Hamiltonization of Nonholonomic Systems and the Inverse Problem of the Calculus of Variations

We introduce a method which allows one to recover the equations of motion of a class of nonholonomic systems by finding instead an unconstrained Hamiltonian system on the full phase space, and to restrict the resulting canonical equations to an appropriate submanifold of phase space. We focus first on the Lagrangian picture of the method and deduce the corresponding Hamiltonian from the Legendre transformation. We illustrate the method with several examples and we discuss its relationship to the Pontryagin maximum principle.Comment: 23 pages, accepted for publication in Rep. Math. Phy

Correlação entre estado nutricional e ingestão alimentar em pacientes de hemodiálise

BACKGROUND: Patients in end-stage renal disease often suffer from poor appetite, various comorbidities, and dietary restrictions. Despite regular hemodialysis, nutritional imbalances are frequently reported. Aiming to correlate nutritional status with food ingestion, a prospective study was done in an outpatient group. METHODS: Stable patients undergoing chronic hemodialysis for at least 3 months (n = 44) were investigated by dietary recall and standard anthropometric, biochemical, and bioimpedance determinations, including subjective and objective global assessment. The mean age of the group was 47.0 ± 16.9 years, and 63.6% were men. Body mass index was 22.2 ± 3.9 kg/m² (mean ± SD), calorie intake was 1471 ± 601 kcal/day (20.7 ± 6.7 kcal/kg/day), and protein ingestion was 74.3 ± 16.6 g protein/day (1.2 g/kg/day). Dietary and clinical findings were correlated with nutritional indices by linear regression analysis. RESULTS: Malnutrition estimated by subjective global assessment was very common (>;90%), despite the fact that body mass index and serum albumin were within an acceptable range in the majority of the population. Objective global assessment yelded roughly comparable numerical findings, with 6.8% being well nourished, 61.4% at nutritional risk or lightly undernourished, 29.6% moderately malnourished, and 2.3% severely malnourished. Total calorie intake was devoid of associations, but protein, carbohydrate, and lipid input positively correlated with triceps skinfold (P=.02). Lipid ingestion was the only marker directly associated with arm circumference, and it correlated with body mass index, as well as with total body fat (bioimpedance analysis) (POBJETIVOS: Pacientes em fase final de enfermidade renal frequentemente sofrem de falta de apetite, várias comorbidades e restrições dietéticas, e a despeito de hemodiálise regular, desequilíbrios nutricionais são frequentemente relatados. Com o propósito de correlacionar estado nutricional com ingestão alimentar, um estudo prospectivo foi realizado com pacientes ambulatoriais. MÉTODOS: Doentes estáveis sibmetidos a hemodiálise crônica por no mínimo 3 meses (n= 44) foram investigados mediante recordatório alimentar e determinações convencionais antropométricas, bioquímicas e de bioimpedância , incluindo-se avaliação global subjetiva e também objetiva. A idade do grupo era de 47.0 ± 16.9 anos com 63.6% de homens. O índice de massa corporal situava-se em 22.2 ± 3.9 kg/m2, a ingestão calórica foi de 1471 ± 601 kcal/dia (20.7 ± 6.7 kcal/kg/dia) e o consumo proteico atingiu 74.3 ± 16.6 g proteina/dia (1.2 g/kg/dia) . As variáveis dietéticas e clínicas foram correlacionadas com os índices nutricionais através da análise de regressão linear. RESULTADOS: A desnutrição estimada pela avalia;áo global subjetiva foi muito comum (>;90%), apesar de que o índice de massa corporal e a taxa de albumina estavam aceitáveis na maioria da população. A avaliação objetiva global evidenciou resultados numericamente parecidos, com 6,8% bem nutridos, 61,4% com risco nutricional ou desnutrição leve, 29,6% no patamar moderado e 2,3% exibindo desnutrição grave. O ganho calórico total não apresentou associações, todavia ingressos de proteina, carboidratos e lípides se correlacionaram positivamente com a prega cutânea do tríceps (P=0.02). Apenas a ingestão lipídica associou-se diretamente com a circunferência do braço, demonstrando ainda correlação com o índice de massa corporal bem como com a gordura corpórea total (bioimpedância) (

Gauge Theories with Lorentz-Symmetry Violation by Symplectic Projector Method

The violation of Lorentz symmetry is studied from the point of view of a canonical formulation. We make the usual analysis on the constraints structure of the Carroll-Field-Jackiw model. In this context we derive the equations of motion for the physical variables and check out the dispersion relations obtained from them. Therefore, by the analysis using Symplectic Projector Method (SPM), we can check the results about this type of Lorentz breaking with those in the recent literature: in this sense we can confirm that the configuration of $v^{\mu}$ space-like is stable, and the $v^{\mu}$ time-like carry tachionic modes.Comment: 7 pages and no figure

Time of arrival in the presence of interactions

We introduce a formalism for the calculation of the time of arrival t at a space point for particles traveling through interacting media. We develop a general formulation that employs quantum canonical transformations from the free to the interacting cases to construct t in the context of the Positive Operator Valued Measures. We then compute the probability distribution in the times of arrival at a point for particles that have undergone reflection, transmission or tunneling off finite potential barriers. For narrow Gaussian initial wave packets we obtain multimodal time distributions of the reflected packets and a combination of the Hartman effect with unexpected retardation in tunneling. We also employ explicitly our formalism to deal with arrivals in the interaction region for the step and linear potentials.Comment: 20 pages including 5 eps figure

Seagrass and submerged aquatic vegetation (VAS) habitats off the Coast of Brazil: state of knowledge, conservation and main threats

Seagrass meadows are among the most threatened ecosystems on earth, raising concerns about the equilibrium of coastal ecosystems and the sustainability of local fisheries. The present review evaluated the current status of the research on seagrasses and submerged aquatic vegetation (SAV) habitats off the coast of Brazil in terms of plant responses to environmental conditions, changes in distribution and abundance, and the possible role of climate change and variability. Despite an increase in the number of studies, the communication of the results is still relatively limited and is mainly addressed to a national or regional public; thus, South American seagrasses are rarely included or cited in global reviews and models. The scarcity of large-scale and long-term studies allowing the detection of changes in the structure, abundance and composition of seagrass habitats and associated species still hinders the investigation of such communities with respect to the potential effects of climate change. Seagrass meadows and SAV occur all along the Brazilian coast, with species distribution and abundance being strongly influenced by regional oceanography, coastal water masses, river runoff and coastal geomorphology. Based on these geomorphological, hydrological and ecological features, we characterised the distribution of seagrass habitats and abundances within the major coastal compartments. The current conservation status of Brazilian seagrasses and SAV is critical. The unsustainable exploitation and occupation of coastal areas and the multifold anthropogenic footprints left during the last 100 years led to the loss and degradation of shoreline habitats potentially suitable for seagrass occupation. Knowledge of the prevailing patterns and processes governing seagrass structure and functioning along the Brazilian coast is necessary for the global discussion on climate change. Our review is a first and much-needed step toward a more integrated and inclusive approach to understanding the diversity of coastal plant formations along the Southwestern Atlantic coast as well as a regional alert the projected or predicted effects of global changes on the goods and services provided by regional seagrasses and SAV

Thrombosis in vasculitis: from pathogenesis to treatment

In recent years, the relationship between inflammation and thrombosis has been deeply investigated and it is now clear that immune and coagulation systems are functionally interconnected. Inflammation-induced thrombosis is by now considered a feature not only of autoimmune rheumatic diseases, but also of systemic vasculitides such as Behçet’s syndrome, ANCA-associated vasculitis or giant cells arteritis, especially during active disease. These findings have important consequences in terms of management and treatment. Indeed, Behçet’syndrome requires immunosuppressive agents for vascular involvement rather than anticoagulation or antiplatelet therapy, and it is conceivable that also in ANCA-associated vasculitis or large vessel-vasculitis an aggressive anti-inflammatory treatment during active disease could reduce the risk of thrombotic events in early stages. In this review we discuss thrombosis in vasculitides, especially in Behçet’s syndrome, ANCA-associated vasculitis and large-vessel vasculitis, and provide pathogenetic and clinical clues for the different specialists involved in the care of these patients