427 research outputs found

    Unusual Beaver, Castor canadensis, Dams in Central Yukon

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    North American Beavers (Castor canadensis) are remarkable for their ability to build dams and modify their habitat. Dams are typically made of the boles and branches of trees and large shrubs, and reinforced with mud and rocks. Here, we report two unusual Beaver dams in central Yukon, Canada, that are made primarily of medium-sized rocks. This observation points to the adaptability of Beavers in using available materials to build their dams

    A proposed baroclinic wave test case for deep‐ and shallow‐atmosphere dynamical cores

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    Idealised studies of key dynamical features of the atmosphere provide insight into the behaviour of atmospheric models. A very important, well understood, aspect of midlatitude dynamics is baroclinic instability. This can be idealised by perturbing a vertically sheared basic state in geostrophic and hydrostatic balance. An unstable wave mode then results with exponential growth (due to linear dynamics) in time until, eventually, nonlinear effects dominate and the wave breaks. A new, unified, idealised baroclinic instability test case is proposed. This improves on previous ones in three ways. First, it is suitable for both deep‐ and shallow‐atmosphere models. Second, the constant surface pressure and zero surface geopotential of the basic state makes it particularly well‐suited for models employing a pressure‐ or height‐based vertical coordinate. Third, the wave triggering mechanism selectively perturbs the rotational component of the flow; this, together with a vertical tapering, significantly improves dynamic balance.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/108108/1/qj2241.pd

    Permafrost Development in the Intertidal Zone at Churchill, Manitoba: A Possible Mechanism for Accelerated Beach Lift

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    Boreholes drilled in the Beech Bay area during July to November 1929 indicated that a sill of permafrost had extended below the high-water line, tapering in depth towards low water. The boreholes revealed thick layers of fine sediments on top of deep underlain bedrock. Recent borings determined the upper limits of permafrost in 1981. Examination of the data shows that there has been a permafrost expansion into the emerging tidal zone. These observations suggest an additional mechanism for accelerated uplift of coastal exposed "soft" sediments: the vertical expansion of refrozen, water-saturated silts and clays as new permafrost forms. The existing rates of isostatic uplift are enhanced by the process.Key words: permafrost, active zone, isostatic uplift, Breech Bay, Churchill, Hudson BayDes carottes prises dans la région de la baie Beech entre juillet et novembre 1929 ont indiqué qu'un seuil de pergélisol s'étendait au-dessous du niveau des hautes mers, diminuant en profondeur en approchant le niveau des basses mers. Les carottes révèlant des couches épaisses de fins sédiments reposant sur un profond soubassement. Des carottes récentes ont déterminé les limites supérieures du pergélisol en 1981. L'étude des données signales une expansion du pergélisol dans la zone intertidale surgissante. Ces observations suggèrent un mécanisme additionnel accélérant la levée des sédiments "mous" exposés le long des côtes par l'expansion verticale de vases et de glaises saturés d'eau et congelées à nouveau sous de nouvelles formes de pergélisol. Le taux de levée isostatique est augmenté par le processus.Mots clés: pergélisol, zone active, levée isostatique, baie Beech, la baie d'Hudso

    The Effect of Obesity on Nocturnal Blood Pressure Patterns

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    Abnormal nocturnal blood pressure (BP) during sleep is considered an indication of many cardio­vascular diseases.[1] For healthy individuals, noc­turnal BP drops 5-10% on ambulatory BP monitor­ing (ABPM). Individuals with abnormal nocturnal BP are classified in three distinct ways: (1) an ab­sence of BP drop, (2) a lack of typical nocturnal dip (LND), or (3) a rise of BP at night (RBPN).[3] In this study, we examine a potential correlation between obesity and abnormal nocturnal BP and the impact of weight loss on nocturnal BP patterns. For our study, we recruited 30 individuals with LND, 30 with RBPN, and 20 with normal nocturnal BP (control) and placed them all on a prescribed DASH diet previously demonstrated to improve daytime BP.[9] Baseline ABPM readings and body mass index (BMI) measurements for each individ­ual were compared before and after two months of dieting. After two months on the DASH diet, the control group had the lowest BMI followed by the LND group and the RBPN group. These results demonstrate a linear correlation between BMI and nocturnal BP. Individuals who lost less than 5% of their original weight experienced a 3% increase in BP at night. Those who lost more than 5% weight experienced a 8.5% decrease in BP nocturnally, effectively restoring their healthy nocturnal BP pat­tern. Thus, obesity may contribute to nocturnal BP abnormalities, and weight loss may improve this condition.Une pression artĂ©rielle (PA) nocturne anormale durant le sommeil est considĂ©rĂ©e un indicateur de nombreuses maladies cardiovasculaires.[1] Chez les personnes saines, la PA nocturne diminue de façon physiologique d’environ 5-10 % mesurĂ©e grĂące au moniteur ambulatoire de pression artĂ©rielle (MAPA). Les personnes ayant une PA nocturne anormale sont classĂ©es de trois façons distinctes: 1) une absence d’une diminution de PA, 2) un manque de « dipping » nocturne typique (MDN), ou 3) une augmentation de la PA durant la nuit (APAN).[3] Dans cette Ă©tude, nous examinons la possibilitĂ© d’une corrĂ©lation entre l’obĂ©sitĂ© et la PA nocturne anormale et l’impact d’une perte de poids sur les motifs de la PA nocturne. Pour notre Ă©tude, nous avons recrutĂ© 30 individus avec MDN, 30 avec APAN, et 20 individus avec une PA nocturne normale (groupes contrĂŽle), et les avons mis sur le rĂ©gime DASH qui a prĂ©cĂ©demment dé­montrĂ© une amĂ©lioration de PA durant la journĂ©e.[9] Des mesures de base avec MAPA ainsi que des mesures d’indice de masse corporelle (IMC) furent prises pour chaque individu, et par la suite utilisĂ©es afin de les comparer avec les mesures de MAPA et d’IMC suites aux deux mois du rĂ©gime. AprĂšs avoir suivi le rĂ©gime DASH pendant une durĂ©e de deux mois, le groupe contrĂŽle avait la plus faible IMC suivie par le groupe du MDN, et le groupe APAN eu le plus haut IMC global. Ces rĂ©sultats dĂ©montrent une relation linĂ©aire entre l’IMC et des anomalies de PA nocturnes. Les individus qui ont perdus <5 % de poids ont su voir une augmentation de PA d’un taux de 3 % la nuit. Ceux qui ont perdu ≄ 5 % de poids ont eu une diminution de leur PA de 8,5% la nuit ce qui rĂ©tablit un motif sains de PA nocturne. Par con­sĂ©quent, conformĂ©ment Ă  cette Ă©tude on peut con­clure que l’obĂ©sitĂ© contribue Ă  des anormalitĂ©s de la PA nocturne, et la perte de poids peut amĂ©liorer cette conditions

    A Randomised, Blinded, Placebo-Controlled, Dose Escalation Study of the Tolerability and Efficacy of Filgrastim for Haemopoietic Stem Cell Mobilisation in Patients With Severe Active Rheumatoid Arthritis

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    Autologous haemopoietic stem cell transplantation (HSCT) represents a potential therapy for severe rheumatoid arthritis (RA). As a prelude to clinical trails, the safety and efficacy of haemopoietic stem cell (HSC) mobilisation required investigation as colony-stimulating factors (CSFs) have been reported to flare RA. A double-blind, randomised placebo-controlled dose escalation study was performed. Two cohorts of eight patients fulfilling strict eligibility criteria for severe active RA (age median 40 years, range 24-60 years; median disease duration 10.5 years, range 2-18 years) received filgrastim (r-Hu-methionyl granulocyte(G)-(SF) at 5 and 10 microg/kg/day, randomised in a 5:3 ratio with placebo. Patients were unblinded on the fifth day of treatment and those randomised to filgrastim underwent cell harvesting (leukapheresis) daily until 2 X 10^6/kg CD34+ cells (haemopoietic stem and progenitor cells) were obtained. Patients were assessed by clinical and laboratory parameters before, during and after filgrastim administration. RA flare was defined as an increase of 30% or more in two of the following parameters: tender joint count, swollen joint count or pain score. Efficacy was assessed by quantitation of CD34+ cells and CFU-GM. One patient in the 5 microg/kg/day group and two patients in the 10 microg/kg/day group fulfilled criteria for RA flare, although this did not preclude successful stem cell collection. Median changes in swollen and tender joint counts were not supportive of filgrastim consistently causing exacerbation of disease, but administration of filgrastim at 10 microg/kg/day was associated with rises in median C-reactive protein and median rheumatoid factor compared with placebo. Other adverse events were well recognised for filgrastim and included bone pain (80%) and increases in alkaline phosphatase (four-fold) and lactate dehydrogenase (two-fold). With respect to efficacy, filgrastim at 10 microg/kg/day was more efficient with all patients (n = 5) achieving target CD34+ cell counts with a single leukapheresis (median = 2.8, range = 2.3-4.8 X 10^6/kg, median CFU-GM = 22.1, range = 4.2-102.9 X 10^4/kg), whereas 1-3 leukaphereses were necessary to achieve the target yield using 5 microg/kg/day. We conclude that filgrastim may be administered to patients with severe active RA for effective stem cell mobilisation. Flare of RA occurs in a minority of patients and is more likely with 10 than 5 microg/kg/day. However, on balance, 10 microg/kg/day remains the dose of choice in view of more efficient CD34+ cell mobilisation

    Strong and auxiliary forms of the semi-Lagrangian method for incompressible flows

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    We present a review of the semi-Lagrangian method for advection-diusion and incompressible Navier-Stokes equations discretized with high-order methods. In particular, we compare the strong form where the departure points are computed directly via backwards integration with the auxiliary form where an auxiliary advection equation is solved instead; the latter is also referred to as Operator Integration Factor Splitting (OIFS) scheme. For intermediate size of time steps the auxiliary form is preferrable but for large time steps only the strong form is stable

    Bridging the gap between the gas and solution phase : solvent specific photochemistry in 4-tert-butylcatechol

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    Eumelanin is a naturally synthesized ultraviolet light absorbing biomolecule, possessing both photoprotective and phototoxic properties. We infer insight into these properties of eumelanin using a bottom-up approach, by investigating a subunit analogue, 4-tert-butylcatechol. Utilizing a combination of femtosecond transient electronic absorption spectroscopy and time-re-solved velocity map ion imaging, our results suggest an environmental-dependent relaxation pathway, following irradiation at 267 nm to populate the S1 (1ππ*) state. Gas-phase and non-polar solution-phase measurements reveal that the S1 state decays through coupling onto the S2 (1πσ*) state that is dissociative along the non-intramolecular hydrogen bonded ‘free’ O–H bond. This process is mediated by tunneling beneath an S1/S2 conical intersection and occurs in 4.9 ± 0.6 ps in the gas-phase and 27 ± 7 ps in the non-polar cyclohexane solution. Comparative studies on the deuterated isotopologue of 4-tert-butylcatechol in both the gas- and solution-phase (cyclohexane) reveals an average kinetic isotope effect of ~19 and ~7, respectively, supportive of O–H dissociation mediated by a quantum tunneling mechanism. In contrast, in the polar acetonitrile, the S1 state decays on a much longer timescale of 1.7 ± 0.1 ns. We propose that the S1 decay is now multicomponent, likely driven by internal conversion, intersystem crossing and fluorescence, as well as O–H dissociation. The attribution of conformer driven excited state dynamics to explain how the S1 state decays in the gas- and non-polar solution-phase versus the polar solution-phase, elegantly demonstrates the influence the environment has on the ensuing excited state dynamics