What Is a “Massive” Concrete Structure at Early Ages? Some Dimensional Arguments

The risk of early-age concrete cracking depends on the capacity of hardening concrete to support the thermal stresses caused by the exothermic nature of the hydration process. This has been recognized for “massive” concrete structures. However, with the increasing use of high performance concretes, it is apparent that this problem also concerns traditionally “thin” structural members (columns, beams). The definition of a “massive” concrete structure, and how the structural dimension affects intensity and occurrence of chemically-induced strucctural degradation is the main focus of this paper. Based on dimensional analysis of the governing equations, a characteristic length scale, the hydration heat diffusion length, is derived; beyond this length the structure needs to be considered as “massive,” and latent hydration heat effects affect the long-term structural integrity. From experimental data of normal strength concrete and high performance concrete, it is shown that this hydration heat diffusion length of high performance concrete is of the order of ?h = 0.2 m, and lh = 0.3 m for normal strength concrete. Through a number of case studies, the relevant similarity parameters of the risk of early-age concrete cracking are identified, which allow's the monitoring of the structural performance of early-age concrete structures.     

Thermodynamic Temperature of High-Temperature Fixed Points Traceable to Blackbody Radiation and Synchrotron Radiation

Absolute spectral radiometry is currently the only established primary thermometric method for the temperature range above 1300 K. Up to now, the ongoing improvements of high-temperature fixed points and their formal implementation into an improved temperature scale with the mise en pratique for the definition of the kelvin, rely solely on single-wavelength absolute radiometry traceable to the cryogenic radiometer. Two alternative primary thermometric methods, yielding comparable or possibly even smaller uncertainties, have been proposed in the literature. They use ratios of irradiances to determine the thermodynamic temperature traceable to blackbody radiation and synchrotron radiation. At PTB, a project has been established in cooperation with VNIIOFI to use, for the first time, all three methods simultaneously for the determination of the phase transition temperatures of high-temperature fixed points. For this, a dedicated four-wavelengths ratio filter radiometer was developed. With all three thermometric methods performed independently and in parallel, we aim to compare the potential and practical limitations of all three methods, disclose possibly undetected systematic effects of each method and thereby confirm or improve the previous measurements traceable to the cryogenic radiometer. This will give further and independent confidence in the thermodynamic temperature determination of the high-temperature fixed point’s phase transitions.     

Betriebsleittechnik – Funktionsumfang und Stand der Systeme

Process Control Engineering – Function and State of the Art of the Systems On considering material flow in a chemical engineering company it is possible to identify associated business processes whose support by appropriate information processing systems will permit efficient control of material flow and material conversion as production goal. Such consideration indicates not only the principal functions of information processing but also the necessary integration of process-oriented information systems such as those relating to formulation, production planning, and operating data processing. Various concepts are currently under discussion for such integration.     

A nonparametric changepoint model for stratifying continuous variables under order restrictions and binary outcome

Modelling using monotonic regression can be a useful alternative to parametric approaches when optimal stratification for continuous predictors is of interest. This method is described here in the context of binary response. Within this framework we aim to address two points. First, we propose a method to enhance the parsimony of the model, by applying a reducing procedure based on a sequence of Fisher exact tests and a bootstrap method to select between full monotonic and reduced model. Secondly, we discuss the case of multiple predictors: an iterative algorithm (an extension of the Pool Adjacent Violators Algorithm) can be applied when more than one predictor variable is taken into account. The resulting model is a monotonic surface and can be applied alternatively to the additive monotonic models as described by Morton-Jones and colleagues when the explanatory variables are assumed to interact. The monotonic-surface model provides also a multivariate extension of the monotonic likelihood ratio test. This test is discussed here and an approach based on permutations to assess the p-value is proposed. Finally, we combine both ideas (reduced monotonic regression and monotonic-surface estimation) to a simple and easy to interpret model, which leads to a combination of the predictors in a few constant risk groups. Despite the fact that the proposed approach becomes somewhat cumbersome due to the lack of asymptotic methods to infer, it is attractive because of its simplicity and stability. An application will outline the benefit of using bivariate step functions in modelling.     

Major benefit from antiplatelet therapy for patients at high risk for adverse cardiac events after coronary Palmaz-Schatz stent placement: analysis of a prospective risk stratification protocol in the Intracoronary Stenting and Antithrombotic Regimen (ISAR) trial

BACKGROUND: The Intracoronary Stenting and Antithrombotic Regimen (ISAR) Trial is a randomized study in which antiplatelet therapy is compared with anticoagulant therapy after coronary stent placement, showing a significantly lower rate of noncardiac and cardiac events with antiplatelet therapy. The present study is a report of the analysis of a prospective risk stratification protocol in the ISAR Trial and the association with the incidence of adverse cardiac events and stent vessel occlusion. METHODS AND RESULTS: In all 517 patients randomized in the ISAR Trial, risk stratification was done with a list of 18 clinical, procedural, and angiographic variables: 165 patients with two or fewer criteria were classified as low risk, 148 patients with three criteria were classified as intermediate risk, and 204 patients with four or more criteria were classified as high risk. Within a 30-day follow-up, cardiac event rate (death, myocardial infarction, repeat intervention) was 6.4% for high-risk, 3.4% for intermediate-risk, and 0% for low-risk patients (P<.01). Stent vessel occlusion occurred in 5.9%, 2.7%, and 0%, respectively (P<.01). There was no significant difference between anticoagulant and antiplatelet therapy in the low- and intermediate-risk groups. In high-risk patients, however, the cardiac event rate was 12.6% with anticoagulant therapy and 2.0% with antiplatelet therapy (P=.007), and the rate of stent vessel occlusion was 11.5% and 0%, respectively (P<.001). CONCLUSIONS: This risk stratification protocol can help to identify patients at risk for adverse cardiac events and stent vessel occlusion. Patients in the high-risk group had the most benefit from antiplatelet therapy. These data suggest that antiplatelet therapy is the therapy of choice after coronary stenting specifically for patients with acute ischemic syndromes, difficult procedures, or suboptimal final results.     

Untersuchungen zur Langkettenverzweigung in Polyäthylenen

Polyethylene samples of various densities and melt flow indices resulting from different polymerization processes have been investigated with respect to long chain branching (LKV). For that purpose several polymer fractions have been characterized by measurement of weight average molecular weights M_w and intrinsic viscosities [η], the latter ranging from 0,2 to 3,2 with high pressure samples and from 0,2 to 10 with low pressure material. The intrinsic viscosity difference of branched (high pressure) polyethylene compared to linear (low pressure) polyethylene is used as a measure of LKV. With high pressure polyethylene LKV increases with decreasing density. This dependence is strongest within the medium molecular weight range. Samples with varying LKV but constant density can be obtained by appropriate change of polymerization conditions. No LKV has been observed with low pressure polyethylene. This means a marked difference compared to high pressure material of equal density. Branching with low pressure polymers can therefore be ascribed to the short chain type only, which in particular results from copolymerization. Several mathematical approaches have been checked whether or not they can yield suitable information about n, the number of long chain branches per molecule. The best fit with our experimental data is obtained using the expression [η]v/[η]₁ = g^1,3 (n = f(g)) and assuming, that the average concentration of long chain branch points does not depend on molecular weight for fractions of the same sample (n/M = const.). If LKV ist taken into consideration, logarithmic normal molecular weight distributions are obtained for many high pressure polyethylenes (similar to low pressure material). Data are reported in support of the view, that performance characteristics are dependent on LKV. There is some evidence, that melt flow properties of polyethylene are improved with increasing LKV.     

Is concrete a poromechanics materials?—A multiscale investigation of poroelastic properties

Materials and Structures - There is an ongoing debate, in Concrete Science and Engineering, whether cementitious materials can be viewed as poromechanics materials in the sense of the porous media...     

Reference-free total reflection X-ray fluorescence analysis of semiconductor surfaces with synchrotron radiation

Total reflection X-ray fluorescence (TXRF) analysis is a well-established method to monitor lowest level contamination on semiconductor surfaces. Even light elements on a wafer surface can be excited effectively when using high-flux synchrotron radiation in the soft X-ray range. To meet current industrial requirements in nondestructive semiconductor analysis, the Physikalisch-Technische Bundesanstalt (PTB) operates dedicated instrumentation for analyzing light element contamination on wafer pieces as well as on 200- and 300-mm silicon wafer surfaces. This instrumentation is also suited for grazing incidence X-ray fluorescence analysis and conventional energy-dispersive X-ray fluorescence analysis of buried and surface nanolayered structures, respectively. The most prominent features are a high-vacuum load-lock combined with an equipment front end module and a UHV irradiation chamber with an electrostatic chuck mounted on an eight-axis manipulator. Here, the entire surface of a 200- or a 300-mm wafer can be scanned by monochromatized radiation provided by the plane grating monochromator beamline for undulator radiation in the PTB laboratory at the electron storage ring BESSY II. This beamline provides high spectral purity and high photon flux in the range of 0.078-1.86 keV. In addition, absolutely calibrated photodiodes and Si(Li) detectors are used to monitor the exciting radiant power respectively the fluorescence radiation. Furthermore, the footprint of the excitation radiation at the wafer surface is well-known due to beam profile recordings by a CCD during special operation conditions at BESSY II that allow for drastically reduced electron beam currents. Thus, all the requirements of completely reference-free quantitation of TXRF analysis are fulfilled and are to be presented in the present work. The perspectives to arrange for reference-free quantitation using X-ray tube-based, table-top TXRF analysis are also addressed.     

Scratch test model for the determination of fracture toughness

We revisit the scratch test within the framework of linear elastic fracture mechanics. In the analysis, we employ an Airy stress function approach to determine stresses and displacement in the vicinity of the scratch-blade–material interface, which serve as input for the evaluation of the energy release rate by means of the J-Integral. In contrast to previous models, the energy release rate thus found scales with the sum of the applied forces squared. This entails a linear relation between the applied forces and , where w is the scratch width and d the scratch depth. This analytical scaling is validated using experimental scratch data on cement paste and sandstone, which shows that the proposed approach provides a convenient way to determine the fracture toughness from scratch tests carried out with different scratch widths and depths.