1,533 research outputs found
A concurrency semantics for relaxed atomics that permits optimisation and avoids thin-air executions
Copyright is held by the owner/author(s). Despite much research on concurrent programming languages, especially for Java and C/C++, we still do not have a satisfactory definition of their semantics, one that admits all common optimisations without also admitting undesired behaviour. Especially problematic are the "thin-Air" examples involving high-performance concurrent accesses, such as C/C++11 relaxed atomics. The C/C++11 model is in a per-candidate-execution style, and previous work has identified a tension between that and the fact that compiler optimisations do not operate over single candidate executions in isolation; rather, they operate over syntactic representations that represent all executions. In this paper we propose a novel approach that circumvents this difficulty. We define a concurrency semantics for a core calculus, including relaxed-Atomic and non-Atomic accesses, and locks, that admits a wide range of optimisation while still forbidding the classic thin-Air examples. It also addresses other problems relating to undefined behaviour. The basic idea is to use an event-structure representation of the current state of each thread, capturing all of its potential executions, and to permit interleaving of execution and transformation steps over that to reflect optimisation (possibly dynamic) of the code. These are combined with a non-multi-copy-Atomic storage subsystem, to reflect common hardware behaviour. The semantics is defined in a mechanised and executable form, and designed to be implementable above current relaxed hardware and strong enough to support the programming idioms that C/C++11 does for this fragment. It offers a potential way forward for concurrent programming language semantics, beyond the current C/C++11 and Java models.This work was partly funded by the EPSRC Programme Grant REMS:
Rigorous Engineering for Mainstream Systems, EP/K008528/
Propagators in Lagrangian space
It has been found recently that propagators, e.g. the cross-correlation
spectra of the cosmic fields with the initial density field, decay
exponentially at large-k in an Eulerian description of the dynamics. We explore
here similar quantities defined for a Lagrangian space description. We find
that propagators in Lagrangian space do not exhibit the same properties: they
are found not to be monotonic functions of time, and to track back the linear
growth rate at late time (but with a renormalized amplitude). These results
have been obtained with a novel method which we describe alongside. It allows
the formal resummation of the same set of diagrams as those that led to the
known results in Eulerian space. We provide a tentative explanation for the
marked differences seen between the Eulerian and the Lagrangian cases, and we
point out the role played by the vorticity degrees of freedom that are specific
to the Lagrangian formalism. This provides us with new insights into the
late-time behavior of the propagators.Comment: 14 pages, 5 figure
Non Gaussian extrema counts for CMB maps
In the context of the geometrical analysis of weakly non Gaussian CMB maps,
the 2D differential extrema counts as functions of the excursion set threshold
is derived from the full moments expansion of the joint probability
distribution of an isotropic random field, its gradient and invariants of the
Hessian. Analytic expressions for these counts are given to second order in the
non Gaussian correction, while a Monte Carlo method to compute them to
arbitrary order is presented. Matching count statistics to these estimators is
illustrated on fiducial non-Gaussian "Planck" data.Comment: 4 pages, 1 figur
Production Of Dna Minicircles Less Than 250 Base Pairs Through A Novel Concentrated Dna Circularization Assay Enabling Minicircle Design With Nf-κb Inhibition Activity
Double-stranded DNA minicircles of less than 1000 bp in length have great interest in both fundamental research and therapeutic applications. Although minicircles have shown promising activity in gene therapy thanks to their good biostability and better intracellular trafficking, minicircles down to 250 bp in size have not yet been investigated from the test tube to the cell for lack of an efficient production method. Herein, we report a novel versatile plasmidfree method for the production of DNA minicircles comprising fewer than 250 bp. We designed a linear nicked DNA double-stranded oligonucleotide bluntended substrate for efficient minicircle production in a ligase-mediated and bending protein-assisted circularization reaction at high DNA concentration of 2M. This one pot multi-step reaction based-method yields hundreds of micrograms of minicircle with sequences of any base composition and position and containing or not a variety of site-specifically chemical modifications or physiological supercoiling. Biochemical and cellular studies were then conducted to design a 95 bp minicircle capable of binding in vitro two NF-κB transcription factors per minicircle and to efficiently inhibiting NF-κB-dependent transcriptional activity in human cells. Therefore, our production method could pave the way for the design of minicircles as new decoy nucleic acids. © The Author(s) 2016.45
Seismic diagnostics for transport of angular momentum in stars 1. Rotational splittings from the PMS to the RGB
Rotational splittings are currently measured for several main sequence stars
and a large number of red giants with the space mission Kepler. This will
provide stringent constraints on rotation profiles. Our aim is to obtain
seismic constraints on the internal transport and surface loss of angular
momentum of oscillating solar-like stars. To this end, we study the evolution
of rotational splittings from the pre-main sequence to the red-giant branch for
stochastically excited oscillation modes. We modified the evolutionary code
CESAM2K to take rotationally induced transport in radiative zones into account.
Linear rotational splittings were computed for a sequence of
models. Rotation profiles were derived from our evolutionary models and
eigenfunctions from linear adiabatic oscillation calculations. We find that
transport by meridional circulation and shear turbulence yields far too high a
core rotation rate for red-giant models compared with recent seismic
observations. We discuss several uncertainties in the physical description of
stars that could have an impact on the rotation profiles. For instance, we find
that the Goldreich-Schubert-Fricke instability does not extract enough angular
momentum from the core to account for the discrepancy. In contrast, an increase
of the horizontal turbulent viscosity by 2 orders of magnitude is able to
significantly decrease the central rotation rate on the red-giant branch. Our
results indicate that it is possible that the prescription for the horizontal
turbulent viscosity largely underestimates its actual value or else a mechanism
not included in current stellar models of low mass stars is needed to slow down
the rotation in the radiative core of red-giant stars.Comment: 15 pages, 13 figures, accepted for publication in A&
Unstable Disk Galaxies. I. Modal Properties
I utilize the Petrov-Galerkin formulation and develop a new method for
solving the unsteady collisionless Boltzmann equation in both the linear and
nonlinear regimes. In the first order approximation, the method reduces to a
linear eigenvalue problem which is solved using standard numerical methods. I
apply the method to the dynamics of a model stellar disk which is embedded in
the field of a soft-centered logarithmic potential. The outcome is the full
spectrum of eigenfrequencies and their conjugate normal modes for prescribed
azimuthal wavenumbers. The results show that the fundamental bar mode is
isolated in the frequency space while spiral modes belong to discrete families
that bifurcate from the continuous family of van Kampen modes. The population
of spiral modes in the bifurcating family increases by cooling the disk and
declines by increasing the fraction of dark to luminous matter. It is shown
that the variety of unstable modes is controlled by the shape of the dark
matter density profile.Comment: Accepted for publication in The Astrophysical Journa
Reduced Gutzwiller formula with symmetry: case of a finite group
We consider a classical Hamiltonian on , invariant by a
finite group of symmetry , whose Weyl quantization is a
selfadjoint operator on . If is an irreducible
character of , we investigate the spectrum of its restriction
to the symmetry subspace of
coming from the decomposition of Peter-Weyl. We give
reduced semi-classical asymptotics of a regularised spectral density describing
the spectrum of near a non critical energy . If
is compact, assuming that periodic orbits are
non-degenerate in , we get a reduced Gutzwiller trace formula
which makes periodic orbits of the reduced space appear. The
method is based upon the use of coherent states, whose propagation was given in
the work of M. Combescure and D. Robert.Comment: 20 page
Slowly, rotating non-stationary, fluid solutions of Einstein's equations and their match to Kerr empty space-time
A general class of solutions of Einstein's equation for a slowly rotating
fluid source, with supporting internal pressure, is matched using Lichnerowicz
junction conditions, to the Kerr metric up to and including first order terms
in angular speed parameter. It is shown that the match applies to any
previously known non-rotating fluid source made to rotate slowly for which a
zero pressure boundary surface exists. The method is applied to the dust source
of Robertson-Walker and in outline to an interior solution due to McVittie
describing gravitational collapse. The applicability of the method to
additional examples is transparent. The differential angular velocity of the
rotating systems is determined and the induced rotation of local inertial frame
is exhibited
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