CPU相关概念浅议

CPU由运算器和控制器两部分组成,是英文CentralPro-cessingUnit(中央处理单元)的缩写,是计算机的核心器件。CPU的运算能力和控制能力,一定程度上决定着计算机的运行效率。随着芯片制造技术和指令执行理论的发展,CPU的性能日益提高,从而有力地推动了计算机的发展和普及,有关CPU的概念(术语)也成为我们关注的焦点。正确理解这些概念,对于我们选购和使用计算机都会有很大的帮助。1主频与外频1.1主频主频指的是CPU片内振荡器的振荡频率,计算机的大部分工作以此频率为基准。将此频率分频后成为机器周期脉冲,其周期称为机器周期。计算机中…     

An anthropomorphic multimodality (CT/MRI) head phantom prototype for end-to-end tests in ion radiotherapy

With the increasing complexity of external beam therapy “end-to-end” tests are intended to cover every step from therapy planning through to follow-up in order to fulfill the higher demands on quality assurance. As magnetic resonance imaging (MRI) has become an important part of the treatment process, established phantoms such as the Alderson head cannot fully be used for those tests and novel phantoms have to be developed. Here, we present a feasibility study of a customizable multimodality head phantom. It is initially intended for ion radiotherapy but may also be used in photon therapy.As basis for the anthropomorphic head shape we have used a set of patient computed tomography (CT) images. The phantom recipient consisting of epoxy resin was produced by using a 3D printer. It includes a nasal air cavity, a cranial bone surrogate (based on dipotassium phosphate), a brain surrogate (based on agarose gel), and a surrogate for cerebrospinal fluid (based on distilled water). Furthermore, a volume filled with normoxic dosimetric gel mimicked a tumor.The entire workflow of a proton therapy could be successfully applied to the phantom. CT measurements revealed CT numbers agreeing with reference values for all surrogates in the range from 2 HU to 978 HU (120 kV). MRI showed the desired contrasts between the different phantom materials especially in T2-weighted images (except for the bone surrogate). T2-weighted readout of the polymerization gel dosimeter allowed approximate range verification.     

Increased serum high-density lipoprotein cholesterol in hypertensive men treated with the potent vasodilator carprazidil

The effects of the potent arteriolar vasodilator carprazidil on serum lipoproteins and various clinical, biochemical and endocrine parameters were assessed in 15 men with mild to moderate essential hypertension. Following a carprazidil monotherapy (average dose 50 to 60 mg/d) of 8 weeks (N = 15) or 16 weeks (N = 12) duration, blood pressure was decreased significantly (P less than 0.01), while serum high-density lipoprotein cholesterol (+ 26% and + 24%, respectively; P less than 0.01) and the alpha-lipoprotein fraction (+ 26% and + 41%) were increased. Low- and very low-density lipoprotein cholesterol, triglycerides, as well as mean body weight, blood and plasma volume, heart rate, and plasma renin, aldosterone, norepinephrine, and epinephrine were not consistently altered. These results indicate that treatment of hypertensive men with carprazidil in modest dosage may have a favorable influence both on blood pressure and serum lipoproteins.     

Effect of prolonged exercise on serum lipids and lipoproteins

It has been shown that physical exercise lowers serum triglyceride levels and may increase high density lipoprotein-cholesterol levels. Understanding of the mechanisms responsible for these beneficial adaptations is still incomplete. Twenty-six men, who played soccer continuously for 64 hours to establish a world's record, were monitored for acute changes in lipid metabolism. Food intake was determined before and during the exercise period. Blood specimens were taken before and repeatedly during the match for the measurement of triglycerides (TG), total cholesterol (CH), glycerol, apolipoprotein A-I (apoA-I), and cholesterol in various lipoprotein fractions (quantitative lipoprotein electrophoresis). During exercise TG levels decreased from 116 +/- 26 to 66 +/- 13 mg/dL and CH from 180 +/- 22 to 135 +/- 25 mg/dL. Both TG and glycerol showed an initial increase followed by a continuous decrease. Alpha-CH increased by 19% whereas beta-CH and pre-beta-CH decreased markedly (39% and 78%, respectively). In contrast to alpha-CH, apo A-1 fell only slightly by 10%. These results indicate that the effect of chronic exercise on lipids and lipoproteins can be mimicked by acute prolonged exercise. Similar mechanisms may be involved in these adaptations. Moreover, the extreme length of physical exertion substantially lowered CH.     

Clinical course of cardiovascular involvement in the mucocutaneous lymph node syndrome: Relation between clinical signs of carditis and development of coronary arterial aneurysm

Seventy-nine patients with mucocutaneous lymph node syndrome were evaluated prospectively by clinical examination, electrocardiography, chest radiography, M mode and two dimensional echocardiography and thallium-201 myocardial scanning. Serial changes were categorized according to the duration of illness: stage I (1 to 10 days), stage II (11 to 20 days), stage III (21 to 30 days), stage IV (31 to 60 days) and stage V (61 days to 40 months). The presence of myocarditis in stages I and II was suggested in 40 of 79 patients (50.6 percent) by electrocardiographic, echocardiographic, radiographic and clinical abnormalities. Myocarditis was accompanied by pericarditis in six patients and by both endocarditis and pericarditis in one patient. These signs of inflammation were resolved by stage III in all but three patients with electrocardiographic abnormalities. In the active stage, large coronary arterial lesions were suspected only because of an abnormal spherical echo-free space in the region of the coronary arteries on two dimensional echocardiograph as well as electrocardiographic evidence of deep Q waves in leads II, III and aVF. One or more coronary aneurysms developed in 11 patients, primarily in stage II; regression of the aneurysm was noted in 5 of these patients during stages III, IV and V. Aneurysm regression demonstrated by angiography did not correlate with echocardiographic changes in aneurysm size in one patient. Moreover, the occurrence of coronary aneurysm did not correlate with the presence of signs of carditis, because the frequency of carditis was the same in patients with and without aneurysm.     

Noninvasive visualization of coronary arterial aneurysm in infants and young children with mucocutaneous lymph node syndrome with two dimensional echocardiography

Real time two dimensional echocardiographic studies of the main coronary arteries were performed in 30 normal subjects and 58 patients with the mucocutaneous lymph node syndrome. Four echocardiographic coronary arterial patterns were observed: linear, dilated, fusiform or spherical. In normal subjects the left main coronary artery generally had a linear pattern but had a dilated pattern in two patients. The right coronary artery could not be visualized clearly. In 7 of the 58 patients with the mucocutaneous lymph node syndrome, a portion of the left main coronary artery had a fusiform or spherical pattern, or both, and the stem of the right coronary artery also had a spherical pattern in 2 patients. In all five patients who had coronary angiography, the procedure confirmed an aneurysm in the left main coronary artery or its branching point and the stem of the left anterior descending coronary artery or the stem of the right coronary artery, or both. In three of the five patients, coronary arterial aneurysms were predicted before coronary angiography was performed. Thus, two dimensional echocardiography is a reliable noninvasive method for evaluating coronary arterial aneurysms in infants and young children.     

Immune reactions in infective endocarditis. II. Relevance of circulating immune complexes, serum inhibition factors, lymphocytotoxic reactions, and antibody-dependent cellular cytotoxicity against cardiac target cells

Circulating immune complexes (IC) were detected in 35 out of 41 patients (85%) with infective endocarditis of known bacterial origin in contrast to only 9 out of 20 patients (45%) with endocarditis but negative blood cultures (p less than 0.05). Peak IC levels of 33.25 +/- 24.33 micrograms/ml in the early period fell significantly to 8.38 +/- 13.37 micrograms/ml after antibiotic treatment (p less than 0.001). High levels of IC coincided with relative hypocomplementemia. Erythrocyturia was observed in 51 of 58 IC-positive patients demonstrating peripheral sequelae of circulating IC. Incidence and concentrations of IC correlated neither with the mere presence of the rheumatoid factor nor with the titers of antimyolemmal antibodies, nor with antibody mediated cytolysis in the presence of complement. Serum inhibition factors (SIF) and E-rosette inhibitory factors (RIF) were not demonstrated, indicating that IC in endocarditis do not suppress phytohemagglutinin-induced lymphocyte proliferation or the E-rosetting of T cells. Significant lymphocytotoxicity against heterologous cardiac target cells without serum (LC) could be demonstrated in 11 out of 23 patients (48%) with endocarditis as compared to its absence in controls (n = 33, p less than 0.01). In assays of antibody-dependent cellular cytotoxicity (ADCC), either enhancement or blocking of lymphocytotoxicity by autologous serum or both was observed. The modulation of lymphocytotoxicity was most likely due to antimyolemmal antibodies, to IC, or to both, although effects of other serum factors cannot be ruled out completely.     

Studies on the pathogenesis of the dawn phenomenon in insulin-dependent diabetic patients

To assess the role of hormonal factors in the pathogenesis of the dawn phenomenon, nocturnal (9:00 PM to 9 AM) concentrations of blood glucose, free insulin, and counterregulatory hormones were determined in eight insulin-dependent diabetic patients under feedback-controlled and continuous insulin infusions after previous blood glucose normalization. Under feedback control, mean insulin requirements, necessary for maintenance of euglycemia rose significantly in the early morning (11:00 PM to 3 AM: 8.4 +/- 1.4; 5 AM to 9 AM: 12.6 +/- 1.5 mU/kg/h; P less than 0.01). Mean free-insulin concentrations did not increase simultaneously. Correspondingly, mean insulin-clearance rates under continuous insulin infusion were higher in the morning (11:00 AM to 3 AM: 359 +/- 58; 5 AM to 9 AM: 459 +/- 72 mL/min/m2; P less than 0.05). Increases of insulin clearance rates were most marked (greater than 15%) in patients whose blood glucose rose during continuous insulin administration. Glucagon and norepinephrine concentrations were stable throughout both parts of the study. Cortisol and growth hormone exhibited the known nocturnal rhythms. Epinephrine levels were at the lower limit of detection at night and rose to normal basal concentrations at 9:00 AM. We conclude that increases of insulin clearance rates may be an important factor for the development of the dawn phenomenon while the role of most counter-regulatory hormones is still uncertain.     

Effects of antihypertensives on plasma lipids and lipoprotein metabolism

There is good epidemiologic evidence that hypertension is associated with a high risk of cardiovascular disease. However, primary intervention trials have failed to demonstrate that a reduction in blood pressure in hypertensive patients reduces morbidity and mortality from cardiac events. Since various antihypertensive drugs adversely affect lipoprotein metabolism, these drugs may increase associated coronary risk and offset the beneficial effects of lowering blood pressure. This article reviews the effects of various antihypertensive drugs on plasma lipids, lipoproteins, and apolipoproteins. They can be summarized as follows: thiazide-type diuretics cause a marked elevation of plasma triglycerides and very low-density lipoprotein (VLDL) and minor increases in total cholesterol and low-density lipoprotein (LDL), but have little effects on high-density lipoprotein (HDL). The nonselective β-blockers do not significantly affect total cholesterol and LDL, but increase total triglycerides and VLDL and decrease HDL. The changes in plasma lipids and lipoproteins caused by cardioselective β-blockers and β-blockers with intrinsic sympathomimetic activity are qualitatively similar but less pronounced. Calcium antagonists and angiotensin-converting enzyme inhibitors appear to have no significant effects on plasma lipids. α₁-inhibitors reduce total triglycerides, total cholesterol, VLDL, and LDL and increase HDL. The possible mechanisms by which antihypertensive drugs affect cellular lipid metabolism (e.g., LDL receptor, lipid synthesis, lipoprotein lipase, lecithin cholesteryl acyltransferase, acylcholesteryl acyltransferase, and cholesteryl ester hydrolase) are described. The clinical significance of changes in blood lipids and cellular lipid metabolism caused by antihypertensive drugs is not yet totally clear. Nevertheless, before antihypertensive drug treatment is initiated, blood lipid levels should be measured to identify preexisting hyperlipidemia. Blood lipoprotein levels should be monitored during long-term antihypertensive therapy to reconsider the therapeutic regimen if adverse lipid changes are observed.     

Reversal of diuretic-induced increases in serum low-density-lipoprotein cholesterol by the betablocker pindolol

Seventeen patients with mild to moderate essential hypertension received during three consecutive 4 wk periods a matched placebo, the thiazide-like diuretic, clopamide in a low dosage of 5 mg/day, or this diuretic combined with the betablocker, pindolol in a low dosage of 10 mg/day. Compared to placebo conditions, clopamide monotherapy significantly increased serum low-density lipoprotein cholesterol (LDL-C) by 13% (p < 0.025). Following addition of pindolol, serum LDL-C was restored to control values. These variations in serum LDL-C were unrelated to concomitant changes in blood pressure, plasma potassium, renin activity or aldosterone levels. Blood pressure in the supine position was reduced from $\text{152}\text{99}\text{±}\text{13}\text{9}\text{mm Hg (+SD)}$ to $\text{141}\text{93}\text{±}\text{15}\text{7}\text{mm Hg}$ following diuretic-monotherapy and to $\text{139}\text{90}\text{±}\text{12}\text{9}\text{mm Hg}$ following diuretic-betablocker combination treatment. These findings suggest that antihypertensive combination treatment with low doses of clopamide and pindolol is not only effective and well tolerated, but may also avoid the increase in serum LDL-C levels occurring when the thiazide-like diuretic is given alone.