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In Europe, the risk assessment for bees at the European Union or national level has always focussed on potential impacts on honeybees. During the revision of the European Food Safety Authority bee guidance it was explicitly stated that bumblebees and solitary bees should be considered as well and consequently concerns were raised regarding the representativeness of honeybees for these other bee species. These concerns originate from differences in size as well as differences in behavioral and life history traits of other bee species. In response to this concern, the non-Apis working group of the International Commission for Plant-Pollinator Relationships initiated a ring-test of a semifield tunnel study design using the bumblebee Bombus terrestris. Nine laboratories participated, validating and improving the proposed design over a 2-year period. The intention of the ring-test experiments was to develop and if possible, establish a test protocol to conduct more standardized semifield tests with bumblebees. In the present study, the results of the ring-tests are summarized and discussed to give recommendations for a promising experimental design. Environ Toxicol Chem 2022;41:2548-2564. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

There are various differences in size, behavior, and life history traits of non-Apis bee species compared with honey bees (Apis mellifera; Linnaeus, 1758). Currently, the risk assessment for bees in the international and national process of authorizing plant protection products has been based on honey bee data as a surrogate organism for non-Apis bees. To evaluate the feasibility of a semifield tunnel test for Osmia bicornis (Linnaeus, 1758) and Osmia cornuta (Latreille, 1805), a protocol was developed by the non-Apis working group of the International Commission for Plant-Pollinator Relationships, consisting of experts from authorities, academia, and industry. A total of 25 studies were performed over a 2-yr period testing a replicated control against a replicated positive control using either a dimethoate or diflubenzuron treatment. Studies were regarded to be valid, if ≥30% of released females were found to occupy the nesting units in the night/morning before the application (establishment). Thirteen studies were regarded to be valid and were analyzed further. Parameters analyzed were nest occupation, flight activity, cell production (total and per female), cocoon production (total and per female), emergence success, sex ratio, and mean weight of females and males. Dimethoate was a reliable positive control at the tested rate of 75 g a.i./ha, once >30% females had established, displaying acute effects such as reduction in flight activity, increase in adult mortality (shown by nest occupation), and reproduction ability of the females (total cell and cocoon production). On the other hand, no effects on larval and pupal development were observed. The growth regulator diflubenzuron had statistically significant effects on brood development, causing mortality of eggs and larvae at a rate of approximately 200 g a.i./ha, whereas fenoxycarb did not cause any significant effects at the tested rates of 300 and 600 g a.i./ha. In conclusion, the ring-test protocol proved to be adequate once the study comprised a well-established population of female Osmia bees, and the results improved in the second year as the laboratories increased their experience with the test organism. It is noted that the success of a study strongly depends on the experience of the experimenter, the crop quality, the quality of the cocoons, and the weather conditions. Based on these finding, recommendations for a semifield study design with Osmia spp. are proposed. Environ Toxicol Chem 2021;40:236-250. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

The aim of the study was to investigate the potential impact of the insecticide chlorantraniliprole on queen-right bumblebee (Bombus terrestris) colonies under semi-field conditions in Phacelia tanacetifolia. The P. tanacetifolia crop was grown in soil treated with modelled worst-case 20-year plateau concentration of chlorantraniliprole in the top 20 cm of soil (equivalent to 0.088 mg a.s./kg). Additionally, two chlorantraniliprole spray applications at 60 g a.s./ha were made. In treatment T1 both spray applications took place before P. tanacetifolia flowering at growth stages BBCH 51–55 and BBCH 55–59. In T2 one spray application was conducted before P. tanacetifolia flowering at BBCH 55–59 and one application during P. tanacetifolia flowering and during daily bee flight at BBCH 61–62. The application in the control (C) and reference item treatment (R) (400 g dimethoate a.s./ha) was carried out during full P. tanacetifolia flowering and bumblebee flight. The bumblebee colonies were exposed to the treated flowering P. tanacetifolia crop for 20 days in the tunnels and afterwards the colonies were kept on a monitoring site. Results of this study indicate no significant differences between the chlorantraniliprole groups T1 and T2 and the control regarding all parameters assessed (i.e. adult and larval mortality, flight activity at the hive entrance, colony weight development, condition of the colonies and production of young queens and males). Overall, no effects of chlorantraniliprole on B. terrestris colonies including queen/male production, adult and larval survival, colony development and forager flight activity were found in this worst-case exposure set-up.

To date, regulatory pesticide risk assessments have relied on the honey bee (Apis mellifera L.) (Hymenoptera: Apidae) as a surrogate test species for estimating the risk of pesticide exposure to all bee species. However, honey bees and non-Apis bees may differ in their susceptibility and exposure to pesticides. In 2017, a workshop ('Pesticide Exposure Assessment Paradigm for Non-Apis Bees') was held to assess if honey bee risk assessment frameworks are reflective of non-Apis bee pesticide exposure. In this article, we summarize the workshop discussions on bumble bees (Bombus spp.). We review the life history and foraging behavior of bumble bees and honey bees and discuss how these traits may influence routes and levels of exposure for both taxa. Overall, the major pesticide exposure routes for bumble bees and honey bees are similar; however, bumble bees face additional exposure routes (direct exposure of foraging queens and exposure of larvae and adults to soil residues). Furthermore, bumble bees may receive comparatively higher pesticide doses via contact or oral exposure. We conclude that honey bee pesticide risk assessments may not always be protective of bumble bees, especially queens, in terms of exposure. Data needed to reliably quantify pesticide exposure for bumble bees (e.g., food consumption rates, soil residue levels) are lacking. Addressing these knowledge gaps will be crucial before bumble bee exposure can be incorporated into the pesticide risk assessment process. Because bumble bees exhibit appreciable interspecific variation in colony and behavioral characteristics, data relevant to pesticide exposure should be generated for multiple species.

There are various differences in size, behavior, and life history traits of non‐Apis bee species compared with honey bees (Apis mellifera; Linnaeus, 1758). Currently, the risk assessment for bees in the international and national process of authorizing plant protection products has been based on honey bee data as a surrogate organism for non‐Apis bees. To evaluate the feasibility of a semifield tunnel test for Osmia bicornis (Linnaeus, 1758) and Osmia cornuta (Latreille, 1805), a protocol was developed by the non‐Apis working group of the International Commission for Plant‐Pollinator Relationships, consisting of experts from authorities, academia, and industry. A total of 25 studies were performed over a 2‐yr period testing a replicated control against a replicated positive control using either a dimethoate or diflubenzuron treatment. Studies were regarded to be valid, if ≥30% of released females were found to occupy the nesting units in the night/morning before the application (establishment). Thirteen studies were regarded to be valid and were analyzed further. Parameters analyzed were nest occupation, flight activity, cell production (total and per female), cocoon production (total and per female), emergence success, sex ratio, and mean weight of females and males. Dimethoate was a reliable positive control at the tested rate of 75 g a.i./ha, once >30% females had established, displaying acute effects such as reduction in flight activity, increase in adult mortality (shown by nest occupation), and reproduction ability of the females (total cell and cocoon production). On the other hand, no effects on larval and pupal development were observed. The growth regulator diflubenzuron had statistically significant effects on brood development, causing mortality of eggs and larvae at a rate of approximately 200 g a.i./ha, whereas fenoxycarb did not cause any significant effects at the tested rates of 300 and 600 g a.i./ha. In conclusion, the ring‐test protocol proved to be adequate once the study comprised a well‐established population of female Osmia bees, and the results improved in the second year as the laboratories increased their experience with the test organism. It is noted that the success of a study strongly depends on the experience of the experimenter, the crop quality, the quality of the cocoons, and the weather conditions. Based on these finding, recommendations for a semifield study design with Osmia spp. are proposed. Environ Toxicol Chem 2021;40:236–250. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC., For ecotoxicological testing of pesticides, a protocol was developed and ring‐tested by the non‐Apis working group of the International Commission for Plant‐Pollinator Relationships to conduct semifield tunnel tests with the solitary bee species Osmia bicornis (Linnaeus, 1758) and Osmia cornuta (Latreille, 1805).

Parameters within hysteresis operators modeling real world objects have to be identified from measurements and are therefore subject to corresponding errors. To investigate the influence of these errors, the methods of Uncertainty Quantification (UQ) are applied. Results of forward UQ for a play operator with a stochastic yield limit are presented. Moreover, inverse UQ is performed to identify the parameters in the weight function in a Prandtl-Ishlinskiĭ operator and the uncertainties of these parameters.

There has been increasing interest in the effects of neonicotinoid insecticides on wild bees. In solitary bee species the direct link between each individual female and reproductive success offers the opportunity to evaluate effects on individuals. The present study investigated effects of exposure to winter oilseed rape grown from thiamethoxam-treated seed on reproductive behavior and output of solitary red mason bees (Osmia bicornis) released in 6 pairs of fields over a 2-yr period and confined to tunnels in a single year. After adjustment to the number of females released, there was significantly lower production of cells and cocoons/female in tunnels than in open field conditions. This difference may be because of the lack of alternative forage within the tunnels. Under open field conditions, palynology of the pollen provisions within the nests demonstrated a maximum average of 31% oilseed rape pollen at any site, with Quercus (oak) contributing up to 86% of the pollen. There were no significant effects from exposure to oilseed rape grown from thiamethoxam-treated seed from nest establishment through cell production to emergence under tunnel or field conditions. Environ Toxicol Chem 2018;37:1071-1083. © 2017 SETAC.

Parameters within hysteresis operators modeling real-world objects have to be identified from measurements and are therefore subject to error in measurement. To investigate the influence of these errors, the methods of Uncertainty Quantification (UQ) are applied.

In this paper, the optimal control of traveling magnetic fields in a process of crystal growth from the melt of semiconductor materials is considered. As controls, the phase shifts of the voltage in the coils of a heater-magnet module are employed to generate Lorentz forces for stirring the crystal melt in an optimal way. By the use of a new industrial heater-magnet module, the Lorentz forces have a stronger impact on the melt than in earlier technologies. It is known from experiments that during the growth process, temperature oscillations with respect to time occur in the neighborhood of the solid-liquid interface. These oscillations may strongly influence the quality of the growing single crystal. As it seems to be impossible to suppress them completely, the main goal of optimization has to be less ambitious, namely one tries to achieve oscillations that have a small amplitude and a frequency which is sufficiently high such that the solid-liquid interface does not have enough time to react to the oscillations. In our approach, we control the oscillations at a finite number of selected points in the neighborhood of the solidification front. The system dynamics is modeled by a coupled system of partial differential equations that account for instationary heat conduction, turbulent melt flow, and magnetic field. We report on numerical methods for solving this system and for the optimization of the whole process. Different objective functionals are tested to reach the goal of optimization.

The representation formula for hysteresis operators acting on scalar-valued continuous input functions being piecewise monotone that was derived in Brokate and Sprekels (1996) [1] has been extended to results for hysteresis operators acting on vectorial input function, see Klein (2012, 2014) [2] , [3] , [4] , [5] . In the current paper, the representation result is extended to rate-independent systems, as considered for example in Mielke (2005) [9] . The input functions are requested to be continuous and to be piecewise strictly monotaffine, i.e. to be piecewise the composition of a strictly monotone increasing function with an affine function, the strictly monotone function being applied first.

As the number of fuel-cell vehicles on the roads increase, the vehicle designs are gaining more importance. Clearly, one major topic in this field is the optimization of powertrain designs. In this design process, the aim of the car manufacturers is to meet the expectations of the potential customer best, while creating a sustainable product. However, due to several trade-offs in the design, it would be non-realistic to expect a single solution that fulfills all design objectives. Therefore, a systematical approach, which includes a trade-off analysis and evaluation methods for this multiobjective design problem, is required. In this paper, a suitable methodology is presented and applied in a case study, where an optimum powertrain design for a typical European long-range passenger car is sought. Simulation-aided powertrain models and scalable component models are used to increase the accuracy of the design process. Furthermore, various visual and quantitative evaluation techniques are applied in order to support the decision making process.

Suggested by conversations in 1991 (Mark Krasnosel'skiĭ and Aleksei Pokrovskiĭ with TIS), this paper generalizes earlier work (Krasnosel'skiĭ-Pokrovskiĭ 1974) of theirs by defining a setting of hybrid systems with isotone switching rules for a partially ordered set of modes and then obtaining a periodicity result in that context. An application is given to a partial differential equation modeling calcium release and diffusion in cardiac cells.

Energy management is integral to the design of fuel-cell (FC) hybrid vehicles (FCHVs), as well as topology and component sizing. Therefore, an optimal energy management strategy is crucial for a successful FCHV concept. The goal in this optimization process is to coordinate the energy sources and power components on a vehicle in such a way that the total consumption is minimized. We defined a new strategy that quantifies the shifts in the operating point (OP) of the FC system by using the specific fuel consumption due to load shifting and adapts the conditions for a possible shifting of the OP of the FC system to reduce the total fuel consumption. This paper shows the simulation results of the proposed strategy in comparison with existing strategies. The main focus is given on the improvement in fuel consumption, the effect of the new approach on utilization of the power sources concerning their aging mechanisms, and the effect of varying conditions by time. The results indicate that the goal of reduction in total fuel consumption is achieved.

Sweeping processes are a class of evolution differential inclusions arising in elastoplasticity and were introduced by J.J. Moreau in the early seventies. The solution operator of the sweeping processes represents a relevant example of rate independent operator. As a particular case we get the so called play operator, which is a typical example of a hysteresis operator. The continuity properties of these operators were studied in several works. In this note we address the continuity with respect to the strict metric in the space of functions of bounded variation with values in the metric space of closed convex subsets of a Hilbert space. We provide counterexamples showing that for all BV-formulations of the sweeping process the corresponding solution operator is not continuous when its domain is endowed with the strict topology of BV and its codomain is endowed with the L1-topology. This is at variance with the play operator which has a BV-extension that is continuous in this case.

Within the regulatory framework for authorisation of plant protection products (PPPs) (EU Directive 91/414/1991/EEC replaced by Regulation (EC) 1107/2009), higher tier risk assessments and earthworm field tests are conducted in different countries across Europe. This paper describes dominant earthworm species for regulatory and biogeographical regions in agricultural landscapes across Europe and examines regional differences in earthworm communities and densities and their respective response to a toxic reference. For the assessment of earthworm abundance and species distribution, data of untreated control plots from 30 earthworm field studies were analysed; each conducted according to the ISO 11268–3 (1999) guideline by European Crop Protection Association member companies in the context of registration of PPPs. For the evaluation of the response to PPPs under different regional and climatic conditions, the effect on earthworm abundance was assessed by comparing plots treated with toxic references with untreated control plots. Additionally, a comparative literature review was included providing an overview of earthworm species composition and densities in agricultural crops from 14 European countries. The assessment of earthworm field studies from six different European countries revealed that common earthworm species of anecic and endogeic ecological groups are present at most field sites. Dominant species groups of endogeic and anecic earthworms can be defined that are abundant in all assessed countries. These are the endogeic species Aporrectodea caliginosa, Aporrectodea rosea and Allolobophora chlorotica, and the anecic species Lumbricus terrestris (Northern and Central Europe) and Lumbricus friendi (Southern Europe). Taking into account the high variability in total earthworm abundances, it can be concluded that the variability within regions was larger than the variability between regions. Analysis of the earthworm community and data of toxic references lead to the conclusion that testing in different zones is not considered necessary.

Dynamic testing of a phosphoric acid-based high temperature PEM fuel cell shows a peculiar phenomenon. A certain current loss is observed after temperature cycling at constant voltage. This loss is incidentally recovered by applying a cell voltage spike to open circuit voltage. Experimental investigations into temperature, cell voltage, and ageing effects show that this phenomenon might occur due to the orientation of the adsorbed phosphate species on the platinum catalyst surface. Along with some supporting literature and experimental results, a hypothesis is presented in order to explain this occurrence. Phosphoric acid adsorption hysteresis on platinum catalyst due to temperature cycling could cause the temporary cell current loss. Electrode potential-dependent molecule symmetry of adsorbed phosphate ions could bring about the cell current recovery.

During unidirectional solidification of multicrystalline (mc) silicon, the adjustment of controllable mixing patterns with high stirring efficiency can be obtained by application of a double-frequency travelling magnetic field (TMF). It is assumed that such Lorentz force mode is generated within KRISTMAG ® heater magnet modules (HMM) positioned around a rectangular crystallization container with silicon melt. The induced flow distributions were studied numerically by 3D magnetic and transient flow calculations. The electromagnetic interference due to the presence of two frequencies and its effect on the resulting Lorentz force density have been estimated analytically. The results show that the flow can be intentionally intensified in the bulk volume without generation of hazardous high velocities in the peripheral region, i.e. near container walls. No considerable resonance effect has been found. As a result the TMF penetration and, hence, the melt mixing level within the central region is enhanced. Additionally, a general improvement of the process purity can be predicted.

The paper is concerned with a class of optimal heating problems in semiconductor single crystal growth processes. To model the heating process, time-harmonic Maxwell equations are considered in the...

In this work, hysteresis operators mapping continuous vector-valued input functions being piecewise monotaffine, i.e. being piecewise the composition of a monotone with an affine function, to vector-valued output functions are considered. It is shown that the operator can be generated by a unique defined function on the convexity triple free strings. A formulation of a congruence property for periodic inputs is presented and reformulated as a condition for the generating string function.

We present numerical simulations of vapor pressure controlled (VCz) and liquid encapsulated Czochralski (LEC) crystal growth of GaAs under the influence of a traveling magnetic field (TMF) with melt diameters of approximately 6 in and melt heights of approximately 1.8 in. The TMF is generated by an internal heater-magnet module (HMM) inside the pressure chamber in the growth arrangement and has been developed within the project KRIST MAG ˜ , see http://www.kristmag.com . For the global simulation, i.e. for the computation in the entire pressure chamber, the software WIAS-HiTNIHS is used. We validate this software by comparing measured and simulated Lorentz forces. Furthermore, we discuss how to account for effects of non-axisymmetric parts of the growth configuration during the axisymmetric computations performed by WIAS-HiTNIHS . Results computed by stationary global simulations are used as input data for transient local simulations of the melt. For the local simulations, we use the code NAVIER to solve the Navier–Stokes equations with the Boussinesq approximation together with the energy equation in an axisymmetric setting. Numerical simulations of the melt in an LEC configuration with an HMM are presented, showing that the Lorentz force generated by a TMF induced from the HMM can damp the temperature oscillations in the Taylor cell below the crystal.

A software for the numerical simulation of crystal growth from the melt under the influence of a traveling magnetic field was developed by coupling a global stationary simulation of the temperature distribution and the electro-magnetic fields to a local transient simulation of the melt. Numerical results of the simulation of the vapor pressure controlled Czochralski (VCz) growth of GaAs are presented.

We present numerical computations of the temperature fields in axisymmetric growth apparatus for sublimation growth of silicon carbide (SiC) bulk single crystals by physical vapor transport (PVT) (modified Lely method). The results are computed using our software WIAS-HiTNIHS , the WIAS High Temperature Numerical Induction Heating Simulator; pronunciation: ∼ hit-nice , by solving the energy balance in the entire growth apparatus, taking into account the heat conduction in the solid parts as well as in gas cavities, and also accounting for the radiative heat transfer between the surfaces of the gas cavities. The insulation in a PVT growth apparatus usually consists of graphite felt, where the fibers are aligned in one particular direction, resulting in an anisotropic thermal conductivity. We show that neglecting this anisotropy can overestimate the SiC crystal's temperature by 70 K or underestimate the required heating power by 800 W.

In some recent papers, the concept of outward pointing operators has been used as a tool within the mathematical investigation of equations involving hysteresis operators, and has been considered for the stop operator, the play operator, and Prandtl–Ishlinskii operators. Now, for Preisach operators, conditions will be discussed which ensure that this condition is satisfied.

The goal of this work is to canonize arbitrary Borel measurable mappings on the Milliken space, which is the space of all increasing infinite sequences of pairwise disjoint nonempty finite subsets of the set of all nonnegative integers. The main result refers to the metric topology on the Milliken space. The result is a common generalization of a theorem of Taylor and a theorem of Promel and Voigt.

The paper deals with the long-time behaviour of evolution systems involving hysteresis operators. Introducing the concept of outwards pointing hysteresis operators allows to generalize methods that have been used to derive uniform a priori bounds for solutions to equations involving the superposition with nonlinear functions. This is done to derive a large-time asymptotic result for a coupled system of PDEs and ODEs modelling nonlinear thermo-visco-plastic developments. Moreover, a class of generalized Prandtl–Ishlinskii operator will be introduced and results concerning the thermodynamic consistency and the outwards pointing property of these operators will be presented.

We present a transient mathematical model for the sublimation growth of silicon carbide (SiC) single crystals by the physical vapor transport (PVT) method. The model of the gas phase consists of balance equations for mass, momentum, and energy, as well as reaction-diffusion equations. Due to physical and chemical reactions, the gas phase is encompassed by free boundaries. Nonlinear heat transport equations are considered in the various solid components of the growth system. Discontinuous and nonlocal interface conditions are formulated to account for temperature steps between gas and solid as well as for diffuse-gray radiative heat transfer between cavity surfaces. An axisymmetric induction heating model is devised using a magnetic scalar potential. For a nonlinear evolution problem arising from the model, a finite volume scheme is stated, followed by a discrete existence and uniqueness result. We conclude by presenting and analyzing results of transient numerical experiments relevant to the physical growth process.

The paper deals with the long-time behaviour of evolution systems described by ODEs and PDEs with hysteresis operators. The analysis is based on two concepts. The first one is the outward pointing property of the involved hysteresis operators which implies uniform a priori bounds for solutions, the second one is related to the hysteresis modelling itself and consists in introducing a class of thermodynamically consistent generalized Prandtl–Ishlinskii operators as a model for a nonlinear elastoplastic material law. A stability result for solutions in one-dimensional visco-elasto-plasticity is derived as an illustration of the theory.

In this article, we use numerical simulation to investigate transient temperature phenomena during sublimation growth of SiC single crytals via physical vapor transport (also called the modified Lely method). We consider the evolution of temperatures at the SiC source and at the SiC seed crystal, which are highly relevant to the quality of the grown crystals, but inaccessible to direct measurements. The simulations are based on a transient mathematical model for the heat transport, including heat conduction, radiation, and radio frequency (RF) induction heating. Varying the position of the induction coil as well as the heating power, it is shown that the measurable temperature difference between the bottom and the top of the growth apparatus can usually not be used as a simple indicator for the respective temperature difference between SiC source and seed. Moreover, it is shown that there can be a time lag of 1.5 h between the heating of the temperature measuring points and the heating of the interior of the SiC source.

This article presents transient numerical simulations of the temperature evolution during sublimation growth of SiC single crystals via physical vapor transport (also called the modified Lely method) including diffusion and radiation, investigating the influence of induction heating. Using the imposed voltage as input data, the heat sources are computed via an axisymmetric complex-valued magnetic scalar potential that is determined as the solution of an elliptic PDE. The presented results include stationary simulations of magnetic potential distributions and resulting heat sources as well as transient simulations of the temperature evolution during the heating process. We examine the effects of imposed voltage (i.e. heating power), of different coil positions, and of a moving induction coil on the evolution of the global temperature field and on the temperature at the source, at the seed, and at the blind holes. All material data used are either included or referenced.

In this paper, a phase field system of Penrose–Fife type with non–conserved order parameter is considered. A class of time–discrete schemes for an initial–boundary value problem for this phase–field system is presented. In three space dimensions, convergence is proved and an error estimate linear with respect to the time–step size is derived.

Scattering of helium atoms by cyclopentane, pyrrolidine and tetrahydrofurane molecules was ob-served in crossed molecular beam experiments. The intensity of scattered helium atoms, depending on the scattering angle, was measured with high resolution, and the damping of the diffraction oscillations of the differential cross sections was used to extract elastic anisotropic interaction potentials for these molecules. The evaluation included a geometric transformation concerning the puckered states of the envelope and the twisted conformation of the molecules. The potentials were found to be rather similar.

Differential cross section measurements are reported for scattering of an improved He-atomic beam by crossed beams of Pyrrole, Furane and Thiophene. The damping of the DCS diffraction oscillations is used to extract reliable anisotropic intermolecular potentials, applying the infinite order sudden approximation (IOSA).

In fuel cell systems with an anode recirculation cycle that runs overstoichiometrically, an undesired enrichment of nitrogen and water vapor occurs due to their diffusion through the membrane-electrode-assembly (MEA). This causes an impairment of the power density. So far, this phenomenon was avoided by a time dependent purge strategy. During this process a lot of unconsumed hydrogen gets wasted. A more efficient purge strategy that reduces the waste and improves the system efficiency, which operates load dependently by means of the mass transfer coefficient, is introduced. A comparison of the system efficiency with and without the load-dependent-purge-strategy (LPS) is made and discussed in order to demonstrate the effectiveness of the new method. Static as well as dynamic system simulations were performed for this purpose. A notable improvement of the system efficiency of up to 10% with LPS was achieved. With LPS the purge power losses could be markedly reduced. This reformation also induces an improvement of the system efficiency, which brings us a considerable step forward towards a longer reach. Moreover, LPS is not restricted to a certain fuel cell system and thus affords a more flexible and versatile employment than its predecessor.

In Brokate-Sprekels 1996, it is shown that hysteresis operators acting on scalar-valued, continuous, piecewise monotone input functions can be represented by functionals acting on alternating strings. In a number of recent papers, this representation result is extended to hysteresis operators dealing with input functions in a general topological vector space. The input functions have to be continuous and piecewise monotaffine, i.e. being piecewise the composition of two functions such that the output of a monotone increasing function is used as input for an affine function. &nbsp In the current paper, a representation result is formulated for hysteresis operators dealing with input functions being left-continuous and piecewise monotaffine and continuous. The operators are generated by functions acting on an admissible subset of the set of all strings of pairs of elements of the vector space.

Differential cross sections have been measured by scattering He atoms from CFnCl4-n (1≤n≤4) in crossed molecular beams. The damping of the diffraction oscillations was used to extract interaction potentials for these molecules which range from nearly isotropic to rather anisotropic. Macroscopic binary parameters, as second virial coefficients, diffusion coefficients and viscosities were calculated from these potentials

This paper deals with the mathematical modeling and simulation of crystal growth processes by the so-called Czochralski method and related methods, which are important industrial processes to grow large bulk single crystals of semiconductor materials such as, e. g., silicon (Si) or gallium arsenide (GaAs) from the melt. In particular, we investigate a recently developed technology in which traveling magnetic fields are applied in order to control the behavior of the turbulent melt flow. Since numerous different physical effects like electromagnetic fields, turbulent melt flows, high temperatures, heat transfer via radiation, etc., play an important role in the process, the corresponding mathematical model leads to an extremely difficult system of initial-boundary value problems for nonlinearly coupled partial differential equations. In this paper, we describe a mathematical model that is under use for the simulation of real-life growth scenarios, and we give an overview of mathematical results and numerical simulations that have been obtained for it in recent years.

A simple model for the start-up of a proton exchange membrane fuel cell stack is proposed. The model covers a wide temperature range from temperatures below the freezing point of water to usual operation temperatures of a low-temperature fuel cell. Model equations are derived from first principles. They account for the effects of ice and liquid water on the stack behavior. The model is validated by experimental data published by Schießwohl [2009, “Experimental Investigation of Parameters Influencing the Freeze Start Ability of a Fuel Cell System,” J. Power Sources, 193(1), pp. 107–115.], and a good qualitative agreement is found. The applicability of the model to problems of operation strategies and stack design is demonstrated by simulation studies.

International audience; This paper presents investigations into the chronoamperometric experiments performed on polybenzimidazole (PBI) / phosphoric acid based high temperature polymer electrolyte membrane fuel cells (HT-PEM FC). Electrolyte loadings in the membrane electrode assembly (MEA) are varied to realize three different degrees of flooding of the electrode. Steady state as well as dynamic measurements at three different temperatures (160°C, 120°C and 80°C) is made via chronoamperometry on these cells. The transient current behavior resulting from a voltage step change from open circuit voltage (~ 1 V) to low voltages (0.1 V) are recorded and analyzed. Analysis using the Cottrell plot depicts the underlying mass transport processes in the three different electrodes, catalyst utilization as well as a better description of the three phase boundary reaction zone. An extension of the Cottrell equation is deduced to describe a regular commercial fuel cell behavior.

In some recent papers, the concept of outward pointing operators has been used as a tool within the mathematical investigation of equations involving hysteresis operators and has been considered for the stop operator, the play operator, Prandtl-Ishlinskii˘ operators and Preisach operators. Now, for inverse Preisach operators conditions will be discussed which ensure that the outward pointing property is satisfied. As an application of the theory, a stability result for solutions of a P.D.E. with hysteresis appearing in the context of electromagnetic processes is derived.

Credit Suisse is following an ongoing initiative to implement a complete process orientation in its securities operations applications. Part of this initiative forms the monitoring of processes with the intention to obtain more information about executed process instances and thereby identify opportunities for continuous process improvement. Therefore, ARIS Process Performance Manager first was evaluated in a pilot study and subsequently implemented into the existing application landscape for securities processing. Today, the operations unit monitors its compliance to the time standards for execution defined in the service level agreements (SLA) between the different business units. Moreover, loops in the execution of processes or the cost drivers, like required manual interventions or delays due to communication with external parties become transparent.

Using a mathematical heat transfer model including anisotropic heat conduction, radiation, and radio frequency (RF) heating, we perform numerical computations of the temperature field in an axisymmetric growth apparatus during sublimation growth of silicon carbide (SiC) bulk single crystals by physical vapor transport (PVT) (modified Lely method). Because it is not unusual for the thermal insulation of a PVT growth apparatus to possess an anisotropic thermal conductivity, we numerically study the influence that this anisotropic thermal conductivity has on the temperature field in the growth chamber. Moreover, we also study the influence of the thickness of the insulation. Our results show that, depending on the insulation's orientation, even a moderate anisotropy in the insulation can result in temperature variations of more than 100 K at the growing crystal's surface, which should be taken into account for the simulation as well as for the design of a PVT growth apparatus.

Using transient and stationary mathematical heat transfer models including heat conduction, radiation, and radio frequency (RF) induction heating, we numerically investigate the time evolution of temperature gradients in axisymmetric growth apparatus during the sublimation growth of silicon carbide (SiC) bulk single crystals by physical vapor transport (PVT) (modified Lely method). Temperature gradients in the bulk and on the surface of the growing crystal can cause defects. Here, the evolution of these gradients is studied numerically during the heating, growth, and cooling stages, varying the apparatus design, namely the amount of the source powder charge as well as the size of the upper blind hole used for cooling of the seed. Our results show that a smaller upper blind hole can reduce the temperature gradients both in the bulk and on the surface of the crystal without reducing the surface temperature itself.

The project aims at providing numerical tools to control and optimize sublimation growth of SiC bulk single crystals via the Modified Lely Method. It is in cooperation with the experimental group of Dr. Dietmar Siche at the Institute of Crystal Growth in Berlin. In the course of the project the Modified Lely Method is mathematically modeled and numerically simulated. We present a transient model which for the gas phase consists of balance equations for mass, momentum and energy, and reaction-diffusion equations. The model for the solid components takes into account heat transfer via conduction inside the solid materials and via radiation between solid surfaces of cavities. Results of transient numerical simulations of the temperature evolution inside the growth apparatus are depicted, illustrating the paramount influence of radiation at growth temperature.