bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of electrolytes on cataphoretically deposited LaB6 cathodes
Authors: Khairnar Rajendra S. , Joag D. S. , Kulkarni S. K. , Nigavekar A. S. , Kanitkar P. L.
Published: March 2003

Various electrolytes were used to deposit LaB6 on carburized tantalum by the cataphoretic method. The effect of four electrolytes viz., HCl, NH4NO3, La(NO3)3, and HNO3 on LaB6 coatings has been investigated. It is observed that use of HCl as an electrolyte provides LaB6 coatings with small grain size, low porosity, good adhesion, and ability to withstand a large number of thermal shocks. These properties make HCl the most suitable electrolyte for cataphoretic deposition of LaB6 for thermionic emission.
Tomography of neutral beams
Authors: Cottrell G. A.
Published: March 2003

This paper describes a new diagnostic technique to decode information contained in the spectral and spatial distribution of photons emitted by fast neutral beam particles and provide an estimate of the 2-D beam density distribution function in a cross-sectional slice. By scanning Doppler-shifted Hα radiation from the fast beam particles at a number of peripheral locations around the beam axis, tomographic reconstructions of the beam distribution with spatial resolution Δx≂2 cm and time resolution Δt≂10 ms can be made. Using a maximum entropy reconstruction algorithm (making no symmetry assumptions), experimental reconstructions are presented of the 2-D profile of the beam generated by the prototype JET source for each of the Doppler-shifted line radiation components. Applications of this image processing technique in other areas of high-temperature plasma diagnostic development are discussed briefly.
Potassium-seeded wall-stabilized arc source for Stark broadening studies
Authors: Hohimer J. P.
Published: March 2003

A potassium-seeded wall-stabilized arc source has been developed to provide a stable well-characterized plasma in which to measure the Stark broadening parameters of potassium excited-state transitions. Low-pressure (20-Torr argon) operation of the arc source reduces the argon collisional broadening contribution to the Stark-broadened line shapes, while a heated channel wall minimizes radial cataphoresis in the mixed-gas plasma. The arc source is designed for end-on observation and is compatible with far-infrared laser interferometry which is used to determine the effective plasma path length and on-axis electron density over the current operating range of 5–35 A.
Beam properties of a high-perveance single-aperture dc extraction system
Authors: Piosczyk B. , Dammertz G.
Published: March 2003

In continuous operation a positive hydrogen ion beam up to 240 mA has been extracted at 50 kV out of a single aperture, corresponding to a perveance of 2.1×10−8 A/V3/2. The effective mass of the extracted ion beam was measured to be about 1.8 amu. The current density distribution of the extracted ion beam was measured with a small calorimetric probe. It was found that the beam distribution strongly depends on the matching between the plasma current density and the extraction voltage. At overmatched conditions the ion beam may even become hollow. The distribution of the extracted ion beam depends on the pressure along the beam path. At pressures above 3×10−4 Torr H2, the distribution was observed to be Gaussian. At a pressure 2×10−5 Torr H2, the intensity in the wings of the beam is relatively high with respect to the intensity in the beam center. The beam divergence decreases with the square root of the extraction voltage. The space-charge potential of the neutralized beam is estimated to be about 5.6 V at 2×10−5 Torr decreasing to 1.6 V at 10−3 Torr independent of the beam energy.
Ion energy measurement in an intense pulsed ion beam
Authors: Camarcat N. , Tournier B. , Bourgeois C. , Delvaux J. , Bailly-Salins R.
Published: March 2003

Three independent techniques are used to measure the mean ion energy in an intense ion beam accelerated with a standard pinch-reflex diode. The experimental accelerating voltage agrees with a numerical simulation. The resulting deuteron energy is consistent with the activation results of a BN target and with the hydrodynamic motion of subrange and overrange aluminum foils bombarded by the beam. The accelerating voltage is also used to compare the experimental and computed neutron yields when the beam strikes a CD2 target. The total ion current measured with an electrical diagnostic is five to ten times greater than the corresponding deuteron component. This is significantly greater than values reported previously.
Measuring of soft x-ray flashes with the x-ray acoustic effect
Authors: Germer R.
Published: March 2003

An x-ray acoustic detector was found to be sensitive to extremely soft x-ray flashes (5 eV–10 keV, T≤1 μs). The total dose of the flash is measured by the x-ray acoustic effect. The absorbed energy induces an acoustical pulse that is registered with a microphone. The microphone signal only depends on the absorbed energy. It is independent of the wavelength of the x-rays. The dynamic range is limited only by the linearity of thermal properties of the x-ray absorber and by the noise of the preamplifier. The measuring of continuous x radiation is possible using a chopper and lock-in techniques.
Viscometric temperature measurement in electric or magnetic fields
Authors: Seyed-Yagoobi Jamal , Chato John C. , Crowley Joseph M.
Published: March 2003

In the presence of electrostatic or electromagnetic fields, the viscometric thermometer is one of the few possible and feasible methods of temperature measurement. The device can be operated in a constant pressure or a constant flow mode. The former system is simpler and easier to build and operate but it requires a relatively long reading time of 1 to 2 min and, consequently, can be used only in ‘‘steady-state’’ flows where the variations in temperature are much slower than the reading time required. Different configurations and measurement procedures are described. In particular, a viscometric thermometer was designed and built for the constant pressure mode which enabled us to obtain the temperature distribution inside the channel of an electrohydrodynamic pump.
Effect of low-frequency ambient magnetic fields on the control unit and rf head of a commercial SQUID magnetometer
Authors: Marcus Charles M.
Published: March 2003

The control unit and rf head of the SHE model 330X rf SQUID system are shown to be sensitive to ambient ac magnetic fields below 1 Hz, which cause the appearance of false signals corresponding to a magnetometer signal of 10−6 φ0 per gauss of field applied. The control unit shows a sensitivity that is linear with frequency, suggesting that the signal is generated by Faraday induction. In contrast, the rf head response is independent of frequency and shows a strong second-harmonic conversion. This response may be due to the magnetic field sensitivity of the ferrite core inductor in the tuned amplifier of the rf head. These signals induced by ambient fields are a potential source of error in Stanford’s Relativity Gyroscope experiment, which uses SQUID’s on board a rolling satellite as part of the gyroscope readout system. The extent of the magnetic field sensitivity in these components necessitates the use of additional magnetic shielding aboard the satellite.
Ultrahigh-vacuum sample transfer device with low-temperature capability
Authors: DiNardo N. J. , Demuth J. E. , Thompson W. A. , Ledermann P. G.
Published: March 2003

The design of a novel sample transfer device for use in surface studies in an ultrahigh-vacuum environment is discussed. The principle feature of this design is a broad sample temperature range (∼32–∼1270 K).
Angular displacement measurement system for use in damped torsion pendulums
Authors: Durbin D. P. , Henning H. C. , El-Aasser M. S. , Vanderhoff J. W.
Published: March 2003

A simple electro-optical system has been developed for measuring successive angular displacement cycles of a damped torsion pendulum. The system permits convenient, reproducible measurements of the air/liquid interfacial viscosity of aqueous surfactant systems.
Microprocessor-based far infrared spectrophotometer
Authors: Hatzopoulos A. , Halatsis C.
Published: March 2003

This work describes a microprocessor-based data acquisition and analysis of a far infrared (FIR) spectrophotometer. The work shows how a microprocessor can be used to renovate an old instrument (a Beckman FS720 FIR spectrophotometer) into a modern and versatile instrument.
Reliable slip-on vacuum coupling for low-temperature apparatus
Authors: Stasiak J. W. , Guernsey R. W.
Published: March 2003

A reliable slip-on vacuum coupling scheme for low-temperature applications is described. The novel aspect of this concept is the use of silicone fluid as the sealing agent. The stem and coupling joint described has performed without failure at room temperature, immersed in normal 4He and in superfluid 4He.
Retractable capillary doser
Authors: Fowler G. L. , Panitz J. A.
Published: March 2003

A retractable capillary doser is described which can place a reproducible coverage of molecules on a substrate in an ultrahigh-vacuum environment. An integral valve assembly controls the flow of molecules from the doser volume to the substrate. Automatic operation is achieved by controlling the valve and the position of the doser orifice from a commercial IEEE interface.
Long-range potential energy curves for the X 1Σ+ and a 3Σ+ states of NaRb
Authors: Zemke Warren T. , Stwalley William C.
Published: March 2003

This article critically examines spectroscopic data for the two lowest states (X 1Σ+ and a 3Σ+) for NaRb, which dissociate to ground state Na and Rb atoms. A more precise triplet state RKR potential curve is reported. A complete hybrid potential for the triplet state is determined, based on the improved RKR curve plus Coulombic and exchange contributions at long range. A new, more precise dissociation energy for the a 3Σ+ state is determined: De=183.0±0.10 cm−1. Previously unpublished and improved Dunham coefficients for the singlet state are reported, which cover the bottom 57% of the well. A complete hybrid potential energy curve for the singlet state is determined, based on the RKR curve plus Coulombic and exchange contributions at long range. The X 1Σ+ state potential curve now covers 100% of the well and a new, precise dissociation energy is determined: De=5030.75±0.10 cm−1. Three additional unobserved energy levels are predicted for the a 3Σ+ state of Na8523Rb, all within 1.1 cm−1 of the dissociation limit.
A theoretical study of the nitrogen clusters formed from the ions N3−, N5+, and N5−
Authors: Gagliardi Laura , Orlandi Giorgio , Evangelisti Stefano , Roos Björn O.
Published: March 2003

The results of a theoretical study on the formation of the nitrogen cluster N10 from the ionic species N5+ and N5− are presented. The possibility to form N8 from N5+ and N3− has also been studied but no stable form was found. Structural and vibrational data are given for the different clusters. It is suggested that the anion N5− might be stable enough to be synthesized. The calculations have been carried out using multiconfigurational self-consistent-field wave functions and second-order perturbation theory.
The role of the ground and excited potential energy surfaces in the O(1D and 3P)+SiH4 reactions: A theoretical study
Authors: Nguyen Thanh Lam , Mebel Alexander M. , Lin Sheng H.
Published: March 2003

The O(1D and 3P)+SiH4 reactions have been studied using ab initio/Rice–Ramsperger–Kassel–Marcus calculations to investigate possible formation mechanisms of various products in combustion and chemical vapor deposition processes. The relative branching ratios for various products formed through the O(1D)+SiH4 reaction involving the long-lived H3SiOH intermediate are calculated as 55.5% for the H2SiO/HSiOH+2H channel, 28.4% for the SiO+2H2 channel, 9.9% for the OH+SiH3 channel, 3.2% for the H2O+SiH2 channel, and 3.0% for the HSiO/SiOH+H2+H channel. These results significantly differ from those obtained in experiment, implying that the O(1D)+SiH4 reaction can take place through a mechanism other than the insertion mechanism. While the O(3P)+SiH4 reaction takes place by the abstraction mechanism, the O(1D)+SiH4 reaction can occur through both insertion and addition/abstraction mechanisms. The addition/abstraction mechanism occurring on the first excited potential energy surface is demonstrated to provide a significant contribution to the reaction products and to account for the forward scattering of the OH products observed in experiment. Finally, heats of formation for various species involving Si atom are computed employing the Gaussian 3 theory.
Pattern formation and evolution in diblock copolymer thin films above the order–disorder transition
Authors: Masson J.-L. , Limary R. , Green P. F.
Published: March 2003

Research on diblock copolymer thin films has been devoted primarily toward understanding and controlling microstructural and topographical features at temperatures below the order–disorder transition (ODT), where ordered phase separated structures exist. Recently, we showed that the topography of thin liquid diblock films above the ODT form a hierarchy of patterns, depending on the film thickness. One of these topographies is a “spinodal-like” pattern. Through the use of a pair correlation analysis we show that the structural evolution of this pattern is characterized by four stages. The first involves the amplification of surface perturbations, followed by the formation of an interconnected, “spinodal-like,” pattern. The onset of the third stage is associated with the breakup of the interconnected pattern and the eventual formation of droplets of irregular shapes. The final stage involves evolution toward the formation of circular droplets.
Emission from ferroelectric cathodes versus temperature and the relevant physics
Authors: Boscolo I. , Cialdi S.
Published: March 2003

We show that electron emission from a relaxor ferroelectric cathode varies with the temperature as the dielectric constant. Consequently, there is no variation when the material makes the antiferroparaelectric phase transition. In addition, we have found that the emission increases with the polarizability of the material. The emission is originated by an induced change of the normal and/or spontaneous polarization. The maximum efficiency of the process, that is the ratio between the emitted charge of energetic electrons and the charge supplied to the sample by the excitation pulse, resulted in about 20%. The good emission of energetic electrons from a ceramic cathode at few hundred degrees temperature, makes this kind of cathode a proper electron injector for ion sources.
Configurational entropy for adsorbed linear species (k-mers)
Authors: Romá F. , Ramirez-Pastor A. J. , Riccardo J. L.
Published: March 2003

The configurational entropy of interacting linear molecules (k-mers) absorbed on a regular lattice is addressed through analytical as well as numerical methods. The general definitions for computational exact calculations of k-mers lattice-gas entropy are presented. In addition, theoretical basis for accurate analytical estimations of the entropy of reference states are given. The coverage and temperature dependence of the configurational entropy of interacting adsorbed dimers on one and two-dimensional lattices are obtained. A novel phase behavior of k-mers lattice-gas is shown and discussed.
Exotic phase transitions in disordered globular networks
Authors: Gutman Lorin , Shakhnovich Eugene
Published: March 2003

We present a comprehensive numerical study of phase diagram and conformational transitions in disordered globular networks with physical/chemical crosslinks. Physically crosslinked random heteropolymer (RHP) networks at positive intersegment interaction dissimilarity, i.e., χf>0, exhibit three globular phases: frozen globular with microdomain structure, random globular, and frozen-random-globular phase, while chemically crosslinked RHPs at positive χf exhibit one random-globular phase and three frozen-globular phases; in contrast with RHPs with physical crosslinks, phase changes in chemically crosslinked RHP networks do not require reentrant passages via a random-globular phase. Based on physical grounds we explain the origins of the phase changes predicted and discuss the order of the phase transitions predicted.
Experimental and theoretical differential cross sections for the reactions Cl+H2/D2
Authors: Skouteris Dimitris , Werner Hans-Joachim , Aoiz F. Javier , Bañares Luis , Castillo Jesus F. , Menéndez Marta , Balucani Nadia , Cartechini Laura , Casavecchia Piergiorgio
Published: March 2003

Experimental and theoretical differential cross sections for the reactions between Cl atoms and two isotopic variants of molecular hydrogen (H2 and D2) are presented. The experimental results have been obtained by using the crossed molecular beam method with mass spectrometric detection. The theoretical results have been computed using both the quasiclassical trajectory and quantum mechanical (QM) methods. The potential energy surface employed for the calculations is the ab initio BW2 surface by Bian and Werner [J. Chem. Phys. 112, 220 (2000)]. The theoretical results have been directly compared to the experiments in the laboratory frame at a collision energy (Ec) of 4.25 and 5.85 kcal/mol for the Cl+H2 reaction and of 4.9 and 6.3 kcal/mol for the Cl+D2 reaction. The agreement between QM results and experiment is quite satisfactory for the Cl+D2 reaction, especially for the low collision energy, while for Cl+H2 is less good, especially when considering data at the lower Ec.
Exchange energy functionals based on the full fourth-order density matrix expansion
Authors: Maximoff Sergey N. , Scuseria Gustavo E.
Published: March 2003

We have derived the fourth-order generalized density matrix expansion and used it to construct various exchange-energy functionals. The fourth-order terms depend on several quantities containing invariants of the second-order derivative matrices of the orbitals and the electron density. The impact of these variables on the accuracy of exchange functionals has never been studied before and we here demonstrate their importance. The new exchange functionals show excellent accuracy (as compared to Hartree–Fock exchange energies) surpassing those of our previously developed exchange functionals.
Nonadiabatic g–u mixing of the F 1Σg+ and 2 1Σu+ states of Li6Li7
Authors: Li Li , Kasahara Shunji , Kabir Md. Humayun , Sahashi Yukiko , Baba Masaaki , Katô Hajime
Published: March 2003

Transitions from the A 1Σu+ (v=4, J=11 and 9) level to the F 1Σg+ (v=3, J=10) and 2 1Σu+ (v=2, J=10) levels of the Li6Li7 molecule, were observed using Doppler-free two-step polarization labeling spectroscopy. The intensity ratio of the two transitions was approximately 150:1. The energy spacing between the deperturbed F 1Σg+ (v=3, J=10) and 2 1Σu+ (v=2, J=10) levels was calculated to be 0.11 cm−1. The 2 1Σu+←A 1Σu+ transition becomes allowed due to an interaction between gerade and ungerade states resulting from the mass difference of the nuclei. The interaction energy between the F 1Σg+ (v=3, J=10) and 2 1Σu+ (v=2, J=10) levels was calculated to be 0.009 cm−1 from an analysis of the deperturbed level energies and the ratio of the line intensities.
Quantum dissipative master equations: Some exact results
Authors: Zhao Y. , Chen G. H.
Published: March 2003

With the help of quantum characteristic functions some exact results are found for two quantum dissipative master equations which contain dissipative Liouvillian operators of the Lindblad-type corresponding to two forms of dissipation mechanisms. Population relaxation is used to demonstrate how dynamic information can be retrieved from these solutions.
Single vibronic level emission spectroscopy of jet-cooled HSiF and DSiF
Authors: Hostutler David A. , Clouthier Dennis J. , Judge R. H.
Published: March 2003

Using the technique of single vibronic level emission spectroscopy, the ground state vibrational manifolds of jet-cooled HSiF and DSiF have been studied. The radicals were produced in a pulsed electric discharge jet using trifluorosilane (HSiF3 or DSiF3) as the precursor. The gas phase ground state harmonic vibrational frequencies of both isotopomers have been determined for the first time. A normal coordinate analysis using the vibrational frequencies and literature values for the centrifugal distortion constants allowed the determination of all six ground state force constants. Our previous ground state rotational constants have been combined with the calculated harmonic contributions to the α constants to obtain an average (rz) structure and an estimate of the equilibrium (rez) structure. The reliability of the force constants has been evaluated by Franck–Condon simulations of the emission spectra and comparisons of the calculated and experimentally determined inertial defects.
Satellite transition magic-angle spinning nuclear magnetic resonance spectroscopy of half-integer quadrupolar nuclei
Authors: Gan Zhehong
Published: March 2003

The theory of satellite transition magic-angle spinning nuclear magnetic resonance (NMR) spectroscopy of half-integer quadrupolar spins is presented and a two-dimensional experiment that uses satellite transitions to obtain isotropic NMR spectra is described. Correlation of satellite and central transitions under magic-angle spinning generates coherence transfer echoes leading to isotropic NMR spectra of half-integer quadrupolar nuclei. Pulse sequences of the two-dimensional satellite transition experiment are described. Satellite transition excitation and coherence transfer are studied with numerical simulations. Experimental results with model samples show high efficiencies of the experiment for acquisition of high-resolution isotropic NMR of half-integer quadrupolar nuclei.
Isomerizations and relative kinetic stability of LJn clusters in a carrier gas
Authors: Curotto E.
Published: March 2003

A number of simulations of LJ7@He(ρ) and LJ28@He(ρ), for several values of the density of the carrier gas ρ are carried out. Heat capacity data demonstrate that the cluster becomes kinetically more stable at higher values of ρ. Using a structural characterization strategy, it is found that the isomeric distributions are affected by changes in ρ. The relative isomer probability curves are integrated over the simulation temperature range. The resulting quantities increase as a function of ρ monotonically but nonlinearly for Ar7. The patterns for the integrated probabilities for Ar28 are less obvious.
A nonanalytic model for the generic van der Waals equation of state and the critical behavior of simple fluids
Authors: Eu Byung Chan
Published: March 2003

In this paper, we assume a phenomenological model for the generic van der Waals equation of state to study the subcritical behavior of fluids. In the present model each generic van der Waals parameter consists of the corresponding van der Waals parameter and nonanalytic contributions. By explicitly assuming nonanalytic functions of density for the generic van der Waals parameters, we show that critical exponents of thermodynamic variables near the critical point can be directly related to the nonanalyticity of the generic van der Waals parameters. The critical exponents can be determined in comparison with the experimental values. Thus the generic van der Waals equation of state is shown to be an economic way of phenomenologically relating the critical exponents to the nonanalyticity of the equation of state as functions of density and temperature.
Direct semiclassical simulation of photochemical processes with semiempirical wave functions
Authors: Granucci G. , Persico M. , Toniolo A.
Published: March 2003

We describe a new method for the simulation of excited state dynamics, based on classical trajectories and surface hopping, with direct semiempirical calculation of the electronic wave functions and potential energy surfaces (DTSH method). Semiempirical self-consistent-field molecular orbitals (SCF MO’s) are computed with geometry-dependent occupation numbers, in order to ensure correct homolytic dissociation, fragment orbital degeneracy, and partial optimization of the lowest virtuals. Electronic wave functions are of the MO active space configuration interaction (CI) type, for which analytic energy gradients have been implemented. The time-dependent electronic wave function is propagated by means of a local diabatization algorithm which is inherently stable also in the case of surface crossings. The method is tested for the problem of excited ethylene nonadiabatic dynamics, and the results are compared with recent quantum mechanical calculations.
Interpolated potential-energy surface and reaction dynamics for BH++H2
Authors: Fuller Rebecca O. , Bettens Ryan P. A. , Collins Michael A.
Published: March 2003

An ab initio potential-energy surface for the ground doublet state of BH3+ has been constructed at the QCISD(T)/6-311G(d,p) level of theory. Classical simulations of the collision between BH+ and H2(D2) and isotopic analogs show that the deep BH3+ well gives rise to substantial “scrambling” of the hydrogen and deuterium atoms leading to BHD++D, BD++HD, and BD2++H products.
Milliwatt operation of AlGaN-based single-quantum-well light emitting diode in the ultraviolet region
Authors: Nishida Toshio , Saito Hisao , Kobayashi Naoki
Published: March 2003

By introducing a single-quantum-well active layer and a high-Al-content carrier blocking layer, the output power of an AlGaN-based ultraviolet light-emitting diode has been improved by one order of magnitude. Optical output of 1 mW was achieved at the emission peak wavelength of 341–343 nm.
Identification of refractory-metal-free C40 TiSi2 for low temperature C54 TiSi2 formation
Authors: Li K. , Chen S. Y. , Shen Z. X.
Published: March 2003

A refractory-metal-free C40 TiSi2 phase formed by pulsed-laser annealing is identified experimentally by combined convergent beam electron diffraction (CBED) study and CBED pattern simulation. The simulation shows that the C40 TiSi2 has a hexagonal structure with the space group P6222 (180) and lattice parameters a=0.471 nm and c=0.653 nm. Upon further furnace annealing or rapid thermal annealing, C54 TiSi2 can be directly achieved from C40 TiSi2 at low temperatures (600–700 °C). This observation suggests that pulsed-laser annealing is promising for extension of TiSi2 into the subquarter micron region in semiconductor device fabrication.
Efficient tunable luminescence of SiGe alloy sheet polymers
Authors: Vogg G. , Meyer A. J.-P. , Miesner C. , Brandt M. S. , Stutzmann M.
Published: March 2003

Crystalline SiGe alloy sheet polymers were topotactically prepared from epitaxially grown calcium germanosilicide Ca(Si1−xGex)2 precursor films in the whole composition range. These polygermanosilynes are found to be a well-defined mixture of the known siloxene and polygermyne sheet polymers with the OH groups exclusively bonded to silicon. The optical properties determined by photoluminescence and optical reflection measurements identify the mixed SiGe sheet polymers as direct semiconductors with efficient luminescence tunable in the energy range between 2.4 and 1.3 eV.
Large-signal coherent control of normal modes in quantum-well semiconductor microcavity
Authors: Lee Y.-S. , Norris T. B. , Maslov A. , Citrin D. S. , Prineas J. , Khitrova G. , Gibbs H. M.
Published: March 2003

We demonstrate coherent control of the cavity-polariton modes of a quantum-well semiconductor microcavity in a two-color scheme. The cavity enhancement of the excitonic nonlinearity gives rise to a large signal; modulating the relative phase of the excitation pulses between zero and π produces a differential reflectivity (ΔR/R) of up to 20%. The maximum nonlinear signal is obtained for cocircular pump and probe polarization. Excitation-induced dephasing is responsible for the incoherent nonlinear response, and limits the contrast ratio of the optical switching.
Injectorless quantum-cascade lasers
Authors: Wanke Michael C. , Capasso Federico , Gmachl Claire , Tredicucci Alessandro , Sivco Deborah L. , Hutchinson Albert L. , Chu S.-N. George , Cho Alfred Y.
Published: March 2003

An “injectorless” quantum-cascade (QC) laser is presented. The requirement of using injector regions to transport electrons from the lower laser level and other low-lying energy levels of one active region to the upper laser level of the next electron-downstream active region was eliminated by using an appropriately designed double-quantum-well “chirped” superlattice active region. The major advantage of the “injectorless” QC laser is the close packing of the active regions and the concomitant large optical confinement factor. Using a cascade of 75 consecutive active regions, designed for emission at λ=11.5 μm, a pulsed peak output power of 270 mW is achieved at 7 K and approximately 10 mW at the maximum operating temperature of 195 K.
Stacks of intrinsic Josephson junctions singled out from inside Bi2Sr2CaCu2O8+x single crystals
Authors: Wang H. B. , Wu P. H. , Yamashita T.
Published: March 2003

Using a double-side fabrication method, a stack of intrinsic Josephson junctions plus a bow-tie antenna and chokes were made in a slice 200 nm thick and singled out from inside a bulk Bi2Sr2CaCu2O8+x single crystal. The junctions in the fabricated stack were very uniform, and the number of junctions involved was rather controllable. Potentially it would be possible to use this method to fabricate integrated circuits based on intrinsic Josephson junctions in high TC superconductors.
Ultrafast carrier and phonon dynamics in ion-irradiated graphite
Authors: Ishioka K. , Hase M. , Kitajima M. , Ushida K.
Published: March 2003

The effect of defects on the dynamics of photoexcited carriers and coherent acoustic phonon in graphite is investigated by means of reflectivity measurements with femtosecond time resolution. Point defects are introduced by irradiating graphite with 5 keV He+ ions. Introduction of the defects enhances the carrier relaxation by opening a decay channel via vacancy states, which competes efficiently with carrier–phonon scattering. The coherent phonon relaxation is also accelerated due to an additional scattering by defects. The linear fluence dependence of the decay rate is understood as scattering of propagating acoustic phonon by single vacancies.
High diffraction efficiency polarization gratings recorded by biphotonic holography in an azobenzene liquid crystalline polyester
Authors: Sánchez C. , Alcalá R. , Hvilsted S. , Ramanujam P. S.
Published: March 2003

High diffraction efficiencies have been achieved with polarization gratings recorded in thin films of an azobenzene side-chain liquid crystalline polyester by means of biphotonic processes. Efficiency values up to 30% have been reached after an induction period of 300 s and subsequent evolution with the sample in darkness. These values are at least two orders of magnitude higher than those previously reported for biphotonic recording. The gratings can be erased with unpolarized blue light and partial recovery of the diffraction efficiency has been observed after the erasure process when the sample is kept in darkness. Red light illumination of the erased film increases the recovered efficiency value and the recovery rate.
Calibrated fluorescence imaging of tissue in vivo
Authors: Qu Jianan Y. , Hua Jianwen
Published: March 2003

A calibrated fluorescence imaging system utilizing a combination of fluorescence and cross-polarization imaging technology is described and applied to tissue examination in vivo. The results show that the inhomogeneity of fluorescence excitation and collection across the irregular surface of the examined tissue is calibrated to a great extent by taking the ratio of the raw fluorescence image to the cross-polarized reflection image. The effects of optical properties of tissue on the calibrated fluorescence signals are studies on simulated tissue phantoms systematically. Using the calibrated fluorescence imaging technology, we demonstrate that different tissue can be clearly separated endoscopically and in vivo based on the calibrated fluorescence signal.
Synthesis of extremely small InP quantum dots and electronic coupling in their disordered solid films
Authors: Mićić Olga I. , Ahrenkiel S. P. , Nozik Arthur J.
Published: March 2003

Extremely small colloidal InP quantum dots (QDs) with diameters ranging from 15 to 23 Å were synthesized, and the optical properties of close-packed arrays of these dots were studied. The isolated QDs in dilute colloidal solution exhibit pronounced discrete absorption spectra, indicating a narrow size distribution. The absorption spectra of close-packed solids of ∼18 Å diameter QDs with interdot spacings of 9 and 18 Å show that the absorption onsets and excitonic peaks are, respectively, redshifted and broadened in going from dilute solution to close-packed solids. These results can be explained by electron delocalization in disordered close-packed solids; the spacing of electronic levels in the QDs is reduced and produces a redshift in the absorption spectra.
Study of dipole interaction in micron-width NiFe/Cu/NiFe/NiO wire using exchange anisotropy
Authors: Kimura Takashi , Itagaki Yoshio , Wakaya Fujio , Gamo Kenji
Published: March 2003

The dipole interaction between a NiFe layer pinned by a NiO and a free NiFe layer in a micron-wide NiFe/Cu/NiFe/NiO wire was studied by changing the direction of the exchange bias from the NiO layer. The effect of the dipole interaction when the exchange bias was perpendicular to the wire axis was larger than that when the exchange bias was parallel to the wire axis, and was consistently explained by the stray field caused by the magnetic charges of the pinned layer. It was demonstrated that this method, using exchange anisotropy, is useful for investigating the dipole interaction between ferromagnetic materials separated by a nonmagnetic material in small-scale magnetic multilayers.
Electroluminescence from a forward-biased Schottky barrier diode on modulation Si δ-doped GaAs/InGaAs/AlGaAs heterostructure
Authors: Babiński Adam , Witczak P. , Twardowski A. , Baranowski J. M.
Published: March 2003

Electroluminescence (EL) from a forward-biased Schottky barrier diode on modulation Si δ-doped pseudomorphic GaAs/InGaAs/AlGaAs heterostructure with high mobility electron gas is investigated in this work. It has been found that the EL from the InGaAs quantum well can be observed at temperatures up to 90 K. The EL line shape depends on the current density, which reflects the filling of the InGaAs channel with electrons. The total integrated EL intensity depends linearly on the current density. We propose that hole diffusion from an inversion layer at the Schottky barrier is responsible for the observed optical recombination with electrons in the InGaAs quantum well.
Polarity dependence of hexagonal GaN films on two opposite c faces of Al2O3 substrate
Authors: Han Peide , Wang Zhanguo , Duan Xiaofeng , Zhang Ze
Published: March 2003

GaN films were grown in pairs on two opposite c faces of Al2O3 substrate by low-pressure metal-organic vapor phase epitaxy, and studied by scanning electron microscopy and converged beam electron diffraction. It is found that GaN film on the c-Al2O3 whose c face is forward to its crystal seed has [0001] polarity, and the other film on the c-Al2O3 whose c face is backward to its crystal seed has [0001̄] polarity.
Stability and production of positron–diatomic molecule complexes
Authors: Mella Massimo , Bressanini Dario , Morosi Gabriele
Published: March 2003

The energies at geometries close to the equilibrium for the e+LiF and e+BeO ground states were computed by means of diffusion Monte Carlo simulations. These results allow us to predict the equilibrium geometries and the vibrational frequencies for these exotic systems, and to discuss their stability with respect to the various dissociation channels. Since the adiabatic positron affinities were found to be smaller than the dissociation energies for both complexes, we propose these two molecules as possible candidates in the challenge to produce and detect stable positron–molecule systems. Moreover, low-energy positron scattering on LiF and BeO targets may show vibrational Feshbach resonances as fingerprints of the existence of stable ground states of e+LiF and e+BeO.
Nucleation and growth of well-aligned, uniform-sized carbon nanotubes by microwave plasma chemical vapor depositon
Authors: Wang N. , Yao B. D.
Published: March 2003

The nucleation and growth of carbon nanotubes assisted by microwave plasma on metal surfaces have been observed by transmission electron microscopy. Microwave plasma generated nanoparticles of various sizes on metal surfaces. Initially, the nanoparticles were embedded in an amorphous carbon layer and led to the formation of carbon tube nuclei. At the early stage of growth, the carbon tube diameters ranged from 10 to 100 nm. Carbon tubes with diameters of 40–50 nm had a high growth rate in the vertical direction, resulting in the formation of tube arrays.
Cyclotron resonance of a two-dimensional Wigner solid
Authors: Monarkha Yu. P.
Published: March 2003

Cyclotron resonance absorption from a two-dimensional electron solid formed on a free surface of liquid helium is analyzed by means of the memory function formalism. The presence of the low-frequency phonon mode of the Wigner solid in a strong magnetic field is shown to broaden significantly the electron dynamical structure factor (DSF) as a function of frequency, strengthening the contribution from multiphonon emission terms of the high-frequency mode. Thus in most cases the linewidth is formed by nonlinear terms of the DSF expansion in the cyclotron motion factor exp(−iωct) rather than by the linear terms analyzed previously. The inclusion of all these multiphonon terms changes the sign of the many-electron effect and agrees well with available experimental data, eliminating the discrepancy between theory and experiment.
Plastic-deformation-induced low-temperature anomalies of the resistivity of polycrystalline copper and aluminum
Authors: Dmitriev V. M. , Lebedeva I. L. , Prentslau N. N.
Published: March 2003

The temperature dependence of the electrical resistivity ρ of pure polycrystalline aluminum and copper after plastic deformation is investigated in the temperature interval 4.2–300 K. Using heat treatment as a tool for changing the crystallite size d and structural perfection of the sample, it is determined how ρ depends on the ratio of d to the electron mean free path le and on the degree of deformation of the Cu and Al. At temperatures below 10 K the ρ(T) curves of the deformed samples of polycrystalline copper and aluminum exhibit minima and maxima. At higher temperatures a more complicated dependence of ρ(d/le) is observed. It is found that in the region of the anomalous skin effect the experimentally determined and theoretically calculated values of the surface resistance Rs agree only in the case when the electron mean free path is smaller than the size of the crystallites.
Magnetic state in URu2Si2, UPd2Al3, and UNi2Al3 probed by point contacts
Authors: Naidyuk Yu. G. , Kvitnitskaya O. E. , Jansen A. G. M. , Wyder P. , Geibel C. , Menovsky A. A.
Published: March 2003

The antiferromagnetic (AFM) state is investigated in the three heavy-fermion compounds URu2Si2, UPd2Al3, and UNi2Al3 by measuring dV/dI(V) curves of point contacts at different temperatures 1.5–20 K and magnetic fields 0–28 T. The zero-bias maximum in dV/dI(V) for URu2Si2 points to a partially gapped Fermi surface related to the itinerant nature of the AFM state, contrary to the case of UPd2Al3, where analogous features have not been found. The AFM state in UNi2Al3 has more similarities with URu2Si2. For URu2Si2, the same critical field of about 40 T along the easy axis c is found for all features in dV/dI(V), corresponding to the Néel temperature, the gap in the electronic density of states, and presumably the ordered moments.
Quantum biexcitonic liquid in monoclinic ZnP2 crystals
Authors: Gorban I. S. , Yeshchenko O. A. , Dmitruk I. M. , Biliy M. M.
Published: March 2003

A phonon–roton dispersion relation is proposed for the elementary excitations of a quantum biexcitonic liquid in semiconductors. The proposed dispersion relation is used as a starting point for a calculation of the photoluminescence spectrum of the liquid and an analysis of its behavior under variation of temperature and density of the biexcitonic liquid. The parameters of the dispersion curve of elementary excitations of the quantum biexcitonic liquid are evaluated by fitting the calculated photoluminescence spectrum to the experimental spectrum of the biexcitonic liquid of semiconducting β-ZnP2 crystals. Experimental studies of how the photoluminescence spectrum of a biexcitonic liquid in β-ZnP2 depends on the temperature and the intensity of the laser excitation confirm the initial theoretical model. The dependence of the temperature of the crystals on the excitation intensity is measured, and for some of the samples an anomalous dependence is found: the temperature of the crystal decreases as the excitation intensity increases. This effect is probably a consequence of the giant thermal conductivity of the superfluid biexcitonic liquid in β-ZnP2 crystals.
The influence of small impurities of He4 on the melting curve of He3
Authors: Ganshin A. N. , Grigor’ev V. N. , Maı̆danov V. A. , Penzev A. A. , Rudavskiı̆ E. Ya. , Rybalko A. S. , Syrnikov E. V.
Published: March 2003

The melting curve of He3 containing a small He4 impurity is measured in the temperature range 20–600 mK. It is found that the coordinates of the minimum of the melting curve are shifted, that hysteresis appears, and that the slope of the melting curve at low temperatures is changed. The data obtained agree with a calculation that takes into account the change in the coordinates of the minimum due to the entropy of mixing of the He–43He solution. The results of the experiment are used to estimate the error arising when the melting curve of He3 is used to determine the temperature.
Protein:protein interactions and the pairing of boundary elements in vivo
Authors: Blanton Jason , Gaszner Miklos , Schedl Paul
Published: March 2003

Although it is now well-established that boundary elements/insulators function to subdivide eukaryotic chromosomes into autonomous regulatory domains, the underlying mechanisms remain elusive. One idea is that boundaries act as barriers, preventing the processive spreading of “active” or “silenced” chromatin between domains. Another is that the partitioning into autonomous functional units is a consequence of an underlying structural subdivision of the chromosome into higher order “looped” domains. In this view, boundaries are thought to delimit structural domains by interacting with each other or with some other nuclear structure. The studies reported here provide support for the looped domain model. We show that theDrosophila scsandscs‘boundary proteins, Zw5 and BEAF, respectively, interact with each other in vitro and in vivo. Moreover, consistent with idea that this protein:protein interaction might facilitate pairing of boundary elements, we find that thatscsandscs‘are in close proximity to each other inDrosophilanuclei.
Facilitation of dendritic mRNA transport by CPEB
Authors: Huang Yi-Shuian , Carson John H. , Barbarese Elisa , Richter Joel D.
Published: March 2003

In neurons, the proteins derived from mRNAs localized in dendrites have been implicated in synaptic plasticity. The cytoplasmic polyadenylation element (CPE), a cis element in the 3′-UTRs of specific dendritic mRNAs, promotes cytoplasmic polyadenylation-induced translation in response to synaptic stimulation. Here, we demonstrate that the CPE and its binding protein CPEB facilitate mRNA transport to dendrites. In rat hippocampal neurons infected with recombinant viruses, the CPE is sufficient to direct a reporter RNA into dendrites. CPEB-GFP protein forms RNA-containing particles that are transported into dendrites in a microtubule-dependent fashion at an average velocity of 4–8 μm/min. Such particles also contain maskin, a CPEB-associated factor that mediates cap-dependent translational repression of CPE-containing mRNA, and the molecular motors dynein and kinesin. Overexpression of CPEB in neurons promotes the transport of CPE-containing endogenous MAP2 mRNA to dendrites, whereas overexpression of a mutant CPEB that is defective for interaction with molecular motors inhibits this transport. In neurons derived from CPEB knockout mice, the dendritic transport of a CPE-containing reporter RNA is reduced. These results suggest a mechanism whereby CPE-containing mRNAs can be transported to dendrites in a translationally dormant form, but activated at synapses in response to NMDA receptor stimulation.
Essential and dispensable roles of ATR in cell cycle arrest and genome maintenance
Authors: Brown Eric J. , Baltimore David
Published: March 2003

A Cre/lox-conditional mouse line was generated to evaluate the role of ATR in checkpoint responses to ionizing radiation (IR) and stalled DNA replication. We demonstrate that after IR treatment, ATR and ATM each contribute to early delay in M-phase entry but that ATR regulates a majority of the late phase (2–9 h post-IR). Double deletion ofATRandATMeliminates nearly all IR-induced delay, indicating that ATR and ATM cooperate in the IR-induced G2/M-phase checkpoint. In contrast to the IR-induced checkpoint, checkpoint delay in response to stalled DNA replication is intact inATRknockout cells andATR/ATMandATR/p53double-knockout cells. The DNA replication checkpoint remains intact inATRknockout cells even though the checkpoint-stimulated inhibitory phosphorylation of Cdc2 on T14/Y15 and activating phosphorylation of the Chk1 kinase no longer occur. Thus, incomplete DNA replication in mammalian cells can prevent M-phase entry independently of ATR and inhibitory phosphorylation of Cdc2. When DNA replication inhibitors are removed, ATR knockout cells proceed to mitosis but do so with chromosome breaks, indicating that ATR provides a key genome maintenance function in S phase.
The nucleotides responsible for the direct physical contact between the chromatin insulator protein CTCF and theH19imprinting control region manifest parent of origin-specific long-distance insulation and methylation-free domains
Authors: Pant Vinod , Mariano Piero , Kanduri Chandrasekhar , Mattsson Anita , Lobanenkov Victor , Heuchel Rainer , Ohlsson Rolf
Published: March 2003

The repression of the maternally inheritedIgf2allele has been proposed to depend on a methylation-sensitive chromatin insulator organized by the 11 zinc finger protein CTCF at theH19imprinting control region (ICR). Here we document that point mutations of the nucleotides in physical contact with CTCF within the endogenousH19ICR lead to loss of CTCF binding andIgf2imprinting only when passaged through the female germline. This effect is accompanied by a significant loss of methylation protection of the maternally derivedH19ICR. Because CTCF interacts with other imprinting control regions, it emerges as a central factor responsible for interpreting and propagating gamete-derived epigenetic marks and for organizing epigenetically controlled expression domains.
Rent Sharing in Multi‐Site Hog Production
Authors: Cozzarin Brian P. , Westgren Randall E.
Published: March 2003

A firm‐level model of three‐site hog production is used compare a franchise organizational structure to a three‐firm alliance. The results of the simulations imply that the franchise system is better equipped to mitigate underproduction in the nursery and finishing units, the nursery and finishing units lose relatively more profit than they otherwise would in an alliance. The pig‐space guatantee does little to offset the financial risk for the nursery and finishing units when underproduction occurs upstream (breeding, gestation, and farrowing unit).