2,280 research outputs found
Edge states control droplet break-up in sub-critical extensional flows
A fluid droplet suspended in an extensional flow of moderate intensity may
break into pieces, depending on the amplitude of the initial droplet
deformation. In subcritical uniaxial extensional flow the non-breaking base
state is linearly stable, implying that only a finite amplitude perturbation
can trigger break-up. Consequently, the stable base solution is surrounded by
its finite basin of attraction. The basin boundary, which separates initial
droplet shapes returning to the non-breaking base state from those becoming
unstable and breaking up, is characterized using edge tracking techniques. We
numerically construct the edge state, a dynamically unstable equilibrium whose
stable manifold forms the basin boundary. The edge state equilibrium controls
if the droplet breaks and selects a unique path towards break-up. This path
physically corresponds to the well-known end-pinching mechanism. Our results
thereby rationalize the dynamics observed experimentally [Stone & Leal, J.
Fluid Mech. 206, 223 (1989)
A semantic language for querying anonymous web sources
A great deal of work has been carried out in recent years to facilitate access to data and information available on the Web. Proposals converge in two additional areas which consist in providing the sources with semantic annotations and in designing languages and tools that are capable of using these annotations. However, a large number of sources have not yet been annotated suitably. Besides, languages and existing tools do not allow the user to formulate "blind" queries without knowing the sources. To overcome these two limitations, in this paper we propose a flexible query language which allows a user to query sources in an anonymous way without knowing their existence and their structure. Queries can be solved by a system which in advance discovers potential sources and memorizes their schemas. We clarify how such a system can function
The Earth as an extrasolar planet: The vegetation spectral signature today and during the last Quaternary climatic extrema
The so-called Vegetation Red-Edge (VRE), a sharp increase in the reflectance
around , is a characteristic of vegetation spectra, and can therefore
be used as a biomarker if it can be detected in an unresolved extrasolar
Earth-like planet integrated reflectance spectrum. Here we investigate the
potential for detection of vegetation spectra during the last Quaternary
climatic extrema, the Last Glacial Maximum (LGM) and the Holocene optimum, for
which past climatic simulations have been made. By testing the VRE
detectability during these extrema when Earth's climate and biomes maps were
different from today, we are able to test the vegetation detectability on a
terrestrial planet different from our modern Earth. Data from the Biome3.5
model have been associated to visible GOME spectra for each biome and cloud
cover to derive Earth's integrated spectra for given Earth phases and observer
positions. The VRE is then measured. Results show that the vegetation remains
detectable during the last climatic extrema. Compared to current Earth, the
Holocene optimum with a greener Sahara slightly increases the mean VRE on one
hand, while on the other hand, the large ice cap over the northern Hemisphere
during the LGM decreases vegetation detectability. We finally discuss the
detectability of the VRE in the context of recently proposed space missions.Comment: 31-page manuscript, 12 figures, accepted for publication in Int. J.
of Astrobiolog
Fluorescence and phosphorescence from individual C molecules excited by local electron tunneling
Using the highly localized current of electrons tunneling through a double
barrier Scanning Tunneling Microscope (STM) junction, we excite luminescence
from a selected C molecule in the surface layer of fullerene
nanocrystals grown on an ultrathin NaCl film on Au(111). In the observed
luminescence fluorescence and phosphorescence spectra, pure electronic as well
as vibronically induced transitions of an individual C molecule are
identified, leading to unambiguous chemical recognition on the single-molecular
scale
Dynamical Coulomb Blockade Observed in Nano-Sized Electrical Contacts
Electrical contacts between nano-engineered systems are expected to
constitute the basic building blocks of future nano-scale electronics. However,
the accurate characterization and understanding of electrical contacts at the
nano-scale is an experimentally challenging task. Here we employ
low-temperature scanning tunneling spectroscopy to investigate the conductance
of individual nano-contacts formed between flat Pb islands and their supporting
substrates. We observe a suppression of the differential tunnel conductance at
small bias voltages due to dynamical Coulomb blockade effects. The differential
conductance spectra allow us to determine the capacitances and resistances of
the electrical contacts which depend systematically on the island--substrate
contact area. Calculations based on the theory of environmentally assisted
tunneling agree well with the measurements.Comment: 5 pages, 3 figures, to appear in PR
All-optical Reservoir Computing
Reservoir Computing is a novel computing paradigm which uses a nonlinear
recurrent dynamical system to carry out information processing. Recent
electronic and optoelectronic Reservoir Computers based on an architecture with
a single nonlinear node and a delay loop have shown performance on standardized
tasks comparable to state-of-the-art digital implementations. Here we report an
all-optical implementation of a Reservoir Computer, made of off-the-shelf
components for optical telecommunications. It uses the saturation of a
semiconductor optical amplifier as nonlinearity. The present work shows that,
within the Reservoir Computing paradigm, all-optical computing with
state-of-the-art performance is possible
Discordant Increases in CD4+ T Cells in Human Immunodeficiency Virus-Infected Patients Experiencing Virologic Treatment Failure: Role of Changes in Thymic Output and T Cell Death
Some patients infected with human immunodeficiency virus (HIV) who are experiencing antiretroviral treatment failure have persistent improvement in CD4+ T cell counts despite high plasma viremia. To explore the mechanisms responsible for this phenomenon, 2 parameters influencing the dynamics of CD4+ T cells were evaluated: death of mature CD4+ T cells and replenishment of the CD4+ T cell pool by the thymus. The improvement in CD4+ T cells observed in patients with treatment failure was not correlated with spontaneous, Fas ligand-induced, or activation-induced T cell death. In contrast, a significant correlation between the improvement in CD4+ T cell counts and thymic output, as assessed by measurement of T cell receptor excision circles, was observed. These observations suggest that increased thymic output contributes to the dissociation between CD4+ T cell counts and viremia in patients failing antiretroviral therapy and support a model in which drug-resistant HIV strains may have reduced replication rates and pathogenicity in the thymu
H2O and δD profiles remotely-sensed from ground in different spectral infrared regions
We present ground-based FTIR (Fourier Transform Infrared) water vapour analyses performed in four different spectral regions: 790–880, 1090–1330, 2650–3180, and 4560–4710 cm−1. All four regions allow the retrieval of lower, middle, and upper tropospheric water vapour amounts with a vertical resolution of about 3, 6, and 10 km, respectively. In addition the analyses at 1090–1330 and 2650–3180 cm−1 allow the retrieval of lower and middle/upper tropospheric δD values with vertical resolutions of 3 and 10 km, respectively. A theoretical and empirical error assessment – taking coincident Vaisala RS92 radiosonde measurements as a reference – suggests that the H2O data retrieved at high wavenumbers are slightly more precise than those retrieved at low wavenumbers. We deduce an H2O profile precision and accuracy of generally better than 20% except for the low wavenumber retrieval at 790–880 cm−1, where the assessed upper precision limit of middle/upper tropospheric H2O is 35%. The scatter between the H2O profiles produced by the four different retrievals is generally below 20% and the bias below 10%, except for the boundary layer, where it can reach 24%. These values well confirm the theoretical and empirical error assessment and are rather small compared to the huge tropospheric H2O variability of about one order of magnitude thereby demonstrating the large consistency between the different H2O profile retrievals. By comparing the two δD profile versions we deduce a precision of about 8 and 17‰ for the lower and middle/upper troposphere, respectively. However, at the same time we observe a systematic difference between the two retrievals of up to 40‰ in the middle/upper troposphere which is a large value compared to the typical tropospheric δD variability of only 80‰.M. Schneider has been supported by the Deutsche Forschungsgemeinschaft via the project RISOTO (Geschaftszeichen SCHN 1126/1-1 and 1-2)
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