3,059 research outputs found
Extraction of the atmospheric neutrino fluxes from experimental event rate data
The precise knowledge of the atmospheric neutrino fluxes is a key ingredient
in the interpretation of the results from any atmospheric neutrino experiment.
In the standard atmospheric neutrino data analysis, these fluxes are
theoretical inputs obtained from sophisticated numerical calculations. In this
contribution we present an alternative approach to the determination of the
atmospheric neutrino fluxes based on the direct extraction from the
experimental data on neutrino event rates. The extraction is achieved by means
of a combination of artificial neural networks as interpolants and Monte Carlo
methods.Comment: 6 pages, 2 figs, to appear in the proceedings of the 2nd
International Conference on Quantum Theories and Renormalization Group in
Gravity and Cosmology, Barcelona, July 200
Neural network approach to parton distributions fitting
We will show an application of neural networks to extract information on the
structure of hadrons. A Monte Carlo over experimental data is performed to
correctly reproduce data errors and correlations. A neural network is then
trained on each Monte Carlo replica via a genetic algorithm. Results on the
proton and deuteron structure functions, and on the nonsinglet parton
distribution will be shown.Comment: 4 pages, 5 eps figures. Talk given by Andrea Piccione at the "X
International Workshop on Advanced Computing and Analysis Techniques in
Physics Research", ACAT 2005, DESY-Zeuthen, Germany, 22-27 May 2005.
Corrected fig.
Giant planets around two intermediate-mass evolved stars and confirmation of the planetary nature of HIP67851 c
Precision radial velocities are required to discover and characterize planets
orbiting nearby stars. Optical and near infrared spectra that exhibit many
hundreds of absorption lines can allow the m/s precision levels required for
such work. However, this means that studies have generally focused on
solar-type dwarf stars. After the main-sequence, intermediate-mass stars
(former A-F stars) expand and rotate slower than their progenitors, thus
thousands of narrow absorption lines appear in the optical region, permitting
the search for planetary Doppler signals in the data for these types of stars.
We present the discovery of two giant planets around the intermediate-mass
evolved star HIP65891 and HIP107773. The best Keplerian fit to the HIP65891 and
HIP107773 radial velocities leads to the following orbital parameters: P=1084.5
d; msin = 6.0 M; =0.13 and P=144.3 d; msin = 2.0
M; =0.09, respectively. In addition, we confirm the planetary nature
of the outer object orbiting the giant star HIP67851. The orbital parameters of
HIP67851c are: P=2131.8 d, msin = 6.0 M and =0.17. With
masses of 2.5 M and 2.4 M HIP65891 and HIP107773 are two of the
most massive stars known to host planets. Additionally, HIP67851 is one of five
giant stars that are known to host a planetary system having a close-in planet
( 0.7 AU). Based on the evolutionary states of those five stars, we
conclude that close-in planets do exist in multiple systems around subgiants
and slightly evolved giants stars, but probably they are subsequently destroyed
by the stellar envelope during the ascent of the red giant branch phase. As a
consequence, planetary systems with close-in objects are not found around
horizontal branch stars.Comment: Accepted for publication in A&
Neural network determination of parton distributions: the nonsinglet case
We provide a determination of the isotriplet quark distribution from
available deep--inelastic data using neural networks. We give a general
introduction to the neural network approach to parton distributions, which
provides a solution to the problem of constructing a faithful and unbiased
probability distribution of parton densities based on available experimental
information. We discuss in detail the techniques which are necessary in order
to construct a Monte Carlo representation of the data, to construct and evolve
neural parton distributions, and to train them in such a way that the correct
statistical features of the data are reproduced. We present the results of the
application of this method to the determination of the nonsinglet quark
distribution up to next--to--next--to--leading order, and compare them with
those obtained using other approaches.Comment: 46 pages, 18 figures, LaTeX with JHEP3 clas
Intuïcions dels alumnes de secundària sobre la probabilitat. Una recerca sobre la influència del treball empíric en el cas d'un esdeveniment compost
En aquest article es presenta una investigació
relacionada amb dos conceptes probabilístics, l'espai
mostral i la probabilitat d'un esdeveniment compost,
realitzada amb alumnes de 2n d'ESO. En el camp de la
probabilitat és sabut que un ensenyament efectiu s'ha
de fomentar en el coneixement previ per part dels
professors de les intuïcions que presenten els
alumnes. En aquest sentit, un dels objectius d'aquest
treball és determinar i classificar les intuïcions dels
alumnes en relació amb els dos conceptes esmentats.
Aquesta tasca s'ha realitzat seguint els paràmetres
següents: el conjunt d'estratègies desenvolupades, la
comprensió de les situacions presentades i la
naturalesa de les argumentacions en relació amb els
diferents significats que pot prendre la probabilitat.
Per a l'obtenció de les dades s'ha utilitzat una de les
proves d'avaluació de les competències bàsiques
aplicades pel Departament d'Educació en els anys
2006-2007. Paral·lelament, s'ha analitzat la influència
del treball empíric en la formació i la modificació de
les intuïcions dels alumnes. En aquest sentit, els
resultats de la investigació assenyalen un camí a
seguir per ajudar els estudiants a crear intuïcions
correctes, i a la vegada mostren que certes intuïcions
que poden interferir en aquest camí sovint són
evitables amb l'ajut de l'experimentació.This paper presents an investigation with two
probabilistic concepts, the sample space and the
probability of a compound event, made with
13-14 years students. In the field of probability it is
known that effective teaching should be preceded
by research into the primary intuitive substrate of
the relevant subject. In this sense, one of the
objectives of this study is to determinate and
classify the students intuitions about the two
concepts mentioned above. This task was carried
out according to the following parameters: the set
of strategies developed, the understanding of the
situations presented and the nature of the
students arguments in relation to the different
meanings of the concept of probability. To obtain
the data, we used one of the basic skills test
implemented by the Education Department in
2006-2007. Simultaneously, we analyzed the
influence of empirical work in the formation and
modification of the students intuitions. In this
sense, the results of the investigation indicate a
way forward to help students create correct
intuitions showing, at the same time, that the
existence of certain intuitions that can interfere in
their way are often avoidable with the help of
experimentation
Spin Coulomb drag in the two-dimensional electron liquid
We calculate the spin-drag transresistivity
in a two-dimensional electron gas at temperature in the random phase
approximation. In the low-temperature regime we show that, at variance with the
three-dimensional low-temperature result [], the spin transresistivity of a two-dimensional {\it spin unpolarized}
electron gas has the form . In the
spin-polarized case the familiar form is
recovered, but the constant of proportionality diverges logarithmically as
the spin-polarization tends to zero. In the high-temperature regime we obtain
(where
is the effective Rydberg energy) {\it independent} of the density.
Again, this differs from the three-dimensional result, which has a logarithmic
dependence on the density. Two important differences between the spin-drag
transresistivity and the ordinary Coulomb drag transresistivity are pointed
out: (i) The singularity at low temperature is smaller, in the Coulomb
drag case, by a factor where is the Fermi wave vector and
is the separation between the layers. (ii) The collective mode contribution
to the spin-drag transresistivity is negligible at all temperatures. Moreover
the spin drag effect is, for comparable parameters, larger than the ordinary
Coulomb drag effect.Comment: 6 figures; various changes; version accepted for publicatio
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