8,586 research outputs found
Generalized Chaplygin Gas Models tested with SNIa
The so called Generalized Chaplygin Gas (GCG) with the equation of state was recently proposed as a candidate for dark
energy in the Universe. In this paper we confront the GCG with SNIa data.
Specifically we have tested the GCG cosmology in three different classes of
models with (1) , ; (2) ,
and (3) , , as well as the
model withouth any assumption on . The best fitted models are
obtained by minimalizing the function and levels in the
plane. We supplemented our analysis with confidence intervals
in the plane, as well as one-dimensional probability
distribution functions for models parameter. The general conclusion is that
SNIa data strongly support the Chaplygin gas (with ). Extending our
analysisby relaxing the flat prior lead to the result that even though the best
fitted values of are formally non-zero, still they are close to flat
case. It should be viewed as an advantage of the GCG model since in similar
analysisof CDM model high negative value of were found to
be bestfitted to the data and independent inspiration from CMBR and
extragalactic astronomy has been invoked to fix the curvature problem. Our
results show clearly that in Generalized Chaplygin Gas cosmology distant
supernovae should be brighter than in CDM model.This prediction seems
to be confirmed with new Riess high redshift SNIa sample. Moreover, we argue
that with the future SNAP data it would be possible to differentiate between
models with various value of parameter and/or discriminated between
GCG, Cardassian and CDM modelsComment: 54 pages 29 figures improved version analysis flat prior relaxed high
redshift Riess SNIa sample include
Poland Divided: Spatial Differences in the June 2003 EU Accession Referendum. Jean Monnet/Robert Schuman Paper Series, Vol. 4 No. 1, January 2004
(From the introduction). Thus, our purpose here is to describe and analyze geographical patterns within Poland of approval, disapproval, and abstention from this crucial vote on joining the EU, and to link those outcomes to the social and economic situation obtaining in the regions. From these associations we can shed additional light on how Poland divided on this pivotal issue and posit some challenges for both Polish and EU policy makers in the years ahead. To guide us we refer to several studies of the emergence of electoral politics in former- Soviet states (notably Russia and Ukraine) and in Central and Eastern Europe that have pointed to the salience of geographical differences in voting outcomes and voter turnout in the postcommunist period. (7) Complementing research based on individual level, or survey, data, these geographic studies using aggregate data relate variations in the social, economic, and demographic traits of regions to party, candidate, and issue preferences across these same units. For example, it has been almost universally the case in the post-communist countries that rural, older, agricultural populations have voted mainly for parties of the left and against reform, while urban, better-educated, white collar areas have, for the most part, favored parties and candidates that have advocated reform and privatization. These outcomes match very closely the kinds of divisions within societies that we find in surveys. Clearly, however, we must recognize the limitations of aggregate data analysis, especially the need to avoid imputing individual action from collective figures. Surveys, of course, have advantages over one-time aggregate data, including their ability to probe attitudes and to conduct sampling over time. However, polling results have their own limitations especially that they tend to be a–spatial (and therefore cannot usually be used to illuminate important regional issues), and that respondents are not always truthful, particularly on sensitive subjects. But taken together, survey and aggregate data provide us with a higher degree of confidence in the analysis of the correlates of voting behavior. Following the methodology used in these other geographic studies of post-communist states, here we will test several propositions relating to the affinity for EU membership within different segments of Poland’s electorate. We will do this by cross-tabulating results of the June accession referendum with key social and economic variables among the 373 powiaty of Poland. According to the administrative reform of 1999, Poland is divided into 16 provinces (województwa, or voivodships), which are in turn divided into sub-regions (podregiony) and further into the powiaty. (8) The powiat scale of analysis is ideal for our purposes; powiaty are “county” level units or individual cities “with powiat status” (what we will call here “urban powiaty”) that provide an excellent degree of spatial resolution and, most importantly, for which the Polish government provides superb, detailed socioeconomic data and electoral results. (9) Powiaty typically range from 50,000 to 150,000 inhabitants and between 500-2,000 km2. Urban powiaty range from relatively small to medium-sized urban centers with populations around 100,000 people to the largest cities such as Poznań (572,000), Wrocław (624,000), Kraków (741,000) and Łódz (786,526). The Warsaw conurbation comprises the powiat of Warsaw (1.610 million). (10) As will be seen, there is a remarkable diversity within Poland—not unexpectedly in such a large and heterogeneous country—with regard both to social and economic conditions and to the demonstrated preferences of voters, with the two being related
Comment on: Nonlocal Realistic Leggett Models Can be Considered Refuted by the Before-Before Experiment
It is shown here that Suarez [Found. Phys. 38, 583 (2008)] wrongly presents
the assumptions behind the Leggett's inequalities, and their modified form used
by Groeblacher et al. [Nature 446, 871 (2007)] for an experimental
falsification of a certain class of non-local hidden variable models.Comment: comment submitted to Found. Phy
Neutrino-driven explosions twenty years after SN1987A
The neutrino-heating mechanism remains a viable possibility for the cause of
the explosion in a wide mass range of supernova progenitors. This is
demonstrated by recent two-dimensional hydrodynamic simulations with detailed,
energy-dependent neutrino transport. Neutrino-driven explosions were not only
found for stars in the range of 8-10 solar masses with ONeMg cores and in case
of the iron core collapse of a progenitor with 11 solar masses, but also for a
``typical'' progenitor model of 15 solar masses. For such more massive stars,
however, the explosion occurs significantly later than so far thought, and is
crucially supported by large-amplitude bipolar oscillations due to the
nonradial standing accretion shock instability (SASI), whose low (dipole and
quadrupole) modes can develop large growth rates in conditions where convective
instability is damped or even suppressed. The dominance of low-mode deformation
at the time of shock revival has been recognized as a possible explanation of
large pulsar kicks and of large-scale mixing phenomena observed in supernovae
like SN 1987A.Comment: 11 pages, 6 figures; review proceeding for "Supernova 1987A: 20 Years
After: Supernovae and Gamma-Ray Bursters" AIP, New York, eds. S. Immler, K.W.
Weiler, and R. McCra
Unexpected reemergence of von Neumann theorem
Is is shown here that the "simple test of quantumness for a single system" of
arXiv:0704.1962 (for a recent experimental realization see arXiv:0804.1646) has
exactly the same relation to the discussion of to the problem of describing the
quantum system via a classical probabilistic scheme (that is in terms of hidden
variables, or within a realistic theory) as the von Neumann theorem (1932). The
latter one was shown by Bell (1966) to stem from an assumption that the hidden
variable values for a sum of two non-commuting observables (which is an
observable too) have to be, for each individual system, equal to sums of
eigenvalues of the two operators. One cannot find a physical justification for
such an assumption to hold for non-commeasurable variables. On the positive
side. the criterion may be useful in rejecting models which are based on
stochastic classical fields. Nevertheless the example used by the Authors has a
classical optical realization
Quantum Field Theory on Spacetimes with a Compactly Generated Cauchy Horizon
We prove two theorems which concern difficulties in the formulation of the
quantum theory of a linear scalar field on a spacetime, (M,g_{ab}), with a
compactly generated Cauchy horizon. These theorems demonstrate the breakdown of
the theory at certain `base points' of the Cauchy horizon, which are defined as
`past terminal accumulation points' of the horizon generators. Thus, the
theorems may be interpreted as giving support to Hawking's `Chronology
Protection Conjecture', according to which the laws of physics prevent one from
manufacturing a `time machine'. Specifically, we prove: Theorem 1: There is no
extension to (M,g_{ab}) of the usual field algebra on the initial globally
hyperbolic region which satisfies the condition of F-locality at any base
point. In other words, any extension of the field algebra must, in any globally
hyperbolic neighbourhood of any base point, differ from the algebra one would
define on that neighbourhood according to the rules for globally hyperbolic
spacetimes. Theorem 2: The two-point distribution for any Hadamard state
defined on the initial globally hyperbolic region must (when extended to a
distributional bisolution of the covariant Klein-Gordon equation on the full
spacetime) be singular at every base point x in the sense that the difference
between this two point distribution and a local Hadamard distribution cannot be
given by a bounded function in any neighbourhood (in MXM) of (x,x). Theorem 2
implies quantities such as the renormalized expectation value of \phi^2 or of
the stress-energy tensor are necessarily ill-defined or singular at any base
point. The proofs rely on the `Propagation of Singularities' theorems of
Duistermaat and H\"ormander.Comment: 37 pages, LaTeX, uses latexsym and amsbsy, no figures; updated
version now published in Commun. Math. Phys.; no major revisions from
original versio
The Consistent Newtonian Limit of Einstein's Gravity with a Cosmological Constant
We derive the `exact' Newtonian limit of general relativity with a positive
cosmological constant . We point out that in contrast to the case with
, the presence of a positive in Einsteins's equations
enforces, via the condition , on the potential , a range
, within which the
Newtonian limit is valid. It also leads to the existence of a maximum mass,
. As a consequence we cannot put the boundary
condition for the solution of the Poisson equation at infinity. A boundary
condition suitably chosen now at a finite range will then get reflected in the
solution of provided the mass distribution is not spherically symmetric.Comment: Latex, 15 pages, no figures, errors correcte
Intelligent fuzzy controller for event-driven real time systems
Most of the known linguistic models are essentially static, that is, time is not a parameter in describing the behavior of the object's model. In this paper we show a model for synchronous finite state machines based on fuzzy logic. Such finite state machines can be used to build both event-driven, time-varying, rule-based systems and the control unit section of a fuzzy logic computer. The architecture of a pipelined intelligent fuzzy controller is presented, and the linguistic model is represented by an overall fuzzy relation stored in a single rule memory. A VLSI integrated circuit implementation of the fuzzy controller is suggested. At a clock rate of 30 MHz, the controller can perform 3 MFLIPS on multi-dimensional fuzzy data
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