1,665 research outputs found
Onderzoek naar verschillen in frequentieverdeling van hoge grondwaterstanden tengevolge van verschillen in neerslag
Momenteel worden in Nederland bij het bepalen van drainafstanden de stationaire formules van Hooghoudt (1940) en Ernst (1954) gebruikt, In het bij deze formules gehanteerde kriterium wordt dientengevolge geen rekening gehouden met het niet-stationaire karakter van de grondwaterstroming naar de ontwateringsmiddelen. In opdracht van de 'DRAINAGE CONTACTGROEP' is in het hier gepresenteerde onderzoek nader onderzoek gedaan naar dit aspekt van het drainagekriterium
Statistical analysis of time-resolved emission from ensembles of semiconductor quantum dots: Interpretation of exponential decay models
We present a statistical analysis of time-resolved spontaneous emission decay curves from ensembles of emitters, such as semiconductor quantum dots, with the aim of interpreting ubiquitous non-single-exponential decay. Contrary to what is widely assumed, the density of excited emitters and the intensity in an emission decay curve are not proportional, but the density is a time integral of the intensity. The integral relation is crucial to correctly interpret non-single-exponential decay. We derive the proper normalization for both a discrete and a continuous distribution of rates, where every decay component is multiplied by its radiative decay rate. A central result of our paper is the derivation of the emission decay curve when both radiative and nonradiative decays are independently distributed. In this case, the well-known emission quantum efficiency can no longer be expressed by a single number, but is also distributed. We derive a practical description of non-single-exponential emission decay curves in terms of a single distribution of decay rates; the resulting distribution is identified as the distribution of total decay rates weighted with the radiative rates. We apply our analysis to recent examples of colloidal quantum dot emission in suspensions and in photonic crystals, and we find that this important class of emitters is well described by a log-normal distribution of decay rates with a narrow and a broad distribution, respectively. Finally, we briefly discuss the Kohlrausch stretched-exponential model, and find that its normalization is ill defined for emitters with a realistic quantum efficiency of less than 100%.\ud
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Signatures of Interchange Reconnection: STEREO, ACE and Hinode Observations Combined
Combining STEREO, ACE and Hinode observations has presented an opportunity to
follow a filament eruption and coronal mass ejection (CME) on the 17th of
October 2007 from an active region (AR) inside a coronal hole (CH) into the
heliosphere. This particular combination of `open' and closed magnetic
topologies provides an ideal scenario for interchange reconnection to take
place. With Hinode and STEREO data we were able to identify the emergence time
and type of structure seen in the in-situ data four days later. On the 21st,
ACE observed in-situ the passage of an ICME with `open' magnetic topology. The
magnetic field configuration of the source, a mature AR located inside an
equatorial CH, has important implications for the solar and interplanetary
signatures of the eruption. We interpret the formation of an `anemone'
structure of the erupting AR and the passage in-situ of the ICME being
disconnected at one leg, as manifested by uni-directional suprathermal electron
flux in the ICME, to be a direct result of interchange reconnection between
closed loops of the CME originating from the AR and `open' field lines of the
surrounding CH.Comment: 13 pages, 13 figures, accepted Annales Geophysica
Star Formation Histories of Nearby Elliptical Galaxies. II. Merger Remnant Sample
This work presents high spectroscopic observations of a sample of six
suspected merger remnants, selected primarily on the basis of H{\sc i} tidal
debris detections. Single stellar population analysis of these galaxies
indicates that their ages, metallicities, and -enhancement ratios are
consistent with those of a representative sample of nearby elliptical galaxies.
The expected stellar population of a recent merger remnant, young age combined
with low [/Fe], is not seen in any H{\sc i}-selected galaxy. However,
one galaxy (NGC~2534), is found to deviate from the -plane in the sense
expected for a merger remnant. Another galaxy (NGC~7332), selected by other
criteria, best matches the merger remnant expectations.Comment: 12 pages, 10 figures, accepted by A
Interaction effects on dynamic correlations in non-condensed Bose gases
We consider dynamic, i.e., frequency-dependent, correlations in non-condensed
ultracold atomic Bose gases. In particular, we consider the single-particle
correlation function and its power spectrum. We compute this power spectrum for
a one-component Bose gas, and show how it depends on the interatomic
interactions that lead to a finite single-particle relaxation time. As another
example, we consider the power spectrum of spin-current fluctuations for a
two-component Bose gas and show how it is determined by the spin-transport
relaxation time.Comment: 9 pages, 3 figure
Eruption of a Kink-Unstable Filament in Active Region NOAA 10696
We present rapid-cadence Transition Region And Coronal Explorer (TRACE)
observations which show evidence of a filament eruption from active region NOAA
10696, accompanied by an X2.5 flare, on 2004 November 10. The eruptive
filament, which manifests as a fast coronal mass ejection some minutes later,
rises as a kinking structure with an apparently exponential growth of height
within TRACE's field of view. We compare the characteristics of this filament
eruption with MHD numerical simulations of a kink-unstable magnetic flux rope,
finding excellent qualitative agreement. We suggest that, while tether
weakening by breakout-like quadrupolar reconnection may be the release
mechanism for the previously confined flux rope, the driver of the expansion is
most likely the MHD helical kink instability.Comment: Accepted by ApJ Letters. 4 figures (Fig. 3 in two parts). For MPEG
files associated with Figure 1, see:
http://www.mssl.ucl.ac.uk/~drw/papers/kink/ktrace.mpg
http://www.mssl.ucl.ac.uk/~drw/papers/kink/kmdi.mpg
http://www.mssl.ucl.ac.uk/~drw/papers/kink/ksimu.mp
Monte Carlo simulations of ordering in ferromagnetic-antiferromagnetic bilayers
Monte Carlo simulations have been used to study phase transitions on coupled
anisotropic ferro/antiferromagnetic (FM/AFM) films of classical Heisenberg
spins. We consider films of different thicknesses, with fully compensated
exchange across the FM/AFM interface. We find indications of a phase transition
on each film, occuring at different temperatures. It appears that both
transition temperatures depend on the film thickness.Comment: Revtex, 4 pages, 4 figure
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