7,326 research outputs found
Delivering sound energy along an arbitrary convex trajectory
Accelerating beams have attracted considerable research interest due to their peculiar properties and various applications. Although there have been numerous research on the generation and application of accelerating light beams, few results have been published on the generation of accelerating acoustic beams. Here we report on the experimental observation of accelerating acoustic beams along arbitrary convex trajectories. The desired trajectory is projected to the spatial phase profile on the boundary which is discretized and sampled spatially. The sound field distribution is formulated with the Green function and the integral equation method. Both the paraxial and the non-paraxial regimes are examined and observed in the experiments. The effect of obstacle scattering in the sound field is also investigated and the results demonstrate that the approach is robust against obstacle scattering. The realization of accelerating acoustic beams will have an impact on various applications where acoustic information and energy are required to be delivered along an arbitrary convex trajectory
Quantifying the toroidal flux of preexisting flux ropes of coronal mass ejections
Funding: SOHO is a project of international cooperation between ESA and NASA. C.X., X.C. and M.D.D. are funded by NSFC grants 11722325, 11733003, 11790303, 11790300, Jiangsu NSF grants BK20170011, and "Dengfeng B" program of Nanjing University.In past decades, much progress has been achieved in understanding the origin and evolution of coronal mass ejections (CMEs). In situ observations of the counterparts of CMEs, especially magnetic clouds (MCs) near the Earth, have provided measurements of the structure and total flux of CME flux ropes. However, it has been difficult to measure these properties in an erupting CME flux rope, in particular in a preexisting flux rope. In this work, we propose a model to estimate the toroidal flux of a preexisting flux rope by subtracting the flux contributed by magnetic reconnection during the eruption from the flux measured in the MC. The flux contributed by the reconnection is derived from geometric properties of two-ribbon flares based on a quasi-2D reconnection model. We then apply the model to four CME/flare events and find that the ratio of toroidal flux in the preexisting flux rope to that in the associated MC lies in the range 0.40–0.88. This indicates that the toroidal flux of the preexisting flux rope makes an important contribution to that of the CME flux rope and is usually at least as large as the flux arising from the eruption process for the selected events.Publisher PDFPeer reviewe
Experimental Test of Tracking the King Problem
In quantum theory, the retrodiction problem is not as clear as its classical
counterpart because of the uncertainty principle of quantum mechanics. In
classical physics, the measurement outcomes of the present state can be used
directly for predicting the future events and inferring the past events which
is known as retrodiction. However, as a probabilistic theory,
quantum-mechanical retrodiction is a nontrivial problem that has been
investigated for a long time, of which the Mean King Problem is one of the most
extensively studied issues. Here, we present the first experimental test of a
variant of the Mean King Problem, which has a more stringent regulation and is
termed "Tracking the King". We demonstrate that Alice, by harnessing the shared
entanglement and controlled-not gate, can successfully retrodict the choice of
King's measurement without knowing any measurement outcome. Our results also
provide a counterintuitive quantum communication to deliver information hidden
in the choice of measurement.Comment: 16 pages, 5 figures, 2 table
Engineering band structures and topological invariants by transformation optics
By introducing the transformation optics method to periodic systems, we show
the tunability of the band structures by comparing the results from original
spaces and transformed spaces. Interestingly, we find the topological invariant
Chern number will change sign when the orientation of the Brillouin zone
flipped. The new platform we provided for engineering the band diagram and
topological invariant might lead to the development of both transformation
optics and photonic topological states.Comment: 6 pages, 3 figure
Tris(1H-imidazole-κN 3)(7-oxabicycloÂ[2.2.1]heptane-2,3-dicarboxylÂato-κ3 O 2,O 3,O 7)cobalt(II) 3.35-hydrate
In the crystal structure of the title compound, [Co(C8H8O5)(C3H4N2)3]·3.35H2O, the central CoII ion is in a slightly distorted octaÂhedral environment, coordinated by the bridgÂing O atom from the bicycloÂ[2.2.1]heptane ligand, by two carboxylÂate O atoms from two different carboxylÂate groups and by three N atoms from imidazole ligands. Uncoordinated water molÂecules, some of them disordered, are present in the crystal structure. In the crystal structure, molÂecules are linked by O—H⋯O, N—H⋯O and O—H⋯N hydrogen-bonding interÂactions
Supermassive Black Holes with High Accretion Rates in Active Galactic Nuclei. IV. H Time Lags and Implications for Super-Eddington Accretion
We have completed two years of photometric and spectroscopic monitoring of a
large number of active galactic nuclei (AGNs) with very high accretion rates.
In this paper, we report on the result of the second phase of the campaign,
during 2013--2014, and the measurements of five new H time lags out of
eight monitored AGNs. All five objects were identified as super-Eddington
accreting massive black holes (SEAMBHs). The highest measured accretion rates
for the objects in this campaign are , where
,
is the mass accretion rates, is the Eddington luminosity and
is the speed of light. We find that the H time lags in SEAMBHs are
significantly shorter than those measured in sub-Eddington AGNs, and the
deviations increase with increasing accretion rates. Thus, the relationship
between broad-line region size () and optical luminosity at
5100\AA, , requires accretion rate as an additional
parameter. We propose that much of the effect may be due to the strong
anisotropy of the emitted slim-disk radiation. Scaling by
the gravitational radius of the black hole, we define a new radius-mass
parameter () and show that it saturates at a critical accretion rate of
, indicating a transition from thin to slim
accretion disk and a saturated luminosity of the slim disks. The parameter
is a very useful probe for understanding the various types of accretion onto
massive black holes. We briefly comment on implications to the general
population of super-Eddington AGNs in the universe and applications to
cosmology.Comment: 53 pages, 12 figures, 7 tables, accepted for publication in The
Astrophysical Journa
Direct conversion of astrocytes into neuronal cells by drug cocktail
Direct conversion of astrocytes into neuronal cells by
drug cocktail
Cell Research advance online publication 2 October 2015; doi:10.1038/cr.2015.120
Dear Editor,
Neurological disorder is one of the greatest threats
to public health according to the World Health Organization.
Because neurons have little or no regenerative
capacity, conventional therapies for neurological disorders
yielded poor outcomes. While the introduction of
exogenous neural stem cells or neurons holds promise,
many challenges still need to be tackled, including cell
resource, delivery strategy, cell integration and cell
maturation. Reprogramming of fibroblasts into induced
pluripotent stem cells or directly into desirable neuronal
cells by transcription factors (TFs) or small molecules
can solve some problems, but other issues remain to be
addressed, including safety, conversion efficiency and
epigenetic memory [1, 2].
Astrocytes are considered to be the ideal starting
candidate cell type for generating new neurons, due to
their proximity in lineage distance to neurons and ability
to proliferate after brain damage. Many studies have
already revealed that astrocytes of the central nervous
system can be reprogrammed into induced neuronal cells
by virus-mediated overexpression of specific TFs in vitro
and in vivo [3-6]. However, application of this virus-mediated
direct conversion is still limited due to concerns
on clinical safety. We have previously reported direct
conversion of somatic cells into neural progenitor cells
(NPCs) in vitro by cocktail of small molecules under hypoxia
[7]. Here we set out to explore whether astrocytes
can be induced into neuronal cells by the chemical cocktail
in vitro
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