Witnessed Entanglement

We present a new measure of entanglement for mixed states. It can be approximately computable for every state and can be used to quantify all different types of multipartite entanglement. We show that it satisfies the usual properties of a good entanglement quantifier and derive relations between it and other entanglement measures.Comment: Revised version. 7 pages and one figur

Quantum Correlations and Coherence in Spin-1 Heisenberg Chains

We explore quantum and classical correlations along with coherence in the ground states of spin-1 Heisenberg chains, namely the one-dimensional XXZ model and the one-dimensional bilinear biquadratic model, with the techniques of density matrix renormalization group theory. Exploiting the tools of quantum information theory, that is, by studying quantum discord, quantum mutual information and three recently introduced coherence measures in the reduced density matrix of two nearest neighbor spins in the bulk, we investigate the quantum phase transitions and special symmetry points in these models. We point out the relative strengths and weaknesses of correlation and coherence measures as figures of merit to witness the quantum phase transitions and symmetry points in the considered spin-1 Heisenberg chains. In particular, we demonstrate that as none of the studied measures can detect the infinite order Kosterlitz-Thouless transition in the XXZ model, they appear to be able to signal the existence of the same type of transition in the biliear biquadratic model. However, we argue that what is actually detected by the measures here is the SU(3) symmetry point of the model rather than the infinite order quantum phase transition. Moreover, we show in the XXZ model that examining even single site coherence can be sufficient to spotlight the second-order phase transition and the SU(2) symmetry point.Comment: 8 pages. 5 figure

Estrutura genética e demográfica do caranguejo-uçá (Ucides cordatus) na costa do Brasil

O caranguejo Ucides cordatus, popularmente conhecido no Brasil como caranguejo-uçá, é encontrado em manguezais desde o estado de Santa Catarina até a Flórida, nos Estados Unidos. No Brasil, a grande demanda por esta espécie na indústria alimentícia é a causa da cata de várias toneladas de indivíduos todos os anos. Somados a este fator, a destruição dos manguezais e o surgimento de uma doença letal vêm sendo apontados como agentes causadores de severas reduções nos estoques naturais de U. cordatus. Uma vez que reduções populacionais severas tendem a provocar eventos de efeito gargalo e, consequentemente, redução da aptidão dos indivíduos ao longo do tempo, estudos de genética de populações que se dediquem a entender o padrão da distribuição genética, quantificar o fluxo gênico e avaliar as tendências demográficas das populações, são essenciais na elaboração de estratégias de manejo e de conservação. Portanto, neste trabalho, utilizamos sequências de 568 pb da subunidade 1 do gene mitocondrial citocromo c oxidase de 181 espécimes de U. cordatus coletados em 15 localidades ao longo da costa brasileira, entre os estados de Santa Catarina e Maranhão, que compreendem praticamente toda a região de ocorrência da espécie no Brasil. Do total de sequências, 80 haplótipos foram revelados, caracterizando uma elevada diversidade haplotípica (h=0,925). Por outro lado, a diversidade nucleotídica foi baixa (π =0,00462), dada a diferença de poucos pares de bases entre os haplótipos. A relação hierárquica entre os haplótipos não demonstrou nenhuma estruturação geográfica da diversidade genética. Além disso, a análise de variância molecular e os valores da estatística-Φ (Φst=0,00231) revelaram que a maior parte da variação genética em U. cordatus está contida no nível intrapopulacional (98,8%), e apenas uma fração sutil entre os grupos de populações (2,5%). Os valores de Fs de Fu e D de Tajima revelaram-se negativos, indicando que as populações de U. cordatus sofreram eventos de expansão populacional recente. Este cenário também foi confirmado através da análise de mismatch distribution, na qual distribuições unimodais foram encontradas para todas as populações. Nossos dados são concordantes com trabalhos prévios que indicam que o fluxo gênico em U. cordatus é suficientemente amplo a fim de produzir homogeneidade genética entre as populações. Este perfil é condizente com a estratégia de exportação das larvas desta espécie para alto mar, no qual fatores oceanográficos, como correntes marinhas, podem agir de forma a ampliar a dispersão destas formas imaturas

Separable Multipartite Mixed States - Operational Asymptotically Necessary and Sufficient Conditions

We introduce an operational procedure to determine, with arbitrary probability and accuracy, optimal entanglement witness for every multipartite entangled state. This method provides an operational criterion for separability which is asymptotically necessary and sufficient. Our results are also generalized to detect all different types of multipartite entanglement.Comment: 4 pages, 2 figures, submitted to Physical Review Letters. Revised version with new calculation

TRANSIENT MODELLING OF A NATURAL CIRCULATION LOOP UNDER VARIABLE PRESSURE

The objective of the present work is to model the transient operation of a natural circulation loop, which is one-tenth scale in height to a typical Passive Residual Heat Removal system (PRHR) of an Advanced Pressurized Water Nuclear Reactor and was designed to meet the single and two-phase ow similarity criteria to it. The loop consists of a core barrel with electrically heated rods, upper and lower plena inter- connected by hot and cold pipe legs to a seven-tube shell heat exchanger of countercurrent design, and an expansion tank with a descending tube. A long transient characterized the loop operation, during which a phenomenon of self-pressurization, without self-regulation of the pressure, was experimentally observed. This represented a unique situation, named natural circulation under variable pressure (NCVP). The self-pressurization was originated in the air trapped in the expansion tank and compressed by the loop water dilatation, as it heated up during each experiment. The mathematical model, initially oriented to the single-phase ow, included the heat capacity of the structure and employed a cubic polynomial approximation for the density, in the buoyancy term calculation. The heater was modelled taking into account the di erent heat capacities of the heating elements and the heater walls. The heat exchanger was modelled considering the coolant heating, during the heat exchanging process. The self-pressurization was modelled as an isentropic compression of a perfect gas. The whole model was computationally im-plemented via a set of nite di erence equations. The corresponding computational algorithm of solution was of the explicit, marching type, as for the time discretization, in an upwind scheme, regarding the space discretization. The computational program was implemented in MATLAB. Several experiments were carried out in the natural circulation loop, having the coolant ow rate and the heating power as control parameters. The variables used in the comparison between experimental and calculated data were some relevant loop temperatures and pressures. The results obtained from the computational model agree qualitatively well with the experimental NCVP data

Interannual variability of the South Indian Countercurrent

Author Posting. © American Geophysical Union, 2016. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 121 (2016): 3465–3487, doi:10.1002/2015JC011417.In the present work, we investigate the interannual variability of the South Indian Countercurrent (SICC), a major and still understudied current of the Indian Ocean circulation. To characterize the interannual variability of the SICC, four different data sets (altimetry, GLORYS, OFAM3, and SODA) are analyzed using multiple tools, which include Singular Spectrum Analysis and wavelet methods. The quasi-biennial band dominates the SICC low-frequency variance, with the main peak in the 1.5–1.8 year interval. A secondary peak (2.1–2.5 year) is only found in the western basin. Interannual and decadal-type modulations of the quasi-biennial signal are also identified. In addition, limitations of SODA before the 1960s in the SICC region are revealed. Within the quasi-biennial band, the SICC system presents two main patterns with a multiple jet structure. One pattern is characterized by a robust northern jet, while in the other the central jet is well developed and northern jet is weaker. In both patterns, the southern jet has always a strong signature. When the northern SICC jet is stronger, the northern cell of the subtropical gyre has a triangular shape, with its southern limb having a strong equatorward slant. The quasi-biennial variability of the SICC is probably related to the Indian Ocean tropical climate modes that are known to have a strong biennial characteristic.ARC Discovery Project Grant Number: DP130102088; NSF Grant Number: OCE-091716; Ocean Science Division of VM Oceanica2016-11-2

A Robust Semidefinite Programming Approach to the Separability Problem

We express the optimization of entanglement witnesses for arbitrary bipartite states in terms of a class of convex optimization problems known as Robust Semidefinite Programs (RSDP). We propose, using well known properties of RSDP, several new sufficient tests for the separability of mixed states. Our results are then generalized to multipartite density operators.Comment: Revised version (minor spell corrections) . 6 pages; submitted to Physical Review