1,159 research outputs found
Effective Interactions for the Three-Body Problem
The three-body energy-dependent effective interaction given by the
Bloch-Horowitz (BH) equation is evaluated for various shell-model oscillator
spaces. The results are applied to the test case of the three-body problem
(triton and He3), where it is shown that the interaction reproduces the exact
binding energy, regardless of the parameterization (number of oscillator quanta
or value of the oscillator parameter b) of the low-energy included space. We
demonstrate a non-perturbative technique for summing the excluded-space
three-body ladder diagrams, but also show that accurate results can be obtained
perturbatively by iterating the two-body ladders. We examine the evolution of
the effective two-body and induced three-body terms as b and the size of the
included space Lambda are varied, including the case of a single included
shell, Lambda hw=0 hw. For typical ranges of b, the induced effective
three-body interaction, essential for giving the exact three-body binding, is
found to contribute ~10% to the binding energy.Comment: 19 pages, 9 figures, submitted to PR
Localized fluidization in a granular medium: Parametric study with a physical model of “sand boiling”
The present study investigates steady-state localized fluidization within a granular bed by means of experiments on a physical model using a direct internal visualization by means of combined optical techniques. The experimental setup allows access to a broad range of control parameters with the purpose of extending previous findings on this specific configuration, in particular regarding the critical flow rate needed to generate a chimney fluidization. A saturation of this critical flow rate with bed height is and can be explained by a purely hydrodynamic effect related to the geometry and the permeability of the bed which rule together the development of the upward fluid flow through the initially static granular bed. A quantitative model based on CFD simulations is successfully developed in good agreement with the experimental findings
Multi-Pion States in Lattice QCD and the Charged-Pion Condensate
The ground-state energies of systems containing up to twelve 's in a
spatial volume V ~ (2.5 fm)^3 are computed in dynamical, mixed-action lattice
QCD at a lattice spacing of ~ 0.125 fm for four different values of the light
quark masses. Clean signals are seen for each ground state, allowing for a
precise extraction of both the scattering length and
-interaction from a correlated analysis of systems containing
different numbers of 's. This extraction of the scattering
length is consistent with than that from the -system alone. The
large number of systems studied here significantly strengthens the arguments
presented in our earlier work and unambiguously demonstrates the presence of a
low energy -interaction. The equation of state of a
gas is investigated using our numerical results and the density dependence of
the isospin chemical potential for these systems agrees well with the
theoretical expectations of leading order chiral perturbation theory. The
chemical potential is found to receive a substantial contribution from the
-interaction at the lighter pion masses. An important
technical aspect of this work is the demonstration of the necessity of
performing propagator contractions in greater than double precision to extract
the correct results.Comment: 38 pages, 20 figure
Bit-Vector Model Counting using Statistical Estimation
Approximate model counting for bit-vector SMT formulas (generalizing \#SAT)
has many applications such as probabilistic inference and quantitative
information-flow security, but it is computationally difficult. Adding random
parity constraints (XOR streamlining) and then checking satisfiability is an
effective approximation technique, but it requires a prior hypothesis about the
model count to produce useful results. We propose an approach inspired by
statistical estimation to continually refine a probabilistic estimate of the
model count for a formula, so that each XOR-streamlined query yields as much
information as possible. We implement this approach, with an approximate
probability model, as a wrapper around an off-the-shelf SMT solver or SAT
solver. Experimental results show that the implementation is faster than the
most similar previous approaches which used simpler refinement strategies. The
technique also lets us model count formulas over floating-point constraints,
which we demonstrate with an application to a vulnerability in differential
privacy mechanisms
A qualitative study on redefining normality in relatives of patients with advanced cancer
OBJECTIVE: To obtain insight into adaptation processes of redefining normality and its influencing factors in relatives of patients with advanced cancer.METHODS: An exploratory qualitative study among relatives of patients with advanced cancer was conducted. Participants were purposively recruited. Ten in-depth individual (relative only) and 16 dyad (relative and patient together) interviews were conducted, transcribed verbatim, and analyzed by means of thematic analysis, drawing on elements of grounded theory, combining both inductive and deductive elements.RESULTS: Two adaptation processes of (redefining) normality were identified: assimilation and accommodation. The latter was found to be the main way of adapting to new events. Assimilative coping strategies entailed "continuing to do the same activities as done before the disease," "difficulty accepting the situation," "avoiding to think about the disease," and "living in the short term." Accommodative strategies involved "arranging practical matters," "thinking about the future," "doing what is feasible," "engaging in new activities," "accepting the situation," "seeking distraction," "living in the short term," and "focusing on what truly matters in life." The interplay between the diagnosis and treatment of cancer, a deteriorating disease status, and the accompanying uncertainty about the future was of influence on the relatives' coping strategies.CONCLUSION: When the new situation is too divergent to assimilate, accommodation may be necessary for relatives to cope with the growing complexity of the consequences of their loved one's illness. Accommodative coping then involves accepting the changing reality and actively making the necessary adjustments to build resilience and cope with the new circumstances.</p
Demonstrating high-precision photometry with a CubeSat: ASTERIA observations of 55 Cancri e
ASTERIA (Arcsecond Space Telescope Enabling Research In Astrophysics) is a 6U
CubeSat space telescope (10 cm x 20 cm x 30 cm, 10 kg). ASTERIA's primary
mission objective was demonstrating two key technologies for reducing
systematic noise in photometric observations: high-precision pointing control
and high-stabilty thermal control. ASTERIA demonstrated 0.5 arcsecond RMS
pointing stability and 10 milliKelvin thermal control of its camera
payload during its primary mission, a significant improvement in pointing and
thermal performance compared to other spacecraft in ASTERIA's size and mass
class. ASTERIA launched in August 2017 and deployed from the International
Space Station (ISS) November 2017. During the prime mission (November 2017 --
February 2018) and the first extended mission that followed (March 2018 - May
2018), ASTERIA conducted opportunistic science observations which included
collection of photometric data on 55 Cancri, a nearby exoplanetary system with
a super-Earth transiting planet. The 55 Cancri data were reduced using a custom
pipeline to correct CMOS detector column-dependent gain variations. A Markov
Chain Monte Carlo (MCMC) approach was used to simultaneously detrend the
photometry using a simple baseline model and fit a transit model. ASTERIA made
a marginal detection of the known transiting exoplanet 55 Cancri e
(~\Rearth), measuring a transit depth of ppm. This is the
first detection of an exoplanet transit by a CubeSat. The successful detection
of super-Earth 55 Cancri e demonstrates that small, inexpensive spacecraft can
deliver high-precision photometric measurements.Comment: 23 pages, 9 figures. Accepted in A
Enhancing Optical Up-Conversion Through Electrodynamic Coupling with Ancillary Chromophores
In lanthanide-based optical materials, control over the relevant operating characteristics–for example transmission wavelength, phase and quantum efficiency–is generally achieved through the modification of parameters such as dopant/host combination, chromophore concentration and lattice structure. An alternative avenue for the control of optical response is through the introduction of secondary, codoped chromophores. Here, such secondary centers act as mediators, commonly bridging the transfer of energy between primary absorbers of externally sourced optical input and other sites of frequency-converted emission. Utilizing theoretical models based on experimentally feasible, three-dimensional crystal lattice structures; a fully quantized theoretical framework provides insights into the locally modified mechanisms that can be implemented within such systems. This leads to a discussion of how such effects might be deployed to either enhance, or potentially diminish, the efficiency of frequency up-conversion
Rapid integrated assessment of food safety and nutrition related to pork consumption of regular consumers and mothers with young children in Vietnam
Pork is the most common and widely consumed meat product in Vietnam. The study aimed to assess nutrition and food safety risks and opportunities associated with pork value chains in Vietnam. Twenty-nine focus group discussions (FGD) were conducted in Hung Yen and Nghe An provinces with 164 participants who were both regular pork consumers and mothers with young children. In each province, three districts were selected, and in each district we selected one commune. To assess the quality of pork, we took 30 swab samples of pig carcasses at slaughterhouses, 90 pork samples at slaughterhouses and markets and analysed all samples for total bacterial count (TBC), coliforms, water holding capacity and pH. The results showed that pork was the main livestock product consumed and women are responsible for buying and preparing food for daily meals. Pork was the main animal sourced food (ASF) for Vietnamese consumers, for 50–60% of ASF. There was little knowledge of zoonotic diseases. The findings suggest further studies to address consumers’ concern on chemical contamination. Most market pork samples were not within the allowable range of limits standards of Vietnam for bacterial contamination: 90% of samples were above the official permissible limit for TBC and 98% did not meet standards for coliforms. Fifty percent of samples had acceptable pH but only 5% had acceptable water holding capacity. There were no significant differences in pork quality between intensifying Hung Yen and traditional Nghe An provinces, although there was a tendency for samples from Hung Yen to have better compliance. This rapid assessment revealed considerable interest and knowledge on pork nutrition and safety and found some behavioural but few quality and safety differences between traditional and intensifying systems. This indicated marketed pork is of low quality and safety, and a lack of support to consumers in making good choices
Micromechanical features of jet erosion - A numerical perspective
The erosion mechanisms driving the particle detachment of a soil under an impinging jet are here analysed from a micromechanical perspective combining the numerical Discrete Element and Lattice Boltzmann methods (DEM-LBM). Firstly, the local hydrodynamic conditions of both free and impinging jets are examined and briefly discussed, particularly on the relevance of the superficial irregularities of the granular assembly, which can dominate the local distribution of hydrodynamic variables over the impingement area. Profiles of both macromechanic and discrete (micromechanic) variables will be put forward. Then, the onset of erosion is reviewed from a topological point of view (locality of first grain motion) on the basis of a parametric study. Finally, the variation of the critical inflow velocity for the initiation of erosion in dependence on the particle size is also examined and briefly discussed
Short-term variability of a sample of 29 trans-Neptunian objects and Centaurs
We present results of 6 years of observations, reduced and analyzed with the
same tools in a systematic way. We report completely new data for 15 objects,
for 5 objects we present a new analysis of previously published results plus
additional data and for 9 objects we present a new analysis of data already
published. Lightcurves, possible rotation periods and photometric amplitudes
are reported for all of them. The photometric variability is smaller than
previously thought: the mean amplitude of our sample is 0.1mag and only around
15% of our sample has a larger variability than 0.15mag. The smaller
variability than previously thought seems to be a bias of previous
observations. We find a very weak trend of faster spinning objects towards
smaller sizes, which appears to be consistent with the fact that the smaller
objects are more collisionally evolved, but could also be a specific feature of
the Centaurs, the smallest objects in our sample. We also find that the smaller
the objects, the larger their amplitude, which is also consistent with the idea
that small objects are more collisionally evolved and thus more deformed.
Average rotation rates from our work are 7.5h for the whole sample, 7.6h for
the TNOs alone and 7.3h for the Centaurs. All of them appear to be somewhat
faster than what one can derive from a compilation of the scientific literature
and our own results. Maxwellian fits to the rotation rate distribution give
mean values of 7.5h (for the whole sample) and 7.3h (for the TNOs only).
Assuming hydrostatic equilibrium we can determine densities from our sample
under the additional assumption that the lightcurves are dominated by shape
effects, which is likely not realistic. The resulting average density is
0.92g/cm^3 which is not far from the density constraint that one can derive
from the apparent spin barrier that we observe.Comment: Accepted for publication in A&
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