不测土条件下半定量施肥原理和模型评述

1　不测土条件下半定量推荐施肥的需求矿质营养学说是施肥最基本原理 ,它的诞生标志着人类主动施肥时期的开始。从早期的定性施肥阶段 ,发展到今天的定量施肥阶段 ,如何确定施肥量一直是施肥技术的核心和难点。测土是定量施肥或精确施肥的前提。然而 ,测土本身存在各种偏差或精度、测土需要费用 ,本文仅对代表性的不测土施肥模型及其原理进行评述。即使有了土壤有效养分的测定结果 ,如何将其转化为一季内土壤提供的养分量一直是个理论难题 ,特别是Ｎ素土壤供应量更为难测或难以估算。因此 ,如何在使用定量施肥模型的同时 ,而又将土壤养分因…     

Validity of hair mineral testing

The variance of testing was compared between the College of American Pathologists clinical survey and that of a recent review about hair mineral testing. The review suggested that the accuracy of hair mineral testing was unreliable. In general, there was a greater range of variance in the College of American Pathologists testing results. These latter results are based on laboratory testing and are used as a “yardstick” to determine if a laboratory passes or fails that analyte and are considered a “gold standard.” An extract, which resulted from a method that avoided the washing step, was compared among five laboratories. Very good precision resulted, indicating that the varied washing steps used by the laboratories in a recent review were probably the source of much variance. Analysis of hair analysis seemed to yield important information in several historical or forensic cases involving Ludwig von Beethoven, Napoleon Bonaparte, ex-US-presidents Zachary Taylor and Andrew Jackson, and Charles Hall, an Arctic explorer. Several elements that were reviewed, including arsenic, cadmium, cobalt, germanium, lead, lithium, manganese, mercury, nickel, and thallium, showed relationships between body burden, dosage, and exposure or toxicity. Evidence of toxicity could not be found by measuring hair aluminum or vanadium. Chromium, selenium, and zinc seemed to have nutritional value. Ratios of hair elements with clinical importance could not be found.     

Laboratory culture of Chironomus tentans for use in toxicity testing: optimum initial egg-stocking densities

The midge Chironomus tentans Fabricius is a commonly used freshwater invertebrate in sediment toxicity tests. Rigorous laboratory culturing techniques are needed to provide organisms of uniform quality and known age for use in testing and for the continuation of the culture itself. This study was conducted to determine the effect of initial culture stocking density on: (1) post-hatch (larval) dry weight, body length and head-capsule width at 10 and 20 days; (2) time to emergence; (3) number and sex of emergent adults; (4) number of larvae and pupae at test termination (day 42 post hatch); and (5) adult dry weight. Three egg stocking densities were used 690 (1.1 eggs cm^–2), 1043 (1.7 eggs cm^–2) and 1463 (2.4 eggs cm^–2). Mean weight of larvae at 10 days in high density tanks (0.13 mg/organism) was significantly higher (P=0.003) than both the medium and low density tanks (0.10 and 0.09 mg/organism, respectively). No significant differences between the three stocking densities were observed for the body length or head-capsule width at either 10 or 20 days post-hatch. Although not statistically significant, larval dry weight decreased with increased stocking density at day 20. A significantly (P=0.02) greater number of females (173±28) emerged from the low stocking density compared to both the medium and high stocking densities (123±45 and 118±54, respectively). Peak adult emergence for the low and medium stocking densities occurred between days 22 and 25 post-hatch, whereas peak adult emergence occurred between days 30 and 33 for the high stocking density. Survival relative to the initial number of eggs stocked was significantly greater (P=0.007) in the low density treatment compared to that in either the medium or the high density treatments. Mean adult weight exhibited an inverse relationship with initial stocking densities. At test end, there was not a significant difference in the mean number of organisms surviving and emerging in the three density levels. The central tendency for number of organisms surviving for all three treatments was 504 organisms per tank (0.82 organisms cm^–2). The results of this experiment suggest that an optimal egg stocking density of 1.0 egg cm^–2 (600 eggs/tank) be used with the feeding rate identified. This would ensure uniform larvae at the appropriate developmental stage (2nd–3rd instar) needed for toxicological research/testing (e.g. 10 days post-hatch), as well as producing sufficient emergence of males and females for future culture establishment.     

Maximally efficient two-stage screening

In DNA library screening, blood testing, and monoclonal antibody generation, significant savings in the number of assays can be realized by employing group sampling. Practical considerations often limit the number of stages of group testing that can be performed. We address situations in which only two stages of testing are used. We define efficiency to be the expected number of positives isolated per assay performed and assume gold-standard tests with unit sensitivity and specificity. Although practical tests never are golden, polymerase chain reaction (PCR) methods provide procedures for screening recombinant libraries that are strongly selective yet retain high sensitivity even when samples are pooled. Also, results for gold-standard tests serve as bounds on the performance of practical testing procedures. First we derive formulas for the efficiency of certain extensions of the popular rows-and-columns technique. Then we derive an upper bound on the efficiency of any two-stage strategy that lies well below the classical upper bound for situations with no constraint on the number of stages. This establishes that a restriction to only two stages necessitates performing many more assays than efficient multistage procedures need. Next, we specialize the bound to cases in which each item belonging only to pools that tested positive in stage 1 must be tested individually in stage 2. The specialized bound for such positive procedures is tight because we show that an appropriate multidimensional extension of the rows-and-columns technique achieves it. We also show that two-stage positive procedures in which the stage-1 groups are selected at random perform suboptimally, thereby establishing that efficient tests must be structured carefully.     

Equivalence of regression curves sharing common parameters

In clinical trials, the comparison of two different populations is a common problem. Nonlinear (parametric) regression models are commonly used to describe the relationship between covariates, such as concentration or dose, and a response variable in the two groups. In some situations, it is reasonable to assume some model parameters to be the same, for instance, the placebo effect or the maximum treatment effect. In this paper, we develop a (parametric) bootstrap test to establish the similarity of two regression curves sharing some common parameters. We show by theoretical arguments and by means of a simulation study that the new test controls its significance level and achieves a reasonable power. Moreover, it is demonstrated that under the assumption of common parameters, a considerably more powerful test can be constructed compared with the test that does not use this assumption. Finally, we illustrate the potential applications of the new methodology by a clinical trial example.     

Do European Standard Disinfectant tests truly simulate in‐use microbial and organic soiling conditions on food preparation surfaces?

Aims: The results from European standard disinfectant tests are used as one basis to approve the use of disinfectants in Europe. The design of these laboratory‐based tests should thus simulate as closely as possible the practical conditions and challenges that the disinfectants would encounter in use. No evidence is available that the organic and microbial loading in these tests simulates actual levels in the food service sector. Methods and Results: Total organic carbon (TOC) and total viable count (TVC) were determined on 17 visibly clean and 45 visibly dirty surfaces in two restaurants and the food preparation surfaces of a large retail store. These values were compared to reference values recovered from surfaces soiled with the organic and microbial loading, following the standard conditions of the European Surface Test for bactericidal efficacy, EN 13697. Conclusions: The TOC reference values for clean and dirty conditions were higher than the data from practice, but cannot be regarded as statistical outliers. This was considered as a conservative assessment; however, as additional nine TOC samples from visibly dirty surfaces were discarded from the analysis, as their loading made them impossible to process. Similarly, the recovery of test organisms from surfaces contaminated according to EN 13697 was higher than the TVC from visibly dirty surfaces in practice; though they could not be regarded as statistical outliers of the whole data field. No correlation was found between TVC and TOC in the sampled data, which re‐emphasizes the potential presence of micro‐organisms on visibly clean surfaces and thus the need for the same degree of disinfection as visibly dirty surfaces. Significance and Impact of the Study: The organic soil and the microbial burden used in EN disinfectant standards represent a realistic worst‐case scenario for disinfectants used in the food service and food‐processing areas.     

Molecular testing of BRAF,RAS and TERT on thyroid FNAs with indeterminate cytology improves diagnostic accuracy

Objective

Liquid‐based (LB)‐FNA is widely recognized as a reliable diagnostic method to evaluate thyroid nodules. However, up to 30% of LB‐FNA remain indeterminate according to the Bethesda system. Use of molecular biomarkers has been recommended to improve its pathological accuracy but implementation of these tests in clinical practice may be difficult. Here, we evaluated feasibility and performance of molecular profiling in routine practice by testing LB‐FNA for BRAF, N/HRAS and TERT mutations.

Methods

We studied a large prospective cohort of 326 cases, including 61 atypia of undetermined significance, 124 follicular neoplasms, 72 suspicious for malignancy and 69 malignant cases. Diagnosis of malignancy was confirmed by histology on paired surgical specimen.

Results

Mutated LB‐FNAs were significantly associated with malignancy regardless of the cytological classification. Overall sensitivity was 60% and specificity 89%. Importantly, in atypia of undetermined significance and follicular neoplasm patients undergoing surgery according to the Bethesda guidelines, negative predictive values were 85.4% and 90% respectively. TERT promoter mutation was rare but very specific for malignancy (5.5%) suggesting that it could be of interest in patients with indeterminate cytology.

Conclusions

Mutation profiling can be successfully performed on thyroid LB‐FNA without any dedicated sample in a pathology laboratory. It is an easy way to improve diagnostic accuracy of routine LB‐FNA and may help to better select patients for surgery and to avoid unnecessary thyroidectomies.

     

Permutation tests for random effects in linear mixed models

Inference regarding the inclusion or exclusion of random effects in linear mixed models is challenging because the variance components are located on the boundary of their parameter space under the usual null hypothesis. As a result, the asymptotic null distribution of the Wald, score, and likelihood ratio tests will not have the typical χ(2) distribution. Although it has been proved that the correct asymptotic distribution is a mixture of χ(2) distributions, the appropriate mixture distribution is rather cumbersome and nonintuitive when the null and alternative hypotheses differ by more than one random effect. As alternatives, we present two permutation tests, one that is based on the best linear unbiased predictors and one that is based on the restricted likelihood ratio test statistic. Both methods involve weighted residuals, with the weights determined by the among- and within-subject variance components. The null permutation distributions of our statistics are computed by permuting the residuals both within and among subjects and are valid both asymptotically and in small samples. We examine the size and power of our tests via simulation under a variety of settings and apply our test to a published data set of chronic myelogenous leukemia patients.