292 research outputs found
A Bit-String Model for Biological Aging
We present a simple model for biological aging. We studied it through
computer simulations and we have found this model to reflect some features of
real populations.Comment: LaTeX file, 4 PS figures include
KSTAR: An algorithm to predict patient-specific kinase activities from phosphoproteomic data
Kinase inhibitors as targeted therapies have played an important role in improving cancer outcomes. However, there are still considerable challenges, such as resistance, non-response, patient stratification, polypharmacology, and identifying combination therapy where understanding a tumor kinase activity profile could be transformative. Here, we develop a graph- and statistics-based algorithm, called KSTAR, to convert phosphoproteomic measurements of cells and tissues into a kinase activity score that is generalizable and useful for clinical pipelines, requiring no quantification of the phosphorylation sites. In this work, we demonstrate that KSTAR reliably captures expected kinase activity differences across different tissues and stimulation contexts, allows for the direct comparison of samples from independent experiments, and is robust across a wide range of dataset sizes. Finally, we apply KSTAR to clinical breast cancer phosphoproteomic data and find that there is potential for kinase activity inference from KSTAR to complement the current clinical diagnosis of HER2 status in breast cancer patients
Impact of Corporate Governance Practices on Firm Capital Structure and Profitability: A Study of Selected Hotels and Restaurant Companies in Sri Lanka.
Corporate governance issues have been a growing area of management research especially among large and listed firms. Good corporate governance practices are regarded as important in reducing risk for investors, attracting investment capital and improving the performance of companies. Companies need financial resources and better earnings to promote their objectives. Therefore, factorsmay affect the capital structure and profitability of companies should be considered carefully. The purpose of the present study is to investigate whether there is any relationship among some specific characters of corporate governance, capital structure and profitability of listedHotels &Restaurant companies in Colombo Stock Exchange (CSE). To do so, 18 companies were selected from those which were listed inCSE during the 2007-2012. The ‘Board Composition(BC)’, ‘Board Size (BS)’ and ‘CEOduality (CEOD)’ were considered as independent variables, whereas,’ Debt Ratio(DR)’,‘Debt-to-Equity Ratio(DER)’,‘Returns on Equity(ROE)’,and ‘Return on Assets(ROA)’ as dependent variable. The results indicate a positive relationship between ‘BS; BC; CEOD; ROE; ROA and DERwhereas negative relationship between BS; BID and DR.in addition CEOD have a positive relationship with DR.In addition, none of the variables have a significant relationship with capital structure and profitability. Key words: Corporate Governance; Capital Structure and Profitability
The magnetic fields of large Virgo cluster spirals: Paper II
The Virgo cluster of galaxies provides excellent conditions for studying
interactions of galaxies with the cluster environment. Both the high-velocity
tidal interactions and effects of ram pressure stripping by the intracluster
gas can be investigated in detail. We extend our systematic search for possible
anomalies in the magnetic field structures of Virgo cluster spirals in order to
characterize a variety of effects and attribute them to different disturbing
agents. Six angularly large Virgo cluster spiral galaxies (NGC4192, NGC4302,
NGC4303, NGC4321, NGC4388, and NGC4535) were targets of a sensitive total power
and polarization study using the 100-m radio telescope in Effelsberg at 4.85GHz
and 8.35GHz (except for NGC4388 observed only at 4.85GHz, and NGC4535 observed
only at 8.35GHz). Magnetic field structures distorted to various extent are
found in all galaxies. Three galaxies (NGC4302, NGC4303, and NGC4321) show some
signs of possible tidal interactions, while NGC4388 and NGC4535 have very
likely experienced strong ram-pressure and shearing effects, respectively,
visible as distortions and asymmetries of polarized intensity distributions. As
in our previous study, even strongly perturbed galaxies closely follow the
radio-far-infrared correlation. In NGC4303 and NGC4321, we observe symmetric
spiral patterns of the magnetic field and in NGC4535 an asymmetric pattern.
Magnetic fields allow us to trace even weak interactions that are difficult to
detect with other observations. Our results show that the degree of distortions
of a galaxy is not a simple function of the distance to the cluster center but
reflects also the history of its interactions. The angle between the velocity
vector and the rotation vector of a galaxy may be a general parameter that
describes the level of distortions of galactic magnetic fields.Comment: 12 pages, 18 figures, 2 tables. Accepted for publication in Astronomy
and Astrophysic
The influence of the cluster environment on the large-scale radio continuum emission of 8 Virgo cluster spirals
The influence of the environment on the polarized and total power radio
continuum emission of cluster spiral galaxies is investigated. We present deep
scaled array VLA 20 and 6 cm observations including polarization of 8 Virgo
spiral galaxies. These data are combined with existing optical, HI, and Halpha
data. Ram pressure compression leads to sharp edges of the total power
distribution at one side of the galactic disk. These edges coincide with HI
edges. In edge-on galaxies the extraplanar radio emission can extend further
than the HI emission. In the same galaxies asymmetric gradients in the degree
of polarization give additional information on the ram pressure wind direction.
The local total power emission is not sensitive to the effects of ram pressure.
The radio continuum spectrum might flatten in the compressed region only for
very strong ram pressure. This implies that neither the local star formation
rate nor the turbulent small-scale magnetic field are significantly affected by
ram pressure. Ram pressure compression occurs mainly on large scales (>=1 kpc)
and is primarily detectable in polarized radio continuum emission.Comment: 16 pages, 10 figures, accepted for publication in A&
On the influence of ram-pressure stripping on the star formation of simulated spiral galaxies
We investigate the influence of ram-pressure stripping on the star formation
and the mass distribution in simulated spiral galaxies. Special emphasis is put
on the question where the newly formed stars are located. The stripping radius
from the simulation is compared to analytical estimates. Disc galaxies are
modelled in combined N-body/hydrodynamic simulations (GADGET-2) with
prescriptions for cooling, star formation, stellar feedback, and galactic
winds. These model galaxies move through a constant density and temperature
gas, which has parameters comparable to the intra-cluster medium (ICM) in the
outskirts of a galaxy cluster (T=3 keV ~3.6x10^7 K and rho=10^-28 g/cm^3). With
this numerical setup we analyse the influence of ram-pressure stripping on the
star formation rate of the model galaxy. We find that the star formation rate
is significantly enhanced by the ram-pressure effect (up to a factor of 3).
Stars form in the compressed central region of the galaxy as well as in the
stripped gas behind the galaxy. Newly formed stars can be found up to hundred
kpc behind the disc, forming structures with sizes of roughly 1 kpc in diameter
and with masses of up to 10^7 M_sun. As they do not possess a dark matter halo
due to their formation history, we name them 'stripped baryonic dwarf'
galaxies. We also find that the analytical estimate for the stripping radius
from a Gunn & Gott (1972) criterion is in good agreement with the numerical
value from the simulation. Like in former investigations, edge-on systems lose
less gas than face-on systems and the resulting spatial distribution of the gas
and the newly formed stars is different.Comment: 8 pages, 7 figures, accepted for publication in A&
Metal enrichment of the intra-cluster medium over a Hubble time for merging and relaxed galaxy clusters
We investigate the efficiency of galactic mass loss, triggered by
ram-pressure stripping and galactic winds of cluster galaxies, on the chemical
enrichment of the intra-cluster medium (ICM). We combine N-body and
hydrodynamic simulations with a semi-numerical galaxy formation model. By
including simultaneously different enrichment processes, namely ram-pressure
stripping and galactic winds, in galaxy-cluster simulations, we are able to
reproduce the observed metal distribution in the ICM. We find that the mass
loss by galactic winds in the redshift regime z>2 is ~10% to 20% of the total
galactic wind mass loss, whereas the mass loss by ram-pressure stripping in the
same epoch is up to 5% of the total ram-pressure stripping mass loss over the
whole simulation time. In the cluster formation epochs z<2 ram-pressure
stripping becomes more dominant than galactic winds. We discuss the
non-correlation between the evolution of the mean metallicity of galaxy
clusters and the galactic mass losses. For comparison with observations we
present two dimensional maps of the ICM quantities and radial metallicity
profiles. The shape of the observed profiles is well reproduced by the
simulations in the case of merging systems. In the case of cool-core clusters
the slope of the observed profiles are reproduced by the simulation at radii
below ~300 kpc, whereas at larger radii the observed profiles are shallower. We
confirm the inhomogeneous metal distribution in the ICM found in observations.
To study the robustness of our results, we investigate two different
descriptions for the enrichment process interaction.Comment: 11 pages, 13 figures, accepted for publication in A&A, high
resolution version can be found at
<http://astro.uibk.ac.at/~wolfgang/kapferer.pdf
Evolutionary paths to and from the red sequence: Star formation and HI properties of transition galaxies at z~0
(Abridged) We investigate the properties of galaxies between the blue and the
red sequence (i.e., the transition region) by combining UV and NIR imaging to
HI line observations for a volume-limited sample of nearby galaxies. We confirm
the existence of a tight relation between colour and HI-fraction across all the
range of colours, although outside the blue cloud this trend becomes gradually
weaker. Transition galaxies are divided into two different families, according
to their atomic hydrogen content. HI-deficient galaxies are the majority of
transition galaxies in our sample. They are found in high density environments
and all their properties are consistent with a quenching of the star formation
via gas stripping. However, while the migration from the blue cloud is
relatively quick (i.e., <=1 Gyr), a longer amount of time (a few Gyr at least)
seems required to completely suppress the star formation and reach the red
sequence. At all masses, migrating HI-deficient galaxies are mainly disks,
implying that the mechanism responsible for today's migration in clusters
cannot have played a significant role in the creation of the red sequence at
high-redshift. Conversely, HI-normal transition galaxies are a more
heterogeneous population. A fraction of these objects show evidence for
accretion/minor-merging events suggesting that at least part of the HI
reservoir has an external origin. The detailed evolution of such systems is
still unclear, but our analysis suggests that some galaxies might have migrated
back from the red sequence after accretion events. Our study clearly shows the
variety of evolutionary paths leading to the transition region and suggests
that the transition galaxies may not be always associated with systems quickly
migrating from the blue to the red sequence.Comment: 19 pages, 11 Figures, 1 Table. MNRAS in press. High resolution
version available at
http://www.astro.cardiff.ac.uk/pub/Luca.Cortese/papers/mnras09_1159_hires.p
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