9,014 research outputs found
An analytical proof of Hardy-like inequalities related to the Dirac operator
We prove some sharp Hardy type inequalities related to the Dirac operator by
elementary, direct methods. Some of these inequalities have been obtained
previously using spectral information about the Dirac-Coulomb operator. Our
results are stated under optimal conditions on the asymptotics of the
potentials near zero and near infinity.Comment: LaTex, 22 page
Self-adjointness of Dirac operators via Hardy-Dirac inequalities
Distinguished selfadjoint extensions of Dirac operators are constructed for a
class of potentials including Coulombic ones up to the critical case,
. The method uses Hardy-Dirac inequalities and quadratic form
techniques.Comment: PACS 03.65.P, 03.3
Distinguished self-adjoint extensions of Dirac operators via Hardy-Dirac inequalities
We prove some Hardy-Dirac inequalities with two different weights including
measure valued and Coulombic ones. Those inequalities are used to construct
distinguished self-adjoint extensions of Dirac operators for a class of
diagonal potentials related to the weights in the above mentioned inequalities.Comment: 16 page
Neural networks and spectra feature selection for retrival of hot gases temperature profiles
Proceeding of: International Conference on Computational Intelligence for Modelling, Control and Automation, 2005 and International Conference on Intelligent Agents, Web Technologies and Internet Commerce, Vienna, Austria 28-30 Nov. 2005Neural networks appear to be a promising tool to solve the so-called inverse problems focused to obtain a retrieval of certain physical properties related to the radiative transference of energy. In this paper the capability of neural networks to retrieve the temperature profile in a combustion environment is proposed. Temperature profile retrieval will be obtained from the measurement of the spectral distribution of energy radiated by the hot gases (combustion products) at wavelengths corresponding to the infrared region. High spectral resolution is usually needed to gain a certain accuracy in the retrieval process. However, this great amount of information makes mandatory a reduction of the dimensionality of the problem. In this sense a careful selection of wavelengths in the spectrum must be performed. With this purpose principal component analysis technique is used to automatically determine those wavelengths in the spectrum that carry relevant information on temperature distribution. A multilayer perceptron will be trained with the different energies associated to the selected wavelengths. The results presented show that multilayer perceptron combined with principal component analysis is a suitable alternative in this field.Publicad
Ammonia observations in the LBV nebula G79.29+0.46. Discovery of a cold ring and some warm spots
The surroundings of Luminous Blue Variable (LBV) stars are excellent
laboratories to study the effects of their high UV radiation, powerful winds,
and strong ejection events onto the surrounding gas and dust. The LBV
G79.29+0.46 powered two concentric infrared rings which may interact with the
infrared dark cloud (IRDC) G79.3+0.3. The Effelsberg 100m telescope was used to
observe the NH_3 (1,1), (2,2) emission surrounding G79.29+0.46 and the IRDC. In
addition, we observed particular positions in the (3,3) transition toward the
strongest region of the IRDC. We report here the first coherent shell-like
structure of dense NH_3 gas associated with an evolved massive star. The shell,
two or three orders of magnitude more tenuous than the IRDC, is well traced in
both ammonia lines, and surrounds the ionized nebula. The NH_3 emission in the
IRDC is characterized by a low and uniform rotational temperature (T_rot ~ 10
K) and moderately high opacities in the (1,1) line. The rest of the observed
field is spotted by warm or hot zones (T_rot > 30 K) and characterized by
optically thin emission of the (1,1) line. The NH_3 abundances are about
10^{-8} in the IRDC, and 10^{-10}-10^{-9} elsewhere. The warm temperatures and
low abundances of NH_3 in the shell suggest that the gas is being heated and
photo-dissociated by the intense UV field of the LBV star. An outstanding
region is found to the south-west (SW) of the LBV star within the IRDC. The
NH_3 (3,3) emission at the centre of the SW region reveals two velocity
components tracing gas at temperatures > 30K. The northern edge of the SW
region agrees with the border of the ring nebula and a region of continuum
enhancement; here, the opacity of the (1,1) line and the NH_3 abundance do not
decrease as expected in a typical clump of an isolated cold dark cloud. This
strongly suggests some kind of interaction between the ring nebula and the
IRDC.Comment: 15 pages, 13 figures, accepted by A&A. Note the change of title with
respect to previous versio
Journal Staff
Electrical properties and strain gauge factor of Cr/SiOx cermet films with compositions 50/50 and 70/30 wt% were investigated in order to evaluate their use in strain gauge devices. The films were deposited by flash evaporation. The microstructures and resulting phases were characterized by electron diffraction and electron microscopy. The influence of the thickness and deposition rate on the sheet resistance, the temperature coefficient of resistance and the gauge factor were investigated. The results are consistent with a mixed conduction mechanism with metallic and a thermally activated tunneling components, between interconnected and discrete conductive phases, respectively.Se investigaron las propiedades eléctricas y el factor extensométrico de películas del cermet- Cr/SiOx en composiciones 50/50 y 70/30 % en peso, para evaluar su uso en dispositivos "strain gauge". Las películas fueron depositadas por evaporación "flash". Las estructuras y fases resultantes fueron caracterizadas por microscopía y difracción de electrones. Se estudió la influencia del espesor y la velocidad del depósito sobre la resistencia laminar, el coeficiente térmico de resistencia y el factor extensométrico. Los resultados son consistentes con un mecanismo de conducción mixto, con una componente metálica y otra por efecto túnel térmicamente activado, entre fases conductoras interconectadas y discretas, respectivamente
Faint emission lines in the Galactic H II regions M16, M20 and NGC 3603
We present deep echelle spectrophotometry of the Galactic {\hii} regions M16,
M20 and NGC 3603. The data have been taken with the Very Large Telescope
Ultraviolet-Visual Echelle Spectrograph in the 3100 to 10400 \AA range. We have
detected more than 200 emission lines in each region. Physical conditions have
been derived using different continuum and line intensity ratios. We have
derived He, C and O abundances from pure recombination
lines as well as abundances from collisionally excited lines for a large number
of ions of different elements. We have obtained consistent estimations of the
temperature fluctuation parameter, {\ts}, using different methods. We also
report the detection of deuterium Balmer lines up to D (M16) and to
D (M20) in the blue wings of the hydrogen lines, which excitation
mechanism seems to be continuum fluorescence. The temperature fluctuations
paradigm agree with the results obtained from optical CELs and the more
uncertain ones from far IR fine structure CELs in NGC 3603, although, more
observations covering the same volume of the nebula are necessary to obtain
solid conclusions.Comment: 22 pages, 13 Tables, 7 Figures. Accepted for publication by MNRA
On the abundance discrepancy problem in HII regions
The origin of the abundance discrepancy is one of the key problems in the
physics of photoionized nebula. In this work, we analize and discuss data for a
sample of Galactic and extragalactic HII regions where this abundance
discrepancy has been determined. We find that the abundance discrepancy factor
(ADF) is fairly constant and of the order of 2 in all the available sample of
HII regions. This is a rather different behaviour than that observed in
planetary nebulae, where the ADF shows a much wider range of values. We do not
find correlations between the ADF and the O/H, O++/H+ ratios, the ionization
degree, Te(High), Te(Low)/ Te(High), FWHM, and the effective temperature of the
main ionizing stars within the observational uncertainties. These results
indicate that whatever mechanism is producing the abundance discrepancy in HII
regions it does not substantially depend on those nebular parameters. On the
contrary, the ADF seems to be slightly dependent on the excitation energy, a
fact that is consistent with the predictions of the classical temperature
fluctuations paradigm. Finally, we obtain that Te values obtained from OII
recombination lines in HII regions are in agreement with those obtained from
collisionally excited line ratios, a behaviour that is again different from
that observed in planetary nebulae. These similar temperature determinations
are in contradiction with the predictions of the model based on the presence of
chemically inhomogeneous clumps but are consistent with the temperature
fluctuations paradigm. We conclude that all the indications suggest that the
physical mechanism responsible of the abundance discrepancy in HII regions and
planetary nebulae are different.Comment: 14 pages, 8 figures, 9 tables. Accepted for publication in the Ap
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