稳定机床制动性能,提高生产效率——机床主轴制动的改造

机床工作时按操作者意图的理想状态是该停即停、该动即动。本文从电磁制动的驱动电路入手,通过机床主轴制动的改造,提高制动的速度与稳定性,避免抱死。

Mechanism of Downcutting Erosion of Debris Flow over a Movable Bed

The phenomenon of debris flow is intermediate between mass movement and solid transport. Flows can be sudden, severe and destructive. Understanding debris flow erosion processes is the key to providing geomorphic explanations, but progress has been limited because the physical-mechanical properties, movement laws and erosion characteristics are different from those of sediment-laden flow. Using infinite slope theory, this research examines the process and mechanism of downcutting erosion over a moveable bed in a viscous debris flow gully. It focuses specifically on the scour depth and the critical slope for viscous debris flow,and formulas for both calculations are presented.Both scour depth and the critical conditions of downcutting erosion are related to debris flow properties(sand volume concentration and flow depth) and gully properties(longitudinal slope,viscous and internal friction angle of gully materials,and coefficient of kinetic friction). In addition, a series of flume experiments was carried out to characterize the scouring process of debris flows with different properties. The calculated values agreed well with the experimental data. These theoretical formulas are reasonable, and using infinite slope theory to analyze down cutting erosion from viscous debris flow is feasible.

Anomalous origin of left pulmonary artery branch from the aorta with Fallot's tetralogy:one case report

We report the case of a ten-year-old boy who had often presented with respiratory distress since born. Chest X-ray showed an enlarged right ventricle. Echocardiography demonstrated characteristic features of Fallot＇s tetralogy and the left pulmonary artery could not be visualized. However, cardiac catheterization disclosed that the left pulmonary artery had an anomalous origin in the ascending aorta. The patient underwent total surgical correction of the defects. Nine days later, he was discharged. We present the results of a literature review of the incidence, physiopathological, clinical, diagnostic, and surgical characteristics of this rare disease.

Aortic stenosis： insights on pathogenesis and clinical implications

Aortic stenosis （AS） is a common valvular heart disease in the Western populations, with an estimated overall prevalence of 3% in adults over 75 years. To understand its patho-biological processes represents a priority. In elderly patients, AS usually involves trileaflet valves and is referred to as degenerative calcific processes. Scientific evidence suggests the involvement of an active ＂atherosclerosis-like＂ pathogenesis in the initiation phase of degenerative AS. To the contrary, the progression could be driven by different forces （such as mechanical stress, genetic factors and interaction between inflammation and calcification）. The improved understanding presents potentially new therapeutic targets for preventing and inhibiting the development and progression of the disease. Furthermore, in clinical practice the management of AS patients implies the evaluation of generalized atherosclerotic manifestations （i.e., in the coronary and carotid arteries） even for prognostic reasons. In counselling elderly patients, the risk stratification should address individual frailty beyond the generic risk scores. In these regard, the co-morbidities, and in particular those linked to the global atherosclerotic burden, should be carefully investigated in order to define the risk/benefit ratio for invasive treatment strategies. We present a detailed overview of insights in pathogenesis of AS with possible practical implications.

Postprandial transduodenal bolus transport is regulated by complex peristaltic sequence

AIM: To study the relationship between the patterns of postprandial peristalsis and transduodenal bolus transport in healthy subjects. METHODS: Synchronous recording of chyme transport and peristaltic activity was performed during the fasting state and after administration of a test meal using a special catheter device with cascade configuration of impedance electrodes and solid-state pressure transducers. The catheter was placed into the duodenum, where the f irst channel was located in the f irst part of the duodenum and the last channel at the duodenojejunal junction. After identif ication of previously def ined chyme transport patterns the associated peristaltic patterns were analyzed. RESULTS: The interdigestive phase 3 complex was reliably recorded with both techniques. Of 497 analyzed impedance bolus transport events, 110 (22%) were short-spanned propulsive, 307 (62%) long-spanned propulsive, 70 (14%) complex propulsive, and 10 (2%) retrograde transport. Short-spanned chyme transports were predominantly associated with stationary or propagated contractions propagated over short distance. Long-spanned and complex chyme transports were predominantly associated with propulsive peristaltic patterns, which were frequently complex and comprised multiple contractions. Propagated double wave contraction, propagated contraction with a clustered contraction, and propagated cluster of contractions have been identif ied to be an integralted part of a peristaltic sequence in human duodenum. CONCLUSION: Combined impedancometry and manometry improves the analysis of the peristaltic patterns that are associated with postprandial transduodenal chymetransport. Postprandial transduodenal bolus transport is regulated by propulsive peristaltic patterns, which are frequently complex but well organized. This f inding should be taken into consideration in the analysis of intestinal motility studies.

A numerical error analysis method and its application on a 4RRR parallel kinematic machine

To guarantee the accuracy of error analysis and evaluate the manufacturing tolerance s influence,anumerical error analysis method for parallel kinematic machines (PKMs) is presented in this paper.Quasi-Newton method and genetic algorithm are introduced for the forward kinematic solution.Based onthe inverse and forward kinematic solutions,the end-effector s error calculation procedure is developed.To solve the accuracy problem caused by the length and angular parameters' different units,a normalizationmethod is proposed based on the manufacturing tolerance.Comparison between the error analysis resultscalculated by the traditional method and the numerical method for a 4RRR PKM shows that,this numericalerror analysis method is more accurate,simpler,and can evaluate the machine s real error basedon the manufacturing tolerance.

Roles and mechanisms of ginsenoside in cardiovascular diseases: progress and perspectives

Ginseng is among the oldest traditional Chinese medicinal herbs and is widely used in China and Southeast Asia. Over the past 50 years, considerable research has focused on the chemical constituents, pharmacological action, and clinical applications of ginseng. In this review, we examine the current state of research on ginseng, including the main active ingredient ginsenoside, its pharmacological effects on the cardiovascular system, and mechanisms of action. We focus on what is known of the effects of ginseng against atherosclerosis, arrhythmia, myocardial ischemia, and its inhibition of ventricular remodeling, providing a basis for expanding the clinical applications of ginseng.