109 research outputs found
Hydrogen temperature gradient in the transition region of a solar coronal hole.
No full textThe Lyman series of hydrogen was observed by SUMER on SOHO on the north polar limb of the Sun with a total exposure time of more than ten hours. The resulting line profiles have been analysed using the technique described by Marsch et al. (1999). The data analysis corroborates earlier findings on the Lyman lines, but also yields phenomena which cannot be fully understood at the present time. Firstly, the Line width of the Lyman lines increases with decreasing series or quantum number. Secondly, the hydrogen temperature gradient in the height range from 12 000 km to 18 000 km is unexpectedly small and does not reveal a steep jump as might be expected from modelling of the transition region. The average temperature increases only slightly from 1 10(5) K to 2 10(5) K. Possible explanations of these observations are given and models are briefly discussed.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000088424400033&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701Astronomy & AstrophysicsSCI(E)19ARTICLE1381-38535
MODELING RESULTS ON SPATIAL TRANSPORT AND SPECTRAL TRANSFER OF SOLAR-WIND ALFVENIC TURBULENCE
No full textIn this paper a set of time stationary transport equations for incompressible MHD fluctuations in the solar wind is derived from previous general transport equations (Marsch and Tu, 1989; Zhou and Matthaeus, 1990a), which have been found to give solutions with fast time variations. The present derivation is based on the assumption that the fluctuations are composed of small-scale convected structures and short-wavelength Alfven waves. The different contributions of these two types of fluctuations to the total correlation functions can be evaluated by means of temporal and spatial averaging of the correlations over the small scales. Two linearly decoupled sets of transport equations then result, which separately describe the spatial evolution of the turbulent energies and cross correlations of the structures and waves. For the propagating Alfven waves a multiple-scale analysis yields two WKB-type transfer equations for the autocorrelation functions expressed in terms of Elsasser velocity fields. For the structures a third additional equation is derived, which determines the evolution of the residual energy, that is, the difference between the kinetic and magnetic energy of the convected fluctuations. The final set of equations is slowly varying in time and thus satisfactory from the point of view of conventional statistical turbulence theory. The nonlinearities are modeled by cascading flux functions, which are determined by dimensional analysis following the Kolmogorov phenomenology and based on the time stationarity assumption. The new equations are consistent with this assumption and equivalent to the equations obtained by Tu and Marsch (1993). The present derivation aims at clarifying the relations between the general and the time stationary set of transport equations. Consequently, stationary equations governing the spatial and spectral evolution of the power frequency spectra e+/- for Alfvenic fluctuations, described in terms of the two Elsasser variables, are established and integrated numerically. As a first step to study the effects of the nonlinear terms, we neglect the coupling terms related to convected structures. This approximation may apply to the fluctuations observed in fast streams near 0.3 AU. We integrate the resulting two coupled transport equations in frequency-distance-space by employing a new technique based on the method of characteristics. Interplanetary parametric decay instabilities are also included in the model. The numerical results obtained show that (1) The cascade process which is based on local nonlinear interactions in frequency space cannot transport any initial value of the normalized cross-helicity from the low-frequency boundary to the higher-frequency range. Cascade processes alone invariably result in dynamic alignment and cause the spectra of e+ as well as e- to steepen at higher frequencies. (2) However, a parametric-decay-like source term can enforce the normalized cross-helicity to decrease with increasing heliocentric distance and can also produce and sustain a flatter part in the spectrum of e in the high-frequency range. These results are in qualitative agreement with the observations. Research topics which should be dealt with in the future to complete the present preliminary numerical work are also pointed out.Astronomy & AstrophysicsSCI(E)40ARTICLEA1221045-210599
Wave dissipation by ion cyclotron resonance in the solar corona.
No full textIt has recently been suggested that small-scale reconnection occurring in the chromospheric network creates high-frequency Alfven waves, and that these waves may represent the main energy source for the heating of the solar corona and generation of the solar wind. However, if these waves exist, they will be absorbed preferentially by the minor heavy ions with low gyrofrequencies, and thus it is unclear whether there is actually enough wave energy left over for the heating and acceleration of the major solar wind ions, namely protons and alpha particles, in the extended corona after the absorption by heavy ions (Cranmer 2000). We have studied this problem with the multi-fluid model presented by Tu & Marsch (2001), which includes the self-consistent treatment of the damping of the waves as well as the associated acceleration and heating of the ions. We found that if the wave power density is sufficiently large, say about 1000 nT(2) Hz(-1) at 160 Hz and 2.5 R-circle dot, then the wave absorption by a prominent minor ion such as O+5 is small, and most of the wave energy is left for absorption by protons. This occurs because the minor ions are quickly (within several gyroperiods) accelerated and then are induced to partially surfing the waves. However, if the wave power is too low, say lower than 10 nT(2) Hz(-1) at 160 Hz and 2.5 R-circle dot, then the damping of the wave power by the O+5 ions is severe, and little wave energy is left for protons.Astronomy & AstrophysicsSCI(E)35ARTICLE31071-107636
Construcción de un plásmido para la elaboración de bancos de genes
No full textTesis (Ingeniería Biotecnológica), Instituto Politécnico Nacional, UPIBI, 2010, 1 archivo PDF, (22 páginas). tesis.ipn.m
Heating and acceleration of coronal ions interacting with plasma waves through cyclotron and Landau resonance.
No full textOn the basis of quasi-linear theory, the parallel and perpendicular wave heating and acceleration rates for gyrotropic particle velocity distribution functions are derived. These rates can be used in anisotropic multicomponent fluid equations, in order to describe the wave-particle interactions of ions with, for examples, kinetic Alfven and electromagnetic or electrostatic ion cyclotron, respectively, magnetosonic waves propagating along or obliquely to the mean magnetic field. The waves of coronal origin propagating away from the Sun into the interplanetary medium can resonantly heat the solar wind ions and accelerate minor ions preferentially with respect to the protons. Such processes are required in order to explain and understand the measured characteristics of ion velocity distributions in the solar wind and to interpret the recent spectroscopic evidence obtained from EUV emission line measurements made by the Solar and Heliospheric Observatory (SOHO) spacecraft, which indicate cyclotron-resonance-related line broadenings and shifts.Astronomy & AstrophysicsSCI(E)58ARTICLEA1227-23810
Non-Gaussian probability distributions of solar wind fluctuations
No full textThe probability distributions of field
differences ∆x(τ)=x(t+τ)-x(t),
where the variable x(t) may denote any solar wind scalar field or
vector field component at time t, have been calculated from time series
of Helios data obtained in 1976 at heliocentric distances near 0.3 AU. It is
found that for comparatively long time lag τ, ranging from a few hours
to 1 day, the differences are normally distributed according to a Gaussian. For
shorter time lags, of less than ten minutes, significant changes in shape are
observed. The distributions are often spikier and narrower than the equivalent
Gaussian distribution with the same standard deviation, and they are enhanced
for large, reduced for intermediate and enhanced for very small values of
∆x. This result is in accordance with fluid observations and
numerical simulations. Hence statistical properties are dominated at small scale
τ by large fluctuation amplitudes that are sparsely distributed, which
is direct evidence for spatial intermittency of the fluctuations. This is in
agreement with results from earlier analyses of the structure functions of
∆x. The non-Gaussian features are differently developed for
the various types of fluctuations. The relevance of these observations to the
interpretation and understanding of the nature of solar wind magnetohydrodynamic
(MHD) turbulence is pointed out, and contact is made with existing theoretical
concepts of intermittency in fluid turbulence
On cyclotron wave heating and acceleration of solar wind ions in the outer corona.
No full textThe preferential heating and acceleration of O+5 ions, as observed by Ultraviolet Coronagraph Spectrometer (UVCS) on Solar and Heliospheric Observatory (SOHO) [Kohl et al., 1998] in the solar coronal holes have been interpreted and modeled by invoking wave-particle cyclotron resonance [Cranmer et al., 1999a, 1999b], However, in the model of Cranmer et al. [1999a, 1999b] and in other subsequent models the assumption of a rigid slope of the wave spectrum was made in calculating the wave energy absortion by the different ion species. In the present paper it is shown that a self-consistent treatment of the wave damping and absorption is necessary and leads to substantially different results. On the basis of quasi-linear theory, the interaction between the ions and the ion-cyclotron waves [Marsch et al.: 1982a; Marsch, 1998] is studied. The total energy conservation equation, including the kinetic energy of the resonant particles and the wave energy, is derived and discussed in detail. The spectral evolution equation for cyclotron waves, when being controlled by the wave growth/damping rate and WI(B effects, is solved self-consistently together with the full set of anisotropic multifluid equations for the ions including the cyclotron-resonance wave heating and acceleration rates. From the numerical results we reach the following conclusions: (1) It is physically questionable to use a spectrum with a fixed spectral slope near the cyclotron resonance when one calculates the partition of wave energy among the different ionic species and the kinetic degrees of freedom parallel and perpendicular to the magnetic field. This assumption neglects the important effects of wave absorption and the concurrent reshaping of the wave spectrum, and thus leads in the dissipation domain to extremely low amplitudes of the waves and to difficulties in supplying enough energy to balance the wave absorption at the cyclotron resonances. (2) If the spectrum is allowed to evolve self-consistently and concurrently with the particles' heating and acceleration through wave absorption, such a high perpendicular temperature and corresponding large temperature anisotropy as observed by UVCS do not occur or cannot be maintained. We conclude that the UVCS oxygen ion observations have not yet been explained satisfactorily by the cyclotron-resonance theory.Astronomy & AstrophysicsSCI(E)98ARTICLEA58233-825210
Spatial evolution of the magnetic field spectral exponent in the solar wind: Helios and Ulysses comparison
No full textThe spatial evolution of the spectral exponent of magnetic field fluctuations in the solar wind is investigated by a comparison of spectra and length functions obtained from Hellos for in-ecliptic and from Ulysses for high-latitude observations. A similar radial evolution trend is found in both data sets for the B-z component of the magnetic field, which is least affected by compressive interactions. Yet the fluctuations seem to evolve more slowly in the polar flows as compared with the Alfvenic fluctuations found by the Hellos experiments in coronal-hole-related flows near the Sun in the ecliptic plane.Astronomy & AstrophysicsSCI(E)11ARTICLEA511149-1115210
Producción de la transposasa de TN5 en Escherichia coli BL21 para su funcionamiento in vitro
No full textTesis (Ingeniería Biotecnológica), Instituto Politécnico Nacional, UPIBI, 2013, 1 archivo PDF, (60 páginas). tesis.ipn.m
Construcción de la proteína híbrida-inteína transposasa en pTYB11
No full textTesis (Ingeniería Biotecnológica), Instituto Politécnico Nacional, UPIBI, 2006, 1 archivo PDF, (41 páginas). tesis.ipn.m
- …
