A genetic algorithm for the automated generation of molecules within constraints

Summary A genetic algorithm has been designed which generates molecular structures within constraints. The constraints may be any useful function, for example an enzyme active site, a pharmacophore or molecular properties from pattern recognition or rule-induction analyses. The starting point may be random or may utilise known molecules. These are modified to grow into families of structures which, using the evolutionary operators of selection, crossover and mutation evolve to better fit the constraints. The basis of the algorithm is described together with some applications in lead generation, 3D database construction and drug design. Genetic algorithms of this type may have wider applications in chemistry, for example in the design and optimisation of new polymers, materials (e.g. superconducting materials) or synthetic enzymes.     

Avoiding linear dependencies in LFSR test pattern generators

Linear Feedback Shift Registers (LFSRs) constitute a very efficient mechanism for generating pseudoexhaustive or pseudo-random test sets for the built-in self-testing of digital circuits. However, a well-known problem with the use of LFSRs is the occurrence of linear dependencies in the generated patterns. In this paper, we show for the first time that the amount of linear dependencies can be controlled by selecting appropriate characteristic polynomials and reordering the LFSR cells. We identify two classes of such polynomials which, by appropriate LFSR cell ordering, guarantee that a large ratio of linear dependencies cannot occur. Experimental results show significant enhancements on the fault coverage for pseudo-random testing and support the theoretical relation between minimization of linear dependencies and effective fault coverage.This work was partially supported by NSF grant MIP-9409905, a 1993–94 ACM/IEEE Design Automation Scholarship and a grant from Nissan Corporation. A preliminary version of this work appeared in A Class of Good Characteristic Polynomials for LFSR Test Pattern Generators, in Proc. of IEEE International Conference on Computer Design, Oct. 1994, pp. 292–295, where it received the ICCD'94 Best Paper Award.     

热致液晶乙基纤维素与尼龙－1010共混物的研究

在自制单螺杆小型挤出机上通过熔融共混的办法，制备了不同配比（５／９５—２５／７５）的ＥＣ／Ｎｙｌｏｎ—１０１０共混物．用ＷＡＸＤ、ＤＳＣ、毛细管流变仪、力学性能测试等方法对共混物进行了研究．发现共混后尼龙－１０１０的形态结构有明显改变，其强度、模量都有提高，在高剪切速率下，共混物粘度大大降低．配比为１５８５时，这些性能的改进尤为明显．     

Do proficiency tests always verify laboratories’ performance? The case of FAPAS PT 0270

In this paper, the case of FAPAS PT 0270 “Doramectin and Oxfendazole in Sheep Liver” is discussed. During evaluation of the data received from participants (determination of total, oxidised oxfendazole residue and calculation of the sum of oxfendazole and oxfendazole sulfone residues), significant differences were observed between the results obtained by use of two analytical approaches. This phenomenon can be explained by the route of oxfendazole metabolism, which results in the presence of fenbendazole in the sample. This was not predicted by the provider; consequently, not all the necessary tests on the material were conducted. Due to the high uncertainty of the z-scores in this test, the results of the PT cannot be used for purposes of evaluation, and the benefits of participation in PT 0270 are questionable.     

废弃线路板化学分析采样、制样及检测方法

介绍废弃线路板中有回收价值元素和有害物质分析的采样、制样及检测技术。样品经过分类采样、剪切破碎和高温灰化制样,采用样品全分析或副批混合样分析。通过提高称样量、多次测定求平均值的办法,火试金富集-重量法测定贵金属金、银。湿法王水溶解样品,碘量法测定主体元素铜。电感耦合等离子体发射光谱(ICP-AES)法测定其它杂质元素,被测元素质量浓度在0~10μg/mL范围内与光谱强度呈良好线性关系,相关系数均大于0.9998。测定结果的相对标准偏差小于10%(n=5),加标回收率为97.0%~102.5%。该方法简单、快速,有效地解决了线路板样品不均匀而难采样,以及硬度、韧性强制样难,金属易包裹难分解的技术瓶颈,测定结果准确,具有代表性。该方法适用于废弃线路板化学成分分析,其它废弃电子产品检测可参考此方法。     

Analysis of tinuvin 1577 polymer additive in edible oils using on-line coupled HPLC-GC

An application of automated on-line HPLC-HRGC is described for direct analysis of edible oils for migrated polymer additives. The sample preparation, separating the additive from the oil triglycerides, is carried out using normal phase HPLC. The fraction of the eluent containing the additive is automatically transferred to a HRGC where a second and final separation of the additive from minor oil components takes place. The method compares well with off-line separation methods. Migration data for Tinuvin 1577 from PET and PC polymers as well as an unspecified experimental polymer is given. The advantages and disadvantages of using different edible oils as food simulants are discussed.     

Multipurpose chamber for the implementation of gas diffusion, dialysis, solid-phase extraction and precipitation/dissolution in continuous flow analyzers

A multipurpose chamber capable of implementing a variety of continuous separation techniques is reported. The proposed module can be used in conjunction with flow manifolds coupled on-line to optical detectors in order to develop simple autoanalyzers for full sample pretreatment. The analytical applicability of such a device is discussed with specific regard to gas diffusion, dialysis, solid-phase extraction (SPE), and precipitation/dissolution techniques. Its versatility and simplicity are among the main advantages. Four different automated analyzers based on the use of the multipurpose chamber have been developed for monitoring of different quality control parameters of liquid food samples, namely, carbon dioxide in beer, ascorbic acid in fruit juice, caffeine in soft drinks and lactose, fat and protein in milk. The results obtained were compared with those provided by the existing alternatives for the same applications in terms of sensitivity and precision.     

A result on hypothesis testing for a multivariate normal distribution when some observations are missing

Let U_i = (X_i, Y_i), i = 1, 2,…, n, be a random sample from a bivariate normal distribution with mean μ = (μ_x, μ_y) and covariance matrix

. Let X_i, i = n + 1,…, N represent additional independent observations on the X population. Consider the hypothesis testing problem H₀ : μ = 0 vs. H₁ : μ ≠ 0. We prove that Hotelling's T² test, which uses (X_i, Y_i), i = 1, 2,…, n (and discards X_i, i = n + 1,…, N) is an admissible test. In addition, and from a practical point of view, the proof will enable us to identify the region of the parameter space where the T²-test cannot be beaten. A similar result is also proved for the problem of testing μ_x ? μ_y = 0. A Bayes test and other competitors which are similar tests are discussed.     

A quality systems approach for identifying and controlling sources of error with point of care testing devices

Historically, due to the size and nature of the instrumentation, highly skilled laboratory professionals performed clinical testing in centralized laboratories. Today’s clinicians demand realtime test data at the point of care. This has led to a new generation of compact, portable instruments permitting ”laboratory” testing to be performed at or near the patient’s bedside by nonlaboratory workers who are unfamiliar with testing practices. Poorly controlled testing processes leading to poor quality test results are an insidious problem facing point of care testing today. Manufacturers are addressing this issue through instrument design. Providers of clinical test results, regardless of location, working with manufacturers and regulators must create and manage complete test systems that eliminate or minimize sources of error. The National Committee for Clinical Laboratory Standards (NCCLS) in its EP18 guideline, ”Quality management for unit-use testing,” has developed a quality management system approach specifically for test devices used for point of care testing (POCT). Simply stated, EP18 utilizes a ”sources of error” matrix to identify and address potential errors that can impact the test result. The key is the quality systems approach where all stakeholders – professionals, manufacturers and regulators – collaboratively seek ways to manage errors and ensure quality. We illustrate the use of one quality systems approach, EP18, as a means to advance the quality of test results at point of care. Received: 26 June, 2002 Accepted: 17 July 2002 Presented at the European Conference on Quality in the Spotlight in Medical Laboratories, 7–9 October 2001, Antwerp, Belgium Abbreviations NCCLS National Committee for Clinical Laboratory Standards (formerly) · POCT point of care testing · QC quality control · HACCP hazard analysis critical control points · CLIA clinical laboratory improvement amendments (of 1988) Correspondence to S. S. Ehrmeyer     

Evaluation of the use of consensus values in proficiency testing programmes

Proficiency testing (PT) is an essential tool used by laboratory accreditation bodies to assess the competency of laboratories. Because of limited resources of PT providers or for other reasons, the assigned reference value used in the calculation of z-score values has usually been derived from some sort of consensus value obtained by central tendency estimators such as the arithmetic mean or robust mean. However, if the assigned reference value deviates significantly from the ‘true value’ of the analyte in the test material, laboratories’ performance will be evaluated incorrectly. This paper evaluates the use of consensus values in proficiency testing programmes using the Monte Carlo simulation technique. The results indicated that the deviation of the assigned value from the true value could be as large as 40%, depending on the parameters of the proficiency testing programmes under investigation such as sample homogeneity, number of participant laboratories, concentration level, method precision and laboratory bias. To study how these parameters affect the degree of discrepancy between the consensus value and the true value, a fractional factorial design was also applied. The findings indicate that the number of participating laboratories and the distribution of laboratory bias were the prime two factors affecting the deviation of the consensus value from the true value.