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Articles 121 - 150 of 2524
Full-Text Articles in Physical Sciences and Mathematics
Design And Implementation Of A Practical Security-Conscious Electronic Polling System, Lorrie Cranor, Ron Cytron
Design And Implementation Of A Practical Security-Conscious Electronic Polling System, Lorrie Cranor, Ron Cytron
Lorrie F Cranor
We present the design and implementation of Sensus, a practical, secure and private system for conducting surveys and elections over computer networks. Expanding on the work of Fujioka, Okamoto, and Ohta, Sensus uses blind signatures to ensure that only registered voters can vote and that each registered voter only votes once, while at the same time maintaining voters' privacy. Sensus allows voters to verify independently that their votes were counted correctly, and anonymously challenge the results should their votes be miscounted. We outline seven desirable properties of voting systems and show that Sensus satisfied these properties well, in some cases …
“I Read My Twitter The Next Morning And Was Astonished” A Conversational Perspective On Twitter Regrets, Manya Sleeper, Justin Cranshaw, Patrick Kelley, Blase Ur, Alessandro Acquisti, Lorrie Cranor, Norman Sadeh
“I Read My Twitter The Next Morning And Was Astonished” A Conversational Perspective On Twitter Regrets, Manya Sleeper, Justin Cranshaw, Patrick Kelley, Blase Ur, Alessandro Acquisti, Lorrie Cranor, Norman Sadeh
Lorrie F Cranor
We present the results of an online survey of 1,221 Twitter users, comparing messages individuals regretted either saying during in-person conversations or posting on Twitter. Participants generally reported similar types of regrets in person and on Twitter. In particular, they often regretted messages that were critical of others. However, regretted messages that were cathartic/expressive or revealed too much information were reported at a higher rate for Twitter. Regretted messages on Twitter also reached broader audiences. In addition, we found that participants who posted on Twitter became aware of, and tried to repair, regret more slowly than those reporting in-person regrets. …
Forecasting Climate Change Impacts On The Distribution Of Wetland Habitat In The Midwestern United States, Heath Garris, Randall Mitchell, Lauchlan Fraser, Linda Barrett
Forecasting Climate Change Impacts On The Distribution Of Wetland Habitat In The Midwestern United States, Heath Garris, Randall Mitchell, Lauchlan Fraser, Linda Barrett
Randall J. Mitchell
Shifting precipitation patterns brought on by climate change threaten to alter the future distribution of wetlands. We developed a set of models to understand the role climate plays in determining wetland formation on a landscape scale and to forecast changes in wetland distribution for the Midwestern United States. These models combined 35 climate variables with 21 geographic and anthropogenic factors thought to encapsulate other major drivers of wetland distribution for the Midwest. All models successfully recreated a majority of the variation in current wetland area within the Midwest, and showed that wetland area was significantly associated with climate, even when …
What Students Think And How They Really Perform In Chemistry, Ross Hudson
What Students Think And How They Really Perform In Chemistry, Ross Hudson
Dr Ross Hudson
This research was part of a larger study into student performance in senior chemistry with regard to question type and content. This paper examines student perceptions about question type and context and compares these perceptions to actual performance. How students perceive different types of questions and how it influences their self-belief and motivation were the focus of this study. Student responses to different styles or types of questions have been well researched over time. In this study Year 11 chemistry students were quizzed about their preferences to Multiple-Choice questions and Open Response question types and how the presence of each …
A Better Direction For California's Climate Change Policy, David Gamage, Mark Gergen
A Better Direction For California's Climate Change Policy, David Gamage, Mark Gergen
Mark P. Gergen
No abstract provided.
Few-Boson Processes In The Presence Of An Attractive Impurity Under One-Dimensional Confinement, Nirav Mehta, Connor Morehead
Few-Boson Processes In The Presence Of An Attractive Impurity Under One-Dimensional Confinement, Nirav Mehta, Connor Morehead
Nirav P Mehta
We consider a few-boson system confined to one dimension with a single distinguishable particle of lesser mass. All particle interactions are modeled with δ functions, but due to the mass imbalance the problem is nonintegrable. Universal few-body binding energies, atom-dimer and atom-trimer scattering lengths, are all calculated in terms of two parameters, namely the mass ratio mL/mH, and ratio gHH/gHL of the δ-function couplings. We specifically identify the values of these ratios for which the atom-dimer or atom-trimer scattering lengths vanish or diverge. We identify regions in this parameter space in which various few-body inelastic processes become energetically allowed. In …
Managing People And Technology: The Challenges In Csr And Energy Efficient Shipping, Momoko Kitada, Aykut Ölçer
Managing People And Technology: The Challenges In Csr And Energy Efficient Shipping, Momoko Kitada, Aykut Ölçer
Aykut Ölçer
This paper addresses the challenges of managers in the shipping industry to implement energy efficient measures in ship operations and their roles of managing both people and technology under the fulfilment of their corporate social responsibility (CSR). An increasing pressure on shipping companies to concern about marine environment, including energy efficiency, has led managers to consider CSR as their ethical business practices. It is an accepted norm that shipping is generally the most environmentally friendly mode of transport in terms of CO2 produced per ton nautical mile. Despite an extensive amount of research available to improve energy efficiency in shipping, …
Earth Ethics, James Martin-Schramm, Daniel Spencer, Laura A. Stivers
Earth Ethics, James Martin-Schramm, Daniel Spencer, Laura A. Stivers
Laura Stivers
Imaging Diffractometer With Holographic Encoding Enhancements For Laser Sensing And Characterization, Joesph Binford, Bradley Duncan, Jack Parker, Elizabeth Beecher, Mark Delong
Imaging Diffractometer With Holographic Encoding Enhancements For Laser Sensing And Characterization, Joesph Binford, Bradley Duncan, Jack Parker, Elizabeth Beecher, Mark Delong
Bradley D. Duncan
What is believed to be a novel holographic optical encoding scheme has been developed to enhance the performance of laser sensors designed for the measurement of wavelength and angular trajectory. A prototype holographic imaging diffractometer has been created to reconstruct holographic cueing patterns superimposed in the focal plane of wide-angle scene imagery. Based on experimental pattern metric measurements at the focal plane, a theoretical model is used to compute the laser source wavelength and its apparent propagation direction within the sensor's field of view. The benefits of incorporating holographic enhancements within an imager-based sensor architecture are discussed.
Optical Sparse Aperture Imaging, Nicholas Miller, Matthew Dierking, Bradley Duncan
Optical Sparse Aperture Imaging, Nicholas Miller, Matthew Dierking, Bradley Duncan
Bradley D. Duncan
The resolution of a conventional diffraction-limited imaging system is proportional to its pupil diameter. A primary goal of sparse aperture imaging is to enhance resolution while minimizing the total light collection area; the latter being desirable, in part, because of the cost of large, monolithic apertures. Performance metrics are defined and used to evaluate several sparse aperture arrays constructed from multiple, identical, circular subapertures. Subaperture piston and∕or tilt effects on image quality are also considered. We selected arrays with compact nonredundant autocorrelations first described by Golay. We vary both the number of subapertures and their relative spacings to arrive at …
Monte Carlo Simulation Of Multiple Photon Scattering In Sugar Maple Tree Canopies, Michael Greiner, Bradley Duncan, Matthew Dierking
Monte Carlo Simulation Of Multiple Photon Scattering In Sugar Maple Tree Canopies, Michael Greiner, Bradley Duncan, Matthew Dierking
Bradley D. Duncan
Detecting objects hidden beneath forest canopies is a difficult task for optical remote sensing systems. Rather than relying upon the existence of gaps between leaves, as other researchers have done, our ultimate goal is to use light scattered by leaves to image through dense foliage. Herein we describe the development of a Monte Carlo model for simulating the scattering of light as it propagates through the leaves of an extended tree canopy. We measured several parameters, including the gap fraction and maximum leaf-area density, of a nearby sugar maple tree grove and applied them to our model. We report the …
Improving Mid-Frequency Contrast In Sparse Aperture Optical Imaging Systems Based Upon The Golay-9 Array, Andrew Stokes, Bradley Duncan, Matthew Dierking
Improving Mid-Frequency Contrast In Sparse Aperture Optical Imaging Systems Based Upon The Golay-9 Array, Andrew Stokes, Bradley Duncan, Matthew Dierking
Bradley D. Duncan
Sparse aperture imaging systems are capable of producing high resolution images while maintaining an overall light collection area that is small compared to a fully filled aperture yielding the same resolution. This is advantageous for applications where size, volume, weight and/or cost are important considerations. However, conventional sparse aperture systems pay the penalty of reduced contrast at midband spatial frequencies. This paper will focus on increasing the midband contrast of sparse aperture imaging systems based on the Golay-9 array. This is one of a family of two-dimensional arrays we have previously examined due to their compact, non-redundant autocorrelations. The modulation …
Periodic, Pseudo-Noise Waveforms For Multi-Function Coherent Ladar, Matthew Dierking, Bradley Duncan
Periodic, Pseudo-Noise Waveforms For Multi-Function Coherent Ladar, Matthew Dierking, Bradley Duncan
Bradley D. Duncan
We report the use of periodic, pseudonoise waveforms in a multifunction coherent ladar system. We exploit the Doppler sensitivity of these waveforms, as well as agile processing, to enable diverse ladar functions, including high range resolution imaging, macro-Doppler imaging, synthetic aperture ladar, and range-resolved micro-Doppler imaging. We present analytic expressions and simulations demonstrating the utility of pseudonoise waveforms for each of the ladar modes. We also discuss a laboratory pseudonoise ladar system that was developed to demonstrate range compression and range-resolved micro-Doppler imaging, as well as the phase recovery common to each of the coherent modes.
Holographic Aperture Ladar, Bradley Duncan, Matthew Dierking
Holographic Aperture Ladar, Bradley Duncan, Matthew Dierking
Bradley D. Duncan
Holographic aperture ladar is a variant of synthetic aperture ladar that seeks to increase cross-range scene resolution by synthesizing a large effective aperture through the motion of a smaller receiver and through the subsequent proper phasing and correlation of the detected signals in postprocessing. Unlike in conventional synthetic aperture ladar, however, holographic aperture ladar makes use of a two- dimensional translating sensor array, not simply a translating point detector. Also unlike in conventional synthetic aperture ladar, holographic aperture images will be formed in the two orthogonal cross-range dimensions parallel and perpendicular to the sensor platform’s direction of motion. The central …
Experimental Demonstration Of A Stripmap Holographic Aperture Ladar System, Jason Stafford, Bradley Duncan, Matthew Dierking
Experimental Demonstration Of A Stripmap Holographic Aperture Ladar System, Jason Stafford, Bradley Duncan, Matthew Dierking
Bradley D. Duncan
By synthesizing large effective apertures through the translation of a smaller imaging sensor and the subsequent proper phasing and correlation of detected signals in postprocessing, holographic aperture ladar (HAL) systems seek to increase the resolution of remotely imaged targets. The stripmap HAL process was demonstrated in the laboratory, for the first time to our knowledge. Our results show that the stripmap HAL transformation can precisely account for off-axis transmitter induced phase migrations. This in turn allows multiple pupil plane field segments, sequentially collected across a synthetic aperture, to be coherently mosaiced together. As a direct consequence, we have been able …
Effects Of Spatial Modes On Ladar Vibration Signature Estimation, Douglas Jameson, Matthew Dierking, Bradley Duncan
Effects Of Spatial Modes On Ladar Vibration Signature Estimation, Douglas Jameson, Matthew Dierking, Bradley Duncan
Bradley D. Duncan
Ladar-based vibrometry has been shown to be a powerful technique in enabling the plant identification of machines. Rather than sensing the geometric shape of a target laser vibrometers sense motions of the target induced by moving parts within the system. Since the target need not be spatially resolved, vibration can be sensed reliably and provide positive identification at ranges beyond the imaging limits of the aperture. However, as the range of observation increases, the diffraction-limited beam size on the target increases as well, and may encompass multiple vibrational modes on the target's surface. As a result, vibration estimates formed from …
Bidirectional Scattering Distribution Functions Of Maple And Cottonwood Leaves, Michael Greiner, Bradley Duncan, Matthew Dierking
Bidirectional Scattering Distribution Functions Of Maple And Cottonwood Leaves, Michael Greiner, Bradley Duncan, Matthew Dierking
Bradley D. Duncan
We present our investigations into the optical scattering properties of both sugar maple (Acer saccarum) and eastern cottonwood (Populus deltoides) leaves in the near-IR wavelength regime. The bidirectional scattering distribution function (BSDF) describes the fractions of light reflected by and transmitted through a leaf for a given set of illumination and observation angles. Experiments were performed to measure the BSDF of each species at a discrete set of illumination and observation angles. We then modeled the BSDFs in such a way that other researchers may interpolate their values for scattering in any direction under illumination at any angle.
Demonstrated Resolution Enhancement Capability Of A Stripmap Holographic Aperture Ladar System, Samuel Venable, Bradley Duncan, Matthew Dierking, David Rabb
Demonstrated Resolution Enhancement Capability Of A Stripmap Holographic Aperture Ladar System, Samuel Venable, Bradley Duncan, Matthew Dierking, David Rabb
Bradley D. Duncan
Holographic aperture ladar (HAL) is a variant of synthetic aperture ladar (SAL). The two processes are related in that they both seek to increase cross-range (i.e., the direction of the receiver translation) image resolution through the synthesis of a large effective aperture. This is in turn achieved via the translation of a receiver aperture and the subsequent coherent phasing and correlation of multiple received signals. However, while SAL imaging incorporates a translating point detector, HAL takes advantage of a two-dimensional translating sensor array. For the research presented in this article, a side-looking stripmap HAL geometry was used to sequentially image …
Saturated Semiconductor Optical Amplifier Phase Modulation For Long Range Laser Radar Applications, Jennifer Carns, Bradley Duncan, Matthew Dierking
Saturated Semiconductor Optical Amplifier Phase Modulation For Long Range Laser Radar Applications, Jennifer Carns, Bradley Duncan, Matthew Dierking
Bradley D. Duncan
We investigate the use of a semiconductor optical amplifier operated in the saturation regime as a phase modulator for long range laser radar applications. The nature of the phase and amplitude modulation resulting from a high peak power Gaussian pulse, and the impact this has on the ideal pulse response of a laser radar system, is explored. We also present results of a proof-of-concept laboratory demonstration using phase-modulated pulses to interrogate a stationary target.
Coupling Efficiencies For General Target Illumination Ladar Systems Incorporating Single Mode Optical Fiber Receivers, Christopher Brewer, Bradley Duncan, Kenneth Barnard, Edward Watson
Coupling Efficiencies For General Target Illumination Ladar Systems Incorporating Single Mode Optical Fiber Receivers, Christopher Brewer, Bradley Duncan, Kenneth Barnard, Edward Watson
Bradley D. Duncan
A rigorous method for modeling received power coupling efficiency (ηF/R) and transmitted power coupling efficiency (ηF/T) in a general-target-illumination ladar system is presented. For our analysis we concentrate on incorporating a single-mode optical fiber into the ladar return signal path. By developing expressions for both ηF/R and ηF/T for a simple, diffuse target, our model allows for varying range, beam size on target, target diameter, and coupling optics. Through numerical analysis ηF/R is shown to increase as the range to target increases and decrease as target diameter increases, and ηF/T is shown to decrease with target range. A baseline signal-to-noise …
Parametric Extension Of The Classical Exposure Schedule Theory For Angle-Multiplexed Photorefractive Recording Using The Common-Aperture Beam Geometry, Mark Delong, Bradley Duncan, Jack Parker
Parametric Extension Of The Classical Exposure Schedule Theory For Angle-Multiplexed Photorefractive Recording Using The Common-Aperture Beam Geometry, Mark Delong, Bradley Duncan, Jack Parker
Bradley D. Duncan
The gradual reorientations in crystal geometry encountered during angle-multiplexed holographic recording with obliquely incident recording beams can create significant parametric exposure-time and recording-angle dependencies in both grating writing- and erasure-time constants. We present a parametric extension of the classically derived backward-recursion algorithm that compensates for the intermingling effects of recording geometry, writing-beam intensity variations, and unique crystal behavior. We present experimental data for a sequence of 301 holograms recorded with the goal of equal hologram strength and, separately, the same sequence recorded with the goal of equal hologram reconstruction intensity—which are different cases for a steeply incident readout beam.
Space-Bandwidth Product Enhancement Of A Monostatic, Multi-Aperture Infrared Image Upconversion Ladar Receiver Incorporating Periodically Polled Linbo3, Christopher Brewer, Bradley Duncan, Phillip Maciejewski, Sean Kirkpatrick, Edward Watson
Space-Bandwidth Product Enhancement Of A Monostatic, Multi-Aperture Infrared Image Upconversion Ladar Receiver Incorporating Periodically Polled Linbo3, Christopher Brewer, Bradley Duncan, Phillip Maciejewski, Sean Kirkpatrick, Edward Watson
Bradley D. Duncan
We investigate the space-bandwidth product of a ladar system incorporating an upconversion receiver. After illuminating a target with an eye-safe beam, we direct the return into a piece of periodically poled LiNbO3 where it is upconverted into the visible spectrum and detected with a CCD camera. The theoretical and experimental transfer functions are then found. We show that the angular acceptance of the upconversion process severely limits the receiver field of regard for macroscopic coupling optics. This limitation is overcome with a pair of microlens arrays, and a 43% increase in the system’s measured space-bandwidth product is demonstrated.
Real-Time Non-Linear Image Processing Using An Active Optical Scanning Technique, Bradley Duncan, Ting-Chung Poon, Ron Piper
Real-Time Non-Linear Image Processing Using An Active Optical Scanning Technique, Bradley Duncan, Ting-Chung Poon, Ron Piper
Bradley D. Duncan
Real-time non-linear image processing has been achieved using an active optical scanning technique. This paper reports experimental results in edge extraction for both binary and grey-scale transmissive objects. Binary edge extraction is achieved using morphological transformations, while grey-scale edge extraction is achieved using a threshold decomposition technique. Advantages and limitation of both techniques are identified.
Gaussian Beam Analysis Of Optical Scanning Holography, Bradley Duncan, Ting-Chung Poon
Gaussian Beam Analysis Of Optical Scanning Holography, Bradley Duncan, Ting-Chung Poon
Bradley D. Duncan
A detailed theoretical treatment based on Gaussian beam theory is provided for optical scanning holography [ J. Opt. Soc. Am. A 2, 512 ( 1985)]. Topics addressed include the derivation of the impulse response for the optical scanning holographic system, methods of achieving off-axis holographic recordings, reconstructed image resolution, magnification, and distortion. Also presented is experimental verification of the technique based on measurements of the hologram of a simple transmissive slit object.
Optical-Fiber Preamplifiers For Ladar Detection And Associated Measurements For Improving The Signal-To-Noise Ratio, Michael Salisbury, Paul Mcmanamon, Bradley Duncan
Optical-Fiber Preamplifiers For Ladar Detection And Associated Measurements For Improving The Signal-To-Noise Ratio, Michael Salisbury, Paul Mcmanamon, Bradley Duncan
Bradley D. Duncan
In an effort to increase achievable postdetection signal-tonoise ratios (SNRs) of continuous-wave, 1-gm all-solid-state ladar systems, a prototype rare-earth-doped optical-fiber amplifier has been included in the optical return signal path of both a heterodyne and a directdetection ladar system. We provide numerical predictions for SNR increases according to our previously developed theory. We also detail our experimental efforts and provide the results of SNR measurements for four distinct cases: direct ladar detection with and without a fiber amplifier, and heterodyne ladar detection with and without a fiber amplifier. Experimentally measured increases in SNRs for ladar systems incorporating an optical-fiber amplifier …
Volume Holographic Memory For Laser Threat Discrimination, Mark Delong, Bradley Duncan, Jack Parker
Volume Holographic Memory For Laser Threat Discrimination, Mark Delong, Bradley Duncan, Jack Parker
Bradley D. Duncan
Using conventional volume-holographic angle multiplexing in an Fe:LiNbO3 crystal, we have developed a compact laser threat discriminator, intended for aircraft integration, that optically detects laser spatial coherence and angle of arrival while simultaneously rejecting incoherent background sources, such as the Sun. The device is intended for a specific type of psychophysical laser attack against U.S. Air Force pilots, namely, third-world-country exploitation of inexpensive and powerful cw Ar-ion or doubled Nd:YAG lasers in the visible spectrum to blind or disorient U.S. pilots. The component does not solve the general tactical laser weapon situation, which includes identifying precision-guided munitions, range finders, and …
Analysis Of Ladar Range Resolution Enhancement By Sinusoidal Phase Modulation, Leonard Masters, Martin Mark, Bradley Duncan
Analysis Of Ladar Range Resolution Enhancement By Sinusoidal Phase Modulation, Leonard Masters, Martin Mark, Bradley Duncan
Bradley D. Duncan
The ability of a ladar system to resolve two or more separate returns from a combined echo is related to the effective correlation bandwidth of the pulse emitted by the ladar system. Phase modulation of an outgoing pulse introduces additional frequency components, which increases the effective correlation bandwidth of the pulse and thus improves the range resolution of the system. In this paper, we discuss the general theoretical basis for achieving improved range resolution using a modulated waveform and a matched filter receiver. We then demonstrate these concepts by considering the particular case of improved range resolution for a sinusoidally …
Aberration Production Using A High-Resolution Liquid-Crystal Spatial Light Modulator, Jason Schmidt, Matthew Goda, Bradley Duncan
Aberration Production Using A High-Resolution Liquid-Crystal Spatial Light Modulator, Jason Schmidt, Matthew Goda, Bradley Duncan
Bradley D. Duncan
Phase-only liquid-crystal spatial light modulators provide a powerful means of wavefront control. With high resolution and diffractive (modulo 2𝜋) operation, they can accurately represent large-dynamic-range phase maps. As a result, they provide an excellent means of producing electrically controllable, dynamic, and repeatable aberrations. However, proper calibration is critical to achieving accurate phase maps. Several calibration methods from previous literature were considered. With simplicity and accuracy in mind, we selected one method for each type of necessary calibration. We augmented one of the selected methods with a new step that improves its accuracy. After calibrating our spatial light modulator with our …
Fibre-Optic Network Architectures For On-Board Digital Avionics Signal Distribution, Mohammad Alam, Mohammed Atiquzzaman, Bradley Duncan, Hung Nguyen, Richard Kunath
Fibre-Optic Network Architectures For On-Board Digital Avionics Signal Distribution, Mohammad Alam, Mohammed Atiquzzaman, Bradley Duncan, Hung Nguyen, Richard Kunath
Bradley D. Duncan
Continued progress in both civil and military radio-frequency (RF) digital avionics applications is overstressing the capabilities and reliability of existing RF communication networks based on coaxial cables on board modern aircrafts. Future avionics systems will require high-bandwidth on-board communication links that are lightweight, immune to electromagnetic interference, and highly reliable. Fibre-optic networks can meet all these challenges in a cost-effective manner. Recently, on-board fibre-optic communication systems, where a fibre-optic network acts like a local area network (LAN) for digital data communications, have become a topic of extensive research and development. However, modern digital avionics systems require a system capable of …
Real-Time Reconstruction Of Scanned Optical Holograms Using An Electron Beam Addressed Spatial Light Modulator, Bradley Duncan, Ting-Chung Poon, Ming Hsien Wu, K. Shinoda, Y. Suzuki
Real-Time Reconstruction Of Scanned Optical Holograms Using An Electron Beam Addressed Spatial Light Modulator, Bradley Duncan, Ting-Chung Poon, Ming Hsien Wu, K. Shinoda, Y. Suzuki
Bradley D. Duncan
Real-time holographic recording has recently been demonstrated (1990, Jpn J. Appl. Phys., 29 L1840) using the optical heterodyne scanning technique proposed by Poon (1985, Jp. Opt. Soc. Am. A, 2 521). In this paper we discuss the reconstruction of holograms generated by the heterodyne scanning technique. The primary concentration is on real-time reconstruction using an electron beam addressed spatial light modulator (EBSLM). For comparison, coherent reconstruction methods are also presented. Additional topics to be addressed are the spatial frequency limitations of the EBSLM and the derivation of the incoherent point spread function (PSF) of the holographic imaging system. Based upon …