bluuebunny/crossref_metadata_2025 huggingface dataset:
OCS in para-hydrogen clusters: Rotational dynamics and superfluidity
Authors: Paesani F. , Zillich R. E. , Kwon Y. , Whaley K. B.
Published: May 2005

We present a detailed analysis of the rotational excitations of the linear OCS molecule solvated by a variable number of para-hydrogen molecules (9⩽N⩽17). The effective rotational constant extracted from the fit of the rotational energy levels decreases up to N=13, indicating near-rigid coupling between OCS rotations and para-hydrogen motion. Departure from rigidity is instead seen for larger clusters with 14⩽N⩽17. Path-integral Monte Carlo calculations show that the N dependence of the effective rotational constant can be explained in terms of a partial superfluid response of para-hydrogen to rotations about an axis perpendicular to the OCS axis. Complete para-hydrogen superfluid response to rotations about the OCS axis is found for N⩾10.
Three-dimensional Child–Langmuir law for uniform hot electron emission
Authors: Koh W. S. , Ang L. K. , Kwan T. J. T.
Published: May 2005

This paper presents a three-dimensional (3D) model of Child–Langmuir (CL) law for uniform hot electron emission in planar and cylindrical gap, including the effects of finite emission energy. It is found that the enhancement of 3D CL law (in terms of 1D CL law) can be written in a general form of JC[3D]∕JC[1D]=1+F×G, where F is the normalized mean position of 1D electron flow in classical, weakly relativistic, and quantum regime, and G is the geometrical correction factor depending on the geometrical properties of the finite emitting patches on the cathode. In particular, we present the analytical solutions for various emitting patches, such as rectangle, ellipse, square, circle, triangle, and polygon, which agree very well with 3D particle-in-cell simulation. For a cylindrical gap of finite width, it is also found that the convergent flow (cathode outside) has larger enhancement than the divergent flow (cathode inside) at a given aspect ratio of outer radius to inner radius of the gap. Smooth transition from various operating regimes is demonstrated.
Development of an ITER relevant advanced scenario at ASDEX Upgrade
Authors: Gruber O. , Sips A. C. C. , Staebler A. , Dux R. , Hobirk J. , Horton L. D. , Maggi C. F. , Manini A. , Maraschek M. , Neu R. ,   ASDEX Upgrade Team, Na Y. S.
Published: May 2005

The “improved H-mode,” realized in ASDEX Upgrade [A. Herrmann and O. Gruber, Fusion Sci. Technol. 44, 569 (2003)] in 1998, demonstrates that advanced requirements beyond the standard H-mode for confinement [confinement enhancement factor H98(y,2)>1], stability (normalized beta βN∼3–3.5) and, at densities close to Greenwald density, exhaust can be simultaneously met and maintained stationary for several resistive diffusion times. The q profile is characterized by low central magnetic shear and axis safety factor q0>1 that is obtained by particular heating and current ramp-up scenarios and maintained via benign instabilities. Core transport is still governed by drift-wave turbulence with stiff temperature profiles, but density profiles are more strongly peaked and contribute to the increase in confinement. Neoclassical tearing modes remain small, enabling routine operation up to βN∼3 at international thermonuclear experimental reactor (ITER) relevant collisionalities, for normalized Lamor radii down to four times the ITER value and for a broad range of q95=3.2–4.5. Using tailored heat deposition including central wave heating a compromise was found in density peaking for enhanced confinement and limiting the high-Z impurity concentrations even with a tungsten-coated first wall and divertor. As far as the ITER [ITER EDA Documentation Series No. 24, 2002] relevance of this regime is concerned, its compatibility with significant central electron heating, high edge densities, and type-II edge localized modes is of importance. The GLF23 turbulence model predicts still peaked density profiles and sufficient transport to avoid impurity accumulation. The fusion performance in terms of βNH98(y,2)∕q952 is nearly doubled compared with the ITER base-line scenario at low-q values, while at medium q’s bootstrap current fractions up to 50% and long inductive pulse lengths allow ITER “hybrid” operation.
Effects of ion energy on the crystal size and hydrogen bonding in plasma-deposited nanocrystalline silicon thin films
Authors: Lebib S. , Roca i Cabarrocas P.
Published: May 2005

We present a detailed study of the effects of the substrate temperature, radio-frequency (rf) power, and total pressure on the crystal size and hydrogen bonding in nanocrystalline silicon thin films codeposited on the grounded and rf electrodes of an asymmetric radio frequency glow discharge reactor. Raman spectroscopy, x-ray diffraction, and spectroscopic ellipsometry measurements show that by varying the deposition parameters we can obtain crystal sizes in the range of 3–10nm and crystalline fractions in the range of 20% up to 97%. The obtaining of small crystallite sizes (4–5nm) in films submitted to high-energy (100–300eV) ion bombardment is highlighted by infrared-absorption and hydrogen evolution measurements, which display characteristic features of hydrogen bonded at the surface of the crystallites. Therefore, hydrogen bonding is a unique way to demonstrate the presence of small crystallites in films at the transition between amorphous and nanocrystalline, films which look amorphous when characterized by standard techniques such as Raman spectroscopy and x-ray diffraction.
Distinguishing bipartitite orthogonal states using LOCC: Best and worst cases
Authors: Nathanson Michael
Published: May 2005

Two types of results are presented for distinguishing pure bipartite quantum states using local operations and classical communications. We examine sets of states that can be perfectly distinguished, in particular showing that any three orthogonal maximally entangled states in C3⊗C3 form such a set. In cases where orthogonal states cannot be distinguished, we obtain upper bounds for the probability of error using LOCC taken over all sets of k orthogonal states in Cn⊗Cm. In the process of proving these bounds, we identify some sets of orthogonal states for which perfect distinguishability is not possible.
Electrical performance of contaminated rough surfaces in contact
Authors: Kogut L.
Published: May 2005

The inevitable presence of thin insulating films at the contact interface of electrical contacts has an adverse effect on their performances. An attempt is made to study the electrical performance of degraded electrical contacts where insulating films reside at the contact interface of conductive rough surfaces. The degradation mechanism is based on gradual growth of an insulating film and the characteristics of the insulating film are assumed to be known without considering details regarding the physical and chemical origins of the growth mechanisms. The present study relies on recently developed theories for electrical contact resistance of clean and fully contaminated rough surfaces, thus bridging the gap between these two extreme cases. For thick insulating films no current flow occurs across contaminated asperity contacts, whereas for thin insulating films tunneling currents are taken into account. A relationship is obtained between the degraded electrical contact resistance and the metallic conductance area. The effect of tunneling currents on the performance of partially contaminated surfaces is negligible due to the considerable current flow across the metallic asperity contacts. The electrical performance of fully contaminated surfaces is sensitive to the thickness and integrity of the insulating films and, therefore, can be exploited to study the durability of thin insulating films.
Photonic band-gap engineering of quasiperiodic photonic crystals
Authors: Wang Yiquan , Jian Shuisheng , Han Shouzhen , Feng Shuai , Feng Zhifang , Cheng Bingying , Zhang Daozhong
Published: May 2005

Band-gap engineering of quasiperiodic photonic crystals (QPC) is studied. Owing to the specific structural properties of the QPC, the distribution—especially its maximum position—of the electric field at different upper gap edge frequencies is quite varied. Therefore, by inserting metallic cylinders at different positions, the width of the gaps can be separately adjusted. This could hardly be realized in a periodic photonic crystal.
Energy transport in the Vaidya system
Authors: Krisch J. P. , Glass E. N.
Published: May 2005

Energy transport mechanisms can be generated by imposing relations between null tetrad Ricci components. Several kinds of mass and density transport generated by these relations are studied for the generalized Vaidya system.
On the Casimir of the group ISL(n,R) and its algebraic decomposition
Authors: Pecina-Cruz J. N.
Published: May 2005

In this paper, an explicit expression for the Casimir operator (or the Casimir invariant) of the inhomogeneous group ISL(n,R) in its enveloping algebra is proposed, which using contractions of the tensorial indices of the generating operators Pρ and Eμν may be presented in the following [slightly more comprehensible as Eq. (1)] form. The Casimir is obtained by symmetrizing this expression. This tensor form is useful in the classification of particles in affine gravitational gauge theories; such as that based on ISL(4,R). It is also proven that the Casimir of ISL(n,R) can be decomposed in terms of the Casimirs of its little groups, a key point in the posterior construction of its irreducible representations.
Magnetic circular dichroism study of Fe∕Co∕Cu(001) using electron yield x-ray absorption spectroscopy with different probe depths
Authors: Gao Xingyu , Xu Hai , Wee A. T. S. , Kuch W. , Tieg C. , Wang Shouguo
Published: May 2005

To obtain depth-resolved magnetic information from Fe films grown on fcc Co∕Cu(001), we have used various signal sources for the detection of x-ray absorption spectroscopy. These include total electron yield (TEY) and partial electron yield (PEY) of inelastic electrons at various kinetic energies between 70 and 470eV as well as PEY using photoelectrons at a fixed binding energy (constant initial state: CIS) near the Fermi level. Inelastic electron yield at electron emission angles up to 87° from the surface normal was found to be as nonsurface sensitive as TEY, however, the CIS mode shows a shorter information depth, comparable to the inelastic mean free path of photoelectrons. No difference in the dichroic signal at the Fe L3 edge was found between the CIS and TEY modes for a 2-monolayer (ML) Fe∕Co film, but an 8-ML Fe∕Co film showed a much higher dichroic signal in the CIS mode than that in the TEY mode. This is consistent with a homogeneous magnetic film at an Fe thickness of 2 ML and a nonhomogeneous magnetic film with a live ferromagnetic layer on the surface with nonferromagnetic underlayers at an Fe thickness of 8 ML. Thus, it is possible to extract depth-resolved magnetic information from x-ray magnetic circular dichroism by combining the surface sensitive CIS mode with other detection modes with less surface sensitivity.
Interfacial reaction in the growth of epitaxial SrTiO3 thin films on (001) Si substrates
Authors: He J. Q. , Jia C. L. , Vaithyanathan V. , Schlom D. G. , Schubert J. , Gerber A. , Kohlstedt H. H. , Wang R. H.
Published: May 2005

The SrTiO3∕Si interface was investigated by transmission electron microscopy for SrTiO3 films grown on (001) Si by molecular-beam epitaxy with different native oxide (SiO2) removal treatments, and Sr∕Ti flux ratios. The interface and film microstructure were independent of the process used to remove the native oxide, but the interface reactivity was dependent on the Sr∕Ti flux ratio. A low Sr∕Ti flux ratio (∼0.8) resulted not only in a layer of amorphous material at the film∕substrate interface but also in the formation of crystalline C49 TiSi2 precipitates at that interface. These results are consistent with thermodynamic expectations in which it is paramount to maintain separation between TiO2 and the underlying silicon.
Paraelectric and ferroelectric order in two-state dipolar fluids
Authors: Matyushov Dmitry V. , Okhrimovskyy Andriy
Published: May 2005

Monte Carlo simulations are used to examine the cooperative creation of a polar state in fluids of two-state particles with nonzero dipole in the excited state. With lowering temperature such systems undergo a second-order transition from nonpolar to polar, paraelectric phase. The transition is accompanied by a dielectric anomaly of polarization susceptibility increasing by three orders of magnitude. The paraelectric phase is then followed by a formation of a nematic ferroelectric which further freezes into a fcc ferroelectric crystal by a first-order transition. A mean-field model of phase transitions is discussed.
Experimental study of the production of vortex rings using a variable diameter orifice
Authors: Allen J. J. , Naitoh T.
Published: May 2005

A method for producing a vortex ring with an apparatus that utilizes a time varying aperture that closes during ring production is shown to have the capability for the production of rings of low nondimensional energy similar to a Hill’s spherical vortex. This represents a difference of more than 50%, in terms of the nondimensional energy, of those which have been produced with fixed diameter generators. Experiments show that modulation of the rate at which the vortex ring generator produces kinetic energy, circulation, and impulse is the critical factor in determining what type of ring is formed.
Geometric manipulation of the high-field linear magnetoresistance in InSb epilayers on GaAs (001)
Authors: Branford W. R. , Husmann A. , Solin S. A. , Clowes S. K. , Zhang T. , Bugoslavsky Y. V. , Cohen L. F.
Published: May 2005

We address the inherent high-field magnetoresistance (MR) of indium antimonide epilayers on GaAs (001), studying the modification of the MR when processed into a set of geometries. The changes produced by the geometries are quite subtle. The extraordinary MR geometry produces the highest low-field MR while the Corbino geometry produces the largest high-field magnetoresistance. We demonstrate that any material with an unsaturating linear intrinsic MR, will also have an unsaturating linear Corbino MR, and that the ideal material for linear MR sensors in conventional geometries would have a high mobility and a small, linear intrinsic MR.
Experimental demonstration of a phase-locked laser array using a self-Fourier cavity
Authors: Corcoran Christopher J. , Durville Frederic
Published: May 2005

A coherent phase-locked laser array has been experimentally demonstrated by combining the outputs of seven individual fiber lasers together in a self-Fourier cavity. By analyzing the interference fringes of the laser output in the far field of the array, a fringe visibility was measured of V=0.87, indicating a coherence of 0.73. The total output power of this laser array when operated as a coherent ensemble was 0.4watts.
Large negative magnetoresistance in a ferromagnetic shape memory alloy: Ni2+xMn1−xGa
Authors: Biswas C. , Rawat R. , Barman S. R.
Published: May 2005

5% negative magnetoresistance (MR) at room temperature has been observed in bulk Ni2+xMn1−xGa. This indicates the possibility of using Ni2+xMn1−xGa as magnetic sensors. We have measured MR in the ferromagnetic state for different compositions (x=0–0.2) in the austenitic, premartensitic, and martensitic phases. MR is found to increase with x. While MR for x=0 varies almost linearly in the austenitic and premartensitic phases, in the martensitic phase it shows a cusplike shape. This has been explained by the changes in twin and domain structures in the martensitic phase. In the austenitic phase, which does not have twin structure, MR agrees with theory based on s-d scattering model.
Instability measurements in amorphous hydrogenated silicon using capacitance-voltage techniques
Authors: Paul S. , Flewitt A. J. , Milne W. I. , Robertson J.
Published: May 2005

In the field of flat panel displays, the current leading technology is the active matrix liquid-crystal display; this uses an amorphous hydrogen silicon (a-Si:H) based thin-film transistors (TFTs) as the switching element in each pixel. However, under gate bias a-Si:H TFTs suffer from instability, as is evidenced by a shift in the gate threshold voltage. The shift in the gate threshold voltage is generally measured from the gate transfer characteristics, after subjecting the TFT to prolonged gate bias. However, a major drawback of this measurement method is that it cannot distinguish whether the shift is caused by the change in the midgap states in the a-Si:H channel or by charge trapping in the gate insulator. In view of this, we have developed a capacitance-voltage method to measure the shift in threshold voltage. We employ metal-insulator-semiconductor structures to investigate the threshold voltage shift as they are simpler to fabricate than TFTs.
Surface distribution studies and improved photoluminescence characteristics of silica coated ZnS:Mn nanophosphor layers
Authors: Haranath D. , Chander Harish , Bhalla Nitesh , Sharma Pooja , Sood K. N.
Published: May 2005

A simple methodology is presented for dispersing the silica-capped ZnS:Mn nanophosphors with controlled particle density as two-dimensional (2D) layers. Si wafer and borosilicate glass slides were taken as substrates for this method. Size-controlled ZnS:Mn nanoparticles were capped with silica for their surface passivation, growth retardation, and stabilization against environmental attacks. By varying the molar concentration of ZnS:Mn nanoparticles in silica sol, a controlled particle density on the substrates has been achieved. The morphological investigations of the layers showed that the surface distribution of the nanophosphor particles within the active area is uniform for a given molar concentration. The room-temperature photoluminescence (PL) studies of these layers showed a broad and intense peak at ∼593nm indicating a blueshift of about 7 nm compared to their conventional bulk counterparts due to quantum size effect. However, annealing of the layers improved the PL intensity by several orders attributing to the more efficient T14→A16 transitions of Mn in the nano-ZnS particles. The methodology presented of 2D layers is useful for microelectronics industry and for nanobased futuristic electroluminescent devices.
Room-temperature electric-field controlled spin dynamics in (110) InAs quantum wells
Authors: Hall K. C. , Gündoğdu K. , Hicks J. L. , Kocbay A. N. , Flatté M. E. , Boggess T. F. , Holabird K. , Hunter A. , Chow D. H. , Zinck J. J.
Published: May 2005

We report the demonstration of room temperature gate control over the electron spin dynamics using the Rashba effect in a (110) InAs∕AlSb two-dimensional electron gas. Our calculations predict that the strong spin–orbit interaction in this system produces pseudomagnetic fields exceeding 1 T when only 140 mV is applied across a single quantum well. Using this large pseudomagnetic field, we demonstrate low-power spin manipulation on a picosecond time scale. Our findings are promising for the prospect of nonmagnetic low-power, high-speed spintronics.
Ferroelectric properties of sol-gel delivered epitaxial Pb(Zrx,Ti1−x)O3 thin films on Si using epitaxial γ-Al2O3 Layers
Authors: Akai Daisuke , Yokawa Mikako , Hirabayashi Keisuke , Matsushita Koji , Sawada Kazuaki , Ishida Makoto
Published: May 2005

This letter reports on the fabrication and investigation of ferroelectric epitaxial Pb(Zr,Ti)O3(PZT)∕Pt films on Si substrates using epitaxial γ-Al2O3 buffer layer for Si integrated ferroelectric devices. (001) and (111) epitaxial γ-Al2O3 films were grown on Si(001) and Si(111) substrates, respectively, using chemical vapor deposition. PZT films with various compositions were epitaxially grown on epitaxial Pt coated substrates using a sol-gel method. Epitaxial PZT films exhibited better ferroelectric and pyroelectric properties than polycrystalline PZT films. In particular, maximum pyroelectric coefficients of the epitaxial films were obtained, with values of 1.8×10−8C∕cm2K for the PZT(001) film with a Zr∕Ti ratio of 40∕60 and 1.4×10−8C∕cm2K for the PZT(111) film with a Zr∕Ti ratio of 52∕48.
Effects of solvent and annealing on the improved performance of solar cells based on poly(3-hexylthiophene): Fullerene
Authors: Al-Ibrahim Maher , Ambacher Oliver , Sensfuss Steffi , Gobsch Gerhard
Published: May 2005

Polymer solar cells based on poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) were fabricated using two different solvents. P3HT:PCBM films casted from chlorobenzene solution absorb more red light than the films casted from chloroform solution. After thermal annealing, the films casted from chloroform show higher absorption than the films casted from chlorobenzene. Solar cells made from P3HT:PCBM chlorobenzene solution show no change in the white light power conversion efficiency (2.2%) after annealing. Solar cells processed from P3HT:PCBM chloroform solution show a white light power conversion efficiency of 1.5% without thermal annealing and 3.4% after the thermal annealing. The stated efficiencies are not corrected for the spectral mismatch.
Over 1.3μm continuous-wave laser emission from InGaSb quantum-dot laser diode fabricated on GaAs substrates
Authors: Yamamoto Naokatsu , Akahane Kouichi , Gozu Shinichirou , Ohtani Naoki
Published: May 2005

A silicon atom irradiation technique is proposed to create high-density InGaSb quantum dots (QDs) on a GaAs substrate. This technique irradiates Si atoms immediately before InGaSb QD growth, and the density of QDs with Si atoms is about 100 times higher than that without Si atoms. The high-density InGaSb QDs show long-wavelength photo- and electroluminescence emissions around 1.3 and 1.5μm in the optical communications waveband. An Sb-based QD laser diode (LD) containing an InGaSb QD active layer was fabricated on a GaAs substrate. This Sb-based QD-LD shows a 1.37μm continuous-wave laser emission at room temperature.
Model for an inversionless two-color laser
Authors: Lee C.-R. , Li Y.-C. , Men F. K. , Pao C.-H. , Tsai Y.-C. , Wang J.-F.
Published: May 2005

We propose a model, by taking advantage of quantum interference in a semiconductor quantum-well structure, for two-color lasing without population inversion. In the suggested three-well system, transitions of the lowest three excited states, being coupled to a common continuum by tunneling, to the ground state have been studied. Our results show that the emission spectrum can be arranged in accordance with the initial conditions of the excited states. With the emission peaks located in the vicinities of the absorption zeros resulting from destructive interferences, the nonreciprocal emission-absorption spectra provide a choice of inversionless lasing at two frequencies.
Highly efficient blue organic light-emitting devices incorporating a composite hole transport layer
Authors: Liao Chi-Hung , Lee Meng-Ting , Tsai Chih-Hung , Chen Chin H.
Published: May 2005

Organic light-emitting devices (OLEDs) incorporating the copper phthalocyanine (CuPc)∕N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine composite hole transport layer have been fabricated. Under optimal condition, the highly efficient sky-blue OLED based on the aminosubstituted distyrylarylene fluorescent dye, doped in the stable diphenyanthracene blue host achieved a luminance efficiency of 16.2cd∕A with a Commission Internationale d’ Eclairage (CIE)x,y color coordinate of [0.15, 0.29] at 6.4V (20mA∕cm2) and an external quantum efficiency of 8.7%.
Artificial silver ragwort surface
Authors: Gu Zhong-Ze , Wei Hong-Mei , Zhang Rui-Qian , Han Guo-Zhi , Pan Chao , Zhang Hong , Tian Xing-Jun , Chen Zhi-Ming
Published: May 2005

Creatures adapted to environmental conditions in a variety of ways, on the macroscopic as well as the microscopic scale. The evolved structures always give a hint about the design of functional materials. Recently, inspired by the trichomes on the surface of silver ragwort, we fabricated a surface with superhydrophobicity and light-shielding simultaneously by simply transforming polystyrene to the trichomeslike structure.
Dynamic amplitude-phase coupling in quantum-dot lasers
Authors: Gehrig E. , Hess O.
Published: May 2005

The well-known α-factor is a convenient measure to describe the magnitude of the amplitude-phase coupling of semiconductor lasers. But is the α-factor really a parameter? First-principle simulations of InGaAs quantum-dot lasers and amplifiers show that in spatially extended quantum-dot laser structures, the amplitude phase coupling is far from being a constant. Our computation of the α-factor demonstrates the same large and excitation-dependent variation and scatter as corresponding to experimentally determined values. Our results therefore provide a key to the interpretation and give a measure of applicability of the α-factor for the classification of quantum-dot lasers.
Mechanism of nanoblister formation in Ga+ self-ion implanted GaN nanowires
Authors: Dhara S. , Datta A. , Wu C. T. , Chen K. H. , Wang Y. L. , Muto S. , Tanabe T. , Shen C. H. , Hsu C. W. , Chen L. C. , Maruyama T.
Published: May 2005

The formation of voids and bubbles during ion implantation is an important area of material research. Void and bubble formation can result in swelling and embrittlement of metallic or semiconducting materials, and increase catalytic effects in the nanopores of the bubble. Here, we report the observation of metallic nanoblister formation in GaN nanowires under self-ion implantation using a Ga+ focused ion beam. The mechanism of the blister formation was resolved using high-resolution transmission electron microscopy equipped with electron energy loss spectroscopy and plasmon imaging.
Control of the reactivity at a metal∕silica interface
Authors: Jarrige I. , Jonnard P. , Vickridge I.
Published: May 2005

The reactivity at the Mo∕SiO2 interface is studied as a function of the method of preparation of the silica layer. Three preparation methods for the silicon substrate are considered: plasma-enhanced chemical vapor deposition, and wet and dry thermal oxidations. Respective hydrogen contents in the silica layer of 3.4, 0.5, and 0.4at.% are induced. We report on the formation of molybdenum silicides (MoSi2 and Mo5Si3) at the Mo∕SiO2 interfaces from an x-ray emission spectroscopy study of the interfacial Si 3p occupied valence states. The interfacial reactivity increases with the hydrogen content of the silica film, which is explained by the ease with which the Si–H bonds break during the early stage of the deposition of the metal by cathodic sputtering.
Characterization of density profile of laser-produced Sn plasma for 13.5nm extreme ultraviolet source
Authors: Tao Y. , Nishimura H. , Fujioka S. , Sunahara A. , Nakai M. , Okuno T. , Ueda N. , Nishihara K. , Miyanaga N. , Izawa Y.
Published: May 2005

We investigated the electron density profile corresponding to the dominant extreme ultraviolet (EUV) emission from a laser-produced Sn plasma using a combination of a green and an UV interferometer. A comparison between experimental results and a one-dimensional radiation hydrodynamic simulation shows reasonable agreement, and the discrepancy could be attributed to three-dimensional plasma expansion. It was found that, due to opacity effects, most of the EUV light comes from an under-dense plasma region.
Room-temperature photoluminescence and resonance-enhanced Raman scattering in highly degenerate InN films
Authors: Naik V. M. , Naik R. , Haddad D. B. , Thakur J. S. , Auner G. W. , Lu H. , Schaff W. J.
Published: May 2005

We report the results of room-temperature photoluminescence (PL) and resonance-enhanced Raman scattering studies on highly degenerate (carrier concentration >3×1020cm−3) InN films grown on c-plane sapphire substrates by plasma source molecular-beam epitaxy. Carrier concentration-dependent PL emission peak is observed in the 1.4–1.8 eV range. These films show strong resonance-enhanced first- and second-order Raman scattering under 785 nm (1.58 eV) excitation energy and not with 514.5 nm (2.41 eV) excitation, suggesting the existence of electronic states ∼1.5eV in these samples. The PL emission peak energies and their dependence on the carrier concentration are consistent with the observed optical absorption edges. These results are compared to the data on single crystalline, low degenerate InN film grown by molecular-beam epitaxy, which shows a band-gap energy of ∼0.6eV. The results imply a large shift in the optical absorption edges due to band filling effects in the highly degenerate InN samples.
Space-charge-limited current involving carrier injection into impurity bands of high-k insulators
Authors: Goldenblum A. , Pintilie I. , Buda M. , Popa A. , Botila T. , Dimoulas A. , Vellianitis G.
Published: May 2005

Photoelectrical measurements have shown that the current flow through La2Hf2O7 and LaAlO3 high-k insulator layers deposited on silicon takes place via impurity channels. A space charge limited current is evidenced, for different insulator thicknesses and temperatures, by the square law dependence of current versus voltage. The analysis demonstrates that this space charge limited (SCL) current in thin insulator films can be explained only by the presence of impurity channels situated near the Fermi level of the injecting contact. Many other aspects related to the SCL current behavior were found.
The use of oscillatory signals in the study of genetic networks
Authors: Lipan Ovidiu , Wong Wing H.
Published: May 2005

The structure of a genetic network is uncovered by studying its response to external stimuli (input signals). We present a theory of propagation of an input signal through a linear stochastic genetic network. We found that there are important advantages in using oscillatory signals over step or impulse signals and that the system may enter into a pure fluctuation resonance for a specific input frequency.
Role of peripheral corticotropin-releasing factor and urocortin II in intestinal inflammation and motility in terminal ileum
Authors: la Fleur Susanne E. , Wick Elizabeth C. , Idumalla Prema S. , Grady Eileen F. , Bhargava Aditi
Published: May 2005

Corticotropin-releasing factor (CRF) and the closely related family of neuropeptides urocortins (Ucns) are ancient paracrine-signaling peptides secreted in both the central and peripheral neural circuits. CRF and Ucns released from the CNS (central) regulate a plethora of physiological processes that include food intake, inflammation, and bowel motility and permeability. In the gastrointestinal tract, CRF actions are largely proinflammatory, whereas the effects of the Ucn subtypes can be either pro- or antiinflammatory. Central (intracerebroventricular) or peripheral (i.p.) administration of CRF or Ucns inhibits gastric emptying and promotes colonic motility. To ascertain the role of peripherally expressed CRF and UcnII in gastrointestinal inflammation and motility, we generated ileum-specific phenotypic knockouts of these peptides by using RNA interference. Long dsRNA effectively silenced basal expression of CRF and UcnII in ileum. Control dsRNA or saline treatment did not affect CRF or UcnII expression. In an experimental model of toxin-induced intestinal inflammation, inhibition of CRF ablated the inflammatory response (measured by epithelial damage, mucosal edema, and neutrophil infiltration). UcnII dsRNA treatment did not alter the inflammatory response to toxin. Furthermore, ileal motility was increased after site-specific inhibition of both CRF and UcnII. Thus, we demonstrate that ileal-specific CRF promotes inflammation and both CRF and UcnII modulate bowel motility.
Structural properties of Aβ protofibrils stabilized by a small molecule
Authors: Williams Angela D. , Sega Matt , Chen Maolian , Kheterpal Indu , Geva Merav , Berthelier Valerie , Kaleta David T. , Cook Kelsey D. , Wetzel Ronald
Published: May 2005

Metastable oligomeric and protofibrillar forms of amyloidogenic proteins have been implicated as on-pathway assembly intermediates in amyloid formation and as the major toxic species in a number of amyloid diseases including Alzheimer's disease. We describe here a chemical biology approach to structural analysis of Aβ protofibrils. Library screening yielded several molecules that stimulate Aβ aggregation. One of these compounds, calmidazolium chloride (CLC), rapidly and efficiently converts Aβ(1-40) monomers into clusters of protofibrils. As monitored by electron microscopy, these protofibrils persist for days when incubated in PBS at 37°C, with a slow transition to fibrillar structures apparent only after several weeks. Like normal protofibrils, the CLC-Aβ aggregates exhibit a low thioflavin T response. Like Aβ fibrils, the clustered protofibrils bind the anti-amyloid Ab WO1. The CLC-Aβ aggregates exhibit the same protection from hydrogen-deuterium exchange as do protofibrils isolated from a spontaneous Aβ fibril formation reaction: ≈12 of the 39 Aβ(1-40) backbone amide protons are protected from exchange in the protofibril, compared with approximately twice that number in amyloid fibrils. Scanning proline mutagenesis analysis shows that the Aβ molecule in these protofibrillar assemblies exhibits the same flexible N and C termini as do mature amyloid fibrils. The major difference in Aβ conformation between fibrils and protofibrils is added structural definition in the 22-29 segment in the fibril. Besides aiding structural analysis, compounds capable of facilitating oligomer and protofibril formation might have therapeutic potential, if they act to sequester Aβ in a form and/or location that cannot engage the toxic pathway.
De novo
cis-regulatory module elicitation for eukaryotic genomes
Authors: Gupta Mayetri , Liu Jun S.
Published: May 2005

Transcription regulation is controlled by coordinated binding of one or more transcription factors in the promoter regions of genes. In many species, especially higher eukaryotes, transcription factor binding sites tend to occur as homotypic or heterotypic clusters, also known as cis-regulatory modules. The number of sites and distances between the sites, however, vary greatly in a module. We propose a statistical model to describe the underlying cluster structure as well as individual motif conservation and develop a Monte Carlo motif screening strategy for predicting novel regulatory modules in upstream sequences of coregulated genes. We demonstrate the power of the method with examples ranging from bacterial to insect and human genomes.
The Nkx6.1 homeodomain transcription factor suppresses glucagon expression and regulates glucose-stimulated insulin secretion in islet beta cells
Authors: Schisler Jonathan C. , Jensen Per Bo , Taylor David G. , Becker Thomas C. , Knop Filip Krag , Takekawa Shiro , German Michael , Weir Gordon C. , Lu Danhong , Mirmira Raghavendra G. , Newgard Christopher B.
Published: May 2005

We have previously described rat insulinoma INS-1-derived cell lines with robust or poor glucose-stimulated insulin secretion (GSIS). In the current study, we have further resolved these lines into three classes: class 1, glucose-unresponsive/glucagon-expressing; class 2, glucose-unresponsive/glucagon-negative; and class 3, glucose-responsive/glucagon-negative. The transcription factor Nkx2.2 was expressed with relative abundance of 3.3, 1.0, and 1.0 in class 1, class 2, and class 3 cells, respectively, whereas Nkx6.1 expression had the opposite trend: 1.0, 2.6, and 6.4 in class 1, class 2, and class 3 cells, respectively. In class 1 cells, overexpressed Nkx6.1 suppressed glucagon expression but did not affect the levels of several other prominent beta cell transcription factors. RNA interference (RNAi)-mediated suppression of Nkx6.1 in class 3 cells resulted in a doubling of glucagon mRNA, with no effect on Pdx1 levels, whereas suppression of Pdx1 in class 3 cells caused a 12-fold increase in glucagon transcript levels, demonstrating independent effects of Nkx6.1 and Pdx1 on glucagon expression in beta cell lines. RNAi-mediated suppression of Nkx6.1 expression in class 3 cells also caused a decrease in GSIS from 13.9- to 3.7-fold, whereas suppression of Pdx1 reduced absolute amounts of insulin secretion without affecting fold response. Finally, RNAi-mediated suppression of Nkx6.1 mRNA in primary rat islets was accompanied by a significant decrease in GSIS relative to control cells. In sum, our studies have revealed roles for Nkx6.1 in suppression of glucagon expression and control of GSIS in islet beta cells.
Predicted highly expressed genes in archaeal genomes
Authors: Karlin Samuel , Mrázek Jan , Ma Jiong , Brocchieri Luciano
Published: May 2005

Based primarily on 16S rRNA sequence comparisons, life has been broadly divided into the three domains of Bacteria, Archaea, and Eukarya. Archaea is further classified into Crenarchaea and Euryarchaea. Archaea generally thrive in extreme environments as assessed by temperature, pH, and salinity. For many prokaryotic organisms, ribosomal proteins (RP), transcription/translation factors, and chaperone genes tend to be highly expressed. A gene is predicted highly expressed (PHX) if its codon usage is rather similar to the average codon usage of at least one of the RP, transcription/translation factors, and chaperone gene classes and deviates strongly from the average gene of the genome. The thermosome (Ths) chaperonin family represents the most salient PHX genes among Archaea. The chaperones Trigger factor and HSP70 have overlapping functions in the folding process, but both of these proteins are lacking in most archaea where they may be substituted by the chaperone prefoldin. Other distinctive PHX proteins of Archaea, absent from Bacteria, include the proliferating cell nuclear antigen PCNA, a replication auxiliary factor responsible for tethering the catalytic unit of DNA polymerase to DNA during high-speed replication, and the acidic RP
P
0
, which helps to initiate mRNA translation at the ribosome. Other PHX genes feature Cell division control protein 48 (Cdc48), whereas the bacterial septation proteins FtsZ and minD are lacking in Crenarchaea. RadA is a major DNA repair and recombination protein of Archaea. Archaeal genomes feature a strong Shine-Dalgarno ribosome-binding motif more pronounced in Euryarchaea compared with Crenarchaea.
Serum IgG mediates mucosal immunity against rotavirus infection
Authors: Westerman Larry E. , McClure Harold M. , Jiang Baoming , Almond Jeffrey W. , Glass Roger I.
Published: May 2005

We evaluated the protective role of passively transferred circulating antibodies in protecting non-human primates against experimental rotavirus infection. Pooled sera with rotavirus-specific IgG titers that were either high (1:10,000), intermediate (1:300), or negative (<1:25) were infused i.v. into naïve pigtailed macaques (ages 3-6 months). Rotavirus-specific IgG could be detected in the sera at 18 h in all animals infused with antibody-containing serum, and fecal IgG titers could be detected only in animals given high-titer pooled sera. When orally challenged with 106fluorescent-forming units of a simian rotavirus strain, YK-1, at 18 h after serum transfer, control animals shed virus starting 1-3 days after challenge and continued to shed virus at high titers for 6-8 days, whereas passively immunized macaques did not shed virus or had delayed shedding at low titers for only a limited time. The observation that passively transferred antibodies can suppress or delay viral infection in rotavirus-challenged pigtailed macaques has important implications for the design and testing of parenteral candidate rotavirus vaccines.
Conservation and evolvability in regulatory networks: The evolution of ribosomal regulation in yeast
Authors: Tanay Amos , Regev Aviv , Shamir Ron
Published: May 2005

Transcriptional modules of coregulated genes play a key role in regulatory networks. Comparative studies show that modules of coexpressed genes are conserved across taxa. However, little is known about the mechanisms underlying the evolution of module regulation. Here, we explore the evolution of cis-regulatory programs associated with conserved modules by integrating expression profiles for two yeast species and sequence data for a total of 17 fungal genomes. We show that although the cis-elements accompanying certain conserved modules are strictly conserved, those of other conserved modules are remarkably diverged. In particular, we infer the evolutionary history of the regulatory program governing ribosomal modules. We show how a cis-element emerged concurrently in dozens of promoters of ribosomal protein genes, followed by the loss of a more ancient cis-element. We suggest that this formation of an intermediate redundant regulatory program allows conserved transcriptional modules to gradually switch from one regulatory mechanism to another while maintaining their functionality. Our work provides a general framework for the study of the dynamics of promoter evolution at the level of transcriptional modules and may help in understanding the evolvability and increased redundancy of transcriptional regulation in higher organisms.
Four-dimensional ultrafast electron microscopy
Authors: Lobastov Vladimir A. , Srinivasan Ramesh , Zewail Ahmed H.
Published: May 2005

Electron microscopy is arguably the most powerful tool for spatial imaging of structures. As such, 2D and 3D microscopies provide static structures with subnanometer and increasingly with ångstrom-scale spatial resolution. Here we report the development of 4D ultrafast electron microscopy, whose capability imparts another dimension to imaging in general and to dynamics in particular. We demonstrate its versatility by recording images and diffraction patterns of crystalline and amorphous materials and images of biological cells. The electron packets, which were generated with femtosecond laser pulses, have a de Broglie wavelength of 0.0335 Å at 120 keV and have as low as one electron per pulse. With such few particles, doses of few electrons per square ångstrom, and ultrafast temporal duration, the long sought after but hitherto unrealized quest for ultrafast electron microscopy has been realized. Ultrafast electron microscopy should have an impact on all areas of microscopy, including biological imaging.
Coevolution of TCR-MHC interactions: Conserved MHC tertiary structure is not sufficient for interactions with the TCR
Authors: Kim Hye-Jung , Guo Donglin , Sant'Angelo Derek B.
Published: May 2005

The specificity for self-MHC that is necessary for T cell function is a consequence of intrathymic selection during which T cell antigen receptors (TCRs) expressed by immature thymocytes are tested for their affinity for self-peptide:self-MHC. The germ-line-encoded segments of the TCR, however, are believed to have an innate specificity for structural features of MHC molecules. We directly tested this hypothesis by generating a transgenic mouse system in which the protein HLA-DM is expressed at the surface of thymic cortical epithelial cells in the absence of classical MHC molecules. The specialized intracellular function of HLA-DM has removed this MHC class II-like protein from the evolutionary forces that have been hypothesized to shape TCR-MHC interactions. Our study shows that a structural mimic of MHC class II is not sufficient to appropriately interact with the TCRs expressed by developing thymocytes. This result emphasizes the unique complementarity of TCR-MHC interactions that are maintained by the evolutionary pressures dictated by positive selection.
Analysis of the population of competing British sport horses as measured by lifetime performance: structural distributions at different levels of competition
Authors: Whitaker TC , Hill J
Published: May 2005

A preliminary investigation into the structure of the competing sport horse population within the UK for the year 2000 was undertaken, comprising 30 974 horses and 39 679 individual performances. All performance data were expressed as total lifetime winnings. The level of non-winning horses, expressed as a percentage, was high in all disciplines: dressage 22%, eventing 50% and show jumping 23%. The percentage of horses competing in disciplines at the highest recognized level was small: dressage 2.5%, eventing 10% and show jumping 6.5%. Highest earners for all disciplines all earned considerably more than the threshold for highest performance level in their respective discipline (×2.2 dressage, ×24 eventing, ×365 show jumping). Data for all three disciplines were highly skewed. Structural analysis of the distributions by level showed a highly skewed hypogeometric distribution at the lowest level of competition for all disciplines, uniform distribution at intermediate levels (bimodal tendencies were observed within dressage) and normal distribution at advanced levels. Product–moment correlations showed a significant correlation between show jumping and eventing (0.228, P<0.01). Problems with data availability and presentation may mean that up to 12.9% of the population may have had a confounding effect on the results of this study.
Exercise stress, intestinal permeability and gastric ulceration in racing Alaskan sled dogs
Authors: Royer Christopher M , Willard Michael , Williamson Katherine , Steiner Jörg M , Williams David A , David Michael
Published: May 2005

Sustained strenuous exercise has been shown to produce gastrointestinal disease in athletic species, but the causative factors remain unknown. Since exercise results in oxidative stress and hypercortisolaemia, we tested the hypothesis that oxidative and physiological stress cause gastrointestinal disease in racing Alaskan sled dogs. Dogs from three racing teams were examined before (pre) and immediately after (post) completing a 1770-km sled dog race in approximately 11 days. Serum cortisol and isoprostane concentrations were compared with markers of gastrointestinal barrier integrity and endoscopic evidence of gastric ulceration. Gastric barrier integrity was assessed by measuring the urinary recovery of sucrose and intestinal barrier integrity was assessed using the urinary recovery ratio of lactulose to rhamnose (L/R), administered together by orogastric gavage. Exercise produced a significant increase in median serum cortisol (pre: 1040, 717–2946 pg ml−1(range); post: 8072, 2228–29 571 pg ml−1;P<0.0001) and L/R recovery ratio (pre: 0.110, 0.060–0.270; post: 0.165, 0.080–0.240;P=0.009) but not isoprostane (pre: 1007, 656–2305 pg ml−1; post: 1164, 23–4710 pg ml−1;P=0.194) concentration. The increased serum cortisol concentration was not correlated with a change in L/R recovery ratio or urine sucrose concentration. Dogs with abnormal gastric endoscopy results (61% of finishers) had higher serum cortisol concentrations than dogs with normal endoscopy results (P=0.0007). We have demonstrated concurrent hypercortisolaemia and gastrointestinal barrier dysfunction with no correlation of the two. Thus, our data do not provide support for the hypothesis that increased serum cortisol concentration causes exercise-induced gastrointestinal disease.