143,490 research outputs found
Diquarks and the Semi-Leptonic Decay of in the Hybrid Scheme
In this work we use the heavy-quark-light-diquark picture to study the
semileptonic decay in the so-called
hybrid scheme. Namely, we apply the heavy quark effective theory (HQET) for
larger (corresponding to small recoil), which is the invariant mass
square of , whereas the perturbative QCD approach for smaller
to calculate the form factors. The turning point where we require the form
factors derived in the two approaches to be connected, is chosen near
. It is noted that the kinematic parameter which is
usually adopted in the perturbative QCD approach, is in fact exactly the same
as the recoil factor used in HQET where , are the
four velocities of and respectively. We find that the
final result is not much sensitive to the choice, so that it is relatively
reliable. Moreover, we apply a proper numerical program within a small range
around to make the connection sufficiently smooth and we
parameterize the form factor by fitting the curve gained in the hybrid scheme.
The expression and involved parameters can be compared with the ones gained by
fitting the experimental data. In this scheme the end-point singularities do
not appear at all. The calculated value is satisfactorily consistent with the
data which is recently measured by the DELPHI collaboration within two standard
deviations.Comment: 16 pages, including 4 figures, revtex
Multi-Curve Model for Steel Pier Hysteretic Curve
A multi-curve fitting model for a steel pier hysteretic curve is developed The scheme of the curve fitting is separated for the phase before and after the ultimate strength An quadratic equation is defined in the local coordinate at the hysteretic curve having the largest curvature in each cycle By using this model, saving the cost for the computer calculation using elasto-plastic finite displacement program is expected and also simple treatment in the hybrid test is considered
Kinetics of the thermal degradation of Erica arborea by DSC: Hybrid kinetic method
The scope of this work was the determination of kinetic parameters of the
thermal oxidative degradation of a Mediterranean scrub using a hybrid method
developed at the laboratory. DSC and TGA were used in this study under air
sweeping to record oxidative reactions. Two dominating and overlapped
exothermic peaks were recorded in DSC and individualized using an experimental
and numerical separation. This first stage allowed obtaining the enthalpy
variation of each exothermic phenomenon. In a second time, a model free method
was applied on each isolated curve to determine the apparent activation
energies. A reactional kinetic scheme was proposed for the global exotherm
composed of two independent and consecutive reactions. In fine mean values of
enthalpy variation and apparent activation energy previously determined were
injected in a model fitting method to obtain the reaction order and the
preexponential factor of each oxidative reaction. We plan to use these data in
a sub-model to be integrated in a wildland fire spread model
Hydrogen vs. Battery in the long-term operation. A comparative between energy management strategies for hybrid renewable microgrids
The growth of the world’s energy demand over recent decades in relation to energy intensity and demography is clear. At the same time, the use of renewable energy sources is pursued to address decarbonization targets, but the stochasticity of renewable energy systems produces an increasing need for management systems to supply such energy volume while guaranteeing, at the same time, the security and reliability of the microgrids. Locally distributed energy storage systems (ESS) may provide the capacity to temporarily decouple production and demand. In this sense, the most implemented ESS in local energy districts are small–medium-scale electrochemical batteries. However, hydrogen systems are viable for storing larger energy quantities thanks to its intrinsic high mass-energy density. To match generation, demand and storage, energy management systems (EMSs) become crucial. This paper compares two strategies for an energy management system based on hydrogen-priority vs. battery-priority for the operation of a hybrid renewable microgrid. The overall performance of the two mentioned strategies is compared in the long-term operation via a set of evaluation parameters defined by the unmet load, storage efficiency, operating hours and cumulative energy. The results show that the hydrogen-priority strategy allows the microgrid to be led towards island operation because it saves a higher amount of energy, while the battery-priority strategy reduces the energy efficiency in the storage round trip. The main contribution of this work lies in the demonstration that conventional EMS for microgrids’ operation based on battery-priority strategy should turn into hydrogen-priority to keep the reliability and independence of the microgrid in the long-term operation
Fuzzy set methods for object recognition in space applications
Progress on the following tasks is reported: (1) fuzzy set-based decision making methodologies; (2) feature calculation; (3) clustering for curve and surface fitting; and (4) acquisition of images. The general structure for networks based on fuzzy set connectives which are being used for information fusion and decision making in space applications is described. The structure and training techniques for such networks consisting of generalized means and gamma-operators are described. The use of other hybrid operators in multicriteria decision making is currently being examined. Numerous classical features on image regions such as gray level statistics, edge and curve primitives, texture measures from cooccurrance matrix, and size and shape parameters were implemented. Several fractal geometric features which may have a considerable impact on characterizing cluttered background, such as clouds, dense star patterns, or some planetary surfaces, were used. A new approach to a fuzzy C-shell algorithm is addressed. NASA personnel are in the process of acquiring suitable simulation data and hopefully videotaped actual shuttle imagery. Photographs have been digitized to use in the algorithms. Also, a model of the shuttle was assembled and a mechanism to orient this model in 3-D to digitize for experiments on pose estimation is being constructed
Identification of Musical Instruments by means of the Hough-Transformation
In order to distinguish between the sounds of different musical instruments, certain instrument-specific sound features have to be extracted from the time series representing a given recorded sound. The Hough Transform is a pattern recognition procedure that is usually applied to detect specific curves or shapes in digital pictures (Shapiro, 1978). Due to some similarity between pattern recognition and statistical curve fitting problems, it may as well be applied to sound data (as a special case of time series data). The transformation is parameterized to detect sinusoidal curve sections in a digitized sound, the motivation being that certain sounds might be identified by certain oscillation patterns. The returned (transformed) data is the timepoints and amplitudes of detected sinusoids, so the result of the transformation is another ?condensed? time series. This specific Hough Transform is then applied to sounds played by different musical instruments. The generated data is investigated for features that are specific for the musical instrument that played the sound. Several classification methods are tried out to distinguish between the instruments and it turns out that RDA (a hybrid method combining LDA and QDA) (Friedman, 1989) performs best. The resulting error rate is better than those achieved by humans (Bruderer, 2003). --
Measurement of the energy resolution and calibration of hybrid pixel detectors with GaAs:Cr sensor and Timepix readout chip
This paper describes an iterative method of per-pixel energy calibration of
hybrid pixel detectors with GaAs:Cr sensor and Timepix readout chip. A
convolution of precisely measured spectra of characteristic X-rays of different
metals with the resolution and the efficiency of the pixel detector is used for
the calibration. The energy resolution of the detector is also measured during
the calibration. The use of per-pixel calibration allows to achieve a good
energy resolution of the Timepix detector with GaAs:Cr sensor: 8% and 13% at 60
keV and 20 keV, respectively
Cloud Atlas: High-Contrast Time-Resolved Observations of Planetary-Mass Companions
Directly-imaged planetary-mass companions offer unique opportunities in
atmospheric studies of exoplanets. They share characteristics of both brown
dwarfs and transiting exoplanets, therefore, are critical for connecting
atmospheric characterizations for these objects. Rotational phase mapping is a
powerful technique to constrain the condensate cloud properties in ultra-cool
atmospheres. Applying this technique to directly-imaged planetary-mass
companions will be extremely valuable for constraining cloud models in low mass
and surface gravity atmospheres and for determining the rotation rate and
angular momentum of substellar companions. Here, we present Hubble Space
Telescope Wide Field Camera 3 near-infrared time-resolved photometry for three
planetary-mass companions, AB Pic B, 2M0122B, and 2M1207b. Using two-roll
differential imaging and hybrid point spread function modeling, we achieve
sub-percent photometric precision for all three observations. We find tentative
modulations () for AB Pic B and 2M0122B but cannot reach
conclusive results on 2M1207b due to strong systematics. The relatively low
significance of the modulation measurements cannot rule out the hypothesis that
these planetary-mass companions have the same vertical cloud structures as
brown dwarfs. Our rotation rate measurements, combined with archival period
measurements of planetary-mass companions and brown dwarfs do not support a
universal mass-rotation relation. The high precision of our observations and
the high occurrence rates of variable low-surface gravity objects encourage
high-contrast time-resolved observations with the James Webb Space Telescope.Comment: Accepted for publication in AAS Journa
Depth sensing indentation of organic-inorganic hybrid coatings deposited onto a polymeric substrate
PEO-Si/SiO2 hybrid coatings deposited onto a PVC substrate were micromechanically characterized using depth sensing indentation. The effect of curing time and coating thickness was investigated. Elastic moduli of coated systems determined by the Oliver–Pharr approach displayed a continuous decreasing trend with increasing indentation depth, reflecting that the hybrids are stiffer than the substrate. Aiming to extract coating-only elastic modulus a simple method based on FE simulations was developed. The method was applied to evaluate the moduli of the hybrid coatings and the values were compared with those obtained by applying different approaches available in literature. The elastic modulus of PEO-Si/SiO2 hybrids was proven to be practically independent of curing time after 24 h. However, large curing times resulted in coatings being more prone to failure.Fil: Fasce, Laura Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Seltzer, Rocío. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Frontini, Patricia Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentin
- …