Models for the 3-D axisymmetric gravitational potential of the Milky Way Galaxy - A detailed modelling of the Galactic disk

Aims. Galaxy mass models based on simple and analytical functions for the density and potential pairs have been widely proposed in the literature. Disk models constrained by kinematic data alone give information on the global disk structure only very near the Galactic plane. We attempt to circumvent this issue by constructing disk mass models whose three-dimensional structures are constrained by a recent Galactic star counts model in the near-infrared and also by observations of the hydrogen distribution in the disk. Our main aim is to provide models for the gravitational potential of the Galaxy that are fully analytical but also with a more realistic description of the density distribution in the disk component. Methods. From the disk model directly based on the observations (here divided into the thin and thick stellar disks and the HI and H$_2$ disks subcomponents), we produce fitted mass models by combining three Miyamoto-Nagai disk profiles of any "model order" (1, 2, or 3) for each disk subcomponent. The Miyamoto-Nagai disks are combined with models for the bulge and "dark halo" components and the total set of parameters is adjusted by observational kinematic constraints. A model which includes a ring density structure in the disk, beyond the solar Galactic radius, is also investigated. Results. The Galactic mass models return very good matches to the imposed observational constraints. In particular, the model with the ring density structure provides a greater contribution of the disk to the rotational support inside the solar circle. The gravitational potential models and their associated force-fields are described in analytically closed forms, and in addition, they are also compatible with our best knowledge of the stellar and gas distributions in the disk component. The gravitational potential models are suited for investigations of orbits in the Galactic disk.Comment: 22 pages, 13 figures, 11 tables, accepted for publication in A&

Coding for Cryptographic Security Enhancement using Stopping Sets

In this paper we discuss the ability of channel codes to enhance cryptographic secrecy. Toward that end, we present the secrecy metric of degrees of freedom in an attacker's knowledge of the cryptogram, which is similar to equivocation. Using this notion of secrecy, we show how a specific practical channel coding system can be used to hide information about the ciphertext, thus increasing the difficulty of cryptographic attacks. The system setup is the wiretap channel model where transmitted data traverse through independent packet erasure channels with public feedback for authenticated ARQ (Automatic Repeat reQuest). The code design relies on puncturing nonsystematic low-density parity-check codes with the intent of inflicting an eavesdropper with stopping sets in the decoder. Furthermore, the design amplifies errors when stopping sets occur such that a receiver must guess all the channel-erased bits correctly to avoid an expected error rate of one half in the ciphertext. We extend previous results on the coding scheme by giving design criteria that reduces the effectiveness of a maximum-likelihood attack to that of a message-passing attack. We further extend security analysis to models with multiple receivers and collaborative attackers. Cryptographic security is enhanced in all these cases by exploiting properties of the physical-layer. The enhancement is accurately presented as a function of the degrees of freedom in the eavesdropper's knowledge of the ciphertext, and is even shown to be present when eavesdroppers have better channel quality than legitimate receivers.Comment: 13 pages, 8 figure

Optimal switching of a nanomagnet assisted by microwaves

We develop an efficient and general method for optimizing the microwave field that achieves magnetization switching with a smaller static field. This method is based on optimal control and renders an exact solution for the 3D microwave field that triggers the switching of a nanomagnet with a given anisotropy and in an oblique static field. Applying this technique to the particular case of uniaxial anisotropy, we show that the optimal microwave field, that achieves switching with minimal absorbed energy, is modulated both in frequency and in magnitude. Its role is to drive the magnetization from the metastable equilibrium position towards the saddle point and then damping induces the relaxation to the stable equilibrium position. For the pumping to be efficient, the microwave field frequency must match at the early stage of the switching process the proper precession frequency of the magnetization, which depends on the magnitude and direction of the static field. We investigate the effect of the static field (in amplitude and direction) and of damping on the characteristics of the microwave field. We have computed the switching curves in the presence of the optimal microwave field. The results are in qualitative agreement with micro-SQUID experiments on isolated nanoclusters. The strong dependence of the microwave field and that of the switching curve on the damping parameter may be useful in probing damping in various nanoclusters.Comment: 9 pages, 8 figure

Integração das tecnologias sociais Barraginhas e Lago de Múltiplo Uso.

A integração das tecnologias sociais barraginhas e lago de múltiplo uso vêm garantindo sustentabilidade hídrica para agricultores familiares, viabilizando criatórios de peixes e irrigação de hortas. No município de Araçaí-MG, comunidade Fazendinhas Pai José, em um solo seco sob vegetação de Cerrado, com predominância de latossolos vermelho e amarelo, porosos e profundos, após reuniões com a comunidade, foram construídas 96 barraginhas no ano de 2008 e 90 em 2009, para colher a água dos escorrimentos superficiais das chuvas: as enxurradas. Ao contê-las, foram reduzidas também as erosões e assoreamentos. As barraginhas são carregadas e descarregadas de 10 a 12 vezes por ano, infiltrando e elevando o lençol freático, umedecendo o solo em torno das mesmas e nas baixadas, amenizando secas, revitalizando córregos. Foi observado aumento do nível das cisternas de quatro para 10 a 11m de coluna de água, gerando nos agricultores sentimento de abundância. Isso viabilizou a construção de lagos impermeabilizado com lona de plástico comum para armazenamento de água durante o período seco, pelo bombeamento de água das cisternas, o que viabilizou a criação de peixes e ainda irrigação de hortas. De forma complementar, no período chuvoso, os lagos são abastecidos também por água captada por telhados. A experiência já foi reaplicada em mais dois municípios vizinhos e poderá ser extrapolada aos estados do Brasil central, onde predominam solos e condições similares

Integração entre Barraginhas e lagos de múltiplo uso: o aproveitamento eficiente da água de chuva para o desenvolvimento rural.

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Litter deposition in integrated agricultural systems in the Brazilian Cerrado.

In agro-ecosystems, litter is a major component, comprising material that is deposited in the soil by fauna and flora. Integrated crop-livestock systems (ICL) and crop-livestock-forest systems (ICLF) are expected to enhance the use of plant biological cycle. Therefore, this study aimed to characterize litter deposition in integrated systems at the Brazilian Savannah, the Cerrado in Mato Grosso do Sul State, Brazil

Flashing annihilation term of a logistic kinetic as a mechanism leading to Pareto distributions

It is shown analytically that the flashing annihilation term of a Verhulst kinetic leads to the power--law distribution in the stationary state. For the frequency of switching slower than twice the free growth rate this provides the quasideterministic source of a Levy noises at the macroscopic level.Comment: 1 fi