3,531 research outputs found
Twisted Permutation Codes
We introduce twisted permutation codes, which are frequency permutation
arrays analogous to repetition permutation codes, namely, codes obtained from
the repetition construction applied to a permutation code. In particular, we
show that a lower bound for the minimum distance of a twisted permutation code
is the minimum distance of a repetition permutation code. We give examples
where this bound is tight, but more importantly, we give examples of twisted
permutation codes with minimum distance strictly greater than this lower bound.Comment: 20 page
The dissipative linear Boltzmann equation for hard spheres
We prove the existence and uniqueness of an equilibrium state with unit mass
to the dissipative linear Boltzmann equation with hard--spheres collision
kernel describing inelastic interactions of a gas particles with a fixed
background. The equilibrium state is a universal Maxwellian distribution
function with the same velocity as field particles and with a non--zero
temperature lower than the background one, which depends on the details of the
binary collision. Thanks to the H--theorem we then prove strong convergence of
the solution to the Boltzmann equation towards the equilibrium.Comment: 17 pages, submitted to Journal of Statistical Physic
Integral representation of the linear Boltzmann operator for granular gas dynamics with applications
We investigate the properties of the collision operator associated to the
linear Boltzmann equation for dissipative hard-spheres arising in granular gas
dynamics. We establish that, as in the case of non-dissipative interactions,
the gain collision operator is an integral operator whose kernel is made
explicit. One deduces from this result a complete picture of the spectrum of
the collision operator in an Hilbert space setting, generalizing results from
T. Carleman to granular gases. In the same way, we obtain from this integral
representation of the gain operator that the semigroup in L^1(\R \times \R,\d
\x \otimes \d\v) associated to the linear Boltzmann equation for dissipative
hard spheres is honest generalizing known results from the first author.Comment: 19 pages, to appear in Journal of Statistical Physic
Use of glide-ins in CMS for production and analysis
With the evolution of various grid federations, the Condor glide-ins represent a key feature in providing a homogeneous pool of resources using late-binding technology. The CMS collaboration uses the glide-in based Workload Management System, glideinWMS, for production (ProdAgent) and distributed analysis (CRAB) of the data. The Condor glide-in daemons traverse to the worker nodes, submitted via Condor-G. Once activated, they preserve the Master-Worker relationships, with the worker first validating the execution environment on the worker node before pulling the jobs sequentially until the expiry of their lifetimes. The combination of late-binding and validation significantly reduces the overall failure rate visible to CMS physicists. We discuss the extensive use of the glideinWMS since the computing challenge, CCRC-08, in order to prepare for the forthcoming LHC data-taking period. The key features essential to the success of large-scale production and analysis on CMS resources across major grid federations, including EGEE, OSG and NorduGrid are outlined. Use of glide-ins via the CRAB server mechanism and ProdAgent, as well as first hand experience of using the next generation CREAM computing element within the CMS framework is discussed
Behavioural responses in a congested sea: an observational study on a coastal nest-guarding fish
The deleterious effects of anthropogenic noise on animal communication are nowadays recognised, not only in urban environments but also in terrestrial habitats and along coasts and in open waters. Yet, the assessment of short- and long-term exposure consequences of anthropogenic noise in marine organisms remains challenging, especially in fish and invertebrates. Males of the Mediterranean damselfish Chromis chromis vocalise and perform visual displays (multimodal communication) to attract mates. The frequency-range of courtship vocalisations overlaps with low-frequency noise generated by maritime activities, resulting in a reduced detection distance among conspecifics. We quantified the number of courtship-related visual displays performed by males living in areas with different levels of maritime traffic. We also tried to manipulate ambient noise in the field to test male short-term response to increased noise levels. Males living in busier areas (near to a harbour) performed significantly more visual displays than those living in less congested areas. When exposed to artificially-increased ambient noise level (playback of boat noise), males did not adjust the number of visual displays accordingly. Yet, we note how assessing the actual effect of maritime traffic in marine populations in their natural environments is particularly difficult, as the effects of boat noise cannot be easily disentangled from a variety of other intrinsic or environmental factors, discussed in the paper. We thus present suggestions to obtain more robust analyses of variations of courtship behaviours in territorial fishes. We hope this will facilitate a further understanding of the potential long-term effects of anthropogenic noise, whose analyses should be prioritised in the context of environmental impact assessment, resource management and biodiversity conservation
Mesoscopic modelling of financial markets
We derive a mesoscopic description of the behavior of a simple financial
market where the agents can create their own portfolio between two investment
alternatives: a stock and a bond. The model is derived starting from the
Levy-Levy-Solomon microscopic model (Econ. Lett., 45, (1994), 103--111) using
the methods of kinetic theory and consists of a linear Boltzmann equation for
the wealth distribution of the agents coupled with an equation for the price of
the stock. From this model, under a suitable scaling, we derive a Fokker-Planck
equation and show that the equation admits a self-similar lognormal behavior.
Several numerical examples are also reported to validate our analysis
New near-IR observations of mesospheric CO2 and H2O clouds on Mars
Carbon dioxide clouds, which are speculated by models on solar and
extra-solar planets, have been recently observed near the equator of Mars. The
most comprehensive identification of Martian CO2 ice clouds has been obtained
by the near-IR imaging spectrometer OMEGA. CRISM, a similar instrument with a
higher spatial resolution, cannot detect these clouds with the same method due
to its shorter wavelength range. Here we present a new method to detect CO2
clouds using near-IR data based on the comparison of H2O and CO2 ice spectral
properties. The spatial and seasonal distributions of 54 CRISM observations
containing CO2 clouds are reported, in addition to 17 new OMEGA observations.
CRISM CO2 clouds are characterized by grain size in the 0.5-2\mum range and
optical depths lower than 0.3. The distributions of CO2 clouds inferred from
OMEGA and CRISM are consistent with each other and match at first order the
distribution of high altitude (>60km) clouds derived from previous studies. At
second order, discrepancies are observed. We report the identification of H2O
clouds extending up to 80 km altitude, which could explain part of these
discrepancies: both CO2 and H2O clouds can exist at high, mesospheric
altitudes. CRISM observations of afternoon CO2 clouds display morphologies
resembling terrestrial cirrus, which generalizes a previous result to the whole
equatorial clouds season. Finally, we show that morning OMEGA observations have
been previously misinterpreted as evidence for cumuliform, and hence
potentially convective, CO2 clouds.Comment: Vincendon, M., C. Pilorget, B. Gondet, S. Murchie, and J.-P. Bibring
(2011), New near-IR observations of mesospheric CO2 and H2O clouds on Mars,
J. Geophys. Res., 116, E00J0
Involvement of CREB-regulated transcription coactivators (CRTC) in transcriptional activation of steroidogenic acute regulatory protein (Star) by ACTH
Modeling Parkinsonâs disease neuropathology and symptoms by intranigral inoculation of preformed human α-synuclein oligomers
The accumulation of aggregated α-synuclein (αSyn) is a hallmark of Parkinsonâs disease (PD). Current evidence indicates that small soluble αSyn oligomers (αSynOs) are the most toxic species among the forms of αSyn aggregates, and that size and topological structural properties are crucial factors for αSynOs-mediated toxicity, involving the interaction with either neurons or glial cells. We previously characterized a human αSynO (H-αSynO) with specific structural properties promoting toxicity against neuronal membranes. Here, we tested the neurotoxic potential of these H-αSynOs in vivo, in relation to the neuropathological and symptomatic features of PD. The H-αSynOs were unilaterally infused into the rat substantia nigra pars compacta (SNpc). Phosphorylated αSyn (p129-αSyn), reactive microglia, and cytokine levels were measured at progressive time points. Additionally, a phagocytosis assay in vitro was performed after microglia pre-exposure to αsynOs. Dopaminergic loss, motor, and cognitive performances were assessed. H-αSynOs triggered p129-αSyn deposition in SNpc neurons and microglia and spread to the striatum. Early and persistent neuroinflammatory responses were induced in the SNpc. In vitro, H-αSynOs inhibited the phagocytic function of microglia. H-αsynOs-infused rats displayed early mitochondrial loss and abnormalities in SNpc neurons, followed by a gradual nigrostriatal dopaminergic loss, associated with motor and cognitive impairment. The intracerebral inoculation of structurally characterized H-αSynOs provides a model of progressive PD neuropathology in rats, which will be helpful for testing neuroprotective therapies
Optical simulations for the Wolter-I collimator in the VERT-X calibration facility
The VERT-X X-ray calibration facility, currently in prototypal realization phase supported by ESA, will be a vertical X-ray beamline able to test and calibrate the entire optical assembly of the ATHENA X-ray telescope. Owing to its long focal length (12 m), a full-illumination test of the entire focusing system would require a parallel and uniform X-ray beam as large as the optical assembly itself (2.5 m). Moreover, the module should better be laid parallel to the ground in order to minimize the effects of gravity deformations. Therefore, the ideal calibration facility would consist of a vertical beam, with the source placed at very large distance (>> 500 m) under high vacuum (10-6 mbar). Since such calibration systems do not exist, and also appear to be very hard to manufacture, VERT-X will be based on a different concept, i.e., the raster scan of a tightly (â 1 arcsec) collimated X-ray beam, generated by a microfocus source and made parallel via a precisely shaped Wolter-I mirror. In this design, the mirror will be made of two segments (paraboloid + hyperboloid) that, for the X-ray beam collimation to be preserved, will have to be accurately finished and maintain their mutual alignment to high accuracy during the scan. In this paper, we show simulations of the reflected wavefront based on physical optics and the expected final imaging quality, for different polishing levels and misalignments for the two segments of the VERT-X collimator
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