Compositional Dependence of the Performance of Poly(p‐phenylene vinylene):Methanofullerene Bulk‐Heterojunction Solar Cells

The dependence of the performance of OC₁C₁₀‐PPV:PCBM (poly(2‐methoxy‐5‐(3′,7′‐dimethyloctyloxy)‐p‐phenylene vinylene):methanofullerene [6,6]‐phenyl C₆₁‐butyric acid methyl ester)‐based bulk heterojunction solar cells on their composition has been investigated. With regard to charge transport, we demonstrate that the electron mobility gradually increases on increasing the PCBM weight ratio, up to 80 wt.‐%, and subsequently saturates to its bulk value. Surprisingly, the hole mobility in the PPV phase shows an identical behavior and saturates beyond 67 wt.‐% PCBM, a value which is more than two orders of magnitude higher than that of the pure polymer. The experimental electron and hole mobilities were used to study the photocurrent generation of OC₁C₁₀‐PPV:PCBM bulk‐heterojunction (BHJ) solar cells. From numerical calculations, it is shown that for PCBM concentrations exceeding 80 wt.‐% reduced light absorption is responsible for the loss of device performance. From 80 to 67 wt.‐%, the decrease in power conversion efficiency is mainly due to a decreased separation efficiency of bound electron–hole (e–h) pairs. Below 67 wt.‐%, the performance loss is governed by a combination of a reduced generation rate of e–h pairs and a strong decrease in hole transport.     

Color‐separating backlight for improved LCD efficiency

Abstract— A large part of the light generated in a backlight is usually absorbed in the color filters of the liquid‐crystal display. A new backlight system that uses a grating to split the white light into different colors and a lens array to focus this light onto the pixels is presented. The absorbing filters can be eliminated and efficiency is improved. The system is characterized, as well as its different components.     

Distributed multilevel optimization for complex structures

Optimization problems concerning complex structures with many design variables may entail an unacceptable computational cost. This problem can be reduced considerably with a multilevel approach: A structure consisting of several components is optimized as a whole (global) as well as on the component level. In this paper, an optimization method is discussed with applications in the assessment of the impact of new design considerations in the development of a structure. A strategy based on fully stressed design is applied for optimization problems in linear statics. A global model is used to calculate the interactions (e.g., loads) for each of the components. These components are then optimized using the prescribed interactions, followed by a new global calculation to update the interactions. Mixed discrete and continuous design variables as well as different design configurations are possible. An application of this strategy is presented in the form of the full optimization of a vertical tail plane center box of a generic large passenger aircraft. In linear dynamics, the parametrization of the component interactions is problematic due to the frequency dependence. Hence, a modified method is presented in which the speed of component mode synthesis is used to avoid this parametrization. This method is applied to a simple test case that originates from noise control.     

ΔE effect for polycrystalline ferromagnetic rods

We performed experimental and computational studies of the acoustic transfer power coefficient for carbon steel cylindric bars placed in axial magnetic field. By experiment, the transmission coefficients of velocity were measured for ferromagnetic bars during the first magnetization curve below saturation. Using the magnetic and magnetostriction material measurements we obtained the profile of the magnetostriction along the distance for a ferromagnetic cylindrical rod placed in a magnetic field parallel with its axis. The data were compared with numerical results obtained by computer simulation, under the assumption of spatial dependent acoustic impedance and phase velocity, leading to the conclusion that the Young modulus is affected by the magnetoelastic interaction according to a linear decrease.     

On dynamically generated ontology translators in agent communication*

In this paper, we consider communication between agents that employ different vocabularies to represent information. In particular, we develop a communication mechanism in which translators between the vocabularies of agents are generated. Instead of being defined in advance, these translators are dynamically constructed during execution of the system, and are based both on the information that the agents exchange and on their underpinning ontologies. Moreover, these translators are not necessarily defined for the total vocabulary of the agents, but instead, only for the parts that have been involved in communication steps. The framework can for instance be used to study and to analyze experiments as performed in the research on the origins of language, like language games, in which the purpose of communication is to come to a mutual understanding of the agents' vocabularies. © 2001 John Wiley & Sons, Inc.     

Assessment of dryland condition using spatial anomalies of vegetation index values

A landscape's long‐term capacity to retain, utilize and recycle local resources is an objective basis for assessing its ecological functionality or condition. In subtropical and tropical drylands, where plant growth is moisture‐limited for much of the time, land condition is reflected in the local water balance. The ratio of long‐term actual evapotranspiration and precipitation (E _a/P) is proposed as an objective indicator of dryland condition. A spatial modelling framework is developed for the quantification of E _a/P over large areas using remotely sensed vegetation density patterns. Model parameters are defined by two particular situations: (i) non‐vegetated sites, where E _a/P depends on the long‐term runoff coefficient of bare soil surfaces (RC_bs), and (ii) non‐degraded sites with a vegetation density close to the potential value for which E _a/P?1.0. Specht's evaporative coefficient is used as an independent variable for the prediction of the potential vegetation density, whereas RC_bs is estimated with the curve number method.

The performance of the method was evaluated in a 900 km² area in south‐east Spain, where predicted land condition was found to be in good agreement with qualitative field observations on the nature and intensity of land degradation processes.     

Optimal regenerator performance in Stirling engines

The key component of a Stirling engine is its regenerative heat exchanger. This device is subject to losses due to dissipation arising from the flow through the regenerator as well as due to imperfect heat transfer between the regenerator material and the gas. The magnitudes of these losses are characterized by the Stanton number St and the Fanning friction factor f, respectively. Using available data for the ratio St/f, results are found for the Carnot efficiency and the power output of the regenerator. They depend on the conductance and on the ratio of pressures at the two sides of the regenerator. Optimum results for efficiency and power output of the regenerator are derived in the limit of zero Mach number. The results are applied to the Stirling engine. The efficiency and the power output of the engine are found for given amplitude of the compression piston. Optimization with respect to regenerator conductance and piston phase angle leads to a maximum possible value of the power output. Under optimal conditions, the Carnot efficiency just below this maximum is close to 100%. Copyright © 2009 John Wiley & Sons, Ltd.     

Mechanism and Kinetics of some Reactions on Silica-Alumina Catalysts

The dehydration of alcohol when its vapor is led over alumina, or some other heterogeneously acting catalysts, is already known from the end of the eighteenth century.     

Recruitment of ZipA to the septal ring of Escherichia coli is dependent on FtsZ and independent of FtsA

Cell division in prokaryotes is mediated by the septal ring. In Escherichia coli, this organelle consists of several essential division proteins, including FtsZ, FtsA, and ZipA. To gain more insight into how the structure is assembled, we studied the interdependence of FtsZ, FtsA, and ZipA localization using both immunofluorescence and Gfp tagging techniques. To this end, we constructed a set of strains allowing us to determine the cellular location of each of these three proteins in cells from which one of the other two had been specifically depleted. Our results show that ZipA fails to accumulate in a ring shape in the absence of FtsZ. Conversely, depletion of ZipA does not abolish formation of FtsZ rings but leads to a significant reduction in the number of rings per unit of cell mass. In addition, ZipA does not appear to require FtsA for assembly into the septal ring and vice versa. It is suggested that septal ring formation starts by assembly of the FtsZ ring, after which ZipA and FtsA join this structure in a mutually independent fashion through direct interactions with the FtsZ protein.