212,552 research outputs found
Oblique Long Waves on Beach and Induced Longshore Current
This study considers the 3D runup of long waves on a uniform beach of constant or variable downward slope that is connected to an open ocean of uniform depth. An inviscid linear long-wave theory is applied to obtain the fundamental solution for a uniform train of sinusoidal waves obliquely incident upon a uniform beach of variable downward slope without wave breaking. For waves at nearly grazing incidence, runup is significant only for the waves in a set of eigenmodes being trapped within the beach at resonance with the exterior ocean waves. Fourier synthesis is employed to analyze a solitary wave and a train of cnoidal waves obliquely incident upon a sloping beach, with the nonlinear and dispersive effects neglected at this stage. Comparison is made between the present theory and the ray theory to ascertain a criterion of validity. The wave-induced longshore current is evaluated by finding the Stokes drift of the fluid particles carried by the momentum of the waves obliquely incident upon a sloping beach. Currents of significant velocities are produced by waves at incidence angles about 45 [degrees] and by grazing waves trapped on the beach. Also explored are the effects of the variable downward slope and curvature of a uniform beach on 3D runup and reflection of long waves
Pseudo-magnetoexcitons in strained graphene bilayers without external magnetic fields
The structural and electronic properties of graphene leads its charge
carriers to behave like relativistic particles, which is described by a
Dirac-like Hamiltonian. Since graphene is a monolayer of carbon atoms, the
strain due to elastic deformations will give rise to so-called `pseudomagnetic
fields (PMF)' in graphene sheet, and that has been realized experimentally in
strained graphene sample. Here we propose a realistic strained graphene bilayer
(SGB) device to detect the pseudo-magnetoexcitons (PME) in the absence of
external magnetic field. The carriers in each graphene layer suffer different
strong PMFs due to strain engineering, which give rise to Landau quantization.
The pseudo-Landau levels (PLLs) of electron-hole pair under inhomogeneous PMFs
in SGB are analytically obtained in the absence of Coulomb interactions. Based
on the general analytical optical absorption selection rule for PME, we show
that the optical absorption spectrums can interpret the corresponding formation
of Dirac-type PME. We also predict that in the presence of inhomogeneous PMFs,
the superfluidity-normal phase transition temperature of PME is greater than
that under homogeneous PMFs.}Comment: 16 pages, 6 figure
Anomalous Currents on Closed Surfaces: Extended Proximity, Partial Quantization, and Qubits
Motivated by the surface of topological insulators, the Dirac anomaly's
discontinuous dependence on sign of the mass, , is investigated on
closed topologies when mass terms are weak or only partially cover the surface.
It is found that, unlike the massive Dirac theory on an infinite plane, there
is a smoothly decreasing current when the mass region is not infinite; also, a
massive finite region fails to exhibit a Hall current edge--exerting an
extended proximity effect, which can, however, be uniformly small--and
oppositely orientated Hall phases are fully quantized while accompanied by
diffuse chiral modes. Examples are computed using Dirac energy eigenstates on a
flat torus (genus one topology) and closed cap cylinder (genus zero topology)
for various mass-term geometries. Finally, from the resulting the properties of
the surface spectra, a potential application for a flux-charge qubit is
presented.Comment: 22 pages, 13 figures. References and focus updated. Added effective
action arguments. Same text as published versio
Ballistic electronic transport in Quantum Cables
We studied theoretically ballistic electronic transport in a proposed
mesoscopic structure - Quantum Cable. Our results demonstrated that Qauntum
Cable is a unique structure for the study of mesoscopic transport. As a
function of Fermi energy, Ballistic conductance exhibits interesting stepwise
features. Besides the steps of one or two quantum conductance units (),
conductance plateaus of more than two quantum conductance units can also be
expected due to the accidental degeneracies (crossings) of subbands. As
structure parameters is varied, conductance width displays oscillatory
properties arising from the inhomogeneous variation of energy difference
betweeen adjoining transverse subbands. In the weak coupling limits,
conductance steps of height becomes the first and second plateaus for
the Quantum Cable of two cylinder wires with the same width.Comment: 11 pages, 5 figure
Chiral superfluid states in hybrid graphene heterostructures
The use of high quality hexagonal boron nitride (hBN) as a dielectric
material has made possible the realization of graphene devices with very high
mobility. In addition hBN can be made as thin as few atomic layers and, as
recently demonstrated experimentally, can be used to isolate electrically two
graphene layers only few nanometers apart. The combined use of graphene and hBN
has therefore opened the possibility to create novel electronic structures. In
this work we study the "hybrid" heterostructure formed by one sheet of single
layer graphene (SLG) and one sheet of bilayer graphene (BLG) separated by a
thin film of hBN. In general it is expected that interlayer interactions can
drive the system to a spontaneously broken symmetry state characterized by
interlayer phase coherence. The peculiarity of the SLG-BLG heterostructure is
that the electrons in the layers (SLG and BLG) have different chiralities. We
find that the difference of chirality between electrons in the two layers
causes the spontaneously broken symmetry state to be N-fold degenerate.
Moreover, we find that some of the degenerate states are chiral superfluid
states, topologically distinct from the usual layer-ferromagnetism. The chiral
nature of the ground state opens the possibility to realize protected midgap
states. The N-fold degeneracy of the ground state makes the physics of SLG-BLG
hybrid systems analogous to the physics of helium-3, in particular given the
recent discovery of chiral superfluid states in this system.Comment: 5 pages, 4 figure
Improved quark mass density- dependent model with quark and non-linear scalar field coupling
The improved quark mass density- dependent model which includes the coupling
between the quarks and a non-linear scalar field is presented. Numerical
analysis of solutions of the model is performed over a wide range of
parameters. The wave functions of ground state and the lowest one-particle
excited states with even and odd parity are given. The root-mean squared
radius, the magnetic moment and the ratio between the axial-vector and the
vector beta-decay coupling constants of the nucleon are calculated. We found
that the present model is successful to describe the properties of nucleon.Comment: 7pages, 6 figure
The State Equation of the Yang-Mills field Dark Energy Models
In this paper, we study the possibility of building Yang-Mills(YM) field dark
energy models with equation of state (EoS) crossing -1, and find that it can
not be realized by the single YM field models, no matter what kind of
lagrangian or initial condition. But the states of and
all can be naturally got in this kind of models. The former is like
a quintessence field, and the latter is like a phantom field. This makes that
one can build a model with two YM fields, in which one with the initial state
of , and the other with . We give an example model of
this kind, and find that its EoS is larger than -1 in the past and less than -1
at the present time. We also find that this change must be from to
, and it will go to the critical state of with the expansion
of the Universe, which character is same with the single YM field models, and
the Big Rip is naturally avoided.Comment: 20 pages, 4 figures. minor typos correcte
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