bluuebunny/crossref_metadata_2025 huggingface dataset:
The partitioning of energy amongst vibration, rotation, and translation during the dissociation of p-difluorobenzene–Ar neutral and cation complexes
Authors: Bellm Susan M. , Lawrance Warren D.
Published: January 2003

The dissociation dynamics of p-difluorobenzene–Ar and p-difluorobenzene-Ar+ have been investigated from the 51¯ level in S1 and the 292¯ level in D0, respectively. The technique of velocity map imaging has been used to determine the translational energy release distributions. In the case of 51¯ p-difluorobenzene–Ar, dispersed fluorescence spectra provide the distribution of vibrational energy in the p-difluorobenzene fragment. A significant fraction of the p-difluorobenzene products are formed in the 00 level. From the translational energy release data the rotational energy distribution within 00 can be inferred. The results show that the average rotational energy is 380 cm−1, >5 times the average translational energy of 70 cm−1. This rotational excitation infers that dissociation occurs with the Ar atom significantly displaced from its equilibrium position above the center of the aromatic ring. From the average rotational energy it is determined that the Ar atom is, on average, displaced by 1.8–3.7 Å from the center of the aromatic ring at dissociation, i.e., the Ar atom is beyond the carbon atoms. In the case of dissociation from the 292¯ level of p-difluorobenzene-Ar+, the vibrational distribution within the p-difluorobenzene+ product is not known, however it can be inferred from previous studies of dissociation within S1. As for the 51¯ p-difluorobenzene–Ar case, the evidence suggests that dissociation leads to significant rotational excitation of p-difluorobenzene+. There are a limited number of destination vibrations within the p-difluorobenzene and p-difluorobenzene+ fragments for dissociation from 51¯ (S1) and 292¯ (D0), respectively. Hence there are only a few, widely separated, values for the combined translational and rotational energy available. Despite this, the translational energy release distributions in both cases are smooth and structureless. In the limit of no rotational excitation of the polyatomic fragment, the translational energy release distributions would show peaks only at energies corresponding to populated vibrational states of the product. The absence of such peaks indicates that rotational excitation of the product occurs for all vibrational states, reducing the average translational energy released and smearing the distribution.
Semiclassical dynamics with quantum trajectories: Formulation and comparison with the semiclassical initial value representation propagator
Authors: Garashchuk Sophya , Rassolov Vitaly A.
Published: January 2003

We present a time-dependent semiclassical method based on quantum trajectories. Quantum-mechanical effects are described via the quantum potential computed from the wave function density approximated as a linear combination of Gaussian fitting functions. The number of the fitting functions determines the accuracy of the approximate quantum potential (AQP). One Gaussian fit reproduces time-evolution of a Gaussian wave packet in a parabolic potential. The limit of the large number of fitting Gaussians and trajectories gives the full quantum-mechanical result. The method is systematically improvable from classical to fully quantum. The fitting procedure is implemented as a gradient minimization. We also compare AQP method to the widely used semiclassical propagator of Herman and Kluk by computing energy-resolved transmission probabilities for the Eckart barrier from the wave packet time-correlation functions. We find the results obtained with the Herman–Kluk propagator to be essentially equivalent to those of AQP method with a one-Gaussian density fit for several barrier widths.
Entanglement-assisted coherent control in nonreactive diatom–diatom scattering
Authors: Gong Jiangbin , Shapiro Moshe , Brumer Paul
Published: January 2003

Intriguing quantum effects that result from entangled molecular rovibrational states are shown to provide a novel means for controlling both differential and total collision cross sections in identical particle diatom–diatom scattering. Computational results on elastic and inelastic scattering of para–H2 and para–H2 are presented, with the collision energy ranging from 400 cm−1 to the ultracold regime. The experimental realization and possible extension to other systems are discussed.
Accurate double many-body expansion potential energy surface for triplet H3+. I. The lowest adiabatic sheet (a3Σu+)
Authors: Cernei Mihail , Alijah Alexander , Varandas António J. C.
Published: January 2003

We report on a global potential energy hypersurface for the lowest triplet state of H3+ based on the double many-body expansion (DMBE) method and ab initio data points of V5Z quality. These data points are represented with a root mean square deviation of only 3.46 cm−1 in the energy region below the H2+(X2Σg+)+H(2S) dissociation threshold and with less than 15 cm−1 up to the three-particle breakup energy. As expected from a DMBE approach, all dissociation limits are represented accurately and are approached in a physically correct manner.
An accurate determination of rovibrational spectra using the externally corrected coupled-cluster approaches: LiH ground state
Authors: Li Xiangzhu , Paldus Josef
Published: January 2003

Recently acquired highly precise spectroscopic data for the ground state of LiH and its various isotopomers are employed to carry out a critical assessment of the performance of the externally corrected coupled-cluster (CC) approaches. Both the amplitude and energy-corrected approaches are considered, in particular the reduced multireference CC method with singles and doubles (RMR CCSD) and the asymmetric energy formula based CCSD-[MR] method, both exploiting the same modest-size multireference configuration interaction (MR CISD) wave function, based on an M-dimensional reference space, as the source of higher than pair clusters. To assess the size of the basis set errors relative to those of the methods employed, the comparison is also made with the full CI (FCI) results at the cc-pVTZ level. The rovibrational energy levels and the corresponding transition frequencies are then computed for various isotopomers of LiH using the theoretically determined potentials at the cc-pVXZ (X=D, T, Q, and 5) and the extrapolated completebasis-set-limit levels and a comparison is made with the experiment as well as with the existing theoretical results, particularly those exploiting the CC approaches. The role of adiabatic corrections is also assessed. It is shown that both the RMR CCSD and CCSD-[4R] methods, yielding an almost indistinguishable results, are capable of accounting for the nondynamical correlation effects that are lacking in the standard single-reference CCSD approaches.
Proton transfer in gas-phase ammonium dinitramide clusters
Authors: Alavi Saman , Thompson Donald L.
Published: January 2003

Proton transfer in gaseous ammonium dinitramide (ADN) clusters up to (ADN)2 is studied by using density-functional theory. Proton transfer between the hydrogen dinitramide and ammonia units does not occur in the ADN monomer, rather the ammonia–hydrogen dinitramide complex is stabilized by strong hydrogen bonding. However, proton transfer between hydrogen dinitramide and ammonia is observed in the ADN dimer [NH3HN(NO2)2]2, ADN solvated with a single ammonia molecule [NH3NH(NO2)2]NH3, and ADN solvated with a hydrogen dinitramide molecule [NH3HN(NO2)2]HN(NO2)2. Structural changes in the complexes relative to the free molecules and the binding energies of the clusters are given. Using population analysis, the total electrostatic interaction energy in each cluster is calculated. The electrostatic energy is a measure that distinguishes between the ionic or hydrogen-bonded nature of the clusters. Some implications of proton transfer in ADN clusters on the decomposition mechanism of ADN are discussed.
The electron cusp condition and the virial ratio as indicators of basis set quality
Authors: Rosas-Garcia Victor M. , Crawford T. Daniel
Published: January 2003

We consider two measures of the quality of one-electron basis sets for quantum-chemical calculations: The electron–electron coalescence curvature and the correlation energy virial ratio. The former is based on the Kato cusp condition that many-electron wave functions must exhibit discontinuous first derivatives with respect to r12 as the coordinates of any two electrons coalesce. The latter is based on a simple modification of the quantum-mechanical virial theorem that makes use of only the correlation contributions to the kinetic and potential energy expectation values. The two measures are tested using coupled cluster wave functions for helium, neon, argon, calcium, and phosphorus atoms and are found to indicate good correlation with the quality of the basis set. These techniques may provide a foundation for the development of reliable basis set diagnostics for a variety of quantum-chemical applications.
Comment on “On the interpretation of force-extension curves of single protein molecules” [J. Chem. Phys. 116, 7760 (2002)]
Authors: Neumann Richard M.
Published: January 2003

Makarov et al., in comparing the force laws obtained using constant-force (Gibbs) and constant-displacement (Helmholtz) ensembles in real and in ideal chains, define chain extension in terms of the average end-to-end displacement, 〈r〉, in the Gibbs derivation. In our comment, we point out that this definition is not the extension which is measured in typical fixed-force, single-molecule, stretching experiments. We also clarify the relationship between the force laws obtained from the different ensembles for the ideal Gaussian chain.
Response to “Comment on ‘On the interpretation of force-extension curves of single protein molecules’ ” [J. Chem. Phys. 118, 2964 (2003)]
Authors: Makarov Dmitrii E. , Wang Zhisong , Hansma Helen G.
Published: January 2003

We argue that the average scalar extension of a molecule 〈|r|〉 is not what is measured in a typical single protein stretching experiment, contrary to Neumann’s belief. We further show that Neumann’s “disagreement” with our results is based on his misinterpretation of our work.
Calculations of nuclear magnetic shielding in paramagnetic molecules
Authors: Rinkevicius Zilvinas , Vaara Juha , Telyatnyk Lyudmyla , Vahtras Olav
Published: January 2003

We propose and evaluate first principles methods for calculating the nuclear shielding tensor in open-shell, paramagnetic molecules, dealing with the case of small spin–orbit coupling that, in turn, implies the best applicability to light, organic compounds. The formalism is consistent up to second order in the fine structure constant, and includes orbital, fully anisotropic dipolar, and isotropic contact contributions to the tensor. The proposed method is implemented within the ab initio single- and multiconfiguration self-consistent field as well as density functional theory frameworks. The applications include small main-group radicals and larger nitroxide radicals. The analysis of the results and comparison with the experimental nuclear magnetic resonance data, which are available for the latter compounds, indicate promising accuracy and applicability of the density functional theory method to chemically interesting problems.
Logarithmic decay of the orientational correlation function in supercooled liquids on the Ps to Ns time scale
Authors: Cang Hu , Novikov V. N. , Fayer M. D.
Published: January 2003

Dynamics of supercooled ortho-terphenyl, salol, benzophenone, 2-biphenylmethanol, and dibutylphthalate have been studied using optical heterodyne detected optical Kerr effect experiments over a broad range of time, <1 ps to tens of ns. On time scales longer than those influenced by intramolecular vibrational dynamics, “intermediate” power law decays with temperature independent exponents close to −1 have been observed from ∼2 ps to 1–10 ns in all five samples. The intermediate power law decays occur over a wide range of temperatures from well above to somewhat below Tc, the mode-coupling theory (MCT) critical temperature. The intermediate power law corresponds to approximately a logarithmic decay of the polarizability–polarizability (orientational) correlation function. The amplitude of the intermediate power law increases with increasing temperature as [(T−Tc)/Tc]1/2. The intermediate power law decay is followed by a second longer time scale power law, and the final portion of the decay is exponential. As a framework for discussion, the results are compared to the quantitative predictions of the MCT. The observations are in contrast to the standard MCT for the longer time portions of the decays. The observed intermediate power law decays may be consistent with MCT if the dynamics occur in the part of the MCT parameter space near a high order singularity (end point case).
Numerical simulation of magnetic susceptibility effects in nuclear magnetic resonance spectroscopy
Authors: Mayer Christian , Terheiden Annegret
Published: January 2003

A numerical algorithm is proposed which is suitable to calculate the magnetic field distribution as well as the corresponding nuclear magnetic resonance time signals and frequency spectra induced by susceptibility effects. It accounts for a wide variety of system parameters such as various sample geometries, free and hindered self-diffusion, inhomogeneous susceptibility, and variable spin concentration. It is suitable to cover multiple experimental conditions such as single pulses, echoes, sample spinning at any tilt angle, and field gradient experiments. Typical results are shown that demonstrate the separate and combined influences of self-diffusion and sample spinning on spectral line shapes. Calculated frequency shifts are compared with known analytical expressions and with experimental data on dispersions of magnetic nanoparticles.
A Monte Carlo study of effects of chain stiffness and chain ends on dilute solution behavior of polymers. I. Gyration-radius expansion factor
Authors: Yamakawa Hiromi , Yoshizaki Takenao
Published: January 2003

A Monte Carlo (MC) study is made of the mean-square radius of gyration 〈S2〉 and the gyration-radius expansion factor αS for the freely rotating chain of bond angle 109° and with the Lennard-Jones (LJ) 6-12 intramolecular potentials between beads in a cutoff version for the number n of bonds in the chain ranging from 10 to 1500 at the reduced temperature ranging from 3.6 to 8.0, which is defined as the absolute temperature multiplied by the Boltzmann constant and divided by the depth of the well of the LJ potential. It is shown that the ratio 〈S2〉/n approaches asymptotically a constant independent of n for very large n at the value 3.72±0.05 of the reduced temperature, which value is equal to the reduced Θ temperature Θ* of the MC model system, and that possible effects of chain ends on 〈S2〉 and therefore on αS are negligibly small. Taking the values of 〈S2〉 at Θ* as the unperturbed ones, αS2 is evaluated from those at various reduced temperatures higher than Θ*. It is then found that the behavior of αS2 may be well explained in the quasi-two-parameter scheme or is in good agreement with that of real experimental data. Further, the binary cluster integral for a bead in the chain is found to be much smaller in magnitude than that for a single isolated bead at reduced temperatures higher than Θ*, the result being consistent with a previous finding.
Fabrication of nanometer-scale mechanical devices incorporating individual multiwalled carbon nanotubes as torsional springs
Authors: Williams P. A. , Papadakis S. J. , Patel A. M. , Falvo M. R. , Washburn S. , Superfine R.
Published: January 2003

We report on the fabrication of nanometer-scale mechanical devices incorporating multiwalled carbon nanotubes (MWNTs) as the torsional spring elements. We have employed electron beam lithography to pattern device elements directly onto individual MWNTs on a silicon dioxide substrate. The structures were suspended by etching the substrate and subsequent critical-point drying of the sample. We also briefly present characterization of the torsional properties of an individual MWNT. The techniques described are applicable to other nanometer-scale rod-like objects.
Single-step fabrication of silicon-cone arrays
Authors: Wysocki G. , Denk R. , Piglmayer K. , Arnold N. , Bäuerle D.
Published: January 2003

A regular lattice of SiO2 microspheres on a quartz support is used as a microlens system for laser-induced single-step fabrication of arrays of silicon cones on a (100) Si surface. The experiments were performed with single-pulse 248 nm KrF laser radiation.
Photon noise correlations in electrically coupled semiconductor lasers
Authors: Mayer P. M. , Rana F. , Ram R. J.
Published: January 2003

Measurements of the correlation between the photon noise of two semiconductor lasers sharing a bias circuit are presented. The photon noise of the electrically coupled lasers is found to be correlated by as much as 70%. The photon noise correlations are measured at low frequencies as a function of the bias current for lasers connected in series and in parallel, and for high and low impedance biases. The magnitude and sign of the noise correlations are consistent with theoretical expectations.
Spin wave resonance in Ga1−xMnxAs
Authors: Goennenwein S. T. B. , Graf T. , Wassner T. , Brandt M. S. , Stutzmann M. , Philipp J. B. , Gross R. , Krieger M. , Zürn K. , Ziemann P. , Koeder A. , Frank S. , Schoch W. , Waag A.
Published: January 2003

We report ferromagnetic resonance experiments on Ga1−xMnxAs thin films. For the dc magnetic field perpendicular to the sample plane, we observe up to eight distinct resonances, which we attribute to spin wave modes. To account for the spacing of the resonances, we infer a linear gradient in the magnetic properties, which is ascribed to a linear variation of the uniaxial magnetic anisotropy with film thickness. Values of D=(1±0.4)×10−9 Oe cm2 for the spin stiffness and JMnMn≈1 meV for the exchange integral between Mn spins are obtained.
Magnetoelastic and thermoelastic shape memory effect in a Co–Ni single crystal
Authors: Zhou W. M. , Liu Y. , Jiang B. H. , Qi X. , Liu Y. N.
Published: January 2003

This letter reports on a study of the magnetomechanical and thermomechanical behavior of a Co–32Ni single crystal. When magnetized along the [001]fcc direction at room temperature in austenite coexited with martensitic state, field-induced strains as high as 4.2% were measured at a field of 12 kOe. The magnetic field-induced strains were recovered during demagnetization, exhibiting a magnetic hysteresis of 5–6 kOe. No field-induced strain was detected if a magnetic field was loaded along another direction. When deformed in compression along the [001]fcc direction at room temperature to a prestrain of 5.4%, about 1.5% strain was recovered during subsequent heating, yielding a recovery rate of 27.8%. For specimens deformed in other crystal directions, no obvious recoverable strain was measured. These experimental phenomena are discussed and interpreted in terms of reversible motions of Shockley partial dislocations.
High brightness laser source based on polarization coupling of two diode lasers with asymmetric feedback
Authors: Thestrup Birgitte , Chi Mingjun , Sass Bjarne , Petersen Paul Michael
Published: January 2003

In this letter, we show that polarization coupling and asymmetric diode-laser feedback can be used to combine two diode-laser beams with low spatial coherence into a single beam with high spatial coherence. The coupled laser source is based on two similar laser systems each consisting of a 1 μm×200 μm broad area laser diode applied with a specially designed feedback circuit. When operating at two times threshold, 50% of the freely running system output power is obtained in a single beam with an M2 beam quality factor of 1.6±0.1, whereas the M2 values of the two freely running diode lasers are 29±1 and 34±1, respectively.
Integrated diffractive terahertz elements
Authors: Stoyanov Nikolay S. , Feurer T. , Ward David W. , Nelson Keith A.
Published: January 2003

Femtosecond laser machining with high-energy pulses is used for fabrication of diffractive elements in LiNbO3 crystalline samples. This permits terahertz generation, frequency dispersion, detection, and analysis within a single integrated platform that is well suited for applications in terahertz spectroscopy or signal processing.
Comparison of magnetocurrent and transfer ratio in magnetic tunnel transistors with spin-valve bases containing Cu and Au spacer layers
Authors: van Dijken Sebastiaan , Jiang Xin , Parkin Stuart S. P.
Published: January 2003

The magnetocurrent of magnetic tunnel transistors with spin-valve base structures is found to be nearly insensitive to whether the spacer layer material in the spin valve is Cu or Au. By contrast, the in-plane magnetoresistance of the same spin valves differs by almost a factor of two. Furthermore, the transfer ratio of the transistor structure is an order of magnitude lower for Au compared to Cu spacer layers. We attribute these different behaviors to the significant role of spin-dependent interface scattering for electrons near the Fermi energy but to much weaker such scattering for hot electrons in the energy range considered (∼1–2 eV).
Leakage currents in high-permittivity thin films
Authors: Schroeder Herbert , Schmitz Sam , Meuffels Paul
Published: January 2003

Quite often leakage current data through high-permittivity thin films exhibit straight lines in the “Schottky” plot, i.e., log (current density j) versus sqrt (mean applied field), which suggests an electrode-limited current by field-enhanced thermionic emission. Unfortunately, the extracted permittivity at optical frequencies seldom is in agreement with experimental values and often is unacceptably small, i.e., <1. We suggest a model demonstrating that the leakage current in high-permittivity thin films is bulk-limited, but still is showing the characteristic dependence of thermionic emission. This is due to a combination of boundary conditions of the model, low-permittivity thin layers (“dead layer”) at the electrodes and current injection/recombination terms at the injecting/collecting electrodes, respectively.
Modeling of transport in polycrystalline organic semiconductor films
Authors: Verlaak S. , Arkhipov V. , Heremans P.
Published: January 2003

We propose a grain-boundary barrier model with an energy distribution of interfacial traps to describe charge transport in polycrystalline organic thin films. The model is applied to the interpretation of charge transport in unintentionally doped pentacene films. It gives an acceptable explanation for the concomitant increase in threshold voltage and mobility, and allows an understanding of the difference between the dopant-concentration and gate-voltage dependences of the mobility.
Space-charge region-dominated steady-state photoconductance in low-lifetime Si wafers
Authors: Bail M. , Schulz M. , Brendel R.
Published: January 2003

We investigate the steady-state photoconductance of an oxidized low-lifetime monocrystalline Si wafer with an inversion layer at its surfaces. Photogenerated electrons and holes reduce the band bending and decrease the width of the carrier depleted space-charge region. Mobile charge carriers are stored on both sides of the space-charge region and dominate the photoconductivity at a low illumination intensity. This charge storage effect disappears under accumulation. We present an analytic model for the experimental observations. It is necessary to account for the charge storage effect when deducing low (<10 μs) minority carrier lifetimes on surface-inverted solar Si wafers from one-sun steady-state photoconductance measurements.
Sm
x
Nd
1−x
NiO
3
thin-film solid solutions with tunable metal–insulator transition synthesized by alternate-target pulsed-laser deposition
Authors: Ambrosini Andrea , Hamet Jean-François
Published: January 2003

Thin-film solid solutions of SmxNd1−xNiO3 were synthesized on NdGaO3 substrates by pulsed-laser deposition using alternating NdNiO3 and SmNiO3 targets. The films were characterized by x-ray diffraction and variable-temperature four-probe conductivity measurements. The films grow in the {100}pseudocubic direction. There is a nearly linear increase of the metal–insulator transition from 199 K for x=0 to 378 K for x=1, with the composition corresponding to x=0.6 displaying a transition near room temperature.
Dielectric relaxation and strain behavior of 95.5% Pb(Zn1/3Nb2/3)O3–4.5% PbTiO3 single crystals at cryogenic temperatures
Authors: Yu Zhi , Ang Chen , Furman E. , Cross L. E.
Published: January 2003

The dielectric behavior of 95.5% Pb(Zn1/3Nb2/3)O3–4.5% PbTiO3 single crystals oriented along 〈001〉 direction with and without dc electric field has been studied at cryogenic temperatures. A pronounced low-temperature dielectric relaxation process was observed below 200 K; the relaxation rate follows the Arrhenius law (τ0=∼1.0×10−15 s and U=0.24 eV). An additional dielectric anomaly showed up around 250 K at 10 kHz under a dc electric field. These results indicate rather complicated polarization mechanisms at cryogenic temperatures which clearly need more detailed study. The strain levels at cryogenic temperatures suggest that this material is very promising for space applications, in which the performance at cryogenic temperatures is critical.
Aligned carbon nanotubes patterned photolithographically by silver
Authors: Huang Shaoming , Mau Albert H. W.
Published: January 2003

Selective growth of aligned carbon nanotubes (CNTs) by pyrolysis of iron (II) phthalocyanine (FePc) on quartz substrate patterned photolithographically by metallic silver has been demonstrated. Micro/nanopattern of aligned CNTs can be achieved by using a photomask with features on a microscale. With convenient use of simple high-contract black and white films as a photomask, aligned nanotubes patterned with 20 μm resolution in large scale can be fabricated. This practical fabrication of aligned CNTs on patterned conducting substrate could be applied to various device applications of CNTs.
Observation of light polarization-dependent structural changes in chalcogenide glasses
Authors: Chen Gang , Jain Himanshu , Vlcek Miroslav , Khalid Syed , Li Jun , Drabold David A. , Elliott Stephen R.
Published: January 2003

The atomistic origin of photoinduced vector (polarization-dependent) phenomena in As–Se films is determined by extended x-ray absorption fine structure with in situ exposure to polarized laser light. A vector structural change is observed directly for any material: there is an expansion of the nearest-neighbor distance around the Se atoms, the magnitude of which depends on the direction of light polarization; the effect around As atoms is relatively smaller. The results point to the origin of scalar as well as vector changes in properties, which either persist after the light is removed, or exist only when light is incident on the sample.
Wafer-fused AlGaAs/GaAs/GaN heterojunction bipolar transistor
Authors: Estrada Sarah , Xing Huili , Stonas Andreas , Huntington Andrew , Mishra Umesh , DenBaars Steven , Coldren Larry , Hu Evelyn
Published: January 2003

We describe an n-AlGaAs/p-GaAs/n-GaN heterojunction bipolar transistor, formed via wafer fusion of a p-GaAs base to an n-GaN collector. Wafer fusion was carried out at 750 °C for 1 h. Devices utilized a thick base (0.15 μm) and exhibited limited common-emitter current gain (0.2–0.5) at an output current density of ∼100 A/cm2. Devices were operated to VCE greater than 20 V, with a low VCE offset (1 V). Improvements in both device structure and wafer fusion conditions should provide further improvements in device performance.
Growth and structural analysis of metalorganic chemical vapor deposited (112̄0) MgxZn1−xO (0<x<0.33) films on (011̄2) R-plane Al2O3 substrates
Authors: Muthukumar S. , Zhong J. , Chen Y. , Lu Y. , Siegrist T.
Published: January 2003

Mg x Zn 1−x O  (0<x<0.33) thin films were grown on R-plane (011̄2) sapphire substrate by metalorganic chemical vapor deposition. It was found that a thin ZnO buffer layer with a minimum thickness of ∼50 Å is needed to achieve wurtzite-type MgxZn1−xO films on R-plane sapphire. The x-ray Δω(112̄0) rocking curve and Δ2θ(112̄0) full width at half maximum for Mg0.18Zn0.82O film were measured to be 0.275° and 0.18°, respectively, indicating strong mosaicity and strain in the films. In-plane reflections show the lower lattice mismatch along the c axis of the MgxZn1−xO films on R-plane sapphire. Optical transmission spectra indicate the good quality of the films.
Blocking phenomena in granular magnetic alloys through magnetization, Hall effect, and magnetoresistance experiments
Authors: Denardin J. C. , Pakhomov A. B. , Brandl A. L. , Socolovsky L. M. , Knobel M. , Zhang X. X.
Published: January 2003

Magnetization and magnetotransport were measured in CoxAg1−x granular composites as a function of temperature and applied magnetic field. A transition from blocked to superparamagnetic behavior with increasing temperatures can be observed in magnetization, giant magnetoresistance and the extraordinary Hall effect measurements. However, the blocking temperature determined from magnetotransport measurements is systematically lower than the one estimated from magnetic measurements. This is due to the selective magnetic scattering, which is enhanced for smaller particles, while the magnetization probes the whole particle size distribution.
Formation and structure of inverted hexagonal pyramid defects in multiple quantum wells InGaN/GaN
Authors: Watanabe K. , Yang J. R. , Huang S. Y. , Inoke K. , Hsu J. T. , Tu R. C. , Yamazaki T. , Nakanishi N. , Shiojiri M.
Published: January 2003

We have determined the structure of inverted hexagonal pyramid defects (IHPs) in multiple quantum wells InGaN/GaN by high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM). HAADF STEM images reveal definitely that the IHP nucleates at a threading dislocation and grows in the form of a thin six-walled structure with InGaN/GaN {101̄1} layers. It has been found that IHPs start even at In-rich dots under adverse growth conditions.
Ion densities in an ac metal halide arc discharge
Authors: Karabourniotis D. , Drakakis E.
Published: January 2003

The time-dependent density of mercury ions, sodium ions, and electrons is determined experimentally at the center of a high-pressure mercury discharge with sodium iodide as additive operated on alternating current within transparent quartz tube. The technique used is based on emission lines, and is independent of thermodynamic equilibrium assumptions. The results show that at sinusoidal low-frequency excitation the electrons come mainly from mercury ionization, the electron and mercury-ion densities vary strongly within the ac cycle, whereas the modulation of the sodium-ion density is significantly less pronounced. Results are also obtained assuming thermodynamic equilibrium and compared with the initial ones.
Rovibrational state-selected study of H2+ (X,ν+=0–17, N+=1)+Ar using the pulsed field ionization-photoelectron-secondary ion coincidence scheme
Authors: Qian X.-M. , Zhang T. , Chiu Y.-H. , Levandier D. J. , Miller J. S. , Dressler R. A. , Ng C. Y.
Published: January 2003

A high-resolution pulsed field ionization photoelectron-secondary ion coincidence (PFI-PESICO) method has been developed for absolute cross section measurements of state-selected ion–molecule reactions. Employing this new PFI-PESICO scheme, we have measured rovibrational-state-selected absolute cross sections for the reaction of H2+(X,ν+=0–17, N+=1)+Ar at the center-of-mass collision energies of 1.1 and 2.4 eV. The ν+=17 state is the second to the last vibrational level of H2+(X), which lies a mere 0.03 eV below the H2+(X) dissociation limit. The absolute cross sections observed for the formation of Ar+ and ArH+ [σv+(Ar++ArH+)] from H2+(X,ν+=0–4, N+=1) are consistent with previous experiments, exhibiting strong enhancement of the reaction cross section for ν+=2. However, the σv+(Ar++ArH+) values for H2+(X,ν+=5–14, N+=1)+Ar are found to be nearly constant. The drop in σv+(Ar++ArH+) observed for H2+(X,ν+=15–17, N+=1)+Ar is attributed to the further dissociation of product ArH+.
Separation of hot-electron and self-heating effects in two-dimensional AlGaN/GaN-based conducting channels
Authors: Vitusevich S. A. , Danylyuk S. V. , Klein N. , Petrychuk M. V. , Avksentyev A. Yu. , Sokolov V. N. , Kochelap V. A. , Belyaev A. E. , Tilak V. , Smart J. , Vertiatchikh A. , Eastman L. F.
Published: January 2003

We address experimental and theoretical study of a two-dimensional electron gas transport at low and moderate electric fields. The devices under study are group-III nitride-based (AlGaN/GaN) gateless heterostructures grown on sapphire. The transmission line model patterns of different channel lengths, L, and of the same channel width are used. A strong dependence of the device I–V characteristics on the channel length has been found. We have developed a simple theoretical model to adequately describe the observed peculiarities in the I–V characteristics measured in steady-state and pulsed (10−6 s) regimes. The effect of the Joule heating of a heterostructure is clearly distinguished. The thermal impedance and the channel temperature rise caused by the Joule self-heating have been extracted for the devices of different L at different values of dissipated power. The current reduction due to both self-heating and hot-electron effects is determined quantitatively as a function of the electric field.
Atomic-scale strain field and In atom distribution in multiple quantum wells InGaN/GaN
Authors: Watanabe K. , Nakanishi N. , Yamazaki T. , Yang J. R. , Huang S. Y. , Inoke K. , Hsu J. T. , Tu R. C. , Shiojiri M.
Published: January 2003

We present an atomic-scale structural and compositional analysis of ultrathin layers in multiple quantum well InGaN/GaN, by high-angle annular dark field (HAADF) scanning transmission electron microscopy (STEM). A high-quality HAADF STEM image processed by two-dimensional smoothing and deconvolution provides precise atomic-column positions and clear contrast, thereby allowing us to map the strain field and In atom distribution in successive GaN and InGaN layers. We conclude from these maps that there is a local fluctuation of In atoms in the InGaN layers and the In-rich regions, considered as quantum dots, cause large expansion only along the [0001] direction.
Polymer-based surface-plasmon-polariton stripe waveguides at telecommunication wavelengths
Authors: Nikolajsen Thomas , Leosson Kristjan , Salakhutdinov Ildar , Bozhevolnyi Sergey I.
Published: January 2003

Long-range surface-plasmon-polariton (LR–SPP) waveguiding along thin gold stripes embedded in polymer is investigated in the wavelength range of 1510–1620 nm. LR–SPP intensity distributions at the output are measured for different stripe widths and thicknesses. Coupling loss of ∼0.5 dB is achieved when exciting the fundamental LR–SPP mode along 10-nm-thick stripes of 6–10 μm width with a polarization maintaining fiber. LR–SPP propagation loss of 6–8 dB/cm is estimated (at 1550 nm) and attributed to scattering from inhomogeneities of the metal stripe and polymer cladding.
Ca-doping-induced enhancement of the critical currents of coated conductors grown by ion-beam-assisted deposition
Authors: Weber A. , Hammerl G. , Schmehl A. , Schneider C. W. , Mannhart J. , Schey B. , Kuhn M. , Nies R. , Utz B. , Neumueller H.-W.
Published: January 2003

One of the most promising technologies for the fabrication of high-Tc cables is the ion-beam-assisted deposition (IBAD) technique. The performance of the superconductors fabricated by IBAD, and the fabrication costs, are to a great extent determined by the critical current densities of the superconductors’ grain boundaries. Since, in bicrystalline samples, overdoping has been found to improve the transport properties of grain boundaries in high-Tc superconductors, we have explored whether overdoping also enhances the critical currents of IBAD samples. The measurements show that, depending on the critical current density of the superconducting film, Jc (77 K) is increased by factors up to 2.2, also in applied magnetic fields of several tesla.
White light-emitting diodes of GaN-based Sr2SiO4:Eu and the luminescent properties
Authors: Park Joung Kyu , Lim Mi Ae , Kim Chang Hae , Park Hee Dong , Park Joon Taik , Choi Se Young
Published: January 2003

We have synthesized a Eu2+-activated Sr2SiO4 yellow phosphor and investigated an attempt to develop white light-emitting diodes (LEDs) by combining it with a GaN blue LED chip. Two distinct emission bands from the GaN-based LED and the Sr2SiO4:Eu phosphor are clearly observed at 400 nm and at around 550 nm, respectively. These two emission bands combine to give a spectrum that appears white to the naked eye. Our results showed that GaN (400-nm chip)-based Sr2SiO4:Eu exhibits a better luminous efficiency than that of the industrially available product InGaN (460-nm chip)-based YAG:Ce.
Optically controlled three-dimensional rotation of microscopic objects
Authors: Bingelyte V. , Leach J. , Courtial J. , Padgett M. J.
Published: January 2003

We demonstrate that microscopic objects held in optical tweezers can be set into controlled rotation about any axis of choice. Our approach relies on the use of a spatial light modulator to create a pair of closely separated optical traps holding different parts of the same object. The pair of traps can be made to revolve around each other in any plane, rotating the trapped object with them. This technique overcomes the previous restriction on the orientation of the rotation axis to be parallel to the beam axis, and extends the versatility of optical tweezers as micromanipulation tools.
Explaining gender segregation
Authors: Blackburn Robert M. , Browne Jude , Brooks Bradley , Jarman Jennifer
Published: January 2003

Occupational gender segregation — the tendency for women and men to work in different occupations — is an important feature of all societies, and particularly the wealthy industrialized ones. To understand this segregation, and to explain its significance, we need to distinguish between vertical segregation entailing inequality and horizontal segregation representing difference without inequality, with overall segregation being the resultant of these components. Three major theoretical approaches to understanding occupational gender segregation are examined: human capital/rational choice, patriarchy, and preference theories. All are found to be inadequate; they tend to confuse overall segregation with its vertical component, and each entails a number of other faults. It is generally assumed or implied that greater empowerment of women would reduce gender segregation. This is the reverse of what actually happens; in countries where the degree of women's empowerment is greater, the level of gender segregation is also greater. An alternative theoretical approach based on processes of social reproduction is shown to be more useful.
Employment, flexible working and the family
Authors: Crompton Rosemary
Published: January 2003

This paper assesses some of the implications of one of the major social changes to have taken place in the West during the second half of the twentieth century — that is, the increased employment of women, together with normative changes in gender relations and in women's expectations. These changes have been linked to an increase in individualism, which itself is associated with the transcendence of ‘first modernity’. Thus it is suggested that new approaches to social analysis are required (Beck). Here it is argued that, rather than develop completely new approaches in order to grasp the changes that are under way, the ‘economic’ and the ‘social’ (that is, employment and the family) should be seen as intertwined, rather than approached as separate phenomena. Past debates in feminism, changes in the family, and flexible employment are critically examined. The growing tensions between employment and family life are discussed. It is argued that these changes are associated with the intensification of capitalist development, rather than reflecting a fundamental transformation of society. Existing approaches to the analysis of social change, including Polanyi's analysis of the development of ‘counter‐movements’ against the ‘self‐regulating’ market, will, therefore, still be relevant to our enquiries. In the concluding section, a programme of research that would examine these changes is outlined.
Culture, the ‘sick role’ and the consumption of health
Authors: Shilling Chris
Published: January 2003

This paper revisits Parsons's conception of the ‘sick role’ and examines the relevance of his writings on the cultural understanding of sickness to the consumption of health in the contemporary era. In terms of current developments, I focus on the development of pro‐active approaches towards the healthy body, and the growth of ‘information rich’ consumers of health care. These have become prominent themes in sociology, and while Parsons's writings are usually viewed as anachronistic I argue they remain highly pertinent to understanding the emergence of informed, body conscious lay people. If Parsons's analysis of health is more relevant to current circumstances than many critics assume, however, it is not unproblematic. The residual categories associated with the sick role obscure the continued utility of his work on the general cultural values informing health care. It is Parsons's analysis of these values, I suggest, that needs rescuing from restricted understandings of the sick role and highlighting as an important resource for contemporary theorists.
Global anti‐corporate struggle: a preliminary analysis 1
Authors: Crossley Nick
Published: January 2003

This paper offers a preliminary analysis of the recent wave of anti‐corporate protest that has swept across numerous countries throughout the world. In the first part of the paper the social structure of this phenomenon is examined. Specifically, it is argued that it should be understood as a ‘field’, in Pierre Bourdieu's sense of the term. In the second part of the paper the factors which account for the emergence of this field are explored, using a ‘value‐added’ model which focuses upon the interplay of strains, situational definitions, focal events, opportunities and the circulation of protest relevant resources. The paper is conceived as a preliminary analysis which outlines a framework and draws out important themes. It is not offered as a complete account but rather as a basis from which more specific and focused studies might stem.
Effect of Sulfosulfuron on the Urine and Urothelium of Male Rats
Authors: Arnold Lora L. , Cano Martin , St John Margaret K. , Healy Charles E. , Cohen Samuel M.
Published: January 2003

Sulfosulfuron, developed as a herbicide, caused increased microcrystalluria and the formation of urinary tract calculi when fed to male and female rats in a chronic 2-year study at doses of 5,000 ppm and 20,000 ppm. Hyperplasia was also seen in urinary bladders at 5,000 ppm and 20,000 ppm, almost exclusively in the presence of observable calculi/microcalculi. Urinary bladder tumors were found in 2 females in the 5000 ppm group, both in the presence of calculi. No increased microcrystalluria, calculi, or tumors were found at doses of 500 ppm and lower. In the current study, 5 groups of male Sprague—Dawley rats were fed sulfosulfuron at doses of 50, 500, 5,000, and 20,000 ppm for 10 weeks. Ten animals were co-administered 5,000 ppm sulfosulfuron with 12,300 ppm NH 4Cl to determine if inhibition of the formation of calculi would prevent any urothelial effects of treatment with sulfosulfuron. Ten animals in the control group and in the high-dose sulfosulfuron group were fed only basal diet for an additional 10 weeks to determine if the effects of sulfosulfuron on the bladder epithelium were reversible. There was an increased incidence of microcrystalluria observed at 5,000 and 20,000 ppm. There was no increase in microcrystalluria observed in the urine of rats co-administered sulfosulfuron and NH4Cl. Urinary bladder calculi were found in the bladder of 1 animal fed 20,000 ppm. Examination by light microscopy showed diffuse papillary/nodular hyperplasi a of the bladder epithelium in this animal. No increased microcrystalluria was observed after withdrawal of the chemical from the diet and the bladder epithelium was normal by light microscopy. The hyperplastic effects associated with the feeding of high doses of sulfosulfuron occur only with the appearance of urinary tract calculi. Based on these results and anatomical differences between rats and humans, it may be concluded that the hyperplastic and carcinogenic effects of sulfosulfuron in rats are high-dose, threshold phenomena that are not likely to occur in humans under environmentally relevant exposures.
“Have You Seen This?” Diffuse Hepatic Apoptosis
Authors: Greaves Peter , Edwards Richard , Cohen Gerald M. , Macfarlane Marion
Published: January 2003

One important cell death pathway involves binding of the cell surface receptor Fas, which recruits and activates specifi c initiator and effector caspases. In this study Balb/c mice were injected with monoclonal antibody to Fas either alone or followed by the tripeptide caspase inhibitor Z-VAD.fmk. At four hours mice were killed along with concurrent controls and tissues processedforhistological examination and immunocytochemica l staining for cleaved caspase-3. The livers in all animals treated with Fas alone showed massive apoptosis and positive staining for cleaved caspase-3 whereas those treated with Fas and Z-VAD.fmk or controls showed little or no apoptosis or staining for cleaved caspase-3. These features suggest that massive apoptosis may be important in fulminant liver disease.
Altered Hox Gene Expression and Cellular Pathogenesis of 5-Aza-2' -Deoxycytidine-Induced Murine Hindlimb Dysmorphogenesis
Authors: Branch S. , Henry-Sam G.
Published: January 2003

The DNA demethylating agent, 5-aza-2'-deoxycytidine (d-AZA), elicits temporally related morphological defects and altered gene expression in mouse hindlimbs. Segmental formation of limb regions (stylopod, zeugopod, and autopod) is partially dependent on Hox gene activation. The objective of this study was to understand the role of altered expression of key hox genes in the early pathogenesi s of d-AZA-induced hindlimb defects in mice. Semiquantitative RT-PCR was used to analyze hox gene expression (Hox C-11 and Hox A and D homologs, paralogs 9—13). Untreated and treated fore and hindlimb buds were collected 12 and 24 hours after IP injection (1 mg/kg) of d-AZA at 9 am on gestational (GD) 10 and processed for RT-PCR. Additional pregnant mice were treated similarly and whole embryos collected 12 and 24 hours posttreatment and processed for histopathological analysis. No changes in hox gene expression were detected in the forelimb tissue. There was a 2-fold down-regulation of hoxA-11 and C-11 in the 12-hour hindlimb bud tissue. No changes in the HoxD series were detected in the hindlimb bud tissue. The 12- and 24-hour untreated mice exhibited some of the morphological features consistent with physiological apoptosis. Most tissues of the treated mice exhibited cellular changes consistent with cell death associated with the cytotoxicity of the compound. The data reported supports the hypothesis that altered gene expression and not cytotoxicity alone is associated with d-AZA-induced hindlimb dysmorphogenesis .