Cosmic String Wakes in Scalar-Tensor Gravities

The formation and evolution of cosmic string wakes in the framework of a scalar-tensor gravity are investigated in this work. We consider a simple model in which cold dark matter flows past an ordinary string and we treat this motion in the Zel'dovich approximation. We make a comaprison between our results and previous results obtained in the context of General Relativity. We propose a mechanism in which the contribution of the scalar field to the evolution of the wakes may lead to a cosmological observation.Comment: Replaced version to be published in the Classical and Quantum Gravit

Fast pick up technique for high quality heterostructures of bilayer graphene and hexagonal boron nitride

We present a fast method to fabricate high quality heterostructure devices by picking up crystals of arbitrary sizes. Bilayer graphene is encapsulated with hexagonal boron nitride to demonstrate this approach, showing good electronic quality with mobilities ranging from 17 000 cm^2/V/s at room temperature to 49 000 cm^2/V/s at 4.2 K, and entering the quantum Hall regime below 0.5 T. This method provides a strong and useful tool for the fabrication of future high quality layered crystal devices.Comment: 5 pages, 3 figure

Como a planta de arroz se desenvolve.

Planta. Raízes. Caule. Perfilhamento. Folha. Panícula. Espigueta. Flor. Grão. Germinação. Plântula. Fases de crescimento da planta de arroz. Produção de matéria seca. Produção. Características da planta relacionadas com a capacidade de produção. Exigências de radiação solar pela cultura do arroz.bitstream/item/100485/1/Encarte.pdfEncarte

Controlling spin relaxation in hexagonal BN-encapsulated graphene with a transverse electric field

We experimentally study the electronic spin transport in hBN encapsulated single layer graphene nonlocal spin valves. The use of top and bottom gates allows us to control the carrier density and the electric field independently. The spin relaxation times in our devices range up to 2 ns with spin relaxation lengths exceeding 12 $\mu$m even at room temperature. We obtain that the ratio of the spin relaxation time for spins pointing out-of-plane to spins in-plane is $\tau_{\bot} / \tau_{||} \approx$ 0.75 for zero applied perpendicular electric field. By tuning the electric field this anisotropy changes to $\approx$0.65 at 0.7 V/nm, in agreement with an electric field tunable in-plane Rashba spin-orbit coupling

Maintenance of spiral morphology and formation of biofilms on copper surfaces by water-exposed Helicobacter pylori

There is still a lack of consensus on the way Helicobacter pylori is transmitted, but biofilms in drinking water are suspected to create a safe haven for the subsistence of the bacterium and hence promote a waterborne route of infection. Cultivability in water is low when compared to other waterborne pathogens, a situation that is attributed to the conversion of the highly infectious spiral form to the generally regarded as inactive coccoid form of the bacterium. In this study, the adhesion ability to abiotic surfaces (such as copper and PVC), morphology and cultivability of water-exposed H. pylori was assessed. In copper, the bacterium was able to retain spiral morphology and form 3D structures for over two months whereas in PVC conversion to the coccoid form occurred in approximately 1 week. Even though the logical interpretation for these results would be that copper favours the bacterium survival, standard plating experiments have shown precisely the opposite: cultivability decreases faster for the cells exposed to copper. Besides demonstrating the deleterious action that copper surfaces have on H. pylori, this study also indicates that at least for this case, H. pylori coccoid morphology is in fact a manifestation of cell adaptation to the environment.Fundação para a Ciência e Tecnologia (FCT) European Commission Research Project SAFER

Local cosmic string in generalised scalar tensor theory

A recent investigation shows that a local gauge string with a phenomenological energy momentum tensor, as prescribed by Vilenkin, is inconsistent in Brans-Dicke theory. In this work it has been shown that such a string is consistent in a more general scalar tensor theory where $\omega$ is function of the scalar field.A set of solutions of full nonlinear Einstein's equations for interior region of such a string are presented.Comment: 7 pages, latex format, minor changes according to referee's suggestions, revised version submitted in Phys.Rev.

Relativistic Green functions in a plane wave gravitational background

We consider a massive relativistic particle in the background of a gravitational plane wave. The corresponding Green functions for both spinless and spin 1/2 cases, previously computed by A. Barducci and R. Giachetti \cite{Barducci3}, are reobtained here by alternative methods, as for example, the Fock-Schwinger proper-time method and the algebraic method. In analogy to the electromagnetic case, we show that for a gravitational plane wave background a semiclassical approach is also sufficient to provide the exact result, though the lagrangian involved is far from being a quadratic one.Comment: Last paper by Professor Arvind Narayan Vaidya, 18 pages, no figure