9,189 research outputs found
Velocity, energy and helicity of vortex knots and unknots
In this paper we determine the velocity, the energy and estimate writhe and
twist helicity contributions of vortex filaments in the shape of torus knots
and unknots (toroidal and poloidal coils) in a perfect fluid. Calculations are
performed by numerical integration of the Biot-Savart law. Vortex complexity is
parametrized by the winding number , given by the ratio of the number of
meridian wraps to that of the longitudinal wraps. We find that for vortex
knots and toroidal coils move faster and carry more energy than a reference
vortex ring of same size and circulation, whereas for knots and poloidal
coils have approximately same speed and energy of the reference vortex ring.
Helicity is dominated by the writhe contribution. Finally, we confirm the
stabilizing effect of the Biot-Savart law for all knots and unknots tested,
that are found to be structurally stable over a distance of several diameters.
Our results also apply to quantized vortices in superfluid He.Comment: 17 pages, 8 figures, 2 table
Preliminary findings from a survey on the MD state of the practice
In the context of an Italian research project, this paper reports on an on-line survey, performed with 155 software professionals, with the aim of investigating about their opinions and experiences in modeling during software development and Model-driven engineering usage. The survey focused also on used modeling languages, processes and tools. A preliminary analysis of the results confirmed that Model-driven engineering, and more in general software modeling, are very relevant phenomena. Approximately 68% of the sample use models during software development. Among then, 44% generate code starting from models and 16% execute them directly. The preferred language for modeling is UML but DSLs are used as wel
Distributed storage and cloud computing: a test case
Since 2003 the computing farm hosted by the INFN Tier3 facility in Trieste supports the activities of many scientific communities. Hundreds of jobs from 45 different VOs, including those of the LHC experiments, are processed simultaneously. Given that normally the requirements of the different computational communities are not synchronized, the probability that at any given time the resources owned by one of the participants are not fully utilized is quite high. A balanced compensation should in principle allocate the free resources to other users, but there are limits to this mechanism. In fact, the Trieste site may not hold the amount of data needed to attract enough analysis jobs, and even in that case there could be a lack of bandwidth for their access. The Trieste ALICE and CMS computing groups, in collaboration with other Italian groups, aim to overcome the limitations of existing solutions using two approaches: sharing the data among all the participants taking full advantage of GARR-X wide area networks (10 GB/s) and integrating the resources dedicated to batch analysis with the ones reserved for dynamic interactive analysis, through modern solutions as cloud computing
Model-independent constraints on contact interactions from LEP2 data analysis
We derive model-independent constraints on four-fermion contact
interaction-type dynamics from the published preliminary LEP2 experimental data
on e^+e^- annihilation into \mu^+\mu^- and \tau^+\tau^- pairs, measured at
different energies between 130 and 207 GeV. The basic observables are chosen to
be the total cross section and the forward-backward asymmetry, and the analysis
realistically takes into account data uncertainties and correlations among
measurements at the various energies. The combination of data from different
energy points plays an important role in the determination of regions allowed
for the contact interaction coupling constants. In contrast to the more common
one-parameter analyses, we only obtain constraints on pairs of parameters
rather than limits on individual ones.Comment: 13 pages, LaTeX, including figures. v2: Included discussion of tau
data, version to appear in EPJ
Chromosome walking: A novel approach to analyse amino acid content of human proteins ordered by gene position
Molecular beam epitaxy of InAs nanowires in SiO2 nanotube templates: challenges and prospects for integration of III-Vs on Si
Guided growth of semiconductor nanowires in nanotube templates has been
considered as a potential platform for reproducible integration of III-Vs on
silicon or other mismatched substrates. Herein, we report on the challenges and
prospects of molecular beam epitaxy of InAs nanowires on SiO2/Si nanotube
templates. We show how and under which conditions the nanowire growth is
initiated by In-assisted vapor-liquid-solid growth enabled by the local
conditions inside the nanotube template. The conditions for high yield of
vertical nanowires are investigated in terms of the nanotube depth, diameter
and V/III flux ratios. We present a model that further substantiates our
findings. This work opens new perspectives for monolithic integration of III-Vs
on the silicon platform enabling new applications in the electronics,
optoelectronics and energy harvesting arena
The analysis of glutamate and glutamine frequencies in human proteins as marker of tissue oxygenation
relA over-expression reduces tumorigenicity and activates apoptosis in human cancer cells
We previously demonstrated that bcl-2 over-expression increases the malignant behaviour of the MCF7 ADR human breast cancer cell line and enhances nuclear factor-kappa B (NF-k B) transcriptional activity. Here, we investigated the direct effect of increased NF-k B activity on the tumorigenicity of MCF7 ADR cells by over-expressing the NF-k B subunit relA/p65. Surprisingly, our results demonstrated that over-expression of relA determines a considerable reduction of the tumorigenic ability in nude mice as indicated by the tumour take and the median time of tumour appearance. In vitro studies also evidenced a reduced cell proliferation and the activation of the apoptotic programme after relA over-expression. Apoptosis was associated with the production of reactive oxygen species, and the cleavage of the specific substrate Poly-ADP-ribose-polymerrase. Our data indicate that there is no general role for NF-k B in the regulation of apoptosis and tumorigenicity. In fact, even though inhibiting NF-k B activity has been reported to be lethal to tumour cells, our findings clearly suggest that an over-induction of nuclear NF-k B activity may produce the same effect. © 2001 Cancer Research Campaign http://www.bjcancer.co
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