bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamics of anions and cations in cesium hydrogensulfide (CsHS, CsDS): Neutron and x-ray diffraction, calorimetry and proton NMR investigations
Authors: Haarmann F. , Jacobs H. , Kockelmann W. , Senker J. , Müller P. , Kennedy C. A. , Marriott R. A. , Qiu L. , White M. A.
Published: September 2002

Protonated and deuterated samples of the hydrogensulfide of cesium were studied by high-resolution neutron powder diffraction, calorimetry and proton NMR investigations in a wide temperature range. Primarily due to reorientational disorder of the anions, three modifications of the title compounds are known: an ordered low-temperature modification—LTM (tetragonal, I4/m, Z=8), a dynamically disordered middle-temperature modification—MTM (tetragonal, P4/mbm, Z=2), and a high-temperature modification—HTM (cubic, Pm3̄m, Z=1). The LTM⇄MTM phase transition is continuous. Its order parameter, related to an order/disorder and to a displacive part of the phase transition, coupled bilinearly, follows a critical law. The critical temperature TC=123.2±0.5 K determined by neutron diffraction of CsDS is in good agreement with TC=121±2 K obtained by calorimetric investigations. For the protonated title compound a shift to TC=129±2 K was observed by calorimetric measurements. The entropy change of this transition is (0.24±0.04) R and (0.27±0.04) R for CsHS and CsDS, respectively. The MTM⇄HTM phase transition is clearly of first order. The transition temperatures of CsHS and CsDS are T=207.9±0.3 K and T=213.6±0.3 K with entropy changes of (0.86±0.01) R and (0.81±0.01) R, respectively. Second moments (M2) of the proton NMR absorption signal of MTM and HTM are in reasonable agreement with M2 calculated for the known crystal structures. A minimum in spin-lattice relaxation times (T1) in the MTM could not be assigned by dipolar coupling to a two-site 180° reorientation of the anions, a model of motion presumed by the knowledge of the crystal structure. The activation enthalpies determined by fits of T1 presuming a thermal activated process are in the order of molecular reorientations (Ea=13.5±0.5 kJ mol−1 for the MTM and Ea=9.3±0.3 kJ mol−1 for the HTM). In the HTM at T>330 K translational motion of the cations determines T1 (Ea=13.8±0.4 kJ mol−1).
Assertion and validation of the performance of the B3LYP⋆ functional for the first transition metal row and the G2 test set
Authors: Salomon Oliver , Reiher Markus , Hess Bernd Artur
Published: September 2002

The exact exchange part in hybrid density functionals is analyzed with respect to the prediction of ground state multiplicities. It has been found [M. Reiher, O. Salomon, and B. A. Hess, Theor. Chem. Acc., 107, 48 (2001)] that pure and hybrid density functionals yield energy splittings between high-spin and low-spin states of Fe–sulfur complexes that differ by more than 100 kJ/mol and thus fail to reliably predict the correct multiplicity of the ground state. This deviation can lead to meaningless reaction energetics for metal-catalyzed reactions. The finding that the energy splitting depends linearly on the exact exchange admixture parameter led to a new parametrization of the B3LYP functional which was dubbed B3LYP⋆. In the present paper we investigate the generality and transferability of this functional. We study the extent to which the exact exchange admixture affects the thermochemistry validated with respect to the reference data set of molecules from the G2 test set. Metallocenes and bis(benzene) metal complexes of the first transition metal period are chosen to test the transferability of the findings for Fe–sulfur complexes. Moreover, the slope of the linear dependence of the energy splitting of high-spin and low-spin states on the amount of admixture of exact exchange is studied in detail.
Adaptive nudged elastic band approach for transition state calculation
Authors: Maragakis P. , Andreev Stefan A. , Brumer Yisroel , Reichman David R. , Kaxiras Efthimios
Published: September 2002

We present a method for the location of transition states in complicated physical systems. Our algorithm is a variation of the well-established nudged elastic band method and leads to significant improvements in efficiency and accuracy. We assess the applicability of our method by testing it on several systems of practical interest representing a variety of physical situations. At the molecular level, we apply the method to tautomerization processes in nucleic acid bases and the double proton transfer in nucleic acid base pairs. For bulk systems, we considered the concerted exchange mechanism in Si, which is a complicated pathway for defect-free diffusion in the diamond lattice. For surface systems, we considered ad-dimer diffusion mechanisms on Si(100). We incorporated the climbing image extension of the nudged elastic band method and compared it against the original approach on two-dimensional model potential energy surfaces. Based on favorable comparisons with related methods and the general implementation of our method, we believe that this is well suited for efficient estimates of activation barriers with sophisticated electronic structure codes.
A lower bound on the quantum capacity of channels with correlated errors
Authors: Hamada Mitsuru
Published: September 2002

The highest fidelity of quantum error-correcting codes of length n and rate R is proven to be lower bounded by 1−exp[−nE(R)+o(n)] for some function E(R) on noisy quantum channels that are subject to not necessarily independent errors. The E(R) is positive below some threshold R0, which implies R0 is a lower bound on the quantum capacity. This work is an extension of the author’s previous works [M. Hamada, Phys. Rev. A, 65, 052305 (2002); quant-ph/0109114, LANL (2001); M. Hamada, quant-ph/0112103, LANL (2001)], which presented the bound for channels subject to independent errors, or channels modeled as tensor products of copies of a completely positive linear map. The relation of the channel class treated in this article to those in the previous works is similar to that of Markov chains to sequences of independent identically distributed random variables.
Solution to Michaelis–Menten enzyme kinetic equation via undetermined gauge functions: Resolving the nonlinearity of Lineweaver–Burk plot
Authors: Murugan R.
Published: September 2002

A composite approximate solution of Michaelis–Menten enzyme kinetic equation, which could describe both transient and slow dynamics, was obtained by ordinary perturbation methods in terms of undetermined gauge functions up to a first-order level. It was found that the zeroth-order perturbation function itself solved the paradox due to steady-state approximation and predicted well the maximum enzyme-substrate complex ([ES]max) and time tm to attain it. Extensive kinetic simulations using a chemical kinetic simulator proved the validity of these results. A comparison between simulated and predicted results showed that error in the prediction of tm was negligible when perturbation parameter falls in the range of (0<ε≪1). Apart from these, also the effect of transient dynamics on the linearity of Lineweaver–Burk plot (especially near the origin) has been explained.
Frontside versus backside reactivity in electron transfer to oriented tert butyl bromide and methyl bromide
Authors: Brooks Philip R. , Harris Sean A.
Published: September 2002

Electron transfer collisions between beams of neutral K atoms and neutral alkyl bromide (R–Br) molecules (R=CH3,t-C4H9) are observed by detecting positive and negative ions in coincidence for energies ≳4 eV, the minimum energy for overcoming the Coulomb attraction between ions. The molecules are state selected by a hexapole electric field and oriented prior to the electron transfer. The steric asymmetry for both molecules above ≈6 eV shows that “frontside,” or Br end attack, is favored to form Br−, with t-C4H9Br being more asymmetric than CH3Br. The asymmetry maximizes near 5 eV and as the energy decreases, apparently changes sign to favor “backside,” or alkyl-end attack. Free electrons (and K+) are detected from t-C4H9Br and show a similar change in preferred orientation: at low energies alkyl end attack is favored, and at high energies Br end is favored. These observations suggest that the electron is transferred into different orbitals with different spatial distributions as the energy is varied. Steric factors are evaluated from the experimental data. The steric factor for t-C4H9Br is generally smaller than for CH3Br and above about 5 eV, both increase with energy in Arrhenius-type dependence. The apparent “steric activation energy” is ≈2.2 eV for CH3Br and 3.9 eV for t-C4H9Br.
Green electroluminescence from a Tb-doped AlN thin-film device on Si
Authors: Lu F. , Carius R. , Alam A. , Heuken M. , Buchal Ch.
Published: September 2002

Green photoluminescence and electroluminescence (EL) from Tb implanted AlN films have been observed at room temperature. The AlN films of 180 nm thickness were grown on n-type Si(111) by metalorganic chemical vapor deposition. X-ray diffraction shows that the AlN is polycrystalline. The AlN films were doped by ion implantation of Tb to a peak concentration of 1 at. %. A postimplantation annealing step was required to obtain optically active Tb ions. A dc EL device was fabricated using a transparent ZnO:Al top electrode. The strong room-temperature green light emission was observable with the naked eye. It was obtained with a drive current density of 2–70 mA/cm2 at a drive voltage of 70–100 V. The emission lines between 490 and 650 nm originate from Tb3+ transitions from the D45 level to ground state multiplets. The observed luminescence lifetimes are approximately 0.5 ms.
The anionic complex Cl−⋯ HCCH: Results of large-scale coupled cluster calculations
Authors: Botschwina Peter , Oswald Rainer
Published: September 2002

On the basis of large-scale coupled-cluster calculations the dissociation energy of the complex Cl−⋯ HCCH is predicted to be D0=3600 cm−1, with an uncertainty of the order of 1%. The ground state rotational constant is obtained to be 2053 (10) MHz and the wave number of the hydrogen-bonded CH stretching vibration is 2877±10 cm−1. Anharmonicity constants for the stretching vibrations are discussed in comparison with those calculated earlier for Br−⋯ HCCH and I−⋯ HCCH [P. Botschwina and H. Stoll, Phys. Chem. Chem. Phys. 3, 1965 (2001)].
Longitudinal and transverse piezoelectric coefficients of lead zirconate titanate/vinylidene fluoride-trifluoroethylene composites with different polarization states
Authors: Zeng R. , Kwok K. W. , Chan H. L. W. , Choy C. L.
Published: September 2002

Composite films comprising lead zirconate titanate (PZT) ceramic particles dispersed in a vinylidene fluoride-trifluoroethylene copolymer matrix have been prepared by compression molding. The ceramic and copolymer phases of the composite films are polarized separately, resulting in samples with three different polarization states: only the ceramic phase polarized, both phases polarized in the same direction, and two phases polarized in opposite directions. The effect of polarization state on the longitudinal and transverse piezoelectric coefficients (d33 and d31) of the composite film has been investigated as functions of ceramic volume fraction φc. When the ceramic and copolymer phases of a composite film are polarized in the same direction, their piezoelectric activities partially cancel each other, thereby giving almost zero piezoelectric activity at φc∼0.4. On the other hand, when the phases of a composite film are polarized in opposite directions, their piezoelectric activities reinforce. However, depolarization of the ceramic phase is observed at high φc, leading to a decrease in the piezoelectric activity. The observed d33 and d31 values for the composite films agree well with theoretical predictions.
The entanglement of purification
Authors: Terhal Barbara M. , Horodecki Michał , Leung Debbie W. , DiVincenzo David P.
Published: September 2002

We introduce a measure of both quantum as well as classical correlations in a quantum state, the entanglement of purification. We show that the (regularized) entanglement of purification is equal to the entanglement cost of creating a state ρ asymptotically from maximally entangled states, with negligible communication. We prove that the classical mutual information and the quantum mutual information divided by two are lower bounds for the regularized entanglement of purification. We present numerical results of the entanglement of purification for Werner states in H2⊗H2.
Monte Carlo wave packet study of negative ion mediated vibrationally inelastic scattering of NO from the metal surface
Authors: Li Shenmin , Guo Hua
Published: September 2002

The scattering dynamics of vibrationally excited NO from a metal surface is investigated theoretically using a dissipative model that includes both the neutral and negative ion states. The Liouville–von Neumann equation is solved numerically by a Monte Carlo wave packet method, in which the wave packet is allowed to “jump” between the neutral and negative ion states in a stochastic fashion. It is shown that the temporary population of the negative ion state results in significant changes in vibrational dynamics, which eventually lead to vibrationally inelastic scattering of NO. Reasonable agreement with experiment is obtained with empirical potential energy surfaces. In particular, the experimentally observed facile multiquantum relaxation of the vibrationally highly excited NO is reproduced. The simulation also provides interesting insight into the scattering dynamics.
Dielectric measurement to probe electron ordering and electron-spin interaction
Authors: Zheng X. G. , Sakurai Y. , Okayama Y. , Yang T. Q. , Zhang L. Y. , Yao X. , Nonaka K. , Xu C. N.
Published: September 2002

Here we found that dielectric measurement can be a sensitive probe to detect the behavior of electrons and electron-spin interaction in a strongly electron-correlated system. The CuO single crystal samples with and without excess holes were investigated by dielectric measurements in combination with magnetic susceptibility measurement. Only for the semiconducting single crystal with holes was dynamic dielectric relaxation with prominent frequency dispersion and large dielectric constants observed, suggesting localization of holes in the lattice. Coupling of hole and spin was directly observed by dielectric anomalies at the magnetic phase transitions. A pseudoferroelectric-like characteristic in the E–P plot was also observed. This study verifies that the holes are strongly coupled both to the vibrational and magnetic degrees of freedom in CuO. It also suggests the possibility of using dielectric measurement as a tool to investigate the coupling of electron and spin in strong correlated systems.
Determination of inter- and intragranular currents in high temperature superconducting tapes and coated conductors
Authors: Tönies S. , Vostner A. , Weber H. W.
Published: September 2002

The inter- and intragranular critical current densities were determined for different types of coated conductors as well as mono- and multifilamentary (BiPb)2Sr2Ca2Cu3Ox tapes. Either the inter- or the intragranular critical current density was changed systematically by bending the tapes or by neutron irradiation, respectively. Thus, we are able to assess these two critical current densities, even in samples with very good grain connectivity.
Electron-beam enhancement of the metal vapor vacuum arc ion source
Authors: Batalin V. A. , Bugaev A. S. , Gushenets V. I. , Hershcovitch A. , Johnson B. M. , Kolomiets A. A. , Kuibeda R. P. , Kulevoy T. V. , Oks E. M. , Pershin V. I. , Petrenko S. V. , Seleznev D. N. , Yushkov G. Yu.
Published: September 2002

We report detailed investigations of the electron-beam metal vapor vacuum arc (E-MEVVA) ion source. The experiments were performed in Moscow and Tomsk with nearly the same design of ion sources. We recently reported the first conclusive demonstration of electron-beam enhancement of MEVVA performance using lead and bismuth cathodes, which yielded maximum ion charge states of Pb7+ and Bi8+ for E-MEVVA, as compared to Pb2+ and Bi2+ for conventional MEVVA operation. In this article we report extensive results for additional cathode materials, further details of the Moscow and Tomsk ion sources, and a discussion of electron beam effects on E-MEVVA performance. These results can be considered as a proof of the E-MEVVA principle.
Solid-state decomposition of silicon carbide for growing ultra-thin heteroepitaxial graphite films
Authors: Charrier A. , Coati A. , Argunova T. , Thibaudau F. , Garreau Y. , Pinchaux R. , Forbeaux I. , Debever J.-M. , Sauvage-Simkin M. , Themlin J.-M.
Published: September 2002

Using grazing-incidence x-ray diffraction and scanning tunneling microscopy (STM), we show that the thermal decomposition of an electronic-grade wafer of 6H-SiC after annealing at increasing temperatures TA between 1080 and 1320 °C leads to the layer-by-layer growth of unconstrained, heteroepitaxial single-crystalline graphite. The limited width of the in-plane diffraction rod profiles of graphite reveals large terraces, with an average size larger than 200 Å and a very small azimuthal disorientation. The overlayer is unstrained and adopts the crystalline parameter of bulk graphite even at the smallest coverage studied, which corresponds to a single graphene plane, as inferred from the flat out-of-plane diffraction profile. By increasing TA, additional graphene planes can be grown below this graphite layer from the solid-state decomposition of SiC, forming the AB stacking of Bernal graphite. A C-rich precursor is evidenced in STM by an intrinsic (6×6) reconstruction made of ordered ring or starlike structures. The resulting epitaxial film is indistinguishable from a bulk graphite single crystal.
Qubits as parafermions
Authors: Wu L.-A. , Lidar D. A.
Published: September 2002

Qubits are neither fermions nor bosons. A Fock space description of qubits leads to a mapping from qubits to parafermions: particles with a hybrid boson-fermion quantum statistics. We study this mapping in detail, and use it to provide a classification of the algebras of operators acting on qubits. These algebras in turn classify the universality of different classes of physically relevant qubit-qubit interaction Hamiltonians. The mapping is further used to elucidate the connections between qubits, bosons, and fermions. These connections allow us to share universality results between the different particle types. Finally, we use the mapping to study the quantum computational power of certain anisotropic exchange Hamiltonians. In particular, we prove that the XY model with nearest-neighbor interactions only is not computationally universal. We also generalize previous results about universal quantum computation with encoded qubits to codes with higher rates.
Thermal stability of polycrystalline silicon electrodes on ZrO2 gate dielectrics
Authors: Perkins Charles M. , Triplett Baylor B. , McIntyre Paul C. , Saraswat Krishna C. , Shero Eric
Published: September 2002

Thermal stability of gate stack structures composed of ZrO2 gate dielectrics and silicon electrodes was investigated. The ZrO2 films were deposited by atomic layer deposition, while the polycrystalline silicon electrodes were deposited using different variants of chemical (CVD) and physical vapor deposition (PVD). Zirconium silicide formation was noted in all CVD-electroded samples after subsequent annealing treatments at temperatures above 750 °C, but not in the room temperature PVD-electroded samples, even after gate annealing at 1050 °C. The dependence of zirconium silicide formation on the Si deposition process was explained using thermodynamic arguments which explicitly include the effects of oxygen deficiency of the metal oxide films.
Topological quantum memory
Authors: Dennis Eric , Kitaev Alexei , Landahl Andrew , Preskill John
Published: September 2002

We analyze surface codes, the topological quantum error-correcting codes introduced by Kitaev. In these codes, qubits are arranged in a two-dimensional array on a surface of nontrivial topology, and encoded quantum operations are associated with nontrivial homology cycles of the surface. We formulate protocols for error recovery, and study the efficacy of these protocols. An order-disorder phase transition occurs in this system at a nonzero critical value of the error rate; if the error rate is below the critical value (the accuracy threshold), encoded information can be protected arbitrarily well in the limit of a large code block. This phase transition can be accurately modeled by a three-dimensional Z2 lattice gauge theory with quenched disorder. We estimate the accuracy threshold, assuming that all quantum gates are local, that qubits can be measured rapidly, and that polynomial-size classical computations can be executed instantaneously. We also devise a robust recovery procedure that does not require measurement or fast classical processing; however, for this procedure the quantum gates are local only if the qubits are arranged in four or more spatial dimensions. We discuss procedures for encoding, measurement, and performing fault-tolerant universal quantum computation with surface codes, and argue that these codes provide a promising framework for quantum computing architectures.
Spectroscopic characterization of stress-induced leakage current in sub 5-nm-thick silicon oxide film
Authors: Komiya Kenji , Omura Yasuhisa
Published: September 2002

This article proposes a spectroscopic characterization technique for examining the stress-induced leakage current in sub 5-nm-thick silicon oxide films. The fluctuation power of stress-induced leakage currents suggests that defects have a single, dominant energy level. Monte Carlo simulations are carried out to verify the defect model and stress-induced leakage current characteristics. It is clearly demonstrated using simulations and spectroscopic analyses that the stress-dependent magnitude of the leakage current is characterized by defect location and defect energy level. Defect distribution is extracted from stress-induced leakage current characteristics based on a physics-based practical defect model; the defect distribution differs from past predictions. It is also identified from simulations that defect regions, which contribute to the stress-induced leakage current observed at high gate voltages, exist mainly at a depth of about 1.2 nm from the SiO2/Si substrate interface with the distribution width of 0.6 nm. Finally, simulations suggest that the stress-induced leakage current observed at low gate voltages results from structural modification of the gate electrode/SiO2 interface.
Effects of magnetic field on pulse wave forms in plasma immersion ion implantation in a radio-frequency, inductively coupled plasma
Authors: Tong Honghui , Fu Ricky K. Y. , Tang Deli , Zeng Xuchu , Chu Paul K.
Published: September 2002

The time-dependent current wave forms measured using a pulse biased planar electrode in hydrogen radio-frequency (rf), inductively coupled plasma, plasma immersion ion implantation experiments are observed to vary in the presence of an external magnetic field B. Results further indicate that the magnitude of the pulse current is related to the strength and direction of the magnetic field, rf power, and pressure, but the pulse current curves can be primarily correlated with B. The plasma discharges are enhanced in all cases due to magnetic confinement of the electrons, enlargement of the plasma generation volume, and increase in the rf power absorbing efficiency. The plasma density diagnosed by Langmuir probe diminishes in front of the sample chuck with B, whereas the plasma is confined nearby the sidewall of the vacuum chamber at high magnetic field. The high degree of plasma density nonuniformity at high B in front of the sample chuck is not desirable for the processing of planar samples such as silicon wafers and must be compensated. The reduction in the plasma density and plasma density gradient in the sheath can be accounted for by the changes in the pulse current wave forms.
Characterization of spin valves fabricated on opaque substrates by optical ferromagnetic resonance
Authors: Barman A. , Kruglyak V. V. , Hicken R. J. , Marrows C. H. , Ali M. , Hindmarch A. T. , Hickey B. J.
Published: September 2002

We have used a transmission line deposited on a transparent substrate to deliver an optically triggered magnetic field pulse to a spin valve structure deposited upon an opaque substrate. The ensuing ferromagnetic resonance oscillations have been studied in optical pump-probe experiments in which the probe passes through the transmission line substrate. The resonance frequencies have been modeled by solving the Landau–Lifshitz equation and are used in determining the anisotropy, exchange bias, and interlayer coupling parameters of the sample.
Thin-film lasers based on dye-deoxyribonucleic acid-lipid complexes
Authors: Kawabe Y. , Wang L. , Nakamura T. , Ogata N.
Published: September 2002

Amplified spontaneous emission (laser action without cavities) from deoxyribonucleic acid (DNA) derivative films was achieved by doping with a hemicyanine dye which is well known as a nonlinear optical molecule. The amplification confirmed by spectral narrowing and superlinear dependence of the emission intensity on the pumping was observed from the complex films when the film samples were irradiated with a nanosecond laser at the intensity above a threshold value (∼20 μJ). The durability and low threshold values suggest the possibility of DNA complexes as a practical candidate for thin-film dye lasers.
Evidence of ionized metal clusters in ion plating discharges
Authors: Wilson A. D. , Davison A. , Leyland A. , Matthews A. , Fancey K. S.
Published: September 2002

A quadropole mass-energy analyzer has been used to detect positively charged metal ions at the substrate (cathode) of an ion plating system. By studying titanium, evaporated into thermionically supported argon glow discharges at pressures of 1–4 Pa, we have detected the presence of ionized clusters of the vapor material up to the analyzer mass limit of 2500 a.m.u. In contrast, a similar analysis from an equivalent titanium-only discharge has revealed a relatively insignificant cluster detection rate. The results support an earlier prognosis that these clusters may nucleate and grow through vapor cooling, caused by collisions with gas atoms in the discharge.
Continuous-wave 1664.7 nm fiber source utilizing four-wave mixing and stimulated Raman scattering
Authors: de Matos C. J. S. , Chestnut D. A. , Taylor J. R.
Published: September 2002

We present a continuous-wave light source based on four-wave mixing and first- and second-order stimulated Raman scattering in a 9 km dispersion-shifted optical fiber. The source operates at 1664.7 nm with a 1.7 nm linewidth and a power up to 371 mW. Applications could be found in spectroscopy.
Nanoscale patterning of magnetic islands by imprint lithography using a flexible mold
Authors: McClelland Gary M. , Hart Mark W. , Rettner Charles T. , Best Margaret E. , Carter Kenneth R. , Terris Bruce D.
Published: September 2002

A nanomolding process for producing 55-nm-diameter magnetic islands over 3-cm-wide areas is described. A master pattern of SiO2 pillars is used to form a polymeric mold, which is in turn used to mold a photopolymer resist film. This latter film is used as a resist for etching SiO2, yielding a pattern of pillars. Finally, an 11-nm-CoPt multilayer is deposited. Magnetic force microscopy reveals that the film on top of each pillar is a magnetically isolated single domain that switches independently.
Observation of two- and three-dimensional magnesium oxide nanostructures formed by thermal treatment of magnesium diboride powder
Authors: Klug Kevin L. , Dravid Vinayak P.
Published: September 2002

A simple thermal treatment has been used to produce a variety of elongated single crystalline magnesium oxide nanostructures. Incipient evaporation of a magnesium diboride starting powder combined with a mixed oxygen/argon process gas provided the constituents for nanostructure growth. Electron diffraction and energy dispersive x-ray spectroscopy confirm the single crystalline nature and chemical composition of the objects, and the atomic surface plane is observed to be of the (001) type. Transmission electron microscopy and scanning electron microscopy reveal several MgO morphologies including linear nanobelts and two- and three-dimensional entities that contain approximately ninety degree angles. Atomic steps are observed on the inner edges of these angles, but are absent from the outer rims. The experimental conditions used to form these nanoscale materials and possible applications are described.
Photorefractive x-ray imaging
Authors: Berben D. , Andreas B. , Buse K.
Published: September 2002

Photorefractive effects that are affected by x-rays are used to design an x-ray imaging system with outstanding spatial resolution. An elementary holographic reflection grating is recorded in a photorefractive iron-doped lithium niobate crystal. The x-rays yield a conductivity pattern that erases the hologram locally. The diffracted visible light now bears the x-ray image. In first experiments, structures of 25 μm size are easily resolved with a dose of 90 Gray and a signal-to-noise ratio of 6. The detector is fully reversible, has a logarithmic response, and is able to operate for hard x rays (>100 keV).
Structural and optical properties of wurtzite MgxZn1−xS (0⩽x⩽0.25) films grown on (0001) Al2O3 by pulsed-laser deposition
Authors: Ong H. C. , Dai J. Y.
Published: September 2002

Wurtzite MgxZn1−xS (0⩽x⩽0.25) thin films have been epitaxially grown on (0001) Al2O3 using pulsed-laser deposition. High-quality films can be prepared at a growth temperature of 450–550 °C with (0001) ω-rocking curve full width at half maximum as narrow as 0.09°. High-resolution cross-sectional transmission electron microscopy of the films deposited at 500 °C shows the presence of the mixture of zinc-blende and wurtzite phases at the interface, and therefore the interfacial region is highly defective. However, above the critical thickness of ∼5 nm, the film bulk consists of pure wurtzite material with a very high level of crystallinity. The band edge of MgxZn1−xS films examined by transmission spectroscopy at room temperature increases from 3.75 eV at x=0 to 3.95 at x=0.25.
SnO
2
nanocrystals in SiO2: A wide-band-gap quantum-dot system
Authors: Chiodini N. , Paleari A. , DiMartino D. , Spinolo G.
Published: September 2002

Nanoclusters of crystalline SnO2 have been grown in glass, starting from tin-doped silica prepared by a sol–gel method. Based upon a particular choice of molecular precursors, nanocrystallites with a mean radius of about 1 nm and a quite narrow size dispersion were obtained, resulting in wide-band-gap (>4 eV) quantum dots (QDs). In this system, differently from other semiconductor-doped glasses, both the glassy host and the nanophase are oxides of IV-group elements. Owing to their thermochemical compatibility, the two phases give stable optical-grade glass ceramics with potential applications in photonics, opening up the field to technological employments of wide-band-gap QDs.
Microcavity organic light-emitting diodes on silicon
Authors: Jean Frédérique , Mulot Jean-Yves , Geffroy Bernard , Denis Christine , Cambon Pierre
Published: September 2002

We study resonant-cavity organic light-emitting diodes made on silicon substrates. The device structure is Al/indium–tin–oxide (ITO)/copper phthalocyanine (CuPc)/a triphenylamine derivative (TPD)/tris-(8-hydroxyquinoline) aluminum (Alq3)/cathode, where the cathode is a semitransparent Al layer or a LiF/Al stack. We use a model based on the transfer-matrix method to deduce the wavelength dependence of the ITO refractive index, and to calculate the spectra and the angular emission diagrams of the diodes. Microcavities limit the spectral and spatial distributions of the emitted light in accordance with the model. Current–voltage characteristics of various devices prove that a thin LiF layer improves the injection of electrons in Alq3 from semitransparent aluminum cathodes.
Generation of low-frequency components due to phase-amplitude modulation of subcycle far-infrared pulses in near-field diffraction
Authors: Mitrofanov Oleg , Pfeiffer L. N. , West K. W.
Published: September 2002

We observe carrier phase dependent generation of low-frequency spectral components in the near-field zone of a subwavelength aperture illuminated by subcycle far-infrared (terahertz) pulses. Diffraction induced π/2-phase shift of the pulse carrier results in the spectral intensity variation of the low-frequency components. The effect appears only if the pulse duration is shorter than the period of the carrier oscillation.
Surface acoustic wave propagation in aluminum nitride-unpolished freestanding diamond structures
Authors: Mortet V. , Elmazria O. , Nesladek M. , Assouar M. B. , Vanhoyland G. , D’Haen J. , D’Olieslaeger M. , Alnot P.
Published: September 2002

High-quality surface acoustic wave (SAW) filters based on aluminum nitride (AlN)/diamond layered structures were prepared using the nucleation side of polycrystalline chemical vapor deposition (CVD) diamond, removed from a silicon substrate by wet etching. Highly oriented AlN thin films with optimized piezoelectric properties and with various thicknesses were sputtered onto the nucleation side of freestanding diamond. The effect of AlN thickness on the SAW phase velocity, the coupling coefficient, and the device characteristics were investigated. Experimental results show that the Rayleigh wave and the higher modes are generated. These results agree well with calculated dispersion curves and demonstrate that a high electromechanical coupling coefficient together with a high phase velocity can be obtained by using the nucleation side of freestanding CVD diamond layer.
Evaluation of silicon surface nitridation effects on ultra-thin ZrO2 gate dielectrics
Authors: Nieh Renee , Choi Rino , Gopalan Sundar , Onishi Katsunori , Kang Chang Seok , Cho Hag-Ju , Krishnan Siddarth , Lee Jack C.
Published: September 2002

The effects of silicon surface nitridation on metal–oxide–semiconductor capacitors with zirconium oxide (ZrO2) gate dielectrics were investigated. Surface nitridation was introduced via ammonia (NH3) annealing prior to ZrO2 sputter-deposition, and tantalum nitride (TaN) was used for the gate electrode. It was found that capacitors with the nitridation had thinner equivalent oxide thickness (∼8.7 Å), comparable leakage current, and slightly increased capacitance–voltage hysteresis as compared to samples without nitridation. Additionally, transmission electron microscopy pictures revealed that nitrided samples had a thicker interfacial layer (IL), which had a higher dielectric constant than that of the non-nitrided IL.
A single
Photorhabdus
gene,
makes caterpillars floppy
(
mcf
), allows
Escherichia coli
to persist within and kill insects
Authors: Daborn P. J. , Waterfield N. , Silva C. P. , Au C. P. Y. , Sharma S. , ffrench-Constant R. H.
Published: September 2002

Photorhabdus luminescens
, a bacterium with alternate pathogenic and symbiotic phases of its lifestyle, represents a source of novel genes associated with both virulence and symbiosis. This entomopathogen lives in a “symbiosis of pathogens” with nematodes that invade insects. Thus the bacteria are symbiotic with entomopathogenic nematodes but become pathogenic on release from the nematode into the insect blood system. Within the insect, the bacteria need to both avoid the peptide- and cellular- (hemocyte) mediated immune response and also to kill the host, which then acts as a reservoir for bacterial and nematode reproduction. However, the mechanisms whereby
Photorhabdus
evades the insect immune system and kills the host are unclear. Here we show that a single large
Photorhabdus
gene,
makes caterpillars floppy
(
mcf
), is sufficient to allow
Esherichia coli
both to persist within and kill an insect. The predicted high molecular weight Mcf toxin has little similarity to other known protein sequences but carries a BH3 domain and triggers apoptosis in both insect hemocytes and the midgut epithelium.
Differential presentation of a soluble exogenous tumor antigen, NY-ESO-1, by distinct human dendritic cell populations
Authors: Nagata Yasuhiro , Ono Satoru , Matsuo Mitsutoshi , Gnjatic Sacha , Valmori Danila , Ritter Gerd , Garrett Wendy , Old Lloyd J. , Mellman Ira
Published: September 2002

Dendritic cells (DCs) play a critical role in initiating antigen-specific immune responses, because they are able to capture exogenous antigens for presentation to naïve T cells on both MHC class I and II molecules. As such, DCs represent important elements in the development of vaccine therapy for cancer. Although DCs are known to present antigens from phagocytosed tumor cells or preprocessed peptides, we explored whether they might also present soluble recombinant NY-ESO-1, a well characterized cancer antigen. We compared the abilities of human monocyte-derived DCs and DCs derived
in vitro
from CD34-positive stem cells to present NY-ESO-1 epitopes to MHC class I-restricted cytotoxic T cells. Although monocyte-derived DCs did not efficiently crosspresent free NY-ESO-1 protein, IgG-immune complexes containing NY-ESO-1 were avidly presented after uptake by Fcγ receptors (FcγRII). In contrast, CD34-derived DCs were unable to process either soluble or immune complexed NY-ESO-1, although they efficiently presented preprocessed NY-ESO-1 peptides. This difference did not necessarily correlate with endocytic capacity. Although monocyte-derived DCs exhibited greater fluid-phase uptake than CD34-derived DCs, the two populations did not differ with respect to their surprisingly limited capacity for Fcγ receptor-mediated endocytosis. These results indicate that monocyte-derived DCs will be easier to load by using protein antigen
in vitro
than CD34-derived DCs, and that the latter population exhibits a restricted ability to crosspresent soluble exogenous antigens.
An improved genetic model generates high-resolution mapping of QTL for protein quality in maize endosperm
Authors: Wu Rongling , Lou Xiang-Yang , Ma Chang-Xing , Wang Xuelu , Larkins Brian A. , Casella George
Published: September 2002

The genetic mapping of polymorphic markers in a cross between two inbred plant lines has proven to be a powerful method for detecting quantitative trait loci (QTL) underlying complex traits. However, existing methods of QTL mapping were developed for disomic inheritance of both marker and QTL loci in a diploid population. To map QTL influencing traits expressed in the endosperm, a triploid embryo-nourishing tissue resulting from double fertilization, existing QTL mapping models require modification to consider the trisomic inheritance of the endosperm and the generation difference between the mapping population and the endosperm. Such a model requires simultaneous use of two successive generations, which theoretically can lead to an increase in resolution for QTL mapping compared with the use of a single backcross or F2generation. Using a newly developed model based on these considerations, we demonstrate the improved resolution of QTL, influencing protein quality traits in maize endosperm. The increased resolution made possible with this approach makes identified QTL accessible to positional cloning.
Gene expression during the priming phase of liver regeneration after partial hepatectomy in mice
Authors: Su Andrew I. , Guidotti Luca G. , Pezacki John Paul , Chisari Francis V. , Schultz Peter G.
Published: September 2002

Understanding the gene-expression patterns during liver regeneration may help to reveal how regenerative processes are initiated and controlled as well as shed new light onto processes that lead to liver disease. Using high-density oligonucleotide arrays, we have examined the gene-expression program in the livers of mice after partial hepatectomy. A time course was constructed for gene expression between 0 and 4 h after partial hepatectomy, corresponding to the priming phase of liver regeneration. The genomic program for liver regeneration involves transcription-factor generation, stress and inflammatory responses, cytoskeletal and extracellular matrix modification, and regulation of cell-cycle entry. The genome-wide changes that are observed provide a detailed and comprehensive map of the initial priming stage of liver regeneration.
Sympatric speciation by sexual conflict
Authors: Gavrilets Sergey , Waxman David
Published: September 2002

It is well established that sexual conflict can drive an endless coevolutionary chase between the sexes potentially leading to genetic divergence of isolated populations and allopatric speciation. We present a simple mathematical model that shows that sexual conflict over mating rate can result in two other general regimes. First, rather than “running away” from males, females can diversify genetically into separate groups, effectively “trapping” the males in the middle at a state characterized by reduced mating success. Female diversification brings coevolutionary chase to the end. Second, under certain conditions, males respond to female diversification by diversifying themselves. This response results in the formation of reproductively isolated clusters of genotypes that emerge sympatrically.
Assigning numbers to the arrows: Parameterizing a gene regulation network by using accurate expression kinetics
Authors: Ronen Michal , Rosenberg Revital , Shraiman Boris I. , Alon Uri
Published: September 2002

A basic challenge in systems biology is to understand the dynamical behavior of gene regulation networks. Current approaches aim at determining the network structure based on genomic-scale data. However, the network connectivity alone is not sufficient to define its dynamics; one needs to also specify the kinetic parameters for the regulation reactions. Here, we ask whether effective kinetic parameters can be assigned to a transcriptional network based on expression data. We present a combined experimental and theoretical approach based on accurate high temporal-resolution measurement of promoter activities from living cells by using green fluorescent protein (GFP) reporter plasmids. We present algorithms that use these data to assign effective kinetic parameters within a mathematical model of the network. To demonstrate this, we employ a well defined network, the SOS DNA repair system of
Escherichia coli
. We find a strikingly detailed temporal program of expression that correlates with the functional role of the SOS genes and is driven by a hierarchy of effective kinetic parameter strengths for the various promoters. The calculated parameters can be used to determine the kinetics of all SOS genes given the expression profile of just one representative, allowing a significant reduction in complexity. The concentration profile of the master SOS transcriptional repressor can be calculated, demonstrating that relative protein levels may be determined from purely transcriptional data. This finding opens the possibility of assigning kinetic parameters to transcriptional networks on a genomic scale.
The molecular structure of spider dragline silk: Folding and orientation of the protein backbone
Authors: van Beek J. D. , Hess S. , Vollrath F. , Meier B. H.
Published: September 2002

The design principles of spider dragline silk, nature's high-performance fiber, are still largely unknown, in particular for the noncrystalline glycine-rich domains, which form the bulk of the material. Here we apply two-dimensional solid-state NMR to determine the distribution of the backbone torsion angles (φ,ψ) as well as the orientation of the polypeptide backbone toward the fiber at both the glycine and alanine residues. Instead of an “amorphous matrix,” suggested earlier for the glycine-rich domains, these new data indicate that all domains in dragline silk have a preferred secondary structure and are strongly oriented, with the chains predominantly parallel to the fiber. As proposed previously, the alanine residues are predominantly found in a β sheet conformation. The glycine residues are partly incorporated into the β sheets and otherwise form helical structures with an approximate 3-fold symmetry.
Early restriction of peripheral and proximal cell lineages during formation of the lung
Authors: Perl Anne-Karina T. , Wert Susan E. , Nagy Andras , Lobe Corrinne G. , Whitsett Jeffrey A.
Published: September 2002

To establish the timing of lineage restriction among endodermal derivatives, we developed a method to label permanently subsets of lung precursor cells at defined times during development by using Cre recombinase to activate floxed alkaline phosphatase or green fluorescent protein genes under control of doxycycline-dependent surfactant protein C promoter. Extensive or complete labeling of peripheral lung, thyroid, and thymic epithelia, but not trachea, bronchi, or gastrointestinal tract occurred when mice were exposed to doxycycline from embryonic day (E) 4.5 to E6.5. Nonoverlapping cell lineages of conducting airways (trachea and bronchi), as distinct from those of peripheral airways (bronchioles, acini, and alveoli), were established well before formation of the definitive lung buds at E9–9.5. At E11.5, the labeled precursors of peripheral lung were restricted to relatively few cells along the bronchial tubes and clusters in bronchial tips and lateral buds. Thereafter, these cells underwent marked expansion to form the entire gas-exchange region in the lung. This study demonstrates early restriction of endodermal progenitor cells forming peripheral as compared with proximal airways, identifies distinct cell lineages in conducting airways, and distinguishes neuroepithelial and tracheal–bronchial gland cell lineages from those lining peripheral regions of the lung. This system for conditional gene addition or deletion is useful for the study of lung morphogenesis and gene function
in vivo
, and identifies progenitor cells that may serve as useful targets for cell or gene replacement for pulmonary disorders.
Monoallelic expression and methylation of imprinted genes in human and mouse embryonic germ cell lineages
Authors: Onyango Patrick , Jiang Shan , Uejima Hiroshi , Shamblott Michael J. , Gearhart John D. , Cui Hengmi , Feinberg Andrew P.
Published: September 2002

Imprinting is an epigenetic modification leading to monoallelic expression of some genes, and disrupted imprinting is believed to be a barrier to human stem cell transplantation, based on studies that suggest that epigenetic marks are unstable in mouse embryonic germ (EG) and embryonic stem (ES) cells. However, stem cell imprinting has not previously been examined directly in humans. We found that three imprinted genes,
TSSC5, H19,
and
SNRPN,
show monoallelic expression in
in vitro
differentiated human EG-derived cells, and a fourth gene,
IGF2,
shows partially relaxed imprinting at a ratio from 4:1 to 5:1, comparable to that found in normal somatic cells. In addition, we found normal methylation of an imprinting control region (ICR) that regulates
H19
and
IGF2
imprinting, suggesting that imprinting may not be a significant epigenetic barrier to human EG cell transplantation. Finally, we were able to construct an
in vitro
mouse model of genomic imprinting, by generating EG cells from 8.5-day embryos of an interspecific cross, in which undifferentiated cells show biallelic expression and acquire preferential parental allele expression after differentiation. This model should allow experimental manipulation of epigenetic modifications of cultured EG cells that may not be possible in human stem cell studies.