LCD TV中的电源转换链与开关电源拓扑

电视机的升级 自从英国广播公司(BBC)于1936年在伦敦开通世界上首个公共电视广播以来,电视机技术已取得了长足的发展:从BBC于1953年首先开通彩色电视广播,到日本NHK于1981年进行首例高清电视(HDTV)系统演示等,不一而足.     

Framework for the evolution of acquiring knowledge modules to integrate the acquisition of high-level cognitive skills and professional competencies: Principles and case studies

The changing profile of students, the expectations of business and the capabilities offered by Information and Communication Technologies (ICT) makes it necessary to change teaching practices, particularly in higher education. This paper proposes a methodological framework destined to force disciplinary course modules to evolve in order to integrate high-level cognitive skills and professional competencies. In this paper, we examine this framework in terms of the primary currents in educational psychology: behaviorism, cognitivism, constructivism and social constructivism. We present and analyze three case studies showing the evolution of three disciplinary course modules. We show that the lessons taught in these three modules are more motivating and more efficient, producing results that are closer to what employers are asking of their employees.     

Idiopathic verapamil-responsive left ventricular tachycardia: clinical characteristics and long-term follow-up of 33 patients

Long-term prognosis, pharmacological prophylaxis and transcatheter ablation in a large group of patients with idiopathic verapamil-responsive left ventricular tachycardia (IVRLVT) are reported in this study. Thirty-three patients with a mean age of 27 +/- 16 years at their first IVRLVT episode, were studied retrospectively. Ventricular tachycardia was of the right bundle branch block morphology in all cases, with left axis deviation in 29 and right axis deviation in five (one patient had the two morphologies). Mitral valve prolapse was present in four patients; no heart disease was found in the remaining 29. Ventricular tachycardia could be electrophysiologically induced in 90% of the patients; Holter monitoring showed only sporadic ventricular extrasystoles in 76%; late potentials were found in 33% of the cases. At the end of a follow-up of 5.7 +/- 4.7 years, no patient had died. Thirty-one patients (94%) received a mean of 2.5 +/- 1.2 drugs; beta-blockers were effective in 71% of the cases, verapamil in 25%, class 1 drugs in 22%, class 3 drugs in 18%. Two patients who never received prophylaxis and four in whom it was stopped, were controlled with verapamil in case of recurrence. Six patients underwent catheter ablation; two with DC shock in whom it was successful in one, and four with radiofrequency energy, with a total success rate. The good prognosis of IVRLVT has been confirmed in a long-term follow-up; a new finding is the high efficacy of beta-blockers for prophylaxis. Radiofrequency transcatheter ablation is an effective and safe therapy for patients with symptoms not controlled by drug treatment.     

Four-layer bandaging and healing rates of venous leg ulcers

This paper reports the healing rates of venous leg ulcers in a community setting (Exeter and District Community Health Services NHS Trust) using the Charing Cross four-layer compression system. We report on 514 venous leg ulcers and show healing rates of 40% at 12 weeks, 50% at 17 weeks, 57% at 24 weeks and 80% predicted at 2 years. Patients were treated in one of 16 community leg ulcer clinics or in their homes. Nurses were allowed to use this system only after full training by the leg ulcer management service. Nurses had to prove their competence in leg ulcer assessment, Doppler measurement and the technique of four-layer compression. Even in patients whose leg ulcers did not heal, it was felt that the four-layer compression system was comfortable, convenient and cost effective with only weekly changes of bandages being necessary.