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Results for “Canadian Journal of Physics”

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At least 19 recordsLinked to original sources
USGS2003

Temperature, pressure, and compositional effects on anomalous or "self" preservation of gas hydrates

We previously reported on a thermal regime where pure, polycrystalline methane hydrate is preserved metastably in bulk at up to 75 K above its nominal temperature stability limit of 193 K at 0.1 MPa, following rapid release of the sample pore pressure. Large fractions (>50 vol.%) of methane hydrate can be preserved for 2-3 weeks by this method, reflecting the greatly suppressed rates of dissociation that characterize this "anomalous preservation" regime. This behavior contrasts that exhibited by methane hydrate at both colder (193-240 K) and warmer (272-290 K) isothermal test conditions, where dissociation rates increase monotonically with increasing temperature. Here, we report on recent experiments that further investigate the effects of temperature, pressure, and composition on anomalous preservation behavior. All tests conducted on sI methane hydrate yielded self-consistent results that confirm the highly temperature-sensitive but reproducible nature of anomalous preservation behavior. Temperature-stepping experiments conducted between 250 and 268 K corroborate the relative rates measured previously in isothermal preservation tests, and elevated pore-pressure tests showed that, as expected, dissociation rates are further reduced with increasing pressure. Surprisingly, sII methane-ethane hydrate was found to exhibit no comparable preservation effect when rapidly depressurized at 268 K, even though it is thermodynamically stable at higher temperatures and lower pressures than sI methane hydrate. These results, coupled with SEM imaging of quenched sample material from a variety of dissociation tests, strongly support our earlier arguments that ice-"shielding" effects provided by partial dissociation along hydrate grain surfaces do not serve as the primary mechanism for anomalous preservation. The underlying physical-chemistry mechanism(s) of anomalous preservation remains elusive, but appears to be based more on textural or morphological changes within the hydrate material itself, rather than on compositional zoning or ice-rind development.

Canadian Journal of Physics↗
USGS2003

Temperature dependence of polyhedral cage volumes in clathrate hydrates

The polyhedral cage volumes of structure I (sI) (carbon dioxide, methane, trimethylene oxide) and structure II (sII) (methane-ethane, propane, tetrahydrofuran, trimethylene oxide) hydrates are computed from atomic positions determined from neutron powder-diffraction data. The ideal structural formulas for sI and sII are, respectively, S2L6 ?? 46H2O and S16L???8 ?? 136H2O, where S denotes a polyhedral cage with 20 vertices, L a 24-cage, and L??? a 28-cage. The space-filling polyhedral cages are defined by the oxygen atoms of the hydrogen-bonded network of water molecules. Collectively, the mean cage volume ratio is 1.91 : 1.43 : 1 for the 28-cage : 24-cage : 20-cage, which correspond to equivalent sphere radii of 4.18, 3.79, and 3.37 A??, respectively. At 100 K, mean polyhedral volumes are 303.8, 227.8, and 158.8 A??3 for the 28-cage, 24-cage, and 20-cage, respectively. In general, the 20-cage volume for a sII is larger than that of a sI, although trimethylene oxide is an exception. The temperature dependence of the cage volumes reveals differences between apparently similar cages with similar occupants. In the case of trimethylene oxide hydrate, which forms both sI and sII, the 20-cages common to both structures contract quite differently. From 220 K, the sII 20-cage exhibits a smooth monotonic reduction in size, whereas the sI 20-cage initially expands upon cooling to 160 K, then contracts more rapidly to 10 K, and overall the sI 20-cage is larger than the sII 20-cage. The volumes of the large cages in both structures contract monotonically with decreasing temperature. These differences reflect reoriented motion of the trimethyelene oxide molecule in the 24-cage of sI, consistent with previous spectroscopic and calorimetric studies. For the 20-cages in methane hydrate (sI) and a mixed methane-ethane hydrate (sII), both containing methane as the guest molecule, the temperature dependence of the 20-cage volume in sII is much less than that in sI, but sII is overall larger in volume.

Canadian Journal of Physics↗
USGS2003

Measured temperature and pressure dependence of compressional (Vp) and shear (Vs) wave speeds in compacted, polycrystalline ice lh

We report on laboratory measurements of compressional- and shear-wave speeds in a compacted, polycrystalline ice-Ih sample. The sample was made from triply distilled water that had been frozen into single crystal ice, ground into small grains, and sieved to extract the 180–250 µ m diameter fraction. Porosity was eliminated from the sample by compacting the granular ice between a hydraulically driven piston and a fixed end plug, both containing shear-wave transducers. Based on simultaneous compressional- and shear-wave-speed measurements, we calculated Poisson's ratio and compressional-wave, bulk, and shear moduli from –20 to –5°C and 22 to 33 MPa.

Canadian Journal of Physics↗
USGS2003

Measured temperature and pressure dependence of Vp and Vs in compacted, polycrystalline sI methane and sII methane-ethane hydrate

We report on compressional- and shear-wave-speed measurements made on compacted polycrystalline sI methane and sII methane-ethane hydrate. The gas hydrate samples are synthesized directly in the measurement apparatus by warming granulated ice to 17??C in the presence of a clathrate-forming gas at high pressure (methane for sI, 90.2% methane, 9.8% ethane for sII). Porosity is eliminated after hydrate synthesis by compacting the sample in the synthesis pressure vessel between a hydraulic ram and a fixed end-plug, both containing shear-wave transducers. Wave-speed measurements are made between -20 and 15??C and 0 to 105 MPa applied piston pressure.

Canadian Journal of Physics↗
USGS2003

Neutron powder diffraction studies as a function of temperature of structure II hydrate formed from propane

Neutron powder diffraction data confirm that hydrate samples synthesized with propane crystallize as structure type II hydrate. The structure has been modeled using rigid-body constraints to describe C3H8 molecules located in the eight larger polyhedral cavities of a deuterated host lattice. Data were collected at 12, 40, 100, 130, 160, 190, 220, and 250 K and used to calculate the thermal expansivity from the temperature dependence of the lattice parameters. The data collected allowed for full structural refinement of atomic coordinates and the atomic-displacement parameters.

Canadian Journal of Physics↗
USGS2003

Ductile flow of methane hydrate

Compressional creep tests (i.e., constant applied stress) conducted on pure, polycrystalline methane hydrate over the temperature range 260-287 K and confining pressures of 50-100 MPa show this material to be extraordinarily strong compared to other icy compounds. The contrast with hexagonal water ice, sometimes used as a proxy for gas hydrate properties, is impressive: over the thermal range where both are solid, methane hydrate is as much as 40 times stronger than ice at a given strain rate. The specific mechanical response of naturally occurring methane hydrate in sediments to environmental changes is expected to be dependent on the distribution of the hydrate phase within the formation - whether arranged structurally between and (or) cementing sediments grains versus passively in pore space within a sediment framework. If hydrate is in the former mode, the very high strength of methane hydrate implies a significantly greater strain-energy release upon decomposition and subsequent failure of hydrate-cemented formations than previously expected.

Canadian Journal of Physics↗
USGS1990

Food habits of wintering canvasbacks in Louisiana

We studied the food habits of canvasbacks ( Aythya valisineria ) at Catahoula Lake (inland) and the Mississippi River Delta (coastal), Louisiana, from November 1987 to February 1988. Plant foods comprised >97 aggregate percent dry mass of the canvasback diet. The proportion of plant material eaten did not vary with sex, age, or month, or differ between study sites or nocturnal and diurnal collections. Tubers of chufa flatsedge ( Cyperus esculentus ) and common arrowhead ( Sagittaria latifolia ) made up 94% of the canvasback diet at Catahoula Lake. Common and grassy arrowhead ( Sagittaria graminea ) tubers and American bulrush ( Scirpus americanus ) rhizomes and seeds formed 94% of the canvasback diet at the Mississippi River Delta. Consumption of specific food taxa did not vary with sex, age, or month at either study site. Canvasbacks at the Mississippi River Delta preferred seeds of American bulrush over all other foods, but American bulrush rhizomes were underrepresented in the diet. Densities of subterranean plant foods at Catahoula Lake and the Mississippi River Delta are apparently higher than at other major canvasback concentration areas and enable canvasbacks wintering in Louisiana to improve their physical condition before spring migration.

Louisiana↗
USGS1994

Wolf and bear predation on white-tailed deer fawns in northeastern Minnesota

Whitetailed deer (Odocoileus virginianus) fawn mortality was studied during the summers of 1989 and 1990 in northeastern Minnesota. Estimated pooled mortality rates for 21 radio-tagged fawns were 0.44 for the May-June, 0.13 for the July-October, and 0.51 for the May-October intervals. Predation accounted for all mortalities, with wolves (Canis lupus) responsible for 51% of them and black bears (Ursus americanus) for 49%. Fawns from mothers gt 4 years old weighed more and survived better than fawns from young mothers, which weighed less. Of various related factors (doe age, doe mass, fawn mass, fawn birth date, and fawn blood serum urea nitrogen (SUN)), only SUN was significant between surviving and perishing fawns, fawns with low SUN survived significantly less. Fawn SUN may have been only an indirect indicator of a doe physical, or behavioral factor that was more important to fawn survival.

Canadian Journal of Zoology↗
USGS2000

Stratigraphy and historic accumulation of mercury in recent depositional sediments in the Sudbury River, Massachusetts, USA

The distribution and deposition of sedimentary mercury in the Sudbury River were linked to an industrial complex (Nyanza site) that operated from 1917 through 1978. In two reservoirs just downstream from the Nyanza site, estimated rates of mercury accumulation increased markedly in the 1920s and 1930s, were greatest during 1976-1982, decreased within 5 years after industrial operations ceased, and have decreased further since capping of contaminated soil at the Nyanza site was completed in 1991. The most contaminated sediments were typically buried, yet the 0- to 1-cm stratum remained substantially contaminated in all cores. Mercury accumulating in the surficial, reservoir sediments was probably from continuing, albeit much lesser, inputs from the Nyanza site, whereas recent inputs to downstream wetland areas were attributed to recycling of sedimentary mercury or to mercury from unidentified local sources. In the reservoirs, burial of highly contaminated sediments is gradually decreasing the amount of sedimentary mercury available for methylation. In downstream wetlands, however, sedimentary mercury seemed to be more available than that in the reservoirs for physical transport and biogeochemical cycling.

Canadian Journal of Fisheries and Aquatic Sciences↗
USGS1986

In situ and laboratory geotechnical tests of the Pierre Shale near Hayes, South Dakota — A characterization of engineering behavior

A geotechnical investigation of the Pierre Shale near Hayes, South Dakota, was conducted by the U.S. Geological Survey as a basis for evaluating problems in deep excavations into that formation. The physical and mechanical properties of the shale were determined through use of core holes drilled to a maximum depth of 184 m. In situ borehole determinations included a gravimeter survey, pressuremeter testing, thermal profile measurements, and borehole velocity measurements. Onsite and offsite laboratory measurements included rebound measurements, sonic velocity measurements of shear and primary waves, X-ray mineralogy and major element determinations, size analyses, fracture analyses, fabric analyses, and determination of thermal properties.Below 15–22 m, the shale is an unweathered, saturated, overconsolidated, underpressured clay shale with a clay-mineral content ranging between 50 and 100%, dominantly composed of mixed-layer illitic smectites. The physical and mechanical properties vary widely. The variation is related to the clay mineral content (especially in bentonite zones), a large transverse mechanical anisotropy, and zones of fractures and microfractures, which may result from rebound caused by erosion. These may contribute to slope instability over large areas. The thermal and mechanical properties change markedly if the shale is permitted to dry out. The state of stress and overconsolidation appear to be functions of the depositional and erosional history of the deposit. Both are markedly affected by the large fracture zones. The properties of the clay shale indicate problems that may be encountered in excavation and use of deep underground facilities. Key words : anisotropy, characterization, clay shale, consolidation state, physical properties, rebound, relaxation, stress state, thermal properties.

South Dakota↗
USGS1998

Urinary 3-methylhistidine and progressive winter undernutrition in white-tailed deer

Physiological indicators of muscle catabolism would aid assessment of winter nutritional restriction of ungulates, and urinary 3-methylhistidine has exhibited potential in this regard in several species. We examined the effect of chronic moderate and severe nutritional restriction during winter on urinary 3-methylhistidine:creatinine ratios in seven adult white-tailed deer ( Odocoileus virginianus ) and the relationship of these ratios to urinary urea nitrogen:creatinine ratios. Mean base line estimates of urinary 3-methylhistidine:creatinine ratio for the control and severely restricted deer (0.043 and 0.086 µmol:mg, respectively) were similar ( P = 0.280) and remained unchanged in the control deer throughout the study. In contrast, mean 3-methylhistidine:creatinine ratios increased dramatically as nutritional restriction and cumulative mass loss progressed; the quadratic component of the data for the chronically restricted deer was significant ( P < 0.001). Likewise, there was a strong curvilinear relationship ( R 2 = 0.82) between cumulative mass loss (up to 29%) of the pooled deer and urinary 3-methylhistidine:creatinine ratios. Further, urinary urea nitrogen:creatinine ratios were strongly related to 3-methylhistidine:creatinine ratios ( r 2 = 0.89). Our study indicates that further investigation of 3-methylhistidine as an indicator of physical condition and muscle protein breakdown is warranted.

Canadian Journal of Zoology↗
USGS2016

Getting quantitative about consequences of cross-ecosystem resource subsidies on recipient consumers

Most studies of cross-ecosystem resource subsidies have demonstrated positive effects on recipient consumer populations, often with very large effect sizes. However, it is important to move beyond these initial addition–exclusion experiments to consider the quantitative consequences for populations across gradients in the rates and quality of resource inputs. In our introduction to this special issue, we describe at least four potential models that describe functional relationships between subsidy input rates and consumer responses, most of them asymptotic. Here we aim to advance our quantitative understanding of how subsidy inputs influence recipient consumers and their communities. In the papers following, fish were either the recipient consumers or the subsidy as carcasses of anadromous species. Advancing general, predictive models will enable us to further consider what other factors are potentially co-limiting (e.g., nutrients, other population interactions, physical habitat, etc.) and better integrate resource subsidies into consumer–resource, biophysical dynamics models.

Canadian Journal of Fisheries and Aquatic Sciences↗
USGS2008

Landscape-scale evaluation of genetic structure among barrier-isolated populations of coastal cutthroat trout, Oncorhynchus clarkii clarkii

Relationships among landscape structure, stochastic disturbance, and genetic diversity were assessed by examining interactions between watershed-scale environmental factors and genetic diversity of coastal cutthroat trout (Oncorhynchus clarkii clarkii) in 27 barrier-isolated watersheds from western Oregon, USA. Headwater populations of coastal cutthroat trout were genetically differentiated (mean FST = 0.33) using data from seven microsatellite loci (2232 individuals), but intrapopulation microsatellite genetic diversity (mean number of alleles per locus = 5, mean He = 0.60) was only moderate. Genetic diversity of coastal cutthroat trout was greater (P = 0.02) in the Coast Range ecoregion (mean alleles = 47) than in the Cascades ecoregion (mean alleles = 30), and differences coincided with indices of regional within-watershed complexity and connectivity. Furthermore, regional patterns of diversity evident from isolation-by-distance plots suggested that retention of within-population genetic diversity in the Coast Range ecoregion is higher than that in the Cascades, where genetic drift is the dominant factor influencing genetic patterns. Thus, it appears that physical landscape features have influenced genetic patterns in these populations isolated from short-term immigration. ?? 2008 NRC.

Canadian Journal of Fisheries and Aquatic Sciences↗
USGS1981

Ecological studies of vesicular arbuscular mycorrhizae in a barrier sand dune

An ecological survey of the vegetation of a barrier dune on the south coast of Rhode Island showed Ammophila breviligulata , Solidago sempervirens , Lathyrus japonicus , and Myrica pensylvanica to be the dominant plant species. All plants were mycorrhizal. Six species of vesicular–arbuscular (VA) fungi occurred in association with these plants, with Gigaspora gigantea and Acaulospora scrobiculata the most abundant. Also present were Gigaspora calospora , Glomus etunicatus , Glomus fasciculatus , and an undescribed species of Gigaspora . Spore densities and frequencies were measured in a transect across the dune and were compared with plant cover and physical factors (pH, soil moisture, organic matter, soil nutrients, chlorides, and sand grain size). Areas on the dune with greatest vegetation cover by Ammophila were associated with greatest spore densities and fungal diversity in the rhizosphere. For most plant species, maximum spore density occurred in the front half of the plant's distribution range, nearest the dune crest. There was little correlation between spore populations in the soil and physical characteristics, with the exception of sand grain size. The importance of considering VA mycorrhizae in sand dune stabilization programs is discussed.

Rhode Island↗
USGS2012

Range overlap and individual movements during breeding season influence genetic relationships of caribou herds in south-central Alaska

North American caribou ( Rangifer tarandus ) herds commonly exhibit little nuclear genetic differentiation among adjacent herds, although available evidence supports strong demographic separation, even for herds with seasonal range overlap. During 1997–2003, we studied the Mentasta and Nelchina caribou herds in south-central Alaska using radiotelemetry to determine individual movements and range overlap during the breeding season, and nuclear and mitochondrial DNA (mtDNA) markers to assess levels of genetic differentiation. Although the herds were considered discrete because females calved in separate regions, individual movements and breeding-range overlap in some years provided opportunity for male-mediated gene flow, even without demographic interchange. Telemetry results revealed strong female philopatry, and little evidence of female emigration despite overlapping seasonal distributions. Analyses of 13 microsatellites indicated the Mentasta and Nelchina herds were not significantly differentiated using both traditional population-based analyses and individual-based Bayesian clustering analyses. However, we observed mtDNA differentiation between the 2 herds (F STM = 0.041, P < 0.001). Although the Mentasta and Nelchina herds exhibit distinct population dynamics and physical characteristics, they demonstrate evidence of gene flow and thus function as a genetic metapopulation.

Alaska↗
USGS1979

Arctic stream processes--an annotated bibliography

This bibliography selectively summarizes investigations to date (1978) dealing with the physical processes of streams in the Arctic. The specialized annotations include aspects of stream processes described in subordinate parts of general papers on the arctic environment and therefore not evident in author-abstract bibliographies. Foreign contributions--Canadian, Scandinavian, and Russian--are summarized, in the case of Russian literature primarily by means of papers in translation journals. Until 1970 the role of streams in development of the arctic landscape was commonly considered subordinate to that of glacial and frost-related processes. This conclusion changed, however, with the findings of the many new studies begun in response to oil and gas discoveries in the late 1960's. The conclusions of these studies, made to provide both the engineering data for resource development and the information to assess the impacts of that development, were in general agreement that stream processes throughout most of the Arctic were significantly more important than previously had been thought.

Water Supply Paper↗
USGS2017

Testing for synchrony in recruitment among four Lake Michigan fish species

In the Great Lakes region, multiple fish species display intra-specific spatial synchrony in 28 recruitment success, with inter-annual climate variation hypothesized as the most likely driver. 29 In Lake Michigan, we evaluated whether climatic or other physical variables could also induce 30 spatial synchrony across multiple species, including bloater ( Coregonus hoyi ), rainbow smelt 31 ( Osmerus mordax ), yellow perch ( Perca flavescens ), and alewife ( Alosa pseudoharengus ). The 32 residuals from stock-recruitment relationships revealed yellow perch recruitment to be correlated 33 with recruitment of both rainbow smelt (r = 0.37) and alewife (r = 0.36). Across all four species, 34 higher than expected recruitment occurred in 5 years between 1978 and 1987 and then switched 35 to lower than expected recruitment in 5 years between 1996 and 2004. Generalized additive 36 models revealed warmer spring and summer water temperatures and lower wind speeds 37 corresponded to higher than expected recruitment for the nearshore-spawning species, and 38 overall variance explained ranged from 14% (yellow perch) to 61% (alewife). For all species 39 but rainbow smelt, higher recruitment also occurred in extremely high or low years of the North 40 Atlantic Oscillation index. Future development of indices that describe the physical Great Lakes 41 environment could improve understanding of how climate can synchronize fish populations 42 within and across species.

Great Lakes↗
USGS2012

Structure of marine predator and prey communities along environmental gradients in a glaciated fjord

Spatial patterns of marine predator communities are influenced to varying degrees by prey distribution and environmental gradients. We examined physical and biological attributes of an estuarine fjord with strong glacier influence to determine the factors that most influence the structure of predator and prey communities. Our results suggest that some species, such as walleye pollock ( Theragra chalcogramma ), black-legged kittiwake ( Rissa tridactyla ), and glaucous-winged gull ( Larus glaucescens ), were widely distributed across environmental gradients, indicating less specialization, whereas species such as capelin ( Mallotus villosus ), harbor seal ( Phoca vitulina ), and Kittlitz's murrelet ( Brachyramphus brevirostris ) appeared to have more specialized habitat requirements related to glacial influence. We found that upper trophic level communities were well correlated with their mid trophic level prey community, but strong physical gradients in photic depth, temperature, and nutrients played an important role in community structure as well. Mid-trophic level forage fish communities were correlated with the physical gradients more closely than upper trophic levels were, and they showed strong affinity to tidewater glaciers. Silica was closely correlated with the distribution of fish communities, the mechanisms of which deserve further study.

Alaska↗