Small-signal modeling and control of the quasi-square-wave boostconverter

Sampled-data techniques are used to examine the dynamic characteristics and closed-loop performance of the quasi-square-wave boost converter. Direct duty-ratio control and current-mode control are considered. With direct duty-ratio control, the system poles remain well damped under all load conditions, and there is no zero in the control-to-output transfer function. Good closed-loop performance is therefore achieved. Under current-mode control, the requirement for a stabilizing ramp is seen to depend on load conditions, and the achievable voltage control-loop bandwidth is smaller than that using direct duty-ratio control; however, there is a significant reduction in the magnitude of the DC source to output-voltage frequency response     

Regional chemotherapy of liver tumors

In the absence of adequate autogenous vein for tibial artery bypass in limb salvage surgery, the use of prosthetic grafts with a distal anastomotic vein cuff or patch has shown promising results. Here, we describe how the Florester Internal Vessel Occluder (Meadox UK, Bedfordshire, UK) can facilitate the construction of a distal anastomotic vein cuff.     

Numerical investigation of nitriding of refractory metals (with account of the phase constitution diagrams for metal-gas systems)

A mathematical model of dissolution of gas in a metal is suggested with account of phase formation in accordance with the phase constitution diagram (PCD). The stage-by-stage saturation process to the final product formation is shown for an individual particle, through which a reaction wave passes, depending on the diffusion permeability of the metal and solubility conditions that obey Sieverts's law. The effect of the filtration supply of the oxidant to the reaction zone and the process exothermicity on the course of the process is shown.Institute of Structural Macrokinetics, Russian Academy of Sciences, Chernogolovka, Russia. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 65, No. 4, pp. 447–450, October, 1993.     

Ambulatory subcutaneous internal sphincterectomy]

The internal anal sphincterotomy operation represents the best therapy for the treatment of those anal lesions, above all anal fissures, which cause hypertrophy and spasms of the internal anal sphincter. The Authors report their experience of 253 operations of internal subcutaneous sphincterotomy carried out between 1989 and 1995 under local anaesthesia in the outpatient clinic. The excellent results achieved prove that the procedure can easily be carried out under local anaesthesia in an outpatient clinic and, therefore, it is preferable to the surgical technique of isolation of the internal sphincter, not only for its practicality but also for the improved results.     

High speed p-type SiGe modulation-doped field-effect transistors

We report on the fabrication and characterization of high-speed p-type modulation-doped field-effect transistors (MODFETs) with 0.7-μm and 1-μm gate-lengths having unity current-gain cut-off frequencies (f_T) of 9.5 GHz and 5.3 GHz, respectively. The devices were fabricated on a high hole mobility SiGe heterostructure grown by ultra-high-vacuum chemical vapor deposition (UHV-CVD). The dc maximum extrinsic transconductance (g_m) is 105 mS/mm (205 mS/mm) at room temperature (77 K) for the 0.7-μm gate length devices. The fabricated devices show good pinch-off characteristics and have a very low gate leakage current of a few μA/mm at room temperature and a few nA/mm at 77 K