959 research outputs found
Improved linear response for stochastically driven systems
The recently developed short-time linear response algorithm, which predicts
the average response of a nonlinear chaotic system with forcing and dissipation
to small external perturbation, generally yields high precision of the response
prediction, although suffers from numerical instability for long response times
due to positive Lyapunov exponents. However, in the case of stochastically
driven dynamics, one typically resorts to the classical fluctuation-dissipation
formula, which has the drawback of explicitly requiring the probability density
of the statistical state together with its derivative for computation, which
might not be available with sufficient precision in the case of complex
dynamics (usually a Gaussian approximation is used). Here we adapt the
short-time linear response formula for stochastically driven dynamics, and
observe that, for short and moderate response times before numerical
instability develops, it is generally superior to the classical formula with
Gaussian approximation for both the additive and multiplicative stochastic
forcing. Additionally, a suitable blending with classical formula for longer
response times eliminates numerical instability and provides an improved
response prediction even for long response times
Fragmentation channels of relativistic Be nuclei in peripheral interactions
Nuclei of Li were accelerated at the JINR Nuclotron. After the
charge-exchange reaction involving these nuclei at an external target a second
Be beam of energy 1.23A GeV was formed. This beam was used to expose
photo-emulsion chambers. The mean free path for inelastic Be interactions
in emulsion =14.00.8 cm coincides within the errors with those
for Li and Li nuclei. More than 10% of the Be events are associated
with the peripheral interactions in which the total charge of the relativistic
fragments is equal to the charge of the Be and in which charged mesons are
not produced. An unusual ratio of the isotopes is revealed in the composition
of the doubly charged Be fragments: the number of He fragments is twice
as large as that of He fragments. In 50% of peripheral interactions, a
Be nucleus decays to two doubly charged fragments. The present paper gives
the channels of the Be fragmentation to charged fragments. In 50% of
events, the Be fragmentation proceeds only to charged fragments involving
no emission of neutrons. Of them, the He+He channel dominates, the
He+d+p and Li+pchannels constitute 10% each. Two events involving no
emission of neutrons are registered in the 3-body He+t+p and He+d+d
channels. The mean free path for the coherent dissociation of relativistic
Be nuclei to He+He is 71 m. The particular features of the
relativistic Be fragmentation in such peripheral interactions are explained
by the He+He 2-cluster structure of the Be nucleus.Comment: 10 pages, 3 figures, 3 tables, conference: Conference on Physics of
Fundamental Interactions, Moscow, Russia, 5-9 Dec 200
The Euler-Maruyama approximation for the absorption time of the CEV diffusion
A standard convergence analysis of the simulation schemes for the hitting
times of diffusions typically requires non-degeneracy of their coefficients on
the boundary, which excludes the possibility of absorption. In this paper we
consider the CEV diffusion from the mathematical finance and show how a weakly
consistent approximation for the absorption time can be constructed, using the
Euler-Maruyama scheme
The d' dibaryon in the quark-delocalization, color-screening model
We study the questions of the existence and mass of the proposed dibaryon in the quark-delocalization, color-screening model
(QDCSM). The transformation between physical and symmetry bases has been
extended to the cases beyond the SU(2) orbital symmetry. Using parameters fixed
by baryon properties and scattering, we find a mild attraction in the
channel, but it is not strong enough to form a deeply bound state
as proposed for the state. Nor does the (isospin) I=2 N
configuration have a deeply bound state. These results show that if a narrow
dibaryon state does exist, it must have a more complicated structure.Comment: 12 pp. latex, no figs., 2 tables, additional refs., Report-no was
adde
Joule Heating and Current-Induced Instabilities in Magnetic Nanocontacts
We consider the electrical current through a magnetic point contact in the
limit of a strong inelastic scattering of electrons. In this limit local Joule
heating of the contact region plays a decisive role in determining the
transport properties of the point contact. We show that if an applied constant
bias voltage exceeds a critical value, the stationary state of the system is
unstable, and that periodic, non-harmonic oscillations in time of both the
electrical current through the contact and the local temperature in the contact
region develop spontaneously. Our estimations show that the necessary
experimental conditions for observing such oscillations with characteristic
frequencies in the range Hz can easily be met. We also show a
possibility to manipulate upon the magnetization direction of a magnetic grain
coupled through a point contact to a bulk ferromagnetic by exciting the
above-mentioned thermal-electric oscillations.Comment: 9 pages, 6 figures, submitted to Physical Review
Pentaquark baryons in SU(3) quark model
We study the SU(3) group structure of pentaquark baryons which are made of
four quarks and one antiquark. The pentaquark baryons form {1}, {8}, {10},
{10}-bar, {27}, and {35} multiplets in SU(3) quark model. First, the flavor
wave functions of all the pentaquark baryons are constructed in SU(3) quark
model and then the flavor SU(3) symmetry relations for the interactions of the
pentaquarks with three-quark baryons and pentaquark baryons are obtained.Comment: REVTeX, 36 pages, 8 figures, references added, section for mass sum
rules is added, to appear in Phys. Rev.
Equilibrium states for potentials with \sup\phi - \inf\phi < \htop(f)
In the context of smooth interval maps, we study an inducing scheme approach
to prove existence and uniqueness of equilibrium states for potentials
with he `bounded range' condition \sup \phi - \inf \phi < \htop, first used
by Hofbauer and Keller. We compare our results to Hofbauer and Keller's use of
Perron-Frobenius operators. We demonstrate that this `bounded range' condition
on the potential is important even if the potential is H\"older continuous. We
also prove analyticity of the pressure in this context.Comment: Added Lemma 6 to deal with the disparity between leading eigenvalues
and operator norms. Added extra references and corrected some typo
Radial distribution of a single-pass amplified radiation in the active elements of CuBr lasers
The paper presents the results of study of single-pass amplified radiation distribution of copper bromide vapor laser active elements used in high-speed laser monitors. The possibility of modifying the profile of a single-pass amplified light beam by changing the copper bromide vapor concentration is demonstrated. This means of influence on the radiation profile seems to be easiest due to implementation by varying only one parameter of operation. Gaussian, ring-shaped or flat profiles can be achieved depending on the temperature of the containers with copper bromide. The diameter of the beam becomes narrower when increasing the concentration of copper bromide vapor. This feature is characteristic of the discharge tubes as small (diameter 2.5, length 5 cm) and large (diameter 5 cm, length 90 cm) active volume
Hemilability of phosphine-thioether ligands coordinated to trinuclear Mo3S4 cluster and its effect on hydrogenation catalysis
Ligand-exchange reactions of [Mo3S4(tu)8(H2O)]Cl44H2O (tu = thiourea) with
(PhCH2CH2)2PCH2CH2SR ligands, where R = Ph (PS1), pentyl (PS2) or Pr (PS3) afford new
complexes isolated as [Mo3S4Cl3(PS1)3]PF6 ([1]PF6), [Mo3S4Cl3(PS2)3]PF6 ([2]PF6) and
[Mo3S4Cl3(PS3)3]PF6 ([3]PF6) salts in 30-50% yields as the major reaction products. The crystal
structures of [1]PF6 and [2]PF6 were determined by X-ray diffraction (XRD) analysis. Each of
the three phosphine-thioether ligands is coordinated in a bidentate chelating mode to a different
molybdenum atom of the Mo3S4 trinuclear cluster, herewith all the phosphorus atoms of the
phosphino-thioether ligand are located trans to the capping sulfur (3-S). A second product that
forms in the reaction of [Mo3S4(tu)8(H2O)]Cl44H2O with PS1 corresponds to the neutral
[Mo3S4Cl4(PS1)2(PS1*)] complex. Its XRD analysis reveals both bidentate (PS1) and
monodentate (PS1*) coordinating modes of the same ligand. In the latter mode the phosphinethioether
is coordinated to a Mo atom only via the P atom. All compounds were characterized by
1H, 31P{1H} NMR, electrospray-ionization (ESI) mass spectrometry and cyclic voltammetry
(CV). Reactions of [1]PF6, [2]PF6 and [3]PF6 with an excess of Bu4NCl in CD2Cl2 were followed
by 31P{1H} NMR. The spectra indicate equilibrium between cationic [Mo3S4Cl3(PSn)3]
+
and
neutral [Mo3S4Cl4(PSn)2(PSn*)] (n = 1, 2) species. The equilibrium constants were determined
as 2.5 ± 0.2103
, 43 ± 2 Đ
-1
and 30 ± 2 Đ
-1
(at 25°C) for [1]PF6, [2]PF6 and [3]PF6, indicating
quantitative differences in hemilabile behavior of the phosphino-thioether ligands, depending on
the substituent at sulfur. Clusters [1]PF6, [2]PF6 and [3]PF6 were tested as catalysts in reduction
of nitrobenzene to aniline with Ph2SiH2 under mild conditions. Significant differencies in the
catalytic activity were observed, which can be attributed to different hemilabile behavior of the
PS1 and PS2/PS3 ligands
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