107,565 research outputs found
Soliton Resonances for MKP-II
Using the second flow - the Derivative Reaction-Diffusion system, and the
third one of the dissipative SL(2,R) Kaup-Newell hierarchy, we show that the
product of two functions, satisfying those systems is a solution of the
modified Kadomtsev-Petviashvili equation in 2+1 dimension with negative
dispersion (MKP-II). We construct Hirota's bilinear representation for both
flows and combine them together as the bilinear system for MKP-II. Using this
bilinear form we find one and two soliton solutions for the MKP-II. For special
values of parameters our solution shows resonance behaviour with creation of
four virtual solitons. Our approach allows one to interpret the resonance
soliton as a composite object of two dissipative solitons in 1+1 dimensions.Comment: 11 pages, 2 figures, Talk on International Conference "Nonlinear
Physics. Theory and Experiment. III", 24 June-3 July, 2004, Gallipoli(Lecce),
Ital
Common gauge origin of discrete symmetries in observable sector and hidden sector
An extra Abelian gauge symmetry is motivated in many new physics models in
both supersymmetric and nonsupersymmetric cases. Such a new gauge symmetry may
interact with both the observable sector and the hidden sector. We
systematically investigate the most general residual discrete symmetries in
both sectors from a common Abelian gauge symmetry. Those discrete symmetries
can ensure the stability of the proton and the dark matter candidate. A hidden
sector dark matter candidate (lightest U-parity particle or LUP) interacts with
the standard model fields through the gauge boson Z', which may selectively
couple to quarks or leptons only. We make a comment on the implications of the
discrete symmetry and the leptonically coupling dark matter candidate, which
has been highlighted recently due to the possibility of the simultaneous
explanation of the DAMA and the PAMELA results. We also show how to construct
the most general U(1) charges for a given discrete symmetry, and discuss the
relation between the U(1) gauge symmetry and R-parity.Comment: Version to appear in JHE
Lyman alpha line formation in starbursting galaxies II. Extremely Thick, Dustless, and Static HI Media
The Lya line transfer in an extremely thick medium of neutral hydrogen is
investigated by adopting an accelerating scheme in our Monte Carlo code to skip
a large number of core or resonant scatterings. This scheme reduces computing
time significantly with no sacrifice in the accuracy of the results. We applied
this numerical method to the Lya transfer in a static, uniform, dustless, and
plane-parallel medium. Two types of photon sources have been considered, the
midplane source and the uniformly distributed sources. The emergent profiles
show double peaks and absorption trough at the line-center. We compared our
results with the analytic solutions derived by previous researchers, and
confirmed that both solutions are in good agreement with each other. We
investigated the directionality of the emergent Lya photons and found that limb
brightening is observed in slightly thick media while limb darkening appears in
extremely thick media. The behavior of the directionality is noted to follow
that of the Thomson scattered radiation in electron clouds, because both Lya
wing scattering and Thomson scattering share the same Rayleigh scattering phase
function. The mean number of wing scatterings just before escape is in exact
agreement with the prediction of the diffusion approximation. The Lya photons
constituting the inner part of the emergent profiles follow the relationship
derived from the diffusion approximation. We present a brief discussion on the
application of our results to the formation of Lya broad absorption troughs and
P-Cygni type Lya profiles seen in the UV spectra of starburst galaxies.Comment: 24 papges, 12 figures, The revised version submitted to Ap
Coulomb corrections to bremsstrahlung in electric field of heavy atom at high energies
The differential and partially integrated cross sections are considered for
bremsstrahlung from high-energy electrons in atomic field with the exact
account of this field. The consideration exploits the quasiclassical electron
Green's function and wave functions in an external electric field. It is shown
that the Coulomb corrections to the differential cross section are very
susceptible to screening. Nevertheless, the Coulomb corrections to the cross
section summed up over the final-electron states are independent of screening
in the leading approximation over a small parameter ( is
a screening radius, is the electron mass, ). Bremsstrahlung from
an electron beam of the finite size on heavy nucleus is considered as well.
Again, the Coulomb corrections to the differential probability are very
susceptible to the beam shape, while those to the probability integrated over
momentum transfer are independent of it, apart from the trivial factor, which
is the electron-beam density at zero impact parameter. For the Coulomb
corrections to the bremsstrahlung spectrum, the next-to-leading terms with
respect to the parameters ( is the electron energy) and
are obtained.Comment: 13 pages, 4 figure
Pseudorandom Generators for Width-3 Branching Programs
We construct pseudorandom generators of seed length that -fool ordered read-once branching programs
(ROBPs) of width and length . For unordered ROBPs, we construct
pseudorandom generators with seed length . This is the first improvement for pseudorandom
generators fooling width ROBPs since the work of Nisan [Combinatorica,
1992].
Our constructions are based on the `iterated milder restrictions' approach of
Gopalan et al. [FOCS, 2012] (which further extends the Ajtai-Wigderson
framework [FOCS, 1985]), combined with the INW-generator [STOC, 1994] at the
last step (as analyzed by Braverman et al. [SICOMP, 2014]). For the unordered
case, we combine iterated milder restrictions with the generator of
Chattopadhyay et al. [CCC, 2018].
Two conceptual ideas that play an important role in our analysis are: (1) A
relabeling technique allowing us to analyze a relabeled version of the given
branching program, which turns out to be much easier. (2) Treating the number
of colliding layers in a branching program as a progress measure and showing
that it reduces significantly under pseudorandom restrictions.
In addition, we achieve nearly optimal seed-length
for the classes of: (1) read-once polynomials on
variables, (2) locally-monotone ROBPs of length and width
(generalizing read-once CNFs and DNFs), and (3) constant-width ROBPs of length
having a layer of width in every consecutive
layers.Comment: 51 page
How dsDNA breathing enhances its flexibility and instability on short length scales
We study the unexpected high flexibility of short dsDNA which recently has
been reported by a number of experiments. Via the Langevin dynamics simulation
of our Breathing DNA model, first we observe the formation of bubbles within
the duplex and also forks at the ends, with the size distributions independent
of the contour length. We find that these local denaturations at a
physiological temperature, despite their rare and transient presence, can lower
the persistence length drastically for a short DNA segment in agreement with
experiment
Wavelength- and material-dependent absorption in GaAs and AlGaAs microcavities
The quality factors of modes in nearly identical GaAs and
Al_{0.18}Ga_{0.82}As microdisks are tracked over three wavelength ranges
centered at 980 nm, 1460 nm, and 1600 nm, with quality factors measured as high
as 6.62x10^5 in the 1600-nm band. After accounting for surface scattering, the
remaining loss is due to sub-bandgap absorption in the bulk and on the
surfaces. We observe the absorption is, on average, 80 percent greater in
AlGaAs than in GaAs and in both materials is 540 percent higher at 980 nm than
at 1600nm.Comment: 4 pages, 2 figures, 1 table, minor changes to disucssion of Qrad and
Urbach tai
SPH Simulations of Galactic Gaseous Disk with Bar: Distribution and Kinematic Structure of Molecular Clouds toward the Galactic Center
We have performed Smoothed Particle Hydrodynamic (SPH) simulations to study
the response of molecular clouds in the Galactic disk to a rotating bar and
their subsequent evolution in the Galactic Center (GC) region. The Galactic
potential in our models is contributed by three axisymmetric components
(massive halo, exponential disk, compact bulge) and a non-axisymmetric bar.
These components are assumed to be invariant in time in the frame corotating
with the bar. Some noticeable features such as an elliptical outer ring, spiral
arms, a gas-depletion region, and a central concentration have been developed
due to the influence of the bar. The rotating bar induces non-circular motions
of the SPH particles, but hydrodynamic collisions tend to suppress the random
components of the velocity. The velocity field of the SPH particles is
consistent with the kinematics of molecular clouds observed in HCN (1-0)
transition; these clouds are thought to be very dense clouds. However, the l-v
diagram of the clouds traced by CO is quite different from that of our SPH
simulation, being more similar to that obtained from simulations using
collisionless particles. The diagram of a mixture of collisional and
collisionless particles gives better reproduction of the kinematic structures
of the GC clouds observed in the CO line. The fact that the kinematics of HCN
clouds can be reproduced by the SPH particles suggests that the dense clouds in
the GC are formed via cloud collisions induced by rotating bar.Comment: 31 pages, 10 pigures, accepted for publication in Ap
Water Use Efficiency in a Furrow System
An existing volumetric balance approach in conjunction with the Kostiakov infiltration equation for determining soil infiltration parameters in a furrow is used to study furrow irrigation in the local environment. Other parameters required include furrow geometry, assumed subsurface profile and flow advance data. A set of adjacent
furrows is used to indicate the performance of the field system. The procedure outlined here can be used to evaluate efficiency of continuous mode furrow irrigation. The spatial and temporal variation of infiltration
characteristics of a soil are well known. As such, the performance of a furrow irrigation system which uses the soil as a medium of conveyance varies with the ever-changing infiltration behaviour. There is therefore a
need for an evaluation procedure to determine water use efficiency which can be followed throughout the irrigation season so as to enable the irrigator to make any necessary changes to improve its performance. This
determination of irrigation performance hinges very much on the correct evaluation of the infiltration process, in this case, in dynamic infiltration water flowing overland in small channels. An evaluation example is given
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