3,218 research outputs found
Dark Matter Halo Mass Function From HPC N-body Simulations
Dark matter (DM) dominates the matter in the Universe. Because of self-gravity, DM collapses and becomes clumpy, building the large-scale hierarchical structures. Baryons assemble within DM potential wells and form galaxies.
Because we can not directly observe DM halos, numerical simulations is the only way one can study their dynamics and other properties. Using N-body simulations, we can obtain the Halo Mass Function (HMF), which provides the abundance of DM halos as a function of their mass. The HMF depends weakly on cosmological redshift and is one of the basic tools in modern cosmology.
We use GIZMO --- a flexible, multi-method magneto-radiation-hydrodynamics code with self-gravity. It is designed to simultaneously capture advantages of both hydrodynamics via grid-based/adaptive mesh refinement (AMR) schemes and collisionless dynamics of stars and DM
Modeling Evolution of Galactic Bars at Cosmic Dawn
We study evolution of galactic bars using suite of very high-resolution
zoom-in cosmological simulations of galaxies at z ~ 9-2. Our models were chosen
to lie within similar mass DM halos, log(Mvir/Mo) ~ 11.65 +- 0.05, at z=6, 4,
and 2, in high and low overdensity environments. We apply two galactic wind
feedback mechanisms for each model. All galaxies develop sub-kpc stellar bars
differing in their properties. We find that (1) The high-z bars form in
response to various perturbations: mergers, close flybys, cold accretion
inflows along the cosmological filaments, etc.; (2) These bars account for
large-mass fraction of galaxies; (3) Bars display large corotation-to-bar-size
ratios, and are weaker compared to their low-redshift counterparts, by
measuring their Fourier amplitudes, and are very gas-rich; (4) Their pattern
speed does not exhibit monotonic decline with time due to braking against DM,
as at low z; (5) Bar properties, including their stellar population (SFRs and
metal enrichment) depend sensitively on prevailing feedback; (6) Finally, we
find that bars can weaken substantially during cosmological evolution, becoming
weak oval distortions -- hence bars are destroyed and reformed multiple times
unlike their low-z counterparts. In all cases, bars in our simulations have
been triggered by interactions. In summary, stellar bars appear to be not only
contemporary phenomenon, but based on increased frequency of mergers, flybys
and the strength of cold accretion flows at high z, we expect them to be
ubiquitous at redshifts > 2 -- the epoch of rapid galaxy growth and larger
stellar dispersion velocities.Comment: Astrophysical Journal (in press), 24 pages, 16 figure
GASS High Velocity Clouds in the Region of the Magellanic Leading Arm
We present a catalog of high-velocity clouds in the region of the Magellanic
Leading Arm. The catalog is based on neutral hydrogen (\HI) observations from
the Parkes Galactic All-Sky Survey (GASS). Excellent spectral resolution allows
clouds with narrow-line components to be resolved. The total number of detected
clouds is 419. We describe the method of cataloging and present the basic
parameters of the clouds. We discuss the general distribution of the
high-velocity clouds and classify the clouds based on their morphological type.
The presence of a significant number of head-tail clouds and their distribution
in the region is discussed in the context of Magellanic System simulations. We
suggest that ram-pressure stripping is a more important factor than tidal
forces for the morphology and formation of the Magellanic Leading Arm and that
different environmental conditions might explain the morphological difference
between the Magellanic Leading Arm and Magellanic Stream. We also discuss a
newly identified population of clouds that forms the LA IV and a new diffuse
bridge-like feature connecting the LA II and III complexes.Comment: 20 pages, 24 figures, accepted by ApJ on December 14, 201
A direct interaction between fascin and microtubules contributes to adhesion dynamics and cell migration
Fascin is an actin-binding and bundling protein that is highly upregulated in most epithelial cancers. Fascin promotes cell migration and adhesion dynamics in vitro and tumour cell metastasis in vivo. However, potential non-actin bundling roles for fascin remain unknown. Here we show for the first time that fascin can directly interact with the microtubule cytoskeleton and that this does not depend upon fascin-actin bundling. Microtubule binding contributes to fascin-dependent control of focal adhesion dynamics and cell migration speed. We also show that fascin forms a complex with focal adhesion kinase (FAK) and Src, and that this signalling pathway lies downstream of fascin-microtubule association in the control of adhesion stability. These findings shed light on new non actin-dependent roles for fascin and may have implications for the design of therapies to target fascin in metastatic disease
A Hardware-in-Loop Simulation of DC Microgrid using Multi-Agent Systems
Smart-grid is a complex system that incorporates distributed control, communication, optimization, and management functions in addition to the legacy functions such as generation, storage, and control. The design and test of new smart-grid algorithms require an efficient simulator. Agent-based simulation platforms are the most popular tools that work well in the control and monitoring functionalities of the power electric network such as the microgrid. Most existing simulation tools necessitate either simulated or static data. In this paper, we propose a hardware-in-loop simulator for de-microgrid. The simulator reads the power generated by the PV panels and the battery SoC using Raspberry PI. A physical agent that runs on Raspberry PI sends the real-time data to a de-microgrid simulator that runs on a PC. As a proof of concept, we implemented a load-shedding algorithm using the proposed system
Time series analysis of dengue fever and weather in Guangzhou, China
<p>Abstract</p> <p>Background</p> <p>Monitoring and predicting dengue incidence facilitates early public health responses to minimize morbidity and mortality. Weather variables are potential predictors of dengue incidence. This study explored the impact of weather variability on the transmission of dengue fever in the subtropical city of Guangzhou, China.</p> <p>Methods</p> <p>Time series Poisson regression analysis was performed using data on monthly weather variables and monthly notified cases of dengue fever in Guangzhou, China for the period of 2001-2006. Estimates of the Poisson model parameters was implemented using the Generalized Estimating Equation (GEE) approach; the quasi-likelihood based information criterion (QICu) was used to select the most parsimonious model.</p> <p>Results</p> <p>Two best fitting models, with the smallest QICu values, are selected to characterize the relationship between monthly dengue incidence and weather variables. Minimum temperature and wind velocity are significant predictors of dengue incidence. Further inclusion of minimum humidity in the model provides a better fit.</p> <p>Conclusion</p> <p>Minimum temperature and minimum humidity, at a lag of one month, are positively associated with dengue incidence in the subtropical city of Guangzhou, China. Wind velocity is inversely associated with dengue incidence of the same month. These findings should be considered in the prediction of future patterns of dengue transmission.</p
Role of Inn1 and its interactions with Hof1 and Cyk3 in promoting cleavage furrow and septum formation in S. cerevisiae
Cytokinesis requires coordination of actomyosin ring (AMR) contraction with rearrangements of the plasma membrane and extracellular matrix. In Saccharomyces cerevisiae, new membrane, the chitin synthase Chs2 (which forms the primary septum [PS]), and the protein Inn1 are all delivered to the division site upon mitotic exit even when the AMR is absent. Inn1 is essential for PS formation but not for Chs2 localization. The Inn1 C-terminal region is necessary for localization, and distinct PXXP motifs in this region mediate functionally important interactions with SH3 domains in the cytokinesis proteins Hof1 (an F-BAR protein) and Cyk3 (whose overexpression can restore PS formation in inn1Î cells). The Inn1 N terminus resembles C2 domains but does not appear to bind phospholipids; nonetheless, when overexpressed or fused to Hof1, it can provide Inn1 function even in the absence of the AMR. Thus, Inn1 and Cyk3 appear to cooperate in activating Chs2 for PS formation, which allows coordination of AMR contraction with ingression of the cleavage furrow
Charged-Higgs phenomenology in the Aligned two-Higgs-doublet model
The alignment in flavour space of the Yukawa matrices of a general
two-Higgs-doublet model results in the absence of tree-level flavour-changing
neutral currents. In addition to the usual fermion masses and mixings, the
aligned Yukawa structure only contains three complex parameters, which are
potential new sources of CP violation. For particular values of these three
parameters all known specific implementations of the model based on discrete
Z_2 symmetries are recovered. One of the most distinctive features of the
two-Higgs-doublet model is the presence of a charged scalar. In this work, we
discuss its main phenomenological consequences in flavour-changing processes at
low energies and derive the corresponding constraints on the parameters of the
aligned two-Higgs-doublet model.Comment: 46 pages, 19 figures. Version accepted for publication in JHEP.
References added. Discussion slightly extended. Conclusions unchange
Protein Pattern Formation
Protein pattern formation is essential for the spatial organization of many
intracellular processes like cell division, flagellum positioning, and
chemotaxis. A prominent example of intracellular patterns are the oscillatory
pole-to-pole oscillations of Min proteins in \textit{E. coli} whose biological
function is to ensure precise cell division. Cell polarization, a prerequisite
for processes such as stem cell differentiation and cell polarity in yeast, is
also mediated by a diffusion-reaction process. More generally, these functional
modules of cells serve as model systems for self-organization, one of the core
principles of life. Under which conditions spatio-temporal patterns emerge, and
how these patterns are regulated by biochemical and geometrical factors are
major aspects of current research. Here we review recent theoretical and
experimental advances in the field of intracellular pattern formation, focusing
on general design principles and fundamental physical mechanisms.Comment: 17 pages, 14 figures, review articl
Astrophysical Constraints on Dark Matter
Astrophysics gives evidence for the existence of Dark Matter and puts
constraints on its nature. The Cold Dark Matter model has become "standard"
cosmology combined with a cosmological constant. There are indications that
"Cold" Dark Matter could be "warmer" than initially discussed. This paper
reviews the main information on the Cold/Warm nature of Dark Matter.Comment: Proceedings of the 3rd International conference on Directional
Detection of Dark Matter (CYGNUS 2011), Aussois, France, 8-10 June 201
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