174 research outputs found
Provisioning Spot Market Cloud Resources to Create Cost-effective Virtual Clusters
Infrastructure-as-a-Service providers are offering their unused resources in
the form of variable-priced virtual machines (VMs), known as "spot instances",
at prices significantly lower than their standard fixed-priced resources. To
lease spot instances, users specify a maximum price they are willing to pay per
hour and VMs will run only when the current price is lower than the user's bid.
This paper proposes a resource allocation policy that addresses the problem of
running deadline-constrained compute-intensive jobs on a pool of composed
solely of spot instances, while exploiting variations in price and performance
to run applications in a fast and economical way. Our policy relies on job
runtime estimations to decide what are the best types of VMs to run each job
and when jobs should run. Several estimation methods are evaluated and
compared, using trace-based simulations, which take real price variation traces
obtained from Amazon Web Services as input, as well as an application trace
from the Parallel Workload Archive. Results demonstrate the effectiveness of
running computational jobs on spot instances, at a fraction (up to 60% lower)
of the price that would normally cost on fixed priced resources.Comment: 14 pages, 4 figures, 11th International Conference on Algorithms and
Architectures for Parallel Processing (ICA3PP-11); Lecture Notes in Computer
Science, Vol. 7016, 201
Coiling Instabilities in Multilamellar Tubes
Myelin figures are densely packed stacks of coaxial cylindrical bilayers that
are unstable to the formation of coils or double helices. These myelin figures
appear to have no intrinsic chirality. We show that such cylindrical membrane
stacks can develop an instability when they acquire a spontaneous curvature or
when the equilibrium distance between membranes is decreased. This instability
breaks the chiral symmetry of the stack and may result in coiling. A
unilamellar cylindrical vesicle, on the other hand, will develop an
axisymmetric instability, possibly related to the pearling instability.Comment: 6 pages, 2 figure
A First Step Towards Automatically Building Network Representations
To fully harness Grids, users or middlewares must have some knowledge on the
topology of the platform interconnection network. As such knowledge is usually
not available, one must uses tools which automatically build a topological
network model through some measurements. In this article, we define a
methodology to assess the quality of these network model building tools, and we
apply this methodology to representatives of the main classes of model builders
and to two new algorithms. We show that none of the main existing techniques
build models that enable to accurately predict the running time of simple
application kernels for actual platforms. However some of the new algorithms we
propose give excellent results in a wide range of situations
Large Scale Power Spectrum from Peculiar Velocities Via Likelihood Analysis
The power spectrum (PS) of mass density fluctuations, independent of
`biasing', is estimated from the Mark III catalog of peculiar velocities using
Bayesian statistics. A parametric model is assumed for the PS, and the free
parameters are determined by maximizing the probability of the model given the
data. The method has been tested using detailed mock catalogs. It has been
applied to generalized CDM models with and without COBE normalization.
The robust result for all the models is a relatively high PS, with at . An
extrapolation to smaller scales using the different CDM models yields . The peak is weakly constrained to the range
. These results are consistent with a direct
computation of the PS (Kolatt & Dekel 1996). When compared to galaxy-density
surveys, the implied values for () are of order
unity to within 25%.
The parameters of the COBE-normalized, flat CDM model are confined by a 90%
likelihood contour of the sort , where
and for models with and without tensor
fluctuations respectively. For open CDM the powers are and (no tensor fluctuations). A -shape model free of COBE
normalization yields only a weak constraint: .Comment: 19 pages, 8 figures, 2 tables. Accepted for publication in The
Astrophysical Journa
Morphology of axisymmetric vesicles with encapsulated filaments and impurities
The shape deformation of a three-dimensional axisymmetric vesicle with
encapsulated filaments or impurities is analyzed by integrating a dissipation
dynamics. This method can incorporate systematically the constraint of a fixed
surface area and/or a fixed volume. The filament encapsulated in a vesicle is
assumed to take a form of a rod or a ring so as to imitate cytoskeletons. In
both cases, results of the shape transition of the vesicle are summarized in
phase diagrams in the phase space of the vesicular volume and a rod length or a
ring radius.
We also study the dynamics of a vesicle with impurities coupled to the
membrane curvature. The phase separation and the associated shape deformation
in the early stage of the dynamical evolution can well be explained by the
linear stability analysis. Long runs of simulation demonstrate the nonlinear
coarsening of the wavy deformation of the vesicle in the late stage.Comment: 9 pages, 9 figure
The Velocity Function of Galaxies
We present a galaxy circular velocity function, Psi(log v), derived from
existing luminosity functions and luminosity-velocity relations. Such a
velocity function is desirable for several reasons. First, it enables an
objective comparison of luminosity functions obtained in different bands and
for different galaxy morphologies, with a statistical correction for dust
extinction. In addition, the velocity function simplifies comparison of
observations with predictions from high-resolution cosmological N-body
simulations.
We derive velocity functions from five different data sets and find rough
agreement among them, but about a factor of 2 variation in amplitude. These
velocity functions are then compared with N-body simulations of a LCDM model
(corrected for baryonic infall) in order to demonstrate both the utility and
current limitations of this approach. The number density of dark matter halos
and the slope of the velocity function near v_*, the circular velocity
corresponding to an ~L_* spiral galaxy, are found to be comparable to that of
observed galaxies. The primary sources of uncertainty in construction of
Psi(log v) from observations and N-body simulations are discussed and
explanations are suggected to account for these discrepancies.Comment: Latex. 28 pages, 4 figures. Accepted by Ap
Multibudded tubules formed by COPII on artificial liposomes
COPII-coated vesicles form at the endoplasmic reticulum for cargo transport to the Golgi apparatus. We used in vitro reconstitution to examine the roles of the COPII scaffold in remodeling the shape of a lipid bilayer. Giant Unilamellar Vesicles were examined using fast confocal fluorescence and cryo-electron microscopy in order to avoid separation steps and minimize mechanical manipulation. COPII showed a preference for high curvature structures, but also sufficient flexibility for binding to low curvatures. The COPII proteins induced beads-on-a-string-like constricted tubules, similar to those previously observed in cells. We speculate about a mechanical pathway for vesicle fission from these multibudded COPII-coated tubules, considering the possibility that withdrawal of the Sar1 amphipathic helix upon GTP hydrolysis leads to lipid bilayer destabilization resulting in fission
3D reconstruction and comparison of shapes of DNA minicircles observed by cryo-electron microscopy
We use cryo-electron microscopy to compare 3D shapes of 158 bp long DNA minicircles that differ only in the sequence within an 18 bp block containing either a TATA box or a catabolite activator protein binding site. We present a sorting algorithm that correlates the reconstructed shapes and groups them into distinct categories. We conclude that the presence of the TATA box sequence, which is believed to be easily bent, does not significantly affect the observed shapes
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