High power factor PWM rectifiers with an analog pulsewidthprediction controller

A single-phase PWM bridge rectifier controlled by a pulsewidth prediction (PWP) method to operate switching devices to realize a high power factor and to reduce the AC-side current harmonics is proposed. The PWP controller provides instantaneous current control with either a constant frequency carrier or a piecewisely fixed multiple-frequency carrier in one source-voltage cycle. The paper describes the control methods and implementation of analog PWP controllers, and performance characteristics of the rectifier. Unity displacement power factor was obtained and the AC-side current harmonics were reduced. Experimental results show the usefulness of the proposed method and applicability to rectifiers in UPS systems, etc     

Change of internal/pore structure in alumina green body during initial sintering

A novel characterization method was applied to study the morphological changes of large pores in a ceramic green body during the early stage of densification at 1100°C for 1–64 h. Large processing pores were present in the green body. They were preserved after densification up to a relative density of 83.9% with their shape and size unchanged significantly. The pore size distribution determined by mercury porosimetry showed the growth of matrix pores of small size, but failed to show the change of large processing pores with densification.     

Particle deposition and removal in wet cleaning processes for ULSImanufacturing

Particle deposition on wafer surfaces in solutions can be described by the well-documented principles of colloid science. Particle concentration, solution pH, and ionic strength in solutions are all important factors which determine the number of particles which deposit on wafer surfaces immersed in liquids. maximum particle deposition is observed in high ionic strength acidic solutions and is reduced as solution pH increase. Particle removal efficiencies in various solutions were also investigated; NH₄OH-H₂O₂-H ₂O solutions were optimized in NH₄OH content around the ratio of 0.05:1.15 (0.05 part NH₄OH, 1 part H₂O₂, 5 parts H₂O). Wafer damage as measured by surface micro-roughness was not increased during NH₄ OH-H₂O₂-H₂O treatment using this ratio     

Restriction map polymorphism in the forked and vermilion regions of Drosophila melanogaster

Restriction map polymorphism at two X linked foci, forked and vermilion of Drosophila melanogaster was studied in three natural populations. The estimates of nucleotide variation were theta = 0.003 and pi = 0.002 for the forked region and theta = 0.004 and pi = 0.002 for the vermilion region. Three insertions (> 500 bp) were observed at each locus. Typical of other regions of this species each of these large insertions was unique in the sample. Non-random association among polymorphisms was common at the vermilion locus, while the forked locus was not polymorphic enough to test linkage disequilibrium. The amounts of restriction site and size variation in the vermilion and forked were within the range observed for other loci of D. melanogaster.     

Blood supply to the retina in the laboratory shrew (Suncus murinus)

BACKGROUND: The benefit of splenectomy, performed for complications of chronic lymphocytic leukemia (CLL) including autoimmune hemolytic anemia, thrombocytopenia, hypersplenism, and symptomatic splenomegaly, has not been clearly demonstrated. The objective of this study was to determine if splenectomy achieves a predictable hematologic and survival advantage over conventional chemotherapy in patients with CLL. STUDY DESIGN: A retrospective review was performed of 77 consecutive patients with CLL who underwent splenectomy between 1970 and 1994 at the University of Texas M. D. Anderson Cancer Center. Indications for splenectomy, pre- and postoperative hematologic profiles, response to splenectomy, and time to progression and death were recorded. Kaplan-Meier life tables were constructed, and a comparison to an age- and gender-matched cohort of CLL patients treated with fludarabine and no splenectomy was performed using log rank statistical analysis. RESULTS: Seventy-six percent of the patients studied were Rai stage III/IV. Twenty of 29 patients with hemoglobin counts (Hb) < or = 10 g/dL and 11 of 18 patients with platelet counts (plt) < 50 x 10(9)/L achieved an excellent hematologic response to splenectomy. Splenectomy significantly improved survival in patients with Hb < or = 10 g/dL or plt < or = 50 x 10(9)/L (p = 0.025). Thrombocytopenia did not significantly increase postoperative morbidity, and mortality rate was not significantly different between treatment groups. CONCLUSIONS: Splenectomy significantly improves survival in selected subgroups of patients with advanced-stage CLL over that achieved with conventional chemotherapy. Based on these results, splenectomy should be performed early in the course of the disease in CLL patients with either an Hb < or = 10 g/dL or plt < or = 50 x 10(9)/L.     

Surgical stratification of patients with atrial fibrillation secondary to organic cardiac lesions

BACKGROUND: While the maze procedure does not always eliminate atrial fibrillation (AF) secondary to organic cardiac lesions, concomitant performance of the procedure is associated with increased surgical complexity and potential risks. METHODS: To stratify the surgical approach for patients with AF secondary to underlying cardiac lesions, we analyzed 24 preoperative and perioperative variables in 115 consecutive patients with AF undergoing a modified maze procedure combined with valvular intervention (101), repair of congenital anomalies (13) and coronary revascularization (1). RESULTS: Patients who remained in AF (18) compared to patients with restored atrial rhythm (97), had a higher incidence of giant left atrium (56% vs 10%, P < 0.0001), larger cardiothoracic ratio (70 +/- 13 vs 62 +/- 8%, P = 0.001) and left atrial dimension (64 +/- 12 vs 55 +/- 12 mm, P = 0.004), a longer history of AF (13.7 +/- 6.8 vs 8.3 +/- 6.9 years, P = 0.003) and lower f-wave voltage (0.10 vs 0.15 mV, P = 0.004). Multivariate logistic regression analysis of 24 preoperative and perioperative variables identified the presence of giant left atrium, cardiothoracic ratio and age at operation as the significant risk factors predisposing patients to persistent postoperative AF. Retrospective estimation identified 73 (63.5%) patients with a high probability of atrial defibrillation (97.3%) and 42 (36.5%) patients with a high risk of failure (38.1%). Regardless of the preoperative risk analysis or the performance of left atrial plication, every patient with a postoperative left atrial dimension less than 40 mm or cardiothoracic ratio below 55% was successfully defibrillated. CONCLUSION: The results suggest performing the maze procedure before "risk factors" develop for patients with predicted maze-amenable AF. While omitting the maze procedure may be prudent for patients with suspected maze-refractory AF, the simultaneous reduction of left atrial size may offset the increased risk from preoperative size factors. A prospective study seems warranted to examine the effects of left atrial plication on postoperative rhythm.     

Effects of acute exposure to simulated altitude on heart rate variability during exercise

It has been shown that fluctuation of human heartbeat intervals [heart rate variability (HRV)] reflects variations in cardiac autonomic nervous system activity. The present study was designed to investigate whether the acute exposure to moderate levels of simulated altitude and the resultant hypoxia could modify HRV during exercise. Seven healthy men completed one resting measurement in the upright sitting position and two submaximal steady-state cycle ergometer exercises at intensities equivalent to 25 and 50% of their estimated maximal work rate. Experiments were conducted in random order at altitude equivalents of 500, 1,500, 2,500, and 3,500 m within 2 h of exposure to that altitude. Beat-to-beat HRV was measured continuously during the tests. HRV data were analyzed by "coarse-graining spectral analysis" (Y. Yamamoto and R.L. Hughson, Physica 68D: 250-264, 1993) to break down their total power (PT) into harmonic and nonharmonic (fractal) components. The harmonic component was further divided into low (0.0- to 0.15-Hz; PL)- and high (> 0.15-Hz; PH)-frequency components, and the indicators of relative sympathetic (SNS) and parasympathetic (PNS) nervous system activities were calculated by PL/PH and PH/PT, respectively. The fractal component was used to calculate the spectral exponent (beta) to evaluate the overall "irregularity" of HRV. The effects of exercise intensity (increase in heart rate, SNS indicator, and beta and decrease in PNS indicator) were significant (P < 0.05) at all altitude levels. The altitude effects (increase in heart rate and SNS indicator and decrease in PNS indicator) were found only during exercise at 3,500 m (P < 0.05). There was no significant effect of altitude on beta (P > 0.05). These data indicate that acute effects of altitude exposure on HRV were found 1) during exercise at moderate altitude (> 2,500 m) and 2) mainly for the harmonic components of HRV.     

Broad Beamwidth and Cross Polarization Free Dipole Antennas With Reactive Loaded Monopoles

A method to broaden the E-plane radiation pattern of a dipole antenna over a ground plane is proposed. Two parasitic monopole elements with reactive loads are placed in the vicinity of the driving dipole element. Another advantage of this antenna is that these monopoles do not cause cross polarization in the H-plane. Based on the electromotive force (EMF) method, a new procedure that optimizes the load values is developed. Numerical verification by the method of moments (MoM) is provided; additionally, each antenna parameter including the optimum reactive load is obtained. The experiment is also presented to demonstrate the performance