Ultrastructure of calcareous dinophytes (Thoracosphaeraceae, Peridiniales) with a focus on vacuolar crystal-like particles.

Biomineralization in calcareous dinophytes (Thoracosphaeracaea, Peridiniales) takes place in coccoid cells and is presently poorly understood. Vacuolar crystal-like particles as well as collection sites within the prospective calcareous shell may play a crucial role during this process at the ultrastructural level. Using transmission electron microscopy, we investigated the ultrastructure of coccoid cells at an early developmental stage in fourteen calcareous dinophyte strains (corresponding to at least ten species of Calciodinellum, Calcigonellum, Leonella, Pernambugia, Scrippsiella, and Thoracosphaera). The shell of the coccoid cells consisted either of one (Leonella, Thoracosphaera) or two matrices (Scrippsiella and its relatives) of unknown element composition, whereas calcite is deposited in the only or the outer layer, respectively. We observed crystal-like particles in cytoplasmic vacuoles in cells of nine of the strains investigated and assume that they are widespread among calcareous dinophytes. However, similar structures are also found outside the Thoracosphaeraceae, and we postulate an evolutionarily old physiological pathway (possibly involved in detoxification) that later was specialized for calcification. We aim to contribute to a deeper knowledge of the biomineralization process in calcareous dinophytes

Structural characterization of classical and memristive circuits with purely imaginary eigenvalues

The hyperbolicity problem in circuit theory concerns the existence of purely imaginary eigenvalues (PIEs) in the linearization of the time-domain description of the circuit dynamics. In this paper we characterize the circuit configurations which, in a strictly passive setting, yield purely imaginary eigenvalues for all values of the capacitances and inductances. Our framework is based on branch-oriented, semistate (differential-algebraic) circuit models which capture explicitly the circuit topology, and uses several notions and results from digraph theory. So-called P-structures arising in the analysis turn out to be the key element supporting our results. The analysis is shown to hold not only for classical (RLC) circuits but also for nonlinear circuits including memristors and other mem-devices

Structural analysis for electric circuits and consequences for MNA

The development of integrated circuits requires powerful numerical simulation programs. Of course, there is no method that treats all the different kinds of circuits successfully. The numerical simulation tools provide reliable results only if the circuit model meets the assumptions that guarantee the successful application of the integration software. Because of the large dimension of many circuits (about $10^7$ circuit elements) it is often difficult to find the circuit configurations that lead to numerical difficulties. In this paper, we analyze electric circuits with respect to their structural properties in order to give circuit designers some help for fixing modelling problems if the numerical simulation fails. We consider one of the most frequently used modelling technique, the modified nodal analysis (MNA), and discuss the index of the differential algebraic equations (DAEs) obtained by this kind of modelling

Turn-key module for neutron scattering with sub-micro-eV resolution

We report the development of a compact turn-key module that boosts the resolution in quasi-elastic neutron scattering by several orders of magnitude down to the low sub-micro-eV range. It is based on a pair of neutron resonance spin flippers that generate a well defined temporal intensity modulation, also known as MIEZE (Modulation of IntEnsity by Zero Effort). The module may be used under versatile conditions, in particular in applied magnetic fields and for depolarising and incoherently scattering samples. We demonstrate the power of MIEZE in studies of the helimagnetic order in MnSi under applied magnetic fields

El origen del endurecimiento de metales y aleaciones nanoestructurados

14 pages, 8 figures.[EN] Nanostructured metals and alloys have a variety of chemical and physical properties that are greatly modified by the nano-scale of their microstructure. At the same time, these materials generally show very high strength, although ductility or toughness may not be good. Strength increases as the microstructure scale reduces from the macro-micro level and even finer, but sometimes the strength appears to fall as the structure scale approaches the nano level. These strength variations are examined here, and the mechanisms responsible for both strengthening and weakening are discussed. The fall in ductility and toughness as materials become nanostructured is a complex topic that requires extensive analysis, but this will not be treated in the present overview.[ES] Los metales y aleaciones nanoestructuradas muestran una serie de propiedades químicas y físicas fuertemente modificadas cuando su microestructura entra en la escala nano. A la vez, estos materiales muestran generalmente alta resistencia pero mediocre ductilidad o tenacidad. La resistencia aumenta cuando baja la escala de la microestructura desde el nivel micro hacia el nivel nano, pero a veces la resistencia parece reducir por las microestructuras mas finas. Se examinan aquí todas estas variaciones y se discuten los mecanismos responsables del endurecimiento y ablandamiento. Los cambios de ductilidad o tenacidad cuando la microestructura entra en la escala nano necesitan un análisis detallado que no se trata en este articulo.Peer reviewe

Index-aware model order reduction for index-2 differential-algebraic equations

A model order reduction (MOR) method for index-2 differential-algebraic equations (DAEs) is introduced, which is based on the intrinsic differential equations contained in the starting system and on the remaining algebraic constraints. This extends the method introduced in a previous paper for index-1 DAEs. This procedure is implemented numerically and the results show numerical evidence of its robustness over the traditional methods

Investigation of an ejector in a R744 refrigerant circuit

Thema dieser Arbeit ist die Untersuchung eines R744-Kältekreislaufes mit Ejektor. Die Arbeit gliedert sich in einen theoretischen und einen experimentellen Teil. Im theoretischen Teil wird der gesamte Kältekreislauf mit Ejektor untersucht. Dabei werden die durch Entropieproduktion auftretenden Verluste analysiert. Als Grundlage für die Berechnung der Drosselverluste und der Entropieproduktion in einem R744-Kältekreislauf wurde eine Wärmepumpe herangezogen. Für die Berechnung zur Effizienzsteiterung wurde eine Omnibusklimaanlage gewählt. Die Entropieanalyse zeigt, dass die Verluste mit Hilfe eines zweiten Verdampfers reduziert werden können. Das Steigerungspotential der energetischen Effizienz eines R744-Ejektorkältekreislaufs mit Hilfe eines zweiten Verdampfers belegen die Berechnungen zur Omnibusklimaanlage. Bestandteil der Berechnungen ist der Vergleich verschiedener Kreislaufverschaltungen. Alle Berechnungen werden mit Modellen einer für die Beschreibungssprache Modelica erstellten Modellbibliothek durchgeführt. Der experimentelle Teil beinhaltet die Untersuchung zur Ejektorgeometrie und die Entwicklung einer Massenstromkorrelation, die für Modelle zur Simulation von Kältekreisläufen genutzt werden kann. Hierfür wurde neben einzelnen Düsen auch ein Ejektor entworfen und gefertigt. Mit Hilfe einer Literaturrecherche konnten die optimalen Geometrieparameter für den Ejektor gefunden werden. Die Ergebnisse der einzelnen Arbeiten aus der Literaturrecherche werden dargestellt und die jeweils optimalen Geometrieparameter werden anschließend zusammengefasst. Der letzte Teil der Arbeit beinhaltet die Beschreibung der einzelnen Parameter und der dimensionslosen Größen der empirischen Massenstromkorrelation. Grundlage für die Entwicklung der Korrelation waren Messungen des Massendurchflusses in den Düsen und dem Ejektor. Vier verschiedenartige Düsen mit unterschiedlichen geometrischen Eigenschaften und eine Ejektortreibdüse wurden untersucht. Für die Düsen und den Ejektor wurde der Massendurchfluss bei verschiedenen Ein- und Austrittszuständen des Kältemittels gemessen. Zunächst wurden nur die einzelnen Düsen untersucht, bei denen das Kältemittel in Form eines Freistrahls aus der Düse austritt. In einem zweiten Schritt wurde der Massendurchfluss durch die Treibdüse im Ejektor gemessen. Die Korrelation wurde erweitert und so angepasst, dass damit der Massenstrom in einem Ejektor berechnet werden kann.The topic of this work is an investigation of an R744 refrigerant circuit with an ejector. The work is divided into a theoretical and an experimental part. In the theoretical part the whole of the cooling cycle with ejector is investigated. As part of this, the losses caused as a result of the generation of entropy are analysed. A heat pump was used as the basis for the calculation of the throttling losses and the generation of entropy in an R744 refrigerant circuit. A bus HVAC unit was selected for the calculation of the increase in efficiency. The entropy analysis shows that the losses can be reduced with the aid of a second evaporator. The potential for improvement in the energy efficiency of an R744 ejector refrigerant circuit with the aid of a second evaporator is proved by the calculations for the bus HVAC unit. An element in the calculations is the comparison of various circuit interconnections. All calculations in the theoretical part of the work are carried out with models of a model library constructed for the description language, Modelica. The experimental part comprises an investigation of the ejector geometry and the development of a mass flow correlation which can be used on models for the simulation of refrigerant circuits. In addition to individual nozzles, an ejector was also designed and manufactured for this. The optimal geometry parameters for the ejector could be found with the help of literature research. The results of the individual items of work from the literature research are presented and each of the optimal geometry parameters are then summarized. The last part of the work consists of the description of the individual parameters and the dimensionless size of the empirical mass flow correlation. The basis for the development of the correlation were measurements of the mass flow in the nozzles and the ejector. Four different kinds of nozzles with various geometric properties and an ejector motive nozzle were investigated. The mass flow for various entry and exit conditions of the refrigerant were measured for the nozzles and the ejector. Initially only those individual nozzles were investigated for which the refrigerant left the nozzle in the form of an open jet. In a second step the mass flow through the jet nozzles in the ejector was measured. The correlation was extended and adjusted in such a way that it could be used to calculate the mass flow in an ejector

Nitrogen deficiency in Arabidopsis affects galactolipid composition and gene expression and results in accumulation of fatty acid phytyl esters

Nitrogen is an essential nutrient for plants because it represents a major constituent of numerous cellular compounds, including proteins, amino acids, nucleic acids and lipids. While N deprivation is known to have severe consequences for primary carbon metabolism, the effect on chloroplast lipid metabolism has not been analysed in higher plants. Nitrogen limitation in Arabidopsis led to a decrease in the chloroplast galactolipid monogalactosyldiacylglycerol (MGDG) and a concomitant increase in digalactosyldiacylglycerol (DGDG), which correlated with an elevated expression of the DGDG synthase genes DGD1 and DGD2. The amounts of triacylglycerol and free fatty acids increased during N deprivation. Furthermore, phytyl esters accumulated containing medium-chain fatty acids (12:0, 14:0) and a large amount of hexadecatrienoic acid (16:3). Fatty acid phytyl esters were localized to chloroplasts, in particular to thylakoids and plastoglobules. Different polyunsaturated acyl groups were found in phytyl esters accumulating in Arabidopsis lipid mutants and in other plants, including 16:3 and 18:3 species. Therefore N deficiency in higher plants results in a co-ordinated breakdown of galactolipids and chlorophyll with deposition of specific fatty acid phytyl esters in thylakoids and plastoglobules of chloroplasts