共查询到20条相似文献,搜索用时 15 毫秒
1.
B.Z. Kopeliovich A.V. Tarasov O.O. Voskresenskaya 《The European Physical Journal A - Hadrons and Nuclei》2001,11(3):345-356
The Born approximation, one photon exchange, used for DIS (deep inelastic scattering) is subject to virtual radiative corrections
which are related to the long-range Coulomb forces. They may be sizeable for heavy nuclei since Zα is not a small parameter. So far, these corrections are known only for two processes, elastic scattering and bremsstrahlung
on the Coulomb field of a point-like target. While the former amplitude acquires only a phase, in the latter case also the
cross-section is modified. Although the problem of Coulomb corrections for DIS on nuclei is extremely difficult, it should
be challenged rather than “swept under the carpet”. The importance of these radiative corrections is questioned in the present
paper. We show that, in the simplest case of a constant hadronic current, the Coulomb corrections provide a phase to the Born
amplitude, therefore the cross-section remains the same. Inclusion of more realistic hadronic dynamics changes this conclusion.
The example of coherent production of vector mesons off nuclei reveals large effects. So far a little progress has been made
deriving lepton wave functions in the Coulomb field of an extended target. Employing available results based on the first-order
approximation in Zα, we conclude that the Coulomb corrections are still important for heavy nuclei. We also consider an alternative approach
for extended nuclear targets, the eikonal approximation, which we demonstrate to reproduce the known exact results for Coulomb
corrections. Calculating electroproduction of vector mesons, we again arrive at a large deviation from the Born approximation.
We conclude that one should accept with caution the experimental results for nuclear effects in DIS based on analyses done
in the Born approximation.
Received: 16 May 2001 / Accepted: 4 July 2001 相似文献
2.
Extended quark distribution functions are presented obtained by fitting a large amount of experimental data of the l-A DIS process on the basis of an improved nuclear density model. The experimental data of l-A DIS processes with A≥3 in the region 0.0010≤x≤0.9500 are quite satisfactorily described by using the extended formulae. Our knowledge of the influence of nuclear matter on the quark distributions is deepened. 相似文献
3.
Ever since the discovery of carbon nanotubes (CNTs) by Iijima in 1991, there have been extensive research efforts on their synthesis, physics, electronics, chemistry, and applications due to the fact that CNTs were predicted to have extraordinary physical, mechanical, chemical, optical, and electronic properties. Among the various forms of CNTs, single-walled and multi-walled, random and aligned, semiconducting and metallic, aligned CNTs are especially important since fundamental physics studies and many important applications will not be possible without alignment. Even though there have been significant endeavors on growing CNTs in an aligned configuration since their discovery, little success had been realized before our first report on growing individually aligned CNTs on various substrates by plasma-enhanced chemical vapor deposition (PECVD) [Science 282 (1998) 1105–1108]. Our report spearheaded a new field on growth, characterization, physics, and applications of aligned CNTs. Up to now, there have been thousands of scientific publications on synthesizing, studying, and utilizing aligned CNTs in various aspects. In this communication, we review the current status of aligned CNTs, the physics for their alignment, their applications in field emission, optical antennas, subwavelength light transmission in CNT-based nanocoax structures, nanocoax arrays for novel solar cell structures, etc. The focus of this review is to examine various aligned CNT systems, either as an individual or as an array, either the orientation is vertical, parallel, or at other angles to the substrate horizon, either the CNT core structures are mostly hollow channels or are composed of complex compartments. Major fabrication methods are illustrated in detail, particularly the most widely used PECVD growth technique on which various device integration schemes are based, followed by applications whereas current limitations and challenges will also be discussed to lay down the foundation for future developments. 相似文献
4.
Kovařík K Schienbein I Olness FI Yu JY Keppel C Morfín JG Owens JF Stavreva T 《Physical review letters》2011,106(12):122301
We perform a global χ2 analysis of nuclear parton distribution functions using data from charged current neutrino-nucleus (νA) deep-inelastic scattering (DIS), charged-lepton-nucleus (?(±)A) DIS, and the Drell-Yan (DY) process. We show that the nuclear corrections in νA DIS are not compatible with the predictions derived from ?(±)A DIS and DY data. We quantify this result using a hypothesis-testing criterion based on the χ2 distribution which we apply to the total χ2 as well as to the χ2 of the individual data sets. We find that it is not possible to accommodate the data from νA and ?(±)A DIS by an acceptable combined fit. Our result has strong implications for the extraction of both nuclear and proton parton distribution functions using combined neutrino and charged-lepton data sets. 相似文献
5.
WANG Yan-Zhao ZHANG Hong-Fei GAO Yong-Hua HOU Zhao-Yu DONG Jian-Min DUAN Chun-Gui ZUO Wei 《中国物理C(英文版)》2009,33(4):263-268
Extended quark distribution functions are presented obtained by fitting a large amount of experi-mental data of the ι-A DIS process on the basis of an improved nuclear density model. The experimental data of ι-A DIS processes with A≥ 3 in the region 0.0010 ≤ x ≤ 0.9500 are quite satisfactorily described by using the extended formulae. Our knowledge of the influence of nuclear matter on the quark distributions is deepened. 相似文献
6.
It is shown that a smectic A droplet deposited on a solid substrate treated for strong homeotropic anchoring is faceted at
the top in spite of the fact that there are no steps at the free surface, but instead edge dislocations in the bulk. The radius
of the facet and the full profile of the curved part of the droplet are determined as a function of the temperature in the
vicinity of a nematic-smectic A phase transition. It is shown that the observed profiles do not correspond to the actual equilibrium
shape, but to metastable configurations close to their point of marginal stability. In addition, we predict that the profiles
must be different for a given temperature depending on whether the droplet has been heated or cooled down to reach this temperature.
Finally, we discuss the problem of the formation of giant dislocations in big droplets (Grandjean terraces). 相似文献
7.
L.R. Hutchings R.W. Richards R.L. Thompson D.G. Bucknall A.S. Clough 《The European physical journal. E, Soft matter》2001,5(4):451-464
Heterotelechelic deuteropolystyrenes have been synthesised with a tertiary amine functionality at one end and a fluorocarbon
group at the other end of the polymer chain. A layer of this polymer, circa 120 ? thick, has been attached to the surface of a silicon substrate and subsequently covered with a much thicker layer of
hydrogenous polystyrene. The combination has then been annealed at 413 K under vacuum for defined times and the subsequent
distribution of the deutero heterotelechelic polymer determined using nuclear reaction analysis and neutron reflectometry.
The influences of annealing time, molecular weight and thickness of the hydrogenous polymer have been examined. Nuclear reaction
analysis showed that an excess of the heterotelechelic polymer formed at both interfaces with a larger excess remaining at
the substrate-polymer interface. When the molecular weight of the hydrogenous polymer is lower than that of the deuteropolymer,
the deutero layer is initially swollen by the hydrogenous polymer but the thickness then decreases as deutero polymer becomes
detached from the silicon substrate and an additional excess layer is eventually formed at the vacuum-polymer surface. When
the molecular weight of the hydrogenous polymer is higher, there is an initial shrinkage of the deuteropolymer layer, but
the original thickness (∼ radius of gyration of the deuteropolymer) is regained on prolonged annealing. There is no evidence
for bridging between the two interfaces by the heterotelechelic polymer. After five days annealing the volume fraction distribution
of the deuteropolymer at the silicon substrate was well described by a self-consistent field model where the only adjustable
parameter was the sticking energy of the tertiary amine group to the silicon substrate for which a value of 8k
B
T was obtained. Comparison of the dependence of the equilibrium layer thickness of the deuteropolymer on the equilibrium grafting
density at the silicon surface with the predictions of scaling theory for brush-like polymer layers suggested that the grafted
molecules were in the ideal, unperturbed brush region.
Received 12 October 2000 and Received in final form 27 March 2001 相似文献
8.
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
9.
C. Ciofi degli Atti L.P. Kaptari S. Scopetta 《The European Physical Journal A - Hadrons and Nuclei》1999,5(2):191-207
It is shown that in semi-inclusive deep inelastic scattering (DIS) of electrons off complex nuclei, the detection, in coincidence
with the scattered electron, of a nucleus (A−1) in the ground state, as well as of a nucleon and a nucleus (A−2), also in the ground state, may provide unique information on several long standing problems, such as: i) the nature and
the relevance of the final state interaction in DIS; ii) the validity of the spectator mechanism in DIS; iii) the medium induced
modifications of the nucleon structure function; iv) the origin of the EMC effect.
Received: 4 March 1999 相似文献
10.
P. Strasser T. Matsuzaki K. Nagamine 《The European Physical Journal A - Hadrons and Nuclei》2002,13(1-2):197-202
X-ray spectroscopy of muonic atoms is an important tool to obtain information on the nuclear charge distribution of nuclei.
It has been successfully used for many years to study stable isotopes in condensed or gaseous states. A new method has been
proposed to extend muonic atom X-ray spectroscopy to the use of radioactive isotope beams to form muonic atoms with unstable
nuclei. This new method allows studies of the nuclear properties and nuclear sizes of unstable atoms by means of the muonic
X-ray method at facilities where both negative muon and radioactive nuclear beams would be available. Progress of a feasibility
study at RIKEN-RAL muon facility is also reported.
Received: 1 May 2001 / Accepted: 4 December 2001 相似文献
11.
R.N. Boyd 《The European Physical Journal A - Hadrons and Nuclei》2002,13(1-2):203-206
There are many explosive processes in nucleosynthesis: big bang nucleosynthesis, the rp-process, the γ-process, the ν-process,
and the r-process. However, I will discuss just the rp-process and the r-process in detail, primarily because both seem to
have been very active research areas of late, and because they have great potential for studies with radioactive nuclear beams.
I will also discuss briefly the γ-process because of its inevitability in conjunction with the rp-process.
Received: 1 May 2001 / Accepted: 4 December 2001 相似文献
12.
M. Sajjad Athar S. Ahmad S. K. Singh 《The European Physical Journal A - Hadrons and Nuclei》2005,24(3):459-474
The charged current lepton production induced by neutrinos in 56Fe nuclei has been studied. The calculations have been done for the quasielastic as well as the inelastic reactions assuming Δ-dominance and take into account the effect of Pauli blocking, Fermi motion and the renormalization of weak transition strengths in the nuclear medium. The quasielastic production cross-sections for lepton production are found to be strongly reduced due to nuclear effects, while there is about 10% reduction in the inelastic cross-sections in the absence of the final-state interactions of the pions. The numerical results for the momentum and angular distributions of the leptons averaged over the various atmospheric-neutrino spectra at the Soudan and Gran Sasso sites have been presented. The effect of nuclear-model dependence and the atmospheric-flux dependence on the relative yield of μ to e has been studied and discussed. 相似文献
13.
The shapefactor, the logft-value, the electron longitudinal polarization and the distribution of electrons emitted from oriented nuclei of36Cl have been calculated by applying two different nuclear models. Firstly a pure 1d3/2→1d3/2 transition has been considered. Secondly a more refined shell model of thes-d shell configuration space has been taken into account. It is shown that there is no great influence of the shell model version to the observables, that the observables depend strongly on the relativistic nuclear matrix elements, that the so-called “two parameter equation” for the shapefactor cannot be used in the case of36Cl and that there is no larger sensitivity of (V+A) admixtures to the electron longitudinal polarization than normally found in allowed decays. Comparisons with the existing experimental data are made. 相似文献
14.
M. Mukherjee D. Beck K. Blaum G. Bollen J. Dilling S. George F. Herfurth A. Herlert A. Kellerbauer H. -J. Kluge S. Schwarz L. Schweikhard C. Yazidjian 《The European Physical Journal A - Hadrons and Nuclei》2008,35(1):1-29
ISOLTRAP is a Penning trap mass spectrometer for high-precision mass measurements on short-lived nuclides installed at the
on-line isotope separator ISOLDE at CERN. The masses of close to 300 radionuclides have been determined up to now. The applicability
of Penning trap mass spectrometry to mass measurements of exotic nuclei has been extended considerably at ISOLTRAP by improving
and developing this double Penning trap mass spectrometer over the past two decades. The accurate determination of nuclear
binding energies far from stability includes nuclei that are produced at rates less than 100 ions/s and with half-lives well
below 100ms. The mass-resolving power reaches 107 corresponding to 10keV for medium heavy nuclei and the uncertainty of the resulting mass values has been pushed down to below
10-8. The article describes technical developments achieved since 1996 and the present performance of ISOLTRAP. 相似文献
15.
C. Ciofi degli Atti B.Z. Kopeliovich 《The European Physical Journal A - Hadrons and Nuclei》2003,17(1):133-144
The Final-State Interaction (FSI) in Deep-Inelastic Scattering (DIS) of leptons off a nucleus A, due to the propagation of the struck nucleon debris and its hadronization in the nuclear environment is considered. The
effective cross-section of such a partonic system with the nucleons of the medium and its time dependence are estimated, for
different values of the Bjorken scaling variable, on the basis of a model which takes into account both the production of
hadrons due to the breaking of the color string, which is formed after a quark is knocked out off a bound nucleon, as well
as the production of hadrons originating from gluon radiation. It is shown that the interaction, the evolution and the hadronization
of the partonic system in the nuclear environment can be thoroughly investigated by a new type of semi-inclusive process,
denoted A(e, e'(A - 1))X, in which the scattered lepton is detected in coincidence with a heavy nuclear fragment, namely a nucleus (A - 1) in low energy and momentum states. As a matter of fact, if the FSI is disregarded, the momentum distribution of (A - 1) is directly related to the momentum distribution of the nucleon before γ* absorption, i.e. the same quantity which appears in the conventional A(e, e'N)X process, where N denotes a nucleon. The rescattering of the struck nucleon debris with the medium damps and distorts the momentum distributions
of (A - 1) in a way which is very sensitive to the details of the effective cross-section of the debris with the nucleons of the
medium. The total cross-section of the process A(e, e'(A - 1))X on 4He, 16O, and 40Ca, related to the probability that after a target nucleon experiences a DIS process, the recoiling (A - 1) nucleus remains intact in spite of the strong FSI, is evaluated, and the distorted momentum distribution of the recoiling
(A - 1) system is obtained. It is shown that both quantities are very sensitive to the details of the early stage of hadronization
of the nucleon debris in the nuclear medium.
Received: 28 June 2002 / Accepted: 15 January 2003 / Published online: 5 May 2003 相似文献
16.
R. Liu M.-L. Liang B. Yuan 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(3):571-578
Pairwise thermal entanglement in the three-qubit XXX
Heisenberg model with next nearest neighbor interaction and a nonuniform
magnetic field has been studied. It's found that the next nearest neighbor
interaction has a great effect on the entanglement between the next nearest
neighbor sites, but has slight effect on the nearest neighbor
entanglement (NNE). Applying a magnetic field at the middle site enhances the
next nearest neighbor entanglement (NNNE) sharply when there is a small field
at the side sites and the next nearest neighbor coupling constant is
positive. A staggered magnetic field helps to maintain nearest neighbor
entanglement obviously. 相似文献
17.
C. M.J. Wijers J.-H. Chu O. Voskoboynikov 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(2):225-241
The influence of the surrounding semiconducting matrix upon the
optical response of embedded nano-objects (quantum dots) has been
investigated. This system can be described by means of a hybrid model, where the full response is a combination of a macroscopic
electrostatic response term and a dynamic response term, obtained quantum mechanically. The result is a modified discrete
dipole model, where excess discrete dipoles having an excess polarizability with respect to a uniform background identical
to the dielectric host material represent the response. In this model all electrodynamic interactions are screened by the
host material. The electrostatic response is obtained by approximating the quantum dots by embedded dielectric oblate ellipsoids.
Closed expressions for the electrostatic response of these ellipsoids have been derived. The electrodynamic nature of the
dynamic quantum mechanical polarizability term however is unclear. It is not certain whether this polarizability is dressed
or bare. Therefore we have investigated in detail the consequences of both options. Although there is no real qualitative
difference between them, the difference is so large that experiment can easily discriminate between both. Results should be
easily measurable anyhow. 相似文献
18.
L. Grodzins 《Hyperfine Interactions》1983,13(1-3):57-64
Mössbauer's discovery vitalized the study of hyperfine interactions on nuclear states. The technique has been used to measure the electromagnetic moments of scores of nuclear levels and the results, especially on rotational states, have been important to our understanding of nuclear structure. Equally signicant for nuclear physics has been the deep insight which Mössbauer studies have given us of the hyperfine interaction itself; using that knowledge, and a variety of techniques, the measurements of nuclear magnetic moments are now reliable and routine. 相似文献
19.
N. Nakaoka K. Watanabe 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):397-400
Capacitances of molecules, fullerenes and carbon nanotubes
under the condition of no electron-tunneling are calculated by
the partitioned real-space density functional method that has
been recently developed. We found that a quantum capacitance of
a spherical jellium bielectrode decreases and approaches the
classical value as the electron density increases. The
capacitances of fullerenes and carbon nanotubes do not depend on
the detailed atomic geometry but on the overall shapes. The
values of the capacitances of these nanostructures are found to
be a few 10-20 F and are compatible
with the experimental ones determined by the scanning tunneling
microscopy studies. 相似文献
20.
D. Stauffer M. Sahimi 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,57(2):147-152
Models that provide insight into how extreme positions regarding any social phenomenon may spread in a society or at the global
scale are of great current interest. A realistic model must account for the fact that globalization, internet, and other means
of mass communications have given rise to scale-free networks of interactions between people. We propose a novel model which
takes into account the nature of the interactions network, and provides some key insights into this phenomenon. These include,
(1) the existence of a
fundamental difference between a hierarchical network whereby people are influenced by those that are higher in the hierarchy
but not by those below them, and a symmetrical network where person-on-person influence works mutually, and (2) that a few
“fanatics” can influence a large fraction of the population either temporarily (in the hierarchical networks) or permanently
(in symmetrical networks). Even if the “fanatics” disappear, the population may still remain susceptible to the positions
originally advocated by them. The
model is, however, general and applicable to any phenomenon for which there is a degree of enthusiasm or susceptibility to
in the population. 相似文献