39,670 research outputs found
Harmonic generation of noble-gas atoms in the Near-IR regime using ab-initio time-dependent R-matrix theory
We demonstrate the capability of ab-initio time-dependent R-matrix theory to
obtain accurate harmonic generation spectra of noble-gas atoms at Near-IR
wavelengths between 1200 and 1800 nm and peak intensities up to 1.8 X 10(14)
W/cm(2) . To accommodate the excursion length of the ejected electron, we use
an angular-momentum expansion up to Lmax = 279. The harmonic spectra show
evidence of atomic structure through the presence of a Cooper minimum in
harmonic generation for Kr, and of multielectron interaction through the giant
resonance for Xe. The theoretical spectra agree well with those obtained
experimentally.Comment: 6 pages, 5 figure
Superconductivity-Induced Transfer of In-Plane Spectral Weight in Bi2Sr2CaCu2O8: Resolving a Controversy
We present a detailed analysis of the superconductivity-induced
redistribution of optical spectral weight in Bi2Sr2CaCu2O8 near optimal doping.
It confirms the previous conclusion by Molegraaf et al. (Science 66, 2239
(2002)), that the integrated low-frequency spectral weight shows an extra
increase below Tc. Since the region, where the change of the integrated
spectral weight is not compensated, extends well above 2.5 eV, this transfer is
caused by the transfer of spectral weight from interband to intraband region
and only partially by the narrowing of the intraband peak. We show that the
opposite assertion by Boris et al. (Science 304, 708 (2004)) regarding this
compound, is unlikely the consequence of any obvious discrepancies between the
actual experimental data.Comment: ReVTeX, 9 pages, 8 encapsulated postscript figures, several typo's
correcte
Effect of long-range Coulomb interaction on shot-noise suppression in ballistic transport
We present a microscopic analysis of shot-noise suppression due to long-range
Coulomb interaction in semiconductor devices under ballistic transport
conditions. An ensemble Monte Carlo simulator self-consistently coupled with a
Poisson solver is used for the calculations. A wide range of injection-rate
densities leading to different degrees of suppression is investigated. A sharp
tendency of noise suppression at increasing injection densities is found to
scale with a dimensionless Debye length related to the importance of
space-charge effects in the structure.Comment: RevTex, 4 pages, 4 figures, minor correction
Investigating laser induced phase engineering in MoS2 transistors
Phase engineering of MoS2 transistors has recently been demonstrated and has
led to record low contact resistances. The phase patterning of MoS2 flakes with
laser radiation has also been realized via spectroscopic methods, which invites
the potential of controlling the metallic and semiconducting phases of MoS2
transistors by simple light exposure. Nevertheless, the fabrication and
demonstration of laser patterned MoS2 devices starting from the metallic
polymorph has not been demonstrated yet. Here, we study the effects of laser
radiation on 1T/1T'-MoS2 transistors with the prospect of driving an in-situ
phase transition to the 2H-polymorph through light exposure. We find that
although the Raman peaks of 2H-MoS2 become more prominent and the ones from the
1T/1T' phase fade after the laser exposure, the semiconducting properties of
the laser patterned devices are not fully restored and the laser treatment
ultimately leads to degradation of the transport channel
Secoviridae: a proposed family of plant viruses within the order Picornavirales that combines the families Sequiviridae and Comoviridae, the unassigned genera Cheravirus and Sadwavirus, and the proposed genus Torradovirus
The order Picornavirales includes several plant viruses that are currently classified into the families Comoviridae (genera Comovirus, Fabavirus and Nepovirus) and Sequiviridae (genera Sequivirus and Waikavirus) and into the unassigned genera Cheravirus and Sadwavirus. These viruses share properties in common with other picornavirales (particle structure, positive-strand RNA genome with a polyprotein expression strategy, a common replication block including type III helicase, a 3C-like cysteine proteinase and type I RNA-dependent RNA polymerase). However, they also share unique properties that distinguish them from other picornavirales. They infect plants and use specialized proteins or protein domains to move through their host. In phylogenetic analysis based on their replication proteins, these viruses form a separate distinct lineage within the picornavirales branch. To recognize these common properties at the taxonomic level, we propose to create a new family termed “Secoviridae” to include the genera Comovirus, Fabavirus, Nepovirus, Cheravirus, Sadwavirus, Sequivirus and Waikavirus. Two newly discovered plant viruses share common properties with members of the proposed family Secoviridae but have distinct specific genomic organizations. In phylogenetic reconstructions, they form a separate sub-branch within the Secoviridae lineage. We propose to create a new genus termed Torradovirus (type species, Tomato torrado virus) and to assign this genus to the proposed family Secoviridae
Potts models in the continuum. Uniqueness and exponential decay in the restricted ensembles
In this paper we study a continuum version of the Potts model. Particles are
points in R^d, with a spin which may take S possible values, S being at least
3. Particles with different spins repel each other via a Kac pair potential. In
mean field, for any inverse temperature there is a value of the chemical
potential at which S+1 distinct phases coexist. For each mean field pure phase,
we introduce a restricted ensemble which is defined so that the empirical
particles densities are close to the mean field values. Then, in the spirit of
the Dobrushin Shlosman theory, we get uniqueness and exponential decay of
correlations when the range of the interaction is large enough. In a second
paper, we will use such a result to implement the Pirogov-Sinai scheme proving
coexistence of S+1 extremal DLR measures.Comment: 72 pages, 1 figur
Thickness dependent interlayer transport in vertical MoS2 Josephson junctions
We report on observations of thickness dependent Josephson coupling and
multiple Andreev reflections (MAR) in vertically stacked molybdenum disulfide
(MoS2) - molybdenum rhenium (MoRe) Josephson junctions. MoRe, a chemically
inert superconductor, allows for oxide free fabrication of high transparency
vertical MoS2 devices. Single and bilayer MoS2 junctions display relatively
large critical currents (up to 2.5 uA) and the appearance of sub-gap structure
given by MAR. In three and four layer thick devices we observe orders of
magnitude lower critical currents (sub-nA) and reduced quasiparticle gaps due
to proximitized MoS2 layers in contact with MoRe. We anticipate that this
device architecture could be easily extended to other 2D materials.Comment: 18 pages, 6 figures including Supporting Informatio
Energetic radiation and the sulfur chemistry of protostellar envelopes: Submillimeter interferometry of AFGL 2591
CONTEXT: The chemistry in the inner few thousand AU of accreting envelopes
around young stellar objects is predicted to vary greatly with far-UV and X-ray
irradiation by the central star. Aim We search for molecular tracers of
high-energy irradiation by the protostar in the hot inner envelope. METHODS:
The Submillimeter Array (SMA) has observed the high-mass star forming region
AFGL 2591 in lines of CS, SO, HCN, HCN(v2=1), and HC15N with 0.6" resolution at
350 GHz probing radial scales of 600-3500 AU for an assumed distance of 1 kpc.
The SMA observations are compared with the predictions of a chemical model
fitted to previous single-dish observations. RESULTS: The CS and SO main peaks
are extended in space at the FWHM level, as predicted in the model assuming
protostellar X-rays. However, the main peak sizes are found smaller than
modeled by nearly a factor of 2. On the other hand, the lines of CS, HCN, and
HC15N, but not SO and HCN(v2=1), show pedestal emissions at radii of about 3500
AU that are not predicted. All lines except SO show a secondary peak within the
approaching outflow cone. A dip or null in the visibilities caused by a sharp
decrease in abundance with increasing radius is not observed in CS and only
tentatively in SO. CONCLUSIONS: The emission of protostellar X-rays is
supported by the good fit of the modeled SO and CS amplitude visibilities
including an extended main peak in CS. The broad pedestals can be interpreted
by far-UV irradiation in a spherically non-symmetric geometry, possibly
comprising outflow walls on scales of 3500 -- 7000 AU. The extended CS and SO
main peaks suggest sulfur evaporation near the 100 K temperature radius.Comment: Astronomy and Astrophysics, in pres
Chemical Modelling of Young Stellar Objects, I. Method and Benchmarks
Upcoming facilities such as the Herschel Space Observatory or ALMA will
deliver a wealth of molecular line observations of young stellar objects
(YSOs). Based on line fluxes, chemical abundances can then be estimated by
radiative transfer calculations. To derive physical properties from abundances,
the chemical network needs to be modeled and fitted to the observations. This
modeling process is however computationally exceedingly demanding, particularly
if in addition to density and temperature, far UV (FUV) irradiation, X-rays,
and multi-dimensional geometry have to be considered.
We develop a fast tool, suitable for various applications of chemical
modeling in YSOs. A grid of the chemical composition of the gas having a
density, temperature, FUV irradiation and X-ray flux is pre-calculated as a
function of time. A specific interpolation approach is developed to reduce the
database to a feasible size. Published models of AFGL 2591 are used to verify
the accuracy of the method. A second benchmark test is carried out for FUV
sensitive molecules. The novel method for chemical modeling is more than
250,000 times faster than direct modeling and agrees within a mean factor of
1.35. The tool is distributed for public use.
In the course of devloping the method, the chemical evolution is explored: We
find that X-ray chemistry in envelopes of YSOs can be reproduced by means of an
enhanced cosmic-ray ionization rate. We further find that the abundance of CH+
in low-density gas with high ionization can be enhanced by the recombination of
doubly ionized carbon (C++) and suggest a new value for the initial abundance
of the main sulphur carrier in the hot-core.Comment: Accepted by ApJS. 24 pages, 15 figures. A version with higher
resolution images is available from
http://www.astro.phys.ethz.ch/staff/simonbr/papgridI.pdf . Online data
available at http://www.astro.phys.ethz.ch/chemgrid.html . Second paper of
this series of papers available at arXiv:0906.058
Some studies on the deformation of the membrane in an RF MEMS switch
Radio Frequency (RF) switches of Micro Electro Mechanical Systems (MEMS) are appealing to the mobile industry because of their energy efficiency and ability to accommodate more frequency bands. However, the electromechanical coupling of the electrical circuit to the mechanical components in RF MEMS switches is not fully understood.
In this paper, we consider the problem of mechanical deformation of electrodes in RF MEMS switch due to the electrostatic forces caused by the difference in voltage between the electrodes. It is known from previous studies of this problem, that the solution exhibits multiple deformation states for a given electrostatic force. Subsequently, the capacity of the switch that depends on the deformation of electrodes displays a hysteresis behaviour against the voltage in the switch.
We investigate the present problem along two lines of attack.
First, we solve for the deformation states of electrodes using numerical methods such as finite difference and shooting methods. Subsequently, a relationship between capacity and voltage of the RF MEMS switch is constructed. The solutions obtained are exemplified using the continuation and bifurcation package AUTO.
Second, we focus on the analytical methods for a simplified version of the problem and on the stability analysis for the solutions of deformation states. The stability analysis shows that there exists a continuous path of equilibrium deformation states between the open and closed state
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