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81.
Alexander Jesacher Christian Maurer Severin Fürhapter Andreas Schwaighofer Stefan Bernet Monika Ritsch-Marte 《Optics Communications》2008,281(8):2207-2212
We propose a non-holographic method to create line traps of arbitrary shape in the sample plane. Setting the phase gradient along theses lines gives control over the transverse forces acting on the confined particles. Phase structures, displayed on a spatial light modulator, are optically processed by a spiral phase filter and imaged onto the object plane of a microscope objective. The resulting bright line structures can be used to trap microparticles. Additionally, they exert transverse scattering forces, which can be exploited for inducing orbital motions or for creating “attracting” or “repelling” points, respectively. We give theoretical and experimental evidence that these scattering forces are proportional to the curvature of the line tweezers. 相似文献
82.
Zhibin Lin 《Applied Surface Science》2007,253(15):6295-6300
The electron temperature dependences of the electron-phonon coupling factor, electron heat capacity and thermal conductivity are investigated for Ni in a range of temperatures typically realized in femtosecond laser material processing applications, from room temperature up to temperatures of the order of 104 K. The analysis is based on the electronic density of states obtained through the electronic structure calculations. Thermal excitation of d band electrons is found to result in a significant decrease in the strength of the electron-phonon coupling, as well as large deviations of the electron heat capacity and the electron thermal conductivity from the commonly used linear temperature dependences on the electron temperature. Results of the simulations performed with the two-temperature model demonstrate that the temperature dependence of the thermophysical parameters accounting for the thermal excitation of d band electrons leads to higher maximum lattice and electron temperatures achieved at the surface of an irradiated Ni target and brings the threshold fluences for surface melting closer to the experimentally measured values as compared to the predictions obtained with commonly used approximations of the thermophysical parameters. 相似文献
83.
An investigation on the possibility of enhancement of soft X-ray (SXR) (900–1600 eV) emission from a fast miniature plasma focus (FMPF) device of 235 J (at 14 kV) storage energy through doping of operating gas was performed. Neon (Ne), the operating gaseous medium, was doped with krypton (Kr) in different volumetric ratios at various operating pressures ranging from 2 to 14 mbar. The 1% Kr doping increased the average optimum SXR emission efficiency from 0.47% to 0.6% without enhancing the hard X-ray (HXR) (>1600 eV) emission. The Kr doping influenced the major pinching characteristics such as focusing efficiency and time to pinch with consequential effect on X-ray emissions. Synchronous operation of the 4 pseudo-spark gap (PSG) switches was mandatory for efficient discharge current delivery to the electrodes. A drastic improvement in the pinching efficiency was obtained with replacement of old and worn out PSG switches with the new ones. Optical imaging of current sheath dynamics was performed using gated ICCD camera to verify the normal operation of the device after the PSGs replacement. A numerical simulation analysis on the 2 cm long stainless steel tapered anode, used in this study, was done to predict the maximum SXR emission efficiency and the peak operating gas pressure. An analysis on the amount of SXR fluence generated at the source position and the proportion of it reaching the target position is also reported. 相似文献
84.
Jian Hua Yin 《数学学报(英文版)》2014,30(3):389-394
Let G be an arbitrary spanning subgraph of the complete graph Kr+1 on r+1 vertices and Kr+1-E(G) be the graph obtained from Kr+1 by deleting all edges of G.A non-increasing sequence π=(d1,d2,...,dn) of nonnegative integers is said to be potentially Kr+1-E(G)-graphic if there is a graph on n vertices that has π as its degree sequence and contains Kr+1-E(G) as a subgraph.In this paper,a characterization of π that is potentially Kr+1-E(G)-graphic is given,which is analogous to the Erdo s–Gallai characterization of graphic sequences using a system of inequalities.This is a solution to an open problem due to Lai and Hu.As a corollary,a characterization of π that is potentially Ks,tgraphic can also be obtained,where Ks,t is the complete bipartite graph with partite sets of size s and t.This is a solution to an open problem due to Li and Yin. 相似文献
85.
J. Larsson A. Allen P.H. Bucksbaum R.W. Falcone A. Lindenberg G. Naylor T. Missalla D.A. Reis K. Scheidt A. Sjögren P. Sondhauss M. Wulff J.S. Wark 《Applied Physics A: Materials Science & Processing》2002,75(4):467-478
We have employed time-resolved X-ray diffraction with picosecond temporal resolution to measure the time-dependent rocking
curves of laser-irradiated asymmetrically cut single InSb crystals. Coherent acoustic phonons were excited in the crystals
by irradiation with 800-nm, 100-fs laser pulses at irradiances between 0.25 and 12 mJ/cm2. The induced time-dependent strain profiles (corresponding to the coherent phonons) were monitored by diffracting collimated,
monochromatic pulses of X-rays from the irradiated crystals. Recording of the diffracted radiation with a fast low-jitter
X-ray streak camera resulted in an overall temporal resolution of better than 2 ps. The strain associated with the coherent
phonons modifies the rocking curve of the crystal in a time-dependent manner, and the rocking curve is recorded by keeping
the angle of incidence of the X-rays upon the crystal fixed, but varying the energy of the incident X-rays around a central
energy of 8.453 keV (corresponding to the peak of the rocking curve of the unperturbed crystal). The observed time-dependent
diffraction from the irradiated crystals is in reasonable agreement with simulations over a wide range of energies from the
unperturbed rocking-curve peak.
Received: 22 March 2002 / Revised version: 25 March 2002 / Published online: 6 June 2002 相似文献
86.
S. Residori N. Olivi-Tran E. Pampaloni 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,12(1):15-20
In the case of 2D optical patterns, frustration comes from the interplay between the physical constraints (light-matter interaction)
and the geometrical constraints (cavity length and structure). Depending on the dynamical parameters, we are able to single
out two distinct behaviors. For small diffusion and close to threshold, the system is forced to fulfill the geometrical constraints
giving rise to a phase dynamics of quasicrystals. For larger diffusion, the system fragmentates into spatial domains giving
rise to a competition between different patterns. By means of a geometrical argument, we show that the spatial distribution
of domains is related to the symmetry imposed by the geometrical constraint and that the domain borders are disinclination
defects. These defects being the nucleation centers of spatial domains, they trigger the onset of pattern competition.
Received 27 December 1999 and Received in final form 29 March 2000 相似文献
87.
The potential induced by the electron-optical-phonon interaction in a quantum well (QW) is investigated by means of the perturbation
theory. We consider the interactions of an electron with both bulklike confined longitudinal optical (LO) phonons and four
branches of interface optical (IO) phonons. The spatial distributionV
i(z) of the induced potential for QW structures with different heterolayer compositions and different well widths is calculated
in detail. The numerical results show that the heterolayer composition of the QW plays an important role in determining the
shape ofV
i(z) and that the existence of IO-phonons is important to the electronic states in QWs. 相似文献
88.
Y. Fujita H. Fujita T. Adachi G.P.A. Berg E. Caurier H. Fujimura K. Hara K. Hatanaka Z. Janas J. Kamiya T. Kawabata K. Langanke G. Martınez-Pinedo T. Noro E. Roeckl Y. Shimbara T. Shinada S.Y. van der Werf M. Yoshifuku M. Yosoi R.G.T. Zegers 《The European Physical Journal A - Hadrons and Nuclei》2002,13(4):411-418
Under the assumption that isospin is a good quantum number, symmetry is expected for the transitions from the ground states
of T = 1, T
z = ±1 nuclei to the common excited states of the T
z = 0 nucleus situated between the two nuclei. The symmetry can be studied by comparing the strengths of Gamow-Teller (GT)
transitions obtained from a (p, n)-type charge-exchange reaction on a target nucleus with T
z = 1 with those from the β-decay of the T
z = - 1 nucleus. The A = 58 system is the heaviest for which such a comparison is possible. As a part of the symmetry study, we measured the GT
transitions from 58Ni (T
z = 1) to 58Cu (T
z = 0) by using the zero-degree (3
He, t) reaction at 150 MeV/nucleon. With the achieved resolution of 50 keV, many hitherto unresolved GT states have been identified.
The GT transition strengths were obtained for states up to 8 MeV excitation, i.e., near to the Q window limitation ( Q
EC = 9.37 MeV) of the β-decay from 58Zn (T
z = - 1) to 58Cu. The strength distribution is compared with that from shell-model calculations.
Received: 24 November 2001 / Accepted: 30 January 2002 相似文献
89.
A. La Magna R. Pucci 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(4):421-429
In this paper we have introduced a variational approach to investigate the ground state of a model which includes both the
Holstein electron-phonon interaction and the extended Hubbard electron-electron interaction. We have considered a variational
state for the phonon subsystem which generalizes the previous used forms. This state allows to take into account the possibility
of extended phonon mediated correlations. The effective electron Hamiltonian, which we have obtained, includes first and second
neighbor electron-electron interaction terms. We have treated exactly, through a Lanczos method, this effective model in the
one-dimensional case. We have applied our method to two Bechgaard salts and in these cases we have estimated the correlation
parameters. We have shown that the introduction of electron-phonon interaction allows an estimate of the on site U and nearest-neighbor V Coulomb repulsion, which are in agreement with the experimental optical spectra of the above mentioned two compounds.
Received: 30 October 1997 / Revised: 28 January 1998 / Accepted: 10 April 1998 相似文献
90.
We extend the theory of large polarons in the frame of a semi classical model. We analyse two physical effects in which the discreteness of the periodic lattice plays a major role: i) In addition to standard Holstein polarons, we show the existence of braggons which are polarons whose energy lies in a lattice gap. According to the type of gap considered, some of the them are ordinary solitons, some others are vector-solitons. ii) The pinning (or Peierls Nabarro) effect of the lattice on the polarons. We show that the coupling of the electrons with acoustic phonons is able to produce polarons or bipolarons in crystallographic situations where the coupling with optical phonons does'nt. The existence of multidimensional polarons and bipolarons is investigated, and we find interesting possibilities in dimension D=2. The binding energy and effective mass of the polarons are determined in the frame of the model, and their dynamical stability is analysed. We also show the existence, for D=1, of tripolarons in which two energy levels are occupied in the potential well created by the electron-lattice interaction. Finally the conditions of validity of the semi-classical approximation are given. 相似文献