共查询到16条相似文献,搜索用时 0 毫秒
1.
V. A. Kudryavtsev L. Pandola V. Tomasello 《The European Physical Journal A - Hadrons and Nuclei》2008,36(2):171-180
Background induced by neutrons in deep underground laboratories is a critical issue for all experiments looking for rare events,
such as dark matter interactions or neutrinoless ββ decay. Neutrons can be produced either by natural radioactivity, via spontaneous
fission or (α, n) reactions, or by interactions initiated by high-energy cosmic rays. In all underground experiments, Monte Carlo simulations
of neutron background play a crucial role for the evaluation of the total background rate and for the optimization of rejection
strategies. The Monte Carlo methods that are commonly employed to evaluate neutron-induced background and to optimize the
experimental setup, are reviewed and discussed. Focus is given to the issue of reliability of Monte Carlo background estimates.
We dedicate this work to the memory of our friend and colleague Nicola Ferrari, who prematurely passed away in July 2006. 相似文献
2.
We investigate the evolutions with density of the QCD scalar susceptibility and of the sigma mass in a chiral relativistic theory of nuclear matter, in the mean-field approximation. In order to reach saturation we need to introduce the scalar response of the nucleons. The consequences are a quite mild density dependence of the sigma mass and the progressive decoupling of the quark density fluctuations from the nucleonic ones at large densities. 相似文献
3.
G. Kaniadakis 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,70(1):3-13
In ordinary statistical mechanics the Boltzmann-Shannon
entropy is related to the Maxwell-Bolzmann distribution
pi by means of a twofold link. The first link is differential and
is offered by the Jaynes Maximum Entropy Principle. Indeed, the
Maxwell-Boltzmann distribution is obtained by maximizing the Boltzmann-Shannon entropy under
proper constraints. The second link is algebraic and imposes that
both the entropy and the distribution must be expressed in
terms of the same function in direct and inverse form. Indeed, the
Maxwell-Boltzmann distribution pi is expressed in terms of the exponential
function, while the Boltzmann-Shannon entropy is defined as the mean value of
-ln (pi).
In generalized statistical mechanics the second link is customarily
relaxed. Of course, the generalized exponential function defining
the probability distribution function after inversion, produces a
generalized logarithm Λ(pi). But, in general, the mean value
of -Λ(pi) is not the entropy of the system. Here we
reconsider the question first posed in [Phys. Rev. E 66,
056125 (2002) and 72, 036108 (2005)], if and how is it
possible to select generalized statistical theories in which the
above mentioned twofold link between entropy and the distribution
function continues to hold, such as in the case of ordinary
statistical mechanics.
Within this scenario, apart from the standard
logarithmic-exponential functions that define ordinary statistical
mechanics, there emerge other new couples of direct-inverse
functions, i.e. generalized logarithms Λ(x) and generalized
exponentials Λ-1(x), defining coherent and
self-consistent generalized statistical theories. Interestingly, all
these theories preserve the main features of ordinary statistical
mechanics, and predict distribution functions presenting power-law
tails. Furthermore, the obtained generalized entropies are both
thermodynamically and Lesche stable. 相似文献
4.
M. J. Ramsey-Musolf 《The European Physical Journal A - Hadrons and Nuclei》2007,32(4):379-388
I discuss the prospects for future studies of parity-violating (PV) interactions at low energies and the insights they might
provide about open questions in the standard model as well as physics that lies beyond it. I cover four types of parity-violating
observables: PV electron scattering; PV hadronic interactions; PV correlations in weak decays and searches for the permanent
electric dipole moments of quantum systems. 相似文献
5.
A.-J. Li C.-L. Wang L. Wang J.-H. Wu J.-Y. Gao 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,42(3):373-379
We investigate the spontaneously generated coherence (SGC) in a Doppler broadened four-level atomic system driven by two coherent
fields. We plot
the spontaneous emission spectra with different parameters and discuss how
the initial atomic conditions and parameters of both fields change the
number of peaks and dark lines of spontaneous emission spectra. Furthermore, we also show how the spontaneous emission spectrum
is modified by
Doppler effects in the viewed direction. Our results have important
references to the experimental observation of SGC in hot atomic vapors. 相似文献
6.
J. M. Friedrich 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):620-625
Results for the spin structure of the nucleon from the COMPASS data taking periods 2002 to 2004 are presented. The quark contribution
to the nucleon spin, following from a QCD fit to the new data, turns out to be significantly larger than it was derived from
the previous world data. The new data favour, on the other side, a comparatively small gluon polarisation in the range x
g ≈ 0.1. In the data taken with the deuteron target polarised transversely the related asymmetries are found to be small on
the level of accuracy reached so far, indicating a cancellation of the proton and neutron contributions. This is in agreement,
for both the Collins and the Sivers asymmetry, with recent theoretical calculations. Also, a step towards the understanding
of angular-momentum contributions with COMPASS is taken by the evaluation of asymmetries in exclusive vector meson production. 相似文献
7.
S. Procureur 《The European Physical Journal A - Hadrons and Nuclei》2007,32(4):483-487
The most recent determinations of the gluon polarization in the nucleon,
, obtained at RHIC and COMPASS experiments, are reviewed. The former accesses the gluon polarization mainly through the production
of neutral pions (PHENIX) or jets (STAR) in polarized proton collisions. The latter uses the photon-gluon fusion in polarized
lepton-nucleon scattering, tagged either by open charm or high-pT hadrons production. All the results are in good agreement, and favour values of ΔG roughly between 0 and 0.5 at a few (GeV/c)2 , thus in contradiction with what could be derived from the Ellis-Jaffe sum rule and the axial anomaly. Much stronger constraints
will be obtained in a near future by both programs, helping us to clarify the role of gluons in the nucleon spin. 相似文献
8.
K. J. Öberg H. Lundberg 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,42(1):15-34
Radiative lifetimes of nine out of the twelve 4f136p levels in Yb III have been measured, seven of these for the first time. A Penning discharge lamp is introduced as a continuous
plasma source, in which the lifetimes are determined with the time-resolved laser-induced fluorescence technique by pumping
from metastable 5d and 6s levels. Spectra of the same source are recorded with a Fourier-transform spectrometer, which are
used to derive branching fractions of the 6p and 7s levels. Combined with the lifetimes, the branching fractions are used
to determine 81 experimental transition probabilities. Wavelengths of 142 Yb III transitions are measured and the uncertainties
of corresponding Ritz wavenumbers are improved by an order of magnitude from the prior values. The energy of the 5d (5/2,5/2)○
0 level has been shifted 144.20 cm-1 to the higher value 45421.045 cm-1. Much emphasis is put on data treatment and error analysis.
Electronic supplementary material Supplementary Online Material 相似文献
9.
Dynamics of ionization mechanisms in relativistic collisions involving heavy and highly-charged ions
D.C. Ionescu A. Belkacem 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(3):301-307
The dynamics of mechanisms associated with the ionization of inner-shell electrons in relativistic collisions involving heavy
and highly-charged ions is investigated within a nonperturbative approach formulated explicitly in the time domain. The theoretical
treatment is based on the exact numerical solution of the time dependent Dirac equation for two Coulomb centers on a lattice
in momentum space. We present results for ionization in encounters between 100 MeV/u Au79+ projectile ions impinging on a hydrogen-like uranium target. By directly visualizing the collision dynamics we identify a
new ionization mechanism in which electrons are emitted from the internuclear region preferentially in the transverse direction
with respect to the projectile trajectory. A striking characteristic of this ionization mechanism is that the velocity of
the electron is higher than the projectile velocity.
Received 26 June 2001 and Received in final form 27 November 2001 相似文献
10.
E. Träbert H.-P. Garnir P.-D. Dumont T. Bastin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(1):25-31
Peculiar properties of ion-atom collision systems, in particular deviations from statistical populations of singlet and triplet
levels, can be studied by optical spectroscopy. We have extended earlier studies by VUV spectroscopy of a number of collision
systems at various collision energies in the 0.01-MeV/nucleon to 1-MeV/nucleon range, involving H2
+, H+, He+, He2+, Ne+, Ar+, and N2
+ as projectiles and Ne, Ar, and N2 as target gases. Statistically significant deviations of the relative intensities of singlet and triplet lines from simple
ratios are observed in the displaced terms of the valence shell of Ne III, corroborating and extending earlier work. For Ar
III, the energy dependences of singlet-to-triplet excitation ratios are very different for different projectiles. For N II,
in contrast, all observed line ratios are practically independent of the projectile energy.
Received 17 November 2000 and Received in final form 31 January 2001 相似文献
11.
de Jeu WH Obraztsov EP Ostrovskii BI Ren W McMullan PJ Griffin AC Sánchez-Ferrer A Finkelmann H 《The European physical journal. E, Soft matter》2007,24(4):399-409
The layer correlations in main-chain smectic liquid-crystal polymer and elastomer systems have been studied using high-resolution
X-ray scattering. In contrast to side-chain smectic polymers, in main-chain systems the polymer chains are oriented parallel
to the layer normal. As a result they couple directly to the lamellar structure and any polymer defect is translated into
layer distortions. For the homopolymers the resulting X-ray lineshapes are well described by Lorentzians. This is interpreted
as an average of algebraically decaying order in domains with dimensions of hundreds of nm and a wide dispersion of sizes.
The elastomers show much broader peaks than the correponding polymers. This is attributed to strong non-uniform strain within
the finite-size domains due to defects of the layer structure.
An erratum to this article is available at . 相似文献
12.
D.V. Fisher Y. Maron 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(3):349-359
Accurate treatment of the plasma density effects requires a detailed knowledge of the spatial distribution of individual ions
around a test ion. In the present work, rigorous expressions are derived for the main 2- and 3-particle spatial distribution
functions involving the nearest neighbor (NN) and the next-nearest neighbor (NNN) ions. These expressions, valid for both
ideal and nonideal plasmas, present the distributions as functionals of the potentials U
NN and U
NNN at the nearest and next-nearest ion locations. All of the distribution functions except one are derived and discussed in
the present work for the first time ever. For utilization of our results in practical calculations, we suggest semi-empirical
expressions for U
NN and U
NNN in the ion-ion coupling parameter range 0 ?Γ < 1. In order to test the accuracy of our expressions for U
NN and U
NNN we conduct Molecular Dynamics (MD) simulations. The simulations utilize the pure Coulomb particle-particle interaction potentials,
regularized at close range to avoid classical Coulomb collapse, and are free from the assumptions made to find U
NN and U
NNN. Thus, the results of the MD simulations provide an independent test of our theoretical results. Excellent agreement has
been found between the results of the theory and of the MD simulations. Finally, we outline the implications of the present
findings on the problem of tunneling and charge exchange in dense plasmas.
Received 27 October 2000 and Received in final form 30 January 2001 相似文献
13.
J. Westergren S. Nordholm A. Rosén 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(1):81-97
The cooling of the metal cluster Pd13 in an atmosphere of rare gas has been studied by means of computer simulation. By simulation, the average energy transfer
in collisions between one cluster and one gas atom has been obtained. Emphasis has been placed on conditions when the temperatures
of the colliding species are almost equal. All modes of motion, inclusive the translation, must be considered in order to
obtain vanishing energy transfer at equilibrium. A simulation scheme is presented by which the energy transfer is zero to
the cluster when the gas and the cluster temperatures are equal. At equilibrium the energy transfer does however not vanish
for all impact parameters. In the collisions with Pd13, the cluster is heated by collisions with a small impact parameter but equally cooled by collisions with a large impact parameter.
Argon and krypton are found to cool Pd13 equally efficiently while neon and helium are less efficient cooling agents.
Received 28 September 2001 / Received in final form 8 August 2002 Published online 12 November 2002
RID="a"
ID="a"e-mail: JanW@phc.gu.se 相似文献
14.
E. Biémont P. Palmeri P. Quinet E. Träbert C.J. Zeippen 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(1):37-44
Transitions between the five fine-structure levels in the 3s
23p
3 ground configuration of Fe XII (P-like) are of interest in astrophysics and terrestrial plasma diagnostics. The decay rates
give rise to level lifetimes in the millisecond range, which have been measured recently at a heavy-ion storage ring. While
most of the 3s
23p
23d levels are short-lived, two of these levels have no E1 decay channels and may also have millisecond lifetimes. We present
HFR and MCDF calculations of the E1, M1, E2 and M2 transition rates between the 3s
23p
3, 3s3p4 and 3s
23p
23d levels and compare the lifetime results to most recent experimental data as well as to other predictions.
Received 2 October 2001 / Received in final form 22 January 2002 Published online 28 June 2002 相似文献
15.
N. El Khayati R. Cherkaoui El Moursli J. Rodríguez-Carvajal G. André N. Blanchard F. Bourée G. Collin T. Roisnel 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(4):429-442
We have studied in detail the crystal and magnetic structures of the oxyphosphates MFePO5 (M: divalent transition metal) using neutron powder diffraction as a function of temperature. All of them are isomorphic
to the mixed valence compound α-Fe2PO5 with space-group Pnma. No disorder exists between the two metallic sites. The M2+O6 octahedra share edges between them and faces with Fe3+O6 octahedra building zigzag chains running parallel to the b-axis that are connected by PO4 tetrahedra. The topology of this structure gives rise to a complex pattern of super-exchange interactions responsible of
the observed antiferromagnetic order. The magnetic structures are all collinear with the spin directed along the b-axis except for M = Co. The experimental magnetic moments of Cu+2 and Ni2+ correspond to the expected ionic value, on the contrary the magnetic moment of Fe3+ is reduced, probably due to covalence effects, and that of Co2+ is greater than the spin-only value indicating a non negligible orbital contribution. Using numerical calculations we have
established a magnetic phase diagram adapted for this type of crystal structure and determined the constraints to be satisfied
by the values of the exchange interactions in order to obtain the observed magnetic structure as the ground state.
Received 15 December 2000 and Received in final form 25 June 2001 相似文献
16.
S. Ghosh M.P. Rishi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(2):275-279
Using hydrodynamical model of semiconductor plasma analytical investigations are made for the amplitude modulation as well
as demodulation of an electromagnetic wave in a transversely magnetised acousto-optic semiconducting plasma. The inclusion
of carriers diffusion adds new dimension in the analysis presented here. Analysis are made under different wave number regions
over a wide range of cyclotron frequency. It has been seen that diffusion of charge carriers modifies amplitude modulation
and demodulation processes effectively. Numerical estimations are made for n-InSb crystal irradiated by pump wave of frequency 1.6 T s-1. Complete absorption of the waves takes place in all the possible wave lengths regimes when the cyclotron frequency becomes exactly equal to (v
2 + )1/2.
Received 28 February 2002 Published online 19 July 2002 相似文献