bleaches, and it takes about 30 minutes to regenerate fully, but most of the adaptation occurs within the first five or ten minutes in the dark. Rhodopsin in the human rods is less sensitive to the longer red wavelengths of light, so many people use red light to help preserve night vision as it only slowly depletes the eye's rhodopsin stores in the rods and instead is viewed by the cones.

Many animals have a tissue layer called the tapetum lucidum in the back of the eye that reflects light back through the retina, increasing the amount of light available for it to capture. This is found in many nocturnalanimals and some deep sea animals, and is the cause of eyeshine. Humans lack a tapetum lucidum.

Nocturnal mammals have rods with unique properties that make enhanced night vision possible. The nuclear pattern of their rods changes shortly after birth to become inverted. In contrast to contemporary rods, inverted rods have heterochromatin in the center of their nuclei and euchromatin and other transcription factors along the border. In addition, the outer nuclear layer (ONL) in nocturnal mammals is thick due to the millions of rods present to process the lower light intensities of a few photons. Rather than being scattered, the light is passed to each nucleus individually.^[3] In fact, an animal's ability to see in low light levels may be similar to what humans see when using first- or perhaps second-generation image intensifiers.^{[citation needed]}

A larger size of pupil relative to the rest of the eye, also aids night vision.^{[citation needed]}

Night vision technologies

Night vision technologies can be broadly divided into three main categories:

Image intensification: Image intensification technologies work on the principle of magnifying the amount of received photons from various natural sources such as starlight or moonlight. Examples of such technologies include night glasses and low light cameras.

Active illumination: Active illumination technologies work on the principle of coupling imaging intensification technology with an active source of illumination in the near infrared (NIR) or shortwave infrared (SWIR) band. Examples of such technologies include low light cameras.

Thermal imaging: Thermal imaging technologies work by detecting the temperature difference between the background and the foreground objects.

Night glasses

Binoculars (night vision goggles on flight helmet) Note: the green color of the objective lenses is the reflection of the Light Interference Filters, not a glow.

Night glasses are telescopes or binoculars with a large diameter objective. Large lenses can gather and concentrate light, thus intensifying light with purely optical means and enabling the user to see better in the dark than with the naked eye alone. Often night glasses also have a fairly large exit pupil of 7 mm or more to let all gathered light into the user's eye. However, many people can't take advantage of this because of the limited dilation of the human pupil. To overcome this, soldiers were sometimes issued atropine eye drops to dilate pupils. Before the introduction of image intensifiers, night glasses were the only method of night vision, and thus were widely utilized, especially at sea. Second World War era night glasses usually had a lens diameter of 56 mm or more with magnification of seven or eight. Major drawbacks of night glasses are their large size and weight.

[edit]Active infrared

Imaging results with (top) and without (bottom) active-infrared.

Active infrared night vision combines infrared illumination of spectral range 700-1000nm (just below the visible spectrum of the human eye) with CCD cameras sensitive to this light. The resulting scene, which is apparently dark to a human observer, appears as a monochrome image on a normal display device.^[4]

Because active infrared night vision systems can incorporate illuminators that produce high levels of infrared light, the resulting images are typically higher resolution than other night vision technologies.^[5]^[6] Active infrared night vision is now commonly found in commercial, residential and government security applications, where it enables effective night time imaging under low light conditions. However, since active infrared light can be detected by night vision goggles, there can be a risk of giving away position in tactical military operations.

[edit]Laser range gated imaging

Laser range gated imaging is another form of active night vision which utilizes a high powered pulsed light source for illumination and imaging. Range gating is a technique which controls the laser pulses in conjunction with the shutter speed of the camera's detectors.^[7] Gated imaging technology can be divided into single shot, where the detector captures the image from a single light pulse to multi-shot, where the detector integrates the light pulses from multiple shots to form an image.

One of the key advantages of this technique is the ability to perform target recognition as opposed to detection with thermal imaging.

Thermal vision

Image intensifier

Main article: Image intensifier

The image intensifier is a vacuum-tube based device that converts visible light from an image so that a dimly lit scene can be viewed by a camera or the naked eye. While many believe the light is "amplified," it is not. When light strikes a charged photocathode plate, electrons are emitted through a vacuum tube that strike the microchannel plate that cause the image screen to illuminate with a picture in the same pattern as the light that strikes the photocathode, and is on a frequency that the human eye can see. This is much like a CRT television, but instead of color guns the photocathode does the emitting.

The image is said to become "intensified" because the output visible light is brighter than the incoming IR light, and this effect directly relates to the difference in passive and active night vision goggles. Currently, the most popular image intensifier is the drop-in ANVIS module, though many other models and sizes are available at the market.

Night vision devices

Main article: Night vision device

A night vision device (NVD) is a device comprising an image intensifier tube in a rigid casing, commonly used by military forces. Lately, night vision technology has become more widely available for civilian use. For example, enhanced vision systems (EVS) have become avalable for aircraft to help pilots with situational awareness and avoid accidents. These systems are included in the latest avionics packages from manufacturers such as Cirrus and Cessna.

A specific type of NVD, the night vision goggle (NVG) is a night vision device with dual eyepieces. The device can utilize either one intensifier tube with the same image sent to both eyes, or a separate image intensifier tube for each eye. Night vision goggle combined with magnification lenses constitutes night vision binoculars. Other types include monocular night vision devices with only one eyepiece which may be mounted to firearms as night sights. NVG and EVS technologies are becoming more popular products for helicopter operations to improve safety. The NTSB is considering EVS as recommended equipment for safety features.

Automotive night vision

Main article: Automotive night vision

This section requires expansion.

Patents

References

^ "Histological study of choroidal melanocytes in animals with tapetum lucidum cellulosum (abstract)".
^ "The Human Eye and Single Photons".
^ Solovei, I.; Kreysing, M., Lanctôt, C., Kösem, S., Peichl, L., Cremer, T., et al. (2009, April 16). "Nuclear Architecture of Rod Photoreceptor Cells Adapts to Vision in Mammalian Evolution.". Cell 137 (2): 945–953. doi:10.1016/j.cell.2009.01.052. PMID 19379699.
^ CCTV Information
^ "Thermal Infrared vs. Active Infrared: A New Technology Begins to be Commercialized".
^ Extreme CCTV Surveillance Systems
^ J. Bentell , P. Nies , J. Cloots , J. Vermeiren , B. Grietens , O. David,A. Shurkun and R. Schneider. FLIP CHIPPED InGAaS PHOTODIODE ARRAYS FOR GATED IMAGING WITH EYE-SAFE LASERS.

External links

Wikimedia Commons has media related to: Night Vision

Night Vision & Electronic Sensors Directorate - Fort Belvoir, Virginia

Thursday, July 21, 2011

Space Shuttle Program Over, Next Come the Pink Slips

Congratulations to the crew of STS-135 Atlantis on the successful completion of their mission, and to all the tens of thousands of fine people who worked on America's Space Shuttle program in the last 30+ years, to make it a great success, except for the two screw-ups, the first of which I blame on Ronald Reagan and Ed Meese.

Next up? The pink slips. 9500 layoffs, I read somewhere. What will they do? Apply for their next job I suppose, and be forced to write stuff like this:

Tuesday, July 19, 2011

Optical Illusions

There are millions of these on youtube, and I'm not going to say I culled the best. I do like the first one because it has Mona Kitty.

Illusions in the Puritan-verse:

Monday, July 18, 2011

The Non-Witten Half of IAS - Princeton

In physics, the AdS/CFT correspondence (anti de Sitter/conformal field theory correspondence), sometimes called the Maldacena duality, is the conjecturedequivalence between a string theory and gravity defined on one space, and a quantum field theory without gravity defined on the conformal boundary of this space, whosedimension is lower by one or more. The name suggests that the first space is the product of anti de Sitter space (AdS) with some closed manifold like sphere, orbifold, ornoncommutative space, and that the quantum field theory is a conformal field theory (CFT).^[1]

An example is the duality between Type IIB string theory on AdS₅ × S⁵ space (a product of five dimensional AdS space with a five dimensional sphere) and a supersymmetricN = 4 Yang–Mills gauge theory (which is a conformal field theory) on the 4-dimensional boundary of AdS₅. It is the most successful realization of the holographic principle, a speculative idea about quantum gravity originally proposed by Gerard 't Hooft and improved and promoted by Leonard Susskind.

The AdS/CFT correspondence was originally proposed by Juan Maldacena in late 1997.^[2] Important aspects of the correspondence were given in articles by Steven Gubser, Igor Klebanov and Alexander Markovich Polyakov,^[3] and by Edward Witten.^[4] The correspondence has also been generalized to many other (non-AdS) backgrounds and their dual (non-conformal) theories. In about five years, Maldacena's article had 3000 citations and became one of the most important conceptual breakthroughs in theoretical physics of the 1990s, providing many new lines of research into both quantum gravity and quantum chromodynamics (QCD).

Maldacena's example

It all began with Maldacena's observation. A stack of N D3-branes in type IIB string theory has massless brane fields residing on it. With respect to the brane, they form Yang–Mills supermultiplets transforming under $\mathcal{N} = 4$ SUSY in 3+1D. The vector hypermultiplets form a gauge group $U(N)\cong SU(N)\times U(1)$ . This isn't quite a conformal field theory, even though it runs to one in the infrared once gravitation and string dynamics decouple. In the infrared, the

U (1)

hypermultiplet decouples, but the

S U (N)

hypermultiplets remain interacting as the beta function is zero. The metric background is given by an extremal 3-brane black hole. The event horizon is infinitely far away; the distance to it diverges logarithmically. The near horizon geometry is approximately $AdS_5 \times S^5$ with the approximation becoming more and more exact closer to the horizon. Now, take the scaling limit as the string scale goes to zero with the string coupling kept fixed. All the string and gravitational dynamics decouple, and the U(1) hypermultiplet too. We are left with a bona fide $\mathcal{N}=4$ superconformal field theory. If we take the limit in which we are always in the near horizon region, the geometry becomes exactly $AdS_5 \times S^5$ . A D3-brane has a self-dual charge under the self-dual NS 5-form flux. A stack of N of them gives rise to an integral flux of N over

S 5

Conformal boundary

A suitable Weyl transformation assures that AdS has a boundary. It turns out that this boundary is a conformal field theory having one less dimension. To make things more concrete, choose a particular coordinatization, the half-space coordinatization:

$ds^2 = (kz)^{-2}\left( dz^2 + \eta_{\mu\nu} \, dx^\mu \, dx^\nu \right).$

After a Weyl transformation ω = kz, we get

$\ ds^2 = dz^2 + \eta_{\mu\nu}\,dx^\mu \,dx^\nu,$

which has the Minkowski metric as the boundary at z = 0. This is called the conformal boundary.

Source fields

Basically, the correspondence runs as follows; if we deform the CFT by certain source fields by adding the source $\int d^dx J_{CFT}(x)\mathcal{O}(x)$ , this will be dual to an AdS theory with a bulk field J with the boundary condition

$\lim_{\text{boundary}} J \omega^{\Delta-d+k} = J_{\text{CFT}} \,$

where Δ is the conformal dimension of the local operator $\mathcal{O}$ and k is the number of covariant indices of $\mathcal{O}$ minus the number of contravariant indices. Only gauge-invariant operators are allowed.

Here, we have a dual source field for every gauge-invariant local operator we have.

Using generating functionals, the relation is expressed as

$\left\langle \mathcal{T}\left\{ \exp\left(\int d^dx J_{4D}(x)\mathcal{O}(x)\right) \right\} \right\rangle_{CFT} = Z_{AdS}\left[\lim_{\text{boundary}} J \omega^{\Delta-d+k} = J_{4D}\right]$

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The left hand side is the vacuum expectation value of the time-ordered exponential of the operators over the conformal field theory. The right hand side is the quantum gravity generating functional with the given conformal boundary condition. The right hand side is evaluated by finding the classical solutions to the effective action subject to the given boundary conditions.

Some AdS₅/CFT₄ examples

The stress-energy operator on the CFT side is dual to the transverse components of the metric on the AdS side. Since the stress-energy operator has a conformal weight of 4, the AdS metric ought to go as

ω - 2

, which is true for AdS. Also, the graviton has to be massless, just as it should.

If there is a global internal symmetry G on the CFT side, its Noether current J will be dual to the transverse components of a gauge connection for a Yang–Mills gauge theory with G as the gauge group on the AdS side. Since J has a conformal weight of 3, the dual Yang–Mills gauge boson ought to have zero bulk mass, just as it should.

A scalar operator with conformal weight Δ will be dual to a scalar bulk field with a bulk mass of $k\sqrt{\Delta(\Delta-4)}$ .

Particles

A CFT bound state of size r is dual to a bulk particle approximately localized at z=r.

Supersymmetry

AdS₅/CFT₄

We need to match up conformal supersymmetry in 4D with AdS supersymmetry in 5D. The symmetry supergroups in both cases happen to match up, as they should. There are $8\mathcal{N}$ real SUSY generators and the bosonic part consists of the conformal AdS group Spin(4,2) times an internal group $SU(\mathcal{N})_T \times U(1)_A$ . See superconformal algebra for more details.

For the case $\mathcal{N}=4$ , we have 32 real SUSY generators and an internal group $SU(4)_T\times U(1)_A$ . Now, $SU(4) \cong \mathrm{Spin}(6)$ and Spin(6) is the isometry group of S⁵ with spinorial fields. The bosonic spatial isometry group of $\mathrm{AdS}_5 \times S^5$ is $\mathrm{Spin}(4,2) \times \mathrm{Spin}(6)$ .

In $\mathcal{N}=(2,0)$ 10D SUSY, we have 32 real SUSY generators. In a generic curved spacetime, some of the SUSY generators will be broken but in the special compactification of $\mathrm{AdS}_5 \times S^5$ with both factors having the same radius, we are left 32 real unbroken generators. However, the bosonic spatial isometries with 55 generators in the flat case is now broken to $\mathrm{Spin}(4,2) \times \mathrm{Spin}(6)$ with 30 generators. $\mathcal{N}=(2,0)$ also has a

U (1) R

symmetry and this is identified with

U (1) A

The source of the curvature lies in the nonzero value of a self-dual 5-form flux belonging to the SUGRA multiplet. The integral of this 5-flux over S⁵ has to be a nonzero integer (if it's zero, we have no stress-energy tensor). Because the part of the 5-flux lying in AdS₅ contains a time component, it gives rise to negative curvature. The part of the 5-flux lying in S⁵ doesn't have a time component, and so, it gives rise to a positive curvature.

The SUGRA multiplet also contains a dilaton and axion field. They correspond to the gauge field coupling and theta angle of the dual superYang–Mills theory.

AdS₄/CFT₃

There are $4\mathcal{N}$ real SUSY generators with $\mathrm{Spin}(\mathcal{N})$ as the obligatory R-symmetry.

[edit]

11D $\mathcal{N}=1$ supergravity contains 32 real SUSY generators. There is a particular compactification, $\mathrm{AdS}_4 \times S^7$ , the Freund–Rubin compactification, which preserves all 32 real generators. The bosonic isometry group is reduced to $\mathrm{Spin}(3,2) \times \mathrm{Spin}(8)$ . After a Kaluza–Klein decomposition over S⁷, we get $\mathcal{N}=8$ SUSY. A 7-form magnetic flux is present over S⁷. Its integral over S⁷ has to be integer and nonzero.

Applications

A plethora of papers is found in the literature which uses techniques of ADS CFT to understand strongly coupled system such as RHIC and condensed matter systems.

References

^ For an authoritative review, see Ofer Aharony, Steven S. Gubser, Juan Maldacena, Hirosi Ooguri and Yaron Oz (2000). "Large N field theories, string theory and gravity". Physics Reports 323: 183–386. arXiv:hep-th/9905111. doi:10.1016/S0370-1573(99)00083-6. (Shorter lectures by Maldacena, based on that review.)
^ Juan M. Maldacena (1998). "The Large N limit of superconformal field theories and supergravity". Advances in Theoretical and Mathematical Physics 2: 231–252. arXiv:hep-th/9711200. Bibcode 1998AdTMP...2..231M.
^ S. S. Gubser, I. R. Klebanov and A. M. Polyakov (1998). "Gauge theory correlators from non-critical string theory". Physics Letters B428: 105–114. arXiv:hep-th/9802109. Bibcode 1998PhLB..428..105G.doi:10.1016/S0370-2693(98)00377-3.
^ Edward Witten (1998). "Anti-de Sitter space and holography". Advances in Theoretical and Mathematical Physics 2: 253–291. arXiv:hep-th/9802150. Bibcode 1998hep.th....2150W.
^ Lubos Motl, "Holography: Vasiliev's higher-spin theories and O(N) models", The Reference Frame, 20 February 2010.
^ Jacques Distler, "Rehren Duality", Musings, 16 October 2006 (accessed 22 July 2009).
^ Urs Schreiber, "Making AdS/CFT Precise", The n-Category Café, 22 July 2007 (accessed 22 July 2009).
^ Karl-Henning Rehren (2005). "QFT Lectures on AdS-CFT". In B. Dragovich et al.. Proceedings of the 3rd Summer School in Modern Mathematical Physics. 2004 Zlatibor Summer School on Modern Mathematical Physics. Belgrade: Institute of Physics. pp. 95–118. arXiv:hep-th/0411086.

External links

AdS/CFT correspondence on arxiv.org.
The Illusion of Gravity – Juan Maldacena, Scientific American.
University of Michigan Lecture
Professor Hirosi Ooguri's notes
Meeting on the subject
Database of articles; Supersymmetric Gauge Theories and the AdS/CFT Correspondence
Shadow World. The state of the AdS/CFT conjecture on its 10th anniversary. Science News magazine, November 17, 2007.

[hide]Quantum gravity

Central concepts

graviton · Planck scale · trans-Planckian problem · quantum foam · AdS/CFT correspondence · IR/UV mixing · causal patch · gravitational anomaly · Weinberg–Witten theorem

Black holes

black hole thermodynamics · black hole information paradox · holographic principle · Bousso's holographic bound · black hole complementarity · gravitational singularity

Quantum field theory
in curved spacetime

Hawking radiation · Unruh radiation · Bunch–Davies vacuum · semiclassical gravity · Casimir effect

Proposed theories

superstring theory	M-theory · supergravity · string field theory · Green-Schwarz mechanism · fuzzball · swampland

canonical quantum gravity	Wheeler–DeWitt equation · loop quantum gravity

Euclidean quantum gravity	Hartle–Hawking state

others	noncommutative geometry · causal dynamical triangulation · causal sets · twistor theory

Toy models

2+1D topological gravity · CGHS model · RST model · Liouville gravity · type 0 string theory · Jackiw–Teitelboim gravity

Applications

quantum cosmology

Others

quantum mechanics of time travel

Multiplication by Infinity

Friday, July 22, 2011

Cat Burglar Identified Using Modern Technology

Contents

Types of ranges

Spectral range

Intensity range

Biological night vision

Night vision technologies

Night glasses

[edit]Active infrared

[edit]Laser range gated imaging

Thermal vision

Image intensifier

Night vision devices

Automotive night vision

See also

Patents

References

External links

Thursday, July 21, 2011

Space Shuttle Program Over, Next Come the Pink Slips

Tuesday, July 19, 2011

Optical Illusions

Monday, July 18, 2011

The Non-Witten Half of IAS - Princeton

Contents

Maldacena's example

Conformal boundary

Source fields

Some AdS₅/CFT₄ examples

Particles

Supersymmetry

AdS₅/CFT₄

AdS₄/CFT₃

Applications

Other topics

See also

References

External links

Friday, July 22, 2011

Cat Burglar Identified Using Modern Technology

Contents

Types of ranges

Spectral range

Intensity range

Biological night vision

Night vision technologies

Night glasses

[edit]Active infrared

[edit]Laser range gated imaging

Thermal vision

Image intensifier

Night vision devices

Automotive night vision

See also

Patents

References

External links

Thursday, July 21, 2011

Space Shuttle Program Over, Next Come the Pink Slips

Tuesday, July 19, 2011

Optical Illusions

Monday, July 18, 2011

The Non-Witten Half of IAS - Princeton

Contents

Maldacena's example

Conformal boundary

Source fields

Some AdS5/CFT4 examples

Particles

Supersymmetry

AdS5/CFT4

AdS4/CFT3

Applications

Other topics

See also

References

External links

Some AdS₅/CFT₄ examples

AdS₅/CFT₄

AdS₄/CFT₃