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X-ray absorption spectroscopy (XAS) and small angle x-ray scattering (SAXS) were utilized to study the effect of fluoride (F-) anion in aqueous solutions. XAS spectra show that F- increases the number of strong H-bonds, likely between F- and water in the first hydration shell. SAXS data show a low-Q scattering intensity increase similar to the effect of a temperature decrease, suggesting an enhanced anomalous scattering behavior in F- solutions. Quantitative analysis revealed that fluoride solutions have larger correlation lengths than chloride solutions with the same cations but shorter compared to pure water. This is interpreted as an increased fraction of tetrahedral low-density structures in the solutions due to the presence of the F- ions, which act as nucleation centers replacing water in the H-bonding network and forming stronger H-bonds, but the presence of the cations restricts the extension of strong H-bonds. [ABSTRACT FROM AUTHOR]

We present a general theoretical approach that combines the iterative technique with the nonlinear transfer matrix method to solve the general problems of three-wave mixing with pump depletion in nonlinear multilayer structures. The theoretical model is directly derived from nonlinear coupled wave equations, shows fast numerical convergence and maintains conservation of total energy perfectly for general structures. We have employed this approach to discuss second harmonic generation in photonic bandgap crystals with slow light effect and obtained a conversion efficiency of about 25% for both the forward and backward second harmonic waves. The detailed wave evolution process and energy conversion mechanism of sum frequency generation and difference frequency generation in perfect and imperfectly quasiphase-matching structures have been systematically investigated and their subtle and strong dependence on the initial conditions of incident waves has been revealed. The developed theoretical approach can be very useful for efficient and quantitative analysis of various nonlinear optical problems and help to design optimum nonlinear multilayer structures for specific high-efficiency nonlinear three-wave mixing processes. [ABSTRACT FROM AUTHOR]

We use conducting atomic force microscopy (AFM) in ultra high vacuum to measure the thermoelectric power of Au, Pt, and 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) films. Tips coated with thick (1200 nm) Pt films or highly doped diamond film give reproducible data. The thermoelectric power of metal junctions formed with diamond tips is high but dominated by the diamond material thus making diamond tips of limited applicability in thermovoltage AFM. Pt coated tips on Au or Pt films gives small thermovoltage signal, making quantitative analysis of the thermopower on metal sample problematic. The thermovoltage AFM technique appears best suited to study organic thin films and the thermoelectric power of 1.5 nm and 2 nm thick PTCDA deposited on Au measured with Pt tips is -342 and -372 μV/K, respectively. The negative sign indicates that the lowest unoccupied molecular orbital level dominates electrical transport. [ABSTRACT FROM AUTHOR]

Near edge x-ray absorption fine structure (NEXAFS) spectroscopy has evolved into a powerful characterization tool for polymeric materials and is increasingly being used to elucidate composition and orientation in thin films of relevance to organic electronic devices. For accurate quantitative compositional analysis, insight into the electronic structure and the ability to assess molecular orientation, reliable reference spectra with known energy resolution and calibrated energy scale are required. We report a set of such NEXAFS spectra from 23 semiconducting polymers and some related materials that are frequently used in organic device research. [ABSTRACT FROM AUTHOR]

Doi and Edwards (DE) proposed that the relaxation of entangled linear polymers under large deformation occurs in two steps: the fast chain contraction (via the longitudinal Rouse mode of the chain backbone) and the slow orientational relaxation (due to reptation). The DE model assumes these relaxation processes to be independent and decoupled. However, this decoupling is invalid for a generalized convective constraint release (CCR) mechanism that releases the entanglement on every occasion of the contraction of surrounding chains. Indeed, the decoupling does not occur in the sliplink models where the entanglement is represented by the binary interaction (hooking) of chains. Thus, we conducted primitive chain network simulations based on a multichain sliplink model to investigate the chain contraction under step shear. The simulation quantitatively reproduced experimental features of the nonlinear relaxation modulus G(t,γ). Namely, G(t,γ) was cast in the time-strain separable form, G(t,γ)=h(γ)G(t) with h(γ)=damping function and G(t)=linear modulus, but this rigorous separability was valid only at times t comparable to the terminal relaxation time, although a deviation from this form was rather small (within ±10%) at t>τR (longest Rouse relaxation time). A molecular origin of this delicate failure of time-strain separability at t∼τR was examined for the chain contour length, subchain length, and subchain stretch. These quantities were found to relax in three steps, the fast, intermediate, and terminal steps, governed by the local force balance between the subchains, the longitudinal Rouse relaxation, and the reptation, respectively. The contributions of the terminal reptative mode to the chain length relaxation as well as the subchain length/stretch relaxation, not considered in the original DE model, emerged because the sliplinks (entanglement) were removed via the generalized CCR mechanism explained above and the reformation of the sliplinks was slow at around the chain center compared to the more rapidly fluctuating chain end. The number of monomers in the subchain were kept larger at the chain center than at the chain end because of the slow entanglement reformation at the center, thereby reducing the tension of the stretched subchain at the chain center compared to the DE prediction. This reduction of the tension at the chain center prevented completion of the length equilibration of subchains at t∼τR (which contradicts to the DE prediction), and it forces the equilibration to complete through the reptative mode at t>τR. The delicate failure of time-strain separability seen for G(t,γ) at t∼τR reflects this retarded length equilibration. [ABSTRACT FROM AUTHOR]

We have calculated the absorption spectrum of dichlorine peroxide (ClOOCl) in the spectral range 250-400 nm. We have employed five different approaches to quantitatively model the absorption cross section (empirical broadening scheme, linearized harmonic reflection principle and full reflection principle with ground state density calculated using harmonic approximation, classical molecular dynamics, and path-integral molecular dynamics). We have also tested various single and multireference methods. We found that (i) the excitation characteristics of ClOOCl are sensitive on molecular geometries and therefore the ground state density has to be properly sampled and that (ii) single-reference methods tend to overestimate the absorption cross section and lead to a blueshift in the absorption maximum. The absorption spectrum calculated at the CASPT2 level with complete active space-configuration interaction (CAS-SCF) transition dipole moment with the ground state sampled via path-integral molecular dynamics is in a good agreement with the experiment. We, however, did not reach full agreement in the atmospherically relevant low-energy tail of the spectrum. The general message is that quantitative predictions are difficult even for a relatively small molecule as ClOOCl and the convergence, with respect to the electronic structure method, basis set used, and ground state sampling, needs to be carefully examined. [ABSTRACT FROM AUTHOR]

The coupled-cluster singles and doubles method augmented with single Slater-type correlation factors (CCSD-F12) determined by the cusp conditions (also denoted as SP ansatz) yields results close to the basis set limit with only small overhead compared to conventional CCSD. Quantitative calculations on many-electron systems, however, require to include the effect of connected triple excitations at least. In this contribution, the recently proposed [A. Köhn, J. Chem. Phys. 130, 131101 (2009)] extended SP ansatz and its application to the noniterative triples correction CCSD(T) is reviewed. The approach allows to include explicit correlation into connected triple excitations without introducing additional unknown parameters. The explicit expressions are presented and analyzed, and possible simplifications to arrive at a computationally efficient scheme are suggested. Numerical tests based on an implementation obtained by an automated approach are presented. Using a partial wave expansion for the neon atom, we can show that the proposed ansatz indeed leads to the expected (Lmax+1)-7 convergence of the noniterative triples correction, where Lmax is the maximum angular momentum in the orbital expansion. Further results are reported for a test set of 29 molecules, employing Peterson's F12-optimized basis sets. We find that the customary approach of using the conventional noniterative triples correction on top of a CCSD-F12 calculation leads to significant basis set errors. This, however, is not always directly visible for total CCSD(T) energies due to fortuitous error compensation. The new approach offers a thoroughly explicitly correlated CCSD(T)-F12 method with improved basis set convergence of the triples contributions to both total and relative energies. [ABSTRACT FROM AUTHOR]

A theoretical description is provided for the nonequilibrium conformational and dynamical properties of a polymer in shear flow. Using a mean-field semiflexible chain model, which accounts for hydrodynamic interactions within the preaveraging approximation, analytical expressions are derived for the dependence of the deformation, orientation, and relaxation times on polymer persistence length and shear rate. Moreover, the rheological properties of a dilute polymer solution are discussed. The model yields shear thinning at large Weissenberg numbers. The analytical results are compared with fluorescence microscopy measurements of individual DNA molecules, which yield qualitative and partial quantitative agreement. [ABSTRACT FROM AUTHOR]

The energy loss functions (ELFs) and optical constants of Si and SiO2 were obtained from quantitative analysis of reflection electron energy loss spectroscopy (REELS) by a new approach. In order to obtain the ELF, which is directly related to the optical constants, we measured series of angular and energy dependent REELS spectra for Si and SiO2. The λ(E)K(ΔE) spectra, which are the product of the inelastic mean free path (IMFP) and the differential inverse IMFP, were obtained from the measured REELS spectra. We used the factor analysis (FA) method to analyze series of λ(E)K(ΔE) spectra for various emission angles at fixed primary beam energy to separate the surface-loss and bulk-loss components. The extracted bulk-loss components enable to obtain the ELFs of Si and SiO2, which are checked by oscillator strength-sum and perfect-screening-sum rules. The real part of the reciprocal of the complex dielectric function was determined by Kramers–Kronig analysis of the ELFs. Subsequently, the optical constants of Si and SiO2 were calculated. The resulting optical constants in terms of the refractive index and the extinction coefficient for Si and SiO2 are in good agreement with Palik’s reference data. The results demonstrate the general applicability of FA as an efficient method to obtain the bulk ELF and to determine the optical properties from REELS measurements. [ABSTRACT FROM AUTHOR]

High-level ab initio benchmark calculations of the 15N and 31P NMR chemical shielding constants for a representative set of molecules are presented. The computations have been carried out at the Hartree–Fock self-consistent field (HF-SCF), density functional theory (DFT) (B-P86 and B3-LYP), second-order Mo\ller–Plesset perturbation theory (MP2), coupled cluster singles and doubles (CCSD), and CCSD augmented by a perturbative treatment of triple excitations [CCSD(T)] level of theory using basis sets of triple zeta quality or better. The influence of the geometry, the treatment of electron correlation, as well as basis set and zero-point vibrational effects on the shielding constants are discussed and the results are compared to gas-phase experimental shifts. As for the first time a study using high-level post-HF methods is carried out for a second-row element, we also propose a family of basis sets suitable for the computation of 31P shielding constants. The mean deviations observed for 15N and 31P are 0.9 [CCSD(T)/13s9p4d3f] and -3.3 ppm [CCSD(T)/15s12p4d3f2g], respectively, when corrected for zero-point vibrational effects. Results obtained at the DFT level of theory are of comparable accuracy to MP2 for 15N and of comparable accuracy to HF-SCF for 31P. However, they are not improved by inclusion of zero-point vibrational effects. The PN molecule is an especially interesting case with exceptionally large electron correlation effects on shielding constants beyond MP2 which, therefore, represents an excellent example for further benchmark studies. [ABSTRACT FROM AUTHOR]

An experimental study has been carried out for the development of quantitative deuterium analysis using the neodymium doped yttrium aluminum garnet laser-induced breakdown spectroscopy (LIBS) with atmospheric pressure surrounding He gas by exploring the appropriate experimental condition and special sample cleaning technique. The result demonstrates the achievement of a full resolution between the D and H emission lines from zircaloy-4 samples, which is prerequisite for the desired quantitative analysis. Further, a linear calibration line with zero intercept was obtained for the emission intensity of deuterium from a number of zircaloy samples doped with predetermined concentrations of deuterium. The result is obtained by setting a +4 mm defocusing position for the laser beam, 6 μs detection gating time, and 7 mm imaging position of the plasma for the detection, which is combined with a special procedure of repeated laser cleaning of the samples. This study has thus provided the basis for the development of practical quantitative deuterium analysis by LIBS. [ABSTRACT FROM AUTHOR]

A detailed analysis of the infrared lineshapes corresponding to the intramolecular bond vibrations of HOD in either H2O or D2O is presented here in order to quantitatively assess the accuracy of centroid molecular dynamics in reproducing the correct features of the infrared spectrum of water at ambient conditions. Through a direct comparison with the results obtained from mixed quantum-classical calculations, it is shown that centroid molecular dynamics provides accurate vibrational shifts and lineshapes when the intramolecular bond stretching vibrations are described by a physically reasonable anharmonic potential. Artificially large redshifts due to a so-called “curvature problem” are instead obtained with an unphysical shifted harmonic potential because the latter allows substantial probability density at zero bond lengths. [ABSTRACT FROM AUTHOR]

Real-time in situ spectroscopic ellipsometry and in situ, angle-resolved x-ray photoelectron spectroscopy (AR-XPS) have been applied to establish the relationships between the growth kinetics and the developing microstructure of ultrathin (<3 nm) oxide films grown on clean Al–1.12 at. % Mg alloy surfaces by thermal oxidation in the temperature range T=300–485 K. To this end, procedures for the depth-resolved quantitative AR-XPS analysis of ultrathin, multiple-element, and/or multiphase oxide overgrowths on binary alloy surfaces were developed. As a result, the relationships between the relative depth distributions of Al and Mg in the developing oxide films, the oxide-film growth kinetics, and the oxidation-induced compositional changes in the AlMg alloy substrate could be established as a function of the oxidation conditions. [ABSTRACT FROM AUTHOR]

We report on structural, electrical, and optical characterizations of midwave infrared InAs/GaSb superlattice (SL) p-i-n photodiodes. High-quality SL samples, with 1 μm thick active region (220 SL periods), exhibited a cut-off wavelength of 4.9 μm at 80 K. Using a capacitance-voltage measurement technique performed on mesa diode, the residual background concentration in the nonintentionally doped region was determined to be 3×1015 cm-3 at 80 K. Extracted from current-voltage characteristics, R0A products above 4×105 Ω cm2 at 80 K were measured, and the quantitative analysis of the J-V curves showed that the dark current density of SL photodiode is dominated by generation-recombination processes. Front-side illuminated photodiodes produced responsivity at 80 K equal to 360 mA/W at 4.5 μm. [ABSTRACT FROM AUTHOR]

Electrochemical proton-coupled electron transfer rate constant expressions that interpolate between the golden rule and solvent-controlled limits are derived. These expressions include the effects of solvent dynamics and thus are applicable for a wide range of vibronic couplings and solvent relaxation times. The golden rule limit is defined in terms of weak vibronic coupling and fast solvent relaxation, and the solvent-controlled limit is defined in terms of strong vibronic coupling and slow solvent relaxation. In the golden rule limit, the rate constant is proportional to the square of the vibronic coupling and is independent of the solvent relaxation time. In the solvent-controlled limit, the rate constant is independent of the vibronic coupling and increases as the solvent relaxation time decreases. The interconversion between the solvent-controlled and golden rule limits can be induced by altering the proton donor-acceptor mode frequency and the overlap between the reactant and product proton vibrational wave functions, as well as the electronic coupling, the solvent relaxation time, and the overpotential. The kinetic isotope effect behaves differently in the solvent-controlled and golden rule limits and thus provides a unique probe for characterizing electrochemical proton-coupled electron transfer processes. The analogous rate constant expressions for electrochemical electron transfer and homogeneous proton-coupled electron transfer are also presented. The impact of electrode overpotential, solvent relaxation time, and proton donor-acceptor mode frequency on the rate constants are analyzed for model systems. [ABSTRACT FROM AUTHOR]

We report on a quantitative analysis of the effect of visible light laser irradiation (VLLI) on hexagonal (α) silicon carbide implanted with nitrogen and aluminum. In both cases of 4H and 6H polytypes we show that a short, but intense, irradiation with the 532 nm wavelength of a frequency-doubled neodymium: ytterbium aluminum garnet (Nd:YAG) laser results in a substantial reduction in the damage level produced by room temperature ion implantation. Up to now the recovery could not be made complete but, in the best conditions, it could reach ∼80% of the initial damage value. This is not enough to qualify VLLI as a full activation step but, rather, suggests to use it as a new processing tool in order to lower the constraints of high temperature ion implantation or, after implantation performed at room temperature, to reduce the total budget for high temperature annealing and activation steps. [ABSTRACT FROM AUTHOR]

A recent extension of scaled-particle theory for cavity solvation in polyatomic solvents developed by Ashbaugh and Pratt [J. Phys. Chem. B 111, 9330 (2007)] is tested against molecular simulations of 13 organic liquids. This molecular scaled-particle theory incorporates the intramolecular structure of the solvent in the calculation of the cavity excluding volume, compared with traditional applications of scaled-particle theory where the solvent is treated as an individual hard sphere with no internal structure. Once the diameters of the constituent carbon interaction sites are specified, molecular scaled-particle theory is able to discriminate between geometrically distinct solvents and provides accurate predictions for cavity solvation free energies and near quantitative predictions of the cavity contact correlation function. The diameters of the solvent interaction sites are argued to be transferable between related groups on different solvents, leading to a truly predictive scaled-particle theory given only information on the solvent pressure, density, and molecular topology. [ABSTRACT FROM AUTHOR]

A theoretical expression is developed for femtosecond coherent anti-Stokes Raman scattering (CARS) to quantitatively account for the vibrational line shape in the presence of nonresonant signal. The contributions of the resonant and nonresonant components are extracted from the emitted signal line shape as a function of Stokes wavelength and as a function of the temporal overlap of the two pump pulses (for spectrally resolved femtosecond CARS). The theory is compared to the measured spectra of the oxygen vibrational transition ΔG01=1556.4 cm-1 for temporal detunings of 0 and 700 fs. [ABSTRACT FROM AUTHOR]

We used an optical tweezer to investigate the adhesion of yeast Saccharomyces cerevisiae onto a glass substrate at the initial contact. Micromanipulation of free-living objects with single-beam gradient optical trap enabled to highlight mechanisms involved in this initial contact. As a function of the ionic strength and with a displacement parallel to the glass surface, the yeast adheres following different successive ways: (i) Slipping and rolling at 1.5 mM NaCl, (ii) slipping, rolling, and sticking at 15 mM NaCl, and (iii) only sticking at 150 mM. These observations were numerous and reproducible. A kinetic evolution of these adhesion phenomena during yeast movement was clearly established. The nature, range, and relative intensity of forces involved in these different adhesion mechanisms have been worked out as a quantitative analysis from Derjaguin–Landau–Verwey–Overbeek (DLVO) and extended DLVO theories. Calculations show that the adhesion mechanisms observed and their affinity with ionic strength were mainly governed by the Lifshitz–van der Waals interaction forces and the electrical double-layer repulsion to which are added specific contact forces linked to “sticky” glycoprotein secretion, considered to be the main forces capable of overcoming the short-range Lewis acid-base repulsions. [ABSTRACT FROM AUTHOR]

We present a fully quantum mechanical calculation for binding interaction between HIV-1 protease (PR) and the water molecule W301 which bridges the flaps of the protease with the inhibitors of PR. The quantum calculation is made possible by applying a recently developed molecular fractionation with conjugate caps (MFCC) method which divides a protein molecule into capped amino acid-based fragments and their conjugate caps. These individual fragments are properly treated to preserve the chemical property of bonds that are cut. Ab initio methods at HF, B3LYP, and MP2 levels with a fixed basis set 6-31+G* have been employed in the present calculation. The MFCC calculation produces a quantum mechanical interaction “map” representing interactions between individual residues of PR and W301. This enables a detailed quantitative analysis on binding of W301 to specific residues of PR at quantum mechanical level. [ABSTRACT FROM AUTHOR]

The guidance of vortices in superconducting Nb films with periodic arrangements of magnetic Ni dots is studied via simultaneous four-probe measurements in standard and Hall configuration. Ni dots are fabricated via e-beam lithography and lift-off technology. Arrays with periodicity down to 400 nm and dot size of 200 nm are obtained. Subsequently, the arrays are covered with a thin superconducting Nb layer. Simultaneous Hall and standard resistive measurements of the flux dynamic in Nb bridges with and without magnetic dots demonstrate and quantify the guidance of flux via the magnetic dots. Guidance of vortices is only possible in a limited current regime; guidance improves with decreasing temperature. Within the identified current regime most of the vortices (>40% for zero field) and in the optimum case all of the vortices are guided by the magnetic dots. [ABSTRACT FROM AUTHOR]

A simple geometrical construct is proposed for a clear-cut classification of the relative orientation between two tetrahedral molecules in terms of six orientational classes. When applied to sort out configurations from condensed phase simulations, it leads to a quantitative characterization of orientational order: A definite percentage for each class is obtained as a function of the distance between molecular centers. The basic picture that emerges, for liquid carbon tetrachloride, is that the dominant configuration for each distance is such that the number of chlorines in between both carbons diminishes with increasing separation, with a configuration here termed edge-to-face being the dominant one at contact. Regarding the range of orientational order, remnants are still noticeable at ≈20 Å, i.e., up to the fourth solvation shell. Beyond this distance the distributions are hardly distinguishable from the analytical predictions for random orientation. The analysis of the small fluctuations at such long distances shows that there are no significant differences betweeen the ranges of positional and orientational order. [ABSTRACT FROM AUTHOR]

The quantitative analysis and spatial chemical visualization of amylopectin and amylose in different varieties of sweet potatoes were studied by merging spectral and image information. Three-dimensional (3D) hyperspectral images carrying 1D spectra and 2D images of hundreds of the samples (amylopectin, n = 644; amylose, n = 665) in near-infrared (NIR) range of 950–1650 nm (426 wavelengths) were acquired. The NIR spectra were mined to correlate with the values of the two indexes using a linear algorithm, generating a best performance with correlation coefficients and root mean square error of prediction (r P and RMSE P) of 0.983 and 0.847 g/100 mg for amylopectin, and 0.975 and 0.500 g/100 mg for amylose, respectively. Then, 14 % of the wavelengths (60 for amylopectin, 61 for amylopectin) were selected to simplify the prediction with r P and RMSE P of 0.970 and 1.103 g/100 mg for amylopectin, and 0.952 and 0.684 g/100 mg for amylose, respectively, comparable to those of full-wavelength models. By transferring the simplified model to original images, the color chemical maps were created and the differences of the two indexes in spatial distribution were visualized. The integration of NIR spectra and 2D image could be used for the more comprehensive evaluation of amylopectin and amylose concentrations in sweet potatoes. [ABSTRACT FROM AUTHOR]

This study investigated the degradation mechanism and microbial communities of a reburied stone-fixed wooden pile (SP) after being excavated and treated with pentachlorophenol/polyethylene glycol (PCP/PEG) preservatives for a 20-year period at the Jin Zhongdu Watergate Heritage Cultural Site. High-throughput sequencing (HTS) techniques were combined with scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectrum analysis, and quantitative chemical analyses. A foundation wooden pile (FP) forming the watergate supports, which has been in service for nearly 870 years at the site, was also examined. The results showed that preservatives still partially remained in the SP after burial. More abundant and richer microbial communities were found in the SP (including brown rot, soft rot, white rot fungi and bacteria) due to the hydrophilic PEG providing more favorable habitats for microbial. Therefore, it was indicated that the PCP had gradually lost its antibacterial function. Although brown rot fungi had not been detected using HTS, typical morphological characteristics were observed in the FP using SEM, thereby the characteristics of brown rot fungi were the results of previous decay. The absence of brown rot may have been attributed the competition among wood rot fungi. • The PCP/PEG preservatives have been disabled for wood piles reburied over 20 years. • Residual PEG faction could be detected by FTIR at bands of 2880 cm−1 and 1110 cm−1. • PEG played a reverse role at in-situ wood reburial protection. • Brown rot fungi were not detected by high-throughput sequencing (HTS). • SEM observed decayed morphologies once whereas HTS indicated current microbiome. [ABSTRACT FROM AUTHOR]

Fixation is a critical step in green tea quality formation. In this study, an integrated analysis of sensory evaluation, electronic tongue, quantitative analysis of major chemical constituents and metabolomics analysis was performed to investigate the effect of fixation temperature (205 °C, 215 °C, 225 °C) on the taste profile of Longjing green tea and the underlying non-volatile metabolites changes. A total of 17 major chemical constituents and 100 non-volatile metabolites were investigated. 31 key differential metabolites were screened. With the increase of fixation temperature, the content of cis -catechins (epicatechin) and dimeric catechins (theaflavin, theaflavin-3′-gallate, theaflavin-3,3′-gallate) were significantly decreased, which may reduce the bitterness. The astringency of tea infusions varied depending mainly on the content changes in flavonol glycosedes, along with trans -catechins (gallocatechin, catechin gallate, gallocatechin gallate). Besides, the contents of amino acids, phenolic acids and carbohydrates were also varied. These substances were altered possibly due to variations in epimerization, oxidative polymerization, and thermal degradation. Longjing tea treated with an appropriate fixation temperature of about 215 °C rendered optimal taste quality. This study could advance the understanding of the fixation regulation of green tea taste and its underlying mechanism. [Display omitted] • Fixation temperature affects the bitterness and astringency of Longjing tea. • Decreases in cis- catechins and theaflavins led to a decrease in bitterness. • Low levels of trans -catechins and flavonol glycosides led to low astringency. • Epimerization and oxidative polymerization of catechins were significantly impacted. • 31 key differential metabolites were screened in differently treated samples. [ABSTRACT FROM AUTHOR]

Submillimetric glass and polymer capillaries are employed in the fabrication of microfluidic devices and laboratory-on-a-chip microsystems. A quantitative analysis of the diffusion-related flow in these micro-channels enhances the accuracy of the designed systems and may unearth concepts of significant practical value. The authors have analyzed the diffusion-physisorption (D-P) of a trace material (TM) through gas- or liquid-filled capillaries in a broad range of bore sizes. A nonlinear partial differential equation rooted in the Langmuir model for adsorption and desorption to a solid surface has been obtained to describe this phenomenon. This equation was further improved to accommodate the presence of any arbitrary temperature distribution along the diffusion path. The solutions revealed that the progress rate of the D-P in submillimetric capillaries, unlike in tubes with diameters larger than a few millimeters, is affected by the physisorption of the diffusing molecules to the internal wall of the capillary and is, therefore, diameter dependent. In this case, accurate theoretical rate predictions required information on the nature of both the TM and internal surface of the capillary. Two scalar parameters were defined that, along with the diffusion coefficient of the TM, could facilitate numerical modeling of the diameter dependant process. For an unknown TM, these parameters can be calculated by the fitting of the numerically generated solutions to the experimentally recorded D-P progress rates and be used to identify the unknown TM. The temporal progresses of the D-P of methanol, ethanol, and 1-butanol traces in air-filled closed-end capillaries of 1.2 and 3 mm internal diameters were experimentally recorded. The results verified the mathematical predictions. [ABSTRACT FROM AUTHOR]

The kinetics of the photodarkening effect has been studied experimentally for amorphous selenium (a-Se) layers at room temperature and at an elevated temperature (35 °C) close to the glass transition. By switching an intense pumping light on and off with a period of 100 s, we have studied the kinetics of both the buildup of photodarkening and its relaxation (recovery). It was found that at 35 °C, only a reversible component of photodarkening has been observed. This result has been interpreted within the framework of a phenomenological model assuming that photodarkening is caused by light-induced transitions of structural units from their ground states into metastable states. Our estimate for the energy barrier EB between these states obtained for the photodarkening process (EB∼0.8 eV) coincides with that obtained from the analysis of the relaxation process. At room temperature, an irreversible component of photodarkening has been observed along with the reversible one. The energy barrier responsible for the relaxation of the reversible component at room temperature appears the same as at 35 °C. This suggests that the energy barrier identified represents a fundamental feature of the photoinduced structural metastability in amorphous selenium. [ABSTRACT FROM AUTHOR]

Porous alumina masks are fabricated by anodization of aluminum films grown on both semiconducting and insulating substrates. For these self-assembled alumina masks, pore diameters and periodicities within the ranges of 10–130 and 20–200 nm, respectively, can be controlled by varying anodization conditions. 20 nm periodicities correspond to pore densities in excess of 1012 per square inch, close to the holy grail of media with 1 Tbit/in.2 density. With these alumina masks, ordered sub-100-nm planar ferromagnetic nanodot arrays covering over 1 cm2 were fabricated by electron beam evaporation and subsequent mask lift-off. Moreover, exchange-biased bilayer nanodots were fabricated using argon-ion milling. The average dot diameter and periodicity are tuned between 25 and 130 nm and between 45 and 200 nm, respectively. Quantitative analyses of scanning electron microscopy (SEM) images of pore and dot arrays show a high degree of hexagonal ordering and narrow size distributions. The dot periodicity obtained from grazing incidence small angle neutron scattering on nanodot arrays covering ∼2.5 cm2 is in good agreement with SEM image characterization. [ABSTRACT FROM AUTHOR]

Interactions between two layered silicate sheets, as found in various nanoscale materials, are investigated as a function of sheet separation using molecular dynamics simulation. The model systems are periodic in the xy plane, open in the z direction, and subjected to stepwise separation of the two silicate sheets starting at equilibrium. Computed cleavage energies are 383 mJ/m2 for K-mica, 133 mJ/m2 for K-montmorillonite (cation exchange capacity=91), 45 mJ/m2 for octadecylammonium (C18)-mica, and 40 mJ/m2 for C18-montmorillonite. These values are in quantitative agreement with experimental data and aid in the molecular-level interpretation. When alkali ions are present at the interface between the silicate sheets, partitioning of the cations between the surfaces is observed at 0.25 nm separation (mica) and 0.30 nm separation (montmorillonite). Originally strong electrostatic attraction between the two silicate sheets is then reduced to 5% (mica) and 15% (montmorillonite). Weaker van der Waals interactions decay within 1.0 nm separation. The total interaction energy between sheets of alkali clay is less than 1 mJ/m2 after 1.5 nm separation. When C18 surfactants are present on the surfaces, the organic layer (>0.8 nm) acts as a spacer between the silicate sheets so that positively charged ammonium head groups remain essentially in the same position on the surfaces of the two sheets at any separation. As a result, electrostatic interactions are efficiently shielded and dispersive interactions account for the interfacial energy. The flexibility of the hydrocarbon chains leads to stretching, disorder, and occasional rearrangements of ammonium head groups to neighbor cavities on the silicate surface at medium separation (1.0–2.0 nm). The total interaction energy amounts to less than 1 mJ/m2 after 3 nm separation. [ABSTRACT FROM AUTHOR]

Based upon a bulk scattering model, we investigated the variation of giant magnetoresistance (GMR) behavior after thermal annealing at Ta=250 °C as a function of the top free layer thickness of a GMR spin valve with nano-oxide layers (NOLs). It was found that the enhancement of GMR ratio after thermal annealing is explained qualitatively in terms of the increase of active GMR region in the free layer and, simultaneously, the increase of intrinsic spin-scattering ratio. These effects are likely due to the improved specular reflection at the well-formed interface of NOL. Furthermore, we developed a modified phenomenological model for sheet conductance change (ΔG) in terms of the top free layer thickness. This modified model was found to be useful in the quantitative analysis of the variation of the active GMR region and the intrinsic spin-scattering properties. The two physical parameters were found to change consistently with the effects of thermal annealing on NOL. [ABSTRACT FROM AUTHOR]

Theoretical calculations by Khanna and Jena predicted KAl13 to be an ionically bonded, cluster-assembled “diatomic molecule,” i.e., K+Al13-. We have conducted both mass spectral and anion photoelectron spectroscopic studies on KAln-, finding a “dip” at n=13 in both their mass spectrum and in their electron affinity versus n trend. While these largely qualitative results are consistent with KAl13 being a salt, they can also be explained in terms of the shell model and thus, by themselves, are not conclusive. Quantitative comparisons between calculated photodetachment transition energies and the photoelectron spectrum of KAl13-, however, allow a strong case to be made for ionic bonding in KAl13. As a prototype for ionic bonding involving intact Al13- subunits, KAl13 may be a stepping stone toward forming ionic, cluster-assembled materials. [ABSTRACT FROM AUTHOR]

A simple theoretical model is developed to predict the state-to-state dynamics of direct chemical reactions. Motivated by traditional ideas from transition state theory, expressions are derived for the reactive S matrix that may be computed using the local transition state dynamics. The key approximation involves the use of quantum bottleneck states to represent the near separable dynamics taking place near the transition state. Explicit expressions for the S matrix are obtained using a Franck-Condon treatment for the inelastic coupling between internal states of the collision complex. It is demonstrated that the energetic thresholds for various initial reagent states of the D+H2 reaction can be understood in terms of our theory. Specifically, the helicity of the reagent states are found to correlate directly to the symmetry of the quantum bottleneck states, which thus possess very different thresholds. Furthermore, the rotational product state distributions for D+H2 are found to be associated with interfering pathways through the quantum bottleneck states. [ABSTRACT FROM AUTHOR]

Quantitative theory of orientational behavior of rodlike polyelectrolytes in dilute solution is developed. We find that in salt-free solutions many-body Coulomb interactions between macro- and counterions favor nematic ordering. It is shown that the orientationally isotropic phase of the solution becomes unstable toward nematic ordering at polymer concentration smaller than the overlap concentration. Our predictions are consistent with experimental observations for synthetic polyelectrolytes poly(p-phenylene)sulfonates in aqueous solutions. [ABSTRACT FROM AUTHOR]

A theoretical investigation of the properties of the Si[sub 3]C[sub 4], Si[sub 4]C[sub 3], and Si[sub 4]C[sub 4] clusters is reported. Systematic explorations of the potential energy surfaces of the three clusters are performed using a combination of ab initio molecular dynamics and local energy minimizations using density functional theory. A large number of isomers with a large variety of geometries has been found. The geometries, energies, and vibrational frequencies yielded are discussed. Furthermore, a quantitative analysis of the interatomic distances, angles, and coordination numbers observed, as well as the conclusions on the bonding properties, are presented. The cluster properties are then compared to those of solid SiC and of the smaller Si–C clusters (with size up to 6) obtained in a previous study. Analysis of our results and comparison with bulk properties show that even clusters as small as Si[sub 3]C[sub 4], Si[sub 4]C[sub 3], and Si[sub 4]C[sub 4] exhibit properties similar to those of the amorphous bulk, in particular as for the structures and bonds formed by C atoms. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Polyfluorenes are possibly the most attractive class of conjugated polymers for blue polymer light emitting devices. Derivatives with dendron side chains have been found to significantly improve the color stability of the devices. Using a quasi-cw photoinduced absorption technique we present a qualitative and quantitative analysis of lifetimes and deactivation mechanisms for the triplet excited states in a dendronically substituted derivative. The triplet lifetimes increase by one order of magnitude in the dendronic derivative compared to those in a standard poly(dialkylfluorene), which has been characterized for comparison. The temperature dependence of triplet lifetimes is interpreted in terms of migration assisted deactivation of triplet excitations. We conclude that the dendrons inhibit the Dexter-transfers of triplet excitations between the polymer chains and so strongly hinder triplet migration. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]