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Artificial accretions with cylindrical symmetry have been grown using a simple wind tunnel. The main features of the apparatus are described. Factors concerning the validity of the simulation of natural hail are discussed. Thin sections of the samples are used to study the crystal fabric of the accretions. This study is devoted mainly to the “dry” regime of growth, and the effects on the fabric of sample rotation during growth and of mixed clouds are reported. In dry growth no effects are observed for rotational speed up to 40 Hz. Marked asperities form on wet and spongy deposits formed at 30–40 Hz; their structure strongly resembles that of icicle lobes in large hailstones. Ice crystals in the airstream are readily captured by and modify the structure of wet and spongy growths. Although ice crystals do not appear to be captured by dry growths in quantities sufficient to influence the growth rates, their presence in the airstream does modify the crystal structure. In following parts of this serie...

This paper is motivated by a general interest in pulsed energy addition to a surface in vacuum at high power fluxes (> 1 MW/cm absorbed). The theoretical treatment assumes a perfect gas without plasma formation, and examples are for aluminum. Transient heat conduction into the surface, vapor flux through a Knudsen layer at the surface, and transient one-dimensional flow of vapor into the surrounding vacuum are included as part of the modeling. Results show that the Knudsen layer remains choked so long as the absorbed power is constant or increasing, and it is unchoked when the absorbed power is decreasing. The problem is fully coupled in the latter case. Quasisteady vapor efflux from the surface is established within a fraction of the pulse time at sufficiently high power fluxes. Impulse coupling coefficients due to vapor recoil are noted.

The structure of ice precipitation in northeastern Colorado, collected within summer cumulus clouds and at the ground beneath thunderstorms, shows that the dominant precipitation formation mechanism is the riming of small ice particles, not liquid coalescence. While direct evidence of a stage involving the vapor growth of ice crystals is rare, such a stage is probably present in most cases.

Radial variations of deuterium content are measured in nine large hailstones from three storms; of tritium content in one of the nine; and tangential variations of deuterium content in a wet-growth layer in five of the nine. Crystal size and air bubble content are noted as well. It is concluded 1) that probably neither air bubble content nor crystal size is as good a relative height indicator as deuterium content; 2) that the trajectories of large hailstones can be very simple, not involving recirculations at larger-than-embryo sizes though two of the nine stones analyzed do show recirculation; 3) that the maximum altitude of growth of several of the large hailstones studied was at a temperature above −25°C; 4) that wet-growth layers can show significant tangential variations in D-content; and 5) that studies of hailstone radial deuterium variations can yield valuable information when applied to many hailstones from single storms or when coupled with deuterium measurements on samples of liquid wa...

IV. Introduction A. State of useful knowledge B. List of symbols C. Basic theory and conventions Atmospheric ice nuclei A. Origin B. Mode of action C. Detection and measurement Some approaches to a more basic understanding A. Epitaxy 6. Adsorption C. Entropy effects D. Two-dimensional nucleation Conclusion 369 371 372 373 377 377 378 381 385 386 388 389 390 393

Thermal hysteresis antifreeze proteins, first discovered in polar marine fishes, are fairly common in overwintering insects where they also help prevent freezing. However, a few species of insects that tolerate freezing also contain these proteins, and in these species the function of the proteins is uncertain. The studies outlined here demonstrate that the thermal hysteresis proteins from the overwintering larvae of the beetle Dendroides canadensis are extremely efficient in inhibiting ice recrystallization. Since recrystallization is a potential source of freezing damage, we suggest that this may be a role of the antifreeze proteins within freeze tolerant insects.

The procedures required in measuring and representing hailstone orientation fabrics, and the reason for the development of one particular fabric, are discussed. Spongy growth has been found to give rise to a fabric with the c axes preferentially perpendicular to the growth direction. The origin of this fabric may be used as a spongy growth criterion. The natural hail examined did not have this fabric, and consequently did not grow spongy.

Discussions of possible causes of preferred crystal orientations in fresh-water ice are presented, with data on ice orientations from several Arctic lakes. Evidently, initial ice orientations are determined by wind conditions. Orientation selection during growth at the bottom of the ice also takes place, but in the lake ice examined it is apparently largely unsystematic. Constitutional supercooling can cause c-axis-horizontal orientations, but it is not of sufficient magnitude in the lakes examined to have much effect. Striations are locally significant but erratic.

The range of lobe structures found in natural hailstones is illustrated and classified on the basis of form and growth conditions. Lobes that form in dry growth are cusped, and probably result from a “collection efficiency” effect, lobes growing faster than their surroundings because they collect more material. These lobes probably only form to a marked extent when a hailstone is tumbling. Lobes in wet or spongy growth, icicle lobes, are not cusped and evidently form more as icicles form, by flow of liquid water over the hailstone surfaces and preferential freezing at the tips of projections. The icicle lobes are less developed in very spongy growth than in slightly spongy growth. Distinct, radial air bubble features in hailstones are associated with the cusp-lines between the dry growth lobes. Less distinct, radial air bubble trains are found along the icicle lobe axes.

The process of the formation of new crystals at the interface between a crystal and its supercooled melt, by classical, heterogeneous nucleation, is examined theoretically and is suggested as a possible explanation for a number of crystal growth phenomena. Nucleation of new crystals at large angle lattice mismatches with the old, but at orientations such that the lattices “fit” across the interface is illustrated. Nucleation of new crystals appears to be responsible for the development of preferred orientations in deposits built up by the accretion of supercooled droplets, is advanced as an explanation for curved crystal growth, and is a possible explanation for some features of spherulites.

Direct observations of the growth of ice on, and perpendicular to, a water‐air interface are described, in an experiment reproducing the conditions of formation of natural lake ice. The final, preferred crystal orientation is affected by the initial orientations and by selective wedging cut of grains of certain orientations, but often the most important factor is grain boundary migration. Boundary migration is driven in part by interfacial energy and probably in part by stress. The origin of the stress is not known. Preferred intergrain orientations are found.

The major purpose of determining the water and ice nucleating effectiveness of atmospheric aerosols is to evaluate their effects upon cloud and precipitation formation. A review of classical heterogeneous nucleation theory shows the nucleating effectiveness to depend in an important way upon so many complex factors that the only possible approach is direct measurement. The same complexities affect both the measuring technique and the action of the aerosol within clouds. Consequently the techniques must be adapted to the kind of natural environment that the aerosol will encounter, in each specific case, before any important conclusions can be drawn from nucleus measurements.

Spendlove, Rex S. (California State Department of Public Health, Berkeley), Edwin H. Lennette, Charles O. Knight, and Jean N. Chin . Production in FL cells of infectious and potentially infectious reovirus. J. Bacteriol. 92: 1036–1040. 1966.—A comparative study was made of the development in, and release from, FL cells of infectious and potentially infectious (chymotrypsin-activatable) reovirus (Lang strain). The latent period was shorter, the rate of synthesis was more rapid, and the total yield was more than 10-fold greater in potentially infectious virus as compared with infectious virus. Almost all of the potentially infectious virus, but only approximately one-third of the infectious virus, was released from the infected cells.

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The results of two new experiments designed to determine the contact angle of water on ice are reported. In one it is shown that the first stage of melting of a clean ice surface is liquid formation at discrete sites, not uniformly over the surface as would be predicted if the contact angle were zero. The water has a downward meniscus and a sharp contact angle against the ice during both melting and freezing. In the second experiment ice discs are grown in water at approximately 0·010°C supercooling, and contacted by air bubbles on their smooth, basal faces. According to this experiment the contact angle of water on ice is zero. These contradictory results may be a result of anisotropic surface energy, or an effect of disequilibrium.

Small volumes of spongy ice were produced by nucleating supercooled water in balloons at temperatures from −3 to −10C. The original freezing structure is faithfully preserved by quenching the spongy ice in a dry ice-alcohol mixture, and this method is suggested as an important collection technique for freshly fallen hailstones. With slower final freezing rates, recrystallization takes place, consisting of either grain growth only, or of nucleation and growth of new grains. Free growth of ice in water at or above −10C is probably not accompanied by spontaneous nucleation of new crystals in these experiments; reports to the contrary may be a result of primary recrystallization, which does occur at normal rates of final freezing.

The principle of formation of etch pits with crystal faces on ice crystals is explained as a natural consequence of evaporation (or any sort of dissolution) at concave surfaces of crystals. A new technique of ice etching using perforated metal foil is described. It is a useful way of determining grain orientations in hail stones.

Ice growing dendritically from supercooled water along some foreign surfaces changes its orientation as it grows, in response to asymmetrical temperature gradients. A qualitative, preliminary description and discussion of this phenomenon is presented. The only stable growth is with the c axis [0001] perpendicular to the surface. Other orientations in general curve toward this. Increased initial supercooling sharpens the curvature, and dissolved NaCl inhibits it. The curvature is discussed in terms of edge dislocations introduced during growth. The density of dislocations responsible for the curvature reaches 108 lines/cm2. Orientations of ice grown in containers is a consequence of curved growth. Direct formation of polycrystalline ice from supercooled water is reported. The method used in observing curved ice growth also allows observation of the formation of striations and related phenomena.

A more detailed examination is made of the stress-generated ice crystallization features already discussed by LaChapelle (1968), using mainly thin-section techniques. The crystallization features on the walls of a tunnel within the Blue Glacier are localized at fine-grained layers and are fed by liquid water traveling along grain boundaries within the wall and within the deposits themselves. The water filling the crevasse encountered at the end of the tunnel was freezing uniformly to the crevasse walls as well as forming Thomson crystals within the water, and the evidence points to an important role for constitutional super-cooling in the Thomson crystal formation. The forms of most of the Thomson crystals are explainable qualitatively by beat flow effects.

Summary Development of viral antigen and infectious virus were followed in HeLa cells infected with type 1 reovirus. The antigen was found to go through a sequence of four stages determined by shape and intracellular location. Six to eight hours after infection, antigen appeared in particulate form in the cytoplasm. The particles coalesced to form a reticulum-like structure disseminated throughout the cytoplasm; the reticulum in most cases subsequently became perinuclear. In the final stage, the antigen lost much of its reticular structure and spread confluently throughout the cytoplasm. The cytoplasm began “bubbling” and cell processes containing viral antigen constricted and pinched off from the cell. Cell-associated virus and viral antigen appeared simultaneously after 6 to 8 hr of infection and increased to a maximal concentration at 24 hr. The rate of virus release was slow and appeared to be related to the “bubbling” phenomenon. The effect of the location of antigen and its slow release from the cell may be related to the slow spread of virus in plaques.

Polygonization of aged sea ice is described and is related to internal stress. The subboundaries of the polygonization structure are accounted for by dislocation phenomena and by the freezing of brine in tapering internal fractures. Movement of subboundaries in ice under stress is illustrated. It is suggested that the very much smaller microstructure found in ice frozen from "fresh" water may have the same origin as polygonization in sea ice. Internal fracturing provides avenues for brine migration and is thought to be a significant factor in natural sea-ice purification. Polygonization structures may significantly affect the strength of sea ice.

The freezing of a spongy ice deposit produces a variety of distinctive internal structures caused by the expansion of the trapped water upon freezing. Cracks, certain arrangements of sub-boundaries, and some particular air bubble structures formed in this way are criteria of spongy hailstone growth, after complete freezing. Conclusions from these criteria applied to natural hail agree with conclusions from orientation fabrics.

It is argued that the mechanism of spongy hailstone growth, in certain conditions, is analogous to growth in conditions of constitutional supercooling. If so, this allows the application of the large body of information on, and theory of, crystallization in constitutional supercooling to be applied to spongy hailstone growth. Justification of this view is from fundamental principles, from observations of spongy icicles, and from the orientation fabrics of artificial spongy hail. Application to natural hail is restricted to cases in which the crystal size is fairly large.

When a rapidly freezing, water-ice interface approaches a water-air interface at a low angle, the water shirnks away from the advancing intersection line. This effect seems to indicate that γ IA γ IW + γ WA . The apparent intersection angle decreases with decreasing freezing rate, -a fact which is explained qualitatively by an increase of the slope of the water-ice interface adjacent to the contact line with decreasing freezing rate, caused by experimental conditions. A minimum value for the receding contact angle of water on ice is 12 ± 1° at slightly below 0°C., at a receding rate of about 1 cm./sec. on a somewhat rough surface. The possible error from the fact that the water-ice interface can not be observed directly is less than three degrees.

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Study of frozen drops preserved as hailstone embryos shows that breaking during freezing is fairly common. Drops in clouds tumble and grow by accretion as they freeze. Both effects are expected to favor shattering, but neither has been simulated properly in laboratory studies of possible ice multiplication.

Nucleation rates on cylindrical nuclei are calculated using the classical theory. For very good but very small nuclei, the minimum cylinder radius that causes nucleation is about half that for spherical nuclei, other things being equal. The ice-supercooled water system is used for illustration.

The spectrum of a petroleum fluid inclusion, obtained from a producing oil well in the Gulf of Mexico, was compared with spectra obtained on three bulk oil samples produced from the same well. Comparison of the spectra of bulk and included petroleum samples shows several major differences. These differences are consistent with the loss of the more volatile components from the bulk oil samples.

Gastric carcinoma has not been recognized as a complication of Gardner's syndrome in the Western world. We report a 37-yr-old white woman with Gardner's syndrome who had gastric adenocarcinoma in association with diffuse gastric polyps. At the time of laparotomy, the disease was metastatic to regional lymph nodes. In addition, the patient had mesenteric and retroperitoneal fibromatosis, thyroid adenomas, a chest wall hemangioma, and fibrocystic disease of the breast. This is the first reported case of gastric adenocarcinoma complicating Gardner's syndrome in North America.

In this paper, a theoretical model is developed for rapid surface vaporization into a surrounding ambient atmosphere. The primary emphasis is on metallic surfaces. Power input levels are taken to be low enough so that thermodynamic equilibrium can be assumed before phase change to gas. At high evaporation rates there will be a narrow Knudsen layer region in the gaseous flow just outside the phase interface in which translational nonequilibrium prevails. The modeling treats this layer as a gasdynamic discontinuity and approximate jump conditions are derived. The flow Mach number just outside the Knudsen layer is dictated by the state well away from the surface. Its determination is discussed both for a simple model of transient flow induced by a laser pulse and for the general case of time-varying power input. Examples assume the metallic surface is aluminum and the surrounding air pressure ranges from 1 atm to hard vacuum.

The melting of pure ice single crystals can be inhibited by the presence of an antifreeze glycopeptide isolated from an Antarctic fish. This inhibition effect exhibits crystallographic dependence and can result in superheating of the crystal by heat conduction across the ice-solution interface. The antifreeze molecules inhibit melting in a manner more or less symmetrical to their well-known effect of inhibiting freezing. The melting effect is best expressed at concave ice interfaces, whereas the freezing effect is best expressed at convex ones. Both are restricted to orientations near (1010) with the particular antifreeze that was used.

We found the clinical features of fibrolamellar hepatoma similar to those of nonfibrolamellar hepatoma with the exception of patient age. Although the histopathologic findings of fibrolamellar hepatoma are distinct and easily recognizable, we found that fibrolamellar hepatomas may be histologically heterogeneous. The overall length of survival of patients with fibrolamellar hepatoma was greater than that of patients with nonfibrolamellar hepatoma, but the survival resection was similar, regardless of histologic characteristics. Differences in overall survival between histologic subtypes probably reflects differences in the rate of resectability between fibrolamellar and nonfibrolamellar hepatomas.

The EEA stapler now offers an alternative to hand-sewn techniques for primary and staged low colorectal anastomoses. The stapler may allow a safer and lower resection than was previously possible. A review of 52 primary and 8 staged EEA anastomoses is presented, with emphasis on the combined stapler technique.

It has long been recognized that lake ice is composed of two layers: a lower, relatively clear layer of “black” ice that forms by downward freezing, and an upper, bubbly layer of “white” ice that forms when snow falls onto an ice sheet and depresses it to the point where water floods the surface, making slush that later freezes solid [1, 2, 3]. The ice on a given lake or pond, at a given time, may be all black or mostly white or any proportion between. The whiteness is caused by light scattering from small air bubbles. The black ice may contain air bubbles too, but they are larger and are aligned vertically, with the freezing direction.

Transverse acoustic waves in pulsed lasers result from nonuniform pumping transverse to the flow direction. This theoretical study is based on linear acoustics and disregards hot/cold gas interfaces. First, transverse waves in an infinite parallel hard-walled duct are considered, in which case cavity medium inhomogeneity typically decays as t ~ ' / 2 . An idealized treatment is next given to show that exponential decay can be expected with an anode absorber. There is an optimum absorber resistivity and improved attenuation rate results with increased backing volume. Tilted sidewalls are the final topic. Decay is again exponential, and rapid attenuation requires fairly large tilt angles. Examples are chosen to apply to CO2 electric discharge, chemical, and excimer lasers.