Status and Prospects of Cubic Silicon Carbide Power Electronics Device Technology

Wide bandgap (WBG) semiconductors are becoming more widely accepted for use in power electronics due to their superior electrical energy efficiencies and improved power densities. Although WBG cubic silicon carbide (3C-SiC) displays a modest bandgap compared to its commercial counterparts (4H-silicon carbide and gallium nitride), this material has excellent attributes as the WBG semiconductor of choice for low-resistance, reliable diode and MOS devices. At present the material remains firmly in the research domain due to numerous technological impediments that hamper its widespread adoption. The most obvious obstacle is defect-free 3C-SiC; presently, 3C-SiC bulk and heteroepitaxial (on-silicon) display high defect densities such as stacking faults and antiphase boundaries. Moreover, heteroepitaxy 3C-SiC-on-silicon means low temperature processing budgets are imposed upon the system (max. temperature limited to ~1400 °C) limiting selective doping realisation. This paper will give a brief overview of some of the scientific aspects associated with 3C-SiC processing technology in addition to focussing on the latest state of the art results. A particular focus will be placed upon key process steps such as Schottky and ohmic contacts, ion implantation and MOS processing including reliability. Finally, the paper will discuss some device prototypes (diodes and MOSFET) and draw conclusions around the prospects for 3C-SiC devices based upon the processing technology presented.     

Präoperative Radiotherapie, totale mesorektale Exzision und postoperative Chemotherapie in der Behandlung der T3- und T4-Rektumkarzinome

Exactly accomplished total mesorectal excision (TME) for rectal cancer treatment has achieved very good results by surgery alone, as recently referred in the literature. However, there are anatomical and biological limits in only surgical treatment, advocating the usefulness of additional adjuvant procedures. In our experience, preoperative hyperfractionated accelerated radiotherapy with 41.6 Gy, TME and postoperative chemotherapy with 5-FU proved a success in locoregional control of the disease, leading to a local recurrence rate of 2% of 50 patients in a mean follow-up of 2.5 years after treatment. Despite of it, in our series distant metastases occurred only in the liver in 12% of patients resected for cure, and continues to be a problem which raises the need for other studies about systemical treatment of the disease.     

Single Shock Endocavitary Low Energy Intracardiac Cardioversion of Chronic Atrial Fibrillation

Background.Discomfort related to low-energy internal cardioversion (LEIC) represents a real problem in patients (pts) with atrial fibrillation (AF). The aim of our study was to verify if a single shock could restore sinus rhythm (SR) with a lower discomfort for the pt.Methods. Thirty pts with chronic AF were randomized to receive a single 350 V shock (15 pts) or multiple shocks of increasing energy (15 pts). Three leads were positioned, respectively, in the coronary sinus and in the lateral right wall for shock delivery, and in the right ventricular apex for R wave synchronization. Truncated, biphasic shocks were used. In the first group a single 350 V shock was directly delivered and a second 400 V shock was given only if SR has not been restored. In the second group, beginning at 50 volts the voltage was increased in steps of 50 volts until SR restoration. No patient was sedated. After each shock the pts were asked to rate their discomfort on a scale of 1 to 5 (1 = not perceived, 5 = severe discomfort)Results. SR was restored in all the subjects. In group 1 SR was obtained in 12/15 (80%) pts with the first 350 V (8.1±0.8 joules) shock, while the remaining 3 patients required the second 400 V (10.2±10.3 joules) shock. In group 2 the mean atrial defibrillation threshold was 346.7±29.7 volts (8.0±1.5 joules). Then discomfort score was 2.5±0.6 in group 1 and 3.3±0.6 in group 2 (p < 0.01).Conclusions. A single shock of 350 V restores SR in the majority of pts with chronic AF; by use this new approach, LEIC is tolerated better than the multiple shocks step-up protocol.     

A new interlocking dynamic compression nail for tibial shaft fractures

The Clos tibial nail is a cannulated cylindrical nail that permits static, dynamic as well as incompression mounting by the insertion of locking screws into distal and proximal holes. From September 1998 to March 1999 we treated 16 tibial shaft fractures with CLOS tibial nails. All fractures were managed with calcanear traction, closed reduction, reaming and fixation. Patients were followed for at least 1 year. The mean time to full weight bearing was 11 (10–14) weeks. There were no cases of delayed union or dynamization. All patients returned to their previous activity levels. Received: 4 September 2000; Accepted: 9 September 2000     

Intracellular mechanisms mediating the neuronal death and astrogliosis induced by the prion protein fragment 106–126

Prion encephalopathies include fatal diseases of the central nervous system of men and animals characterized by nerve cell loss, glial proliferation and deposition of amyloid fibrils into the brain. During these diseases a cellular glycoprotein (the prion protein, PrP^C) is converted, through a not yet completely clear mechanism, in an altered isoform (the prion scrapie, PrP^Sc) that accumulates within the brain tissue by virtue of its resistance to the intracellular catabolism. PrP^Sc is believed to be responsible for the neuronal loss that is observed in the prion disease. The PrP 106–126, a synthetic peptide that has been obtained from the amyloidogenic portion of the prion protein, represents a suitable model for studying the pathogenic role of the PrP^Sc, retaining, in vitro, some characteristics of the entire protein, such as the capability to aggregate in fibrils, and the neurotoxicity. In this work we present the results we have recently obtained regarding the action of the PrP 106–126 in different cellular models. We report that the PrP 106–126 induces proliferation of cortical astrocytes, as well as degeneration of primary cultures of cortical neurons or of neuroectodermal stable cell lines (GH₃ cells). In particular, these two opposite effects are mediated by the same attitude of the peptide to interact with the L-type calcium channels: in the astrocytes, the activity of these channels seems to be activated by PrP 106–126, while, in the cortical neurons and in the GH₃ cells, the same treatment causes a blockade of these channels causing a toxic effect.     

Laparoscopic live donor nephrectomy: pre‐operative assessment of technical difficulty1

Laparoscopic live donor nephrectomy decreases disincentives to live kidney donation. Thus, many centers are interested in adopting this procedure. However, the high stakes involved for both the donor and the recipient, and the technical difficulties of the operation, have tempered the enthusiasm of some surgeons. Ideally, if early in their series, surgeons could select patients that would be the least challenging technically, it would facilitate the dissemination of this operation. The purpose of this study is to determine if anatomic or radiologic parameters can accurately assess pre‐operatively the degree of technical difficulty of laparoscopic live donor nephrectomy for any individual patient.
Abdominal spiral three‐dimensional CT scanning was performed prior to laparoscopic donor nephrectomy. CT scans were reviewed for six radiographic anatomic parameters. Seven clinical anatomic measurements relating to body habitus were recorded upon induction anesthesia at the time of surgery. Demographic data for gender, age, race, weight, height, and smoking history were collected. Following laparoscopic live donor nephrectomy, the following six component parts of the operation were graded on a scale of 1–4 (1=easy, 4=very difficult) for technical difficulty: a) mobilization of the colon; b) mobilization of the upper pole; c) dissection of the renal vein; d) dissection of the renal artery; e) division of the adrenal vein; and f) dissection of the ureter. Also, operative time, estimated blood loss, and intra‐operative fluid requirements were recorded as surrogate markers of operative difficulty.
Forty‐one patients were included in the study. Laparoscopic donor nephrectomy was successfully completed in all cases. The sum of the difficulty scores was 9.9±3.1 (mean) (range, 6–18). No anatomic, demographic, or radiologic parameters were predictive of the total operative difficulty score. Of the surrogate markers, only operative time correlated with total difficulty score (R=0.47, p=0.003). Donor weight and abdominal girth correlated with operative time (R=0.50, p=0.002; R=0.38, p=0.019) but not with total difficulty score (R=0.10, p=0.51; R=?0.02, p=0.90, respectively). When the easiest cases and the hardest cases (≤25th percentile and ≥75th percentile total difficulty score, respectively) were segregated out, again no anatomic, demographic, or radiologic parameters were predictive of operative technical difficulty. In conclusion, laparoscopic live donor nephrectomy technical difficulty could not be predicted by body habitus from the variables examined in this study. Hence, it was equally likely that performing laparoscopic live donor nephrectomy using a heavy donor would be technically easy, as using a thin donor would be difficult. Although, in general, operative time increased with donor size and weight, it appears that laparoscopic live donor nephrectomy operative technical difficulty is dependent upon such factors as amount of laparoscopic working space, quality of tissue planes, and retractability of the colon and mesocolon; factors that, to date, are not quantifiable.     

Fine‐needle aspiration cytology of subcutaneous toxoplasmosis: A case report

Toxoplasmosis is a common opportunistic infection in patients with AIDS in whom it typically presents as encephalitis, pneumonia, lymphadenitis, and myocarditis. Skin involvement is very rare and, to our best knowledge, Toxoplasma gondii forming a subcutaneous mass has not been reported. Here, we report the findings of an interesting case of subcutaneous toxoplasmosis with the cytological appearance of an inflammatory fibrovascular lesion in a HIV‐positive patient and discuss the differential diagnosis. Diagn. Cytopathol. 2010;38:716–720. © 2009 Wiley‐Liss, Inc.     

Synthesis and Characterization of Ethylene/1‐Olefin Copolymers Obtained by “Single Centre” Catalysis

The catalytic system rac‐Me₂Si(Ind)₂ZrCl₂/MAO was used to polymerize ethylene and to copolymerize ethylene with different 1‐olefins (copolymers containing 1‐olefins up to 1‐tetradecene were prepared). In the presence of the 1‐olefin, the catalytic activity increases. As expected, the amount of 1‐olefin inserted in the polymer chain depends on the monomers molar ratio in the polymerization bath. The molecular weight of the copolymer decreases as the concentration of the 1‐olefin increases owing to the relatively easy chain transfer reactions after primary and secondary 1‐olefin insertions and the effect depends on the length of the 1‐olefin. The average ethylene sequence length decreases as the amount of inserted 1‐olefin increases leading to a decrease of the melting temperature, T_m. The crystallinity of polymers with the same 1‐olefin content seems to be lower increasing the length of the 1‐olefin. The comonomer distribution is not influenced by the 1‐olefin length but depends only on the catalytic system.