4,149 research outputs found
Effects of Lorentz invariance violation on cosmic ray photon emission and gamma ray decay processes
In this work, we use Lorentz invariance violation (LIV) introduced as a
generic modification to particle dispersion relations to study some
consequences of single photon emission, known as vacuum Cherenkov radiation,
and photon decay processes in cosmic and gamma rays. These processes are
forbidden in a Lorentz invariant theory but allowed under the hypothesis of
LIV. We show that the emission rate have a dependency on the cosmic ray primary
mass and the electric charge that could modify the UHECR spectrum. Furthermore,
LIV dramatically enhances photon decay into an electro-positron pair above
certain energy threshold. This last effect can then be used to set limits to
the LIV energy scale from the direct observation of very high energy cosmic
photon events by telescopes of gamma-rays.Comment: Proceedings of the 35th International Cosmic Ray Conference (ICRC
2017), Busan, Kore
Palaeoenvironmental signatures revealed from rare earth element (REE) compositions of vertebrate microremains of the Vesiku Bone Bed (Homerian, Wenlock), Saaremaa Island, Estonia
The Estonian Journal of Earth Sciences is an open access journal and applies the Creative Commons Attribution 4.0 International License CC BY to all its papers (http://creativecommons.org/licenses/by/4.0/). The attached file is the published version of the article
Entanglement and alpha entropies for a massive scalar field in two dimensions
We find the analytic expression of the trace of powers of the reduced density
matrix on an interval of length L, for a massive boson field in 1+1 dimensions.
This is given exactly (except for a non universal factor) in terms of a finite
sum of solutions of non linear differential equations of the Painlev\'e V type.
Our method is a generalization of one introduced by Myers and is based on the
explicit calculation of quantities related to the Green function on a plane,
where boundary conditions are imposed on a finite cut. It is shown that the
associated partition function is related to correlators of exponential
operators in the Sine-Gordon model in agreement with a result by Delfino et al.
We also compute the short and long distance leading terms of the entanglement
entropy. We find that the bosonic entropic c-function interpolates between the
Dirac and Majorana fermion ones given in a previous paper. Finally, we study
some universal terms for the entanglement entropy in arbitrary dimensions
which, in the case of free fields, can be expressed in terms of the two
dimensional entropy functions.Comment: 13 pages, 2 figure
Dynamical Encoding by Networks of Competing Neuron Groups: Winnerless Competition
Following studies of olfactory processing in insects and fish, we investigate neural networks whose dynamics in phase space is represented by orbits near the heteroclinic connections between saddle regions (fixed points or limit cycles). These networks encode input information as trajectories along the heteroclinic connections. If there are N neurons in the network, the capacity is approximately e(N-1)!, i.e., much larger than that of most traditional network structures. We show that a small winnerless competition network composed of FitzHugh-Nagumo spiking neurons efficiently transforms input information into a spatiotemporal output
Structure and texture of the quark mass matrix
Starting from a weak basis in which the up (or down) quark matrix is
diagonal, we obtain an exact set of equations for the quark mass matrix
elements in terms of known observables. We make a numerical analysis of the
down (up) quark mass matrix. Using the data available for the quark masses and
mixing angles at different energy scales, we found a numerical expression for
these matrices. We suggest that it is not possible to have an specific texture
from this analysis. We also examine the most general case when the complex
phases are introduced in the mass matrix. We find the numerical value for these
phases as a function of , the CP-violationg phase.Comment: 7 pages, we use the macros of Elsevie
Metallochaperones Are Needed for Mycobacterium tuberculosis and Escherichia coli Nicotinamidase-Pyrazinamidase Activity.
Mycobacterium tuberculosis nicotinamidase-pyrazinamidase (PZAse) is a metalloenzyme that catalyzes conversion of nicotinamide-pyrazinamide to nicotinic acid-pyrazinoic acid. This study investigated whether a metallochaperone is required for optimal PZAse activity. M. tuberculosis and Escherichia coli PZAses (PZAse-MT and PZAse-EC, respectively) were inactivated by metal depletion (giving PZAse-MT-Apo and PZAse-EC-Apo). Reactivation with the E. coli metallochaperone ZnuA or Rv2059 (the M. tuberculosis analog) was measured. This was repeated following proteolytic and thermal treatment of ZnuA and Rv2059. The CDC1551 M. tuberculosis reference strain had the Rv2059 coding gene knocked out, and PZA susceptibility and the pyrazinoic acid (POA) efflux rate were measured. ZnuA (200 μM) achieved 65% PZAse-EC-Apo reactivation. Rv2059 (1 μM) and ZnuA (1 μM) achieved 69% and 34.3% PZAse-MT-Apo reactivation, respectively. Proteolytic treatment of ZnuA and Rv2059 and application of three (but not one) thermal shocks to ZnuA significantly reduced the capacity to reactivate PZAse-MT-Apo. An M. tuberculosis Rv2059 knockout strain was Wayne positive and susceptible to PZA and did not have a significantly different POA efflux rate than the reference strain, although a trend toward a lower efflux rate was observed after knockout. The metallochaperone Rv2059 restored the activity of metal-depleted PZAse in vitro Although Rv2059 is important in vitro, it seems to have a smaller effect on PZA susceptibility in vivo. It may be important to mechanisms of action and resistance to pyrazinamide in M. tuberculosis Further studies are needed for confirmation.IMPORTANCE Tuberculosis is an infectious disease caused by the bacterium Mycobacterium tuberculosis and remains one of the major causes of disease and death worldwide. Pyrazinamide is a key drug used in the treatment of tuberculosis, yet its mechanism of action is not fully understood, and testing strains of M. tuberculosis for pyrazinamide resistance is not easy with the tools that are presently available. The significance of the present research is that a metallochaperone-like protein may be crucial to pyrazinamide's mechanisms of action and of resistance. This may support the development of improved tools to detect pyrazinamide resistance, which would have significant implications for the clinical management of patients with tuberculosis: drug regimens that are appropriately tailored to the resistance profile of a patient's individual strain lead to better clinical outcomes, reduced onward transmission of infection, and reduction of the development of resistant strains that are more challenging and expensive to treat
Vibration-induced granular segregation: a phenomenon driven by three mechanisms
The segregation of large spheres in a granular bed under vertical vibrations
is studied. In our experiments we systematically measure rise times as a
function of density, diameter and depth; for two different sinusoidal
excitations. The measurements reveal that: at low frequencies, inertia and
convection are the only mechanisms behind segregation. Inertia (convection)
dominates when the relative density is greater (less) than one. At high
frequencies, where convection is suppressed, fluidization of the granular bed
causes either buoyancy or sinkage and segregation occurs.Comment: 4 pages. 3 figures, revtex4, to appear in PRL (in press
Rare earth elements (REEs) in vertebrate microremains from the upper Pridoli Ohesaare beds of Saaremaa Island, Estonia: geochemical clues to palaeoenvironment c
This is an open access article, available to all readers online, licensed under the Creative Commons Attribution 4.0 International License (CC BY; http://creativecommons.org/licenses/by/4.0/). The attached file is the published version of the article
Hyperspherical entanglement entropy
The coefficient of the log term in the entanglement entropy associated with
hyperspherical surfaces in flat space-time is shown to equal the conformal
anomaly by conformally transforming Euclideanised space--time to a sphere and
using already existing formulae for the relevant heat--kernel coefficients
after cyclic factoring. The analytical reason for the result is that the
conformal anomaly on the lune has an extremum at the ordinary sphere limit. A
proof is given. Agreement with a recent evaluation of the coefficient is found.Comment: 7 pages. Final revision. Historical comments amended. Minor remarks
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