Über die Bindung der Aerosolteilchen auf der Oberfläche der Wolkenelemente

Summary The importance ofStefan's flow by collection of insoluble aerosol particles on the surface of the evaporating droplets by condensation has recently been emphasized mainly in connection with the possible wash-out mechanism in the atmosphere. A simple theory is deduced for the collection efficiency of insoluble particles on droplets under theStefan's force and a comparision is made with the binding of aerosol particles byBrown's motion and microturbulence of air flow. In general we must take in account the influence ofStefan's flow by calculating the wash-out efficiency.     

The electrostatic force between a charged conducting sphere and a charged dielectric sphere in an arbitrarily oriented external electric field

Summary The electrostatic force between a charged conducting sphere and a charged dielectric sphere in a uniform, arbitrarily oriented external electric field is obtained and presented in terms of force coefficients which depend only on the relative geometry of the two spheres and the dielectric constants of the dielectric sphere and the medium. When the dielectric constant of the dielectric sphere is allowed to approach infinity, the resulting computed force agrees with that ofDavis (1964) for two conducting spheres, and when the external field and the charge on the dielectric sphere are set to zero, the resulting force agrees with that ofHall andBeard (1975) for a charged conducting sphere near an uncharged dielectric sphere.     

Coefficients of volume recombination and some derived characteristics of air ions

Summary General formulas derived for the recombination and combination coefficients of charged and uncharged aerosol particles can be adapted for calculation of the recombination coefficient of small air ions by using an appropriate correction term in the exponential function and by introducingThomson's factor of enhancement of the capturing cross-section due to the central electrical forces acting between the oppositely charged ions.By using this corrected formula for the recombination coefficient, some characteristics of the ions to be recombined can be calculated when values of the recombination coefficients measured in dependence on the pressure are applied.     

On the stresses produced in a liquid-saturated porous solid by normal and tangential forces on a moving strip of finite width

Summary This paper deals with the stresses produced in a semi-infinite liquid-saturated porous solid of the type considered byBiot [1]²), by moving normal and tangential forces acting simultaneously on a moving strip of finite width on the free surface. It has been found that the stresses can be obtained in a closed form. It has also been found that if the velocity of the strip exceeds a certain value, the nature of the stresses changes, and there are discontinuities of stress along certain lines. The results have been applied to study the changes in the stresses produced by moving normal and tangential forces with depth and distance.     

On the disturbances in an infinite viscoelastic medium due to transient normal forces and transient twists on the surface of a spherical cavity

Summary In this note the disturbances in an infinite viscoelastic medium ofViogt type with a spherical cavity have been considered. The problem has been solved separately for (1) transient radial forces and (2) transient twist acting on the inner spherical surface of the cavity. Exact solutions have been obtained in both cases.     

On the chemical composition of atmospheric aerosols — Part III: Trends of the total annual precipitation with respect to the chemical content of rainwater over the United States

Summary Following a recent hypothesis on the role of activated sodium chloride particles as potential nuclei of atmospheric precipitation, further analysis is made of average annual data due toC. Junge on the chemical composition of rainwater salts, and correlation of some parameters with the total amount of rainfall is attempted. It is found that the results obtained are in agreement with the proposed role of activated sodium chloride as a nucleus of a substantial part of the atmospheric precipitation.     

A study of the attachment of radon daughter atoms to aerosol particles

Previous studies of the attachment of radon daughter atoms to aerosol particles in the atmospheric air have given varying results, a few of which did not conform to the diffusion theory developed byLassen andRau (1960). Our studies suggest that the radiolytic aerosols formed by gas-phase reactions in the presence of ionizing radiations interfere in the studies carried out with known aerosols. Radiolytic aerosols are formed spontaneously in the system, depending on the concentrations of aerosol-forming gases in the atmospheric air. It is shown that, under experimental conditions which suppressed the formation of radiolytic aerosols, the attachment rates of Ra-A atoms to aerosol particles in the range of 0.2 to 1.0 m in diameter agree with the diffusion theory developed byLassen andRau (1960). Such investigations of the interactions between atoms, molecules, ions, and aerosol particles are highly useful in atmospheric tracer studies.     

The bubble chamber and mechanism of bubble growth

Summary Although the bubble chamber was only invented byGlaser in 1952, there are today over a hundred chambers in use in physics laboratories throughout the world. In the field of high energy physics they have proved to be an invaluable tool and already much information has been obtained concerning very energetic particle interactions and properties of «strange» particles by the use of both hydrocarbon and liquid hydrogen chambers.     

A comparative study on the growth of cloud drops by condensation using an air parcel model with and without entrainment

During a study of the growth of cloud drops by condensation the evolution of cloud drop size spectra with height above cloud base was determined for maritime aerosols, and for continental aerosols containing aerosol particles of mixed composition. Air parcel models were used in which the parcel was either completely closed to mass and heat transfer (strictly adiabatic models), or open to heat transfer and to partial or complete mass transfer (entrainment models). It was found that adiabatic models and models which consider the entraining of air devoid of aerosol particles predict drop size distributions which are considerably narrower than those observed in non-precipitating cumulus clouds, and have only a single maximum. On the other hand, relative broad drop size distributions and distributions with a double maximum — as they are observed in atmospheric clouds — are predicted if the entrainment of both air and aerosol particles are considered in the condensation model. Our results support the findings ofWarner (1973) which were obtained for a purely maritime aerosol.     

Free vibrations of open-section shear walls

The coupled torsional-flexural vibration of open-section shear walls, braced by connecting beams at each floor level, is analysed on the basis of Vlasov's theory of thin-walled beams. The basic dynamic equations and boundary conditions are derived from Hamilton's principle, and a numerical solution obtained by the Ritz-Galerkin method. In addition to the primary torsional and flexural inertias, secondary effects due to rotatory and warping inertia forces have also been taken into account. The method is suitable for both rigid and flexible base conditions. A series of numerical examples is presented in which analytical results are compared with available experimental data, and the effects of secondary inertia forces, base flexibility and connecting beams upon the vibration characteristics of such shear walls are examined for two different structural forms.     

Models for the origin of accretionary lapilli

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.     

Numerical study on the fracturing mechanism of shock wave interactions between two adjacent blast holes in deep rock blasting

With the application of electronic detonators, millisecond blasting is regarded as a significant promising approach to improve the rock fragmentation in deep rock blasting. Thus, it is necessary to investigate the fracturing mechanisms of short-delay blasting. In this work, a rectangle model with two circle boreholes is modeled as a particles assembly based on the discrete element method to simulate the shock wave interactions induced by millisecond blasting. The rectangle model has a size of 12 × 6 m (L × W) and two blast holes have the same diameter of 12 cm. The shock waves are simplified as time-varying forces applied at the particles of walls of the two boreholes. Among a series of numerical tests in this study, the spacing between two adjacent boreholes and delay time of millisecond blasting are considered as two primary variables, and the decoupling charge with a coefficient of 1.5 is taken into account in each case. The results show that stress superposition is not a key factor for improving rock fragmentation (tensile stress interactions rather than compressive stress superposition could affect the generation of cracks), whereas collision actions from isolated particles or particles with weakened constraints play a crucial role in creating the fracture network. The delay time has an influence on causing cracks in rock blasting, however, whether it works heavily depends on the distance between the two holes.

     

Hotspots,mantle convection and plate tectonics: A synthetic calculation

A model is developed that unifies vigorous hotspots with global-scale mantle convection and plate tectonics. The convection dynamics are assumed to generate flow patterns that emerge as closely packed polygonal cells in approaching the asthenosphere, and whose geometry is completely determined by a defining set of vigorous hotspots. Overlying viscously coupled rigid plates are driven with unique velocities (Euler vectors) at which the area integral of the shear forces is zero; these velocities are dynamically stable. The computed plate velocities, resulting from convection based on 15 hotspots, are compared with the velocities of plate motion models AM1-2 (Minster andJordan, 1978) and HS-NUVEL1 (Gripp andGordon, 1990), which combine transform fault geometries, magnetic anomalies and seismic data. The comparison shows a striking agreement for a majority of the plates. Geophysical implications of this numerical exercise are discussed.     

Some implications of statistical transport theory in rock mechanics

Summary Recently, a new theory of the subsidence of rock masses has been advanced byLitwiniszyn and coworkers, which is based on the notion that the individual rock particles perform random walks. It is shown in the present paper that the final equations of the random walk theory can be justified from general principles of statistical mechanics in which no specific theoretical model of particle behaviour has to be made. The theory appears to account appropriately for subsidence phenomena.The research reported in this paper was supported by the Petroleum Research Fund of the American Chemical Society. Acknowledgment is made to the donors of the Petroleum Research Fund administered by the American Chemical Society for support of this reseach.     

Der Jahresrhythmus des Luftdrucks in den Alpen

Summary By means of charts of distribution of amplitude and phase of the first term of harmonic series of the annual pressure variation in the Alps it is shown that it represents a wave which by increasing her amplitude progresses from the outside to the central part of the mountains. Essentially it illustrates the annual process of heating. In renewing earlier studies byConrad about the average change of the annual pressure variation with height illustrated by harmonic dial the altitude of reversing of the sign of this variation is found surprisingly smaller in the Alps than in other regions of the earth probably on account of the maritime influence.     

On the nature,formation and diversity of particulate coherent structures in microgravity conditions and their relevance to materials science and problems of astrophysical interest

Different phenomena related to the spontaneous accumulation of solid particles dispersed in a fluid medium in microgravity conditions are discussed, with an emphasis on recent discoveries and potential links with the general field of astrophysical fluid-dynamics on the one hand, and with terrestrial applications in the field of materials science on the other hand. With special attention to the typical physical forces at play in such an environment, namely, surface-tension gradients, oscillatory residual gravity components, inertial disturbances and forces of an electrostatic nature, specific experimental and numerical examples are presented to provide inputs for an increased understanding of the underlying cause-and-effect relationships. Studying these systems can be seen as a matter of understanding how macroscopic scenarios arise from the cooperative behaviour of sub-parts or competing mechanisms (nonlinearities and interdependencies on various spatial and temporal scales). Through a critical assessment of the properties displayed by the resulting structures (which appear in the form of one-dimensional circuits formed by aligned particles, planar accumulation surfaces, three-dimensional compact structures resembling “quadrics”, micro-crystallites or fractal aggregates), we discuss a possible classification of the related particle attractors in the space of parameters according to the prevailing effect.     

On non-artesian groundwater flow

Summary The present paper deals with certain problems of non-artesian aquifers, with special reference to non-steady flow due to replenishment from the ground surface. Solutions are obtained by direct integration ofBoussinesq's differential equation (transformed), taking also the inclination of the groundwater surface and the slope of the bottom of the aquifer into account. — The study has some bearing on hydrological investigations. For example, it may be desired to find the location of a moving groundwater divide between two water courses, or to determine the quantity of groundwater passing between them. Problems of this nature are also often met with in water supply (artificial infiltration, etc.) and other fields of engineering practice.     

Soil-structure interaction effects on an instrumented building

The paper highlights the use of fem and bi-directional lumped-mass-storey-stiffness numerical models for the study of the soil–structure interaction (ssi) effects on an instrumented building. Data on the structural response have been obtained through the project for seismic instrumentation of a 16-storey r/c cast-in-place dwelling building (Chisinau, Republic of Moldova) during a series of earthquakes (Gutenberg–Richter M _GR = 5.0−6.7). The effect of soil–structure interaction is clearly observed comparing the responses recorded on foundation and free-field. ssi becomes more pronounced for higher level of ground shaking amplifying the natural period of the structure and slightly suppressing high frequences on the foundation in comparison with the free-field motion.     

Efficiency of trenches along railways for trains moving at sub- or supersonic speeds

A full 3D analytical approach is adopted to account for trenches on one or both sides close to a railroad. Low-frequency ground vibrations are investigated due to the passing of trains, and open trenches are used as wave barriers. The modelling technique is based on Fourier transforms and Fourier series. The ground is modelled as a layered semi-infinite domain and the embankment with finite layers. The trenches are obtained by simulating the upper surface layer with two or three finite rectangular regions with appropriate widths. A particular boundary condition is adopted at the vertical sides of all finite regions to enable the solution procedure. Rails and sleepers are accounted for with Euler–Bernoulli beams and an anisotropic Kirchhoff plate with transversal isotropy. The wheel loads from the boogie wheel pairs of the train are simulated as moving forces. Hence, no irregularities in rails or wheels are accounted for.     

Maximum Entropy Spectral Analysis of the geological time series of the oxygen isotope record from deep-sea cores

A Maximum Entropy Spectral Analysis of the geological time series of the oxygen isotope 18 for the last 782,000 years showed 98,000 years as the most prominent periodicity, followed by 40,000 years of less than half the amplitude and still smaller peaks at 24,000, 67,000, 84,000, 107,000 and 786,000 years. Among the astronomical parameters, only eccentricity showed a similar periodicity viz. 96,000 years. Obliquity had a prominent periodicity at 41,000 years which was reflected in the oxygen isotope series also. Corresponding to the bimodal precession peaks (23,000 and 19,000 years), the oxygen isotope series showed a peak at 24,000 years and smaller peaks at 22,000 and 19,000 years. Our results compare well with those obtained byThomson (1990) with a more sophisticated method.