11,683 research outputs found
Effect of spin orbit scattering on the magnetic and superconducting properties of nearly ferromagnetic metals: application to granular Pt
We calculate the effect of scattering on the static, exchange enhanced, spin
susceptibility and show that in particular spin orbit scattering leads to a
reduction of the giant moments and spin glass freezing temperature due to
dilute magnetic impurities. The harmful spin fluctuation contribution to the
intra-grain pairing interaction is strongly reduced opening the way for BCS
superconductivity. We are thus able to explain the superconducting and magnetic
properties recently observed in granular Pt as due to scattering effects in
single small grains.Comment: 9 pages 3 figures, accepted for publication in Phys. Rev. Letter
Beyond Node Degree: Evaluating AS Topology Models
This is the accepted version of 'Beyond Node Degree: Evaluating AS Topology Models', archived originally at arXiv:0807.2023v1 [cs.NI] 13 July 2008.Many models have been proposed to generate Internet Autonomous System (AS) topologies, most of which make structural assumptions about the AS graph. In this paper we compare AS topology generation models with several observed AS topologies. In contrast to most previous works, we avoid making assumptions about which topological properties are important to characterize the AS topology. Our analysis shows that, although matching degree-based properties, the existing AS topology generation models fail to capture the complexity of the local interconnection structure between ASs. Furthermore, we use BGP data from multiple vantage points to show that additional measurement locations significantly affect local structure properties, such as clustering and node centrality. Degree-based properties, however, are not notably affected by additional measurements locations. These observations are particularly valid in the core. The shortcomings of AS topology generation models stems from an underestimation of the complexity of the connectivity in the core caused by inappropriate use of BGP data
Topology Change and Causal Continuity
The result that, for a scalar quantum field propagating on a ``trousers''
topology in 1+1 dimensions, the crotch singularity is a source for an infinite
burst of energy has been used to argue against the occurrence of topology
change in quantum gravity. We draw attention to a conjecture due to Sorkin that
it may be the particular type of topology change involved in the trousers
transition that is problematic and that other topology changes may not cause
the same difficulties. The conjecture links the singular behaviour to the
existence of ``causal discontinuities'' in the spacetime and relies on a
classification of topology changes using Morse theory. We investigate various
topology changing transitions, including the pair production of black holes and
of topological geons, in the light of these ideas.Comment: Latex, 28 pages, 10 figures, small changes in text (one figure
removed), conclusions remain unchanged. Accepted for publication in Physical
Review
Shot noise and conductivity at high bias in bilayer graphene: Signatures of electron-optical phonon coupling
We have studied electronic conductivity and shot noise of bilayer graphene
(BLG) sheets at high bias voltages and low bath temperature K. As a
function of bias, we find initially an increase of the differential
conductivity, which we attribute to self-heating. At higher bias, the
conductivity saturates and even decreases due to backscattering from optical
phonons. The electron-phonon interactions are also responsible for the decay of
the Fano factor at bias voltages V. The high bias electronic
temperature has been calculated from shot noise measurements, and it goes up to
K at V. Using the theoretical temperature dependence of BLG
conductivity, we extract an effective electron-optical phonon scattering time
. In a 230 nm long BLG sample of mobility
cmVs, we find that decreases with increasing
voltage and is close to the charged impurity scattering time fs
at V.Comment: 7 pages, 7 figures. Extended version of the high bias part of version
1. The low bias part is discussed in arXiv:1102.065
Isotropisation of Generalized Scalar-Tensor theory plus a massive scalar field in the Bianchi type I model
In this paper we study the isotropisation of a Generalized Scalar-Tensor
theory with a massive scalar field. We find it depends on a condition on the
Brans-Dicke coupling function and the potential and show that asymptotically
the metric functions always tend toward a power or exponential law of the
proper time. These results generalise and unify these of De Sitter in the case
of a cosmological constant and of Cooley and Kitada in the case of an
exponential potential.Comment: 10 page
Effects of maternal subnutrition during early pregnancy on cow hematological profiles and offspring physiology and vitality in two beef breeds
This experiment evaluated the effects of subnutrition during early gestation on hematology in cows (Bos Taurus) and on hematological, metabolic, endocrine, and vitality parameters in their calves. Parda de Montaña and Pirenaica dams were inseminated and assigned to either a control (CONTROL, 100% requirements) or a nutrient‐restricted group (SUBNUT, 65%) during the first third of gestation. Dam blood samples were collected on days 20 and 253 of gestation, and calf samples were obtained during the first days of life. Pirenaica dams presented higher red series parameters than Parda de Montaña dams, both in the first and the last months of gestation. During early pregnancy, granulocyte numbers and mean corpuscular hemoglobin were lower in Pirenaica‐SUBNUT than in Pirenaica‐CONTROL cows. Calves from the SUBNUT cows did not show a physiological reduction in red series values in early life, suggesting later maturation of the hematopoietic system. Poor maternal nutrition affected calf endocrine parameters. Newborns from dystocic parturitions showed lower NEFA concentrations and weaker vitality responses. In conclusion, maternal nutrition had short‐term effects on cow hematology, Pirenaica cows showing a higher susceptibility to undernutrition; and a long‐term effect on their offspring endocrinology, SUBNUT newborns showing lower levels of IGF‐1 and higher levels of cortisol.This work was supported by the Spanish Ministry of Economy and Business and the European Union Regional Development Funds (INIA RTA 2013‐00059‐C02 and INIA RZP 2015‐001) and the Government of Aragon under the Grant Research Group Funds (A14_17R). A. Noya received a PhD grant from INIA‐Government of Aragon
Noether Symmetry of the Hyperextended Scalar Tensor theory for the FLRW models
We study in which conditions the Hyperextended Scalar Tensor theory in an
FLRW background admits a Noether symmetry and derive the vectors field
generating it.Comment: 11 page
Quantum Information Processing and Relativistic Quantum Fields
It is shown that an ideal measurement of a one-particle wave packet state of
a relativistic quantum field in Minkowski spacetime enables superluminal
signalling. The result holds for a measurement that takes place over an
intervention region in spacetime whose extent in time in some frame is longer
than the light-crossing time of the packet in that frame. Moreover, these
results are shown to apply not only to ideal measurements but also to unitary
transformations that rotate two orthogonal one-particle states into each other.
In light of these observations, possible restrictions on the allowed types of
intervention are considered. A more physical approach to such questions is to
construct explicit models of the interventions as interactions between the
field and other quantum systems such as detectors. The prototypical
Unruh-DeWitt detector couples to the field operator itself and so most likely
respects relativistic causality. On the other hand, detector models which
couple to a finite set of frequencies of field modes are shown to lead to
superluminal signalling. Such detectors do, however, provide successful
phenomenological models of atom-qubits interacting with quantum fields in a
cavity but are valid only on time scales many orders of magnitude larger than
the light-crossing time of the cavity.Comment: 16 pages, 2 figures. Improved abstract and discussion of 'ideal'
measurements. References to previous work adde
Otimização da separação cromatográfica de dissulfeto de carbono para aplicação na análise de resíduos de ditiocarbamatos por CG/FPD.
Foram otimizadas as condições para separação cromatográfica de CS2 na análise de ditiocarbamatos por cromatografia gasosa utilizando detector fotométrico de chama no modo enxofre. Foram utilizadas as colunas capilares: Chrompack CP-SIL 8-CB de 5% fenil 95% metilpolisiloxano de 50m x 0,32mm x 1,2mm; Restek RTX-1, 100% dimetilpolisiloxano com 30m x 0,32mm x 4mm e a megabore de poliestireno divinilbenzeno, HP PLOT-Q de 30m x 0,53mm x 40mm. Para cada coluna foi obtido o limite de detecção de 0,05mg mL-1; 0,27mg mL-1 e 0,03mg mL-1, respectivamente. A coluna HP Plot-Q foi a que permitiu melhor quantificação do dissulfeto de carbono tendo apresentado resolução e simetria de pico muito superior as demais colunas avaliadas
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