Q-based design equations for resonant metamaterials and experimental validation

Practical design parameters of resonant metamaterials, such as loss tangent, are derived in terms of the quality factor $Q$ of the resonant effective medium permeability or permittivity. Through electromagnetic simulations of loop-based resonant particles, it is also shown that the $Q$ of the effective medium response is essentially equal to the $Q$ of an individual resonant particle. Thus, by measuring the $Q$ of a single fabricated metamaterial particle, the effective permeability or permittivity of a metamaterial can be calculated simply and accurately without requiring complex simulations, fabrication, or measurements. Experimental validation shows that the complex permeability analytically estimated from the measured $Q$ of a single fabricated self-resonant loop agrees with the complex permeability extracted from $S$ parameter measurements of a metamaterial slab to better than 20%. This $Q$ equivalence reduces the design of a metamaterial to meet a given loss constraint to the simpler problem of the design of a resonant particle to meet a specific $Q$ constraint. This analysis also yields simple analytical expressions for estimating the loss tangent of a planar loop magnetic metamaterial due to ohmic losses. It is shown that $\tan \delta \approx 0.001$ is a strong lower bound for magnetic loss tangents for frequencies not too far from 1 GHz. The ohmic loss of the metamaterial varies inversely with the electrical size of the metamaterial particle, indicating that there is a loss penalty for reducing the particle size at a fixed frequency

Finite-Size Effects In A One-Dimensional Kondo-Box

We study the correlation effects induced by a Kondo impurity embedded in a quantum box, using as a model a one-dimensional tight-binding band with a finite number of lattice sites which is coupled to an Anderson impurity. The model is solved by means of the density-matrix renormalization-group (DMRG) including the Lanczos method as well as the correction vector method. We examine systems with more than 500 sites retaining up to 2600 states. We define the Kondo temperature $T_K$ for the case of a discrete conduction electron density of states (level spacing $\Delta E$). The strength of the correlations, indicated by the weight of the Kondo resonance, $W$, is determined by the local conduction density of states at the impurity site, $x_0$. $W$ depends both on the symmetry of the conduction electron wave function at the Fermi edge, $\Psi_0(x)$, and on the impurity position $x_0$. We explain why the size of the Kondo peak fluctuates by changing the particle number $N$ between even and odd. We calculate the spin-correlations of the impurity spin and the spin of the conduction band and define a correlation length for a finite system, $l_k^{\rm num}$. We examine systems where the Kondo cloud --- measured by $l_k^{\rm num}$ --- is fully developed within the finite system. We show how the size of the Kondo peak corresponds to the size of the Kondo cloud

Chromosomenzahlen von Farn- und Samenpflanzen aus Deutschland 1

Die Redaktion möchte in Kochia ein Forum für die Publikation von Chromosomenzahlen bieten. Die Beiträge in dieser Reihe sind als eigenständige Publikationen zu betrachten und zu zitieren. Wir folgen im Aufbau bewusst eingeführten und bewährten Reihen wie derjenigen über Chromosomenzahlen mediterraner Pflanzen in „Flora Mediterranea“. Zählungen von Taxa werden beginnend mit dieser Folge durchnummeriert. Die Herausgeber hoffen, mit dieser Reihe die Ermittlung von Chromosomenzahlen an Taxa der heimischen Flora zu fördern und vorhandenes Material publik zu machen

Distribution of Arabis sagittata in Germany : results of a herbarium study

Als Ergebnis einer Herbarstudie wird erstmals eine deutschlandweite Verbreitungskarte für Arabis sagittata vorgestellt. Die zerstreuten Vorkommen liegen vornehmlich im Mittelgebirgsraum und in Beckenlandschaften nördlich bis zur Mittelgebirgsschwelle. Isolierte Einzelfundstellen gibt es zudem im Norddeutschen Tiefland. Die Ergebnisse weichen regional vom Datenstand publizierter Angaben ab. Dies dürfte teilweise auf Verwechslungen mit A. hirsuta beruhen, aber auch der unzureichenden Dokumentation von Herbarmaterial in öffentlichen und zugänglichen Privatherbarien. Insgesamt lässt die Studie jedoch vermuten, dass das Potenzial von Herbarien für die Erstellung von Verbreitungskarten kritischer Sippen bei weitem nicht ausgeschöpft wird.Arabis sagittata, a critical and much neglected element of Germany’s flora, proved to be a rare taxon with scattered occurrences in the southern and central parts of the country. Due to misidentifications and neglect of herbarium vouchers, specimen based data differ from published records. Both data sets have been combined in showing a first distribution map for Germany. Obviously, the three indigenous taxa of the A. hirsuta group (A. hirsuta, A. nemorensis, A. sagittata) are often misidentified. It is recommended that records of A. sagittata should be based on herbarium specimens only. This study shows that herbaria play an important role in creating distribution maps and that their use is far from being utilized to its full potential

Does segmentation always improve model performance in credit scoring?

Credit scoring allows for the credit risk assessment of bank customers. A single scoring model (scorecard) can be developed for the entire customer population, e.g. using logistic regression. However, it is often expected that segmentation, i.e. dividing the population into several groups and building separate scorecards for them, will improve the model performance. The most common statistical methods for segmentation are the two-step approaches, where logistic regression follows Classification and Regression Trees (CART) or Chi-squared Automatic Interaction Detection (CHAID) trees etc. In this research, the two-step approaches are applied as well as a new, simultaneous method, in which both segmentation and scorecards are optimised at the same time: Logistic Trees with Unbiased Selection (LOTUS). For reference purposes, a single-scorecard model is used. The above-mentioned methods are applied to the data provided by two of the major UK banks and one of the European credit bureaus. The model performance measures are then compared to examine whether there is improvement due to the segmentation methods used. It is found that segmentation does not always improve model performance in credit scoring: for none of the analysed real-world datasets, the multi-scorecard models perform considerably better than the single-scorecard ones. Moreover, in this application, there is no difference in performance between the two-step and simultaneous approache

Support Vector Machines for Credit Scoring and discovery of significant features

The assessment of risk of default on credit is important for financial institutions. Logistic regression and discriminant analysis are techniques traditionally used in credit scoring for determining likelihood to default based on consumer application and credit reference agency data. We test support vector machines against these traditional methods on a large credit card database. We find that they are competitive and can be used as the basis of a feature selection method to discover those features that are most significant in determining risk of default. 1

The value of CO2-geothermal bulk energy storage to CO2

Two primary challenges for modern societies are to reduce the amount of carbon dioxide (CO2) that is emitted to the atmosphere and to increase the penetration of renewable energy technologies into electricity systems. CO2-bulk energy storage (CO2-BES) is a CO2 capture and storage (CCS) approach that can address both of these challenges by using CO2 emitted from large point sources (e.g., fossil fuel power plants, cement manufacturers) that is sequestered in sedimentary basin geothermal resources to take power from, and deliver power to, electricity grids. Electricity can be generated by wind and solar energy technologies regardless of whether there is demand for that electricity because wind and sunlight are variable resources. When over-generation occurs, the excess electricity can be used to compress and inject CO2 into sedimentary basin geothermal resources. Electricity can then be dispatched when needed by producing the pressurized and geothermally-heated CO2 from the storage reservoir and converting the heat to electricity in a CO2-geothermal power plant. In this way, CO2-BES can time-shift excess electricity that is generated by wind and solar energy facilities to when there is demand for that electricity. This ability can increase the utilization of installed wind and solar energy capacity. Thus, CO2-BES can (1) directly reduce CO2 emissions to the atmosphere by isolating them in porous and permeable subsurface reservoirs and (2) indirectly reduce CO2 emissions by displacing electricity from power plants that emit CO2 (e.g., fossil fuel plants) with electricity from wind and solar energy facilities. We present an approach to estimate the value of these direct and indirect benefits. Our approach uses an optimization model that we developed to determine the cost-minimizing dispatch of electricity-generating facilities to meet diurnal demand in regional electricity systems. In our analysis, electricity can be generated by base load and variable load power plants, wind- and solar-energy technologies, and CO2-BES facilities. We varied prices on CO2 emissions (e.g., a CO2 emissions tax) in order to determine the optimal CO2-BES storage capacity for each CO2 price. This method allows us to assign a monetary value to the optimized energy storage capacity. We use time increments of one hour, during which we assume electricity generation and demand are constant. Initial results using hypothetical but realistic scenarios for electricity demand and electricity generation by solar energy technologies suggest that the optimal energy storage capacity of CO2-BES is sensitive to a range of CO2 prices. That is, a small increase in the price on CO2 emissions can cause substantial change in the optimal distribution of electricity generation and the energy storage capacity of CO2-BES. Thus, independent system operators (ISOs) could dispatch CO2-BES without needing additional ancillary service compensation schemes if CO2 emissions were modestly taxed. This work was funded by the U.S. National Science Foundation Sustainable Energy Pathways program (grant 1230691)

The Measured Electric Field Spatial Distribution within a Metamaterial Sub-Wavelength Cavity Resonator

Through experimental investigation, a thin subwavelength cavity resonator was physically realized using a bilayer structure composed of air and a negative permeability metamaterial structure one unit cell in thickness. We designed and built the metamaterial slab with periodic metallic ring structures and measured the spatial electric field magnitude in a cavity formed from this slab and a region of air, showing that a subwavelength cavity can be realized. The measured electric field magnitude distribution in the cavity matched very well with effective medium theory, showing that even a slab one unit cell in thickness may be effectively equivalent to a thin homogeneous medium as far as the construction of a sub-wavelength cavity is concerned, provided that the unit cell size is significantly smaller than the free space wavelength

Numerical simulation of transom-stern waves

The flow field generated by a transom-stern hullform is a complex, broad-banded, three-dimensional phenomenon marked by a large breaking wave. This unsteady multiphase turbulent flow feature is difficult to study experimentally and simulate numerically. The results of a set of numerical simulations, which use the Numerical Flow Analysis (NFA) code, of the flow around the Model 5673 transom stern at speeds covering both wet- and dry-transom operating conditions are shown in the accompanying fluid dynamics video. The numerical predictions for wet-transom and dry-transom conditions are presented to demonstrate the current state of the art in the simulation of ship generated breaking waves. The interested reader is referred to Drazen et al. (2010) for a detailed and comprehensive comparison with experiments conducted at the Naval Surface Warfare Center Carderock Division (NSWCCD).Comment: Fluid Dynamics Video for 2010 APS Division of Fluid Dynamics Gallery of Fluid Motion include