19,678 research outputs found
A Model to Describe Transport Properties in
A pseudo-spin model is proposed, as a means to describe some transport
properties (resistivity and Hall mobility) in
. Our model is based in a double-well
potential where tunneling in a given site and interaction between different
lattice sites are allowed only through the excited states. Doping of the pure
system by the addition of increases the ratio between the activation
energy and the tunneling constant. The model Hamiltonian displays some features
which are present in the hydrogen-bonded ferroelectrics. Its dynamics is
treated in the random phase approximation and the characteristic frequency
(time) is used in a Drude formula in order to obtain some transport properties
of the system, namely the electric resistivity and the Hall mobility. The
quantities calculated in this work are compared with the experimental data of
B. Beschoten, S. Sadewasser, G. G\"{u}ntherodt and C. Quitmann [Phys. Rev.
Lett.77, 1837(1996)].Comment: 14 pages, 4 figure
Amyloid positron emission tomography candidates may focus more on benefits than risks of results disclosure
IntroductionGiven mounting calls to disclose biomarker test results to research participants, we explored factors underlying decisions by patients with mild cognitive impairment to receive amyloid imaging results.MethodsProspective, qualitative interviews were conducted with 59 participants (30Â =Â mild cognitive impairment patients, 29Â =Â care partners) from the scan arm of a randomized controlled trial on the effects of amyloid PET results disclosure in an Alzheimer Disease Research Center setting.ResultsSixtyâthree percent of the participants were female, with an average age of 72.9Â years, and most had greater than a high school level of education (80%). Primary motivations included: (1) better understanding oneâs mild cognitive impairment etiology and prognosis to plan ahead, and (2) learning oneâs brain amyloid status for knowledgeâs sake, regardless of whether the information is actionable. Most participants demonstrated an adequate understanding of the scanâs limitations, yet instances of characterizing amyloid PET as a definitive test for Alzheimerâs disease occurred. Mention of potential drawbacks, such as negative psychological outcomes, was minimal, even among care partners.DiscussionFindings demonstrate a risk of disproportionate focus on possible benefits of testing among amyloid scan candidates and suggest a need to clearly emphasize the limitations of amyloid PET when counseling cognitively impaired patients and their families before testing. Future research should examine whether minimizing drawbacks at the preâimaging stage has adverse consequences on results disclosure.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/152635/1/dad2jdadm201805003.pd
Isocurvature Fluctuations in Tracker Quintessence Models
We consider effects of the isocurvature perturbation in the framework of the
tracker-type quintessence models. During the inflation, fluctuations in the
amplitude of the quintessence field are generated, which provide isocurvature
component of the cosmic density perturbation. Contrary to the conventional
notion, it is shown that effects of the isocurvature fluctuation may become
sizable in some cases, and in particular, the cosmic microwave background
angular power spectrum may be significantly enhanced due to the effect of the
isocurvature mode. Such an enhancement may be detectable in on-going and future
experiments.Comment: 15 pages, 5 figures. Discussion on the scale dependence of the
isocurvature mode is changed. Figures are revise
Deep learning-based optimization for reconfigurable intelligent surface-assisted communications
Proceedings of: 2022 IEEE Wireless Communications and Networking Conference (WCNC), 10-13 April 2022, Austin, USA.Reconfigurable Intelligent Surfaces (RISs) are an emerging technology in the evolution towards the Sixth Generation (6G) of mobile communications. They are capable of enhancing the overall system performance and extending the coverage of the existing cells. They are built by a large amount of low-cost meta-elements that can be configured by tuning their phase shifts, and hence, the channel response can be constructively combined and forwarded to some specific direction. Many algorithms have been proposed to obtain the optimum phase shifts, generally assuming a single-carrier system and/or a medium-size RIS to constrain the complexity of the optimization process. In this work, we propose a flexible and scalable unsupervised learning model, capable of obtaining the best phase shifts for any scenario. Our proposal is able to handle multi-carrier waveforms and very large-size RIS, considering both continuous and discrete phase shifts. Besides, we also propose the use of clustering to reduce further the complexity while maintaining the performance. A comparison in terms of achievable rate and time execution is provided in order to show the superiority of our proposal against the existing solutions.This work has been funded by the Spanish National projects IRENE-EARTH (PID2020-115323RB-C33 / AEI/ 10.13039/501100011033) and AMATISTA (CDTI IDI20200861)
Intermediate-Mass Black Holes in Globular Clusters
There have been reports of possible detections of intermediate-mass black
holes (IMBHs) in globular clusters (GCs). Empirically, there exists a tight
correlation between the central supermassive black hole (SMBH) mass and the
mean velocity dispersion of elliptical galaxies, "pseudobulges" and classical
bulges of spiral galaxies. We explore such a possible correlation for IMBHs in
spherical GCs. In our model of self-similar general polytropic quasi-static
dynamic evolution of GCs, a criterion of forming an IMBH is proposed. The key
result is M(BH) = L o^1/(1-n) where M(BH) is the IMBH mass, o is the GC mean
stellar velocity, L is a coefficient, and 2/3 < n < 1
Phantom-Like Behavior in -Gravity
We investigate possible realization of the phantom-like behavior in the
framework of -gravity models where there are no phantom fields in the
matter sector of the theory. By adopting some observationally reliable ansatz
for , we show that it is possible to realize phantom-like behavior in
-gravity without introduction of phantom fields that suffer from
instabilities and violation of the null energy condition. Depending on the
choice of , the null energy condition is fulfilled in some subspaces of
each model parameter space.Comment: 14 pages, Revised Version, To appear in PL
Probing neutrino masses with future galaxy redshift surveys
We perform a new study of future sensitivities of galaxy redshift surveys to
the free-streaming effect caused by neutrino masses, adding the information on
cosmological parameters from measurements of primary anisotropies of the cosmic
microwave background (CMB). Our reference cosmological scenario has nine
parameters and three different neutrino masses, with a hierarchy imposed by
oscillation experiments. Within the present decade, the combination of the
Sloan Digital Sky Survey (SDSS) and CMB data from the PLANCK experiment will
have a 2-sigma detection threshold on the total neutrino mass close to 0.2 eV.
This estimate is robust against the inclusion of extra free parameters in the
reference cosmological model. On a longer term, the next generation of
experiments may reach values of order sum m_nu = 0.1 eV at 2-sigma, or better
if a galaxy redshift survey significantly larger than SDSS is completed. We
also discuss how the small changes on the free-streaming scales in the normal
and inverted hierarchy schemes are translated into the expected errors from
future cosmological data.Comment: 14 pages, 7 figures. Added results with the KAOS proposal and 1
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