bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantum wave packet and quasiclassical trajectory studies of OH+CO: Influence of the reactant channel well on thermal rate constants
Authors: Medvedev Dmitry M. , Gray Stephen K. , Goldfield Evelyn M. , Lakin Matthew J. , Troya Diego , Schatz George C.
Published: January 2004

We study the OH+CO→H+CO2 reaction with both six-dimensional quantum wave packets (QM) and quasiclassical trajectories (QCT), determining reaction probabilities and thermal rate constants (or coefficients), and studying the influence of the reactant channel hydrogen-bonded complex well on the reaction dynamics. The calculations use the recently developed Lakin–Troya–Schatz–Harding (LTSH) ground electronic state potential energy surface, along with a modified surface developed for this study (mod-LTSH), in which the reactant channel well is removed. Our results show that there can be significant differences between the QM and QCT descriptions of the reaction for ground-state reactants and for energies important to the thermal rate constants. Zero-point energy violation plays an important role in the QCT results, and as a result, the QCT reaction probability (for ground-state reactants and zero impact parameter) is much higher than its QM counterpart at moderate to low reagent translational energies. The influence of the reactant channel well in the QCT results is to enhance reactivity at moderate energies and to suppress reactivity at the very lowest collision energies. The QM results also show the enhancement at moderate energies but, while the very lowest translational energies cannot be adequately converged, they do not indicate any tendency toward suppression as energy is reduced. QCT calculations for excited rotational states of the reactants show that the suppression of reactivity associated with the reactant channel well is less important when the reactants are rotating, and as a result, the influence of the reactant channel well on the thermal rate coefficients is relatively small, being important below 200 K. Our results indicate that there still remain important discrepancies between experiment and theory in this low temperature regime and that further improvements of the potential are needed.
Nonresonant holeburning in the Terahertz range: Brownian oscillator model
Authors: Häberle Uli , Diezemann Gregor
Published: January 2004

The response to the field sequence of nonresonant hole burning, a pump-wait-probe experiment originally designed to investigate slow relaxation in complex systems, is calculated for a model of Brownian oscillators, thus including inertial effects. In the overdamped regime the model predictions are very similar to those of the purely dissipative stochastic models investigated earlier, including the possibility to discriminate between dynamic homogeneous and heterogeneous relaxation. The case of underdamped oscillations is of particular interest when low-frequency excitations in glassy systems are considered. We show that also in this situation a frequency selective modification of the response should be feasable. This means that it is possible to specifically address various parts of the spectrum. An experimental realization of nonresonant holeburning in the Terahertz regime therefore is expected to shed further light on the nature of the vibrations around the so-called boson peak.
Vacuum-ultraviolet spectroscopy of poly(methylphenylsilylene)
Authors: Phifer Carol C. , Thomes William J. , Simmons-Potter Kelly , Potter B. G.
Published: January 2004

The first vacuum-ultraviolet spectrum of a polysilylene (chain-type polysilane) with aromatic substituents is presented. Assignments of the absorption bands of the model compound poly(methylphenylsilylene) are based on previous experimental data and theoretical electronic band structure calculations for poly(alkylsilylenes) and on ultraviolet spectra of phenyl-containing monomers and polymers. Although aryl orbitals mix with the σ-conjugated orbitals located along the catenated silicon backbone, some transitions are largely localized on the phenyl groups. These assignments elucidate the nature of the bonding in polysilylenes and should be useful in understanding photodegradation mechanisms and in the design of related new optical materials.
The behavior of the form factor in two dimensions for linear polymers in different regimes
Authors: Harnett Sr. Joan , Bishop Marvin
Published: January 2004

Off-lattice Monte Carlo simulations employing the PIVOT algorithm are used to generate ideal and excluded volume linear polymers in two dimensions. The form factor at small and large wave vectors is calculated from the resulting configurations and compared to the exact equation for ideal chains and to both scaling and renormalization group predictions for excluded volume chains. It is found that using the des Cloizeaux form for the distance distribution function in an analytic calculation of the form factor leads to close agreement with the Monte Carlo data and that simple expressions for both the small and large wave vector expansions reproduce the essential features of the form factor.
Applications of π-photon-induced transparency in two-frequency pulse electron paramagnetic resonance experiments
Authors: Fedin Matvey , Kälin Moritz , Gromov Igor , Schweiger Arthur
Published: January 2004

An approach to pulse electron paramagnetic resonance (EPR) experiments which are based on two different resonance fields is introduced. Instead of using two microwave (mw) sources or a magnetic field jump, bichromatic pulses consisting of a transverse microwave field with frequency ωmw and a longitudinal radio frequency field with frequency ωrf are employed. Such bichromatic pulses excite a number of multiple photon transitions at frequencies ωmw+kωrf (k∈Z). The π-photon-induced transparency phenomenon is used to select the required transitions. This approach is used in the stimulated soft electron spin echo envelope modulation and the four-pulse double electron-electron resonance experiments. The results obtained using the bichromatic pulse approach are in agreement with those obtained with the standard pulse EPR techniques. It is shown that applying bichromatic pulses is straightforward and advantageous in several respects.
Ab initio torsional potential and transition frequencies of acetaldehyde
Authors: Császár Attila G. , Szalay Viktor , Senent Maria L.
Published: January 2004

High-level ab initio electronic structure calculations, including extrapolations to the complete basis set limit as well as relativistic and diagonal Born–Oppenheimer corrections, resulted in a torsional potential of acetaldehyde in its electronic ground state. This benchmark-quality potential fully reflects the symmetry and internal rotation dynamics of this molecule [J. Chem. Phys. 117, 6489 (2002)] in the energy range probed by spectroscopic experiments in the infrared and microwave regions. The torsional transition frequencies calculated from this potential and the ab initio torsional inverse effective mass function are within 2 cm−1 of the available experimental values. Furthermore, the computed contortional parameter ρ of the rho-axis system Hamiltonian is also in excellent agreement with that obtained from spectral analyses of acetaldehyde.
A concerted three-body formation X+Y+C2H4 in the photodissociation of CH2XCH2Y (X,Y=Br,Cl) at 193 nm
Authors: Lee Ya-Rong , Chen Cheng-Chu , Lin Shen-Maw
Published: January 2004

The photodissociation of CH2XCH2Y (X,Y=Br,Cl) through absorption of 193 nm photons was investigated using product translational spectroscopy. No stable CH2BrCH2 or CH2ClCH2 was detected. The recorded time-of-flight spectra indicate that these internally excited radicals dissociated into Y+C2H4 in a concerted reaction with the first C–X bond rupture. Product anisotropy implies that the overall reaction time for three-body formation is in a fraction of rotational period. According to an asynchronous concerted reaction model, the measured spectra were simulated with product translational energy distributions coupled by asymmetric angular distributions. For the mixed halide, CH2BrCH2Cl, triple products Br+Cl+C2H4 can be originated from the cleavage of either the C–Br bond or the C–Cl bond. The results are discussed and where appropriate, comparisons with previous investigations of the related molecules are included.
Dipole solvation in dielectrics
Authors: Matyushov Dmitry V.
Published: January 2004

This paper presents an exact solution for the free energy of linear solvation of a dipolar solute in an arbitrary dielectric material with a microscopic spectrum of polarization fluctuations. The solution is given in terms of wave vector-dependent longitudinal and transverse structure factors of the polarization fluctuations in the pure dielectric. Good agreement with computer simulations of dipole solvation in dipolar and dipolar–quadrupolar liquids is achieved.
Thermodiffusion of interacting colloids. I. A statistical thermodynamics approach
Authors: Dhont Jan K. G.
Published: January 2004

The thermal diffusion coefficient of colloids consists of two additive contributions, one related to specific interactions between the surfaces of colloidal particles with solvent molecules, and a contribution due to interactions between the colloidal particles. In the present paper, the effect of intercolloidal particle interactions on their thermodiffusive behavior is discussed within a statistical thermodynamics framework. Transport coefficients are expressed in terms of the interaction potential between the colloidal spheres. A special feature of macromolecular systems is that this interaction potential is a potential of mean force, which is temperature dependent. It is shown that under certain conditions this implicit temperature dependence gives rise to negative Soret coefficients, that is, to diffusion of macromolecules to hot regions.
Thermodiffusion of interacting colloids. II. A microscopic approach
Authors: Dhont Jan K. G.
Published: January 2004

A microscopic approach is presented to describe the contribution to the thermal diffusion coefficient of colloids due to intercolloidal particle interactions. An exact expression for the leading-order virial coefficient of the thermal diffusion coefficient of interacting colloidal spheres is derived in terms of the intercolloidal pair-interaction potential and hydrodynamic interaction functions. This general expression is explicitly evaluated for hard-core interactions and for spheres with a short-ranged attractive potential. The derivation is based on a Smoluchowski equation that is generalized to include temperature gradients. For short-ranged attractive potentials, a negative Soret coefficient is predicted under certain conditions, when the depth of the attraction increases with increasing temperature.
Semiclassical calculation of the vibrational echo
Authors: Noid W. G. , Ezra Gregory S. , Loring Roger F.
Published: January 2004

The infrared echo measurement probes the time scales of the molecular motions that couple to a vibrational transition. Computation of the echo observable within rigorous quantum mechanics is problematic for systems with many degrees of freedom, motivating the development of semiclassical approximations to the nonlinear optical response. We present a semiclassical approximation to the echo observable, based on the Herman–Kluk propagator. This calculation requires averaging over a quantity generated by two pairs of classical trajectories and associated stability matrices, connected by a pair of phase-space jumps. Quantum, classical, and semiclassical echo calculations are compared for a thermal ensemble of noninteracting anharmonic oscillators. The semiclassical approach uses input from classical mechanics to reproduce the significant features of a complete, quantum mechanical calculation of the nonlinear response.
Zero kinetic energy photoelectron study of SO2+(X 2A1) using coherent extreme ultraviolet radiation
Authors: Mo Yuxiang , Yang Jie , Chen Guanying
Published: January 2004

Using our newly built extreme ultraviolet (XUV) photoelectron and photoion spectrometer, we have obtained the pulsed field ionization zero kinetic energy (ZEKE) photoelectron spectra of SO2+(X 2A1)←SO2(X 1A1) by coherent XUV radiation in the energy range of 12.29–12.82 eV. The adiabatic ionization potential (IP) of SO2 is 12.3458±0.0002 (eV), which was determined by comparing the partially resolved rotational branch contour with the simulated one. Besides the bending vibrational mode (υ2) which was found to be exclusive in the photoelectron spectra (PE) reported previously, we also observed the other two modes: the symmetric stretching (υ1) and the antisymmetric stretching (υ3) vibrations. The fundamental of the symmetric stretching (υ1) is 1057 cm−1 and the overtone of the antisymmetric stretching (2υ3) is 2494 cm−1. The new vibrational progressions (υ100)+, (1υ20)+, (2υ20)+, and (0υ22)+ have also been observed, and these new observations suggested that the irregular structure of (0υ20)+ assigned to the previous PE spectra should be reconsidered. The comparison of the intensities of these vibrational bands with the calculated Franck–Condon factors with harmonic approximation was also made.
Solvatochromic and thermochromic shifts of electronic spectra of polar solute molecules in a mixture of polar and nonpolar solvent; the role of solvent–solvent interactions
Authors: Gorbatsevich Sergej K. , Smirnova Olga Yu.
Published: January 2004

A theoretical model is proposed to describe the influence of the concentration of a polar solvent and the temperature of a solution on the electronic spectra of a polar solute in a binary solvent mixture. It is shown that the interaction between molecules of the polar solvent in the first solvation shell makes the significant contribution to the formation of absorption and fluorescence bands of the solute. An experimental study of solvatochromic and thermochromic shifts of steady-state fluorescence spectra of 3-amino-N-methylphthalimide in decalin–propanol mixture for different values of propanol mole fraction is carried out. Good qualitative agreement between the experimental data and calculation results is observed.
The melting lines of model silicon calculated from coexisting solid–liquid phases
Authors: Yoo S. , Zeng X. C. , Morris James R.
Published: January 2004

The molecular-dynamics simulation approach [Morris and Song, J. Chem. Phys. 116, 9352 (2002)] is employed to calculate the melting lines for two model systems of silicon: the Stillinger–Weber (SW) model and the Tersoff-89 model. To address the anisotropic stress problem indicated in the previous paper, a slightly improved simulation procedure is used to prepare the coexisting solid and liquid phases at the thermodynamic equilibrium. For the SW silicon, the calculated melting temperature Tm at zero pressure agrees with that based on the free-energy calculation [Broughton and Li, Phys. Rev. B 35, 9120 (1987)]. The dependence of Tm at zero pressure on the selected solid surface orientation is also examined. The relative difference between Tm calculated based on the sharp Si (111)/liquid interface and the faceted Si (100)/liquid interface is less than 1%. Both models predict that the melting line exhibits a negative slope, which is consistent with the fact that the molar volume of the solid is larger than that of liquid upon melting.
Activation barriers and rate constants for hydration of platinum and palladium square-planar complexes: An ab initio study
Authors: Burda Jaroslav V. , Zeizinger Michal , Leszczynski Jerzy
Published: January 2004

In the present work, an ab initio study on hydration (a metal-ligand replacement by water molecule or OH− group) of cis- and transplatin and their palladium analogs was performed within a neutral pseudomolecule approach (e.g., metal-complex+water as reactant complex). Subsequent replacement of the second ligand was considered. Optimizations were performed at the MP2/6-31+G(d) level with single-point energy evaluation using the CCSD(T)/6-31++G(d,p) approach. For the obtained structures of reactants, transition states (TS’s), and products, both thermodynamic (reaction energies and Gibbs energies) and kinetic (rate constants) characteristics were estimated. It was found that all the hydration processes are mildly endothermic reactions—in the first step they require 8.7 and 10.2 kcal/mol for ammonium and chloride replacement in cisplatin and 13.8 and 17.8 kcal/mol in the transplatin case, respectively. Corresponding energies for cispalladium amount to 5.2 and 9.8 kcal/mol, and 11.0 and 17.7 kcal/mol for transpalladium. Based on vibrational analyses at MP2/6-31+G(d) level, transition state theory rate constants were computed for all the hydration reactions. A qualitative agreement between the predicted and known experimental data was achieved. It was also found that the close similarities in reaction thermodynamics of both Pd(II) and Pt(II) complexes (average difference for all the hydration reactions are approximately 1.8 kcal/mol) do not correspond to the TS characteristics. The TS energies for examined Pd(II) complexes are about 9.7 kcal/mol lower in comparison with the Pt analogs. This leads to 106 times faster reaction course in the Pd cases. This is by 1 or 2 orders of magnitude more than the results based on experimental measurements.
Nonadiabatic interactions in wave packet dynamics of the bromoacetyl chloride photodissociation
Authors: Lasorne B. , Bacchus-Montabonel M.-C. , Vaeck N. , Desouter-Lecomte M.
Published: January 2004

The competitive photodissociation of bromoacetyl chloride BrCH2COCl in the first A″1 state (S1) by 248 nm photons is investigated by nonadiabatic wave packet simulations. We show that the preferential breaking of the stronger C–Cl bond (α to the excited carbonyl) over the weaker C–Br bond (β) could be explained by a diabatic trapping or nonadiabatic recrossing as previously proposed. Our energy resolved flux analysis agrees fairly well with the experimental branching ratio (C–Cl:C–Br=1.0:0.4). Even if this does not prove the mechanism, this at least prevents to discard it. A reduced dimensionality approach based on constrained Hamiltonian is used. The nonadiabatic dissociation is studied in the two C–O/C–X (X=Br, Cl) subspaces to emphasize the role of the C–O vibration upon [nO→πCO*] excitation. The internal torsion and wagging dihedral angles are frozen at their Franck–Condon value, according to preliminary dynamical tests. The other inactive coordinates are optimized at the trans and Cs constrained geometry in the first excited state. Corresponding 2D cuts in the potential energy surfaces have been computed at the CASSCF level. The nonadiabatic kinetic couplings are highly peaked along an avoided crossing seam in both cases. A two-state diabatic model with a constant potential coupling is proposed in the two C–O/C–X subspaces. The inclusion of the C–O stretching in the active coordinates improves the value of the branching ratio over our previous 1D computation.
Laser-induced fluorescence spectroscopy of 3,4,9,10-perylenetetracarboxylic-dianhydrid in helium nanodroplets
Authors: Wewer M. , Stienkemeier F.
Published: January 2004

Electronic spectra of the S1←S0 transition of the 3,4,9,10-perylenetetracarboxylic-dianhydrid (PTCDA) monomer isolated in superfluid helium nanodroplets have been measured by means of laser-induced fluorescence. The 000 transition appears at 20 988 cm−1 as the dominant line. We obtain clearly resolved the vibrational structure of the molecule. A comparison to Raman spectra of PTCDA films on metallic substrates and PTCDA crystals as well as with calculated frequencies provides the identification of the different modes. The enhanced resolution in the low temperature helium environment and the obtained line positions provide new information about structural properties of perylene derivatives.
Formation of 90° elastic domains during local 180° switching in epitaxial ferroelectric thin films
Authors: Chen Lang , Ouyang J. , Ganpule C. S. , Nagarajan V. , Ramesh R. , Roytburd A. L.
Published: January 2004

90° elastic domains were observed after local polings in epitaxial ferroelectric Pb(Zr0.2Ti0.8)O3 thin films via piezoresponse force microscopy. An area of internal stress arises under a conductive atomic force microscope tip due to the opposite signs of the converse piezoelectric effects in the switched domain and the unswitched films surrounding. The formation of 90° domains leads to the relaxation of the internal stress and stabilization of 180° domain after turning off the electric field applied by the tip. The criterion that formulates the necessary condition for realization of the relaxation mechanism is presented as well.
Molecular-dynamics studies of surface of ice Ih
Authors: Ikeda-Fukazawa Tomoko , Kawamura Katsuyuki
Published: January 2004

We performed molecular dynamics calculations of surface of ice Ih in order to investigate formation mechanism of melting layer on the surface. The results showed that the vibrational amplitude of the atoms in the surface layer greatly depends on the crystal orientation, whereas that in the ice bulk is isotropic. The anisotropy of the vibration is due to a dangling motion of the free O–H bonds exist at the surface layer. The dangling motion enhances the rotational motion of the water molecules. The vibrational density of state showed a coupling between the rotational vibration and the lattice vibration of the water molecules in the surface layer. The coupling of the vibrations causes a distortion of ice lattice. Through the hydrogen-bonding network, the distortion transmits to the interior of the crystal. We conclude that the dangling motion of the free O–H bonds exist at the surface layer is one of the dominant factors governing the surface melting of ice crystal.
Very large dielectric constant of highly oriented Pb1−xBaxTiO3 thin films prepared by chemical deposition
Authors: Pontes F. M. , Leite E. R. , Mambrini G. P. , Escote M. T. , Longo E. , Varela J. A.
Published: January 2004

Highly (100) oriented Pb0.8Ba0.2TiO3/LaNiO3 structures were grown on LaAlO3(100) substrates by using a wet, soft chemical method and crystallized by the microwave oven technique. The Au/PBT/LaNiO3/LaAlO3 capacitor shows a hysteresis loop with remnant polarization, Pr, of 15 μC/cm2, and coercive field, Ec, of 47 kV/cm at an applied voltage of 3 V, along with a dielectric constant over 1800. Atomic force microscopy showed that Pb0.8Ba0.2TiO3 is composed of large grains about 300 nm. The experimental results demonstrated that the microwave preparation is rapid, clean, and energy efficient. Therefore, we demonstrated that the combination of the soft chemical method with the microwave process is a promising technique to grow highly oriented thin films with excellent dielectric and ferroelectric properties, which can be used in various integrated device applications.
GaN quantum dots doped with Eu
Authors: Hori Y. , Biquard X. , Monroy E. , Jalabert D. , Enjalbert F. , Dang Le Si , Tanaka M. , Oda O. , Daudin B.
Published: January 2004

Molecular-beam-epitaxy growth of Eu-doped GaN quantum dots embedded in AlN has been achieved. The crucial issue of Eu location has been addressed by extended x-ray absorption fine structure measurements. By comparing the signature of the Eu short-range environment for several samples, it is concluded that Eu is mostly incorporated in GaN dots. Intense cathodoluminescence associated with Eu has been measured, with no GaN bandedge emission, evidence that carrier recombination mostly occurs through rare-earth ion excitation. Persistent photoluminescence of Eu-doped GaN quantum dots as a function of the temperature is suggested to be further confirmation of the recombination of confined carriers through Eu ion excitation.
Cross-sectional scanning tunneling microscopy and spectroscopy of InGaP/GaAs heterojunctions
Authors: Dong Y. , Feenstra R. M. , Semtsiv M. P. , Masselink W. T.
Published: January 2004

Compositionally abrupt InGaP/GaAs heterojunctions grown by gas-source molecular-beam epitaxy have been investigated by cross-sectional scanning tunneling microscopy and spectroscopy. Images inside the InGaP layer show nonuniform In and Ga distribution. About 1.5 nm of transition region at the interfaces is observed, with indium carryover identified at the GaAs–on–InGaP interface. Spatially resolved tunneling spectra with nanometer spacing across the interface were acquired, from which band offsets (revealing that nearly all of band offset occurs in the valence band) were determined.
High thermal stability of magnetic tunnel junctions with oxide diffusion barrier layers
Authors: Fukumoto Yoshiyuki , Shimura Ken-ichi , Kamijo Atsushi , Tahara Shuichi , Yoda Hiroaki
Published: January 2004

We developed two types of magnetic tunnel junctions (MTJs) that showed high thermal stability. One is a PtMn exchange-biased spin-valve MTJ with a CoFe/Al-oxide (AlOx)/NiFe free layer and a CoFeTaOx/CoFe pinned layer, and the other is a pseudo-spin-valve (PSV) MTJ with a CoFe/AlOx/NiFe soft layer, where AlOx and CoFeTaOx act as barriers for Ni and Mn diffusion toward the tunnel barrier, respectively. After 390 °C-1H annealing, the PSV MTJs maintained 28% and the SV MTJs 39% of tunnel magnetoresistance. Transmission electron microscopy observation of the SV MTJs after 380 °C-1H annealing revealed that the migrated Mn atoms were trapped at the CoFeTaOx layer.
Correlation of charge transport to intrinsic strain in silicon oxynitride and Si-rich silicon nitride thin films
Authors: Habermehl S. , Apodaca R. T.
Published: January 2004

Poole–Frenkel emission in Si-rich nitride and silicon oxynitride thin films is studied in conjunction with compositional aspects of their elastic properties. For Si-rich nitrides varying in composition from SiN1.33 to SiN0.54, the Poole–Frenkel trap depth (ΦB) decreases from 1.08 to 0.52 eV as the intrinsic film strain (εi) decreases from 0.0036 to −0.0016. For oxynitrides varying in composition from SiN1.33 to SiO1.49N0.35, ΦB increases from 1.08 to 1.53 eV as εi decreases from 0.0036 to 0.0006. In both material systems, a direct correlation is observed between ΦB and εi. Compositionally induced strain relief as a mechanism for regulating ΦB is discussed.
A uniform glow discharge plasma source at atmospheric pressure
Authors: Moon Se Youn , Choe W. , Kang B. K.
Published: January 2004

An atmospheric-pressure, uniform, continuous, glow plasma was produced in ambient air assisted by argon feeding gas, using a 13.56 MHz rf source. Based on the measured current–voltage curve and optical emission spectrum intensity, the plasma showed typical glow discharge characteristics, free from streamers and arc. The measured rotational and vibrational temperatures were in the range of 490 to 630 K and 2000 to 3300 K, respectively, within the operation range of argon flow rate and rf power. From the spatial measurement of total optical emission intensity, and rotational and vibrational temperatures, the plasma shows very high uniformity (over 93%) in the lengthwise direction. The plasma size for this study was 200 mm×50 mm×5 mm, although a plasma was produced in the scaled-up version of 600 mm in length, aiming for large-area plasma applications.
High-speed, short-channel polycrystalline silicon thin-film transistors
Authors: Brotherton S. D. , Glasse C. , Glaister C. , Green P. , Rohlfing F. , Ayres J. R.
Published: January 2004

Results are presented on the performance of low-temperature, short-channel polycrystalline silicon (poly-Si) thin-film transistors (TFTs), with channel length down to 0.5 μm, and scaled gate oxide thickness down to 20 nm. Good TFT switching characteristics were obtained, and the uniformity of short-channel TFTs was shown to have a standard deviation of better then 10%, even for channel widths as small as 4 μm. The 0.5 μm TFTs have been incorporated into a 15-stage complementary pair metal-oxide-Si transistor ring oscillator, which, at a supply voltage of 3 V, operated with a delay/stage of ∼0.1 ns.
Infrared matrix-isolation spectroscopy using pulsed deposition of p-H2
Authors: Wu Yu-Jong , Yang Xueming , Lee Yuan-Pern
Published: January 2004

We employed pulsed deposition of p-H2 onto a cold target to form a matrix sample suitable for measurements of infrared absorption. Unlike the method of rapid vapor deposition at ∼2.5 K, developed by Fajardo et al., this method can be performed at a temperature as high as 5.5 K, achievable with a closed-cycle refrigerator; pumping on liquid helium in a cryostat is eliminated. Compared with the enclosed-cell method developed by Oka, Shida, Momose, and co-workers, this method is more versatile in sample preparation, especially for samples at a greater concentration or with high reactivity. Two experiments were tested: the pulse-deposited sample of CH4/p-H2 yields an infrared absorption spectrum nearly identical to that recorded with rapid vapor deposition, and a sample of vinyl chloride (C2H3Cl) in solid p-H2 irradiated with laser emission at 193 nm yields C2H5, in contrast to formation of HCl, C2H2, and a complex of HCl⋅C2H2 observed upon photolysis of C2H3Cl in an Ar matrix. These experiments are also compared with those with n-H2 or Ne as the matrix host.
Quantum mechanical map for protein-ligand binding with application to β-trypsin/benzamidine complex
Authors: Zhang Da W. , Xiang Yun , Gao Ai M. , Zhang John Z. H.
Published: January 2004

We report full ab initio Hartree–Fock calculation to compute quantum mechanical interaction energies for β-trypsin/benzamidine binding complex. In this study, the full quantum mechanical ab initio energy calculation for the entire protein complex with 3238 atoms is made possible by using a recently developed MFCC (molecular fractionation with conjugate caps) approach in which the protein molecule is decomposed into amino acid-based fragments that are properly capped. The present MFCC ab initio calculation enables us to obtain an “interaction spectrum” that provides detailed quantitative information on protein-ligand binding at the amino acid levels. These detailed information on individual residue-ligand interaction gives a quantitative molecular insight into our understanding of protein-ligand binding and provides a guidance to rational design of potential inhibitors of protein targets.
Two-dimensional coupled photonic crystal resonator arrays
Authors: Altug Hatice , Vučković Jelena
Published: January 2004

We present the design and fabrication of photonic crystal structures exhibiting electromagnetic bands that are flattened in all crystal directions, i.e., whose frequency variation with a wave vector is minimized. Such bands can be used to reduce group velocity of light propagating in an arbitrary crystal direction, which is of importance for the construction of miniaturized tunable optical delay components and low-threshold photonic crystal lasers, and the study of nonlinear optics phenomena.
Growth of monodispersed cobalt nanoparticles on 6H–SiC(0001) honeycomb template
Authors: Chen Wei , Loh Kian Ping , Xu Hai , Wee A. T. S.
Published: January 2004

We demonstrated an effective way of controlling the size dispersion of surface adsorbed nanoclusters by utilizing a reconstructed template with regular periodic porosity in the nanoscale range. Monodispersed cobalt (Co) nanoclusters of 3 nm sizes have been grown on the reconstructed 6H–SiC(0001) surface by electron-beam evaporation on the C-terminated 6∛×6∛R30° template at room temperature. In situ scanning tunneling microscopy was used to study the nucleation process of the Co nanoclusters on this template. We found that the average cluster size remains constant for different Co coverage, and the cluster density is linearly dependent on the coverage. The monodispersion of the cluster size is suggested to be due to the physical confinement of the Co clusters by the porous honeycomb structure of the SiC reconstructed surface. X-ray photoelectron spectroscopy reveals that the carbon-rich hexagon template prevents cobalt silicide formation up to an annealing temperature of 1150 °C.
Ordering formation of columnar lattices in magnetic fluid thin films subjected to oscillating perpendicular magnetic fields
Authors: Jiang I. M. , Tsai M. S. , Lu C. K. , Shih C. C. , Chiang J. C. , Horng H. E.
Published: January 2004

Applying an oscillating magnetic field perpendicularly on the high-quality magnetic fluid thin film, the phase separation of particles in the liquid matrix will occur. The concentrated phase makes up the cylindrical columns that can form two-dimensional lattices. The ordered structure of magnetic fluid thin films is the basis for the potential optical application. We explore the dynamical ordering formation of columnar lattices in magnetic fluid thin films subjected to oscillating perpendicular magnetic fields in this study.
Hydrothermal route to ZnO nanocoral reefs and nanofibers
Authors: Choy Jin-Ho , Jang Eue-Soon , Won Jung-Hee , Chung Jae-Hun , Jang Du-Jeon , Kim Young-Woon
Published: January 2004

ZnO nanocoral reefs and nanofibers are synthesized on the glass substrate dip coated with ZnO seed with nanoparticles with an average size of 5 nm under a hydrothermal reaction. The ratios of length to diameter for the former and the latter are determined to be 100 and 1000, respectively. In addition, we found that a threshold power density for UV lasing action could be remarkably reduced from 40 kW/cm2 for the nanocoral reefs to 8 kW/cm2 for the nanofibers by increasing the cavity length of ZnO nanowires.
An angle modulation reflectance spectroscopy characterization of a GaAs/GaAlAs asymmetric microcavity structure
Authors: Lin D. Y.
Published: January 2004

A GaAs/GaAlAs-based asymmetric microcavity structure was studied by an angle modulation reflectance (AMR) and reflectivity measurements at different angles of incidence (θinc) ranging from 10° to 65°. The AMR technique possesses the enhanced capability of showing only the angle-dependent cavity mode (CM) feature and interference features related to the properties of the distributed Bragg reflectors (DBRs). By comparison of the AMR spectra and the numerical first derivative (with respect to energy) of the R spectra, the relative strength and positions of the 1C–1H and 1C–1L excitonic transitions can be extracted through a careful line-shape fit. The resonance enhancement between the CM and excitonic transitions are also discussed.
Tungsten inverse opals: The influence of absorption on the photonic band structure in the visible spectral region
Authors: von Freymann Georg , John Sajeev , Schulz-Dobrick Martin , Vekris Evangellos , Tétreault Nicolas , Wong Sean , Kitaev Vladimir , Ozin Geoffrey A.
Published: January 2004

We report on the fabrication and characterization of tungsten inverse opals for the visible and near-infrared spectral region. The crucial influence of the strong absorption in this spectral region is experimentally investigated by means of a gradient deposition technique and characterization with reflectance and transmittance spectroscopy. With increasing metal infiltration, we observe the breakdown of the photonic band structure, resulting first in a sphere-cavity-like behavior and finally in a behavior similar to that of a periodically structured metal surface.
Sensitive measurements of electric field distributions in low-pressure Ar plasmas by laser-induced fluorescence-dip spectroscopy
Authors: Takizawa K. , Sasaki K. , Kono A.
Published: January 2004

Laser-induced fluorescence-dip (LIF-dip) spectroscopy of Ar was used for measuring the distributions of sheath electric fields in low-pressure, inductively-coupled Ar plasmas. A sensitive detection limit of 3 V/cm obtained by LIF-dip allowed the measurement in the presheath region. The distributions of electric fields observed experimentally were compared with those of theoretical calculations based on a simple fluid model. As a result, reasonable agreement between the experiment and the theory was obtained in the electric fields in the sheath region, while the electric fields in the presheath region observed experimentally were higher than the theoretical results.
Full S matrix calculation via a single real-symmetric Lanczos recursion: The Lanczos artificial boundary inhomogeneity method
Authors: Zhang Hong , Smith Sean C.
Published: January 2004

We present an efficient and robust method for the calculation of all S matrix elements (elastic, inelastic, and reactive) over an arbitrary energy range from a single real-symmetric Lanczos recursion. Our new method transforms the fundamental equations associated with Light’s artificial boundary inhomogeneity approach [J. Chem. Phys. 102, 3262 (1995)] from the primary representation (original grid or basis representation of the Hamiltonian or its function) into a single tridiagonal Lanczos representation, thereby affording an iterative version of the original algorithm with greatly superior scaling properties. The method has important advantages over existing iterative quantum dynamical scattering methods: (a) the numerically intensive matrix propagation proceeds with real symmetric algebra, which is inherently more stable than its complex symmetric counterpart; (b) no complex absorbing potential or real damping operator is required, saving much of the exterior grid space which is commonly needed to support these operators and also removing the associated parameter dependence. Test calculations are presented for the collinear H+H2 reaction, revealing excellent performance characteristics.
Vibrational mode selectivity in hyperfine interactions: Polarization quantum beat spectroscopy of HCF(Ã1A″)
Authors: Ionescu Ionela , Fan Haiyan , Annesley Chris , Xin Ju , Reid Scott A.
Published: January 2004

We report on the vibrational mode dependence of the F19 and H1 hyperfine interaction constants in the Ã1A″ state of HCF, determined using polarization quantum beat spectroscopy. The nuclear spin/overall rotation coupling constants display a pronounced energy dependence and mode selectivity which can be traced to variations in both the A rotational constant and nuclear spin/electron orbital coupling constant a. In particular, modes containing C–F stretching excitation display significantly larger F19 spin-rotation constants, which is explained in terms of a decrease in back donation of electron density into the C 2pπ orbitals.
Granulocyte CEACAM3 Is a Phagocytic Receptor of the Innate Immune System that Mediates Recognition and Elimination of Human-specific Pathogens
Authors: Schmitter Tim , Agerer Franziska , Peterson Lisa , Münzner Petra , Hauck Christof R.
Published: January 2004

Carcinoembryonic antigen-related cell adhesion molecules (CEACAMs) are used by several human pathogens to anchor themselves to or invade host cells. Interestingly, human granulocytes express a specific isoform, CEACAM3, that participates together with CEACAM1 and CEACAM6 in the recognition of CEACAM-binding microorganisms. Here we show that CEACAM3 can direct efficient, opsonin-independent phagocytosis of CEACAM-binding Neisseria, Moraxella, and Haemophilus species. CEACAM3- but not CEACAM6-mediated uptake is blocked by dominant-negative versions of the small GTPase Rac. Moreover, CEACAM3 engagement triggers membrane recruitment and increased GTP loading of Rac that are not observed upon bacterial binding to CEACAM6. Internalization and Rac stimulation are also inhibited by compromising the integrity of an immunoreceptor tyrosine-based activation motif (ITAM)–like sequence in the cytoplasmic tail of CEACAM3 or by interference with Src family protein tyrosine kinases that phosphorylate CEACAM3. In contrast to interfering with CEACAM6, blockage of CEACAM3-mediated events reduces the ability of primary human granulocytes to internalize and eliminate CEACAM-binding bacteria, indicating an important role of CEACAM3 in the control of human-specific pathogens by the innate immune system.
Schnurri-3 (KRC) Interacts with c-Jun to Regulate the IL-2 Gene in T Cells
Authors: Oukka Mohamed , Wein Marc N. , Glimcher Laurie H.
Published: January 2004

The activator protein 1 (AP-1) transcription factor is a key participant in the control of T cell proliferation, cytokine production, and effector function. In the immune system, AP-1 activity is highest in T cells, suggesting that a subset of T cell–specific coactivator proteins exist to selectively potentiate AP-1 function. Here, we describe that the expression of Schnurri-3, also known as κ recognition component (KRC), is induced upon T cell receptor signaling in T cells and functions to regulate the expression of the interleukin 2 (IL-2) gene. Overexpression of KRC in transformed and primary T cells leads to increased IL-2 production, whereas dominant-negative KRC, or loss of KRC protein in KRC-null mice, results in diminished IL-2 production. KRC physically associates with the c-Jun transcription factor and serves as a coactivator to augment AP-1–dependent IL-2 gene transcription.
Increased Expression of Interleukin 23 p19 and p40 in Lesional Skin of Patients with Psoriasis Vulgaris
Authors: Lee Edmund , Trepicchio William L. , Oestreicher Judith L. , Pittman Debra , Wang Frank , Chamian Francesca , Dhodapkar Madhav , Krueger James G.
Published: January 2004

Psoriasis is a type I–deviated disease characterized by the presence of interferon (IFN)-γ and multiple IFN-related inflammatory genes in lesions. Because interleukin (IL)-23 is now recognized to play a role in the recruitment of inflammatory cells in a T helper cell (Th)1-mediated disease, we examined psoriasis skin lesions for production of this newly described cytokine. IL-23 is composed of two subunits: a unique p19 subunit and a p40 subunit shared with IL-12. We found a reliable increase in p19 mRNA by quantitative reverse transcription polymerase chain reaction in lesional skin compared with nonlesional skin (22.3-fold increase; P = 0.001). The p40 subunit, shared by IL-12 and IL-23, increased by 11.6-fold compared with nonlesional skin (P = 0.003), but the IL-12 p35 subunit was not increased in lesional skin. IL-23 was expressed mainly by dermal cells and increased p40 immunoreactivity was visualized in large dermal cells in the lesions. Cell isolation experiments from psoriatic tissue showed strong expression of p19 mRNA in cells expressing monocyte (CD14+ CD11c+ CD83−) and mature dendritic cell (DC) markers (CD14− CD11c+ CD83+), whereas in culture, the mRNAs for p40 and p19 were strongly up-regulated in stimulated monocytes and monocyte-derived DCs, persisting in the latter for much longer periods than IL-12. Our data suggest that IL-23 is playing a more dominant role than IL-12 in psoriasis, a Th1 type of human inflammatory disease.
Bone Marrow Allograft Rejection Mediated by a Novel Murine NK Receptor, NKG2I
Authors: Koike Junzo , Wakao Hiroshi , Ishizuka Yuko , Sato Taka-aki , Hamaoki Masaru , Seino Ken-ichiro , Koseki Haruhiko , Nakayama Toshinori , Taniguchi Masaru
Published: January 2004

Natural killer (NK) cells mediate bone marrow allograft rejection. However, the molecular mechanisms underlying such a rejection remain elusive. In previous analyses, it has been shown that NK cells recognize allogeneic target cells through Ly-49s and CD94/NKG2 heterodimers. Here, we describe identification and characterization of a novel murine NK receptor, NKG2I, belonging to the NKG2 family. NKG2I, which was composed of 226 amino acids, showed ∼40% homology to the murine NKG2D and CD94 in the C-type lectin domain. Flow cytometric analysis with anti-NKG2I monoclonal antibody (mAb) revealed that expression of NKG2I was largely confined to NK and NKT cells, but was not seen in T cells. Furthermore, anti-NKG2I mAb inhibited NK cell–mediated cytotoxicity, whereas cross-linking of NKG2I enhanced interleukin 2– and interleukin 12–dependent interferon-γ production. Similarly, the injection of anti-NKG2I mAb before the allogeneic bone marrow transfer in vivo impinged on the function of NKG2I, resulting in the enhanced colony formation in the spleen. NKG2I is a novel activating receptor mediating recognition and rejection of allogeneic target cells.
Fyn and PTP-PEST–mediated Regulation of Wiskott-Aldrich Syndrome Protein (WASp) Tyrosine Phosphorylation Is Required for Coupling T Cell Antigen Receptor Engagement to WASp Effector Function and T Cell Activation
Authors: Badour Karen , Zhang Jinyi , Shi Fabio , Leng Yan , Collins Michael , Siminovitch Katherine A.
Published: January 2004

Involvement of the Wiskott-Aldrich syndrome protein (WASp) in promoting cell activation requires its release from autoinhibitory structural constraints and has been attributed to WASp association with activated cdc42. Here, however, we show that T cell development and T cell receptor (TCR)-induced proliferation and actin polymerization proceed normally in WASp−/− mice expressing a WASp transgene lacking the cdc42 binding domain. By contrast, mutation of tyrosine residue Y291, identified here as the major site of TCR-induced WASp tyrosine phosphorylation, abrogated induction of WASp tyrosine phosphorylation and its effector activities, including nuclear factor of activated T cell transcriptional activity, actin polymerization, and immunological synapse formation. TCR-induced WASp tyrosine phosphorylation was also disrupted in T cells lacking Fyn, a kinase shown here to bind, colocalize with, and phosphorylate WASp. By contrast, WASp was tyrosine dephosphorylated by protein tyrosine phosphatase (PTP)-PEST, a tyrosine phosphatase shown here to interact with WASp via proline, serine, threonine phosphatase interacting protein (PSTPIP)1 binding. Although Fyn enhanced WASp-mediated Arp2/3 activation and was required for synapse formation, PTP-PEST combined with PSTPIP1 inhibited WASp-driven actin polymerization and synapse formation. These observations identify key roles for Fyn and PTP-PEST in regulating WASp and imply that inducible WASp tyrosine phosphorylation can occur independently of cdc42 binding, but unlike the cdc42 interaction, is absolutely required for WASp contributions to T cell activation.
Inflammation Controls B Lymphopoiesis by Regulating Chemokine CXCL12 Expression
Authors: Ueda Yoshihiro , Yang Kaiyong , Foster Sandra J. , Kondo Motonari , Kelsoe Garnett
Published: January 2004

Inflammation removes developing and mature lymphocytes from the bone marrow (BM) and induces the appearance of developing B cells in the spleen. BM granulocyte numbers increase after lymphocyte reductions to support a reactive granulocytosis. Here, we demonstrate that inflammation, acting primarily through tumor necrosis factor α (TNFα), mobilizes BM lymphocytes. Mobilization reflects a reduced CXCL12 message and protein in BM and changes to the BM environment that prevents homing by cells from naive donors. The effects of TNFα are potentiated by interleukin 1 β (IL-1β), which acts primarily to expand the BM granulocyte compartment. Our observations indicate that inflammation induces lymphocyte mobilization by suppressing CXCL12 retention signals in BM, which, in turn, increases the ability of IL-1β to expand the BM granulocyte compartment. Consistent with this idea, lymphocyte mobilization and a modest expansion of BM granulocyte numbers follow injections of pertussis toxin. We propose that TNFα and IL-1β transiently specialize the BM to support acute granulocytic responses and consequently promote extramedullary lymphopoiesis.