Electronic transport calculations for lightly-doped thermoelectrics using density functional theory: Application to high-performing Cu-doped zinc antimonides

We propose a new method for accurately calculating electrical transport properties of a lightly-doped thermoelectric material from density functional theory (DFT) calculations, based on experimental data and density functional theory results for the corresponding undoped material. We employ this approach because hybrid DFT calculations are prohibitive for the large supercells required to model low dopant concentrations comparable to those achieved experimentally for high-performing thermoelectrics. Using zinc antimonide as our base material, we find that the electrical transport properties calculated with DFT and Boltzmann transport theory exhibit the same trends with changes in chemical potential as those computed with hybrid DFT, and propose a fitting algorithm that involves adjusting the computed Fermi energy so that the resulting Seebeck coefficient trends with temperature match experimental trends. We confirm the validity of this approach in reproducing the experimental trends in electrical conductivity and Seebeck coefficient versus temperature for Bi-doped $\beta-$Zn$_4$Sb$_3$. We then screen various transition metal cation dopants, including copper and nickel, and find that a Cu dopant concentration of 2.56% in Zn$_{39}$Sb$_{30}$ exhibited a 14% increase in the thermoelectric power factor for temperatures between 300-400 K. We thus propose that transition metal dopants may significantly improve the thermoelectric performance of the host material, compared to heavy and/or rare-earth dopants

Reliability modelling of uninterruptible power supply using probability tree method

The unreliability of public power lines have led to the need of uninterruptible power supply (UPS). Utility power failures will cause unacceptably high risk to the profitability, existence and growth of the vital aspect of business that depends heavily on uninterrupted power supply. For this reason it is important to develop a method to estimate the reliability of such system, to ensure that it will perform satisfactorily when needed. This paper describes and discusses an approach to predict the reliability parameters of the UPS system using the probability tree method. Important UPS reliability parameters such as failure rates (lambda), mean time between failures (MTBF), and reliability (R), can be obtained from this method. These quantitative reliability parameters can play an essential role in selection and application of the UPS. The method was applied to different topologies of UPS systems and comparisons were made between the results obtained form probability tree method and the reliability block diagram (RBD) method

Estimating von-Karman's constant from Homogeneous Turbulence

A celebrated universal aspect of wall-bounded turbulent flows is the von Karman log-law-of-the-wall, describing how the mean velocity in the streamwise direction depends on the distance from the wall. Although the log-law is known for more than 75 years, the von Karman constant governing the slope of the log-law was not determined theoretically. In this Letter we show that the von-Karman constant can be estimated from homogeneous turbulent data, i.e. without information from wall-bounded flows.Comment: 4 pages, 3 figs, PRL, submitte

Theory of the Three-Group Evolutionary Minority Game

Based on the adiabatic theory for the evolutionary minority game (EMG) that we proposed earlier[1], we perform a detail analysis of the EMG limited to three groups of agents. We derive a formula for the critical point of the transition from segregation (into opposing groups) to clustering (towards cautious behaviors). Particular to the three-group EMG, the strategy switching in the "extreme" group does not occur at every losing step and is strongly intermittent. This leads to an correction to the critical value of the number of agents at the transition, $N_c$. Our expression for $N_c$ is in agreement with the results obtained from our numerical simulations.Comment: 4 pages and 2 figure

Software Engineering Laboratory (SEL) Data Base Maintenance System (DBAM) user's guide and system description

The Software Engineering Laboratory (SEL) Data Base Maintenance System (DBAM) is explained. The various software facilities of the SEL, DBAM operating procedures, and DBAM system information are described. The relationships among DBAM components (baseline diagrams), component descriptions, overlay descriptions, indirect command file listings, file definitions, and sample data collection forms are provided