A method for software reliability analysis and predictionapplication to the TROPICO-R switching system

An evaluation method which allows existing reliability growth models to provide better predictions of software behavior is presented. The method is primarily based on the analysis of the trend exhibited by the data collected on the program (which is determined by reliability growth tests). Reliability data are then partitioned according to the trend, and two types of reliability growth models can be applied: when the data exhibit reliability decrease followed by reliability growth, an S-shaped model can be applied, and in case of reliability growth, most of the other existing reliability growth models can be applied. The hyperexponential model is shown to allow prediction of the software residual failure rate in operation, and this failure rate is used as a qualification index for the software product. The method is illustrated through its application to the Brazilian electronic switching system TROPICO-R     

Ion implantation in gallium arsenide MESFET technology

The authors emphasize controlled shallow doping of GaAs by ion implantation and its limitations to state-of-the-art GaAs IC technology. The authors discuss the electrical activation behavior of implanted silicon in GaAs upon subsequent capless or silicon nitride capped rapid thermal annealing (RTA). It is demonstrated that atomic H diffuses into the implanted region of GaAs from a plasma-enhanced chemical vapor deposition Si₃N₄ cap during the deposition as well as during subsequent annealing, and the H retards the electrical activation kinetics of the implanted Si. Thru-Si cap dopant implants into GaAs have been studied to enhance dopant concentration in the surface region of the GaAs by recoil-implanted Si from the cap. Application of ion implantation to achieve buried-p layers in GaAs is also briefly discussed     

Effect of dietary fat on lymphocyte proliferation and metabolism

Dendritic cells (DC) are bone marrow-derived leukocytes that act as powerful stimulators of primary and secondary immune responses. Langerhans cells (LC), which are immature DC in epidermis and genital mucosa, are generally believed to be the initial cells infected with HIV following mucosal exposure to virus. Interestingly, freshly isolated LC express the HIV coreceptor CCR5, but not CXCR4, on their cell surfaces. This expression pattern would theoretically allow only macrophage-tropic [and not T cell (TC)-tropic] HIV to be transmitted across intact mucosal epithelium. In vitro, it is known that HIV infects LC (and other DC) in a CD4- and HIV coreceptor-dependent manner. In addition, HIV can be captured by prominent stellate processes on the surface of LC/DC. HIV-infected DC, as well as DC that have captured HIV, efficiently transmit virus to TC during antigen-specific TC activation. Thus, DC may be involved in HIV plasma viremia increases observed following antigenic exposure, e.g. immunizations, in chronically HIV-infected individuals by (1) activating latently infected TC or (2) activating and transmitting virus to new target TC. In summary, DC most likely play a major role in primary HIV infection by allowing virus to breach mucosal surfaces, and can act during both initial and chronic phases of HIV disease by facilitating infection and depletion of TC.     

Effects of the memory enhancer linopirdine (Dup 996) on cerebral glucose metabolism in naive and hypoxia-exposed rats

Phencyclidine (PCP), a psychotomimetic drug of abuse, produces mental changes and manifestations in humans which are reminiscent of schizophrenia, though the mechanism of these actions remains unknown. We report here a biphasic time course of PCP action on regional cerebral glucose metabolism extending over 48 h. A single dose of PCP (8.6 mg/kg) produces an initial increase in glucose metabolism (at 3 h) and a later decrease in glucose metabolism (at 24 h) without a return to baseline until 48 h. A single lower dose of PCP (0.86 mg/kg), a dose which is considered selective for action at the NMDA-PCP receptor, produces no early metabolic change (at 3 h), but replicates the regional hypometabolism albeit less intense at 24 h. The delayed cerebral hypometabolism does not appear to be related to PCP-induced intracellular vacuolization, seen in the retrosplenial cortex. These metabolic changes may be associated with the psychotomimetic effects of PCP and thus may be relevant to psychosis in humans.     

Characterization of Ni-Mo/Al2O3 catalysts prepared by simltaneous impregnation of the active components

Three Ni-Mo/Al₂O₃, catalysts were prepared, containing similar amounts of NiO (2.8%) and MoO₃ (13.5%), by simultaneous impregnation of the active components, varying the nature of the solubilizing agent (ammonia, citric acid and phosphoric acid). The catalysts were characterized with respect to texture (surface area and pore volume), presence of crystalline phases (XRD), distribution of active components (EPMA) and nature of the active phases (DRS). Catalytic activity was measured using thiophene hydrogenolysis as a model reaction. A commercial Ni-Mo catalyst of similar composition was characterized by the same methods.

The catalyst prepared in the phosphoric acid medium (catalyst P) had a significantly lower surface area. In phosphorus-containing catalysts there was a marked tendency of this element to be deposited on the external region of the catalyst extrudates. The DRS spectra showed that Mo was present predominantly as polymolybdate species in all cases. In the industrial catalyst (catalyst I) the presence of nickel spinel was clearly observed. Catalyst P had an absorption minimum in the visible region displaced to higher wavelength compared to the catalysts prepared in ammonia (catalyst A) and citric acid (catalyst C) media. The observed order of activity was P > C > A > I.     

The influence of layered compounds on the properties of starch/layered compound composites

Glycerol‐plasticized starch films were modified by addition of various layered compounds as fillers, two being of natural origin (kaolinite, a neutral mineral clay, and hectorite, a cationic exchanger mineral clay) and two synthetic (layered double hydroxide, LDH, an anionic exchanger, and brucite, having a neutral structure). The effects of the filler type and the plasticizer were analyzed by X‐ray diffraction, dynamic mechanical analysis and thermogravimetry. The storage modulus was higher for kaolinite > brucite > hectorite than for LDH starch composites. However, only the hectorite filler presented a shift of the interplanar basal distance to higher values, which represents the intercalation of glycerol molecules between the clay layers. The glycerol intercalation is minimized in plasticized–oxidized starch films where the oxidized starch chains are preferentially intercalated. Copyright © 2003 Society of Chemical Industry     

Double semiconductor substrate in overlay shielded superconducting microstrip lines

The Transverse Transmission Line (TTL) is used in the theory of the overlay shielded microstrip lines considering the superconductor strip on two semiconductor regions. The superconductor effect is included with the boundary condition of the surface impedance, that is related to the complex conductivity of the material, calculated from the advanced two-fluid model. Applying the moment method the complex propagation constant of the structure, including the phase constant and the attenuation constant, is obtained. Results are presented for the complex propagation constant, versus the frequency and the temperature, of this overlay superconducting microstrip lines.     

Continuous-time tracking problems in an H∞setting: a game theory approach

This paper investigates the problem of finite-horizon H_∞ tracking for linear time-varying systems. Three tracking problems are considered, depending on whether the reference signal is perfectly known in advance, measured on-line, or previewed in fixed interval of time ahead. No a priori knowledge of a dynamic model for the reference signal is assumed. A game theory approach to the latter tracking problems is presented where, given a specific reference signal, the controllers play against nature which can choose any initial state and any bounded energy disturbance input and measurement noise. Necessary and sufficient conditions for the existence of a saddle-point equilibrium are determined, and H_∞ tracking controllers for both the cases of state and output feedback are derived. Tracking problems for time-invariant systems on infinite-horizon are also analyzed, and time invariant tracking controllers are obtained for zero initial conditions