Simulations for the Development of Thermoelectric Measurements

In thermoelectricity, continuum theoretical equations are usually used for the calculation of the characteristics and performance of thermoelectric elements, modules or devices as a function of external parameters (material, geometry, temperatures, current, flow, load, etc.). An increasing number of commercial software packages aimed at applications, such as COMSOL and ANSYS, contain vkernels using direct thermoelectric coupling. Application of these numerical tools also allows analysis of physical measurement conditions and can lead to specifically adapted methods for developing special test equipment required for the determination of TE material and module properties. System-theoretical and simulation-based considerations of favorable geometries are taken into account to create draft sketches in the development of such measurement systems. Particular consideration is given to the development of transient measurement methods, which have great advantages compared with the conventional static methods in terms of the measurement duration required. In this paper the benefits of using numerical tools in designing measurement facilities are shown using two examples. The first is the determination of geometric correction factors in four-point probe measurement of electrical conductivity, whereas the second example is focused on the so-called combined thermoelectric measurement (CTEM) system, where all thermoelectric material properties (Seebeck coefficient, electrical and thermal conductivity, and Harman measurement of zT) are measured in a combined way. Here, we want to highlight especially the measurement of thermal conductivity in a transient mode. Factors influencing the measurement results such as coupling to the environment due to radiation, heat losses via the mounting of the probe head, as well as contact resistance between the sample and sample holder are illustrated, analyzed, and discussed. By employing the results of the simulations, we have developed an improved sample head that allows for measurements over a larger temperature interval with enhanced accuracy.     

Control of Dynamic Brake Through Heuristic Rule

In this paper, it is shown that the application of a dynamic brake or thyristorcontrolled braking resistor (TCBR) at the generator terminals enhances the power transfer limit over a transmission line greatly. Two types of dynamic brake configuration have been considered here: a 3-phase, bidirectional, fullwave, Y-connected, phase controlled conventional brake and a 3-phase, fullwave, thyristor-controlled rectifier bridge. A simple rule-based '' ON-OFF'' control law based on the local measurement of generator output power and its derivative is proposed in this paper. Detail digital simulation studies using the PSCAD/EMTDC package have been carried out. It was found that with the insertion of the dynamic brake circuit and its associated control, the system is able to recover following 3-line-to-ground faults even at very heavy power transfer levels, which is not possible otherwise.     

Triazolinyl-controlled radical polymerization as innovative route to poly(hydroxyethyl methacrylate)

Summary 2,2'-Azoisobutyronitril (AIBN) initiated radical polymerization of trimethylsilyloxyethyl methacrylate (TMS-HEMA) was carried out in N,N-dimethylformamide (DMF) with the triazolinyl radical (T•) as additive. The latter effected a controlled polymerization process at least up to 60 % monomer conversion. The obtained poly(TMS-HEMA) with triazolin endfunctionality was applied to polymerize styrene, resulting in the formation of poly(TMS-HEMA)-block-polystyrene. Received: 22 February 2001/Accepted: 6 March 2001     

Tensor scale: An analytic approach with efficient computation and applications

Scale is a widely used notion in computer vision and image understanding that evolved in the form of scale-space theory where the key idea is to represent and analyze an image at various resolutions. Recently, we introduced a notion of local morphometric scale referred to as “tensor scale” using an ellipsoidal model that yields a unified representation of structure size, orientation and anisotropy. In the previous work, tensor scale was described using a 2-D algorithmic approach and a precise analytic definition was missing. Also, the application of tensor scale in 3-D using the previous framework is not practical due to high computational complexity. In this paper, an analytic definition of tensor scale is formulated for n-dimensional (n-D) images that captures local structure size, orientation and anisotropy. Also, an efficient computational solution in 2- and 3-D using several novel differential geometric approaches is presented and the accuracy of results is experimentally examined. Also, a matrix representation of tensor scale is derived facilitating several operations including tensor field smoothing to capture larger contextual knowledge. Finally, the applications of tensor scale in image filtering and n-linear interpolation are presented and the performance of their results is examined in comparison with respective state-of-art methods. Specifically, the performance of tensor scale based image filtering is compared with gradient and Weickert’s structure tensor based diffusive filtering algorithms. Also, the performance of tensor scale based n-linear interpolation is evaluated in comparison with standard n-linear and windowed-sinc interpolation methods.     

Spectral characteristics of a binary dye-mixture laser

We have investigated laser action in a binary mixture of dyes, Rh-6G and DCM, resulting in tunable laser emission over an extended frequency region. The two dyes absorb the same pump radiation but fluoresce over frequency ranges that are shifted with respect to each other, thereby resulting in extended tunability. Following a time-dependent analysis of a rate-equation model that describe the operation of such a laser, theoretical estimates for optimum dye concentrations and the corresponding extension of the laser tuning range have been obtained.     

Moving from Weakly Endochronous Systems to Delay-Insensitive Circuits

We consider the problem of synthesizing the asynchronous wrappers and glue logic needed for the correct GALS implementation of a modular synchronous system. Our approach is based on the weakly endochronous synchronous model, which defines high-level, implementation-independent conditions guaranteeing correct desynchronization at the level of the abstract synchronous model. We can therefore factor the synthesis problem into (1) a high-level, implementation-independent phase insuring the weak endochrony of each synchronous module and (2) the actual wrapper synthesis phase, highly simplified by the high-level assumptions, yet flexible enough to produce various, efficient implementations.We focus here on the synthesis of delay-insensitive asynchronous wrappers from weakly endochronous synchronous modules, and show how this can be done for a simple DLX processor model.     

Determination of oxidative stability of oils and fats

In a new approach to evaluating the oxidative stability of oils and fats, the consumption of oxygen by a sample confined in a reactor of adjustable temperature is monitored with a gas-phase flow injection analysis (FIA) system. Temperature-dependent data are collected in a low-oxygen-content atmosphere. For a variety of samples, log(oxygen consumption) is linearly related to the reciprocal of the absolute temperature (minimum linear r(2) > 0.99). This makes it possible to extrapolate the temperature-dependent data to predict the stability of the samples at other temperatures, e.g., typical ambient storage temperatures at which the direct determination of oxidative stability would be too slow for most samples. The proposed method is instrumentally simple and is easily automated. The sample throughput rate is an order of magnitude faster relative to current alternatives; temperature-dependent stability characterization for a sample (three temperatures, triplicate measurement at each temperature) requires ≤ 2 h. The reproducibility of the results is excellent. For a cottonseed-oil sample studied over 3 days, the slope and intercept of the log(O(2) consumption) vs 1/T linear plot (for all the 45 measurements made) exhibited uncertainties of 2.1% and 2.0% for the slope and the intercept, respectively, with a linear r(2) value of 0.9929. In a high-temperature (160 °C) oxidation experiment with various oils, the oxygen consumption was well-correlated (linear r(2) 0.9692) with the concomitant decrease in iodine absorption number (IAN). In contrast, it was poorly and negatively correlated with an increase in the peroxide value.     

Stability of Interesterified Fats

The stability characteristics of a number of interesterified fat products made from vegetable oil-mixtures were studied and compared to those of a commercial hydrogenated stuff, vanaspati. It was found that the interesterified products, after addition of antioxidants had comparable stability to vanaspati in most cases, and, hence would not offer any storage problem.