10,197 research outputs found
Simulation of Transport and Gain in Quantum Cascade Lasers
Quantum cascade lasers can be modeled within a hierarchy of different
approaches: Standard rate equations for the electron densities in the levels,
semiclassical Boltzmann equation for the microscopic distribution functions,
and quantum kinetics including the coherent evolution between the states. Here
we present a quantum transport approach based on nonequilibrium Green
functions. This allows for quantitative simulations of the transport and
optical gain of the device. The division of the current density in two terms
shows that semiclassical transitions are likely to dominate the transport for
the prototype device of Sirtori et al. but not for a recent THz-laser with only
a few layers per period. The many particle effects are extremely dependent on
the design of the heterostructure, and for the case considered here, inclusion
of electron-electron interaction at the Hartree Fock level, provides a sizable
change in absorption but imparts only a minor shift of the gain peak.Comment: 12 pages, 5 figures included, to appear in in "Advances in Solid
State Physics", ed. by B. Kramer (Springer 2003
Simulations of mid infrared emission of InAsN semiconductors
This paper delivers an approximation to the complex many body problem of luminescence in semiconductors to the case of mid infrared luminescence of dilute nitrides. The results are compared with recent experimental data for InAsN semiconductors
Extrinsic Curvature and the Einstein Constraints
The Einstein initial-value equations in the extrinsic curvature (Hamiltonian)
representation and conformal thin sandwich (Lagrangian) representation are
brought into complete conformity by the use of a decomposition of symmetric
tensors which involves a weight function. In stationary spacetimes, there is a
natural choice of the weight function such that the transverse traceless part
of the extrinsic curvature (or canonical momentum) vanishes.Comment: 8 pages, no figures; added new section; significant polishing of tex
Spatial connectivity of aquatic macrophytes and flood cycle influence species richness of an ant community of a Brazilian floodplain
Despite the environmental and economic importance of Pantanal, there are few studies quantifying the influence of sazonality and spatial variation on biological diversity in this ecosystem. In this context, the present work aimed to study the assemblage of ants associated with macrophytes during the flood and dry period of Paraguay river, in marginal environments in the Pantanal of Porto Murtinho, Mato Grosso do Sul. We observed a wide variation in the temporal distribution of the diversity of the assemblages of ants, since from 37 species, 36 occurred in the dry and 20 in the flood period. Of the total of macrophyte species observed, in only 12.5% we found a more specific correlation with ants that were nesting in spaces provided by plants representing a total of 10.52% of the species analized.
Ethical Aspects Concerning Endodontic Instrument Fracture
Aim: The aim of this study was to address several ethical aspects concerning the behavior of endodontists and general dentists regarding endodontic instrument fracture during root canal treatment. Methods: The responses of a group of professionals (endodontists and general dentists) to a questionnaire were reviewed and analyzed statistically by Fisher's Exact and chi-square tests at 5% significance level. Results: Forty-six percent of the interviewees responded that they would try to solve the problem without informing the patient about the accident. Only 28.1% of the participants affirmed that they would let the patient know right at the moment of occurrence. Conclusions: The outcomes of this survey demonstrate that most professionals are afraid of informing their patient about an accidental endodontic instrument breakage during treatment and might be subject to lawsuits.72515351538Leite, V.G., Odontologia legal (1962) Bahia: Era NovaCoehn, S., Burns, R.C., (1980) Caminhos da polpa, , 2.ed. Rio de Janeiro: Guanabara Koogan;Frank, A.L., The dilemma of the fractured instrument (1983) J Endod, 9, pp. 515-516Cohen, S., Endodontic treatment: Avoid these malpractice traps (1988) Dent Manag, 28 (36-38), p. 40Imura, N., Zuolo, M.L., (1988) Procedimentos clĂnicos em endodontia, , SĂŁo Paulo: Pancast;Walton, R.E., Torabinejad, M., (1997) Principios e prática em endodontia, , 2.ed. SĂŁo Paulo: Santos;Itoh, A., Higuchi, N., Minami, G., Yasue, T., Yoshida, T., Maseki, T., A survey of filling methods, intracanal medications, and instruments breakage (1999) J Endod, 25, pp. 823-824Ree, M.H., Timmerman, M.F., Wesselink, P.R., Factors influencing referral for specialist endodontic treatment amongst a group of Dutch general practitioners (2003) Int Endod J, 36, pp. 129-134De Deus, Q.D., (1992) Endodontia, , 5.ed. Rio de Janeiro: Medsi;Leonardo, M.R., Leal, J.M., (1998) Endodontia: Tratamento dos canais radiculares, , 3.ed. SĂŁo Paulo: Panamericana
Therapeutic strategies for IVD regeneration through hyaluronan/SDF-1-based hydrogel and intravenous administration of MSCs
Intervertebral disc (IVD) degeneration involves a complex cascade of events, including degradation of the native extracellular matrix, loss of water content, and decreased cell numbers. Cell recruitment strategies for the IVD have been increasingly explored, aiming to recruit either endogenous or transplanted cells. This study evaluates the IVD therapeutic potential of a chemoattractant delivery system (HAPSDF5) that combines a hyaluronan-based thermoreversible hydrogel (HAP) and the chemokine stromal cell derived factor-1 (SDF-1). HAPSDF5 was injected into the IVD and was combined with an intravenous injection of mesenchymal stem/stromal cells (MSCs) in a pre-clinical in vivo IVD lesion model. The local and systemic effects were evaluated two weeks after treatment. The hydrogel by itself (HAP) did not elicit any adverse effect, showing potential to be administrated by intradiscal injection. HAPSDF5 induced higher cell numbers, but no evidence of IVD regeneration was observed. MSCs systemic injection seemed to exert a role in IVD regeneration to some extent through a paracrine effect, but no synergies were observed when HAPSDF5 was combined with MSCs. Overall, this study shows that although the injection of chemoattractant hydrogels and MSC recruitment are feasible approaches for IVD, IVD regeneration using this strategy needs to be further explored before successful clinical translation.Funding: This research was funded by Portuguese funds through FCT-Fundação para a Ciência e a Tecnologia (IUD/BIM/04293/2019) and by EUROSPINE TRF (2017_05)
A computational approach to forecasting and minimizing electricity costs in the short-term market for distributors in Brazil
In Brazil, the electric power distributors must buy electricity on auctions one, three and five years ahead. If there is inefficiency in the contracting of electric energy, the chamber of Commercialization of Electric Energy, which enables the commercialization, can apply penalties. Thus, this paper proposes a computational approach to forecasting electricity by the class of the consumer using a multi-layer perceptron artificial neural network with a backpropagation algorithm and a prediction using time series techniques through the Bayesian and Akaike selection criteria. The forecast of electricity consumption can serve as support in the purchase of electricity in auctions in the regulated contracting environment and in the process of settlement of differences and for energy management, customer service, and distributor billing. The results show that a multilayer network with a backpropagation algorithm is able to learn the behavior of the data that influences the electric energy consumed by consumption class and can be used to follow the evolution in the demand of each class of consumption and, consequently, to help distributors in the process of contracting of electricity, reduce losses like fines, and reduce the costs of the energy distributor
Sistemas aquosos bifásicos uma ferramenta sustentável para a extração de ácido clavulânico a partir de diferentes fontes
O ácido clavulânico (AC) Ă© um inibidor de β-lactamases que tem vindo a ser largamente utilizado na área mĂ©dica. Embora seja de extrema importância, o desenvolvimento de processos alternativos de produção e purificação Ă© ainda insignificante, sendo fundamental o estudo de tĂ©cnicas de extração mais biocompatĂveis, como os Sistemas Aquosos Bifásicos (SABs). Assim, este trabalho objetivou o estudo de Sistemas Aquosos Bifásicos baseados em polĂmeros como uma ferramenta alternativa para a extração de AC. Foram testados dois SPAB compostos por Polietileno Glicol (PEG) com massa molecular (M) de 4000 g/mol e Poliacrilato de SĂłdio de 8000 g/mol, nos quais foi alterado o eletrĂłlito indutor da formação de fases, em particular, sulfato de sĂłdio (Na2SO4,) e cloreto de sĂłdio (NaCl). Ademais, este trabalho visou tambĂ©m avaliar a eficiĂŞncia de extração do AC, bem como compreender o efeito dos contaminantes no processo de migração. Para tal, foi avaliada a extração do AC a partir de trĂŞs fontes distintas: solução pura (99,9%); solução comercial (60%); diretamente a partir do sobrenadante de um meio fermentando de Streptomyces clavuligerus. Os resultados obtidos demonstraram que independentemente da fonte inicial do AC, ambos os SABs polimĂ©ricos promoveram uma partição preferencial do AC para a fase rica em PEG, sendo o coeficiente de partição maior nos sistemas com Na2SO4 do que com NaCl. ApĂłs identificar a grande capacidade de partição de AC, o SAB com PEG/NaPA/Na2SO4 foi tambĂ©m utilizado para avaliar a partição de proteĂnas presente no meio fermentado, sendo tambĂ©m obtida uma preferencial partição destas para a fase rica em PEG. Assim, apesar da baixa capacidade de purificação de AC frente a proteĂnas contaminantes, os SABs estudados demonstraram que podem ser uma tĂ©cnica alternativa sustentável e bastante econĂ´mica para uma etapa inicial de clarificação/concentração de bioprodutos a partir de caldos fermentados
Improved methods for detection of β-galactosidase (lacZ) activity in hard tissue
The ß-galactosidase gene (lacZ) of Escherichia coli is widely used as a reporter gene. The expression of lacZ can be detected by enzyme-based histochemical staining using chromogenic substrates such as 5-bromo-4-chloro-3-indolyl-ß-D: -galactoside (X-gal). Because the enzymatic activity of lacZ is vulnerable to high temperatures and acid treatment for demineralization, detection of lacZ on paraffinized sections is difficult, especially for hard tissues, which require demineralization before sectioning in paraffin. To circumvent this problem, whole-mount X-gal staining before sectioning is performed. However, detection of lacZ activity in the center of larger portions of hard whole adult tissues is challenging. In this study, focusing on fixation procedures, we determined the conditions conducive to improved detection of lacZ activity in deeper areas of whole tissues. We used an annexin a5 (Anxa5)-lacZ reporter mouse model in which the Anxa5 expression in hard tissue is indicated by lacZ activity. We found that lacZ activity could be detected throughout the periodontal ligament of adult mice when fixed in 100% acetone, whereas it was not detected in the periodontal ligament around the root apex fixed in glutaraldehyde and paraformaldehyde. This staining could not be detected in wild-type mice. Acetone maintains the lacZ activity within 48 h of fixation at both 4°C and at room temperature. In conclusion, acetone is the optimal fixative to improve permeability for staining of lacZ activity in large volumes of adult hard tissues
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