5,690 research outputs found
Characterization of double potentials in human atrial flutter: Studies during transient entrainment
AbstractDouble potentials, defined as atrial electrograms with two discrete deflections per beat separated by an isoelectric interval or a low amplitude baseline, have been observed during right atrial endocardial mapping of human atrial flutter. In this study, bipolar atrial electrograms were recorded during atrial flutter (mean cycle length 235 ± 27 ms [± SEM]) from the high Right atrium, the His bundle region, the coronary sinus and at least 30 right atrial endocardial napping sites in 10 patients. Double potentials were recorded from the right atrium in all patients during atrial flutter.Double potentials were evaluated during transient entrainment of atrial flutter by rapid high right atrial pacing in 5 of the 10 patients. In four of these five patients during such transient entrainment 1) one deflection of the double potential was captured with a relatively short activation time (mean interval 89 ± 45 ms) and the other deflection was captured with a relatively long activation time (mean interval 233 ± 24 ms), producing a paradoxical decrease in the short interdeflection interval from a mean of 75 ± 20 ms to a mean of 59 ± 24 ms; and 2) the configuration of the double potential remained similar to that observed during spontaneous atrial flutter. On pacing termination 1) the two double potential deflections were found to be associated with two different atrial flutter complexes in the electrocardiogram (ECG); 2) the previous double potential deflection relation resumed; and 3) when sinus rhythm was present, the double potentials were replaced by a broad, low amplitude electrogram recording at the same site. These functional double potentials probably represent collision of activation wave fronts in a functional center of the artial flutter reentrant circuit and therefore may serve as a marker for an area of functional block. In one of the five patients, double potentials were recorded from the site during transient entrainment of atrial flutter, during spontaneous atrial flutter and during sinus rhythm. These were called persistent double potentials and were associated with the same atrial flutter complex in the ECG, indicating that not all double potentials recorded during atrial flutter represent the same phenomenon
Passive anaphylaxis and IgE antibody production are compromised in tumor necrosis factor- and in granulocyteâmacrophage colony stimulating factor-deficient mice
ABSTRACTBackgroundA number of recent studies has demonstrated a critical role for mast cells and mast cell-derived cytokines, especially tumour necrosis factor (TNF), in the control of host defense mechanisms during inflammation. In the presesnt study, we investigated whether TNF-deficient (TNFâ/â) and granulocyte-macrophage colony stimulating factor (GM-CSF)-deficient (GM-CSFâ/â) mice expressed defects in normal mast cell function.MethodsBecause the first step in the passive cutaneous anaphylactic (PCA) reaction is fixation of the antibody to mast cells, we tried to obtain a PCA in TNFâ/â and GM-CSFâ/âmice.ResultsWhile an anti-dinitrophenyl IgE monoclonal antibody induced a strong PCA reaction in wild-type mice, it was not possible to obtain a PCA reaction in either TNFâ/â or GM-CSFâ/â mice. We next examined whether mast cells were present in these mice and if so, did they have functional FcΔRI receptors on their surface. The number of mast cells in smears from the peritoneal fluid of the TNFâ/â and GM-CSFâ/â mice was similar to that seen in wild-type mice. However, the expression of FcΔRI on mast cells from the peritoneal fluid of TNFâ/â and GM-CSFâ/â mice, measured by either rosetting assay or FACScan analysis, was compromised compared with wild-type mice. Previous studies have established that defects in FCΔRI expression often have found that IgE production was compromised in both TNFâ/â and GM-CSFâ/â mice.ConclusionsThe observed defects may partially explain the immunodeficiency of these cytokine-deficient animals during infection
Simulations of Galactic Cosmic Ray Impacts on the Herschel/PACS bolometer Arrays with Geant4 Code
The effects of the in-flight behaviour of the bolometer arrays of the
Herschel/PACS instrument under impacts of Galactic cosmic rays are explored.
This instrument is part of the ESA-Herschel payload, which will be launched at
the end of 2008 and will operate at the Lagrangian L2 point of the Sun-Earth
system. We find that the components external to the detectors (the spacecraft,
the cryostat, the PACS box, collectively referred to as the `shield') are the
major source of secondary events affecting the detector behaviour. The impacts
deposit energy on the bolometer chips and influence the behaviour of nearby
pixels. 25% of hits affect the adjacent pixels. The energy deposited raises the
bolometer temperature by a factor ranging from 1 to 6 percent of the nominal
value. We discuss the effects on the observations and compare simulations with
laboratory tests.Comment: Experimental Astronomy, 2008, in pres
Formation of a Massive Black Hole at the Center of the Superbubble in M82
We performed 12CO(1-0), 13CO(1-0), and HCN(1-0) interferometric observations
of the central region (about 450 pc in radius) of M82 with the Nobeyama
Millimeter Array, and have successfully imaged a molecular superbubble and
spurs. The center of the superbubble is clearly shifted from the nucleus by 140
pc. This position is close to that of the massive black hole (BH) of >460 Mo
and the 2.2 micron secondary peak (a luminous supergiant dominated cluster),
which strongly suggests that these objects may be related to the formation of
the superbubble. Consideration of star formation in the cluster based on the
infrared data indicates that (1) energy release from supernovae can account for
the kinetic energy of the superbubble, (2) the total mass of stellar-mass BHs
available for building-up the massive BH may be much higher than 460 Mo, and
(3) it is possible to form the middle-mass BH of 100-1000 Mo within the
timescale of the superbubble. We suggest that the massive BH was produced and
is growing in the intense starburst region.Comment: 9 pages, 3 figures, to appear in ApJ Lette
Interaction and dynamical binding of spin waves or excitons in quantum Hall systems
Interaction between spin waves (or excitons) moving in the lowest Landau
level is studied using numerical diagonalization. Becuse of complicated
statistics obeyed by these composite particles, their effective interaction is
completely different from the dipole-dipole interaction predicted in the model
of independent (bosonic) waves. In particular, spin waves moving in the same
direction attract one another which leads to their dynamical binding. The
interaction pseudopotentials V_[up,up](k) and V_[up,down](k) for two spin waves
with equal wavevectors k and moving in the same or opposite directions have
been calculated and shown to obey power laws V(k) ~ k^alpha at small k. A high
value of alpha_[up,up]~4 explains the occurrence of linear bands in the spin
excitation spectra of quantum Hall droplets.Comment: 6 pages, 4 figures, submitted to PR
Effect of Edge-Preserving Adaptive Image Filter on Low-Contrast Detectability in CT Systems: Application of ROC Analysis
Objective. For the multislice CT (MSCT) systems with a larger
number of detector rows, it is essential to
employ dose-reduction techniques. As reported in
previous studies, edge-preserving adaptive image
filters, which selectively eliminate only the
noise elements that are increased when the
radiation dose is reduced without affecting the
sharpness of images, have been developed. In the
present study, we employed receiver operating
characteristic (ROC) analysis to assess the
effects of the quantum denoising system (QDS),
which is an edge-preserving adaptive filter that we
have developed, on low-contrast resolution, and
to evaluate to what degree the radiation dose
can be reduced while maintaining acceptable
low-contrast resolution.
Materials and Methods. The low-contrast phantoms (Catphan 412) were scanned at various tube current settings, and ROC analysis was then performed for the groups of images obtained with/without the use of QDS at each tube current to determine whether or not a target could be identified. The tube current settings for which the area under the ROC curve (Az value) was approximately 0.7 were determined for both groups of images with/without the use of QDS. Then, the radiation dose reduction ratio when QDS was used was calculated by converting the determined tube current to the radiation dose.
Results. The use of the QDS edge-preserving adaptive image filter allowed the radiation dose to be reduced by up to 38%.
Conclusion. The QDS was found to be useful for reducing the radiation dose without affecting the low-contrast resolution in MSCT studies
Unidentified Infrared Emission Bands in the Diffuse Interstellar Medium
Using the Mid-Infrared Spectrometer on board the Infrared Telescope in Space
and the low-resolution grating spectrometer (PHT-S) on board the Infrared Space
Observatory, we obtained 820 mid-infrared (5 to 12 m) spectra of the
diffuse interstellar medium (DIM) in the Galactic center, W51, and Carina
Nebula regions. These spectra indicate that the emission is dominated by the
unidentified infrared (UIR) emission bands at 6.2, 7.7, 8.6, and 11.2 m.
The relative band intensities (6.2/7.7 m, 8.6/7.7 m, and 11.2/7.7
m) were derived from these spectra, and no systematic variation in these
ratios was found in our observed regions, in spite of the fact that the
incident radiation intensity differs by a factor of 1500. Comparing our results
with the polycyclic aromatic hydrocarbons (PAHs) model for the UIR band
carriers, PAHs in the DIM have no systematic variation in their size
distribution, their degree of dehydrogenation is independent of the strength of
UV radiation field, and they are mostly ionized. The latter finding is
incompatible with past theoretical studies, in which a large fraction of
neutral PAHs is predicted in this kind of environment. A plausible resolution
of this discrepancy is that the recombination coefficients for electron and
large PAH positive ion are by at least an order of magnitude less than those
adopted in past theoretical studies. Because of the very low population of
neutral state molecules, photoelectric emission from interstellar PAHs is
probably not the dominant source of heating of the diffuse interstellar gas.
The present results imply constant physical and chemical properties of the
carriers of the UIR emission bands in the DIM.Comment: 13 pages, 6 figures. Accepted for publication in Ap
NMA CO (J=1-0) Observations of the Halpha/Radio Lobe Galaxy NGC 3079: Gas Dynamics in a Weak Bar Potential and Central Massive Core
within 24 lines with 80 characters) We present ^12CO (1-0) observations in
the central 4.5 kpc (1 arcmin) of the Halpha/Radio lobe galaxy NGC 3079 with
the Nobeyama Millimeter Array. The molecular gas shows four components: a main
disk, spiral arms, a nuclear disk, and a nuclear core. The main disk extends
beyond our spatial coverage. The spiral arms are superimposed on the main disk.
The nuclear disk with about 600 pc radius has an intense concentration of
molecular gas. Its appearance on PV diagrams is indicative of oval motions of
the gas, rather than circular. The nuclear core is more compact than our
resolution. Though it is unresolved, the nuclear core shows a very high
velocity about 200 km/s even at the radius of about 100 pc on the PV diagram.
We propose a model that NGC 3079 contains a weak bar. This model explains the
observed features: the main disk and spiral arms result from gaseous x1-orbits
and associated crowding respectively. The nuclear disk arises from gaseous
x2-orbits. From the appearance of the spiral arms on the PV diagram, the
pattern speed of the bar is estimated to be 55+-10 km/s/kpc. The high velocity
of the nuclear core cannot be explained by our model for a bar. Thus we
attribute it to a central massive core with a dynamical mass of 10^9 Msun
within the central 100 pc. This mass is three orders of magnitude more massive
than that of a central black hole in this galaxy.Comment: 43 pages, 17 figures; ApJ, 573, 105, 200
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