94 research outputs found
Changes in the cholinergic system of rat sciatic nerve and skeletal muscle following suspension induced disuse
Muscle disused induced changes in the cholinergic system of sciatic nerve, slow twitch soleus (SOL) and fast twitch extensor digitorum longus (EDL) muscle were studied in rats. Rats with hindlimbs suspended for 2 to 3 weeks showed marked elevation in the activity of choline acetyltransferase (ChAT) in sciatic nerve (38%), in SOL (108%) and in EDL (67%). Acetylcholinesterase (AChE) activity in SOL increased by 163% without changing the molecular forms pattern of 4S, 10S, 12S, and 16S. No significant changes in activity and molecular forms pattern of AChE were seen in EDL or in AChE activity of sciatic nerve. Nicotinic receptor binding of 3H-acetylcholine was increased in both muscles. When measured after 3 weeks of hindlimb suspension the normal distribution of type 1 fibers in SOL was reduced and a corresponding increase in type IIa and IIb fibers is seen. In EDL no significant change in fiber proportion is observed. Muscle activity, such as loadbearing, appears to have a greater controlling influence on the characteristics of the slow twitch SOL muscle than upon the fast twitch EDL muscle
The combination of ground-based astrometric compilation catalogues with the HIPPARCOS Catalogue. II. Long-term predictions and short-term predictions
The combination of ground-based astrometric compilation catalogues, such as
the FK5 or the GC, with the results of the ESA Astrometric Satellite HIPPARCOS
produces for many thousands of stars proper motions which are significantly
more accurate than the proper motions derived from the HIPPARCOS observations
alone. In Paper I (Wielen et al. 1999, A&A 347, 1046) we have presented a
method of combination for single stars (SI mode). The present Paper II derives
a combination method which is appropriate for an ensemble of 'apparently
single-stars' which contains undetected astrometric binaries. In this case the
quasi-instantaneously measured HIPPARCOS proper motions and positions are
affected by 'cosmic errors', caused by the orbital motions of the photo-centers
of the undetected binaries with respect to their center-of-mass. In contrast,
the ground-based data are 'mean values' obtained from a long period of
observation. We derive a linear 'long-term prediction' (LTP mode) for epochs
far from the HIPPARCOS epoch T_H ~ 1991.25, and a linear 'short-term
prediction' (STP mode) for epochs close to T_H. The most accurate prediction
for a position at an arbitrary epoch is provided by a smooth, non-linear
transition from the STP solution to the LTP solution. We present an example for
the application of our method, and we discuss the error budget of our method
for the FK6 (a combination of the FK5 with HIPPARCOS) and for the combination
catalog GC+HIP. For the basic fundamental stars, the accuracy of the FK6 proper
motions in the LTP mode is better than that of the HIPPARCOS proper motions
(taking here the cosmic errors into account) by a factor of more than 4.Comment: Slightly revised version. Accepted for publication in Astronomy and
Astrophysic
The search for the origin of the Local Bubble redivivus
We present a new unbiased search and analysis of all B stars in the solar
neighbourhood (within a volume of 400 pc diameter) using the Arivel data base
to track down the remains of the OB associations, which hosted the supernovae
responsible for the Local Bubble in the interstellar gas. We find after careful
dereddening and by comparison with theoretical isochrones, that besides the
Upper Scorpius the Upper Centaurus Lupus and Lower Centaurus Crux subgroups are
the youngest stellar associations in the solar neighbourhood with ages of 20 to
30 Myr, in agreement with previous work. In search for the ``smoking gun'' of
the origin of the Local Bubble, we have traced the paths of the associations
back into the past and found that they entered the present bubble region 10 to
15 Myr ago. We argue that the Local Bubble began to form then and estimate that
14 to 20 supernovae have gone off since. It is shown that the implied energy
input is sufficient to excavate a bubble of the presently observed size.Comment: 10 pages, 8 figures, accepted by Mon. Not. R. Astron. So
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