1,576 research outputs found
Experimental study of acoustic displays of flight parameters in a simulated aerospace vehicle
Evaluating acoustic displays of target location in target detection and of flight parameters in simulated aerospace vehicle
Inferring neural dynamics during burst suppression using a neurophysiology-inspired switching state-space model
Burst suppression is an electroencephalography (EEG) pattern associated with
profoundly inactivated brain states characterized by cerebral metabolic
depression. Its distinctive feature is alternation between short temporal
segments of near-isoelectric inactivity (suppressions) and relatively
high-voltage activity (bursts). Prior modeling studies suggest that
burst-suppression EEG is a manifestation of two alternating brain states
associated with consumption (during a burst) and production (during a
suppression) of adenosine triphosphate (ATP). This finding motivates us to
infer latent states characterizing alternating brain states and underlying ATP
kinetics from instantaneous power of multichannel EEG using a switching
state-space model. Our model assumes Gaussian distributed data as a broadcast
network manifestation of one of two global brain states. The two brain states
are allowed to stochastically alternate with transition probabilities that
depend on the instantaneous ATP level, which evolves according to first-order
kinetics. The rate constants governing the ATP kinetics are allowed to vary as
first-order autoregressive processes. Our latent state estimates are determined
from data using a sequential Monte Carlo algorithm. Our
neurophysiology-informed model not only provides unsupervised segmentation of
multi-channel burst-suppression EEG but can also generate additional insights
on the level of brain inactivation during anesthesia.Comment: To appear in the proceedings of the 2020 IEEE Asilomar Conference on
Signals, Systems, and Computer
Reconstruction of extensive air shower images of the first Large Size Telescope prototype of CTA using a novel likelihood technique
Ground-based gamma-ray astronomy aims at reconstructing the energy and
direction of gamma rays from the extensive air showers they initiate in the
atmosphere. Imaging Atmospheric Cherenkov Telescopes (IACT) collect the
Cherenkov light induced by secondary charged particles in extensive air showers
(EAS), creating an image of the shower in a camera positioned in the focal
plane of optical systems. This image is used to evaluate the type, energy and
arrival direction of the primary particle that initiated the shower. This
contribution shows the results of a novel reconstruction method based on
likelihood maximization. The novelty with respect to previous likelihood
reconstruction methods lies in the definition of a likelihood per single camera
pixel, accounting not only for the total measured charge, but also for its
development over time. This leads to more precise reconstruction of shower
images. The method is applied to observations of the Crab Nebula acquired with
the Large Size Telescope prototype (LST-1) deployed at the northern site of the
Cherenkov Telescope Array.Comment: Proceedings of the 37th International Cosmic Ray Conference (ICRC
2021), Berlin, Germany. https://pos.sissa.it/395/71
Quantum Chemistry, Anomalous Dimensions, and the Breakdown of Fermi Liquid Theory in Strongly Correlated Systems
We formulate a local picture of strongly correlated systems as a Feynman sum
over atomic configurations. The hopping amplitudes between these atomic
configurations are identified as the renormalization group charges, which
describe the local physics at different energy scales. For a metallic system
away from half-filling, the fixed point local Hamiltonian is a generalized
Anderson impurity model in the mixed valence regime. There are three types of
fixed points: a coherent Fermi liquid (FL) and two classes of self-similar
(scale invariant) phases which we denote incoherent metallic states (IMS). When
the transitions between the atomic configurations proceed coherently at low
energies, the system is a Fermi liquid. Incoherent transitions between the low
energy atomic configurations characterize the incoherent metallic states. The
initial conditions for the renormalization group flow are determined by the
physics at rather high energy scales. This is the domain of local quantum
chemistry. We use simple quantum chemistry estimates to specify the basin of
attraction of the IMS fixed points.Comment: 12 pages, REVTE
Information Policy Country Report: South Africa
Information policy country report prepared for School of Information 507: Foundations of Information Policy Analysis and Design.http://deepblue.lib.umich.edu/bitstream/2027.42/64841/1/IPOL Country Report - South Africa (2009).pd
Etiology of Burst Suppression EEG Patterns
Burst-suppression electroencephalography (EEG) patterns of electrical activity, characterized by intermittent high-power broad-spectrum oscillations alternating with isoelectricity, have long been observed in the human brain during general anesthesia, hypothermia, coma and early infantile encephalopathy. Recently, commonalities between conditions associated with burst-suppression patterns have led to new insights into the origin of burst-suppression EEG patterns, their effects on the brain, and their use as a therapeutic tool for protection against deleterious neural states. These insights have been further supported by advances in mechanistic modeling of burst suppression. In this Perspective, we review the origins of burst-suppression patterns and use recent insights to weigh evidence in the controversy regarding the extent to which burst-suppression patterns observed during profound anesthetic-induced brain inactivation are associated with adverse clinical outcomes. Whether the clinical intent is to avoid or maintain the brain in a state producing burst-suppression patterns, monitoring and controlling neural activity presents a technical challenge. We discuss recent advances that enable monitoring and control of burst suppression
Superconductivity in the Two-Band Hubbard Model in Infinite Dimensions
We study a two-band Hubbard model in the limit of infinite dimensions, using
a combination of analytical methods and Monte-Carlo techniques. The normal
state is found to display various metal to insulators transitions as a function
of doping and interaction strength. We derive self-consistent equations for the
local Green's functions in the presence of superconducting long-range order,
and extend previous algorithms to this case. We present direct numerical
evidence that in a specific range of parameter space, the normal state is
unstable against a superconducting state characterized by a strongly frequency
dependent order-parameter.Comment: 12 pages (14 figures not included, available upon request), Latex,
LPTENS Preprint 93/1
Compressibility of the Two-Dimensional infinite-U Hubbard Model
We study the interactions between the coherent quasiparticles and the
incoherent Mott-Hubbard excitations and their effects on the low energy
properties in the Hubbard model. Within the framework of a
systematic large-N expansion, these effects first occur in the next to leading
order in 1/N. We calculate the scattering phase shift and the free energy, and
determine the quasiparticle weight Z, mass renormalization, and the
compressibility. It is found that the compressibility is strongly renormalized
and diverges at a critical doping . We discuss the nature
of this zero-temperature phase transition and its connection to phase
separation and superconductivity.Comment: 4 pages, 3 eps figures, final version to appear in Phys. Rev. Let
Prevalence of comorbidities in rheumatoid arthritis and evaluation of their monitoring: results of an international, cross-sectional study (COMORA)
Background: Patients with rheumatoid arthritis (RA) are at increased risk of developing comorbid conditions.<p></p>
Objectives: To evaluate the prevalence of comorbidities and compare their management in RA patients from different countries worldwide.<p></p>
Methods Study design: international, cross-sectional. Patients: consecutive RA patients. Data collected: demographics, disease characteristics (activity, severity, treatment), comorbidities (cardiovascular, infections, cancer, gastrointestinal, pulmonary, osteoporosis and psychiatric disorders).<p></p>
Results: Of 4586 patients recruited in 17 participating countries, 3920 were analysed (age, 56±13 years; disease duration, 10±9 years (mean±SD); female gender, 82%; DAS28 (Disease Activity Score using 28 joints)–erythrocyte sedimentation rate, 3.7±1.6 (mean±SD); Health Assessment Questionnaire, 1.0±0.7 (mean±SD); past or current methotrexate use, 89%; past or current use of biological agents, 39%. The most frequently associated diseases (past or current) were: depression, 15%; asthma, 6.6%; cardiovascular events (myocardial infarction, stroke), 6%; solid malignancies (excluding basal cell carcinoma), 4.5%; chronic obstructive pulmonary disease, 3.5%. High intercountry variability was observed for both the prevalence of comorbidities and the proportion of subjects complying with recommendations for preventing and managing comorbidities. The systematic evaluation of comorbidities in this study detected abnormalities in vital signs, such as elevated blood pressure in 11.2%, and identified conditions that manifest as laboratory test abnormalities, such as hyperglycaemia in 3.3% and hyperlipidaemia in 8.3%.<p></p>
Conclusions: Among RA patients, there is a high prevalence of comorbidities and their risk factors. In this multinational sample, variability among countries was wide, not only in prevalence but also in compliance with recommendations for preventing and managing these comorbidities. Systematic measurement of vital signs and laboratory testing detects otherwise unrecognised comorbid conditions.<p></p>
Overscreened multi-channel SU(N) Kondo model : large-N solution and Conformal Field Theory
The multichannel Kondo model with SU(N) spin symmetry and SU(K) channel
symmetry is considered. The impurity spin is chosen to transform as an
antisymmetric representation of SU(N), corresponding to a fixed number of
Abrikosov fermions . For more
than one channel (K>1), and all values of N and Q, the model displays non-Fermi
behaviour associated with the overscreening of the impurity spin. Universal
low-temperature thermodynamic and transport properties of this non-Fermi liquid
state are computed using conformal field theory methods. A large-N limit of the
model is then considered, in which K/N and Q/N are held fixed. Spectral
densities satisfy coupled integral equations in this limit, corresponding to a
(time-dependent) saddle-point. A low frequency, low-temperature analysis of
these equations reveals universal scaling properties in the variable
, also predicted from conformal invariance. The universal scaling
form is obtained analytically and used to compute the low-temperature universal
properties of the model in the large-N limit, such as the T=0 residual entropy
and residual resistivity, and the critical exponents associated with the
specific heat and susceptibility. The connections with the ``non-crossing
approximation'' and the previous work of Cox and Ruckenstein are discussed.Comment: 39 pages, RevTeX, including 5 figures in encapsulated postscript
forma
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