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Decrease in saccadic performance after many visually guided saccadic eye movements in monkeys

PURPOSE: To investigate the influence of repeated saccades and of background illumination on the metrics and dynamics of visually guided targeting saccades. METHODS: Eye movements were measured by magnetic search coil technique in seven trained monkeys (Macaca mulatta) while they performed many visually guided saccades in the dark or in dim background light. RESULTS: After 2000 to 7000 saccades in the dark, peak eye velocity on the average decreased by 20%, saccadic gain decreased slightly by 4.5%, and saccadic latency increased by 15%. All parameters also showed increased variability. In contrast, when testing was done in dim light, there was little to no change in average saccadic metrics and latency. CONCLUSIONS: The changes in saccadic metrics and dynamics in the dark do not reflect a change of the ocular plant but may reflect a change in the cortical or cerebellar influences on the brain stem burst generator linked to the monkeys attentional state. Background light mostly prevents this change.     

Three-dimensional extension of non-linear shell formulation based on the enhanced assumed strain concept

Conventional shell formulations, such as 3- or 5-parameter theories or even 6-parameter theories including the thickness change as extra parameter, require a condensation of the constitutive law in order to avoid a significant error due to the assumption of a linear displacement field across the thickness. This means that the normal stress in thickness direction has to either vanish or be constant. In general, these extra constraints cannot be satisfied explicitly or they Sead to elaborate strain expressions. The main objective of the present study is to introduce directly a complete 3-D constitutive law without modification. Therefore, a 7-parameter theory is utilized which includes a linear varying thickness stretch as extra variable allowing also large strain effects. In order to preserve the basic features of a displacement formulation the extra strain term is incorporated via the enhanced assumed strain concept recently proposed by Simo and Rifai to improve the performance of finite elements. Since the extra strain parameter can be eliminated on the element level after discretization, the formulation preserves the formal structure of a 6-parameter shell theory. The resulting hybrid-mixed shell formulation is applied to large deformation problems with hyperelasticity, small and large strain plasticity.     

Die Abscheidung von polychlorierten Dioxinen und Furanen aus Abgasen mit Aktivkoksverfahren

Removal of Polychlorinated Dioxins and Furans from Off-Gases by Activated Charcoal. Discussions on solid waste incineration are dominated by the formation and emission of polychlorinated dibenzodioxins (PCDD) and dibenzofurans (PCDF). The predominant part of these substances remains in the fly ash, and less than 20% is present in the off-gases. Very stringent emission limits have been stipulated during recent years in many countries. The adsorption of PCDD/PCDF on carbonaceous materials has proved to be a very effective technique for their removal. Experimental results relating to gas clean-up, adsorber types, and concepts for the integration in plants are described.     

Über „Gährung” und „gährende Pflänzchen”: Aus den Anfängen der Gärungsforschung im 19. Jahrhundert

The cultural history of alcoholic fermentation goes back to very early periods of human being. But only in the 19th century the nature of the biological production of alcohol was discovered. In that time chemistry and botany had a different, complementary view to alcoholic fermentation. While the positions of chemists are well-known and much discussed in the historiography of science the contribution of botanists to fermentation research is almost entirely forgotten nowadays. The work of the mycologist Oscar Brefeld, who studied yeast fermentation from 1873 to 1876, illustrates the special botanical view to the ontogenetical side of alcoholic fermentation, to morphological and physiological differences between growing and dying, fermenting and fermented yeast cells, and to the energetic and ecological role of fermentation as well as its universality in vegetable kingdom.     

Effect of the filler morphology on the crystallization behavior and dielectric properties of the polyvinylidene fluoride-based composite

Ceramic/polymer composites can be chemically stable, mechanically strong, and flexible, which make them candidates for electric devices, such as pressure or temperature sensors, energy storage or harvesting devices, actuators, and so forth. Depending on the application, various electrical properties are of importance. Polymers usually have low dielectric permittivity, but increased dielectric permittivity can be achieved by the addition of the ceramic fillers with high dielectric constant. With the aim to enhance dielectric properties of the composite without loss of flexibility, 5 wt% of BaTiO₃-Fe₂O₃ powder was added into a polyvinylidene fluoride matrix. The powder was prepared by different synthesis conditions to produce core/shell structures. The effect of the phase composition and morphology of the BaTiO₃-Fe₂O₃ core/shell filler on the structure and lattice dynamics of the polymer composites was investigated. Based on the results of the thermal analysis, various parameters of ceramic/polymer composites were determined. Differences in the phase composition and morphology of the filler have an influence on the formation of various polyvinylidene fluoride allomorphs and the degree of crystallinity. Furthermore, the dielectric performances of pure polyvinylidene fluoride and the polymer/ceramic composites were measured.     

Vulnerability and Robustness of a Security Skyscraper Subjected to Aircraft Impact

Abstract: Ultra‐high‐performance concrete (UHPC) is particularly suitable for application in aircraft‐impact‐resistant high‐rise buildings for combined load‐bearing and protective structures. The material provides very high—steel‐like—compressive strength, sufficient ductility, and fire resistance due to the addition of steel and polypropylene fibers. The following contribution is focused on two key aspects: hydro‐code simulations of structural UHPC walls which protect vertical escape and rescue routes and structural dynamic simulations of the global structure to investigate the impact resistance considering the sudden loss of external columns. A high‐speed dynamic material model for UHPC is obtained by implementing the results of a series of Hopkinson‐Bar experiments which were recently published. The strain‐rate‐dependent material properties are implemented in the established RHT‐Concrete‐Model for hydro‐code applications being furthermore extended by a tensile softening law for fiber‐reinforced UHPC. Based on this material model a series of aircraft‐engine impact experiments are configurated supported by three‐dimensional nonlinear hydro‐code prognosis simulations. With a total of six impact experiments on combined fiber‐ and rebar‐reinforced UHPC panels, all relevant damage states of the structural wall are obtained. The experimental results are compared to the hydro‐code prognosis simulations to validate the simulative approach and the material model for UHPC. In addition to the local impact behavior, structural dynamic numerical simulations of a global high‐rise structure are presented being focused on the effect of the sudden and notional loss of columns in coincidence with the aircraft impact load function.     

Rissbildung und Zugtragverhalten von mit Fasern verstärktem Stahlbeton am Beispiel ultrahochfesten Betons

Crack Formation and Tensile Behaviour of Concrete Members Reinforced with Rebars and Fibres exemplified by Ultra‐High‐Performance Concrete Part 1: Crack Mechanical Relationships When combining conventional non‐pre‐stressed or pre‐stressed reinforcement with fibres, differences in the load‐carrying and deformation behaviour arise in comparison to the well‐known reinforced and pre‐stressed concrete. This fact holds true comparably for all concrete classes. However, it is of special interest for ultra‐high‐performance concretes (UHPC), because fibres are added to these concretes generally to improve ductility. With regard to durability, the positive influence of the fibres on the crack formation process and the crack widths in the serviceability range is significant. Especially for enhanced requirements concerning the crack width (order of magnitude: 0.1 mm) with combined reinforcement of rebars and fibres an essential improve compared to reinforced concrete can be achieved. The analysis of the crack formation process presumes the understanding of the different behaviours of the two reinforcing elements ”rebars” and ”fibres”. In part 1 of this contribution, the therefore required mechanical relationships are presented and linked with each other considering equilibrium and compatibility. In part 2 the derived relationships are validated on the basis of experimental investigations on tensile members with combined reinforcement made of UHPC. The application is furthermore illustrated by means of two examples. Because of its universal formulation, the presented proposal is generally applicable to all types of concrete reinforced with rebars and fibres, i.e. it is not limited to ultra‐high‐performance concrete.