A Dual Diffusion Chamber for Observing Ice Crystal Growth on c-Axis Ice Needles

We describe a dual diffusion chamber for observing ice crystal growth from water vapor in air as a function of temperature and supersaturation. In the first diffusion chamber, thin c-axis ice needles with tip radii ~100 nm are grown to lengths of ~2 mm. The needle crystals are then transported to a second diffusion chamber where the temperature and supersaturation can be independently controlled. By creating a linear temperature gradient in the second chamber, convection currents are suppressed and the supersaturation can be modeled with high accuracy. The c-axis needle crystals provide a unique starting geometry compared with other experiments, and the dual diffusion chamber allows rapid quantitative observations of ice growth behavior over a wide range of environmental conditions

Field Report on the Excavation of Indian Villages in the Vicinity of the Spiro Mounds, Leflore County, Oklahoma

A wealth of strikingly unusual and beautiful objects of Indian manufacture were excavated from the burials of the Spiro Mound, Leflore (sic.) County, Oklahoma during 1936-37. Engraved Gulf Coast conch shells, shell beads of a dozen types, river pearls, effigy pipes, long delicately chipped flint blades, feather and textile cloths and precisely incised pottery vessels were excavated in quantities. So unusual was this material that, at the time, the archaeological science was unable to answer a host of questions which immediately arose concerning the identity of the tribe who had made the artifacts and who were buried with them. How long ago had they occupied the region? From where had they come, and where did they go? The chronological relationship of the Spiro Mound Culture to the known cultures of the United States was of particular concern to the investigators. How and where did this tribe fit into the picture of America\u27s past

An experimental apparatus for observing deterministic structure formation in plate-on-pedestal ice crystal growth

We describe an experimental apparatus for making detailed morphological observations of the growth of isolated plate-like ice crystals from water vapor. Each crystal develops a plate-on-pedestal (POP) geometry, in which a large, thin, plate-like crystal grows out from the top edge of an initially prismatic seed crystal resting on a substrate. With the POP geometry, the substrate is not in contact with the growing plate (except at its center), so substrate interactions do not adversely affect the crystal growth. By controlling the temperature and supersaturation around the crystal, we can manipulate the resulting ice growth behavior in predictable ways, producing morphologies spanning the full range from simple faceted hexagonal plates to complex dendritic structures. We believe that the experimental apparatus described here will allow unprecedented investigations of ice crystal growth behaviors under controlled conditions, identifying and exploring robust morphological features in detail. Such investigations will provide valuable observational inputs for developing numerical modeling techniques that can accurately reproduce the faceted and branched structures that frequently emerge during diffusion-limited crystal growth

Toward a Comprehensive Model of Snow Crystal Growth: 6. Ice Attachment Kinetics near -5 C

I examine a variety of snow crystal growth measurements taken at a temperature of -5 C, as a function of supersaturation, background gas pressure, and crystal morphology. Both plate-like and columnar prismatic forms are observed under different conditions at this temperature, along with a diverse collection of complex dendritic structures. The observations can all be reasonably understood using a single comprehensive physical model for the basal and prism attachment kinetics, together with particle diffusion of water vapor through the surrounding medium and other well-understood physical processes. A critical model feature is structure-dependent attachment kinetics (SDAK), for which the molecular attachment kinetics on a faceted surface depend strongly on the nearby mesoscopic structure of the crystal

A Versatile Apparatus for Measuring the Growth Rates of Small Ice Prisms from the Vapor Phase

I describe an adaptable apparatus for making precision measurements of the growth of faceted ice prisms from water vapor as a function of temperature, supersaturation, and background gas pressure. I also describe procedures for modeling growth data to disentangle a variety of physical effects and better understand systematic errors and measurement uncertainties. By enabling precise ice-growth measurements over a broad range of environmental conditions, this apparatus is well suited for investigating the molecular attachment kinetics at the ice/vapor interface, which is needed to understand and model snow crystal growth dynamics

On the Equilibrium Shape of an Ice Crystal

We examine the shape of a an isolated, dislocation-free ice crystal when it is in equilibrium with the vapor phase in an isothermal closed environment, as a function of temperature. From our analysis we draw the following conclusions: 1) The equilibrium shape has not yet been definitively measured for ice crystals; 2) The surface energy anisotropy is likely cusp-like near the facet angles, and the size of the cusps can be estimated from crystal growth measurements; 3) The equilibrium shape is likely nearly spherical with only small faceted regions; 4) The time needed to reach equilibrium is likely prohibitively long, except under special circumstances; and 5) Surface energy effects likely play a relatively smaller role in ice crystal growth dynamics when compared to the role of attachment kinetics

The Eufaula Mound: Contributions to the Spiro Focus

The main aim of the paper is the comparison of two archaeological sites, (1) the Eufaula site of McIntosh County, and (2) the Spiro site of Leflore County, Okla. Purpose of the comparison is to indicate the relationship between the 2 sites, thereby establishing a Spiro Focus, the ramifications and general affiliations of which will be suggested. The thesis is based on original research coming out of my experience as Project Superintendent of various units of the Oklahoma WP A Project. The Project, sponsored by the university of Oklahoma and directed by Dr. F.E. Clements, has carried on large scale excavations in Oklahoma since 1936. At that time the Spiro l\found group, in the east central part of the state, was opened up. In the two years from 1936 to 1938 a crew of 70 WP A laborers, under the direction of trained archaeologists, unearthed quantities of archeological material. The main bulk of material from the Great Temple Mound was excavated under the direction of Mr. Joe Finkelstein. 1 It was my privilege to analyze the material excavated by him. I also excavated the Spiro Village and a series of villages in the vicinity of the Mound group. 2 Both groups of data will be utilized