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1.
2.
D. Grant Richards Kevin G. Whithear Peter C. Scott Robin B. Gasser 《Acta parasitologica / Witold Stefański Institute of Parasitology, Warszawa, Poland》2006,51(2):156-159
Coccidiosis of chickens, caused by species of Eimeria (Protozoa, Apicomplexa), is an intestinal disease of major economic importance worldwide. In the present study, the reproductive
characteristics of a precocious line (designated E. tenella Rt3+15) from Australia were investigated in chicken embryos and the implications of the findings briefly discussed. 相似文献
3.
头顶一颗珠地下根茎无性繁殖研究 总被引:1,自引:0,他引:1
头顶一颗珠为国家二类保护植物,又为名贵药材,其根茎无性繁殖比种子有性繁殖缩短生育期2a;从出苗到入药提早12mo;平均单株根茎干重增加6%;无性繁殖系数可达10~12,在生产上有利用价值 相似文献
4.
F.D. CASTILLO M. J. BENSON D. L. WINGATE T. SAMARAS N. M. SPYROU 《Neurogastroenterology and motility》1994,6(1):11-19
Abstract Detection of peristalsis in the human small intestine has been limited in the past by both the available measurement techniques and the complexity of this activity. Recent developments in ambulant recording have provided a means of monitoring the occurrence of intestinal contractions at multiple sites in the small bowel, but the problem of complexity remains. Using digital data recorded from an intra-luminal strain-gauge transducer in the proximal gut, an algorithm was implemented to identify and classify contractile events within the small bowel. By modelling propagated activity the effect of varying transducer spacing and the number of transducers used was assessed. The question of variability of apparent velocity of peristaltic contractions was examined using successive cross-correlation calculations to extract underlying phase differences between samples of 512 minutes of manometric recording over 150 mm of human small bowel. The effective velocity was found to have a median value of 14 mm sec-1 and an inter quartile range of 12–18 mm see-1 ). It is proposed that, in dynamically tracking variations in phase difference between adjacent recording sites, cross-correlation techniques should be used to control the parameters used for the recognition of propagated contractile events and thereby improve the specificity of this process. 相似文献
5.
JORGE M. DAVIDENKO M.D. MARIO DELMAR M.D. Ph .D. JACQUES BEAUMONT Ph .D. DONALD C. MICHAELS Ph .D. PACO LORENTE Ph .D. JOSÉ JALIFE M.D. 《Journal of cardiovascular electrophysiology》1994,5(11):945-960
Inhibition and Facilitation in Cardiac Muscle. Introduction: The effects of subthreshold electrical pulses on the response to subsequent stimulation have been described previously in experimental animal studies as well as in the human heart. In addition, previous studies in cardiac Purkinje fibers have shown that diastolic excitability may decrease after activity (active inhibition) and, to a lesser extent, following subthreshold responses (electrotonic inhibition). However, such dynamic changes in excitability have not been explored in isolated ventricular muscle, and it is uncertain whether similar phenomena may play any role in the activation pal-terns associated with propagation abnormalities in the myocardium. Methods and Results: Experiments were performed in isolated sheep Purkinje fibers and papillary muscles, and in enzymatically dissociated guinea pig ventricular myocytes. In all types of preparations introduction of a conditioning subthreshold pulse between two subthreshold pulses was followed by a transient decay in excitability (electrotonic inhibition). The degree of inhibition was directly related to the amplitude and duration of the conditioning pulse and inversely related to the postconditioning interval. Yet, inhibition could be demonstrated long after (> 1 sec) the end of the conditioning pulse. Electrotonic inhibition was found at all diastolic intervals and did not depend on the presence of a previous action potential. In Purkinje fibers, conditioning action potentials led to active inhibition of subsequent responses. In contrast, in muscle cells, such action potentials had a facilitating effect (active facilitation). Electrotonic inhibition and active facilitation were observed in both sheep ventricular muscle and guinea pig ventricular myocytes. Accordingly, during repetitive stimulation with pulses of barely threshold intensity, we observed: (1) bistability (i.e., with the same stimulating parameters, stimulus: response patterns were either 1:1 or 1:0, depending on previous history), and (2) abrupt transitions between 1:1 and 1:0 (absence of intermediate wenckebach-like patterns). Simulations utilizing an ionic model of cardiac myocytes support the hypothesis that electrotonic inhibition in well-polarized ventricular muscle is the result of partial activation of Ik following subthreshold pulses. On the other hand, active facilitation may be the result of an activity-induced decrease in the conductance of IK1. Conclusion: Diastolic excitability of well-polarized ventricular myocardium may be transiently depressed following local responses and transiently enhanced following action potentials. On the other hand, diastolic excitability decreases during quiescence. Active facilitation and electrotonic inhibition may have an important role in determining the dynamics of excitation of the myocardium in the presence of propagation abnormalities. 相似文献
6.
Propagation of hepatitis A virus in human embryo fibroblasts 总被引:8,自引:0,他引:8
Verena Gauss-Müller Gert G. Frisner Friedrich Deinhardt 《Journal of medical virology》1981,7(3):233-239
human diploid fibroblasts and human primary liver cell carcinoma cells (PLC/PRF/5) were infected with hepatitis A virus (HAV) adapted to growth in cell culture or derived directly from human stool. Viral antigen was expressed in PLC/PRF/5 cells 28 days after infection with cell culture-adapted HAV, and 50 days after infection with virus from human stool. In human fibroblasts the periods until first expression of viral antigen were 90 and 210 days, respectively. During further passages of HAV in fibroblasts the time of first appearance of antigen decreased to about 28 days. Biophysical properties of HAV extracted from infected fibroblasts were comparable to those of HAV derived directly from human stool. Immunofluorescence studies showed that the antigen was located exclusively within the cytoplasm of the infected fibroblasts. Kinetics of antigen production indicated that an equilibrium between virus multiplication and cell metabolism was reached in persistently infected fibroblasts. 相似文献
7.
提倡优生就是防止有遗传疾病和先天畸形婴儿的出生。采取相应的优生措施是做到优生的基本条件。随着人们对优生的愈来愈重视,优生学的研究也取得了越来越多的成就。 相似文献
8.
S. Cheng P. V. Komi H. Kyröläinen D. H. Kim K. Häkkinen 《European journal of applied physiology》1989,59(1-2):128-130
Summary Vibrational wave propagation was tested in vivo on the tibial bone of both legs of 56 female volunteers. The impact was produced
by a hammer with a force strain gauge and the response was monitored by two accelerometers. The peak amplitude of the accelerations,
the velocity of the acceleration wave propagation and damping were analysed for comparison among the different age groups.
The results showed significant negative correlations between age and the peak amplitude of acceleration, and the velocity
of acceleration wave propagation (p<0.01). The damping time of the acceleration wave also had a negative correlation with age. These findings suggested that
age differences were related to the differences in the mechanical properties of bone. With reduction of bone mineral density,
the velocity of the vibrational wave propagation would decrease, with simultaneous increase in impedance. In addition, wave
absorption would be accelerated. It is suggested that this method could be used as an indicator of bone density. The method
could also be developed to provide an index to monitor the progress of osteoporosis.
Visiting research assistant from the Department of Sport Medicine, Chengdu College of Physical Education, Chengdu, People's
Republic of China
Visiting research assistant from Seoul National University, Seoul, South Korea 相似文献
9.
Various investigators have used the monodomain model to study cardiac propagation behaviour. In many cases, the governing
non-linear parabolic equation is solved using the finite-difference method. An adequate discretisation of cardiac tissue with
realistic dimensions, however, often leads to a large model size that is computationally demanding. Recently, it has been
demonstrated, for a two-dimensional homogeneous monodomain, that the Chebyshev pseudospectral method can offer higher computational
efficiency than the finite-difference technique. Here, an extension of the pseudospectral approach to a three-dimensional
inhomogeneous case with fibre rotation is presented. The unknown transmembrane potential is expanded in terms of Chebyshev
polynomial trial functions, and the monodomain equation is enforced at the Gauss-Lobatto node points. The forward Euler technique
is used to advance the solution in time. Numerical results are presented that demonstrate that the Chebyshev pseudospectral
method offered an even larger improvement in computational performance over the finite-difference method in the three-dimensional
case. Specifically, the pseudospectral method allowed the number of nodes to be reduced by ≈85 times, while the same solution
accuracy was maintained. Depending on the model size, simulations were performed with ≈18–41 times less memory and ≈99–169
times less CPU time. 相似文献
10.
A computer model of a one-dimensional cardiac fibre of resistively coupled cells is used to investigate the influence of the
junction resistance on the nature of conduction. The results of the simulations are presented and indicate that the effect
of the junction on both intracellular and extracellular waveshape and on the velocity of propagation depends on the size and
frequency of the coupling resistance and the kinetics of the active membrane. Significant changes in these factors are not
observed without the generation of prepotentials in the action potential upstroke. The absence of this ‘signature’ in microelectrode
recordings of activity in ventricular muscle suggests that under normal conditions cardiac tissue behaves as a functional
syncytium. 相似文献