共查询到20条相似文献，搜索用时 31 毫秒
1.
M. A. R. Matos V. M. F. Morais C. C. S. Sousa M. V. Roux R. Notario 《Molecular physics》2013,111(13-14):1789-1796
The standard (p°?=?0.1?MPa) molar energies of combustion in oxygen, at T?=?298.15?K, of 1-naphthalenemethanol and 2-naphthalenemethanol were measured by static bomb calorimetry. The values of the standard molar enthalpies of sublimation, at T?=?298.15?K, were obtained by Calvet microcalorimetry. Combining these results the standard molar enthalpies of formation of the compounds, in the gas phase, at T?=?298.15?K, have been calculated.
Energetics of naphthalene derivatives, IV+: a calorimetric and calculational thermochemical study of the isomeric naphthalenemethanols
Published online:
04 December 2010Table 相似文献
2.
Studies of single-particle momentum distributions in light atoms and molecules are reviewed with specific emphasis on experimental measurements using the deep inelastic neutron scattering technique at eV energies. The technique has undergone a remarkable development since the mid-1980s, when intense fluxes of epithermal neutrons were made available from pulsed neutron sources. These types of measurements provide a probe of the short-time dynamics of the recoiling atoms or molecules as well as information on the local structure of the materials. The paper introduces both the theoretical framework for the interpretation of deep inelastic neutron scattering experiments and thoroughly illustrates the physical principles underlying the impulse approximation from light atoms and molecules. The most relevant experimental studies performed on a variety of condensed matter systems in the last 20 years are reviewed. The experimental technique is critically presented in the context of a full list of published work. It is shown how, in some cases, these measurements can be used to extract directly the effective Born–Oppenheimer potential. A summary of the progress made to date in instrument development is also provided. Current data analysis and the interpretation of the results for a variety of physical systems is chosen to illustrate the scope and power of the method. The review ends with a brief consideration of likely developments in the foreseeable future. Particular discussion is given to the use of the VESUVIO spectrometer at ISIS.
Measurement of momentum distribution of lightatoms and molecules in condensed matter systems using inelastic neutron scattering
Published online:
19 February 2007Table 相似文献
3.
《光谱学快报》2013,46(4):501-516
ABSTRACT A spectrophotometric and a spectrofluorimetric methods are developed for the determination of two nonsteroidal anti-inflammatory drugs meloxicam I and tenoxicam II in the presence of their degradation products, namely 5-methyl-2-aminothiazole (III), benzothiazine carboxylic acid (IV), for meloxicam, pyridine-2-amine (V) and methyl 4-hydroxy-2-methyl-2H-thienol[2,3-e]1,2-thiazine-3-carboxylate-1, 1-dioxide (VI) for tenoxicam, Fig. 1.
STABILITY-INDICATING METHODS FOR DETERMINATION OF MELOXICAM AND TENOXICAM IN THE PRESENCE OF THEIR DEGRADATION PRODUCTS
Published online:
01 September 2006 Figure 1. The structure of the studied drugs and their degradation products. 相似文献
4.
Disorder and long-range interactions are two of the key components that make material failure an interesting playfield for the application of statistical mechanics. The cornerstone in this respect has been lattice models of the fracture in which a network of elastic beams, bonds, or electrical fuses with random failure thresholds are subject to an increasing external load. These models describe on a qualitative level the failure processes of real, brittle, or quasi-brittle materials. This has been particularly important in solving the classical engineering problems of material strength: the size dependence of maximum stress and its sample-to-sample statistical fluctuations. At the same time, lattice models pose many new fundamental questions in statistical physics, such as the relation between fracture and phase transitions. Experimental results point out to the existence of an intriguing crackling noise in the acoustic emission and of self-affine fractals in the crack surface morphology. Recent advances in computer power have enabled considerable progress in the understanding of such models. Among these partly still controversial issues, are the scaling and size-effects in material strength and accumulated damage, the statistics of avalanches or bursts of microfailures, and the morphology of the crack surface. Here we present an overview of the results obtained with lattice models for fracture, highlighting the relations with statistical physics theories and more conventional fracture mechanics approaches.
Statistical models of fracture
Published online:
28 November 2010Table 相似文献
5.
Most studies on granular physics have focused on dry granular media, with no liquids between the grains. However, in geology and many real world applications (e.g. food processing, pharmaceuticals, ceramics, civil engineering, construction, and many industrial applications), liquid is present between the grains. This produces inter-grain cohesion and drastically modifies the mechanical properties of the granular media (e.g. the surface angle can be larger than 90 degrees). Here we present a review of the mechanical properties of wet granular media, with particular emphasis on the effect of cohesion. We also list several open problems that might motivate future studies in this exciting but mostly unexplored field.
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6.
F. Sciortino 《物理学进展》2013,62(6-7):471-524
This review focuses on recent developments in the theoretical, numerical and experimental study of slow dynamics in colloidal systems, with a particular emphasis on the glass transition phenomenon. Colloidal systems appear to be particularly suited for tackling the general problem of dynamic arrest, since they show a larger flexibility compared to atomic and molecular glasses because of their size and the possibility of manipulating the physical and chemical properties of the samples. Indeed, a wealth of new effects, not easily observable in molecular liquids, have been predicted and measured in colloidal systems. The slow dynamic behavior of three classes of colloidal suspension is reviewed – hard colloids, short-range attractive colloids and soft colloidal systems – selecting the model systems among the most prominent candidates for grasping the essential features of dynamic arrest. Emphasis is on the possibility of performing a detailed comparison between experimental data and theoretical predictions based on the mode coupling theory of the glass transition. Finally, the importance of understanding the system's kinetic arrest phase diagram, i.e. the regions in phase space where disordered arrested states can be expected, is stressed. When and how these states are kinetically stabilized with respect to the ordered lowest free energy phases is then examined in order to provide a framework for interpreting and developing new ideas in the study of new materials.
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7.
We review the present state of understanding of solid friction at low velocities and for systems with negligibly small wear effects. We first analyze in detail the behavior of friction at interfaces between macroscopic hard rough solids, whose main dynamical features are well described by the Rice–Ruina rate and state-dependent constitutive law. We show that it results from two combined effects: (i) the threshold rheology of nanometer-thick junctions jammed under confinement into a soft glassy structure and (ii) the geometric aging, i.e. slow growth of the real area of contact via asperity creep interrupted by sliding. Closer analysis leads to identifying a second aging-rejuvenation process, at work within the junctions themselves. We compare the effects of structural aging at such multicontact, very highly confined, interfaces with those met under different confinement levels, namely boundary lubricated contacts and extended adhesive interfaces involving soft materials (hydrogels, elastomers). This leads us to propose a classification of frictional junctions in terms of the relative importance of jamming and adsorption-induced metastability.
Solid friction from stick–slip down to pinning and aging
Published online:
28 November 2010Table 相似文献
8.
Although nineteen years have passed since the discovery of high temperature cuprate superconductivity 1, there is still no consensus on its physical origin. This is in large part because of a lack of understanding of the state of matter out of which the superconductivity arises. In optimally and underdoped materials, this state exhibits a pseudogap at temperatures large compared to the superconducting transition temperature 2, 3. Although discovered only three years after the pioneering work of Bednorz and Müller, the physical origin of this pseudogap behavior and whether it constitutes a distinct phase of matter is still shrouded in mystery. In the summer of 2004, a band of physicists gathered for five weeks at the Aspen Center for Physics to discuss the pseudogap. In this perspective, we would like to summarize some of the results presented there and discuss the importance of the pseudogap phase in the context of strongly correlated electron systems.
The pseudogap: friend or foe of high T c ?
Published online:
19 February 2007Table 相似文献
9.
A large number of multifaceted quantum transport processes in molecular systems and physical nanosystems, such as e.g. nonadiabatic electron transfer in proteins, can be treated in terms of quantum relaxation processes which couple to one or several fluctuating environments. A thermal equilibrium environment can conveniently be modelled by a thermal bath of harmonic oscillators. An archetype situation provides a two-state dissipative quantum dynamics, commonly known under the label of a spin-boson dynamics. An interesting and nontrivial physical situation emerges, however, when the quantum dynamics evolves far away from thermal equilibrium. This occurs, for example, when a charge transferring medium possesses nonequilibrium degrees of freedom, or when a strong time-dependent control field is applied externally. Accordingly, certain parameters of underlying quantum subsystem acquire stochastic character. This may occur, for example, for the tunnelling coupling between the donor and acceptor states of the transferring electron, or for the corresponding energy difference between electronic states which assume via the coupling to the fluctuating environment an explicit stochastic or deterministic time-dependence. Here, we review the general theoretical framework which is based on the method of projector operators, yielding the quantum master equations for systems that are exposed to strong external fields. This allows one to investigate on a common basis, the influence of nonequilibrium fluctuations and periodic electrical fields on those already mentioned dynamics and related quantum transport processes. Most importantly, such strong fluctuating fields induce a whole variety of nonlinear and nonequilibrium phenomena. A characteristic feature of such dynamics is the absence of thermal (quantum) detailed balance.
Quantum dynamics in strong fluctuating fields
Published online:
19 February 2007Table 相似文献
10.
C. H. Marrows 《物理学进展》2013,62(8):585-713
Electrical currents flowing in ferromagnetic materials are spin-polarised as a result of the spin-dependent band structure. When the spatial direction of the polarisation changes, in a domain structure, the electrons must somehow accommodate the necessary change in direction of their spin angular momentum as they pass through the wall. Reflection, scattering, or a transfer of angular momentum onto the lattice are all possible outcomes, depending on the circumstances. This gives rise to a variety of different physical effects, most importantly a contribution to the electrical resistance caused by the wall, and a motion of the wall driven by the spin-polarised current. Historical and recent research on these topics is reviewed.
Spin-polarised currents and magnetic domain walls
Published online:
19 February 2007Table 相似文献
11.
Michael Zaiser 《物理学进展》2013,62(1-2):185-245
From the traditional viewpoint of continuum plasticity, plastic deformation of crystalline solids is, at least in the absence of so-called plastic instabilities, envisaged as a smooth and quasi-laminar flow process. Recent theoretical and experimental investigations, however, demonstrate that crystal plasticity is characterized by large intrinsic spatio-temporal fluctuations with scale-invariant characteristics: In time, deformation proceeds through intermittent bursts with power-law size distributions; in space, deformation patterns and deformation-induced surface morphology are characterized by long-range correlations, self-similarity and/or self-affine roughness. We discuss this scale-invariant behaviour in terms of robust scaling associated with a non-equilibrium critical point (‘yielding transition’).
Scale invariance in plastic flow of crystalline solids
Published online:
01 February 2007Table 相似文献
12.
13.
J. A. Åström 《物理学进展》2013,62(3-4):247-278
Recent developments in statistical models for fragmentation of brittle material are reviewed. The generic objective of these models is understanding the origin of the fragment size distributions (FSDs) that result from fracturing brittle material. Brittle fragmentation can be divided into two categories: (1) Instantaneous fragmentation for which breakup generations are not distinguishable and (2) continuous fragmentation for which generations of chronological fragment breakups can be identified. This categorization becomes obvious in mining industry applications where instantaneous fragmentation refers to blasting of rock and continuous fragmentation to the consequent crushing and grinding of the blasted rock fragments. A model of unstable cracks and crack-branch merging contains both of the FSDs usually related to instantaneous fragmentation: the scale invariant FSD with the power exponent (2?1/D) and the double exponential FSD which relates to Poisson process fragmentation. The FSDs commonly related to continuous fragmentation are: the lognormal FSD originating from uncorrelated breakup and the power-law FSD which can be modeled as a cascade of breakups. Various solutions to the generic rate equation of continuous fragmentation are briefly listed. Simulations of crushing experiments reveal that both cascade and uncorrelated fragmentations are possible, but that also a mechanism of maximizing packing density related to Apollonian packing may be relevant for slow compressive crushing.
Statistical models of brittle fragmentation
Published online:
28 November 2010Table 相似文献
14.
15.
Matthias Eschrig 《物理学进展》2013,62(1-2):47-183
We review recent experimental and theoretical results on the interaction between single-particle excitations and collective spin excitations in the superconducting state of high-Tc cuprates. We concentrate on the traces that sharpen features in the magnetic-excitation spectrum (measured by inelastic neutron scattering) and imprint in the spectra of single-particle excitations (measured, e.g. by angle-resolved photoemission spectroscopy, tunnelling spectroscopy, and indirectly also by optical spectroscopy). The ideal object to obtain a quantitative picture for these interaction effects is a spin-1 excitation around 40?meV, termed ‘resonance mode’. Although the total weight of this spin-1 excitation is small, the confinement of its weight to a rather narrow momentum region around the antiferromagnetic wavevector makes it possible to observe strong self-energy effects in parts of the electronic Brillouin zone. Notably, the sharpness of the magnetic excitation in energy has allowed these self-energy effects to be traced in the single-particle spectrum rather precisely. Namely, the doping and temperature dependence together with the characteristic energy and momentum behaviour of the resonance mode has been used as a tool to examine the corresponding self-energy effects in the dispersion and in the spectral line-shape of the single-particle spectra, and to separate them from similar effects due to the electron–phonon interaction. This leads to the unique possibility to single out the self-energy effects due to the spin–fermion interaction and to directly determine the strength of this interaction in high-Tc cuprate superconductors. The knowledge of this interaction is important for the interpretation of other experimental results as well as for the quest for the still unknown pairing mechanism in these interesting superconducting materials.
The effect of collective spin-1 excitations on electronic spectra in high- Tc superconductors
Published online:
01 February 2007Table 相似文献
16.
《物理学进展》2013,62(4):263-376
Memento, homo, qui pulvis est et pulverem reverteris. Genesis 3 Polvos serán, mas polvo enamorado. Francisco de Quevedo The physics of granular materials in ambient gases is governed by interparticle forces, gas–particle interaction, geometry of particle positions and geometry of particle contacts. At low consolidations these are strongly dependent on the external forces, boundary conditions and on the assembling procedure. For dry fine powders of micron and sub-micron particle size interparticle attractive forces are typically much higher than particle weight, and particles tend to aggregate. Because of this, cohesive powders fracture before breaking, flow and avalanche in coherent blocks much larger than the particle size. Similarly the drag force for micron sized particles is large compared to their weight for velocities as low as 1?mm/s. Due to this extreme sensitivity to interstitial gas flow, powders transit directly from plastic dense flows to fluidization without passing through collisional regimes with negligible gas interaction. These two features, strong attractive forces and strong gas interaction make powder behaviour differ qualitatively from the behaviour of large, noncohesive grains. In this paper we investigate the implications of these two features on the bulk powder behaviour. More in particular, the aim of this paper is to examine the relationship between attractive interparticle forces at grain level, with solid bulk properties at low consolidations (solid fraction, stresses), fluidization (aggregation, settling) and flow regime boundaries (plastic flow, inertial flow, fluidization and suspension). Many of the experimental results reported here are for dry and uncharged fine powders made of polymer particles of the order of 10 microns in diameter. However, the basic concepts and methodology are of general applicability.
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17.
Charles S. Fadley 《Synchrotron Radiation News》2013,26(5):26-31
Traditional angle-resolved photoemission (ARPES) with excitation in the ca. 20 to 150 eV range has clearly evolved to be the technique of choice for studying the electronic structure of surfaces and complex new strongly correlated and magnetic materials. However, it is clear that ARPES with excitation only up to 150 eV or so remains a very surface-sensitive probe, thus necessitating careful in-situ sample treatment, cleaving, or even synthesis to avoid the measurement of surface-associated artifacts. A key measure of this surface sensitivity is the electron inelastic mean free path (IMFP orΛe), which measures the mean depth of electron emission without inelastic scattering, and both experimental [1, 2] and theoretical [3] IMFP studies showing that the only reliable way to increase bulk or buried layer/interface sensitivity for all material types is to go to higher photon energies in the soft X-ray (ca. 0.5–2 keV) or hard X-ray (ca. 2–10 keV) regime. 相似文献
18.
T. Földes D. Golebiowski T.P. Softley G. Di Lonardo L. Fusina 《Molecular physics》2014,112(18):2407-2418
Jet-cooled spectra of 14NH3 and 15NH3 in natural abundance were recorded using cavity ring-down (CRDS, 6584–6670 cm?1) and cavity enhanced absorption (CEAS, 6530–6700 cm?1) spectroscopy. Line broadening effects in the CRDS spectrum allowed lines with J ″-values between 0 and 3 to be identified. Intensity ratios in 14NH3 between the jet-cooled CRDS and literature room-temperature data from Sung et al. (J. Quant. Spectrosc. Radiat. Transfer, 113 (2012), 1066) further assisted the line assignments. Ground state combination differences were extensively used to support the assignments, providing reliable values for J, K and inversion symmetry of the ground state vibrational levels. CEAS data helped in this respect for the lowest J lines, some of which are saturated in the CRDS spectrum. Further information on a/s doublets arose from the observed spectral structures. Thirty-two transitions of 14NH3 were assigned in this way and a limited but significant number (19) of changes in the assignments results, compared to Sung et al. or to Cacciani et al. (J. Quant. Spectrosc. Radiat. Transfer, 113 (2012), 1084). Sixteen known and 25 new low-J transitions were identified for 15NH3 in the CRDS spectrum but the much scarcer literature information did not allow for any more refined assignment. The present line position measurements improve on literature values published for 15NH3 and on some line positions for 14NH3. 相似文献
19.
The thermodynamic behaviour of two-dimensional single-component elastic crystalline solids is developed: the surface Euler's equation, the surface Gibbs equation, the surface Gibbs–Duhem equation, and the conditions to be expected at equilibrium, including the stress-deformation behaviour of the crystal. The analysis recognizes that the surface Helmholtz free energy is an explicit function of the lattice vectors defining the crystalline structure. As an application, we obtain the stress-deformation behaviour of single-wall carbon nanotubes which are composed of a regular two-dimensional array of hexagonal lattices of carbon atoms. Using two potentials, Tersoff [1]–Brenner [2] and Brenner et al. [3] to describe interatomic potentials and hence the specific surface Helmholtz free energy, we compute the surface elastic properties for the single-wall carbon nanotubes. These are compared with the available experimental values. 相似文献
20.
Kai-Bin Fu 《哲学杂志》2013,93(15):1873-1882
Abstract Si et al. [1] pointed out that it was inappropriate to use continuity of displacement at interfaces during phase transitions or in the case of reactions at interfaces as in the case of oxidation, since appropriate reference configurations cannot be identified. They instead derived a new compatibility constraint, when atleast one of the adjoining phases is crystalline. The test of these ideas offered by Slattery et al. [2] was successful, but it likely was too simple, since the deformations were so small. A more stringent and successful test has recently been offered by [3]. Here, we analyze oxidation on the surface of a cylinder both using an extension of the compatibility constraint and using continuity of displacement, comparing the results with the experimental observations of Imbrie and Lagoudas [4]. 相似文献