Organic hospital food is desired by patients and engages the kitchen

In December 2005 a questionnaire survey was conducted at the University Hospital in Trondheim, Norway. Patients and personnel expressed that food is important for their health and well-being. Good taste, appearance and right nutrition were mentioned as being important factors for food quality. About 80 % of the respondents were positive to the use of organic food at the hospital, even though only about half of them agreed that it is worth the price. The absence of pesticides, artificial fertilizers and preservatives in food was ranked to be more important than organic production of food. All respondents seemed to be critical to the use of pesticides and preservatives in food production and processing

Signatures of criticality arise in simple neural population models with correlations

Large-scale recordings of neuronal activity make it possible to gain insights into the collective activity of neural ensembles. It has been hypothesized that neural populations might be optimized to operate at a 'thermodynamic critical point', and that this property has implications for information processing. Support for this notion has come from a series of studies which identified statistical signatures of criticality in the ensemble activity of retinal ganglion cells. What are the underlying mechanisms that give rise to these observations? Here we show that signatures of criticality arise even in simple feed-forward models of retinal population activity. In particular, they occur whenever neural population data exhibits correlations, and is randomly sub-sampled during data analysis. These results show that signatures of criticality are not necessarily indicative of an optimized coding strategy, and challenge the utility of analysis approaches based on equilibrium thermodynamics for understanding partially observed biological systems.Comment: 36 pages, LaTeX; added journal reference on page 1, added link to code repositor

Fast simulation of a flat cross wedge rolling process

In this paper, a new approach for a Fast Simulation of flat cross wedge rolling processes is presented. The approach is based on a preliminary research project of the Institute of Forming Technology and Machines (IFUM) of the Leibniz Universität Hannover, in which a software prototype for a Fast Simulation of a radial-axial ring rolling process was developed. Both simulations are based on geometric-kinematic models that allow a faster calculation of the material flow compared to the Finite Element-simulation (FE-simulation). The goal of the Fast Simulation for the flat cross wedge process is to support the designer in the challenging design phase of the flat cross wedge tool as well as in the planning phase of the process parameters. In this phase it shall be easier in future to determine the best geometric parameters for the design of flat cross wedge tools, to attain the necessary material flow and geometry, before starting with the first FE-simulation. With this preliminary information from the Fast Simulation it will be possible to reduce the number of iteration loops for the time-consuming FE-simulations of incremental forming processes

Aerodynamic Admittance Models for Buffeting Excitation of High and Slender Structures

Die dynamische Reaktion hoher, schlanker Bauwerke infolge Böenerregung wird maßgeblich durch die aerodynamische Admittanz bestimmt, welche die räumlich-zeitliche Übertragung der Windturbulenz auf die Druckverteilung an der Oberfläche eines Körpers beschreibt. Zur Ermittlung böeninduzierter Windlasten wird gewöhnlich von einem quasi-stationären Modell der aerodynamischen Admittanz ausgegangen. Die aerodynamische Übertragung wird dabei als unabhängig sowohl von der Zeit als auch von der Frequenz unterstellt. Der tatsächlich stark nichtlineare Zusammenhang zwischen den Geschwindigkeits- und Richtungsfluktuationen der Turbulenz sowie den resultierenden Windlasten wird mittels diskutabler Methoden linearisiert. Solche Vereinfachungen können insbesondere bei hochturbulenter Strömung zu einer beträchtlichen Unterschätzung der fluktuierenden Windkräfte führen. Um beurteilen zu können, inwieweit konventionelle Admittanzansätze die Realität beschreiben, wurden neben theoretischen Untersuchungen Naturmessungen durchgeführt. Der Fachwerkschaft eines 344 m hohen Mastes wurde über eine Fläche von 360 m² mit auf Kraftmesszellen lagernden Fassadenelementen verkleidet. Durch die simultane Messung der auf die Fassaden wirkenden Windkräfte sowie des ungestörten Strömungsfeldes werden aerodynamische Admittanzmodelle vor dem Hintergrund einer sicheren Bemessung hoher, schlanker Bauwerke überprüft.The dynamic response of high and slender structures induced by turbulence buffeting is decisively determined by the aerodynamic admittance, which describes the spatial and temporal transfer function between the wind turbulence and the wind loads acting on a body´s surface. For the determination of turbulence-induced wind loads a quasi-steady admittance model is usually chosen. Such a model starts from the assumption that the aerodynamic transfer function is constant with respect to both time and frequency. The actually highly nonlinear relationship between the fluctuations of wind speed and wind direction on the one hand, and the resulting wind forces on the other, is linearised by methods which have to be discussed. Particularly in high-turbulent flow, the conventional linearised descriptions of the originally nonlinear wind-speed-to-wind-force relationship will produce a highly incorrect estimation of the dynamic part of the wind load. Besides theoretical investigations the effect of different quasi-steady approaches of the aerodynamic admittance function on the fluctuations of the wind loads are studied by full-scale measurements. The lattice shaft structure of a 344 m high guyed mast was equipped with cladding elements, which covered an area of 360 m² and are supported by load cells. When simultaneously measuring the wind forces acting on these elements and of the undisturbed turbulent flow, aerodynamic admittance models are checked for a safe design of high and slender structures such as masts and towers

Analysis of machine influence on process stability in sheet bulk metal forming

This contribution deals with the process-machine interaction while forming parts by sheet-bulk metal forming. The goal of this process is to form complex functional elements, such as gearing and carrier elements, by means of controlled thickening of the metal sheet. The high process forces in vertical as well as in horizontal direction to form these elements, cause displacements of the tool and press components, which lead to parts defects retroactively. This work demonstrates these challenges with regard to manufacturing of asymmetrical parts and introduces a suitable approach to represent the process-machine interaction by modelling.DFG/TCRC/7

Enhancement of the interface of friction welded steel-aluminium joints

Lightweight multi-material components are of great importance for the transport industry. Not only the component’s weight can be decreased, but also its local properties can be adapted to different loading profiles. Tailored Forming is a novel concept for producing multi-material components. By using a joining process, the creation of a bond between different materials takes place in the first step of the process chain. In the subsequent steps, multi-material workpieces are processed in their joined state while maintaining or improving the joint strength. This study focuses on steel-aluminium joints, which were created by friction welding and further processed by induction heating and impact extrusion. A counter pressure superposition mechanism was implemented in the extrusion tooling to control the stress state during plastic deformation. Flow behaviours of steel and aluminium are largely different at a given temperature, which necessitates a near step-function temperature distribution in the hybrid billet to obtain matching flow stresses. An inductive heating strategy was developed which led to a temperature gradient in the billets before extrusion. Extruded billets were analysed by destructive testing methods and metallography. The bond could be maintained after extrusion when counter pressure superposition was used; but no improvement could be obtained. Without counter force superposition, however, cracks were observed in the joining interface and the joint strength decreased. This paper discusses the aforementioned findings in the current process design and makes suggestions on how the involved processes should be reconfigured to improve the joint strength. © 2020, The Author(s)

Нагрев и пределы частотного регулирования асинхронного двигателя, работающего с наименьшими годовыми приведенными затратами

Исследуется тепловой режим асинхронного двигателя, оптимизированного по минимуму годовых приведенных затрат при переменной частоте питающего напряжения. Определены пределы регулирования скорости. Показана целесообразность оптимизации двигателя по экономическому критерию

Numerical investigations on the influence of the weld surface and die geometry on the resulting tensile stresses in the joining zone during an extrusion process

Bulk metal components are often used in areas which are subjected to very high loads. For most technical components, a distinction between structural and functional areas can be made. These areas usually have very different loading profiles, sometimes with contradictory requirements. Nevertheless, nowadays almost only monomaterials are used for the production of bulk metal components. With increasing requirements towards more and more efficient products with lower weight, compact design and extended functionality, these materials are reaching their material-specific limits. A significant increase of product quality and economic efficiency can be expected exclusively with locally adapted properties by combining different materials within one component. In this regard, the focus of this contribution is the production of a hybrid pinion shaft made of the material combination steel (37CrS4) and aluminium (AW6082). The tool concept for extrusion of the hybrid preform, the simulation-based design of the forming process as well as the material characterisation are presented. With the help of the FE-simulation, different serially arranged semi-finished component geometries were investigated in order to minimise the occurring tensile stresses in the component during the extrusion process to prevent failure during forming

Investigation of the influence of an oscillation superposition on the wear behaviour in an industrial-like process

In cold forging processes as well as in sheet-bulk metal forming, vast contact stresses result in severe tool wear and thus in tool failures. In order to achieve a sustainable production, a new manufacturing process is developed within the subproject T06 in the transregional collaborative research centre 73 at the Institute of Forming Technology and Machines (IFUM). In this subproject the influence of an oscillation superposition on a forming process is investigated. The new type of sheet-bulk metal forming (SBMF) process manufactures a component with internal and external gearing. Contact normal stresses and thus tool wear could be reduced by applying an oscillation superposition in the main force flow of the machine. To verify the positive results in other processes, the oscillation method is applied to an industrial-like process based on anchor bolt manufacturing of Fischerwerke GmbH & Co. KG. For this purpose, a representative tool system is developed using numerical simulation. The numerical simulation is also used to investigate resulting local contact stresses and relative sliding velocities. Furthermore, cylinder compression tests with and without oscillation superposition are conducted for the workpiece stainless steel 1.4362 (AISI S32304), in order to qualify the reduction of contact stress

Neuromuscular function and fatigue resistance of the plantar flexors following short-term cycling endurance training

Previously published studies on the effect of short-term endurance training on the neuromuscular function of the plantar flexors have shown that the H-reflex elicited at rest and during weak voluntary contractions was increased following the training regime. However, these studies did not test H-reflex modulation during isometric maximum voluntary contraction (iMVC) and did not incorporate a control group in their study design to compare the results of the endurance training group to individuals without the endurance training stimulus. Therefore, this randomized controlled study was directed to investigate the neuromuscular function of the plantar flexors at rest and during iMVC before and after eight weeks of cycling endurance training. Twenty-two young adults were randomly assigned to an intervention group and a control group. During neuromuscular testing, rate of torque development, isometric maximum voluntary torque and muscle activation were measured. Triceps surae muscle activation and tibialis anterior muscle co-activation were assessed by normalized root mean square of the EMG signal during the initial phase of contraction (0-100, 100-200 ms) and isometric maximum voluntary contraction of the plantar flexors. Furthermore, evoked spinal reflex responses of the soleus muscle (H-reflex evoked at rest and during iMVC, V-wave), peak twitch torques induced by electrical stimulation of the posterior tibial nerve at rest and fatigue resistance were evaluated. The results indicate that the endurance training did not lead to a significant change in any variable of interest. Data of the present study conflict with the outcome of previously published studies that have found an increase in H-reflex excitability after endurance training. However, these studies had not included a control group in their study design as was the case here. It is concluded that short-term cycling endurance training does not necessarily enhance H-reflex responses and fatigue resistance