nature publishing group original contributionsInsomniacs are known to have a higher risk of developing hypertension, but less attention has been focused on patients with hypertension with respect to the further aggravation of the hypertensive states because of poor quality sleep. 1-4 Indeed, a great many of hypertensive patients suffer additional distress because of poorer quality sleep, 5-7 and the degree of poor sleep quality is associated with the severity of the hypertension. [7][8][9][10] These observations suggest the possibility that hypertension and the disrupted sleep might share a common etiology, namely adrenergic overdrive. However, the pathophysiology behind sleep disturbance related to essential hypertension is much less well understood.An association between sympathetic hyperactivity and sleep disturbance has been shown in a rodent model of essential hypertension, spontaneously hypertensive rats (SHR). 11 Compared with normotensive rats, SHR sleeps poorly in terms of fewer episodes, shorter accumulated time and more interruption of quiet sleep (QS; synonymous with non-rapid eye movement sleep), 11 with sympathetic hyperactivity more evident than while awake. The norepinephrine levels are higher in the cerebrospinal fluid of hypertensive patients 12,13 and rats, 14 as well as in some brain areas of SHR. [15][16][17] Norepinephrine is an important monoamine that promotes arousal, and therefore this increased norepinephrine secretion in individuals with essential hypertension might be responsible for not only their elevated blood pressure but also their poorer quality of sleep.Several attempts have been made to investigate the acute effect of adrenergic agonists or antagonists on sleep-wake cycles in normotensive rats; however, the results were inconsistent. 18 In this context, QS time has been found to be prolonged by α1-antagonists and shortened by α1-agonists, 19,20 whereas no consistent modification to QS has been observed the first two authors contributed equally to this paper. BackgroundInadequate sleep may aggravate hypertension, but the pathophysiology of sleep disturbance in hypertension remains unknown. Among spontaneously hypertensive rats (SHr), sleep disturbance co-occurred with sympathetic hyperactivity; therefore, we hypothesized that the sleep disturbance can be alleviated by antagonizing the adrenergic overdrive.
Tool magazine and automatic tool changer is important parts to fulfill the machining center tool reserve and automatic changing of the spindle tool. The reliability of them directly affects the performance of the host. But recently there are no researches on the reliability evaluation methods, so considering this situation, the reliability evaluation researches on CNC machine tools and their main parts at home and abroad are analyzed and concluded. Combining the collected failure data of the circular tool magazine and automatic tool changer, use MTBF (Mean Time between Failures), MTTR (Mean Time To Repair) and the inherent availability index to realize the reliability evaluation of the circular tool magazine and automatic tool changer. Thus put forward a method to study the reliability evaluation of circular tool magazine and automatic tool changer.
As the tool magazine and automatic tool changer (ATC) are the important function units to reserve and change tools for the machining center, the tool-changing rate affects their reliability life which directly influences the performance level of the machining center. However, the reliability of the tool magazine and ATC has not yet got a reasonable evaluation index. Directing at the features of the tool magazine and ATC system, the mean tool change numbers between failures evaluation index is proposed, which is used to calculate the mean time to repair and estimate the collected failure data of the chain-type tool magazine and ATC. It can be seen that the tool magazine with continuous tool-changing adopts the mean tool change numbers between failures as the reliability evaluation index.
According to the existing problems in production planning management mode and management processes of Chinese medium and small manufacture enterprise, referring to the advanced management concept of MRPII/ERP, a master production schedule system which is suitable for management state of Chinese medium and small manufacture enterprise is researched and developed. The operation process, data flow and ER model of the master production schedule system are discussed and researched. Finally, Microsoft vb.net is selected as the development tool of the master production schedule system and Microsoft SQL Server 2000 is used as the database management system, a master production schedule prototype system is designed and implemented.
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