共查询到20条相似文献,搜索用时 31 毫秒
1.
F. Herfurth A. Kellerbauer F. Ames G. Audi D. Beck K. Blaum G. Bollen O. Engels H.-J. Kluge D. Lunney R.B. Moore M. Oinonen E. Sauvan C. Scheidenberger S. Schwarz G. Sikler C. Weber 《The European Physical Journal A - Hadrons and Nuclei》2002,15(1-2):17-20
Mass measurements of 34Ar, 73-78Kr, and 74,76Rb were performed with the Penning-trap mass spectrometer ISOLTRAP. Very accurate Q
EC-values are needed for the investigations of the
t-value of 0+ → 0+ nuclear β-decays used to test the standard model predictions for weak interactions. The necessary accuracy on the Q
EC-value requires the mass of mother and daughter nuclei to be measured with δm/m ⩽ 3 . 10-8. For most of the measured nuclides presented here this has been reached. The 34Ar mass has been measured with a relative accuracy of 1.1 . 10-8. The Q
EC-value of the 34Ar 0+ → 0+ decay can now be determined with an uncertainty of about 0.01%. Furthermore, 74Rb is the shortest-lived nuclide ever investigated in a Penning trap.
Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002
RID="a"
ID="a"e-mail: frank.herfurth@cern.ch 相似文献
2.
L. Zhang W. Kleemann J. Dec R. Wang M. Itoh 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(2):163-171
The dielectric permittivity ε′ - i
of SrTi 18O 3 (STO18) is studied under a dc electric field E as a function of the temperature, T. In ε′
vs.
T, a double-peak is found when 0 < E < 30 KV/m. While the peak at high-T is attributed to the smeared ferroelectric phase transition, the low-T one is induced by domain wall motion. The transverse Ising model including an external homogeneous and quenched random-fields
is successfully used to describe both the smeared phase transition and the domain wall response in the low-T domain state. The calculations are in good agreement with the experimental results.
Received 4 January 2002 / Received in final form 25 March 2002 Published online 19 July 2002 相似文献
3.
V.Yu. Irkhin M.I. Katsnelson 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(4):481-486
Peculiarities of transport properties of three- and two-dimensional half-metallic ferromagnets are investigated, which are
connected with the absence of spin-flip scattering processes. The temperature and magnetic field dependences of resistivity
in various regimes are calculated. The resistivity is proportional to T
9/2 for T < T
* and to T
7/2 for T > T
*, T* being the crossover temperature for longitudinal scattering processes. The latter scale plays also an important role in magnetoresistance.
The contribution of non-quasiparticle (incoherent) states to the transport properties is discussed. It is shown that they
can dominate in the temperature dependence of the impurity-induced resistivity and in the tunnel junction conductivity.
Received 16 September 2002 / Received in final form 6 November 2002 Published online 31 December 2002 相似文献
4.
The ZEUS Collaboration S. Chekanov et al. 《The European Physical Journal C - Particles and Fields》2002,25(2):169-187
Diffractive dissociation of virtual photons, , has been studied in ep interactions with the ZEUS detector at HERA. The data cover photon virtualities 0.17 < Q
2
< 0.70 GeV2 and 3 < Q
2
< 80 GeV2 with 3 < MX < 38 GeV, where MX is the mass of the hadronic final state. Diffractive events were selected by two methods: the first required the detection
of the scattered proton in the ZEUS leading proton spectrometer (LPS); the second was based on the distribution of MX. The integrated luminosities of the low- and high-Q2 samples used in the LPS-based analysis are 0.9 pb-1 and 3.3 pb-1, respectively. The sample used for the MX-based analysis corresponds to an integrated luminosity of 6.2 pb-1. The dependence of the diffractive cross section on W, the virtual photon-proton centre-of-mass energy, and on Q2 is studied. In the low-Q2 range, the energy dependence is compatible with Regge theory and is used to determine the intercept of the Pomeron trajectory.
The W dependence of the diffractive cross section exhibits no significant change from the low-Q2 to the high-Q2 region. In the low-Q2 range, little Q2 dependence is found, a significantly different behaviour from the rapidly falling cross section measured for Q
2
> 3 GeV2. The ratio of the diffractive to the virtual photon-proton total cross section is studied as a function of W and Q2. Comparisons are made with a model based on perturbative QCD.
Received: 27 March 2002 / Published online: 9 August 2002 相似文献
5.
Bo-Wen Xiao Xin Qian Bo-Qiang Ma 《The European Physical Journal A - Hadrons and Nuclei》2002,15(4):523-527
The electromagnetic form factor of the kaon meson is calculated in the light-cone formalism of the relativistic constituent
quark model. The calculated K+ form factor is consistent with almost all of the available experimental data at low-energy scale, while other properties
of the kaon could also be interrelated in this representation with reasonable parameters. Predictions of the form factors
for the charged and neutral kaons at a higher-energy scale are also given, and we find the non-zero K0 form factor at Q
2≠ 0 due to the mass difference between the strange and down quarks inside K0.
Received: 21 June 2002 / Accepted: 29 July 2002 / Published online: 3 December 2002
RID="a"
ID="a"e-mail: mabq@phy.pku.edu.cn
Communicated by A. Sch?fer 相似文献
6.
We extract the neutron charge form factor G
n
E(Q
2) from the charge form factor of deuteron G
d
C(Q
2) obtained from T
20(Q
2) data at 0≤Q
2≤ 1.717 (GeV/c)2. The extraction is based on the relativistic impulse approximation in the instant form of the relativistic Hamiltonian dynamics.
Our results (12 new points) are compatible with existing values of the neutron charge form factor of other authors. We propose
a fit for the whole set (36 points) taking into account the data for the slope of the form factor at Q
2 = 0.
Received: 26 July 2002 / Accepted: 18 September 2002 / Published online: 4 February 2003
RID="a"
ID="a"e-mail: krutov@ssu.samara.ru
RID="b"
ID="b"e-mail: troitsky@theory.sinp.msu.ru
Communicated by V.V. Anisovich 相似文献
7.
《The European Physical Journal C - Particles and Fields》2009,62(4):659-695
Spin Density Matrix Elements (SDMEs) describing the angular distribution of exclusive ρ
0 electroproduction and decay are determined in the HERMES experiment with 27.6 GeV beam energy and unpolarized hydrogen and
deuterium targets. Eight (fifteen) SDMEs that are related (unrelated) to the longitudinal polarization of the beam are extracted
in the kinematic region 1<Q
2<7 GeV2, 3.0<W<6.3 GeV, and −t<0.4 GeV2. Within the given experimental uncertainties, a hierarchy of relative sizes of helicity amplitudes is observed. Kinematic
dependences of all SDMEs on Q
2 and t are presented, as well as the longitudinal-to-transverse ρ
0 electroproduction cross-section ratio as a function of Q
2. A small but statistically significant deviation from the hypothesis of s-channel helicity conservation is observed. An indication is seen of a contribution of unnatural-parity-exchange amplitudes;
these amplitudes are naturally generated with a quark-exchange mechanism. 相似文献
8.
V.S. Shelkovsky S.G. Stepanian I.K. Galetich M.V. Kosevich L. Adamowicz 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(3):421-430
A combined experimental-theoretical approach to modeling of building blocks of recognition complexes formed by nucleic acid
bases and the amino-acids side-chain amino group is reviewed. The approach includes the temperature dependent field-ionization
mass spectrometry and ab initio quantum chemical calculations. The mass spectrometric technique allows determination of interaction enthalpies of biomolecules
in the gas phase, and the results it produces are directly comparable to the results obtained through theoretical modeling.
In our works we have analyzed both thermodynamic and structural aspects of the recognition complexes of four canonical nucleic
acid bases and acrylamide, which models the side chain of asparagine and glutamine. It has been shown that all bases can interact
with amide group of the amino acids via their Watson-Crick sites when being incorporated into a single strand DNA or RNA. Stability of the complexes studied, expressed
as - ΔH (kJ mole-1) decreases as: m9Gua (- 59.5) > m
1Cyt (- 57.0) > m
9Ade (- 52.0) ≫m
1Ura (- 40.6). We have determined that in the double stranded DNA only purine bases can be recognized.
Received 5 February 2002 and Received in final form 14 March 2002 Published online 13 September 2002 相似文献
9.
B. Canals D.A. Garanin 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(4):439-447
Thermodynamic quantities and correlation functions (CFs) of the classical antiferromagnet on the checkerboard lattice are
studied for the exactly solvable infinite-component spin-vector model, D↦∞. In contrast to conventional two-dimensional magnets with continuous symmetry showing extended short-range order at distances
smaller than the correlation length, r
ξ
c∝ exp(T
*/T), correlations in the checkerboard-lattice model decay already at the scale of the lattice spacing due to the strong degeneracy
of the ground state characterized by a macroscopic number of strongly fluctuating local degrees of freedom. At low temperatures,
spin CFs decay as <
>∝ 1/r
2 in the range a
0≪r≪ξ
c∝T
-1/2, where a0 is the lattice spacing. Analytical results for the principal thermodynamic quantities in our model are very similar with
MC simulations, exact and analytical results for the classical Heisenberg model (D = 3) on the pyrochlore lattice. This shows that the ground state of the infinite-component spin vector model on the checkerboard
lattice is a classical spin liquid.
Received 16 November 2001 and Received in final form 12 February 2002 相似文献
10.
K. Blaum G. Bollen F. Herfurth A. Kellerbauer H.-J. Kluge M. Kuckein E. Sauvan C. Scheidenberger L. Schweikhard 《The European Physical Journal A - Hadrons and Nuclei》2002,15(1-2):245-248
The cyclotron frequencies of singly charged carbon clusters Cn
+ (n ≥ 2) were measured with the Penning-trap mass spectrometer ISOLTRAP at ISOLDE/CERN. The present limit of mass accuracy δm/m = 1.2 . 10-8 and the extent of the mass-dependent systematic shift (δm/m)sys = 1.7(0.6) . 10-10/u
. (m - m
ref) of the setup were investigated for the first time. In addition, absolute mass measurements by use of pure clusters of the
most abundant carbon isotope 12C are now possible at ISOLTRAP.
Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002
RID="a"
ID="a"Present address: CERN, CH-1211 Geneva 23, Switzerland; e-mail: klaus.blaum@cern.ch 相似文献
11.
G.I. Japaridze S. Sarkar 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(2):139-144
A one-dimensional model of interacting electrons with on-site U, nearest-neighbor V, and pair-hopping interaction W is studied at half-filling using the continuum limit field theory approach. The ground state phase diagram is obtained for
a wide range of coupling constants. In addition to the insulating spin-density wave (SDW) and charge-density wave (CDW) phases
for large U and V, respectively, we identify a bond-charge-density-wave (BCDW) phase W < 0, | U - 2V| < | 2W| and a bond-spin-density-wave (BSDW) for W > 0, | U - 2V| < W. The possibility of bond-located ordering results from the site-off-diagonal nature of the pair-hopping term and is a special
feature of the half-filled band case. The BCDW phase corresponding to an enhanced Peierls instability in the system. The BdSDW
is an unconventional insulating magnetic phase, characterized by a gapless spin excitation spectrum and a staggered magnetization
located on bonds between sites. The general ground state phase diagram including insulating, metallic, and superconducting
phases is discussed. A transition to the η-superconducting phase at | U - 2V| ≪ 2t?W is briefly discussed.
Received 20 February 2002 / Received in final form 11 April 2002 Published online 19 July 2002 相似文献
12.
W. Melnitchouk 《The European Physical Journal A - Hadrons and Nuclei》2003,17(2):223-234
We explore the relationship between exclusive and inclusive electromagnetic scattering from the pion, focusing on the transition
region at intermediate Q2. Combining Drell-Yan data on the leading twist quark distribution in the pion with a model for the resonance region at large
x, we calculate QCD moments of the pion structure function over a range of Q2, and quantify the role of higher twist corrections. Using a parameterization of the pion elastic form factor and phenomenological
models for the π↦ρ transition form factor, we further test the extent to which local duality may be valid for the pion.
Received: 10 February 2003 / Accepted: 12 March 2003 / Published online: 27 May 2003 相似文献
13.
D. Stauffer A. Aharony L. da Fontoura Costa J. Adler 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(3):395-399
Neural networks are supposed to recognise blurred images (or patterns) of N pixels (bits) each. Application of the network to an initial blurred version of one of P pre-assigned patterns should converge to the correct pattern. In the “standard" Hopfield model, the N “neurons” are connected to each other via N2 bonds which contain the information on the stored patterns. Thus computer time and memory in general grow with N2. The Hebb rule assigns synaptic coupling strengths proportional to the overlap of the stored patterns at the two coupled
neurons. Here we simulate the Hopfield model on the Barabási-Albert scale-free network, in which each newly added neuron is
connected to only m other neurons, and at the end the number of neurons with q neighbours decays as 1/q
3. Although the quality of retrieval decreases for small m, we find good associative memory for 1 ≪ m ≪ N. Hence, these networks gain a factor N/m ≫ 1 in the computer memory and time.
Received 12 January 2003 Published online 11 April 2003
RID="a"
ID="a"e-mail: stauffer@thp.uni-koeln.de 相似文献
14.
Coupled thermal and carrier transports (electron/hole generation, recombination, diffusion and drifting) in laser photoetching
of GaAs thin film is investigated. A new volumetric heating mechanism originating from SRH (Shockley–Read–Hall) non-radiative
recombination and photon recycling is proposed and modeled based on recent experimental findings. Both volumetric SRH heating
and Joule heating are found to be important in the carrier transport, as well as the etching process. SRH heating and Joule
heating are primarily confined within the space-charge region, which is about 20 nm from the GaAs surface. The surface temperature
rises rapidly as the laser intensity exceeds 105 W/m2. Below a laser intensity of 105 W/m2, the thermal effect is negligible. The etch rate is found to be dependent on the competition between photovoltaic and photothermal
effects on surface potential. At high laser intensity, the etch rate is increased by more than 100%, due to SRH and Joule
heating.
Received: 24 January 2002 / Accepted: 11 April 2002 / Published online: 10 September 2002
RID="*"
ID="*"Corresponding author. Fax: +1-310/206-2302, E-mail: xiang@seas.ucla.edu 相似文献
15.
S. Djeniže A. Srećković S. Bukvić 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(1):11-16
We have obtained transition probabilities (Einstein's A values) of thirteen transitions in doubly (N III), six in triply (N IV) and two in four times (N V) ionized nitrogen spectra
belonging to the 3s-3p and 3p-3d transitions using a relative line intensity ratio (RLIR) technique. The linear low-pressure pulsed arc was used as an optically
thin plasma source operated at 51 400 K electron temperature and 2.2×1023 m-3 electron density in nitrogen plasma. Our A values are compared to recent theoretical and experimental data.
Received 18 December 2001 / Received in final form 29 January 2002 Published online 28 June 2002 相似文献
16.
D. Stauffer P.M.C. de Oliveira 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(4):587-592
The density of never changed opinions during the Sznajd consensus-finding process decays with time t as 1/t
θ. We find θ ≃ 3/8 for a chain, compatible with the exact Ising result of Derrida et al. In higher dimensions, however, the exponent differs from the Ising θ. With simultaneous updating of sublattices instead of
the usual random sequential updating, the number of persistent opinions decays roughly exponentially. Some of the simulations
used multi-spin coding.
Received 22 August 2002 / Received in final form 12 November 2002 Published online 31 December 2002 相似文献
17.
Stochastic multiresonance in a bistable sawtooth potential driven by correlated multiplicative and additive noise 总被引:1,自引:0,他引:1
J. Wang L. Cao D.J. Wu 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(1):123-128
We present an analytic investigation of the signal-to-noise ratio (SNR) by studying the bistable sawtooth system driven by correlated Gaussian white noises. The analytic expression of SNR is obtained. Based on it, we detect the phenomenon of stochastic multiresonance, which arises from the dependence of SNR upon the noises correlation coefficient. Furthermore, there exists not only resonance, but also suppression in the SNR∼D (the additive noise intensity) curve and the SNR∼Q (the multiplicative noise intensity) curve.
Received 26 February 2002 / Received in final form 12 July 2002 Published online 17 September 2002 相似文献
18.
M.P. Rekalo E. Tomasi-Gustafsson 《The European Physical Journal A - Hadrons and Nuclei》2003,16(4):563-567
We discuss the applicability of pQCD to the elastic scattering of electrons on protons and deuterons. We analyze the Q2-dependence of the reduced deuteron form factor, taking into account the recent data on the electric proton form factor and
we find that the value of the QCD-scale parameter Λ differs essentially from the value Λ = 0.1 GeV, previously found using
the dipole parametrization of the electromagnetic nucleon form factors GE and GM. Moreover, the predicted scaling behavior of the reduced deuteron form factor cannot be recovered in the Dirac and Pauli
representations for the nucleon electromagnetic form factors.
Received: 14 October 2002 / Accepted: 12 November 2002 / Published online: 11 March 2003
RID="a"
ID="a"Permanent address: National Science Center KFTI, 310108 Kharkov, Ukraine.
RID="b"
ID="b"e-mail: etomasi@cea.fr
Communicated by V.V. Anisovich 相似文献
19.
M. Jazbinšek M. Zgonik S. Takekawa M. Nakamura K. Kitamura H. Hatano 《Applied physics. B, Lasers and optics》2002,75(8):891-894
The wavelength dependence of the space-charge field as induced in near-stoichiometric LiTaO3 crystals is investigated by measuring the bulk photogalvanic effect and the photoconductivity. LiTaO3 crystals of composition nearer to stoichiometry exhibit a pronounced reduction of the saturated space-charge field, which
results from a larger increase in the photoconductivity relative to the photogalvanic effect. Especially, at near-UV wavelengths,
the saturated space-charge field of the order of 0.1 kV/cm reaches a minimum that is two orders of magnitude lower than typical
values observed in undoped near-stoichiometric LiNbO3.
Received: 11 July 2002 / Revised version: 2 September 2002 / Published online: 20 December 2002
RID="*"
ID="*"Corresponding author. Fax: +41-1/633-1056, E-mail: mojca@fiz.uni-lj.si 相似文献