134 research outputs found
Low-energy Antiproton Interaction with Helium
An ab initio potential for the interaction of the neutral helium atom with
antiprotons and protons is calculated using the Born-Oppenheimer approximation.
Using this potential, the annihilation cross section for antiprotons in the
energy range 0.01 microvolt to 1 eV is calculated.Comment: 13 pages, 7 figures, LaTe
Correlated sampling in quantum Monte Carlo: a route to forces
In order to find the equilibrium geometries of molecules and solids and to
perform ab initio molecular dynamics, it is necessary to calculate the forces
on the nuclei. We present a correlated sampling method to efficiently calculate
numerical forces and potential energy surfaces in diffusion Monte Carlo. It
employs a novel coordinate transformation, earlier used in variational Monte
Carlo, to greatly reduce the statistical error. Results are presented for
first-row diatomic molecules.Comment: 5 pages, 2 postscript figure
Digging into NGC 6334I(N): Multiwavelength Imaging of a Massive Protostellar Cluster
We present a high-resolution, multi-wavelength study of the massive
protostellar cluster NGC 6334I(N) that combines new spectral line data from the
Submillimeter Array (SMA) and VLA with a reanalysis of archival VLA continuum
data, 2MASS and Spitzer images. As shown previously, the brightest 1.3 mm
source SMA1 contains substructure at subarcsecond resolution, and we report the
first detection of SMA1b at 3.6 cm along with a new spatial component at 7 mm
(SMA1d). We find SMA1 (aggregate of sources a, b, c, and d) and SMA4 to be
comprised of free-free and dust components, while SMA6 shows only dust
emission. Our 1.5" resolution 1.3 mm molecular line images reveal substantial
hot-core line emission toward SMA1 and to a lesser degree SMA2. We find CH3OH
rotation temperatures of 165\pm 9 K and 145\pm 12 K for SMA1 and SMA2,
respectively. We estimate a diameter of 1400 AU for the SMA1 hot core emission,
encompassing both SMA1b and SMA1d, and speculate that these sources comprise a
>800 AU separation binary that may explain the previously-suggested precession
of the outflow emanating from the SMA1 region. The LSR velocities of SMA1,
SMA2, and SMA4 all differ by 1-2 km/s. Outflow activity from SMA1, SMA2, SMA4,
and SMA6 is observed in several molecules including SiO(5--4) and IRAC 4.5
micron emission; 24 micron emission from SMA4 is also detected. Eleven water
maser groups are detected, eight of which coincide with SMA1, SMA2, SMA4, and
SMA6. We also detect a total of 83 Class I CH3OH 44GHz maser spots which likely
result from the combined activity of many outflows. Our observations paint the
portrait of multiple young hot cores in a protocluster prior to the stage where
its members become visible in the near-infrared.Comment: Accepted to ApJ, 24 pages, a full high resolution version is
available at http://www.cv.nrao.edu/~cbrogan/ms.long.pd
Two-Center Integrals for r_{ij}^{n} Polynomial Correlated Wave Functions
All integrals needed to evaluate the correlated wave functions with
polynomial terms of inter-electronic distance are included. For this form of
the wave function, the integrals needed can be expressed as a product of
integrals involving at most four electrons
Boundary Conditions on Internal Three-Body Wave Functions
For a three-body system, a quantum wave function with definite
and quantum numbers may be expressed in terms of an internal wave
function which is a function of three internal coordinates. This
article provides necessary and sufficient constraints on to
ensure that the external wave function is analytic. These
constraints effectively amount to boundary conditions on and its
derivatives at the boundary of the internal space. Such conditions find
similarities in the (planar) two-body problem where the wave function (to
lowest order) has the form at the origin. We expect the boundary
conditions to prove useful for constructing singularity free three-body basis
sets for the case of nonvanishing angular momentum.Comment: 41 pages, submitted to Phys. Rev.
A Cloud-Based Framework for Machine Learning Workloads and Applications
[EN] In this paper we propose a distributed architecture to provide machine learning practitioners with a set of tools and cloud services that cover the whole machine learning development cycle: ranging from the models creation, training, validation and testing to the models serving as a service, sharing and publication. In such respect, the DEEP-Hybrid-DataCloud framework allows transparent access to existing e-Infrastructures, effectively exploiting distributed resources for the most compute-intensive tasks coming from the machine learning development cycle. Moreover, it provides scientists with a set of Cloud-oriented services to make their models publicly available, by adopting a serverless architecture and a DevOps approach, allowing an easy share, publish and deploy of the developed models.This work was supported by the project DEEP-Hybrid-DataCloud ``Designing and Enabling E-infrastructures for intensive Processing in a Hybrid DataCloud'' that has received funding from the European Union's Horizon 2020 Research and Innovation Programme under Grant 777435Lopez Garcia, A.; Marco De Lucas, J.; Antonacci, M.; Zu Castell, W.; David, M.; Hardt, M.; Lloret Iglesias, L.... (2020). A Cloud-Based Framework for Machine Learning Workloads and Applications. IEEE Access. 8:18681-18692. https://doi.org/10.1109/ACCESS.2020.2964386S1868118692
Random-phase approximation and its applications in computational chemistry and materials science
The random-phase approximation (RPA) as an approach for computing the
electronic correlation energy is reviewed. After a brief account of its basic
concept and historical development, the paper is devoted to the theoretical
formulations of RPA, and its applications to realistic systems. With several
illustrating applications, we discuss the implications of RPA for computational
chemistry and materials science. The computational cost of RPA is also
addressed which is critical for its widespread use in future applications. In
addition, current correction schemes going beyond RPA and directions of further
development will be discussed.Comment: 25 pages, 11 figures, published online in J. Mater. Sci. (2012
Molecular excitation in the Interstellar Medium: recent advances in collisional, radiative and chemical processes
We review the different excitation processes in the interstellar mediumComment: Accepted in Chem. Re
ATLAS liquid argon calorimeter front end electronics
The ATLAS detector has been designed for operation at CERN's Large Hadron Collider. ATLAS includes a complex system of liquid argon calorimeters. This paper describes the architecture and implementation of the system of custom front end electronics developed for the readout of the ATLAS liquid argon calorimeters
The Eruption of the Candidate Young Star ASASSN-15qi
Outbursts on young stars are usually interpreted as accretion bursts caused by instabilities in the disk or the star-disk connection. However, some protostellar outbursts may not fit into this framework. In this paper, we analyze optical and near-infrared spectra and photometry to characterize the 2015 outburst of the probable young star ASASSN-15qi. The mag brightening in the band was sudden, with an unresolved rise time of less than one day. The outburst decayed exponentially by 1 mag for 6 days and then gradually back to the pre-outburst level after 200 days. The outburst is dominated by emission from K gas. An explosive release of energy accelerated matter from the star in all directions, seen in a spectacular cool, spherical wind with a maximum velocity of 1000 km/s. The wind and hot gas both disappeared as the outburst faded and the source the source returned to its quiescent F-star spectrum. Nebulosity near the star brightened with a delay of 10-20 days. Fluorescent excitation of H is detected in emission from vibrational levels as high as , also with a possible time delay in flux increase. The mid-infrared spectral energy distribution does not indicate the presence of warm dust emission, although the optical photospheric absorption and CO overtone emission could be related to a gaseous disk. Archival photometry reveals a prior outburst in 1976. Although we speculate about possible causes for this outburst, none of the explanations are compelling
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