Digital Commons Network^™

Low Temperature, Postgrowth Self-Doping Of Cdte Single Crystals Due To Controlled Deviation From Stoichiometry, V. Lyahovitskaya, L. Chernyak, J. Greenberg, L. Kaplan, David Cahen

Faculty Bibliography 2000s

Careful analysis of the Cd-Te pressure-temperature-composition phase diagram, shows a deviation of CdTe stoichiometry only in the Te-depletion direction between 450 and 550 degrees C. Combined control over the semiconductor composition, via intrinsic defects, and over the atmosphere and cooling rate can, therefore, yield a process for intrinsic doping of CdTe at these relatively low temperatures. We present results that support this. Quenching of CdTe, following its annealing in Te atmosphere at 400-550 degrees C, leads to p-type conductivity with a hole concentration of similar to 2 x 10(16) cm(-3). Slow cooling of the samples, after 550 degrees C annealing …

All-Fiber Connectorized Compact Fiber Optic Delay-Line Modules Using Three-Dimensional Polarization Optics, Nicholas Madamopoulos, Nabeel A. Riza

Faculty Bibliography 2000s

Compact and all-fiber connectorized photonic delay-line modules based on three-dimensional bulk polarization optics are proposed and experimentally demonstrated. The modules are built on a single optical microbench and demonstrate optical leakage noise performance of -40 dB at switching speeds of 10 mu s. Insertion loss analysis is also performed. A special gradient-index lens fiber optic collimator design is proposed to further reduce the optical insertion loss of the delay-line module. A wavelength-dependent design is also proposed for expanding the applicability of the PDL module to multichannel operation.

Single Axial-Mode Selection In A Far-Infrared P-Ge Laser, A. V. Muravjov, S. H. Withers, H. Weidner, R. C. Strijbos, S. G. Pavlov, V. N. Shastin, R. E. Peale

Faculty Bibliography 2000s

Single axial-mode operation of the pulsed far-infrared p-Ge laser with an intracavity Fabry-Perot type frequency selector has been observed by means of Fourier-transform spectroscopy. A spectral resolution better than 1 GHz has been achieved on an ordinary continuous-scan spectrometer using the event-locked technique for pulsed emission sources. A laser active-cavity finesse of at least unity has been directly confirmed from the measured emission spectral width. Analysis of the envelope of the corresponding interferogram suggests that the finesse exceeds 10.

Relative Electrical Resistivities And Poling Of Nonlinear Optical Polymeric Waveguides, Tomáš Pliška, Joachim Meier, Arne Eckau, Vincent Ricci, Anne-Claire Le Duff, Michael Canva, George I. Stegeman, Paul Raymond, Francois Kajzar, Kwok Pong Chan

Faculty Bibliography 2000s

A method based on Maker fringe measurements of nonlinear optical coefficients has been used to determine the relative dc electrical resistivities of a series of linear and nonlinear optical polymers. The method can be used to identify low resistivity linear cladding materials for optimized electric field poling of nonlinear optical polymeric waveguides. As an example of the application of the technique we have studied the resistivity of poly(methyl methacrylate)-polystyrene (PMMA-PS) copolymers with varying content of the two components. The resistivity of PMMA was found to be one order of magnitude lower than that of PS.

Evidence Of Scattering Anisotropy Effects On Boundary Conditions Of The Diffusion Equation, G. Popescu, C. Mujat, A. Dogariu

Faculty Bibliography 2000s

We present experimental evidence that the diffusion process close to the boundary is fundamentally different from the bulk diffusion in the sense that it is affected by the scattering properties of the individual centers. Systematic measurements show a nontrivial behavior of the extrapolation length ratio on the scattering anisotropy of individual particles. The results are compared with other works and are supported by an independent Monte Carlo simulation. A simple analytical model that emphasizes the influence of the last scattering event successfully describes the results.

Comparison Of Infrared Frequency Selective Surfaces Fabricated By Direct-Write Electron-Beam And Bilayer Nanoimprint Lithographies, Irina Puscasu, G. Boreman, R. C. Tiberio, D. Spencer, R. R. Krchnavek

Faculty Bibliography 2000s

We report on the fabrication of crossed-dipole resonant filters by direct-write electron-beam and nanoimprint lithographies. Such structures have bean used as spectrally selective components at visible, microwave; and infrared wavelengths. Imprinting is accomplished in a modified commercial hot press at 155 degreesC. The replica is then etched in oxygen plasma and developed in chlorobenzene to selectively dissolve the poly(methylmethacrylate and methacrylic acid) and poly(methylmethacrylate) bilayer resist. This step enhances undercut and improves lift-off metalization. Infrared fourier transform spectroscopy was performed to characterize the transmission response of the frequency selective surfaces (FSSs) fabricated. The resonant behavior for the direct-write FSS was …

Microwave Response Near Zero Magnetic Field In Transition-Metal-Doped Silicate Glasses, R. R. Rakhimov, H. R. Ries, D. E. Jones, L. B. Glebov, L. N. Glebova

Faculty Bibliography 2000s

A sharp microwave response centered at zero magnetic field was observed in manganese- and iron-doped Na2O-CaO-MgO-SiO2 glasses with phase opposite to the normal Mn+2 and Fe+3 paramagnetic signals. The response can be described as magneto-induced microwave conductivity in the dielectric glass that derives from spin-dependent charge migration within the first coordination sphere of the paramagnetic ion. In contrast to the spin-polarized tunneling in ferromagnets between different valence states of metals, the observed effect is due to spin-dependent tunneling that occurs in the vicinity of manganese or iron in diluted paramagnetic systems.

Small-Tilt Micromirror-Device-Based Multiwavelength Three-Dimensional 2x2 Fiber Optic Switch Structures, Nabeel A. Riza, Sarun Sumriddetchkajorn

Faculty Bibliography 2000s

Small-tilt micromirror-based 2x2 fiber optic switch array structures are proposed using fixed mirrors and fiber interconnections. A multiwavelength 2x2 fiber optic switch based on this small-tilt micromirror is experimentally demonstrated. The key innovation in this architecture is the use of a specially located fixed mirror to form a symmetric 2x2 retroreflective switching structure. These 2x2 fiber optic switch structures can also provide a fault-tolerant design using a macropixel approach. A two-dimensional digital micromirror device (2D-DMD) from Texas Instruments (TI) designed to operate in the visible band is used to represent the small-tilt micromirrors in our experimental demonstration. Multiwavelength switch operation …

Wide-Angle, Off-Axis, See-Through Head-Mounted Display, Jannick P. Rolland

Faculty Bibliography 2000s

A 60-deg-field-of-view optical see-through head-mounted display (HMD) using off-axis optics has been designed for 3-D medical imaging visualization. Two basic on-axis optical design concepts for see-though HMDs are reviewed first, to motivate the design of an off-axis optical form. An off-axis design is then presented. Because HMDs are typically designed from the pupil of the eye to the miniature display, it is common to assess final performance according to the display characteristics. Such analysis, however, does not provide information that is easily translated into task-based performance metric. Therefore, we present an analysis of the performance of the design from a …

Optical Versus Video See-Through Mead-Mounted Displays In Medical Visualization, Jannick P. Rolland, Henry Fuchs

Faculty Bibliography 2000s

We compare two technological approaches to augmented reality for 3-D medical visualization: optical and video see-through devices. We provide a context to discuss the technology by reviewing several medical applications of augmented-reality research efforts driven by real needs in the medical field, both in the United States and in Europe. We then discuss the issues for each approach, optical versus video, from both a technology and human-factor point of view. Finally, we point to potentially promising future developments of such devices including eye tracking and multifocus planes capabilities, as well as hybrid optical/video technology.

Fast Algorithms For Histogram Matching: Application To Texture Synthesis, J. P. Rolland, V. Vo, B. Bloss, C. K. Abbey

Faculty Bibliography 2000s

Texture synthesis is the ability to create ensembles of images of similar structures from sample textures that have been photographed. The method we employ for texture synthesis is based on histogram matching of images at multiple scales and orientations. This paper reports two fast and in one case simple algorithms for histogram matching We show that the sort-matching and the optimal cumulative distribution function (CDF)-matching (OCM) algorithms provide high computational speed compared to that provided by the conventional approach. The sort-matching algorithm also provides exact histogram matching. Results of texture synthesis using either method show no subjective perceptual differences. The …

Oxidation And Chemical State Analysis Of Polycrystalline Magnetron Sputtered (Ti,Al)N Films At Ambient And Liquid N-2 Temperatures, S. Seal, A. Kale, K. B. Sundaram, D. Jimenez

Faculty Bibliography 2000s

In order to improve the functional properties of hard coatings, recent investigations have been directed towards Ti-N based multicomponent materials. The nitride (Ti, Al)N, in particular, with a Ti:Al ratio of 1:1 seems to be a promising alternative to the widely used TiN, exhibits better oxidation resistance and hence improved performance over that of TiN. (Ti, Al)N coatings were de sputter deposited onto 316SS substrates under ambient and liquid nitrogen temperatures. As deposited films were oxidized in a vertical fused-silica tube furnace in pure O-2 flowing atmosphere at temperatures ranging from 700 to 900 degrees C. Scanning electron microscope and …

Systems Engineering Analysis Of Aplanatic Wolter Type I X-Ray Telescopes, Patrick L. Thompson, James E. Harvey

Faculty Bibliography 2000s

It is well known that normal-incidence aplanatic telescope designs perform better at small field angles than ones corrected only for spherical aberration. This is why most large astronomical telescopes fabricated in the past fifty years have been of the Ritchey-Chretien (aplanatic) design rather than of the classical Cassegrain design. For the relatively new field of x-ray astronomy, the Welter type I grazing incidence design has been extensively utilized. It consists of a paraboloidal primary mirror coaxial with a confocal hyperboloidal secondary mirror. Aplanatic versions of the Welter type I grazing incidence x-ray telescope have been discussed in detail in the …

Interface Structures In Gaas Wafer Bonding: Application To Compliant Substrates, R. R. Vanfleet, M. Shverdin, J. Silcox, Z. H. Zhu, Y. H. Lo

Faculty Bibliography 2000s

The interface of direct bonded GaAs to GaAs has been studied by scanning transmission electron microscopy and electron energy loss spectroscopy. Voids are seen along the boundary with most being partially filled with a gallium particle. Two general sizes of voids are seen. The large voids (d similar to 45 nm) are distributed in an approximately linear relationship and the smaller (d similar to 12 nm) randomly. In compliant substrates, one of the layers is made thin (less than or equal to 10 nm) and twisted similar to 45 degrees. The larger voids often extend past this thin compliant layer, …

Clutter Modeling In Infrared Images Using Genetic Programming, Liviu I. Voicu, Mosleh Uddin, Harley R. Myler, Anthony Gallagher, Julien Schuler

Faculty Bibliography 2000s

Background clutter characterization in infrared imagery has become an actively researched field, and several clutter models have been reported. These models attempt to evaluate the target detection and recognition probabilities that are characteristic of a certain scene when specific target and human visual perception features are known. The prior knowledge assumed and required by these models is a severe limitation. Furthermore, the attempt to model subjective and intricate mechanisms such as human perception with general mathematical formulas is controversial, in this paper, we introduce the idea of adaptive models that are dynamically derived from a set of examples by a …

"Happy Days Are Here Again": Cocoa Farmers, Middlemen Traders And The Structural Adjustment Program In Southwestern Nigeria, 1986-1990s, Ezekiel Ayodele Walker

Faculty Bibliography 2000s

This article examines the impact of the Structural Adjustment Program (SAP) that was installed by the military regime of Ibrahim Babangida in 1986 on the cocoa economy of southwestern Nigeria. The structural adjustment program resulted in the dissolution of the Cocoa Board. The scrapping of the Cocoa Board engendered significant changes in the marketing of cocoa, as Nigerian, and non-Nigerian exporters (Syrians and Lebanese) sought to gain control of the cocoa trade. This resulted in a price war that led to a monumental increase in the price of cocoa. The cocoa boom from 1987 to 1988 was compounded by the …

Two Estimators Of The Mean Of A Counting Process With Panel Count Data, Jon A. Wellner, Ying Zhang

Faculty Bibliography 2000s

We study two estimators of the mean function of a counting process based on "panel count data." The setting for "panel count data" is one in which n independent subjects, each with a counting process with common mean function, are observed at several possibly different times during a study. Following a model proposed by Schick and Yu, we allow the number of observation times, and the observation times themselves, to be random variables. Our goal is to estimate the mean function of the counting process. We show that the estimator of the mean function proposed by Sun and Kalbfleisch can …

Multiple Source Pools And Dispersal Barriers For Galapagos Plant Species Distribution, J. Alan Yeakley, John F. Weishampel

Faculty Bibliography 2000s

We reexamined geographic factors explaining the number of plant species on islands in the Galapagos Archipelago. We hypothesized that plant species richness (S) was related to the number of source pools and that plant species dispersal preferentially followed direct, oceanic pathways. To test different dispersal pathways from multiple source pools, the total number of islands within a given dispersal radius (i) was posed as the sum of the number of line-of-sight islands (C-i) and of the number of islands without line-of-sight connection (B-i). In partial regression analyses, controlling for nearest island area (A(2)) and for recipient island elevation (E) and …

Parameters Influencing Sediments Resuspension And The Link To Sorption Of Inorganic Compounds, Eid A. Alkhatib, Keith Castor

Chemistry & Physics Faculty Publications

In the aquatic environment, the accumulation of chemicalcontaminants by sediments poses a potential threat to endemiclife forms and drinking water resources. Trace metals such asCd, Cu, Cr, Ni, Pb, and toxic organic compounds, are among awide variety of contaminants having an affinity for sediments.In this study, experiments were performed simulating sedimentresuspension in the lower Housatonic River, Connecticut, using aParticle Entrainment Simulator. Analyses of grain sizedistributions, porosities and total organic contents of thesediments suggested that these parameters influence theredistribution and entrainment of settleable solids in the watercolumn. These findings were established by evaluating the impactof one parameter on sediment resuspension as …

Tight Bounds On The Algebraic Connectivity Of A Balanced Binary Tree, Jason J. Molitierno, Michael Neumann, Bryan L. Shader

Mathematics Faculty Publications

In this paper, quite tight lower and upper bounds are obtained on the algebraic connectivity, namely, the second-smallest eigenvalue of the Laplacian matrix, of an unweighted balanced binary tree with k levels and hence n = 2^k - 1 vertices. This is accomplished by considering the inverse of a matrix of order k - 1 readily obtained from the Laplacian matrix. It is shown that the algebraic connectivity is 1/(2^k - 2k + 3) + 0(1/2^2k).

Poetry As Theory: Lope De Vega's Epistola As Arbiter Of Proper Discourse, Mark J. Mascia

Languages Faculty Publications

The purpose of this article is to examine the ways in which Lope de Vega manipulates epistolas to serve his own ends with regards to language, both on a narrowly literary level and on a broader personal and even national one. What emerges is an epistola which blends both the self-evident art of poetry writing and critical speculation upon it, one which Lope consciously uses as a literary mode of vindication and defense for his ideas regarding proper discourse and as an attack on any type of discourse of which he disapproves.

Characterization Of The Interactions Within The Ccr4 -Not Complex And The Interactions Between Adr1 And Tfiid Components, Yongli Bai

Doctoral Dissertations

The mechanisms of transcriptional regulation are well conserved from yeast to human cells. Most genes are regulated at the transcriptional level, particularly, at the transcription initiation step. In Saccharomyces cerevisiae at least one transcriptional activator, ADR1, and one transcription complex, CCR4-NOT, participate in the activation of the ADH2 gene. The core 1 x 106 dalton CCR4-NOT complex consists of CCR4, CAF1, the five NOT proteins (NOT1-NOT5), and three other uncharacterized proteins. Deletion of NOT3, NOT4, or NOT5 did not affect the association of CCR4 with CAF1 in the gel filtration analysis. In contrast, NOT2 inactivation caused partial destabilization of the …

Modeling The Friction Effects Of Eelgrass On The Tidal Flow In Great Bay, New Hampshire, Safak Nur Erturk

Doctoral Dissertations

In this study the frictional effects of eelgrass (Zostera marina L.) on the tidal flow in Great Bay, NH is modeled using a bottom friction coefficient adjustment approach. A two-dimensional, non-linear, time stepping, finite element model, ADAM is used. ADAM model incorporates two-dimensional wave physics, with a porous medium beneath the sediment surface to simulate wetting and drying process on the tidal flats. The effectiveness of ADAM model in simulating the tidal flow in Great Bay with wetting and drying on the tidal flats is verified. The model is calibrated by adjusting the bottom friction coefficient for the M2, M2S2 …

A Comparison Of Direct Methods For Valuing Environmental Amenities: A Case Study Of The White Mountain National Forest, Wendy Harper

Doctoral Dissertations

New Hampshire's White Mountain National Forest is well known for its mountain scenery as well as its many recreational opportunities. Upcoming changes in the electric utility industry may work to change the average level of visibility in the White Mountain National Forest. While the contingent valuation method has been extensively used to value public goods (in instances such as the case above), some view the procedure with skepticism. As a result, alternative methods such as conjoint analysis have been receiving more attention. This dissertation presents the results of a face-to-face survey that attempted to directly compare conjoint analysis and contingent …

Internet Use And Its Relation To Mental And Physical Health Among Older Adults, Michael Anthony Mangan

Doctoral Dissertations

This exploratory study examined relations between frequency of Internet use among adults 65 and older and perceptions of social support and personal control. Additionally, standard multiple regression procedures were employed to assess the usefulness of frequency of Internet use, perceived social support, and perceived control as predictors of mental and physical health. Results were that frequency of Internet use was uncorrelated with perceptions of social support and personal control and was not predictive of mental or physical health. Perceived social support and perceived control emerged as predictors of mental and physical health. Recommendations for future research that refines measurement of …

The Moses Illusion In Reading Comprehension, Anne E. Cook

Doctoral Dissertations

The Moses Illusion refers to participants' failure to detect distortions in questions such as, "How many animals of each kind did Moses take on the Ark?" although it was actually Noah's Ark. The Illusion is thought to depend on the semantic relation between the distorted term (e.g., Moses) and the correct term (e.g., Noah). The Illusion literature has been limited mostly to investigations of semantic memory and to a single-question format. The experiments reported in this dissertation examined whether the Illusion extends to longer passages of text and whether it is influenced by the presence of the correct term in …

Landscape-Scale Prediction Of Forest Productivity By Hyperspectral Remote Sensing Of Canopy Nitrogen, Marie-Louise Smith

Doctoral Dissertations

Foliar nitrogen concentration represents a direct and primary link between carbon and nitrogen cycling in terrestrial ecosystems. Although foliar N is used by many ecosystem models to predict leaf-level photosynthetic rates, it has rarely been examined as a direct scalar to stand-level carbon gain. Significant improvements in remote sensing detector technology in the list decade now allow for improved landscape-level estimation of the biochemical attributes of forest ecosystems.

In this study, relationships among forest growth (aboveground net primary productivity (ANPP) and aboveground woody biomass production (AWBP)), canopy chemistry and structure, and high resolution imaging spectrometry were examined for 88 long-term …

The Effects Of Ultraviolet Radiation, Highway Contamination, And Synergism Of The Two On Spotted Salamander Embryos, Sarah Letitia Turtle

Doctoral Dissertations

In this study, I examined the effects of ultraviolet radiation, highway contamination and a synergism of both factors on the spotted salamander, Ambystoma maculatum embryos in field and laboratory experiments. There are numerous reports of amphibian population declines from around the world. There are several possible factors causing the decline, including, habitat loss, environmental pollution, disease, and ultraviolet B radiation (UVB, 290--320 nm). Results of studies conducted to date seem to indicate that the impacts of these factors vary greatly among species and across geography. Amphibians have unique characteristics and life histories that make them more vulnerable to changes in …

Modeling Plant-Soil-Atmosphere Carbon Dioxide Exchange Using Optimality Principles, Kevin Patrick Tu

Doctoral Dissertations

The exchange of carbon dioxide (CO2) between terrestrial ecosystems and the atmosphere plays a central role in the ecology of the biosphere and the climate system. Towards quantification of ecosystem-atmosphere CO 2 exchange, a generalized model of plant-soil-atmosphere CO2 exchange (OPTICAL) was described and evaluated using eddy covariance measurements of net ecosystem exchange of CO2 (NEE) in arctic, boreal, temperate, and tropical landscapes. The model requires no calibration and is based on theories of plant resource optimization and plant-soil nutrient feedbacks. The model predicts canopy photosynthetic capacity (Pcmax), canopy photosynthesis (P c), plant respiration (Rp), and soil heterotrophic respiration (RH). …

Lifers: A Study Of At -Risk Adolescent Readers, Pamela Nottage Mueller

Doctoral Dissertations

In this study I put a face and voice to the at-risk adolescent reader. No strangers to failure, these are students who by and large have struggled with reading their entire educational lives but who for whatever reason have been unable to escape the cycle of frustration in which they find themselves caught. These are students who have a great deal to say but who until now have had no forum in which to say it. These are students who deserve to be heard.

For my primary source of data, I utilized Seidman's phenomenological approach to interviewing, conducting a series …