1,387 research outputs found
Hydrodynamical simulations of galaxy properties: Environmental effects
Using N-body+hydro simulations we study relations between the local
environments of galaxies on 0.5 Mpc scale and properties of the luminous
components of galaxies. Our numerical simulations include effects of star
formation and supernova feedback in different cosmological scenarios: the
standard Cold Dark Matter model, the Broken Scale Invariance model (BSI), and a
model with cosmological constant (LCDM).
In this paper, we concentrate on the effects of environment on colors and
morphologies of galaxies, on the star formation rate and on the relation
between the total luminosity of a galaxy and its circular velocity. We
demonstrate a statistically significant theoretical relationship between
morphology and environment. In particular, there is a strong tendency for
high-mass galaxies and for elliptical galaxies to form in denser environments,
in agreement with observations. We find that in models with denser environments
(CDM scenario) ~ 13 % of the galactic halos can be identified as field
ellipticals, according to their colors. In simulations with less clustering
(BSI and LCDM), the fraction of ellipticals is considerably lower (~ 2-3 %).
The strong sensitivity of morphological type to environment is rather
remarkable because our results are applicable to ``field'' galaxies and small
groups. If all galaxies in our simulations are included, we find a
statistically significant dependence of the galaxy luminosity - circular
velocity relation on dark matter overdensity within spheres of radius 0.5 Mpc,
for the CDM simulations. But if we remove ``elliptical'' galaxies from our
analysis to mimic the Tully-Fisher relation for spirals, then no dependence is
found in any model.Comment: 44 pages, 21 figures (17 included). Submitted to New Astronomy. GIFF
color plots and the complete paper in Postscript (including color figures)
can be found at http://astrosg.ft.uam.es/~gustavo/newas
Hydrodynamical simulations of galaxy formation: effects of supernova feedback
We numerically simulate some of the most critical physical processes in
galaxy formation: The supernova feedback, in conjunction with gasdynamics and
gravity, plays a crucial role in determining how galaxies arise within the
context of a model for large-scale structure. Our treatment incorporates a
multi-phase model of the interstellar medium and includes the effects of
cooling, heating and metal enrichment by supernovae, and evaporation of cold
clouds. The star formation happens inside the clouds of cold gas, which are
produced via thermal instability. We simulate the galaxy formation in standard
biased CDM model for a variety of parameters and for several resolutions in the
range 2--20kpc. In our picture, supernova feedback regulates the
evolution of the gas components and star formation. The efficiency of cloud
evaporation by supernova strongly influences star formation rates. This
feedback results in a steady rate of star formation in large galaxies (mass
larger than 2-3x10^{11}\Msun) at a level of (1-10)\Msun\yr for .
Supernova feedback has an even stronger effect on the evolution of dwarf
galaxies, most of which have a small fraction of stars and extremely low
luminosities: . In the case of both large and small galaxies, the
distribution of luminous matter (stars) is strongly BIASED with respect to the
dark matter. We find an approximate biasing measure of the form for z=0 and overdensities exceeding 1000. Deviations
from this relation (a factor 2-3) depend on the environment. For halo masses
exceeding 2x10^{10}\Msun, the dependence of the absolute magnitude on the
total mass can be approximated as M_V=-18.5-4\log(M_{tot}/10^{11}\Msun), with
a scatter of less than 0.5mag.Comment: 17 pages LATEX (uses mn.sty). 12 PostScript figures and the text are
available at ftp://charon.nmsu.edu/pub/aklypin/HYDRO Corrected ftp adderes
Luminosity- and morphology-dependent clustering of galaxies
How does the clustering of galaxies depend on their inner properties like
morphological type and luminosity? We address this question in the mathematical
framework of marked point processes and clarify the notion of luminosity and
morphological segregation. A number of test quantities such as conditional
mark-weighted two-point correlation functions are introduced. These descriptors
allow for a scale-dependent analysis of luminosity and morphology segregation.
Moreover, they break the degeneracy between an inhomogeneous fractal point set
and actual present luminosity segregation. Using the Southern Sky Redshift
Survey~2 (da Costa et al. 1998, SSRS2) we find both luminosity and
morphological segregation at a high level of significance, confirming claims by
previous works using these data (Benoist et al. 1996, Willmer et al. 1998).
Specifically, the average luminosity and the fluctuations in the luminosity of
pairs of galaxies are enhanced out to separations of 15Mpc/h. On scales smaller
than 3Mpc/h the luminosities on galaxy pairs show a tight correlation. A
comparison with the random-field model indicates that galaxy luminosities
depend on the spatial distribution and galaxy-galaxy interactions. Early-type
galaxies are also more strongly correlated, indicating morphological
segregation. The galaxies in the PSCz catalog (Saunders et al. 2000) do not
show significant luminosity segregation. This again illustrates that mainly
early-type galaxies contribute to luminosity segregation. However, based on
several independent investigations we show that the observed luminosity
segregation can not be explained by the morphology-density relation alone.Comment: aastex, emulateapj5, 20 pages, 13 figures, several clarifying
comments added, ApJ accepte
Changing social contracts in climate-change adaptation
Risks from extreme weather events are mediated through
state, civil society and individual action
1
,
2
. We propose evolving
social contracts as a primary mechanism by which adaptation
to climate change proceeds. We use a natural experiment
of policy and social contexts of the UK and Ireland affected
by the same meteorological event and resultant flooding in
November 2009. We analyse data from policy documents and
from household surveys of 356 residents in western Ireland and
northwest England. We find significant differences between
perceptions of individual responsibility for protection across
the jurisdictions and between perceptions of future risk from
populations directly affected by flooding events. These explain
differences in stated willingness to take individual adaptive
actions when state support retrenches. We therefore show
that expectations for state protection are critical in mediating
impacts and promoting longer-term adaptation. We argue
that making social contracts explicit may smooth pathways to
effective and legitimate adaptation
Accepting higher morbidity in exchange for sacrificing fewer animals in studies developing novel infection-control strategies.
Preventing bacterial infections from becoming the leading cause of death by the year 2050 requires the development of novel, infection-control strategies, building heavily on biomaterials science, including nanotechnology. Pre-clinical (animal) studies are indispensable for this development. Often, animal infection outcomes bear little relation to human clinical outcome. Here, we review conclusions from pathogen-inoculum dose-finding pilot studies for evaluation of novel infection-control strategies in murine models. Pathogen-inoculum doses are generally preferred that produce the largest differences in quantitative infection outcome parameters between a control and an experimental group, without death or termination of animals due to having reached an inhumane end-point during the study. However, animal death may represent a better end-point for evaluation than large differences in outcome parameters or number of days over which infection persists. The clinical relevance of lower pre-clinical outcomes, such as bioluminescence, colony forming units (CFUs) retrieved or more rapid clearance of infection is unknown, as most animals cure infection without intervention, depending on pathogen-species and pathogen-inoculum dose administered. In human clinical practice, patients suffering from infection present to hospital emergency wards, frequently in life-threatening conditions. Animal infection-models should therefore use prevention of death and recurrence of infection as primary efficacy targets to be addressed by novel strategies. To compensate for increased animal morbidity and mortality, animal experiments should solely be conducted for pre-clinical proof of principle and safety. With the advent of sophisticated in vitro models, we advocate limiting use of animal models when exploring pathogenesis or infection mechanisms
Dynamical effects of the neutrino gravitational clustering at Planck angular scales
We study the CMB anisotropy induced by the non-linear perturbations in the
massive neutrino density associated to the non-linear gravitational clustering
proceses. Our results show that for the neutrino fraction in agreement with
that indicated by the astroparticle and nuclear physics experiments and a
cosmological accreting mass comparable with the mass of known clusters, the
angular resolution and the sensitivity of the CMB anisotropy measurements from
the Planck surveyor will allow the detection of the dynamical effects of the
neutrino gravitational clustering.Comment: 40 pages and 12 figures, submitted to ApJ (14 March 2002
Waveguide model of the hearing aid earmold system
BACKGROUND: The earmold system of the Behind-The-Ear hearing aid is an acoustic system that modifies the spectrum of the propagated sound waves. Improper selection of the earmold system may result in deterioration of sound quality and speech intelligibility. Computer modeling methods may be useful in the process of hearing aid fitting, allowing physician to examine various earmold system configurations and choose the optimum one for the hearing aid user. METHODS: In this paper, a computer model adequate for this task is proposed. This model is based on the waveguide modeling method. The waveguide model simulates the propagation of sound waves in the system of cylindrical tubes. Frequency response of the hearing aid receiver is simulated in the model and the influence of the ear canal and the eardrum on the earmold system is taken into account. The model parameters are easily calculated from parameters of a physical hearing aid system. Transfer function of the model is calculated and frequency response plots are obtained using the Matlab system. RESULTS: The frequency response plots of the earmold model were compared to the measurement plots of the corresponding physical earmold systems. The same changes in frequency responses caused by modification of length or diameter of a selected waveguide section, are observed in both measurement data of a real earmold system and in computed model responses. CONCLUSION: Comparison of model responses obtained for various sets of parameters with measurement data proved that the proposed model accurately simulates the real earmold system and the developed model may be used to construct a computer system assisting the physician who performs earmold system fitting
The Tension on dsDNA Bound to ssDNA/RecA Filaments May Play an Important Role in Driving Efficient and Accurate Homology Recognition and Strand Exchange
It is well known that during homology recognition and strand exchange the
double stranded DNA (dsDNA) in DNA/RecA filaments is highly extended, but the
functional role of the extension has been unclear. We present an analytical
model that calculates the distribution of tension in the extended dsDNA during
strand exchange. The model suggests that the binding of additional dsDNA base
pairs to the DNA/RecA filament alters the tension in dsDNA that was already
bound to the filament, resulting in a non-linear increase in the mechanical
energy as a function of the number of bound base pairs. This collective
mechanical response may promote homology stringency and underlie unexplained
experimental results
Dimensions of professional competences for interventions towards sustainability
This paper investigates sustainability competences through the eyes of professional practitioners in the field of sustainability and presents empirical data that have been created using an action research approach. The design of the study consists of two workshops, in which professional practitioners in interaction with each other and the facilitators are invited to explore and reflect on the specific knowledge, skills, attitudes and behaviours necessary to conduct change processes successfully towards sustainability in a variety of business and professional contexts. The research focuses on the competences associated with these change processes to devise, propose and conduct appropriate interventions that address sustainability issues. Labelled âintervention competenceâ, this ability comprises an interlocking set of knowledge, skills, attitudes and behaviours that include: appreciating the importance of (trying to) reaching decisions or interventions; being able to learn from lived experience of practice and to connect such learning to oneâs own scientific knowledge; being able to engage in political-strategic thinking, deliberations and actions, related to different perspectives; the ability for showing goal-oriented, adequate action; adopting and communicating ethical practices during the intervention process; being able to cope with the degree of complexity, and finally being able to translate stakeholder diversity into collectively produced interventions (actions) towards sustainability. Moreover, this competence has to be practised in contexts of competing values, non-technical interests and power relations. The article concludes with recommendations for future research and practice
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