44 research outputs found
Stochastic motion of test particle implies that G varies with time
The aim of this letter is to propose a new description to the time varying
gravitational constant problem, which naturally implements the Dirac's large
numbers hypothesis in a new proposed holographic scenario for the origin of
gravity as an entropic force. We survey the effect of the Stochastic motion of
the test particle in Verlinde's scenario for gravity\cite{Verlinde}. Firstly we
show that we must get the equipartition values for which
leads to the usual Newtonian gravitational constant. Secondly,the stochastic
(Brownian) essence of the motion of the test particle, modifies the Newton's
2'nd law. The direct result is that the Newtonian constant has been time
dependence in resemblance as \cite{Running}.Comment: Accepted in International Journal of Theoretical Physic
Density correlations and dynamical Casimir emission of Bogoliubov phonons in modulated atomic Bose-Einstein condensates
We present a theory of the density correlations that appear in an atomic
Bose-Einstein condensate as a consequence of the dynamical Casimir emission of
pairs of Bogoliubov phonons when the atom-atom scattering length is modulated
in time. Different regimes as a function of the temporal shape of the
modulation are identified and a simple physical picture of the phenomenon is
discussed. Analytical expressions for the density correlation function are
provided for the most significant limiting cases. This theory is able to
explain some unexpected features recently observed in numerical calculations of
Hawking radiation from analog black holes
Understanding Hawking radiation from simple models of atomic Bose-Einstein condensates
This chapter is an introduction to the Bogoliubov theory of dilute Bose
condensates as applied to the study of the spontaneous emission of phonons in a
stationary condensate flowing at supersonic speeds. This emission process is a
condensed-matter analog of Hawking radiation from astrophysical black holes but
is derived here from a microscopic quantum theory of the condensate without any
use of the analogy with gravitational systems. To facilitate physical
understanding of the basic concepts, a simple one-dimensional geometry with a
stepwise homogenous flow is considered which allows for a fully analytical
treatment.Comment: 41 pages. to appear in the proceedings of the IX SIGRAV School on
'Analogue Gravity', Como (Italy), May 201
Measurement of Z0 decays to hadrons, and a precise determination of the number of neutrino species
We have made a precise measurement of the cross section for e+e--->Z0-->hadrons with the L3 detector at LEP, covering the range from 88.28 to 95.04 GeV. From a fit to the Z0 mass, total width, and the hadronic cross section to be MZ0=91.160 +/- 0.024 (experiment) +/-0.030(LEP) GeV, [Gamma]Z0=2.539+/-0.054 GeV, and [sigma]h(MZ0)=29.5+/-0.7 nb. We also used the fit to the Z0 peak cross section and the width todetermine [Gamma]invisible=0.548+/-0.029 GeV, which corresponds to 3.29+/-0.17 species of light neutrinos. The possibility of four or more neutrino flavors is thus ruled out at the 4[sigma] confidence level.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28683/3/0000500.pd
A measurement of the Z0 leptonic partial widths and the vector and axial vector coupling constants
We have measured the partial widths of the Z0 into lepton pairs, and the forward-backward charge asymmetry for the process e+e--->[mu]+[mu]- using the L3 detector at LEP. We obtain an average [Gamma]ll of 83.0+/-2.1+/-1.1 MeV.From this result and the asymmetry measurement, we extract the values of the vector and axial vector couplings of the Z0 to leptons: grmv=-0.066-0.027+0.046 and grmA= -0.495-0.007+0.007.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28666/3/0000483.pd
Decomposing rhythm processing: Electroencephalography of perceived and self-imposed rhythmic patterns
Contains fulltext :
99240.pdf (publisher's version ) (Open Access)Perceiving musical rhythms can be considered a process of attentional chunking over time, driven by accent patterns. A rhythmic structure can also be generated internally, by placing a subjective accent pattern on an isochronous stimulus train. Here, we investigate the event-related potential (ERP) signature of actual and subjective accents, thus disentangling low-level perceptual processes from the cognitive aspects of rhythm processing. The results show differences between accented and unaccented events, but also show that different types of unaccented events can be distinguished, revealing additional structure within the rhythmic pattern. This structure is further investigated by decomposing the ERP into subcomponents, using principal component analysis. In this way, the processes that are common for perceiving a pattern and self-generating it are isolated, and can be visualized for the tasks separately. The results suggest that top-down processes have a substantial role in the cerebral mechanisms of rhythm processing, independent of an externally presented stimulus.12 p
Improving boys' reading comprehension with readers theatre
Research on readers theatre has indicated that it can improve elementary students\u27 reading achievement and can be motivating, engaging and enjoyable, even for reluctant or struggling readers. Because of the potential for improvement and the engagement factor, the purpose of this study was to examine the effects of readers theatre on young male students, a population that tends to be more reluctant to read. This matched quasiâexperimental study examined the differential effects of readers theatre on secondâgrade boys\u27 decoding, word knowledge and reading comprehension. Students were pretested and posttested using the GatesâMacGinitie Reading Test. With the use ofa propensity score matching procedure, 46 students were matched from a sample of 76 on the basis of pretest scores, Englishâlanguage learner status, atârisk status and whether the students received special education services. A repeated measures analysis of variance detected a time effect on the reading comprehension measure, which was qualified by an interaction effect, indicating that boys in the treatment group outperformed those in the businessâasâusual comparison group. Implementing readers theatre in elementary classrooms may be an effective means for engaging young male students in the reading process and improving their reading comprehension. Additional implications for instruction, limitations and directions for future research are also discussed