Temperature dependence of the characteristic travel distance

The effect of temperature variation on the environmental fate of organic chemicals can be evaluated in steady-state multimedia box models by expressing chemical partitioning data and reaction rate coefficients as functions of temperature. Using such a modelthetemperature dependence of the characteristic travel distance in air L(A), which is a measure for the atmospheric long-range transport potential of organic chemicals, is calculated. Simulations are reported for a set of 40 chemicals of environmental interest. Increasing temperature is shown to have two opposing effects on L(A). Rates of chemical transformations in the atmosphere (k(air)) and surface media are increased, which reduces L(A). Rates of atmospheric deposition (k(dep)) are reduced leading to increased mobility and L(A). Accordingly, L(A) can monotonically increase or decrease with increasing temperature, or it can have a maximum in the modeled temperature range, but it cannot have a minimum. For chemicals with a strong temperature dependence of k(air) relative to k(dep), L(A) will increase with increasing temperature. Results for selected polychlorinated biphenyls are compared to monitoring data yielding qualitative agreement when chemical properties are adjusted to mean temperatures for the measurement period. The results demonstrate that the temperature dependence of the characteristic travel distance is highly dependent on chemical characteristics and can be counterintuitive. The use of mass balance models is thus essential. The difference between the L(A) values at 5 degrees C and 30 degrees C can be up to a factor of 6. Accordingly, chemical ranking with respect to L(A) can change significantly if performed at different temperatures. Implications of the different temperature dependencies on long-range transport to polar regions are discussed.     

Qualms regarding the optimality of cumulative path length control in CSA/CMA-evolution strategies

Cumulative step-size adaptation (CSA) based on path length control is regarded as a robust alternative to the standard mutative self-adaptation technique in evolution strategies (ES), guaranteeing an almost optimal control of the mutation operator. This paper shows that the underlying basic assumption in CSA--the perpendicularity of expected consecutive steps--does not necessarily guarantee optimal progress performance for (mu/mu(I), lambda) intermediate recombinative ES.     

Benchmark database on the evolution of two-phase flows in a vertical pipe

Based on many years of experience, a new extensive and high-quality database was obtained for steady-state upward air-water flows in a vertical pipe with an inner diameter of 195.3 mm using the wire-mesh sensor technology. During the experiments, the sensor was always mounted on the top of the test section while the distance between gas injection and measuring plane was varied up to 18 different L/D by using gas injection chambers at different vertical positions. The gas was injected via holes in the pipe wall. In this new test series the pressure was kept at 0.25 MPa (absolute) at the location of the active gas injection while the temperature was constant at 30 °C ± 1 K. The experiments were done for 48 combinations of air and water superficial velocities varying from 0.04 m/s to 1.6 m/s for water and 0.0025 m/s to 3.2 m/s for air. From the raw data time-averaged data as: radial gas volume fraction profiles, bubble size distributions, radial volume fraction profiles decomposed according to the bubble size and the radial profiles of the gas velocity were calculated. The consistency of this data was thoroughly checked. They are characterized by a high resolution in space, which makes them suitable for the development and validation of CFD-grade closure models, e.g. for bubble forces and coalescence and break-up. It is also an ideal base to validate CFD approaches for poly-dispersed flow. For this reason it is proposed to use the database as a benchmark for modelling poly-dispersed flows.     

Controlled p-doping of pigment layers by cosublimation: Basic mechanisms and implications for their use in organic photovoltaic cells

We present a systematic study on doping of vanadyl- and zinc-pathalocyanine by a fully fluorinated form of tetracyano-quinodimethane as an example of controlled doping of thin organic films by cosublimation of matrix and dopant. The films are characterized in situ by temperature dependent Seebeck and conductivity measurements. We observe a drastic increase of conductivity and a corresponding shift of the Fermi level towards the valence states with increasing dopant concentration. We thus conclude that doping has the potential of both reducing the series resistance and increasing the photovoltage of organic solar cells. As a first step to exploit this potential, we present two different ways of preparing diodes with rectification ratios in excess of 10⁴ using doped phthalocyanines. By adding an undoped interlayer between the contact and the doped layer, we have produced diodes which work already in the strict absence of oxygen and are stable in air. To increase the efficiency of charge carrier generation in photovoltaic cells, we need to use photoactive donor–acceptor-heterojunctions. We present here first examples of pn- and pin-type heterojunctions combining p-doped and nominally undoped layers.     

Mathematical Description of Experimentally Determined Charge Distributions of a Unipolar Diffusion Charger

The charge distributions of an improved opposed flow unipolar diffusion charger were measured using a tandem differential mobility analyzer (DMA) set up in a size range of approximately 20–400 nm. The charger is intended to be used in a portable aerosol sizer to measure particle size distributions. The determined charge distributions were represented by lognormal distributions, and a set of equations and coefficients was developed to calculate the charge distributions. These equations can be easily implemented in software for size distribution measurements. The agreement between the mathematically derived and measured charge distributions is very good, with regression coefficients R ² > 0.96. The investigations showed that approximately 55% of 20-nm particles remain uncharged, while up to 25 elementary charges need to be considered for multiple charge correction of 400-nm particles. Comparison with the Fuchs theory delivered satisfying agreement with the measured average charge levels, but charge distributions cannot be described by the Fuchs theory, likely caused by the charger geometry.

Copyright 2012 American Association for Aerosol Research     

Determination of the equivalent circuit of gunn-elements for X-band oscillator applications

The main purpose of this paper is to develope a procedure for the computer-aided determination of the equivalent circuit of Gunn-elements. In order to determine the equivalent circuit, the Gunne-element is first measured in a test oscillator. Varying the elements of the circuit the calculated frequency and power distribution is adjusted to the measured one by means of an iterative method. The equivalent circuit of Gunn-elements obtained in this way is used for the dimensioning of Gunn-element-oscillators in the X-band in finline technique.     

An integrated approach for validating micro mechanical systems based on simulation and test

Miniaturization of macroscopic mechanical systems enables the opening of new areas of application for micro technological systems. Because of technological restrictions, especially when applying miniaturized conventional manufacturing techniques, shape and material deviations cannot be scaled down in the same dimension like micro parts. Thus, the long-term objective is to ensure the functioning by appropriate design measures. In doing so, determination of the transfer behavior by modeling and simulation is required. This work presents two ways for ensuring the required properties of micro gears and describes how the results do correlate. The experimental way uses the radial composite inspection as it is used in the macroscopic world. The simulative way deploys a rolling simulation by utilization of finite element analysis. The virtual prototypes are originated on measured real test gears. When comparing experiment and simulation of the rolling behavior, in some short and long wave areas deviations can be recognized. These can be ascribed to the reduction from three to two dimensions when modeling. Other deviations might be based on inaccuracies when mounting into the test rig. In other areas quite good correlations of test and simulation could be ascertained.     

Performance of Micro-fabricated Magnetic Calorimeters Arrays for X-Ray Spectroscopy

We have been developing array technology for fabricating magnetic calorimeters for X-ray astronomy. The magnetization change in each pixel of the paramagnetic sensor material due to the heat input of an absorbed X-ray is sensed by a meander shaped coil. With this geometry it is possible to obtain excellent energy sensitivity, low magnetic cross-talk and large format arrays fabricated on wafers that are separate from the SQUID read-out. A magnetic bias field for each pixel is generated by the use of a persistent current that is stored. We report on the results from our prototype arrays, which are coupled to low noise DC-SQUIDs. The first test results are presented and the sensitivity is compared with calculations.     

Thermomechanische Behandlung von Manganhartstählen

Die durch Walzen oder Schmieden im Bereich von 700 bis 1050°C thermomechanisch behandelten Manganhartstähle X 120 Mn 12 und X 120 MnCrSiV 12 werden unter Einbeziehung einer anschließenden Haltedauer bei Umformtemperatur bzw. bei 440°C bezüglich ihres Gefüges und ihrer Eigenschaften vergleichend untersucht. Es zeigt sich, daß die Legierungszusätze an Chrom, Silicium und Vanadin eine höhere Umformtemperatur zur Erzielung einer gewünschten Verfestigung zulassen und damit die thermomechanische Behandlung erleichtern. Der Verschleißwiderstand wird nicht beeinträchtigt.