Histochemical evaluation of placental dipeptidyl peptidase IV (CD26) in pre-eclampsia: enzyme activity in villous trophoblast indicates an enhanced likelihood of gestational hypertensive disorders

Nitric oxide (NO) acts as a modulator of neuronal transmission in mature neuronal systems, including the retina. Recently, NO has also been suggested to have a trophic function during development. We examined immunocytochemically the distribution of NO-producing cells in developing and transplanted rabbit retinas. An antibody detecting the neuronal isoform of its biosynthetic enzyme, nitric oxide synthase (NOS), was used on normal developing retinas [starting at embryonic day (E) 15] and on rabbit retinal transplants after various survival times (1-139 days after surgery). Weakly stained cell bodies were first observed in the proximal margin of the neuroblastic layer at E 29. Stained processes projecting towards a developing inner plexiform layer were also visible at this time point. Immunoreactive cells were located at later stages in the innermost part of the inner nuclear layer and in the ganglion cell layer, and are likely to correspond mainly to amacrine cells. NOS-labelled cells were also found in retinal transplants. The first NOS-labelled cells appeared, as in normal developing retinas, in ages corresponding to E 29 and were still detected in transplants corresponding to postnatal day 123. NOS-labelled cells were seen in areas between rosettes, where amacrine cells are located. NOS-labelled processes were at times seen to project for long distances, forming very distinct plexuses. NOS-containing amacrine cells thus appear both in the transplants and in developing retinas in the embryonic stages, long before synaptic function involving these cells can be expected, suggesting a role for NO not only in neuromodulation but also in retinal development.     

Surface and interface properties of PdCr/SiC Schottky diode gas sensor annealed at 425°C

The surface and interface properties of Pd_0.9Cr_0.1/SiC Schottky diode gas sensors both before and after annealing are investigated using Auger electron spectroscopy (AES), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). At room temperature the alloy reacted with SiC and formed Pd_xSi only in a very narrow interfacial region. After annealing for 250 h at 425°C, the surface of the Schottky contact area has much less silicon and carbon contamination than that found on the surface of an annealed Pd/SiC structure. Palladium silicides (Pd_xSi) formed at a broadened interface after annealing, but a significant layer of alloy film is still free of silicon and carbon. The chromium concentration with respect to palladium is quite uniform down to the deep interface region. A stable catalytic surface and a clean layer of Pd_0.9Cr_0.1 film are likely responsible for significantly improved device sensitivity.     

Breakdown degradation associated with elementary screw dislocations in 4H-SiC pn junction rectifiers

It is well-known that SiC wafer quality deficiencies are delaying the realization of outstandingly superior 4H-SiC power electronics. While efforts to date have centered on eradicating micropipes (i.e., hollow core super-screw dislocations with Burgers vector>2c), 4H-SiC wafers and epilayers also contain elementary screw dislocations (i.e., Burgers vector=1c with no hollow core) in densities on the order of thousands per cm², nearly 100-fold micropipe densities. This paper describes an initial study into the impact of elementary screw dislocations on the reverse-bias current–voltage (I–V) characteristics of 4H-SiC p⁺n diodes. First, synchrotron white beam X-ray topography (SWBXT) was employed to map the exact locations of elementary screw dislocations within small-area 4H-SiC p⁺n mesa diodes. Then the high-field reverse leakage and breakdown properties of these diodes were subsequently characterized on a probing station outfitted with a dark box and video camera. Most devices without screw dislocations exhibited excellent characteristics, with no detectable leakage current prior to breakdown, a sharp breakdown I–V knee, and no visible concentration of breakdown current. In contrast, devices that contained at least one elementary screw dislocation exhibited 5–35% reduction in breakdown voltage, a softer breakdown I–V knee, and visible microplasmas in which highly localized breakdown current was concentrated. The locations of observed breakdown microplasmas corresponded exactly to the locations of elementary screw dislocations identified by SWBXT mapping. While not as detrimental to SiC device performance as micropipes, the undesirable breakdown characteristics of elementary screw dislocations could nevertheless adversely affect the performance and reliability of 4H-SiC power devices.     

An amorphous silicon thin film transistor: Theory and experiment

The volt-ampere characteristics for a thin film transistor fabricated with vacuum deposited amorphous silicon as the semiconductor is presented. The substrate is single crystalline silicon with a 3000 Å layer of thermally grown silicon dioxide as the insulator. The gate is a buried N⁺ phosphorus diffused region while the source and drain contacts are interdigited fingers of aluminum. By using the Cohen-Fritzsche-Ovshinsky model for the density of localized states in the mobility gap, the V_G vs I_D characteristic at small values of V_D is predicted and experimentally verified. This characteristic is used to theoretically predict the family of I_D curves for the TFT over a range of V_G and V_D. The theory and experiment agree exceptionally well below the gate-drain pinch-off, thereby verifying the theory of a TFT with a uniform distribution of traps in the band-gap.     

Electrical characterization of a JFET-accessed GaAs dynamic RAMcell

A complete one-transistor dynamic RAM cell in GaAs is discussed. Read and write operations is monitored by observing the capacitance of the storage node. Storage times on the order of a few seconds are obtained at room temperature with an activation energy slightly less than half the zero-temperature bandgap     

How many severely injured multiple-trauma patients can benefit from the biomechanical advantage of early mobilization following femoral intramedullary nailing?

The benefit of early operative stabilization of femoral fractures is established in patients with multiple injuries. In the last few years the unreamed femoral nail is favoured for internal fixation of femoral fractures despite pathophysiological concerns. The foremost advantage of femoral nails compared with plate fixation is the possibility of early full weight bearing. The aim of this retrospective study was to investigate, under consideration of the severity of injury, the extent of injury, and the clinical course, if multiple injured patients with concomitant femoral fractures benefit from the preferred intramedullary nailing with early weight bearing. Three hundred and two (23.8%) out of 1271 multiple injured patients (ISS > 17) had a concomitant femoral fracture. Fourty-seven out of 302 patients were children under 16 years of age, remaining 255 patients. Eighteen out of 255 patients died within the first 21 days after trauma and 66 patients required mechanical ventilation for more than three weeks (171/255). Thirty patients suffered from severe head injury (AIS-head > 3) and seven from severe pulmonary contusion with concomitant abdominal injury (134/255). Two patients had grade III open femoral fractures with vascular injury. Ipsilateral unstable pelvic fractures were seen in 11 patients, seven patients had ipsilateral intraarticular femoral fractures, and ipsilateral intraarticular fractures of the lower leg or foot were observed in 40 patients (74/255). The results demonstrate, that only 74 (29%) out of 255 multiple injured patients (> 16 years of age) had a theoretical benefit of early weight bearing. Seventy percent of the patients did not benefit from intramedullary nailing considering full weight bearing. With regard to pathophysiological concerns alternative methods of fracture fixation should be discussed for these patients. Primary fracture fixation with external fixators and secondary internal fixation proved to be a save alternative method. The complication rate of plating is comparable to intramedullary nailing but associated with less severe systemic risks. Primary plating of femoral fractures would not delay mobilization of most multiple injured patients.     

Elimination of the sidewall defects in selective epitaxial growth(SEG) of silicon for a dielectric isolation technology

Selective epitaxial growth (SEG) of silicon has not had widespread use as a dielectric isolation technology due to the near sidewall defects at the SiO₂/Si interface. These defects are located in the first 1-2 μm of the SEG/sidewall SiO₂ interface. Diode junctions intersecting the sidewall and 5 μm removed from the sidewall were fabricated in SEG material using thermally grown silicon dioxide (OX) and thermally nitrided thermal silicon dioxide (NOX) as the field insulating mask. Averaged over 16 devices of each type, diodes fabricated with NOX had much better low current I-V characteristics and minimum ideality factors (1.03) than diodes fabricated with OX field oxides (1.23). Junctions intersecting the NOX field insulator had nearly identical characteristics to bulk SEG     

The role of ion and solvent transport during the redox process of conducting polymers

The understanding of the redox behavior of conducting polymers is essential for a successful application of these so-called synthetic metals as functional coatings. The redox process involves the exchange of ions and solvent molecules. This so called doping/dedoping process involves changes of the mechanical and the electronic structure of the polymer. This paper discusses investigations at poly(3,4-ethylenedioxythiophene (PEDOT) and poly(pyrrole) (Ppy) by the electrochemical quartz crystal microbalance (EQCM) technique and electrochemical impedance spectroscopy (EIS). In the case of PEDOT a determination of the anion and the solvent fluxes was possible, and it was found that most anions replace solvent molecules upon their incorporation. The doping/dedoping mechanism of Ppy is more complicated. Here, the first redox cycles are characterized by a complex interplay of cation, anion and solvent fluxes with irreversible changes of the polymer structure. However, in combination with EIS new insights of the ion and solvent exchange and its influence on the electronic properties can be achieved.     

The p+n−n+ pulsed diode at extreme current densities—II: The forward pulsed case and its anomalous voltage response

The voltage transient response of the p⁺n^?n⁺ diode structure to a single intense current pulse in the forward direction is presented for current densities up to 10⁴ A/cm². The anomalous voltage response is studied by computer simulation of the device and compared with the experimental results. The response at these current densities becomes very dependent upon the carrier lifetimes and the recombination law chosen for the n⁺ region. At the larger current densities Avalanche generation and Auger recombination can exist simultaneously, yielding a larger than expected voltage across the device even as steady state is approached.