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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.
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
4.
Using the flux-transport equation in the absence of sources, we study the relation between a highly peaked polar magnetic field and the poleward meridional flow that concentrates it. If the maximum flow speed
m greatly exceeds the effective diffusion speed /R, then the field has a quasi-equilibrium configuration in which the poleward convection of flux via meridional flow approximately balances the equatorward spreading via supergranular diffusion. In this case, the flow speed () and the magnetic field B() are related by the steady-state approximation () (/R)B()/B() over a wide range of colatitudes from the poles to midlatitudes. In particular, a general flow profile of the form sin
p
cos
q
which peaks near the equator (q p) will correspond to a cos
n
magnetic field at high latitudes only if p = 1 and
m = n /R. Recent measurements of n 8 and 600 km2 s–1 would then give
m 7 m s–1. 相似文献
5.
A. M. I. Osman 《Astrophysics and Space Science》1985,116(2):299-311
Surface photometry of the UV continuum galaxy NGC 838 has been carried out in theB, V system using photographic plates obtained with the 74 Kottamia telescope, Egypt. Isophotes, luminosity profiles, integrated photographic magnitudes, effective diameters and other photometric parameters are derived.The photoelectrically calibrated total apparent magnitudes areB
T
=13.57 with maximum diameters 1.57×1.34 (at threshold
m
=27.7 mag.//) andV
T
=12.91 with maximum diameters 1.54×1.32 (at threshold
m
=27.7 mag./). The integrated colour index(B–V)
T
=0.66 and the effective surface brightness
e
(B=19.0 mag./) and
e
(V=19.7 mag./. The major axis is at position angle =85°±1°.The nucleus of NGC 838 is quite blue (integrated colour(B–V)=0.41 forr
*<0.1) compared to normal galaxies while the colour becomes redder from the nucleus outwards. The UV excess, H emission and radio continuum emission previously observed from this galaxy by other investigators may be attributed to a recent burst of star formation in the nucleus of the galaxy of duration slightly greater than 2×107 yr. 相似文献
6.
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
7.
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
8.
RecentUBV photometry of the RS CVn binary CF Tuc is discussed and analysed. If we combine the results with previously published spectroscopy we find radii of 1.63R
for the hotter (6000 K) and 3.11R
for the cooler (4500 K) component; both stars having a mass of about 1.3M
. The distance to the system is put at 86±15 pc.Though the photometric data is incomplete in the coverage of some regions out of the minima, there is no significant evidence of the wave-type distortions — a known hallmark of RS CVn stars — and the data can be modeled by a standard eclipsing binary system in which the statistical test of goodness-of-fit (2) produces quite acceptable values for reasonable estimates of observational accuracy (0.01 mag). We, therefore, have no need to postulate any additional photometric complications, and feel entitled to some confidence in the reliability of the derived parameter set. 相似文献
9.
The observation of [OI] 6300 » emission in the coma of Halley's comet 1982i, using the imaging Fabry-Pérot spectrometer, was carried out from Gurushikhar (2439N, 7243E, 1700m altitude), Mt. Abu, India on March 15, 1986 (R = 0.90 AU, = 0.96 AU). The analysis of the interferogram show the absence of the differential velocity of neutral oxygen above 5 km s–1. 相似文献
10.
I. W. Roxburgh 《Solar physics》1972,27(2):478-480
Three different asymptotic branches of the two-fluid equations are found with
e
m
,
p
n
, where, is the inverse distance from the Sun, with (m, n) = (2/7, 2/7), (2/7, 6/7), (4/3, 4/3); other special solutions are also found but they correspond to special choices of density and temperature at the corona. In all the (4/3, 4/3) solutions, the electron and proton temperatures tend to equality at large distances.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
11.
It is shown that X-ray radiation of neutron stars with magnetic fieldsB=1011–1013 G near cyclotron resonances=s
B
(s=1,2,...) is deeply affected by such quantum effects as electron-positron vacuum polarization (significant at V=3×1028
n
e
–1
(B/B
C
4)1, whereB
C
=4.4×1013G), the quantizing character of the magnetic field (significant atV=3 x 1028
n
e
–1
(B/B
c)41 whereB
c
=4.4 x 1013G), the non-harmonic character of the Landau levels, and the quantum recoil of electrons. The latter two factors shift the resonances by the frequency –s
2
B
(B/2B
c
)sin2, being the angle between the direction of radiation propagation and the magnetic field. IfVV
0 (for 1,V
0–1=(mc
2/2T)1/2), the normal mode (NM) polarizations, as well as the absorption coefficientk
1 of the extraordinary NM in the Doppler core of the first resonance (|–| B cos ), is only slightly affected by varyingb and/orV, whereas for the ordinary NM (at 1)k
2k
1
2[b + (3 + tan2–2V)2]k
1. For sufficiently largeb and/orV the quantum effects amplify resonant absorption of the ordinary NM at
B
, with spin-flip transitions playing a major role atb1+V
2. IfVV
0, the coefficientsk
1 andk
2 in the Doppler core of the resonance are of the same order and acquire some peculiar features (shifts, intersections, etc.), with the NM polarizations depending sharply on and being strongly non-orthogonal. AtVV
0,k
2=k
1(cos2 +B/2B
C
) and the polarizations are almost linear. Near high resonances (s2), as a rule,k
1,2(1 + b)
s–1
2s–3 i.e., absorption increases withb due to replacement of the thermal energy of the transverse motion of electron,T, by the magnetic energy
B
. The above effects should be taken into account for an interpretation of observational data on X-ray pulsars (e.g., Her X-1) and other X-ray sources associated with neutron stars. 相似文献
12.
Hong-Nan Zhou 《Astrophysics and Space Science》1988,141(2):199-206
The contact binary system CC Com (=12h09m33s.8, =+22°4339, (1950);V
max=11.31, (B-V)max=1.24) is a W UMa-type system with the shortest known period. The photometric solution of CC Com is presented using the Wilson and Devinney method. The results show that the CC Com belongs to the late-type eclipsing binary with the spectral type K5V and K6V, low temperatureT
1=4300 K,T
2=4265 K, the mass ratioq=0.5873±0.0021, and the inclinationi=87°.719±1°.44. The best regions of the gravity darkening exponents , the bolomotric albedov, and the limb-darkening coefficients are tested. It is found that 0.1250.065, 0.1v0.5, =0.5 are better regions for CC Com. The third body ofl
3 is not found to be significant. The results are combined with the spectroscopic results of Rucinski to provide an estimate of the absolute parameters. 相似文献
13.
Polarization properties of solar and stellar radio emission require, in some cases, emission below the third or fourth coronal electron gyro level, < 3,_c; 4, _c. In the context of plasma radiation, the source parameters should be such that the intermediate magnetic field condition 1 <
p
2
/
c
2
< 3 is satisfied. Supposing this condition, we investigate the generation of electrostatic waves in a warm background plasma with a high-energy component of magnetically trapped electrons. We invoke the conversion of upper-hybrid waves and Bernstein waves into electromagnetic radiation as being responsible for intense radio emission from a coronal magnetic loop. Moreover, odd-half harmonic emissions in the solar radio spectrum as well as the o-mode polarization at the second harmonic of the plasma frequency are natural consequence of this proposed model. 相似文献
14.
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
15.
16.
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
17.
S. T. Revankar 《Astrophysics and Space Science》1982,86(1):13-23
Free convection effects on MHD flow past a semi infinite porous flat plate is studied when the time dependent suction velocity changes in step function form. The solution of the problem is obtained in closed form for the fluid with unit Prandtl number. It is observed that for both cooling and heating of the plate the suction velocity enhances the velocity field. The heat transfer is higher with increase in suction velocity.Notations
B
intensity of magnetic field
-
G
Grashof number
-
H
magnetic field parameter,H=(M+1/4)
1/2–1/2
-
M
magnetic field parameter
-
N
u
Nusselt number
-
P
Prandtl number of the fluid
-
r
suction parameter
-
T
temperature of the fluid
-
T
w
temperature of the plate
-
T
temperature of the fluid at infinity
-
t
time
-
t
non-dimensional time
-
u
velocity of the fluid parallel to the plate
-
u
non-dimensional velocity
-
U
velocity of the free stream
-
suction velocity
- 1
suction velocity att0
- 2
suction velocity att>0
-
x,y
coordinate axes parallel and normal to the plate, respectively
-
y
non-dimensional distance normal to the plate
-
coefficient of volume expansion
-
thermal diffusivity
-
kinematic viscosity
-
electric conductivity of the fluid
-
density of the fluid
-
non-dimensional temperature of the fluid
-
shear stress at the plate
-
non dimensional shear stress
- erf
error function
- erfc
complementary error function 相似文献
18.
James H. Bartlett 《Celestial Mechanics and Dynamical Astronomy》1989,46(2):129-145
The area preserving mapping x = x + a(y – y
3), y = y – a(x – x3), for 0.3 a 2.0 has been studied to locate approximately the x-axis points bounding almost stable regions. For each value of a, these are fixed points with variational trace just greater than 2.0. Transition to chaos can occur rapidly as a increases (with n/k fixed). 相似文献
19.
A family of symplectic integrators adapted for the integration of perturbed Hamiltonian systems of the form H=A+B was given in (McLachlan, 1995). We give here a constructive proof that for all integer p, such integrator exists, with only positive steps, and with a remainder of order O(p + 22), where is the stepsize of the integrator. Moreover, we compute the analytical expressions of the leading terms of the remainders at all orders. We show also that for a large class of systems, a corrector step can be performed such that the remainder becomes O(p +42). The performances of these integrators are compared for the simple pendulum and the planetary three-body problem of Sun–Jupiter–Saturn. 相似文献
20.
Corrado Massa 《Astrophysics and Space Science》1996,246(1):153-158
The consequences of a cosmological term varying asS
–2 in a spatially isotropic universe with scale factorS and conserved matter tensor are investigated. One finds a perpetually expanding universe with positive and gravitational constantG that increases with time. The hard equation of state 3P>U (U mass-energy density,P scalar pressure) applied to the early universe leads to the expansion lawSt (t cosmic time) which solves the horizon problem with no need of inflation. Also the flatness problem is resolved without inflation. The model does not affect the well known predictions on the cosmic light elements abundance which come from standard big bang cosmology.In the present, matter dominated universe one findsdG/dt=2H/U (H is the Hubble parameter) which is consistent with observations provided <10–57 cm–2. Asymptotically (S) the term equalsGU/2, in agreement with other studies. 相似文献