Search results for "force"
showing 10 items of 3423 documents
Anomalous behavior of the second magnetization peak inLa1.81Sr0.19CuO4single crystals: Possible influence of two-band superconductivity
2008
We report an anomalous temperature $T$ variation of the field ${H}_{\text{on}}$ for the onset of the second magnetization peak in ${\text{La}}_{1.81}{\text{Sr}}_{0.19}{\text{CuO}}_{4}$ single crystals with the external magnetic field $H$ oriented parallel to the $c$ axis. While the peak field ${H}_{p}$ has a continuous decrease with increasing $T$, ${H}_{\text{on}}$ exhibits a sudden decrease for $T\ensuremath{\sim}11--15\text{ }\text{K}$. This behavior appears to be related to the particular $T$ dependence of the superfluid density in the case of two-band superconductivity affecting the $T$ variation of the elastic energy of the vortex system at low $H$.
Guided vortex motion in Nb films on facetted substrate surfaces
2003
Abstract Anisotropy of the pinning force in a superconductor can cause a guiding effect on the vortices, which leads to the appearance of new components in the galvanomagnetic quantities of the sample. In this case one can observe an additional odd magnetoresistive component with respect to magnetic field reversal. Furthermore, an even contribution to the Hall voltage is observed. Guided motion of vortices in Nb films on facetted α-Al2O3 (1 0 1 0) was found by measuring the longitudinal and transversal resistivities of three films with transport current directed parallel, perpendicular and at an angle of 45° with respect to the facet ridges. Field inversion was used to separate the even and…
Atomic-resolution imaging of the polar (0001¯) surface of LiNbO3in aqueous solution by frequency modulation atomic force microscopy
2012
S. Rode,1 R. Holscher,2 S. Sanna,2 S. Klassen,1 K. Kobayashi,3 H. Yamada,3 W. G. Schmidt,2 and A. Kuhnle1,* 1Institut fur Physikalische Chemie, Fachbereich Chemie, Johannes Gutenberg-Universitat Mainz, Jakob-Welder-Weg 11, 55099 Mainz, Germany 2Lehrstuhl fur Theoretische Physik, Universitat Paderborn, 33095 Paderborn, Germany 3Department of Electronic Science and Engineering, Kyoto University, Katsura, Nishikyo, Kyoto 615-8510, Japan (Received 31 March 2012; revised manuscript received 12 June 2012; published 29 August 2012)
Atomistic Simulations of Solid Friction
2002
Friction between two solid bodies in relative sliding motion takes place on a large spectrum of length and time scales: From the nanometer/second scale in an atomic force microscope up to the extremely macroscopic scales of tectonic motion. Despite our familiarity with the effects of friction, fundamental questions remain unanswered. The atomistic origins of well-established phenomenological friction laws are controversial. Many explanations, seemingly well-established, have recently been called into question by new experimental results. Computer simulations have also revealed flaws in previous theoretical approaches and led to new insights into the atomistic processes responsible for frict…
Breaking Symmetry Effects on Heavy Tetraquarks
2017
In this contribution we present symmetry arguments that can be applied to study the stability of four-quark systems with two different masses. The role played by different symmetry breaking effects and the non-Abelian algebra of color forces is discussed in detail. In the particular case of hidden-flavor all-heavy four-quark states, QQ (Q) over bar(Q) over bar, the system becomes unstable for standard color-additive models. Differences and similarities between Qq (Q) over bar(q) over bar and QQ (q) over bar(q) over bar configurations are presented. In the latter case, its stability when the mass ratio M/m increases was established almost forty years ago. In the former case, we find a kind o…
Simultaneous Determination of Force Constants and Dipole Moment Derivatives of Methane.
1998
The expressions of the effective Hamiltonian and dipole moment spectroscopic parameters in the tetrahedral formalism are used simultaneously to fit the force field and dipole moment derivatives of the methane molecule. Data, the so-called "observed parameters," are the values of the spectroscopic parameters determined from the frequencies and line strengths analyses. The ambiguities of most parameters (in the polyad scheme) are treated consistently with the Hamiltonian reduction chosen in the frequency analyses. As an illustration, the method is applied to the tetrahedral XY4 isotopic species only. The quadratic and cubic force field constants have been determined in addition to the linear …
Emergence of Coherence through Variation of Intermolecular Distances in a Series of Molecular Dimers
2015
Quantum coherences between electronically excited molecules are a signature of entanglement and play an important role for energy transport in molecular assemblies. Here we monitor and analyze for a homologous series of molecular dimers embedded in a solid host the emergence of coherence with decreasing intermolecular distance by single-molecule spectroscopy and quantum chemistry. Coherent signatures appear as an enhancement of the purely electronic transitions in the dimers which is reflected by changes of fluorescence spectra and lifetimes. Effects that destroy the coherence are the coupling to the surroundings and to vibrational excitations. Complementary information is provided by excit…
Charge compensation by long-period reconstruction in strongly polar lithium niobate surfaces
2013
The microscopic structure of the polar (000$\overline{1}$) and (0001) surfaces of lithium niobate is investigated by atomic-resolution frequency modulation atomic force microscopy and first-principles calculations. It is found that the surface reconstructs at annealing temperatures sufficiently high to drive off external adsorbates. In particular a ($\sqrt{7}\ifmmode\times\else\texttimes\fi{}\sqrt{7}$)$R$19.1${}^{\ensuremath{\circ}}$ reconstruction is found for the (000$\overline{1}$) surface. Density-functional theory calculations show that---apart from the $(\sqrt{7}\ifmmode\times\else\texttimes\fi{}\sqrt{7})$---a series of adatom-induced surface reconstructions exist that lower the surfa…
Status of the EPIC thin and medium filters on-board XMM-Newton after more than 10 years of operation I: laboratory measurements on back-up filters
2013
After more than ten years of operation of the EPIC camera on board the X-ray observatory XMM-Newton, we have reviewed the status of its Thin and Medium filters by performing both laboratory measurements on back-up filters, and analysis of data collected in-flight. We have selected a set of Thin and Medium back-up filters among those still available in the EPIC consortium, and have started a program to investigate their status by different laboratory measurements including: UV/VIS transmission, X-ray transmission, RAMAN IR spectroscopy, X-Ray Photoelectron Spectroscopy, and Atomic Force Microscopy. We report the results of the measurements conducted up to now, and point out some lessons lear…
Escape Transition of a Grafted Polymer Chain
2000
The escape transition of a flexible polymer chain of chain length N, end-grafted at a hard wall and compressed by a piston of radius R in good solvent conditions, is studied by Monte Carlo simulation and by phenomenological arguments. In contrast to previous theories which have predicted a jump in the force f at a critical value H t of the height H of the piston above the wall, we find that the transition (which is sharp only for N → ∞) is characterized by a flat region of f in the f — H isotherm, i. e. a jump in the height occurs at the transition from H esc , t to H imptt , with (H imp , t — H esc , t )/H esc , t ≈ 0.26. At the transition the constant force f t is predicted and observed t…