bluuebunny/crossref_metadata_2025 huggingface dataset:
Low genetic connectivity in an estuarine fish with pelagic larvae
Authors: Bradbury I R , Campana S E , Bentzen P
Published: March 2008

We evaluated the spatial scale of metapopulation structure and genetic connectivity in rainbow smelt, Osmerus mordax, using eight microsatellite loci at 22 spawning locations throughout Newfoundland and Labrador. Consistent with low gene flow and limited dispersal, significant genetic structuring (FST≈ 0.11) was present at small spatial scales (<200 km). Moreover, strong isolation by distance (IBD, P < 0.001, r2= 0.47) was observed, which was linear at small scales and nonlinear at large distances (>200 km). We hypothesized that despite high dispersal potential associated with a pelagic larval stage, behaviours restricting gene flow may result in structuring at the estuary scale. Multidimensional scaling and neighbour-joining of multilocus genotypes indicate some bay-scale associations. However, a comparison of FSTvalues and IBD residuals at both estuary and bay scales indicated low structure within and elevated structure among estuaries. Estuarine structuring was further supported by the presence of significant small-scale IBD within several coastal embayments (50–100 km), as well as Bayesian clustering consistent with estuarine-scale independence. Finally, estimates of dispersal based on the IBD relationship are consistent with local estuarine recruitment (<1.5 km·generation–1). We conclude that the unexpectedly high genetic structure observed is consistent with behavioral influences reducing dispersal, supporting previous work implicating active larval retention.
Water-yield estimates for critical loadings assessment: comparisons of gauging methods versus an isotopic approach
Authors: Bennett K E , Gibson J J , McEachern P M
Published: March 2008

An isotope mass balance technique is applied to quantify water yield and refine a steady-state critical acid loadings assessment for 49 lakes in hydrologically complex, wetland-rich terrain of northeastern Alberta. The approach uses physical and climatological data combined with site-specific measurements of evaporative isotopic enrichment of 2H and 18O in lake water to measure lake residency and ungauged runoff to lakes. Mean water yields to individual lakes across the region over a 3-year period are estimated to range from 5 to 395 mm·year–1, with a standard deviation of two times the predicted estimates based on interpolation of gauged stream flow from broad-scale watersheds in the area. Comparison of the method with longer-term Water Survey of Canada hydrometric data suggests very similar average water yields for moderate- to large-sized watersheds. However, the isotope-based estimates appear to capture extreme low water yields in flat, disconnected areas and extreme high water yields in other areas thought to be related to stronger connections to regional groundwater flow systems. For aquatic ecosystems of northeastern Alberta, an area expected to be affected by acid deposition from regional oil sands development, continued refinement of the technique is important to accurately assess critical loads for ungauged systems, particularly those in low-yield settings.
Otolith chemistry indicates population structuring by the Antarctic Circumpolar Current
Authors: Ashford Julian R , Jones Cynthia M , Hofmann Eileen E , Everson Inigo , Moreno Carlos A , Duhamel Guy , Williams Richard
Published: March 2008

Large-scale transport of seawater in ocean currents may generate spatially complex population structure through the advection of life stages of marine fish species. To test this, we compared the chemistry of otolith nuclei from Patagonian toothfish (Dissostichus eleginoides), presently managed as spatially discrete populations corresponding to fishing management areas along the Antarctic Circumpolar Current (ACC), which transports water eastward around the Southern Ocean. The chemistry of otolith nuclei, laid down during early life, differed significantly between fishing areas off South America and the Antarctic and between some Antarctic areas. However, we found significant discrepancies from expectation for a population structure corresponding to fishing areas. We also found evidence of four groups of fish with different early life chemistry: one associated with South America and three Antarctic groups showing mixing consistent with advective transport along the ACC. These results suggest that toothfish populations are structured by their physical environment; population abundance and persistence may rely on a restricted number of breeding members with access to spawning grounds, whereas fisheries may rely substantially on nonbreeding vagrants transported from fishing areas upstream.
Stocking success of local-origin fry and impact of hatchery ancestry: monitoring a new steelhead (Oncorhynchus mykiss) stocking program in a Minnesota tributary to Lake Superior
Authors: Caroffino David C , Miller Loren M , Kapuscinski Anne R , Ostazeski Joseph J
Published: March 2008

The inception of a hatchery program to rebuild a naturalized steelhead (Oncorhynchus mykiss) population in Minnesota waters of Lake Superior gave us the rare opportunity to monitor the success of fry stocking and determine if hatchery ancestry can reduce fitness of stocked fish in the early generations of a stocking program. Through genetic monitoring of two year classes, we determined that hatchery adults produced 1.3-6.2 times as many age-2 juveniles per female than naturally spawning fish. Survival of stocked fry of parents born in a hatchery relative to those of parents born in the wild was 70% in paired-stocking comparisons. These results suggest that stocking local-origin fry can increase the short-term abundance of depleted populations and that fish with no hatchery history are a better source for supplemental stocking. Additionally, sampling small numbers of adults for broodstock created genetically distinct groups, which could potentially cause long-term genetic change in the population. Genetic monitoring of adults will be essential to determining whether differences observed persist through the life cycle of the stocked fish.
Water velocity influences prey detection and capture by drift-feeding juvenile coho salmon (Oncorhynchus kisutch) and steelhead (Oncorhynchus mykiss irideus)
Authors: Piccolo John J , Hughes Nicholas F , Bryant Mason D
Published: March 2008

We examined the effects of water velocity on prey detection and capture by drift-feeding juvenile coho salmon (Oncorhynchus kisutch) and steelhead (sea-run rainbow trout, Oncorhynchus mykiss irideus) in laboratory experiments. We used repeated-measures analysis of variance to test the effects of velocity, species, and the velocity × species interaction on prey capture probability, prey detection distance, and swimming speeds during prey capture. We used 3D video analysis to assess the spatial and temporal characteristics of prey detection and capture. Coho and steelhead showed significant, velocity-dependent decreases in capture probability (~65% to 10%, with an increase of velocity from 0.29 to 0.61 m·s-1) and prey detection distance, with no effect of species and no velocity × species interaction. Neither velocity nor species affected prey interception speed; fish intercepted prey at their predicted maximum sustainable swimming speed (Vmax) at all velocities. Speed of return to the focal point increased significantly with increasing velocity, with no effect of species. At faster velocities, return speeds were faster than Vmax, indicating potential increases in energetic cost because of anaerobic swimming. The 3D analysis suggests that the reduction in capture probability was due to both reduced prey detection distance and a uniform decline in detection probability within the prey capture area.
Hatchery-induced morphological variation in an endangered fish: a challenge for hatchery-based recovery efforts
Authors: Belk Mark C , Benson Lisa J , Rasmussen Josh , Peck Steven L
Published: March 2008

Recovery plans for many endangered fishes include production of large numbers of individuals in hatcheries to augment wild populations. However, effects of hatchery culture on phenotypic development are poorly documented for most species. June sucker (Chasmistes liorus) is an endangered lake sucker endemic to Utah Lake (Utah, USA), and recovery plans include raising thousands of juveniles to stock in the lake. To determine effects of hatchery culture on morphology of young June sucker, we raised individuals from four different families in both lake and hatchery environments and compared shape variation among families and between environments. We compared shape from three perspectives: lateral body, ventral mouth, and lateral head views. Mean shape varied between hatchery-reared and lake-reared individuals in each of the three views. In addition, hatchery-reared individuals exhibited higher variance in shape both within and among families compared with shape variance in lake-reared individuals. Hatchery-reared individuals exhibited divergent phenotypes compared with lake-reared individuals. These results suggest that exposure to the native environment during early life stages may be important for phenotypic development suitable to native habitats. Hatcheries should incorporate designs and practices to minimize divergent phenotypic development of individuals.
Genetic and environmental correlates of morphological variation in a marine fish: the case of Baltic Sea herring (Clupea harengus)
Authors: Jørgensen Hanne B.H. , Pertoldi Cino , Hansen Michael M , Ruzzante Daniel E , Loeschcke Volker
Published: March 2008

Baltic Sea herring (Clupea harengus) have been shown to exhibit morphological differences across the marked salinity and temperature gradients in the region. Here we analyse genetic (nine microsatellite loci), morpho metric (skull shape), and meristic (pectoral fin rays and number of vertebrae) variations across seven samples of spawning herring collected from four spawning locations in the Baltic Sea to examine whether morphological variation correlates with genetic and (or) environmental factors. Results suggest that herring is adapting to its environment through a combination of selection and plastic responses. Skull shape, including and excluding size variation, differed significantly among samples, both temporally and spatially. Genetic and morphometric distances were correlated, especially when size variation was excluded from the analysis. When size variation was included, skull shape variation was more closely correlated with environmental distances among spawning locations. Vertebrate number differed among samples and was correlated with environmental distances, whereas the number of fin rays was not. Genetic and geographic distances among samples were not correlated.
Predicting smallmouth bass (Micropterus dolomieu) occurrence across North America under climate change: a comparison of statistical approaches
Authors: Sharma Sapna , Jackson Donald A
Published: March 2008

Smallmouth bass (Micropterus dolomieu) is a warm-water fish species that is native to central and eastern North America. Climate change scenarios predict further extension northward of suitable habitat for smallmouth bass, which may negatively affect native fish species. We developed and compared predictive models of the distribution of bass in North America using four statistical approaches: logistic regression, classification tree, discriminant analysis, and artificial neural networks. We collected 4181 geo-referenced records of smallmouth bass occurrence and matched them with climate data. Artificial neural networks performed the best with the highest sensitivity (correctly predicting species presence) and specificity (correctly predicting absence), followed by discriminant analysis. Artificial neural networks indicated that winter air temperatures were the most important predictors of smallmouth bass occurrence, whereas the other approaches indicated that summer air temperatures were the best predictors of bass occurrence. Logistic regression and classification tree exhibited very low sensitivity, but very high specificity as a result of the large proportion of absences within the data set. Business-as-usual climate change scenarios suggest that smallmouth bass are expected to have suitable thermal habitat throughout most of Canada and the continental United States by 2100.
Testing the assumption of annual shell ring deposition in freshwater mussels
Authors: Haag Wendell R , Commens-Carson Amy M
Published: March 2008

We tested the assumption of annual shell ring deposition by freshwater mussels in three rivers using 17 species. In 2000, we notched shell margins, returned animals to the water, and retrieved them in 2001. In 2003, we measured shells, affixed numbered tags, returned animals, and retrieved them in 2004 and 2005. We validated deposition of a single internal annulus per year in all species and in 94% of specimens. Most unvalidated shells were old individuals with tightly crowded rings. Handling produced a conspicuous disturbance ring in all specimens and often resulted in shell damage. Observed growth was similar to but slightly lower than growth predicted by von Bertalanffy length-at-age models developed independently from shell annuli; further, handling specimens in 2 consecutive years reduced growth more than handling only once. These results show that mussels are extremely sensitive to handling. Brief handling does not likely increase short-term mortality, but repeated handling could decrease long-term fitness. Handling effects should be considered in sampling programs or when interpreting results of mark-recapture studies designed to estimate mussel growth. Production of annual shell rings is a pervasive phenomenon across species, space, and time, and validated shell rings can provide accurate estimates of age and growth.
Carbocentric limnology: looking back, looking forward
Authors: Prairie Yves T
Published: March 2008

In this perspective article, I argue that dissolved organic carbon occupies a central role in the functioning of lake ecosystems, comparable in importance to that played by nutrients. Because lakes receive so much dissolved organic carbon from the terrestrial landscape, its accumulation in water bodies usually represents the largest pool of lacustrine organic matter within the water column. The transformation of even a small fraction of this external carbon by the microbial community can alter significantly the metabolic balance of lake ecosystems, simultaneously releasing carbon dioxide to the atmosphere and burying organic carbon in lake sediments. At the landscape level, even if they occupy a small fraction of the landscape, lakes play a surprisingly important role in the regional carbon budget, particularly when considered at the appropriate temporal scale.
Atomic lifetime measurements employing an electron beam ion trap
Authors: Träbert E
Published: March 2008

Transition probabilities relate to atomic structure and dynamics in ways that are different from straightforward spectra. Besides being a tool for fundamental physics studies, the knowledge of transition probabilities is essential for applications in plasma physics and astrophysics. Techniques and procedures used for measuring the lifetimes of levels in highly charged ions by employing an electron beam ion trap are reviewed to illustrate the state of the art. Examples are drawn from experiments that involve observations in the visible, extreme-ultraviolet, and X-ray ranges, and cover atomic lifetimes in the femtosecond to second range.PACS Nos.: 32.70.Cs, 32.30.Jc, 32.30.Rj
The role of EBIT in X-ray laser research
Authors: Nilsen J
Published: March 2008

In the early 1980s, the X-ray laser program required a new level of understanding and measurements of the atomic physics of highly charged ions. The electron beam ion trap (EBIT) was developed and built at Lawrence Livermore National Laboratory (LLNL) as part of the effort to understand and measure the cross sections and wavelengths of highly charged ions. This paper explains some of the early history of EBIT and how it was used to help develop X-ray lasers. EBIT’s capability was unique and some of the experimental results obtained over the years, related to X-ray lasers, will be shown. As X-ray lasers have now become a table-top tool, new areas of research that involve understanding the index of refraction in partially ionized plasmas will be discussed. In addition, new areas where EBIT may be able to further contribute will be suggested.PACS Nos.: 52.38.–r, 52.25.Os, 52.70.–m, 42.55.Vc, 07.60.Ly, 29.30.Kv, 31.15.–p
High-precision relativistic atomic structure calculations and the EBIT: Tests of quantum electrodynamics in highly charged ions
Authors: Cheng K T , Chen M H , Johnson W R , Sapirstein J
Published: March 2008

High-precision relativistic atomic-structure calculations based on the relativistic many-body perturbation theory and the relativistic configuration-interaction method are shown to provide stringent tests of strong-field quantum electrodynamic (QED) corrections when compared with electron beam ion trap measurements of the spectra of highly charged, many-electron ions. It is further shown that theory and experiment are accurate enough to test not just the leading screened QED corrections but also smaller contributions from higher order Breit interactions, relaxed-core QED corrections, two-loop Lamb shifts, negative-energy state corrections, nuclear polarizations, and nuclear recoils. PACS Nos. 31.30.Jv, 32.30.Rj, 31.25.–v, 31.15.Ar
Relativistic many-body calculations of atomic properties in Pd-like ions
Authors: Safronova U I , Bista R , Bruch R , Merabet H
Published: March 2008

Wavelengths, transition rates, and line strengths are calculated for the 85 possible multipole transitions between the excited 4p6 4d9 4f, 4p6 4d9 5l, 4p5 4d10 4f, and 4p5 4d10 5l states and the ground 4p6 4d10 state in Pd-like ions with the nuclear charges ranging from Z = 47 to 100. Relativistic many-body perturbation theory (RMBPT), including the Breit interaction, is used to evaluate energies and transition rates for multipole transitions in hole–particle systems. This method is based on the relativistic many-body perturbation theory, agrees with MCDF calculations in lowest order, includes all second-order correlation corrections, and includes corrections from negative energy states. The calculations start from a [Zn]4p64d10 Dirac–Fock potential. First-order perturbation theory is used to obtain intermediate-coupling coefficients, and second-order RMBPT is used to determine the matrix elements. The contributions from negative-energy states are included in the second-order multipole matrix elements. The resulting transition energies and transition rates are compared with experimental values and with results from other recent calculations. Trends of the transitions rates for the selected multipole transitions as function of Z are illustrated graphically. The Z dependence of the energy splitting for all triplet terms of the 4p64d9 4f and 4p64d9 5l configurations are shown for Z = 47–100. PACS Nos.: 31.15.Ar, 31.15.Md, 32.70.Cs, 32.30.Rj, 31.25.Jf
Milestones in EBIT spectroscopy and why it almost did not work
Authors: Marrs R E
Published: March 2008

The electron beam ion trap (EBIT) spectroscopy that now seems routine would not be possible without considerable good luck in several areas of EBIT technology. Among these are X-ray background, ion cooling, neutral gas density, and electron current density and energy control. A favorable outcome in these areas has enabled clean X-ray spectra, sufficient intensity for high-resolution spectroscopy, production of very high-charge states, and a remarkable variety of spectroscopic measurements. During construction of the first EBIT 20 years ago, it was not clear that any of this was possible.PACS Nos.: 34.80.Kw, 32.30.Rj
Spectroscopy on magnetically confined plasmas using electron beam ion trap spectrometers
Authors: Graf A T , Brockington S , Horton R , Howard S , Hwang D , Beiersdorfer P , Clementson J , Hill D , May M , Mclean H , Wood R , Bitter M , Terry J , Rowan W L , Lepson J K , Delgado-Aparicio L
Published: March 2008

Multiple spectrometers originally designed for and used at the University of California Lawrence Livermore National Laboratory’s electron beam ion trap have found use at various magnetically confined plasma facilities. Three examples will be described. First is a soft X-ray/EUV grating spectrometer (6–150 Å), which is operating at the National Spherical Torus Experiment. Second is an EUV spectrometer with wavelength coverage up to 400 Å, which has just recently started operating at the Sustained Spheromak Physics Experiment. The last is a high-resolution transmission-grating spectrometer for visible light that has been used at the Compact Toroid Injection Experiment and is currently at the Alcator C-Mod tokamak.PACS Nos.: 39.30.+w, 52.55.–s, 32.30.Rj, 07.60.Rd, 52.70.La
Semiclassical quantization of non-Hermitian multidimensional systems using Hamilton–Jacobi equation
Authors: Nanayakkara A
Published: March 2008

The Hamilton–Jacobi equation of motion is solved in action variables for non-Hermitian systems. Both real and complex semiclassical eigenvalues are obtained that make action variables into integers. This study shows, regardless of the existence of periodic or quasi-periodic classical trajectories, Hamilton–Jacobi methods can be applied to quantize some complex non-Hermitian systems with a good accuracy.

PACS Nos.: 23.23.+x, 56.65.Dy
De Broglie waves as an effect of clock desynchronization
Authors: Baylis William E
Published: March 2008

De Broglie waves are a simple consequence of special relativity applied to the complex-phase oscillations of stationary states. As de Broglie showed in his doctoral thesis, the synchronized oscillations of an extended system at rest, even a classical one, become de Broglie-like waves when boosted to finite velocity. The waves illustrate the well-known but seldom demonstrated relativistic effect of clock desynchroniation (or dephasing) in moving frames. Although common manifestations of stationary-state oscillations in interference experiments are sensitive only to energy differences, de Broglie wavelengths are inversely proportional to rest-frame oscillation frequency, and their observed values require that the oscillation frequencies are proportional to the the total absolute energy, including the rest component mc2.

PACS Nos.: 03.65.Ta, 03.30.+p, 01.65.+g
A varying-c cosmology
Authors: Shojaie H , Farhoudi M
Published: March 2008

We develop a new model for the Universe based on two key assumptions: first, the inertial energy of the Universe is a constant, and second, the total energy of a particle, the inertial plus the gravitational potential energy produced by the other mass in the Universe, is zero. This model allows the speed of light and the total mass of the Universe to vary as functions of cosmological time, where we assume the gravitational constant to be a constant. By means of these assumptions, the relations between the scale factor and the other parameters are derived. The Einstein equation, by making it compatible with varying-c, is used and the Friedmann equations in this model are obtained. Assuming the matter content of the Universe to be perfect fluids, the model fixes γ to be 2/3. That is, the whole Universe always exhibits a negative pressure. Moreover, the behaviour of the scale factor is the same for any value of the curvature. It is also shown that the Universe began from a big bang with zero initial mass and expands forever even with positive curvature, but it is always decelerating. At the end, solutions to some famous problems, mainly of the standard big bang model, and an explanation for the observational data about the accelerating Universe are provided.

PACS Nos.: 98.80.Bp, 98.80.Jk
Relations entre l’entropie physique, le codage de l’information et l’énergie de simulation
Authors: Bigerelle M , Iost A
Published: March 2008

It is shown that an isomorphism exists between the mixing entropy and the size of a computer program that simulates the physical system. This isomorphism must be constructed with respect to some theorems, and it is shown that the composition of two isomorphisms, one based on a run length encoding and another by encoding sequences in a dictionary allows us to quantify the entropy of binary and ternary systems at the equilibrium. Finally, it is shown that the energy consumed by a physical system encoded by this system and executed on a Turing machine is proportional to the free energy of the thermodynamic system.
Measurements of the intercombination and forbidden lines from the spectra of helium-like ions in tokamaks and electron beam ion traps
Authors: Bitter M , Hill K W , Goeler S von , Stodiek W , Beiersdorfer P , Rice J E , Ince-Cushman A
Published: March 2008

The paper reviews the results from tokamak experiments and measurements on electron beam ion traps for the line ratios x/w, y/w, and z/w in the spectra of helium-like ions with Z in the range from 14 to 28. With the exception of the DITE experiments, where these line ratios were found to be in agreement with theoretical predictions, all other tokamak experiments yielded values that were significantly greater than predicted. The reasons for these discrepancies are not yet understood. It is possible that radial profile effects were not properly taken into account in the majority of the tokamak experiments. The paper also gives a short historical review of the X-ray diagnostic developments and presents very recent data from a new type of X-ray imaging crystal spectrometer, which records spatially resolved spectra with a spatial resolution of about 1 cm in the plasma. These new data can be Abel inverted, so that it will be possible to determine line ratios at each radial position in the plasma. Effects of radial profiles, which may have affected the chord-integrated measurements of the past, will thus be eliminated in the future. PACS Nos.: 52.55.Fa, 32.30.Rj
Anticipated X-ray and VUV spectroscopic data from ITERwith appropriate diagnostic instrumentation
Authors: Peacock N J , O’Mullane M G , Barnsley R , Tarbutt M
Published: March 2008

The radiation characteristics of anticipated sample elements, from H through W, in the International Thermonuclear Experimental Reactor (ITER) have been modelled using the diffusion equilibrium model SANCO for the ion concentrations coupled with the spectral signature of the ions, throughout the X-ray and VUV regions (0.1–100 keV), using the Atomic Data and Analysis Structure population code and database, ADAS. The spectral signature varies greatly depending on whether the viewing line-of-sight (LOS) encompasses the divertor and (or) core regions of the plasma volume. Bound–bound transitions required for line profile analyses of nonfuel core ions can locally dominate the continuum spectrum in the 0.1–10 keV region at acceptably low elemental concentrations. While the background continuum is the main source of noise in the line profile analyses, the intensity and features of the continuum when divided into many spectral bands covering 0.1–100 keV are themselves powerful diagnostics of the plasma composition, Zeff, and the electron temperature. The spectral signature of the divertor LOSs where 1 < Te < 300 eV is dominated typically and exclusively by lines in the XUV–VUV region, restricted in the case of W to λ > 40 Å. Appropriate instrumentation, relying on imaging Bragg reflectors and diffractors and position-sensitive energy-resolving detectors, is designed to cover the full spatial extent of the core plasma. Estimates of the core signal/noise based on experience with tritium experiments on the Joint European Torus indicates substantial signal levels with tolerable neutron-induced noise and component degradation. The divertor diagnostics make use of a suite of aspheric diffraction grating spectrometers designed to measure impurity ion influxes and are essential for plasma control. The EBIT could be conceived as a neutron-free adjunct facility to the ITER spectroscopic programme. At its simplest level, it provides standards for instrument performance and for the spectroscopic signature of selected ions subjected to electronic and atomic collisions over a wide range of ITER-relevant impacting energies.PACS Nos.: 52.58.Lq, 52.55.Fa, 52.70–m, 52.25.Vy, 87.64.Gb
The XRS microcalorimeter spectrometer at the Livermore electron beam ion trap
Authors: Porter F S , Beck B R , Beiersdorfer P , Boyce K R , Brown G V , Chen H , Gygax J , Kahn S M , Kelley R L , Kilbourne C A , Magee E , Thorn D B
Published: March 2008

NASA’s X-ray spectrometer (XRS) microcalorimeter instrument has been operating at the electron beam ion trap (EBIT) facility at Lawrence Livermore National Laboratory since July of 2000. The spectrometer is currently undergoing its third major upgrade to become an easy to use and extremely high-performance instrument for a broad range of EBIT experiments. The spectrometer itself is broadband, capable of simultaneously operating from 0.1 to 12 keV and has been operated at up to 100 keV by manipulating its operating conditions. The spectral resolution closely follows the spaceflight version of the XRS, beginning at 10 eV FWHM at 6 keV in 2000, upgraded to 5.5 eV in 2003, and will hopefully be ~3.8 eV in the fall of 2007. Here we review the operating principles of this unique instrument, the extraordinary science that has been performed at EBIT over the last six years, and prospects for future upgrades. Specifically, we discuss upgrades to cover the high-energy band (to at least 100 keV) with a high quantum efficiency detector and prospects for using a new superconducting detector to reach 0.8 eV resolution at 1 keV and 2 eV at 6 keV with high counting rates. PACS Nos.: 52.25.Os, 52.70.La, 95.85.Nv, 32.30.Rj, 07.85.Fv, 78.70.En
Analog and digital simulations of Maxwellian plasmas forastrophysics
Authors: Savin D W , Badnell N R , Beiersdorfer P , Beck B R , Brown G V , Bryans P , Gorczyca T W , Gu M F , Kahn S M , Laming J M , Liedahl D A , Mitthumsiri W , Scofield J H , Wong K L
Published: March 2008

Many astrophysical and laboratory plasmas possess Maxwell–Boltzmann (MB) electron energy distributions (EEDs). Interpreting or predicting the properties of these plasmas requires accurate knowledge of atomic processes such as radiative lifetimes, electron impact excitation and de-excitation, electron impact ionization, radiative recombination, dielectronic recombination, and charge transfer, all for thousands of levels or more. Plasma models cannot include all of the needed levels and atomic data. Hence, approximations need to be made to make the models tractable. Here we report on an “analog” technique we have developed for simulating a Maxwellian EED using an electron beam ion trap and review some recent results using this method. A subset of the atomic data needed for modeling Maxwellian plasmas relates to calculating the ionization balance. Accurate fractional abundance calculations for the different ionization stages of the various elements in the plasma are needed to reliably interpret or predict the properties of the gas. However, much of the atomic data needed for these calculations have not been generated using modern theoretical methods and are often highly suspect. Here we will also review our recent updating of the recommended atomic data for “digital’ computer simulations of MB plasmas in collisional ionization equilibrium (CIE), describe the changes relative to previously recommended CIE calculations, and discuss what further recombination and ionization data are needed to improve this latest set of recommended CIE calculations. PACS Nos.: 34.70.+e,34.80.Dp, 34.80.Kw, 34,80,Lx, 52.50.–j, 52.20.Fs, 52.20.Hv, 52.25.Jm, 52,72.+v, 52.75.–d, 95.30.Dr, 95.30.Ky, 98.38.Bn, 98.58.Bz
Proposed wavelength measurements of silicon X-ray spectra: Application to Vela X-1
Authors: Liedahl D A , Brown G V
Published: March 2008

When a stellar wind from a massive star is captured by a neutron star in close orbit, gravitational potential energy is converted into hard X-radiation near the surface of the neutron star. The X-radiation, in turn, modifies the wind through heating and photoionization, which affects the dynamics of mass capture. We have begun a project to further elucidate this process, which involves time-dependent three-dimensional hydrodynamics, large-scale atomic physics calculations, and radiation transport, integrated in an attempt to derive a self-consistent “first principles” description of the mass transfer process. We anticipate that the high-resolution silicon X-ray spectrum, produced by innershell photoionization and photoexcitation, as measured by the Chandra observatory, will provide benchmarks for these calculations. However, theoretical wavelengths, which are required in order to draw inferences concerning the velocity field of the wind, are uncertain at the level of the likely Doppler shifts in the stellar wind. EBIT measurements could lead to a reliable set of wavelengths, thereby providing observational constraints on the physics that powers some of the brightest X-ray sources in the Galaxy. PACS Nos.: 32.30.Rj, 32.80.Fb, 32.80.Hd, 52.25.Os, 52.72.+v, 97.10.Me, 97.80.Jp
Turbulent boundary layer over a deep cavity: friction coefficient and streamwise velocity components
Authors: Hassan M El , Labraga L , Keirsbulck L
Published: March 2008

Deep cavities are present in car vehicles in numerous forms. Although drag downstream cavities have interested many authors, this aspect was never treated for particularly deep cavities. The objective of the present investigation is to study the effect of a deep cavity, characterized by its length-to-depth ratio L/H = 0.2, on both the skin friction coefficient and the statistic components of the streamwise velocity. Laser Doppler velocimetry (LDV) was used for the mean velocity and its statistic components measurements. Results obtained by other authors allowed a comparison between shallow and deep cavity configurations. The main conclusion is that with the same flow conditions, the drag increase downstream from the cavity is less important compared to the square cavity. A localized skewness coefficient decrease and a flatness coefficient increase could be related to intermittence ejection of flow from the downstream part of the cavity. This hypothesis was confirmed thanks to particle image velocimetry (PIV) measurements.

PACS No.: 47.27.nb
Laboratory astrophysics in the extreme ultraviolet
Authors: Lepson J K , Beiersdorfer P , Bitter M , Kahn S M
Published: March 2008

Electron beam ion traps are uniquely well suited for laboratory astrophysics because they can produce nearly any charge state of any element in a collisionally excited plasma that is comparable in density and temperature to many astronomical sources. The Lawrence Livermore EBIT facility has been optimized for laboratory astrophysics with a suite of dedicated instruments and has made significant advances in this field. This paper reviews some of the work performed at LLNL in compiling comprehensive spectral catalogues, discovery of a magnetic field line diagnostic in the EUV and soft X-ray regimes, and density diagnostics on EBIT and at the NSTX tokamak.PACS Nos.: 95.30.Ky, 32.30.Rj, 95.75.–z, 95.85.Nv, 97.10.Ex, 95.55.Ka, 95.85.Mt, 52.55.Fa
Guiding of highly charged ions through insulating nanocapillaries
Authors: Schuch R , Johansson A , Kumar R T , Sahana M B , Skog P , Soroka I L , Vikor Gy , Zhang H Q
Published: March 2008

The guiding of highly charged ions through nanocapillaries in different insulating materials, such as polyethylene terephthalate, SiO2, and Al2O3 has been investigated by our group, using 7 keV Ne7+ ions. We find transmission of ions incident at angles larger than the angle given by the capillary aspect ratio in all these materials. The measured angular distributions, however, vary with the membrane material. In this report we compare the experimental findings with the different membranes. PACS Nos.: 79.20.Rf, 34.50.Dy, 81.07.De
Observations of scour around offshore structures
Authors: Dahlberg Rune
Published: March 2008

By placement of a structure on the seabottom, the freefield current pattern is changed. The size and geometrical shape of the structure influence the resulting current pattern. This paper deals with observations of scour around gravity structures, piled structures, and pipelines as well as the experience gained with various scour protection methods. Basic considerations required for estimation of scour potential are included for completeness. The observations show that significant scour occurs mainly in shallow waters, especially in areas with active sand waves where some of the piled structures and pipelines included in this study were located. All the major gravity platforms were in deeper waters which explains the moderate scour observed around these structures. The only exception was a square shaped based which experienced significant scour at the corners. Keywords: offshore structure, erosion, protection, case history, field performance data.
The permeability of natural soft clays. Part I: Methods of laboratory measurement
Authors: Tavenas F. , Leblond P. , Jean P. , Leroueil S.
Published: March 2008

The methods of measuring the permeability of clays in the laboratory are investigated. Constant head tests in the triaxial are best suited for testing large specimen under field stress conditions provided the cell is modified to eliminate leakage. Using this type of test, the validity of Darcy's law is confirmed.Falling head tests in the oedometer are very simple to perform and subject to minimal sources of errors. However, small size specimens may not be totally representative.Indirect evaluations of the permeability from consolidation tests are shown to be unreliable particularly in structured natural clays: evaluation of k from cv measurements in step-loaded tests gives much too low values, constant rate of strain tests strongly overestimate k in the vicinity of σp′ and give nonrepresentative e vs. lg k relations; controlled gradient tests tend to underestimate k at all void ratios. Keywords: permeability, clays, laboratory tests, test equipment, consolidation tests.
Some difficulties associated with the limit equilibrium method of slices
Authors: Ching R. K. H. , Fredlund D. G.
Published: March 2008

Several commonly encountered problems associated with the limit equilibrium methods of slices are discussed. These problems are primarily related to the assumptions used to render the inherently indeterminate analysis determinate. When these problems occur in the stability computations, unreasonable solutions are often obtained. It appears that problems occur mainly in situations where the assumption to render the analysis determinate seriously departs from realistic soil conditions. These problems should not, in general, discourage the use of the method of slices. Example problems are presented to illustrate these difficulties and suggestions are proposed to resolve these problems. Keywords: slope stability, limit equilibrium, method of slices, factor of safety, side force function.
Preconsolidation pressure of Champlain clays. Part II. Laboratory determination
Authors: Leroueil S. , Tavenas F. , Samson L. , Morin P.
Published: March 2008

A series of conventional and special consolidation tests was carried out on clay samples from 11 sites in the Champlain sea basin. The results show that, for a given clay at a given depth, there is a unique preconsolidation pressure – strain rate relationship independent of the tests carried out and that the relationships obtained in different Champlain clays can be normalized.Correlations between the preconsolidation pressure values obtained from the different special consolidation tests and the conventional test are established, and a method of estimating in-situ preconsolidation pressure is suggested. Keywords: preconsolidation pressure, laboratory, testing techniques, strain rate.
A simple stress path analog for the triaxial test
Authors: Vaid Y. P. , Negussey Dawit
Published: March 2008

A simple pneumatic stress path triaxial testing device has been designed. The components of the apparatus and the operation of the system is described. Typical results of drained tests on a sand are presented in order to illustrate the capabilities of the device as a stress path analog and to highlight briefly the stress path dependence of soil behaviour. Keywords: triaxial equipment, pneumatic, stress path.
Creep in brittle rock after an increment of uniaxial load
Authors: Cruden D.M.
Published: March 2008

An analytical extension of a theory of brittle creep predicts that the form of the creep curve of brittle rock after an increment of uniaxial, compressive load depends on a creep parameter, n, of the rock and the size of the load increment and varies with time.With large load increments and large values of n, creep behaviour quickly loses any trace of creep at the lower load. For smaller increments and smaller values of n, the subsequent creep shows a distinctive mode of approach to normal creep behaviour at the higher load. The early portion of this creep curve can be used to estimate the creep parameters of the material.Experiments on Pennant sandstone are used to show how estimates of the physical parameters controlling the variation of creep with stress and time can be derived, for the first time, from increment creep tests on a single specimen. Keywords: creep, rock, brittle materials, crack, corrosion.
Improvement of sensitive silty clay by electroosmosis
Authors: Morris Derek V. , Hillis Sydney F. , Caldwell Jack A.
Published: March 2008

A laboratory test program was undertaken in order to assess the probable effectiveness of electroosmotic treatment in the field in reducing the water content and sensitivity of a deposit of soft sensitive silty clay. The results of treatment on tube samples indicate that substantial reductions in water content and liquidity index would be expected, particularly close to the anode. Static and dynamic triaxial tests on both treated and untreated specimens indicated major improvement in both static strength and the resistance to cyclic loading of the soil. Both of these are necessary if construction of a major embankment on this material is to proceed. Key words: electroosmosis, soil improvement, sensitive soils, cyclic testing.
Effects of freeze–thaw and softening on a natural clay at low stresses
Authors: Graham J. , Au V. C. S.
Published: March 2008

Weathering processes such as softening and freeze–thaw cycling affect the properties of clays. Care must therefore be taken when selecting strength and compressibility parameters for analysis of natural slopes, compacted clay embankments, and trench excavations in which significant proportions of the cross section can be affected by climatic weathering.Samples of plastic Lake Agassiz clay from Winnipeg were consolidated anisotropically in the laboratory to axial stresses less than or equal to the in situ effective overburden pressure. They were therefore all overconsolidated with respect to the field preconsolidation pressure. The samples were then loaded under drained or undrained conditions along steeply rising stress paths in p′, q stress space. One group of samples was tested immediately to identify the "undisturbed" behavior, a second group was subjected to freeze–thaw cycles, and a third group allowed to swell freely before testing.The freeze–thaw cycling produced increased compressibility and pore-water pressures, and reduced strengths at low stresses compared with the behavior of undisturbed clay. Freezing also caused the development of a clearly defined fissure structure. Softening at low stresses with access to water produced less marked effects. Key words: clay, undisturbed, freeze–thaw, softening, strength, yielding, pore-water pressures.
Static and low-frequency response of pile groups
Authors: Sharnouby Bahaa El , Novak Milos
Published: March 2008

A simple, efficient method is presented for the analysis of large pile groups subjected to vertical loads, horizontal loads, and moments acting either statically or dynamically with low frequencies. The soil profile and the arrangement of the piles may be arbitrary but the solution is particularly efficient for groups with double symmetry or axisymmetry. The group is analyzed directly, avoiding the use of interaction factors, but the interaction factors are also presented. The piles can be of any type, i.e., floating, end-bearing, socketed, or with a pedestal.
Unfrozen water content in saline soils: results using time-domain reflectometry
Authors: Patterson D. E. , Smith M. W.
Published: March 2008

The use of time-domain reflectometry (TDR) for determining the phase composition of saline permafrost from measurement of the apparent dielectric constant, Ka, is examined.Combined TDR–dilatometry experiments were performed to assess whether the TDR method could be used on frozen soil samples with high pore water salinity. In general, unfrozen water content determinations by TDR were within ±0.025 cm3∙cm−3 of those obtained by dilatometry, with no marked influence due to salinity. A novel probe design for use on saline core samples shows promise as a means for determining unfrozen water contents in the field.
Geochemical evolution of inactive pyritic tailings in the Elliot Lake uranium district
Authors: Dubrovsky N. M. , Cherry J. A. , Reardon E. J. , Vivyurka A. J.
Published: March 2008

Geochemical data obtained between 1979 and 1983 from a network of piezometer nests and cores from three inactive uranium tailings impoundments in the Elliot Lake district indicate that oxidation of pyrite taking place in the shallow part of the zone above the water table is causing the chemistry of the pore water above and below the water table to change. A two-layer hydrochemical zonation has developed in which infiltration water from rain and snow has resulted in an upper zone of low-pH water with high concentrations of SO4, Fe, and heavy metals. This zone is gradually expanding downward at rates generally between 0.2 and 2 m/year, causing displacement of the original mill process water, which has neutral pH and low concentrations of heavy metals. High concentrations of Fe(III) at shallow depth in the zone above the water table indicate that ferric iron is an important oxidizer of pyrite in the presence of free oxygen.The pe of the groundwaters is controlled by the ferric–ferrous redox couple, and trends in the data indicate iron solubility control by siderite at high pH, by ferric hydroxide at moderate to slightly acid pH values, and possibly by jarosite at low pH. Aluminum solubility controls are complex, and precipitation of amorphous aluminum hydroxide, allophane, and basic aluminum sulfates may occur over different pH ranges. Transport of low-pH conditions is retarded relative to the rate of groundwater flow in the tailings, because of the buffering effect of small amounts of carbonate minerals added during tailings neutralization; primary aluminosilicates such as sericite; and secondary aluminum hydroxides.Field data show that the flux of dissolved iron from the vadose zone to the groundwater zone in the Nordic Main tailings has been decreasing in recent years. However, mass-balance calculations indicate a potential for the generation of high-Fe groundwater for several decades to several hundred years. A long-term potential for acid and iron production is also shown by data from two tailings impoundments that have been inactive 8–10 years longer than the Nordic Main area. Presently only a small portion of the Nordic Main and West Arm tailings areas has become acidic through the entire tailings thickness; however, under existing infiltration conditions more extensive acidification will occur in future decades.
Synthesis of isoxazole conjugates of sugars via 1,3-dipolar cycloaddition
Authors: Vaidya Vipraja V , Wankhede Karuna S , Salunkhe Manikrao M , Trivedi Girish K
Published: March 2008

Isoxazole conjugates of sugar have been synthesized by the aid of 1,3-dipolar cycloaddition in a click chemistry approach. The sugar-derived propargyl ethers underwent 1,3-dipolar cycloadditions smoothly with in situ generated nitrile oxides from aromatic oximes in good yields. The reaction exhibited a high degree of regioselectivity.Key words: isoxazole conjugates, 1,3-dipolar cycloadditions, nitrile oxides.