26,445 research outputs found
Modulated amplitude waves with nonzero phases in Bose-Einstein condensates
In this paper we give a frame for application of the averaging method to
Bose-Einstein condensates (BECs) and obtain an abstract result upon the
dynamics of BECs. Using aver- aging method, we determine the location where the
modulated amplitude waves (periodic or quasi-periodic) exist and we also study
the stability and instability of modulated amplitude waves (periodic or
quasi-periodic). Compared with the previous work, modulated amplitude waves
studied in this paper have nontrivial phases and this makes the problem become
more diffcult, since it involves some singularities.Comment: 17 pages, 2 figure
An ab initio investigation on the endohedral metallofullerene Gd 3 N â C 80
First-principles electronic structure studies on the ground state geometry and electronic and magnetic properties of bare and hydrogen coated metallofullerene Gd3NâC80 have been carried out within a density functional formalism. The correlation effects are incorporated either through a generalized gradient corrected functional or through an on-site Coulomb interaction (LDA+U). It is shown that the bare Gd3NâC80 possess a ferromagnetic ground state with a large spin moment of 21ÎŒB that is highly stable against spin fluctuations. The simulated Raman spectrum shows that the low-energy peaks are contributed by the floppy movement of N atom. As to the effect of addition of hydrogens, it is shown that the most favorable site for the hydrogen adsorption is an on-top site where the H atom is located above a five-member carbon ring with a binding energy of 1.92eV, while the least stable site corresponds to an on-top absorption above a six-member ring. A study of the energetics upon multiple adsorption of H shows that the binding energy of the H to metallofullerene drops after 11 H atoms. This shows that it should be possible to attach multiple ligands offering the potential that the Gd3NâC80 can be functionalized with ligands or assembled in cluster assemblies
Axisymmetric Self-Similar Equilibria of Self-Gravitating Isothermal Systems
All axisymmetric self-similar equilibria of self-gravitating, rotating,
isothermal systems are identified by solving the nonlinear Poisson equation
analytically. There are two families of equilibria: (1) Cylindrically symmetric
solutions in which the density varies with cylindrical radius as R^(-alpha),
with 0 <= alpha <= 2. (2) Axially symmetric solutions in which the density
varies as f(theta)/r^2, where `r' is the spherical radius and `theta' is the
co-latitude. The singular isothermal sphere is a special case of the latter
class with f(theta)=constant. The axially symmetric equilibrium configurations
form a two-parameter family of solutions and include equilibria which are
surprisingly asymmetric with respect to the equatorial plane. The asymmetric
equilibria are, however, not force-free at the singular points r=0, infinity,
and their relevance to real systems is unclear. For each hydrodynamic
equilibrium, we determine the phase-space distribution of the collisionless
analog.Comment: 13 pages, 7 figures, uses emulateapj.sty. Submitted to Ap
Trivial topological phase of CaAgP and the topological nodal-line transition in CaAg(P1-xAsx)
By performing angle-resolved photoemission spectroscopy and first-principles
calculations, we address the topological phase of CaAgP and investigate the
topological phase transition in CaAg(P1-xAsx). We reveal that in CaAgP, the
bulk band gap and surface states with a large bandwidth are topologically
trivial, in agreement with hybrid density functional theory calculations. The
calculations also indicate that application of "negative" hydrostatic pressure
can transform trivial semiconducting CaAgP into an ideal topological nodal-line
semimetal phase. The topological transition can be realized by partial
isovalent P/As substitution at x = 0.38.Comment: 20 pages, 4 figure
Competition and adaptation in an Internet evolution model
We model the evolution of the Internet at the Autonomous System level as a
process of competition for users and adaptation of bandwidth capability. We
find the exponent of the degree distribution as a simple function of the growth
rates of the number of autonomous systems and the total number of connections
in the Internet, both empirically measurable quantities. This fact place our
model apart from others in which this exponent depends on parameters that need
to be adjusted in a model dependent way. Our approach also accounts for a high
level of clustering as well as degree-degree correlations, both with the same
hierarchical structure present in the real Internet. Further, it also
highlights the interplay between bandwidth, connectivity and traffic of the
network.Comment: Minor content changes and inset of fig.
Nonsaturating magnetoresistance and nontrivial band topology of type-II Weyl semimetal NbIrTe4
Weyl semimetals, characterized by nodal points in the bulk and Fermi arc
states on the surface, have recently attracted extensive attention due to the
potential application on low energy consumption electronic materials. In this
report, the thermodynamic and transport properties of a theoretically predicted
Weyl semimetal NbIrTe4 is measured in high magnetic fields up to 35 T and low
temperatures down to 0.4 K. Remarkably, NbIrTe4 exhibits a nonsaturating
transverse magnetoresistance which follows a power-law dependence in B.
Low-field Hall measurements reveal that hole-like carriers dominate the
transport for T 80 K, while the significant enhancement of electron
mobilities with lowering T results in a non-negligible contribution from
electron-like carriers which is responsible for the observed non-linear Hall
resistivity at low T. The Shubnikov-de Haas oscillations of the Hall
resistivity under high B give the light effective masses of charge carriers and
the nontrivial Berry phase associated with Weyl fermions. Further
first-principles calculations confirm the existence of 16 Weyl points located
at kz = 0, 0.02 and 0.2 planes in the Brillouin zone.Comment: 5 figures, 1 tabl
Phase Diagram of Rydberg atoms in a nonequilibrium optical lattice
We study the quantum nonequilibrium dynamics of ultracold three-level atoms
trapped in an optical lattice, which are excited to their Rydberg states via a
two-photon excitation with nonnegligible spontaneous emission. Rich quantum
phases including uniform phase, antiferromagnetic phase and oscillatory phase
are identified. We map out the phase diagram and find these phases can be
controlled by adjusting the ratio of intensity of the pump light to the control
light, and that of two-photon detuning to the Rydberg interaction strength.
When the two-photon detuning is blue-shifted and the latter ratio is less than
1, bistability exists among the phases. Actually, this ratio controls the
Rydberg-blockade and antiblockade effect, thus the phase transition in this
system can be considered as a possible approach to study both effects.Comment: 5 pages,5 figure
What about a beta-beam facility for low energy neutrinos?
A novel method to produce neutrino beams has recently been proposed : the
beta-beams. This method consists in using the beta-decay of boosted radioactive
nuclei to obtain an intense, collimated and pure neutrino beam. Here we propose
to exploit the beta-beam concept to produce neutrino beams of low energy. We
discuss the applications of such a facility as well as its importance for
different domains of physics. We focus, in particular, on neutrino-nucleus
interaction studies of interest for various open issues in astrophysics,
nuclear and particle physics. We suggest possible sites for a low energy
beta-beam facility.Comment: 4 pages, 1 figur
Theory of I-V Characteristics of Magnetic Josephson Junctions
We analyze the electrical characteristics of a circuit consisting of a free
thin-film magnetic layer and source and drain electrodes that have opposite
magnetization orientations along the free magnet's two hard directions. We find
that when the circuit's current exceeds a critical value there is a sudden
resistance increase which can be large in relative terms if the currents to
source or drain are strongly spin polarized and the free magnet is thin. This
behavior can be partly understood in terms of a close analogy between the
magnetic circuit and a Josephson junction
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