2,915 research outputs found
The drive system of the Major Atmospheric Gamma-ray Imaging Cherenkov Telescope
The MAGIC telescope is an imaging atmospheric Cherenkov telescope, designed
to observe very high energy gamma-rays while achieving a low energy threshold.
One of the key science goals is fast follow-up of the enigmatic and short lived
gamma-ray bursts. The drive system for the telescope has to meet two basic
demands: (1) During normal observations, the 72-ton telescope has to be
positioned accurately, and has to track a given sky position with high
precision at a typical rotational speed in the order of one revolution per day.
(2) For successfully observing GRB prompt emission and afterglows, it has to be
powerful enough to position to an arbitrary point on the sky within a few ten
seconds and commence normal tracking immediately thereafter. To meet these
requirements, the implementation and realization of the drive system relies
strongly on standard industry components to ensure robustness and reliability.
In this paper, we describe the mechanical setup, the drive control and the
calibration of the pointing, as well as present measurements of the accuracy of
the system. We show that the drive system is mechanically able to operate the
motors with an accuracy even better than the feedback values from the axes. In
the context of future projects, envisaging telescope arrays comprising about
100 individual instruments, the robustness and scalability of the concept is
emphasized.Comment: 15 pages, 12 (10) figures, submitted to Astroparticle Physics, a high
resolution version of the paper (particularly fig. 1) is available at
http://publications.mppmu.mpg.de/2008/MPP-2008-101/FullText.pd
An Empirical Investigation of the Predictors of Executive Career Success
The present study examined the degree to which demographic, human capital,motivational, organizational, and industry/region variables predicted executive career success. Career success was assumed to comprise objective (pay, ascendancy) and subjective (job satisfaction, career satisfaction) elements. Results obtained from a sample of 1,388 U.S.executives suggested that demographic, human capital, motivational, and organizational variables explained significant variance in objective career success and in career satisfaction. Particularly interesting were findings that educational level, quality, prestige, and degree type all predicted financial success. In contrast, only the motivational and organizational variables explained significant amounts of variance in job satisfaction. These findings suggest that the variables that lead to objective career success often are quite different from those that lead to subjectively defined success
Adsorption on carbon nanotubes: quantum spin tubes, magnetization plateaus, and conformal symmetry
We formulate the problem of adsorption onto the surface of a carbon nanotube
as a lattice gas on a triangular lattice wrapped around a cylinder. This model
is equivalent to an XXZ Heisenberg quantum spin tube. The geometric frustration
due to wrapping leads generically to four magnetization plateaus, in contrast
to the two on a flat graphite sheet. We obtain analytical and numerical results
for the magnetizations and transition fields for armchair, zig-zag and chiral
nanotubes. The zig-zags are exceptional in that one of the plateaus has
extensive zero temperature entropy in the classical limit. Quantum effects lift
up the degeneracy, leaving gapless excitations which are described by a
conformal field theory with compactification radius quantized by the tube
circumference.Comment: 5 pages, 6 figure
Reference range: Which statistical intervals to use?
Reference ranges, which are data-based intervals aiming to contain a pre-specified large proportion of the population values, are powerful tools to analyse observations in clinical laboratories. Their main point is to classify any future observations from the population which fall outside them as atypical and thus may warrant further investigation. As a reference range is constructed from a random sample from the population, the event âa reference range contains (100 P)% of the populationâ is also random. Hence, all we can hope for is that such event has a large occurrence probability. In this paper we argue that some intervals, including the P prediction interval, are not suitable as reference ranges since there is a substantial probability that these intervals contain less than (100 P)% of the population, especially when the sample size is large. In contrast, a (P,Îł) tolerance interval is designed to contain (100 P)% of the population with a pre-specified large confidence Îł so it is eminently adequate as a reference range. An example based on real data illustrates the paperâs key points
MWL observations of VHE blazars in 2006
In 2006 the MAGIC telescope observed the well known very high energy (VHE, >
80 GeV) blazars Mrk 421 and Mrk 501 in the course of multi-wavelength
campaigns, comprising measurements in the optical, X-ray and VHE regime. MAGIC
performed additional snapshot observations on Mrk 421 around the MWL campaigns
and detected the source each night with high significance, establishing once
more flux variability on nightly scales for this object. For certain nights,
the integral flux exceeded the one of Crab significantly, whereas the truly
simultaneous observations have been conducted in a rather low flux state. The
MAGIC observations contemporaneous to XMM-Newton revealed clear intra-night
variability. No significant correlation between the spectral index and the flux
could be found for the nine days of observations. The VHE observations of Mrk
501 have been conducted during one of the lowest flux states ever measured by
MAGIC for this object. The VHE and optical light curves do not show significant
variability, whereas the flux in X-rays increased by about 50 %. In this
contribution, the results of the MAGIC observations will be presented in
detail.Comment: Contribution to the 31st ICRC, Lodz, Poland, July 200
A study of environmental characterization of conventional and advanced aluminum alloys for selection and design. Phase 2: The breaking load test method
A technique is demonstrated for accelerated stress corrosion testing of high strength aluminum alloys. The method offers better precision and shorter exposure times than traditional pass fail procedures. The approach uses data from tension tests performed on replicate groups of smooth specimens after various lengths of exposure to static stress. The breaking strength measures degradation in the test specimen load carrying ability due to the environmental attack. Analysis of breaking load data by extreme value statistics enables the calculation of survival probabilities and a statistically defined threshold stress applicable to the specific test conditions. A fracture mechanics model is given which quantifies depth of attack in the stress corroded specimen by an effective flaw size calculated from the breaking stress and the material strength and fracture toughness properties. Comparisons are made with experimental results from three tempers of 7075 alloy plate tested by the breaking load method and by traditional tests of statistically loaded smooth tension bars and conventional precracked specimens
Robustness considerations in selecting efficient two-color microarray designs
The main goal of microarray experiments is to select a small subset of genes that are differentially expressed among competing mRNA samples. For a given set of such mRNA samples, it is possible to consider a number of two-color cDNA microarray designs with a fixed number of arrays. Appropriate criteria can be used to select an efficient design from such a set of alternative experimental designs. In practice, however, microarray expression data often contain missing observations and the most efficient design (with complete observations) for a specific setup may not be efficient in the presence of missing observations. In this article, we propose two criteria to address the robustness of microarray designs against missing observations. We demonstrate the simultaneous use of efficiency and robustness criteria to select good microarray designs for both one-factor and multi-factor experiments. Contact: [email protected]
EQUILIBRIUM OF CHILDREN PRACTISING JUDO
INTRODUCTION Human body equilibrium is the index of one's health, physical development, fitness and athletic mastery level. Coordinational abilities of children aged 4-5 in maintaining statodynamic stability have been studied when solving equilibrium motor tasks ( P. Perrin, 1989; V. N. Boloban, 1990; K. Bretz, R. J. Kaske, 1994; A.U. Kholtobina, 1994, et al.) . METHODOLOGY Measurements have been made by means of ADAMtype equipment complex (Software: lngchicurbĂŒro - Dr. K.Bretz, 1992). Different methods of solving equilibrium motor tasks by children have been determined. Their stabilograms consist of such individual parameters as: amplitude, frequency of vibration, duration of test task performance, special location in time function (on isoline, above or below it ) , and in âstabilograph-subjectâ coordinate system. RESULTS Spectral Fourier-analysis of stabilograms demonstrates that body stability is generally determined by vibrations having the frequencies 0.5-1.5 Hz. In the frequencies above 2-3 Hz, children subjects do not yet possess voluntary motions to regulate body postures. Coordination indices of children's body orthograde position demonstrate necessity of special training to provide body equilibrium. Developed didactical means, methods and control elements provide efficient formation of statodynamic stability skill. Stabilogram indices allow to determine coordinational abilities in children and forecast development of their voluntary motions in the structure of professional orientation
Long term monitoring of bright TeV Blazars with the MAGIC telescope
The MAGIC telescope has performed long term monitoring observations of the
bright TeV Blazars Mrk421, Mrk501 and 1ES1959+650. Up to 40 observations, 30 to
60 minutes each have been performed for each source evenly distributed over the
observable period of the year. The sensitivity of MAGIC is sufficient to
establish a flux level of 25% of the Crab flux for each measurement. These
observations are well suited to trigger multiwavelength ToO observations and
the overall collected data allow an unbiased study of the flaring statistics of
the observed AGNs.Comment: 4 pages, 4 figures, to appear in the proceedings of the 30th
International Cosmic Ray Conference, Merida, July 200
Avalanche statistics of sand heaps
Large scale computer simulations are presented to investigate the avalanche
statistics of sand piles using molecular dynamics. We could show that different
methods of measurement lead to contradicting conclusions, presumably due to
avalanches not reaching the end of the experimental table.Comment: 6 pages, 4 figure
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