7,323 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
Impact Ionization in ZnS
The impact ionization rate and its orientation dependence in k space is
calculated for ZnS. The numerical results indicate a strong correlation to the
band structure. The use of a q-dependent screening function for the Coulomb
interaction between conduction and valence electrons is found to be essential.
A simple fit formula is presented for easy calculation of the energy dependent
transition rate.Comment: 9 pages LaTeX file, 3 EPS-figures (use psfig.sty), accepted for
publication in PRB as brief Report (LaTeX source replaces raw-postscript
file
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
Toward the End of Time
The null-brane space-time provides a simple model of a big crunch/big bang
singularity. A non-perturbative definition of M-theory on this space-time was
recently provided using matrix theory. We derive the fermion couplings for this
matrix model and study the leading quantum effects. These effects include
particle production and a time-dependent potential. Our results suggest that as
the null-brane develops a big crunch singularity, the usual notion of
space-time is replaced by an interacting gluon phase. This gluon phase appears
to constitute the end of our conventional picture of space and time.Comment: 31 pages, reference adde
Population Cancer Risks Associated with Coal Mining: A Systematic Review
BACKGROUND: Coal is produced across 25 states and provides 42% of US energy. With production expected to increase 7.6% by 2035, proximate populations remain at risk of exposure to carcinogenic coal products such as silica dust and organic compounds. It is unclear if population exposure is associated with increased risk, or even which cancers have been studied in this regard.
METHODS: We performed a systematic review of English-language manuscripts published since 1980 to determine if coal mining exposure was associated with increased cancer risk (incidence and mortality).
RESULTS: Of 34 studies identified, 27 studied coal mining as an occupational exposure (coal miner cohort or as a retrospective risk factor) but only seven explored health effects in surrounding populations. Overall, risk assessments were reported for 20 cancer site categories, but their results and frequency varied considerably. Incidence and mortality risk assessments were: negative (no increase) for 12 sites; positive for 1 site; and discordant for 7 sites (e.g. lung, gastric). However, 10 sites had only a single study reporting incidence risk (4 sites had none), and 11 sites had only a single study reporting mortality risk (2 sites had none). The ecological study data were particularly meager, reporting assessments for only 9 sites. While mortality assessments were reported for each, 6 had only a single report and only 2 sites had reported incidence assessments.
CONCLUSIONS: The reported assessments are too meager, and at times contradictory, to make definitive conclusions about population cancer risk due to coal mining. However, the preponderance of this and other data support many of Hill\u27s criteria for causation. The paucity of data regarding population exposure and risk, the widespread geographical extent of coal mining activity, and the continuing importance of coal for US energy, warrant further studies of population exposure and risk
Improving Predictions for Helium Emission Lines
We have combined the detailed He I recombination model of Smits with the
collisional transitions of Sawey & Berrington in order to produce new accurate
helium emissivities that include the effects of collisional excitation from
both the 2 (3)S and 2 (1) S levels. We present a grid of emissivities for a
range of temperature and densities along with analytical fits and error
estimates.
Fits accurate to within 1% are given for the emissivities of the brightest
lines over a restricted range for estimates of primordial helium abundance. We
characterize the analysis uncertainties associated with uncertainties in
temperature, density, fitting functions, and input atomic data. We estimate
that atomic data uncertainties alone may limit abundance estimates to an
accuracy of 1.5%; systematic errors may be greater than this. This analysis
uncertainty must be incorporated when attempting to make high accuracy
estimates of the helium abundance. For example, in recent determinations of the
primordial helium abundance, uncertainties in the input atomic data have been
neglected.Comment: ApJ, accepte
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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