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1.
I. Malakpur 《Astrophysics and Space Science》1973,24(2):577-583
We identify the different absorption systems of Nova Delphini 1967 by studying the radial velocity variation of the absorption lines with time. The ‘premaximum’ system was visible at the time of the first observation and its velocity decreased very quickly in the early stages of the nova's development. This velocity started to increase from 16 January, 1968. We show that the ‘diffuse-enhanced’ system overtook the ‘premaximum’ system and caused its velocity to increase. The ‘principal’ system became visible on 27 August, 1967, and showed a continuous slow increase of the radial velocity, with a sudden increase near 21 April, 1968, due to a collision between the ‘principal’ and the ‘diffuse-enhanced’ systems. The ‘diffuse-enhanced’ system, visible from 17 December, 1967, disappeared on 21 April, 1968. The ‘diffuse-enhanced’ system overtook and merged with the principal shell on 21 April, 1968. Finally, we see that the ‘orion’ system became visible on 11 May, 1968 and disappeared on 9 August, 1968. This is not due to a collision, but could be produced by a change of the degree of ionization of the absorbing atoms or by the decrease of the density of the cloud of gas responsible for this system. There were also some absorption systems having a constant velocity, only visible for lines of Ca II. These systems could be produced by ejection of circumstellar gas. We show that the Nova entered the nebular stage around 28 July, 1968. 相似文献
2.
I. Malakpur 《Astrophysics and Space Science》1974,27(2):467-484
We have found that the gas of the premaximum, diffuse-enhanced and orion systems is produced by the nova itself and is ejected by shock waves in the form of discrete layers. The principal envelope originates in the gas responsible for the premaximum system, as a result of considerable, sudden increase of the radiation pressure of Lα, a certain time after the beginning of the nova explosion. The radiation pressure accelerates a part of the premaximum envelope and it is this accelerated part of the premaximum envelope that forms the principal envelope of nova. This acceleration is then transferred to the outer regions of the envelope. The mass of the principal envelope therefore increases continuously. We have rejected all the previous theories that have been proposed for the formation of the principal envelope, because the authors of the theories have supposed that the principal envelope is formed at the moment of the luminosity maximum, while in the case of Nova Delphini 1967, we have found that the principal envelope was formed about 125 days before the luminosity maximum. By accepting that the premaximum, diffuse-enhanced and orion layers are ejected by shock waves and that the principal system is produced by radiation pressure, we can interpret the luminosity curve and the variation of the radial velocity of each system as a function of time and the observed sporadic changes of luminosity or radial velocity. We have found that the luminosity comes from the gas associated with the principal envelope and that its mass is about 80% of the mass of the all matters ejected by a nova, during its activity. We have discussed the cause of the nova explosion and have concluded that there is no satisfactory theory of novae. 相似文献
3.
The theoretical implications of an isolation mechanism that utilizes progressively increasing frictional resistance is investigated. This type of frictional resistance can be provided by the tightening together of a set of friction plates by compressive forces that increase with relative separations of the building and the foundation. The mathematical model of the device is developed and its numerical solutions are obtained. It is shown that in comparison with dry friction alone significant reductions in acceleration transmissibility and relative displacement transmissibility can be obtained. 相似文献
4.
Various results concerning the pre-December 1967 maximum phase of this nova, are brought together. It is concluded from a comparison of the Paschen and Balmer absorption line intensities, that most H emission was produced at the centre of the envelope, and that continuous ejection occurred in this phase. Gravitational deceleration my explain certain properties of the H profiles. 相似文献
5.
The sliding behaviour of a rigid mass supported on a randomly vibrating foundation through a non-symmetric Coulomb-friction contact is studied both analytically and by numerical simulation. The analysis is based on a stationary solution of the associated Fokker-Planck equation, and makes use of equivalent linearization and of a suitable decomposition of the non-zero mean non-stationary sliding process. It is shown that the analytical results yield several exact asymptotic expansions for both small and large values of time. An extensive Monte Carlo type numerical simulation study produces non-stationary response statistics which are in very good accord with the analytical results. Furthermore, it is found that Gumbel's Extreme Value Distribution reproduces with remarkable accuracy the observed cumulative frequency of maximum slip displacement. The results of this paper may find application in seismic design of embankment dams, earth retaining walls and base ‘isolation’ systems. 相似文献
6.
A series of numerical experiments on the performance of different base isolation systems for a non-uniform shear beam structure is carried out. Several base isolation systems are considered and the peak relative displacements and the maximum absolute accelerations of the base-isolated structure and its base raft under a variety of conditions are evaluated. Several sensitivity analyses for variations in properties of the base isolator and the structure are carried out. A number of different earthquake excitations are also used in the study. The results show that performances of the base isolation systems are not sensitive to small variations in their natural period, damping or friction coefficient. The presence of a frictional element in the isolators reduces their sensitivity to severe variations in frequency content and amplitude of the ground acceleration. In particular, the resilient-friction base isolators with or without sliding upper plate perform reasonably well under a variety of loading conditions. The rubber bearing type, however, leads to the lowest peak transmitted accelerations for moderate intensity earthquakes. 相似文献
7.
A comparative study of performances of different base isolators for shear beam type structures is carried out. Several leading base isolation systems, including the laminated rubber bearing with and without lead plug, the resilient-friction base isolator with and without sliding upper plate, and the EDF system are considered. Displacement and acceleration response spectra for a shear beam structure subject to the accelerograms of the N00W component of El Centro 1940 and the N90W component of Mexico City 1985 earthquakes and their magnified forms are evaluated. A series of parametric studies is carried out and advantages and disadvantages of various base isolation systems are identified. Comparisons of the results with the response spectra of a fixed-base structure show that the base isolation systems are, in general, highly effective in reducing the peak acceleration transmitted to the superstructure. Thus, the deflections and stresses generated in a base-isolated structure are significantly lower than those of a fixed-base one. Furthermore, the results of the study also show that the friction-type base isolators are less sensitive to severe variations in frequency content and amplitude of the ground acceleration. 相似文献
8.
A linear multistorey structure with a seismic base isolation system consisting of rubber bearings and frictional elements is considered. The non-linear equations of motion are derived for the first mode vibration and the stochastic response to a white noise ground acceleration is determined. Based on this response, suitable objective functions are defined and the optimum design of the isolation system is performed. It is shown that a small amount offriction increases the effectiveness of the system compared with the same system but without frictional elements. 相似文献
9.
Optimal control of base-isolated and non-base-isolated buildings subjected to earthquake excitation is considered. The control force at any instant is determined on-line through minimizing a quadratic time-dependent performance index based on the total energy imparted to the structure and the control effect. This control algorithm is based upon the use of discrete actuators and sensors that exert the control force and monitor the response of the building. Having constant gain matrices makes this algorithm efficient and easy to implement. The effect of time delay on the efficiency of the algorithm is investigated. Comparisons have been made to demonstrate the effectiveness of the proposed method. 相似文献
10.
I. Malakpur 《Astrophysics and Space Science》1977,47(1):17-24
The aim of this paper has been to study the neutral helium triplet emission lines identified in the spectrum of the envelope of Nova Delphini. By comparing the observed flux of the neutral helium lines with that calculated theoretically by Robbins, we find that the optical thickness in the center of the line 3889 is of the order of 21.50 for summer 1969. The optical thickness obtained by this method is here denoted tran(3889).On the other hand, we obtain the number of neutral helium atoms in the 23S state [N(23S)] by considering the equilibrium between the mechanisms that populate and depopulate this state. We then find that the depopulation by photoionization due to the radiation of Ly (Hi), transitions to the 21S, 21p and 23p states by electron collision, photoionization due to the continuum radiation of the central star, are 82.70%, 13.20%, 2.40%, 0.90% and 0.80% respectively. We find that the mechanism of the photoionization by Ly is the dominant mechanism of depopulation of 23S state. We calculated ( 3889) of the order of 82.37, fromN(23S), obtained in the preceding paragraph. The optical thickness obtained by this method is here denoted bal(3889).The difference between tran(3889) and bal(3889) is very large and it cannot be attributed to calculation errors. We have considered all the mechanisms that can depopulate the 23S state, so we then conclude that the difference between tran(3889) and bal(3889) is due to the heterogeneity of the envelope of the Nova, already found by us in our previous study of the profiles of the permitted and forbidden lines. Finally, we find from this study a filling factor of the order of 0.30. 相似文献