Optics Research Papers - Academia.edu (original) (raw)

We propose a new sensing device based on all-optical nano-objects placed in a suspended periodic array. We demonstrate that the intensity-based sensing mechanism can measure environment refractive index change of the order of 1.8×10−6,... more

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- Optics

In recent years, several New England projects have promoted professional development and curriculum design in optics and photonics. Funded in part by the Advanced Technological Education (ATE) program of the National Science Foundation (NSF), these projects have prepared middle and high school teachers, college faculty and career counselors from more than 100 New England institutions to introduce fiber optics, telecommunications and photonics technology education. Four of these projects will be discussed here: (1) The New England Board of Higher Education's (NEBHE) Fiber Optics Technology Education Project, (FOTEP) was designed to teach fiber optics theory and to provide laboratory experiences at the secondary and postsecondary levels. (2) Springfield Technical Community College's Northeast Center for Telecommunications Technologies (NCTT) is developing curricula and instructional materials in lightwave, networking and wireless telecommunications technologies. (3) The Harvard-Smithsonian Center for Astrophysics project ComTech developed a 12-week, hands-on curriculum and teaching strategies for middle and high school science and technology teachers in telecommunications and focused on optical communication (fiber optics). (4) NEBHE's project PHOTON is preparing middle, secondary and postsecondary instructors to introduce theory and laboratory experiences in photonics, including geometric and wave optics as well as principles of lasers and photonics applications.

- by Nicholas Massa
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- Optics, Curriculum Design, Fiber Optics, Telecommunications

A new method of designing nonimaging concentrators is presented and two new types of concentrators are developed. The first is an aspheric lens, and the second is a lens-mirror combination. A ray tracing of three-dimensional concentrators (with rotational symmetry) is also done, showing that the lens-mirror combination has a total transmission as high as that of the full compound parabolic concentrators, while their depth is much smaller than the classical parabolic mirror-nonimaging concentrator combinations. Another important feature of this concentrator is that the optically active surfaces are not in contact with the receiver, as occurs in other nonimaging concentrators in which the rim of the mirror coincides with the rim of the receiver.

- by Juan C Miñano
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- Mechanical Engineering, Optics, Ray Tracing, Applied Optics
- by Elvira Bojilova
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- Optics, Print Culture, Art History, Art Theory

— This paper aims to develop a cost-effective device to make a star tracking system using an Arduino DUE [6] and Stellarium [1]. It also includes the processing of the image via MATLAB Ⓡ [2] that is obtained from the telescope in near... more

- by Saswata Dasgupta and +2
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- Optics, Image Processing, Arduino, Telescope Making

This paper reports on the use of cellulose paper simultaneously as electrolyte, separation of electrodes, and physical support of a rechargeable battery. The deposition on both faces of a paper sheet of metal or metal oxides thin layers with different electrochemical potentials, respectively as anode and cathode, such as Cu and Al, lead to an output voltage of 0.70 V and a current density that varies between 150 nA/cm 2 and 0.5 mA/cm 2 , subject to the paper composition, thickness and the degree of OH x species adsorbed in the paper matrix. The electrical output of the paper battery is independent of the electrodes thickness but strongly depends on the atmospheric relative humidity (RH), with a current density enhancement by more than 3 orders of magnitude when RH changes from 60% to 85%. Besides flexibility, low cost, low material consumption, environmental friendly, the power output of paper batteries can be adapted to the desired voltage-current needed, by proper integration. A 3-V prototype was fabricated to control the ON/OFF state of a paper transistor.

- by Bruno Bras
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- Optics, Medical Imaging, Fiber Optics, Telecommunications
- by Fred Zheng
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- Optics
- by Lina Cardenas
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- Optics
- by vijay katta
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- Electrical Engineering, Control Systems Engineering, Applied Mathematics, Physics
- by Arsh Khan
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- Electrical Engineering, Applied Mathematics, Optics, Solid State Physics

We have demonstrated a one-dimensional array of individually addressable electrowetting tunable liquid lenses that compensate for more than one wave of phase distortion across a wavefront. We report a scheme for piston control using tunable liquid lens arrays in volume-bound cavities that alter the optical path length without affecting the wavefront curvature. Liquid lens arrays with separately tunable focus or phase control hold promise for laser communication systems and adaptive optics.

- by Robert Niederriter
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- Mechanical Engineering, Optics, Applied Optics, Optical physics

Evaluar el impacto de las lentes de contacto desechables en la calidad visual, comparando aberraciones ópticas, en ojos miopes, con y sin lentes de contacto. Método: Las aberraciones ópticas se midieron mediante el sistema del Trazado de Rayos Láser, el cuál es un método de medida objetivo, sobre un conjunto de 18 ojos, en 3 condiciones diferentes: a ojo desnudo, ojo más lentes de prueba, ojo con lentes de contacto desechables. Resultados: Existe una alta variabilidad entre sujetos, pero la tendencia general es que las lentes de prueba no modifican las aberraciones, mientras que las lentes de contacto tienden a incrementar las aberraciones oculares para pupilas grandes cerca de un 40% en promedio. Sin embargo tal incremento es mucho menor para pupilas más pequeñas. Conclusión: Este estudio revela que no se produce efectos significativos en la calidad de visión en pacientes que usan lentes de contacto desechables bajo condiciones de luz diurna, así como un pequeño descenso en visión nocturna. Palabras clave: Aberraciones, lentes de contacto blandas, método de trazado de Rayos.

- by ubaid ahmed
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- Physics, Optics, Art, Contact Lenses

The use of bacteriorhodopsin (BR) as an active layer in write-once-read-many optical storage is presented. This novel feature of BR materials may be used on a wide variety of substrates, among them transparent substrates but also paper and plastics. The physical basis of the recording process is polarization-sensitive two-photon absorption. As an example for this new BR application, an identification card equipped with an optical recording strip is presented, which has a capacity of about 1 MB of data. The recording density currently used is 125 kB/cm 2 , which is far from the optical limits but allows operation with cheap terminals using plastic optics. In the examples given, data are stored in blocks of 10 kB each. A special optical encryption procedure allows the stored data to be protected from unauthorized reading. The molecular basis of this property is again the polarization-sensitive recording mechanism. The unique combination of optical storage, photochromism, and traceability of the BR material is combined on the single-molecule level. BR introduces a new quality of storage capability for applications with increased security and anticounterfeiting requirements.

- by Norbert Hampp
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- Optics, Biomedical Engineering, Photochemistry, Computer Security
- by Mario Armenise
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- Applied Mathematics, Physics, Acoustics, Optics

We present both a computational and an experimental approach to the problem of biological aerosol characterization, joining the expertises reached in the field of theoretical optical scattering by complex, arbitrary shaped particles... more

- by Rosalba Saija
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- Optics, Pattern Recognition, Feature Extraction, Electromagnetic Field

The maximum distance to which the secondary mirror can be moved with respect to its primary in a true Cassegrain telescope with limited image deterioration is found to be proportional to the fourth power of the focal ratio of the primary mirror. This limit is independent of all other parameters describing the system when the magnification of the secondary is greater than about 3.

- by Roger Clark
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- Mechanical Engineering, Optics, Medical Imaging, Fiber Optics

It is shown that the Fraunhofer diffraction pattern of a tilted aperture screen can be interpreted as a ' monocular view of the Ewald sphere. Two of those patterns recorded at opposite tilting angles are used to give a stereoscopic impression of the Ewald sphere. Experimental results are shown, and the approximations involved are discussed.

- by R. Bamler
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- Mechanical Engineering, Optics, Medical Imaging, Fiber Optics
- by Ahmad Amjadi
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- Optics, Optical physics, Probability Density Function, Electric Field

An hybrid atomic force-scanning near-field optical microscope (AFM-SNOM) has been realized starting from a home-built AFM. The instrument uses a tetrahedral SiN tip for force and near field detection and is designed to provide, besides simple imaging, a full three-dimensional (3-D) mapping of force, friction and light intensity on the sample. High-resolution optical images of dielectric samples are presented together with curves describing the behavior of the collected optical intensity as a function of tip-object distance. AFM images and forcedistance curves are reported as well and are compared with those obtained from the optical channel. Subwavelength features of the samples can be easily appreciated in both kinds of images, and the refractive index of the object can be computed from the attenuation constant of the tunneling light detected by the tip, with the AFM curve providing a convenient way of detecting the contact point. The spatial resolution of this kind of measurement is far better than that obtainable with any other index-measuring device. Homogeneous glass samples as well as monomode channel waveguides were analyzed in our experiments. The refractive index of several different prisms, made either of BK7 (n = 1:519 at = 532 nm) or of SF58 (n = 1:932) glass, could be measured with our near-field technique. As for the channel waveguides, the accuracy of our measurements lets us detect their presence and lateral extension in the substrate but is not yet sufficient to allow the reconstruction of their index profile.

- by franco quercioli
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- Optics, Medical Imaging, Fiber Optics, Telecommunications

A theory is presented which relates the minimum detectable contrast level for an object in the presence of noise to the statistics of the speckle. Consideration is given to smoothing of the noise by multiple looks and by area. Measurements of the minimum detectable contrast are made for two types of speckle noise. First, a coherent, plane wave is added to an ideal diffuse wave and the threshold of detection is established as a function of the beam ratio. Secondly, these results are compared to the technique of speckle smoothing using an N-fold intensity superposition of fully developed theory is observed.

- by Nicholas George
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- Optics, Medical Imaging, Fiber Optics, Telecommunications

The paper presents the research results of pegmatites from Karelian deposits. The aim of this research was to find
selective features of microcline, biotite, muscovite, quartz, and plagioclase for determining the opportunity of their
selection from original ore by optical sorting method which based on color differences of analyzed objects. Studies have
shown that the solution of the problem of these minerals separation is possible in 3 stages. In the first stage groups
"microcline", "muscovite and biotite", "quartz and plagioclase," are separated according to the values of channels hue H
and lightness L in the color model HLS. In the second stage biotite and muscovite are separated from each other by the
values of the channel hue H and saturation S. Finally, in the third stage couple "quartz - plagioclase" are separated. But
these minerals are indistinguishable from each other by color, so it's proposed to separate them by selective feature
"surface structure".

- by Artem Alekhin and +1
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- Optics, Image Processing, Mining, Optical Sorting

Wavelength scanning interferometry is a known technique to precisely measure the surface topography and plate thickness for transparent materials, such as glass. However, conventional methods have some problems in the practical applications that they require precise sample surface position adjustments relative to the reference surface, and highly accurate linear wavelength scanning. We propose a leastsquares model-fitting algorithm which estimates the surface topography and plate thickness from the interferograms obtained by arbitrary wavelength shift. The LD wavelength tuned by temperature control is measured by a wavelength meter, and the measured values are used in the data analysis. The validity of the proposed method is proved by computer simulations and actual experiments. The atual test results showed good agreement with those by a conventional method, and a onesigma repeatability of 2 nm was obtained.

- by Katsuichi Kitagawa
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- Optics, Interferometry
- by Sead Doric and +1
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- Engineering, Physics, Optics, Semiconductor Lasers

In the past decades, spectral-domain optical coherence tomography (SD-OCT) has transformed into a widely popular imaging technology which is used in many research and clinical applications. Despite such fast growth in the field, the technology has not been readily accessible to many research laboratories either due to the cost or inflexibility of the commercially available systems or due to the lack of essential knowledge in the field of optics to develop custom-made scanners that suit specific applications. This paper aims to provide a detailed discussion on the design and development process of a typical SD-OCT scanner. The effects of multiple design parameters, for the main optical and optomechanical components, on the overall performance of the imaging system are analyzed and discussions are provided to serve as a guideline for the development of a custom SD-OCT system. While this article can be generalized for different applications, we will demonstrate the design of a SD-OCT s...

- by Israel de la Rosa
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- Computer Science, Optics

We discuss an optical system that encodes an input signal to a polarization state, using a spatial light modulator (SLM). Using two SLMs the optical system multiplexes two 2D signals in the polarization domain, and we demonstrate the multiplexing of two binary images. The encryption and decryption of two binary images using an XOR operation is also presented.

- by john sheridan
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- Mechanical Engineering, Computer Science, Optics, Encryption

The James Webb Space Telescope (JWST) Optical Simulation Testbed (JOST) is a tabletop workbench to study aspects of wavefront sensing and control for a segmented space telescope, including both commissioning and maintenance activities. JOST is complementary to existing optomechanical testbeds for JWST (e.g. the Ball Aerospace Testbed Telescope, TBT) given its compact scale and flexibility, ease of use, and colocation at the JWST Science & Operations Center. We have developed an optical design that reproduces the physics of JWST's three-mirror anastigmat using three aspheric lenses; it provides similar image quality as JWST (80% Strehl ratio) over a field equivalent to a NIRCam module, but at HeNe wavelength. A segmented deformable mirror stands in for the segmented primary mirror and allows control of the 18 segments in piston, tip, and tilt, while the secondary can be controlled in tip, tilt and x, y, z position. This will be sufficient to model many commissioning activities, to investigate field dependence and multiple field point sensing & control, to evaluate alternate sensing algorithms, and develop contingency plans. Testbed data will also be usable for cross-checking of the WFS&C Software Subsystem, and for staff training and development during JWST's five-to ten-year mission.

- by Mamadou Moustapha N'diaye
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- Aerospace Engineering, Algorithms, Physics, Optics

Tohoku University researchers have revealed more details about omnidirectional photoluminescence (ODPL) spectroscopy-a method for probing semiconducting crystals with light to detect defects and impurities. [32] Researchers have measured an optical clock's ticking with record-breaking accuracy while also showing the clock can be operated with unprecedented consistency. [31] The optical tweezer is revealing new capabilities while helping scientists understand quantum mechanics, the theory that explains nature in terms of subatomic particles. [30] In the perspective, Gabor and Song collect early examples in electron metamaterials and distil emerging design strategies for electronic control from them. [29] Lawrence Livermore National Laboratory (LLNL) researchers are working to make better electronic devices by delving into the way nanocrystals are arranged inside of them. [28] Self-assembly and crystallisation of nanoparticles (NPs) is generally a complex process, based on the evaporation or precipitation of NP-building blocks. [27] New nanoparticle-based films that are more than 80 times thinner than a human hair may help to fill this need by providing materials that can holographically archive more than 1000 times more data than a DVD in a 10-by-10-centimeter piece of film. [26] Researches of scientists from South Ural State University are implemented within this area. [25] Following three years of extensive research, Hebrew University of Jerusalem (HU) physicist Dr. Uriel Levy and his team have created technology that will enable computers and all optic communication devices to run 100 times faster through terahertz microchips. [24] When the energy efficiency of electronics poses a challenge, magnetic materials may have a solution. [23] An exotic state of matter that is dazzling scientists with its electrical properties, can also exhibit unusual optical properties, as shown in a theoretical study by researchers at A*STAR. [22]

- by George Rajna
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- Optics
- by Armando Marques-Guedes
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- History, Cultural History, Sociology, Political Sociology

A theory of the influence of measurement conditions on temperature measurement accuracy with infrared systems has been recently presented. A comparison study of the shortwave 13-5-µm2 and longwave 18-12-µm2 measuring IR cameras was conducted on the basis of this theory. The results of the simulations show that the shortwave systems in typical measurement conditions generally offer better accuracy in temperature measurement than do the longwave systems. Some experiments that use a commercially available IR camera were carried out to verify the theory. The results of these experiments and a discussion about the theory limitations are presented.

- by Krzysztof Chrzanowski
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- Mechanical Engineering, Optics, Medical Imaging, Remote Sensing

Drawing of the hollow all-polymer Bragg fibers based on PMMA/PS and PVDF/PC materials combinations are demonstrated. Hole collapse during drawing effects the uniformity of a photonic crystal reflector in the resultant fiber. We first investigate how the core collapse effects fiber transmission properties. We then present modelling of fluid dynamics of hollow multilayer polymer fiber drawing. Particularly, hole collapse during

- by Charles Dubois
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- Optics, Fluid Dynamics, Photonic Crystal, Optical physics

We present a novel and simple method to measure both the value of the second-order dispersion coefficient and the nonlinear coefficient in optical fibers. This method is based on the higher-order soliton-effect pulse compression phenomenon and is valid for dispersion values greater than 0.5 ps/km/nm. A non-zero dispersion-shifted fiber, a standard single-mode fiber and a highly-dispersive highly-nonlinear fiber have been measured using this method.

- by Achille Monteville and +1
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- Optics, Higher Order Thinking, Pulse Compression, Optical physics

Visible Laser Light Communication System (VLLC) is a wireless communication system, using laser as the medium. In the data transfer process, it is possible to have optical interference where 2 laser beams coincide with one point on the reflector. Research on the effect of laser source interference has been carried out by several researchers including mitigation actions to reduce its effects. This experiment uses 2 optical distance sensors that produce a laser with a wavelength of 650 nm with a power <=4.1 mW and with the direction of the laser beam both of them cross each other. To determine the effect of the interference of two laser beams when crossing the communication process in the visible light communication system, a reflector is used which can capture the two laser beams and the reflector can be shifted gradually so that a condition can be obtained where the two laser beams meet at one point. From the measurements made at the points after the laser beam crossing, the meas...

- by Pranoto Laksono
- •
- Materials Science, Optics, Laser, Optoelectronics

The S-Bend structures are heavily exploited to join optical components. Reducing the power loss caused by the curve is the main objective in the design step of these components. However integrated optical circuits require S-Bend waveguide to be low loss and compact sized. In this paper, we present a contribution to link the curved structure to the straight waveguide by using the simulated bend function available in the Beam propagation tool of the Rsoft commercial software package. Simulation results confirm that this approach allows a reduction of the size of the curved structure with offset with relatively minimum of losses for photonic field.

- by BRIK Fatima
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- Optics, Integrated Optics, Offset, Radius of Curvature

Two twelve-channel arrays based on surface-etched slot gratings, one with nonuniformly spaced slots and another with uniformly spaced slots are presented for laser operation in the O-band. A wavelength tuning range greater than 40 nm, with a side-mode suppression ratio (SMSR) > 40 dB over much of this range and output power greater than 20 mW, was obtained for the array with non-uniform slots over a temperature range of 15°C-60°C. The introduction of multiple slot periods, chosen such that there is minimal overlap among the side reflection peaks, is employed to suppress modes lasing one free spectral range (FSR) from the intended wavelength. The tuning range of the array with uniformly spaced slots, on the other hand, was found to be discontinuous due to mode-hopping to modes one FSR away from the intended lasing mode which are not adequately suppressed. Spectral linewidth was found to vary across devices with the lowest measured linewidths in the range of 2 MHz to 4 MHz.

- by Nicolás Abadía and +1
- •
- Electrical Engineering, Physics, Optics, Optical Fiber Communications
- by Nanguang Chen
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- Optics
- by Jabez McClelland
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- Applied Mathematics, Optics, Medical Imaging, Fiber Optics

We have developed a super compact optical fluorescence spectrometer. Our innovative design combines advantages of guided wave planar optics and free-space microoptics. This innovation allows for miniaturization that is not achievable with pure planar or pure free-space optics. A prototype device has volume of its optical part below 1cm3. The spectrometer covers 450nm-650nm spectral range, and provides spectral resolution of

- by G. Auner
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- Optics, Image Processing, Lab On A Chip, Free Space Optics

Received XX Month XXXX; revised XX Month, XXXX; accepted XX Month XXXX; posted XX Month XXXX (Doc. ID XXXXX); published XX Month XXXX The simultaneous measurement of numerical aperture (NA) and mode field diameter (MFD) of single-mode fibers (SMF) was performed on several commercial fibers by means of digital image processing of the output light projected into a screen. In addition, the changes induced by core diffusion in an ultra-high (UH) NA fiber at several heat depositions from a CO2 laser source were measured. The measurement method demonstrated to be useful to monitor the adiabaticity of this process, by taking the product of the NA and MFD in order to verify if it remains constant. The method provides a cheap alternative to measure these optical fiber parameters by using simple optomechanical elements, readily available smartphone camera and can be easily implemented in the laboratory.

- by Daniel Toral
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- Optics

We model the double phase-conjugate mirror (DPCM) as a function of time, the average direction of propagation of the two beams forming the DPCM, and one transverse coordinate. Calculations show that the conjugation fidelity and reflectivity have different dependencies on the photorefractive coupling coefficient times length; the fidelity turns on abruptly with a threshold, whereas the reflectivity increases smoothly. The DPCM behaves as an oscillator at and above threshold: the time required for the reflectivity to reach the steady state dramatically slows down near threshold (like critical slowing down in lasers); above threshold the DPCM is self-sustaining even if the random noise terms used to start the process are set to zero. A decrease in the noise level improves the fidelity but increases the response time. The use of unbalanced input beam ratios results in asymmetric conjugation such that the fidelity obtained on the side of the weaker input beam is significantly reduced. The slowing down diminishes with increasing noise level or unbalanced input intensities.

- by Doruk Engin and +1
- •
- Applied Mathematics, Optics, Medical Imaging, Fiber Optics

A coherent processor is presented which is capable of performing a large class of 1-D linear space-variant operations. The only components of the processor are a 1-D input, a mask whose transmittance is specified by the desired linear operation, and an output plane. Compared with other 1-D processors, this processor has advantages of real space compactness and total elimination of vignetting. Experimental results are presented for the specific operations of convolution and spectrum scaling.

- by John F. Walkup
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- Mechanical Engineering, Optics, Medical Imaging, Fiber Optics

An experiment to investigate the potential of a laser-induced plasma method for determining concrete compressive strength was conducted by focusing a Nd:YAG laser on concrete samples with different degrees of compressive strength. This technique was developed in light of the role of the shock wave in the generation of a laser-induced plasma. It was found that the speed of the shock front depends on the hardness of the sample. It was also found that a positive relationship exists between the speed of the shock front and the ionization rate of the ablated atoms. Hence, the ratio of the intensity between the Ca(II) 396.8 nm and Ca(I) 422.6 nm emission lines detected from the laser-induced plasma can be used to examine the hardness of the material. In fact, it was observed that the ratio changes with respect to the change in the concrete compressive strength. The findings also show that the ratio increases with time after the cement is mixed with water.

- by Nasrullah Idris
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- Mechanical Engineering, Optics, Analytical Chemistry, Medical Imaging

We propose and demonstrate a 10 Gb/s wavelength division multiplexed passive optical network (WDM-PON) where subcarriers are employed to transmit the downstream data and optical carriers of the downlink subcarrier modulated (SCM) lights are reused to injection lock Fabry-Perot laser diodes (FP-LDs) for uplink transmission. Experiment results show that a very good BER performance can be achieved for both uplink and downlink at 10 Gb/s. The impact of optical carrier to subcarrier ratio and wavelength mismatching is also investigated.

- by Wen-De Zhong
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- Optics, Optical physics, Fabry Perot, Electrical And Electronic Engineering

We demonstrate the transfer of information encoded as orbital angular momentum (OAM) states of a light beam. The transmitter and receiver units are based on spatial light modulators, which prepare or measure a laser beam in one of eight pure OAM states. We show that the information encoded in this way is resistant to eavesdropping in the sense that any attempt to sample the beam away from its axis will be subject to an angular restriction and a lateral offset, both of which result in inherent uncertainty in the measurement. This gives an experimental insight into the effects of aperturing and misalignment of the beam on the OAM measurement and demonstrates the uncertainty relationship for OAM.

An external reflection scanning near-field optical microscope with shear force regulation of the tip-surface distance is described. Near-field optical and shear force topographical images are compared for various samples. It is shown that the most important correlative relationships between these images can be deduced from symmetry considerations. The possibility of extracting additional information from the optical images is demonstrated on images of human blood cells.

- by Igor Smolyaninov
- •
- Mechanical Engineering, Optics, Medical Imaging, Fiber Optics

The generation of terahertz (THz) transients in photoconductive emitters has been studied by varying the spatial extent and density of the optically excited photocarriers in asymmetrically excited, biased low-temperature-grown GaAs antenna structures. We find a pronounced dependence of the THz pulse intensity and broadband (>6.0 THz) spectral distribution on the pump excitation density and simulate this with a three-dimensional carrier dynamics model. We attribute the observed variation in THz emission to changes in the strength of the screening field.

- by J. Lloyd-Hughes
- •
- Optics, Quantum Physics, Terahertz, Density dependence

We analyze interactions between moving dissipative solitons in one- and multidimensional cubic-quintic complex Ginzburg-Landau equations with a linear potential and effective viscosity. The interactions between the solitons are analyzed by using balance equations for the energy and momentum. We demonstrate that the separation between two solitons forming a bound state decreases with the increase of the slope of the linear potential.

- by Boris Malomed
- •
- Optics, Quantum Physics, Optical physics, Electrical And Electronic Engineering

This paper reports on a study that was designed to investigate the knowledge about image formation exhibited by students following instruction in geometrical optics in an activity-based college physics course for prospective elementary teachers. Students were interviewed individually, using several tasks involving simple apparatus (plane and curved mirrors, lenses, and prisms). The diagrams drawn by the students and the verbal comments they made provide evidence that their knowledge can be described as an intermediate state, a hybridization of preinstruction knowledge (which is dominated by a holistic conceptualization) and formal physics knowledge. We infer from our data the core concepts and main ideas of the postinstruction students' hybrid knowledge. Finally, by comparing preinstruction and formal physics conceptualizations of image formation we argue that a strong type of knowledge restructuring (in the sense

- by Dan Roginsky
- •
- Physics, Optics, Science Education, Higher Education

We present a model of energy consumption in IP networks. Using this model, we identify energy ldquohotspotsrdquo and estimate how energy consumption will grow with increasing network capacity. Todaypsilas Internet uses less than 1% of the available electricity supply. However, network energy consumption could grow substantially as access rates increase.

- by Kerry Hinton
- •
- Optics, Medical Imaging, Fiber Optics, Telecommunications