Multiscale Colloidal Assembly of Silica Nanoparticles into Microspheres with Tunable Mesopores

Colloidal assembly of silica (nano)particles is a powerful method to design functional materials across multiple length scales. Although this method has enabled the fabrication of a wide range of silica‐based materials, attempts to design and synthesize porous materials with a high level of tuneability and control over pore dimensions have remained relatively unsuccessful. Here, the colloidal assembly of silica nanoparticles into mesoporous silica microspheres (MSMs) is reported using a discrete set of silica sols within the confinement of a water‐in‐oil emulsion system. By studying the independent manipulation of different assembly parameters during the sol–gel process, a design strategy is outlined to synthesize MSMs with excellent reproducibility and independent control over pore size and overall porosity, which does not require additional ageing or post‐treatment steps to reach pore sizes as large as 50 nm. The strategy presented here can provide the necessary tools for the microstructural design of the next generation of tailor‐made silica microspheres for use in separation applications and beyond.     

Modeling biological gradient formation: combining partial differential equations and Petri nets

Both Petri nets and differential equations are important modeling tools for biological processes. In this paper we demonstrate how these two modeling techniques can be combined to describe biological gradient formation. Parameters derived from partial differential equation describing the process of gradient formation are incorporated in an abstract Petri net model. The quantitative aspects of the resulting model are validated through a case study of gradient formation in the fruit fly.     

Wirtschaftliche Einsatzbereiche von Wärmepumpen- und Mehrstufenschaltungen in der Rektifiziertechnik

Economic applications of heat pumps and of multi-column heat integrated systems in distillation processes . The influence of relevant parameters (e.g. relative volatility, flow rate, pressure) on the economics of distillation plants involving heat pumps and heat integrated columns is simulated by a computer program. The different structures of possible energy supply (cogeneration heat-power plant, direct heating) have been taken into account in the models employed. The areas of economic application of the various energy conserving systems are shown in diagrams. These allow a preliminary selection of the most economic variant. The application of heat pumps outside the field of cryogenic engineering is restricted to some special cases like the separation of closeboiling mixtures. In those cases, where a minimum plant size and steam price is exceeded heat integrated columns promise an economic advantage, provided that cheaper configurations of direct heat recovery are impossible.     

Alternative strategies to full employment in a regional labor market

The subject of the paper is the development of employment and man-power in the county of Borken, situated in the North-West of the FRG close to the Dutch border. It discusses alternative strategies on the labor demand and supply sides which may serve to reach full employment. The analysis includes forecasts of the supply and the derived demand for labor in 1990, disaggregated into 33 sectors and 43 occupations. The main objective is to estimate that sectoral structure of labor demand and that professional structure of labor supply which in combination would lead to full employment by 1990. Alternative optimizations show that an overall increase of employment as well as an increased professional flexibility of the labor force are necessary to reach the employment objective. The optimal strategies indicate the direction which sector adaption and professional formation policies should take.     

In Situ Investigation of the Bainitic Transformation from Deformed Austenite During Continuous Cooling in a Low Carbon Mn-Si-Cr-Mo Steel

Metallurgical and Materials Transactions A - The effects of hot deformation on the bainitic transformation of a low carbon steel during continuous cooling were comprehensively studied through in...     

Multiscale characterization of pathological bone tissue

Bone is a complex natural material with a complex hierarchical multiscale organization, crucial to perform its functions. Ultrastructural analysis of bone is crucial for our understanding of cell to cell communication, the healthy or pathological composition of bone tissue, and its three-dimensional (3D) organization. A variety of techniques has been used to analyze bone tissue. This article describes a combined approach of optical, scanning electron, and transmission electron microscopy for the ultrastructural analysis of bone from the nanoscale to the macroscale, as illustrated by two pathological bone tissues. By following a top-down approach to investigate the multiscale organization of pathological bones, quantitative estimates were made in terms of calcium content, nearest neighbor distances of osteocytes, canaliculi diameter, ordering, and D-spacing of the collagen fibrils, and the orientation of intrafibrillar minerals which enable us to observe the fine structural details. We identify and discuss a series of two-dimensional (2D) and 3D imaging techniques that can be used to characterize bone tissue. By doing so we demonstrate that, while 2D imaging techniques provide comparable information from pathological bone tissues, significantly different structural details are observed upon analyzing the pathological bone tissues in 3D. Finally, particular attention is paid to sample preparation for and quantitative processing of data from electron microscopic analysis.     

National Styles? Jacques Loeb's Analysis of German and American Science Around 1900 in his Correspondence with Ernst Mach

Abstract.   In modern discourse about the history of science, it seems to be widely accepted that at the end of the nineteenth century, Germany was one of the leading countries in the production of science. In the past, historians of science tried to trace back a specific 'German style' of science that—in combination with other factors—determined this German dominance around 1900, especially in the life sciences. Considering the theoretical concept of 'national styles', it has to be kept in mind that around 1900, contemporaries already proclaimed 'national styles' of science as representations of national identity. Thus, the question arises as to how far existing historiographical conceptions of national styles may include earlier claims and prejudices. Careful reconstructions of contemporary discourses on national styles and inquiries into the 'stylisation' of a dominant, successful 'German style' are necessary. One of the contemporary critics of a 'German style' of science was the physiologist Jacques Loeb (1859–1924), who emigrated to the USA in 1891. Loeb corresponded regularly with the physicist and philosopher Ernst Mach (1838–1916). Ernst Mach can be considered Loeb's intellectual father with whom he corresponded about strategic, philosophical, and epistemological questions. Using the Loeb–Mach correspondence, the aim of the paper is to reconstruct Loeb's conception of a 'German style' of science and its differences to an 'American style'. Changes in his views are discussed as well as the roots of his views and some of their consequences. Finally, Loeb's ideas on national styles and his working profiles before and after his emigration are compared to historiographical analyses of 'American' or 'German' styles of science around 1900.     

Parameter identification for a macroscopic granular soil model applied to dense Berlin Sand

The present paper outlines the macroscopic stress-strain behaviour of cohesionless soils by the example of dense Berlin Sand. Granular materials as sand show very complex stress-strain relations depending on the stress state and the load history. Examination of these relations is performed at a representative elementary volume (REV) consisting of a sufficient amount of particles. In triaxial tests quasi-static loads are applied to axisymmetric samples, representing the REV, with simultaneous measurement of the response of the granular structure. Within the constitutive equations of the elasto-plastic model, the elastic response is described by a materially non-linear elasticity law. Plastic deformations are considered in the context of a single-surface yield function with isotropic hardening properties. Non-associated flow is realized with an additional plastic potential function. Isotropic behaviour is assumed and the study is restricted to small strains. The parameter identification for the model under study is shown for dense Berlin Sand on the basis of triaxial tests. Received: 2 July 1999