Coulomb blockade in an atomically thin quantum dot coupled to a tunable Fermi reservoir

Gate-tunable quantum-mechanical tunnelling of particles between a quantum confined state and a nearby Fermi reservoir of delocalized states has underpinned many advances in spintronics and solid-state quantum optics. The prototypical example is a semiconductor quantum dot separated from a gated contact by a tunnel barrier. This enables Coulomb blockade, the phenomenon whereby electrons or holes can be loaded one-by-one into a quantum dot. Depending on the tunnel-coupling strength, this capability facilitates single spin quantum bits or coherent many-body interactions between the confined spin and the Fermi reservoir. Van der Waals (vdW) heterostructures, in which a wide range of unique atomic layers can easily be combined, offer novel prospects to engineer coherent quantum confined spins, tunnel barriers down to the atomic limit or a Fermi reservoir beyond the conventional flat density of states. However, gate-control of vdW nanostructures at the single particle level is needed to unlock their potential. Here we report Coulomb blockade in a vdW heterostructure consisting of a transition metal dichalcogenide quantum dot coupled to a graphene contact through an atomically thin hexagonal boron nitride (hBN) tunnel barrier. Thanks to a tunable Fermi reservoir, we can deterministically load either a single electron or a single hole into the quantum dot. We observe hybrid excitons, composed of localized quantum dot states and delocalized continuum states, arising from ultra-strong spin-conserving tunnel coupling through the atomically thin tunnel barrier. Probing the charged excitons in applied magnetic fields, we observe large gyromagnetic ratios (~8). Our results establish a foundation for engineering next-generation devices to investigate either novel regimes of Kondo physics or isolated quantum bits in a vdW heterostructure platform.Comment: Published in Nature Nanotechnology. 7 pages + 14 supplementary information pages. 14 figure

Spin–layer locking of interlayer excitons trapped in moiré potentials

Van der Waals heterostructures offer attractive opportunities to design quantum materials. For instance, transition metal dichalcogenides (TMDs) possess three quantum degrees of freedom: spin, valley index, and layer index. Further, twisted TMD heterobilayers can form moir\'e patterns that modulate the electronic band structure according to atomic registry, leading to spatial confinement of interlayer exciton (IXs). Here we report the observation of spin-layer locking of IXs trapped in moir\'e potentials formed in a heterostructure of bilayer 2H-MoSe$_2$ and monolayer WSe$_2$. The phenomenon of locked electron spin and layer index leads to two quantum-confined IX species with distinct spin-layer-valley configurations. Furthermore, we observe that the atomic registries of the moir\'e trapping sites in the three layers are intrinsically locked together due to the 2H-type stacking characteristic of bilayer TMDs. These results identify the layer index as a useful degree of freedom to engineer tunable few-level quantum systems in two-dimensional heterostructures.Comment: 10 pages, 4 figures. Supplementary Material available at: https://www.dropbox.com/s/8331cfoasdofwkq/Brotons-Gisbert_Suppl_Info.pdf?dl=

Mortalidade por esclerose lateral amiotrófica no município de São Paulo de 2002 a 2006

OBJECTIVE: To describe the mortality rates of amyotrophic lateral sclerosis (ALS) in the city of São Paulo as a function of demographics, year, and region. METHOD: This was a retrospective descriptive study. Information was obtained from death certificates registered at the Program for the Improvement of Mortality Information, Municipal Health Department (PRO-AIM/SMS), coded as G12.2 according to International Classification of Diseases (ICD-10), from 2002 to 2006. RESULTS: Over the studied time, were found 326 deaths (51.6% women, overall mean age of 64.1 years). Highest deaths percentages happened in those from 60 to 69 and 70 to 79 years and in white individuals. ALS mortality rates ranged 0.44/100,000 in 2002 and 0.76/100,000 in 2006. No significant changes overtime in administrative districts were found. CONCLUSION: ALS mortality rates in São Paulo were lower in comparison to other countries, however any risk factor in our environment, lifestyle or genetic characteristics were found.OBJETIVO: Descrever a taxa de mortalidade da esclerose lateral amiotrófica (ELA) no município de São Paulo (MSP) de 2002 a 2006, segundo tempo, pessoa e espaço. MÉTODO: Estudo descritivo retrospectivo, utilizando dados das declarações de óbitos do Programa de Aprimoramento das Informações de Mortalidade (PROAIM/SMS), com G12.2 segundo Classificação Internacional de Doenças (CID 10), de 2002 a 2006. RESULTADOS: Foram encontrados 326 óbitos, 51,6% mulheres, média de idade de 64,1 anos. Maiores percentuais de mortes foram encontrados nas faixas etárias de 60-69 anos e 70-79 anos e na raça branca. As taxas de mortalidade por ELA variaram de 0,44/100.000 em 2002 para 0,76/100.000 em 2006. Não houve mudanças significativas nos distritos administrativos em relação ao tempo. CONCLUSÃO: Taxas de mortalidade por ELA no MSP são menores, comparadas às de outros países; mas nenhum fator de risco foi encontrado no estudo em relação ao ambiente, modo de vida e características genéticas.Federal University of São Paulo Paulista School of MedicineSecretary of Health Program for the Improvement of Mortality InformationUNIFESP, EPMSciEL

Deep Near-infrared Spectroscopy of Passively Evolving Galaxies at z ≳ 1.4

We present the results of new near-IR spectroscopic observations of passive galaxies at z ≳ 1.4 in a concentration of BzK-selected galaxies in the COSMOS field. The observations have been conducted with Subaru/MOIRCS, and have resulted in absorption lines and/or continuum detection for 18 out of 34 objects. This allows us to measure spectroscopic redshifts for a sample that is almost complete to K_AB = 21. COSMOS photometric redshifts are found in fair agreement overall with the spectroscopic redshifts, with a standard deviation of ~0.05; however, ~30% of objects have photometric redshifts systematically underestimated by up to ~25%. We show that these systematic offsets in photometric redshifts can be removed by using these objects as a training set. All galaxies fall in four distinct redshift spikes at z = 1.43, 1.53, 1.67, and 1.82, with this latter one including seven galaxies. SED fits to broadband fluxes indicate stellar masses in the range of ~4-40 × 10^10 M_☉ and that star formation was quenched ~1 Gyr before the cosmic epoch at which they are observed. The spectra of several individual galaxies have allowed us to measure their Hδ_F indices and the strengths of the 4000 Å break, which confirms their identification as passive galaxies, as does a composite spectrum resulting from the co-addition of 17 individual spectra. The effective radii of the galaxies have been measured on the COSMOS HST/ACS i_(F814W)-band image, confirming the coexistence at these redshifts of passive galaxies, which are substantially more compact than their local counterparts with others that follow the local effective radius-stellar mass relation. For the galaxy with the best signal-to-noise spectrum we were able to measure a velocity dispersion of 270 ± 105 km s^(–1) (error bar including systematic errors), indicating that this galaxy lies closely on the virial relation given its stellar mass and effective radius

Flipping exciton angular momentum with chiral phonons in MoSe2_2/WSe2_2 heterobilayers

Identifying quantum numbers to label elementary excitations is essential for the correct description of light-matter interaction in solids. In monolayer semiconducting transition metal dichalcogenides (TMDs) such as MoSe$_2$ or WSe$_2$, most optoelectronic phenomena are described well by labelling electron and hole states with the spin projection along the normal to the layer (S$_z$). In contrast, for WSe$_2$/MoSe$_2$ interfaces recent experiments show that taking S$_z$ as quantum number is not a good approximation, and spin mixing needs to be always considered. Here we argue that the correct quantum number for these systems is not S$_z$, but the $z$-component of the total angular momentum -- J$_z$ = L$_z$ + S$_z$ -- associated to the C$_3$ rotational lattice symmetry, which assumes half-integer values corresponding modulo 3 to distinct states. We validate this conclusion experimentally through the observation of strong intervalley scattering mediated by chiral optical phonons that -- despite carrying angular momentum 1 -- cause resonant intervalley transitions of excitons, with an angular momentum difference of 2.Comment: are welcom

Perfil de pacientes que evoluem para óbito por tuberculose no município de São Paulo, 2002

OBJECTIVE: To profile adult patients dying of tuberculosis in the city of São Paulo with respect to biological, environmental and institutional factors. METHODS: Descriptive study covering all tuberculosis deaths (N=416) among individuals aged over 15 years in 2002. Data were obtained from hospital records, the local Mortality Information System, Coroner's Service, and tuberculosis Surveillance System. The estimates of relative risk and 95% confidence intervals (95% CI) were based on the reference group, i.e., females aged 15 to 29 years, originally from the State of São Paulo (Brazil). A comparative analysis was conducted using Pearson's chi-square test and Fisher's exact test for categorical variables and Kruskal-Wallis test for continuous variables. RESULTS: Of all tuberculosis deaths identified, 78% had pulmonary form. Tuberculosis diagnosis was made after death in 30% and in primary health care units in 14%. Of them, 44% had not started treatment; 49% were not notified; and 76% were men. The median age was 51 years; 52% had up to four years of schooling; 4% were probably living in the streets. Mortality rate increased with age; it was 5.0/100,000 for the entire city, ranging between zero to 35 according to the district. Previous treatment was reported for 82 out of 232 patients, and of them, 41 defaulted treatment. Diabetes (16%), chronic obstructive pulmonary disease (19%), HIV infection (11%), smoking (71%), and alcohol abuse (64%) were also reported. CONCLUSIONS: Adult males over 50, migrants and living in lower Human Development Index districts were more likely to die of tuberculosis. Low schooling and comorbidities are relevant characteristics. Low involvement of primary care units in tuberculosis diagnosis and high underreporting of cases were also seen.OBJETIVO: Describir el perfil de pacientes adultos residentes en el municipio de São Paulo (Sureste de Brasil) que evolucionaron a óbito asociado con tuberculosis, según factores biológicos, ambientales e institucionales. MÉTODOS: Se realizó estudio descriptivo, abarcando todos los óbitos por tuberculosis (N=416) ocurridos en 2002, entre mayores de 15 años. Los datos analizados fueron obtenidos del Sistema Municipal de Informaciones de Mortalidad, prontuarios hospitalares, Servicio de Verificación de Óbitos y Sistema de Vigilancia de Tuberculosis. Los cálculos de riesgos relativos e intervalos de confianza de 95% (IC 95%) tuvieron como referencia el sexo femenino, grupo de 15 a 29 años, y los naturales del Estado de Sao Paulo. El análisis comparativo uso la prueba de Chi-cuadrado de Pearson y el exacto de Fisher para variables categóricas y la prueba de Kruskal-Wallis para variables continuas. RESULTADOS: Del total de óbitos, 78% presentaron la forma pulmonar; el diagnóstico fue efectuado posterior a la muerte en 30% y en unidades de atención primaria en 14% de los casos; 44% no iniciaron tratamiento; 49% no fueron notificados; 76% eran hombres y la edad mediana fue de 51 años; 52% tenían cuatro años de estudio, 4% probablemente vivían en las calles. Las tasas de mortalidad aumentaban con la edad, con un valor de 5,0/100.000 en el municipio, variando de cero a 35, dependiendo del distrito. Para 82 de 232 pacientes con registro de tratamiento, había registro de tratamiento anterior, y de esos, 41 lo habían abandonado. Se comprobó presencia de diabetes (16%), enfermedad pulmonar obstructiva crónica (19%), HIV (11%), tabaquismo (71%) y alcoholismo (64%) en los pacientes. CONCLUSIONES: Los hombres por encima de los 50 años, migrantes y residentes en distritos con bajo Índice de Desarrollo Humano presentaron mayores riesgos de óbito. La baja escolaridad y presentar co-morbilidad son características importantes. Se observo baja participación de las unidades básicas de salud en el diagnóstico y una elevada sub-notificación.OBJETIVO: Descrever o perfil de pacientes adultos residentes no município de São Paulo que evoluíram para óbito associado à tuberculose, segundo fatores biológicos, ambientais e institucionais. MÉTODOS: Estudo descritivo, abrangendo todos os óbitos por tuberculose (N=416) ocorridos em 2002, entre maiores de 15 anos. Os dados analisados foram obtidos do Sistema Municipal de Informações de Mortalidade, prontuários hospitalares, Serviço de Verificação de Óbitos e Sistema de Vigilância de Tuberculose. Os cálculos dos riscos relativos e intervalos de confiança de 95% (IC 95%) tiveram como referência o sexo feminino, grupo de 15 a 29 anos, e os naturais do Estado de São Paulo. A análise comparativa usou o teste do qui-quadrado de Pearson e o exato de Fisher para variáveis categóricas e o teste Kruskal-Wallis para variáveis contínuas. RESULTADOS: Do total de óbitos, 78% apresentavam a forma pulmonar; o diagnóstico foi efetuado após a morte em 30% e em unidades de atendimento primário em 14% dos casos; 44% não iniciaram tratamento; 49% não foram notificados; 76% eram homens e a mediana da idade foi de 51 anos; 52% tinham até quatro anos de estudo, 4% eram prováveis moradores de rua. As taxas de mortalidade aumentavam com a idade, sendo de 5,0/100.000 no município, variando de zero a 35, conforme o distrito. Para 82 de 232 pacientes com registro de tratamento, havia referência de tratamento anterior, e desses, 41 o haviam abandonado. Constatou-se presença de diabetes (16%), doença pulmonar obstrutiva crônica (19%), HIV (11%), tabagismo (71%) e alcoolismo (64%) nos pacientes. CONCLUSÕES: Homens acima de 50 anos, migrantes e residentes em distritos com baixo Índice de Desenvolvimento Humano apresentam maiores riscos de óbito. A pouca escolaridade e apresentar co-morbidades são características importantes. Observou-se baixa participação das unidades básicas de saúde no diagnóstico e a elevada sub-notificação

Manual de Segurança Alimentar – Da Origem ao Consumo

A Sociedade é cada vez mais exigente, e para satisfazer o consumidor quer em qualidade quer em segurança alimentar, a legislação em vigor deve ser cumprida com rigor, de forma a garantir que os produtos da origem até ao consumo sejam alimentos seguros. O presente trabalho aborda a importância da segurança alimentar, desde a origem ao consumo, com destaque às exigências sanitárias contidas no Regulamento (CE) 852/2004, em vigor desde 1 de janeiro de 2006, tendo sempre em conta as boas práticas de higiene dos manipuladores intervenientes, das instalações, equipamentos, receção das matérias-primas, armazenagem das mesmas e respetivo processamento dos alimentos. Aborda-se ainda a Norma ISO 22000, que especifica os requisitos para um sistema de gestão da segurança alimentar e que combina os elementos-chave geralmente reconhecidos como essenciais, que permitem assegurar a segurança dos géneros alimentícios ao longo da cadeia alimentar até ao seu consumo final. Para além destes temas, são abordados ainda dois exemplos práticos relativos à implementação da segurança alimentar desde a origem da matéria-prima, até ao consumo de alimentos em dois setores. O primeiro é o de uma empresa do setor de distribuição, enquadrando-se nesta o fornecedor de origem, onde se realizam as etapas de abate, desmancha e embalamento, e o segundo é do setor da restauração

Engineering 2D material exciton lineshape with graphene/h-BN encapsulation

Control over the optical properties of atomically thin two-dimensional (2D) layers, including those of transition metal dichalcogenides (TMDs), is needed for future optoelectronic applications. Remarkable advances have been achieved through alloying, chemical and electrical doping, and applied strain. However, the integration of TMDs with other 2D materials in van der Waals heterostructures (vdWHs) to tailor novel functionalities remains largely unexplored. Here, the near-field coupling between TMDs and graphene/graphite is used to engineer the exciton lineshape and charge state. Fano-like asymmetric spectral features are produced in WS$_{2}$, MoSe$_{2}$ and WSe$_{2}$ vdWHs combined with graphene, graphite, or jointly with hexagonal boron nitride (h-BN) as supporting or encapsulating layers. Furthermore, trion emission is suppressed in h-BN encapsulated WSe$_{2}$/graphene with a neutral exciton redshift (44 meV) and binding energy reduction (30 meV). The response of these systems to electron-beam and light probes is well-described in terms of 2D optical conductivities of the involved materials. Beyond fundamental insights into the interaction of TMD excitons with structured environments, this study opens an unexplored avenue toward shaping the spectral profile of narrow optical modes for application in nanophotonic devices

Evaluation of eleven immunochromatographic assays for SARS-CoV-2 detection: investigating the dengue cross-reaction

COVID-19 disease is spread worldwide and diagnostic techniques have been studied in order to contain the pandemic. Immunochromatographic (IC) assays are feasible and a low-cost alternative especially in low and middle-income countries, which lack structure to perform certain diagnostic techniques. Here we evaluate the sensitivity and specificity of eleven different IC tests in 145 serum samples from confirmed cases of COVID-19 using RT-PCR and 100 negative serum samples from blood donors collected in February 2019. We also evaluated the cross-reactivity with dengue using 20 serum samples from patients with confirmed diagnosis for dengue collected in early 2019 through four different tests. We found high sensitivity (92%), specificity (100%) and an almost perfect agreement (Kappa 0.92) of IC assay, especially when we evaluated IgG and IgM combined after 10 days from the onset of symptoms with RT-PCR. However, we detected cross-reactivity between dengue and COVID-19 mainly with IgM antibodies (5 to 20% of cross-reaction) and demonstrated the need for better studies about diagnostic techniques for these diseases