A bayesian semiparametric analysis for additive Hazard models with censored observations

The hazard function, also called the risk function or intensity function, is usually used to model survival data or other waiting times, such as unemployment times. In contrast to the proportional hazard model, the additive risk model assumes that the hazard function is the sum of rather than the product of, the baseline hazard function and a non-negative function of covariates. We propose to introduce the covariates into the model through a Gamma hazard function, while the baseline hazard function is left unspecified. Following the Bayesian paradigm, we obtain an approximation to the posterior distribution using Markov Chain Monte Carlo techniques. The subject-specific survival estimation is also studied. A real example using unemployment data is provided. This work was partially supported by the Spanish Education and Science Council Project PB96-0776.     

Changes in culturability and virulence of Salmonella typhimurium during long-term starvation under desiccating conditions

The survival of Salmonella typhimurium under desiccation and starvation conditions commonly associated with farm buildings was investigated in a desiccation model system: filtration onto polycarbonate membranes placed in a sealed desiccator with 0.0067 g/m³ absolute humidity. Heterogeneities within bacterial populations in relation to time of desiccation were investigated on a single-cell basis by epifluorescence microscopy coupled with an image analysis system in conjunction with fluorescent dyes Chemchrome V6 and DAPI. Changes in cellular states were compared to the results of plate counts (colony forming units, CFU) on selective (modified semi-solid Rappaport Vassiliadis (MSRV)) and non-selective (nutrient agar (NA) and R2A agar) media, and to the measurements of infectivity and virulence using two animal models (chicks and mice). During 9 weeks of experimental desiccation, total cell counts (DAPI) of starved S. typhimurium remained stable, as did esterase activity (Chemchrome V6), but DAPI fluorescence intensity decreased slowly. Bacterial cells entered gradually into non-culturable states (decrease of CFU counts on MSRV, NA and R2A agar media) and the total loss of culturability on NA (defined as probability of presence of 1 CFU on the membrane inferior to 10⁻⁶) was obtained after 9 weeks. Loss of chick infectivity and mice virulence in animal models occurred more rapidly, within three weeks of experimental desiccation.     

Effect of p53 on lung carcinoma cells irradiated by carbon ions or X-rays

The study is to investigate the feasibility and advantages of heavy ion beams on radiotherapy. The cellular cycle and apoptosis, cell reproductive death and p53 expression evaluated with flow cytometry, clonogenic survival assays and Western blot analysis were examined in lung carcinoma cells after exposure to 89.63 MeV/u carbon ion and 6 MV X-ray irradiations, respectively. The results showed that the number colonyforming assay of A549 was higher than that of H1299 cells in two radiation groups; A549 cellular cycle was arrested in G2/M in 12 h and the per-centage of apoptosis ascended at each time point of carbon ion radiation with doses, the expression of p53 upregulated with doses exposed to X-ray or carbon ion. The cell number in G2/M of H1299 and apoptosis were increasing at all time points with doses in 12C6+ ion irradiation group. The results suggested that the effects of carbon ions or X rays ir-radiation on lung carcinoma cells were different, 12C6+ ion irradiation could have more effect on upregulating the ex-pression of p53 than X-ray, and the upregulated expression of p53 might produce the cellular cycle G2/M arrested, apoptosis increasing; and p53 gene might affect the lung cancer cells radiosensitivity.     

The selection and characterization of the mutants in bioflocculant bacteria C8 induced by 3 MeV helium ion irradiation

A 3 MeV He²⁺ beam was used to irradiate C8 (a flocculant-producing bacteria) with a fluence ranging from 10¹¹ to 10¹³ ions/cm². The effects on the survival ratio, TTC-dehydrogenase activity, flocculating activity and RAPD analysis are reported. The survival ratio curve caused by irradiation is proved to be “saddle-shaped”. Eleven mutants were obtained, all of which had a significant change in dehydrogenase activity and most showed a positive change in flocculating activity. RAPD measurements were used to analyse the DNA of mutants with a flocculating activity over 80%, which indicated that all their DNA had been changed by irradiation.     

一种高速Viterbi译码器的优化设计及Verilog实现

文章设计了一种高速Viterbi译码器，该设计基于卷积码编码及其Viterbi译码原理，完成了Viterhi译码的核心单元算法的优化，并采用Verilog语言编程实现了卷积码编码器和译码器。仿真和综合的结果表明本文设计的译码器速率达50Mbit／s，同时译码器的电路规模也通过算法得到了优化。     

Life history of Trogoderma granarium Everts (Coleoptera: Dermestidae) on peeled barley,peeled oats and triticale

The life history of the khapra beetle, Trogoderma granarium Everts (Coleoptera: Dermestidae), was investigated on cracked peeled barley, cracked peeled oats and cracked triticale. The results suggest that the biological and demographic parameters of T. granarium are affected by the tested commodities. The developmental time of total immature period of T. granarium was significantly lower on barley (35.06 days) than on oats (42.87 days) and triticale (43.58 days). Mean longevities of adult females were 7.00, 7.89 and 8.24 days, and for adult males were 5.79, 6.05 and 5.49 days when T. granarium fed on barley, oats and triticale, respectively. The highest fecundity recorded when T. granarium fed on barley (39.0 eggs/female) or triticale (35.2 eggs/female), but it was significantly lower when this species fed on oats (25.4 eggs/female). While the net reproductive rate did not differ significantly when T. granarium fed on barley (14.6 females/female), oats 10.2 (females/female) and triticale (11.0 females/female), the mean generation time was significantly lower when fed on barley (40.5 days) than on oats (48.7 days) and triticale (46.1 days). The intrinsic rate of increase of T. granarium did not differ significantly when fed on barley and triticale (0.066 and 0.052 females/female/day, respectively), but it was significantly lower when fed on oats (0.047 females/female/day). The biological and demographic parameters of T. granarium may be incorporated in population models that evaluate the population dynamics aiming to the optimization of management strategies against this noxious species.     

Sensory cut-off point obtained from survival analysis statistics

In the present work we applied interval-censored survival analysis techniques to estimate sensory cut-off points based on consumer’s decision to accept or reject food products taking into account the inherent variability in sensory measurements. We compared the values obtained using this survival analysis methodology with those obtained by applying a previous regression based method. Cut-off point (COP) estimations were made for acid flavor in yogurt, strawberry flavor in a strawberry flavored drink and appearance quality index in broccoli. For two of these products the regression based cut-off points were unrealistic, and would lead to much too conservative COP’s, leading to unnecessary rejection of samples in quality control inspections or very short shelf-lives. For one of the products (strawberry flavored drink), the survival and regression-based COP’s were comparable. The survival analysis methodology is recommended for estimating sensory cut-off points in food products.     

Joint latent class model of survival and longitudinal data: An application to CPCRA study

There has been an increasing interest in the joint analysis of repeated measures and time to event data. In many studies, there could also exist heterogeneous subgroups. Thus a new model is proposed for the joint analysis of longitudinal and survival data with underlying subpopulations identified by latent class model. Within each latent class, a joint model of longitudinal and survival data with shared random effects is adopted. The proposed model is applied to Terry Beirn Community Programs for Clinical Research on AIDS study (CPCRA) to characterize the underlying heterogeneity of the cohort and to study the relation between longitudinal CD4 measures and time to death. The proposed model is desirable when the heterogeneity among subjects cannot be ignored and both the longitudinal and survival outcomes are of interest.     

Confidence regions having different shapes for the failure distribution function

A failure distribution represents an attempt to describe mathematically the length of life of a device.Most often the possibility remains that the analysts may be hesitant or unwilling to entertain any well known theoretical failure distribution.Therefore, one must rely on actual observations of the time to failure to construct an empirical cumulative failure distribution function. We present some useful results in constructing statistical confidence regions for the entire failure cumulative distribution function (cdf), F(x) from which a random sample has been drawn. The bandwidth of these regions becomes narrower in some parts of the distribution where we may want to have more precise information about failure cdf than is afforded by the ordinary Kolmogorov-Smirnov (K−S) confidence region. The problem of constructing the best, having minimum risk, confidence region from a decision theoretic approach is also considered.Illustrative numerical examples are presented.