Inductance and resistance calculations for isolated conductors

In this review paper we present various analytical and numerical calculations for computing the high frequency and low frequency inductance and resistance of isolated conductors. The high frequency estimates are obtained using conformal mapping theory. In both cases, a uniformly distributed return current at an arbitrary radius is assumed. Formulae are presented for the inductance of a strip conductor of zero thickness. The inductance is computed both for dc and for ac infinite conductivity. For regular polygons the conformal mapping is defined by a power series, while finite element analysis is used to compute the dc inductance. Conformal mapping theory is used to obtain estimates of the resistance and inductance of a rectangular conductor when the skin depth is small compared to the thickness of the conductor. A method is then presented for calculating the resistance when the skin depth exceeds the thickness of the conductor but remains small in relation to the width of the conductor. Finite element analysis is used to confirm that one of the two resistance estimates always gives a reasonable estimate of the resistance

Spatial and temporal variation in crop diversity in agroforestry homegardens of southern Ethiopia

A key assumption in many homegarden studies is that homegardens are ecologically and socio-economically sustainable due to their species diversity. The precise relation between diversity and sustainability is still heavily debated, however. A basic question is how diversity in homegardens can best be characterized in view of the various dimensions of species diversity and their variation in time and space. This paper assesses different types of species diversity in the homegardens of Sidama region of southern Ethiopia. In a survey of crop species in 144 homegardens a total of 78 cultivated crop species (excluding trees) belonging to 10 functional groups were recorded; there were on average 16 crop species and 8 functional groups per farm. Within homegardens, plots differ in species composition and crop diversity. Four types of homegarden systems are distinguished differing in both type and area-share of dominant species, relative orientation at subsistence or cash production and overall crop diversity. The gradual replacement of enset by maize and of coffee by more financially attractive cash crops khat and pineapple causes a decrease in overall crop diversity. Our data demonstrate that it is incorrect to consider homegardens as generic systems with a uniform distribution of species diversity: important within and between homegarden variation exists. Ecological and socio-economic sustainability is not just related to species diversity per se, but rather to more specific features such as presence of keystone species and diversity in functional species groups. Socio-economic sustainability in terms of adjustment to socio-economic change implies dynamics in species diversit

Broadband double-layered coplanar patch antennas with adjustable CPW feeding structure

In this paper, we have presented the double-layered coplanar patch antennas of enhanced impedance bandwidth and adjustable conductor-backed coplanar waveguide feed lines. The proposed structure retains the advantage of laying the coplanar patch and coplanar waveguide (CPW) feed line on the same surface, which makes direct integration with other devices easier. In addition, the substrate thickness of the radiating patch can be adjusted to achieve a wider impedance bandwidth while the dimensions of the CPW feed line are kept unchanged. Simulation has been done by using commercial electromagnetic (EM) simulation software. Four testing antennas, which have centre frequency at about 10 GHz, were designed. The four testing antennas had the same total thickness, but different thickness combinations. From the measured return loss, gain, and radiation patterns of the antennas, it was demonstrated that different thickness combinations do not affect the characteristics of the antennas seriously. Therefore, the dimensions of the CPW feed structure of the antennas can be adjusted individually and can be selected for different applications

Effect of starch level and roughage intake on animal perfomance, rumen wall characteristics and liver abscesses in intensively fed Frisian bulls

Organic dairy cows in Denmark has a higher frequency of liver abscesses, which is probably due to higher starch levels in the feed rations to high yielding cows compaired to conventional cows. Following abstract is based on experiments on young bulls and demonstrates whether replacing high-starch feeds with low-starch feed, such as dried grass pellets and sugar beet pulp, can reduce the problems with liver abscessation without reducing the performance level. The low-starch feed would be relevant to organic dairy production. In total, 41 Danish Friesian bulls (154±20 kg LW) were allocated into four treatment groups in a 2x2 factorial design fed either a high starch (N) or a high fibrous concentrate (F) and either chopped barley straw (S) or a mixture of 75% chopped barley straw and 25% sugar beet molasses (Sm). In the F ration, 25% of the wheat from N was replaced by dried sugar beet pulp and grass pellets giving a starch level of 24.3% and 39.1% (wt) and an energy content of 0.99 and 1.04 Scandinavian Feed Units/kg feed, respectively. The ad libitum fed bulls were slaughtered at 11.5±0.2 mo. weighing 429±41 kg LW on average. Feed intake was higher for F than N (p=0.005) (7.1 vs. 6.4 kg/d), whereas the addition of molasses increased straw intake from 0.5 to 0.9 kg/d (p<0.001). The higher intake of Sm compared with S reduced concentrate intake (p<0.05), but did not affect total net energy intake. The average daily gain (1370 g/d) did not differ between groups. The rumen wall was more severely damaged with N compared with F (p<0.05) and with S compared with Sm (p<0.003). The higher straw intake prevented rumen wall damage, but did not reduce the number of animals with liver abscesses, like the lower starch level did (1 vs. 9 animals, p<0.005)

Noble-metal-free sunlight harvesting meta-surface for water evaporation

We present ultrathin multilayer metamaterial absorbers based on abundant, low-cost materials, to effectively harness solar energy for heating and evaporation of water

Above- and below-ground competition in high and low irradiance: tree seedling responses to a competing liana Byttneria grandifolia

Abstract: In tropical forests, trees compete not only with other trees, but also with lianas, which may limit tree growth and regeneration. Liana effects may depend on the availability of above- and below-ground resources and differ between tree species. We conducted a shade house experiment to test the effect of light (4% and 35% full sun, using neutral-density screen) on the competitive interactions between seedlings of one liana (Byttneria grandifolia) and three tree species (two shade-tolerant trees, Litsea dilleniifolia and Pometia tomentosa, and one light-demanding tree, Bauhinia variegata) and to evaluate the contribution of both above- and below-ground competition. Trees were grown in four competition treatments with the liana: no competition, root competition, shoot competition and root and shoot competition. Light strongly affected leaf photosynthetic capacity (light-saturated photosynthetic rate, Pn), growth and most morphological traits of the tree species. Liana-induced competition resulted in reduced Pn, total leaf areas and relative growth rates (RGR) of the three tree species. The relative importance of above- and below-ground competition differed between the two light levels. In low light, RGR of the three tree species was reduced more strongly by shoot competition (23.1¿28.7% reduction) than by root competition (5.3¿26.4%). In high light, in contrast, root competition rather than shoot competition greatly reduced RGR. Liana competition affected most morphological traits (except for specific leaf area and leaf area ratio of Litsea and Pometia), and differentially altered patterns of biomass allocation in the tree seedlings. These findings suggest that competition from liana seedlings can greatly suppress growth in tree seedlings of both light-demanding and shade-tolerant species and those effects differ with competition type (below- and above-ground) and with irradianc

Bistability conditions between lasing and non-lasing states for vertical-cavity surface-emitting lasers with frequency-selective optical feedback

This paper gives analytical treatment and experimental details on on/off-bistability in vertical-cavity surface-emitting lasers with frequency-selective feedback by a grating. In particular, the conditions for the coexistence of lasing and nonlasing states and an abrupt turn-on behaviour at threshold are derived using an envelope approximation. The theoretical and experimental results are in satisfactory agreement