Evolving wormhole geometries within nonlinear electrodynamics

In this work, we explore the possibility of evolving (2+1) and (3+1)-dimensional wormhole spacetimes, conformally related to the respective static geometries, within the context of nonlinear electrodynamics. For the (3+1)-dimensional spacetime, it is found that the Einstein field equation imposes a contracting wormhole solution and the obedience of the weak energy condition. Nevertheless, in the presence of an electric field, the latter presents a singularity at the throat, however, for a pure magnetic field the solution is regular. For the (2+1)-dimensional case, it is also found that the physical fields are singular at the throat. Thus, taking into account the principle of finiteness, which states that a satisfactory theory should avoid physical quantities becoming infinite, one may rule out evolving (3+1)-dimensional wormhole solutions, in the presence of an electric field, and the (2+1)-dimensional case coupled to nonlinear electrodynamics.Comment: 17 pages, 1 figure; to appear in Classical and Quantum Gravity. V2: minor corrections, including a referenc

Neutral C60 effusive source for atomic collisions with fullerene

Review of scientific instruments, Vol.72, Nº9A neutral C60 effusive source was assembled in a crossed molecular-beam apparatus in order to perform atom–molecule electron transfer collisions and its calibration by time-of-flight mass spectrometry. This source consists of a stainless-steel oven where the C60 sublimation takes place. Typical operation temperatures are in the range of 723 up to 888 K. Through this setup the study of the ion pair formation process K C60→K C60 where K is a potassium atom can be performed in a wide range of collision energies 10 up to 500 eV . The results show evidence of negative ion formation being the ratio of intensities between the parent ion and fragment ions clearly dependent on the collision energy used

Deconvolving the information from an imperfect spherical gravitational wave antenna

We have studied the effects of imperfections in spherical gravitational wave antenna on our ability to properly interpret the data it will produce. The results of a numerical simulation are reported that quantitatively describe the systematic errors resulting from imperfections in various components of the antenna. In addition, the results of measurements on a room-temperature prototype are presented that verify it is possible to accurately deconvolve the data in practice.Comment: 5 pages, 2 figures, to be published in Europhysics Letter

A New Integrated Approach for Fast Intrinsic Dielectric Breakdown

FCT-MCTES Portugal through UID/EEA/00066/2013 is gratefully acknowledged.A non-equilibrium phenomenological description for a complete dielectric breakdown sequence in perfect solid electric insulators, from the dynamics of instability to the growth of branching patterns, is implemented. It represents an original treatment which allows overcoming the current lack of such a complete physical description, involving thermodynamics, and in particular equations on maximum dissipation energy for dielectric breakdown are developed. From the assumption that there is a time delay in the energy rates and propagation speeds between the system input and output, a principle of maximum energy dissipation is postulated and corresponding dynamic evolution equations were obtained. It is shown that the delay in those speeds gives rise to the appearance of iterated equations which in turn leads to the logistic maps describing the dynamic evolution of the system. The results can describe the instability process along with dissipation patterns formation. The vast theoretical and experimental analogies between mechanical fracture and dielectric rupture, lead us to foresee the potential applicability of this model in the prediction of dielectric rupture patterns. This work opens then the possibility to predict the consequent branching patterns by using a maximum energy dissipation principle, contributing in a significant way for energy efficiency engineering.publishersversionpublishe

Thermal diagnostic of the Optical Window on board LISA Pathfinder

Vacuum conditions inside the LTP Gravitational Reference Sensor must comply with rather demanding requirements. The Optical Window (OW) is an interface which seals the vacuum enclosure and, at the same time, lets the laser beam go through for interferometric Metrology with the test masses. The OW is a plane-parallel plate clamped in a Titanium flange, and is considerably sensitive to thermal and stress fluctuations. It is critical for the required precision measurements, hence its temperature will be carefully monitored in flight. This paper reports on the results of a series of OW characterisation laboratory runs, intended to study its response to selected thermal signals, as well as their fit to numerical models, and the meaning of the latter. We find that a single pole ARMA transfer function provides a consistent approximation to the OW response to thermal excitations, and derive a relationship with the physical processes taking place in the OW. We also show how system noise reduction can be accomplished by means of that transfer function.Comment: 20 pages, 14 figures; accepted for publication in Class. Quantum Gra

Perfil de expressão gênica global no músculo esquelético de ovinos por meio de microarrays.

O perfil de expressão gênica global no músculo esquelético de cordeiros de quatro grupos genéticos de ovinos foi comparado por meio de microarrays de oligonucleotídeos. As análises indicaram 262 transcritos diferencialmente expressos entre os grupos genéticos. Um total de 23 transcritos de funções conhecidas foram diferencialmente expressos, sendo dez deles apenas na comparação Morada Nova x Somalis Brasileira. Dentre os genes diferencialmente expressos, aqueles envolvidos com características de importância para a produção de carne, destacaram-se: MyoD e IGFBP4 (desenvolvimento muscular), PGDS e SCD (biosíntese de ácidos graxos), C/EBP δ e PPARγ (adipogênese) e PYGL, GLUT-3, GGTA1 e ATP5G1 (metabolismo energético). Os resultados da técnica de microarray foram validados por meio de qPCR. Estes transcritos podem ser considerados marcadores expressos úteis para a seleção de cordeiros nas condições estudadas. A seleção para polimorfismos nestes genes pode conferir maior marmoreio e deposição de massa muscular, que são características ligadas diretamente a quantidade, a qualidade e a aceitação da carne. Global gene expression profile in skeletal muscle of sheep by microarray. Abstract: The global gene expression profile in muscle of four genetic groups of hair sheep were compared by oligonucleotide microarray. The analyses showed that 262 transcripts were differentially expressed among the four genetic groups. A total of 23 genes of known function were differentially expressed, with 10 transcripts differentially expressed only in the comparison between Morada Nova x Brazilian Somali. Among the differentially expressed genes, those involved with important features for the production of meat, stood out: IGFBP4 and MyoD (muscle growth), and PGDS (SCD biosynthesis of fatty acids), C/EBPδ and PPARγ (adipogenesis) and PYGL, GLUT-3, and GGTA1 ATP5G1 (energy metabolism). The results of the microarray were validated by qPCR. These transcripts can be considered useful markers expressed in the selection of lambs under the conditions studied here. Screening for polymorphisms in these genes may confer greater marbling deposition and muscle mass, which are features directly linked to quantity, quality and acceptability of meat

On the Sensitivity of a Hollow Sphere as a Multi-modal Resonant Gravitational Wave Detector

We present a numerical analysis to simulate the response of a spherical resonant gravitational wave detector and to compute its sensitivity. Under the assump- tion of optimal filtering, we work out the sensitivity curve for a sphere first taking into account only a single transducer, and then using a coherent analysis of the whole set of transducers.Comment: 24 pages, 11 figures, published versio

Traversable wormholes coupled to nonlinear electrodynamics

In this work we explore the possible existence of static, spherically symmetric and stationary, axisymmetric traversable wormholes coupled to nonlinear electrodynamics. Considering static and spherically symmetric (2+1) and (3+1)-dimensional wormhole spacetimes, we verify the presence of an event horizon and the non-violation of the null energy condition at the throat. For the former spacetime, the principle of finiteness is imposed, in order to obtain regular physical fields at the throat. Next, we analyze the (2+1)-dimensional stationary and axisymmetric wormhole, and also verify the presence of an event horizon, rendering the geometry non-traversable. Relatively to the (3+1)-dimensional stationary and axisymmetric wormhole geometry, we find that the field equations impose specific conditions that are incompatible with the properties of wormholes. Thus, we prove the non-existence of the general class of traversable wormhole solutions, outlined above, within the context of nonlinear electrodynamics.Comment: 9 pages, Revtex4. V2: major change in title; considerable additions in the Introduction and in the rotating solution, no physics changes; correction of a reference, one reference added; now 10 pages. This version to appear in Classical and Quantum Gravit