6,508 research outputs found
IMPECCABLE: Integrated Modeling PipelinE for COVID Cure by Assessing Better LEads
The drug discovery process currently employed in the pharmaceutical industry typically requires about 10 years and $2–3 billion to deliver one new drug. This is both too expensive and too slow, especially in emergencies like the COVID-19 pandemic. In silico methodologies need to be improved both to select better lead compounds, so as to improve the efficiency of later stages in the drug discovery protocol, and to identify those lead compounds more quickly. No known methodological approach can deliver this combination of higher quality and speed. Here, we describe an Integrated Modeling PipEline for COVID Cure by Assessing Better LEads (IMPECCABLE) that employs multiple methodological innovations to overcome this fundamental limitation. We also describe the computational framework that we have developed to support these innovations at scale, and characterize the performance of this framework in terms of throughput, peak performance, and scientific results. We show that individual workflow components deliver 100 × to 1000 × improvement over traditional methods, and that the integration of methods, supported by scalable infrastructure, speeds up drug discovery by orders of magnitudes. IMPECCABLE has screened ∼ 1011 ligands and has been used to discover a promising drug candidate. These capabilities have been used by the US DOE National Virtual Biotechnology Laboratory and the EU Centre of Excellence in Computational Biomedicine
The Formation of the First Stars. I. The Primordial Star Forming Cloud
To constrain the nature of the very first stars, we investigate the collapse
and fragmentation of primordial, metal-free gas clouds. We explore the physics
of primordial star formation by means of three-dimensional simulations of the
dark matter and gas components, using smoothed particle hydrodynamics, under a
wide range of initial conditions, including the initial spin, the total mass of
the halo, the redshift of virialization, the power spectrum of the DM
fluctuations, the presence of HD cooling, and the number of particles employed
in the simulation. We find characteristic values for the temperature, T ~ a few
100 K, and the density, n ~ 10^3-10^4 cm^-3, characterising the gas at the end
of the initial free-fall phase. These values are rather insensitive to the
initial conditions. The corresponding Jeans mass is M_J ~ 10^3 M_sun. The
existence of these characteristic values has a robust explanation in the
microphysics of H2 cooling, connected to the minimum temperature that can be
reached with the H2 coolant, and to the critical density at which the
transition takes place betweeb levels being populated according to NLTE, and
according to LTE.
In all cases, the gas dissipatively settles into an irregular, central
configuration which has a filamentary and knotty appearance. The fluid regions
with the highest densities are the first to undergo runaway collapse due to
gravitational instability, and to form clumps with initial masses ~ 10^3 M_sun,
close to the characteristic Jeans scale. These results suggest that the first
stars might have been quite massive, possibly even very massive with M_star >
100 M_sun.Comment: Minor revisions. 26 pages, including 24 figures and 5 tables. ApJ, in
press. To appear in the Dec. 20, 2001 issue (v563
Revisiting Actor Programming in C++
The actor model of computation has gained significant popularity over the
last decade. Its high level of abstraction makes it appealing for concurrent
applications in parallel and distributed systems. However, designing a
real-world actor framework that subsumes full scalability, strong reliability,
and high resource efficiency requires many conceptual and algorithmic additives
to the original model.
In this paper, we report on designing and building CAF, the "C++ Actor
Framework". CAF targets at providing a concurrent and distributed native
environment for scaling up to very large, high-performance applications, and
equally well down to small constrained systems. We present the key
specifications and design concepts---in particular a message-transparent
architecture, type-safe message interfaces, and pattern matching
facilities---that make native actors a viable approach for many robust,
elastic, and highly distributed developments. We demonstrate the feasibility of
CAF in three scenarios: first for elastic, upscaling environments, second for
including heterogeneous hardware like GPGPUs, and third for distributed runtime
systems. Extensive performance evaluations indicate ideal runtime behaviour for
up to 64 cores at very low memory footprint, or in the presence of GPUs. In
these tests, CAF continuously outperforms the competing actor environments
Erlang, Charm++, SalsaLite, Scala, ActorFoundry, and even the OpenMPI.Comment: 33 page
TIES 20: Relative Binding Free Energy with a Flexible Superimposition Algorithm and Partial Ring Morphing
The TIES (Thermodynamic Integration with Enhanced Sampling) protocol is a formally exact alchemical approach in computational chemistry to the calculation of relative binding free energies. The validity of TIES relies on the correctness of matching atoms across compared pairs of ligands, laying the foundation for the transformation along an alchemical pathway. We implement a flexible topology superimposition algorithm which uses an exhaustive joint-traversal for computing the largest common component(s). The algorithm is employed to enable matching and morphing of partial rings in the TIES protocol along with a validation study using 55 transformations and five different proteins from our previous work. We find that TIES 20 with the RESP charge system, using the new superimposition algorithm, reproduces the previous results with mean unsigned error of 0.75 kcal/mol with respect to the experimental data. Enabling the morphing of partial rings decreases the size of the alchemical region in the dual-topology transformations resulting in a significant improvement in the prediction precision. We find that increasing the ensemble size from 5 to 20 replicas per λ window only has a minimal impact on the accuracy. However, the non-normal nature of the relative free energy distributions underscores the importance of ensemble simulation. We further compare the results with the AM1-BCC charge system and show that it improves agreement with the experimental data by slightly over 10%. This improvement is partly due to AM1-BCC affecting only the charges of the atoms local to the mutation, which translates to even fewer morphed atoms, consequently reducing issues with sampling and therefore ensemble averaging. TIES 20, in conjunction with the enablement of ring morphing, reduces the size of the alchemical region and significantly improves the precision of the predicted free energies
Characterization of exoplanets from their formation I: Models of combined planet formation and evolution
A first characterization of many exoplanets has recently been achieved by the
observational determination of their radius. For some planets, a measurement of
the luminosity has also been possible, with many more directly imaged planets
expected in the future. The statistical characterization of exoplanets through
their mass-radius and mass-luminosity diagram is thus becoming possible. This
is for planet formation and evolution theory of similar importance as the
mass-distance diagram. Our aim in this and a companion paper is to extend our
formation model into a coupled formation and evolution model. We want to
calculate in a self-consistent way all basic characteristics (M,a,R,L) of a
planet and use the model for population synthesis calculations. Here we show
how we solve the structure equations describing the gaseous envelope not only
during the early formation phase, but also during gas runaway accretion, and
during the evolutionary phase at constant mass on Gyr timescales. We then study
the in situ formation and evolution of Jupiter, the mass-radius relationship of
giants, the influence of the core mass on the radius and the luminosity both in
the "hot start" and the "cold start" scenario. We put special emphasis on the
comparison with other models. We find that our results agree very well with
those of more complex models, despite a number of simplifications. The upgraded
model yields the most important characteristics of a planet from its beginning
as a seed embryo to a Gyr old planet. This is the case for all planets in a
synthetic planetary population. Therefore, we can now use self-consistently the
statistical constraints coming from all major observational techniques. This is
important in a time where different techniques yield constraints on very
diverse sub-populations of planets, and where its is challenging to put all
these constraints together in one coherent picture.Comment: Accepted to A&A. Identical as v1 except for additional online data
reference and corrected typos. 23 pages, 11 figure
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