Thermal inclusions: how one spin can destroy a many-body localized phase

Many-body localized (MBL) systems lie outside the framework of statistical mechanics, as they fail to equilibrate under their own quantum dynamics. Even basic features of MBL systems such as their stability to thermal inclusions and the nature of the dynamical transition to thermalizing behavior remain poorly understood. We study a simple model to address these questions: a two level system interacting with strength $J$ with $N\gg 1$ localized bits subject to random fields. On increasing $J$, the system transitions from a MBL to a delocalized phase on the \emph{vanishing} scale $J_c(N) \sim 1/N$, up to logarithmic corrections. In the transition region, the single-site eigenstate entanglement entropies exhibit bi-modal distributions, so that localized bits are either "on" (strongly entangled) or "off" (weakly entangled) in eigenstates. The clusters of "on" bits vary significantly between eigenstates of the \emph{same} sample, which provides evidence for a heterogenous discontinuous transition out of the localized phase in single-site observables. We obtain these results by perturbative mapping to bond percolation on the hypercube at small $J$ and by numerical exact diagonalization of the full many-body system. Our results imply the MBL phase is unstable in systems with short-range interactions and quenched randomness in dimensions $d$ that are high but finite.Comment: 17 pages, 12 figure

Técnicas para melhorar a durabilidade da construção em terra

Umas das principais fragilidades da construção em terra é a sua durabilidade face à ação da água, seja pelas chuvas, inundações ou ascensão da água por capilaridade, situações que acontecem sobretudo em países com elevado índice de pluviosidade. Contudo, as construções vernaculares têm demonstrado que é possível construir de forma durável, apesar de este conhecimento parecer ter sido esquecido ao longo dos anos. Por outro lado também têm sido desenvolvidas novas tecnologias para compactação, estabilização e impermeabilização de solos para melhorar a durabilidade da construção em terra. Todavia, a sustentabilidade da solução construtiva pode ser comprometida pelo uso excessivo de cimento ou materiais excessivamente impermeabilizantes. Neste artigo, pretende-se identificar e avaliar estratégias para proteção face à ação da água que têm sido utilizadas desde a Antiguidade até aos nossos dias. Deste modo, será possível perceber como inúmeros edifícios construídos em terra foram preservados ao longo de séculos, resistindo a condições climáticas severas

Determining North Atlantic meridional transport variability from pressure on the western boundary: a model investigation.

In this paper we investigate the possibility of determining North Atlantic meridional transport variability using pressure on the western boundary, focusing on the 42degN latitude of the Halifax WAVE array. We start by reviewing the theoretical foundations of this approach. Next we present results from a model analysis, both statistical and dynamic, that demonstrate the feasibility of the approach. We consider how well we can quantify the meridional transport variability at 42degN given complete knowledge of bottom pressure across the basin, and to what degree this quantification is degraded by first ignoring the effect of intervening topography, and then by using only bottom pressure on the western boundary. We find that for periods of greater than one year we can recover more than 90% of the variability of the main overturning cell at 42degN using only the western boundary pressure, provided we remove the depth-average boundary pressure signal. This signal arises from a basin mode of bottom pressure variability, which has power at all timescales, but that does not in truth have a meridional transport signal associated with it, and from the geostrophic depth-independent compensation of the Ekman transport. An additional benefit of the removal of the depth-average pressure is that this high-frequency Ekman signal, which is essentially noise as far as monitoring the MOC for climatically important changes is concerned, is clearly separated from other modes

Path Integral Approach to Strongly Nonlinear Composite

We study strongly nonlinear disordered media using a functional method. We solve exactly the problem of a nonlinear impurity in a linear host and we obtain a Bruggeman-like formula for the effective nonlinear susceptibility. This formula reduces to the usual Bruggeman effective medium approximation in the linear case and has the following features: (i) It reproduces the weak contrast expansion to the second order and (ii) the effective medium exponent near the percolation threshold are $s=1$, $t=1+\kappa$, where $\kappa$ is the nonlinearity exponent. Finally, we give analytical expressions for previously numerically calculated quantities.Comment: 4 pages, 1 figure, to appear in Phys. Rev.

Aproveitamento sustentável de recursos geotérmicos no campo geotérmico da Ribeira Grande, São Miguel, Açores

ABSTRACT: The use of geothermal resources for power production on São Miguel Island has almost 40 years of accumulated experience. In the last decade, the stable power output from Pico Vermelho and Ribeira Grande geothermal plants have been providing up to 44% of the electricity needs of São Miguel Island. Throughout the history of the project, EDA RENOVÁVEIS has been carefully monitoring the Ribeira Grande reservoir conditions and well discharges to assess the resource response to the production load. The results from the last 10 years of monitoring data indicate that production did not cause any significant impact on the reservoir pressure or temperature and it can be maintained in the long-term without the risk of over-exploiting the geothermal resource.RESUMO: O uso de recursos geotérmicos para produção de eletricidade na ilha de São Miguel tem quase 40 anos de experiência acumulada. Na última década, a estabilidade da produção das centrais geotérmicas do Pico Vermelho e da Ribeira Grande tem garantido até 44% das necessidades de energia elétrica da ilha de São Miguel. Ao longo da história do projeto, a EDA RENOVÁVEIS tem promovido a monitorização do reservatório geotérmico da Ribeira Grande, bem como dos parâmetros de produção dos poços geotérmicos, com vista a avaliar a resposta do recurso ao esforço de exploração. Os resultados dos últimos 10 anos de monitorização indicam que a exploração do recurso geotérmico não causou impacto significativo quer na pressão, quer na temperatura do reservatório, prevendo-se que esta poderá manter-se a longo prazo sem o risco de sobre-exploração do recurso geotérmico.info:eu-repo/semantics/publishedVersio

Phosphorylation of the carboxy-terminal domain of histone H1: effects on secondary structure and DNA condensation

Linker histone H1 plays an important role in chromatin folding. Phosphorylation by cyclin-dependent kinases is the main post-translational modification of histone H1. We studied the effects of phosphorylation on the secondary structure of the DNA-bound H1 carboxy-terminal domain (CTD), which contains most of the phosphorylation sites of the molecule. The effects of phosphorylation on the secondary structure of the DNA-bound CTD were site-specific and depended on the number of phosphate groups. Full phosphorylation significantly increased the proportion of β-structure and decreased that of α-helix. Partial phosphorylation increased the amount of undefined structure and decreased that of α-helix without a significant increase in β-structure. Phosphorylation had a moderate effect on the affinity of the CTD for the DNA, which was proportional to the number of phosphate groups. Partial phosphorylation drastically reduced the aggregation of DNA fragments by the CTD, but full phosphorylation restored to a large extent the aggregation capacity of the unphosphorylated domain. These results support the involvement of H1 hyperphosphorylation in metaphase chromatin condensation and of H1 partial phosphorylation in interphase chromatin relaxation. More generally, our results suggest that the effects of phosphorylation are mediated by specific structural changes and are not simply a consequence of the net charge

Cephalopod Brains: An Overview of Current Knowledge to Facilitate Comparison With Vertebrates.

Cephalopod and vertebrate neural-systems are often highlighted as a traditional example of convergent evolution. Their large brains, relative to body size, and complexity of sensory-motor systems and behavioral repertoires offer opportunities for comparative analysis. Despite various attempts, questions on how cephalopod 'brains' evolved and to what extent it is possible to identify a vertebrate-equivalence, assuming it exists, remain unanswered. Here, we summarize recent molecular, anatomical and developmental data to explore certain features in the neural organization of cephalopods and vertebrates to investigate to what extent an evolutionary convergence is likely. Furthermore, and based on whole body and brain axes as defined in early-stage embryos using the expression patterns of homeodomain-containing transcription factors and axonal tractography, we describe a critical analysis of cephalopod neural systems showing similarities to the cerebral cortex, thalamus, basal ganglia, midbrain, cerebellum, hypothalamus, brain stem, and spinal cord of vertebrates. Our overall aim is to promote and facilitate further, hypothesis-driven, studies of cephalopod neural systems evolution

Modeling Heterogeneous Materials via Two-Point Correlation Functions: I. Basic Principles

Heterogeneous materials abound in nature and man-made situations. Examples include porous media, biological materials, and composite materials. Diverse and interesting properties exhibited by these materials result from their complex microstructures, which also make it difficult to model the materials. In this first part of a series of two papers, we collect the known necessary conditions on the standard two-point correlation function S2(r) and formulate a new conjecture. In particular, we argue that given a complete two-point correlation function space, S2(r) of any statistically homogeneous material can be expressed through a map on a selected set of bases of the function space. We provide new examples of realizable two-point correlation functions and suggest a set of analytical basis functions. Moreover, we devise an efficient and isotropy- preserving construction algorithm, namely, the Lattice-Point algorithm to generate realizations of materials from their two- point correlation functions based on the Yeong-Torquato technique. Subsequent analysis can be performed on the generated images to obtain desired macroscopic properties. These developments are integrated here into a general scheme that enables one to model and categorize heterogeneous materials via two-point correlation functions.Comment: 37 pages, 26 figure