4,195 research outputs found
On the influence of statistics on the determination of the mean value of the depth of shower maximum for ultra high energy cosmic ray showers
The chemical composition of ultra high energy cosmic rays is still uncertain.
The latest results obtained by the Pierre Auger Observatory and the HiRes
Collaboration, concerning the measurement of the mean value and the
fluctuations of the atmospheric depth at which the showers reach the maximum
development, Xmax, are inconsistent. From comparison with air shower
simulations it can be seen that, while the Auger data may be interpreted as a
gradual transition to heavy nuclei for energies larger than ~ 2-3x10^18 eV, the
HiRes data are consistent with a composition dominated by protons. In Ref. [1]
it is suggested that a possible explanation of the observed deviation of the
mean value of Xmax from the proton expectation, observed by Auger, could
originate in a statistical bias arising from the approximated exponential shape
of the Xmax distribution, combined with the decrease of the number of events as
a function of primary energy. In this paper we consider a better description of
the Xmax distribution and show that the possible bias in the Auger data is at
least one order of magnitude smaller than the one obtained when assuming an
exponential distribution. Therefore, we conclude that the deviation of the
Auger data from the proton expectation is unlikely explained by such
statistical effect.Comment: To be published in Journal of Physics G: Nuclear and Particle Physic
An improved direct colorimetric method for the quantitative analysis of urinary hippuric acid as an index of toluene exposure
An improved direct colorimetric method for determining the concentration of urinary hippuric acid as an index of toluene exposure was described. One tenth ml of urine was diluted with 0.4 ml 0.01 M phosphate buffer H 6.9 and mixed with 0.5 ml pyridine. The mixture was layered on 0.2 ml benzenesulfonyl chloride. The reaction was started by mixing for one min with a mechanical shaker. The colored solution was allowed to stand for 30 min, diluted with 5 ml ethanol, and absorbance measured at 410 nm within 30 min after the dilution. The coefficient of variation of this method was 6% and the recovery 103% when urine contains about 0.2-0.5 mg hippuric acid per ml of urine. The concentration was linear up to 2.0 mg per ml hippuric acid in a specimen.</p
Magnetized strangelets at finite temperature
The main properties of magnetized strangelets, namely, their energy per
baryon, radius and electric charge, are studied. Temperature effects are also
taken into account in order to study their stability compared to the 56Fe
isotope and non-magnetized strangelets using the liquid drop model. Massive
quarks are considered with the aim to have a more realistic description for
strangelets in the astrophysical context and the environment of heavy ion
colliders, playing also an important role in the thermodynamical quantities of
the quark gas. It is concluded that the presence of a magnetic field tends to
stabilize more the strangelets, even when temperature effects are taken into
account. Magnetized strangelets in a paired superconductor phase (magnetized
color flavor locked phase) are also discussed. It is shown that they are more
stable than ordinary magnetized strangelets for typical gap values of the order
of O(100) MeV.Comment: 10 pages, 10 figures, discussion extended, new references adde
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Learning the preferences of physicians for the organization of result lists of medical evidence articles
Objectives
Despite many clinical decision support systems (CDSSs) being rated as highly usable, CDSSs have not been widely adopted in clinical practice. We posit that there are factors aside from usability that impact adoption of CDSSs; in particular we are interested in the role played by MDs intrinsic motivation to use computer-based support. Our research aim is to investigate the relationship between usability and intrinsic motivation in order to learn about adoption of CDSS in clinical practice.
Methods
Following the evaluation of a CDSS, 19 MDs completed a 2 part questionnaire about their intrinsic motivation to use computer-based support in general and the usability of the evaluated CDSS.
Results
The analysis of MDs motivation to use computer-based support demonstrated that MDs are comfortable using computer-based support and in general find using it quite easy (a motivation rating of 0.66 on a (0, 1) scale was computed). However MDs also reported a perceived lack of competence associated with a lack of prior experience using technology in practice, which results in pressure and tension. The considered CDSS scored highly on all usability dimensions and a usability rating of 0.74 was recorded. The examination of the relationship between motivation and usability suggested that users who were motivated to use computer-based support experienced better usability than those who reported low levels of motivation.
Conclusions
Our small case study suggests that an important factor supplementing the usability of CDSSs is intrinsic motivation to use computer-based support in general. We posit that the lack of such a measure thus far in CDSS evaluation may to some extent explain seeming MD satisfaction with CDSSs on one hand, but their limited adoption on the other. We recommend that clinical managers responsible for deploying CDSS should invest in training MDs to use technology underlying computer-based support applications instead of focusing only on the features of the specific CDSS to be deployed
Estimating the inelasticity with the information theory approach
Using the information theory approach, in both its extensive and nonextensive
versions, we estimate the inelasticity parameter of hadronic reactions
together with its distribution and energy dependence from and
data. We find that the inelasticity remains essentially constant in energy
except for a variation around , as was originally expected.Comment: 14 pages, 8 figures. Misprints correcte
Observations of red-giant variable stars by Aboriginal Australians
Aboriginal Australians carefully observe the properties and positions of
stars, including both overt and subtle changes in their brightness, for
subsistence and social application. These observations are encoded in oral
tradition. I examine two Aboriginal oral traditions from South Australia that
describe the periodic changing brightness in three pulsating, red-giant
variable stars: Betelgeuse (Alpha Orionis), Aldebaran (Alpha Tauri), and
Antares (Alpha Scorpii). The Australian Aboriginal accounts stand as the only
known descriptions of pulsating variable stars in any Indigenous oral tradition
in the world. Researchers examining these oral traditions over the last
century, including anthropologists and astronomers, missed the description of
these stars as being variable in nature as the ethnographic record contained
several misidentifications of stars and celestial objects. Arguably,
ethnographers working on Indigenous Knowledge Systems should have academic
training in both the natural and social sciences.Comment: The Australian Journal of Anthropology (2018
Statistical Asynchronous Regression: Determining the Relationship Between two Quantities that are not Measured Simultaneously
We introduce the Statistical Asynchronous Regression (SAR) method: a
technique for determining a relationship between two time varying quantities
without simultaneous measurements of both quantities. We require that there is
a time invariant, monotonic function Y = u(X) relating the two quantities, Y
and X. In order to determine u(X), we only need to know the statistical
distributions of X and Y. We show that u(X) is the change of variables that
converts the distribution of X into the distribution of Y, while conserving
probability. We describe an algorithm for implementing this method and apply it
to several example distributions. We also demonstrate how the method can
separate spatial and temporal variations from a time series of energetic
electron flux measurements made by a spacecraft in geosynchronous orbit. We
expect this method will be useful to the general problem of spacecraft
instrument calibration. We also suggest some applications of the SAR method
outside of space physics.Comment: 27 pages, 10 figures, stronger motivations and rewriting to make the
paper more accessible to a general audience. in press in J. Geophys. Res.
(Space Physics
Combining Multi-Fidelity Modelling and Asynchronous Batch Bayesian Optimization
Bayesian Optimization is a useful tool for experiment design. Unfortunately, the classical, sequential setting of Bayesian Optimization does not translate well into laboratory experiments, for instance battery design, where measurements may come from different sources and their evaluations may require significant waiting times. Multi-fidelity Bayesian Optimization addresses the setting with measurements from different sources. Asynchronous batch Bayesian Optimization provides a framework to select new experiments before the results of the prior experiments are revealed. This paper proposes an algorithm combining multi-fidelity and asynchronous batch methods. We empirically study the algorithm behavior, and show it can outperform single-fidelity batch methods and multi-fidelity sequential methods. As an application, we consider designing electrode materials for optimal performance in pouch cells using experiments with coin cells to approximate battery performance
Nonextensive thermal sources of cosmic rays?
The energy spectrum of cosmic rays (CR) exhibits power-like behavior with a
very characteristic "knee" structure. We consider a possibility that such a
spectrum could be generated by some specific nonstatistical temperature
fluctuations in the source of CR with the "knee" structure reflecting an abrupt
change of the pattern of such fluctuations. This would result in a generalized
nonextensive statistical model for the production of CR. The possible physical
mechanisms leading to these effects are discussed together with the resulting
chemical composition of the CR, which follows the experimentally observed
abundance of nuclei.Comment: 16 pages, 3 figures, rewritten and updated version, to be published
in Centr. Eur. J. Phy
Equivalence of volume and temperature fluctuations in power-law ensembles
Relativistic particle production often requires the use of Tsallis statistics
to account for the apparently power-like behavior of transverse momenta
observed in the data even at a few GeV/c. In such an approach this behavior is
attributed to some specific intrinsic fluctuations of the temperature in
the hadronizing system and is fully accounted by the nonextensivity parameter
. On the other hand, it was recently shown that similar power-law spectra
can also be obtained by introducing some specific volume fluctuations,
apparently without invoking the introduction of Tsallis statistics. We
demonstrate that, in fact, when the total energy is kept constant, these volume
fluctuations are equivalent to temperature fluctuations and can be derived from
them. In addition, we show that fluctuations leading to multiparticle power-law
Tsallis distributions introduce specific correlations between the considered
particles. We then propose a possible way to distinguish the fluctuations in
each event from those occurring from event-to-event. This could have
applications in the analysis of high density events at LHC (and especially in
ALICE).Comment: Revised version with new figure, footnotes and references adde
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