Search results for " density"

Time-dependent density-functional theory in the projector augmented-wave method

2008

We present the implementation of the time-dependent density-functional theory both in linear-response and in time-propagation formalisms using the projector augmented-wave method in real-space grids. The two technically very different methods are compared in the linear-response regime where we found perfect agreement in the calculated photoabsorption spectra. We discuss the strengths and weaknesses of the two methods as well as their convergence properties. We demonstrate different applications of the methods by calculating excitation energies and excited state Born–Oppenheimer potential surfaces for a set of atoms and molecules with the linear-response method and by calculating nonlinear e…

Power Density Optimization of EMI Filters for Power Electronic Converters

The switching power converters are used in a broad variety of applications, from the consumer electronics to the DC distribution systems, from the vehicle applications (road vehicles, marine vehicles, aircraft) to the industrial automation. In each of these application fields, the conversion systems which present more compact size and reduced weight, at the same power, are strongly required in relation to stringent design constraints. In this context, the optimization of the power density of the converter becomes an essential requirement. The increase of the switching frequency of the static devices allows an improvement of the power density, thanks to the possibility of reducing the sizes …

The Role of Preschool Hours in Achieving Physical Activity Recommendations for Preschoolers

2021

Research on physical activity (PA) in different educational settings could elucidate which interventions promote a healthy school lifestyle in early childhood education (ECE). The aims of this study were: (a) to analyse the PA levels of preschoolers during school hours, as well as the rate of compliance with specific recommendations on total PA (TPA) and moderate-vigorous PA (MVPA)

Nested assemblages resulting from host size variation: the case of endoparasite communities in fish hosts

2001

Nested species subsets are a common pattern in many types of communities found in insular or fragmented habitats. Nestedness occurs in some communities of ectoparasites of fish, as does the exact opposite departure from random assembly, anti-nestedness. Here, we looked for nested and anti-nested patterns in the species composition of communities of internal parasites of 23 fish populations from two localities in Finland. We also compared various community parameters of nested and anti-nested assemblages of parasites, and determined whether nestedness may result simply from a size-related accumulation of parasite species by feeding fish hosts. Nested parasite communities were characterised b…

Diel vertical movements of zooplankton in lake La Cruz (Cuenca, Spain)

2000

The study of diel vertical movements of zooplankton in a small meromictic karstic lake (lake La Cruz), presenting highly stratified waters, was performed using two different methodologies: (i) samples were taken along the vertical profile and were compared at different hours in a diel cycle; (ii) some plankton traps were located at different depths, covering different periods of time, to catch organisms going upwards and downwards. The main subject of this study has been the vertical movements affecting rotifers since they were dominant in the zooplankton of this lake, but we have also included the results obtained for other zooplankton groups. The results indicate an almost general movemen…

Forest Fragmentation Increases Nest Predation in the Eurasian Treecreeper

2004

We used long-term breeding data to monitor the influences of fragmentation and habitat composi- tion at different spatial scales on the reproductive success of Eurasian Treecreepers (Certhia familiaris) breeding in nest boxes. We collected data from the same forest patches (2.7-65.1 ha in size) during seven breeding sea- sons. Nest predation varied considerably over the years and was the primary cause of nesting failure (mean annual rate of 21.6 ± 12.8%). Nest predation explained most of the variation in fledgling production during the study period. Landscape-level fragmentation (radius of 500 m from territory center) affected nest predation more than did fragmentation on the territory scal…

Norm-Based Trade Union Membership: Evidence for Germany

2004

AbstractIn the absence of closed shops and discriminatory wage policies, union membership can be explained by the existence of social norms.We describe a model, incorporating institutional features of the German labour market, which explicitly allows for social custom effects in the determination of union membership. Using panel data for Germany, we find evidence for according effects which restrict freeriding. The impact of social norms tends to increase with net union density. Hence, observed reductions in the demand for union membership can weaken the impact of a norm and accentuate the free-rider problem.

ESCAPE TIMES IN STOCK MARKETS

2005

We study the statistical properties of escape times for stock price returns in the Wall Street market. In particular we get the escape time distribution for real data from daily transactions and for three models: (i) the Wiener process with drift and a constant market volatility, (ii) Heston and (iii) GARCH models, where the volatility is a stochastic process. We find that the first model is unable to catch all the features of the escape time distribution of real data. Moreover, the Heston model describes the probability density function for both return and escape times better than the GARCH model.

Measurement of ultra-low heating rates of a single antiproton in a cryogenic Penning trap

2019

Physical review letters 122(4), 043201 (2019). doi:10.1103/PhysRevLett.122.043201

Enhanced flexible algorithm for the optimization of slot filling factors in electrical machines †

2020

The continuous development in the field of industrial automation and electric mobility has led to the need for more efficient electrical machines with a high power density. The improvement of electrical machines’ slot filling factors is one of the measures to satisfy these requirements. In recent years, this topic has aroused greater interest in the industrial sector, since the evolution of the winding technological manufacturing processes allows an economically sustainable realization of ordered winding arrangements, rather than random ones. Moreover, the manufacture of electrical machines’ windings must be preceded by an accurate design phase in which it is possible to evaluate the maximu…