398 research outputs found
Flume tests on fluvial erosion mechanisms in tillbed channels
Semi-alluvial stream channels eroded into till and other glacial sediments are common in areas of extensive glacial deposition such as the Great Lakes region and northern interior plains of North America. The mechanics of erosion and erosional weakness of till results in the dominance of fluvial scour and mass erosion due to spontaneous fracture at planes of weakness under shearing flow. There have been few controlled tests looking at erosional mechanisms and resistance of till in river channels.We subjected small blocks of till to unidirectional flows in a laboratory flume to measure the threshold shear stress for erosion and observed the erosion mechanics. Critical shear stress for erosion varied from 7 to 8 Pa for samples with initial saturated moisture content in which a combination of fluvial scour and mass cracking/block erosion dominated. When dried, micro-fissures occurred in the sample and erosional resistance of the till was extremely low at \u3c1 Pa with erosion appearing to be by fluvial scour. When mobile gravel was added to the test conditions, the gravel reduced the erosion threshold slightly because of the enhanced scour around and below the gravel particles and the tendency for the gravel to aid in crack enlargement. Thus a partial or thin gravel cover over the till may provide no protection from erosion. The erosion processes and effects reflect the complex and contingent mechanics and properties of till, and suggest that the erosion characteristics of till bed semi-alluvial channels differ from abrasion or plucking dominated processes in more resistant bedroc
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Beyond Crossing Fibers: Bootstrap Probabilistic Tractography Using Complex Subvoxel Fiber Geometries
Diffusion magnetic resonance imaging fiber tractography is a powerful tool for investigating human white matter connectivity in vivo. However, it is prone to false positive and false negative results, making interpretation of the tractography result difficult. Optimal tractography must begin with an accurate description of the subvoxel white matter fiber structure, includes quantification of the uncertainty in the fiber directions obtained, and quantifies the confidence in each reconstructed fiber tract. This paper presents a novel and comprehensive pipeline for fiber tractography that meets the above requirements. The subvoxel fiber geometry is described in detail using a technique that allows not only for straight crossing fibers but for fibers that curve and splay. This technique is repeatedly performed within a residual bootstrap statistical process in order to efficiently quantify the uncertainty in the subvoxel geometries obtained. A robust connectivity index is defined to quantify the confidence in the reconstructed connections. The tractography pipeline is demonstrated in the human brain
Swirling astrophysical flows - efficient amplifiers of Alfven waves
We show that a helical shear flow of a magnetized plasma may serve as an
efficient amplifier of Alfven waves. We find that even when the flow is purely
ejectional (i.e., when no rotation is present) Alfven waves are amplified
through the transient, shear-induced, algebraic amplification process. Series
of transient amplifications, taking place sequentially along the flow, may
result in a cascade amplification of these waves. However, when a flow is
swirling or helical (i.e., some rotation is imposed on the plasma motion),
Alfven waves become subject to new, much more powerful shear instabilities. In
this case, depending on the type of differential rotation, both usual and
parametric instabilities may appear. We claim that these phenomena may lead to
the generation of large amplitude Alfven waves and the mechanism may account
for the appearance of such waves in the solar atmosphere, in accretion-ejecion
flows and in accretion columns. These processes may also serve as an important
initial (linear and nonmodal) phase in the ultimate subcritical transition to
MHD Alfvenic turbulence in various kinds of astrophysical shear flows.Comment: 12 pages, 11 figures, accepted for publication (25-11-02) in
Astronomy and Astrophysic
An Investigation of Cancer Rates in the Argentia Region, Newfoundland and Labrador: An Ecological Study
Background. The Argentia region of Newfoundland and Labrador, Canada, was home to a US naval base during a 40-year period between the 1940s and the 1990s. Activities on the base resulted in contamination of the soil and groundwater in the region with chemicals such as heavy metals and dioxins, and residents have expressed concern about higher rates of cancer in their community. This study investigated the rate of cancer diagnosis that is disproportionately high in the Argentia region. Methods. Cases of cancer diagnosed between 1985 and 2011 were obtained for the Argentia region, two comparison communities, and the province of Newfoundland and Labrador. Crude and age-standardized incidence rates of cancer diagnosis were calculated and compared. The crude incidence rate was adjusted for differences in age demographics using census data, and age-standardized incidence rates were compared. Results. Although the Argentia region had a higher crude rate of cancer diagnosis, the age-standardized incidence rate did not differ significantly from the comparison communities or the provincial average. Argentia has an aging population, which may have influenced the perception of increased cancer diagnosis in the community. Conclusions. We did not detect an increased burden of cancer in the Argentia region
HST Snaphot Study of Variable Stars in Globular Clusters: Inner Region of NGC 6441
[Abridged] We present the results of a Hubble Space Telescope snapshot
program to survey the inner region of the globular cluster NGC 6441 for its
variable stars. A total of 57 variable stars was found including 38 RR Lyrae
stars, 6 Population II Cepheids, and 12 long period variables. Of the RR Lyrae
stars observed in this survey, 26 are pulsating in the fundamental mode with a
mean period of 0.753d and 12 are first-overtone mode pulsators with a mean
period of 0.365d. These values match up very well with those found in
ground-based surveys. Combining all the available data for NGC 6441, we find
mean periods of 0.759d and 0.375d for the RRab and RRc stars, respectively. We
also find that the RR Lyrae in this survey are located in the same regions of a
period-amplitude diagram as those found in ground-based surveys. Although NGC
6441 is a metal-rich globular cluster, its RR Lyrae more closely resemble those
in Oosterhoff type II globular clusters. However, even compared to typical
Oosterhoff type II systems, the mean period of its RRab stars is unusually
long. We also derived I-band period-luminosity relations for the RR Lyrae
stars. Of the six Population II Cepheids, five are of W Virginis type and one
is a BL Herculis variable stars. This makes NGC 6441, along with NGC 6388, the
most metal-rich globular cluster known to contain these types of variable
stars. Another variable, V118, may also be a Population II Cepheid given its
long period and its separation in magnitude from the RR Lyrae stars. We argue
that there does not appear to be a change in the period-luminosity relation
slope between the BL Herculis and W Virginis stars, but that a change of slope
does occur when the RV Tauri stars are added to the period-luminosity relation.Comment: 28 pages, including 9 figures and 8 tables, emulateapj5/apjfonts
style. Accepted by the Astronomical Journal. Approximate publication date
September 2003. We recommend the interested reader to download the preprint
with full-resolution figures, which can be found at
http://www.astro.puc.cl/~mcatelan/Pritzl.zi
Decline in Lung Function From Mid-to Late-Life With Central Arterial Stiffness: The Atherosclerosis Risk in Communities Study
We investigated the association of lung function at mid-life, later in life, and its 20-year decline, with arterial stiffness later in life. We examined 5720 Atherosclerosis Risk in Communities Study participants who attended Visits 1 (1987-1989) and 5 (2011-2013). Lung function measures were forced expiratory volume in one second (FEV1) and forced vital capacity (FVC), obtained at Visits 1, 2 (1990–1992), and 5. Central artery stiffness (carotid-femoral pulse wave velocity [cfPWV]) was measured at Visit 5. We evaluated associations of lung function with later-life central artery stiffness and cfPWV >75th percentile by multivariable linear and logistic regressions. Lung function at Visit 1 (FEV1 β: −26, 95% Confidence Interval [CI]: −48, −5; FVC β: −14, 95% CI: −32, 5) and Visit 5 (FEV1 β: −22, 95% CI: −46, 2; FVC β: −18, 95% CI: −38, 2) were inversely associated with cfPWV at Visit 5, and with odds of high cfPWV in fully adjusted models. Twenty-year decline in lung function was not associated with continuous or dichotomous measures of arterial stiffness (FEV1 β: 11, 95% CI: −46, 68; FVC β: −4, 95% CI: −52, 43). Lung function at mid-life and late-life was inversely associated with arterial stiffness in later life
Label-free detection of DNA hybridization based on hydration-induced tension in nucleic acid films
The properties of water at the nanoscale are crucial in many areas of biology, but the confinement of water molecules in sub-nanometre channels in biological systems has received relatively little attention. Advances in nanotechnology make it possible to explore the role played by water molecules in living systems, potentially leading to the development of ultrasensitive biosensors. Here we show that the adsorption of water by a self-assembled monolayer of single-stranded DNA on a silicon microcantilever can be detected by measuring how the tension in the monolayer changes as a result of hydration. Our approach relies on the microcantilever bending by an amount that depends on the tension in the monolayer. In particular, we find that the tension changes dramatically when the monolayer interacts with either complementary or single mismatched single-stranded DNA targets. Our results suggest that the tension is mainly governed by hydration forces in the channels between the DNA molecules and could lead to the development of a label-free DNA biosensor that can detect single mutations. The technique provides sensitivity in the femtomolar range that is at least two orders of magnitude better than that obtained previously with label-free nanomechanical biosensors and with label-dependent microarrays.D.R. acknowledges the fellowship funded by the Autonomic Community of Madrid (CAM). J.T, M.C, J.M and D.R acknowledge financial support by Spanish Ministry of Science (MEC) under grant No. TEC2006-10316 and CAM under grant No. 200550M056. C.B. acknowledges funding provided by MEC under grant No. BIO2007-67523. Work at Centro de Astrobiología was supported by European Union (EU), Instituto Nacional de Técnica Aeroespacial (INTA), MEC and CAM. All the authors acknowledge A. Cebollada, J.M. García-Martín, J. García, J.L. Costa-Kramer, M. Arroyo-Hernández and J.V. Anguita for their assistance in the gold deposition on the cantilevers.Peer reviewe
Derivation of an endogenous small RNA from double-stranded Sox4 sense and natural antisense transcripts in the mouse brain
Natural antisense transcripts (NATs) are involved in cellular development and regulatory processes. Multiple NATs at the Sox4 gene locus are spatiotemporally regulated throughout murine cerebral corticogenesis. In the study, we evaluated the potential functional role of Sox4 NATs at Sox4 gene locus. We demonstrated Sox4 sense and NATs formed dsRNA aggregates in the cytoplasm of brain cells. Over expression of Sox4 NATs in NIH/3T3 cells generally did not alter the level of Sox4 mRNA expression or protein translation. Upregulation of a Sox4 NAT known as Sox4ot1 led to the production of a novel small RNA, Sox4_sir3. Its biogenesis is Dicer1-dependent and has characteristics resemble piRNA. Expression of Sox4_sir3 was observed in the marginal and germinative zones of the developing and postnatal brains suggesting a potential role in regulating neurogenesis. We proposed that Sox4 sense-NATs serve as Dicer1-dependent templates to produce a novel endo-siRNA- or piRNA-like Sox4_sir3
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Wheat head armyworm true or false : a tale from the Pacific Northwest
The wheat head armyworm (Faronta diffusa) is a troublesome pest in cereal grains in the Pacific Northwest. This publication describes the life cycle, behavior, distribution, and feeding of the wheat head armyworm. Guidance on identification and control of the pest is also provided.Published December 2009. A more recent revision exists. Facts and recommendations in this publication may no longer be valid. Please look for up-to-date information in the OSU Extension Catalog: http://extension.oregonstate.edu/catalogKeywords: wheat head armyworm (WHA), Faronta diffusa, WH
The cognitive-affective-conative model of destination image: a confirmatory analysis
Destination image influences tourist behaviour before, during and after travel, as it is an important instrument which contributes to tourists’ loyalty. Although Gartner (1993) advocates that the cognitive, affective and conative dimensions of destination image are hierarchically interrelated, there is no empirical evidence to support the complete model. This study aims to test the hierarchical nature of the relationship between the dimensions of destination image. The results of structural equation modelling confirm Gartner’s theoretical model, validating the theory that the influence of the cognitive component on the conative dimension is higher when mediated by the affective component, raising managerial implications
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