1,065,633 research outputs found
Boussinesq-like multi-component lattice equations and multi-dimensional consistency
We consider quasilinear, multi-variable, constant coefficient, lattice
equations defined on the edges of the elementary square of the lattice, modeled
after the lattice modified Boussinesq (lmBSQ) equation, e.g., . These equations are classified into three canonical forms and
the consequences of their multidimensional consistency
(Consistency-Around-the-Cube, CAC) are derived. One of the consequences is a
restriction on form of the equation for the variable, which in turn implies
further consistency conditions, that are solved. As result we obtain a number
of integrable multi-component lattice equations, some generalizing lmBSQ.Comment: 24 page
Accelerating universes driven by bulk particles
We consider our universe as a 3d domain wall embedded in a 5d dimensional
Minkowski space-time. We address the problem of inflation and late time
acceleration driven by bulk particles colliding with the 3d domain wall. The
expansion of our universe is mainly related to these bulk particles. Since our
universe tends to be permeated by a large number of isolated structures, as
temperature diminishes with the expansion, we model our universe with a 3d
domain wall with increasing internal structures. These structures could be
unstable 2d domain walls evolving to fermi-balls which are candidates to cold
dark matter. The momentum transfer of bulk particles colliding with the 3d
domain wall is related to the reflection coefficient. We show a nontrivial
dependence of the reflection coefficient with the number of internal dark
matter structures inside the 3d domain wall. As the population of such
structures increases the velocity of the domain wall expansion also increases.
The expansion is exponential at early times and polynomial at late times. We
connect this picture with string/M-theory by considering BPS 3d domain walls
with structures which can appear through the bosonic sector of a
five-dimensional supergravity theory.Comment: To appear in Phys. Rev. D, 16 pages, 3 eps figures, minor changes and
references adde
Far-infrared constraints on the contamination by dust-obscured galaxies of high-z dropout searches
The spectral energy distributions (SED) of dusty galaxies at intermediate redshift may look similar to very high-redshift galaxies in the optical/near infrared (NIR) domain. This can lead to the contamination of high-redshift galaxy searches based on broad-band optical/NIR photometry by lower redshift dusty galaxies because both kind of galaxies cannot be distinguished. The contamination rate could be as high as 50%. This work shows how the far-infrared (FIR) domain can help to recognize likely low-z interlopers in an optical/NIR search for high-z galaxies. We analyze the FIR SEDs of two galaxies that are proposed to be very high-redshift (z > 7) dropout candidates based on deep Hawk-I/VLT observations. The FIR SEDs are sampled with PACS/Herschel at 100 and 160 μm, with SPIRE/Herschel at 250, 350 and 500 μm and with LABOCA/APEX at 870 μm. We find that redshifts > 7 would imply extreme FIR SEDs (with dust temperatures >100 K and FIR luminosities >10^(13) L_⊙). At z ~ 2, instead, the SEDs of both sources would be compatible with those of typical ultra luminous infrared galaxies or submillimeter galaxies. Considering all available data for these sources from visible to FIR we re-estimate the redshifts and find z ~ 1.6–2.5. Owing to the strong spectral breaks observed in these galaxies, standard templates from the literature fail to reproduce the visible-to-near-IR part of the SEDs even when additional extinction is included. These sources strongly resemble dust-obscured galaxies selected in Spitzer observations with extreme visible-to-FIR colors, and the galaxy GN10 at z = 4. Galaxies with similar SEDs could contaminate other high-redshift surveys
Resolution of the Proton Spin Problem
A number of lines of investigation into the structure of the nucleon have
converged to the point where we believe that one has a consistent explanation
of the well known proton spin crisis.Comment: 10 pages, 1 figur
Leakage-current lineshapes from inelastic cotunneling in the Pauli spin blockade regime
We find the leakage current through a double quantum dot in the Pauli spin
blockade regime accounting for inelastic (spin-flip) cotunneling processes.
Taking the energy-dependence of this spin-flip mechanism into account allows
for an accurate description of the current as a function of applied magnetic
fields, gate voltages, and an inter-dot tunnel coupling. In the presence of an
additional local dephasing process or nonuniform magnetic field, we obtain a
simple closed-form analytical expression for the leakage current giving the
full dependence on an applied magnetic field and energy detuning. This work is
important for understanding the nature of leakage, especially in systems where
other spin-flip mechanisms (due, e.g., to hyperfine coupling to nuclear spins
or spin-orbit coupling) are weak, including silicon and carbon-nanotube or
graphene quantum dots.Comment: 11 pages, 10 figures; v2: Typos corrected, colorbar added to fig. 7,
final version published in Phys. Rev.
Magnetic remanence of Josephson junction arrays
In this work we study the magnetic remanence exhibited by Josephson junction
arrays in response to an excitation with an AC magnetic field. The effect,
predicted by numerical simulations to occur in a range of temperatures, is
clearly seen in our tridimensional disordered arrays. We also discuss the
influence of the critical current distribution on the temperature interval
within which the array develops a magnetic remanence. This effect can be used
to determine the critical current distribution of an array.Comment: 8 pages, 4 figures, Talk to be presented on 44th Annual Conference on
Magnetism & Magnetic Materials, San Jose, CA, USA Accepted to be published in
Journal of Applied Physic
Detection of steam in the circumstellar disk around a massive Young Stellar Object
We report on the observation of hot water vapor (steam) in the inner AU of a
young massive star located in the star-forming region IRAS 08576-4334. The
water lines are detected in a medium resolution (R=10,000) K-band spectrum
taken by the infrared spectrometer ISAAC mounted on the VLT-ANTU. The water
vapor is at a mean temperature of 1565+/-510 K, cooler than the hot CO found in
the same object, which is at 1660K and the column density is N(H2O)=(2.5 +/-
0.4)x1E18 cm-2. The profile of both H2O and CO lines is best reproduced by the
emission from a Keplerian disk. To interpret the data, we also investigate the
formation of molecules and especially CO and water vapor in the inner hot and
dense part of disks around young high mass stars using a pseudo time-dependent
gas-phase chemical model. Molecules are rapidly photodissociated but this
destruction is compensated by an efficient formation due to fast
neutral-neutral reactions. The ability of CO molecules to self-shield
significantly enhances its abundance. Water molecules are sufficiently abundant
to be detectable. The observed H2O/CO ratio is reproduced by gas at 1600K and
an enhanced UV field over gas density ratio I_UV/nH=1E(-4)- 1E(-6). The
simulations support the presence of CO and H2O molecules in the inner disks
around young massive stars despite the strong UV radiation and show that the OH
radical plays an essential role in hot gas chemistry.Comment: 15 pages, 11 figures, Accepted to A&
Stationary and transient leakage current in the Pauli spin blockade
We study the effects of cotunneling and a non-uniform Zeeman splitting on the
stationary and transient leakage current through a double quantum dot in the
Pauli spin blockade regime. We find that the stationary current due to
cotunneling vanishes at low temperature and large applied magnetic field,
allowing for the dynamical preparation of a pure spin ground state, even at
large voltage bias. Additionally, we analyze current that flows between
blocking events, characterized, in general, by a fractional effective charge
. This charge can be used as a sensitive probe of spin relaxation
mechanisms and can be used to determine the visibility of Rabi oscillations.Comment: v1: 4 pages; v2: 4 pages+ additional supplementary material, version
to appear in PR
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