3,657 research outputs found
Ultracold Bose gases in time-dependent 1D superlattices: response and quasimomentum structure
The response of ultracold atomic Bose gases in time-dependent optical
lattices is discussed based on direct simulations of the time-evolution of the
many-body state in the framework of the Bose-Hubbard model. We focus on
small-amplitude modulations of the lattice potential as implemented in several
recent experiment and study different observables in the region of the first
resonance in the Mott-insulator phase. In addition to the energy transfer we
investigate the quasimomentum structure of the system which is accessible via
the matter-wave interference pattern after a prompt release. We identify
characteristic correlations between the excitation frequency and the
quasimomentum distribution and study their structure in the presence of a
superlattice potential.Comment: 4 pages, 4 figure
A method to estimate relative orientations of body segments during movement using accelerometry
Quantitative assessment of human body movements includes the analysis of joint orientations. We propose a new method to estimate relative orientation between body segments using a single 3D accelerometer per segment
Multiresolution kernel matrix algebra
We propose a sparse arithmetic for kernel matrices, enabling efficient
scattered data analysis. The compression of kernel matrices by means of
samplets yields sparse matrices such that assembly, addition, and
multiplication of these matrices can be performed with essentially linear cost.
Since the inverse of a kernel matrix is compressible, too, we have also fast
access to the inverse kernel matrix by employing exact sparse selected
inversion techniques. As a consequence, we can rapidly evaluate series
expansions and contour integrals to access, numerically and approximately in a
data-sparse format, more complicated matrix functions such as and
. By exploiting the matrix arithmetic, also efficient Gaussian process
learning algorithms for spatial statistics can be realized. Numerical results
are presented to quantify and quality our findings
The effects of mergers and acquisitions on the firm size distribution
This paper provides new empirical evidence on the effects of mergers and acquisitions (M&As) on the shape of the firm size distribution, by using data of the population of manufacturing firms in the Netherlands. Our analysis shows that M&As do not affect the size distribution when we consider the entire population of firms. When we focus on the firms involved in an M&A event, we observe a shift of the firm size distribution towards larger sizes. Firm size distribution becomes more concentrated around the mean, less skewed to the right hand side, and thinner at the tails as a whole. The shift toward higher sizes due to M&A is not uniform but affects firms of different sizes in different ways. While the number of firms in the lower tail decreased, the number of firms in the central size classes increased substantially and outweighed the increase in the number (and mean size) of firms in the upper tail of the distribution (consequently the overall market concentration measured by the Herfindahl index declines). M&As lead to a departure from log-normality of the firm size distribution, suggesting that external growth does not follow Gibrat's law. Our counterfactual analysis highlights that only internal growth does not affect the shape of the size distribution of firms. On the contrary, it suggests that the change in the size distribution is almost entirely due to the external growth of the firms
Adensamentos periódicos do rebanho bovino de corte no Pantanal e seus reflexos na eficiência reprodutiva: um relato.
Os adensamentos consistem em promover, periodicamente, rodeios (agrupar o rebanho de cria), sob a hipótese de que a aproximação de touros e vacas conduz a um maior índice de prenhez. Este trabalho teve como objetivo relatar a experiência de um estudo realizado para averiguar se essa pratica tem, efetivamente, o efeito esperado, bem como relatar as dificuldades encontradas. Foi conduzido numa propriedade particular representativa do Pantanal de Rio Verde de Mato Grosso, MS, no período de 1987 a 1990. Utilizaram-se 766 vacas neloradas e 46 touros da raça Nelore, mantidos em duas invernadas (pastagem nativa) de, aproximadamente, 1.500 hectares cada, cuja lotação foi de 3 hectares/unidade animal e a relação touro/vaca foi de 1:16. O ensaio envolveu dois tratamentos (T1 e T2). O T1 obedeceu ao manejo tradicional da região (testemunha). No T2, o rebanho foi submetido a adensamentos a cada 21 dias, durante a estação de monta (setembro a março). O adensamento consistiu em levar todo o gado para um piquete a parte, com 19 hectares, mantendo-o por 48 horas. Os resultados obtidos não são conclusivos por falta de controle das condições experimentais. Discutem-se as dificuldades encontradas nesse ensaio, bem como são apresentadas sugestões para futuros trabalhos a serem conduzidos na região.bitstream/item/139369/1/cir-tec-28.pd
Transport properties of a superconducting single-electron transistor coupled to a nanomechanical oscillator
We investigate a superconducting single-electron transistor capacitively
coupled to a nanomechanical oscillator and focus on the double Josephson
quasiparticle resonance. The existence of two coherent Cooper pair tunneling
events is shown to lead to pronounced backaction effects. Measuring the current
and the shot noise provides a direct way of gaining information on the state of
the oscillator. In addition to an analytical discussion of the linear-response
regime, we discuss and compare results of higher-order approximation schemes
and a fully numerical solution. We find that cooling of the mechanical
resonator is possible, and that there are driven and bistable oscillator states
at low couplings. Finally, we also discuss the frequency dependence of the
charge noise and the current noise of the superconducting single electron
transistor.Comment: 19 pages, 11 figures, published in PR
Electrostatic extraction of cold molecules from a cryogenic reservoir
We present a method which delivers a continuous, high-density beam of slow
and internally cold polar molecules. In our source, warm molecules are first
cooled by collisions with a cryogenic helium buffer gas. Cold molecules are
then extracted by means of an electrostatic quadrupole guide. For ND the
source produces fluxes up to molecules/s with
peak densities up to molecules/cm. For
HCO the population of rovibrational states is monitored by depletion
spectroscopy, resulting in single-state populations up to .Comment: 4 pages, 4 figures, changes to the text, updated figures and
reference
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