3,536 research outputs found
Coronal heating in coupled photosphere-chromosphere-coronal systems: turbulence and leakage
Coronal loops act as resonant cavities for low frequency fluctuations that
are transmitted from the deeper layers of the solar atmosphere and are
amplified in the corona, triggering nonlinear interactions. However trapping is
not perfect, some energy leaks down to the chromosphere, thus limiting the
turbulence development and the associated heating. We consider the combined
effects of turbulence and leakage in determining the energy level and
associated heating rate in models of coronal loops which include the
chromosphere and transition region. We use a piece-wise constant model for the
Alfven speed and a Reduced MHD - Shell model to describe the interplay between
turbulent dynamics in the direction perpendicular to the mean field and
propagation along the field. Turbulence is sustained by incoming fluctuations
which are equivalent, in the line-tied case, to forcing by the photospheric
shear flows. While varying the turbulence strength, we compare systematically
the average coronal energy level (E) and dissipation rate (D) in three models
with increasing complexity: the classical closed model, the semi-open corona
model, and the corona-chromosphere (or 3-layer) model, the latter two models
allowing energy leakage. We find that:
(i) Leakage always plays a role (even for strong turbulence), E and D are
systematically lower than in the line-tied model. (ii) E is close to the
resonant prediction, i.e., assuming effective turbulent correlation time longer
than the Alfven coronal crossing time (Ta). (iii) D is close to the value given
by the ratio of photospheric energy divided by Ta (iv) The coronal spectra
exibits an inertial range with 5/3 spectral slope, and a large scale peak of
trapped resonant modes that inhibit nonlinear couplings. (v) In the realistic
3-layer model, the two-component spectrum leads to a damping time equal to the
Kolmogorov time reduced by a factor u_rms/Va_coronaComment: 15 pages, 15 figures, Accepted for publication in A&
Evaluation of the PlayStation 2 as a cluster computing node
Cluster computing is currently a popular, cost-effective solution to the increasing computational demands of many applications in scientific computing and image processing. A cluster computer is comprised of several networked computers known as nodes. Since the goal of cluster computing is to provide a cost-effective means to processing computationally demanding applications, nodes that can be obtained at a low price with minimal performance tradeoff are always attractive. Presently, the most common cluster computers are comprised of networks of workstations constructed from commodity components. Recent trends have shown that computers being developed and deployed for purposes other than traditional personal computers or workstations have presented new candidates for cluster computing nodes. The new computing node candidates being considered may provide a competitive and even less expensive alternative to the cluster computing nodes being used today. Machines such as video game consoles, whose prices are kept extremely low due to intense marketplace competition, are a prime example of such machines. The Sony PlayStation 2, in particular, provides the user with low-level hardware devices that are often found in more expensive machines. This work presents and evaluation of the PlayStation 2 video game console as a cluster computing node for scientific and image processing applications. From this evaluation, a determination is made as to whether the PlayStation 2 is a viable alternative to the cluster computing nodes being used today
Support and power plant documentation for the gas turbine powered bus demonstration program
The operational experience obtained for the GT404-4 gas turbine engines in the intercity and intracity Bus Demonstration Programs is described for the period January 1980 through September 1981. Support for the engines and automatic transmissions involved in this program provided engineering and field service, spare parts and tools, training, and factory overhauls. the Greyhound (intercity) coaches accumulated 183,054 mi (294,595 km) and 5154 hr of total operation. The Baltimore Transit (intracity) coaches accumulated 40,567 mi (65,285 km) and 1840 hr of total operation. In service, the turbine powered Greyhound and Transit coaches achieved approximately 25% and 40% lower fuel mileage, respectively, than did the production diesel powered coaches. The gas turbine engine will require the advanced ceramic development currently being sponsored by the DOE and NASA to achieve fuel economy equivalent not only to that of today's diesel engines but also to the projected fuel economy of the advanced diesel engines of the 1990s. Sufficient experience was not achieved with the coaches prior to the start of service to identify and eliminate many of the problems associated with the startup of new equipment. Because of these problems, the mean miles between incident were unacceptably low. The future gas turbine system should be developed sufficiently to establish satisfactory durability prior to evaluation in revenue service. Commercialization of the gas turbine bus engine remains a viable goal for the future
Integrals of Motion for Critical Dense Polymers and Symplectic Fermions
We consider critical dense polymers . We obtain for this model
the eigenvalues of the local integrals of motion of the underlying Conformal
Field Theory by means of Thermodynamic Bethe Ansatz. We give a detailed
description of the relation between this model and Symplectic Fermions
including the indecomposable structure of the transfer matrix. Integrals of
motion are defined directly on the lattice in terms of the Temperley Lieb
Algebra and their eigenvalues are obtained and expressed as an infinite sum of
the eigenvalues of the continuum integrals of motion. An elegant decomposition
of the transfer matrix in terms of a finite number of lattice integrals of
motion is obtained thus providing a reason for their introduction.Comment: 53 pages, version accepted for publishing on JSTA
Ensayo numérico del calentamiento en un transformador eléctrico
Los componentes activos de un transformador eléctrico son los devanados y el núcleo magnético. Las pérdidas en estos componentes originan calentamientos que, si son desmesurados, aceleran el deterioro del aislamiento de los bobinados y de toda la máquina. A partir de un ensayo numérico en el interior de un trans- formador, se ha desarrollado un estudio del flujo fluidodinámico y del proceso de evacuación de calor. El ob- jetivo final es la optimización del diseño y operación de estas máquinas. Los fenómenos se verifican en el fluido interno, desde las fuentes de energía, las pérdidas, hacia la cuba. Concretamente, se considera un transformador de distribución y la predicción de temperatura como parámetro más representativo. Los ensayos han sido ejecu- tados mediante el Método de Elementos Finitos, con el cual se resuelve numéricamente un modelo matemático basado en las ecuaciones de Navier-Stokes incompresible y la ecuación de transporte de energía térmica, aco- pladas con un término de flotación proporcional a la temperatura incorporado a la ecuación de momento. El ele- vado número de Prandtl del aceite de transformadores obliga a utilizar mallas muy refinadas en las interfaces sólido - fluido. También se destaca la heterogeneidad de los devanados, en los cuales se requiere estudiar la dis- tribución de temperaturas, con marcada anisotropía del arrollamiento de menor tensión. Los resultados numéri- cos se han correlacionado positivamente con datos experimentales del ensayo de calentamiento (IRAM 2018, 1995) de un transformador de distribución (13.2/0.4 - 0.231 kV 315 kVA) de la firma Tadeo Czerweny S.A. Se presentan resultados de la simulación ejecutada, correspondientes al régimen fluidodinámico y térmico, conclu- yéndose que los mismos son consistentes con los fenómenos, y que el procedimiento aplicado es una herramien- ta robusta para el estudio de problemas de campo como el considerado. En el Anexo se registran los procedi- mientos para determinar las conductividades térmicas de los bobinados.Fil: Ferreiro, Alejandro R.. Facultad de Ciencias Exactas y Tecnologías
Gral. Savio y La Forja; ArgentinaFil: Nigro, Norberto Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química (i); Argentina. Universidad Nacional del Litoral; Argentin
Surveillance and Control of Malaria Transmission Using Remotely Sensed Meteorological and Environmental Parameters
Meteorological and environmental parameters important to malaria transmission include temperature, relative humidity, precipitation, and vegetation conditions. These parameters can most conveniently be obtained using remote sensing. Selected provinces and districts in Thailand and Indonesia are used to illustrate how remotely sensed meteorological and environmental parameters may enhance the capabilities for malaria surveillance and control. Hindcastings based on these environmental parameters have shown good agreement to epidemiological records
The Baxter Q Operator of Critical Dense Polymers
We consider critical dense polymers , corresponding to a
logarithmic conformal field theory with central charge . An elegant
decomposition of the Baxter operator is obtained in terms of a finite
number of lattice integrals of motion. All local, non local and dual non local
involutive charges are introduced directly on the lattice and their continuum
limit is found to agree with the expressions predicted by conformal field
theory. A highly non trivial operator is introduced on the lattice
taking values in the Temperley Lieb Algebra. This function provides a
lattice discretization of the analogous function introduced by Bazhanov,
Lukyanov and Zamolodchikov. It is also observed how the eigenvalues of the
operator reproduce the well known spectral determinant for the harmonic
oscillator in the continuum scaling limit.Comment: improved version, accepted for publishing on JSTA
Perceptions of Reading Instruction
It follows that there exists an obvious need for elementary reading programs to be closely articulated with the developing and changing reading requirements of pupils as they progress through the elementary grades. There is an even more obvious need for close cooperation between teachers and administrators in order to implement reading programs that meet pupil requirements
Reward preferences of pathological gamblers under conditions of uncertainty: an experimental study
Among many personality traits, impulsivity represents one of the most important traits associated with pathological gambling. Empirical research has highlighted the multidimensional nature of impulsivity, which includes different heterogeneous traits and behavioral tendencies. The present study experimentally examined reward preferences of pathological gamblers under conditions of uncertainty using the Balloon Analogue Risk Task. Furthermore it also examined the relationship between impulsivity, time perspective, inability to tolerate delay in gratification, and risktaking. The present study is the first to simultaneously examine all these variables simultaneously in a sample of pathological gamblers (n=54) and healthy controls (n=54) from Italy. All participants participated in the Balloon Analogue Risk Task (BART) and were also administered Italian versions of the South Oaks Gambling Screen, the Barratt Impulsiveness Scale, the Consideration of Future Consequences, and the Monetary Choice Questionnaire. Analyses revealed that compared to HCs, PGs were more risk prone on the BART, and reported elevated levels of impulsivity, steeper discounting rates and a shorter time perspective. All the measures correlated with the gambling severity and strong correlations between the BIS, CFC-14 and BART were observed. Logistic regression analysis demonstrated that impulsivity and risk-taking were strong predictors of pathological gambling
The chromosphere: gateway to the corona, or the purgatory of solar physics?
I argue that one should attempt to understand the solar chromosphere not only
for its own sake, but also if one is interested in the physics of: the corona;
astrophysical dynamos; space weather; partially ionized plasmas; heliospheric
UV radiation; the transition region. I outline curious observations which I
personally find puzzling and deserving of attention.Comment: To appear in the proceedings of the 25th NSO Workshop "Chromospheric
Structure and Dynamics. From Old Wisdom to New Insights", Memorie della
Societa' Astronomica Italiana, Eds. Tritschler et a
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