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2007

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Articles 18391 - 18420 of 22017

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Large-Aperture Chirped Volume Bragg Grating Based Fiber Cpa System, Kai-Hsiu Liao, Ming-Yuan Cheng, Emilie Flecher, Vadim I. Smirnov, Leonid B. Glebov, Almantas Galvanauskas Jan 2007

Large-Aperture Chirped Volume Bragg Grating Based Fiber Cpa System, Kai-Hsiu Liao, Ming-Yuan Cheng, Emilie Flecher, Vadim I. Smirnov, Leonid B. Glebov, Almantas Galvanauskas

Faculty Bibliography 2000s

A fiber chirped pulse amplification system at 1558nm was demonstrated using a large-aperture volume Bragg grating stretcher and compressor made of Photo-Thermal-Refractive (PTR) glass. Such PTR-glass based gratings represent a new type of pulse stretching and compressing devices which are compact, monolithic and optically efficient. Furthermore, since PTR glass technology enables volume gratings with transverse apertures which are large, homogeneous and scalable, it also enables high pulse energies and powers far exceeding those achievable with other existing compact pulse-compression technologies. Additionally, reciprocity of chirped gratings with respect to stretching and compression also enables to address a long-standing problem in CPA …

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Excess Radiation From The Large Planets, Richard L. Liboff Jan 2007

Excess Radiation From The Large Planets, Richard L. Liboff

Faculty Bibliography 2000s

An alternative model is proposed for the excess radiation emitted by the larger planets, each with a liquid metallic hydrogen annular domain about a central core of ice and rocks. This model is based on the mutual attraction between elements of an aggregate of charged bosons in a charge-neutralizing background, in equilibrium at very high pressure, and the property that spin-1 deuterons are bosons. Assuming valid parameters for Jupiter, it is derived that the deuteron density in Saturn is approximately equal to that in Jupiter and that particles emitted in reactions in the liquid metal domain are thermalized in the …

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Characterization Study Of Bonded And Unbonded Polydimethylsiloxane Aimed For Bio-Micro-Electromechanical Systems-Related Applications, Miao Liu, Quanfang Chen Jan 2007

Characterization Study Of Bonded And Unbonded Polydimethylsiloxane Aimed For Bio-Micro-Electromechanical Systems-Related Applications, Miao Liu, Quanfang Chen

Faculty Bibliography 2000s

Authors have demonstrated that by controlling the mixing ratio of polydimethylsiloxane's (PDMS's) two components-base polymer (part A) and a curing agent (part B)-different mechanical properties of PDMS can be achieved. Test results show that the Young's modulus decreases as the increasing of mixing ratios (A: B). However, there is a transitional mixing ratio (part A:part B=10) after which the Young's modulus is almost independent of the mixing ratio. The PDMS's thickness plays an important role in determining the mechanical properties. The results show that the thinner the PDMS, the stiffer it behaves. The bonding strength between two cured PDMS parts …

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Electron Irradiation-Induced Increase Of Minority Carrier Diffusion Length, Mobility, And Lifetime In Mg-Doped Aln/Algan Short Period Superlattice, O. Lopatiuk-Tirpak, L. Chernyak, B. A. Borisov, V. V. Kuryatkov, S. A. Nikishin, K. Gartsman Jan 2007

Electron Irradiation-Induced Increase Of Minority Carrier Diffusion Length, Mobility, And Lifetime In Mg-Doped Aln/Algan Short Period Superlattice, O. Lopatiuk-Tirpak, L. Chernyak, B. A. Borisov, V. V. Kuryatkov, S. A. Nikishin, K. Gartsman

Faculty Bibliography 2000s

Minority carrier diffusion length in a p-type Mg-doped AlN/Al(0.08)Ga(0.92)N short period superlattice was shown to undergo a multifold and persistent (for at least 1 week) increase under continuous irradiation by low-energy beam of a scanning electron microscope. Since neither the diffusion length itself nor the rate of its increase exhibited any measurable temperature dependence, it is concluded that this phenomenon is attributable to the increase in mobility of minority electrons in the two-dimensional electron gas, which in turn is limited by defect scattering. Cathodoluminescence spectroscopy revealed similar to 40% growth of carrier lifetime under irradiation with an activation energy of …

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Cathodoluminescence Studies Of Carrier Concentration Dependence For The Electron-Irradiation Effects In P-Gan, O. Lopatiuk-Tirpak, L. Chernyak, Y. L. Wang, F. Ren, S. J. Pearton, K. Gartsman, Y. Feldman Jan 2007

Cathodoluminescence Studies Of Carrier Concentration Dependence For The Electron-Irradiation Effects In P-Gan, O. Lopatiuk-Tirpak, L. Chernyak, Y. L. Wang, F. Ren, S. J. Pearton, K. Gartsman, Y. Feldman

Faculty Bibliography 2000s

Electron-irradiation increase of nonequilibrium carrier lifetime was studied as a function of hole concentration in Mg-doped GaN. Temperature-dependent cathodoluminescence (CL) studies yielded activation energies of 344, 326, 237, and 197 meV for samples with hole concentrations of 2x10(16), 9x10(16), 3x10(18), and 7x10(18) cm(-3), respectively. The systematic decay of activation energy with carrier concentration was found to be consistent with Mg acceptors, indicating the involvement of the latter levels in irradiation-induced lifetime changes.

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Doping Level Dependence Of Electron Irradiation-Induced Minority Carrier Diffusion Length Increase In Mg-Doped Gan, O. Lopatiuk-Tirpak, L. Chernyak, Y. L. Wang, F. Ren, S. J. Pearton, K. Gartsman Jan 2007

Doping Level Dependence Of Electron Irradiation-Induced Minority Carrier Diffusion Length Increase In Mg-Doped Gan, O. Lopatiuk-Tirpak, L. Chernyak, Y. L. Wang, F. Ren, S. J. Pearton, K. Gartsman

Faculty Bibliography 2000s

The electron irradiation-induced increase of minority carrier diffusion length was studied as a function of hole concentration in Mg-doped GaN. Variable-temperature electron beam induced current measurements yielded activation energies of 264, 254, 171, and 144 meV for samples with hole concentrations of 2x10(16), 9x10(16), 3x10(18), and 7x10(18) cm(-3), respectively. This carrier concentration dependence of the activation energy for the effects of electron irradiation was found to be consistent with Mg acceptors, indicating the involvement of the latter levels in the irradiation-induced diffusion length increase.

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Influence Of Electron Injection On The Temporal Response Of Zno Homojunction Photodiodes, O. Lopatiuk-Tirpak, G. Nootz, E. Flitsiyan, L. Chernyak, L. J. Mandalapu, Z. Yang, J. L. Liu, K. Gartsman, A. Osinsky Jan 2007

Influence Of Electron Injection On The Temporal Response Of Zno Homojunction Photodiodes, O. Lopatiuk-Tirpak, G. Nootz, E. Flitsiyan, L. Chernyak, L. J. Mandalapu, Z. Yang, J. L. Liu, K. Gartsman, A. Osinsky

Faculty Bibliography 2000s

The effects of solid-state electron injection on the peak amplitude and decay time of photosignal in a ZnO-based homojunction UV photodiode were studied using temporal photoresponse measurements under femtosecond pulses of 355 nm radiation. The injection of about 50 C of charge, carried out by applying forward bias to the junction, resulted in a nearly twofold increase of the peak photoresponse and a corresponding increase of the decay constant. Both observations are shown to be a consequence of electron trapping. The long-term stability of the induced changes is also discussed.

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Heteropolymer Translocation Through Nanopores, Kaifu Luo, Tapio Ala-Nissila, See-Chen Ying, Aniket Bhattacharya Jan 2007

Heteropolymer Translocation Through Nanopores, Kaifu Luo, Tapio Ala-Nissila, See-Chen Ying, Aniket Bhattacharya

Faculty Bibliography 2000s

The authors investigate the translocation dynamics of heteropolymers driven through a nanopore using a constant temperature Langevin thermostat. Specifically, they consider heteropolymers consisting of two types of monomers labeled A and B, which are distinguished by the magnitude of the driving force that they experience inside the pore. From a series of studies on polymers with sequences A(m)B(n) the authors identify both universal as well as specific sequence properties of the translocating chains. They find that the scaling of the average translocation time as a function of the chain length N remains unaffected by the heterogeneity, while the residence time …

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Inhibition Of Hydrogen Uptake In Escherichia Coli By Expressing The Hydrogenase From The Cyanobacterium Synechocystis Sp Pcc 6803, Toshinari Maeda, Gönül Vardar, William T. Self, Thomas K. Wood Jan 2007

Inhibition Of Hydrogen Uptake In Escherichia Coli By Expressing The Hydrogenase From The Cyanobacterium Synechocystis Sp Pcc 6803, Toshinari Maeda, Gönül Vardar, William T. Self, Thomas K. Wood

Faculty Bibliography 2000s

Background: Molecular hydrogen is an environmentally- clean fuel and the reversible ( bidirectional) hydrogenase of the cyanobacterium Synechocystis sp. PCC 6803 as well as the native Escherichia coli hydrogenase 3 hold great promise for hydrogen generation. These enzymes perform the simple reaction 2H(+) + 2e-. H-2 ( g). Results: Hydrogen yields were enhanced up to 41- fold by cloning the bidirectional hydrogenase ( encoded by hoxEFUYH) from the cyanobacterium into E. coli. Using an optimized medium, E. coli cells expressing hoxEFUYH also produced twice as much hydrogen as the well- studied Enterobacter aerogenes HU- 101, and hydrogen gas bubbles are …

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A Mobile Head-Worn Projection Display, Ricardo Martins, Vesselin Shaoulov, Yonggang Ha, Jannick Rolland Jan 2007

A Mobile Head-Worn Projection Display, Ricardo Martins, Vesselin Shaoulov, Yonggang Ha, Jannick Rolland

Faculty Bibliography 2000s

A recent advancement was achieved in the integration and miniaturization of a binocular head-worn projection display (HWPD) conceived for fully mobile users. The devised display, referred to as Mobile HWPD (M-HWPD), offers see-through capability through custom-designed, light-weight projection optics and an integrated commercial-off-the-shelf (COTS) retro-reflective screen to display full color stereoscopic rendered images augmenting the real world. Moreover, the light-weight optical device (i.e., approximately 8g per eye) has the ability to project clear images at three different locations within near- or far-field observation depths without loss of image quality. In this paper, we first demonstrate the miniaturization of the optics, …

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Modulation Of Human Neural Stem Cell Differentiation In Alzheimer (App23) Transgenic Mice By Phenserine, Amelia Marutle, Masao Ohmitsu, Mats Nilbratt, Nigel H. Greig, Agneta Nordberg, Kiminobu Sugaya Jan 2007

Modulation Of Human Neural Stem Cell Differentiation In Alzheimer (App23) Transgenic Mice By Phenserine, Amelia Marutle, Masao Ohmitsu, Mats Nilbratt, Nigel H. Greig, Agneta Nordberg, Kiminobu Sugaya

Faculty Bibliography 2000s

In a previous study, we found that human neural stem cells (HNSCs) exposed to high concentrations of secreted amyloid-precursor protein (sAPP) in vitro differentiated into mainly astrocytes, suggesting that pathological alterations in APP processing during neurodegenerative conditions such as Alzheimer's disease (AD) may prevent neuronal differentiation of HNSCs. Thus, successful neuroplacement therapy for AD may require regulating APP expression to favorable levels to enhance neuronal differentiation of HNSCs. Phenserine, a recently developed cholinesterase inhibitor (ChEI), has been reported to reduce APP levels in vitro and in vivo. In this study, we found reductions of APP and glial fibrillary acidic protein …

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Low-Threshold And High Efficiency Lasing Upon Band-Edge Excitation In A Cholesteric Liquid Crystal, Yuko Matsuhisa, Yuhua Huang, Ying Zhou, Shin-Tson Wu, Ryotaro Ozaki, Yuuki Takao, Akihiko Fujii, Masanori Ozaki Jan 2007

Low-Threshold And High Efficiency Lasing Upon Band-Edge Excitation In A Cholesteric Liquid Crystal, Yuko Matsuhisa, Yuhua Huang, Ying Zhou, Shin-Tson Wu, Ryotaro Ozaki, Yuuki Takao, Akihiko Fujii, Masanori Ozaki

Faculty Bibliography 2000s

A low threshold and high efficiency laser based on dye-doped cholesteric liquid crystals (CLCs) is demonstrated using an input excitation with the same handedness of circular polarization as the helical structure of the sample at the shorter wavelength band edge of the reflection band. The responsible mechanism originates from the dramatic increase of the optical density of state (DOS) at the band edges. The calculated DOS of the CLC system confirms the authors' experimental results.

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Cholesteric Liquid Crystal Laser In A Dielectric Mirror Cavity Upon Band-Edge Excitation, Yuko Matsuhisa, Yuhua Huang, Ying Zhou, Shin-Tson Wu, Yuuki Takao, Akihiko Fujii, Masanori Ozaki Jan 2007

Cholesteric Liquid Crystal Laser In A Dielectric Mirror Cavity Upon Band-Edge Excitation, Yuko Matsuhisa, Yuhua Huang, Ying Zhou, Shin-Tson Wu, Yuuki Takao, Akihiko Fujii, Masanori Ozaki

Faculty Bibliography 2000s

Low threshold laser action of dye-doped cholesteric liquid crystals ( CLCs) is demonstrated using an input circularly polarized light whose handedness is the same as the cholesteric helix of the sample at the high-energy band edge of the reflection band. The mechanism originates from the dramatic increase of the photon density of state at the band edges. We also demonstrate an enhanced laser action of a CLC in a dielectric multilayer cavity. In such a device configuration, the band-edge excitation at high-energy band edge improves the lasing performance not only for the same handedness circularly polarized pump beam as the …

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Invariant Resolution Dynamic Focus Ocm Based On Liquid Crystal Lens, S. Murali, K. S. Lee, J. P. Rolland Jan 2007

Invariant Resolution Dynamic Focus Ocm Based On Liquid Crystal Lens, S. Murali, K. S. Lee, J. P. Rolland

Faculty Bibliography 2000s

A primary limitation of optical coherence microscopy is the lack of sufficient lateral resolution over a usable imaging volume for diagnostic applications, even with high-numerical aperture imaging optics. In this paper, we first motivate the benefit of refocusing at multiple depths in a highly scattering biological sample using optical coherence microscopy, which experimentally shows invariant 2.5 mu m axial and 6.5 mu m lateral resolution throughout the sample. We then present the optical system design of a hand-held probe with the advanced capability to dynamically focus with no moving parts to a depth of 2 mm in skin-equivalent tissue at …

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Power-Law Eigenvalue Density, Scaling, And Critical Random-Matrix Ensembles, K. A. Muttalib, Mourand E. H. Ismail Jan 2007

Power-Law Eigenvalue Density, Scaling, And Critical Random-Matrix Ensembles, K. A. Muttalib, Mourand E. H. Ismail

Faculty Bibliography 2000s

We consider a class of rotationally invariant unitary random matrix ensembles where the eigenvalue density falls off as an inverse power law. Under a scaling appropriate for such power-law densities (different from the scaling required in Gaussian random matrix ensembles), we calculate exactly the two-level kernel that determines all eigenvalue correlations. We show that such ensembles belong to the class of critical ensembles.

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Formation, Thermal Stability, And Surface Composition Of Size-Selected Aufe Nanoparticles, A. Naitabdi, Roldan Cuenya Jan 2007

Formation, Thermal Stability, And Surface Composition Of Size-Selected Aufe Nanoparticles, A. Naitabdi, Roldan Cuenya

Faculty Bibliography 2000s

The surface composition of isolated Au0.5Fe0.5 nanoparticles (NPs) synthesized by micelle encapsulation and supported on TiO2(110) has been investigated. The study reveals that phase-segregated structures are present after annealing at 300 degrees C. A subsequent thermal treatment at 700 degrees C resulted in the formation of a AuFe alloy. At this temperature, a state characteristic of Fe was identified at the NPs' surface. Annealing at 900 degrees C resulted in the disappearance of the Fe surface state, which is attributed to Au segregation to the surface. The initial hexagonal NP arrangement on the TiO2(110) surface was preserved up to 900 …

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Pet, A Non-Ab Toxin, Is Transported And Translocated Into Epithelial Cells By A Retrograde Trafficking Pathway, Fernando Navarro-García, Adrián Canizalez-Roman, Kaitlin E. Burlingame, Ken Teter, Jorge E. Vidal Jan 2007

Pet, A Non-Ab Toxin, Is Transported And Translocated Into Epithelial Cells By A Retrograde Trafficking Pathway, Fernando Navarro-García, Adrián Canizalez-Roman, Kaitlin E. Burlingame, Ken Teter, Jorge E. Vidal

Faculty Bibliography 2000s

The plasmid-encoded toxin (Pet) of enteroaggregative Escherichia coli is a 104-kDa autotransporter protein that exhibits proteolytic activity against the actin-binding protein alpha-fodrin. Intracellular cleavage of epithelial fodrin by Pet disrupts the actin cytoskeleton, causing both cytotoxic and enterotoxic effects. Intoxication requires the serine protease activity of Pet and toxin endocytosis from clathrin-coated pits. The additional events in the intracellular trafficking of Pet are largely uncharacterized. Here, we determined by confocal microscopy that internalized Pet is transferred from the early endosomes to the Golgi apparatus and then travels to the endoplasmic reticulum (ER). Pet associates with the Sec61p translocon before it …

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Anchoring Energy And Cell Gap Effects On Liquid Crystal Response Time, Xiangyi Nie, Ruibo Lu, Haiqing Xianyu, Thomas X. Wu, Shin-Tson Wu Jan 2007

Anchoring Energy And Cell Gap Effects On Liquid Crystal Response Time, Xiangyi Nie, Ruibo Lu, Haiqing Xianyu, Thomas X. Wu, Shin-Tson Wu

Faculty Bibliography 2000s

The anchoring energy and cell gap effects on liquid crystal response time (tau(0)) is analyzed theoretically and validated experimentally. Analytical expressions are derived using two different approaches: effective cell gap and surface dynamic equation methods. Consistent results are deduced from these two approaches. A simplified equation tau(0)similar to d(x) also fits the experimental data well, where d is the liquid crystal cell gap and x is the exponent. Under two extreme (strong and weak) anchoring limits, the exponent x approaches 2 and 1, respectively. This information is helpful for optimizing liquid crystal devices for display applications.

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Spectral Filtering In A Diode-Pumped Nd : Ylf Regenerative Amplifier Using A Volume Bragg Grating, A. V. Okishev, C. Dorrer, V. I. Smirnov, L. B. Glebov, J. D. Zuegel Jan 2007

Spectral Filtering In A Diode-Pumped Nd : Ylf Regenerative Amplifier Using A Volume Bragg Grating, A. V. Okishev, C. Dorrer, V. I. Smirnov, L. B. Glebov, J. D. Zuegel

Faculty Bibliography 2000s

Instrument-limited suppression of out-of-band Amplified Spontaneous Emission (ASE) is demonstrated in a Nd:YLF Diode-Pumped Regenerative Amplifier (DPRA) using a Volume Bragg Grating (VBG) as a spectrally selective reflective element. A VBG with 99.4% diffraction efficiency and 230-pm-FWHM reflection bandwidth produced a 43-pm-FWHM output spectral width in an unseeded DPRA compared to 150-pm FWHM in the same DPRA with no VBG. Instrument-limited ASE suppression is even observed when the DPRA seed pulse energy approaches the ASE background.

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Space Velocities Of L- And T-Type Dwarfs, M. R. Zapatero Osorio, E. L. Martin, V. J. S. Béjar, H. Bouy, R. Deshpande, R. J. Wainscoat Jan 2007

Space Velocities Of L- And T-Type Dwarfs, M. R. Zapatero Osorio, E. L. Martin, V. J. S. Béjar, H. Bouy, R. Deshpande, R. J. Wainscoat

Faculty Bibliography 2000s

We have obtained radial velocities of a sample of 18 ultracool dwarfs (M6.5-T8) using high-resolution, near-infrared spectra obtained with NIRSPEC and the Keck II telescope. We have confirmed that the radial velocity of G1 570D is coincident with that of the K-type primary star G1 570A, thus providing additional support for their true companionship. The presence of planetary-mass companions around 2MASS J05591914-1404488 (T4.5 V) has been analyzed using five NIRSPEC radial velocity measurements obtained over a period of 4.37 yr. We have computed UVW space motions for a total of 21 L and T dwarfs within 20 pc of the …

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Lithium In Lp 944-20, Ya. V. Pavlenko, H. R. A. Jones, E. L. Martín, E. Guenther, M. A. Kenworthy, M. R. Zapatero Osorio Jan 2007

Lithium In Lp 944-20, Ya. V. Pavlenko, H. R. A. Jones, E. L. Martín, E. Guenther, M. A. Kenworthy, M. R. Zapatero Osorio

Faculty Bibliography 2000s

We present a new estimate of the lithium abundance in the atmosphere of the brown dwarf LP 944-20. Our analysis is based on a self-consistent analysis of low-, intermediate- and high-resolution optical and near-infrared spectra. We obtain log N(Li) = 3.25 +/not superset of 0.25 using fits of our synthetic spectra to the Li I resonance line doublet profiles observed with Very Large Telescope/Ultraviolet-Visual Echelle Spectrograph (VLT/UVES) and Anglo-Australian Telescope/Segmented Pupil/Image Reformatting Array of Lenslets (AAT/SPIRAL). This lithium abundance is over two orders of magnitude larger than previous estimates in the literature. In order to obtain good fits of the …

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Bayesian Decision Theoretic Scale-Adaptive Estimation Of A Log-Spectral Density, Marianna Pensky, Brani Vidakovic, Daniela De Canditiis Jan 2007

Bayesian Decision Theoretic Scale-Adaptive Estimation Of A Log-Spectral Density, Marianna Pensky, Brani Vidakovic, Daniela De Canditiis

Faculty Bibliography 2000s

The problem of estimating the log-spectrum of a stationary time series by Bayesian shrinkage of empirical wavelet coefficients is studied. A model in the wavelet domain that accounts for distributional properties of the log-periodogram at levels of fine detail and approximate normality at coarse levels in the wavelet decomposition, is proposed. The smoothing procedure, called BAMS-LP (Bayesian Adaptive Multiscale Shrinker of Log-Periodogram), ensures that the reconstructed log-spectrum is sufficiently noise-free. It is also shown that the resulting Bayes estimators are asymptotically optimal (in the mean-squared error sense). Comparisons with non-wavelet and wavelet-non-Bayesian methods are discussed.

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Frequentist Optimality Of Bayes Factor Estimators In Wavelet Regression Models, Marianna Pensky, Theofanis Sapatinas Jan 2007

Frequentist Optimality Of Bayes Factor Estimators In Wavelet Regression Models, Marianna Pensky, Theofanis Sapatinas

Faculty Bibliography 2000s

We investigate the theoretical performance of Bayes factor estimators in wavelet regression models with independent and identically distributed errors that are not necessarily normally distributed. We compare these estimators in terms of their frequentist optimality in Besov spaces for a wide variety of error and prior distributions. Furthermore, we provide sufficient conditions that determine whether the underlying regression function belongs to a Besov space a-priori with probability one. We also study an adaptive estimator by considering an empirical Bayes estimation procedure of the Bayes factor estimator for a certain combination of error and prior distributions. Simulated examples are used to …

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Discovery Of Radio Emission From The Tight M8 Binary Lp 349-25, Ngoc Phan-Bao, Rachel A. Osten, Jeremy Lim, Eduardo L. Martin, Paul T. P. Ho Jan 2007

Discovery Of Radio Emission From The Tight M8 Binary Lp 349-25, Ngoc Phan-Bao, Rachel A. Osten, Jeremy Lim, Eduardo L. Martin, Paul T. P. Ho

Faculty Bibliography 2000s

We present radio observations of eight ultracool dwarfs with a narrow spectral type range (M8-M9.5) using the Very Large Array at 8.5 GHz. Only the tight M8 binary LP 349 - 25 was detected. LP 349 - 25 is the tenth ultracool dwarf system detected in radio wavelengths and its trigonometric parallax pi = 67.6 mas, recently measured by Gatewood and coworkers, makes it the furthest ultracool system detected by the Very Large Array to date, and the most radio luminous outside of obvious flaring activity or variability. With a separation of only 1.8 AU, masses of the components of …

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Polarization-Induced Spectral Changes On Propagation Of Stochastic Electromagnetic Beams, Jixiong Pu, Olga Korotkova, Emil Wolf Jan 2007

Polarization-Induced Spectral Changes On Propagation Of Stochastic Electromagnetic Beams, Jixiong Pu, Olga Korotkova, Emil Wolf

Faculty Bibliography 2000s

It was shown some years ago that the spectrum of a stochastic scalar field depends not only on the source spectrum but also on the degree of coherence of the source. In this paper we show that there are electromagnetic fields for which not only the state of coherence of the source, but also its degree of polarization affect the spectrum of the radiated field. We illustrate the analysis by diagrams which show the far-zone spectra of some stochastic electromagnetic beams generated by sources of different states of coherence and different degrees of polarization. The spectra of the radiated field …

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Analysis Of Beam Wander Effects For A Horizontal-Path Propagating Gaussian-Beam Wave: Focused Beam Case, Jaume Recolons, Larry C. Andrews, Ronald L. Phillips Jan 2007

Analysis Of Beam Wander Effects For A Horizontal-Path Propagating Gaussian-Beam Wave: Focused Beam Case, Jaume Recolons, Larry C. Andrews, Ronald L. Phillips

Faculty Bibliography 2000s

Failure of the first-order Rytov approximation to properly predict the scintillation index of a large-aperture focused beam, or an uplink collimated (or focused) beam, has been discussed in several recent publications, which cite beam wander effects as the main reason for this failure. We use computer simulations to examine several aspects of beam wander phenomena on a propagating convergent beam in the weak-fluctuation regime over a horizontal path at high altitude for which the refractive index structure parameter is on the order of C-n(2)= 1.39 x 10(-16) m(-2/3). Simulation results are presented at various ranges up to 10 km for …

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Liquid-Crystal-Based Linear Polarization Rotator, Hongwen Ren, Shin-Tson Wu Jan 2007

Liquid-Crystal-Based Linear Polarization Rotator, Hongwen Ren, Shin-Tson Wu

Faculty Bibliography 2000s

A liquid-crystal (LC)-based polarization rotator which can rotate the polarization axis of an incident linearly polarized light from 0 degrees to 90 degrees is demonstrated. In the LC cell, the top substrate has a uniform rubbing but the bottom substrate has two orthogonal rubbings which are separated by a nonrubbing zone. Between these two rubbed strips, the LC directors twist continuously from 0 degrees to 90 degrees. As a result, the optic axis of the incident linearly polarized light can be rotated continuously depending on the beam position.

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Liquid Crystal Lens With Large Focal Length Tunability And Low Operating Voltage, Hongwen Ren, David W. Fox, Benjamin Wu, Shin-Tson Wu Jan 2007

Liquid Crystal Lens With Large Focal Length Tunability And Low Operating Voltage, Hongwen Ren, David W. Fox, Benjamin Wu, Shin-Tson Wu

Faculty Bibliography 2000s

We demonstrate a tunable focus liquid crystal (LC) lens by sandwiching a homogeneous LC layer between a planar electrode and a curved electrode. The curved electrode which is made of conductive polymer has parabolic shape with a large apex distance. Such design dramatically reduces the phase loss which leads to a short focal length (similar to 15 cm). By using a thin top glass substrate on the curved electrode side, the operating voltage of the lens cell for achieving the shortest focal length is reduced to similar to 23 V-rms. This LC lens has advantages in large focal length tunability, …

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Variable-Focus Liquid Lens, Hongwen Ren, Shin-Tson Wu Jan 2007

Variable-Focus Liquid Lens, Hongwen Ren, Shin-Tson Wu

Faculty Bibliography 2000s

A variable-focus liquid lens using a transparent flat cell is demonstrated. The top substrate has an aperture which is sealed with a thin elastic membrane on the outer surface and the bottom aperture is sealed on the inner surface of the bottom substrate. By applying a pressure to the outer membrane inward causes the liquid to redistribute and swell the inner membrane outward which, in turn, forms a plano-convex lens. To prove principles, a water lens with 5 mm aperture was fabricated. The resolution is better than 25 1p/mm and the response time is similar to 40 ms. Potential applications …

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Single Glass Substrate Liquid Crystal Device Using Electric Field-Enforced Phase Separation And Photoinduced Polymerization, Hongwen Ren, Shin-Tson Wu, Yi-Hsin Lin Jan 2007

Single Glass Substrate Liquid Crystal Device Using Electric Field-Enforced Phase Separation And Photoinduced Polymerization, Hongwen Ren, Shin-Tson Wu, Yi-Hsin Lin

Faculty Bibliography 2000s

An in-plane switching liquid crystal (LC) cell using a glass substrate and a photoinduced polymer layer is demonstrated. The fabrication process is based on the electrodynamics of dielectric fluids. When the fringing field is present, the LC molecules tend to aggregate in the strong electric field regions while the monomers diffuse to the weak field regions. After photopolymerization, the LC molecules are confined by a thin polymer layer and polymer walls which define the cell gap. This approach enables single-substrate large panel display devices to be fabricated.

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