Competing risks as a multi-state model

This paper deals with the competing risks model as a special case of a multi-state model. The properties of the model are reviewed and contrasted to the so-called latent failure time approach. The relation between the competing risks model and right-censoring is discussed and regression analysis of the cumulative incidence function briefly reviewed. Two real data examples are presented and a guide to the practitioner is given.     

Light-scattering studies of packed stationary phases for capillary electrochromatography

Multiply scattered light through turbid media, packed particles, or compressed powders will inherently have a significantly longer optical path length than that of light which is not scattered. The concept of using the multiply scattered light potentially generated in the packed stationary phase of a capillary electrochromatography (CEC) column for enhanced detection as a result of its increased optical path length was examined. Ultraviolet (UV) light at 365 nm or laser light at 635 nm was focused to a small spot onto the packed section of a 3 microns spherisorb ODS1 CEC column (100 microns i.d.). The light was transported inside the capillary, and an image of the multiply scattered light several millimeters along the capillary was collected using a charged-couple device detector. Even if the spot size was less than 100 microns in diameter, evidence of light scattering was observed at a detection spatial off-set distance of 1-2 mm from the illumination point. When the calcium channel blocking drug felodipine was flushed through the column, the light intensity value dropped (increase in absorbance) to a greater degree at a spatial off-set (1.5 mm) than at the illumination point. The greater absorbance values at the spatial off-set were examined experimentally when felodipine was eluted from the column in the CEC mode in 6 min using MeCN/50 mM TRIS (pH 8.0) (80:20, v/v) at an applied voltage of 300 V/cm and an injection time of 2 s at 10 kV. A factor of 8.5 increase in absorbance was observed at a spatial off-set of 1 mm compared to the value obtained at the illumination point. An efficiency value of approximately 234,000 plates m-1 was obtained for this higher felodipine peak. Higher noise values, however, were also observed with this increase in absorbance. Using a spectrophotometer or an open capillary to obtain reference values for optical length, it was possible to estimate the average optical path length of light traveled through the packed stationary phase when transmitted at a spatial off-set. It was concluded that, although an increase in absorbance of 8.5 was observed at a spatial off-set, this most likely arises from the light being "redirected" and scattered in a straightforward fashion along the capillary. It was expected that if substantial multiple scattering did occur inside the packed stationary phase, a significantly larger absorbance increase would be attained. A number of proposals are thus given to explain the relatively low degree of multiple scattering in this stationary phase and suggestions offered on means to attain even higher absorbance increases at a spatial off-set. Additional potential applications are also discussed.     

隔河岩水利枢纽水文预报的现状与展望

文章叙述了清江流域概况及水文特性;水文自动化测报系统简况;隔河岩工程施工洪水预报中采用的方法;隔河岩工程施工洪水预报中采用的方法;水文预报现状及展望,洪水预报采用水箱模型,精度高,取得了较好经济效益。     

以矩阵为变量的线性方程组

本文讨论以矩阵为变量的线性方程组，给出相容性的充要条件。     

几种重金属对紫背萍的过氧化氢酶（CAT）活性的影响

通过测定试验植物的过氧化氢酶分解过氧化氢后所放出氧气的量，确定紫背萍的过氧化氢酶的活性。结果表明，紫背萍在暴露到镉，锌，铜和铁的不同浓度时，其ＣＡＴ活性明显升高这表明４种重金属对紫背萍的ＣＡＴ活性均有刺激作用。结果不表明，此 萍在有铁存在的两种金属的复合作用下，其ＣＡＴ活性明显降低。     

Determination of oxidative stability of oils and fats

In a new approach to evaluating the oxidative stability of oils and fats, the consumption of oxygen by a sample confined in a reactor of adjustable temperature is monitored with a gas-phase flow injection analysis (FIA) system. Temperature-dependent data are collected in a low-oxygen-content atmosphere. For a variety of samples, log(oxygen consumption) is linearly related to the reciprocal of the absolute temperature (minimum linear r(2) > 0.99). This makes it possible to extrapolate the temperature-dependent data to predict the stability of the samples at other temperatures, e.g., typical ambient storage temperatures at which the direct determination of oxidative stability would be too slow for most samples. The proposed method is instrumentally simple and is easily automated. The sample throughput rate is an order of magnitude faster relative to current alternatives; temperature-dependent stability characterization for a sample (three temperatures, triplicate measurement at each temperature) requires ≤ 2 h. The reproducibility of the results is excellent. For a cottonseed-oil sample studied over 3 days, the slope and intercept of the log(O(2) consumption) vs 1/T linear plot (for all the 45 measurements made) exhibited uncertainties of 2.1% and 2.0% for the slope and the intercept, respectively, with a linear r(2) value of 0.9929. In a high-temperature (160 °C) oxidation experiment with various oils, the oxygen consumption was well-correlated (linear r(2) 0.9692) with the concomitant decrease in iodine absorption number (IAN). In contrast, it was poorly and negatively correlated with an increase in the peroxide value.     

Dye removal from wastewater using activated carbon developed from sawdust: adsorption equilibrium and kinetics

Mahogany sawdust was used to develop an effective carbon adsorbent. This adsorbent was employed for the removal of direct dyes from spent textile dyeing wastewater. The experimental data were analysed by the Langmuir and Freundlich models of adsorption. Equilibrium data fitted well with the Langmuir model. The rates of adsorption were found to conform to the pseudo-second-order kinetics with good correlation. The equilibrium adsorption capacity of the sawdust carbon was determined with the Langmuir equation as well as the pseudo-second-order rate equation and found to be >300 mg dye per gram of the adsorbent. The most ideal pH for adsorption of direct dyes onto sawdust carbon was found to be 3 and below. The results indicate that the Mahogany sawdust carbon could be employed as a low cost alternative to commercial activated carbon in the removal of dyes from wastewater.