4,607 research outputs found
Possible Constraints on the Time Variation of the Fine Structure Constant from Cosmic Microwave Background Data
The formation of the cosmic microwave background radiation (CMBR) provides a
very powerful probe of the early universe at the epoch of recombination.
Specifically, it is possible to constrain the variation of fundamental physical
constants in the early universe. We have calculated the effect of a varying
electromagnetic coupling constant (\alpha) on the CMBR and find that new
satellite experiments should provide a tight constraint on the value of \alpha
at recombination which is complementary to existing constraints. An estimate of
the obtainable precision is |\dot{\alpha}/\alpha| \leq 7 x 10^{-13} y^{-1} in a
realistic experiment.Comment: 5 pages, 3 postscript figures, matches version to appear in Phys.
Rev.
Probing neutrino decays with the cosmic microwave background
We investigate in detail the possibility of constraining neutrino decays with
data from the cosmic microwave background radiation (CMBR). Two generic decays
are considered \nu_H -> \nu_L \phi and \nu_H -> \nu_L \nu_L_bar \nu_L. We have
solved the momentum dependent Boltzmann equation in order to account for
possible relativistic decays. Doing this we estimate that any neutrino with
mass m > 1 eV decaying before the present should be detectable with future CMBR
data. Combining this result with other results on stable neutrinos, any
neutrino mass of the order 1 eV should be detectable.Comment: 8 pages, 4 figures, to appear in Phys. Rev.
Tissue dyslipidemia in salmonella-infected rats treatTissue dyslipidemia in salmonella-infected rats treated with amoxillin and pefloxac
Background: This study investigated the effects of salmonella infection and its chemotherapy on lipid metabolism
in tissues of rats infected orally with Salmonella typhimurium and treated intraperitoneally with pefloxacin and
amoxillin.
Methods: Animals were infected with Salmonella enterica serovar Typhimurium strain TA 98. After salmonellosis was
confirmed, they were divided into 7 groups of 5 animals each. While one group served as infected control group, three
groups were treated with amoxillin (7.14 mg/kg body weight, 8 hourly) and the remaining three groups with
pefloxacin (5.71mg/kg body weight, 12 hourly) for 5 and 10 days respectively. Uninfected control animals received
0.1ml of vehicle. Rats were sacrificed 24h after 5 and 10 days of antibiotic treatment and 5 days after discontinuation of
antibiotic treatment. Their corresponding controls were also sacrificed at the same time point. Blood and tissue lipids
were then evaluated.
Results: Salmonella infection resulted in dyslipidemia characterised by increased concentrations of free fatty acids
(FFA) in plasma and erythrocyte, as well as enhanced cholesterogenesis, hypertriglyceridemia and phospholipidosis in
plasma, low density lipoprotein-very low density lipoprotein (LDL-VLDL), erythrocytes, erythrocyte ghost and the
organs. The antibiotics reversed the dyslipidemia but not totally. A significant correlation was observed between fecal
bacterial load and plasma cholesterol (r=0.456, p<0.01), plasma triacyglycerols (r=0.485, p<0.01), plasma phospholipid
(r=0.414, p<0.05), plasma free fatty acids (r=0.485, p<0.01), liver phospholipid (r=0.459, p<0.01) and brain phospholipid
(r=0.343, p<0.05).
Conclusion: The findings of this study suggest that salmonella infection in rats and its therapy with pefloxacin and
amoxillin perturb lipid metabolism and this perturbation is characterised by cholesterogenesis
Commuting self-adjoint extensions of symmetric operators defined from the partial derivatives
We consider the problem of finding commuting self-adjoint extensions of the
partial derivatives {(1/i)(\partial/\partial x_j):j=1,...,d} with domain
C_c^\infty(\Omega) where the self-adjointness is defined relative to
L^2(\Omega), and \Omega is a given open subset of R^d. The measure on \Omega is
Lebesgue measure on R^d restricted to \Omega. The problem originates with I.E.
Segal and B. Fuglede, and is difficult in general. In this paper, we provide a
representation-theoretic answer in the special case when \Omega=I\times\Omega_2
and I is an open interval. We then apply the results to the case when \Omega is
a d-cube, I^d, and we describe possible subsets \Lambda of R^d such that
{e^(i2\pi\lambda \dot x) restricted to I^d:\lambda\in\Lambda} is an orthonormal
basis in L^2(I^d).Comment: LaTeX2e amsart class, 18 pages, 2 figures; PACS numbers 02.20.Km,
02.30.Nw, 02.30.Tb, 02.60.-x, 03.65.-w, 03.65.Bz, 03.65.Db, 61.12.Bt,
61.44.B
New constraint on the cosmological background of relativistic particles
We have derived new bounds on the relativistic energy density in the Universe
from cosmic microwave background (CMB), large scale structure (LSS), and type
Ia supernova (SNI-a) observations. In terms of the effective number of neutrino
species a bound of N_\nu = 4.2^{+1.2}_{-1.7} is derived at 95% confidence. This
bound is significantly stronger than previous determinations, mainly due to
inclusion of new CMB and SNI-a observations. The absence of a cosmological
neutrino background (N_\nu = 0) is now excluded at 5.4 \sigma. The value of
N_\nu is compatible with the value derived from big bang nucleosynthesis
considerations, marking one of the most remarkable successes of the standard
cosmological model. In terms of the cosmological helium abundance, the CMB,
LSS, and SNI-a observations predict a value of 0.240 < Y < 0.281.Comment: 10 pages, 3 figures, references adde
New constraints on neutrino physics from Boomerang data
We have performed a likelihood analysis of the recent data on the Cosmic
Microwave Background Radiation (CMBR) anisotropy taken by the Boomerang
experiment. We find that this data places a strong upper bound on the radiation
density present at recombination. Expressed in terms of the equivalent number
of neutrino species the bound is N_nu < 13, and the standard model
prediction, N_nu = 3.04, is completely consistent the the data. This bound is
complementary to the one found from Big Bang nucleosynthesis considerations in
that it applies to any type of radiation, i.e. it is not flavour sensitive. It
also applies to the universe at a much later epoch, and as such places severe
limits on scenarios with decaying neutrinos. The bound also yields a firm upper
limit on the lepton asymmetry in the universe.Comment: 4 pages, 2 postscript figures, matches version to appear in PR
Translation Representations and Scattering By Two Intervals
Studying unitary one-parameter groups in Hilbert space (U(t),H), we show that
a model for obstacle scattering can be built, up to unitary equivalence, with
the use of translation representations for L2-functions in the complement of
two finite and disjoint intervals.
The model encompasses a family of systems (U (t), H). For each, we obtain a
detailed spectral representation, and we compute the scattering operator, and
scattering matrix. We illustrate our results in the Lax-Phillips model where (U
(t), H) represents an acoustic wave equation in an exterior domain; and in
quantum tunneling for dynamics of quantum states
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Motivations for innovation in the built environment: new directions for research
Innovation in the built environment involves multiple actors with diverse motivations. Policy-makers find it difficult to promote changes that require cooperation from these numerous and dispersed actors and to align their sometimes divergent interests. Established research traditions on the economics and management of innovation pay only limited attention to stakeholder choices, engagement and motivation. This paper reviews the insights that emerge as research in these traditions comes into contact with work on innovation from sociological and political perspectives. It contributes by highlighting growing areas of research on user involvement in complex innovation, collective action, distributed innovation and transition management. To differing extents, these provide approaches to incorporate the motivations of different actors into theoretical understanding. These indicate new directions for research that promise to enrich understanding of innovation
Neutrino masses and cosmic radiation density: Combined analysis
We determine the range of neutrino masses and cosmic radiation content
allowed by the most recent CMB and large-scale structure data. In contrast to
other recent works, we vary these parameters simultaneously and provide
likelihood contours in the two-dimensional parameter space of N_eff}, the usual
effective number of neutrino species measuring the radiation density, and \sum
m_nu. The allowed range of \sum m_nu and N_eff has shrunk significantly
compared to previous studies. The previous degeneracy between these parameters
has disappeared, largely thanks to the baryon acoustic oscillation data. The
likelihood contours differ significantly if \sum m_nu resides in a single
species instead of the standard case of being equally distributed among all
flavors. For \sum m_nu=0 we find 2.7 < N_eff < 4.6 at 95% CL while \sum m_nu <
0.62 eV at 95% CL for the standard radiation content.Comment: 8 pages, 2 figure
Cosmological limit on the neutrino mass
We have performed a careful analysis of constraints on the neutrino mass from
current cosmological data. Combining data from the cosmic microwave background
and the 2dF galaxy survey yields an upper limit on the sum of the three
neutrino mass eigenstates of \sum m_nu < 3 eV (95% conf.), without including
additional priors. Including data from SNIa observations, Big Bang
nucleosynthesis, and HST Hubble key project data on H_0 tightens the limit to
\sum m_nu < 2.5 eV (95% conf.). We also perform a Fisher matrix analysis which
illustrates the cosmological parameter degeneracies affecting the determination
of \sum m_nu.Comment: 6 pages, 2 figures, uses Revtex
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