Land Snail Extinctions at Kalaeloa, O'ahu

A decline over time in the proportion of native land snail taxa believed to be extinct today at Kalae10a has been interpreted and widely cited as an example of Polynesian influence on the Hawaiian environment. This interpretation is shown to be based on an inappropriate measure of decline and nonstandard calibrations of 14C dates. An analysis of change over time in the diversity of land snail taxa from Kalaeloa sinkholes and recalibration of 14C dates using Bayesian techniques reveals a different pattern, which is interpreted as having two components. There is a long-term, gradual decline in the diversity of native, extinct land snail taxa, explained as the result of desiccation of the sinkhole environment due to a drop in the water table when sea level fell from its mid-Holocene high stand. There is also an abrupt disruption of the land snail fauna late in the stratigraphic sequence. It is argued that this disruption dates to the historic period, when the environment of the 'Ewa plain was drastically altered for sugarcane production and when the vegetation that now dominates the region was introduced. Aside from the appearance of the snail Lamellaxis gracilis, which was introduced to the Islands by Polynesians, the land snail assemblages from the Kalaeloa sinkholes yield no evidence for Polynesian influence on the environment

Engineering materials for hydrogen separation

To address the need for enhanced hydrogen separation techniques using metal membranes, a different fabrication technique was utilized that would overcome these concerns. The objectives for the fabrication were: obtaining a highly clean surface on the refractory foil, forming a palladium coating without subsequent surface contamination, and providing a high degree of purity, crystallinity, and crystallographic orientation. To achieve these objectives, the process of physical vapor deposition was used. Within a high vacuum chamber, both sides of a tantalum or vanadium foil were ion milled to remove the surface oxide and, without ever breaking the vacuum, both sides of the cleaned foil were coated with thin palladium layers. The palladium was deposited using either e-beam evaporation or sputtering. Foils produced by this technique have yielded exceptionally high hydrogen flow rates

Archaeological sequence diagrams and Bayesian chronological models

This paper develops directed graph representations for a class of archaeological sequence diagrams, such as the Harris Matrix, that do not include information on duration. These "stratigraphic directed graphs" differ from previous software implementations of the Harris Matrix, which employ a mix of directed graph and other data structures and algorithms. A "chronological directed graph" to represent the relationships in a Bayesian chronological model that correspond to the possibilities inherent in a sequence diagram, and an algorithm to map a stratigraphic directed graph to a chronological directed graph are proposed and illustrated with an example. These results are intended to be a proof of concept for the design of a front-end for Bayesian calibration software that is based directly on the archaeological stratigrapher's identification of contexts, observations of stratigraphic relationships, inferences concerning parts of once-whole contexts, and selection of materials for radiocarbon dating

Josephson Coupling and Fiske Dynamics in Ferromagnetic Tunnel Junctions

We report on the fabrication of Nb/AlO_x/Pd_{0.82}Ni_{0.18}/Nb superconductor/insulator/ferromagnetic metal/superconductor (SIFS) Josephson junctions with high critical current densities, large normal resistance times area products, high quality factors, and very good spatial uniformity. For these junctions a transition from 0- to \pi-coupling is observed for a thickness d_F ~ 6 nm of the ferromagnetic Pd_{0.82}Ni_{0.18} interlayer. The magnetic field dependence of the \pi-coupled junctions demonstrates good spatial homogeneity of the tunneling barrier and ferromagnetic interlayer. Magnetic characterization shows that the Pd_{0.82}Ni_{0.18} has an out-of-plane anisotropy and large saturation magnetization, indicating negligible dead layers at the interfaces. A careful analysis of Fiske modes provides information on the junction quality factor and the relevant damping mechanisms up to about 400 GHz. Whereas losses due to quasiparticle tunneling dominate at low frequencies, the damping is dominated by the finite surface resistance of the junction electrodes at high frequencies. High quality factors of up to 30 around 200 GHz have been achieved. Our analysis shows that the fabricated junctions are promising for applications in superconducting quantum circuits or quantum tunneling experiments.Comment: 15 pages, 9 figure

The stone adze and obsidian assemblage from the Talasiu site, Kingdom of Tonga

Typological and geochemical analyses of stone adzes and other stone tools have played a significant role in identifying directionality of colonisation movements in early migratory events in the Western Pacific. In later phases of Polynesian prehistory, stone adzes are important status goods which show substantial spatial and temporal variation. However, there is a debate when standardisation of form and manufacture appeared, whether it can be seen in earliest populations colonising the Pacific or whether it is a later development. We present in this paper a stone adze and obsidian tool assemblage from an early Ancestral Polynesian Society Talasiu site on Tongatapu, Kingdom of Tonga. The site shows a wide variety of adze types; however, if raw material origin is taken into account, emerging standardisation in adze form might be detected. We also show that Tongatapu was strongly connected in a network of interaction to islands to the North, particularly Samoa, suggesting that these islands had permanent populations

Land Snail Extinctions at Kalaeloa, O`ahu

In this article we show that the interpretation of Polynesian influence drawn from the stratigraphic record of sub-fossil land snails at Kalaeloa (O'ahu, Hawai'i) is based on a unique stratigraphic sequence at a single sinkhole. The interpretation was then applied to other land snail sequences, despite their lack of evidence for Polynesian influence. We present a reanalysis of the stratigraphic record to conclude that Polynesians had little, if any, effect on land snail populations in sinkholes. We show that directional change in land snail populations was underway before Polynesians colonised the islands. Decreases in the diversity of snail populations, possibly indicative of environmental stress, do occur near the end of the stratigraphic sequence. Based on available dating evidence, however, these changes probably took place in the post-Contact period when the regional environment was radically altered by sugar cane cultivation

Composite metal membranes for hydrogen separation applications

A novel multilayer metal membrane has been developed that can be used for the separation of hydrogen from feed streams with near perfect selectivity. The membrane is comprised of very thin layers of fully dense palladium film deposited on both sides of a thin Group V metal foil, ion-milled prior to sputtering of the palladium. Palladium loading are kept low using the thin film deposition technology: 0.0012 grams of palladium per square centimeter of membrane is typically used, although thinner coatings have been employed. This membrane operates at temperatures on the order of 300 C and is capable of high rates of hydrogen flow. Flows are dependent on the pressure differential applied to the membrane, but flows of 105 sccm/cm{sup 2} and higher are regularly observed with differentials below one atmosphere. Long term testing of the membrane for a period in excess of 775 hours under constant conditions showed stable flows and an 85% hydrogen recovery efficiency. A system has been successfully applied to the hydrogen handling system of a proton exchange membrane fuel cell and was tested using a pseudo-reformate feed stream without any degradation in performance

MOCVD of field emission phosphors using a liquid delivery system

Thin film phosphors for field emission displays show the potential to overcome the life-limiting problems that traditional powders face because of their high surface areas. By depositing a fully dense thin film, the surface area can be dramatically reduced, while the electrical and thermal conductivity is increased. Metal organic chemical vapor deposition offers the ability to deposit high quality, dense films that are crystalline as deposited and at temperatures low enough to allow for inexpensive glass. Deposition has been produced from mixtures of Y(tmhd){sub 3}, TEOS, Tb(tmhd){sub 3}, and O{sub 2} using a liquid delivery system. Coatings were shown to be composed of Y, Si, and Tb by x-ray fluorescence, but x-ray diffraction did not show any crystallinity. Excitation using radioluminescence produced a peak in the visible green at approximately 540 nm, indicative of the excitation of a Tb{sup 3+}. The morphology of the deposition was smooth, with surface features on the order of one micron and below. Some limited microcracking was also observed from the morphology because of the thermal expansion mismatch

Investigation of the nucleation and growth of thin-film phosphors

The deposition of CaGa{sub 2}S{sub 4}:Ce has been accomplished using a commercial liquid delivery system on two substrate surfaces: ZnS and SrS. However, the film deposited on ZnS was not of satisfactory quality because of the formation of an amorphous layer and a high amount of residual porosity within the deposition. The use of a SrS layer on top of the ZnS improved the nucleation by reducing the interfacial energy between the substrate and deposition. It greatly reduced the porosity in the coating and reduced the formation of the amorphous layer. The crystallinity of the CaGa{sub 2}S{sub 4} 400 peak was also increased by a factor of ten when a layer of SrS was used. Further, the FWHM of the 400 peaks from the two depositions was not significantly different, indicating that the crystallite size and strain was approximately the same. The B{sub 40} was increased by a factor of two, from 1.84 cd/m{sup 2} for ZnS to 3.67 cd/m{sup 2} for SrS. This increase is an improvement in the performance of the films and is attributable to the increase in the crystallinity

Bayesian chronology construction and substance time

Two views of archaeological time are distinguished; an event view that models stratigraphic relations, and a substance view that models genealogical relations among artifacts, including the three modes of change represented by branching, transformation, and reticulation. Chronology construction is more complex in substance time than it is in event time, which only concerns transformation. Allen's interval algebra can be used to specify the chronological relations associated with the modes of change, and these relations can be identified by post-processing the output from Bayesian chronological models. A worked example illustrates how identifying the chronological relations can aid construction of a phyletic seriation of beads recovered from Anglo-Saxon female graves. These results might encourage archaeologists to carry out chronology construction in substance time as an aid to historical inference