135 research outputs found
Some aspects of the energy balance closure problem
International audienceAfter briefly discussing several reasons for the energy balance closure problem in the surface layer, the paper focuses on the influence of the low frequency part of the turbulence spectrum on the residual. Changes in the turbulent fluxes in this part of the turbulence spectrum were found to have a significant influence on the changes of the residual. Using the ogive method, it was found that the eddy-covariance method underestimates turbulent fluxes in the case of ogives converging for measuring times longer than the typical averaging interval of 30 min. Additionally, the eddy-covariance method underestimates turbulent fluxes for maximal ogive functions within the averaging interval, both mainly due to advection and non-steady state conditions. This has a considerable influence on the use of the eddy-covariance method
Memristive operation mode of a site-controlled quantum dot floating gate transistor
The authors gratefully acknowledge financial support from the European Union (FPVII (2007-2013) under Grant Agreement No. 318287 Landauer) as well as the state of Bavaria.We have realized a floating gate transistor based on a GaAs/AlGaAs heterostructure with site-controlled InAs quantum dots. By short-circuiting the source contact with the lateral gates and performing closed voltage sweep cycles, we observe a memristive operation mode with pinched hysteresis loops and two clearly distinguishable conductive states. The conductance depends on the quantum dot charge which can be altered in a controllable manner by the voltage value and time interval spent in the charging region. The quantum dot memristor has the potential to realize artificial synapses in a state-of-the-art opto-electronic semiconductor platform by charge localization and Coulomb coupling.Publisher PDFPeer reviewe
Energy balance closure for the LITFASS-2003 experiment
In the first part, this paper synthesises the main results from a series of previous studies on the closure of the local energy balance at low-vegetation sites during the LITFASS-2003 experiment. A residual of up to 25% of the available energy has been found which cannot be fully explained either by the measurement uncertainty of the single components of the surface energy balance or by the length of the flux-averaging period. In the second part, secondary circulations due to heterogeneities in the surface characteristics (roughness, thermal and moisture properties) are discussed as a possible cause for the observed energy balance non-closure. This hypothesis seems to be supported from the fluxes derived from area-averaging measurement techniques (scintillometers, aircraft)
A Hubble Space Telescope Imaging Survey of Nearby Active Glactic Nuclei
We obtained 500-second F606W WFPC2 images of 256 of the nearest (z<0.035)
Seyfert 1,Seyfert 2, and starburst galaxies. Less than 10% show tidal features
or multiple nuclei. The incidence of inner starburst rings is about 10% in both
classes of Sy galaxies. In contrast, galaxies with H II region emission line
spectra appear substantially more irregular because of their much higher
specific rates of star formation. An unresolved central continuum source in our
HST images is a virtually perfect indicator of a Sy1 spectrum. 52% of these Sy1
point sources are saturated in our images; we use their wings to estimate their
magnitudes. The converse is not however true, as over a third of Sy's with
direct spectroscopic evidence for broad Balmer wings show no nuclear point
source. Like the Sy2's, they have central surface brightnesses consistent with
those expected for the bulges of normal galaxies. The frequency of bars in
Sy1's and 2's and non-Sys are the same. The Sy2 galaxies are significantly more
likely to show nuclear dust absorption, especially in lanes and patches which
are irregular or reach close to the nucleus. The difference cannot be explained
by different average redshifts or selection techniques. This is confirmed by
our morphology classifications, which show that Sy1 nuclei reside in earlier
type galaxies than Sy2 nuclei. This intrinsic difference in host galaxy
properties may undermine the strong unification hypothesis for Sy galaxies that
they appear different due to the orientation of their central engine. The
excess galactic dust we see in Sy2's may cause substantial absorption which
obscures their hypothesized broad emission-line regions and central nonstellar
continua. This galactic dust could produce much of the absorption in Sy2 nuclei
which had instead been attributed to a thick dusty accretion torus.Comment: The text of the paper is 23 pages (ms.tex), there are 8 tables, and 9
figures. Figures 1, 2, and 3 are the image gallery (45 pages) and are NOT
included here. They can be ftp'ed from ftp.astro.ucla.edu. Log in as
anonymous and give your e-mail address as the password. The images are in the
/pub/submit/vg/AGNgallery . Figures 4-9 are in eps format and are included
here and can be printed using the lpr command in unix system
Quality control of CarboEurope flux data ? Part II: Inter-comparison of eddy-covariance software
International audienceAs part of the quality assurance and quality control activities within the CarboEurope-IP network, a comparison of eddy-covariance software was conducted. For four five-day datasets, CO2 flux estimates were calculated by seven commonly used software packages to assess the uncertainty of CO2 flux estimates due to differences in post-processing. The datasets originated from different sites representing different commonly applied instrumentation and different canopy structures to cover a wide range of realistic conditions. Data preparation, coordinate rotation and the implementation of the correction for high frequency spectral losses were identified as crucial processing steps leading to significant discrepancies in the CO2 flux results. The overall comparison indicated a good although not yet perfect agreement among the different software within 5?10% difference for 30-min CO2 flux values. Conceptually different ideas about the selection and application of processing steps were a main reason for the differences in the CO2 flux estimates observed. A balance should be aspired between scientific freedom on the one hand, in order to advance methodical issues, and standardisation of procedures on the other hand, in order to obtain comparable fluxes for multi-site synthesis studies
Evaluation of Microsatellite Typing, ITS Sequencing, AFLP Fingerprinting, MALDI-TOF MS, and Fourier-Transform Infrared Spectroscopy Analysis of<i> Candida auris</i>
Candida auris is an emerging opportunistic yeast species causing nosocomial outbreaks at a global scale. A few studies have focused on the C. auris genotypic structure. Here, we compared five epidemiological typing tools using a set of 96 C. auris isolates from 14 geographical areas. Isolates were analyzed by microsatellite typing, ITS sequencing, amplified fragment length polymorphism (AFLP) fingerprint analysis, matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS), and Fourier-transform infrared (FTIR) spectroscopy methods. Microsatellite typing grouped the isolates into four main clusters, corresponding to the four known clades in concordance with whole genome sequencing studies. The other investigated typing tools showed poor performance compared with microsatellite typing. A comparison between the five methods showed the highest agreement between microsatellite typing and ITS sequencing with 45% similarity, followed by microsatellite typing and the FTIR method with 33% similarity. The lowest agreement was observed between FTIR spectroscopy, MALDI-TOF MS, and ITS sequencing. This study indicates that microsatellite typing is the tool of choice for C. auris outbreak investigations. Additionally, FTIR spectroscopy requires further optimization and evaluation before it can be used as an epidemiological typing method, comparable with microsatellite typing, as a rapid method for tracing nosocomial fungal outbreaks
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