7,897 research outputs found
Uncertainties in Atmospheric Neutrino Fluxes
An evaluation of the principal uncertainties in the computation of neutrino
fluxes produced in cosmic ray showers in the atmosphere is presented. The
neutrino flux predictions are needed for comparison with experiment to perform
neutrino oscillation studies. The paper concentrates on the main limitations
which are due to hadron production uncertainties. It also treats primary cosmic
ray flux uncertainties, which are at a lower level. The absolute neutrino
fluxes are found to have errors of around 15% in the neutrino energy region
important for contained events underground. Large cancellations of these errors
occur when ratios of fluxes are considered, in particular, the
ratio below GeV, the
ratio below GeV and
the up/down ratios above GeV are at the 1% level. A detailed
breakdown of the origin of these errors and cancellations is presented.Comment: 14 pages, 22 postscript figures, written in Revte
String spectra near some null cosmological singularities
We construct cosmological spacetimes with null Kasner-like singularities as
purely gravitational solutions with no other background fields turned on. These
can be recast as anisotropic plane-wave spacetimes by coordinate
transformations. We analyse string quantization to find the spectrum of string
modes in these backgrounds. The classical string modes can be solved for
exactly in these time-dependent backgrounds, which enables a detailed study of
the near singularity string spectrum, (time-dependent) oscillator masses and
wavefunctions. We find that for low lying string modes(finite oscillation
number), the classical near-singularity string mode functions are non-divergent
for various families of singularities. Furthermore, for any infinitesimal
regularization of the vicinity of the singularity, we find a tower of string
modes of ultra-high oscillation number which propagate essentially freely in
the background. The resulting picture suggests that string interactions are
non-negligible near the singularity.Comment: Latex, 30pgs; v2. minor clarifications, references adde
Executive function in first-episode schizophrenia
BACKGROUND: We tested the hypothesis that schizophrenia is primarily a frontostriatal disorder by examining executive function in first-episode patients. Previous studies have shown either equal decrements in many cognitive domains or specific deficits in memory. Such studies have grouped test results or have used few executive measures, thus, possibly losing information. We, therefore, measured a range of executive ability with tests known to be sensitive to frontal lobe function.
METHODS: Thirty first-episode schizophrenic patients and 30 normal volunteers, matched for age and NART IQ, were tested on computerized test of planning, spatial working memory and attentional set shifting from the Cambridge Automated Neuropsychological Test Battery. Computerized and traditional tests of memory were also administered for comparison. RESULTS: Patients were worse on all tests but the profile was non-uniform. A componential analysis indicated that the patients were characterized by a poor ability to think ahead and organize responses but an intact ability to switch attention and inhibit prepotent responses. Patients also demonstrated poor memory, especially for free recall of a story and associate learning of unrelated word pairs.
CONCLUSIONS: In contradistinction to previous studies, schizophrenic patients do have profound executive impairments at the beginning of the illness. However, these concern planning and strategy use rather than attentional set shifting, which is generally unimpaired. Previous findings in more chronic patients, of severe attentional set shifting impairment, suggest that executive cognitive deficits are progressive during the course of schizophrenia. The finding of severe mnemonic impairment at first episode suggests that cognitive deficits are not restricted to one cognitive domain
Null cosmological singularities and free strings
We continue exploring free strings in the background of null Kasner-like
cosmological singularities, following arXiv:0904.4532 [hep-th]. We study the
free string Schrodinger wavefunctional along the lines of arXiv:0807.1517
[hep-th]. We find the wavefunctional to be nonsingular in the vicinity of
singularities whose Kasner exponents satisfy certain relations. We compare this
with the description in other variables. We then study certain regulated
versions of these singularities where the singular region is replaced by a
substringy but nonsingular region and study the string spectra in these
backgrounds. The string modes can again be solved for exactly, giving some
insight into how string oscillator states get excited near the singularity.Comment: Latex, 24pgs, v3. PRD version, various clarifications on AdS/CFT
connections added, references adde
A Barren Landscape?
We consider the generation of a non-perturbative superpotential in F-theory
compactifications with flux. We derive a necessary condition for the generation
of such a superpotential in F-theory. For models with a single volume modulus,
we show that the volume modulus is never stabilized by either abelian
instantons or gaugino condensation. We then comment on how our analysis extends
to a larger class of compactifications. From our results, it appears that among
large volume string compactifications, metastable de Sitter vacua (should any
exist) are non-generic.Comment: 14 pages, comments adde
Survey of ETA prediction methods in public transport networks
The majority of public transport vehicles are fitted with Automatic Vehicle Location (AVL) systems generating a continuous stream of data. The availability of this data has led to a substantial body of literature addressing the development of algorithms to predict Estimated Times of Arrival (ETA). Here research literature reporting the development of ETA prediction systems specific to busses is reviewed to give an overview of the state of the art. Generally, reviews in this area categorise publications according to the type of algorithm used, which does not allow an objective comparison. Therefore this survey will categorise the reviewed publications according to the input data used to develop the algorithm. The review highlighted inconsistencies in reporting standards of the literature. The inconsistencies were found in the varying measurements of accuracy preventing any comparison and the frequent omission of a benchmark algorithm. Furthermore, some publications were lacking in overall quality. Due to these highlighted issues, any objective comparison of prediction accuracies is impossible. The bus ETA research field therefore requires a universal set of standards to ensure the quality of reported algorithms. This could be achieved by using benchmark datasets or algorithms and ensuring the publication of any code developed
A three-dimensional calculation of atmospheric neutrinos
A Monte-Carlo calculation of the atmospheric neutrino fluxes [1,2] has been
extended to take account of the three-dimensional (3D) nature of the problem,
including the bending of secondary particles in the geomagnetic field. Emphasis
has been placed on minimizing the approximations when introducing the 3D
considerations. In this paper, we describe the techniques used and quantify the
effects of the small approximations which remain. We compare 3D and 1D
calculations using the same physics input in order to evaluate the conditions
under which the 3D calculation is required and when the considerably simpler 1D
calculation is adequate. We find that the 1D and 3D results are essentially
identical for neutrino energy greater than 5 GeV except for small effects in
the azimuthal distributions due to bending of the secondary muon by the
geomagnetic field during their propagation in the atmosphere.Comment: 24 pages, 15 figures, LaTeX, to be submitted to Physical Review
Finite-element analysis of contact between elastic self-affine surfaces
Finite element methods are used to study non-adhesive, frictionless contact
between elastic solids with self-affine surfaces. We find that the total
contact area rises linearly with load at small loads. The mean pressure in the
contact regions is independent of load and proportional to the rms slope of the
surface. The constant of proportionality is nearly independent of Poisson ratio
and roughness exponent and lies between previous analytic predictions. The
contact morphology is also analyzed. Connected contact regions have a fractal
area and perimeter. The probability of finding a cluster of area drops as
where increases with decreasing roughness exponent. The
distribution of pressures shows an exponential tail that is also found in many
jammed systems. These results are contrasted to simpler models and experiment.Comment: 13 pages, 15 figures. Replaced after changed in response to referee
comments. Final two figures change
Radiation Hardness Studies in a CCD with High-Speed Column Parallel Readout
Charge Coupled Devices (CCDs) have been successfully used in several high
energy physics experiments over the past two decades. Their high spatial
resolution and thin sensitive layers make them an excellent tool for studying
short-lived particles. The Linear Collider Flavour Identification (LCFI)
collaboration is developing Column-Parallel CCDs (CPCCDs) for the vertex
detector of the International Linear Collider (ILC). The CPCCDs can be read out
many times faster than standard CCDs, significantly increasing their operating
speed. The results of detailed simulations of the charge transfer inefficiency
(CTI) of a prototype CPCCD are reported and studies of the influence of gate
voltage on the CTI described. The effects of bulk radiation damage on the CTI
of a CPCCD are studied by simulating the effects of two electron trap levels,
0.17 and 0.44 eV, at different concentrations and operating temperatures. The
dependence of the CTI on different occupancy levels (percentage of hit pixels)
and readout frequencies is also studied. The optimal operating temperature for
the CPCCD, where the effects of the charge trapping are at a minimum, is found
to be about 230 K for the range of readout speeds proposed for the ILC. The
results of the full simulation have been compared with a simple analytic model.Comment: 3 pages, 6 figures; presented at IEEE'07, ALCPG'07, ICATPP'0
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