1,766 research outputs found
Physics of brain dynamics: Fokker-Planck analysis reveals changes in EEG delta-theta interactions in anaesthesia
We use drift and diffusion coefficients to reveal interactions between different oscillatory processes underlying a complex signal and apply the method to EEG delta and theta frequencies in the brain. By analysis of data recorded from rats during anaesthesia, we consider the stability and basins of attraction of fixed points in the phase portrait of the deterministic part of the retrieved stochastic process. We show that different classes of dynamics are associated with deep and light anaesthesia, and we demonstrate that the predominant directionality of the interaction is such that theta drives delt
Discovery and evolution of the new black hole candidate Swift J1539.2-6227 during its 2008 outburst
We report on the discovery by the Swift Gamma-Ray Burst Explorer of the black
hole candidate Swift J1539.2-6227 and the subsequent course of an outburst
beginning in November 2008 and lasting at least seven months. The source was
discovered during normal observations with the Swift Burst Alert Telescope
(BAT) on 2008 November 25. An extended observing campaign with the Rossi X-Ray
Timing Explorer (RXTE) and Swift provided near-daily coverage over 176 days,
giving us a good opportunity to track the evolution of spectral and timing
parameters with fine temporal resolution through a series of spectral states.
The source was first detected in a hard state during which strong low-frequency
quasi-periodic oscillations (QPOs) were detected. The QPOs persisted for about
35 days and a signature of the transition from the hard to soft intermediate
states was seen in the timing data. The source entered a short-lived thermal
state about 40 days after the start of the outburst. There were variations in
spectral hardness as the source flux declined and returned to a hard state at
the end of the outburst. The progression of spectral states and the nature of
the timing features provide strong evidence that Swift J1539.2-6227 is a
candidate black hole in a low-mass X-ray binary system.Comment: Accepted by the Astrophysical Journa
Enhancement of noncontact friction between closely spaced bodies by two-dimensional systems
. We consider the effect of an external bias voltage and the spatial
variation of the surface potential, on the damping of cantilever vibrations.
The electrostatic friction is due to energy losses in the sample created by the
electromagnetic field from the oscillating charges induced on the surface of
the tip by the bias voltage and spatial variation of the surface potential. A
similar effect arises when the tip is oscillating in the electrostatic field
created by charged defects in a dielectric substrate. The electrostatic
friction is compared with the van der Waals friction originating from the
fluctuating electromagnetic field due to quantum and thermal fluctuation of the
current density inside the bodies. We show that the electrostatic and van der
Waals friction can be greatly enhanced if on the surfaces of the sample and the
tip there are two-dimension (2D) systems, e.g. a 2D-electron system or
incommensurate layers of adsorbed ions exhibiting acoustic vibrations. We show
that the damping of the cantilever vibrations due to the electrostatic friction
may be of similar magnitude as the damping observed in recent experiments of
Stipe \textit{et al} [B.C.Stipe, H.J.Mamin, T.D.Stowe, T.W.Kenny, and D.Rugar,
Phys.Rev. Lett.% \textbf{87}, 0982001]. We also show that at short separation
the van der Waals friction may be large enough to be measured experimentally.Comment: 11 pages, 2 figure
Patterns of Adherence to Oral Hypoglycemic Agents and Glucose Control among Primary Care Patients with Type 2 Diabetes
Researchers sought to examine whether there are patterns of oral hypoglycemic-agent adherence among primary-care patients with type 2 diabetes that are related to patient characteristics and clinical outcomes. Longitudinal analysis via growth curve mixture modeling was carried out to classify 180 patients who participated in an adherence intervention according to patterns of adherence to oral hypoglycemic agents across 12 weeks. Three patterns of change in adherence were identified: adherent, increasing adherence, and nonadherent. Global cognition and intervention condition were associated with pattern of change in adherence (p \u3c .05). Patients with an increasing adherence pattern were more likely to have an Hemoglobin A1c) \u3c 7%; adjusted odds ratio = 14.52, 95% CI (2.54, 82.99) at 12 weeks, in comparison with patients with the nonadherent pattern. Identification of patients with type 2 diabetes at risk of nonadherence is important for clinical prognosis and the development and delivery of interventions
A Brief Adherence Intervention that Improved Glycemic Control: Mediation by Patterns of Adherence
This study examined whether longitudinal adherence profiles mediated the relationship between a brief adherence intervention and glycemic control among patients with type 2 diabetes. Adherence was assessed using the Medication Event Monitoring System. Longitudinal analysis via growth curve mixture modeling was carried out to classify patients according to patterns of adherence to oral hypoglycemic agents. Hemoglobin A1c assays were used to measure glycemic control as the clinical outcome. Across the whole sample, longitudinal adherence profiles mediated 35.2% (13.2, 81.0%) of the effect of a brief adherence intervention on glycemic control [from odds ratio (OR) = 8.48, 95% confidence interval (CI) (3.24, 22.2) to 4.00, 95% CI (1.34, 11.93)]. Our results suggest that patients in the intervention had better glycemic control largely due to their greater likelihood of adherence to oral hypoglycemic agents
Patterns of Adherence to Oral Hypoglycemic Agents and Glucose Control among Primary Care Patients with Type 2 Diabetes
Researchers sought to examine whether there are patterns of oral hypoglycemic-agent adherence among primary-care patients with type 2 diabetes that are related to patient characteristics and clinical outcomes. Longitudinal analysis via growth curve mixture modeling was carried out to classify 180 patients who participated in an adherence intervention according to patterns of adherence to oral hypoglycemic agents across 12 weeks. Three patterns of change in adherence were identified: adherent, increasing adherence, and nonadherent. Global cognition and intervention condition were associated with pattern of change in adherence (p \u3c .05). Patients with an increasing adherence pattern were more likely to have an Hemoglobin A1c) \u3c 7%; adjusted odds ratio = 14.52, 95% CI (2.54, 82.99) at 12 weeks, in comparison with patients with the nonadherent pattern. Identification of patients with type 2 diabetes at risk of nonadherence is important for clinical prognosis and the development and delivery of interventions
Free-Boundary Dynamics in Elasto-plastic Amorphous Solids: The Circular Hole Problem
We develop an athermal shear-transformation-zone (STZ) theory of plastic
deformation in spatially inhomogeneous, amorphous solids. Our ultimate goal is
to describe the dynamics of the boundaries of voids or cracks in such systems
when they are subjected to remote, time-dependent tractions. The theory is
illustrated here for the case of a circular hole in an infinite two-dimensional
plate, a highly symmetric situation that allows us to solve much of the problem
analytically. In spite of its special symmetry, this example contains many
general features of systems in which stress is concentrated near free
boundaries and deforms them irreversibly. We depart from conventional
treatments of such problems in two ways. First, the STZ analysis allows us to
keep track of spatially heterogeneous, internal state variables such as the
effective disorder temperature, which determines plastic response to subsequent
loading. Second, we subject the system to stress pulses of finite duration, and
therefore are able to observe elasto-plastic response during both loading and
unloading. We compute the final deformations and residual stresses produced by
these stress pulses. Looking toward more general applications of these results,
we examine the possibility of constructing a boundary-layer theory that might
be useful in less symmetric situations.Comment: 30 pages (preprint format), 9 figure
The X-ray Spectra of Black Hole X-ray Novae in Quiescence as Measured by Chandra
We present Chandra observations of black hole X-ray novae V404 Cyg, A0620-00,
GRO J1655-40 and XTE J1550-564 in quiescence. Their quiescent spectra can be
well fitted by a power-law model with slope . While a coronal
(Raymond-Smith) model is also a statistically acceptable representation of the
spectra, the best fit temperatures of these models is times higher
than that seen in active stellar coronae. These four spectra of quiescent X-ray
novae are all consistent with that expected for accretion via an
advection-dominated accretion flow (ADAF) and inconsistent with that expected
from a stellar corona. This evidence for continued accretion in quiescence
further strengthens the case for the existence of event horizons in black
holes. Both A0620-00 and GRO J1655-40 were fainter than in previous
observations, while V404 Cyg was more luminous and varied by a factor of 2 in a
few ksec. A reanalysis of the X-ray data for XTE J1550-564 shows that (like
V404 Cyg and A0620-00) its luminosity exceeds the maximum prediction of the
coronal model by a large factor. The 0.3-7 keV luminosity of the four sources
studied ranges from erg/s.Comment: 9 pages, 6 figures, accepted for publication in Ap
- …