3,504 research outputs found
Charge and momentum transfer in supercooled melts: Why should their relaxation times differ?
The steady state values of the viscosity and the intrinsic ionic-conductivity
of quenched melts are computed, in terms of independently measurable
quantities. The frequency dependence of the ac dielectric response is
estimated. The discrepancy between the corresponding characteristic relaxation
times is only apparent; it does not imply distinct mechanisms, but stems from
the intrinsic barrier distribution for -relaxation in supercooled
fluids and glasses. This type of intrinsic ``decoupling'' is argued not to
exceed four orders in magnitude, for known glassformers. We explain the origin
of the discrepancy between the stretching exponent , as extracted from
and the dielectric modulus data. The actual width of the
barrier distribution always grows with lowering the temperature. The contrary
is an artifact of the large contribution of the dc-conductivity component to
the modulus data. The methodology allows one to single out other contributions
to the conductivity, as in ``superionic'' liquids or when charge carriers are
delocalized, implying that in those systems, charge transfer does not require
structural reconfiguration.Comment: submitted to J Chem Phy
Electric and magnetic fields effects on the excitonic properties of elliptic core-multishell quantum wires
The effect of eccentricity distortions of core-multishell quantum wires on
their electron, hole and exciton states is theoretically investigated. Within
the effective mass approximation, the Schrodinger equation is numerically
solved for electrons and holes in systems with single and double radial
heterostructures, and the exciton binding energy is calculated by means of a
variational approach. We show that the energy spectrum of a core-multishell
heterostructure with eccentricity distortions, as well as its magnetic field
dependence, are very sensitive to the direction of an externally applied
electric field, an effect that can be used to identify the eccentricity of the
system. For a double heterostructure, the eccentricities of the inner and outer
shells play an important role on the excitonic binding energy, specially in the
presence of external magnetic fields, and lead to drastic modifications in the
oscillator strength.Comment: 17 pages, 10 figure
Ocorrência de horizontes antrópicos (Terra Preta de Índio) em Neossolos Quartzarênicos no município de Parintins - AM - Brasil.
Este trabalho teve por objetivo caracterizar três perfis com horizonte antrópico na localidade conhecida como comunidade do Lago da Valeria, no município de Parintins - AM
Evaluation of manioc (Manihot esculenta Crantz) cultivation in mixed cropping systems.
Avaliação da cultura da mandioca (Manihot esculenta Crantz) em sistema e policultivo: Yields and survival rates will be presented for three manioc cultivars(Pao IM 226, Vinagre IM 157 and Mandioca IM 116), planted between the rows in two mixed cropping systems, which were treated by application of 30% or 100% of the recommended fertilizer dose and inoculation or not with mycorrhizal fungi spores. With regard to yield, there is no statistically significant difference between the treatments viewed in isolation. However, there are statistically significant differences between the cultivars Pao (10.6 tons/ha) and Vinagre (5.5 tons/ha) in system 2; between 100% fertilization (5.2 tons/ha) and 30% fertilization (3.7 tons/ha) in system 3, and between the Pao cultivars in systems 2 (10.6 tons/ha) and 3 (5.4 tons/ha). The resprouting rates of the cutting were considered to be low. There was no statistically significant difference in survival rates between the treatments. The yields are lower than those normally obtained in the region, i.e., 20.0 tons/ha for Pao, 14.0 tons/ha for Vinagre and 16,0 tons/ha for manioc in monoculture
Colorectal Endoscopic Submucosal Dissection in a Western Center: Analysis of Outcomes and Safety Profile
Introduction: Endoscopic submucosal dissection (ESD) is a well-established endoscopic technique for the treatment of gastrointestinal lesions. Colorectal ESD outcomes are less reported in the Western literature, and Portuguese data are still very scarce. Our aim was to describe our experience on colorectal ESD regarding its outcomes and safety profile. Methods: We conducted a retrospective evaluation of recorded data on ESDs performed between 2015 and 2020. Only ESDs performed on epithelial neoplastic lesions were selected for further analysis. Results: Of a total of 167 colorectal ESDs, 153 were included. Technical success was achieved in 147 procedures (96%). The lesions were located in the colon (n = 24) and rectum (n = 123). The en bloc resection rate was 92% and 97%, the R0 resection rate was 83% and 82%, and the curative resection rate was 79% and 78% for the colon and the rectum, respectively. The need for a hybrid technique was the only risk factor for piecemeal or R1 resection. We report a perforation rate of 3.4% and a 4.1% rate of delayed bleeding; all the adverse events were manageable endoscopically, without the need of blood transfusions or surgery. Most of the lesions were laterally spreading tumours of the granular mixed type (70%), and 20% of the lesions were malignant (12% submucosal and 8% intramucosal cancer). Conclusion: Our series on colorectal ESD reports a very good efficacy and safety profile. This technique can be applied by endoscopists experienced in ESD
Improving light harvesting in polymer photodetector devices through nanoindented metal mask films
To enhance light harvesting in organic photovoltaic devices, we propose the incorporation of a metal (aluminum) mask film in the system’s usual layout. We fabricate devices in a sandwich geometry, where the mask (nanoindented with a periodic array of holes of sizes d and spacing s) is added between the transparent electrode and the active layer formed by a blend of the semiconducting polymer P3HT and substituted fullerene. Its function is to promote trapping of the incident light into the device’s cavity (the region corresponding to the active layer). For d, we set a value that allows light diffraction through the holes in the relevant absorption range of the polymer. To optimize the mask structure, we consider a very simple model to determine the s leading to trapped fields that are relatively intense and homogeneous within the device. From measurements of the action spectra, we show that, indeed, such architecture can considerably improve the resulting photocurrent efficiencies—one order of magnitude in the best situation studied.
Conditions for Neonatal Resuscitation in Portuguese Delivery Rooms: a National Survey (2009)
Introdução: Desde 1989 que em Portugal as taxas de mortalidade materna, perinatal e neonatal apresentam uma diminuição significativa, em parte devido à rede perinatal implementada.
Auditorias às condições existentes nos diferentes níveis de cuidados constituem um instrumento fundamental para identificar desvios da normalidade definida e podem ser um contributo para a melhoria de cuidados.
Objectivos: Conhecer as condições e práticas de assistência nas salas de parto nacionais e, quando se justificar, propôr medidas de melhoria dos cuidados neonatais.
Material e métodos: Foi enviado, por via electrónica, um questionário a 35 centros hospitalares com maternidade. O inquérito incluía questões relacionadas com os recursos humanos, equipamento disponível, características das salas de partos, práticas usadas na estabilização/ reanimação do recém-nascido, número de partos e número de recém-nascidos transferidos após o nascimento por ano, bem como questões relacionadas com a articulação com as equipas de obstetrícia.
Resultados: Responderam 30 (86%) centros, 16 de apoio perinatal diferenciado. Oito (27%)
centros têm pediatra presente em todos os partos, os restantes centros têm pediatra disponível para as situações de maior risco. Entre o material não disponível em alguns centros salienta-se o equipamento de monitorização cardio-respiratória, dispositivo de apoio ventilatório com pressão
controlada, misturador de oxigénio, ventilador, CPAP (continuous positive airway pressure), incubadora de transporte e material para toracocentese e paracentese. Os critérios usados para oxigenoterapia e uso de surfactante “profiláctico” não são os mesmos entre os diversos centros.
Todos os centros referiram a necessidade transferir recém-nascidos após o nascimento, quer por falta de diferenciação de cuidados quer por falta de vagas para internamento. Os centros de apoio perinatal referiram pior colaboração por parte das equipas de obstetrícia.
Conclusâo: Os cuidados prestados ao recém-nascido nas salas de partos nacionais podem e
devem ser melhorados. É necessário adequar o equipamento e recursos humanos às necessidades de cada centro. É necessário actualizar protocolos de práticas como oxigenoterapia e uso de surfactante “profiláctico”, reduzir o transporte após o nascimento e melhorar a comunicação com as equipas de obstetrícia
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