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The transition from arid glacial to moist early Holocene conditions represented a profound change in northern lowland Neotropical climate. Here we report a detailed record of changes in moisture availability during the latter part of this transition ({approx}11,250 to 7,500 cal yr BP) inferred from sediment cores retrieved in Lake Peten Itza, northern Guatemala. Pollen assemblages demonstrate that a mesic forest had been largely established by {approx}11,250 cal yr BP, but sediment properties indicate that lake level was more than 35 m below modern stage. From 11,250 to 10,350 cal yr BP, during the Preboreal period, lithologic changes in sediments from deep-water cores (>50 m below modern water level) indicate several wet-dry cycles that suggest distinct changes in effective moisture. Four dry events (designated PBE1-4) occurred at 11,200, 10,900, 10,700, and 10,400 cal yr BP and correlate with similar variability observed in the Cariaco Basin titanium record and glacial meltwater pulses into the Gulf of Mexico. After 10,350 cal yr BP, multiple sediment proxies suggest a shift to a more persistently moist early Holocene climate. Comparison of results from Lake Peten Itza with other records from the circum-Caribbean demonstrates a coherent climate response during the entire span of our record. …

Three specific failure criteria for the transversely isotropic fiber composite case will be discussed. All three use the polynomial expansion method. The three criteria are the Tsai-Wu criterion, the Hashin criterion and the Christensen criterion. All three criteria will be given in forms that admit direct and easy comparison, which has not usually been done. The central differences between these three criteria will be discussed, and steps will be taken toward the evaluation of them.

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In Biot's theory of poroelasticity, elastic materials contain connected voids or pores and these pores may be filled with fluids under pressure. The fluid pressure then couples to the mechanical effects of stress or strain applied externally to the solid matrix. Eshelby's formula for the response of a single ellipsoidal elastic inclusion in an elastic whole space to a strain imposed at a distant boundary is a very well-known and important result in elasticity. Having a rigorous generalization of Eshelby's results valid for poroelasticity means that the hard part of Eshelby's work (in computing the elliptic integrals needed to evaluate the fourth-rank tensors for inclusions shaped like spheres, oblate and prolate spheroids, needles and disks) can be carried over from elasticity to poroelasticity--and also thermoelasticity--with only relatively minor modifications. Effective medium theories for poroelastic composites such as rocks can then be formulated easily by analogy to well-established methods used for elastic composites. An identity analogous to Eshelby's classic result has been derived [Physical Review Letters 79:1142-1145 (1997)] for use in these more complex and more realistic problems in rock mechanics analysis. Descriptions of the application of this result as the starting point for new methods of estimation are presented, including …

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I discuss the Color Glass Condensate as a media. I argue that Pomerons, Odderons and Reggeons are the small fluctuation excitations of this media. I argue that understanding the effects of Pomeron loops leads to the idea that this media has a duality symmetry. I discuss the implications of the Color Glass Condensate for the initial conditions at RHIC.

The Kinetic Stabilizer (K-S) concept [1] represents a means for stabilizing axisymmetric mirror and tandem-mirror (T-M) magnetic fusion systems against MHD interchange instability modes. Magnetic fusion research has given us examples of axisymmetric mirror confinement devices in which radial transport rates approach the classical ''Spitzer'' level, i.e. situations in which turbulence if present at all, is at too low a level to adversely affect the radial transport [2,3,4]. If such a low-turbulence condition could be achieved in a T-M system it could lead to a fusion power system that would be simpler, smaller, and easier to develop than one based on closed-field confinement, e.g., the tokamak, where the transport is known to be dominated by turbulence. However, since conventional axisymmetric mirror systems suffer from the MHD interchange instability, the key to exploiting this new opportunity is to find a practical way to stabilize this mode. The K-S represents one avenue to achieving this goal. The starting point for the K-S concept is a theoretical analysis by Ryutov [5]. He showed that a MHD-unstable plasma contained in an axisymmetric mirror cell can be MHD-stabilized by the presence of a low-density plasma on the expanding field lines outside the mirrors. If this …

Today's large-scale scientific simulations produce data sets tens to hundreds of terabytes in size. The DataFoundry project is developing querying and analysis tools for these data sets. The Approximate Ad-Hoc Query Engine for Simulation Data (AQSIM) uses a multi-resolution, tree-shaped data structure that allows users to place runtime limits on queries over scientific simulation data. In this AQSIM data hierarchy, each node in the tree contains an abstract model describing all of the information contained in the subtree below that node. AQSIM is able to create the data hierarchy in a single pass. However, the nodes in the hierarchy frequently have low node fanout, which leads to inefficient I/O behavior during query processing. Low node fanout is a common problem in tree-shaped indices. This paper presents a set of one-pass tree ''pruning'' algorithms that efficiently restructure the data hierarchy by removing inner nodes, thereby increasing node fanout. As our experimental results show, the best approach is a combination of two algorithms, one that focuses on increasing node fanout and one that attempts to reduce the maximum tree height.

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The Savannah River Site (SRS) and Hanford site are in the process of stabilizing millions of gallons of radioactive waste slurries remaining from production of nuclear materials for the Department of Energy (DOE). The Defense Waste Processing Facility (DWPF) at SRS is currently vitrifying the waste in borosilicate glass while the facilities at the Hanford site are in the design/construction phase. Both processes utilize slurry-fed joule heated melters to vitrify the waste slurries. The rheological properties of the waste slurries limit the total solids content that can be processed by the remote equipment during the pretreatment and melter feed processes. The use of a surface active agent, or surfactant, to increase the solids loading that can be fed to the melters would increase melt rate by reducing the heat load on the melter required to evaporate the water in the feed. The waste slurries are non-Newtonian fluids with rheological properties that were modeled using the Bingham Plastic mod el (this model is typically used by SRNL when studying the DWPF process1).The results illustrate that altering the surface chemistry of the particulates in the waste slurries can lead to a reduction in the yield stress. Dolapix CE64 is an effective surfactant …

Event horizons and closed time-like curves cannot exist in the real world for the simple reason that they are inconsistent with quantum mechanics. Following ideas originated by Robert Laughlin, Pawel Mazur, Emil Mottola, David Santiago, and the speaker it is now possible to describe in some detail what happens physically when one approaches and crosses a region of space-time where classical general relativity predicts there should be an infinite red shift surface. This quantum critical physics provides a new perspective on a variety of enigmatic astrophysical phenomena including supernovae explosions, gamma ray bursts, positron emission, and dark matter.

This paper presents a novel slideway bearing design comprised of a thin-film (0.1 mm-0.2 mm) of ultra-high molecular weight polyethylene (UHMWPE) bound to a rigid hemispherical substrate. Two prototype bearing designs were fabricated and tested to characterize the coefficient of friction (dynamic and static) and wear of the polymer. In addition, similar bearings were incorporated into a kinematically constrained rectilinear carriage to determine the repeatability of motion during multiple traverses. The first bearing had a radius of curvature on the order of 2.38 mm incorporating an UHMWPE film thickness between 0.1 mm and 0.2 mm. The friction coefficient was measured to be between 0.155 and 0.189 for normal loads of 11.5 N and 2.2 N, respectively at a surface speed of 4.2 mm {center_dot} s{sup -1}. This bearing failed after a traverse of approximately 700 m at a load of 11.5 N. A similar evaluation procedure was carried out on a bearing of radius 6.35 mm resulting in a friction coefficient between 0.125 and 0.185 at loads of 27.8 N and 2.2 N, respectively, and the bearing endured a traverse of over 2.2 km at a load of approximately 28 N (in both air and vacuum conditions) with a surface …

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The Layzer model for the nonlinear evolution of bubbles in the Rayleigh-Taylor instability has recently been generalized to the case of spherically imploding interfaces [D. S. Clark and M. Tabak, to appear, PRE (2005).]. The spherical case is more relevant to, e.g., inertial confinement fusion or various astrophysical phenomena when the convergence is strong or the perturbation wavelength is comparable to the interface curvature. Here, the model is further extended to the case of bubble growth during the deceleration (stagnation) phase of a spherical implosion and to the growth of spikes during both the acceleration and deceleration phases. Differences in the nonlinear growth rates for both bubbles and spikes are found when compared with planar results. The model predictions are verified by comparison with numerical hydrodynamics simulations.

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This article is a response to an article by M. Adell et al. [Phy. Rev. Lett. 94, 139701 (2005)] about semiconductor-based spintronics research.

Interactions between surface and ground water are a key component of the hydrologic budget on the watershed scale. Models that honor these interactions are commonly based on the conductance concept that presumes a distinct interface at the land surface, separating the surface from the subsurface domain. These types of models link the subsurface and surface domains via an exchange flux that depends upon the magnitude and direction of the hydraulic gradient across the interface and a proportionality constant (a measure of the hydraulic connectivity). Because experimental evidence of such a distinct interface is often lacking in field systems, there is a need for a more general coupled modeling approach. A more general coupled model is presented that incorporates a new two-dimensional overland flow simulator into the parallel three-dimensional variable saturated subsurface flow code ParFlow. In ParFlow, the overland flow simulator takes the form of an upper boundary condition and is, thus, fully integrated without relying on the conductance concept. Another important advantage of this approach is the efficient parallelism incorporated into ParFlow, which is efficiently exploited by the overland flow simulator. Several verification and simulation examples are presented that focus on the two main processes of runoff production: excess infiltration …

Bikini Island was contaminated March 1, 1954 by the Bravo detonation (U.S nuclear test series, Castle) at Bikini Atoll. About 90% of the estimated dose from nuclear fallout to potential island residents is from cesium-137 ({sup 137}Cs) transferred from soil to plants that are consumed by residents. Thus, radioecology research efforts have been focused on removing {sup 137}Cs from soil and/or reducing its uptake into vegetation. Most effective was addition of potassium (K) to soil that reduces {sup 137}Cs concentration in fruits to 3-5% of pretreatment concentrations. Initial observations indicated this low concentration continued for some time after K was last applied. Long-term studies were designed to evaluate this persistence in more detail because it is very important to provide assurance to returning populations that {sup 137}Cs concentrations in food (and, therefore, radiation dose) will remain low for extended periods, even if K is not applied annually or biennially. Potassium applied at 300, 660, 1260, and 1970 kg ha{sup -1} lead to a {sup 137}Cs concentration in drinking coconut meat that is 34, 22, 10, and about 4 % of original concentration, respectively. Concentration of {sup 137}Cs remains low 8 to 10 y after K is last applied. An explanation …

A large fraction of the expected number of source detections of the forthcoming observatory Gamma-ray Large Area Space Telescope (GLAST) will be initially unidentified. We argue that traditional methodological approaches to identify individual detections and/or populations of gamma-ray sources present procedural limitations. These limitations will hamper our ability to classify the populations lying in the anticipated dataset with the required degree of confidence, in particular for those for which no member has yet been detected convincingly with the predecessor experiment EGRET. Here we suggest a new paradigm for achieving the classification of gamma-ray source populations that is based on implementing an a priori protocol to search for theoretically-motivated candidates. It is essential that such paradigm will be defined before the data is unblinded, in order to protect the discovery potential of the sample. Key to the new procedure is a quantitative assessment of the confidence level by which new populations can be claimed to have been discovered. When needed, small number statistics is applied for population studies in gamma-ray astronomy. Although we refer here explicitly only to the case of GLAST, the scheme we present can certainly be adapted to other experiments confronted with a similar combination of problems.

Oceanic uptake and transport of bomb radiocarbon as {sup 14}CO{sub 2} created by atmospheric nuclear weapons testing in the 1950s and 1960s has been a useful diagnostic to determine the carbon transfer between the ocean and atmosphere. In addition, the distribution of radiocarbon in the ocean can be used as a tracer of oceanic circulation. Results obtained from samples collected in the Gulf of Alaska in the summer of 2002 provide a direct comparison with results in the 1970s during GEOSECS and in the early 1990s during WOCE. The open gyre values are 20-40{per_thousand} more negative than those documented in 1991 and 1993 (WOCE) although the general trends as a function of latitude are reproduced. Surface values are still significantly higher than pre-bomb levels ({approx}-105{per_thousand} or lower). In the central gyre, we observe {Delta}{sup 14}C-values that are lower in comparison to GEOSECS (stn 218) and WOCE P16/P17 to a density of {approx}26.8{sigma}t. This observation is consistent with the overall decrease in surface {Delta}{sup 14}C values, and reflects the erosion of the bomb-{sup 14}C transient. We propose that erosion of the bomb-{sup 14}C transient is accomplished by entrainment of low {sup 14}C water via vertical exchange within the Gulf of Alaska …

A near-infrared camera in use at the Canada-France-Hawaii Telescope (CFHT) and at the 1.6-m telescope of the Observatoire du Mont-Megantic is described. The camera is based on a Hawaii-1 1024 x 1024 HgCdTe array detector. Its main feature is to acquire three simultaneous images at three wavelengths across the methane absorption bandhead at 1.6 {micro}m, enabling, in theory, an accurate subtraction of the stellar point spread function (PSF) and the detection of faint close methanated companions. The instrument has no coronoagraph and features fast data acquisition, yielding high observing efficiency on bright stars. The performance of the instrument is described, and it is illustrated by laboratory tests and CFHT observations of the nearby stars GL526, {nu}-And and {chi}-And. TRIDENT can detect (6{sigma}) a methanated companion with {Delta}H = 9.5 at 0.5'' separation from the star in one hour of observing time. Non-common path aberrations and amplitude modulation differences between the three optical paths are likely to be the limiting factors preventing further PSF attenuation. Instrument rotation and reference star subtraction improve the detection limit by a factor of 2 and 4 respectively. A PSF noise attenuation model is presented to estimate the non-common path wavefront difference effect on PSF subtraction …

We review several proposals for generation of solitary attosecond pulses using two types of free electron lasers which are envisioned as future light sources for studies of ultra-fast dynamics using soft and hard x-rays.

The published scientific literature is scanned and periodically evaluated for neutron and non-neutron nuclear data and the resulting recommendations are published [1,2]. After the literature has been scanned and appropriate data collected, there are often problems with regard to the treatment of the various types of data during this evaluation process and with regard to the method by which the recommendations are drawn from the assessment of the collection of individual measurements. Some-problems with uncertainties are presented.