1,748 research outputs found
Accounting for the foreground contribution to the dust emission towards Kepler's supernova remnant
âThe definitive version is available at www3.interscience.wiley.com '. Copyright Royal Astronomical Society. DOI: 10.1111/j.1365-2966.2009.15061.xWhether or not supernovae contribute significantly to the overall dust budget is a controversial subject. Submillimetre (sub-mm) observations, sensitive to cold dust, have shown an excess at 450 and 850 ÎŒm in young remnants Cassiopeia A (Cas A) and Kepler. Some of the sub-mm emission from Cas A has been shown to be contaminated by unrelated material along the line of sight. In this paper, we explore the emission from material towards Kepler using sub-mm continuum imaging and spectroscopic observations of atomic and molecular gas, via H i, 12CO(J= 2â1) and 13CO(J= 2â1). We detect weak CO emission (peak T*A = 0.2â1 K, 1â2 km sâ1 full width at half-maximum) from diffuse, optically thin gas at the locations of some of the sub-mm clumps. The contribution to the sub-mm emission from foreground molecular and atomic clouds is negligible. The revised dust mass for Kepler's remnant is 0.1â1.2 Mâ , about half of the quoted values in the original study by Morgan et al., but still sufficient to explain the origin of dust at high redshifts.Peer reviewe
Mode coupling in the nonlinear response of black holes
We study the properties of the outgoing gravitational wave produced when a
non-spinning black hole is excited by an ingoing gravitational wave.
Simulations using a numerical code for solving Einstein's equations allow the
study to be extended from the linearized approximation, where the system is
treated as a perturbed Schwarzschild black hole, to the fully nonlinear regime.
Several nonlinear features are found which bear importance to the data analysis
of gravitational waves. When compared to the results obtained in the linearized
approximation, we observe large phase shifts, a stronger than linear generation
of gravitational wave output and considerable generation of radiation in
polarization states which are not found in the linearized approximation. In
terms of a spherical harmonic decomposition, the nonlinear properties of the
harmonic amplitudes have simple scaling properties which offer an economical
way to catalog the details of the waves produced in such black hole processes.Comment: 17 pages, 20 figures, abstract and introduction re-writte
A spherical perfect lens
It has been recently proved that a slab of negative refractive index material
acts as a perfect lens in that it makes accessible the sub-wavelength image
information contained in the evanescent modes of a source. Here we elaborate on
perfect lens solutions to spherical shells of negative refractive material
where magnification of the near-field images becomes possible. The negative
refractive materials then need to be spatially dispersive with and . We concentrate on lens-like solutions for the
extreme near-field limit. Then the conditions for the TM and TE polarized modes
become independent of and respectively.Comment: Revtex4, 9 pages, 2 figures (eps
The general Leigh-Strassler deformation and integrability
The success of the identification of the planar dilatation operator of N=4
SYM with an integrable spin chain Hamiltonian has raised the question if this
also is valid for a deformed theory. Several deformations of SYM have recently
been under investigation in this context. In this work we consider the general
Leigh-Strassler deformation. For the generic case the S-matrix techniques
cannot be used to prove integrability. Instead we use R-matrix techniques to
study integrability. Some new integrable points in the parameter space are
found.Comment: 22 pages, 8 figures, reference adde
Neutralino-Nucleon Cross Section and Charge and Colour Breaking Constraints
We compute the neutralino-nucleon cross section in several supersymmetric
scenarios, taking into account all kind of constraints. In particular, the
constraints that the absence of dangerous charge and colour breaking minima
imposes on the parameter space are studied in detail. In addition, the most
recent experimental constraints, such as the lower bound on the Higgs mass, the
branching ratio, and the muon are considered. The
astrophysical bounds on the dark matter density are also imposed on the
theoretical computation of the relic neutralino density, assuming thermal
production. This computation is relevant for the theoretical analysis of the
direct detection of dark matter in current experiments. We consider first the
supergravity scenario with universal soft terms and GUT scale. In this scenario
the charge and colour breaking constraints turn out to be quite important, and
\tan\beta\lsim 20 is forbidden. Larger values of can also be
forbidden, depending on the value of the trilinear parameter . Finally, we
study supergravity scenarios with an intermediate scale, and also with
non-universal scalar and gaugino masses where the cross section can be very
large.Comment: Final version to appear in JHE
Maternal Oral Bacterial Levels Predict Early Childhood Caries Development
Objective: To calculate the association of maternal salivary bacterial challenge (mutans streptococci [MS] and lactobacilli [LB]) from pregnancy through 24 monthsâ postpartum with child caries incidence (â„1 cavitated or restored teeth) at 36 months. Materials & Methods: Dental, salivary bacterial, sociodemographic, and behavioral measures were collected at three- to six-month intervals from a birth cohort of low-income Hispanic mother-child dyads (N = 243). We calculated the relative child caries incidence, adjusted for confounding, following higher maternal challenge of MS (>4500 colony-forming units per milliliter of saliva [CFU/mL]) and LB (>50 CFU/mL) based on multivariable models. Results: Salivary MS and LB levels were greater among mothers of caries-affected children versus caries-free children. Mothers with higher salivary MS challenge were more likely to have MS-positive children (>0 CFU/mL), but maternal LB challenge was not a statistically significant predictor of child LB-positive status. Adjusting for sociodemographics, feeding and care practices, and maternal dental status, higher maternal salivary challenge of both MS and LB over the study period predicted nearly double the child caries incidence versus lower MS and LB (cumulative incidence ratio: 1.9; 95% confidence interval: 1.1, 3.8). Conclusion: Maternal salivary bacterial challenge not only is associated with oral infection among children but also predicts increased early childhood caries occurrence
Nonequilibrium evolution in scalar O(N) models with spontaneous symmetry breaking
We consider the out-of-equilibrium evolution of a classical condensate field
and its quantum fluctuations for a scalar O(N) model with spontaneously broken
symmetry. In contrast to previous studies we do not consider the large N limit,
but the case of finite N, including N=1, i.e., plain theory.
The instabilities encountered in the one-loop approximation are prevented, as
in the large-N limit, by back reaction of the fluctuations on themselves, or,
equivalently, by including a resummation of bubble diagrams.
For this resummation and its renormalization we use formulations developed
recently based on the effective action formalism of Cornwall, Jackiw and
Tomboulis. The formulation of renormalized equations for finite N derived here
represents a useful tool for simulations with realistic models. Here we
concentrate on the phase structure of such models. We observe the transition
between the spontaneously broken and the symmetric phase at low and high energy
densities, respectively. This shows that the typical structures expected in
thermal equilibrium are encountered in nonequilibrium dynamics even at early
times, i.e., before an efficient rescattering can lead to thermalization.Comment: 31 pages, 19 Figures, LaTeX; extended discussion on the basis of:
fluctuations, eff. potential, correlations, analytic calculation of
parametric resonance for "pion"_and_ "sigma" field
Finite temperature behaviour of the ISS-uplifted KKLT model
We study the static phase structure of the ISS-KKLT model for moduli
stabilisation and uplifting to a zero cosmological constant. Since the
supersymmetry breaking sector and the moduli sector are only gravitationally
coupled, we expect negligible quantum effects of the modulus upon the ISS
sector, and the other way around. Under this assumption, we show that the ISS
fields end up in the metastable vacua. The reason is not only that it is
thermally favoured (second order phase transition) compared to the phase
transition towards the supersymmetric vacua, but rather that the metastable
vacua form before the supersymmetric ones. This nice feature is exclusively due
to the presence of the KKLT sector. We also show that supergravity effects are
negligible around the origin of the field space. Finally, we turn to the
modulus sector and show that there is no destabilisation effect coming from the
ISS sector.Comment: 23 pages, 3 figures, mistake corrected, one plot updated, physical
conclusions unchange
Clonal dissemination of Klebsiella pneumoniae ST258 harbouring KPC-2 in Argentina
AbstractThe present work describes the abrupt emergence of Klebsiella pneumoniae carbapenemase (KPC) and characterizes the first 79 KPC-producing enterobacteria from Argentina (isolated from 2006 to 2010). The emergence of blaKPC-2 was characterized by two patterns of dispersion: the first was the sporadic occurrence in diverse enterobacteria from distant geographical regions, harbouring plasmids of different incompatibility groups and blaKPC-2 in an unusual genetic environment flanked by ISKpn8-ÎblaTEM-1 and ISKpn6-like. blaKPC-2 was associated with IncL/M transferable plasmids; the second was the abrupt clonal spread of K. pneumoniae ST258 harbouring blaKPC-2 in Tn4401a
Near-infrared-actuated devices for remotely controlled drug delivery
A reservoir that could be remotely triggered to release a drug would enable the patient or physician to achieve on-demand, reproducible, repeated, and tunable dosing. Such a device would allow precise adjustment of dosage to desired effect, with a consequent minimization of toxicity, and could obviate repeated drug administrations or device implantations, enhancing patient compliance. It should exhibit low off-state leakage to minimize basal effects, and tunable on-state release profiles that could be adjusted from pulsatile to sustained in real time. Despite the clear clinical need for a device that meets these criteria, none has been reported to date to our knowledge. To address this deficiency, we developed an implantable reservoir capped by a nanocomposite membrane whose permeability was modulated by irradiation with a near-infrared laser. Irradiated devices could exhibit sustained on-state drug release for at least 3 h, and could reproducibly deliver short pulses over at least 10 cycles, with an on/off ratio of 30. Devices containing aspart, a fast-acting insulin analog, could achieve glycemic control after s.c. implantation in diabetic rats, with reproducible dosing controlled by the intensity and timing of irradiation over a 2-wk period. These devices can be loaded with a wide range of drug types, and therefore represent a platform technology that might be used to address a wide variety of clinical indications
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