Scheduled maintainance policies of repairable computer systems

For systems which can undergo repair, it is common to use regular maintance policies as a means to achieve availability requirements. We develop a solution method to analyze various scheduled maintainance policies of repairable computer systems. The analysis is applicable to systems with failure behaviour which can be modeled by a continuous-time MArkov process, and thus important characteristics can be included in the model. Furthermore, we do not use the assumption of perfect repair, which is unrealistic for most systems. We obtain both transient and steady-state measures. The solution approach is based on the randomization technique and possesses advantagessuch as numerical stability and ease of implementation.Para sistemas que podem ser reparados, é comum o uso de políticas de manutenção regular como meio de se obter desejada confiabilidade. Neste artigo, desenvolvemos um método de solução para analisar várias políticas de manutenção de sistemas de computação reparáveis. A análise se aplica a sistemas cujo comportamento de falha pode ser modelado por um processo de Markov de tempo contínuo e, por conseguinte, características importantes podem ser incluídas no modelo. Além do mais, não é necessário supor que o sistema é reparado com perfeição ao término de um período de manutenção. Esta suposição não é realística na maioria dos casos. São obtidas tanto medidas transientes quanto medidas em estado estacionário. O método de solução é baseado na técnica de aleatorização e possui vantagens tais como estabilidade numérica e facilidade de implementação

The Kindred Bonds of Mentally Ill Homeless Persons

While the unraveling of the kinship bond has long been suspected to play a role in the epidemiology of homelessness, the connection between kinship and homelessness has been little studied. Based on a normative analysis of the role of family structure in response to adversity, this article explores the impact of the amount and quality of kinship ties on episodes of homelessness experienced by discharged psychiatric patients in Ohio. Survey data derived from personal interviews with both former patients and their kin indicate more strain in relations with kin of the homeless than the nonhomeless. The strain in the kinship bond appears to emanate from a greater prevalence of chronic disabilities that undermine independent functioning and tax the resources of relatives who choose to remain involved. Consistent with this interpretation, patients with histories of homelessness reported more psychiatric symptoms, more deficits in daily living skills, and more contact with the criminal justice system. In general, patient variables were better able than family variables to differentiate the homeless from the nonhomeless. Nonetheless, the formulation of public policies for reducing the incidence and prevalence of homelessness will surely need to take account of the kinship bond and how it can be strengthened

Advanced information processing system: Hosting of advanced guidance, navigation and control algorithms on AIPS using ASTER

This program demonstrated the integration of a number of technologies that can increase the availability and reliability of launch vehicles while lowering costs. Availability is increased with an advanced guidance algorithm that adapts trajectories in real-time. Reliability is increased with fault-tolerant computers and communication protocols. Costs are reduced by automatically generating code and documentation. This program was realized through the cooperative efforts of academia, industry, and government. The NASA-LaRC coordinated the effort, while Draper performed the integration. Georgia Institute of Technology supplied a weak Hamiltonian finite element method for optimal control problems. Martin Marietta used MATLAB to apply this method to a launch vehicle (FENOC). Draper supplied the fault-tolerant computing and software automation technology. The fault-tolerant technology includes sequential and parallel fault-tolerant processors (FTP & FTPP) and authentication protocols (AP) for communication. Fault-tolerant technology was incrementally incorporated. Development culminated with a heterogeneous network of workstations and fault-tolerant computers using AP. Draper's software automation system, ASTER, was used to specify a static guidance system based on FENOC, navigation, flight control (GN&C), models, and the interface to a user interface for mission control. ASTER generated Ada code for GN&C and C code for models. An algebraic transform engine (ATE) was developed to automatically translate MATLAB scripts into ASTER

Hydrogenation of CO on a silica surface: an embedded cluster approach

The sequential addition of H atoms to CO adsorbed on a siliceous edingtonite surface is studied with an embedded cluster approach, using density functional theory for the quantum mechanical (QM) cluster and a molecular force field for the molecular mechanical (MM) cluster. With this setup, calculated QM/MM adsorption energies are in agreement with previous calculations employing periodic boundary conditions. The catalytic effect of the siliceous edingtonite (100) surface on CO hydrogenation is assessed because of its relevance to astrochemistry. While adsorption of CO on a silanol group on the hydroxylated surface did not reduce the activation energy for the reaction with a H atom, a negatively charged defect on the surface is found to reduce the gas phase barriers for the hydrogenation of both CO and H2C = O. The embedded cluster approach is shown to be a useful and flexible tool for studying reactions on (semi-)ionic surfaces and specific defects thereon. The methodology presented here could easily be applied to study reactions on silica surfaces that are of relevance to other scientific areas, such as biotoxicity of silica dust and geochemistry

Parental Attitudes toward Genetic Testing for Pediatric Deafness

Recent molecular genetic advances have resulted in genetic testing becoming an option for deaf individuals and their families. However, there is little information about the interest in such testing. To investigate this issue, parents with normal hearing who have one or more deaf children were surveyed about their attitudes toward diagnostic, carrier, and prenatal genetic testing for deafness. This population was chosen because it represents the majority of individuals who are encountered in clinical practice, given that 90%–95% of deaf individuals are born to persons with normal hearing. Of 328 surveys distributed, 96 were completed and returned. Of the respondents, 96% recorded a positive attitude toward genetic testing for deafness, including prenatal testing, although none would use this information to terminate an affected pregnancy. All respondents had a poor understanding of genetics, with 98% both incorrectly estimating the recurrence risk of deafness and misunderstanding the concept of inheritance. Notably, these findings were similar in the group who had had genetic testing for their children and in the group who had not, suggesting either that the parents who received genetic testing did not receive genetic counseling or that the counseling was not effective. On the basis of these results, it was concluded that this population is interested in the use of genetic testing and that testing should not be done without first providing formal genetic counseling. Appropriate counseling can help parents to understand the risks, benefits, and limitations of genetic testing

Performability analysis of computer systems : from model specification to solution

Computer system relialbility/availability modeling deals with the representation of changes in the structure of the system being modeled, which are generally due to faults, and how such changes affect the availability of the system. On the other hand, performance modeling involves representing the probabilistic nature of user demands and predicting the system capacity to perform useful work, under the assumption that the system structure remains constant. With the advent of degradable systems, the system may be restructurcd in responsc to faults and may continue to perform useful ,work, even though operating at lower capacity. Performability modeling considers the effect of structural changes and their impact on the overall performance of the system. The complexity of current computer systems and the variety of different problems to be analyzed, including the simultaneous evaluation of performance and availability, demonstrate the need for sophisticated tools that allow the specification of general classes of problems while incorporating powerful analytic and/or simulation techniques. Concerning model specification, a recently proposed object oriented modeling paradigm that accommodates a wide variety of applications is discussed and compared with other approaches. With respect to solution methods, a brief overview of past work on performability evaluation of Malkov models is presented. Then it is shown that many performability related measures can be calclllated using the uniformization or randomization technique by marking distinguished states and/or transitions of the Malkov model of the system being studied. Finally, the state space explosion ploblem is addressed and several techniques for dealing with the ploblem are discussed.Modelagem de disponibilidade/confiabilidade de sistemas de computação diz respeito à representação de mudanças na estrutura do sistema sendo modelado, geralmente, causadas por falhas, e como essas mudanças afetam a disponibilidade do sistema. Modelagem de desempenho, por outro lado, é voltada para a representação da natureza probabilística das demandas dos usuários e tenta prever a capacidade do sistema pra realizar tarefas, supondo-se que a estrutura do sistema permanece constante. Com o advento de sistemas desagradáveis, o sistema pode ser reestruturado em consequência a falhas e pode continuar a realizar tarefas, mesmo a uma capacidade reduzida. Análise de desempenhabilidade ('performability') considera o efeito das mudanças estruturais e o seu impacto no desempenho lobal do sistema. A complexibilidade dos atuais sistemas de computação, e a variedade de diferentes problemas a serem analisados, incluindo avaliação simultânea de desempenho e disponibilidade, demonstram a necessidade de ferramentas sofisticadas que permitam a especificação de uma classe geral de problemas além de incorporarem técnicas poderosas analíticas e/ou de simulação. No que diz respeito a especificação do modelo, é discutido um paradigma orientado a objeto, recentemente proposto, que acomoda uma grande variedade de aplicações. As principais vantagens deste paradigma são discutidas e é feita uma comparação com outras técnicas. No que diz respeito a métodos de solução, é feito um breve apanhado de desempenhabilidade de modelos Markov. É mostrado então, que muitas medidas relacionadas a desempenhabilidade podem ser calculadas usando-se a técnica de aleatorização (uniformização), marcando-se estados e/ou transições do modelo Markoviano do sistema sendo estudado. Finalmente, o problema de explosão de estados é abordado, e várias técnicas para lidar com o problema são discutidas

Antigenic specificity of antibody-dependent cell-mediated cytotoxicity directed against human immunodeficiency virus in antibody-positive sera

Antibody-dependent cell-mediated cytotoxicity (ADCC) specific for human immunodeficiency virus (HIV) has been described for HIV-infected individuals. To determine the antigenic specificity of this immune response and to define its relationship to the disease state, an ADCC assay was developed using Epstein-Barr virus-transformed lymphoblastoid cell line targets infected with vaccinia virus vectors expressing HIV proteins. The vaccinia virus vectors induced appropriate HIV proteins (envelope glycoproteins gp160, gp120, and gp41 or gag proteins p55, p40, p24, and p17) in infected lymphoblastoid cell lines as demonstrated by radioimmunoprecipitation and syncytia formation with c8166 cells. Killer cell-mediated, HIV-specific ADCC was found in sera from HIV-seropositive but not HIV-seronegative hemophiliacs. This HIV-specific response was directed against envelope glycoprotein but was completely absent against target cells expressing the HIV gag proteins. The ADCC directed against gp160 was present at serum dilutions up to 1/316,000. There was no correlation between serum ADCC titer and the stage of HIV-related illness as determined by T-helper-cell numbers. These experiments clearly implicated gp160 as the target antigen of HIV-specific ADCC activity following natural infection. Vaccines which stimulate antibodies directed against gp160, which are capable of mediating ADCC against infected cells, could be important for protection against infection by cell-associated virus

Detection of major histocompatibility complex class I-restricted, HIV-specific cytotoxic T lymphocytes in the blood of infected hemophiliacs

Major histocompatibility (MHC)-restricted, human immunodeficiency virus type one (HIV-1)-specific, cytotoxic T lymphocytes (CTLs) were detected in the peripheral blood mononuclear cells (PBMCs) of HIV-1-infected individuals. Using a system of autologous B and T lymphoblastoid cell lines infected with recombinant vaccinia vectors (VVs) expressing HIV-1 gene products, we were able to detect HIV-1-specific cytolytic responses in the PBMCs of 88% of HIV-1-seropositive hemophiliac patients in the absence of in vitro stimulation. These cytolytic responses were directed against both HIV-1 envelope and gag gene products. The responses were resistant to natural killer (NK) cell depletion and were inhibited by monoclonal antibodies (MoAbs) to the T cell receptor, CD8 surface antigens, and MHC class I antigens, suggesting a classical MHC class I restricted, virus-specific CTL response

The Lantern Vol. 28, No. 1, January 1961

• I Felt Horror That Day • John Ten • Term Paper: Circa 3032 A.D. • Villanelle • Lament • Joy of Bearded Boy • U.S. Foreign Policy: The Future • Contrast • Camp Crowder • Whispered Sounds • Pity, Love • Not Quite Free • Experiences of a Heroin Addict • The Hawk • The Second Apple • Reaction • Poor Family, Moving • Torch Ends Sputter in the Pall • Late Date • She\u27ll Call Mehttps://digitalcommons.ursinus.edu/lantern/1079/thumbnail.jp