Cloud Stability Research Articles

RETENTION OF D‐LIMONENE DURING FREEZE DRYING OF ORANGE JUICE

Retention of d‐limonene during freeze drying of citrus juices from several sources was investigated as a multi‐phase problem. Reconstituted to 25 and 10° Brix, commercial frozen concentrates show high retention (between 90 and lOO%), whereas fresh‐squeezed juice shows a relatively low retention (about 30%), comparable to that found previously for synthetic emulsions. Retention data for pasteurized fresh juice after substantial agitation and for never‐concentrated, commercial pasteurized juices show an intermediate value (between 60 and 70%). Presence and stability of cloud are shown to correlate closely with improved d‐limonene retention in commercial frozen concentrates. On this basis, a simple model is developed which predicts the retention level for this type of juice in the asymptotic region. The results for the other types of juice studied are interpreted with the aid of microscopic determinations of oil droplet size and the model derived for synthetic emulsions.

Morphology of the magnetospheric barium release

The magnetospheric barium release experiment of September 21, 1971, was observed by a high-performance image intensifier television camera system from Kitt Peak National Observatory, Tucson, Arizona. The system produced high-resolution video recordings of the dynamic morphology of the barium ion cloud. The system was calibrated for absolute sensitivity, thus enabling the reconstruction of the barium density profiles in the cloud. The ionized plasma expands along the field line with the velocity somewhat greater than the neutral expansion velocity. Perpendicular to the magnetic field line, the expansion of the cloud is limited by the forces exerted by the earth's magnetic field. Thus, the cloud takes up a field-aligned filamentary structure. As early as 30 sec after release, two major filaments could be distinguished. Two minutes after release, the cloud already consisted of at least 8 or 10 filamentary striationlike structures. These are formed in the low-density expanded part of the cloud. These striations and the diffuse parts of the cloud move in a direction perpendicular to the magnetic field with a velocity different from that of the main dense core of the cloud. This differential velocity moves the lower-density parts away from the main core. These lower-density parts appear to be highly structured in the form of fieldaligned striations. During the first 8 min after release, the high-density main core part erodes to a very narrow strip, which is about 12 km wide. This width of the central core is less than the diameter of the gyro-orbit of the initial velocity barium ions in the ambient magnetic field. The rapid fragmentation of the cloud to such narrow forms has interesting implications for the stability of dense magnetospheric plasma clouds.

Pectinase stabilization of orange juice cloud

Pectinase stabilization of orange juice cloud

Modification of laboratory fog with organic surface films

Laboratory fogs were generated under controlled and reproducible conditions in a 600-meter3 chamber and seeded with aerosols of various compounds that form organic surface films at air-water interfaces. The fogs were programmed through several slow expansions and compressions to assure adequate time to permit the coating of the fog drops with a surface film and to avoid nucleation on aerosols of the surface active material. Visibility characteristics and droplet data were obtained for both seeded and control fogs. Cetyl alcohol stabilized fogs significantly during compressions and periods of constant pressure. This observation was substantiated by measurements of visibility, drop size, drop concentration, and liquid water content of the fogs. The cetyl alcohol, a linear molecule, formed tightly packed surface films around the fog drops, which inhibited the transport of water molecules across the water-drop-air interface and thereby appreciably retarded the evaporation rate of the fog droplets. Oleyl alcohol, a nonlinear molecule, formed fluid surface films that did not retard evaporation or alter fog visibility. The data suggest that droplet growth on treated nuclei can be retarded but that under the controlled conditions of these experiments fog formation was not significantly altered by the chemical seeding. It is concluded that additional experiments designed to limit natural fog formation with evaporation retardants are not warranted. In the natural atmosphere the release of organic compounds from human activity may cause inadvertent cloud and fog stabilization; the determination of the chemistry and physics of this process represents an important and relatively unexplored area of environmental inquiry.

Where Stars Form

Where Stars Form

Water Cloud Stabilization with Chlorinated Silanes

Water Cloud Stabilization with Chlorinated Silanes

Striations in ionospheric ion clouds, 1

We discuss the occurrence of striated irregularities in ionospheric ion clouds. Striations can either be impressed on the cloud from the ambient medium or generated by the cloud itself. If they are impressed on the cloud, the Striations are simply tracers of small-scale electric fields in their environment. To ascertain whether this is indeed the case, we investigate the stability of the cloud. It is pointed out that the cloud cannot be considered an isolated object and that its interaction with the ionosphere is essential if we consider striation formation by the cloud itself. In this part 1, the short-circuiting effect on cloud-generated polarization fields is considered in detail. The effect of the simultaneously generated image Striations is discussed for a homogeneous ionosphere. This effect is very strong, but for its final evaluation one needs a more realistic model of the ionosphere. This treatment will be the subject of part 2.

Growth and stability of artificial ion clouds in the ionosphere

A number of instabilities that may account for sudden onset of striations in ionospheric barium clouds are considered. The E×B instability, driven by confined action of the ambient ionospheric electric field and the cloud density gradient, is shown to be the most likely cause. The equilibrium state of the cloud is obtained by an expansion technique, yielding ion density, internal electric field, and cloud velocity. The linearized small oscillation equations are then obtained and are reduced to two-dimensional form. A trial solution yields an instability threshold (expressed either as critical electric field or as onset time delay) that is of reasonable magnitude.

Unstable flow in martensite and ferrite

It is proposed that unstable plastic flow of iron alloys containing carbon or nitrogen occurs when (∂ lnν/∂τ*)T becomes negative (v is the average velocity of the dislocations andτ* the effective stress acting upon them) at the maximum in the force-velocity curve deduced from either the Snoek or the Cottrell steady-state drag model. In addition, a nucleating event is necessary. A model is developed which predicts relationships between the applied stress, the strain rate and the temperature at the onset of unstable flow, and also the activation energy associated with the event. Experiments have been carried out on iron-carbon and iron-nickel-carbon alloys covering a range of carbon concentration in solution. The alloys were either annealed ferrite or martensite and, thus, the extremes of the range of possible dislocation density were examined. Two distinct types of plastic instability were identified: jerky flow, the result of Snoek interaction, and serrated flow due to Cottrell drag. All the qualitative and quantitative features of the phenomenon which were examined were found to be in complete accord with the model. The average velocity of the dislocations as a function of the temperature at the start of unstable flow has been deduced from the model and an estimate of the density of dislocations moving at the time has been made using measured values of the critical strain rate. The strain rate and temperature at which unstable flow disappears were measured as a function of the carbon concentration and the two types of substructure. The data show that an explanation based on the assumption that the phenomenon involved is the same as that producing the Koster internal-friction peak is untenable. An alternative suggestion, based on the relative stability of a Cottrell cloud and a carbide precipitate, is discussed briefly and qualitatively.

Physico‐chemical characteristics of orange juice cloud

AbstractOrange juice is a suspension of heterogeneous particles in a clear serum. The size of the particles varies between 0·05 μm and a few hundred μm. The particles with a size below 2 μm constitute the stable ‘cloud’. This fraction consists of needle‐like crystals of hesperidin, chromoplastids, amorphous (rag) particles and oil globules attached to some of these particles. The adsorption of oil globules on the rag particles enhances their stability in suspension, by decreasing their density. The hesperidin crystals are formed partly by crystallisation immediately after juice extraction. All the cloud particles exhibit a negative charge, which decreases with decreasing pH. However, it seems that hydration rather than electrical charge is responsible for the stabilisation of the cloud. Heat treatment of the juice causes an increase in the number of fine particles at the expense of coarser ones. In this process some extraction of pectin into the serum also takes place but this has little significance on the cloudiness and cloud stability of the juice.

The Influence of Cloud Nucleus Population on the Microstructure and Stability of Convective Clouds

The Influence of Cloud Nucleus Population on the Microstructure and Stability of Convective Clouds

The Influence of Cloud Nucleus Population on the Microstructure and Stability of Convective Clouds

Measurements of the concentration of cloud droplets and of the supersaturation spectrum of the cloud nucleus population in the air below cloud base showed a strong correlation between these properties. It is concluded that variations in the cloud nucleus content of the air are primarily responsible for variations of cloud droplet concentrations and colloidal stability.

The Microstructure and Colloidal Stability of Warm Clouds

Observations on the droplet spectra of different kinds of warm clouds have shown that systematic differences in microstructure exist between the various cloud types. These differences in microstructure are related in a simple way to differences in observed colloidal stability.

The Microstructure and Colloidal Stability of Warm Clouds

The Microstructure and Colloidal Stability of Warm Clouds

The Microstructure and Colloidal Stability of Warm Clouds: Part I - The Relation between Structure and Stability

Observations on the droplet spectra of different kinds of warm clouds have shown that systematic differences in microstructure exist between the various cloud types. These differences in microstructure are related in a simple way to differences in observed colloidal stability.

The Microstructure and Colloidal Stability of Warm Clouds: Part II - The Causes of the Variations in Microstructure

An attempt is made to explore the causes of the differences in microstructure between the Hawaiian orographic cloud, maritime cumuli and continental cumuli, observations on which were discussed in Part I of this series.

The Growth of Cloud Drops by Condensation. II. The Formation of Large Cloud Drops

The observed stability of many deep non-freezing clouds suggests that there is a gap between the sizes normally reached by droplets due to condensation and the sizes at which coalescence of drops becomes effective in producing rain. One way such clouds could yield rain would be for condensation to give rise to some drops bigger than usual. Conditions for the growth of some drops to a relatively large size by condensation are investigated theoretically. This requires that in some air parcels an undue proportion of the available water vapour should condense on relatively few nuclei. The types of vertical motion and nucleus spectra which could yield this result are investigated. Slow motions are favourable. Suitable spectra are : (i) a few " giant ' nuclei (M = 10-10, 10-12) ; (ii) all but a few nuclei relatively small. Rain itself tends to produce type (ii) spectrum, so that it could perhaps act regeneratively. It is found that very large cloud drops can be formed by condensation under conditions which, on present knowledge, seem likely to occur at times, but not normally. The hypothesis that the factors studied here largely determine colloidal stability in non-freezing cloud is therefore satisfactory, inasmuch as it leaves room for both stability and instability.

Collisions of Cloud Droplets

WHETHER cloud droplets coalesce on impact is a problem of obvious theoretical and practical interest, having bearings on theories of rain formation, methods of fog dispersal, the stability of clouds, etc. A major obstacle in the way of providing an answer to this question is the difficulty of simulating in the laboratory the conditions that obtain naturally in clouds. Nevertheless, in July 1941, I made some experiments in connexion with this subject at the Imperial College with the aid of facilities kindly provided by Prof. (now Sir George) Thomson, and with the help of Dr. J. Mazur, and the results obtained may be of interest to others concerned with the same problem.