bluuebunny/crossref_metadata_2025_split huggingface dataset:
A theory of relaxation processes with application to a two-dimensional rotor
Authors: Fulton Robert L. 
Published: July 2002

A general theory of the relaxation of a system in contact with a second system (called the heat bath) which need not be in equilibrium is presented. The theory, which avoids the use of projection operators, is developed in such a fashion that the effects of the interaction between the system and the heat bath can be consistently approximated by an ordering in terms of the degree of the fluctuation in the heat bath variables. This gives a natural classification in terms of differing regimes, the lowest nontrivial of which is the quadratic, or Gaussian, regime. The cubic and higher order fluctuations represent increasingly complex regimes. The exact equations of motion for the average of the single time system variables and for the two-time correlation functions involving the system variables are found in the Gaussian regime. (The general theory is not limited to the two-time correlation functions.) In the classical limit these lead to equations of motion for the three quantities: the average of the single time variables; the two-time, or pair, fluctuations; and the average of the Poisson bracket of a pair of system variables (the
dissipative function) for systems in and not in equilibrium. Some exact consequences of the equations when the heat bath and the system are in thermal equilibrium are found. In particular the exact equilibrium distribution function of the system variables is determined and it is demonstrated that the system variables obey the fluctuation–dissipation theorem. Various approximation schemes are devised. When the bath and the system are in thermal equilibrium the approximate equations of motion obey the fluctuation–dissipation theorem and have as a possible steady state solution the exact equilibrium distribution. The theory is applied to the relaxation of a rigid rotor constrained to rotate in two dimensions. The first corrections to the diffusion constant D due to the nonzero correlation times of the bath variables and a finite moment of inertia of the rotor are found. Connection is made with dielectric friction when the rotor is endowed with a permanent dipole moment which interacts with the bath variables via an electric field. A symmetrized version of the Nee–Zwanzig friction constant gives one contribution to the diffusion constant. In addition, when the moment of inertia is finite and the correlation time of the bath variables is nonzero, there is a contribution which tends to increase the diffusion constant.
On the characterization of regions of avoided surface crossings using an analytic gradient based method
Authors: Yarkony David R. 
Published: July 2002

The characterization of regions of avoided surface crossings in polyatomic systems using multiconfiguration self-consistent field/configuration interaction(CI) wave functions is considered. It is shown that when the difference density matrices ΔγIJ =γI−γJ and ΔΓIJ =ΓI−ΓJ are introduced construction of the energy difference gradient ∂/∂Rα [EI(R)−EJ(R) ] becomes formally equivalent to the construction of the energy gradient (∂/∂Rα)EI(R). Here EI(R) is electronic potential energy surface at the CI level and γI and ΓI are the standard one- and two-particle density matrices.
The formalism presented here provides a unified approach for the evaluation of three important classes of derivatives, energy gradients (using standard density matrices γI and ΓI ), energy difference gradients (using difference density matrices ΔγIJ and ΔΓIJ) and intersurface nonadiabatic derivative couplings (using transition density matrices γIJ and ΓIJ). The algorithms for the evaluation of the energy difference gradient permit efficient exploitation of the formal similarities which exist between the Newton–Raphson procedure for the minimization of EI(R) and that for ΔEIJ(R)2 =[EI(R)−EJ(R) ]2. These similarities can be used to advantage in the characterization of ΔEIJ(R)2 surfaces. The use of this formalism to analyze regions of avoided surface crossings is considered. In particular the methodology introduced here is used to locate an energetically accessible portion of a seam of avoided crossings for the two lowest potential energy surfaces of the Na–HCl system.
These surfaces describe the electronic quenching reaction Na(2P)+HCl→NaCl+H. This avoided crossing seam is the analog of a (C2v) allowed crossing seam in the Na(2P)+H2→Na(2S)+H2 nonreactive quenching problem.
Forces on nuclei in interacting molecules: New analytical results obtained with nonlocal polarizability densities
Authors: Hunt K. L. C. , Liang Y. Q. 
Published: July 2002

When the charge overlap between interacting molecules or ions A and B is weak or negligible, the first-order interaction energy depends only upon the molecular positions, orientations, and the unperturbed charge distributions of the molecules. In contrast, the first-order force on a nucleus in molecule A as computed from the Hellmann–Feynman theorem depends not only on the unperturbed charge distribution of molecule B, but also on the electronic polarization induced in A by the field from B. At second order, the interaction energy depends on the first-order, linear response of each molecule to its neighbor, while the Hellmann–Feynman force on a nucleus in A depends on second-order and nonlinear responses to B. One purpose of this work is to unify the physical interpretations of interaction energies and Hellmann–Feynman forces at each order, using nonlocal polarizability densities and connections that we have recently established among permanent moments, linear response, and nonlinear response tensors. Our theory also yields new information on the origin of terms in the long-range forces on molecules, through second order in the interaction.
One set of terms in the force on molecule A is produced by the field due to the unperturbed charge distribution of B and by the static reaction field from B, acting on the nuclear moments of A. This set originates in the direct interactions between the nuclei in A and the charge distribution of B. A second set of terms results from the permanent field and the reaction field of B acting on the permanent electronic moments of A. This set results from the attraction of nuclei in A to the electronic charge in A itself, polarized by linear response to B. Finally, there are terms in the force on A due to the perturbation of B by the static reaction field from A; these terms stem from the attraction of nuclei in A to the electronic charge in A, hyperpolarized by the field from B. For neutral, dipolar molecules A and B at long range, the forces on individual nuclei vary as R−3 in the intermolecular separation R; but when the forces are summed over all of the nuclei, the vector sum varies as R−4. This result, an analogous conversion at second order (from R−6 forces on individual nuclei to an R−7 force when summed over the nuclei), and the long-range limiting forces on ions are all derived from new sum rules obtained in this work.
Silyl group internal rotation in S1 phenylsilane and phenylsilane cation: Experiments and ab initio calculations
Authors: Lu Kueih-Tzu , Weisshaar James C. 
Published: July 2002

Resonant two-photon ionization (R2PI) and pulsed field ionization (PFI) were used to measure S1–S0 and cation–S1 spectra of internally cold phenylsilane. We measure the adiabatic ionization potentials IP(phenylsilane)=73 680±5 cm−1, IP(phenylsilane ⋅Ar)=73 517±5 cm−1 and IP(phenylsilane ⋅Ar2)=73 359±5 cm−1. We assign many low lying torsion–vibration levels of the S1 (Ã 1A1) state and of X̃ 2B1 of phenylsilane+. In both states, the pure torsional transitions are well fit by a simple sixfold hindered rotor Hamiltonian. The results for the rotor inertial constant B and internal rotation potential barrier V6 are, in S1, B=2.7±0.2 cm−1 and V6=−44±4 cm−1; in the cation, B=2.7±0.2 cm−1 and V6=+19±3 cm−1. The sign of V6 and the conformation of minimum energy are inferred from spectral intensities of bands terminating on the 3a″1 and 3a″2 torsional levels. In S1 the staggered conformation is most stable, while in the cation ground state the eclipsed conformation is most stable. For all sixfold potentials whose absolute phase is known experimentally, the most stable conformer is staggered in the neutral states (S0 and S1 p-fluorotoluene, S1 toluene, S1 p-fluorotoluene) and eclipsed in the cationic states (ground state toluene+ and phenylsilane+). In phenylsilane+ we estimate several potential energy coupling matrix elements between torsional and vibrational states.
For small V6, the term PαPa in the rigid-frame model Hamiltonian strongly mixes the 6a′1 and 6a′2 torsional states, which mediates further torsion–vibrational coupling. In addition, the cation X̃ 2B1 vibrational structure is badly perturbed, apparently by strong vibronic coupling with the low-lying Ã 2A2 state. Accordingly, ab initio calculations find a substantial in-plane distortion of the equilibrium geometry of the X̃ 2B1 state, while the Ã 2A2 state is planar and symmetric. The calculations also correctly predict the lowest energy conformer for S0 states and for cation ground states. Finally, we adapt the natural resonance theory (NRT) of Glendening and Weinhold to suggest why sixfold barriers for methyl and silyl rotors are uniformly small, while some threefold barriers are quite large. The phase of the sixfold potential is apparently determined by a subtle competition between two types of rotor-ring potential terms: attractive donor–acceptor interactions and repulsive van der Waals interactions (steric effects).
High gradient phenomena in two-dimensional vortex interactions
Authors: Yao H. B. , Zabusky N. J. , Dritschel D. G. 
Published: July 2002

Hyperdiffusion, a simple linear eddy diffusivity scheme, is commonly used in atmospheric and oceanic simulations because it increases the range of inertially behaving spatial scales for a given model resolution. Compared with molecular diffusion (which is utterly negligible in the atmosphere and oceans), hyperdiffusion more sharply confines the dissipation to the smallest scales of the numerical model. But is this all that hyperdiffusion does? In this paper, the inelastic interaction of two distributed vortices of unequal size is examined. Contour surgery (CS) simulations are compared with pseudospectral (PS) simulations employing hyperdiffusion or molecular diffusion. The example illustrates what is believed to be the most fundamental characteristic of two-dimensional (2-D) (and layerwise-2-D) vortex dynamics, namely, the formation of exceedingly high vorticity gradients. There is an excellent agreement between the hyperdiffusive PS and CS calculations at early times (i.e., for a few vortex rotation periods). Thereafter, significant discrepancies develop, beginning abruptly from the time when vorticity-gradient intensification is arrested by diffusion. A rapid inward erosion of the smaller of the two vortices then takes place. This erosion takes place under the joint action of (hyper) diffusion and stripping (the peeling of the vortex periphery by the external flow). With hyperdiffusion, the erosion is accompanied by a serious numerical artifact: a climb in the peak vorticity by 30% in this example. Eventually, the erosion reaches the vortex center and the vortex is sheared into a filament. In the CS calculation, there is no erosion, no climb in peak vorticity, and the vortex appears to last indefinitely.
In the PS calculations, the viscosity or hyperdiffusion is adjusted according to the resolution to give the largest possible inertial range while ensuring numerical stability. It is found that vortices that are spanned by fewer than 10–20 grid points are eroded away in only a few vortex rotation periods (a time scale that is very much shorter than one would estimate from pure viscous decay). These findings bring into question the results of many 2- turbulence simulations using hyperdiffusion, for hyperdiffusion simulates neither inviscid dynamics nor molecular-diffusive dynamics.
Differential Effects of Tri‐n‐Butylstannyl Benzoates on Induction of Apoptosis in K562 and MCF‐7 Cells
Authors: Ray Dipankar , Sarma Koushik Das , Antony Abraham 
Published: July 2002

AbstractTributyltin compounds have been shown to induce apoptosis by causing extracellular Ca2+ influx and generating reactive oxygen species (ROS). Several organotin compounds were reported to have differential cytotoxicity on various human cell lines depending on the length of the alkyl chain. In this report, the cytotoxic effects of three tri‐n‐butylstannyl (halo)benzoate compounds‐tri‐n‐butylstannyl benzoate (TBSB), tri‐n‐butylstannyl 2,6‐difluorobenzoate (TBSDFB) and tri‐n‐butylstannyl‐2‐iodobenzoate (TBSIB)‐were studied on lymphocytic cells of human leukemic K562 lineage and epithelial cells of human breast cancer MCF‐7 cells lineage. K562 cells were found to be more sensitive to these compounds than MCF‐7 cells. Although the induction of apoptosis by the above compounds in K562 cells resulted from the extracellular Ca2+ influx and the generation of ROS, the initial amount of extracellular Ca2+ influx was greater in TBSB‐treated K562 cells than the cells treated with either TBSDFB or TBSIB. Similarly, DNA fragmentation by endonucleases was observed as an early event in TBSB‐treated K562 cells, which might be correlated with the initially greater extracellular Ca2+ influx. In contrast, MCF‐7 cells were found to undergo apoptosis mainly because of the generation of ROS. The present results suggest that the differential effects of tributyltin compounds on induction of apoptosis in K562 and MCF‐7 cells are largely attributable to the extent of extracellular Ca2+ influx.
The Membrane Protein Alkaline Phosphatase Is Delivered to the Vacuole by a Route That Is Distinct from the VPS-dependent Pathway
Authors: Piper Robert C. , Bryant Nia J. , Stevens Tom H. 
Published: July 2002

Membrane trafficking intermediates involved in the transport of proteins between the TGN and the lysosome-like vacuole in the yeast Saccharomyces cerevisiae can be accumulated in various vps mutants. Loss of function of Vps45p, an Sec1p-like protein required for the fusion of Golgi-derived transport vesicles with the prevacuolar/endosomal compartment (PVC), results in an accumulation of post-Golgi transport vesicles. Similarly, loss of VPS27 function results in an accumulation of the PVC since this gene is required for traffic out of this compartment.
The vacuolar ATPase subunit Vph1p transits to the vacuole in the Golgi-derived transport vesicles, as defined by mutations in VPS45, and through the PVC, as defined by mutations in VPS27. In this study we demonstrate that, whereas VPS45 and VPS27 are required for the vacuolar delivery of several membrane proteins, the vacuolar membrane protein alkaline phosphatase (ALP) reaches its final destination without the function of these two genes. Using a series of ALP derivatives, we find that the information to specify the entry of ALP into this alternative pathway to the vacuole is contained within its cytosolic tail, in the 13 residues adjacent to the transmembrane domain, and loss of this sorting determinant results in a protein that follows the VPS-dependent pathway to the vacuole.
Using a combination of immunofluorescence localization and pulse/chase immunoprecipitation analysis, we demonstrate that, in addition to ALP, the vacuolar syntaxin Vam3p also follows this VPS45/27-independent pathway to the vacuole. In addition, the function of Vam3p is required for membrane traffic along the VPS-independent pathway.
Fast computation of 3D radon transform via a direct Fourier method.
Authors: Lanzavecchia S , Luigi Bellon P 
Published: July 2002

Abstract
MOTIVATION: Arrays of three-dimensional (3D) data are ubiquitous in structural biology, biomedicine and clinical imaging. The Radon transform can be implied in their manipulation mainly for the solution of the inverse tomographic problem, since experimental data are often collected as projections or as samples of the Radon space. In electron tomography, new applications of the transform may become convenient if a fast and accurate transformation algorithm is adopted. RESULTS: A direct Fourier method (DFM) is proposed to compute the 3D Radon transform from a sampled function with compact support. This paper describes an already known two-step algorithm and illustrates its DFM implementation by coordinate transformations in 2D Fourier space. The algorithm is easily inverted to obtain a density distribution from the Radon transform. The main applications are in the field of electron tomography, especially in processes of angular refinement, since whatever projection of a structure can be retrieved from its Radon transform in a fast and accurate way. The times required to compute a number of projections with use of the Radon transform are compared with those required by other algorithms. Further uses of the Radon transform can be foreseen in applications based on 'projection onto convex sets' (POCS). AVAILABILITY: Software is available free of charge upon request to the authors. CONTACT: salvator@csmtbo.mi.cnr.it
Stable Cycling of Room‐Temperature Sodium‐Sulfur Batteries Based on an In Situ Crosslinked Gel Polymer Electrolyte
Authors: Murugan Saravanakumar , Klostermann Sina V. , Schützendübe Peter , Richter Gunther , Kästner Johannes , Buchmeiser Michael R. 
Published: June 2022

AbstractHigh‐temperature sodium‐sulfur battery (HT Na–S) technology has attracted substantial interest in the stationary energy storage sector due to its low cost and high energy density. However, the currently used solid electrolyte (ß‐alumina) is expensive and can only be operated at high temperatures, which compromises safety. On the other hand, liquid electrolytes in room temperature sodium‐sulfur batteries (RT Na–S) are susceptible to dendrite formation and polysulfide shuttle. Consequently, an electrolyte with both solid (shuttle blocking) and liquid (ionic conductivity) properties to overcome the above‐mentioned issues is highly desired. Herein, a high‐performance quasi‐solid state crosslinked gel polymer electrolyte (GPE) prepared in situ using pentaerythritol triacrylate (PETA) exhibiting high ionic conductivity of 2.33 mS cm−1 at 25 °C is presented. The GPE‐based electrolyte shows high stability resulting in a high discharge capacity of >600 mAh gs−1 after 2500 cycles with an average Coulombic efficiency of 99.91%. Density functional theory calculations reveal a weak interaction between the Na+ ions and the oxygen molecules of the PETA moiety, which leads to a facile cation movement. The crosslinked polymer network is tightly connected to the cathode and can confine sulfides, thereby facilitating the conversion process.
Tuning Electronic and Ionic Transport by Carbon‐Based Additives in Polymer Electrolytes for Thermoelectric Applications
Authors: Frank Maximilian , Pflaum Jens 
Published: June 2022

AbstractThermoelectric materials utilizing ionic transport open‐up entirely new possibilities for the recuperation of waste heat. Remarkably, solid state electrolytes which have entered the focus of battery research in recent years turn‐out to be promising candidates also for ionic thermoelectrics. Here, the dynamics of ionic transport and thermoelectric properties of a methacrylate based polymer blend in combination with a lithium salt is analyzed. Impedance spectroscopy data indicates the presence of just one transport mechanism irrespective of lithium salt concentration. In contrast, the temperature dependent ionic conductivity increases with salt concentration and can be ascribed to a Vogel–Fulcher–Tammann (VFT) behavior. The obtained Seebeck coefficients of 2 mV K−1 allow for high power outputs while the polymer matrix maintains the temperature gradient by its low thermal conductivity. Adding multi‐walled carbon nanotubes to the polymer matrix allows for variation of the Seebeck coefficient as well as the ionic and electronic conductivities. As a result, a transition between a high temperature VFT regime and a low temperature Arrhenius regime appears at a critical temperature, Tc, shifting upon addition of salt. The observed polarity change in Seebeck voltage at Tc suggests a new mode of thermoelectric operation, which is demonstrated by a proof‐of‐concept mixed electronic‐ionic‐thermoelectric generator.
Mechanistic Understanding and Three‐Dimensional Tuning of Fluid Imbibition in Silica‐Coated Cotton Linter Paper Sheets
Authors: Mikolei Joanna J. , Neuenfeld Lukas , Paech Steffen , Langhans Markus , Biesalski Markus , Meckel Tobias , Andrieu‐Brunsen Annette 
Published: June 2022

AbstractPaper‐based microfluidic devices are used in point of care diagnostic, sensor technology or lab‐on‐a‐chip devices. Although a number of studies has been reported, only relatively few paper‐based diagnostic tools are available on the market. A remaining challenge is the mechanistic understanding and precise design of capillary flow in paper. Here, silica coatings are applied to control paper wettability, fiber swelling, and thus fluid transport in all three dimensions of a paper sheet via a simple dip‐coating and post‐treatment process. By adjusting the three‐dimensional silica coating distribution, a three‐dimensional asymmetric wettability gradient within the paper sheet is obtained which controls the fluid distribution and imbibition. The correlation between silica coating amount and silica distribution with the resulting fluid behavior is systematically elaborated by analyzing the interaction between fiber and fluid as well as the fiber swelling by applying confocal microscopy. Three different silica‐amount dependent fluid distribution states are demonstrated. These new insights into the mechanism of fluid imbibition using simple silica coatings enable the specific design of different imbibition mechanisms and thus the adjustment of the microfluidic properties in paper‐based microfluidic devices with control over all three spatial dimensions of a paper sheet in one fabrication step.
Sulfur oxidative coupling of methane process development and its modeling via machine learning
Authors: Scabbia Giovanni , Abotaleb Ahmed , Sinopoli Alessandro 
Published: June 2022

AbstractSulfur oxidative coupling of methane (SOCM) has seen a significant improvement in catalyst design and performances, but there is still a lack of development at process level. We propose an optimized SOCM process flow diagram, with integrated waste heat recovery system and an efficient separation technique. The outcomes of the simulated process were used to design a data‐driven modeling approach, based on machine learning methods, and to evaluate its interpolation accuracy. The simultaneous multi‐input/multioutput relationship between the different parameters of the SOCM system were determined, revealing the optimum reaction conditions for the maximum benzene, toluene and xylene yield, at the minimum CH4 and H2S recycling rate.
Separation ofCH4/N2by an ultra‐stable metal–organic framework with the highest breakthrough selectivity
Authors: Chang Miao , Wang Fei , Wei Yan , Yang Qingyuan , Wang Jie‐Xin , Liu Dahuan , Chen Jian‐Feng 
Published: June 2022

AbstractSelectively separating CH4from N2in natural gas purification is extremely important, but challenging. Herein, a copper‐based metal–organic framework (MOF) NKMOF‐8‐Me with inert pore environment was reported for efficient CH4/N2separation. Adsorption results show that this material owns the highest CH4uptake (1.76 mmol/g) and initial adsorption heat (Qst0) of CH4(28.0 kJ/mol) as well as difference inQst0(9.1 kJ/mol) among all materials with good water stability. Breakthrough experiments confirm that this MOF can completely separate the CH4/N2mixture with the highest CH4/N2breakthrough selectivity (7.8) reported so far. Theoretical calculations reveal the separation mechanism is the short average distance between CH4and pore wall, resulting in a stronger adsorption affinity for CH4. In addition, this MOF exhibits highly structural stability and regeneration. These results guarantee this MOF as a promising adsorbent for the recovery of CH4from coalbed methane.