824 research outputs found
The negative BOLD response as a marker of the seizure onset zone
Epilepsy is a neurological disease affecting 70 million people worldwide. For most individuals, these seizures can be controlled using medications, however nearly 1 in 3 people may need surgery to achieve seizure freedom. For this surgery to be successful, the brain region generating the seizures, which contains the critical seizure onset zone (SOZ), must be accurately identified and removed. Unfortunately, the surgical success rate is low likely due to imprecise determination of the SOZ. As a novel approach to SOZ identification, the collection of intracranial electroencephalography and functional magnetic resonance imaging (iEEG-fMRI) has been proposed as a novel method of identifying the SOZ. However, iEEG-fMRI faces the methodological challenge of artifact introduced from MR scanning which completely obscures the physiological EEG signal. Therefore, the first step towards bringing iEEG-fMRI into the clinical realm is to improve methods for extracting the physiological EEG signal from the iEEG-fMRI data. To this end, the first study in this thesis validated a set of methods aimed at removing fMRI artifact from iEEG, culminating in the creation of the first automatic iEEG pre-processing pipeline. The next step towards clinical utility for iEEG-fMRI is improving our interpretation of iEEG-fMRI results. Traditionally, only positive IED related fMRI activation maps were considered in relation to SOZ localization, and the negative response was ignored. It has been suggested that both positive and negative activation maps should be considered, and the maximal cluster of these two maps, regardless of polarity, should be used to localize the SOZ. In the second study, the concept was tested using iEEG-fMRI and it was found that the use of the maximal negative cluster had limited utility for SOZ localization. The results of this thesis provide a new method for preparing EEG data from iEEG-fMRI experiments and it shows that the bulk of maximal negative fMRI clusters have limited reliability for clinical applications
Detection of off-pulse emission from PSR B0525+21 and PSR B2045-16
We report the detection of off-pulse emission from two long period pulsars
PSR B0525+21 and PSR B2045-16 using the Giant Metrewave Radio Telescope (GMRT).
We recorded high time resolution interferometric data at 325 MHz and gated the
data offline to separate the on- and off-pulse sections of the pulsar. On
imaging the two temporal sections separately, we detected a point source in the
off-pulse images of both the pulsars coincident with the pulsar locations in
the on-pulse images. The long periods (3.75 and 1.96 s respectively) and low
spin-down energies (E ~ 10exp(31) erg s-1) of the two pulsars argue against a
pulsar wind nebula (PWN) origin for the off-pulse emission. The derived
estimates of the ISM particle density required to drive a PWN do not support
such an interpretation. A magnetospheric origin for the off-pulse emission
raises questions regarding the location of the emission region, which is an
important input into pulsar emission models.Comment: 15 pages, 11 figure
Effects of anesthetic and sedative agents on sympathetic nerve activity
Background
The effects of sedative and anesthetic agents on sympathetic nerve activity (SNA) are poorly understood.
Objective
The purpose of this study was to determine the effects of commonly used sedative and anesthetic agents on SNA in ambulatory dogs and humans.
Methods
We implanted radiotransmitters in 6 dogs to record stellate ganglion nerve activity (SGNA), subcutaneous nerve activity (ScNA), and blood pressure (BP). After recovery, we injected dexmedetomidine (3 μg/kg), morphine (0.1 mg/kg), hydromorphone (0.05 mg/kg), and midazolam (0.1 mg/kg) on different days. We also studied 12 human patients (10 male; age 68.0 ± 9.1 years old) undergoing cardioversion for atrial fibrillation with propofol (0.77 ± 0.18 mg/kg) or methohexital (0.65 mg/kg) anesthesia. Skin sympathetic nerve activity (SKNA) and electrocardiogram were recorded during the study.
Results
SGNA and ScNA were significantly suppressed immediately after administration of dexmedetomidine (P = .000 and P = .000, respectively), morphine (P = .011 and P = .014, respectively), and hydromorphone (P = .000 and P = .012, respectively), along with decreased BP and heart rate (HR) (P <.001 for each). Midazolam had no significant effect on SGNA and ScNA (P = .248 and P = .149, respectively) but increased HR (P = .015) and decreased BP (P = .004) in ambulatory dogs. In patients undergoing cardioversion, bolus propofol administration significantly suppressed SKNA (from 1.11 ± 0.25 μV to 0.77 ± 0.15 μV; P = .001), and the effects lasted for at least 10 minutes after the final cardioversion shock. Methohexital decreased chest SKNA from 1.59 ± 0.45 μV to 1.22 ± 0.58 μV (P = .000) and arm SKNA from 0.76 ± 0.43 μV to 0.55 ± 0.07 μV (P = .001). The effects lasted for at least 10 minutes after the cardioversion shock.
Conclusion
Propofol, methohexital, dexmedetomidine, morphine, and hydromorphone suppressed, but midazolam had no significant effects on, SNA
The nature of pulsar radio emission
High-quality averaged radio profiles of some pulsars exhibit double, highly
symmetric features both in emission and absorption. It is shown that both types
of features are produced by a split-fan beam of extraordinary-mode curvature
radiation (CR) that is emitted/absorbed by radially-extended streams of
magnetospheric plasma. With no emissivity in the plane of the stream, such a
beam produces bifurcated emission components (BFCs) when our line of sight
passes through the plane. A distinct example of double component created in
that way is present in averaged profile of the 5 ms pulsar J1012+5307. We show
that the component can indeed be very well fitted by the textbook formula for
the non-coherent beam of curvature radiation in the polarisation state that is
orthogonal to the plane of electron trajectory. The observed width of the BFC
decreases with increasing frequency at the rate that confirms the curvature
origin. Likewise, the double absorption features (double notches) are produced
by the same beam of the extraordinary-mode CR, when it is eclipsed by thin
plasma streams. The intrinsic property of CR to create bifurcated fan beams
explains the double features in terms of very natural geometry and implies the
curvature origin of pulsar radio emission. (abbreviated)Comment: 16 pages, 18 figures, accepted by MNRAS after minor revisio
A model for double notches and bifurcated components in radio profiles of pulsars and magnetars - Evidence for the parallel acceleration maser in pulsar magnetosphere
Averaged pulse profiles of three nearby pulsars: B1929+10, J0437-4715 and
B0950+08 exhibit unusual `double notches'. These W-like looking features
consist of two adjacent V-shaped dips that approach each other at increasing
observation frequency nuobs roughly at a rate sep \propto nuobs^{-1/2}, where
sep is the separation between the notches' minima. We show that basic
properties of the notches, namely their W-like look and the rate of their
converging can be understood within a narrow class of models of coherent radio
emission from pulsars: the free electron maser models based on coherent inverse
Compton scattering of parallel oscillations of ambient electric field. The
observed properties of the pulsars imply that the Fourier spectrum of the
wiggler-like oscillations is narrow and that the broad-band character of the
radio emission reflects the width of the electron energy distribution. Such a
model provides a natural explanation for the frequency-independent separation
between the main pulse and interpulse of B0950+08 as well as for the lack of
radius to frequency mapping in the conal-like emission of J0437-4715. The
frequency behaviour of the main pulse in the profile of the first radio
magnetar XTE J1810-197 can also be explained within this model.Comment: 15 pages, 10 figures, accepted by A&A after minor change
Type IIb Supernova SN 2011dh: Spectra and Photometry from the Ultraviolet to the Near-Infrared
We report spectroscopic and photometric observations of the Type IIb SN
2011dh obtained between 4 and 34 days after the estimated date of explosion
(May 31.5 UT). The data cover a wide wavelength range from 2,000 Angstroms in
the UV to 2.4 microns in the NIR. Optical spectra provide line profiles and
velocity measurements of HI, HeI, CaII and FeII that trace the composition and
kinematics of the SN. NIR spectra show that helium is present in the atmosphere
as early as 11 days after the explosion. A UV spectrum obtained with the STIS
reveals that the UV flux for SN 2011dh is low compared to other SN IIb. The HI
and HeI velocities in SN 2011dh are separated by about 4,000 km/s at all
phases. We estimate that the H-shell of SN 2011dh is about 8 times less massive
than the shell of SN 1993J and about 3 times more massive than the shell of SN
2008ax. Light curves (LC) for twelve passbands are presented. The maximum
bolometric luminosity of erg s occurred
about 22 days after the explosion. NIR emission provides more than 30% of the
total bolometric flux at the beginning of our observations and increases to
nearly 50% of the total by day 34. The UV produces 16% of the total flux on day
4, 5% on day 9 and 1% on day 34. We compare the bolometric light curves of SN
2011dh, SN 2008ax and SN 1993J. The LC are very different for the first twelve
days after the explosions but all three SN IIb display similar peak
luminosities, times of peak, decline rates and colors after maximum. This
suggests that the progenitors of these SN IIb may have had similar compositions
and masses but they exploded inside hydrogen shells that that have a wide range
of masses. The detailed observations presented here will help evaluate
theoretical models for this supernova and lead to a better understanding of SN
IIb.Comment: 23 pages, 14 figures, 9 tables, accepted by Ap
NLTT 41135: a field M-dwarf + brown dwarf eclipsing binary in a triple system, discovered by the MEarth observatory
We report the discovery of an eclipsing companion to NLTT 41135, a nearby M5
dwarf that was already known to have a wider, slightly more massive common
proper motion companion, NLTT 41136, at 2.4 arcsec separation. Analysis of
combined-light and radial velocity curves of the system indicates that NLTT
41135B is a 31-34 +/- 3 MJup brown dwarf (where the range depends on the
unknown metallicity of the host star) on a circular orbit. The visual M-dwarf
pair appears to be physically bound, so the system forms a hierarchical triple,
with masses approximately in the ratio 8:6:1. The eclipses are grazing,
preventing an unambiguous measurement of the secondary radius, but follow-up
observations of the secondary eclipse (e.g. with the James Webb Space
Telescope) could permit measurements of the surface brightness ratio between
the two objects, and thus place constraints on models of brown dwarfs.Comment: 15 pages, 6 figures, 10 tables, emulateapj format. Accepted for
publication in Ap
Kepler-432: a red giant interacting with one of its two long period giant planets
We report the discovery of Kepler-432b, a giant planet ()
transiting an evolved star with an orbital period of days. Radial velocities (RVs) reveal that
Kepler-432b orbits its parent star with an eccentricity of , which we also measure independently with
asterodensity profiling (AP; ), thereby confirming
the validity of AP on this particular evolved star. The well-determined
planetary properties and unusually large mass also make this planet an
important benchmark for theoretical models of super-Jupiter formation.
Long-term RV monitoring detected the presence of a non-transiting outer planet
(Kepler-432c; days), and adaptive optics imaging revealed a nearby
(0\farcs87), faint companion (Kepler-432B) that is a physically bound M dwarf.
The host star exhibits high signal-to-noise asteroseismic oscillations, which
enable precise measurements of the stellar mass, radius and age. Analysis of
the rotational splitting of the oscillation modes additionally reveals the
stellar spin axis to be nearly edge-on, which suggests that the stellar spin is
likely well-aligned with the orbit of the transiting planet. Despite its long
period, the obliquity of the 52.5-day orbit may have been shaped by star-planet
interaction in a manner similar to hot Jupiter systems, and we present
observational and theoretical evidence to support this scenario. Finally, as a
short-period outlier among giant planets orbiting giant stars, study of
Kepler-432b may help explain the distribution of massive planets orbiting giant
stars interior to 1 AU.Comment: 22 pages, 19 figures, 5 tables. Accepted to ApJ on Jan 24, 2015
(submitted Nov 11, 2014). Updated with minor changes to match published
versio
Surface stresses on a thin shell surrounding a traversable wormhole
We match an interior solution of a spherically symmetric traversable wormhole
to a unique exterior vacuum solution, with a generic cosmological constant, at
a junction interface, and the surface stresses on the thin shell are deduced.
In the spirit of minimizing the usage of exotic matter we determine regions in
which the weak and null energy conditions are satisfied on the junction
surface. The characteristics and several physical properties of the surface
stresses are explored, namely, regions where the sign of the tangential surface
pressure is positive and negative (surface tension) are determined. This is
done by expressing the tangential surface pressure as a function of several
parameters, namely, that of the matching radius, the redshift parameter, the
surface energy density and of the generic cosmological constant. An equation
governing the behavior of the radial pressure across the junction surface is
also deduced.Comment: 24 pages, 11 figures, LaTeX2e, IOP style files. Accepted for
publication in Classical and Quantum Gravity. V2: Four references added, now
25 page
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