MRI断层层厚测量方法研究

探讨客观、快速、准确测量二维磁共振图像断层层厚的方法。扫描有层厚测试功能的体模获得相应图像,利用传统测试方法(方法 1:调节窗宽、窗位测量目标物的方法;方法 2:单条层面灵敏度剖面线的方法)与改进的多条灵敏度剖面线平均(方法 3A)及一阶导处理自动搜寻目标物边缘的方法(方法 3B)测量层厚。标称层厚为5 mm,当图像均匀性较好时(98.97%),得到各个方法的层厚均值和标准偏差,方法1、2、3A、3B结果分别为4.96 mm/0.03 mm,4.97 mm/0.06 mm,4.98 mm/0.02 mm,4.97 mm/0.01 mm,单因素方差分析F值为0.48;当图像均匀性较差时(95.35%),方法1、2、3A、3B结果分别为4.82 mm/0.41 mm,4.80 mm/0.46 mm,4.84 mm/0.15 mm,4.85 mm/0.11 mm,F值为0.46。F值结果显示4种层厚测试方法有效,但是标准偏差的差异意味着测试结果的不确定度变化较大。方法 1标准偏差最大,方法3B的标准偏差最小。4种测试方法的结果表明:传统测试方法主观性强,误差大,不确定度大,稳定性欠佳;改进后的方法客观、快速,准确度高。特别是当图像均匀性欠佳时,改进的层厚测试方法抗干扰性强。     

Recommendations for estimation of quality of concrete in finished structures

The object of the present recommendations is to guide the engineer in the selection and the use of the procedures which he should adopt when he is required to estimate the quality of concrete in finished structures. Moreover, these recommendations are intended to provide a general background of the problems involved in this connection. It should be emphasized that the following recommendations are to be regarded as a guide only. They are not meant to be a “standard” or a “code of practice”. In this form, they may be expected to be of great value to engineers who are little familiar with this subject, and who might appreciate assistance in making their own judgements. The recommendations are accompanied with comments, which are set in italics.     

气相色谱-质谱联用仪校准中常见故障问题分析及仪器日常维护

随着当今科技的飞速发展,气相色谱-质谱联用仪（以下简称GC/MS）的应用范围越来越广泛,在食品安全、生物医药、石油及石油化工产品及生态环境的保护等领域得到广泛的应用,究其原因是缘于GC/MS具有定性专属性强、灵敏度高、检测速度快的优势[1]。目前GC/MS虽已广泛应用,但在日常使用中难免会出现一些问题,文章通过介绍GC/MS现场校准过程中常见故障问题及排查解决办法,以及GC/MS的日常使用与维护,进而提高其使用价值。     

Testing methods for concrete durability

Experimental techniques for measuring progressive deterioration of concrete were investigated. Specimens of pastes, mortars, and concretes were subjected to alternate wetting and drying in sodium sulfate solutions and plain water as well as freezing and thawing. The methods used to assess the effects included: changes in weight, length, and flexural strength, changes in ultrasonic pulse time, quantitative and qualitative optical microscopy, scanning electron microscopy, and energy dispersive X-ray analysis. The results of the study show that the ultrasonic pulse method can be used to detect local cracking at an early stage of formation. Of the different testing methods employed, the progressive deterioration was best reflected by the measurements of pulse time. Measurements of flexural strength also adequately reflected the state of corrosion. Measurements of weight did not consistently indicate damage, while those of length were not always reliable.     

Recommendations for the treatment of the variations of concrete strength in codes of practice

Some time ago (Materials and Structures n^o 24, November–December 1971), Mr. Petersons published a paper referring to the work of Working Group III of the Joint CEB/CIB/FIP/RILEM Committee on the Statistical Control of Concrete. In the following, Mr. Teychenné gives a personal view of the ideas actually being discussed by Working Group I. The Joint Committee will at its next session discuss these proposals and hopes to finalize its work in the near future by publishing draft Recommendations on the Statistical Quality Control of Concrete.     

Apparatus for accelerated degradation testing of concrete specimens

To simulate chemical degradation of concrete in an automated and standardized way, an apparatus for accelerated degradation tests was developed. Because alternated wetting and drying often accelerate concrete degradation, cylindrical test specimens are subjected to a cyclic procedure of turning through an aggressive solution and drying by air. After every attack cycle the test specimens are brushed with rotary brushes to simulate mechanical abrasion. The degradation of the concrete, in terms of change of the dimensions of the test specimens, is determined by means of a non-contact distance measurement with laser sensors. Out of the measured data the change of the cylinder radius and the surface roughness are calculated. To illustrate the test procedure, experimental results concerning sulfuric and lactic/acetic acid degradation are provided.

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Résumé Un appareil a été développé pour simuler de manière automatisée et standardisée l'attaque chimique du béton. Vu que l'alternance de submersions et de séchages accélèrent souvent le processus de dégradation, des échantillons cylindriques sont exposés à une procédure cyclique qui les fait tourner dans une solution agressive suivie d'un séchage à l'air. Suite à chaque cycle d'attaque les échantillons sont brossés avec des brosses rotatives pour simuler l'abrasion mécanique. La dégradation des échantillons de béton est mesurée à l'aide de lasers, qui déterminent sans aucun contact, la distance entre le béton et le laser. Sur la base de ces données, le changement du rayon du cylindre et la rugosité de la surface sont calculés.

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Editorial Note Prof. Dr. Ir. Luc Taerwe is a RILEM Senior Member.     

Possible methods for the non-destructive testing of sprayed coatings

The increasing demand for the non-destructive testing of sprayed coatings has prompted a general examination of some of the basic physical properties of solids, and ways of measuring them, in the hope that pointers would emerge to indicate at least an alleviation of—if not a solution to—this problem. The viewpoint adopted was firstly to identify properties of coatings that could be reliably measured, and then to choose those properties that could be related to features of a coating of engineering interest. A further restriction imposed was the existing availability of instruments and techniques for the measurements.The resultant suggestions are therefore largely speculative and embrace thermal, acoustic, and magnetic properties amongst others. The purpose of the paper is to encourage exploration along possibly unconventional lines; thus no firm conclusions are drawn but a list of coating flaws etc. is given with some suggestions for the techniques that might be suitable for their assessment. It is emphasized that all tests must be regarded as comparative.     

Objective Bayesian methods for one-sided testing

The one-sided testing problem can be naturally formulated as the comparison between two nonnested models. In an objective Bayesian setting, that is, when subjective prior information is not available, no general method exists either for deriving proper prior distributions on parameters or for computing Bayes factor and model posterior probabilities. The encompassing approach solves this difficulty by converting the problem into a nested model comparison for which standard methods can be applied to derive proper priors. We argue that the usual way of encompassing does not have a Bayesian justification. and propose a variant of this method that provides an objective Bayesian solution. The solution proposed here is further extended to the case where nuisance parameters are present and where the hypotheses to be tested are separated by an interval. Some illustrative examples are given for regular and non-regular sampling distributions. This paper has been supported by Ministerio de Ciencia y Tecnología under grant BEC20001-2982     

A compound sampling scheme for acceptance testing of concrete

A sampling scheme which consists of the following two sampling rules is considered: (i) the sample mean value of the random samples should not be less than a times the specified standard and (ii) all individual test results should not be less thanb times the specified standard. By varying the constantsa andb and the sampling size, the sampling scheme generates a wide range of operating characteristics (OC) curves. An approximate closed-form solution is proposed for calculating the OC curve of the proposed scheme. Applications of the scheme are also discussed.

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Resume On considère une procédure d’échantillonnage qui consiste à appliquer les deux règles suivantes: (i) la valeur moyenne d’échantillons pris au hasard ne devrait pas être inférieure àa fois la valeur spécifiée officielle: (ii) tous les résultats d’essai individuels ne devraient pas être inférieurs àb fois la valeur spécifiée officielle. La régle d’échantillonnage proposée présente trois paramètres: la taille de l’éprouvette,n, et les constantesa etb. En faisant varier ces trois paramètres, la procédure d’échantillonnage donne lieu à un vaste éventail de courbes de fonctionnement caractéristique. et permet d’établir une courbe OC acceptable pour le producteur et le consommateur. On peut l’utiliser aussi pour produire une nouvelle règle de réception qui donnera une courbe OC similaire à celle d’une procédure d’échantillonnage existante. On propose une solution approchée pour le calcul de la courbe OC de la procédure proposée. On discute aussi les applications de cette procédure.

     

Rheological testing methods for gypsum plaster pastes

The rheological properties of gypsum plaster pastes were studied. The pastes were prepared from a commercial grade calcium sulfate hemihydrate. The water/plaster ratio was varied within the range100/130÷100/190. The rheological tests were performed using the coaxial cylinder viscometer Rotovisko-Haake RV3 within a wide range of shear rates. The results obtained by the application of different experimental procedures were compared and discussed.