Recurrent Acceleration in Dilaton-Axion Cosmology

A class of Einstein-dilaton-axion models is found for which almost all flat expanding homogeneous and isotropic universes undergo recurrent periods of acceleration. We also extend recent results on eternally accelerating open universes.Comment: 8 pages, 7 figures. minor changes. Version 4 corrects a figure captio

Factors Affecting Water Management on the North Slope of Alaska

The North Slope of Alaska is undergoing sudden development following the recent discovery of large oil and gas reserves in the area. The water resources of the region should be carefully managed both to ensure adequate supplies of usable water at reasonable cost, and to guard against excessive deterioration of water quality. The likely effects on the environment of man's activities are investigated and found to be poorly understood at the present time. Research priorities are suggested to supply rapid answers to questions of immediate importance. The applicability of a regional management concept to the North Slope waters is considered and the concept is recommended as part of a broad land and water planning philosophy which would emphasize regional control over state and federal control. The use of economic incentives rather than standards for the control of water quality is not recommended at the present time.The work upon which this report is based was supported primarily by funds provided by the Sea Grant Program of the University of Alaska under grant No. 1-36109

Ancestral Caddo Ceramic Vessels from Sites in the Upper Neches River Basin in Anderson and Cherokee Counties, Texas

Late Caddo period sites belonging to the Frankston phase (ca. A.D. 1400-1680) and the Historic Caddo Allen phase (ca. A.D. 1680-1800) are common in the upper Neches River basin in East Texas, including habitation sites as well as associated and unassociated cemeteries. As is well known, ancestral Caddo cemeteries have burial features with associated funerary offerings, most commonly ceramic vessels. In this article, we document 34 ancestral Caddo ceramic vessels in the collections of the Texas Archeological Research Laboratory at The University of Texas at Austin (TARL) from six different sites in the upper Neches River basin, including the Ballard Estates (41AN53, n=4 vessels), O. L. Ellis (41AN54, n=15), Lee Ellis (41AN56, n=1), Dabbs Estate (41AN57, n=3), A. H. Reagor (41CE15, n=3), and John Bragg (41CE23, n=8 vessels) sites. Our first purpose is to put on record these ceramic vessels from six poorly known ancestral Caddo sites in order to better understand the history of Caddo settlement in the upper Neches River basin, including the history of burial interments at these sites. The second purpose is much broader, and is part of an effort to establish an East Texas Caddo ceramic vessel database that can be employed for a variety of research purposes. The synthesis of the stylistically diverse Caddo ceramic wares in different recognized ancestral communities across the Caddo area, including the upper Neches River basin occupied by a Hasinai Caddo group, would seem to be tailor-made for studies of ancestral Caddo social networks and social identities that rely on large regional ceramic datasets. The formal and statistical assessment of the regional variation in Caddo ceramic assemblages is currently being assembled in a Geographic Information System by Robert Z. Selden, Jr. (Stephen F. Austin State University), and the assemblages include the vessels from the six sites discussed herein. This is based on the delineation of temporal and spatial divisions in the character of Caddo ceramics (i.e., principally data on decorative methods, vessel forms, defined types and varieties, and the use of different tempers) across East Texas sites and other parts of the Caddo area, and then constructing networks of similarities between ceramic assemblages from these sites that can be used to assess the strength of cultural and social relationships among Caddo communities in the region through time and across space. The identification of such postulated relationships can then be explored to determine the underlying reasons for the existence of such relationships, including factors such as the frequency of interaction and direct contact between communities, the trade and exchange of ceramic vessels, population movement, and similarities in the organization of ceramic vessel production. In conjunction with a database on 2D/3D-scanned Caddo ceramic vessels from East Texas sites, the East Texas Caddo ceramic vessel database is made part of a digital database where comprehensive mathematical and quantitative analyses of morphological attributes and decorative elements on vessels can be conducted. Queries to such a combined database of vessels and sherds should lead to better understandings of regional Caddo ceramic stylistic and technological attributes and their spatial and temporal underpinnings. The results of past and current instrumental neutron activation analysis (INAA) and petrographic analysis of Caddo Area ceramics, including East Texas (where there is a robust INAA database) can also be explored as a means to corroborate production locales, and establish the chemical and paste characteristics of local fine ware and utility ware ceramics in assemblages of different ages. These in turn allow the evaluation of the possible movement of ceramic vessels between different Caddo communities in East Texas and the broader Caddo world

Conway's subprime Fibonacci sequences

It's the age-old recurrence with a twist: sum the last two terms and if the result is composite, divide by its smallest prime divisor to get the next term (e.g., 0, 1, 1, 2, 3, 5, 4, 3, 7, ...). These sequences exhibit pseudo-random behaviour and generally terminate in a handful of cycles, properties reminiscent of 3x+1 and related sequences. We examine the elementary properties of these 'subprime' Fibonacci sequences.Comment: 18 pages, 5 figure

The use of niobia in oxidation catalysis

This paper summarises the background to work carried out at the University of Twente on the use of niobia as a catalyst for the oxidative dehydrogenation of propane to propylene and discusses the development of promoted niobia catalysts for this reaction. Results are also presented which illustrate the use of niobia in catalysts for other reactions such as the oxidative coupling of methane, the oxidative dehydrogenation of ethane and the oxidative dehydrogenation of methanol. It appears that niobia and niobia-modified catalysts, when used in high-temperature oxidation processes, can exhibit relatively high selectivities compared with more conventional catalysts

Where is the Inner Edge of an Accretion Disk Around a Black Hole?

What is meant by the "inner edge" of an accretion disk around a black hole depends on the property that defines the edge. We discuss four such definitions using data from recent high-resolution numerical simulations. These are: the "turbulence edge", where flux-freezing becomes more important than turbulence in determining the magnetic field structure; the "stress edge", where plunging matter loses dynamical contact with the outer accretion flow; the "reflection edge", the smallest radius capable of producing significant X-ray reflection features; and the "radiation edge", the innermost place from which significant luminosity emerges. All these edges are dependent on the accretion rate and are non-axisymmetric and time-variable. Although all are generally located in the vicinity of the marginally stable orbit, significant displacements can occur, and data interpretations placing the disk edge precisely at this point can be misleading. If observations are to be used successfully as diagnostics of accretion in strong gravity, the models used to interpret them must take careful account of these distinctions.Comment: accepted by Ap.J., 26 p

Quantum phase transition between one-channel and two-channel Kondo polarons

For a mobile spin-1/2 impurity, coupled antiferromagnetically to a one-dimensional gas of fermions, perturbative ideas have been used to argue in favor of two-channel Kondo behavior of the impurity spin. Here we combine general considerations and extensive numerical simulations to show that the problem displays a novel quantum phase transition between two-channel and one-channel Kondo screening upon increasing the Kondo coupling. We construct a ground-state phase diagram and discuss the various non-trivial crossovers as well as possible experimental realizations.Comment: 5+4 pages, 5+3 fig

Comparison of Compression Schemes for CLARA

CLARA (Compact Linear Advanced Research Accelerator)at Daresbury Laboratory is proposed to be the UK's national FEL test facility. The accelerator will be a ~250 MeV electron linac capable of producing short, high brightness electron bunches. The machine comprises a 2.5cell RF photocathode gun, one 2 m and three 5 m normal conducting S-band (2998MHz) accelerating structures and a variable magnetic compression chicane. CLARA will be used as a test bed for novel FEL configurations. We present a comparison of acceleration and compression schemes for the candidate machine layout.Comment: 3 pages, 5 figures, IPAC 201