bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of ischaemic preconditioning on hepatic oxygenation, microcirculation and function in a rat model of moderate hepatic steatosis
Authors: KOTI Rahul S. , YANG Wenxuan , GLANTZOUNIS Georgios , QUAGLIA Alberto , DAVIDSON Brian R. , SEIFALIAN Alexander M.
Published: December 2004

IPC (ischaemic preconditioning) may protect the steatotic liver, which is particularly susceptible to I/R (ischaemia/reperfusion) injury. Hepatic steatosis was induced in Sprague–Dawley rats with a high-cholesterol (2%) diet for 12 weeks after which rats were subjected to I/R (ischaemia/reperfusion; 45 min of lobar ischaemia followed by 2 h of reperfusion). Rats were divided into three study groups (n=6 each) receiving: (i) sham laparotomy alone, (ii) I/R, and (iii) IPC (5 min of ischaemia, followed by 10 min of reperfusion) before I/R. Hepatic extra- and intra-cellular oxygenation and HM (hepatic microcirculation) were measured with near-infrared spectroscopy and laser Doppler flowmetry respectively. Plasma liver enzymes and hepatic tissue ATP were measured as markers of liver injury. Histology showed moderate-grade steatosis in the livers. At the end of 2 h of reperfusion, I/R significantly decreased extra- and intra-cellular oxygenation concomitant with a failure of recovery of HM (21.1±14.4% of baseline; P<0.001 compared with sham animals). IPC increased intracellular oxygenation (redox state of the copper centre of cytochrome oxidase; P<0.05 compared with rats receiving I/R alone) and flow in HM (70.9±17.1% of baseline; P<0.001 compared with rats receiving I/R alone). Hepatocellular injury was significantly reduced with IPC compared with I/R injury alone (alanine aminotransferase, 474.8±122.3 compared with 5436.3±984.7 units/l respectively; P<0.01; aspartate aminotransferase, 630.8±76.9 compared with 3166.3±379.6 units/l respectively; P<0.01]. In conclusion, IPC has a hepatoprotective effect against I/R injury in livers with moderate steatosis. These data may have important clinical implications in liver surgery and transplantation.
Alterations of serum resistin in normal pregnancy and pre-eclampsia
Authors: CHEN Danqing , DONG Minyue , FANG Qin , HE Jing , WANG Zhengping , YANG Xiaofu
Published: December 2004

Resistin is expressed in human placenta and has been postulated to play a role in regulating energy metabolism in pregnancy. However, changes in serum resistin levels in normal pregnancy and in the setting of pre-eclampsia are far from understood. The purpose of the present study was to clarify the alterations in serum resistin level in normal pregnancy and pre-eclampsia. Blood samples were taken from 28 healthy non-pregnant women, 27 women in the first, 26 in the second and 26 in the third trimesters of normal pregnancy and 25 women with pre-eclampsia. Serum resistin concentrations were determined by using an ELISA, and mean serum resistin levels were compared with one-way ANOVA. Serum resistin levels were not significantly different among non-pregnant women and women in the first and second trimesters of pregnancy (P>0.05 for all). Serum resistin was significantly elevated in the third trimester of normal pregnancy compared with non-pregnant women (P<0.01) and women in the first (P<0.001) and second (P<0.001) trimesters of pregnancy. Serum resistin level was significantly lower in women with pre-eclampsia than women in the third trimester of normal pregnancy (P<0.001), but was comparable with those of non-pregnant women and women in the first and second trimesters of pregnancy (P>0.05 for all). In conclusion, we found an increase in serum resistin in the third trimester of normal pregnancy, but this increase was not present in pre-eclampsia. We postulate that these associations may offer insight into the mechanisms of maternal adaptation to pregnancy and the pathogenesis of pre-eclampsia.
Prostate epithelial cell differentiation and its relevance to the understanding of prostate cancer therapies
Authors: LONG Ronan M. , MORRISSEY Colm , FITZPATRICK John M. , WATSON R. William G.
Published: December 2004

Prostate cancer is the most common malignancy in males in the western world. However, little is known about its origin and development. This review highlights the biology of the normal prostate gland and the differentiation of basal epithelial cells to a secretory phenotype. Alterations in this differentiation process leading to cancer and androgen-independent disease are discussed, as well as a full characterization of prostate epithelial cells. A full understanding of the origin and characteristics of prostate cancer epithelial cells will be important if we are to develop therapeutic strategies to combat the heterogeneous nature of this disease.
Neural stem cells and cell replacement therapy: making the right cells
Authors: BITHELL Angela , WILLIAMS Brenda P.
Published: December 2004

The past few years have seen major advances in the field of NSC (neural stem cell) research with increasing emphasis towards its application in cell-replacement therapy for neurological disorders. However, the clinical application of NSCs will remain largely unfeasible until a comprehensive understanding of the cellular and molecular mechanisms of NSC fate specification is achieved. With this understanding will come an increased possibility to exploit the potential of stem cells in order to manufacture transplantable NSCs able to provide a safe and effective therapy for previously untreatable neurological disorders. Since the pathology of each of these disorders is determined by the loss or damage of a specific neural cell population, it may be necessary to generate a range of NSCs able to replace specific neurons or glia rather than generating a generic NSC population. Currently, a diverse range of strategies is being investigated with this goal in mind. In this review, we focus on the relationship between NSC specification and differentiation and discuss how this information may be used to direct NSCs towards a particular fate.
Single electron emission from the closed-tips of single-walled carbon nanotubes
Authors: Zhou Gang , Duan Wenhui , Gu Binglin
Published: December 2004

The single electron emission behaviors and characteristics from the well-defined quantized energy levels, corresponding to localized electronic states at the dome-structure tips, in single-walled carbon nanotubes (SWNTs) are investigated and illuminated by use of the energy level emission model in combination with the first-principles calculations on the electronic structures. Under the external electric field, the confined electrons are emitted simultaneously from each quantized energy level by virtue of the resonant tunneling effects. With increasing applied voltage, the emission current increases monotonically and exponentially up to the first peak value, and then steps into the increasing and decreasing “sawtoothlike” variations in sequence. The negative differential resistance or conductivity and the maximum current for SWNTs are simulated. The influences of localized electronic states and curvatures of the different closed tips on the single electron emission behaviors of SWNTs are evaluated and discussed. Also a few issues and applications relevant to electron emission of carbon nanotubes are addressed.
Nucleation rates for the condensation of monovalent metals
Authors: Bahadur Ranjit , McClurg Richard B.
Published: December 2004

We show that consideration of both cluster growth and magic numbers are necessary to accurately calculate nucleation rates for the condensation of alkali and coinage metal vapors. The effects are not additive. Rates calculated using the modified theory differ up to several orders of magnitude from typical classical calculations. Calculated rates compare favorably with experimental nucleation onset and rate data for lithium, sodium, cesium, and silver. Verifiable predictions are made for the other alkali and coinage metals.
Measurement of density distributions for colloidal β-FeOOH rods in suspensions exhibiting phase separation: The role of long-range forces in smectic ordering
Authors: Maeda Hideatsu , Maeda Yoshiko
Published: December 2004

We prepared monodisperse colloidal β-FeOOH rods with length-to-width ratios L/W of 3.6–7.0 (L=210–330 nm and W=40–58 nm). Density gradients of the rods occurred in the suspensions by gravity, inducing a phase separation. The denser phase showed smectic (Sm) liquid crystalline structures exhibiting iridescent colors in a wide range of pH from 1.2 (at which the rods interact attractively) to 4.7 (repulsively). The lower density phase was disordered, but frequently emitted diffuse colors locally (at pH>2.6), implying the occurrence of short-range order. The nematic phase was not observed in the β-FeOOH systems, being consistent with theoretical predictions. The particle density distributions were measured over the whole region of the suspensions (separated into two phases) at various pH values using a rapid freezing method. A phase diagram was determined thereby, where the critical (minimal) packing fraction of the particles for the Sm phase showed a nonlinear decrease from 0.43 to 0.12 with increasing pH. Rod-rod spacings in the Sm phase estimated experimentally at various pH were well explained using Derjaguin–Landau–Verwey–Overbeek (DLVO) type pair potentials. It is suggested that Sm ordering can be induced by attractive minima at pH<2.2, while driven by soft repulsions at pH>2.6. The former Sm ordering is expected to be the condensation-type phase transition and the latter the disorder-order transition.
Surfactant free fabrication of polymeric nanoparticles by combined liquid–liquid phase separation and solvent/nonsolvent mixing technology
Authors: Xiong J. Y. , Liu X. Y. , Sawant P. D. , Chen S. B. , Chung T. S. , Pramoda K. P.
Published: December 2004

It is generally agreed that, in most cases, surfactants are required to obtain stable polymeric nanoparticle dispersions. Here, we report a method which can be used to produce surfactant free yet stable polymeric nanoparticle dispersions. This method is based on explored mechanism of selective solvation of nanoparticles and EPD (electron pair donor)/EPA (electron pair acceptor) complexes formed among solvent and nonsolvent molecules. Using polyimide P84 (copolyimide 3,3′ 4,4′-benzophenone tetracarboxylic dianhydride and 80% methylphenylene diamine+20% methylene dianiline) as the model polymer, this mechanism was realized through a combined liquid–liquid phase separation and solvent/nonsolvent mixing technology. Surfactant-free polyimide nanoparticles (<100 nm) were produced. Experimental details and principles of this technology were given based on the ternary diffusion, the liquid–liquid phase separation and the advanced nucleation and growth theory. Two types of methods [denoted as the forward titration method and the backward titration (BT) method] were examined. It was found that the BT method is extremely helpful to prepare polyimide nanoparticles (<100 nm). As another important aspect, explored stabilization mechanism of the resultant nanoparticle dispersions was supported by the comparative experiments, implying that selective solvation of nanoparticles and EPD/EPA complexes may play key roles in stabilization.
Interpolated potential energy surfaces and dynamics for atom exchange between H and H3+, and D and H3+
Authors: Moyano Gloria E. , Pearson David , Collins Michael A.
Published: December 2004

Two ab initio interpolated potential energy surfaces have been constructed to study the dynamics of atomic hydrogen/deuterium exchange in collisions of H3+ with H (D). One of the surfaces is based on energy calculations using quadratic configuration interaction with single and double excitations. The second includes a perturbative treatment of the triple excitations and an additive correction for basis set deficiency. Results from classical dynamics simulation of the exchange reaction on these surfaces are presented and discussed.
First-principles study of the rotational transitions of H2 physisorbed over benzene
Authors: Hamel Sébastien , Côté Michel
Published: December 2004

In the ongoing search for promising compounds for hydrogen storage, novel porous metal-organic frameworks (MOFs) have been discovered recently [M. Eddadoudi, J. Kim, N. L. Rosi, D. Vodak, J. Wachter, M. O’Keeffe, and O. M. Yaghi, Science 295, 469 (2002); N. L. Rosi, J. Eckert, M. Eddadoudi, D. Vodak, J. Kim, M. O’Keeffe, and O. M. Yaghi, Science 300, 1127 (2003)]. Binding sites in these MOFs were deduced from inelastic neutron scattering (INS) spectroscopy of the rotational transitions of the adsorbed molecular hydrogen. In light of this discovery, it is important to have a fundamental understanding of hydrogen adsorption at different sites in this class of MOF materials. As a first step, here we study the case of H2 adsorbed on benzene as a model of the organic linkers in the microporous crystal. We access the density functional theory results by comparing with correlated ab initio methods, e.g., second-order Møller–Plesset and coupled cluster with noniterative triple excitations. Different approximations for the exchange-correlation potentials were accessed for a set of relevant properties (binding energy, energetically favored configuration, and distance between the adsorbents and adsorbates). In particular, theoretical rotational spectra of the adsorbed H2 were obtained that could be compared to the experimental INS spectra.
Simulation of x-ray absorption near edge spectra of electronically excited ruthenium tris-2,2′-bipyridine
Authors: Campbell Luke , Mukamel Shaul
Published: December 2004

The L3 edge x-ray absorption near edge spectrum (XANES) of the ground electronic state and the metal to ligand charge transfer state of ruthenium tris-2,2′-bipyridine is calculated. The final valence states and energies in the presence of the photoelectron and core hole, and the corresponding transition intensities are computed using time dependent density functional theory with the Becke three-parameter density functional with the Lee-Yang-Parr correlation functional. Calculations show a valence shift of the primary XANES peak and the appearance of the new XANES transition to the hole created by the optical excitation, in agreement with experiment [M. Saes, C. Bressler, R. Abela, D. Grolimund, S. L. Johnson, P. A. Heimann, and M. Chergui, Phys. Rev. Lett. 90, 047403 (2003)].
Blue luminescence of Au nanoclusters embedded in silica matrix
Authors: Dhara S. , Chandra Sharat , Magudapathy P. , Kalavathi S. , Panigrahi B. K. , Nair K. G. M. , Sastry V. S. , Hsu C. W. , Wu C. T. , Chen K. H. , Chen L. C.
Published: December 2004

Photoluminescence study using the 325 nm He–Cd excitation is reported for the Au nanoclusters embedded in SiO2 matrix. Au clusters are grown by ion beam mixing with 100 KeV Ar+ irradiation on Au [40 nm]/SiO2 at various fluences and subsequent annealing at high temperature. The blue bands above ∼3 eV match closely with reported values for colloidal Au nanoclusters and supported Au nanoislands. Radiative recombination of sp electrons above Fermi level to occupied d-band holes are assigned for observed luminescence peaks. Peaks at 3.1 and 3.4 eV are correlated to energy gaps at the X- and L-symmetry points, respectively, with possible involvement of relaxation mechanism. The blueshift of peak positions at 3.4 eV with decreasing cluster size is reported to be due to the compressive strain in small clusters. A first principle calculation based on density functional theory using the full potential linear augmented plane wave plus local orbitals formalism with generalized gradient approximation for the exchange correlation energy is used to estimate the band gaps at the X- and L-symmetry points by calculating the band structures and joint density of states for different strain values in order to explain the blueshift of ∼0.1 eV with decreasing cluster size around L-symmetry point.
An application of coupled reference interaction site model/molecular dynamics to the conformational analysis of the alanine dipeptide
Authors: Freedman Holly , Truong Thanh N.
Published: December 2004

We present an application of our recently proposed coupled reference interaction site model (RISM) molecular dynamics (MD) solvation free energy methodology [Freedman and Truong, Chem. Phys. Lett. 381, 362 (2003); J. Chem. Phys. 121, 2187 (2004)] to study the comformational stability of alanine dipeptide in aqueous solution. In this methodology, radial distribution functions obtained from a single MD simulation are substituted into a RISM expression for solvation free energy. Consequently, iterative solution of the RISM equation is not needed. The relative solvation free energies of seven different conformations of the alanine dipeptide in aqueous solution are calculated. Results from the coupled RISM/MD methodology are in good agreement with those from earlier simulations using the accurate free energy perturbation approach, showing that the αR conformation is most stabilized by solution. This study establishes a framework for applying this coupled RISM/MD method to larger biological systems.
Role of nearest-neighbor drops in the kinetics of homogeneous nucleation in a supersaturated vapor
Authors: Grinin A. P. , Zhuvikina I. A. , Kuni F. M. , Reiss H.
Published: December 2004

A theory of simultaneous nucleation and drop growth in a supersaturated vapor is developed. The theory makes use of the concept of “nearest-neighbor” drops. The effect of vapor heterogeneity caused by vapor diffusion to a growing drop, formed previously, is accounted for by considering the nucleation of the nearest-neighbor drop. The diffusional boundary value problem is solved through the application of a recent theory that maintains material balance between the vapor and the drop, even though the drop boundary is a moving one. This is fundamental to the use of the proper time and space dependent vapor supersaturation in the application of nucleation theory. The conditions are formulated under which the mean distance to the nearest-neighbor drop and the mean time to its appearance can be determined reliably. Under these conditions, the mean time provides an estimate of the duration of the nucleation stage, while the mean distance provides an estimate of the number of drops formed per unit volume during the nucleation stage. It turns out, surprisingly, that these estimates agree fairly well with the predictions of the simpler and more standard approach based on the approximation that the density of the vapor phase remains uniform during the nucleation stage. Thus, as a practical matter, in many situations, the use of the simpler and less rigorous method is justified by the predictions of the more rigorous, but more complicated theory.
Rotational spectrum, potential energy surface, and bound states of the weakly bound complex He–N2O
Authors: Song XiaoGeng , Xu Yunjie , Roy Pierre-Nicholas , Jäger Wolfgang
Published: December 2004

Pure rotational transitions of the weakly bound complex He–N2O and three minor isotopomers (He–14N15NO, He–15N14NO, and He–15N15NO) were measured in the frequency region from 6 to 20 GHz. Predictions for the microwave transition frequencies were based on the infrared work by Tang and McKellar [J. Chem. Phys. 117, 2586 (2002)]. In the case of N14 containing isotopomers, nuclear quadrupole hyperfine structure of the rotational transitions was observed and analyzed. The resulting spectroscopic parameters were used to determine geometrical and dynamical information about the complex. An ab initio potential energy surface was calculated at the coupled cluster level of theory with single and double excitations and perturbative inclusion of triple excitations. This surface was constructed using the augmented correlation consistent polarized valence triple zeta basis set for all atoms with the inclusion of bond functions for the van der Waals bond. Bound state calculations were done to determine the energies of low-lying rovibrational levels that are supported by the potential energy surface. The resulting transition energies agree with the experimental values to 1% or better.
Lowest-energy structures of (C60)nX (X=Li+,Na+,K+,Cl−) and (C60)nYCl (Y=Li,Na,K) clusters for n⩽13
Authors: Hernández-Rojas J. , Bretón J. , Gomez Llorente J. M. , Wales D. J.
Published: December 2004

Basin-hopping global optimization is used to find likely candidates for the lowest minima on the potential energy surface of (C60)nX (X=Li+,Na+,K+,Cl−) and (C60)nYCl (Y=Li,Na,K) clusters with n⩽13. The energy is evaluated using the Girifalco form for the C60 intermolecular potential along with a polarization potential, which depends on the first few nonvanishing C60 multipole polarizabilities. We find that the ions occupy interstitial sites of a (C60)n cluster, the coordination shell being triangular for Li+, tetrahedral for Na+ and K+, and octahedral for Cl−. When the required coordination site does not exist in the corresponding (C60)n global minimum, the lowest minimum of the doped system may be based on an alternative geometry. This situation is particularly common in the Cl− complexes, where the (C60)n global minima with icosahedral packing change into decahedral or closed-packed forms for the ions. In all the ions we find a significant binding energy for the doped cluster. In the alkali chloride complexes the preferred coordination for the diatomic moiety is octahedral and is basically determined by the Cl− ion. However, the smaller polarization energies in this case mean that a change in structure from the (C60)n global minimum does not necessarily occur if there is no octahedral site.
Phases, periphases, and interphases equilibrium by molecular modeling. I. Mass equilibrium by the semianalytical stochastic perturbations method and application to a solution between (120) gypsum faces
Authors: Pedesseau Laurent , Jouanna Paul
Published: December 2004

The SASP (semianalytical stochastic perturbations) method is an original mixed macro-nano-approach dedicated to the mass equilibrium of multispecies phases, periphases, and interphases. This general method, applied here to the reflexive relation Ck⇔μk between the concentrations Ck and the chemical potentials μk of k species within a fluid in equilibrium, leads to the distribution of the particles at the atomic scale. The macroaspects of the method, based on analytical Taylor’s developments of chemical potentials, are intimately mixed with the nanoaspects of molecular mechanics computations on stochastically perturbed states. This numerical approach, directly linked to definitions, is universal by comparison with current approaches, DLVO Derjaguin–Landau–Verwey–Overbeek, grand canonical Monte Carlo, etc., without any restriction on the number of species, concentrations, or boundary conditions. The determination of the relation Ck⇔μk implies in fact two problems: a direct problem Ck⇒μk and an inverse problem μk⇒Ck. Validation of the method is demonstrated in case studies A and B which treat, respectively, a direct problem and an inverse problem within a free saturated gypsum solution. The flexibility of the method is illustrated in case study C dealing with an inverse problem within a solution interphase, confined between two (120) gypsum faces, remaining in connection with a reference solution. This last inverse problem leads to the mass equilibrium of ions and water molecules within a 3 Å thick gypsum interface. The major unexpected observation is the repulsion of SO42− ions towards the reference solution and the attraction of Ca2+ ions from the reference solution, the concentration being 50 times higher within the interphase as compared to the free solution. The SASP method is today the unique approach able to tackle the simulation of the number and distribution of ions plus water molecules in such extreme confined conditions. This result is of prime importance for all coupled chemical-mechanical problems dealing with interfaces, and more generally for a wide variety of applications such as phase changes, osmotic equilibrium, surface energy, etc., in complex chemical-physics situations.
Convergence of triples energy in CCSD(T) and CC3 calculations with correlation-consistent basis sets
Authors: Laschuk Eduardo Fischli , Livotto Paolo Roberto
Published: December 2004

The convergence behavior of connected triples correlation energy in CCSD(T) and CC3 calculations with (aug-)cc-pVXZ basis sets has been accurately described in terms of a power law of the type EX=E∞+AX−4. Calculations ranging from double-Z through septuple-Z attest the validity of this X−4 convergence model. Extrapolations generated from (X−1,X)-Z calculations yield energies of nearly (X+1)-Z quality. Typically, the fraction of triples correlation energy recovered is 0.92±0.05 in (D,T) extrapolations; 0.98±0.01 in (T,Q) extrapolations; 1.0002±0.0012 in (Q,5) extrapolations; and 0.9995±0.0005 in (5,6) extrapolations.
Vibronic spectroscopy of unsaturated transition metal complexes: CrC2H, CrCH3, and NiCH3
Authors: Brugh Dale J. , DaBell Ryan S. , Morse Michael D.
Published: December 2004

Vibronically resolved resonant two-photon ionization and dispersed fluorescence spectra of the organometallic radicals CrC2H, CrCH3, and NiCH3 are reported in the visible and near-infrared wavelength regions. For CrC2H, a complicated vibronic spectrum is found in the 11 100–13 300 cm−1 region, with a prominent vibrational progression having ωe′=426.52±0.84 cm−1, ωe′xe′=0.74±0.13 cm−1. Dispersed fluorescence reveals a v″=1 level of the ground state with ΔG1/2″=470±20 cm−1. These vibrational frequencies undoubtedly pertain to the Cr–C2H stretching mode. It is suggested that the spectrum corresponds to the Ã 6Σ+←X̃ 6Σ+ band system, with the CrC2H molecule being linear in both the ground and the excited state. The related CrCH3 molecule displays a vibronic spectrum in the 11 500–14 000 cm−1 region. The upper state of this system displays six sub-bands that are too closely spaced to be vibrational structure, but too widely separated to be K structure. It is suggested that the observed spectrum is a E6←X̃ A16 band system, analogous to the well-known B 6Π←X 6Σ+ band systems of CrF and CrCl. The ground state Cr–CH3 vibration is characterized by ωe″=525±17 cm−1 and ωe″xe″=7.9±6 cm−1. The spectrum of NiCH3 lies in the 16 100–17 400 cm−1 range and has ωe′=455.3±0.1 cm−1 and ωe′xe′=6.60±0.03 cm−1. Dispersed fluorescence studies provide ground state vibrational constants of ωe″=565.8±1.6 cm−1 and ωe″xe″=1.7±3.0 cm−1. Again, these values correspond to the Ni–CH3 stretching motion.
The optimized Rouse–Zimm theory of excluded volume effects on chain dynamics
Authors: Kim Ji-Hyun , Lee Sangyoub
Published: December 2004

Based on the optimized Rouse–Zimm (ORZ) approximation to the Kirkwood diffusion equation, we investigate the effects of excluded volume interactions on the single chain dynamics. By incorporating the nonuniformly expanded moments of interbead distances into the expressions for the diffusion and structure matrices appearing in the ORZ diffusion equation, we obtain the general relaxation spectrum for flexible chains that is valid over the range from θ solvents to good solvents. The present theory involves four parameters: the Kuhn statistical length b0, the bead number N, the excluded volume parameter z, and the hydrodynamic interaction parameter h*. These model parameters are determined from structural data of polymers with the aid of the quasi-two-parameter theory. The set of relaxation times of ORZ normal modes calculated with these bead-and-spring model parameters enables the theoretical prediction of various frictional and dynamical properties of polymers within a unified framework. The present ORZ theory generalizes the Ptitsyn–Eizner-type approaches by incorporating the nonuniform chain expansion effect into the structure matrix as well as the diffusion matrix.
The permanent electric dipole moments of WN and ReN and nuclear quadrupole interaction in ReN
Authors: Steimle Timothy C. , Virgo Wilton L.
Published: December 2004

The high-resolution laser induced fluorescence spectra of tungsten mononitride WN and rhenium mononitride ReN have been recorded in a laser ablation/molecular beam spectrometer. The field free spectrum of the (0,0)A 4Π3/2-X 4Σ1/2− band system of WN186 has been analyzed to produce B″, B′, and γ″ values of 0.4659(2), 0.4554(2), and 0.0518(1) cm−1, respectively. The permanent electric dipole moments μ for the X 4Σ1/2− and A 4Π3/2 state were determined to be 3.77(18) and 2.45(3) D, respectively, from the analysis of the optical Stark effect. The (0,0)[26.0]0+-X0+ band system of ReN was recorded in the presence of a variable static electric field. The ground and excited state electric dipole moments of ReN187 were determined to be μ(X0+)=1.96(8) D and μ([26.0]0+)=3.53(4) D. Splittings in the field free ReN187 spectrum were analyzed to produce Re187 (I=5/2) nuclear electric quadrupole coupling constants e2Qq0 of −0.0304(8) and 0.0328(9) cm−1 for the X0+ and [26.0]0+ states, respectively. A molecular orbital correlation model is used to interpret the observation and a comparison is made to CrN and MoN.
Isomers of OCS2: IR absorption spectra of OSCS and O(CS2) in solid Ar
Authors: Lo Wen-Jui , Chen Hui-Fen , Chou Po-Han , Lee Yuan-Pern
Published: December 2004

Irradiation of an Ar matrix sample containing O3 and CS2 with a KrF excimer laser at 248 nm yielded new lines at 1402.1 (1404.7), 1056.2 (1052.7), and 622.3 (620.5) cm−1; numbers in parentheses correspond to species in a minor matrix site. Secondary photolysis at 308 nm diminished these lines and produced mainly OCS and SO2. Annealing of this matrix to 30 K yielded a second set of new lines at 1824.7 and 617.8 cm−1. The first set of lines are assigned to C=S stretching, O–S stretching, and S–C stretching modes of carbon disulfide S-oxide, OSCS; and the second set of lines are assigned to C=O stretching and OCS bending modes of dithiiranone, O(CS2), respectively, based on results of S34- and O18-isotopic experiments and quantum-chemical calculations. These calculations using density-functional theory (B3LYP/aug-cc-pVTZ) predict four stable isomers of OCS2: O(CS2), SSCO, OSCS, and SOCS, listed in order of increasing energy. According to calculations, O(CS2) has a cyclic CS2 moiety and is the most stable isomer of OCS2. OSCS is planar, with bond angles ∠OSC≅111.9° and ∠SCS≅177.3°; it is less stable than SSCO and O(CS2) by ∼102 and 154 kJ mol−1, respectively, and more stable than SOCS by ∼26 kJ mol−1. Calculated vibrational wave numbers, IR intensities, S34- and O18-isotopic shifts for OSCS and O(CS2) fit satisfactorily with experimental results.
Infrared spectrum of the I−–D2 anion complex
Authors: Wild D. A. , Bieske E. J.
Published: December 2004

The infrared spectrum of the I−–D2 anion complex is measured in the D2 stretch region by monitoring production of I− photofragments. The rotationally resolved spectrum consists of two overlapping Σ-Σ subbands, redshifted by ≈58 cm−1 from the free D2 fundamental vibrational band. These subbands are associated with absorptions by I−–D2 complexes containing ortho and para forms of D2. The measured rotational constants are consistent with a 3.79 Å separation between I− and the D2 center of mass, contracting by 0.08 Å when the D2 subunit is vibrationally excited. Spectroscopic data are used to generate effective radial potential energy curves describing the interaction of ortho and para D2 with I− from which the dissociation energies of I−–D2(ortho) and I−–D2(para) are estimated as D0=236 and 297 cm−1, respectively.
Quasi-elastic neutron scattering study of dimethyl-sulfoxide–water mixtures: Probing molecular mobility in a nonideal solution
Authors: Bordallo H. N. , Herwig K. W. , Luther B. M. , Levinger N. E.
Published: December 2004

The translational and rotational motions of water and dimethyl sulfoxide, [DMSO, (CH3)2SO] have been investigated using quasi-elastic neutron scattering. Water–DMSO mixtures at five DMSO mole fractions, χDMSO, ranging from 0 to 0.75, were measured. Hydrogen–deuterium substitution was used to extract independently the water proton dynamics (d-DMSO–H2O), the DMSO methyl proton dynamics (h-DMSO–D2O) and to obtain background corrections (d-DMSO–D2O). The translational diffusion of water slows down significantly compared to bulk water at all χDMSO>0. The rotational time constant for water exhibits a maximum at χDMSO=0.33 that corresponds to the observed maximum of the viscosity of the mixture. Data for DMSO can be analyzed in terms of a relatively slow tumbling of the molecule about its center-of-mass in conjunction with random translational diffusion. The rotational time constant for this motion exhibits some dependence on χDMSO, while the translational diffusion constant shows no clear variation for χDMSO>0. The results presented reinforce the idea that due to the stronger associative nature of DMSO, DMSO–water aggregates are formed over the whole composition range, disturbing the tetrahedral natural arrangement of the water molecules. As a consequence adding DMSO to water causes a drastic slowing down of the dynamics of the water molecule, and vice versa.
Exchange-correlation potentials for high-electron-density ions in the Be isoelectronic series
Authors: Morrison Robert C. , Bartolotti Libero J.
Published: December 2004

Accurate reference wave functions and their densities have been used to obtain accurate exchange-correlation potentials for the beryllium isoelectronic sequence Be, Ne+6, Ar+14, and Kr+32. The exchange-correlation potentials for the four-electron cations with high Z in this sequence exhibit structure prior to the intershell peak that is not present in neutral atoms. The kinetic energy contribution to the exchange-correlation potential contributes to the early structure as well as to the intershell peak. The near degeneracy in this four-electron sequence plays a significant role in the structure prior to the intershell peak. Several of the quantities on which the Perdew–Burke–Ernzerhoff and Tao–Perdew–Staroverov–Scuseria functionals are dependent are examined. The generalized gradient approximations appear not to account for the near degeneracy in this series.
Coupled ion and network dynamics in polymer electrolytes: Monte Carlo study of a lattice model
Authors: Dürr O. , Dieterich W. , Nitzan A.
Published: December 2004

Monte Carlo simulations are used to study ion and polymer chain dynamic properties in a simplified lattice model with only one species of mobile ions. The ions interact attractively with specific beads in the host chains, while polymer beads repel each other. Cross linking of chains by the ions reduces chain mobilities which in turn suppresses ionic diffusion. Diffusion constants for ions and chains as a function of temperature follow the Vogel–Tammann–Fulcher (VTF) law with a common VTF temperature at low ion concentration, but both decouple at higher concentrations, in agreement with experimental observations. Our model allows us to introduce pressure as an independent variable through calculations of the equation of state using the quasichemical approximation, and to detect an exponential pressure dependence of the ionic diffusion.
Memory effect in the chain-collapse process in a dilute polymer solution
Authors: Maki Yasuyuki , Sasaki Naoki , Nakata Mitsuo
Published: December 2004

The effect of temperature perturbation on a single-chain-collapse process was studied for poly(methyl methacrylate) with the molecular weight Mw=1.05×107 in the mixed solvent of tert-butyl alcohol+water (2.5 vol %). In the chain-collapse process after a quench from the θ temperature to a temperature T1, the temperature was changed from T1 to T2 at the time t1 after the quench and returned to T1 at the time t1+t2. In the three stages at T1, T2, and T1, measurements of the mean-square radius of gyration of polymer chains were carried out by static light scattering and the chain-collapse process was represented by the expansion factor as a function of time. An effect of chain aggregation on the measurements was negligibly small because of the very slow phase separation. For the negative temperature perturbation (T1>T2), the chain-collapse processes observed in the first and third stages were connected smoothly and agreed with the collapse process due to a single-stage quench to T1. A memory of the chain collapse in the first stage at T1 was found to persist into the third stage at the same temperature T1 without being affected by the temperature perturbation of T2 during t2. The memory effect was observed irrespective of the time period of t2. The positive temperature perturbation (T1<T2) showed an acceleration of the chain-collapse process.
Infrared spectrum and predissociation dynamics of H2O+–Ar
Authors: Dopfer O. , Engel V.
Published: December 2004

The infrared (IR) spectrum and vibrational predissociation of the proton-bound H2O+–Ar ionic complex are investigated within an ab initio and quantum dynamical study. For this purpose, a two-dimensional potential energy surface (2D PES) is determined as a function of the HO–H and OH–Ar coordinates. This PES is then employed in a wave-packet calculation to determine spectral properties of the system and to calculate the IR absorption spectrum. The vibrational energy levels and relative IR intensities agree well with the experimental spectrum reported earlier. On the other hand, the predissociation lifetimes in the nanosecond regime derived from the 2D PES are in disagreement with the experimental observations, indicating the importance of the neglected degrees of freedom for a correct description of the dynamics of the complex.
Narrow plasmonic/photonic extinction and scattering line shapes for one and two dimensional silver nanoparticle arrays
Authors: Zou Shengli , Schatz George C.
Published: December 2004

The interaction of light with silver nanoparticle arrays can in some cases produce mixed plasmonic/photonic bands that have extremely narrow (<1 meV) line shapes in extinction and scattering. In this paper we extend computational electrodynamics results of a recent communication [S. Zou, N. Janel, and G. C. Schatz, J. Chem. Phys. 120, 10871 (2004)] where this effect was first described to study how these narrow bands are influenced by a number of structural factors, and to determine how useful these arrays might be for sensing applications. Included are studies of the effect of disorder in the array structure on plasmon intensity and width, of the effect of orientation of the array relative to the polarization and propagation direction of the incident light, and of the effect of particle shape (comparing results for silver spheres and cylindrical disks). Our results show that the narrow lines are remarkably robust to array disorder, but vacancy defects can easily destroy the effect. The narrowest lines are associated with one dimensional arrays in which both polarization and wave vectors are perpendicular to the array axis. For two dimensional arrays, the narrowest lines are associated with the wave vector perpendicular to the plane of the array and polarization in the plane. Arrays composed of oblate cylinders generate more intense and more redshifted plasmon/photonic peaks than do prolate or spherical particles under comparable conditions. Finally, for sensing applications in which analyte binding is determined by the plasmon wavelength shift associated with change in the surface refractive index, we show that the arrays have greater sensitivity than isolated nanoparticles.
Pure surface plasmon resonance enhancement of the first hyperpolarizability of gold core–silver shell nanoparticles
Authors: Abid Jean-Pierre , Nappa Jérôme , Girault Hubert H. , Brevet Pierre-François
Published: December 2004

We report the optical second harmonic (SH) response from gold core–silver shell nanoparticles supported at a liquid–liquid interface in the spectral region where the second harmonic generation (SHG) frequency is resonant with the surface plasmon (SP) resonance excitation of the nanoparticles. We compare these results with that obtained by classical linear optical absorption spectroscopy and show that the nonlinear optical response is dominated by the SP resonance enhancement with negligible contributions from the interband transitions. As a result, the SH spectrum exhibits two clear SP resonance bands attributed to the two SP resonances of the composite nanostructure formed by the gold core–silver shell nanoparticles. Absolute values of the hyperpolarizabilities are measured by hyper Rayleigh scattering (HRS) and compared that of pure gold nanoparticles. The hyperpolarizability measured at a harmonic energy of 3.0 eV, enhanced through excitation of the high energy SP resonance of the nanoparticle, increases with the silver content whereas the hyperpolarizability measured at a harmonic energy of 2.4 eV, enhanced through the excitation of the low energy SP resonance of the nanoparticle, decreases because of the shift of this resonance away from the harmonic frequency. The hyperpolarizability determined by HRS and the square root of the SHG intensities, scaling with the nanoparticle hyperpolarizability, have similar trends with respect to the silver content indicative of closely related adsorption properties yielding similar surface concentrations at the liquid–liquid interface.
Stepwise frequency tuning of a gyrotron backward-wave oscillator
Authors: Chang T. H. , Chen S. H.
Published: December 2004

The gyrotron backward-wave oscillator (gyro-BWO) features broadband tunability, but ragged tuning curves are frequently observed experimentally. Accordingly, a Ka-band gyro-BWO experiment with external circuit mismatch was conducted to examine its tuning properties at two reflected strengths: one is slightly mismatched (15dB reflection) and the other can be categorized as matched (30dB reflection). Stepwise frequency tunings by varying the magnetic field, the beam voltage, and the beam current were observed under mismatched conditions. A self-locking model was introduced using the concept of injection-locking, where the output and reinjected signals tend to form a stable phase relation, favoring certain discrete oscillation frequencies. The observed frequencies agree closely with the calculated frequencies. Smooth tuning curves were also obtained, revealing a remedy for the stepwise tuning of a gyro-BWO.
Experimental observation of Lorenz chaos in the Quincke rotor dynamics
Authors: Peters François , Lobry Laurent , Lemaire Elisabeth
Published: December 2004

In this paper, we report experimental evidence of Lorenz chaos for the Quincke rotor dynamics. We study the angular motion of an insulating cylinder immersed in slightly conducting oil and submitted to a direct current electric field. The simple equations which describe the dynamics of the rotor are shown to be equivalent to the Lorenz equations. In particular, we observe two bifurcations in our experimental system. Above a critical value of the electric field, the cylinder rotates at a constant rate. At a second bifurcation, the system becomes chaotic. The characteristic shape of the experimental first return map provides strong evidence for Lorenz-type chaos.
Power law behavior in chemical reactions
Authors: Claycomb J. R. , Nawarathna D. , Vajrala V. , Miller J. H.
Published: December 2004

Reactions between metals and chloride solutions have been shown to exhibit magnetic field fluctuations over a wide range of size and time scales. Power law behavior observed in these reactions is consistent with models said to exhibit self-organized criticality. Voltage fluctuations observed during the dissolution of magnesium and aluminum in copper chloride solution are qualitatively similar to the recorded magnetic signals. In this paper, distributions of voltage and magnetic peak sizes, noise spectra, and return times are compared for both reactions studied.
Temporal evolution of a localized weak vortex in viscous circular shear flows
Authors: Shukhman I. G. , Levinski V.
Published: December 2004

The evolution of a weak, highly localized, initial vortex in a steady circular flow is addressed. The effect of basic flow curvature, characterized by the ratio between the Coriolis and inertial forces, on the evolution of the initial vortex is studied. It is shown that the vortex remains weak throughout its entire evolution, although in a certain range of orientation angles of the initial vortex plane there occurs a transient algebraic growth of intensity of the vortex characterized by the value of its total enstrophy. Special attention is devoted to comparison of the results obtained with the experimental results reported by Malkiel, Levinski, and Cohen (1999) where the evolution of artificially synthesized localized vortices in a laminar Taylor–Couette flow was investigated. In particular, it was found that the orientation of the plane of vortex localization predicted by the theoretical model differs from the one observed in the experiment. However, the agreement between the theoretical model and experimental results is expected to be sufficiently better for strong initial vortices. The results of direct numerical simulation of the vortex evolution in a plane flow with constant velocity shear, reported recently by Suponitsky et al. (2003, 2004) show promise of achieving this objective. The analytical expression, obtained in this paper for a weak vortex, may serve as a good test for such a numerical simulation of the evolution of strong vortices in a circular flow.
Quasielectrostatic instabilities excited by energetic oxygen ions in the ring current region
Authors: Singh S. V. , Kakad A. P. , Lakhina G. S.
Published: December 2004

Quasielectrostatic instabilities driven by anisotropic oxygen ions are investigated during storms/substorms in three-component ring current plasma consisting of electrons, protons, and energetic oxygen ions having loss-cone distribution. The response of the electrons is fully electromagnetic and that of the protons and oxygen ions is electrostatic. The electrons, protons, and oxygen ions are treated as magnetized. Obliquely propagating modes with frequencies near the harmonics of the oxygen ion cyclotron frequency are found to become unstable due to pressure anisotropy of the energetic oxygen ions. The results are applied to storm-time ring-current region parameters. The loss of energetic particles resulting from wave-particle interaction may provide an alternate mechanism, complimentary to and independent of the charge exchange process for the ring-current decay.
Electron field emission from various morphologies of fluorinated amorphous carbon nanostructures
Authors: Lai S. H. , Chang K. L. , Shih H. C. , Huang K. P. , Lin P.
Published: December 2004

Unlike general fluorination, amorphous fluorinated carbon (a-C:F) nanostructures have been synthesized directly and efficiently by an electron cyclotron resonance chemical vapor deposition (ECR–CVD) system using a mixture of C2H2, CF4, and Ar as precursors. The electron field-emission properties of the a-C:F nanostructures were investigated. The a-C:F nanoporous films with a low turnon field (1.8V∕μm) are apparently lower than other types of a-C:F nanostructures. The a-C:F nanostructures have a greater field-enhancement factor (2500–4000) than other nonaligned multiwall nanotubes. However, the a-C:F nanostructures follow the Fowler–Nordheim characteristics only in the medium emission current region and they deviate from the characteristics in the low and high emission current regions.
Extensions of adiabatic invariant theory for a charged particle
Authors: Weitzner Harold , Chang Choong-Seock
Published: December 2004

The standard theory of Hamiltonian dynamics of a charged particle is extended to allow electric and magnetic fields to vary across magnetic field lines or surfaces on the Larmor radius distance scale. After the development of the general theory, the special cases of toroidally nested magnetic surfaces and of axisymmetry are considered. In a further restriction the situation with spatially slowly varying static magnetic fields but spatially rapidly varying static bounded electrostatic potentials is treated. The dynamics of the perpendicular velocity is represented by a nonlinear oscillator. The adiabatic invariant and drift Hamiltonian are constructed near an O point in the perpendicular velocity phase plane. Motion near a separatrix and X point in physical space is also briefly explored.