411 research outputs found
Transient Analysis of Thermal Bending and Vibration of Steam Turbine Rotor
Rotor-bearing systems often exhibit nonlinear behavior due to hydrodynamic effects and external forces. Finite element methods based on linear analysis are commonly used for rotor dynamic analyses, where nonlinear bearing/damping forces are linearized into equivalent stiffness and damping coefficients. However, this method may not accurately describe strongly nonlinear systems. Engineers use transient analysis and nonlinear models to improve rotor behavior analysis. This study investigates the effects of transient-thermal bending and vibration on a high-pressure steam turbine rotor using the finite element method. A scaled rotor-shaft was used to study thermal bending and vibrations caused by steam heat. The design of the shaft was based on an existing power station high-pressure turbine rotor. Numerical modal analyses were performed using ANSYS software to obtain a partial level of integrity between the numerical model and the analytical model. Natural frequencies were compared between the experimental, numerical, and analytical results, which showed good correlations
The Submillimetre Properties of Ultraluminous Infrared Galaxies
We present the results of SCUBA observations of a complete sample of local
ULIRGs. Twenty of the initial sample of 23 sources are detected at 850 um and
nearly half of the objects are also detected at 450 um. This data is combined
with existing observations of a further seven ULIRGs to produce the largest
sample of submm observations of ULIRGs currently available. We use similar
techniques to the SLUGS survey to fit dust spectral energy distributions (SEDs)
to their far-IR emission. We find that ULIRGs have a higher dust temperature
than lower luminosity objects (42K compared to 35K) and a steeper emissivity
index. For those objects where 450 um fluxes are available we also attempt a
two component dust SED fit, with warm and cool dust and a dust emissivity index
of beta=2. Such a model has been found to be a good fit to lower luminosity
systems. We find that it also works well for ULIRGs, but that ULIRGs have a
smaller cold dust component. Comparison of the dust mass derived for ULIRGs and
more normal spiral galaxies suggests that the dust content of a ULIRG is simply
the combined dust content of the two galaxies whose merger has triggered the
ULIRG activity. We examine the high end of the 850 um luminosity function and
find results consistent with those of the earlier SLUGS survey. We also find
that ULIRGs make up only about 50% of the high end of the 850 um luminosity
function, with LIRGs containing a large mass of cool dust likely to be
responsible for the rest.Comment: Accepted for publication in MNRA
A Multi-Wavelength Infrared Study of NGC 891
We present a multi-wavlength infrared study of the nearby, edge-on, spiral
galaxy NGC 891. We have examined 20 independent, spatially resolved IR images
of this galaxy, 14 of which are newly reduced and/or previously unpublished
images. These images span a wavelength regime from 1.2 microns in which the
emission is dominated by cool stars, through the MIR, in which emission is
dominated by PAHs, to 850 microns, in which emission is dominated by cold dust
in thermal equilibrium with the radiation field. The changing morphology of the
galaxy with wavelength illustrates the changing dominant components. We detect
extra-planar dust emission in this galaxy, consistent with previously published
results, but now show that PAH emission is also in the halo, to a vertical
distance of z >= 2.5 kpc. We compare the vertical extents of various components
and find that the PAHs (from 7.7 and 8 micron data) and warm dust (24 microns)
extend to smaller z heights than the cool dust (450 microns). For six locations
in the galaxy for which the S/N was sufficient, we present SEDs of the IR
emission, including two in the halo - the first time a halo SED in an external
galaxy has been presented. We have modeled these SEDs and find that the PAH
fraction is similar to Galactic values (within a factor of two), with the
lowest value at the galaxy's center, consistent with independent results of
other galaxies. In the halo environment, the fraction of dust exposed to a
colder radiation field, is of order unity, consistent with an environment in
which there is no star formation. The source of excitation is likely from
photons escaping from the disk.Comment: 24 pages, 17 figures, 7 tables, accepted for publication in MNRA
Cool and warm dust emission from M33 (HerM33es)
We study the far-infrared emission from the nearby spiral galaxy M33 in order
to investigate the dust physical properties such as the temperature and the
luminosity density across the galaxy. Taking advantage of the unique wavelength
coverage (100, 160, 250, 350 and 500 micron) of the Herschel Space Observatory
and complementing our dataset with Spitzer-IRAC 5.8 and 8 micron and
Spitzer-MIPS 24 and 70 micron data, we construct temperature and luminosity
density maps by fitting two modified blackbodies of a fixed emissivity index of
1.5. We find that the 'cool' dust grains are heated at temperatures between 11
and 28 K with the lowest temperatures found in the outskirts of the galaxy and
the highest ones in the center and in the bright HII regions. The
infrared/submillimeter total luminosity (5 - 1000 micron) is estimated to be
1.9x10^9 Lsun. 59% of the total luminosity of the galaxy is produced by the
'cool' dust grains (~15 K) while the rest 41% is produced by 'warm' dust grains
(~55 K). The ratio of the cool-to-warm dust luminosity is close to unity
(within the computed uncertainties), throughout the galaxy, with the luminosity
of the cool dust being slightly enhanced in the center of the galaxy.
Decomposing the emission of the dust into two components (one emitted by the
diffuse disk of the galaxy and one emitted by the spiral arms) we find that the
fraction of the emission in the disk in the mid-infrared (24 micron) is 21%,
while it gradually rises up to 57% in the submillimeter (500 micron). We find
that the bulk of the luminosity comes from the spiral arm network that produces
70% of the total luminosity of the galaxy with the rest coming from the diffuse
dust disk. The 'cool' dust inside the disk is heated at a narrow range of
temperatures between 18 and 15 K (going from the center to the outer parts of
the galaxy).Comment: 12 pages, 14 figures, accepted for publication in A&
PACS and SPIRE photometer maps of M33: First results of the Herschel M33 extended survey (HERM33ES)
Within the framework of the HERM33ES key project, we are studying the star
forming interstellar medium in the nearby, metal-poor spiral galaxy M33,
exploiting the high resolution and sensitivity of Herschel. We use PACS and
SPIRE maps at 100, 160, 250, 350, and 500 micron wavelength, to study the
variation of the spectral energy distributions (SEDs) with galacto-centric
distance. Detailed SED modeling is performed using azimuthally averaged fluxes
in elliptical rings of 2 kpc width, out to 8 kpc galacto-centric distance.
Simple isothermal and two-component grey body models, with fixed dust
emissivity index, are fitted to the SEDs between 24 and 500 micron using also
MIPS/Spitzer data, to derive first estimates of the dust physical conditions.
The far-infrared and submillimeter maps reveal the branched, knotted spiral
structure of M33. An underlying diffuse disk is seen in all SPIRE maps (250-500
micron). Two component fits to the SEDs agree better than isothermal models
with the observed, total and radially averaged flux densities. The two
component model, with beta fixed at 1.5, best fits the global and the radial
SEDs. The cold dust component clearly dominates; the relative mass of the warm
component is less than 0.3% for all the fits. The temperature of the warm
component is not well constrained and is found to be about 60K plus/minus 10K.
The temperature of the cold component drops significantly from about 24K in the
inner 2 kpc radius to 13K beyond 6 kpc radial distance, for the best fitting
model. The gas-to-dust ratio for beta=1.5, averaged over the galaxy, is higher
than the solar value by a factor of 1.5 and is roughly in agreement with the
subsolar metallicity of M33.Comment: 5 pages, 3 figures, accepted for publication in the A&A Herschel
Special Issu
Solvothermal synthesis of soluble, surface modified anatase and transition metal doped anatase hybrid nanocrystals
Titanium dioxide, or titania, is perhaps the most well-known and widely studied photocatalytic material, with myriad applications, due to a high degree of tunability achievable through the incorporation of dopants and control of phase composition and particle size. Many of the applications of titanium dioxide require particular forms, such as gels, coatings, or thin films, making the development of hybrid solution processable nanoparticles increasingly attractive. Here we report a simple solvothermal route to highly dispersible anatase phase titanium dioxide hybrid nanoparticles from amorphous titania. Solvothermal treatment of the amorphous titania in trifluoroacetic acid leads to the formation of anatase phase nanoparticles with a high degree of size control and near complete surface functionalisation. This renders the particles highly dispersible in simple organic solvents such as acetone. Dopant ions may be readily incorporated into the amorphous precursor by co-precipitation, with no adverse effect on subsequent crystallisation and surface modification
The Dust & Gas Properties of M83
We examine the dust and gas properties of the nearby, barred galaxy M83,
which is part of the Very Nearby Galaxy Survey. Using images from the PACS and
SPIRE instruments of Herschel, we examine the dust temperature and dust mass
surface density distribution. We find that the nuclear, bar and spiral arm
regions exhibit higher dust temperatures and masses compared to interarm
regions. However, the distribution of dust temperature and mass are not
spatially coincident. Assuming a trailing spiral structure, the dust
temperature peaks in the spiral arms lie ahead of the dust surface density
peaks. The dust mass surface density correlates well with the distribution of
molecular gas as traced by CO (J=3-2) images (JCMT) and the star formation rate
as traced by H?2 with a correction for obscured star formation using 24 micron
emission. Using HI images from THINGS to trace the atomic gas component, we
make total gas mass surface density maps and calculate the gas-to-dust ratio.
We find a mean gas-to-dust ratio of 84 \pm 4 with higher values in the inner
region assuming a constant CO-to-H2 conversion factor. We also examine the
gas-to-dust ratio using CO-to-H2 conversion factor that varies with
metallicity.Comment: 13 pages, 13 figures, accepted to MNRA
Innovation and growth in the UK pharmaceuticals: the case of product and marketing introductions
New drug introductions are key to growth for pharmaceutical firms. However, not all innovations are the same and they may have differential effects that vary by firm size. We use quarterly sales data on UK pharmaceuticals in a dynamic panel model to estimate the impact of product (new drugs) and marketing (additional pack varieties) innovations within a therapeutic class on a firm’s business unit growth. We find that product innovations lead to substantial growth in both the short and long run, whereas a new pack variety only produces short-term effects. The strategies are substitutes but the marginal effects are larger for product innovations relative to additional packs, and the effects are larger for smaller business units. Nonetheless, pack introductions offer a viable short-term growth strategy, especially for small- and medium-sized businesses
Paleogene Radiation of a Plant Pathogenic Mushroom
Background: The global movement and speciation of fungal plant pathogens is important, especially because of the economic losses they cause and the ease with which they are able to spread across large areas. Understanding the biogeography and origin of these plant pathogens can provide insights regarding their dispersal and current day distribution. We tested the hypothesis of a Gondwanan origin of the plant pathogenic mushroom genus Armillaria and the currently accepted premise that vicariance accounts for the extant distribution of the species. Methods: The phylogeny of a selection of Armillaria species was reconstructed based on Maximum Parsimony (MP), Maximum Likelihood (ML) and Bayesian Inference (BI). A timeline was then placed on the divergence of lineages using a Bayesian relaxed molecular clock approach. Results: Phylogenetic analyses of sequenced data for three combined nuclear regions provided strong support for three major geographically defined clades: Holarctic, South American-Australasian and African. Molecular dating placed the initial radiation of the genus at 54 million years ago within the Early Paleogene, postdating the tectonic break-up of Gondwana. Conclusions: The distribution of extant Armillaria species is the result of ancient long-distance dispersal rather than vicariance due to continental drift. As these finding are contrary to most prior vicariance hypotheses for fungi, our result
Methods to study microbial adhesion on abiotic surfaces
Microbial biofilms are a matrix of cells and exopolymeric substances attached to a wet and solid surface and are commonly associated to several problems, such as biofouling and corrosion in industries and infectious diseases in urinary catheters and prosthesis. However, these cells may have several benefits in distinct applications, such as wastewater treatment processes, microbial fuel cells for energy production and biosensors. As microbial adhesion is a key step on biofilm formation, it is very important to understand and characterize microbial adhesion to a surface. This study presents an overview of predictive and experimental methods used for the study of bacterial adhesion. Evaluation of surface physicochemical properties have a limited capacity in describing the complex adhesion process. Regarding the experimental methods, there is no standard method or platform available for the study of microbial adhesion and a wide variety of methods, such as colony forming units counting and microscopy techniques, can be applied for quantification and characterization of the adhesion process.This work was financially supported by: Project UID/EQU/00511/2013-LEPABE, by the FCT/MEC with national funds and co-funded by FEDER in the scope of the P2020 Partnership Agreement; Project NORTE-07-0124-FEDER-000025 - RL2_Environment&Health, by FEDER funds through Programa Operacional Factores de Competitividade-COMPETE, by the Programa Operacional do Norte (ON2) program and by national funds through FCT - Fundacao para a Ciencia e a Tecnologia; European Research Project SusClean (Contract number FP7-KBBE-2011-5, project number: 287514), Scholarships SFRH/BD/52624/2014, SFRH/BD/88799/2012 and SFRH/BD/103810/2014
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