Role of tip size, orientation, and structural relaxations in first-principles studies of magnetic exchange force microscopy and spin-polarized scanning tunneling microscopy

Using first-principles calculations based on density functional theory (DFT), we investigate the exchange interaction between a magnetic tip and a magnetic sample which is detected in magnetic exchange force microscopy (MExFM) and also occurs in spin-polarized scanning tunneling microscopy (SP-STM) experiments. As a model tip-sample system, we choose Fe tips and one monolayer Fe on W(001) which exhibits a checkerboard antiferromagnetic structure and has been previously studied with both SP-STM and MExFM. We calculate the exchange forces and energies as a function of tip-sample distance using different tip models ranging from single Fe atoms to Fe pyramids consisting of up to 14 atoms. We find that modelling the tip by a single Fe atom leads to qualitatively different tip-sample interactions than using clusters consisting of several atoms. Increasing the cluster size changes the calculated forces quantitatively enhancing the detectable exchange forces. Rotating the tip with respect to the surface unit cell has only a small influence on the tip-sample forces. Interestingly, the exchange forces on the tip atoms in the nearest and next-nearest layers from the apex atom are non-negligible and can be opposite to that on the apex atom for a small tip. In addition, the apex atom interacts not only with the surface atoms underneath but also with nearest-neighbors in the surface. We find that structural relaxations of tip and sample due to their interaction depend sensitively on the magnetic alignment of the two systems. As a result the onset of significant exchange forces is shifted towards larger tip-sample separations which facilitates their measurement in MExFM. At small tip-sample separations, structural relaxations of tip apex and surface atoms can either enhance or reduce the magnetic contrast measured in SP-STMComment: 14 pages, 13 figure

Environmental indicators in a sustainable mining

La industria minera en el Perú tiene muchas obligaciones legales, incluso más que cualquier otra industria, por lo que es necesario gestionar y mitigar los posibles impactos ambientales negativos que pueden ocurrir en el área de influencia minera, tanto indirecta como directa. La industria minera debe cuantificar, calificar e interpretar su desempeño en la sustentabilidad y, al mismo tiempo, debe demostrar sus mejoras continuas a corto y largo plazo. El objetivo de este artículo es la aplicación de los indicadores ambientales en el Sistema de Gestión Ambiental de la unidad minera Atacocha (actualmente administrado por el Grupo Nexa), que se estableció como área de estudio. Esto permitirá a los investigadores tener una visión general, aunque limitada, del rendimiento de su Sistema de Gestión Ambiental (Araujo, 2005). De acuerdo con los resultados obtenidos, se concluye que el uso de Indicadores de Gestión Ambiental contribuyen en la evaluación de la gestión y calidad ambiental en proyectos mineros sostenibles. Con estas herramientas, se podrían tomar decisiones para dirigir el proyecto hacia un nuevo paradigma de desarrollo sostenible.Mining industry in Peru has a lot of regulatory requirements, even more than any other industry, that is why it is necessary to manage all the possible negative environmental impacts that can occur in the mining area of influence, both indirect and direct. Mining industry must be able to quantify, qualify and interpret its sustainability performance, and simultaneously, it must demonstrate its continuous improvements in the short and long term. This study aims to apply environmental indicators in the Environmental Management System of Atacocha Mining Unit (currently Nexa Mining Unit), which has been established as the study area. This would allow the researchers to have an overview, although limited, of the performance of its Environmental Management System. According to the results obtained, we could conclude that the use of Environmental Management Indicators contributes in the assessment of the environmental management and quality in sustainable mining projects. With these tools, we could take the project towards a new paradigm of sustainable developmen

Apm4, the mu subunit of yeast AP-2 interacts with Pkc1, and mutation of the Pkc1 consensus phosphorylation site Thr176 inhibits AP-2 recruitment to endocytic sites.

The AP-2 endocytic adaptor has been extensively characterized in mammalian cells and is considered to play a role both in cargo binding and in formation of endocytic sites. However, despite our detailed knowledge of mechanistic aspects of endocytic complex assembly and disassembly in the model organism Saccharomyces cerevisiae, no function of AP-2 had been described in wild-type yeast under normal growth conditions. A recent study however revealed that disruption of the complex caused by deletion of the gene encoding its mu subunit (APM4) caused defects in cell polarity such that responses to pheromone, nutritional status and cell wall damage were affected. Furthermore, a homozygous deletion of the mu subunit gene in Candida albicans affected its ability to grow hyphae. Direct binding to the yeast cell wall stress sensor Mid2 was detected, and in an apm4 deletion strain Mid2 showed reduced re-localization to the mother bud neck region following cell wall damage with calcofluor or to the mating projection tip. Here we demonstrate an interaction between Apm4 and the yeast cell wall integrity pathway component Pkc1 and show that mutation of the predicted Pkc1 site in the Apm4 hinge region affects recruitment of the AP-2 complex to endocytic sites

Extended States in a One-dimensional Generalized Dimer Model

The transmission coefficient for a one dimensional system is given in terms of Chebyshev polynomials using the tight-binding model. This result is applied to a system composed of two impurities located between $N$ sites of a host lattice. It is found that the system has extended states for several values of the energy. Analytical expressions are given for the impurity site energy in terms of the electron's energy. The number of resonant states grows like the number of host sites between the impurities. This property makes the system interesting since it is a simple task to design a configuration with resonant energy very close to the Fermi level $E_F$.Comment: 4 pages, 3 figure

High-speed noise-free optical quantum memory

Quantum networks promise to revolutionise computing, simulation, and communication. Light is the ideal information carrier for quantum networks, as its properties are not degraded by noise in ambient conditions, and it can support large bandwidths enabling fast operations and a large information capacity. Quantum memories, devices that store, manipulate, and release on demand quantum light, have been identified as critical components of photonic quantum networks, because they facilitate scalability. However, any noise introduced by the memory can render the device classical by destroying the quantum character of the light. Here we introduce an intrinsically noise-free memory protocol based on two-photon off-resonant cascaded absorption (ORCA). We consequently demonstrate for the first time successful storage of GHz-bandwidth heralded single photons in a warm atomic vapour with no added noise; confirmed by the unaltered photon statistics upon recall. Our ORCA memory platform meets the stringent noise-requirements for quantum memories whilst offering technical simplicity and high-speed operation, and therefore is immediately applicable to low-latency quantum networks

Sistema híbrido para tomada de decisão em investimentos no mercado de criptomoedas / Hybrid system for decision making in investments in the cryptocurrency market

Os mercados de criptomoedas vem chamando a atenção e atraindo todo tipo de investidores, desde pessoas até instituições financeiras, buscando altos retornos resultado de la significativa variação dos preços e a sua rápida valorização. No entanto, esse mercado é caracterizado pelo nível de volatilidade e incerteza, levando os preços a níveis muito altos e também a níveis baixos, estas características geram uma grande dificuldade para a toma de decisões dos gestores de investimentos. Este artigo propõe um sistema híbrido para a tomada de decisões no gerenciamento de investimentos no mercado de criptomoedas, considerando um perfil de investimento conservador, que busca reduzir o risco e maximizar o retorno do investimento. A metodologia visa, com base no preço histórico das criptomoedas, estabelecer níveis de retorno e estimar as probabilidades de transição dos retornos para cada nível, isso é feito com base na análise das cadeias de Markov, que são integradas nas múltiplas árvores de decisão para identificar a criptomoeda que projeta o maior retorno futuro, considerando que será vendida em um ou dois períodos após a aquisição. Os resultados são comparados com os dados reais e comprova-se a eficiência da metodologia

The Bethe ansatz as a matrix product ansatz

The Bethe ansatz in its several formulations is the common tool for the exact solution of one dimensional quantum Hamiltonians. This ansatz asserts that the several eigenfunctions of the Hamiltonians are given in terms of a sum of permutations of plane waves. We present results that induce us to expect that, alternatively, the eigenfunctions of all the exact integrable quantum chains can also be expressed by a matrix product ansatz. In this ansatz the several components of the eigenfunctions are obtained through the algebraic properties of properly defined matrices. This ansatz allows an unified formulation of several exact integrable Hamiltonians. We show how to formulate this ansatz for a huge family of quantum chains like the anisotropic Heisenberg model, Fateev-Zamolodchikov model, Izergin-Korepin model, $t-J$ model, Hubbard model, etc.Comment: 4 pages and no figure

Association between chronic conditions and health-related quality of life: differences by level of urbanization in Peru.

PURPOSE: To evaluate the role of urbanization as an effect modifier for the association between specific chronic conditions and number of conditions with health-related quality of life (QOL). METHODS: We analyzed cross-sectional data from the CRONICAS Cohort Study conducted in Lima (highly urbanized), Tumbes (semi-urban), as well as rural and urban sites in Puno. Exposures of interest were chronic bronchitis, depressive mood, hypertension, type 2 diabetes, and a composite variable aggregating the number of chronic conditions (the four exposures plus heart disease and stroke). QOL outcomes were assessed with EuroQol's EQ-5D visual analogue scale (EQ-VAS). We fitted linear regressions with robust variance to evaluate the associations of interest. Study site was assessed as a potential effect modifier using the likelihood-ratio (LR) test. RESULTS: We evaluated data on 2433 subjects: 51.3% were female, mean age was 57.2 years. Study site was found to be an effect modifier only for the association between depressive mood and EQ-VAS score (LR test p < 0.001). Compared to those without depressive mood, participants with depressive mood scored -13.7 points on the EQ-VAS in Lima, -7.9 in urban Puno, -11.0 in semi-urban Tumbes, and -2.7 in rural Puno. Study site was not found to be an effect modifier for the association between the number of chronic conditions and EQ-VAS (LR test p = 0.64). CONCLUSION: The impact of depressive mood on EQ-VAS was larger in urban than in rural sites, while site was not an effect modifier for the remaining associations