12,988 research outputs found
Tunneling into fractional quantum Hall liquids
Motivated by the recent experiment by Grayson et.al., we investigate a
non-ohmic current-voltage characteristics for the tunneling into fractional
quantum Hall liquids. We give a possible explanation for the experiment in
terms of the chiral Tomonaga-Luttinger liquid theory. We study the interaction
between the charge and neutral modes, and found that the leading order
correction to the exponent is of the order of
, which reduces the exponent . We
suggest that it could explain the systematic discrepancy between the observed
exponents and the exact dependence.Comment: Latex, 5 page
Adiabatic evolution on a spatial-photonic Ising machine
Combinatorial optimization problems are crucial for widespread applications
but remain difficult to solve on a large scale with conventional hardware.
Novel optical platforms, known as coherent or photonic Ising machines, are
attracting considerable attention as accelerators on optimization tasks
formulable as Ising models. Annealing is a well-known technique based on
adiabatic evolution for finding optimal solutions in classical and quantum
systems made by atoms, electrons, or photons. Although various Ising machines
employ annealing in some form, adiabatic computing on optical settings has been
only partially investigated. Here, we realize the adiabatic evolution of
frustrated Ising models with 100 spins programmed by spatial light modulation.
We use holographic and optical control to change the spin couplings
adiabatically, and exploit experimental noise to explore the energy landscape.
Annealing enhances the convergence to the Ising ground state and allows to find
the problem solution with probability close to unity. Our results demonstrate a
photonic scheme for combinatorial optimization in analogy with adiabatic
quantum algorithms and enforced by optical vector-matrix multiplications and
scalable photonic technology.Comment: 9 pages, 4 figure
Large-scale photonic Ising machine by spatial light modulation
Quantum and classical physics can be used for mathematical computations that
are hard to tackle by conventional electronics. Very recently, optical Ising
machines have been demonstrated for computing the minima of spin Hamiltonians,
paving the way to new ultra-fast hardware for machine learning. However, the
proposed systems are either tricky to scale or involve a limited number of
spins. We design and experimentally demonstrate a large-scale optical Ising
machine based on a simple setup with a spatial light modulator. By encoding the
spin variables in a binary phase modulation of the field, we show that light
propagation can be tailored to minimize an Ising Hamiltonian with spin
couplings set by input amplitude modulation and a feedback scheme. We realize
configurations with thousands of spins that settle in the ground state in a
low-temperature ferromagnetic-like phase with all-to-all and tunable pairwise
interactions. Our results open the route to classical and quantum photonic
Ising machines that exploit light spatial degrees of freedom for parallel
processing of a vast number of spins with programmable couplings.Comment: https://journals.aps.org/prl/accepted/7007eYb7N091546c41ad4108828a97d5f92006df
BIOH2POWER WP1: BIOGASSPECIFICATIONS AND CRITICALANALYSIS OF PRESENT SITUATION ANDFUTURE PERSPECTIVE FOR BIOGASPRODUCTION IN ITALY AND PIEMONTE
The objective of the Work Package 1 on the frame of the BioH2Power project is to define biogas specifications, in terms of quantity and quality, to be used as a reference for desulphurizing/reforming processes, on the basis of the real on-field experience of a major Italian biogas-to-energy enterprise. Asja will carry on its involvement in the research project building upon its 10-years experience in the field of renewable energy generation from biogas. The technological know-how acquired since the beginning of its operation allows Asja to define the major critical factors in the treatment and use of biogas generated from anaerobic digestion of organic matter. Therefore, its role in the research program will be to provide effective knowing of the reality of biogas, on the basis of the plants Asja manages every day all over Italy and abroad. Then an identification of the potential sources of biogas will be provided in collaboration with Politecnico di Torino. DISMIC complements the work covering other biogas sources different from landfill
Solvable Lie algebras are not that hypo
We study a type of left-invariant structure on Lie groups, or equivalently on
Lie algebras. We introduce obstructions to the existence of a hypo structure,
namely the 5-dimensional geometry of hypersurfaces in manifolds with holonomy
SU(3). The choice of a splitting g^*=V_1 + V_2, and the vanishing of certain
associated cohomology groups, determine a first obstruction. We also construct
necessary conditions for the existence of a hypo structure with a fixed
almost-contact form. For non-unimodular Lie algebras, we derive an obstruction
to the existence of a hypo structure, with no choice involved. We apply these
methods to classify solvable Lie algebras that admit a hypo structure.Comment: 21 pages; v2: presentation improved, typos corrected, notational
conflicts eliminated. To appear in Transformation Group
Recommended from our members
Narrative in adolescent specific language impairment (SLI): a comparison with peers across two different narrative genres
Background: Narrative may provide a useful way in which to assess the language ability of adolescents with specific language impairment and may be more ecologically valid than standardized tests. However, the language of this age group is seldom studied and, furthermore, the effect of narrative genre has not been explored in detail.
Methods & Procedures: A total of 99 typically developing adolescents and 19 peers with specific language impairment were given two different types of narrative task: a story-telling condition and a conversational condition. Four areas of narrative (productivity, syntactic complexity, syntactic errors and performance) were assessed.
Outcomes & Results: The group with specific language impairment was poorer on most aspects of narrative confirming recent research that specific language impairment is a long-term disorder. A number of measures also showed interactions between group and genre, with story-telling proving to be a disproportionately more difficult task for the specific language impairment group. Error analysis also suggested that the specific language impairment group was making qualitatively different errors to the typically developing group, even within a genre.
Conclusions: Adolescents with specific language impairment are not only poorer at both types of narrative than peers, but also show different patterns of competence and error, and require more support from the narrative-partner.
Clinical Implications: Assessments of adolescents are less frequent than at younger ages. This is partly because of the sparsity of tests available in this age range. Qualitative analysis of narrative might prove a useful alternative. The findings suggest that in every-day conversation, young people with specific language impairment manage their difficulties more discreetly and this might make them harder to identify in a mainstream setting
The Stellar Content of Obscured Galactic Giant H II Regions: II. W42
We present near infrared J, H, and K images and K-band spectroscopy in the
giant HII region W42. A massive star cluster is revealed; the color-color plot
and K-band spectroscopic morphology of two of the brighter objects suggest the
presence of young stellar objects. The spectrum of the bright central star is
similar to unobscured stars with MK spectral types of O5-O6.5. If this star is
on the zero age main sequence, then the derived spectrophotometric distance is
considerably smaller than previous estimates. The Lyman continuum luminosity of
the cluster is a few times that of the Trapezium. The slope of the K-band
luminosity function is similar to that for the Trapezium cluster and
significantly steeper than that for the massive star cluster in M17 or the
Arches cluster near the Galactic center.Comment: 30 pages, 11 figures, late
Mass-loss rates from early-type stars
The mass loss rates are derived for a number of unevolved O-type stars and a few WN stars from high dispersion IUE spectra of their P Cygni profiles. When combined with other published mass loss rates, it is found that the relationship between log m and M sub BOL is a broad band rather than a linear relation, suggesting that the line radiation driven wind theory may not be sufficient to explain mass loss. The mass loss rates for the WN stars, while more uncertain, confirm that these stars lose mass about 100 times faster than O-stars
Spectroscopic observations of selected stellar systems
Spectra of very luminous, high temperature stars, the o-type stars with the largest masses among stars, and the Wolf-Rayet (W-R) stars are studied. These stars are characterized by strong stellar winds which produce signiicant mass loss. The nature and evolution of these winds are studied to learn the densities, velocity structue, ionization balance, and composition. The IUE satellite provides the best way to study these phenomena because many of the most important ground state and excited state lines of common highly ionized species are found in the spectral range
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