The stability of a trailing-line vortex in compressible flow

We consider the inviscid stability of the Batchelor (1964) vortex in a compressible flow. The problem is tackled numerically and also asymptotically, in the limit of large (aximuthal and streamwise) wavenumbers, together with large Mach numbers. The nature of the solution passes through different regimes as the Mach number increases, relative to the wavenumbers. At very high wavenumbers and Mach numbers, the mode which is present in the incompressible case ceases to be unstable, while new 'center mode' forms, whose stability characteristics, are determined primarily by conditions close to the vortex axis. We find that generally the flow becomes less unstable as the Mach number increases, and that the regime of instability appears generally confined to disturbances in a direction counter to the direction of the rotation of the swirl of the vortex. Throughout the paper, comparison is made between our numerical results and results obtained from the various asymptotic theories

Hemostatic function and progressing ischemic stroke: D-dimer predicts early clinical progression

<p><b>Background and Purpose:</b> Early clinical progression of ischemic stroke is common and is associated with increased risk of death and dependency. We hypothesized that activation of the coagulation system is an important contributor in some cases of deterioration. We aimed to characterize alterations in circulating hemostatic markers in patients with progressing stroke.</p> <p><b>Methods:</b> Consecutive acute ischemic stroke admissions were recruited. Progressing stroke was defined by deterioration in components of the Scandinavian Stroke Scale. Hemostatic markers (coagulation factors VIIc, VIIIc, and IXc, prothrombin fragments 1+2 [F1+2], thrombin-antithrombin complexes [TAT], D- dimer, fibrinogen, von Willebrand factor [vWF] and tissue plasminogen activator) were measured within 24 hours of symptom recognition.</p> <p><b>Results:</b> Fifty-four (25%) of the 219 patients met criteria for progressing stroke. F1+2 (median 1.28 versus 1.06 nmol/L, P=0.01), TAT (5.28 versus 4.07 mug/L, P lt 0.01), D-dimer ( 443 versus 194 ng/mL, P lt 0.001) and vWF (216 versus 198 IU/dL, P lt 0.05) levels were higher in these patients than in stable/improving patients. In logistic regression analysis, with all important clinical and laboratory variables included, only natural log D-dimer (odds ratio [OR]: 1.87; 95% confidence interval [CI]: 1.38 to 2.54; P=0.0001) and mean arterial blood pressure (OR: 1.26 per 10 mm Hg change; 95% CI: 1.05 to 1.51; P=0.01) remained independent predictors of progressing stroke.</p> <p><b>Conclusions:</b> There is evidence of excess thrombin generation and fibrin turnover in patients with progressing ischemic stroke. Measurement of D-dimer levels can identify patients at high risk for stroke progression. Further research is required to determine whether such patients benefit from acute interventions aimed at modifying hemostatic function.</p&gt

The evolutionary sequence of post-starburst galaxies

© 2017 The Authors. There are multiple ways in which to select post-starburst galaxies in the literature. In this work, we present a study into how two well-used selection techniques have consequences on observable post-starburst galaxy parameters, such as colour, morphology and environment, and how this affects interpretations of their role in the galaxy duty cycle. We identify a master sample of Hδ strong (EWHδ> 3Å) post-starburst galaxies from the value-added catalogue in the seventh data release of the Sloan Digital Sky Survey (SDSS DR7) over a redshift range 0.01 -2.5Å) but one having an additional cut onEWHα (> -3Å).We examine the differences in observables and AGN fractions to see what effect the Hα cut has on the properties of post-starburst galaxies and what these differing samples can tell us about the duty cycle of post-starburst galaxies. We find that Hδ strong galaxies peak in the 'blue cloud', E+As in the 'green valley' and pure E+As in the 'red sequence'.We also find that pure E+As have a more early-type morphology and a higher fraction in denser environments compared with the Hδ strong and E+A galaxies. These results suggest that there is an evolutionary sequence in the post-starburst phase from blue discy galaxies with residual star formation to passive red early-types

Detection of changes in temperature extremes during the second half of the 20th century

Since 1950, the warmest and coldest days and nights of the year have become warmer. Comparing these observations with climate model simulations in an optimal detection analysis shows a significant human influence on patterns of change in extremely warm nights. Human influence on cold nights and days is also detected, although less robustly, but there is no detection of a significant human influence on extremely warm days. In the future, extreme temperatures are expected to intensify considerably, with adverse consequences for human health

Environments and Morphologies of Red Sequence Galaxies with Residual Star Formation in Massive Clusters

We present a photometric investigation into recent star formation in galaxy clusters at z ~ 0.1. We use spectral energy distribution templates to quantify recent star formation in large X-ray selected clusters from the LARCS survey using matched GALEX NUV photometry. These clusters all have signs of red sequence galaxy recent star formation (as indicated by blue NUV-R colour), regardless of cluster morphology and size. A trend in environment is found for these galaxies, such that they prefer to occupy low density, high cluster radius environments. The morphology of these UV bright galaxies suggests that they are in fact red spirals, which we confirm with light curves and Galaxy Zoo voting percentages as morphological proxies. These UV bright galaxies are therefore seen to be either truncated spiral galaxies, caught by ram pressure in falling into the cluster, or high mass spirals, with the photometry dominated by the older stellar population.Comment: Accepted for publication in MNRAS, 11 pages, 11 figure

Discharge and suspended sediment dynamics in an Indian Himalayan river system

A pure, clean and reliable water supply is of paramount importance in India where meeting the requirements of a rising population is one of the big challenges of the 21st century. Climate change in the Indian subcontinent, identified by the Intergovernmental Panel on Climate Change (IPCC, 2013) as the region with the highest level of climate instability, is of major concern (Immerzeel et al., 2010; Morton, 2011). In 2010 the floods in the Indus basin were the worst in history (Hobley et al., 2012). Two thousand people died in Pakistan and in the high-altitude desert of Ladakh, intense rain and floods centred around Leh, washed away homes and villages and killed 200 people. At present, 10 % of the earth’s land-mass is covered with snow. Of this total area, 84.16 % is in the Antarctic, 13.9 % in Greenland, 0.77 % in the Himalaya, 0.51 % in North America, 0.37 % in Africa, 0.15 % in South America, and 0.06 % in Europe. Outside the Polar Regions, the Himalaya has the maximum concentration of glaciers – 9.04 % of its area. An additional 30-to-40 % is covered with snow. The glaciers of the Himalaya are the Third Pole (Dyhrenfurth, 2011). They feed the giant rivers of Asia, support half of humanity and can have a significant influence on regional water availability (Immerzeel et al., 2009). Recent studies have confirmed the important role of high mountain areas of the world as sources of freshwater for the population living in the adjacent lowlands (eg. Bandyopadhyay et al., 1997; Viviroli &Weingartner, 2004; Barnett et al., 2005; Viviroli et al., 2007; Thayyen & Gergan, 2010) Despite the hydrological importance of glaciers for the adjoining lowlands, data on the glaciers of the Himalaya, Karakorum, and Hindu Kush ranges are sparse and inconsistent. There is a lack of long-term series and field investigations, especially for glaciers at higher altitudes (Armstrong, 2010; Schmidt & Nüsser, 2012)

The stability of boundary layers on curved heated plates

This paper is made available with the permission of the Australian Mathematical Society Inc. 21/11/08We consider the effect the competing mechanisms of buoyancy-driven acceleration (arising from heating a surface) and streamline curvature (due to curvature of a surface) have on the stability of boundary-layer flows. We confine our attention to vortex type instabilities (commonly referred to as Gortler vortices) which have been identified as one of the dominant mechanisms of instability in both centrifugally and buoyancy driven boundary layers. The particular model we consider consists of the boundary-layer flow over a heated (or cooled) curved rigid body. In the absence of buoyancy forcing the flow is centrifugally unstable to counter-rotating vortices aligned with the direction of the flow when the curvature is concave (in the fluid domain) and stable otherwise. Heating the rigid plate to a level sufficiently above the fluid's ambient (free-stream) temperature can also serve to render the flow unstable. We determine the level of heating required to render an otherwise centrifugally stable flow unstable and likewise, the level of body cooling that is required to render a centrifugally unstable flow stable.Jillian A. K. Stott and James P. Denie