Nondispersive analytical solutions to the Dirac equation

This paper presents new analytic solutions to the Dirac equation employing a recently introduced method that is based on the formulation of spinorial fields and their driving electromagnetic fields in terms of geometric algebras. A first family of solutions describe the shape-preserving translation of a wavepacket along any desired trajectory in the x-y plane. In particular, we show that the dispersionless motion of a Gaussian wavepacket along both elliptical and circular paths can be achieved with rather simple electromagnetic field configurations. A second family of solutions involves a plane electromagnetic wave and a combination of generally inhomogeneous electric and magnetic fields. The novel analytical solutions of the Dirac equation given here provide important insights into the connection between the quantum relativistic dynamics of electrons and the underlying geometry of the Lorentz group

Brazil: economic study of cassava

A series of studies were carried out in Brazil, on a regional basis, to determine how cassava can fit into the Brazilian agricultural economy in the future so as to assist the country in reaching policy goals (improved welfare of the rural community and increased availability of low-priced food). The recent developments in the Brazilian agricultural sector are summarized with emphasis on agricultural policies and on the balance between food production and exports. Urbanization as well as wheat subsidies have reduced the importance of cassava. Current policies, however, are found to favor food crops such as cassava that are produced by the small farmers. Trends in cassava for human food and its future potential role are also analyzed. The role of farinha as a staple food should be improved; increased per capita consumption will depend on better availability, better quality, and lower prices. To increase the consumption of fresh cassava, it is necessary to reduce marketing margins. The reduction of production costs of cassava starch is also crucial. The rapidly expanding feed industry is discussed with reference to cassava supply. Improved production technology would mean increased benefits to both producers and consumers. A dried cassava industry would reduce the need to import maize, stabilize on-farm prices of cassava, and extend the market size of the crop, particularly in NE Brazil. The cost structure of cassava production and processing is analyzed from the viewpoint of the cassava's future role as a source of rural income and its contribution to the food and feed supply. (CIAT)Se realizo una serie de estudios en Brasil, a nivel regional, para determinar el papel de la yuca en la economia agricola brasilera del futuro y ayudar a alcanzar las metas propuestas en las diferentes politicas (mayor bienestar de la comunidad rural y mayor disponibilidad de alimentos a bajo costo). Se resumen los ultimos avances en el sector agricola brasilero, con enfasis en las politicas agricolas y en el balance entre produccion de alimentos y exportaciones. La urbanizacion y los subsidios al trigo le han restado importancia a la yuca. Las politicas actuales, sin embargo, favorecen los cultivos alimenticios, como la yuca, producidos por pequenos agricultores. Tambien se analizan las tendencias del uso de la yuca en la alimentacion humana y su potencial futuro. Se debe mejorar el papel de la farinha como alimento basico; el aumento en el consumo per capita dependera de una mayor disponibilidad, una mejor calidad y precios mas bajos. Para aumentar el consumo de raices frescas es necesario reducir los margenes de mercadeo. Tambien es importante la reduccion de los costos de produccion del almidon de yuca. Se discute la creciente industria de alimentos para animales con referencia a la oferta de yuca. Un tecnologia de produccion mejorada significaria mayor beneficio tanto para los productores como para los consumidores. Una industria de yuca seca reduciria la necesidad de importar maiz, estabilizaria los precios de la yuca a nivel de finca y ampliaria el mercado del cultivo, particularmente en el nordeste del Brasil. Se analiza la estructura de los costos de produccion y procesamiento de la yuca desde el punto de vista de su futuro papel como fuente de ingresos a nivel rural y su contribucion a la oferta de alimentos para humanos y animales. (CIAT

Effect Of Inhibition Of Nitric Oxide Synthase On Blood Pressure And Renal Sodium Handling In Renal Denervated Rats.

The role of sympathetic nerve activity in the changes in arterial blood pressure and renal function caused by the chronic administration of N G-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) synthesis, was examined in sham and bilaterally renal denervated rats. Several studies have demonstrated that sympathetic nerve activity is elevated acutely after L-NAME administration. To evaluate the role of renal nerve activity in L-NAME-induced hypertension, we compared the blood pressure response in four groups (N = 10 each) of male Wistar-Hannover rats weighing 200 to 250 g: 1) sham-operated vehicle-treated, 2) sham-operated L-NAME-treated, 3) denervated vehicle-treated, and 4) denervated L-NAME-treated rats. After renal denervation or sham surgery, one control week was followed by three weeks of oral administration of L-NAME by gavage. Arterial pressure was measured weekly in conscious rats by a tail-cuff method and renal function tests were performed in individual metabolic cages 0, 7, 14 and 21 days after the beginning of L-NAME administration. L-NAME (60 mg kg-1 day-1) progressively increased arterial pressure from 108 +/- 6.0 to 149 +/- 12 mmHg (P<0.05) in the sham-operated group by the third week of treatment which was accompanied by a fall in creatinine clearance from 336 +/- 18 to 222 +/- 59 microl min-1 100 g body weight-1 (P<0. 05) and a rise in fractional urinary sodium excretion from 0.2 +/- 0. 04 to 1.62 +/- 0.35% (P<0.05) and in sodium post-proximal fractional excretion from 0.54 +/- 0.09 to 4.7 +/- 0.86% (P<0.05). The development of hypertension was significantly delayed and attenuated in denervated L-NAME-treated rats. This was accompanied by a striking additional increase in fractional renal sodium and potassium excretion from 0.2 +/- 0.04 to 4.5 +/- 1.6% and from 0.1 +/- 0.015 to 1.21 +/- 0.37%, respectively, and an enhanced post-proximal sodium excretion compared to the sham-operated group. These differences occurred despite an unchanged creatinine clearance and Na+ filtered load. These results suggest that bilateral renal denervation delayed and attenuated the L-NAME-induced hypertension by promoting an additional decrease in tubule sodium reabsorption in the post-proximal segments of nephrons. Much of the hypertension caused by chronic NO synthesis inhibition is thus dependent on renal nerve activity.33347-5

Early Detection Of Metabolic And Energy Disorders By Thermal Time Series Stochastic Complexity Analysis.

Maintenance of thermal homeostasis in rats fed a high-fat diet (HFD) is associated with changes in their thermal balance. The thermodynamic relationship between heat dissipation and energy storage is altered by the ingestion of high-energy diet content. Observation of thermal registers of core temperature behavior, in humans and rodents, permits identification of some characteristics of time series, such as autoreference and stationarity that fit adequately to a stochastic analysis. To identify this change, we used, for the first time, a stochastic autoregressive model, the concepts of which match those associated with physiological systems involved and applied in male HFD rats compared with their appropriate standard food intake age-matched male controls (n=7 per group). By analyzing a recorded temperature time series, we were able to identify when thermal homeostasis would be affected by a new diet. The autoregressive time series model (AR model) was used to predict the occurrence of thermal homeostasis, and this model proved to be very effective in distinguishing such a physiological disorder. Thus, we infer from the results of our study that maximum entropy distribution as a means for stochastic characterization of temperature time series registers may be established as an important and early tool to aid in the diagnosis and prevention of metabolic diseases due to their ability to detect small variations in thermal profile.4770-

Maternal Undernutrition And The Offspring Kidney: From Fetal To Adult Life.

Maternal dietary protein restriction during pregnancy is associated with low fetal birth weight and leads to renal morphological and physiological changes. Different mechanisms can contribute to this phenotype: exposure to fetal glucocorticoid, alterations in the components of the renin-angiotensin system, apoptosis, and DNA methylation. A low-protein diet during gestation decreases the activity of placental 11ß-hydroxysteroid dehydrogenase, exposing the fetus to glucocorticoids and resetting the hypothalamic-pituitary-adrenal axis in the offspring. The abnormal function/expression of type 1 (AT1(R)) or type 2 (AT2(R)) AngII receptors during any period of life may be the consequence or cause of renal adaptation. AT1(R) is up-regulated, compared with control, on the first day after birth of offspring born to low-protein diet mothers, but this protein appears to be down-regulated by 12 days of age and thereafter. In these offspring, AT2(R) expression differs from control at 1 day of age, but is also down-regulated thereafter, with low nephron numbers at all ages: from the fetal period, at the end of nephron formation, and during adulthood. However, during adulthood, the glomerular filtration rate is not altered, due to glomerulus and podocyte hypertrophy. Kidney tubule transporters are regulated by physiological mechanisms; Na(+)/K(+)-ATPase is inhibited by AngII and, in this model, the down-regulated AngII receptors fail to inhibit Na(+)/K(+)-ATPase, leading to increased Na(+) reabsorption, contributing to the hypertensive status. We also considered the modulation of pro-apoptotic and anti-apoptotic factors during nephrogenesis, since organogenesis depends upon a tight balance between proliferation, differentiation and cell death.431010-

Surface recombination measurements on III–V candidate materials for nanostructure light-emitting diodes

Surface recombination is an important characteristic of an optoelectronic material. Although surface recombination is a limiting factor for very small devices it has not been studied intensively. We have investigated surface recombination velocity on the exposed surfaces of the AlGaN, InGaAs, and InGaAlP material systems by using absolute photoluminescence quantum efficiency measurements. Two of these three material systems have low enough surface recombination velocity to be usable in nanoscale photonic crystal light-emitting diodes

Área foliar específica, biomassa e taxa de crescimento relativo de folhas de cultivares comerciais de Panicum maximum sob sombreamento artificial.

É necessário identificar espécies forrageiras adaptadas ao uso em sistemas silvipastoris. Neste trabalho objetivou-se avaliar o comportamento de três cultivares comerciais (cvs. Massai, Mombaça e Tanzânia) de P. maximum sob sombreamento artificial. A cada 35 dias foram feitos cortes do material vegetal e avaliou-se: área foliar específica (AFE, em cm2/g), biomassa seca (g) e taxa de crescimento relativo (TCR, em g/g/semana) das folhas. Utilizou-se o delineamento de blocos casualizados em esquema fatorial, com quatro repetições, os fatores foram: sombreamento (O, 54 e 81 %) e cortes (1, 2, 3 e 4); com análise individual de cada cultivar. Entre os cortes, não houve diferença na AFE em nenhuma das cvs. O sombreamento de 81% quase duplicou a AFE para todas as cvs., quando comparado com a testemunha. Para Tanzânia não houve interação entre cortes e sombreamento na produção de biomassa seca foliar (BSF). As plantas sob sombreamento de 54% produziram mais BSF que as plantas sob o sombreamento de 81 % ou a pleno sol. Para Massai e Mombaça houve interação entre os fatores, em geral, as plantas sob sombreamento produziram mais BSF do que as não sombreadas. Para todas as cvs., as maiores TCRs foram obtidas na primeira avaliação; nos demais intervalos de corte, todas as TCRs foram negativas. Conclui-se que as cvs avaliadas são adaptadas ao sombreamento, de até 81%; com maior produtividade sób sombreamento de 54 ou 81% do que a pleno sol

FUEL CELL: FEASIBILITY ANALYSIS OF ITS APPLICATION IN AUTOMOBILES

The need to reduce the emission of harmful gases into human life, together with the dependence on oil as a primary source of fuel for internal combustion engines (ICE), are part of the current global scenario. This scenario opens space for fuel cells (FC), technology that generates electricity as the main product of oxide-reduction reactions between Hydrogen and Oxygen. An efficient and clean alternative that appears as a possibility for the substitution of ICE. The present article proposes a model of FC and compares it technically with a conventional ICE, in order to prove the efficiency, performance and environmental impact feasibility of the use of this technology in commercial vehicles