243 research outputs found
Origin of the Peaked Structure in the Conductance of One-Dimensional Silicon Accumulation Layers
We have made extensive studies of the temperature, gate voltage, and electric field dependences of the conductance peaks in small silicon inversion layers in order to distinguish between resonant-tunneling models and a hopping model. We find that many of the peaks are consistent only with a hopping model, whereas some could be consistent with an early resonant-tunneling model. None of our structure is consistent with resonant tunneling if the recent formulation of Stone and Lee is correct
Anti-shielding Effect and Negative Temperature in Instantaneously Reversed Electric Fields and Left-Handed Media
The connections between the anti-shielding effect, negative absolute
temperature and superluminal light propagation in both the instantaneously
reversed electric field and the left-handed media are considered in the present
paper. The instantaneous inversion of the exterior electric field may cause the
electric dipoles into the state of negative absolute temperature and therefore
give rise to a negative effective mass term of electromagnetic field (i. e.,
the electromagnetic field propagating inside the negative-temperature medium
will acquire an imaginary rest mass), which is said to result in the potential
superluminality effect of light propagation in this anti-shielding dielectric.
In left-handed media, such phenomena may also arise.Comment: 9 pages, Late
Complete Genome Sequence of Stenotrophomonas maltophilia Strain CF13, Recovered from Sputum from an Australian Cystic Fibrosis Patient.
Stenotrophomonas maltophilia isolate CF13 is a multidrug-resistant isolate that was recovered in Sydney, Australia, in 2011, from a sputum sample from an individual with cystic fibrosis. The genome sequence of CF13 was completed using long- and short-read technologies
Unconventional Fermi surface in an insulating state
Insulators occur in more than one guise, a recent finding was a class of
topological insulators, which host a conducting surface juxtaposed with an
insulating bulk. Here we report the observation of an unusual insulating state
with an electrically insulating bulk that simultaneously yields bulk quantum
oscillations with characteristics of an unconventional Fermi liquid. We present
quantum oscillation measurements of magnetic torque in high purity single
crystals of the Kondo insulator SmB6, which reveal quantum oscillation
frequencies characteristic of a large three-dimensional conduction electron
Fermi surface similar to the metallic rare earth hexaborides such as PrB6 and
LaB6. The quantum oscillation amplitude strongly increases at low temperatures,
appearing strikingly at variance with conventional metallic behaviour
Fast Differentially Private Matrix Factorization
Differentially private collaborative filtering is a challenging task, both in
terms of accuracy and speed. We present a simple algorithm that is provably
differentially private, while offering good performance, using a novel
connection of differential privacy to Bayesian posterior sampling via
Stochastic Gradient Langevin Dynamics. Due to its simplicity the algorithm
lends itself to efficient implementation. By careful systems design and by
exploiting the power law behavior of the data to maximize CPU cache bandwidth
we are able to generate 1024 dimensional models at a rate of 8.5 million
recommendations per second on a single PC
Numerical methods for non-LTE line radiative transfer: Performance and convergence characteristics
Comparison is made between a number of independent computer programs for
radiative transfer in molecular rotational lines. The test models are
spherically symmetric circumstellar envelopes with a given density and
temperature profile. The first two test models have a simple power law density
distribution, constant temperature and a fictive 2-level molecule, while the
other two test models consist of an inside-out collapsing envelope observed in
rotational transitions of HCO+. For the 2-level molecule test problems all
codes agree well to within 0.2%, comparable to the accuracy of the individual
codes, for low optical depth and up to 2% for high optical depths (tau=4800).
The problem of the collapsing cloud in HCO+ has a larger spread in results,
ranging up to 12% for the J=4 population. The spread is largest at the radius
where the transition from collisional to radiative excitation occurs. The
resulting line profiles for the HCO+ J=4-3 transition agree to within 10%,
i.e., within the calibration accuracy of most current telescopes. The
comparison project and the results described in this paper provide a benchmark
for future code development, and give an indication of the typical accuracy of
present day calculations of molecular line transfer.Comment: Accepted for publication in A&
Gyrotropic impact upon negatively refracting surfaces
Surface wave propagation at the interface between different types of gyrotropic materials and an isotropic negatively refracting medium, in which the relative permittivity and relative permeability are, simultaneously, negative is investigated. A general approach is taken that embraces both gyroelectric and gyromagnetic materials, permitting the possibility of operating in either the low GHz, THz or the optical frequency regimes. The classical transverse Voigt configuration is adopted and a complete analysis of non-reciprocal surface wave dispersion is presented. The impact of the surface polariton modes upon the reflection of both plane waves and beams is discussed in terms of resonances and an example of the influence upon the Goos–Hänchen shift is given
Cooling Rates of Molecular Clouds Based on Numerical MHD Turbulence and non-LTE Radiative Transfer
We have computed line emission cooling rates for the main cooling species in
models of interstellar molecular clouds. The models are based on numerical
simulations of super-sonic magneto-hydrodynamic (MHD) turbulence. Non-LTE
radiative transfer calculations have been performed to properly account for the
complex density and velocity structures in the MHD simulations. Three models
are used. Two of the models are based on MHD simulations with different
magnetic field strength and the third includes the computation of self-gravity
(in the super-Alfvenic regime of turbulence). The density and velocity fields
in the simulations are determined self-consistently by the dynamics of
super-sonic turbulence. The models are intended to represent molecular clouds
with linear size L~6 pc and mean density ~300 cm^-3, with the density
exceeding 10^4 cm^-3 in the densest cores. We present 12CO, 13CO, C18O, O2, OI,
CI and H2O cooling rates in isothermal clouds with kinetic temperatures 10-80K.
Analytical approximations are derived for the cooling rates. The inhomogeneity
of the models reduces photon trapping and enhances the cooling in the densest
parts of the clouds. Compared with earlier models the cooling rates are less
affected by optical depth effects and are therefore higher. The main effects
comes, however, from the density variation since cooling efficiency increases
with density. This is very important for the cooling of the clouds as a whole
since most cooling is provided by gas with density above the average.Comment: AASTeX, 19 pages, 15 figures; final, revised version; accepted to Ap
Unconventional quantum vortex matter state hosts quantum oscillations in the underdoped high-temperature cuprate superconductors.
A central question in the underdoped cuprates pertains to the nature of the pseudogap ground state. A conventional metallic ground state of the pseudogap region has been argued to host quantum oscillations upon destruction of the superconducting order parameter by modest magnetic fields. Here, we use low applied measurement currents and millikelvin temperatures on ultrapure single crystals of underdoped [Formula: see text] to unearth an unconventional quantum vortex matter ground state characterized by vanishing electrical resistivity, magnetic hysteresis, and nonohmic electrical transport characteristics beyond the highest laboratory-accessible static fields. A model of the pseudogap ground state is now required to explain quantum oscillations that are hosted by the bulk quantum vortex matter state without experiencing sizable additional damping in the presence of a large maximum superconducting gap; possibilities include a pair density wave.Royal Society
Winton Programme for the Physics of Sustainability
Engineering and Physical Sciences Research Council (EPSRC; studentship and grant numbers EP/R513180/1, EP/M506485/1 and EP/P024947/1)
European Research Council under the European Unions Seventh
Framework Programme (Grant Agreement numbers 337425 and 772891). EPSRC Strategic Equipment Grant EP/M000524/1
Leverhulme Trust by way of the award of a Philip Leverhulme
Prize.
National Key Research and Development Program of China (grant no. 2016YFA0401704).
Work performed at the National High Magnetic Field Laboratory (NHMFL) supported by NSF Cooperative Agreement DMR-1157490, the State of Florida, and the Department of Energy (DOE)
DOE Basic Energy Sciences project: ‘Science of 100 tesla’
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