3,057 research outputs found
A one-dimensional Fermi accelerator model with moving wall described by a nonlinear van der Pol oscillator
A modification of the one-dimensional Fermi accelerator model is considered
in this work. The dynamics of a classical particle of mass , confined to
bounce elastically between two rigid walls where one is described by a
non-linear van der Pol type oscillator while the other one is fixed, working as
a re-injection mechanism of the particle for a next collision, is carefully
made by the use of a two-dimensional non-linear mapping. Two cases are
considered: (i) the situation where the particle has mass negligible as
compared to the mass of the moving wall and does not affect the motion of it;
(ii) the case where collisions of the particle does affect the movement of the
moving wall. For case (i) the phase space is of mixed type leading us to
observe a scaling of the average velocity as a function of the parameter
() controlling the non-linearity of the moving wall. For large
, a diffusion on the velocity is observed leading us to conclude that
Fermi acceleration is taking place. On the other hand for case (ii), the motion
of the moving wall is affected by collisions with the particle. However due to
the properties of the van der Pol oscillation, the moving wall relaxes again to
a limit cycle. Such kind of motion absorbs part of the energy of the particle
leading to a suppression of the unlimited energy gain as observed in case (i).
The phase space shows a set of attractors of different periods whose basin of
attraction has a complicate organization
The Brazilian Interbank Network Structure and Systemic Risk
We explore the structure and dynamics of interbank exposures in Brazil using a unique data set of all mutual exposures of financial institutions in Brazil, as well as their capital reserves, at various periods in 2007 and 2008. We show that the network of exposures can be adequately modeled as a directed scale-free (weighted) graph with heavy-tailed degree and weight distributions. We also explore the relationship between connectivity of a financial institution and its capital buffer. Finally, we use the network structure to explore the extent of systemic risk generated in the system by the individual institutions.
Lepton Flavor Violating Photoleptonic Effect
We study lepton flavor violating analogs of the photoelectric effect, with a
final or instead of an electron: and . On the basis of the general parametrization of the matrix element
of the electromagnetic current we estimate the upper limits for the cross
sections and event rates of these processes, imposed by the current
experimental bounds on and decays.Comment: 6 pages, 1 figure, RevTeX
Antiferromagnetic spin chain behavior and a transition to 3D magnetic order in Cu(D,L-alanine)2: Roles of H-bonds
We study the spin chain behavior, a transition to 3D magnetic order and the
magnitudes of the exchange interactions for the metal-amino acid complex
Cu(D,L-alanine)2.H2O, a model compound to investigate exchange couplings
supported by chemical paths characteristic of biomolecules. Thermal and
magnetic data were obtained as a function of temperature (T) and magnetic field
(B0). The magnetic contribution to the specific heat, measured between 0.48 and
30 K, displays above 1.8 K a 1D spin-chain behavior that can be fitted with an
intrachain antiferromagnetic (AFM) exchange coupling constant 2J0 = (-2.12
0.08) cm, between neighbor coppers at 4.49 {\AA} along chains
connected by non-covalent and H-bonds. We also observe a narrow specific heat
peak at 0.89 K indicating a phase transition to a 3D magnetically ordered
phase. Magnetization curves at fixed T = 2, 4 and 7 K with B0 between 0 and 9
T, and at T between 2 and 300 K with several fixed values of B0 were globally
fitted by an intrachain AFM exchange coupling constant 2J0 = (-2.27 0.02)
cm and g = 2.091 0.005. Interchain interactions J1 between coppers
in neighbor chains connected through long chemical paths with total length of
9.51 {\AA} are estimated within the range 0.1 < |2J1| < 0.4 cm, covering
the predictions of various approximations. We analyze the magnitudes of 2J0 and
2J1 in terms of the structure of the corresponding chemical paths. The main
contribution in supporting the intrachain interaction is assigned to H-bonds
while the interchain interactions are supported by paths containing H-bonds and
carboxylate bridges, with the role of the H-bonds being predominant. We compare
the obtained intrachain coupling with studies of compounds showing similar
behavior and discuss the validity of the approximations allowing to calculate
the interchain interactions.Comment: 10 pages, 4 figure
Information Systems For Shuttle Processing: An Enterprise Approach
The purpose of this paper is to describe a process being utilized by Lockheed Space Operations Company (LSOC) for planning, developing and supporting an integrated information system for the Shuttle Processing Contract (SPC). This process was developed by Electronic Data Systems (EDS) to address the complex modernization and integration issues facing General Motors (GM). LSOC has contracted EDS to participate in adapting the process to the environment at Kennedy Space Center (KSC) for shuttle processing
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Aplicação de Análise e Modelagem Multidimensional para o Monitoramento de ResÃduos Sólidos Industriais
Impact of Level of Use on Plant Vigor and Weight of \u3cem\u3eFestuca humilior\u3c/em\u3e and \u3cem\u3eCalamagrostis vicunarum\u3c/em\u3e
Tussock grasslands of Festuca humilior and Calamagrostis vicunarum cover a significant extension of the central Andes of Peru, constituting a plant association highly appreciated by cattle ranchers. The objective of this research was to estimate the cumulative impact of the level of use of the key grasses Festuca humilior and Calamagrostis vicunarum on plant height, vigor, and weight. This study was conducted in a humid grassland of regular condition located at 4186 masl in the Puna ecoregion. The variables evaluated were: plant height, basal and canopy diameter and plant weight. The experiment lasted two years in which individual plants from both species were cut every four months. The vigor resulted from the regression of the weight (g) and the volume (cm3) of the plant. Height (cm) was the length from the soil surface to the flag leaf. The experimental design was a randomized block design with a 2x3 factorial arrangement, two species and three height removal levels: zero, 40 and 80%. The height, vigor and weight of Festuca humilior and Calamagrostis vicunarum decreased in response to increasing use levels, but the changes were more evident in Festuca than in Calamagrostis. While the decrease in the evaluated variables was constant for Festuca humilior as the level of use increased, Calamagrostis also decreased, but to a lesser extent, remaining almost unchanged when biomass removal levels changed from moderate to heavy, suggesting that this species was more tolerant to grazing. The results helped explaining why in fields dominated by Festuca humilior and sub-dominated by Calamagrostis vicunarum subjected to intense grazing, dominance relationships change in favor of Calamagrostis, a species of lower forage value than Festuca humilior. It is recommended to manage the grazing system under a low-intensity and low frequency regime
Scaling properties for a classical particle in a time-dependent potential well.
Some scaling properties for a classical particle interacting with a time-dependent square-well potential are studied. The corresponding dynamics is obtained by use of a two-dimensional nonlinear area-preserving map. We describe dynamics within the chaotic sea by use of a scaling function for the variance of the average energy, thereby demonstrating that the critical exponents are connected by an analytic relationship
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