Dependability modeling using Petri-nets

This paper describes a methodology to construct dependability models using generalized stochastic Petri nets (GSPN) and stochastic reward nets (SRN). Algorithms are provided to convert a fault tree (a commonly used combinatorial model type) model into equivalent GSPN and SRN models. In a fault-tree model, various kinds of distributions can be assigned to components such as defective failure-time distribution, nondefective failure-time distribution, or a failure probability. The paper describes subnet constructions for each of these different cases, and shows how to incorporate repair in these models     

Granulomatous hepatitis: a retrospective study

51 cases of granulomatous hepatitis were seen among 1234 liver biopsies over a 10 year period. Tuberculosis was the commonest cause seen in 55 percent of cases. Other causes included leprosy, sarcoidosis, histoplasmosis, brucellosis, amoebic liver abscess, lymphoma and malignant granuloma. 12 percent of cases remained undiagnosed. Clinically these patients presented with pyrexia and hepatosplenomegaly. Jaundice was uncommon. Many showed elevated alkaline phosphatase levels, anaemia and raised ESR Granulomatous hepatitis of unknown aetiology with FUO was seen in 6 percent cases only.     

17 beta-estradiol induced prostatitis in the rat is an autoimmune disease

PURPOSE: Studies suggest that alteration in steroid hormone levels may be one of the factors causing nonbacterial prostatitis (NBP) in rats. We hypothesized that hormonally induced prostatitis in the rat may be an autoimmune disease. Studies were carried out to prove this hypothesis. MATERIALS AND METHODS: We injected 17 beta-estradiol (E2; 250 micrograms/kg. subcutaneously) or vehicle into 1-year-old male rats for 30 days, and isolated and cultured the splenocytes in the presence of con-A (Experiment 1). Approximately 10(7) splenocytes were adoptively transferred into young naive syngeneic rats. To find out whether or not the inflammation is mediated by T-lymphocytes, a pure population of T-lymphocytes from E2-treated 3-month-old rats was injected into young naive syngeneic rats (Experiment 2). To rule out the possibility that the inflammation was due to con-A itself, we cross-linked some T-cells with anti-CD3 antibody before adoptive transfer (Experiment 2). RESULTS: The recipients of splenocytes from E2-treated animals presented evidence of inflammation in terms of lymphocytic infiltration and presence of degranulated mast cells. Furthermore, we observed in these animals an increase in histamine-releasing peptide (HRP) levels, an indication of plasma extravasation. The T-cells stimulated by anti-CD3 antibody produced a similar degree of inflammation, thereby ruling out the possibility that the inflammation was due to con-A. The results also indicated that the immune response to antigen(s) is not dependent on the age of the animal but is dependent on a population of CD3+ T-cells. CONCLUSION: Our results demonstrate that hormonal imbalance and autoimmunity in male rats produce the symptoms of nonbacterial prostatitis.     

Chemical composition of mortars from the Ganga canal system

Investigations of the chemical composition of the lime mortars from the Ganga Canal System do not indicate the presence of any calcium hydroxide in the free state. The samples, however, were found to be heavily carbonated, and several compounds have been indicated.     

Myosin light chains (MLCs) heterogeneity in mammalian smooth and cardiac muscle

Tuberous sclerosis (TS) is well known to be occasionally associated with subependymal giant cell astrocytoma (SGCA). SGCA is considered to be a benign tumor in its clinical course and morphology. However, this tumor is grown sometimes so rapid and caused hydrocephalus. To our knowledge, little is known about hemocirculation and metabolism, particularly in relation with proliferating activity of TS and SGCA. We measured hemocirculation and metabolism of SGCA developed in a case of TS using positron emission tomography (PET). A 13-year-old-boy who had frequently developed convulsions four months after birth. He was diagnosed as TS and had been medically treated with anticonvulsants, since multiple intraventricular calcifications were detected by CT, at the age of five months. The convulsions had been well controlled. In March 1993, he presented with syncopal attack and admitted to our hospital. CT showed multiple subependymal nodules. Among the nodules, one of the left anterior horn exceeded 2cm in size obliterated Monro's foramen. The tumor was homogeneously enhanced with contrast medium. The lesion detected by postcontrast T1-weighted MR imaging had almost the same status as that by CT. T2-weighted image revealed cortical tubers as high intensity area at the left frontal and parietooccipital regions. PET was performed with the Headtome IV. Hemocirculation of the tumor was lower than that of contralateral gray matter, which suggested poor blood supply. The oxygen and glucose metabolism of the tumor were decreased compared with contralateral gray matter, indicative of a low activity of proliferation and a clinically benign tumor in the present case.(ABSTRACT TRUNCATED AT 250 WORDS)     

Numerical methods for reliability evaluation of Markov closedfault-tolerant systems

This paper compares three numerical methods for reliability calculation of Markov, closed, fault-tolerant systems which give rise to continuous-time, time-homogeneous, finite-state, acyclic Markov chains. The authors consider a modified version of Jensen's method (a probabilistic method, also known as uniformization or randomization), a new version of ACE (acyclic Markov chain evaluator) algorithm with several enhancements, and a third-order implicit Runge-Kutta method (an ordinary-differential-equation solution method). Modifications to Jensen's method include incorporating stable calculation of Poisson probabilities and steady-state detection of the underlying discrete-time Markov chain. The new version of Jensen's method is not only more efficient but yields more accurate results. Modifications to ACE algorithm are proposed which incorporate scaling and other refinements to make it more stable and accurate. However, the new version no longer yields solution symbolic with respect to time variable. Implicit Runge-Kutta method can exploit the acyclic structure of the Markov chain and therefore becomes more efficient. All three methods are implemented. Several reliability models are numerically solved using these methods and the results are compared on the basis of accuracy and computation cost     

Defects in conducting polymers

New types of defects such as solitons, polarons and bipolarons in conducting polymers have been discussed in this article. In the light of recent experimental results, the bipolaronic model of conduction has been re-examined. It is shown that more elaborate experiments are essential to confirm the hypothesis of charge transport via bipolarons in these newer synthetic metals.     

Material science aspects of phase change optical recording

Chalcogenide thin films are used as the recording medium for phase change-type optical memory discs. The films are switched between amorphous and crystalline states using the heat of a focussed laser beam. Large reflectivity differences between amorphous and crystalline states are then used to store and retrieve the information. An active chalcogenide layer for this purpose should have a high optical absorption coefficient (α), and good structural and thermal stability. It should be possible to switch the chalcogenide layer between amorphous and crystalline states repeatedly within a short duration, the optical contrast should be high, and the material must have large cycling capability. Keeping the above requirements in mind, we have carried out systematic investigation of structural, optical and crystallization behaviour of thin films of various compositions of GaGeTe, Sb₂Te₃ and BiSe. These studies have shown that these materials can be good candidates for use as recording media in erasable phase-change optical recording.     

Pore formation in cast metals and alloys

Porosity occurs in cast solidifying metals and alloys due to negative pressures generated during solidification contraction, and pressure developed by gases dissolved in the motten metal. Both the above processes may act either together or separately to produce such shrinkage or gas defects (collectively termed pores). They are generally unwanted and constitute a major industrial problem. This paper is an attempt to review up-to-date knowledge of the conditions of pore formation in cast metals and alloys. Various mechanisms responsible for pore nucleation and growth are summarized, and experimentally evaluated using an unfed type of mould with aluminium alloy castings. The observations are in support of a non-nucleation mechanism of pore formation playing a major role in the occurrence of such defects in cast metals. Further, in gas-containing alloy melts the critical amounts of gas required for single and multiple pore nucleation have been determined quantitatively and are listed in the text. The gas contents of the melts were measured using an apparatus based on the first bubble technique. It is also experimentally observed that under poor feeding conditions more than one of the non-classical nucleation mechanisms may be functional at the same time for the formation of such defects.Nomenclature P _e Sum of external forces which tend to collapse a pore - P _h Hydrostatic pressure - P _g Internat gas pressure in liquid metal - P _a Atmospheric pressure applied during solidification - P _s Shrinkage pressure - Surface tension at gas-metal interface - P _f Fracture pressure of liquid metal - 2_/r Surface tension resistance - V _i Volume of initial gas content of liquid Metal - P _i Total internal pressure due to gas and/or shrinkage - K _s,K _L Gas solubility constants of solid and liquid metal, respectively - K K_s/K_L - r Radius of liquid channel - R Radius of cylindrical casting - L Length of liquid channel - L _c Length of cylindrical casting - f ₁ Fraction of liquid left in the casting of pure and short freezing-range alloy, r ² L/R ² L _c - V _i ^* Critical gas content - t Tortuosity of channel - n Number of channels (approximately number of dendrite arms per unit area) - f _L Fraction of liquid left in the casting of mushy freezing alloys, r ² nt/R ² - B K _Lnt(1 -K) - nb _i ² B² (approximately) - r* Critical radius for pore nucleation (pore belowr* size cannot exist) - Surface tension of liquid - N Avogadro's number - k Boltzmann constant - h Planck's constant - T Temperature (K) - a,b Inner and outer radii of solidified shell - Y Uniaxial yield stress - , _s Energy per unit area of solid-liquid and solid-vapour interface, respectively - h Thermal diffusivity of solid metal - C_p Specific heat of solid metal - m,K ₁,K ₂ Constants - Fractional contraction of liquid phase on solidification [(solid density — liquid density)/solid density] - /(1 –) - Vortex circulation factor - d Density of liquid - Metal viscosity - h ₁ Thermal conductivity of mould - H Heat of fusion of metal