1,498 research outputs found
Identification of a gene encoding GMP synthetase from a Neurospora crassa cDNA library by bacterial complementation
We report the isolation and identification of a gene encoding GMP synthetase from a Neurospora crassa cDNA library. Phage infection of the purine-requiring Escherichia coli strain SĂ3834 using the NO3- induced cDNA phage library from the Fungal Genetics Stock Center resulted in colonies able to grow on minimal media with no added purine source. A plasmid, termed pGMPS1, was isolated from one of these colonies and shown to reproducibly support growth of strain SĂ3834 in the absence of purines in the media. Identification of this gene as one encoding GMP synthetase is confirmed by DNA sequencing and comparison to the known guaA gene from yeast
Universality in movie rating distributions
In this paper histograms of user ratings for movies (1,...,10) are analysed.
The evolving stabilised shapes of histograms follow the rule that all are
either double- or triple-peaked. Moreover, at most one peak can be on the
central bins 2,...,9 and the distribution in these bins looks smooth
`Gaussian-like' while changes at the extremes (1 and 10) often look abrupt. It
is shown that this is well approximated under the assumption that histograms
are confined and discretised probability density functions of L\'evy skew
alpha-stable distributions. These distributions are the only stable
distributions which could emerge due to a generalized central limit theorem
from averaging of various independent random avriables as which one can see the
initial opinions of users. Averaging is also an appropriate assumption about
the social process which underlies the process of continuous opinion formation.
Surprisingly, not the normal distribution achieves the best fit over histograms
obseved on the web, but distributions with fat tails which decay as power-laws
with exponent -(1+alpha) (alpha=4/3). The scale and skewness parameters of the
Levy skew alpha-stable distributions seem to depend on the deviation from an
average movie (with mean about 7.6). The histogram of such an average movie has
no skewness and is the most narrow one. If a movie deviates from average the
distribution gets broader and skew. The skewness pronounces the deviation. This
is used to construct a one parameter fit which gives some evidence of
universality in processes of continuous opinion dynamics about taste.Comment: 8 pages, 5 figures, accepted for publicatio
Bodies, technologies and action possibilities: when is an affordance?
Borrowed from ecological psychology, the concept of affordances is often said to offer the social study of technology a means of re-framing the question of what is, and what is not, âsocialâ about technological artefacts. The concept, many argue, enables us to chart a safe course between the perils of technological determinism and social constructivism. This article questions the sociological adequacy of the concept as conventionally deployed. Drawing on ethnographic work on the ways technological artefacts engage, and are engaged by, disabled bodies, we propose that the âaffordancesâ of technological objects are not reducible to their material constitution but are inextricably bound up with specific, historically situated modes of engagement and ways of life
Progress in Air Shower Radio Measurements: Detection of Distant Events
Data taken during half a year of operation of 10 LOPES antennas (LOPES-10),
triggered by EAS observed with KASCADE-Grande have been analysed. We report
about the analysis of correlations of radio signals measured by LOPES-10 with
extensive air shower events reconstructed by KASCADE-Grande, including shower
cores at large distances. The efficiency of detecting radio signals induced by
air showers up to distances of 700 m from the shower axis has been
investigated. The results are discussed with special emphasis on the effects of
the reconstruction accuracy for shower core and arrival direction on the
coherence of the measured radio signal. In addition, the correlations of the
radio pulse amplitude with the primary cosmic ray energy and with the lateral
distance from the shower core are studied.Comment: Accepted for publication in Astroparticle Physic
Het kokkelbestand in de Nederlandse kustwateren in 2014
In het voorjaar van 2014 is het kokkelbestand (Cerastoderma edule) in de Waddenzee, de Oosterschelde, de Westerschelde en de Voordelta geĂŻnventariseerd. De inventarisatie wordt jaarlijks uitgevoerd ten behoeve van het beleid voor visserij, en is daarnaast ook van belang voor evaluatie van beheersmaatregelen en effectstudies in het kader van Natura 2000 en de natuurbeschermingswet
Ballistic transport in random magnetic fields with anisotropic long-ranged correlations
We present exact theoretical results about energetic and dynamic properties
of a spinless charged quantum particle on the Euclidean plane subjected to a
perpendicular random magnetic field of Gaussian type with non-zero mean. Our
results refer to the simplifying but remarkably illuminating limiting case of
an infinite correlation length along one direction and a finite but strictly
positive correlation length along the perpendicular direction in the plane.
They are therefore ``random analogs'' of results first obtained by A. Iwatsuka
in 1985 and by J. E. M\"uller in 1992, which are greatly esteemed, in
particular for providing a basic understanding of transport properties in
certain quasi-two-dimensional semiconductor heterostructures subjected to
non-random inhomogeneous magnetic fields
Het mosselbestand en het areaal aan mosselbanken op de droogvallende platen van de Waddenzee in het voorjaar van 2013
Onderzoek naar het areaal en bestand aan litorale mosselbanken in de Waddenzee. Doel is: Het maken van een biomassa-schatting van het mosselbestand op droogvallende platen in de Nederlandse Waddenzee in het voorjaar van 2013. Voor de kartering van het areaal aan mosselbanken worden bij laag water in de beschikbare tijd zo veel mogelijk banken te voet bezocht. Met behulp van GPS-apparatuur worden de positie en omtrek van de banken bepaald. Bij het bepalen van het totale areaal mosselbanken wordt voor de niet bezochte banken uitgegaan van gegevens in eerdere jaren, na middels een vliegtuig inspectie de aanwezigheid van deze banken vastgesteld te hebben
On noise treatment in radio measurements of cosmic ray air showers
Precise measurements of the radio emission by cosmic ray air showers require
an adequate treatment of noise. Unlike to usual experiments in particle
physics, where noise always adds to the signal, radio noise can in principle
decrease or increase the signal if it interferes by chance destructively or
constructively. Consequently, noise cannot simply be subtracted from the
signal, and its influence on amplitude and time measurement of radio pulses
must be studied with care. First, noise has to be determined consistently with
the definition of the radio signal which typically is the maximum field
strength of the radio pulse. Second, the average impact of noise on radio pulse
measurements at individual antennas is studied for LOPES. It is shown that a
correct treatment of noise is especially important at low signal-to-noise
ratios: noise can be the dominant source of uncertainty for pulse height and
time measurements, and it can systematically flatten the slope of lateral
distributions. The presented method can also be transfered to other experiments
in radio and acoustic detection of cosmic rays and neutrinos.Comment: 4 pages, 6 figures, submitted to NIM A, Proceedings of ARENA 2010,
Nantes, Franc
Magnetic translation groups in an n-dimensional torus
A charged particle in a uniform magnetic field in a two-dimensional torus has
a discrete noncommutative translation symmetry instead of a continuous
commutative translation symmetry. We study topology and symmetry of a particle
in a magnetic field in a torus of arbitrary dimensions. The magnetic
translation group (MTG) is defined as a group of translations that leave the
gauge field invariant. We show that the MTG on an n-dimensional torus is
isomorphic to a central extension of a cyclic group Z_{nu_1} x ... x
Z_{nu_{2l}} x T^m by U(1) with 2l+m=n. We construct and classify irreducible
unitary representations of the MTG on a three-torus and apply the
representation theory to three examples. We shortly describe a representation
theory for a general n-torus. The MTG on an n-torus can be regarded as a
generalization of the so-called noncommutative torus.Comment: 29 pages, LaTeX2e, title changed, re-organized, to be published in
Journal of Mathematical Physic
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