6,031 research outputs found
Nonlinear Design Technique for High-Power Switching-Mode Oscillators
A simple nonlinear technique for the design of high-efficiency and high-power switching-mode oscillators is presented. It combines existing quasi-nonlinear methods and the use of an auxiliary generator (AG) in harmonic balance. The AG enables the oscillator optimization to achieve high output power and dc-to-RF conversion efficiency without affecting the oscillation frequency. It also imposes a sufficient drive on the transistor to enable the switching-mode operation with high efficiency. Using this AG, constant-power and constant-efficiency contour plots are traced in order to determine the optimum element values. The oscillation startup condition and the steady-state stability are analyzed with the pole-zero identification technique. The influence of the gate bias on the output power, efficiency, and stability is also investigated. A class-E oscillator is demonstrated using the proposed technique. The oscillator exhibits 75 W with 67% efficiency at 410 MHz
Bifurcation analysis of stabilization circuits in an L-band LDMOS 60-W power amplifier
n this letter, the global stability analysis of an L-band push-pull power amplifier is presented. The analysis is carried out for the amplifier operating in different modes, such as Class AB, Class B, and Class E/F, considering variations in the bias voltages, the input power and the input frequency. After determination of the oscillation mode, three different stabilization techniques are applied and compared: feedback resistors, neutralization capacitors, and odd-mode stabilization resistor. The element values of each stabilization network, ensuring a stable behavior for all the operating conditions, are calculated with a bifurcation-analysis technique. Good agreement is found between measured and simulated results
Analysis and elimination of hysteresis and noisy precursors in power amplifiers
Power amplifiers (PAs) often exhibit instabilities leading to frequency division by two or oscillations at incommensurate frequencies. This undesired behavior can be detected through a large-signal stability analysis of the solution. However, other commonly observed phenomena are still difficult to predict and eliminate. In this paper, the anomalous behavior observed in a Class-E PA is analyzed in detail. It involves hysteresis in the power-transfer curve, oscillation, and noisy precursors. The precursors are pronounced bumps in the power spectrum due to noise amplification under a small stability margin. The correction of the amplifier performance has required the development of a new technique for the elimination of the hysteresis. Instead of a trial-and-error procedure, this technique, of general application to circuit design, makes use of bifurcation concepts to suppress the hysteresis phenomenon through a single simulation on harmonic-balance software. Another objective has been the investigation of the circuit characteristics that make the noisy precursors observable in practical circuits and a technique has been derived for their elimination from the amplifier output spectrum. All the different techniques have been experimentally validated
Pattern for Re-engineering a Classification Scheme, which Follows the Adjacency List Data Model, to a Taxonomy
This pattern for re-engineering non-ontological resources (pr-nor) ïŹts in the schema re-engineering category proposed by [3]. The pattern deïŹnes a procedure that transforms the classiïŹcation scheme components into ontology representational primitives. This pattern comes from the experience of ontology engineers in developing ontologies using classiïŹcation schemes in several projects (seemp 1 , neon 2 , and knowledge web 3 ). The pattern is included in a pool of patterns, which is a key element of our method for re-engineering non-ontological resources into ontologies [2]. The patterns generate the ontologies at a conceptualization level, independent of the ontology implementation language
Spatial deconvolution of spectropolarimetric data: an application to quiet Sun magnetic elements
Observations of the Sun from the Earth are always limited by the presence of
the atmosphere, which strongly disturbs the images. A solution to this problem
is to place the telescopes in space satellites, which produce observations
without any (or limited) atmospheric aberrations. However, even though the
images from space are not affected by atmospheric seeing, the optical
properties of the instruments still limit the observations. In the case of
diffraction limited observations, the PSF establishes the maximum allowed
spatial resolution, defined as the distance between two nearby structures that
can be properly distinguished. In addition, the shape of the PSF induce a
dispersion of the light from different parts of the image, leading to what is
commonly termed as stray light or dispersed light. This effect produces that
light observed in a spatial location at the focal plane is a combination of the
light emitted in the object at relatively distant spatial locations. We aim to
correct the effect produced by the telescope's PSF using a deconvolution
method, and we decided to apply the code on Hinode/SP quiet Sun observations.
We analyze the validity of the deconvolution process with noisy data and we
infer the physical properties of quiet Sun magnetic elements after the
deconvolution process.Comment: 14 pages, 9 figure
Computational analysis of the behavior of atmospheric pollution due to demographic, structural factors, vehicular flow and commerce activities
According to the latest assessments made by the world health organization (WHO2016), the atmospheric pollution (air), has become one of the main causes of morbidity and mortality in the world, with a steep growth of respiratory diseases, increase in lung cancer, ocular complications, and dermis diseases [1,2,3]. Currently, there are governments which still underestimate investments in environmental care, turning their countries into only consumers and predators of the ecosystem [1,2,3]. Worldwide, several cities have been implementing different regional strategies to decrease environmental pollution, however, these actions have not been effective enough and significant indices of contamination and emergency declarations persist [1,2,3]. MedellĂn is one of the cities most affected by polluting gases in Latin America due to the high growth of construction sector, high vehicular flow, increase in commerce, besides a little assertive planting trees system, among other reasons [1,2,3]. With the purpose of providing new researching elements which benefit the improvement of air quality in the cities of the world, it is pretended to mathematically model and computationally implement the behavior of the flow of air, e.g., in zones in the city of MedellĂn to determine the extent of pollution by tightness, impact of current architectural designs, vehicular transport, high commerce flow, and confinement in the public transport system. The simulations allowed to identify spotlights of particulate tightness caused by architectural designs of the city which do not benefit air flow. Also, recirculating gases were observed in different zones of the city. This research can offer greater knowledge around the incidence of pollution generated by structures and architecture. Likewise, these studies can contribute to a better urban, structural and ecological reordering in cities, the implementation of an assertive arborization system, and the possibility to orientate effective strategies over cleaning (purification) and contaminant extracting systems
A Pattern Based Approach for Re-engineering Non-Ontological Resources into Ontologies
With the goal of speeding up the ontology development process, ontology engineers are starting to reuse as much as possible available ontologies and non-ontological resources such as classiïŹcation schemes, thesauri, lexicons and folksonomies, that already have some degree of consensus. The reuse of such non-ontological resources necessarily involves their re-engineering into ontologies. Non-ontological resources are highly heterogeneous in their data model and contents: they encode different types of knowledge, and they can be modeled and implemented in diïŹerent ways. In this paper we present (1) a typology for non-ontological resources, (2) a pattern based approach for re-engineering non-ontological resources into ontologies, and (3) a use case of the proposed approach
Detection of emission in the Si i 1082.7 nm line core in sunspot umbrae
We analyze spectropolarimetric sunspot umbra observations taken in the
near-infrared Si i 1082.7 nm line taking NLTE effects into account. The data
were obtained with the GRIS instrument installed at the German GREGOR
telescope. A point spread function (PSF) was constructed using prior Mercury
observations with GRIS and the information provided by the adaptive optics
system of the GREGOR telescope. The data were then deconvolved from the PSF
using a principal component analysis deconvolution method and were analyzed via
the NICOLE inversion code. The Si i 1082.7 nm line seems to be in emission in
the umbra of the observed sunspot after the effects of scattered light are
removed. We show how the spectral line shape of umbral profiles changes
dramatically with the amount of scattered light. Indeed, the continuum levels
range, on average, from 44% of the quiet Sun continuum intensity to about 20%.
The inferred levels are in line with current model predictions and empirical
umbral models. Current umbral empirical models are not able to reproduce the
emission in the deconvolved umbral Stokes profiles. The results of the NLTE
inversions suggests that to obtain the emission in the Si i 1082.7 nm line, the
temperature stratification should first have a hump located at about log tau -2
and start rising at lower heights when moving into the transition region. This
is, to our knowledge, the first time the Si i 1082.7 nm line is seen in
emission in sunspot umbrae. The results show that the temperature
stratification of current umbral models may be more complex than expected with
the transition region located at lower heights above sunspot umbrae. Our
finding might provide insights into understanding why the sunspot umbra
emission in the millimeter spectral range is less than that predicted by
current empirical umbral models
Asymmetries of the Stokes V profiles observed by HINODE SOT/SP in the quiet Sun
We present the first classification of SOT/SP circular polarization
measurements with the aim of highlighting exhaustively the whole variety of
Stokes V shapes emerging from the quiet Sun. k-means is used to classify HINODE
SOT/SP Stokes V profiles observed in the quiet Sun network and internetwork
(IN). We analyze a 302 x 162 square arcsec field-of-view (FOV) which can be
considered a complete sample of quiet Sun measurements performed at at the disk
center with 0.32 arcsec angular resolution and 0.001 polarimetric sensitivity.
Such a classification allows us to divide the whole dataset in classes, with
each class represented by a cluster profile, i.e., the average of the profiles
in the class. The set of 35 cluster profiles derived from the analysis
completely characterizes SOT/SP quiet Sun measurements. The separation between
network and IN profile shapes is evident - classes in the network are not
present in the IN, and vice versa. Asymmetric profiles are approximatively 93 %
of the total number of profiles. Among these, approximatively 34 % of the
profiles are strongly asymmetric profiles, and they can be divided in three
families: blue-lobe, red-lobe, and Q-like profiles. The blue-lobe profiles tend
to be associated with upflows (granules), whereas the red-lobe and Q-like ones
appear in downflows (intergranular lanes). Such profiles need to be interpreted
considering model atmospheres different from a uniformly magnetized
Milne-Eddington (ME) atmosphere, i.e., characterized by gradients and/or
discontinuities in the magnetic field and velocity along the line-of-sight
(LOS).Comment: 11 pages, 4 figures, accepted for publication in Astronomy and
Astrophysic
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