15,854 research outputs found
Nonequilibrium quantum phase transition in itinerant electron systems
We study the effect of the voltage bias on the ferromagnetic phase transition
in a one-dimensional itinerant electron system. The applied voltage drives the
system into a nonequilibrium steady state with a non-zero electric current. The
bias changes the universality class of the second order ferromagnetic
transition. While the equilibrium transition belongs to the universality class
of the uniaxial ferroelectric, we find the mean-field behavior near the
nonequilibrium critical point.Comment: Final version as accepted to Phys. Rev. Let
Projective measurement in nuclear magnetic resonance
It is demonstrated that nuclear magnetic resonance experiments using
pseudopure spin states can give possible outcomes of projective quantum
measurement and probabilities of such outcomes. The physical system is a
cluster of six dipolar-coupled nuclear spins of benzene in a liquid-crystalline
matrix. For this system with the maximum total spin S=3, the results of
measuring are presented for the cases when the state of the system is one
of the eigenstates of .Comment: 9 pages incluing 3 figure
PkANN - II. A non-linear matter power spectrum interpolator developed using artificial neural networks
In this paper we introduce PkANN, a freely available software package for
interpolating the non-linear matter power spectrum, constructed using
Artificial Neural Networks (ANNs). Previously, using Halofit to calculate
matter power spectrum, we demonstrated that ANNs can make extremely quick and
accurate predictions of the power spectrum. Now, using a suite of 6380 N-body
simulations spanning 580 cosmologies, we train ANNs to predict the power
spectrum over the cosmological parameter space spanning confidence
level (CL) around the concordance cosmology. When presented with a set of
cosmological parameters ( and redshift ), the trained ANN interpolates the power
spectrum for at sub-per cent accuracy for modes up to
. PkANN is faster than computationally expensive
N-body simulations, yet provides a worst-case error per cent fit to the
non-linear matter power spectrum deduced through N-body simulations. The
overall precision of PkANN is set by the accuracy of our N-body simulations, at
5 per cent level for cosmological models with eV for all
redshifts . For models with eV, predictions are
expected to be at 5 (10) per cent level for redshifts (). The
PkANN interpolator may be freely downloaded from
http://zuserver2.star.ucl.ac.uk/~fba/PkANNComment: 21 pages, 14 figures, 2 table
Lunar Resource Assessment: an Industry Perspective
The goals of the U.S. space program are to return to the Moon, establish a base, and continue onward to Mars. To accomplish this in a relatively short time frame and to avoid the high costs of transporting materials from the Earth, resources on the Moon will need to be mined. Oxygen will be one of the most important resources, to be used as a rocket propellant and for life support. Ilmenite and lunar regolith have both been considered as ores for the production of oxygen. Resource production on the Moon will be a very important part of the U.S. space program. To produce resources we must explore to identify the location of ore or feedback and calculate the surface and underground reserves. Preliminary resource production tests will provide the information that can be used in final plant design. Bechtel Corporation's experience in terrestrial engineering and construction has led to an interest in lunar resource assessment leading to the construction of production facilities on the Moon. There is an intimate link between adequate resource assessment to define feedstock quantity and quality, material processing requirements, and the successful production of lunar oxygen. Although lunar resource assessment is often viewed as a research process, the engineering and production aspects are very important to consider. Resource production often requires the acquisition of different types, scales, or resolutions of data than that needed for research, and it is needed early in the exploration process. An adequate assessment of the grade, areal extent, and depth distribution of the resources is a prerequisite to mining. The need for a satisfactory resource exploration program using remote sensing techniques, field sampling, and chemical and physical analysis is emphasized. These data can be used to define the ore for oxygen production and the mining, processing facilities, and equipment required
Review of Recent Searches for Rare and Forbidden Dilepton Decays of Charmed Mesons
I briefly review the results of recent searches for flavor-changing neutral
current and lepton-flavor and lepton-number violating decays of D+, Ds, and D0
mesons (and their antiparticles) into modes containing muons and electrons. The
primary focus is the results from Fermilab charm hadroproduction experiment
E791. E791 examined 24 pi,l,l and K,l,l decay modes of D+ and Ds and l+l- decay
modes of D0. Limits presented by E791 for 22 rare and forbidden dilepton decays
of D mesons were more stringent than those obtained from previous searches, or
else were the first reported.Comment: 8 pages, 1 figure, uses psfig.sty and RevTeX, submitted to Modern
Physics Letters A, based on a Fermilab "Joint Theoretical and Experimental"
tal
Phyllosilicate Transitions in Ferromagnesian Soils: Short-Range Order Materials and Smectites Dominate Secondary Phases
Analyses of X-ray diffraction (XRD) patterns taken by the CheMin instrument on the Curiosity Rover in Gale crater have documented the presence of clay minerals interpreted as smectites and a suite of amorphous to short-range order materials termed X-ray amorphous materials. These X-ray amorphous materials are commonly ironrich and aluminum poor and likely some of them are weathering products rather than primary glasses due to the presence of volatiles. Outstanding questions remain regarding the chemical composition and mineral structure of these X-ray amorphous materials and the smectites present at Gale crater and what they indicate about environmental conditions during their formation. To gain a better understanding of the mineral transitions that occur within ferromagnesian parent materials, we have investigated the development of secondary clay minerals and shortrange order materials in two soil chronosequences with varying climates developing on ultramafic bedrock. Field Sites: We investigated soil weathering within two field locations, the Klamath Mountains of Northern California, and the Tablelands of Newfoundland, Canada. Both sites possess age dated or correlated recently deglaciated soils and undated but substantially older soils. In the Klamath mountains the Trinity Ultramafic Body was deglaciated roughly 15,000 years bp while in the Tablelands a moraine was dated to about 17,600 years bp. The Klamath Mountains feature a seasonally wet and dry climate while the Tablelands are wet year-round with saturated soil conditions observed during sampling and standing water observed within 3 of 4 soil pit sampling locations
Dynamical Mass Generation of Composite Dirac Fermions and Fractional Quantum Hall Effects near Charge Neutrality in Graphene
We develop a composite Dirac fermion theory for the fractional quantum Hall
effects (QHE) near charge neutrality in graphene. We show that the interactions
between the composite Dirac fermions lead to dynamical mass generation through
exciton condensation. The four-fold spin-valley degeneracy is fully lifted due
to the mass generation and the exchange effects such that the odd-denominator
fractional QHE observed in the vicinity of charge neutrality can be understood
in terms of the integer QHE of the composite Dirac fermions. At the filling
factor , we show that the massive composite Dirac fermion liquid is
unstable against chiral p-wave pairing for weak Coulomb interactions and the
ground state is a paired nonabelian state described by the Moore-Read Pfaffian
in the long wavelength limit.Comment: Extended, published version, 9 pages, 3 figure
Nearly optimal solutions for the Chow Parameters Problem and low-weight approximation of halfspaces
The \emph{Chow parameters} of a Boolean function
are its degree-0 and degree-1 Fourier coefficients. It has been known
since 1961 (Chow, Tannenbaum) that the (exact values of the) Chow parameters of
any linear threshold function uniquely specify within the space of all
Boolean functions, but until recently (O'Donnell and Servedio) nothing was
known about efficient algorithms for \emph{reconstructing} (exactly or
approximately) from exact or approximate values of its Chow parameters. We
refer to this reconstruction problem as the \emph{Chow Parameters Problem.}
Our main result is a new algorithm for the Chow Parameters Problem which,
given (sufficiently accurate approximations to) the Chow parameters of any
linear threshold function , runs in time \tilde{O}(n^2)\cdot
(1/\eps)^{O(\log^2(1/\eps))} and with high probability outputs a
representation of an LTF that is \eps-close to . The only previous
algorithm (O'Donnell and Servedio) had running time \poly(n) \cdot
2^{2^{\tilde{O}(1/\eps^2)}}.
As a byproduct of our approach, we show that for any linear threshold
function over , there is a linear threshold function which
is \eps-close to and has all weights that are integers at most \sqrt{n}
\cdot (1/\eps)^{O(\log^2(1/\eps))}. This significantly improves the best
previous result of Diakonikolas and Servedio which gave a \poly(n) \cdot
2^{\tilde{O}(1/\eps^{2/3})} weight bound, and is close to the known lower
bound of (1/\eps)^{\Omega(\log \log (1/\eps))}\} (Goldberg,
Servedio). Our techniques also yield improved algorithms for related problems
in learning theory
Detection of HC11N in the Cold Dust Cloud TMC-1
Two consecutive rotational transitions of the long cyanopolyyne HC11N,
J=39-38, and J=38-37, have been detected in the cold dust cloud TMC-1 at the
frequencies expected from recent laboratory measurements by Travers et al.
(1996), and at about the expected intensities. The astronomical lines have a
mean radial velocity of 5.8(1) km/s, in good agreement with the shorter
cyanopolyynes HC7N and HC9N observed in this very sharp-lined source [5.82(5)
and 5.83(5) km/s, respectively]. The column density of HC11N is calculated to
be 2.8x10^(11) cm^(-2). The abundance of the cyanopolyynes decreases smoothly
with length to HC11N, the decrement from one to the next being about 6 for the
longer carbon chains.Comment: plain tex 10 pages plus 3 ps fig file
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