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91.
李明才 《南京林业大学学报(自然科学版)》1993,17(4):62-65
汽车甩挂运输是先进的公路运输形式之一。从汽车甩挂运输生产工艺的全过程和昼提高车时利用率出发,提出了适合我国目前推行汽车甩挂运输的最佳单程运距为53-100km、133-220km和293-460km。 相似文献
92.
利用部分地考虑能量损失的角关联的改进离子输运双群模型,计算了^4He^+离子垂直入射到C和Cu上的能量沉积参数,改进了早期的离子输运双群模型。 相似文献
93.
采用运行图模拟和理论分析相结合的方法,论证了电气化重载专线维修“天窗”的预留方式,并分析了各种“天窗”的预留方案对输送能力的影响. 相似文献
94.
本文讨论了一类具有一般边界条件的中子迁移方程的适定性.利用Banach空间的锥理论和积分半群理论证明了该方程的具有物理意义的正解的存在唯一性,并且,我们还讨论了相应的迁移算子的本征值的一系列性质. 相似文献
95.
96.
为了估计心脏光学标测过程中不同探测深度对光标测结果的影响,利用电兴奋跨壁传导模型和荧光传输模型,模拟了心室电兴奋跨壁传播时跨膜电位的分布和不同光探测深度的荧光信号,并将深度权重的荧光信号与组织表层细胞的荧光信号做了比较,并分析了产生差异的原因.研究表明:如果大多数荧光来自组织的近表层(小于0.5mm),光探测深度的影响几乎可以忽略;当探测深度增加时(大于等于0.5mm),尤其在螺旋波条件下,两种动作电位在上升时间、幅度和时程上的差异随探测深度的增加而加大,所以需要对以往由心肌表面电标测得到的电生理指标做相应修正. 相似文献
97.
Axonal transport of neurofilaments in normal and disease states 总被引:5,自引:0,他引:5
Miller CC Ackerley S Brownlees J Grierson AJ Jacobsen NJ Thornhill P 《Cellular and molecular life sciences : CMLS》2002,59(2):323-330
Neurofilaments are among the most abundant organelles in neurones. They are synthesised in cell bodies and then transported
into and through axons by a process termed 'slow axonal transport' at a rate that is distinct from that driven by conventional
fast motors. Several recent studies have now demonstrated that this slow rate of transport is actually the consequence of
conventional fast rates of movement that are interrupted by extended pausing. At any one time, most neurofilaments are thus
stationary. Accumulations of neurofilaments are a pathological feature of several human neurodegenerative diseases suggesting
that neurofilament transport is disrupted in disease states. Here, we review recent advances in our understanding of neurofilament
transport in both normal and disease states. Increasing evidence suggests that phosphorylation of neurofilaments is a mechanism
for regulating their transport properties, possibly by promoting their detachment from the motor(s). In some neurodegenerative
diseases, signal transduction mechanisms involving neurofilament kinases and phosphatases may be perturbed leading to disruption
of transport.
Received 11 July 2001; received after revision 30 August 2001; accepted 31 August 2001 相似文献
98.
Horvat A Nikezić G Petrović S Kanazir DT 《Cellular and molecular life sciences : CMLS》2001,58(4):636-644
The subsynaptosomal distribution and specific binding of 17beta-estradiol in vitro to mitochondria isolated from presynaptic nerve endings of female rat brain were examined. 17Beta-estradiol is (i) distributed unequally in synaptosomes and mitochondria posses the highest capacity to bind estradiol with respect to the available amount of the hormone. (ii) Estradiol binds specifically to isolated synaptosomal mitochondria. A Michaelis-Menten plot of specific binding was sigmoidal within a concentration range of 0.1-5 nM of added estradiol, with a saturation plateau at 3 nM. Binding of higher estradiol concentrations demonstrated an exponential Michaelis-Menten plot, indicating non-specific binding to mitochondria. Vmax and Km for the sigmoidal-shape range were estimated as 46 +/- 6 fmol of estradiol/mg of mitochondrial proteins and 0.46 +/- 0.07 nM free estradiol respectively. (iii) Estradiol binding is not affected by the removal of ovaries. The results show that inhibition of Na-dependent Ca2+ efflux from mitochondria by estradiol occurs according to an affinity change of the translocator for Na+, at the same estradiol concentrations that show specific binding to mitochondrial membranes. These data imply that physiological concentrations of estradiol, acting on mitochondrial membrane properties, extragenomically modulate the mitochondrial, and consequently the synaptosomal content of Ca2+, and in that way exert a significant change in nerve cell homeostasis. 相似文献
99.
WANGYutang WENYunyi MANing SHILei 《科学通报(英文版)》2003,48(24):2710-2714
The cardiac protective role of a novel erythro-cyte-derived depressing factor (EDDF) on spontaneous hy-pertensive rats (SHR), calcium overload (CaO) rats and Wistar rats and its mechanism was evaluated. Mean artery pressure (MAP), heart rate (HR) and LVdp/dtmax were measured by physiological recorder. The effect of EDDF on the Ca2+-ATPase activity in myocardial sarcoplasmic reticu-lum (SR) of CaO rats was determined by inorganic phos-phate assay. Calcium transport in myocytes was measured by 45Ca2+ radioactive isotope measurement. The phosphoryla-tion levels of extracellular signal-regulated protein kinases (ERK1/2) in myocardial tissue of SHR and CaO rats were measured by Western blot method. And the ultrastructures of cardiac muscle cells were observed with the transmission electron microscope. The results indicated that EDDF could significantly decrease MAP, HR and LVdp/dtmax in a dose dependent manner (P < 0.05). It seems that the mechanism might relate with activating the Ca2+-APTase, enhancing the uptake and release of Ca2+ from SR (P < 0.05), decreasing the phosphorylation levels of ERK1/2 of myocytes (P < 0.01) and lightening the ultrastructural lesion of cardiac muscle cells. In CaO rats, the Ca2+-ATPase activity decreased clearly com-pared to control (64.99 7.16 vs 94.48 7.68 nmol·min-1 ·mg-1 protein, P < 0.01), while EDDF (100 mg/mL) could significantly increase the activity (87.93 ?9.54 vs 64.99 ?7.16, P < 0.05, n = 7). Both uptake and release rate of Ca2+ (祄ol 45Ca2+/g protein/min) from myocardial SR of CaO rats re-markably decreased compared to control (32.40 ?2.70 and 15.46 ?1.49 vs 61.09 ?10.89 and 25.47 ?4.29, P < 0.05); EDDF (100 mg/mL) could significantly stimulate their activi-ties (50.48 6.76 and 21.76 2.75 vs 32.40 2.70 and 15.46 1.49, P < 0.05). EDDF could evidently down-regulate the phosphorylation of ERK1/2 in myocardial tissue from SHR and CaO rats (P < 0.01), lighten the ultrastructural lesion of cardiac muscle cells of SHR as well. It is concluded that EDDF seems to play protective roles on both structure and function of heart, which closely related with amelioration of Ca2+ transport and inhibition of Ca2+-MAP kinase pathway. 相似文献
100.
Scarborough GA 《Cellular and molecular life sciences : CMLS》2000,57(6):871-883
Living cells require membranes and membrane transporters for the maintenance of life. After decades of biochemical scrutiny, the structures and molecular mechanisms by which membrane transporters catalyze transmembrane solute movements are beginning to be understood. The plasma membrane proton-translocating adenosine triphosphatase (ATPase) is an archetype of the P-type ATPase family of membrane transporters, which are important in a wide variety of cellular processes. The H+-ATPase has been crystallized and its structure determined to a resolution of 8 angstrom in the membrane plane. When considered together with the large body of biochemical information that has been accumulated for this transporter, and for enzymes in general, this new structural information is providing tantalizing insights regarding the molecular mechanism of active ion transport catalyzed by this enzyme. 相似文献