10,445 research outputs found
Controlled photon transfer between two individual nanoemitters via shared high-Q modes of a microsphere resonator
We realize controlled cavity-mediated photon transfer between two single
nanoparticles over a distance of several tens of micrometers. First, we show
how a single nanoscopic emitter attached to a near-field probe can be coupled
to high-Q whispering-gallery modes of a silica microsphere at will. Then we
demonstrate transfer of energy between this and a second nanoparticle deposited
on the sphere surface. We estimate the photon transfer efficiency to be about
six orders of magnitude higher than that via free space propagation at
comparable separations.Comment: accepted for publication in Nano Letter
First Detection of a Strong Magnetic Field on a Bursty Brown Dwarf: Puzzle Solved
We report the first direct detection of a strong, 5 kG magnetic field on the
surface of an active brown dwarf. LSR J1835+3259 is an M8.5 dwarf exhibiting
transient radio and optical emission bursts modulated by fast rotation. We have
detected the surface magnetic field as circularly polarized signatures in the
819 nm sodium lines when an active emission region faced the Earth. Modeling
Stokes profiles of these lines reveals the effective temperature of 2800 K and
log gravity acceleration of 4.5. These parameters place LSR J1835+3259 on
evolutionary tracks as a young brown dwarf with the mass of 554 M and age of 224 Myr. Its magnetic field is at least 5.1 kG and covers
at least 11% of the visible hemisphere. The active region topology recovered
using line profile inversions comprises hot plasma loops with a vertical
stratification of optical and radio emission sources. These loops rotate with
the dwarf in and out of view causing periodic emission bursts. The magnetic
field is detected at the base of the loops. This is the first time that we can
quantitatively associate brown dwarf non-thermal bursts with a strong, 5 kG
surface magnetic field and solve the puzzle of their driving mechanism. This is
also the coolest known dwarf with such a strong surface magnetic field. The
young age of LSR J1835+3259 implies that it may still maintain a disk, which
may facilitate bursts via magnetospheric accretion, like in higher-mass T
Tau-type stars. Our results pave a path toward magnetic studies of brown dwarfs
and hot Jupiters.Comment: ApJ, in pres
Witnessing Entanglement of EPR States With Second-Order Interference
The separability of the continuous-variable EPR state can be tested with
Hanbury-Brown and Twiss type interference. The second-order visibility of such
interference can provide an experimental test of entanglement. It is shown that
time-resolved interference leads to the Hong, Ou and Mandel deep, that provides
a signature of quantum non-separability for pure and mixed EPR states. A
Hanbury-Brown and Twiss type witness operator can be constructed to test the
quantum nature of the EPR entanglement.Comment: 9 pages, 5 figure
Computing evolutionary distinctiveness indices in large scale analysis
We present optimal linear time algorithms for computing the Shapley values and 'heightened evolutionary distinctiveness' (HED) scores for the set of taxa in a phylogenetic tree. We demonstrate the efficiency of these new algorithms by applying them to a set of 10,000 reasonable 5139-species mammal trees. This is the first time these indices have been computed on such a large taxon and we contrast our finding with an ad-hoc index for mammals, fair proportion (FP), used by the Zoological Society of London's EDGE programme. Our empirical results follow expectations. In particular, the Shapley values are very strongly correlated with the FP scores, but provide a higher weight to the few monotremes that comprise the sister to all other mammals. We also find that the HED score, which measures a species' unique contribution to future subsets as function of the probability that close relatives will go extinct, is very sensitive to the estimated probabilities. When they are low, HED scores are less than FP scores, and approach the simple measure of a species' age. Deviations (like the Solendon genus of the West Indies) occur when sister species are both at high risk of extinction and their clade roots deep in the tree. Conversely, when endangered species have higher probabilities of being lost, HED scores can be greater than FP scores and species like the African elephant Loxondonta africana, the two solendons and the thumbless bat Furipterus horrens can move up the rankings. We suggest that conservation attention be applied to such species that carry genetic responsibility for imperiled close relatives. We also briefly discuss extensions of Shapley values and HED scores that are possible with the algorithms presented here
Kinetic modeling and simulation of high-temperature by-product formation from urea decomposition
The Selective catalytic reduction (SCR) technique is widely applied in exhaust gas after-treatment of diesel engines. Depending on operating conditions, injected urea-water solution (UWS) can form liquid films on mixer blades and the pipe wall. Evaporation and subsequent reactions in the wall film can lead to deposits of urea and by-products, respectively. Especially deposits that are not decomposed up to high temperatures are challenging for the SCR technique. Thermogravimetric experiments are conducted for these stable urea by-products, such as ammelide, ammeline and their by-products, such as cyanamide or melamine. An analysis of the evolving gases during thermal decomposition led to a more detailed understanding of the kinetics. The postulated mechanism is able to predict the thermogravimetric analyses results and the effects of variation of the experimental conditions such as initial sample mass and heating rates. The evaluated kinetics, together with the recently developed kinetics for the urea/biuret/triuret/cyanuric acid system Tischer et al. (2019), can now be integrated into CFD simulations of SCR systems to numerically simulate all relevant physical and chemical processes in UWS equipped aftertreatment systems for a wide range of conditions
Iron as recyclable energy carrier: Feasibility study and kinetic analysis of iron oxide reduction
Carbon-free and sustainable energy storage solutions are required to mitigate climate change. One possible solution, especially for stationary applications, could be the storage of energy in metal fuels. Energy can be stored through reduction of the oxide with green hydrogen and be released by combustion. In this work a feasibility study for iron as possible metal fuel considering the complete energy cycle is conducted. On the basis of equilibrium calculations it could be shown that the power-to-power efficiency of the iron/iron oxide cycle is 27 %. As technology development requires a more detailed description of both the reduction and the oxidation, a first outlook is given on the kinetic analysis of the reduction of iron oxides with hydrogen. Thermogravimetric experiments using FeO, FeO and FeO indicate a three-step process for the reduction. The maximum reduction rate can be achieved with a hydrogen content of 25 %. Based on the experimental results a reaction mechanism and accompanied kinetic data were developed for description of FeO reduction with H under varying experimental conditions
Adaptive Evolutionary Clustering
In many practical applications of clustering, the objects to be clustered
evolve over time, and a clustering result is desired at each time step. In such
applications, evolutionary clustering typically outperforms traditional static
clustering by producing clustering results that reflect long-term trends while
being robust to short-term variations. Several evolutionary clustering
algorithms have recently been proposed, often by adding a temporal smoothness
penalty to the cost function of a static clustering method. In this paper, we
introduce a different approach to evolutionary clustering by accurately
tracking the time-varying proximities between objects followed by static
clustering. We present an evolutionary clustering framework that adaptively
estimates the optimal smoothing parameter using shrinkage estimation, a
statistical approach that improves a naive estimate using additional
information. The proposed framework can be used to extend a variety of static
clustering algorithms, including hierarchical, k-means, and spectral
clustering, into evolutionary clustering algorithms. Experiments on synthetic
and real data sets indicate that the proposed framework outperforms static
clustering and existing evolutionary clustering algorithms in many scenarios.Comment: To appear in Data Mining and Knowledge Discovery, MATLAB toolbox
available at http://tbayes.eecs.umich.edu/xukevin/affec
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