bluuebunny/crossref_metadata_2025_split huggingface dataset:
Two‐Dimensional Imaging of OH Radicals in Spark Ignition Kernels by Laser Induced Fluorescence
Authors: Xu J. , Warnatz J. 
Published: July 2012

AbstractTwo‐dimensional laser‐induced fluorescence imaging of OH radicals has been used to observe the temporal and spatial development of the OH distribution during the ignition of a lean methane‐air mixture (ϕ = 0.56) ignited by an electrical spark. A frequency‐doubled dye laser, which is pumped by a XeCl excimer laser, has been used to excite fluorescence from OH radicals. A series of OH concentration maps from a cross‐section through the ignition kernel during the ignition process have been obtained. It can be seen that the gas flow induced by the initial shock wave from the breakdown phases has a significant influence on the development of the ignition kernel. The ignition kernel is produced by a narrow cylindrical plasma channel with high temperature, then expands to an ellipsoid during the ignition. At about 1 ms after the onset of the spark the ignition kernel expands from the ellipsoid to a toroidal shape. A flame front emerges from the ignition kernel at about 10 ms.
Dielectric spectroscopy on CiEj/water mixtures as a function of composition
Authors: Kaatze U. , Gabriel B. , Pottel R. 
Published: July 2012

AbstractAt 25°C the complex dielectric permittivity of mixtures of water with low‐weight poly (ethylene glycol) monoalkyl ethers (CiEj) has been measured as a function of frequency v (1 MHz ≤ v ≤ 55 GHz) and mole fraction x(0 ≤ x ≤ 1). Various relaxation spectral functions are fitted to the measured spectra. It is found that the dielectric relaxation of all liquids (i, j = 2,2; 4,2; 6,2; 4,3; 4,1) can be consistently described by a sum of a Debye term with discrete relaxation time and a Davidson‐Cole term with an underlying unsymmetrical relaxation time distribution. With the exception of the C4E3/H2O mixtures the Debye term vanishes at high content of CiEj molecules (x > 0.25). It is assumed that this term represents a water‐rich subphase while the Davidson‐Cole term reflects a microphase of low water content. With the C4H3/H2O system crankshaft‐like motions of the C4E3 molecule obviously also contribute to the Debye term which exists also in the spectrum of the pure organic liquid. The parameters of all spectra are discussed with respect to the composition of the microphase of low water content, to effects of dipole orientation correlation, and to the mechanism of dielectric relaxation in associated liquids.
Electronic spectra of 7,14‐dithioketo‐5,7,12,14‐tetrahydroquinolino‐[2,3‐b]‐acridine in solution and in the solid state
Authors: Mizuguchi Jin , Rochat Alain Claude , Rihs Grety 
Published: July 2012

Abstract7,14‐Dithioketo‐5,7,12,14‐tetrahydroquinolino‐[2,3‐b]‐acridine (DTQ) is a thionated derivative of quinacridone (QA) that is known as a red pigment. Thionation of QA brings about an intense near‐IR absorption in the solid state which is of practical importance for GaAsAl‐laser printers and optical information storage systems. The electronic properties of DTQ have been investigated in solution and in the solid state in order to characterize the near‐IR absorption from the standpoint of intermolecular hydrogen bonding. The electronic state of the DTQ‐chromophore is found to be most sensitively affected by an environment of proton acceptors which interact with the NH group of the chromophore. In solution, the hydrogen bonds between the NH group and the O atom of a solvent cause a bathochromic shift by 5 – 15 nm relative to the absorption spectrum in dioxane. This is interpreted as being due to electron transfer from the proton to the nitrogen atom, thereby increasing the electron density in the chromophore. A similar increase in electron density is also operative in the solid state through the intermolecular hydrogen bonds between the NH group of one DTQ and the S atom of the neighboring molecule. This is mainly responsible for the bathochromic displacement of DTQ in going from solution to the solid state. The near‐IR absorption is, however, not explicable in terms of the hydrogen bonding interaction alone. Another intermolecular interaction, such as π‐π interactions along the stacking axis, appears to be operative that might lead to a near‐IR absorption.
Hydrogen bonding effect on the electronic spectra in complexes of 1,4‐dithioketo‐3,6‐diphenyl‐pyrrolo‐[3,4‐c]‐pyrrole with n‐methyl‐2‐pyrrolidone and dimethylsulfoxide
Authors: Mizuguchi Jin 
Published: July 2012

Abstract1,4‐Dithioketo‐3,6‐diphenyl‐pyrrolo‐[3,4‐c]‐pyrrole (DTPP) is known as the material suitable for laser printers and optical information storage systems using GaAsAl‐diode lasers. Hydrogen‐bonded complexes of DTPP with N‐methyl‐2‐pyrrolidone (NMP) and Dimethylsulfoxide (DMSO) have been grown from solution as single crystals: DTPP/(NMP)2 and DTPP/(DMSO)2. In both complexes, one DTPP molecule is bonded to two solvent molecules through the hydrogen bonds between the NH group of DTPP and the O atom of the solvent. The hydrogen bonding effect on the electronic spectra has been investigated in these complexes on the basis of the PPP, CNDO/S and INDO/S calculations. The hydrogen bonding in solution and in complexes displaces the longest‐wavelength π ‐ π * visible absorption band towards longer wavelengths. This is interpreted as being due to CT type interaction of hydrogen bonding which involves a partial electron transfer from the oxygen atom to the NH bond. The longest‐wavelength absorption bands in both complexes are polarized along the hydrogen bonding axis, and this agrees with the direction of the transition moment predicted from the calculations. On the other hand, a prominent reflection band appears in DTPP/(DMSO)2 for the polarization perpendicular to the hydrogen bonding axis. This is assigned to an intermolecular CT transition along the stacking columns composed of alternating DTPP and DMSO molecules.
Kinetics and mechanism of the formation of an iron(III) complex with Nα‐pyridoxyl‐L‐tryptophan
Authors: Ozawa Tomohiro , Jitsukawa Koichiro , Einaga Hisahiko 
Published: July 2012

AbstractThe formation of an iron(III) complex with a new multidentate ligand, Nα‐pyridoxyl‐L‐tryptophan(1, H2pltp), has been investigated thermodynamically and kinetically in an aqueous 0.10 mol dm−3 sodium perchlorate solution at 25°C. A 1:2(metal : ligand) complex of 1 forms with much higher stability constant (logβ12/mol−2 dm6 = 38.29±0.28) than the related complex, bis(pyridoxylidene‐L‐tryptophan)iron(III), having the azomethine group (log β12/mol−2 dm6 = 18.38±0.10 [3]). This effect was explained by the contribution of amino nitrogen of higher basicity to the thermodynamic stability. The complex formation reaction proceeds through two parallel pathways of Fe3+ +H3pltp+ and FeOH2+ +H4pltp2+ and also another pathway of FeOH2+ +H3pltp+ with slower coordination of the first ligand to iron(III). The mechanistic rate‐determining step for the formation of the complex was the coordination of the phenolato oxygen to a central metal atom, followed by the rapid donations of the amino nitrogen and carboxylato oxygen atoms.
Structure and morphology of gas phase deposited ice
Authors: Langel W. , Fleger H.‐W. , Knözinger E. 
Published: July 2012

AbstractAmorphous ice was prepared by deposition of H2O vapour diluted in heat exchange gases such as He or Ar at low temperatures (13 to 45 K). This technique is faster than the deposition of pure H2O vapour. The rapid sticking of condensing molecules on the cold solid leads to a poor short range order inside the grains. The high nucleation rate during vapour deposition results in small grain sizes and microporosity. Structure and morphology of the resulting amorphous ice samples were characterized by x‐ray diffraction. The radial distribution function was calculated from the diffraction data of pure ice and proved to be consistent with the Continuous Random Network model. Diffraction patterns of krypton layers on the amorphous ice reflect the morphology of the substrate: at the beginning micropores with a diameter of 15–20 Å and a volume of 0.045 cm3/g are filled. At higher mass coverages outer grain surfaces and large voids are covered by krypton.
The protonation constants of glycine in NaCl at 25 °C based on the pitzer and scatchard models data analysis by ridge regression
Authors: Fiol S. , Brandariz I. , Herrero R. , Vilariño T. , de Vicente M. Sastre 
Published: July 2012

AbstractWe have potentiometrically determined the protonation constants of glycine in NaCl solutions of variable ionic strength. The data thus obtained have been analysed by using the interaction models of Scatchard and Pitzer. The presence of multicollinearity among the explanatory variables of the model has been evidenced through the coefficients of the correlation matrix and the variance inflation factor (VIF). We have applied the ridge regression (RR) to address the problem arising' from multicollinearity and the results are critically compared with those obtained by ordinary least squares regression (OLS).
Zero kinetic energy (ZEKE) photoelectron spectrum and coincident mass spectra of methyl formate
Authors: Waterstradt Eckhard , Jung Rolf , Belling Thomas , Müller‐Dethlefs Klaus 
Published: July 2012

AbstractThe ZEKE photoelectron spectrum of methyl formate in a supersonic jet was recorded using multibunch VUV synchrotron radiation. The adiabatic ionisation potential is determined to 87 390 cm−1 (10.835 eV). Three yet unobserved normal modes of the electronic ground state (ν10, ν11, and ν12) and the progression of a mode previously assigned to ν4 are observed. Ab initio calculations reveal a large Duschinsky rotation upon ionisation of three modes implying that the ν4 progression corresponds to an OCO‐antisymmetrical stretch motion. The finer vibrational structure observed on the electronic ground state above 1500 cm−1 is considerably perturbed due to the anharmonicity of the potential surface.
How does a transition zone affect the electric field enhanced water dissociation in bipolar membranes?
Authors: Mafé Salvador , Ramirez Patricio , Manzanares José A. 
Published: July 2012

AbstractThe changes in the electric field in the space charge regions and the corresponding effect on the water dissociation rate when a transition zone exists between the layers of a bipolar membrane are theoretically studied. A quasi‐equilibrium approach based on the Poisson‐Boltzmann equation for the space charge interfacial regions is used. The transition zone acts to decrease significantly the water dissociation rate. However, for realistic values of the thickness δ of the transition zone and provided that the ohmic drop over δ be small, this decrease in the dissociation rate is not very dependent on δ. The results obtained give theoretical support to some recent experimental findings.
Surface phase transitions of solids. Influence of a surface on order‐disorder transformations in binary alloys
Authors: Peisl J. 
Published: July 2012

AbstractA report is given on a study of the order parameter and the order parameter fluctuations at the Fe3Al (110) surface when it approaches the order‐disorder phase transformation. X‐ray scattering under grazing incidence and exit was employed and gave the necessary surface sensitivity. The temperature dependence of the critical surface scattering at and around the (111) superstructure reflection was investigated. The critical behaviour is strongly influenced by the surface. The new surface exponents have been determined and are β1 = 0.75±0.06, γ‖ = –0.33±0.06, η‖ = 1.52±0.04 and ν = 0.60±0.15. The surface dominated phase transition belongs to the ordinary transition class. Scaling laws can be verified.
Surface melting: A density functional approach
Authors: Löwen H. , Ohnesorge R. , Wagner H. 
Published: July 2012

AbstractA microscopic theory of surface melting is described and applied to Lennard‐Jones systems. Our approach is based on density functional theory with the hard sphere fluid as a reference system. In particular we use a weighted density approximation which yields an accurate Lennard‐Jones bulk phase diagram. Within a practically free minimization of the functional, we find surface melting of a Lennard‐Jones crystal for different surface orientations. Furthermore the hard‐sphere crystal‐fluid interface and the hard‐sphere crystal at a hard wall are explored with density functional theory. It is found that the crystal‐fluid surface tension of hard spheres is extremely small and that the hard wall prefers to be covered by a hard‐sphere‐solid at solid‐liquid coexistence.
Surface diffusion: An STM view
Authors: Frenken J. W. M. , Kuipers L. , Hoogeman M. S. 
Published: July 2012

AbstractWe employ a high‐speed high‐temperature scanning tunneling microscope to investigate two manifestations of surface diffusion. The step fluctuations observed on metal surfaces are shown to be the result of the fast diffusive motion of pre‐existing kinks in the steps. We find that a high density of kinks can be induced by a minute concentration of impurities. At sufficiently high temperatures, surfaces can “jump” to physical contact with the tip of the microscope. Such jumps are followed by a “sintering” process in which a massive connecting neck rapidly builds up between the surface and the tip.
Structural and dynamical properties of surfaces and the effect of premelting
Authors: Schommers W. 
Published: July 2012

AbstractThe effect of premelting is of particular interest in connection with the theory of melting. In this paper, we discuss structural and dynamical properties of surfaces of semi‐infinite crystals as well as of nano‐clusters, which show the effect of premelting. The investigations are based on molecular dynamics calculations: Different models are used for the systematic study of the effect of premelting. In particular, the behaviour of the following functions have been studied: pair correlation function, generalized phonon density of states, and the mean‐square displacement as a function of time. The calculations have been done for krypton since for this substance a reliable interaction potential is available.
A temperature dependent LEED study of the Si(111) surface
Authors: Göbel H. , Mayer C. , Setzer C. , Kling B. , von Blanckenhagen P. , Schommers W. 
Published: July 2012

AbstractThe Si(111) surface shows spontaneous (7×7) reconstruction at low temperatures. At about 1130 K deconstruction to a (1×1) structure takes place. We have studied the reconstructed surface and the quenched, unreconstructed surface by low energy electron diffraction (LEED) as a function of temperature. A kinematical LEED data analysis has been performed in order to be able to discriminate between different structure models.
Phase transitions of two‐dimensional surface compounds at multicomponent alloy surfaces
Authors: Uebing Christian 
Published: July 2012

AbstractIn general the chemical composition of multicomponent alloy surfaces exhibit significant deviations from the bulk composition due to thermally activated segregation processes. Upon cosegregation epitaxially stabilized two‐dimensional surface compounds are formed on substrate surfaces with suitable orientation, e.g. CrN on Fe‐15%Cr‐N (100), CrC on Fe‐15%Cr‐C (100) and VC on Fe‐3%V‐C (100) and Fe‐3%Si‐0.04%V‐C (100). As indicated by sputter depth profiles the thicknesses of such surface compounds correspond to a monolayer.In some of these systems the temperature dependence of surface coverage displays phase transition behavior. On Fe‐3%Si‐0.04%V‐C (100) the VC surface compound is formed at temperatures up to 635 °C. Sharply above that temperature the VC surface compound vanishes. Simultaneously the onset of Si segregation is observed leading to a c(2×2) structure at saturation. Such behavior could be attributed to a temperature‐driven first order phase transition between VC surface compound and c(2×2) Si. A different type of surface phase transitions is observed on Fe‐15%Cr‐N (100). At temperatures T>600°C the two‐dimensional surface compound CrN is epitaxially stabilized on the alloy surface. Upon lowering the temperature the nucleation of three‐dimensional CrN surface precipitates is initiated according to the bulk phase diagram of the Fe‐Cr‐N system. Further growth of such CrN surface precipitates leads to thick CrN films on the substrate surface.Finally Monte Carlo simulations utilizing a lattice gas model of two interpenetrating square sublattices are presented, each sublattice may accommodate one type of adsorbed or segregated species M or X. It is shown that this model is well suited to describe surface compound formation and associated phase transitions.
Structure of the effective hamiltonian for liquid‐vapor interfaces
Authors: Napiórkowski M. 
Published: July 2012

AbstractA nonlocal and non‐Gaussian expression for the effective Hamiltonian of a fluctuating liquid‐vapor interface is derived from the density functional theory for inhomogeneous simple fluids. After applying a gradient expansion one obtains as the leading term the standard capillary‐wave Hamiltonian. The next to leading terms are proportional to the Gaussian curvature and to the mean curvature squared. Microscopic expressions for the coefficients in this expansion are derived. The breakdown of the gradient expansion for long‐range interparticle forces is pointed out; this break‐down is also reflected in the nonanalytical behavior of the (microscopically derived) wave‐vector‐dependent surface tension. The connection between recent scattering experiments and the derived Hamiltonian is discussed.
On the stiffness of an interface near a wall
Authors: Fisher Michael E. , Jin Albert J. , Parry Andrew O. 
Published: July 2012

AbstractThe relevance of the bare stiffness, (l), of an interface at distance l from a planar wall, for the renormalization‐group theory of critical‐wetting instabilities in short‐range, (d = 3)‐dimensional systems is briefly recalled. A careful derivation is presented of an expression for (l) at the van der Waals/mean field level in terms of the order‐parameter profile m∏(z, l) of a planar interface. The analysis completes and improves the treatment of Jin and Fisher [Phys. Rev. B 47, 7365 (1993)].
Gravity, confinement, and phase equilibria
Authors: Indekeu J. O. , Rogiers J. 
Published: July 2012

AbstractWe study a fluid or Ising lattice gas confined between two horizontal walls with separation L, in a gravitational field of strength g. For identical walls (with equal surface fields h1 = hL) the familiar capillary condensation and capillary criticality extend to non‐zero g. Finite‐size scaling predicts that the locus of criticality shrinks to g = 0 for L→∞, in the manner g α L−(βδ/ν+1). For opposing walls (with h1 = –hL) we confirm that bulk two‐phase coexistence is suppressed, for g = 0, to below the wetting temperature Tw. However, for small g (and h1 of appropriate sign) bulk two‐phase coexistence extends to higher temperatures that increase extremely rapidly with g, up to a maximum temperature that is shifted from the L = ∞ bulk critical point in the manner Tc,max(L)–Tc(∞)αL−1/ν, conform with finite‐size scaling.
Diffuse scattering of X‐rays and neutrons from surfaces and interfaces
Authors: Haase A. , Dietrich S. 
Published: July 2012

AbstractBased on a modified first Born‐approximation we derive a general expression for the kinematic cross‐section of x‐rays and neutrons impinging on an arbitrary interfacial structure. The scattering intensity is expressed in terms of the two‐point correlation function of the atomic number densities. Our approach takes into account the exact expression for the refraction of the penetrating waves at the mean interface profile, for example the multiple reflection occurring in a multilayer system, the evanescent waves under the condition of total reflection, or the distortion of the incoming plane wave due to the refraction at a smooth interface. Therefore our results allow a sophisticated analysis of the scattering data in order to extract the lateral correlations from the diffuse scattering intensity. To illustrate this formalism we discuss applications for particularly interesting systems such as liquid‐vapor interfaces, wetting films, and multilayers.
Wetting of heterogeneous substrates
Authors: Napiórkowski M. , Koch W. , Dietrich S. 
Published: July 2012

AbstractOn the basis of a microscopic density functional theory we investigate the structure of van der Waals fluids exposed to the long‐range potentials of spatially and chemically inhomogeneous substrates. As a paradigm of a spatial inhomogeneity we consider a wedge‐shaped substrate. The mean position of the interface between the liquidlike adsorbed film and the bulk vapor phase displays van der Waals tails. Our results differ from those obtained by a phenomenological approach which, under certain approximations, can be derived from the nonlinear integral equation for the interfacial profile. The numerical solution allows us to predict a scaling behavior for the excess coverage as function of the asymptotic film thickness. The chemical inhomogeneity under consideration consists of a flat substrate with two different species each occupying a quarter space. The asymptotic values of the finite film thicknesses are attained according to van der Waals tails. In both systems the formation of adsorbed films is determined by the line contribution to the free energy. For the patched substrate the diverging thickness of the liquid layer is associated with a logarithmic divergence of the line tension.
Divergence of the point tension at wetting
Authors: Abraham D. B. , Latrémolière F. , Upton P. J. 
Published: July 2012

AbstractThe line tension, (free energy associated with the line of contact) is expected to have interesting singular behaviour at the wetting transition, as has already been inferred from mean field theory and scaling arguments. In order to investigate this behaviour, we consider an exactly soluble two‐dimensional Ising model with appropriate wetting boundary conditions and investigate suitable definitions of , now a point tension, associated with the junction of an interface tilted with average angle θc and another lying along the substrate. Size‐dependent fluctuations in the point of contact indicate that be defined through a convolution sum. Hence ≈ ln (1/θc) as θc ↓ 0 (wetting transition), which can be understood as a consequence of the entropic repulsion of the tilted part of the interface against the substrate. This logarithmic divergence is consistent with the recent scaling hypothesis of Indekeu and Robledo.
Wetting dynamics. On the decay of metastable states near a first‐order wetting transition
Authors: Bausch R. , Blossey R. 
Published: July 2012

AbstractFor a system with a first‐order wetting transition we discuss the decay of metastable wetting layers by nucleation. The assumption of detailed balance implies that some essential properties of the decay process follow from statics alone. E.g., the lifetime of the metastable states is predominantly determined by the excess free energy of critical nuclei. The latter are either droplets on a microscopic layer or dents in a macroscopic layer on the wall of the system. We discuss the form and the excess free energy of the critical nuclei in various regions of the phase diagram.
Liquid/liquid interfacial instability in the vicinity of the critical point of a binary liquid mixture
Authors: Wolf H. , Woermann D. 
Published: July 2012

AbstractThe system 2‐butoxyethanol/water is used to study the dynamics of the instability of the liquid/liquid interface in the vicinity of the lower critical point of the system. The values of the viscosity parameter A and the interfacial parameter B which determine the shape of the interfacial instability are changed by varying temperature at which the experiments are carried out. The change of the shape of the interfacial region is monitored using a CCD‐video‐camera. The pictures of the liquid/liquid interface are analysed by determining the number of “viscous fingers”, the width of the mixing zone and the length of the liquid/liquid contour length as function of time. The analysis of the data is based on the work of Tryggvason and Aref (J. Fluid. Mech. 136, 1–30 (1983); 154, 287 (1985)).