1,525 research outputs found
Remote-scope Promotion: Clarified, Rectified, and Verified
Modern accelerator programming frameworks, such as OpenCL, organise threads into work-groups. Remote-scope promotion (RSP) is a language extension recently proposed by AMD researchers that is designed to enable applications, for the first time, both to optimise for the common case of intra-work-group communication (using memory scopes to provide consistency only within a work-group) and to allow occasional inter-work-group communication (as required, for instance, to support the popular load-balancing idiom of work stealing). We present the first formal, axiomatic memory model of OpenCL extended with RSP. We have extended the Herd memory model simulator with support for OpenCL kernels that exploit RSP, and used it to discover bugs in several litmus tests and a work-stealing queue, that have been used previously in the study of RSP. We have also formalised the proposed GPU implementation of RSP. The formalisation process allowed us to identify bugs in the description of RSP that could result in well-synchronised programs experiencing memory inconsistencies. We present and prove sound a new implementation of RSP that incorporates bug fixes and requires less non-standard hardware than the original implementation. This work, a collaboration between academia and industry, clearly demonstrates how, when designing hardware support for a new concurrent language feature, the early application of formal tools and techniques can help to prevent errors, such as those we have found, from making it into silicon
Thermodynamics of the PNJL model with nonzero baryon and isospin chemical potentials
We have extended the Polyakov-Nambu-Jona-Lasinio (PNJL) model for two
degenerate flavours to include the isospin chemical potential (). All
the diagonal and mixed derivatives of pressure with respect to the quark number
(proportional to baryon number) chemical potential () and isospin
chemical potential upto sixth order have been extracted at .
These derivatives give the generalized susceptibilities with respect to quark
and isospin numbers. Similar estimates for the flavour diagonal and
off-diagonal susceptibilities are also presented. Comparison to Lattice QCD
(LQCD) data of some of these susceptibilities for which LQCD data are
available, show similar temperature dependence, though there are some
quantitative deviations above the crossover temperature. We have also looked at
the effects of instanton induced flavour-mixing coming from the chiral
symmetry breaking 't Hooft determinant like term in the NJL part of the model.
The diagonal quark number and isospin susceptibilities are completely
unaffected. The off-diagonal susceptibilities show significant dependence near
the crossover. Finally we present the chemical potential dependence of specific
heat and speed of sound within the limits of chemical potentials where neither
diquarks nor pions can condense.Comment: 15 pages, 7 figures, Added discussions and references, version to
appear in Phys. Rev.
Conserved Density Fluctuation and Temporal Correlation Function in HTL Perturbation Theory
Considering recently developed Hard Thermal Loop perturbation theory that
takes into account the effect of the variation of the external field through
the fluctuations of a conserved quantity we calculate the temporal component of
the Euclidian correlation function in the vector channel. The results are found
to be in good agreement with the very recent results obtained within the
quenched approximation of QCD and small values of the quark mass ()
on improved lattices of size at (),
(), and (), where is
the temporal extent of the lattice. This suggests that the results from lattice
QCD and Hard Thermal Loop perturbation theory are in close proximity for a
quantity associated with the conserved density fluctuation.Comment: 16 pages, 4 figures; One para added in introduction, Fig 1 modified;
Accepted in Phys. Rev.
Colour-singlet clustering of partons and recombination model for hadronization of quark-gluon plasma
colour-singlet restriction, along with flavour and spin symmetry,
on thermal partonic ensemble is shown to recombine the partons with internal
colour structure into colour-singlet multi-quark clusters which can be
identified with various hadronic modes at a given temperature. This provides a
possible basis for recombination model for hadronization of quark-gluon plasma.
This also leads to a natural explanation for the ratio of (anti)protons to
pions and the quark number scaling of the elliptic flow coefficient in
relativistic heavy-ion collisions.Comment: 5 pages; version accepted as a Rapid Communication in Phys. Rev.
Galaxy clustering in 3D and modified gravity theories
We study Modified Gravity (MG) theories by modelling the redshifted matter power spectrum in a spherical Fourier-Bessel (sFB) basis. We use a fully non-linear description of the real-space matter power-spectrum and include the lowest-order redshift-space correction (Kaiser effect), taking into account some additional non-linear contributions. Ignoring relativistic corrections, which are not expected to play an important role for a shallow survey, we analyse two different modified gravity scenarios, namely the generalised Dilaton scalar-tensor theories and the f(R) models in the large curvature regime. We compute the 3D power spectrum C s ℓ (k 1 ,k 2 ) for various such MG theories with and without redshift space distortions, assuming precise knowledge of background cosmological parameters. Using an all-sky spectroscopic survey with Gaussian selection function φ(r)∝exp(−r 2 /r 2 0 ) , r 0 =150h −1 Mpc , and number density of galaxies N ¯ =10 −4 Mpc −3 , we use a χ 2 analysis, and find that the lower-order (ℓ≤25) multipoles of C s ℓ (k,k ′ ) (with radial modes restricted to k25 modes can further reduce the error bars and thus in principle make cosmological gravity constraints competitive with solar system tests. However this will require an accurate modelling of non-linear redshift space distortions. Using a tomographic β(a) -m(a) parameterization we also derive constraints on specific parameters describing the Dilaton models of modified gravity
PNJL model with a Van der Monde term
We extend the Polyakov-Nambu-Jona-Lasinio (PNJL) model for two degenerate
flavours by including the effect of the SU(3) measure with a Van der Monde
(VdM) term. This ensures that the Polyakov loop always remains in the domain
[0,1]. The pressure, energy density, specific heat, speed of sound and
conformal measure show small or negligible effects from this term. However
various quark number and isospin susceptibilities are all found to approach
their respective ideal gas limits around 2 . We compare our methods with
other similar approaches in PNJL model and also present a quantitative
comparison with Lattice QCD data.Comment: 12 pages, 8 eps figures; extended discussion and reference added;
accepted in Phys. Rev.
Inheritance of parthenocarpy in gynoecious cucumber (Cucumis sativus L.) cultivar PPC-2
The gynoecious and parthenocarpic inbred line, Pant Parthenocarpic Cucumber-2 (PPC- 2) was crossed with Indian monoecious and non-parthenocarpic cultivar Pusa Uday to develop F1, F2, B1 and B2 to determine the inheritance of parthenocarpy.The crop was grown under insect proof net house of 40 mesh. The pistillate buds were covered using butter paper bags before anthesis to prevent out-crossing.The observations were recorded separately for the development of early parthenocarpic fruits (i.e.1-7th nodes), late parthenocarpy (8th and above nodes) and non-parthenocarpic fruits. In F1 generation, out of 40 plants screened, 2 plants produced parthenocarpic fruits at lower nodes (1-7th nodes), 37 plants produced parthenocarpic fruits at upper nodes (8th and above), whereas,only 1 plant that did not produced any fruit was considered as non-parthenocarpic. The segregation of F2 population and test crosses for parthenocarpic fruit development suggested that parthenocarpy in gynoecious and parthenocarpic cucumber line PPC-2 is under the control of incomplete dominant gene
Radiative and Collisional Jet Energy Loss in the Quark-Gluon Plasma at RHIC
We calculate and compare bremsstrahlung and collisional energy loss of hard
partons traversing a quark-gluon plasma. Our treatment of both processes is
complete at leading order in the coupling and accounts for the probabilistic
nature of the jet energy loss. We find that the nuclear modification factor
for neutral production in heavy ion collisions is sensitive to
the inclusion of collisional and radiative energy loss contributions while the
averaged energy loss only slightly increases if collisional energy loss is
included for parent parton energies . These results are important for
the understanding of jet quenching in Au+Au collisions at at
RHIC. Comparison with data is performed applying the energy loss calculation to
a relativistic ideal (3+1)-dimensional hydrodynamic description of the
thermalized medium formed at RHIC.Comment: 4 pages, 3 figure
Position-Dependent Correlation Function of Weak Lensing Convergence
We provide a systematic study of the position-dependent correlation function
in weak lensing convergence maps and its relation to the squeezed limit of the
three-point correlation function (3PCF) using state-of-the-art numerical
simulations. We relate the position-dependent correlation function to its
harmonic counterpart, i.e., the position-dependent power spectrum or
equivalently the integrated bispectrum. We use a recently proposed improved
fitting function, BiHalofit, for the bispectrum to compute the theoretical
predictions as a function of source redshifts. In addition to low redshift
results () we also provide results for maps inferred from lensing
of the cosmic microwave background, i.e., . We include a {\em
Euclid}-type realistic survey mask and noise. In agreement with the recent
studies on the position-dependent power spectrum, we find that the results from
simulations are consistent with the theoretical expectations when appropriate
corrections are included.Comment: 7 pages, 7 figure
Distinguishing among Scalar Field Models of Dark Energy
We show that various scalar field models of dark energy predict degenerate
luminosity distance history of the Universe and thus cannot be distinguished by
supernovae measurements alone. In particular, models with a vanishing
cosmological constant (the value of the potential at its minimum) are
degenerate with models with a positive or negative cosmological constant whose
magnitude can be as large as the critical density. Adding information from CMB
anisotropy measurements does reduce the degeneracy somewhat but not
significantly. Our results indicate that a theoretical prior on the preferred
form of the potential and the field's initial conditions may allow to
quantitatively estimate model parameters from data. Without such a theoretical
prior only limited qualitative information on the form and parameters of the
potential can be extracted even from very accurate data.Comment: 15 pages, 5 figure
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