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We investigate theoretically, on the basis of the steady Stokes equations for a viscous incompressible fluid, the flow induced by a stokeslet located on the centre axis of two coaxially positioned rigid disks. The stokeslet is directed along the centre axis. No-slip boundary conditions are assumed to hold at the surfaces of the disks. We perform the calculation of the associated Green's function in large parts analytically, reducing the spatial evaluation of the flow field to one-dimensional integrations amenable to numerical treatment. To this end, we formulate the solution of the hydrodynamic problem for the viscous flow surrounding the two disks as a mixed boundary-value problem, which we then reduce to a system of four dual integral equations. We show the existence of viscous toroidal eddies arising in the fluid domain bounded by the two disks, manifested in the plane containing the centre axis through adjacent counter-rotating eddies. Additionally, we probe the effect of the confining disks on the slow dynamics of a point-like particle by evaluating the hydrodynamic mobility function associated with axial motion. Thereupon, we assess the appropriateness of the commonly employed superposition approximation and discuss its validity and applicability as a function of the geometrical properties of the system. Additionally, we complement our semi-analytical approach by finite-element computer simulations, which reveals a good agreement. Our results may find applications in guiding the design of microparticle-based sensing devices and electrokinetic transport in small-scale capacitors.
In product development, an automated generation of shape variations enables a rapid assessment of potentially appealing design directions. We present a framework for computing a product line-up of automotive body shapes based on spectral methods for mesh processing. We calculate the eigenspace projections of 3D vehicle meshes and identify the relevant style as well as content components based on the eigenvalues. The style of a model is then transferred to arbitrary prototype content car shapes, which allows for a rapid portfolio generation of various car types with minimal user interaction.
Congenital heart disease is the most frequent malformation in newborns. The postoperative mortality of these patients can be assessed with the Risk Adjustment in Congenital Heart Surgery-1 (RACHS-1) score. This study evaluates whether the RACHS-1 score can also be used as a predictor for the length of postoperative ventilation and what is the influence of age.
Material and Methods:
In a retrospective study over the period from 2007 to 2013, all patient records were evaluated: 598 children with congenital heart disease and cardiac surgery were identified and 39 patients have been excluded because of additional comorbidities. For evaluation of mortality, 559 patients could be analysed, after exclusion of 39 deceased patients, 520 cases remained for analysis of postoperative ventilation.
Overall mortality was 7% with a dependency on RACHS-1 categories. The median length of postoperative ventilation rose according to the RACHS-1 categories: RACHS-1 category 1: 9 hours (interquartile range (IQR) 7–13 hours), category 2: 30 hours (IQR 12–85 hours), category 4: 58 hours (IQR 13–135 hours), category 4: 71 hours (IQR 29–165 hours), and category 6: 189 hours (IQR 127–277 hours). Some of the RACHS-1 subgroups differed significantly from the categories, especially the repair of tetralogy of Fallot with a longer ventilation time and strong variability. Younger age was an independent factor for longer postoperative ventilation.
RACHS-1 is a good predictor for the length of postoperative ventilation after cardiac surgery with the exception of some subgroups. Younger age is another independent factor for longer postoperative ventilation. These data provide better insight into ventilation times and allow better planning of operations in terms of available intensive care beds.
Honeybees live both a social life inside of their colony and a life as individuals when foraging. Their cognitive faculties become apparent in their individual life as foragers for provision and information. Identifying them as individuals has crucially allowed studying learning and memory formation under natural conditions and in the laboratory, thus tracing the history of individuals’ experience. Although here I mainly focus on behavioural studies, bees also lend themselves to neurophysiological studies, because of their rather small brains, the excessibility of single neurons and networks, and their robustness. Training experiments reveal that bees perform rather complex tasks (e.g. learning rules, generalization and abstraction, delayed matching to sample, what, when and where tasks). Exploratory learning leads to navigation based on a memory structure, which can be best conceptualized as cognitive maps. Social communication through waggle dance is embedded in this rich spatial memory, allowing bees to choose between alternatives on the base of the expected outcome. While reviewing existing literature on bees’ umwelt and cognition, I will provide practical tips and suggestions on how to best test cognitive skills in these fascinating insects.
Refusal of lifesaving treatment, and such refusal by advance directive, are widely recognized as ethically and legally permissible. Voluntarily stopping eating and drinking (VSED) is not. Ethically and legally, how does VSED compare with these two more established ways for patients to control the end of life? Is it more questionable because with VSED the patient intends to cause her death, or because those who assist it with palliative care could be assisting a suicide?
In fact the ethical and legal basis for VSED is virtually as strong as for refusing lifesaving treatment and less problematic than the basis for refusing treatment by advance directive. VSED should take its proper place among the accepted, permissible ways by which people can control the time and manner of death.
Pedestrian Collision Mitigation Systems (PCMS) are already in the market for some years. Due to continuously evolving EuroNCAP regulations their presence will increase. Visual sensors, already capable of pedestrian classification, provide functional benefits, because the reaction behavior can be optimized when the imminent collision object is recognized as pedestrian or cyclist. Nevertheless their performance will suffer under adverse environmental conditions like darkness, fog, rain or backlight. Even in such unfavorable situations the performance of radar sensors is not significantly deteriorated. Enabling classification capability to automotive radar will further improve road safety and will lower PCMS's overall costs. In this paper, a multi-reflection-point pedestrian target model based on motion analysis is presented. Together with an appropriate sensor model, pedestrian radar signal responses can be provided for a wide range of accident scenarios. Additionally velocity separation requirements that are needed for classification of pedestrians are derived from the simulations. Besides determination of classification features, the model discloses the limits of classical radar signal processing and further offers the opportunity to evaluate parametric spectral analysis. Based on simulated and measured baseband radar signals of pedestrians one of these techniques is deeper analyzed and its enhancement especially on the velocity separation capability is evaluated.
In this paper we present a study of the switching kinetics of SrTiO3 based resistive switching memory devices. A pulse scheme is used to cycle the cells between the high resistive state (HRS) and the low resistive state (LRS) thereby monitoring the transient currents for a precise analysis of the SET and RESET transitions. By variation of the width and amplitude of the applied pulses the switching kinetics are studied between 10-8 and 104 s. Taking the pre-switching currents into account, a power dependency of the SET is found that emphasizes the importance of local Joule heating for the nonlinearity of the switching kinetics.
Resistively switching devices have attracted great attention for potential use in future nonvolatile information storage. Among various oxide materials that show resistive switching (RS) behavior, SrTiO3 (STO) is regarded as a model material to study the effect of valence changes accompanying RS in the oxide . In this class of materials, the RS effect is attributed to rely on the migration of oxygen vacancies and an associated valence change in the cation sublattice. To achieve a switchable state, an initial electroforming step is typically required, which is believed to create conductive regions in the insulating material . Under high electrical stress, an oxygen-deficient region, often referred to as the virtual cathode (VC), is formed . The RS occurs across a very short distance between the VC and the anode, allowing for very short switching times. As the electroforming step greatly impacts the device performance and switching variability, its understanding is essential for device optimization. Electroforming is affected by multiple parameters, e.g. voltage, current, temperature, dopant and defect concentrations, ambient gas atmosphere and time. Distinguishing the influence of the particular parameters is a desirable aim and challenging task. Electrocoloration of Fe-doped STO single crystals has proven a valuable means to visualize valence changes of the Fe ions and is thus suitable to study the formation of the VC. Therefore, we performed electrocoloration experiments and used high resolution transmission light optical microscopy to make the redoxprocesses during electroforming visible. The influence of process driving parameters on the evolution of the VC region is studied. The evolution of the VC is interpreted by drift-diffusion simulation of the time evolution of the oxygen vacancy distribution.
The results of research into the water relations and irrigation requirements of lychee are collated and reviewed. The stages of plant development are summarised, with an emphasis on factors influencing the flowering process. This is followed by reviews of plant water relations, water requirements, water productivity and, finally, irrigation systems. The lychee tree is native to the rainforests of southern China and northern Vietnam, and the main centres of production remain close to this area. In contrast, much of the research on the water relations of this crop has been conducted in South Africa, Australia and Israel where the tree is relatively new. Vegetative growth occurs in a series of flushes. Terminal inflorescences are borne on current shoot growth under cool (<15 °C), dry conditions. Trees generally do not produce fruit in the tropics at altitudes below 300 m. Poor and erratic flowering results in low and irregular fruit yields. Drought can enhance flowering in locations with dry winters. Roots can extract water from depths greater than 2 m. Diurnal trends in stomatal conductance closely match those of leaf water status. Both variables mirror changes in the saturation deficit of the air. Very little research on crop water requirements has been reported. Crop responses to irrigation are complex. In areas with low rainfall after harvest, a moderate water deficit before floral initiation can increase flowering and yield. In contrast, fruit set and yield can be reduced by a severe water deficit after flowering, and the risk of fruit splitting increased. Water productivity has not been quantified. Supplementary irrigation in South-east Asia is limited by topography and competition for water from the summer rice crop, but irrigation is practised in Israel, South Africa, Australia and some other places. Research is needed to determine the benefits of irrigation in different growing areas.
Evidence is provided that the tridymite component observed in the X-ray diffraction patterns of some sewage sludge ashes (SSAs) should not be interpreted as the tridymite modification of SiO2 but as the tridymite form of AlPO4. This proof is based on a combined X-ray Powder Diffraction (XRD), X-ray fluorescence (XRF) and Mossbauer spectroscopy investigation of two SSAs produced at two fluidized bed incineration facilities, located in different municipalities and operated differently. The structural and chemical characterization was carried out on the ‘as received’ SSA samples as well as on the residues of these two SSAs pretreated by leaching in citric acid. In addition, direct proof is presented that the tridymite form of AlPO4 does crystallize from X-ray amorphous precursors under conditions that mimic the huge heating rate and short retention time (just seconds at T ≈ 850 °C) typical for fluidized bed incinerators.
In this work, a novel method for the mode content extrapolation in multimode waveguides with focus on the characterization of mode converters is presented. The proposed method is based on the direct determination of the correlation coefficients between the structural functions of all possible propagating modes and the complex measured near-field pattern. To implement the method, standard near-field equipment is simply required. Test simulations and measurements from 4 to 8 GHz on a 6-in. circular pipe for radar level monitoring are reported in the last section and demonstrate that the proposed technique provides accurate information about the mode content of the structure under test.