21,175 research outputs found
Non-analyticities in three-dimensional gauge theories
Quantum fluctuations generate in three-dimensional gauge theories not only
radiative corrections to the Chern-Simons coupling but also non-analytic terms
in the effective action. We review the role of those terms in gauge theories
with massless fermions and Chern-Simons theories. The explicit form of
non-analytic terms turns out to be dependent on the regularization scheme and
in consequence the very existence of phenomena like parity and framing
anomalies becomes regularization dependent. In particular we find
regularization regimes where both anomalies are absent. Due to the presence of
non-analytic terms the effective action becomes not only discontinuous but also
singular for some background gauge fields which include sphalerons. The
appearence of this type of singularities is linked to the existence of nodal
configurations in physical states and tunneling suppression at some classical
field configurations. In the topological field theory the number of physical
states may also become regularization dependent. Another consequence of the
peculiar behaviour of three-dimensional theories under parity odd
regularizations is the existence of a simple mechanism of generation of a mass
gap in pure Yang-Mills theory by a suitable choice of regularization scheme.
The generic value of this mass does agree with the values obtained in
Hamiltonian and numerical analysis. Finally, the existence of different
regularization regimes unveils the difficulties of establishing a Zamolodchikov
c-theorem for three-dimensional field theories in terms of the induced
gravitational Chern-Simons couplings.Comment: 21 pages; Contribution to Ian Kogan Memorial Collection, ``From
Fields to Strings: Circumnavigating Theoretical Physics'
Recommended from our members
Detection of enteric parasite DNA in household and bed dust samples: potential for infection transmission.
BACKGROUND: Enteric parasites are transmitted in households but few studies have sampled inside households for parasites and none have used sensitive molecular methods. METHODS: We collected bed and living room dust samples from households of children participating in a clinical trial of anthelmintic treatment in rural coastal Ecuador. Dust was examined for presence of DNA specific for 11 enteric parasites (Ascaris lumbricoides, Trichuris trichiura, Ancylostoma duodenale, Necator americanus, Strongyloides stercoralis, Toxocara canis and T. cati, Giardia lamblia, Blastocystis hominis, Cryptosporidium spp., and Entamoeba histolytica) by quantitative PCR (qPCR). RESULTS: Of the 38 households sampled, 37 had positive dust for at least one parasite and up to 8 parasites were detected in single samples. Positivity was greatest for B. hominis (79% of household samples) indicating a high level of environmental fecal contamination. Dust positivity rates for individual pathogens were: S. stercoralis (52%), A. lumbricoides (39%), G. lamblia (39%), Toxocara spp. (42%), hookworm (18%) and T. trichiura (8%). DNA for Cryptosporidium spp. and E. histolytica was not detected. Bed dust was more frequently positive than floor samples for all parasites detected. Positivity for A. lumbricoides DNA in bed (adjusted OR: 10.0, 95% CI: 2.0-50.1) but not floor dust (adjusted OR: 3.6, 95% CI: 0.3-37.9) was significantly associated with active infections in children. CONCLUSIONS: To our knowledge, this is the first use of qPCR on environmental samples to detect a wide range of enteric pathogen DNA. Our results indicate widespread contamination of households with parasite DNA and raise the possibility that beds, under conditions of overcrowding in a humid tropical setting, may be a source of transmission
Non-linear response of single-molecule magnets: field-tuned quantum-to-classical crossovers
Quantum nanomagnets can show a field dependence of the relaxation time very
different from their classical counterparts, due to resonant tunneling via
excited states (near the anisotropy barrier top). The relaxation time then
shows minima at the resonant fields H_{n}=n D at which the levels at both sides
of the barrier become degenerate (D is the anisotropy constant). We showed that
in Mn12, near zero field, this yields a contribution to the nonlinear
susceptibility that makes it qualitatively different from the classical curves
[Phys. Rev. B 72, 224433 (2005)]. Here we extend the experimental study to
finite dc fields showing how the bias can trigger the system to display those
quantum nonlinear responses, near the resonant fields, while recovering an
classical-like behaviour for fields between them. The analysis of the
experiments is done with heuristic expressions derived from simple balance
equations and calculations with a Pauli-type quantum master equation.Comment: 4 pages, 3 figures. Submitted to Phys. Rev. B, brief report
POISSON project - III - Investigating the evolution of the mass accretion rate
As part of the POISSON project (Protostellar Optical-Infrared Spectral Survey
on NTT), we present the results of the analysis of low-resolution NIR spectra
0.9-2.4 um) of two samples of YSOs in Lupus and Serpens (52 and 17 objects),
with masses 0.1-2.0 Msun and ages from 10^5 to a few 10^7 yr. After determining
the accretion parameters of the Lup and Ser targets by analysing their HI
near-IR emission features, we added the results to those from previous regions
(investigated in POISSON with the same methodology). We obtained a final
catalogue (143 objects) of mass accretion rates (Macc) derived in a homogeneous
fashion and analysed how Macc correlates with M* and how it evolves in time. We
derived the accretion luminosity (Lacc) and Macc for Lup and Ser objects from
the Br_gamma line by using relevant empirical relationships from the literature
that connect HI line luminosity and Lacc. To minimise the biases and also for
self-consistency, we re-derived mass and age for each source using the same set
of evolutionary tracks. We observe a correlation MaccM*^2.2, similarly to what
has previously been observed in several star-forming clouds. The time variation
of Macc is roughly consistent with the expected evolution in viscous disks,
with an asymptotic decay that behaves as t^-1.6. However, Macc values are
characterised by a large scatter at similar ages and are on average higher than
the predictions of viscous models. Although part of the scattering may be
related to the employed empirical relationship and to uncertainties on the
single measurements, the general distribution and decay trend of the Macc
points are real. These findings might be indicative of a large variation in the
initial mass of the disks, of fairly different viscous laws among disks, of
varying accretion regimes, and of other mechanisms that add to the dissipation
of the disks, such as photo-evaporation.Comment: 18 pages, 10 figures, accepted by A&
Development and characterization of bioactive alginate microcapsules with cedarwood essential oil
In this work, sodium alginate microcapsules containing cedarwood essential oil (CWO) for uses in anti-acne tonic were prepared by ionic gelification of alginate with calcium chloride (CaCl2) and subsequent addition of glutaraldehyde to improve the crosslinking degree. Alginate microcapsules with cedarwood essential oil were obtained in an encapsulator with a 600 μm nozzle using different alginate concentrations (1, 3 and 4% w/v) , and different compositions of the coagulation solution with CaCl2 concentrations of 0.1, 0.25 and 0.5 M, and addition of glutaraldehyde at two concentrations: 12.5% and 50% (0.1 g L−1 and 10 g L−1, respectively). The effect of alginate concentration was followed by viscosimetry and the influence of the CaCl2 concentration and presence of glutaraldehyde on the microcapsules' shape as well as the total content on encapsulated cedarwood essential oil were evaluated by means of stereoscopic magnifying glass, scanning electron microscopy (SEM) and UV vis spectrophotometry. Results show that proper shape formation is obtained for an alginate concentration of 3% w/v. With regard to the total encapsulated cedarwood oil, as the CaCl2 concentration in the gelifying-coagulating solution increases the efficiency of the encapsulated oil. Best results in terms of micro-bead shape and total amount of encapsulated oil were obtained for a CaCl2 concentration of 0.5 M without glutaraldehyde with a maximum encapsulation of 177.2 mg per gram of microcapsule.Ferrandiz, M.; Lopez, A.; Franco, E.; Garcia-Garcia, D.; Fenollar, D.; Balart, R. (2017). Development and characterization of bioactive alginate microcapsules with cedarwood essential oil. Flavour and Fragrance Journal. 32(3):184-190. doi:10.1002/ffj.3373S18419032
Recommended from our members
Multi-criteria optimization of seismic protective devices utilizing lifecycle performance objectives and application to the design of the tuned mass damper inerter (TMDI) for buildings in Chile
A probabilistic framework for the cost-effective design of supplemental seismic protective devices considering multiple criteria related to their life-cycle performance is reviewed in this contribution. The framework relies on time-history analysis for describing structural behavior, on an assembly-based vulnerability approach for quantifying earthquake losses, and on characterization of the earthquake hazard through stochastic ground motion modeling. Emphasis is placed on application to the design of the tuned mass-damper inerter (TMDI) which if properly tuned can outperform the classical tuned mass damper for the same attached mass due to the presence of the inerter. The latter is a two-terminal device developing a resisting force proportional to the relative acceleration of its terminals by the “inertance” constant. In the herein considered multi-criteria design framework, the life-cycle cost of the TMDI equipped structure is the primary objective composed of the upfront TMDI cost and the anticipated seismic losses over the lifetime of the structure. For enhanced decision support, two additional objectives, namely the repair cost and the inerter force, having specific probability of exceedance over the lifetime of the structure are examined. The repair cost incorporates risk-averse attitudes into the design process, while the inerter force incorporates practical constraints to the transmitted stresses from the TMDI to the host structure. A case study involving an actual 21-storey building constructed in Santiago, Chile shows that optimal TMDI configurations can accomplish simultaneous reduction of life-cycle and repair costs. However, these cost reductions come at the expense of increased inerter forces to be transferred from the TMDI to the host structure. It is further shown that connecting the inerter to lower floors provides considerable benefits across all examined performance criteria as the inerter is engaged in a more efficient way for the same inertance and attached mass ratios
- …