Excitonic effects in the optical properties of CdSe nanowires

Using a first-principle approach beyond density functional theory we calculate the electronic and optical properties of small diameter CdSe nanowires.Our results demonstrate how some approximations commonly used in bulk systems fail at this nano-scale level and how indispensable it is to include crystal local fields and excitonic effects to predict the unique optical properties of nanowires. From our results, we then construct a simple model that describes the optical gap as a function of the diameter of the wire, that turns out to be in excellent agreement with experiments for intermediate and large diameters.Comment: submitte

Construction of the B88 exchange-energy functional in two dimensions

We construct a generalized-gradient approximation for the exchange-energy density of finite two-dimensional systems. Guided by non-empirical principles, we include the proper small-gradient limit and the proper tail for the exchange-hole potential. The observed performance is superior to that of the two-dimensional local-density approximation, which underlines the usefulness of the approach in practical applications

Dark matter effects in modified teleparallel gravity

This work investigates dark matter (DM) effects in compact objects in modified teleparallel gravity (MTG) in which a modification of Teleparallel Equivalent to General Relativity is used. We applied a tetrad to the modified field equations where a set of relations is found. The conservation equation allows us to rewrite our Tolman-Oppenheimer-Volkoff equations with an effective gravitational coupling constant. As input to these new equations, we use a relativistic mean-field (RMF) model with dark matter content included, obtained from a Lagrangian density with both, hadronic and dark particle degrees of freedom, as well as the Higgs boson, used as a mediator in both sectors of the theory. Through numerical calculations, we analyze the mass-radius diagrams obtained from different parametrizations of the RMF-DM model, generated by assuming different values of the dark particle Fermi momentum and running the free parameter coming from the MTG. Our results show that it is possible for the system simultaneously support more DM content, and be compatible with recent astrophysical data provided by LIGO and Virgo Collaboration, as well as by NASA's Neutron star Interior Composition Explorer (NICER).Comment: 8 pages, 2 figure

Atividade alelopática de substâncias químicas isoladas da Acacia mangium e suas variações em função do PH.

Os objetivos deste trabalho foram isolar, identificar e caracterizar a atividade alelopática de substâncias químicas produzidas por Acacia mangium, além de determinar as variações na atividade das substâncias em função da variação do pH da solução. A atividade alelopática foi avaliada em bioensaios de germinação (25 ºC de temperatura e fotoperíodo de 12 horas) e crescimento de radícula e hipocótilo (25 ºC de temperatura e fotoperíodo de 24 horas) das plantas daninhas malícia (Mimosa pudica) e mata-pasto (Senna obtusifolia). Avaliou-se a interferência do pH (3,0 e 9,0) da solução na atividade alelopática das substâncias sobre a germinação das sementes da espécie malícia. Os triterpenoides lupenona (3-oxolup-20(29)-eno) e lupeol (3β-hidroxilup-20(29)-eno), obtidos das folhas caídas da planta doadora, isolados e em par, evidenciaram baixo efeito alelopático inibitório da germinação de sementes e do crescimento do hipocótilo, especialmente do primeiro, cujos efeitos não ultrapassaram o valor de 2,0%. Os efeitos promovidos sobre o crescimento da radícula foram de maior magnitude, atingindo valores superiores a 40%, com destaque para as inibições promovidas pela substância lupenona. Isoladamente, as substâncias promoveram efeitos superiores aos efetivados pelas substâncias analisadas em pares, indicando a existência de antagonismo. O pH da solução influenciou a atividade alelopática das substâncias; para lupenona os efeitos foram mais intensos em pH ácido, enquanto para lupeol os melhores resultados foram verificados em condições alcalinas, mostrando que este fator é ponto importante a ser considerado em trabalhos de campo

Retracing Micro-Epidemics of Chagas Disease Using Epicenter Regression

Vector-borne transmission of Chagas disease has become an urban problem in the city of Arequipa, Peru, yet the debilitating symptoms that can occur in the chronic stage of the disease are rarely seen in hospitals in the city. The lack of obvious clinical disease in Arequipa has led to speculation that the local strain of the etiologic agent, Trypanosoma cruzi, has low chronic pathogenicity. The long asymptomatic period of Chagas disease leads us to an alternative hypothesis for the absence of clinical cases in Arequipa: transmission in the city may be so recent that most infected individuals have yet to progress to late stage disease. Here we describe a new method, epicenter regression, that allows us to infer the spatial and temporal history of disease transmission from a snapshot of a population's infection status. We show that in a community of Arequipa, transmission of T. cruzi by the insect vector Triatoma infestans occurred as a series of focal micro-epidemics, the oldest of which began only around 20 years ago. These micro-epidemics infected nearly 5% of the community before transmission of the parasite was disrupted through insecticide application in 2004. Most extant human infections in our study community arose over a brief period of time immediately prior to vector control. According to our findings, the symptoms of chronic Chagas disease are expected to be absent, even if the strain is pathogenic in the chronic phase of disease, given the long asymptomatic period of the disease and short history of intense transmission. Traducción al español disponible en Alternative Language Text S1/A Spanish translation of this article is available in Alternative Language Text S

Retracing Micro-Epidemics of Chagas Disease Using Epicenter Regression

Vector-borne transmission of Chagas disease has become an urban problem in the city of Arequipa, Peru, yet the debilitating symptoms that can occur in the chronic stage of the disease are rarely seen in hospitals in the city. The lack of obvious clinical disease in Arequipa has led to speculation that the local strain of the etiologic agent, Trypanosoma cruzi, has low chronic pathogenicity. The long asymptomatic period of Chagas disease leads us to an alternative hypothesis for the absence of clinical cases in Arequipa: transmission in the city may be so recent that most infected individuals have yet to progress to late stage disease. Here we describe a new method, epicenter regression, that allows us to infer the spatial and temporal history of disease transmission from a snapshot of a population\u27s infection status. We show that in a community of Arequipa, transmission of T. cruzi by the insect vector Triatoma infestans occurred as a series of focal micro-epidemics, the oldest of which began only around 20 years ago. These micro-epidemics infected nearly 5% of the community before transmission of the parasite was disrupted through insecticide application in 2004. Most extant human infections in our study community arose over a brief period of time immediately prior to vector control. According to our findings, the symptoms of chronic Chagas disease are expected to be absent, even if the strain is pathogenic in the chronic phase of disease, given the long asymptomatic period of the disease and short history of intense transmission

Taenia solium cysticercosis in Eastern and Southern Africa: an emerging problem in agriculture and public health

Pig production has increased tremendously in Eastern and Southern Africa (ESA), particularly in smallholder rural communities. The increase in pig production has mainly been due to land scarcity, increase in pork consumption in many areas including urban centers, and the recognition by many communities of the fast and greater return of the pig industry, compared with other domesticated livestock industries. Concurrent with the increase in smallholder pig keeping and pork consumption, there have been increasing reports of Taenia solium cysticercosis in pigs and humans in the ESA region, although the problems are under-recognized by all levels in many ESA countries. Having recognizing this, scientists researching T. solium in ESA formed a regional cysticercosis working group (CWGESA) to increase awareness of the problem and enable effective and sustainable control of T. solium. This article summarizes the status of T. solium infections in humans and pigs in the ESA countries and highlights the formation and progress of the CWGESA

Análise do potencial alelopático do óleo essencial dos rizomas de Cyperus articulatus (Cyperaceae).

III COBRADAN