共查询到20条相似文献，搜索用时 78 毫秒
1.
An exact analysis of the effects of mass transfer on the flow of a viscous incompressible fluid past an uniformly accelerated vertical porous and non-porous plate has been presented on taking into account the free convection currents. The results are discussed with the effects of the Grashof number Gr, the modified Grashof number Sc, the Schmidt number Sc, and the suction parametera for Pr (the Prandtl number)=0.71 representating air at 20°C.Nomenclature
a
suction parameter
-
C
species concentration
-
C
species concentration at the free stream
-
g
acceleration due gravity
- Gc
modified Grashof number (vg*(C
–C
)/U
0
3
)
- Pr
Prandtl number (C
p/K)
-
T
temperature of the fluid near the plate
-
T
dimensionless temperature near the plate ((T-T
)/(T
-T
))
-
U(t)
dimensionless velocity of the plate (U/U
0)
-
v
normal velocity component
-
v
0
suction/injection velocity
-
x, y
coordinate along and normal to the plate
-
v
kinematic viscosity (/gr)
-
C
p
specific heat at constant pressure
-
C
w
species concentration at the plate
-
C
non-dimensional species concentration ((C-C
)/(C
w
-C
))
- Gr
Grashof number (g(T
w
-T
)/U
0
3
)
-
D
chemical molecular diffusivity
- K
thermal conductivity
- Sc
Schmidt number (/D)
-
T
w
temperature of the plate
-
T
free stream temperature
-
t
time variable
-
t
dimensionless time (tU
0
2
/)
-
U
0
reference velocity
-
u
velocity of the fluid near the plate
-
u
non-dimensional velocity (u/U
0)
-
v
dimensionless velocity (v/U
0)
-
v
0
non-dimensionalv
0
(v
0
/U0)=–at–1/2
-
y
dimensionless ordinate (yU
0/)
-
density of the fluid
-
coefficient of viscosity 相似文献
2.
The effect of small perturbations and in the coriolis and the centrifugal forces respectively on the stability of the triangular points in the restricted problem of three bodies with variable mass has been studied. It is found that the range of stability of triangular points increases or decreases depending upon whether the perturbation point (, ) lies in one or the other of the two parts in which the (, ) plane is divided by the line J8–J9=0 where J8 and J9 depend upon , the constant due to the variation in mass governed by Jeans' law. 相似文献
3.
The synthetic Voigt profile of the following transitions (v=0,v=0), (v=0,v=1), (v=1,v=1), (v=1,v=0) have been computed for different concentrations and temperatures of CO and compaed to the measured intensities of the UV sunspot spectrum by a high resolution spectrograph. From this comparison the solar minimum temperature has been determined. 相似文献
4.
Two dimensional source brightness distributions at 26.4 MHz for solar bursts of spectral type II, III, IV, and V are derived from observations with a multiple-baseline, time-sharing interferometer system. It was designed explicitly to study the large angle (40 halo) component of low frequency solar bursts first reported by Weiss and Sheridan (1962). Thirty-two bursts occurring in the interval of June–August, 1975, were fit with a circular gaussian core and an elliptical gaussian halo component. Half-power halo diameters (E-W×N-S) averaged 30×28 for type III bursts and 42×27, 28×37, 30×25 for type V, II and IV bursts respectively. Typical core sizes fell in the range of 10±4 giving 31 halo to core size ratio. All burst types were found to have some large angle structure: the specific intensity was 10% compared to the core but the total power in each component was comparable. Two processes for producing the core-halo structure of type III bursts are compared: scattering and refraction of a point source and refraction from many sources over an extended region. It is concluded that the core can be explained by either model but the halo is more consistent with emission from an extended source region of 40° in longitude. 相似文献
5.
We report here on high angular resolution observations of solar noise storm sources at a frequency of 75 MHz. The data for the study were obtained at the Gauribidanur Radio Observatory (long.: 77°2612 E, lat.: 13°3612 N) about 100 km north of Bangalore, India, during the solar eclipse of 24 October 1995. Our main conclusion is that there are structures of angular size 2.5 arc min in the outer solar corona. 相似文献
6.
Light refraction by the Sun's atmosphere is calculated.As detected from the Earth, the refraction can deflect a light ray emitted from the Sun's limb by 13 or a starlight ray grazing the solar limb by 26, an effect 15 times larger than the gravitational deflection. 相似文献
7.
Walter Petry 《Astrophysics and Space Science》1986,124(1):63-82
We start from a reference frame for which the pseudo-Euclidean geometry holds, i.e., all laws in have the form of special relativity. The geometry of a reference frame , moving with constant velocity with regard to , is received by using the well-known Galilei-transformation for the covariant space-time vector. In the geometry is different from the pseudo-Euclidean one, i.e., the principle of special relativity does not hold. The velocity of light in is direction dependent but the null result of the Michelson-Morley experiment is received. Several useful transformation formulae are given. In particular, we obtain the Marinov-transformation as transformation from the frame to , and conversely. Maxwell's equations and the equations of motion in the reference frame are given. The theory is applied to some examples, e.g., the Doppler effect, the Fizeau experiment, the field of a charged particle, etc. The method can be generalized to an accelerated reference frame . 相似文献
8.
We analyze a time series of high resolution observations near the solar limb, obtained in H and the Mg b1 line. We identified arch-shaped dark mottles, which are thin, faint H structures observable under very good seeing conditions, best seen in H +0.75 Å. Their mean length is about 15, their mean height about 6 and indicative lifetimes is of the order of 5 min. They show negative (away from the observer) line-of-sight velocities. A possible interpretation is that material flows from the apex towards the feet of the arches. 相似文献
9.
Spectra around the 6374 Å [Fex] and 7892 Å [Fexi] emission lines were obtained simultaneously with the 25-cm coronagraph at Norikura Observatory covering an area of 200 ×500 of the solar corona. The line width, peak intensity and line-of-sight velocity for both the lines were computed using Gaussian fits to the observed line profiles at each location (4 ×4 ) of the observed coronal region. The line-width measurements show that in steady coronal structures the FWHM of the 6374 Å emission line increases with height above the limb with an average value of 1.02 mÅ arc sec–1. The FWHM of the 7892 Å line also increases with height but at a smaller average value of 0.55 mÅ arc sec–1. These observations agree well with our earlier results obtained from observations of the red, green, and infrared emission lines that variation of the FWHM of the coronal emission lines with height in steady coronal structures depends on plasma temperatures they represent. The FWHM gradient is negative for high-temperature emission lines, positive for relatively low-temperature lines and smaller for emission lines in the intermediate temperature range. Such a behaviour in the variation of the FWHM of coronal emission lines with height above the limb suggests that it may not always be possible to interpret an increase in the FWHM of emission line with height as an increase in the nonthermal velocity, and hence rules out the existence of waves in steady coronal structures. 相似文献
10.
We have investigated the role of the 200yr period discovered by Vienne and Duriez (1992) on the tidal evolution of the Mimas–Tethys system through the 2:4 ii present resonance. Three terms are found to generate this period. We present a perturbedpendulum model in which these terms bring about a perturbation to the ideal ii resonance pendulum, which is in a direct ratio to the eccentricity e of Tethys. Although e is now very small, it is shown that this quantity could have been much greater in the past. We also show, thanks to this model, that these terms may have brought about a stochastic layer of noticeable width at the time of capture in the ii resonance, with the consequence that the possible values of the inclination i of Mimas before capture range from 0.4° to 0.6° (these uncertainties arise from the present uncertainties on e). The role of each one of the three terms is examined in the appearance of chaos. A capture into the 1/1 secondary resonance (between the libration period of the primary ii resonance and the period of about 200yr) is found possible. It means that the system could have experienced several captures in the primary resonance, instead of a single one, and that i could have been, with this assumption, much lower than 0.4°. A probability of capture into this secondary resonance as a function of the eccentricity of Tethys on encounter is derived, using Malhotra's method (Malhotra, 1990). Allan's values of i = 0.42° and e 0 (Allan, 1969) are therefore called into question, and taking e 0 is shown to be absolutely necessary if we want to understand the phenomena at work in the Mimas–Tethys system. 相似文献
11.
The HXIS, a joint instrument of the Space Research Laboratory at Utrecht, The Netherlands, and the Department of Space Research of the University of Birmingham, U.K., images the Sun in hard X-rays: Six energy bands in energy range 3.5–30 keV, spatial resolution 8 over Ø 240 and 32 over Ø 624 field of view, and time resolution of 0.5–7 s depending on the mode of operation. By means of a flare flag it alerts all the other SMM instruments when a flare sets in and informs them about the location of the X-ray emission. The experiment should yield information about the position, extension and spectrum of the hard X-ray bursts in flares, their relation to the magnetic field structure and to the quasi-thermal soft X-rays, and about the characteristics and development of type IV electron clouds above flare regions. 相似文献
12.
An analysis of the two-dimensional flow of water at 4°C past an infinite porous plate is presented, when the plate is subjected to a normal suction velocity and the heat flux at the plate is constant. Approximate solutions are derived for the velocity and temperature fields and the skin-friction. The effects ofG (Grashof number) andE (Eckert number) on the velocity and temperature fields are discussed.Nomenclature
u, v
velocity components of the fluid inx, y direction
-
g
acceleration due to gravity
-
coefficient of thermal expansion of water at 4°C
-
v
kinematic viscosity
-
density
-
T
temperature inside thermal boundary layer
-
T
free-stream temperature
-
k
thermal conductivity
-
C
p
specific heat at constant pressure 相似文献
13.
T. P. Singh A. K. Agrawal H. L. Agrawal A. Raptis 《Astrophysics and Space Science》1991,181(2):171-181
The Hall effect on the unsteady hydromagnetic free-convection resulting from the combined effects of thermal and mass diffusion of an electrical-conducting liquid through a porous medium past an infinite vertical porous plate in a rotating system have been analysed. The expressions for the mean velocity, mean skin friction, and mean rate of heat transfer on the plate are derived. The effects of magnetic parameterM, Hall parameterm, Ekman numberE, and permeability parameterK
* on the flow field are discussed with the help of graphs and tables.Nomenclature
C
p
specific heat at constant pressure
-
C
the species concentration inside the boundary layer
-
C
w
the species concentration at porous plate
-
C
the species concentration of the fluid at infinite
-
C
dimensionless species concentration
-
D
chemical molecular diffusivity
-
E
Ekman number
- Ec
Eckert number
-
g
acceleration due to gravity
- Gr
Grashof number
- Gm
modified Grashof number
-
H
0
applied magnetic field
- (J
x, Jy, Jz)
components of current density
-
M
magnetic parameter
-
m
Hall parameter
-
P
Prandtl number
-
q
m
mean rate of heat transfer
- Sc
Schmidt number
-
t
time
-
t
dimensionless time
-
T
temperature of fluid
-
T
w
temperature of the plate
-
T
temperature of fluid at infinite
-
T
dimensionless temperature
- (u, v, w)
components of the velocityq
-
w
0
suction velocity
- (x, y, z)
Cartesian coordinates
-
z
dimensionless coordinate normal to the plate
Greek symbols
coefficient of volume expansion
- *
coefficient of thermal expansion with concentration
-
frequency
-
dimensionless frequency
-
k
thermal conductivity
-
K
*
permeability parameter
-
dinematic viscosity
-
density of the fluid in the boundary layer
-
coefficient of viscosity
- e
magnetic permeability
-
angular velocity
-
electrical conductivity of the fluid
- m
mean skin friction
- mn
mean skin friction in the direction ofx
- mv
mean skin friction in the direction ofy 相似文献
14.
An analysis of the effects of Hall current on hydromagnetic free-convective flow through a porous medium bounded by a vertical plate is theoretically investigated when a strong magnetic field is imposed in a direction which is perpendicular to the free stream and makes an angle to the vertical direction. The influence of Hall currents on the flow is studied for various values of .Nomenclature
c
p
specific heat at constant pressure
-
e
electrical charge
-
E
Eckert number
-
E
electrical field intensity
-
g
acceleration due to gravity
-
G
Grashof number
-
H
0
applied magnetic field
-
H
magnetic field intensity
- (j
x
, j
y
, j
z
)
components of current densityJ
-
J
current density
-
K
permeability of porous medium
-
M
magnetic parameter
-
m
Hall parameter
-
n
e
electron number density
-
P
Prandtl number
-
q
velocity vector
- (T, T
w
, T
)
temperature
-
t
time
- (u, v, w)
components of the velocity vectorq
-
U
0
uniform velocity
-
v
0
suction velocity
- (x, y, z)
Cartesian coordinates
Greek Symbols
angle
-
coefficient of volume expansion
- e
cyclotron frequency
-
frequency
-
dimensionless temperature
-
thermal conductivity
-
coefficient of viscosity
-
magnetic permeability
-
kinematic viscosity
-
mass density of fluid
- e
charge density
-
electrical conductivity
- e
electron collision time 相似文献
15.
Г. Н. Дубошин 《Celestial Mechanics and Dynamical Astronomy》1970,2(4):454-466
(, 1969). ( ), ( ), , , . , (=), , , .. , . , , - ( ), ( ). , .
This paper is a continuation and a generalization of one published earlier (Duboshin, 1969): it discusses the problem whether there exist the Lagrangian and the Eulerian solutions of the generalized three-body (material points) problem. Every point in this generalized problem acts on another, one with a force (attractive or repulsive) directed along the straight line passing through these points, and in an arbitrary manner depending on time, mutual distance and its derivatives, the first and the second. Here, generally speaking, the third axiom of dynamics (law of action and reaction) is not presupposed as fulfilled, that is, it is supposed that every two material points interact in a different way.This most general assumption being made, we establish the conditions which must dictate the laws of the interactions, so that the three points can always remain at the apexes of the equilateral triangle (Langrangian solution), or remain always on a straight line (Eulerian solution).The author believes that such general treatment of the three-body problem can be useful for theoretical studies in celestial mechanics and also for practical applications in the study of isolated stellar systems.相似文献
16.
In the present paper, the effects of free convection currents and the viscous dissipation on the unsteady flow of an electrically conducting and viscous incompressible fluid around an uniformly accelerated vertical porous plate subjected to a suction or injection velocity inversely proportional to the square root of time, in presence of a transverse magnetic field, have been investigated. Analytical solutions for the velocity and the temperature distributions, the skin-friction and the rate of heat transfer are obtained for small magnetic parameterM. During the course of discussion the effects of the Grashof number Gr, the Eckert number Ec, the suction/injection parametera have been considered for unit value of the Prandtl number Pr.Nomenclature
a
suction/injection parameter
-
C
p
specific heat at constant pressure
-
B
0
magnetic induction
-
g
acceleration due to gravity
- Gr
Grashof number (g(T
w
–T
)/U
0
3
)
-
K
thermal conductivity
-
M
magnetic field parameter (B
0
2
/U
0
2
)
- Pr
Prandtl number (C
p/K)
-
T
temperature of the fluid near the plate
-
T
w
temperature of the plate
-
T
temperature of the fluid at infinity
-
t
time
-
t
dimensionless time (tU
0
2
/)
-
u
velocity of the fluid
-
u
non-dimensional velocity (u/U
0)
-
U
velocity of the plate
-
U
dimensionless velocity of the plate (U/U
0)
-
U
0
reference velocity
-
v
0
suction velocity
-
v
0
non-dimensional suction velocity (v
0/U
0)=at
–1/2
- Ec
Eckert number ((U
0)2/3/C
p(T
w
–T
))
-
T
dimensionless temperature of the fluid near the plate ((T–T
)/(T
w
–T
))
-
x, y
coordinates along and normal to the plate
-
x, y
dimensionless coordinates (y=yU
0/)
-
kinematic viscosity
-
coefficient of volume expansion
-
electric conductivity of the fluid
-
y/2t
1/2
-
density of the fluid
-
skin-friction
-
dimensionless skin-friction
-
q
rate of heat transfer
-
q
non-dimensional rate of heat transfer
-
coefficient of viscosity
- e
magnetic permeability
On leave of absence from Department of Mathematics, University of Dhaka, Bangladesh 相似文献
17.
The CCD spectroheliograph-magnetograph is a focal-plane ancillary instrument for the Pulkovo horizontal solar telescope ACU-5. The instrument is placed at an exit port of an isothermal high-resolution diffraction-grating spectrograph. A modified Leighton optical scheme for registration of sunspot magnetic fields is used. The instrument provides FITS-format digital video maps of radial velocities, magnetic fields, and spectroheliograms in any line of the spectral region 3900–11000 Å. The time to obtain one video map of size 91×154 is equal to 10.24 s. The angular resolution of the instrument is 0.8; spectral resolution is 0.01–0.03 Å. Since 1996 the Pulkovo CCD spectroheliograph-magnetograph has been used to obtain high spatial and temporal resolution observations of oscillations of radial velocities and magnetic fields in the photospheric layers of sunspots. 相似文献
18.
Max K. Wallis 《Astrophysics and Space Science》1973,20(1):3-18
The interaction processes governing the penetration of the interstellar gas into the solar neighbourhood are re-examined — as well as photo-ionization and charge-exchange processes, proton elastic collisions and electron ionizations help reduce the nearby gas densities. The total destruction rate varies little during the solar cycle, by perhaps 10%. Particle heating, particularly via the elastic collisions, determines the gas characteristics in the gravitationally focussed tail—enhanced H-density is prevented, while the He-tail is effectively hotter than 103 K.Termination of the solar wind is rediscussed in the light of both electron heating and the stronger gas/plasma interaction. The spiral interplanetary field is taken to break up and the subsonic plasma flow to be controlled by the pressure of slowly cooling electrons. The terminating collisionless shock is then, if it exists at all, very weak (M
1<1.4), subcritical, and energetically unimportant. Cosmic rays are little affected by this sonic transition, but at least the electron component should be modulated by plasma turbulence throughout the ionizing flow.
. , . , . . .相似文献
19.
Г. А. Гурзадян 《Astrophysics and Space Science》1977,46(2):471-484
, , , , ,S
, , , S
Mg. , . , . , ( , ..). B5 B0; (<1%). 相似文献
20.
The location and the stability of the libration points in the restricted problem have been studied when small perturbation and are given to the Coriolis and the centrifugal forces respectively. It is seen that the pointsL
4 andL
5 form nearly equilateral triangles with the primaries and the pointsL
1,L
2,L
3 remain collinear. It is further observed that for the pointsL
4 andL
5, the range of stability increases or decreases depending upon whether the point (, ) lies in one or the other of the two parts in which the (, ) plane is divided by the line 36-19=0 and the stability of the collinear points is not influenced by the perturbations and they remain unstable. 相似文献