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1.
A numerical evaluation of the complete Navier-Stokes equations of motion for steady-state, incompressible flow past an infinite circular cylinder is given in terms of the stream function, vorticity, and pressure distribution past such bodies. A method is described which allows use of these flow characteristics: (1) to approximate the characteristics of air flow past hexagonal columnar ice crystals falling under gravity at terminal velocity in air, (2) to compute the trajectory of supercooled cloud drops relative to such ice crystals, and (3) to determine the efficiency with which short columnar ice crystals and needle shaped ice crystals collide with supercooled cloud drops. It is found that for all columnar type ice crystals riming is negligible if the cloud drop size is less than 5 m, and that for riming to commence short columnar crystals must have diameters larger than 50 m, while needle crystals must have diameters larger than 40 m. It is further shown that the collision efficiency cut-offs at the small drop radius and at the large drop radius end of the collision efficiency diagram can be explained on the basis of the cloud drop trajectories for these drop size ranges.  相似文献   

2.
A theoretical model is presented which allows computing the efficiency with which aerosol particles of radius 0.1r10 m are collected by simple ice crystal plates of radius 50a c 640 m in air of various relative humidities, temperatures and pressures. Particle capture due to thermophoresis, diffusiophoresis and inertial impaction are considered. It is shown that the capture efficiency of an ice crystal in considerably affected by phoretic effects in the range 0.1r1 m. For aerosol particles ofr>1 m the efficiency is strongly controlled by the flow field around the crystal and the density of the aerosol material. Trajectory analysis also predicts that aerosol particles are preferentially captured by the ice crystal rim. Our theoretica results are found to agree satisfactorily with the laboratory studies presently available. Comparison shows that for the same pressure, temperature and relative humidity of the ambient air ice crystal plates are better aerosol particle scavengers than water drops.  相似文献   

3.
Models for the origin of accretionary lapilli   总被引：1，自引：0，他引：1  
Binding between initially cohesionless ash particles to form concentric accretionary lapilli is provided primarily by the capillary forces of liquid bridges from condensed moisture and by electrostatic attraction. Capillary forces are strong bonds if the particles are in close contact, but they decrease rapidly with increasing particle spacing. Electrostatic attraction between charged ash particles is much weaker but effective over larger distances, increasing the frequency of collision between them.Experimental results of liquid film binding of volcanic ash showed that agglomeration was most successful between 15 and 25 wt.%, defining the agglomeration window for the formation of accretionary lapilli. Below 5–10 wt.% and above about 25–30 wt.% of water, concentric agglomeration was inhibited. Particles <350 m could be selected from a wider particle population in the experiments using only small amounts of water, which can explain the growth of accretionary lapilli in pyroclastic surges around agglomeration nuclei. Experiments testing the behavior of volcanic ash in electric fields showed that ash clusters formed instantaneously when the ash entered the field between a corona discharge gun and a grounded metal plate. The maximum grain size incorporated into the artificial clusters was about 180 m but >90 wt.% of ash was <45 m.Accretionary lapilli form in turbulent ash clouds when particles carrying liquid films of condensed moisture collide with each other and when the binding forces exceed the grain dispersive forces. Larger particles >500 m act as agglomeration nuclei in surges, accreting ash <350 m around them. In pyroclastic flows the aggregates are thought to originate from already size-sorted ash at the interface between the lower avalanche part of the flow and its overriding elutriation cloud. The fine-grained rims around accretionary lapilli found close to source are interpreted to be accreted dominantly by electrostatic attraction of very fine ash similar to clustering in elutriation clouds.  相似文献   

4.
Summary This paper discusses the disturbance produced in an infinite layer of non-homogeneous elastic material characterised by =0 n and =0n(n>0) where and are the density and shear modulus respectively of the material, due to periodic torsional force applied on the wall of a cylindrical hole in the layer. The variation of the displacement component with the radius vector is shown graphically and compared with the corresponding homogeneous case.  相似文献   

5.
A theoretical model is presented which allows computing the efficiency with which aerosol particles of 0.001 r1 m are collected by columnar ice crystals in air of various relative humidities, temperatures, and pressures. Particle capture due to Brownian diffusion, thermo- and diffusiophoresis is considered. It is shown that phoretic effects importantly determine the particle capture process of 0.01r1 m. The various pressure-temperature levels studied are found to affect the collection efficiency only ifr>0.1 m. Comparison shows that water drops generally are better aerosol particle scavengers than columnar ice crystals.  相似文献   

6.
The palaeo-intensities (F a) of the geomagnetic field in Egypt at some ages are determined by archaeomagnetic measurements and found to be:F a=36.2 T at 3100 B.C., Fa=46.8 T at 3000 B.C.,F a=36.5 T at 2780 B.C., 49.0 T at 2500 B.C., 36.4 T at 2200 B.C., 57.5 T at 1990 B.C., 62.1 T atca 1400 B.C., 61.5 T at 1400 B.C., 69.9 T at 600 B.C., 59.3 T at 550 B.C., 79.9 T at 460 B.C., 73.7 T at 450 B.C., 69.7 T at 320 B.C., 56.2 T at A.D. 50, 64.9 T, at A.D. 400, 54.4 T at A.D. 300, 57.5 T at A.D. 700 and 43.0 T at A.D. 1975.The palaeo-inclinations (I a) at some ages are found to be:I a=24.2° at 420 B.C., 44° at A.D. 50, 60.7° at A.D. 703 and 42° at A.D. 1795.The measured values ofF a are affected by the anisotropy of magnetic susceptibility of the samples by 13% to 20% of the expected correct value. The suitable correction of this effect is by multiplyingF by 1/((1+0.2(/90)) andF by 1/((1–0.13 (/90)), whereF andF are the resultant values ofF a if the laboratory field is perpendicular or parallel to the wall of the sample during the Thelliers' experiments, respectively, and is the angle between the direction of natural remnant magnetization of the sample and the direction of the laboratory field.The results of this paper, together with the previous results for Egypt and the neighbourhoods, lead to the production of the secular variation curve of the geomagnetic field in Egypt for the last 5000 years. The intensity of the field shows a periodicity of about 400 years with multiples.  相似文献   

7.
Summary In the present note the problem of torsional vibration of a bar in which the moment of inertia and the torsional rigidity are proportional to 0 + 1s, wheres is the spanwise co-ordinate and 0 and 1 are real numbers, has been considered.  相似文献   

8.
The frictional properties of a crushed granite gouge and of gouges rich in montmorillonite, illite, and serpentine minerals have been investigated at temperatures as high as 600°C, confining pressures as high as 2.5 kbar, a pore pressure of 30 bar, and sliding velocities of 4.8 and 4.8×10–2 m/sec. The gouges showed nearly identical strength behaviors at the two sliding velocities; all four gouges, however, showed a greater tendency to stick-slip movement and somewhat higher stress drops in the experiments at 4.8×10–2 m/sec. Varying the sliding velocity also had an effect on the mineral assemblages and deformation textures developed in the heated gouges. The principal mineralogical difference was that at 400°C and 1 kbar confining pressure a serpentine breakdown reaction occurred in the experiments at 4.8×10–2 m/sec but not in those at 4.8 m/sec. The textures developed in the gouge layers were in part functions of the gouge type and the temperature, but changes in the sliding velocity affected, among other features, the degree of mineral deformation and the orientation of some fractures.  相似文献   

9.
Summary Dispersion in Rayleigh waves is discussed for semi-infinite media with = 1(1 ± cos s z) and = 1(1 ± cosh s z), being the rigidity of the medium. A few workers tried with the above Fourier type of model but failed to find the dispersive nature. Because they neglected s due to the complexity of the calculation they arrived at a non dispersive frequency equation. This difficulty is removed in this paper and a dispersive frequency equation is obtained which shows both direct and inverse dispersion. The second model leads to non-convergent solution forz but shows many interesting results which are also discussed.  相似文献   

10.
Summary Rotatory vibrations of a thick spherical shell of isotropic non-homogeneous material with rigidity and density given by (i) = 0 r -2 withQ =Q 0 r -2 e 2mr and (ii) = 0 r m with =Q 0 r n have been discussed and the frequency equation is derived with numerical enumeration of frequency in each case.  相似文献   

11.
Fractals,fault-gouge,and friction   总被引：5，自引：0，他引：5  
The particle-size distribution of a natural fault-gouge has been determined over the range from 5 m to 40 cm. The gouge is self-similar over the range from 5 m to 1 cm having a fractal dimension of 2.60±0.11. The lower and upper fractal limits were also determined. The lower fractal limit occurs at a dimension of about 1–10 m where mineral cleavage and intergranular porosity dominate the cataclasis. The upper fractal limit occurs at particle sizes on the order of 1 cm where the scaled particle density decreases abruptly by a factor of about three. By analogy to soil-mechanics shear box tests and laboratory rock friction experiments, it is argued that the upper fractal limit of the gouge determines the characteristic displacement parameter in stick-slip friction models. A characteristic displacement on the order of 1 cm is consistent with estimates based on numerical simulations of faulting.  相似文献   

12.
The 1981–82 Solar Mesosphere Explorer (SME) mission is described. The SME experiment will provide a comprehensive study of mesospheric ozone and the processes which form and destroy it. Five instruments will be carried on the spinning spacecraft to measure the ozone density and its altitude distribution from 30 to 80 km, monitor the incoming solar ultraviolet radiation, and measure other atmospheric constituent which affect ozone. The polar-orbiting spacecraft will be placed into a 3pm-3 am Sun-synchronous orbit. The atmospheric measurements will scan the Earth's limb and measure: (1) the mesospheric and stratospheric ozone density distribution by inversion of Rayleigh-scattered ultraviolet limb radiance, and the thermal emission from ozone at 9.6 m; (2) the water vapor density distribution by inversion of thermal emission at 6.3 m; (3) the ozone photolysis rate by inversion of the O2(1g) 1.27 m limb radiance; (4) the temperature profile by a combination of narrow-band and wide-band measurements of the 15 m thermal emission by CO2; and, (5) theNO2 density distribution by inversion of Rayleighscattered limb radiance at 0.439 m. The solar ultraviolet monitor will measure both the 0.2–0.31 m spectral region and the Lyman-alpha (0.1216 m) contribution to the solar irradiance. This combination of measurements will provide a rigorous test of the photochemical equilibrium theory of the mesospheric oxygen-hydrogen system, will determine what changes occur in the ozone distribution as a result of changes in the incoming solar radiation, and will detect changes that may occur as a result of meteorological disturbances.  相似文献   

13.
Summary The coefficient of the gamma-ray absorption Cs 137 investigated in eclogites of the Bohemian Massif varies with fresh samples from0.2477 cm –1 to 0.2804 cm –1 . Symplectite is the main factor decreasing the value of down to0.242 cm –1 . On the contrary, the coefficient increases with the increasing content of clinopyroxene and especially of garnet. The linear dependence of the coefficient on the density may be expressed by the equation =0.0682+0.028.  相似文献   

14.
Summary This paper studies the propagation of Surface Waves on a spherically aeolotropic shell surrounded by vacuum. The elastic constantsc ij and density of the material of the shell are assumed to be of the form ij r l and o r m respectively, where ij o are constants andl, m are any integers.  相似文献   

15.
Summary We have discussed in the paper the disturbance produced in an infinite layer of nonhomogeneous elastic material characterised by = 0 Z and = 0 Z where and are the density and shear modulus respectively of the material due to periodic torsional force applied on the wall of a cylindrical hole in the layer. The variation of the displacement component with the depth of the layer is shown graphically and compared with the corresponding homogeneous case.  相似文献   

16.
— Starting with fundamental-mode Rayleigh-wave attenuation coefficient values (R) predicted by previously determined frequency-independent models of shear-wave Q (Q), we have obtained frequency-dependent Q models that explain measured values of R as well as of Lg coda Q and its frequency dependence at 1 Hz (Qo and , respectively) for China and some adjacent regions. The process combines trial-and-error selection of a model for the depth distribution of the frequency dependence parameter () for Q with a formal inversion for the depth distribution of Q at 1 Hz. Fifteen of the derived models have depth distributions of that are constant, or nearly constant, between the surface and a depth of 30 km. distributions that vary with depth in the upper 30 km are necessary to explain the remaining seven models. values for the depth-independent models vary between 0.4 and 0.7 everywhere except in the western portion of the Tibetan Plateau where they range between about 0.1 and 0.3 for three paths. These low values lie in a region where QLg and crustal Q are very low and suggest that they should also be low for high-frequency propagation. The models in which varies with depth all show a decrease in that value ranging between 0.55 and 0.8 in the upper 15 km of the crust and (with two exceptions where =0.0) between 0.3 and 0.55 in the depth range 15–30 km. The distribution of values between 0.6 and 0.8 (the higher part of the range) in the upper crust indicates that high-frequency waves will propagate most efficiently, relative to low-frequency waves, in a band that includes, and strikes north-northeastward from the path between event 212/97 and KMI to the path between event 180/95 and station HIA in the north.Acknowledgement. We thank Lianli Cong for providing his code for plotting crustal Q models and Robert Herrmann for writing the mode summation code for computing Lg synthetics used in this study. Our work benefited from helpful discussions with Jack Xie at Lamont-Doherty Earth Observatory of Columbia University. This research was sponsored by the Defense Threat Reduction Agency Contract No. DTRA-01-00-C-0213.  相似文献   

17.
Summary By comparing the equalities expressing the solar flux within a wide spectral region on the assumption of an extintion within the atmospheric aerosol given by – and that of an extintion represented by 1–1, a relationship is established by means of which: 1) The error is discussed which is done when the air opacity is expressed by 1, in the case when 1; 2) A simple and quick method is worked out for determining the parameters and from actinometric observations, carried out within the spectral regions <525 m and 525 m<<625 m.  相似文献   

18.
The impact of contrail-induced cirrus clouds on regional climate is estimated for mean atmospheric conditions of southern Germany in the months of July and October. This is done by use of a regionalized one-dimensional radiative convective model (RCM). The influence of an increased ice cloud cover is studied by comparing RCM results representing climatological values with a modified case. In order to study the sensitivity of this effect on the radiative characteristics of the ice cloud, two types of additional ice clouds were modelled: cirrus and contrails, the latter cloud type containing a higher number of smaller and less of the larger cloud particles. Ice cloud parameters are calculated on the basis of a particle size distribution which covers the range from 2 to 2000 m, taking into consideration recent measurements which show a remarkable amount of particles smaller than 20 m. It turns out that a 10% increase in ice cloud cover leads to a surface temperature increase in the order of 1K, ranging from 1.1 to 1.2K in July and from 0.8 to 0.9K in October depending on the radiative characteristics of the air-traffic-induced ice clouds. Modelling the current contrail cloud cover which is near 0.5% over Europe yields a surface temperature increase in the order of 0.05 K.  相似文献   

19.
Helicopter measurements of solar irradiance and meteorological data within the atmospheric boundary-layer were made in Lagos during February 1979. Filter samples of aerosols were collected both during flight in February 1979 and at ground level in December 1978. Profile data on spectral aerosol optical depth were obtained and, from these, the aerosol extinction coefficient at two wavelengths (0.5 and 0.88 m) were calculated. Precipitable water was low and was contained mainly within the 750 m layer above ground, suggesting the establishment of a deep unstable boundary layer. Calculated channel energy depletions by aerosols show that, within the first 750 m of the surface, the 0·88 m might be more efficient at attenuating solar energy than 0·5 m. The lagoon (maritime) aerosol sample indicated a more monodisperse size-distribution than the dusty harmattan aerosol sample.  相似文献   

20.
Summary Magnetic field structures at great distances from the Sun have been analyzed qualitatively for a simple vacuum reconnection model of the interplanetary and interstellar magnetic field. In dependence on the mutual orientation of the main solar dipole s and the local interstellar fieldB 0 , either an open or closed configuration of the large-scale field is formed. For(s B 0 )>0, the field lines are represented by a system of magnetic lines open towards interstellar space. In the case of(s B 0 )<0 there exist two zero-points and a separating surface below the heliopause separating the open lines of the interstellar field from the closed lines of the interplanetary field. The magnetic field configuration is characterized by a certain asymmetry, which is considered for(s B 0 )=0.  相似文献   

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