Direct determination of local lattice polarity in crystals

With current advances in sub-angstrom resolution scanning transmission electron microscopy (STEM), it is now possible to image directly local crystal structures of materials where dramatically different atoms are separated from each other at distances about or less than 1 angstrom. We achieved direct imaging of atomic columns of nitrogen in close proximity to columns of aluminum in wurtzite aluminum nitride by using annular dark field imaging in an aberration-corrected STEM. This ability allows direct determination of the local polarity in nanoscale crystals and crystal defects.     

Mechanism for multiplication of atmospheric ice crystals: apparent charge distribution on laboratory crystals

Replication of ice crystals with vapor of methyl 2-cyanoacrylate has produced evidence of whiskers on them; an additional mechanism for the necessary multiplication of ice crystals in the atmosphere is suggested. This replication technique also confirms crystal clustering in the atmosphere and appears to confirm the distribution of electrical charge on ice crystals.     

冷冻浓缩过程冰晶生长的相场法模拟

以水为原料,利用相场模型从微观上对冰晶生长机制进行模拟,结果表明:随着过冷时间的延长,冰晶的分枝逐渐发达;随着过冷度的增高,冰晶的分枝也逐渐发达.表明控制过冷时间和过冷度是冷冻浓缩过程中降低冰晶夹带率的重要措施.     

Temperature-dependence of resistance at an electrotonic synapse

The junctional resistance at septa of the crayfish lateral giant axon is inversely related to temperature with a Q(1l), of about 3 over the range from 5 degrees to 20 degrees C. Nonjunctional axonal membrane is much less affected. Resistance changes occur rapidly with temperature changes. No correlates in ultrastructure of the synapses have been found.     

Kinetics of conversion of air bubbles to air hydrate crystals in antarctic ice

The depth dependence of bubble concentration at pressures above the transition to the air hydrate phase and the optical scattering length due to bubbles in deep ice at the South Pole are modeled with diffusion-growth data from the laboratory, taking into account the dependence of age and temperature on depth in the ice. The model fits the available data on bubbles in cores from Vostok and Byrd and on scattering length in deep ice at the South Pole. It explains why bubbles and air hydrate crystals coexist in deep ice over a range of depths as great as 800 meters and predicts that at depths below approximately 1400 meters the AMANDA neutrino observatory at the South Pole will operate unimpaired by light scattering from bubbles.     

Geomagnetic polarity epochs: a new polarity event and the age of the brunhes-matuyama boundary

Recent paleomagnetic-radiometric data from six rhyolite domes in the Valles Caldera, New Mexico, indicate that the last change in polarity of the earth's magnetic field from reversed to normal (the Brunhes-Matuyama boundary) occurred at about 0.7 million years ago. A previously undiscovered geomagnetic polarity event, herein named the "Jaramillo normal event," occurred about 0.9 million years ago.     

Solid-state ice volcanism on the satellites of uranus

Voyager images of the uranian satellites Ariel and Miranda show flow features with morphologies indicating that ice has been extruded to the satellites' surfaces in the solid state. These images provide the first observational evidence for solid-state ice volcanism in the solar system. Topographic profiles have been measured across a number of flow features on Ariel. With a simple model of extrusion, spreading, and cooling of a viscous flow, the initial viscosity of the flow material is found to have been no more than about 10(16) poise, far lower than expected for H(2)O ice at the ambient surface temperatures in the uranian system. Sharply reduced viscosities may have resulted from incorporation of ices like NH(3) or CH(4) in the uranian satellites.     

Climatic ice core records from the tropical quelccaya ice cap

The Quelccaya Ice Cap in the easternmost glaciated mountain chain of the Peruvian Andes has been studied in four recentfield seasons. Ice cores to a depth of 15 meters have been retrieved at the summit dome (elevation, 5650 meters) and two other locations and used for microparticle, isotope, and beta radioactivity measurements. A concurrent study of the present climate and the heat and mass budgets is being made to permit a paleoclimatic interpretation of deep core records. The results indicate the need for a revision of the isotope "thermometry" for application in the tropics. However, the seasonality of the beta radioactivity, microparticle content, and isotope ratios offers the prospect of a mass balance chronology. This is important in that precipitation is believed to be a more indicative paleoclimatic parameter than temperature in the tropics.     

Convection in the antarctic ice sheet leading to a surge of the ice sheet and possibly to a new ice age

The Antarctic surge theory of Pleistocene glaciation is reexamined in the context of thermal convection theory applied to the Antarctic ice sheet. The ice sheet surges when a water layer at the base of the ice sheet reaches the edge of the ice sheet over broad fronts and has a thickness sufficient to drown the projections from the bed that most strongly hinder basal ice flow. Frictional heat from convection flow promotes basal melting, and, as the ice sheet grows to the continental shelf of Antarctica, a surge of the ice sheet appears likely.     

Geomorphic evidence for the distribution of ground ice on Mars

High-resolution Viking orbiter images show evidence for quasi-viscous relaxation of topography. The relaxation is believed to be due to creep deformation of ice in near-surface materials. The global distribution of the inferred ground ice shows a pronounced latitudinal dependence. The equatorial regions of Mars appear to be ice-poor, while the heavily cratered terrain poleward of +/- 30 degrees latitude appears to be ice-rich. The style of creep poleward of +/- 30 degrees varies with latitude, possibly due to variations in ice rheology with temperature. The distribution suggests that ice at low latitudes, which is not in equilibrium with the present atmosphere, has been lost via sublimation and diffusion through the regolith, thereby causing a net poleward transport of ice over martian history.     

The little ice age as recorded in the stratigraphy of the tropical quelccaya ice cap

The analyses of two ice cores from a southern tropical ice cap provide a record of climatic conditions over 1000 years for a region where other proxy records are nearly absent. Annual variations in visible dust layers, oxygen isotopes, microparticle concentrations, conductivity, and identification of the historical (A.D. 1600) Huaynaputina ash permit accurate dating and time-scale verification. The fact that the Little Ice Age (about A.D. 1500 to 1900) stands out as a significant climatic event in the oxygen isotope and electrical conductivity records confirms the worldwide character of this event.     

Evidence for the exposure of water ice on Titan's surface

The smoggy stratosphere of Saturn's largest moon, Titan, veils its surface from view, except at narrow wavelengths centered at 0.83, 0.94, 1.07, 1.28, 1.58, 2.0, 2.9, and 5.0 micrometers. We derived a spectrum of Titan's surface within these "windows" and detected features characteristic of water ice. Therefore, despite the hundreds of meters of organic liquids and solids hypothesized to exist on Titan's surface, its icy bedrock lies extensively exposed.