623 research outputs found
Mexiletine-quinidine combination: Electrophysiologic correlates of a favorable antiarrhythmic interaction in humans
Combination therapy with mexiletine and quinidine has been shown to be more effective than either agent alone. The ability of mexiletine monotherapy, quinidine monotherapy and mexiletine-quinidine combination therapy to suppress inducible sustained ventricular tachycardia was related to drug-induced changes in ventricular refractoriness, conduction times and monophasic action potential duration recorded from both ventricles. Ventricular tachycardia could no longer be induced in 7 (35%) of the 20 patients studied with combination therapy. This was a significantly higher proportion of patients than that of the groups responding to either monotherapy (quinidine, 10%; mexiletine, 5%).Ventricular effective and functional refractory periods were measured when applying single (S2), double (S3) and triple (S4) extrastimuli. Quinidine monotherapy increased functional and effective refractory periods of both single and multiple extrastimuli. However, when comparing measurements made during mexiletine treatment with those at baseline, mexiletine monotherapy increased only the refractory periods of S4. The effective refractory period of S4 during mexiletine monotherapy (200 ± 20 ins) was significantly longer than at baseline (160 ± 21 ms). Similarly, when comparing measurements made during combination therapy with those during quinidine monotherapy, combination therapy significantly increased the refractory periods only of multiple extrastimuli. The effective refractory period of S4 during combination therapy (253 ± 26 ms) was significantly longer than that of quinidine monotherapy (223 ± 27 ms). The only other significant difference between combination therapy and monotherapy with either agent was a greater prolongation of conduction time to the left ventricular dyskinetic zone with combination therapy.Therefore, mexiletine-quinidine combination therapy is associated with additional prolongation of the refractory periods of multiple extrastimuli and with further prolongation of conduction into the dyskinetic zone of the left ventricle. These electrophysiologic effects may be markers of enhanced antiarrhythmic activity
Identification and control of American germander
1 online resource (PDF, 2 pages)This archival publication may not reflect current scientific knowledge or recommendations. Current information available from the University of Minnesota Extension: https://www.extension.umn.edu
High resolution infrared spectra of bulge globular clusters: Liller~1 and NGC 6553
Using the NIRSPEC spectrograph at Keck II, we have obtained echelle spectra
covering the range 1.5-1.8um for 2 of the brightest giants in Liller 1 and NGC
6553, old metal rich globular clusters in the Galactic bulge. We use spectrum
synthesis for the abundance analysis, and find [Fe/H]=-0.3 +/- 0.2 and
[O/H]=+0.3 +/- 0.2 dex. The composition of the clusters is similar to that of
field stars in the bulge and is consistent with a sceanrio in which the
clusters formed early, with rapid enrichment. We have dificulty achieveing a
good fit to the spectrum of NGC 6553 using either the low or the high values
recently reported in the literature, unless unusually large, or no
alpha-element enhancements are adopted, respectively.Comment: To appear in the Astronomical Journal, March 200
The Accretion of Lyman Alplha Clouds onto Gas-Rech Protogalaxies; A Scenario for the Formation of Globular Star Clusters
A satisfactory theory for the formation of globular star clusters (GCs) has
long been elusive, perhaps because their true progenitors had not yet been
guessed. In this paper I propose a causal relationship between the strongly
decreasing densities of Lyman alpha (LyA) clouds at high redshift and the
formation of GCs - namely that GCs were created by the accretion of LyA clouds
onto protogalaxies. I describe a scenario which involves an inherently stable
and orderly cycling of compression and cooling in the central cores of clouds
during the extended period of dissipation in the outer regins of gas-rich proto
galaxies, culminating in a burst of efficient star formation. I demonstrate
that the comoving density of GCs is comparable to that of LyA clouds at high
redshift, that the energetic requirements for compression to core GC densities
can be met, and that the time-scale for cooling is within obvious limits
imposed by dynamical stability.
This dissipative process requires there to be a large column of dissipated
gas about the attractor in order to form GCs. In addition, the energy
requirements for compression requires attractor masses greater than that
capable of sustaining circular velocities of ~40 km/s. If this scenario is
supported by numerical simulations, then by implication, the GCs were formed at
modest redshifts of z~1-3. This knowledge could help to break the degeneracy
between lookback time and redshift. The model is consistent with a picture of
hierarchical galaxy growth over time scales of many billions of years.Comment: 7 pages. Accepted, 10 June 1999 Astrophysical Journa
APASS Landolt-Sloan BVgri photometry of RAVE stars. I. Data, effective temperatures and reddenings
We provide APASS photometry in the Landolt BV and Sloan g'r'i' bands for all
the 425,743 stars included in the latest 4th RAVE Data Release. The internal
accuracy of the APASS photometry of RAVE stars, expressed as error of the mean
of data obtained and separately calibrated over a median of 4 distinct
observing epochs and distributed between 2009 and 2013, is 0.013, 0.012, 0.012,
0.014 and 0.021 mag for B, V, g', r' and i' band, respectively. The equally
high external accuracy of APASS photometry has been verified on secondary
Landolt and Sloan photometric standard stars not involved in the APASS
calibration process, and on a large body of literature data on field and
cluster stars, confirming the absence of offsets and trends. Compared with the
Carlsberg Meridian Catalog (CMC-15), APASS astrometry of RAVE stars is accurate
to a median value of 0.098 arcsec. Brightness distribution functions for the
RAVE stars have been derived in all bands. APASS photometry of RAVE stars,
augmented by 2MASS JHK infrared data, has been chi2 fitted to a densely
populated synthetic photometric library designed to widely explore in
temperature, surface gravity, metallicity and reddening. Resulting Teff and
E(B-V), computed over a range of options, are provided and discussed, and will
be kept updated in response to future APASS and RAVE data releases. In the
process it is found that the reddening caused by an homogeneous slab of dust,
extending for 140 pc on either side of the Galactic plane and responsible for
E(B-V,poles)=0.036 +/- 0.002 at the galactic poles, is a suitable approximation
of the actual reddening encountered at Galactic latitudes |b|>=25 deg.Comment: Astronomical Journal, in press. Resolution of Figures degrated to
match arXiv file size limit
ISOGAL-DENIS detection of red giants with weak mass loss in the Galactic Bulge
The ISOGAL project is a survey of the stellar populations, structure, and
recent star formation history of the inner disk and bulge of the Galaxy. ISOGAL
combines 15 and 7micron ISOCAM observations with DENIS IJKs data to determine
the nature of a source and the interstellar extinction. In this paper we report
an ISOGAL study of a small field in the inner Galactic Bulge (l=0deg, b=1.0deg,
area=0.035 sq. deg) as a prototype of the larger area ISOGAL survey of the
inner Galaxy. The five wavelengths of ISOGAL+DENIS, together with the
relatively low and constant extinction in front of this specific field, allow
reliable determination of the nature of the sources. The primary scientific
result of this paper is evidence that the most numerous class of ISOGAL
15micron sources are Red Giants in the Galactic bulge and central disk, with
luminosities just above or close to the RGB tip and weak mass-loss rates. They
form loose sequences in the magnitude-colour diagrams [15]/Ks-[15] and
[15]/[7]-[15]. Their large excesses at 15micron with respect to 2micron and
7micron is due to circumstellar dust produced by mass-loss at low rates. These
ISOGAL results are the first systematic evidence and study of dust emission at
this early stage (''Intermediate'' AGB), before the onset of the large
mass-loss phase. It is thus well established that efficient dust formation is
already associated with such low mass-loss rates during this early phase.Comment: 15 pages, 9 figures, accepted for publication in Astronomy and
Astrophysics Journa
An inverse method to interpret colour-magnitude diagrams
An inverse method is developed to determine the star formation history, the
age-metallicity relation, and the IMF slope from a colour-magnitude diagram.
The method is applied to the Hipparcos HR diagram. We found that the thin
disk of our Galaxy shows a peak of stellar formation 1.6 Gyr ago. The stars
close to the Sun have a solar metallicity and a mean IMF index equal to 3.2.
However, the model and the evolutionary tracks do not correctly reproduce the
horizontal giant branch.Comment: 14 pages, 11 figures. To be published in Astronomy & Astrophysic
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