248 research outputs found
Heat and fluid flow in a scraped-surface heat exchanger containing a fluid with temperature-dependent viscosity
Scraped-surface heat exchangers (SSHEs) are extensively used in a wide variety of industrial settings where the continuous processing of fluids and fluid-like materials is involved. The steady non-isothermal flow of a Newtonian fluid with temperature-dependent viscosity in a narrow-gap SSHE when a constant temperature difference is imposed across the gap between the rotor and the stator is investigated. The mathematical model is formulated and the exact analytical solutions for the heat and fluid flow of a fluid with a general dependence of viscosity on temperature for a general blade shape are obtained. These solutions are then presented for the specific case of an exponential dependence of viscosity on temperature. Asymptotic methods are employed to investigate the behaviour of the solutions in several special limiting geometries and in the limits of weak and strong thermoviscosity. In particular, in the limit of strong thermoviscosity (i.e., strong heating or cooling and/or strong dependence of viscosity on temperature) the transverse and axial velocities become uniform in the bulk of the flow with boundary layers forming either just below the blade and just below the stationary upper wall or just above the blade and just above the moving lower wall. Results are presented for the most realistic case of a linear blade which illustrate the effect of varying the thermoviscosity of the fluid and the geometry of the SSHE on the flow
Early development, survival and growth rates of the giant clam Tridacna crocea (Bivalvia: Tridacnidae)
A Connection between Colony Biomass and Death in Caribbean Reef-Building Corals
Increased sea-surface temperatures linked to warming climate threaten coral reef ecosystems globally. To better understand how corals and their endosymbiotic dinoflagellates (Symbiodinium spp.) respond to environmental change, tissue biomass and Symbiodinium density of seven coral species were measured on various reefs approximately every four months for up to thirteen years in the Upper Florida Keys, United States (1994â2007), eleven years in the Exuma Cays, Bahamas (1995â2006), and four years in Puerto Morelos, Mexico (2003â2007). For six out of seven coral species, tissue biomass correlated with Symbiodinium density. Within a particular coral species, tissue biomasses and Symbiodinium densities varied regionally according to the following trends: Mexicoâ„Florida Keysâ„Bahamas. Average tissue biomasses and symbiont cell densities were generally higher in shallow habitats (1â4 m) compared to deeper-dwelling conspecifics (12â15 m). Most colonies that were sampled displayed seasonal fluctuations in biomass and endosymbiont density related to annual temperature variations. During the bleaching episodes of 1998 and 2005, five out of seven species that were exposed to unusually high temperatures exhibited significant decreases in symbiotic algae that, in certain cases, preceded further decreases in tissue biomass. Following bleaching, Montastraea spp. colonies with low relative biomass levels died, whereas colonies with higher biomass levels survived. Bleaching- or disease-associated mortality was also observed in Acropora cervicornis colonies; compared to A. palmata, all A. cervicornis colonies experienced low biomass values. Such patterns suggest that Montastraea spp. and possibly other coral species with relatively low biomass experience increased susceptibility to death following bleaching or other stressors than do conspecifics with higher tissue biomass levels
Genetic basis of control of Rhynchosporium secalis infection and symptom expression in barley
The genetic basis of several different components of resistance to Rhynchosporium secalis in barley was investigated in a mapping population derived from a cross between winter and spring barley types. Both the severity of visual disease symptoms and amount of R. secalis DNA in leaf tissues were assessed in field trials in Scotland in the 2007/2008 and 2008/2009 growing seasons. Relative expression of symptoms was defined as the residual values from a linear regression of amount of R. secalis DNA against visual plot disease score at GS 50. Amount of R. secalis DNA and visual disease score were highly correlated traits and identified nearly identical QTL. The genetic control of relative expression of symptoms was less clear. However, a QTL on chromosome 7H was identified as having a significant effect on the expression of visual disease symptoms relative to overall amount of R. secalis colonisationPeer reviewedFinal Accepted Versio
Hypermagnetic Knots, Chern-Simons Waves and the Baryon Asymmetry
At finite hyperconductivity and finite fermionic density the flux lines of
long range hypermagnetic fields may not have a topologically trivial structure.
The combined evolution of the chemical potentials and of pseudoscalar fields
(like the axial Higgs), possibly present for temperatures in the TeV range, can
twist the hypercharge flux lines, producing, ultimately, hypermagnetic knots
(HK). The dynamical features of the HK depend upon the various particle physics
parameters of the model (pseudoscalar masses and couplings, strength of the
electroweak phase transition, hyperconductivity of the plasma) and upon the
magnitude of the primordial flux sitting in topologically trivial
configurations of the hypermagnetic field. We study different cosmological
scenarios where HK can be generated. We argue that the fermionic number sitting
in HK can be released producing a seed for the Baryon Asymmetry of the Universe
(BAU) provided the typical scale of the knot is larger than the diffusivity
length scale. We derive constraints on the primordial hypermagnetic flux
required by our mechanism and we provide a measure of the parity breaking by
connecting the degree of knottedness of the flux lines to the BAU. We rule out
the ordinary axion as a possible candidate for production (around temperatures
of the order of the GeV) of {\em magnetic} knots since the produced {\em
electromagnetic} helicity is negligible (for cosmological standard) if the
initial amplitude of the axion oscillations is of the order of the Peccei-Quinn
breaking scale.Comment: 30 pages in Revtex style, 8 figure
Radio Properties of Infrared Selected Galaxies in the IRAS 2 Jy Sample
The radio counterparts to the IRAS Redshift Survey galaxies are identified in
the NRAO VLA Sky Survey (NVSS) catalog. Our new catalog of the infrared
flux-limited (S60 >= 2 Jy) complete sample of 1809 galaxies lists accurate
radio positions, redshifts, and 1.4 GHz radio and IRAS fluxes. This sample is
six times larger in size and five times deeper in redshift coverage (to z ~
0.15) compared with those used in earlier studies of the radio and far-infrared
(FIR) properties of galaxies in the local volume. The well known radio-FIR
correlation is obeyed by the overwhelming majority (>98%) of the
infrared-selected galaxies, and the radio AGNs identified by their excess radio
emission constitute only about 1% of the sample, independent of the IR
luminosity. These FIR-selected galaxies can account for the entire population
of late-type field galaxies in the local volume, and their radio continuum may
be used directly to infer the extinction-free star formation rate in most
cases. Both the 1.4 GHz radio and 60 micron infrared luminosity functions are
reasonably well described by linear sums of two Schechter functions, one
representing normal, late-type field galaxies and the second representing
starbursts and other luminous infrared galaxies. The integrated FIR luminosity
density for the local volume is 4.8+/-0.5 x 10^7 L(sun) per Mpc^3, less than
10% of which is contributed by the luminous infrared galaxies with L(FIR) >
10^{11} L(sun) . The inferred extinction-free star formation density for the
local volume is 0.015 +/- 0.005 solar mass per year per Mpc^3.Comment: 34 pages with 15 embedded figures and 7 tables. Latex using aastex
and psfig.sty. To appear in the Astrophysical Journal (2001) (typos corrected
and Fig. 13 replaced in v2.
The SECURE project â Stem canker of oilseed rape: : molecular methods and mathematical modelling to deploy durable resistance
N Evans et al, "The SECURE Project - Stem Canker of oilseed rape: Molecular methods and mathematical modeling to deploy durable resistance", in Vol 4 of the Proceedings of the 12th International Rapeseed Congress : Sustainable Development in Cruciferous Oilseed Crops Production, Wuhan, China, March 26 - 30, 2007. The proceedings are available online at: http://gcirc.org/intranet/irc-proceedings/12th-irc-wuhan-china-2007-vol-4.htmlModelling done during the SECURE project has demonstrated the dynamic nature of the interaction between phoma stem canker (Leptosphaeria maculans), the oilseed rape host (Brassica napus) and the environment. Experiments done with near-isogenic lines of L. maculans to investigate pathogen fitness support field data that suggest a positive effect of the avirulence allele AvrLm4 on pathogen fitness, and that the loss of this allele renders isolates less competitive under field conditions on cultivars without the resistance gene Rlm4. The highlight of molecular work was the cloning of AvrLm1 and AvrLm6. L. maculans is now one of the few fungal species for which two avirulence loci have been cloned. Subsequent research focused on understanding the function of AvrLm1 and AvrLm6 and on the analysis of sequences of virulent isolates to understand molecular evolution towards virulence. Isolates of L. maculans transformed with GFP and/or DsRed were used to follow growth of the fungus in B. napus near-isogenic-lines (NIL) with or without MX (Rlm6) resistance under different temperature and wetness conditions. The results greatly enhanced our knowledge of the infection process and the rate and extent of in planta growth on different cultivars. Conclusions from work to model durability of resistance have been tested under field conditions through a series of experiments to compare durability of resistance conferred by the major resistance gene Rlm6 alone in a susceptible background (EurolMX) or in a resistant background (DarmorMX) under recurrent selection over 4 growing seasons. A major priority of the project was knowledge transfer of results and recommendations to target audiences such as plant breeding companies and extension services. CETIOM developed a âdiversification schemeâ that encourages French growers to make an informed choice about the cultivars that are grown within the rotation based on the resistance genes carried by the individual cultivars. Use of such schemes, in association with survey data on the population structure of L. maculans at both national and European scales will provide opportunities for breeders and the industry to manage available B. napus resistance more effectively.Non peer reviewe
Length of carotid stenosis predicts peri-procedural stroke or death and restenosis in patients randomized to endovascular treatment or endarterectomy.
BACKGROUND: The anatomy of carotid stenosis may influence the outcome of endovascular treatment or carotid endarterectomy. Whether anatomy favors one treatment over the other in terms of safety or efficacy has not been investigated in randomized trials.
METHODS: In 414 patients with mostly symptomatic carotid stenosis randomized to endovascular treatment (angioplasty or stenting; nâ=â213) or carotid endarterectomy (nâ=â211) in the Carotid and Vertebral Artery Transluminal Angioplasty Study (CAVATAS), the degree and length of stenosis and plaque surface irregularity were assessed on baseline intraarterial angiography. Outcome measures were stroke or death occurring between randomization and 30 days after treatment, and ipsilateral stroke and restenosis â„50% during follow-up. RESULTS: Carotid stenosis longer than 0.65 times the common carotid artery diameter was associated with increased risk of peri-procedural stroke or death after both endovascular treatment [odds ratio 2.79 (1.17-6.65), Pâ=â0.02] and carotid endarterectomy [2.43 (1.03-5.73), Pâ=â0.04], and with increased long-term risk of restenosis in endovascular treatment [hazard ratio 1.68 (1.12-2.53), Pâ=â0.01]. The excess in restenosis after endovascular treatment compared with carotid endarterectomy was significantly greater in patients with long stenosis than with short stenosis at baseline (interaction Pâ=â0.003). Results remained significant after multivariate adjustment. No associations were found for degree of stenosis and plaque surface.
CONCLUSIONS: Increasing stenosis length is an independent risk factor for peri-procedural stroke or death in endovascular treatment and carotid endarterectomy, without favoring one treatment over the other. However, the excess restenosis rate after endovascular treatment compared with carotid endarterectomy increases with longer stenosis at baseline. Stenosis length merits further investigation in carotid revascularisation trials
Impacts of climate change on plant diseases â opinions and trends
There has been a remarkable scientific output on the topic of how climate change is likely to affect plant diseases in the coming decades. This review addresses the need for review of this burgeoning literature by summarizing opinions of previous reviews and trends in recent studies on the impacts of climate change on plant health. Sudden Oak Death is used as an introductory case study: Californian forests could become even more susceptible to this emerging plant disease, if spring precipitations will be accompanied by warmer temperatures, although climate shifts may also affect the current synchronicity between host cambium activity and pathogen colonization rate. A summary of observed and predicted climate changes, as well as of direct effects of climate change on pathosystems, is provided. Prediction and management of climate change effects on plant health are complicated by indirect effects and the interactions with global change drivers. Uncertainty in models of plant disease development under climate change calls for a diversity of management strategies, from more participatory approaches to interdisciplinary science. Involvement of stakeholders and scientists from outside plant pathology shows the importance of trade-offs, for example in the land-sharing vs. sparing debate. Further research is needed on climate change and plant health in mountain, boreal, Mediterranean and tropical regions, with multiple climate change factors and scenarios (including our responses to it, e.g. the assisted migration of plants), in relation to endophytes, viruses and mycorrhiza, using long-term and large-scale datasets and considering various plant disease control methods
An Initial Look at the Far Infrared-Radio Correlation within Nearby Star-forming Galaxies using the Spitzer Space Telescope
(Abridged) We present an initial look at the far infrared-radio correlation
within the star-forming disks of four nearby, nearly face-on galaxies (NGC
2403, NGC 3031, NGC 5194, and NGC 6946). Using Spitzer MIPS imaging and WSRT
radio continuum data, observed as part of the Spitzer Infrared Nearby Galaxies
Survey (SINGS), we are able to probe variations in the logarithmic 24mu/22cm
(q_24) and 70mu/22cm (q_70) surface brightness ratios across each disk at
sub-kpc scales. We find general trends of decreasing q_24 and q_70 with
declining surface brightness and with increasing radius. The residual
dispersion around the trend of q_24 and q_70 versus surface brightness is
smaller than the residual dispersion around the trend of q_24 and q_70 versus
radius, on average by ~0.1 dex, indicating that the distribution of star
formation sites is more important in determining the infrared/radio disk
appearance than the exponential profiles of disks. We have also performed
preliminary phenomenological modeling of cosmic ray electron (CRe^-) diffusion
using an image-smearing technique, and find that smoothing the infrared maps
improves their correlation with the radio maps. Exponential kernels tend to
work better than Gaussian kernels which suggests that additional processes
besides simple random-walk diffusion in three dimensions must affect the
evolution of CRe^-s. The best fit smoothing kernels for the two less active
star-forming galaxies (NGC 2403 and NGC 3031) have much larger scale-lengths
than those of the more active star-forming galaxies (NGC 5194 and NGC 6946).
This difference may be due to the relative deficit of recent CRe^- injection
into the interstellar medium (ISM) for the galaxies having largely quiescent
disks.Comment: 41 pages including 6 tables and 12 figures; accepted for publication
in the Astrophysical Journal. A full-resolution color version can be found at
http://www.astro.yale.edu/murphy/a-ph/murphy_FIR-radio.pdf ; Corrected typo
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