共查询到20条相似文献,搜索用时 15 毫秒
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V.A Elyukhin S.F Díaz Albarrn 《Physica E: Low-dimensional Systems and Nanostructures》2005,28(4):552-555
Self-assembling of isoelectronic C and Sn impurities in Ge is predicted. The formation of the 1C4Sn tetrahedral cells is thermodynamically profitable in Ge-rich CxSnyGe1−x−y (4x<y) alloys in the ultra dilute C impurity limit with 1×10-8x1×10-3. The concentrations of Sn atoms when all C atoms are surrounded only by Sn atoms are estimated for the lower molecular beam epitaxy, intermediate annealing and higher bulk crystallization temperatures. The origin of this phenomenon is a considerable decrease of the strain energy after self-assembling. The same self-assembling in Si is thermodynamically non-profitable due to the large cohesive energy of Si–C chemical bonds. 相似文献
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The effect of intermolecular interactions on photoluminescence of a porphyrin side-chain polymer 下载免费PDF全文
Photoluminescence properties and exciton decay dynamics in a porphyrin side-chain
polymer, poly[porphyrin acrylate- acrylonitrile (abbreviated p[(por)A-AN]), have
been investigated by femtosecond time-resolved photoluminescence spectroscopy. All
the luminescences of p[(por)A-AN] films are due to the emissive decay of the
photoexcited singlet excitons in the porphyrins. The luminescence efficiencies and
lifetimes are increased for samples from pure films to dilute blend films. However,
they are increased as the intrachain concentration of the porphyrin sidechain groups
is decreased. The intrachain rotation motions of porphyrin sidechain groups result
in the initial ultrafast luminescence decays, which are much faster than those due
to the interchain interactions. All the samples show no significant red-shift and
broadening of the transient luminescence spectra. The interchain and intrachain
nonradiative exciton relaxation processes may play an important role in the
luminescence dynamics in the p[(por)A-AN] films. The possible origin of different
intrachain and interchain dynamic behaviours in p[(por)A-AN] films is discussed. 相似文献
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N. M. Agababyan G. Ajvazyan V. V. Ammosov M. Atayan N. Grigoryan G. Gulkanyan A. A. Ivanilov G. Karamyan V. A. Korotkov 《Physics of Atomic Nuclei》2002,65(9):1628-1633
The mechanisms of cumulative proton production are studied on the basis of data from the SCAT propane-freon bubble chamber exposed to a wideband neutrino beam at the Serpukhov accelerator. Kinematic correlations between the cumulative proton and muon, as well as pair correlations of the final protons, are analyzed. The former correlations are predicted by the two-nucleon correlation mechanism (TCM), whereas the latter are caused by the mechanism of secondary pion absorption (SPA) in the nucleus. It is shown that the TCM contribution to the cumulative proton production is most significant in the peripheral interactions (about 50%). The SPA contribution accounts for about a quarter of the inclusive cross section of cumulative proton production. 相似文献
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The adduct ions of two tetramolecular G-quadruplexes formed from the d(TGGGGT) and d(TTGGGGGT) single strands with a group of cationic porphyrins, with different charges and substituents, and one neutral porphyrin, were investigated by ESI-MS and ESI-MS/MS in the negative ion mode. Formation of [Q + nNH(4)(+)+P(p+)-(z + n + p)H(+)](z-) adduct ions (where Q = quadruplex, n = number of quartets minus 1, P = porphyrin and p(+) = 0,1,2,3,4) indicates that the porphyrins are bound outside the quadruplexes providing an additional stabilization to those structures. The fragmentation pathways of the [Q + nNH(4)(+)+P(p+)-(z + n + p)H(+)](z-) adduct ions depend on the number of positive charges (p(+)) of the porphyrins and on the overall complex charge (z(-)), but do not show a significant dependence on the type of the substituent groups in the porphyrins. Formation of the 'unfilled' ions [Q + P(p+)-(z + p)H(+)](z-) predominates for porphyrins with a higher number of positive charges. Strand separation with the formation of [T + P(p+)-(z-2 + p)H(+)]((z-2)-) and (SS-2H(+))(2-) ions, where T = [d(TG(4)T)](3) and [d(T(2)G(5)T)](3) and SS = d(TG(4)T) and d(T(2)G(5)T) is only observed for the complexes with a higher overall negative charge. Porphyrin loss with the formation of [Q + nNH(4)(+)-(z + n)H(+)](z-) ions occurs predominantly for the neutral and monocharged porphyrins. The predominant formation of the 'unfilled' ions, [Q + P(p+)-(z + n)H(+)](z-), for porphyrins with a higher number of charges shows that these porphyrins can prevent strand separation and preserve, at least partially, the quadruplex structure. 相似文献
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Simple expressions are derived for the non-eikonal corrections to the Glauber diffraction approximation for the proton-nucleus scattering amplitudes, with the spin dependence of the proton-nucleon amplitudes taken into account. As an example, we study the numerical importance of these corrections for elastic p 58Ni scattering at 800 MeV. 相似文献
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It is widely believed that high-kinetic-energy (>1 keV) recoils in crystalline Si result in the formation of amorphous regions, whereas low-kinetic-energy recoils lead directly to isolated point defects. Here we study the response of a Si crystal using dynamical density-functional calculations and show that recoils of much less than 1 keV result in highly disordered regions that persist for hundreds of femtoseconds. Therefore, beam-induced defect formation is controlled by recrystallization processes during dynamic annealing even following low-energy ion implantation. 相似文献
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Three different approaches to taking into account exchange effects in heavy-ion collisions are studied. Within the first of
them, the lowest eigenstates of the Hamiltonian are treated as forbidden states. In the second approach, the eigenstates of
the normalization kernel of the resonating-group model that correspond to zero eigenvalues are treated as forbidden states.
The third approach takes additionally into account semiforbidden states. The 16O + 16O system is considered. A hybrid approach that combines the methods of discrete and continuous mathematics is developed for
calculating the widths of narrow resonance states. The resonance width calculated within the approach that takes into account
semiforbidden states proves to be sharply different from the widths obtained within traditional approaches. 相似文献
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A simple method was developed for the preparation of cyano- and carboxyl-terminated alkylsiloxane monolayers on the hydroxylated surface of the SiO2/Si substrate through using adsorption and hydrolysis reaction of a short-chain 2-cyanoethyl triethoxysilane [(CH3CH2O)3SiCH2CH2CN]. The contact angle and the X-ray photoelectron spectroscopy (XPS) measurements have proved that the cyano terminal group indeed formed on the substrate and was transformed into the carboxylic terminal group after hydrolysis. The ellipsometry shows the presence of an intact monolayer with thickness of around 0.7 nm before and during the hydrolysis reaction. The surface morphology was observed with atomic force microscopy (AFM) imaging. Those all indicate that uniform and ordered self-assembled monolayers (SAMs) were formed on the substrate. 相似文献
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R. K. Shivpuri D. Grewal V. K. Verma 《Zeitschrift fur Physik C Particles and Fields》1993,58(3):419-422
We discuss here the nuclear effects in multiparticle production processes in 800 GeV proton-emulsion nuclei interactions. The multiplicity of medium energy particles (N g ) was used as a measure of the average number of projectile collisions (<v(N g )>). To study nuclear effects, we determined <v(N g )> and ratio of normalized rapidity density of all produced charged particles in hadron-nucleus to hadron-hadron interaction,R(N η ). It was found that the average multiplicity of shower particles increases with <v(N g )>. From theR(N η ) distribution, we find; a strong maxima in the target fragmentation region, a plateau in the central region and depletion of particle density in the projectile fragmentation region. 相似文献
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通过Monte Carlo模拟和接受率方法研究了限制在圆柱形管道中大胶球之间以及大胶球与管壁之间排空作用的耦合效应.研究发现,当两个大胶球靠近时,大胶球之间的排空作用因与大胶球与管道壁之间的排空作用耦合而得到加强,同样当大胶球与管道壁靠近时,大胶球与管道壁之间的排空作用也因与另一大胶球之间排空作用的耦合而得到了加强.此外,研究还发现,随着圆柱形管道直径的减小,胶球之间、胶球与管道壁之间的排空作用的耦合效应是增强的.
关键词:
排空作用的耦合效应
接受率方法
Monte Carlo模拟 相似文献
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C. Gutiérrez-Wing P. Santiago J.A. Ascencio A. Camacho M. José-Yacamán 《Applied Physics A: Materials Science & Processing》2000,71(3):237-243
In the present work, we report the growth of ordered arrays of gold nanoparticles passivated with n-alkylthiol molecules using
crystallization in toluene vapor. We kept constant the average particle size and the length of the passivating molecule (1-dodecanethiol).
The temperature and time of growth were varied. We show that in the initial stages of the growth, nano-chains of particles
are produced. These nano-chains aggregate to form two-dimensional arrays. In the initial stages the nano-chains form a two-dimensional
square lattice which then relaxes to a close-packed structure. In latter stages of growth a three-dimensional supercrystal
is produced. It is found that the packing of nanoparticles corresponds to an average FCC lattice. However, large variations
on the local parameters of the lattice are observed. Near the edges of the supercrystal the anomalous packing reported by
Zanchet et al. [20] and Fink et al. [21] was observed. The energy of the observed structures is analyzed using molecular dynamics
simulation. It is concluded that using the vapor growth method, it is possible to produce controlled ordered structures from
one to three dimensions.
Received: 24 February 2000 / Accepted: 28 March 2000 / Published online: 13 July 2000 相似文献
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Dynamical effects of spin-dependent interactions in low- and intermediate-energy heavy-ion reactions
It is well known that noncentral nuclear forces, such as the spin–orbital coupling and the tensor force, play important roles in understanding many interesting features of nuclear structures. However, their dynamical effects in nuclear reactions are poorly known because only the spin-averaged observables are normally studied both experimentally and theoretically. Realizing that spin-sensitive observables in nuclear reactions may convey useful information about the in-medium properties of noncentral nuclear interactions, besides earlier studies using the time-dependent Hartree–Fock approach to understand the effects of spin–orbital coupling on the threshold energy and spin polarization in fusion reactions, some efforts have been made recently to explore the dynamical effects of noncentral nuclear forces in intermediate-energy heavy-ion collisions using transport models. The focus of these studies has been on investigating signatures of the density and isospin dependence of the form factor in the spin-dependent single-nucleon potential. Interestingly, some useful probes were identified in the model studies but so far there are still no data to compare with. In this brief review, we summarize the main physics motivations as well as the recent progress in understanding the spin dynamics and identifying spin-sensitive observables in heavy-ion reactions at intermediate energies. We hope the interesting, important, and new physics potentials identified in the spin dynamics of heavy-ion collisions will stimulate more experimental work in this direction. 相似文献