Transient chaos and resonant phase mixing in violent relaxation

This paper explores how orbits in a galactic potential can be impacted by large amplitude time-dependences of the form that one might associate with galaxy or halo formation or strong encounters between pairs of galaxies. A period of time-dependence with a strong, possibly damped, oscillatory component can give rise to large amounts of transient chaos, and it is argued that chaotic phase mixing associated with this transient chaos could play a major role in accounting for the speed and efficiency of violent relaxation. Analysis of simple toy models involving time-dependent perturbations of an integrable Plummer potential indicates that this chaos results from a broad, possibly generic, resonance between the frequencies of the orbits and harmonics thereof and the frequencies of the time-dependent perturbation. Numerical computations of orbits in potentials exhibiting damped oscillations suggest that, within a period of 10 dynamical times t_D or so, one could achieve simultaneously both `near-complete' chaotic phase mixing and a nearly time-independent, integrable end state.Comment: 11 pages and 12 figures: an extended version of the original manuscript, containing a modified title, one new figure, and approximately one page of additional text, to appear in Monthly Notices of the Royal Astronomical Societ

Construyendo significados en mecánica cuántica : fundamentación y resultados de una propuesta innovadora para su introducción en el nivel universitario

El rápido crecimiento de una tecnología basada en los principios de la mecánica cuántica torna imperioso el conocimiento de sus fundamentos por la mayoría de los estudiantes universitarios. Siendo una de las mayores dificultades al estudiar estos temas la creación de la «nueva percepción» que la mecánica cuántica implica para el mundo microscópico, desarrollamos una unidad didáctica introductoria con un abordaje que denominamos fenomenológico-conceptual, con énfasis en las características cuánticas de los sistemas. La unidad incluyó discusiones conceptuales sobre tópicos como los de computación cuántica, efecto túnel, autointerferencia de una partícula, saltos cuánticos y la paradoja del gato de Schrödinger. Los resultados de la implementación de esta estrategia con tres grupos de estudiantes de ingeniería muestran que más de la mitad de los estudiantes participantes consiguieron una comprensión razonable de los conceptos discutidos.Technology based on the principles of Quantum Mechanics is of growing importance so it becomes imperative to offer to the future professionals at least courses on the basics of it. One of the main problems faced by students when learning this subject relates to the difficulty of creating a «new perception» for the microscopic world. To help students in this matter, we used in a introductory unit a phenomenological-conceptual approach with emphasis on the quantum characteristics of the systems, in lieu of searching for classical analogies. The unit included conceptual discussions using topics like quantum computing, teleportation, quantum tunneling, one particle self interference, quantum jumps and the Schrödinger's cat paradox. The results of the implementation of this strategy, with three groups of engineering students, showed that more than half of them attained a good understanding of the central concepts discussed

Degeneration and impaired regeneration of gray matter oligodendrocytes in amyotrophic lateral sclerosis.

Oligodendrocytes associate with axons to establish myelin and provide metabolic support to neurons. In the spinal cord of amyotrophic lateral sclerosis (ALS) mice, oligodendrocytes downregulate transporters that transfer glycolytic substrates to neurons and oligodendrocyte progenitors (NG2(+) cells) exhibit enhanced proliferation and differentiation, although the cause of these changes in oligodendroglia is unknown. We found extensive degeneration of gray matter oligodendrocytes in the spinal cord of SOD1 (G93A) ALS mice prior to disease onset. Although new oligodendrocytes were formed, they failed to mature, resulting in progressive demyelination. Oligodendrocyte dysfunction was also prevalent in human ALS, as gray matter demyelination and reactive changes in NG2(+) cells were observed in motor cortex and spinal cord of ALS patients. Selective removal of mutant SOD1 from oligodendroglia substantially delayed disease onset and prolonged survival in ALS mice, suggesting that ALS-linked genes enhance the vulnerability of motor neurons and accelerate disease by directly impairing the function of oligodendrocytes

Experimental pharmacological research regarding some new quinazolin-4-ones derivatives

A series of new compounds with quinazolin-4-one structure, synthesized by the Pharmaceutical Chemistry Department of the Faculty of Pharmacy of the University of Medicine and Pharmacy “Carol Davila” Bucharest, was studied. Five of them were selected, conventionally named S1, S2, S3, S4, S5, and investigated in terms of their potential influence on the central nervous system (CNS). For this purpose, the antidepressant effect was determined using the forced swimming test; the anxiolytic/ anxiogenic effect was determined using the suspended plus-shaped maze (Ugo Basile); the effect on the motor activity was determined using the Ugo Basile activity cage; and the potential analgesic effect was investigated using the hot plate test (Ugo Basile). Compounds S3 and S5 lowered the motor activity and showed an anxiolytic effect, while S1 and S2 proved to have antidepressant and analgesic effects. A good correlation between antidepressant and analgesic effects was observed, consistent with the fact that analgesic drugs, by increasing norepinephrine and serotonin levels in the pain inhibiting descendent pathways, can be used as co-analgesics in therapy

Composition, richness and abundance of Coleoptera associated to semideciduous forests and ruderal vegetation in Sierra del Rosario, Cuba

En tres bosques semideciduos y en tres tipos de vegetación ruderal del Área Protegida de Recursos Manejados Mil Cumbres (Sierra del Rosario, Pinar del Río, Cuba), se analizan las comunidades de coleópteros y se las compara respecto a la composición, riqueza, abundancia, diversidad, equitatividad, ordenación y complementariedad. La composición de coleópteros conocida hasta el momento es de 166 especies, incluidas en 75 géneros y 34 familias. La vegetación ruderal presentaó mayor riqueza y abundancia que los bosques semideciduos. El bosque y la vegetación ruderal de Pan de Guajaibón exhibieron los valores más altos de riqueza, abundancia y número de especies únicas. Ambas formaciones vegetales de Sierra Chiquita presentaron la mayor diversidad y equitatividad. Las comunidades de coleópteros más afines estaban entre los bosques y entre la vegetaciones ruderales en Forneguera y Pan de Guajaibón. Cada bosque y tipo de vegetación ruderal presentaba especies exclusivas.In three semideciduous forests and in three types of ruderal vegetation within the Mil Cumbres Protected Area of Managed Resources (Sierra del Rosario, Pinar del Río, Cuba), the beetle communities were analyzed and compared for composition, richness, abundance, diversity, equitability, ordination and complementarity. A total of 166 species of 75 genera and 34 families were recorded. Ruderal vegetation showed higher values of richness and abundance than the semideciduous forests. The forest and ruderal vegetation of Pan de Guajaibón showed the highest values of species richness, abundance and number of unique species. Both plant communities of Sierra Chiquita presented the highest diversity and equitability values. The most similar beetle communities were between forests and between ruderal vegetation types at Forneguera and Pan de Guajaibón. Each forest and ruderal vegetation type had exclusive species

Deficiency of Complement Component C1Q Prevents Cerebrovascular Damage and White Matter Loss in a Mouse Model of Chronic Obesity.

Age-related cognitive decline and many dementias involve complex interactions of both genetic and environmental risk factors. Recent evidence has demonstrated a strong association of obesity with the development of dementia. Furthermore, white matter damage is found in obese subjects and mouse models of obesity. Here, we found that components of the complement cascade, including complement component 1qa (C1QA) and C3 are increased in the brain of Western diet (WD)-fed obese mice, particularly in white matter regions. To functionally test the role of the complement cascade in obesity-induced brain pathology, female and male mice deficient in C1QA, an essential molecule in the activation of the classical pathway of the complement cascade, were fed a WD and compared with WD-fed wild type (WT) mice, and t

Oferta, demanda, balanza comercial y competitividad del pescado de México en el mundo

We analyze the international market, fresh or chilled fish and its impact on exports and Mexico's competitiveness in this market from 1995 to 2005. It was found that the production and global consumption of fish present in generally good perspective, the two grew significantly from 1995 to 2005, not the world sugar trade where the trade balance deficit made a condition resulting from increased availability or domestic supply and import of this product in the world market that the annual production target of this or domestic demand and exports. We conclude that despite the unfavorable trend observed in world sugar trade in the period, one can say that this has not been reflected significantly in Mexico, since the competitiveness of fisheries subsector is characterized by significant competitive advantages in the international market (high levels of tradability and relative trade balance) that confer a macroeconomic competitiveness media