72,253 research outputs found
Localized holes and delocalized electrons in photoexcited inorganic perovskites: Watching each atomic actor by picosecond X-ray absorption spectroscopy
We report on an element-selective study of the fate of charge carriers in
photoexcited inorganic CsPbBr3 and CsPb(ClBr)3 perovskite nanocrystals (NCs) in
toluene solutions using time-resolved X-ray absorption spectroscopy with 80 ps
time resolution. Probing the Br K-edge, the Pb L3-edge and the Cs L2-edge, we
find that holes in the valence band are localized at Br atoms, forming small
polarons, while electrons appear as delocalized in the conduction band. No
signature of either electronic or structural changes are observed at the Cs
L2-edge. The results at the Br and Pb edges suggest the existence of a weakly
localized exciton, while the absence of signatures at the Cs edge indicates
that the Cs+ cation plays no role in the charge transport, at least beyond 80
ps. These results can explain the rather modest charge carrier mobilities in
these materials.Comment: 19 pages, 3 figure
IL-15 sustains IL-7R-independent ILC2 and ILC3 development
The signals that maintain tissue-resident innate lymphoid cells (ILC) in different microenvironments are incompletely understood. Here we show that IL-7 receptor (IL-7R) is not strictly required for the development of any ILC subset, as residual cells persist in the small intestinal lamina propria (siLP) of adult and neonatal Il7ra(−/−) mice. Il7ra(−/−) ILC2 primarily express an ST2(−) phenotype, but are not inflammatory ILC2. CCR6(+) ILC3, which express higher Bcl-2 than other ILC3, are the most abundant subset in Il7ra(−/−) siLP. All ILC subsets are functionally competent in vitro, and are sufficient to provide enhanced protection to infection with C. rodentium. IL-15 equally sustains wild-type and Il7ra(−/−) ILC survival in vitro and compensates for IL-7R deficiency, as residual ILCs are depleted in mice lacking both molecules. Collectively, these data demonstrate that siLP ILCs are not completely IL-7R dependent, but can persist partially through IL-15 signalling
Past of a quantum particle: Common sense prevails
We analyze Vaidman's three-path interferometer with weak path marking [Phys.
Rev. A 87, 052104 (2013)] and find that common sense yields correct statements
about the particle's path through the interferometer. This disagrees with the
original claim that the particles have discontinuous trajectories at odds with
common sense. In our analysis, "the particle's path" has operational meaning as
acquired by a path-discriminating measurement. For a quantum-mechanical
experimental demonstration of the case, one should perform a single-photon
version of the experiment by Danan et al. [Phys. Rev. Lett. 111, 240402 (2013)]
with unambiguous path discrimination. We present a detailed proposal for such
an experiment.Comment: v1: 20 pages, 15 figures; v2 and v3: 20 pages, 16 figures, text and
figures edited, references update
Poplar from phytoremediation as a renewable energy source:gasification properties and pollution analysis
Biomass gasification is a very efficient process to produce clean energy in the form of a fuel gas (syngas). Hazelnut shells and poplar have good energy production potential and they are abundant in nature. Hazelnut shells have the characteristics of a very good fuel and poplar is among the fastest growing trees; furthermore, poplar demonstrated the capability to absorb organic contaminants (i.e. heavy metals) from the soil in which they are cultivated. However, poplar is not usually used for biomass gasification and its potential is not fully assessed. Here, 3 types of biomass, hazelnut shells (HS), simple poplar (P) and poplar coming from a phytoremediation procedure (PHYP), were chosen as representative samples to be characterized and tested in a steam gasification process carried out on a bench scale fluidized bed gasifier. A comparison is reported on gasification results, such as gas composition, tar production and gas yield for the biomass feedstocks mentioned above. It was concluded that hazelnut shells and poplar (P and PHYP) could be easily gasified in a fluidized bed gasifier, thus producing a good quality gas with low polluting by-products. The PHYP sample showed lower tar content and higher gas yield. It is guessed that Ca and Mg, found in higher quantities in the PHYP sample, could have had a catalytic effect in tar reforming thus producing lower quantity of heavy hydrocarbons
Breakup of liquid filaments.
Whether a thin filament of liquid separates into two or more droplets or eventually condenses lengthwise to form a single larger drop depends on the liquid's density, viscosity, and surface tension and on the initial dimensions of the filament. Surface tension drives two competing processes, pinching-off and shortening, and the relative time scales of these, controlled by the balance between capillary and viscous forces, determine the final outcome. Here we provide experimental evidence for the conditions under which a liquid filament will break up into drops, in terms of a wide range of two dimensionless quantities: the aspect ratio of the filament and the Ohnesorge number. Filaments which do not break up into multiple droplets demand a high liquid viscosity or a small aspect ratio.This work was supported by EPSRC (RG53364 and RG55605
Long-time relaxation in pilot-wave theory
We initiate the study of relaxation to quantum equilibrium over long
timescales in pilot-wave theory. We simulate the time evolution of the
coarse-grained H-function Hbar(t) for a two-dimensional harmonic oscillator.
For a (periodic) wave function that is a superposition of the first 25 energy
states we confirm an approximately exponential decay of Hbar over five periods.
For a superposition of only the first four energy states we are able to
calculate Hbar(t) over 50 periods. We find that, depending on the set of phases
in the initial wave function, Hbar can decay to a large nonequilibrium residue
exceeding 10% of its initial value or it can become indistinguishable from zero
(the equilibrium value). We show that a large residue in Hbar is caused by a
tendency for the trajectories to be confined to sub-regions of configuration
space for some wave functions, and that this is less likely to occur for larger
numbers of energy states (if the initial phases are chosen randomly). Possible
cosmological implications are briefly discussed.Comment: 23 pages, 11 figures. Significant improvements in v2; new section on
confinement of trajectories. Accepted by J. Phys. A: Math. Theo
exploding clusters dynamics probed by XUV fluorescence
Clusters excited by intense laser pulses are a unique source of warm dense
matter, that has been the subject of intensive experimental studies. The
majority of those investigations concerns atomic clusters, whereas the
evolution of molecular clusters excited by intense laser pulses is less
explored. In this work we trace the dynamics of clusters
triggered by a few-cycle 1.45-m driving pulse through the detection of XUV
fluorescence induced by a delayed 800-nm ignition pulse. Striking differences
among fluorescence dynamics from different ionic species are observed
An extrasolar planetary system with three Neptune-mass planets
Over the past two years, the search for low-mass extrasolar planets has led
to the detection of seven so-called 'hot Neptunes' or 'super-Earths' around
Sun-like stars. These planets have masses 5-20 times larger than the Earth and
are mainly found on close-in orbits with periods of 2-15 days. Here we report a
system of three Neptune-mass planets with periods of 8.67, 31.6 and 197 days,
orbiting the nearby star HD 69830. This star was already known to show an
infrared excess possibly caused by an asteroid belt within 1 AU (the Sun-Earth
distance). Simulations show that the system is in a dynamically stable
configuration. Theoretical calculations favour a mainly rocky composition for
both inner planets, while the outer planet probably has a significant gaseous
envelope surrounding its rocky/icy core; the outer planet orbits within the
habitable zone of this star.Comment: 17 pages, 3 figures, preprint of the paper published in Nature on May
18, 200
- …