8,732 research outputs found
Constraining Fundamental Physics with Future CMB Experiments
The Planck experiment will soon provide a very accurate measurement of Cosmic
Microwave Background anisotropies. This will let cosmologists determine most of
the cosmological parameters with unprecedented accuracy. Future experiments
will improve and complement the Planck data with better angular resolution and
better polarization sensitivity. This unexplored region of the CMB power
spectrum contains information on many parameters of interest, including
neutrino mass, the number of relativistic particles at recombination, the
primordial Helium abundance and the injection of additional ionizing photons by
dark matter self-annihilation. We review the imprint of each parameter on the
CMB and forecast the constraints achievable by future experiments by performing
a Monte Carlo analysis on synthetic realizations of simulated data. We find
that next generation satellite missions such as CMBPol could provide valuable
constraints with a precision close to that expected in current and near future
laboratory experiments. Finally, we discuss the implications of this
intersection between cosmology and fundamental physics.Comment: 11 pages, 14 figure
Electron Emission from Diamondoids: A Diffusion Quantum Monte Carlo Study
We present density-functional theory (DFT) and quantum Monte Carlo (QMC)
calculations designed to resolve experimental and theoretical controversies
over the optical properties of H-terminated C nanoparticles (diamondoids). The
QMC results follow the trends of well-converged plane-wave DFT calculations for
the size dependence of the optical gap, but they predict gaps that are 1-2 eV
higher. They confirm that quantum confinement effects disappear in diamondoids
larger than 1 nm, which have gaps below that of bulk diamond. Our QMC
calculations predict a small exciton binding energy and a negative electron
affinity (NEA) for diamondoids up to 1 nm, resulting from the delocalized
nature of the lowest unoccupied molecular orbital. The NEA suggests a range of
possible applications of diamondoids as low-voltage electron emitters
Distances and Kinematics of Gould Belt Star-Forming Regions with Gaia DR2 results
We present an analysis of the astrometric results from Gaia second data
release (DR2) to Young Stellar Objects (YSOs) in star-forming regions related
to the Gould Belt. These regions are Barnard 59, Lupus 1 to 4, Chamaeleon I and
II, -Chamaeleontis, the Cepheus flare, IC 5146 and Corona Australis.
The mean distance to the YSOs in each region are consistent with earlier
estimations, though a significant improvement to the final errors was obtained.
The mean distances to the star-forming regions were used to fit an ellipsoid of
size pc, and centered at
pc, consistent with recently
determined parameter of the Gould Belt. The mean proper motions were combined
with radial velocities from the literature to obtain the three dimensional
motion of the star-forming regions, which are consistent with a general
expansion of the Gould Belt. We estimate that this expansion is occurring at a
velocity of km s. This is the first time that YSOs motions
are used to investigate the kinematic of the Gould Belt. As an interesting side
result, we also identified stars with large peculiar velocities.Comment: 18 pages, 14 figures, and 5 tables. Accepted for publication in The
Astrophysical Journa
Performance of 4 Pre-Trained Sentence Transformer Models in the Semantic Query of a Systematic Review Dataset on Peri-Implantitis
Systematic reviews are cumbersome yet essential to the epistemic process of medical science. Finding significant reports, however, is a daunting task because the sheer volume of published literature makes the manual screening of databases time-consuming. The use of Artificial Intelligence could make literature processing faster and more efficient. Sentence transformers are groundbreaking algorithms that can generate rich semantic representations of text documents and allow for semantic queries. In the present report, we compared four freely available sentence transformer pre-trained models (all-MiniLM-L6-v2, all-MiniLM-L12-v2, all-mpnet-base-v2, and All-distilroberta-v1) on a convenience sample of 6110 articles from a published systematic review. The authors of this review manually screened the dataset and identified 24 target articles that addressed the Focused Questions (FQ) of the review. We applied the four sentence transformers to the dataset and, using the FQ as a query, performed a semantic similarity search on the dataset. The models identified similarities between the FQ and the target articles to a varying degree, and, sorting the dataset by semantic similarities using the best-performing model (all-mpnet-base-v2), the target articles could be found in the top 700 papers out of the 6110 dataset. Our data indicate that the choice of an appropriate pre-trained model could remarkably reduce the number of articles to screen and the time to completion for systematic reviews
A Binarisation Heuristic for Non-Convex Quadratic Programming with Box Constraints
Non-convex quadratic programming with box constraints is a fundamental problem in the
global optimization literature, being one of the simplest NP-hard nonlinear programs. We
present a new heuristic for this problem, which enables one to obtain solutions of excellent quality
in reasonable computing times. The heuristic consists of four phases: binarisation, convexification,
branch-and-bound, and local optimisation. Some very encouraging computational results are given
On Linearising Mixed-Integer Quadratic Programs via Bit Representation
It is well known that, under certain conditions, one can use bit representation to transform both integer
quadratic programs
and mixed-integer bilinear programs into mixed-integer linear programs (MILPs), and thereby render them
easier to solve using standard software packages. We show how to convert a more general family of
mixed-integer quadratic programs to MILPs, and present several families of strong valid linear inequalities
that can be used to strengthen the continuous relaxations of the resulting MILPs
Surface charging of thick porous water ice layers relevant for ion sputtering experiments
We use a laboratory facility to study the sputtering properties of
centimeter-thick porous water ice subjected to the bombardment of ions and
electrons to better understand the formation of exospheres of the icy moons of
Jupiter. Our ice samples are as similar as possible to the expected moon
surfaces but surface charging of the samples during ion irradiation may distort
the experimental results. We therefore monitor the time scales for charging and
dis- charging of the samples when subjected to a beam of ions. These
experiments allow us to derive an electric conductivity of deep porous ice
layers. The results imply that electron irradiation and sputtering play a
non-negligible role for certain plasma conditions at the icy moons of Jupiter.
The observed ion sputtering yields from our ice samples are similar to previous
experiments where compact ice films were sputtered off a micro-balance.Comment: arXiv admin note: text overlap with arXiv:1509.0400
Bit Representation Can Improve SDP Relaxations of Mixed-Integer Quadratic Programs
A standard trick in integer programming is to replace bounded integer variables with
binary variables, using a bit representation. In a previous paper, we showed that this process
can be used to improve linear programming relaxations of mixed-integer quadratic
programs. In this paper, we show that it can also be used to improve {\em semidefinite}\/
programming relaxations
Cooling Flows of Self-Gravitating, Rotating, Viscous Systems
We obtain self-similar solutions that describe the dynamics of a
self-gravitating, rotating, viscous system. We use simplifying assumptions; but
explicitly include viscosity and the cooling due to the dissipation of energy.
By assuming that the turbulent dissipation of energy is as power law of the
density and the speed v_{rms} and for a power-law dependence of viscosity on
the density, pressure, and rotational velocity, we investigate turbulent
cooling flows. It has been shown that for the cylindrically and the spherically
cooling flows the similarity indices are the same, and they depend only on the
exponents of the dissipation rate and the viscosity model. Depending on the
values of the exponents, which the mechanisms of the dissipation and viscosity
determine them, we may have solutions with different general physical
properties. The conservation of the total mass and the angular momentum of the
system strongly depends on the mechanisms of energy dissipation and the
viscosity model.Comment: 19 pages, 5 figures, To appear in ApJ (scheduled for the v574, July
20, 2002
Scale-free equilibria of self-gravitating gaseous disks with flat rotation curves
We introduce exact analytical solutions of the steady-state hydrodynamic
equations of scale-free, self-gravitating gaseous disks with flat rotation
curves. We express the velocity field in terms of a stream function and obtain
a third-order ordinary differential equation (ODE) for the angular part of the
stream function. We present the closed-form solutions of the obtained ODE and
construct hydrodynamical counterparts of the power-law and elliptic disks, for
which self-consistent stellar dynamical models are known. We show that the
kinematics of the Large Magellanic Cloud can well be explained by our findings
for scale-free elliptic disks.Comment: AAS preprint format, 21 pages, 8 figures, accepted for publication in
The Astrophysical Journa
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