1,094 research outputs found
Acting out our dam future: science-based role-play simulations as mechanisms for learning and natural resource planning
Science often does not make its way into decisions, leading to a problematic gap between scientific and societal progress. To tackle this issue, our research tests a novel science-based negotiation simulation that integrates a role-play simulation (RPS) with a system dynamics model (SDM). In RPSs, stakeholders engage in a mock decision-making process (reflecting real-life institutional arrangements and scientific knowledge) for a set period. System dynamics models (SDMs) are visual tools used to simulate the interactions and feedback within a complex system. We test the integration of the two approaches with stakeholders in New England via a series of two consecutive workshops across two states. The workshops engage stakeholders from diverse groups to foster dialogue, learning, and creativity. Participants discuss a hypothetical (yet realistic) decision scenario to consider scientific information and explore dam management options that meet one another\u27s interests. In the first workshop, participants contributed to the design of the fictionalized dam decision scenario and the SDM. In the second workshop, participants assumed another representative\u27s role and discussed dam management options for the fictionalized scenario. This presentation will briefly report on the practical design of this science-based role-play, and particularly emphasize preliminary results of workshop outcomes, which were evaluated using debriefing sessions, surveys, concept mapping exercises, and interviews. Results will determine the extent to which this new knowledge production process leads to learning, use of science, and more collaborative decision-making about dams in New England and beyond
Star formation rate and metallicity of damped Lyman-alpha absorbers in cosmological SPH simulations
We study the distribution of the star formation rate and metallicity of
damped Lyman-alpha absorbers using cosmological SPH simulations of the Lambda
cold dark matter model in the redshift range z=0-4.5. Our approach includes a
phenomenological model of galactic wind. We find that there is a positive
correlation between the projected stellar mass density and the neutral hydrogen
column density (NHI) of DLAs for high NHI systems, and that there is a good
correspondence in the spatial distribution of stars and DLAs in the
simulations. The evolution of typical star-to-gas mass ratios in DLAs can be
characterised by an increase from about 2 at z=4.5 to 3 at z=3, to 10 at z=1,
and finally to 20 at z=0. We also find that the projected SFR density in DLAs
follows the Kennicutt law well at all redshifts, and the simulated values are
consistent with the recent observational estimates of this quantity by Wolfe et
al. (2003a,b). The rate of evolution in the mean metallicity of simulated DLAs
as a function of redshift is mild, and is consistent with the rate estimated
from observations. The predicted metallicity of DLAs is generally sub-solar in
our simulations, and there is a significant scatter in the distribution of DLA
metallicity for a given NHI. However, we find that the median metallicity of
simulated DLAs is close to that of Lyman-break galaxies, which is higher than
the values typically observed for DLAs by nearly an order of magnitude. This
discrepancy with observations could be due to an inadequate treatment of SN
feedback in our current simulations, perhaps indicating that metals are not
expelled efficiently enough from DLAs by outflows. Alternatively, the current
observations might be missing the majority of the high metallicity DLAs due to
selection effects. (abridged)Comment: 18 pages, 15 figures. Accepted to MNRAS. More visual presentations
and the version with high resolution figures are available at
http://cfa-www.harvard.edu/~knagamine/DLA-pics
Cosmic Variance and Its Effect on the Luminosity Function Determination in Deep High z Surveys
We study cosmic variance in deep high redshift surveys and its influence on
the determination of the luminosity function for high redshift galaxies. For
several survey geometries relevant for HST and JWST instruments, we
characterize the distribution of the galaxy number counts. This is obtained by
means of analytic estimates via the two point correlation function in extended
Press-Schechter theory as well as by using synthetic catalogs extracted from
N-body cosmological simulations of structure formation. We adopt a simple
luminosity - dark halo mass relation to investigate the environment effects on
the fitting of the luminosity function. We show that in addition to variations
of the normalization of the luminosity function, a steepening of its slope is
also expected in underdense fields, similarly to what is observed within voids
in the local universe. Therefore, to avoid introducing artificial biases,
caution must be taken when attempting to correct for field underdensity, such
as in the case of HST UDF i-dropout sample, which exhibits a deficit of bright
counts with respect to the average counts in GOODS. A public version of the
cosmic variance calculator based on the two point correlation function
integration is made available on the web.Comment: ApJ, 676, 767; Public cosmic variance calculator relocated at
https://www.ph.unimelb.edu.au/~mtrenti/cvc/CosmicVariance.htm
Internal properties and environments of dark matter halos
We use seven high-resolution -body simulations to study the correlations
among different halo properties (assembly time, spin, shape and substructure),
and how these halo properties are correlated with the large-scale environment
in which halos reside. The large-scale tidal field estimated from halos above a
mass threshold is used as our primary quantity to characterize the large-scale
environment, while other parameters, such as the local overdensity and the
morphology of large-scale structure, are used for comparison. For halos at a
fixed mass, all the halo properties depend significantly on environment,
particularly the tidal field. The environmental dependence of halo assembly
time is primarily driven by local tidal field. The mass of the unbound fraction
in substructure is boosted in strong tidal force region, while the bound
fraction is suppressed. Halos have a tendency to spin faster in stronger tidal
field and the trend is stronger for more massive halos. The spin vectors show
significant alignment with the intermediate axis of the tidal field, as
expected from the tidal torque theory. Both the major and minor axes of halos
are strongly aligned with the corresponding principal axes of the tidal field.
In general, a halo that can accrete more material after the formation of its
main halo on average is younger, is more elongated, spins faster, and contains
a larger amount of substructure. Higher density environments not only provide
more material for halo to accrete, but also are places of stronger tidal field
that tends to suppress halo accretion. The environmental dependencies are the
results of these two competing effects. The tidal field based on halos can be
estimated from observation, and we discuss the implications of our results for
the environmental dependence of galaxy properties.Comment: Accepted for publication in MNRA
Structure of the Shroom-Rho Kinase Complex Reveals a Binding Interface with Monomeric Shroom That Regulates Cell Morphology and Stimulates Kinase Activity
Shroom-mediated remodeling of the actomyosin cytoskeleton is a critical driver of cellular shape and tissue morphology that underlies the development of many tissues including the neural tube, eye, intestines, and vasculature. Shroom uses a conserved SD2 domain to direct the subcellular localization of Rho-associated kinase (Rock), which in turn drives changes in the cytoskeleton and cellular morphology through its ability to phosphorylate and activate non-muscle myosin II. Here, we present the structure of the human Shroom-Rock binding module, revealing an unexpected stoichiometry for Shroom in which two Shroom SD2 domains bind independent surfaces on Rock. Mutation of interfacial residues impaired Shroom-Rock binding in vitro and resulted in altered remodeling of the cytoskeleton and loss of Shroom-mediated changes in cellular morphology. Additionally, we provide the first direct evidence that Shroom can function as a Rock activator. These data provide molecular insight into the Shroom-Rock interface and demonstrate that Shroom directly participates in regulating cytoskeletal dynamics, adding to its known role in Rock localization
The Evolution of the Dark Halo Spin Parameters lambda and lambda' in a LCDM Universe: The Role of Minor and Major Mergers
The evolution of the spin parameter of dark halos and the dependence on the
halo merging history in a set of dissipationless cosmological LCDM simulations
is investigated. Special focus is placed on the differences of the two commonly
used versions of the spin parameter, namely lambda=J*E^1/2/(G*M^5/2) (Peebles
80) and lambda'=J/(sqrt(2)*M_vir*R_vir*V_vir) (Bullock et al. 01). Though the
distribution of the spin transfer rate defined as the ratio of the spin
parameters after and prior to a merger is similar to a high degree for both,
lambda and lambda', we find considerable differences in the time evolution:
while lambda' is roughly independent of redshift, lambda turns out to increase
significantly with decreasing redshift. This distinct behaviour arises from
small differences in the spin transfer during accretion events. The evolution
of the spin parameter is strongly coupled with the virial ratio
eta:=2*E_kin/|E_pot| of dark halos. Major mergers disturb halos and increase
both their virial ratio and spin parameter for 1-2 Gyrs. At high redshifts
(z=2-3) many halos are disturbed with an average virial ratio of eta = 1.3
which approaches unity until z=0. We find that the redshift evolution of the
spin parameters is dominated by the huge number of minor mergers rather than
the rare major merger events.Comment: 10 pages, 11 figures, submitted to MNRA
Galaxy Clustering Evolution in the UH8K Weak Lensing Fields
We present measurements of the two-point galaxy angular correlation function
as a function of apparent magnitude, color, and morphology. We present new
galaxy number counts to limiting magnitudes of I=24.0 and V=25.0. We find
to be well described by a power-law of slope -0.8. We find the
amplitude of the correlation function to decrease monotonically with
increasingly faint apparent magnitude. We compare with predictions utilizing
redshift distributions based on deep spectroscopic observations. We conclude
that simple redshift-dependent models which characterize evolution by means of
the epsilon parameter inadequately describe the observations. We find a strong
clustering dependence on V-I color because galaxies of extreme color lie at
similar redshifts and the angular correlation functions for these samples are
minimally diluted by chance projections.
We then present the first attempt to investigate the redshift evolution of
clustering, utilizing a population of galaxies of the same morphological type
and absolute luminosity. We study the dependence of on
redshift for Lstar early-type galaxies in the redshift range 0.2<z<0.9.
Although uncertainties are large, we find the evolution in the clustering of
these galaxies to be consistent with stable clustering [epsilon=0]. We find
Lstar early-type galaxies to cluster slightly more strongly (rnought =
5.25\pm0.28 \hMpc assuming epsilon=0) than the local full field population.
This is in good agreement with the 2dFGRS value for Lstar early-type galaxies
in the local universe (abridged).Comment: 41 pages, including 12 figs, 10 tables, to appear in Ap
Low lopinavir plasma or hair concentrations explain second-line protease inhibitor failures in a resource-limited setting.
In resource-limited settings, many patients, with no prior protease inhibitor (PI) treatment on a second-line, high genetic barrier, ritonavir-boosted PI-containing regimen have virologic failure
The Impact of Cooling and Feedback on Disc Galaxies
We present detailed, analytical models for the formation of disc galaxies to
investigate the impact that cooling and feedback have on their structural
properties. In particular, we investigate which observables extracted directly
from the models are best suited as virial mass estimators, and to what extent
they allow the recovery of the model input parameters regarding the feedback
and cooling efficiencies. Contrary to naive expectations, the luminosities and
circular velocities of disc galaxies are extremely poor indicators of total
virial mass. Instead, we show that the product of disc scale length and
rotation velocity squared yields a much more robust estimate. We show that
feedback can cause a narrow correlation between galaxy mass fraction and halo
spin parameter, similar to that found recently by van den Bosch, Burkert and
Swaters from an analysis of dwarf galaxy rotation curves. Finally we
investigate the impact that cooling and feedback have on the colors,
metallicities, star formation histories and Tully-Fisher relation of disc
galaxies.Comment: 20 pages, 12 figures. To be published in MNRA
HI as a Probe of the Large Scale Structure in the Post-Reionization Universe
We model the distribution of neutral Hydrogen (HI hereafter) in the
post-reionization universe. This model uses gravity only N-Body simulations and
an ansatz to assign HI to dark matter haloes that is consistent with
observational constraints and theoretical models. We resolve the smallest
haloes that are likely to host HI in the simulations, care is also taken to
ensure that any errors due to the finite size of the simulation box are small.
We then compute the smoothed one point probability distribution function and
the power spectrum of fluctuations in HI. This is compared with other
predictions that have been made using different techniques. We highlight the
significantly high bias for the HI distribution at small scales. This aspect
has not been discussed before. We then discuss the prospects for detection with
the MWA, GMRT and the hypothetical MWA5000. The MWA5000 can detect visibility
correlations at large angular scales at all redshifts in the post-reionization
era. The GMRT can detect visibility correlations at lower redshifts,
specifically there is a strong case for a survey at z=1.3. We also discuss
prospects for direct detection of rare peaks in the HI distribution using the
GMRT. We show that direct detection should be possible with an integration time
that is comparable to, or even less than, the time required for a statistical
detection. Specifically, it is possible to make a statistical detection of the
HI distribution by measuring the visibility correlation, and, direct detection
of rare peaks in the HI distribution at z = 1.3 with the GMRT in less than 1000
hours of observations.Comment: 15 pages, 11 figures. Accepted for publication in the MNRAS. This is
a merged manuscript also containing material covered in 0908.385
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