Search

A first-order gauge invariant formulation for the two-dimensional quantum rigid rotor is long known in the theoretical physics community as an isolated peculiar model. Parallel to that fact, the longstanding constraints abelianization problem, aiming at the conversion from second to first class systems for quantization purposes, has been approached a number of times in the literature with a handful of different forms and techniques and still continues to be a source of lively and interesting discussions. Connecting these two points, we develop a new systematic method for converting second class systems to first class ones, valid for a class of systems encompassing the quantum rigid rotor as a special case. In particular the gauge invariance of the quantum rigid rotor is fully clarified and generalized in the context of arbitrary translations along the radial momentum direction. Our method differs substantially from previous ones as it does not rely neither on the introduction of new auxiliary variables nor on the a priori interpretation of the second class constraints as coming from a gauge-fixing process.

The present study aimed to investigate human balance control by assessing postural sway on three groups representing three stages of life (6-12, 19-40 and 65-74 years old). There were 14 individuals in each group and they were tested during upright bipedal stance with either eyes open or closed. Focus was given to multiple sway indices representing multi-dimensional features of postural sway in quiet stance and included: the center of pressure area, amplitude, root mean square (RMS), velocity, jerkiness, and sample entropy. Results confirmed that children and seniors swayed more (p<.004), faster (p<.001) and their body sway was shakier (p<.001) than young adults. Seniors also presented faster (p<.006) and shakier (p<.001) sway than children and a more unpredictable pattern of body sway in time (p<.002) than children and young adults. In addition, children presented a more random anterior-posterior sway (p<.034) and a more regular medio-lateral sway (p<.043) than young adults, and a higher synchronization between anterior-posterior and medio-lateral body sway (p<.012) than young adults and seniors. We also observed that postural control of children and young adults becomes relatively more challenged in experimental situations when eyes were closed for most postural indices. In conclusion, this study suggests that multi-dimension posturography is sensitive to detect subtle age-related changes in the postural behavior and each stage of life may have their own signature patterns of postural behavior. Therefore, we expect that quantifications of this nature may be used to assess not only postural instability and fall risk but also to aid the testing of the efficacy of balance interventional protocols.

The aim of this study was to evaluate ruminant and monogastric animal manure co-digested with 10 % of manipueira through process monitoring parameters and biogas production. In this study, eight semi-continuous digesters, with a capacity of 7.8 liters of substrate in fermentation, operated with 30 days of hydraulic retention time, were used. Monitoring analyses were performed in order to assess: pH, total ammonia nitrogen (TAN) concentration, partial alkalinity (PA), content and biogas yield (m3·kg·Volatile Solids (VS)added-1). There was no statistic difference for all the pH values, which reached values around 6.8 to 8.0. For PA, all the substrates reached higher than 1.200 mg·L-1 values as recommended. During the process, there was no risk of failure due to TAN concentration. The average biogas productions accumulated per week were 0.00676; 0.01167; 0.01515 and 0.01856 m3 for substrates composed by dairy cattle, sheep, poultry and swine manure co-digested with manipueira, respectively. The biogas yield for those respective substrates were 0.122; 0.275; 0.535 e 0.843 m3·kg·VSadded-1. The highest biogas yield was obtained for anaerobic co-digestion of swine manure with 10 % (volume/volume) of manipueira., Objetivou-se avaliar o uso de manipueira na co-digestão anaeróbia com dejetos de animais monogástricos e ruminantes, por meio de parâmetros de monitoramento do processo e da produção de biogás. Foram utilizados oito biodigestores semicontínuos com volume útil de 7,8 L de substrato em fermentação operados com tempo de retenção hidráulica de 30 dias. Realizou-se análises de pH, nitrogênio amoniacal, alcalinidade parcial (AP), sólidos totais (ST), sólidos voláteis (SV), e rendimento do biogás (m3 kg SVadicionados-1). Os valores de pH e concentrações de AP apresentaram-se na faixa ideal para a ocorrência do processo de digestão, de 6,0 a 8,0 e acima de 1.200 mg·L-1, respectivamente. Durante o processo não houve risco de falência por concentrações de nitrogênio amoniacal. As produções médias de biogás acumuladas semanais foram de 0,00676, 0,1167, 0,01515 e 0,01856 m3, respectivamente para substratos formados por dejetos de bovinos de leite, ovinos, aves e/ou suínos codigeridos com manipueira. Os rendimentos para os respectivos substratos foram 0,122, 0,275, 0,535 e 0,843 m3 kg SVadicionados-1. Maiores produções de biogás são obtidas na co-digestão anaeróbia de dejetos de suínos com 10 % (volume/volume) de manipueira.

The aim of this study was to evaluate the potential of biogas production from manure of swine fed with diets containing different levels of net energy and ractopamine. The experiment was carried out in a 2x5 factorial arrangement (ractopamine = 0 and 10 ppm, and net energy = 2 300, 2 425, 2 550, 2 675 and 2 800 kcal kg-1). Semi-continuous bench digesters were used at an hidraulic retention time (HRT) of 30 days and daily loads for 90 days. Biogas production was measured weekly; analyzes for pH, ammoniacal nitrogen, alkalinity, total nitrogen and total phosphorus were carried out. The results from monitoring analyses showed that there were no risks of failure of the anaerobic digestion process. There was no interaction between levels of net energy and ractopamine concentration, and there was no effect of ractopamine addition on the biogas production (average of 0.07723 m3 kg-1). There was a linear increase (p< 0.05) for biogas production and volumetric biogas production when net energy in the diets increased. Ractopamine as an additive in the diet for swine does not affect the volumetric biogas potential of the swine manure. Greatest potential for biogas production are obtained from manure from animals fed on higher levels of net energy., Objetivou-se avaliar os potenciais de produção de biogás de dejetos de suínos alimentados com dietas com diferentes níveis de energia líquida e ractopamina. Utilizou-se o delineamento em blocos casualizados (DBC) em esquema fatorial 2x5 (0 e 10 ppm de ractopamina e 2 300; 2 425; 2 550; 2 675 e 2 800 kcal kg-1 de energia líquida). Utilizaram-se biodigestores semicontínuos de bancada com tempo de retenção hidráulica (TRH) de 30 dias e cargas diárias por 90 dias. Foram mensuradas semanalmente as produções de biogás e efetuadas análises de pH, nitrogênio amoniacal, alcalinidade, nitrogênio total e fósforo total. Os resultados das análises de monitoramento mostraram que não houve riscos de falência do processo de biodigestão anaeróbia. Não houve interação entre os níveis de energia líquida e as concentrações de ractopamina, e não houve efeito de suplementação com ou sem ractopamina na produção e nos potenciais de produção de biogás (média de 0,07723 m3 kg-1 de dejetos). Constatou-se aumento linear (p< 0,05) para a produção e potenciais de produção de biogás dos dejetos à medida que os níveis de energia líquida nas dietas aumentaram. O fornecimento da ractopamina para os suínos não interfere nos potenciais de produção de biogás por seus dejetos. Maiores potenciais de produção de biogás são obtidos quando são utilizados dejetos produzidos por animais que receberam maiores níveis de energia líquida.

The aim of this study was to evaluate ruminant and monogastric animal manure co-digested with 10 % of manipueira through process monitoring parameters and biogas production. In this study, eight semi-continuous digesters, with a capacity of 7.8 liters of substrate in fermentation, operated with 30 days of hydraulic retention time, were used. Monitoring analyses were performed in order to assess: pH, total ammonia nitrogen (TAN) concentration, partial alkalinity (PA), content and biogas yield (m3·kg·Volatile Solids (VS)added-1). There was no statistic difference for all the pH values, which reached values around 6.8 to 8.0. For PA, all the substrates reached higher than 1.200 mg·L-1 values as recommended. During the process, there was no risk of failure due to TAN concentration. The average biogas productions accumulated per week were 0.00676; 0.01167; 0.01515 and 0.01856 m3 for substrates composed by dairy cattle, sheep, poultry and swine manure co-digested with manipueira, respectively. The biogas yield for those respective substrates were 0.122; 0.275; 0.535 e 0.843 m3·kg·VSadded-1. The highest biogas yield was obtained for anaerobic co-digestion of swine manure with 10 % (volume/volume) of manipueira., Objetivou-se avaliar o uso de manipueira na co-digestão anaeróbia com dejetos de animais monogástricos e ruminantes, por meio de parâmetros de monitoramento do processo e da produção de biogás. Foram utilizados oito biodigestores semicontínuos com volume útil de 7,8 L de substrato em fermentação operados com tempo de retenção hidráulica de 30 dias. Realizou-se análises de pH, nitrogênio amoniacal, alcalinidade parcial (AP), sólidos totais (ST), sólidos voláteis (SV), e rendimento do biogás (m3 kg SVadicionados-1). Os valores de pH e concentrações de AP apresentaram-se na faixa ideal para a ocorrência do processo de digestão, de 6,0 a 8,0 e acima de 1.200 mg·L-1, respectivamente. Durante o processo não houve risco de falência por concentrações de nitrogênio amoniacal. As produções médias de biogás acumuladas semanais foram de 0,00676, 0,1167, 0,01515 e 0,01856 m3, respectivamente para substratos formados por dejetos de bovinos de leite, ovinos, aves e/ou suínos codigeridos com manipueira. Os rendimentos para os respectivos substratos foram 0,122, 0,275, 0,535 e 0,843 m3 kg SVadicionados-1. Maiores produções de biogás são obtidas na co-digestão anaeróbia de dejetos de suínos com 10 % (volume/volume) de manipueira.

The aim of this study was to evaluate the potential of biogas production from manure of swine fed with diets containing different levels of net energy and ractopamine. The experiment was carried out in a 2x5 factorial arrangement (ractopamine = 0 and 10 ppm, and net energy = 2 300, 2 425, 2 550, 2 675 and 2 800 kcal kg-1). Semi-continuous bench digesters were used at an hidraulic retention time (HRT) of 30 days and daily loads for 90 days. Biogas production was measured weekly; analyzes for pH, ammoniacal nitrogen, alkalinity, total nitrogen and total phosphorus were carried out. The results from monitoring analyses showed that there were no risks of failure of the anaerobic digestion process. There was no interaction between levels of net energy and ractopamine concentration, and there was no effect of ractopamine addition on the biogas production (average of 0.07723 m3 kg-1). There was a linear increase (p< 0.05) for biogas production and volumetric biogas production when net energy in the diets increased. Ractopamine as an additive in the diet for swine does not affect the volumetric biogas potential of the swine manure. Greatest potential for biogas production are obtained from manure from animals fed on higher levels of net energy., Objetivou-se avaliar os potenciais de produção de biogás de dejetos de suínos alimentados com dietas com diferentes níveis de energia líquida e ractopamina. Utilizou-se o delineamento em blocos casualizados (DBC) em esquema fatorial 2x5 (0 e 10 ppm de ractopamina e 2 300; 2 425; 2 550; 2 675 e 2 800 kcal kg-1 de energia líquida). Utilizaram-se biodigestores semicontínuos de bancada com tempo de retenção hidráulica (TRH) de 30 dias e cargas diárias por 90 dias. Foram mensuradas semanalmente as produções de biogás e efetuadas análises de pH, nitrogênio amoniacal, alcalinidade, nitrogênio total e fósforo total. Os resultados das análises de monitoramento mostraram que não houve riscos de falência do processo de biodigestão anaeróbia. Não houve interação entre os níveis de energia líquida e as concentrações de ractopamina, e não houve efeito de suplementação com ou sem ractopamina na produção e nos potenciais de produção de biogás (média de 0,07723 m3 kg-1 de dejetos). Constatou-se aumento linear (p< 0,05) para a produção e potenciais de produção de biogás dos dejetos à medida que os níveis de energia líquida nas dietas aumentaram. O fornecimento da ractopamina para os suínos não interfere nos potenciais de produção de biogás por seus dejetos. Maiores potenciais de produção de biogás são obtidos quando são utilizados dejetos produzidos por animais que receberam maiores níveis de energia líquida.

In this paper, we study zigzag graphene nanoribbons with edges reconstructed with Stone-Wales defects, by means of an empirical (first-neighbor) tight-binding method, with parameters determined by ab initio calculations of very narrow ribbons. We explore the characteristics of the electronic band structure with a focus on the nature of edge states. Edge reconstruction allows the appearance of a new type of edge states. They are dispersive, with nonzero amplitudes in both sublattices; furthermore, the amplitudes have two components that decrease with different decay lengths with the distance from the edge; at the Dirac points one of these lengths diverges, whereas the other remains finite, of the order of the lattice parameter. We trace this curious effect to the doubling of the unit cell along the edge, brought about by the edge reconstruction. In the presence of a magnetic field, the zero-energy Landau level is no longer degenerate with edge states as in the case of the pristine zigzag ribbon.

In this paper, we study zigzag graphene nanoribbons with edges reconstructed with Stone-Wales defects, by means of an empirical (first-neighbor) tight-binding method, with parameters determined by ab initio calculations of very narrow ribbons. We explore the characteristics of the electronic band structure with a focus on the nature of edge states. Edge reconstruction allows the appearance of a new type of edge states. They are dispersive, with nonzero amplitudes in both sublattices; furthermore, the amplitudes have two components that decrease with different decay lengths with the distance from the edge; at the Dirac points one of these lengths diverges, whereas the other remains finite, of the order of the lattice parameter. We trace this curious effect to the doubling of the unit cell along the edge, brought about by the edge reconstruction. In the presence of a magnetic field, the zero-energy Landau level is no longer degenerate with edge states as in the case of the pristine zigzag ribbon.

In this paper, we study zigzag graphene nanoribbons with edges reconstructed with Stone-Wales defects, by means of an empirical (first-neighbor) tight-binding method, with parameters determined by ab initio calculations of very narrow ribbons. We explore the characteristics of the electronic band structure with a focus on the nature of edge states. Edge reconstruction allows the appearance of a new type of edge states. They are dispersive, with nonzero amplitudes in both sublattices; furthermore, the amplitudes have two components that decrease with different decay lengths with the distance from the edge; at the Dirac points one of these lengths diverges, whereas the other remains finite, of the order of the lattice parameter. We trace this curious effect to the doubling of the unit cell along the edge, brought about by the edge reconstruction. In the presence of a magnetic field, the zero-energy Landau level is no longer degenerate with edge states as in the case of the pristine zigzag ribbon.

We demonstrate that the electronic gap of a graphene bilayer can be controlled externally by applying a gate bias. From the magnetotransport data (Shubnikov–de Haas measurements of the cyclotron mass), and using a tight-binding model, we extract the value of the gap as a function of the electronic density.We show that the gap can be changed from zero to midinfrared energies by using fields of & 1 V=nm, below the electric breakdown of SiO2. The opening of a gap is clearly seen in the quantum Hall regime.

We propose a recursive procedure to estimate the microcanonical density of states in multicanonical Monte Carlo simulations which relies only on measurements of moments of the energy distribution, avoiding entirely the need for energy histograms. This method yields directly a piecewise analytical approximation to the microcanonical inverse temperature beta(E) and allows improved control over the statistics and efficiency of the simulations. We demonstrate its utility in connection with recently proposed schemes for improving the efficiency of multicanonical sampling, either with adjustment of the asymptotic energy distribution or with the replacement of single spin flip dynamics with collective updates.

We present an exact solution of a one-dimensional Ising chain with both nearest-neighbor and random long-range interactions. Not surprisingly, the solution confirms the mean-field character of the transition. This solution also predicts the finite-size scaling that we observe in numerical simulations.