An experiment in software reliability: Additional analyses using data from automated replications

A study undertaken to collect software error data of laboratory quality for use in the development of credible methods for predicting the reliability of software used in life-critical applications is summarized. The software error data reported were acquired through automated repetitive run testing of three independent implementations of a launch interceptor condition module of a radar tracking problem. The results are based on 100 test applications to accumulate a sufficient sample size for error rate estimation. The data collected is used to confirm the results of two Boeing studies reported in NASA-CR-165836 Software Reliability: Repetitive Run Experimentation and Modeling, and NASA-CR-172378 Software Reliability: Additional Investigations into Modeling With Replicated Experiments, respectively. That is, the results confirm the log-linear pattern of software error rates and reject the hypothesis of equal error rates per individual fault. This rejection casts doubt on the assumption that the program's failure rate is a constant multiple of the number of residual bugs; an assumption which underlies some of the current models of software reliability. data raises new questions concerning the phenomenon of interacting faults

Preliminary design of the redundant software experiment

The goal of the present experiment is to characterize the fault distributions of highly reliable software replicates, constructed using techniques and environments which are similar to those used in comtemporary industrial software facilities. The fault distributions and their effect on the reliability of fault tolerant configurations of the software will be determined through extensive life testing of the replicates against carefully constructed randomly generated test data. Each detected error will be carefully analyzed to provide insight in to their nature and cause. A direct objective is to develop techniques for reducing the intensity of coincident errors, thus increasing the reliability gain which can be achieved with fault tolerance. Data on the reliability gains realized, and the cost of the fault tolerant configurations can be used to design a companion experiment to determine the cost effectiveness of the fault tolerant strategy. Finally, the data and analysis produced by this experiment will be valuable to the software engineering community as a whole because it will provide a useful insight into the nature and cause of hard to find, subtle faults which escape standard software engineering validation techniques and thus persist far into the software life cycle

Dextromethorphan as a potential neuroprotective agent with unique mechanisms of action

BACKGROUND: Dextromethorphan (DM) is a widely-used antitussive. DM\u27s complex central nervous system (CNS) pharmacology became of interest when it was discovered to be neuroprotective due to its low-affinity, uncompetitive N-methyl-d-aspartate (NMDA) receptor antagonism. REVIEW SUMMARY: Mounting preclinical evidence has proven that DM has important neuroprotective properties in various CNS injury models, including focal and global ischemia, seizure, and traumatic brain injury paradigms. Many of these protective actions seem functionally related to its inhibitory effects on glutamate-induced neurotoxicity via NMDA receptor antagonist, sigma-1 receptor agonist, and voltage-gated calcium channel antagonist actions. DM\u27s protection of dopamine neurons in parkinsonian models may be due to inhibition of neurodegenerative inflammatory responses. Clinical findings are limited, with preliminary evidence indicating that DM protects against neuronal damage. Negative findings seem to relate to attainment of inadequate DM brain concentrations. Small studies have shown some promise for treatment of perioperative brain injury, amyotrophic lateral sclerosis, and symptoms of methotrexate neurotoxicity. DM safety/tolerability trials in stroke, neurosurgery, and amyotrophic lateral sclerosis patients demonstrated a favorable safety profile. DM\u27s limited clinical benefit is proposed to be associated with its rapid metabolism to dextrorphan, which restricts its central bioavailability and therapeutic utility. Systemic concentrations of DM can be increased via coadministration of low-dose quinidine (Q), which reversibly inhibits its first-pass elimination. Potential drug interactions with DM/Q are discussed. CONCLUSIONS: Given the compelling preclinical evidence for neuroprotective properties of DM, initial clinical neuroprotective findings, and clinical demonstrations that the DM/Q combination is well tolerated, this strategy may hold promise for the treatment of various acute and degenerative neurologic disorders. © 2007 Lippincott Williams & Wilkins, Inc

Substrate-Gated Transformation of a Pre-Catalyst into an Iron-Hydride Intermediate [(NO)2_2 (CO)Fe(μ-H)Fe(CO)(NO)2_2]−^− for Catalytic Dehydrogenation of Dimethylamine Borane

Continued efforts are made on the development of earth-abundant metal catalysts for dehydrogenation/hydrolysis of amine boranes. In this study, complex [K-18-crown-6-ether][(NO)$_2$Fe(μ-$^{Me}$Pyr)(μ-CO)Fe(NO)$_2$] (3-K-crown, $^{Me}$Pyr = 3-methylpyrazolate) was explored as a pre-catalyst for the dehydrogenation of dimethylamine borane (DMAB). Upon evolution of H$_{2(g)}$ from DMAB triggered by 3-K-crown, parallel conversion of 3-K-crown into [(NO)$_2$Fe(N,N′-$^{Me}$PyrBH$_2$NMe$_2$)]− (5) and an iron-hydride intermediate [(NO)$_2$(CO)Fe(μ-H)Fe(CO)(NO)$_2$]$^−$ (A) was evidenced by X-ray diffraction/nuclear magnetic resonance/infrared/nuclear resonance vibrational spectroscopy experiments and supported by density functional theory calculations. Subsequent transformation of A into complex [(NO)$_2$Fe(μ-CO)$_2$Fe(NO)$_2$]$^−$ (6) is synchronized with the deactivated generation of H$_{2(g)}$. Through reaction of complex [Na-18-crown-6-ether][(NO)$_2$Fe(η$^2$-BH$_4$)] ($_4$-Na-crown) with CO(g) as an alternative synthetic route, isolated intermediate [Na-18-crown-6-ether][(NO)$_2$(CO)Fe(μ-H)Fe(CO)(NO)$_2$] (A-Na-crown) featuring catalytic reactivity toward dehydrogenation of DMAB supports a substrate-gated transformation of a pre-catalyst [(NO)$_2$Fe(μ-$^{Me}$Pyr)(μ-CO)Fe(NO)$_2$]$^−$ (3) into the iron-hydride species A as an intermediate during the generation of H$_{2(g)}$

A high-frequency divider in 0.18 µm SiGe BiCMOS technology

High speed frequency dividers are critical parts of frequency synthesisers in wireless systems. These dividers allow the output frequency from a voltage controlled oscillator to be compared with a much lower external reference frequency that is commonly used in these synthesisers. Common trade-offs in high frequency dividers are speed of division, power consumption, real estate area, and output signal dynamic range. In this paper we demonstrate the design of a high frequency, low power divider in 0.18 µm SiGe BiCMOS technology. Three dividers are presented, which are a regenerative divider, a master-slave divider, and a combination of regenerative and master-slave dividers to perform a divide-by-8 chain. The dividers are used as part of a 60 GHz frequency synthesizer. The simulation results are in agreement with measured performance of the regenerative divider. At 48 GHz the divider consumes 18 mW from a 1.8 V supply voltage. The master-slave divider operates up to 36 GHz from a very low supply voltage, 1.8 V. The divide-by-8 operates successfully from 40 GHz to 50 GHz.9 page(s