Real space mapping of topological invariants using artificial neural networks

Topological invariants allow to characterize Hamiltonians, predicting the existence of topologically protected in-gap modes. Those invariants can be computed by tracing the evolution of the occupied wavefunctions under twisted boundary conditions. However, those procedures do not allow to calculate a topological invariant by evaluating the system locally, and thus require information about the wavefunctions in the whole system. Here we show that artificial neural networks can be trained to identify the topological order by evaluating a local projection of the density matrix. We demonstrate this for two different models, a 1-D topological superconductor and a 2-D quantum anomalous Hall state, both with spatially modulated parameters. Our neural network correctly identifies the different topological domains in real space, predicting the location of in-gap states. By combining a neural network with a calculation of the electronic states that uses the Kernel Polynomial Method, we show that the local evaluation of the invariant can be carried out by evaluating a local quantity, in particular for systems without translational symmetry consisting of tens of thousands of atoms. Our results show that supervised learning is an efficient methodology to characterize the local topology of a system.Comment: 9 pages, 6 figure

A Retrospective Analysis of Mortality Distribution in Juba Teaching Hospital, Southern Sudan

No Abstrac

Brucellosis in Terekeka County, Central Equatoria State, Southern Sudan

Objectives: To identify factors associated with Brucellosis in patients attending Terekeka Health Facility, Terekeka County, Central Equatoria State, Southern Sudan and to evaluate the utility of the rapid test kit Euracil®.Design: A facility based case-control study.Setting: Terekeka Health Facility, Terekeka County, Central Equatoria State, Southern Sudan.Subjects: Cases were patients presenting at the Terekeka Health Facility with clinical symptoms suggestive of Brucellosis and tested positive for Brucellosis by rapid antigen test while controls were selected from individuals attending Terekeka Health facility with health problems unrelated to brucellosis or febrile illness.Results: A total of fifty eight cases with clinical symptoms suggestive of and tested positive for Brucellosis by rapid antigen test presented. A total of 116 consented controls were recruited into the study. Males accounted for 52% of the cases and 53% of the controls. The mean age was 31 years for both groups. Cases without formal education were 84% while 40% had no source of income, 20% of the cases and 14% of the controls were cattle keepers while 5% of the cases and 13% of the controls were students. In multivariate analysis there were many factors associated with Brucellosislike consumption of raw meat, living with animals at the same place, raising of goats, farm cleaning contact, eating of aborted and wild animals. Logistic regression revealed two factors associated with the disease; consumption of raw milk (OR=3.9, P-value 0.001, 95% CI 1.6666 - 9.0700) was a risk factor while drinking boiled milk was protective(OR= 0.09, p- value 0.000, 95% CI, 0.1 - 0.2).Conclusions: The main age-groups affected were 20 – 30 years with males being affected more than females. Drinking of raw milk was significantly associated with Brucellosis while drinking boiled milk was protective. There should be active public health education on the benefits of boiling milk before consumption. Further studies to elucidate the extent and epidemiology of brucellosis in humans and animals in Southern Sudan are recommended

Sob Os Olhos de Deus e dos Homens: Escravos e Parentesco Ritual na Província do Espírito Santo (1831-1888)

Os estudos sobre parentesco ritual de escravos, sacramentado na pia batismal, têm alcançado maior relevância na historiografia brasileira nos últimos anos e se transformado em objeto central de diversas pesquisas que privilegiam a análise das sociabilidades mais amplas empreendidas pelos cativos no Brasil escravista. O Espírito Santo, durante o Oitocentos, oferece interessante material para discussão a respeito, uma vez que seu território foi marcado pela diversidade de perfis demográficos da população escrava. A partir de registros eclesiásticos de batismo, inventários post mortem, relatórios de presidentes da Província, mapas populacionais, censos e fundos de governadoria se pretendeu identificar padrões de comportamento na formação do parentesco ritual de cativos e compreendê-los a partir da análise do contexto socioeconômico e cultural em que estavam inseridos. Tais tarefas permitiram detectar a influência do compadrio como elemento de formação de diversas comunidades na região central e no sul do Espírito Santo. Além desse viés quantitativo, a pesquisa comportou uma abordagem metodológica qualitativa. Objetivou-se, por meio do cruzamento de dados, expressar a diversidade comportamental dos cativos, privilegiando as interações no interior das escravarias e famílias da sociedade espiritossantense. O trabalho permitiu inserir o Espírito Santo no debate sobre o tema e constatar a influência do catolicismo popular sobre os escravos da região, em outras palavras, observou-se a introdução do elemento sagrado na família escrava bem como seus significados políticos na comunidade através do ritual do compadrio

Unbiased contaminant removal for 3D galaxy power spectrum measurements

Citation: Kalus, B., Percival, W. J., Bacon, D. J., & Samushia, L. (2016). Unbiased contaminant removal for 3D galaxy power spectrum measurements. Monthly Notices of the Royal Astronomical Society, 463(1), 467-476. doi:10.1093/mnras/stw2008We assess and develop techniques to remove contaminants when calculating the 3D galaxy power spectrum. We separate the process into three separate stages: (i) removing the contaminant signal, (ii) estimating the uncontaminated cosmological power spectrum and (iii) debiasing the resulting estimates. For (i), we show that removing the best-fitting contaminant (mode subtraction) and setting the contaminated components of the covariance to be infinite (mode deprojection) are mathematically equivalent. For (ii), performing a quadratic maximum likelihood (QML) estimate after mode deprojection gives an optimal unbiased solution, although it requires the manipulation of large matrices (N-mode being the total number of modes), which is unfeasible for recent 3D galaxy surveys. Measuring a binned average of the modes for (ii) as proposed by Feldman, Kaiser & Peacock (FKP) is faster and simpler, but is sub-optimal and gives rise to a biased solution. We present a method to debias the resulting FKP measurements that does not require any large matrix calculations. We argue that the sub-optimality of the FKP estimator compared with the QML estimator, caused by contaminants, is less severe than that commonly ignored due to the survey window

The Insula and Its Epilepsies

Insular seizures are great mimickers of seizures originating elsewhere in the brain. The insula is a highly connected brain structure. Seizures may only become clinically evident after ictal activity propagates out of the insula with semiology that reflects the propagation pattern. Insular seizures with perisylvian spread, for example, manifest first as throat constriction, followed next by perioral and hemisensory symptoms, and then by unilateral motor symptoms. On the other hand, insular seizures may spread instead to the temporal and frontal lobes and present like seizures originating from these regions. Due to the location of the insula deep in the brain, interictal and ictal scalp electroencephalogram (EEG) changes can be variable and misleading. Magnetic reso- nance imaging, magnetic resonance spectroscopy, magnetoencephalography, positron emission tomography, and single-photon computed tomography imaging may assist in establishing a diagnosis of insular epilepsy. Intracranial EEG recordings from within the insula, using stereo-EEG or depth electrode techniques, can prove insular seizure origin. Seizure onset, most commonly seen as low-voltage, fast gamma activity, however, can be highly localized and easily missed if the insula is only sparsely sampled. Moreover, seizure spread to the contralateral insula and other brain regions may occur rapidly. Extensive sampling of the insula with multiple electrode trajectories is necessary to avoid these pitfalls. Understanding the functional organization of the insula is helpful when interpreting the semiology produced by insular seizures. Electrical stimulation mapping around the central sulcus of the insula results in paresthesias, while stimulation of the posterior insula typically produces painful sensations. Visceral sensations are the next most common result of insular stimulation. Treatment of insular epilepsy is evolving, but poses challenges. Surgical resections of the insula are effective but risk significant morbidity if not carefully planned. Neurostimulation is an emerging option for treatment, especially for seizures with onset in the posterior insula. The close association of the insula with marked autonomic changes has led to interest in the role of the insula in sudden unexpected death in epilepsy and warrants additional study with larger patient cohorts

Self-assembly mechanism in colloids: perspectives from Statistical Physics

Motivated by recent experimental findings in chemical synthesis of colloidal particles, we draw an analogy between self-assembly processes occurring in biological systems (e.g. protein folding) and a new exciting possibility in the field of material science. We consider a self-assembly process whose elementary building blocks are decorated patchy colloids of various types, that spontaneously drive the system toward a unique and predetermined targeted macroscopic structure. To this aim, we discuss a simple theoretical model -- the Kern-Frenkel model -- describing a fluid of colloidal spherical particles with a pre-defined number and distribution of solvophobic and solvophilic regions on their surface. The solvophobic and solvophilic regions are described via a short-range square-well and a hard-sphere potentials, respectively. Integral equation and perturbation theories are presented to discuss structural and thermodynamical properties, with particular emphasis on the computation of the fluid-fluid (or gas-liquid) transition in the temperature-density plane. The model allows the description of both one and two attractive caps, as a function of the fraction of covered attractive surface, thus interpolating between a square-well and a hard-sphere fluid, upon changing the coverage. By comparison with Monte Carlo simulations, we assess the pros and the cons of both integral equation and perturbation theories in the present context of patchy colloids, where the computational effort for numerical simulations is rather demanding.Comment: 14 pages, 7 figures, Special issue for the SigmaPhi2011 conferenc

Effect of Polydispersity and Anisotropy in Colloidal and Protein Solutions: an Integral Equation Approach

Application of integral equation theory to complex fluids is reviewed, with particular emphasis to the effects of polydispersity and anisotropy on their structural and thermodynamic properties. Both analytical and numerical solutions of integral equations are discussed within the context of a set of minimal potential models that have been widely used in the literature. While other popular theoretical tools, such as numerical simulations and density functional theory, are superior for quantitative and accurate predictions, we argue that integral equation theory still provides, as in simple fluids, an invaluable technique that is able to capture the main essential features of a complex system, at a much lower computational cost. In addition, it can provide a detailed description of the angular dependence in arbitrary frame, unlike numerical simulations where this information is frequently hampered by insufficient statistics. Applications to colloidal mixtures, globular proteins and patchy colloids are discussed, within a unified framework.Comment: 17 pages, 7 figures, to appear in Interdiscip. Sci. Comput. Life Sci. (2011), special issue dedicated to Prof. Lesser Blu

Reconstruction of Pacific Ocean Bottom Water Salinity During the Last Glacial Maximum

Knowledge of salinity in the deep ocean is important for understanding past ocean circulation and climate. Based on sedimentary pore fluid chloride measurements of a single Pacific site, Adkins et al. (2002) suggested that, during the Last Glacial Maximum (LGM), the Pacific deep bottom water was saltier than expected based on lower sea level alone. Here we present high-resolution salinity profiles from five sites in the South, Equatorial, and North Pacific Ocean. Our study greatly constrains understanding of LGM salinity in the Pacific Ocean. Our results show that LGM chloride concentrations of deep Pacific bottom water were 4.09 ± 0.4% greater than today\u27s values. Pacific Ocean bottom water salinity was also indistinguishable from being homogeneous across the wide range of latitudes studied here. These LGM salinity reconstructions are on average slightly higher (~1.4 to 1% higher) than expected from sea level of the time, which is generally inferred to have been ~120 to ~135 m lower than today