4,845 research outputs found
Recommendations for a wind profiling network to support Space Shuttle launches
The feasibility is examined of a network of clear air radar wind profilers to forecast wind conditions before Space Shuttle launches during winter. Currently, winds are measured only in the vicinity of the shuttle launch site and wind loads on the launch vehicle are estimated using these measurements. Wind conditions upstream of the Cape are not monitored. Since large changes in the wind shear profile can be associated with weather systems moving over the Cape, it may be possible to improve wind forecasts over the launch site if wind measurements are made upstream. A radar wind profiling system is in use at the Space Shuttle launch site. This system can monitor the wind profile continuously. The existing profiler could be combined with a number of radars located upstream of the launch site. Thus, continuous wind measurements would be available upstream and at the Cape. NASA-Marshall representatives have set the requirements for radar wind profiling network. The minimum vertical resolution of the network must be set so that the wind shears over the depths greater than or = 1 km will be detected. The network should allow scientists and engineers to predict the wind profile over the Cape 6 hours before a Space Shuttle launch
Two-Loop Crossover Scaling Functions of the O(N) Model
Using Environmentally Friendly Renormalization, we present an analytic
calculation of the series for the renormalization constants that describe the
equation of state for the model in the whole critical region. The
solution of the beta-function equation, for the running coupling to order two
loops, exhibits crossover between the strong coupling fixed point, associated
with the Goldstone modes, and the Wilson-Fisher fixed point. The Wilson
functions , and , and thus the
effective critical exponents associated with renormalization of the transverse
vertex functions, also exhibit non-trivial crossover between these fixed
points.Comment: 21 pages, 4 figures, version to appears in IJMPL
Polydispersity Effects in the Dynamics and Stability of Bubbling Flows
The occurrence of swarms of small bubbles in a variety of industrial systems
enhances their performance. However, the effects that size polydispersity may
produce on the stability of kinematic waves, the gain factor, mean bubble
velocity, kinematic and dynamic wave velocities is, to our knowledge, not yet
well established. We found that size polydispersity enhances the stability of a
bubble column by a factor of about 23% as a function of frequency and for a
particular type of bubble column. In this way our model predicts effects that
might be verified experimentally but this, however, remain to be assessed. Our
results reinforce the point of view advocated in this work in the sense that a
description of a bubble column based on the concept of randomness of a bubble
cloud and average properties of the fluid motion, may be a useful approach that
has not been exploited in engineering systems.Comment: 11 pages, 2 figures, presented at the 3rd NEXT-SigmaPhi International
Conference, 13-18 August, 2005, Kolymbari, Cret
Vortices on demand in multicomponent Bose-Einstein condensates
We present a simple mechanism to produce vortices at any desired spatial
locations in harmonically trapped Bose-Einstein condensates (BEC) with
multicomponent spin states coupled to external transverse and axial magnetic
fields. The vortices appear at the spatial points where the spin-transverse
field interaction vanishes and, depending on the multipolar magnetic field
order, the vortices can acquire different predictable topological charges. We
explicitly demonstrate our findings, both numerically and analytically, by
analyzing a 2D BEC via the Gross-Pitaevskii equation for atomic systems with
either two or three internal states. We further show that, by an spontaneous
symmetry breaking mechanism, vortices can appear in any spin component, unless
symmetry is externally broken at the outset by an axial field. We suggest that
this scenario may be tested using an ultracold gas of Rb occupying all
three states in an optical trap.Comment: 11 pages, 9 figures, (Accepted in PRA
Ecología de la germinación de la semillas de Pinus sylvestris L. en el límite sur de su distribución
Seed germination of Pinus sylvestris L. in south eastern Spain was studied under field and growth chamber conditions to assess the effect of the most representative microhabitats of these forests. Under growth chamber conditions, germination was high (almost 95%) in the litter from all microhabitats. Germination under field conditions was highest (up to 95%) in shade-free microhabitats and therefore higher soil temperature (e.g. areas of bare soil and meadows), and lowest (down to 62%) in microhabitats with dense canopy shade and thus lower soil temperature (e.g. under the canopy of pines and under the canopy of juniper). Nevertheless, germination was high also in shaded microhabitats in a year with high rainfall during the germination period, supporting the hypothesis that germination was determined by a combination of appropriate levels of soil temperature, moisture, and light intensity. In contrast, biotic speciesspecific characteristics of the microhabitat were not relevant. Germination may thus reach high percentages in all the microhabitats of the understory during rainy years that ensure appropriate soil moisture during the germination period. However, during dry years germination will concentrate in sunny microhabitats because they reach higher soil temperature early in the season before soil desiccation. These patterns have implications for forest management and stand regeneration via direct seeding.Se analiza la germinación de las semillas de pino silvestre en el límite sur de su distribución (Sierra Nevada) mediante experimentos de campo y de laboratorio en una muestra de diez microhábitats que representan la mayoría de los lugares en los que se encuentran las semillas tras la dispersión en estos bosques. En condiciones de laboratorio, las semillas mostraron una alta tasa de germinación (en torno al 95%) en la hojarasca de todos los microhábitats. En el campo las semillas mostraron una tasa de germinación mayor (en torno al 95%) en microhábitats directamente expuestos al sol y por tanto con mayor temperatura (e.g. suelo sin vegetación y prados de herbáceas) y una menor tasa bajo plantas con copa espesa que generan un microhábitat sombreado y con menor temperatura (bajo copa de pinos adultos y bajo copa de enebros). No obstante, durante un año lluvioso la tasa de germinación en microhábitats sombreados se incrementó considerablemente, sugiriendo que la germinación está controlada por una combinación adecuada de radiación, humedad y temperatura. Por el contrario, no se detectó ningún efecto biótico relacionado con el microhábitat, como alelopatía. La germinación de las semillas de pino silvestre en estos bosques puede por tanto alcanzar valores altos en todos los microhábitats durante años con primavera lluviosa que asegure la confluencia de humedad y temperatura apropiada en el suelo. Sin embargo, en años con primaveras más secas la germinación se concentrará en microhábitats con alta radiación, ya que la mayor temperatura del suelo permitirá una rápida germinación antes de que se produzca la desecación del sustrato. Estos patrones deben tenerse en cuenta a la hora de planificar la regeneración del bosque mediante la siembra de semillas
Domain wall dynamics in expanding spaces
We study the effects on the dynamics of kinks due to expansions and
contractions of the space. We show that the propagation velocity of the kink
can be adiabatically tuned through slow expansions/contractions, while its
width is given as a function of the velocity. We also analyze the case of fast
expansions/contractions, where we are no longer on the adiabatic regime. In
this case the kink moves more slowly after an expansion-contraction cycle as a
consequence of loss of energy through radiation. All these effects are
numerically studied in the nonlinear Klein-Gordon equations (both for the
sine-Gordon and for the phi^4 potential), and they are also studied within the
framework of the collective coordinate evolution equations for the width and
the center of mass of the kink. These collective coordinate evolution equations
are obtained with a procedure that allows us to consider even the case of large
expansions/contractions.Comment: LaTeX, 18 pages, 2 figures, improved version to appear in Phys Rev
Condrosarcoma en pie
El condrosarcoma óseo en el pie es una lesión muy rara. Se presenta 1 caso de bajo
grado de malignidad histológico y primario en su origen, que afecta al primer radio, tratado
mediante resección amplia y sin signos de recidiva a los 3 años y medio de evolución.Bone chondrosarcoma very rarely affccts the foot. We report a case of primary
bone chondrosarcoma vvith low grade malignancy involving the first metatarsal bone. Tumor was
treated by wide resection. Three and half years later, there was not signs of recurrence
Relação entre a qualidade de semente e densidade de plantio na produção de milho.
Trabalho apresentado no X Congresso Brasileiro de Sementes
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