5,264 research outputs found
Spectral properties of a class of random walks on locally finite groups
We study some spectral properties of random walks on infinite countable
amenable groups with an emphasis on locally finite groups, e.g. the infinite
symmetric group. On locally finite groups, the random walks under consideration
are driven by infinite divisible distributions. This allows us to embed our
random walks into continuous time L\'evy processes whose heat kernels have
shapes similar to the ones of alpha-stable processes. We obtain examples of
fast/slow decays of return probabilities, a recurrence criterion, exact values
and estimates of isospectral profiles and spectral distributions, formulae and
estimates for the escape rates and for heat kernels.Comment: 62 pages, 1 figure, 2 table
Quantum Error Correction with the Toric-GKP Code
We examine the performance of the single-mode GKP code and its concatenation
with the toric code for a noise model of Gaussian shifts, or displacement
errors. We show how one can optimize the tracking of errors in repeated noisy
error correction for the GKP code. We do this by examining the
maximum-likelihood problem for this setting and its mapping onto a 1D Euclidean
path-integral modeling a particle in a random cosine potential. We demonstrate
the efficiency of a minimum-energy decoding strategy as a proxy for the path
integral evaluation. In the second part of this paper, we analyze and
numerically assess the concatenation of the GKP code with the toric code. When
toric code measurements and GKP error correction measurements are perfect, we
find that by using GKP error information the toric code threshold improves from
to . When only the GKP error correction measurements are perfect
we observe a threshold at . In the more realistic setting when all error
information is noisy, we show how to represent the maximum likelihood decoding
problem for the toric-GKP code as a 3D compact QED model in the presence of a
quenched random gauge field, an extension of the random-plaquette gauge model
for the toric code. We present a new decoder for this problem which shows the
existence of a noise threshold at shift-error standard deviation for toric code measurements, data errors and GKP ancilla errors.
If the errors only come from having imperfect GKP states, this corresponds to
states with just 4 photons or more. Our last result is a no-go result for
linear oscillator codes, encoding oscillators into oscillators. For the
Gaussian displacement error model, we prove that encoding corresponds to
squeezing the shift errors. This shows that linear oscillator codes are useless
for quantum information protection against Gaussian shift errors.Comment: 50 pages, 14 figure
Schweinehaltung: Beratung zurzeit dringlicher als Forschung
Mit einer Umfrage unter Biobetrieben mit Schweinhaltung haben die Fachgruppen Beratung und Tiergesundheit des FiBL zu ergründen versucht, wo die wichtigsten Probleme in der Zucht und Mast von Bioschweinen liegen und wo Forschungsbedarf besteht. Interessant ist nicht zuletzt die Abhängigkeit der Problemlage von der Anzahl gehaltener Tiere. Die meisten der Schwierigkeiten liessen sich mit verbessertem Management lösen oder vermeiden
Homological Quantum Rotor Codes: Logical Qubits from Torsion
We formally define homological quantum rotor codes which use multiple quantum
rotors to encode logical information. These codes generalize homological or CSS
quantum codes for qubits or qudits, as well as linear oscillator codes which
encode logical oscillators. Unlike for qubits or oscillators, homological
quantum rotor codes allow one to encode both logical rotors and logical qudits,
depending on the homology of the underlying chain complex. In particular, such
a code based on the chain complex obtained from tessellating the real
projective plane or a M\"{o}bius strip encodes a qubit. We discuss the distance
scaling for such codes which can be more subtle than in the qubit case due to
the concept of logical operator spreading by continuous stabilizer
phase-shifts. We give constructions of homological quantum rotor codes based on
2D and 3D manifolds as well as products of chain complexes. Superconducting
devices being composed of islands with integer Cooper pair charges could form a
natural hardware platform for realizing these codes: we show that the
--qubit as well as Kitaev's current-mirror qubit -- also known as the
M\"{o}bius strip qubit -- are indeed small examples of such codes and discuss
possible extensions.Comment: 47 pages, 10 figures, 2 table
Sugar-to-base correlation in nucleic acids with a 5D APSY-HCNCH or two 3D APSY-HCN experiments
A five-dimensional (5D) APSY (automated projection spectroscopy) HCNCH experiment is presented, which allows unambiguous correlation of sugar to base nuclei in nucleic acids. The pulse sequence uses multiple quantum (MQ) evolution which enables long constant-time evolution periods in all dimensions, an improvement that can also benefit non-APSY applications. Applied with an RNA with 23 nucleotides the 5D APSY-HCNCH experiment produced a complete and highly precise 5D chemical shift list within 1.5h. Alternatively, and for molecules where the out-and-stay 5D experiment sensitivity is not sufficient, a set of out-and-back 3D APSY-HCN experiments is proposed: an intra-base (3D APSY-b-HCN) experiment in an MQ or in a TROSY version, and an MQ sugar-to-base (3D APSY-s-HCN) experiment. The two 3D peak lists require subsequent matching via the N1/9 chemical shift values to one 5D peak list. Optimization of the 3D APSY experiments for maximal precision in the N1/9 dimension allowed matching of all 15N chemical shift values contained in both 3D peak lists. The precise 5D chemical shift correlation lists resulting from the 5D experiment or a pair of 3D experiments also provide a valuable basis for subsequent connection to chemical shifts derived with other experiment
La traduction de la demande d'aide sociale : le cas du handicap et de l'insertion des jeunes
En accumulant des données sur deux dispositifs d'attribution des droits sociaux (aides aux jeunes et droits liés au handicap), nous examinons quel est le statut réservé au demandeur, puis les logiques bureaucratiques et morales qui président au tri des demandes par les acteurs des deux dispositifs. Nous nous interrogeons ensuite sur les marges de manœuvre effectives des usagers dans la co-construction de la demande ainsi que sur les façons dont s'élabore la connaissance des besoins auxquels il s'agit de répondre. Cette comparaison montre qu'il n'y a pas une, mais des " magistratures sociales ", plus ou moins participatives, plus ou moins conditionnelles et discrétionnaires, selon le type de bénéficiaires
Wood Density and Hydraulic Properties of Ponderosa Pine From the Willamette Valley VS. the Cascade Mountains
The Willamette Valley (WV) race of ponderosa pine (Pinus ponderosa) is being widely planted for timber in the Willamette Valley, western Oregon, because it grows in habitats that are either too wet or too dry for Douglas-fir (Pseudotsuga menziesii). Compared to the eastern Cascade Mountains (CM), the WV has 3 to 5 times the annual precipitation and warmer temperatures year around. This study characterized the wood quality of the WV race (4 sites) and the CM (4 sites), and also compared the behavior of their wood for water transport for the living trees (1 site in the WV and 1 site in the CM). The average tree ages at the sites ranged from 30 to 83 years at breast height. Between rings 27 and 31, compared to the CM, the WV had denser wood (0.48 vs. 0.40 g/cm3), denser earlywood (0.41 vs. 0.36 g/cm3), and denser latewood (0.62 vs. 0.50 g/cm3), with no significant differences in mean latewood proportion (about 0.35) or mean growth ring width (about 2.5 mm). The pith-to-bark trend in density differed between regions. In the WV, total wood density, earlywood density, and latewood density increased with growth ring from the pith. In the CM, total wood density and latewood density decreased slightly with growth ring width, and earlywood density remained unchanged. An additional sample of younger trees (23 years at breast height) from a genetic trial in the WV in which the seed source was the CM, had low density wood in the first few rings (like the CM trees) but had a steady increase in wood density with growth ring number (like the WV trees). Specific conductivity (ks) of trunk wood was lower in the WV, consistent with its higher wood density and suggestive that the WV race is more drought-adapted than the CM populations. There was no decline in ks from outer to inner sapwood in the WV trees, but a large decline in the CM trees. In water transport experiments, at an applied air pressure of 3.0 MPa, the WV and CM trees had lost 19% and 32% of their ks, respectively, again suggesting that the WV trees are slightly more drought-adapted than are the CM trees. At the other applied air pressures tested (0.5, 2.0. 4.0, and 5.0 MPa), there were no significant differences in loss of conductivity between the two sites. Trunk wood from breast height had a 50% loss of ks at 3.3-3.6 MPa. The loss of relative water content (100% - RWC) was about the same in both sites, except at 4.0 MPa, in which the CM trees had a larger loss of RWC than the WV trees. More work is needed on physiology to better understand the wood density/water transport relations. Ponderosa pine may be more interesting to study than other species because the earlywood, which transports most of the water, shows substantial density differences between geographic regions
Comparative survey of canine parvovirus, canine distemper virus and canine enteric coronavirus infection in free-ranging wolves of central Italy and south-eastern France
Diseases likely affect large carnivore demography and can hinder conservation efforts. We considered three highly contagious viruses that infect a wide range of domestic and wild mammals: canine parvovirus type 2 (CPV-2), canine distemper virus (CDV) and canine enteric coronaviruses (CECoV). Infection by either one of these viruses can affect populations through increased mortality and/or decreased general health. We investigated infection in the wolf populations of Abruzzo, Lazio e Molise National Park (PNALM), Italy, and of Mercantour National Park (PNM), France. Faecal samples were collected during one winter, from October to March, from four packs in PNALM (n = 79) and from four packs in PNM (n = 66). We screened samples for specific sequences of viral nucleic acids. To our knowledge, our study is the first documented report of CECoV infection in wolves outside Alaska, and of the large-scale occurrence of CPV-2 in European wolf populations. The results suggest that CPV-2 is enzootic in the population of PNALM, but not in PNM and that CECoV is episodic in both areas. We did not detect CDV. Our findings suggest that density and spatial distribution of susceptible hosts, in particular free-ranging dogs, can be important factors influencing infections in wolves. This comparative study is an important step in evaluating the nature of possible disease threats in the studied wolf populations. Recent emergence of new viral strains in Europe additionally strengthens the need for proactive monitoring of wolves and other susceptible sympatric species for viral threats and other impairing infections
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