7,821 research outputs found
Coherent coupling between surface plasmons and excitons in semiconductor nanocrystals
We present an experimental demonstration of strong coupling between a surface
plasmon propagating on a planar silver substrate, and the lowest excited state
of CdSe nanocrystals. Variable-angle spectroscopic ellipsometry measurements
demonstrated the formation of plasmon-exciton mixed states, characterized by a
Rabi splitting of 82 meV at room temperature. Such a coherent
interaction has the potential for the development of plasmonic non-linear
devices, and furthermore, this system is akin to those studied in cavity
quantum electrodynamics, thus offering the possibility to study the regime of
strong light-matter coupling in semiconductor nanocrystals at easily accessible
experimental conditions.Comment: 12 pages, 4 figure
Consequences of temperature and temperature variability on swimming activity, group structure, and predation of endangered delta smelt
The effects of water temperature on individual and group movement behaviour in prey fish can affect ecological interactions such as competition and predation, but how variability in temperature influence fish behaviour is less understood. Of particular concern is how increased warming in tidally fluctuating estuaries may impact the native and endangered delta smelt (Hypomesus transpacificus, Osmeridae). To help address this issue, we tested the effects of increased water temperature (fluctuating [17–21°C] and warm [21°C] acclimated treatments) on juvenile delta smelt individual and group behaviour, response to chemical alarm and predator cues, as well as capacity to evade predation. In addition, predation of delta smelt was tested in the presence of a dominant invasive competitor, Mississippi silversides (Menidia beryllina, Atherinopsidae), as well as comparative predation mortality on Mississippi silversides when isolated. After 7 days of increased temperature treatments, delta smelt in the warm treatment increased swimming velocity, decreased turning angle, and altered group structure with larger inter-individual distances compared to fish in the control (17°C) and fluctuating temperature treatments. Following conspecific and predator chemical alarm cues, delta smelt showed anti-predator responses. Control and fluctuating treatment fish responded to conspecific cues with increased swimming speeds, decreased inter-individual distances and near-neighbour distances, and, after 15 min, fish recovered back to baseline behaviours. In contrast, fish in the warm treatment had not recovered after 15 min, and swimming speeds were maintained at roughly 25 cm/s, close to maximum capabilities. Fish in control and fluctuating treatments showed minimal responses to predator cues, whereas delta smelt exposed to warm conditions significantly increased swimming speeds and decreased turning angle. Predation of delta smelt by largemouth bass (Micropterus salmoides, Centrarchidae) was greatest under the warm treatment, correlating with altered behaviours of delta smelt; however, predation of Mississippi silversides was greater than delta smelt, independent of temperature. This study provides novel insight into the group behaviour of delta smelt, their response to predation, and how prolonged exposure to elevated temperature may induce negative individual and group behaviours causing alterations in predator–prey dynamics. This work highlights the importance of testing ecologically realistic temperature fluctuations in experiments as delta smelt had significantly altered responses to elevated temperature, dependent on variability of warming
Low temperature magnetic field effects on the efficiency of aluminium tris(8-hydroxyquinoline) based organic light emitting diodes in the absence of magnetoresistance
Randomized Extended Kaczmarz for Solving Least-Squares
We present a randomized iterative algorithm that exponentially converges in
expectation to the minimum Euclidean norm least squares solution of a given
linear system of equations. The expected number of arithmetic operations
required to obtain an estimate of given accuracy is proportional to the square
condition number of the system multiplied by the number of non-zeros entries of
the input matrix. The proposed algorithm is an extension of the randomized
Kaczmarz method that was analyzed by Strohmer and Vershynin.Comment: 19 Pages, 5 figures; code is available at
https://github.com/zouzias/RE
Profiling human breast epithelial cells using single cell RNA sequencing identifies cell diversity.
Breast cancer arises from breast epithelial cells that acquire genetic alterations leading to subsequent loss of tissue homeostasis. Several distinct epithelial subpopulations have been proposed, but complete understanding of the spectrum of heterogeneity and differentiation hierarchy in the human breast remains elusive. Here, we use single-cell mRNA sequencing (scRNAseq) to profile the transcriptomes of 25,790 primary human breast epithelial cells isolated from reduction mammoplasties of seven individuals. Unbiased clustering analysis reveals the existence of three distinct epithelial cell populations, one basal and two luminal cell types, which we identify as secretory L1- and hormone-responsive L2-type cells. Pseudotemporal reconstruction of differentiation trajectories produces one continuous lineage hierarchy that closely connects the basal lineage to the two differentiated luminal branches. Our comprehensive cell atlas provides insights into the cellular blueprint of the human breast epithelium and will form the foundation to understand how the system goes awry during breast cancer
Torsion and the Gravity Dual of Parity Symmetry Breaking in AdS4/CFT3 Holography
We study four dimensional gravity with a negative cosmological constant
deformed by the Nieh-Yan torsional topological invariant with a
spacetime-dependent coefficient. We find an exact solution of the Euclidean
system, which we call the torsion vortex, having two asymptotic AdS4 regimes
supported by a pseudoscalar with a kink profile. We propose that the torsion
vortex is the holographic dual of a three dimensional system that exhibits
distinct parity breaking vacua. The torsion vortex represents a (holographic)
transition between these distinct vacua. We expect that from the boundary point
of view, the torsion vortex represents a `domain wall' between the two distinct
vacua.
From a bulk point of view, we point out an intriguing identification of the
parameters of the torsion vortex with those of an Abrikosov vortex in a Type I
superconductor. Following the analogy, we find that external Kalb-Ramond flux
then appears to support bubbles of flat spacetime within an asymptotically AdS
geometry.Comment: 26 pages, 4 figures; v2: minor improvements, references adde
Using small molecules to facilitate exchange of bicarbonate and chloride anions across liposomal membranes
Bicarbonate is involved in a wide range of biological processes, which include respiration, regulation of intracellular pH and fertilization. In this study we use a combination of NMR spectroscopy and ion-selective electrode techniques to show that the natural product prodigiosin, a tripyrrolic molecule produced by microorganisms such as Streptomyces and Serratia, facilitates chloride/bicarbonate exchange (antiport) across liposomal membranes. Higher concentrations of simple synthetic molecules based on a 4,6-dihydroxyisophthalamide core are also shown to facilitate this antiport process. Although it is well known that proteins regulate Cl-/HCO3- exchange in cells, these results suggest that small molecules may also be able to regulate the concentration of these anions in biological systems
Duality and scaling in 3-dimensional scalar electrodynamics
Three-dimensional scalar electrodynamics, with a local U(1) gauge symmetry,
is believed to be dual to a scalar theory with a global U(1) symmetry, near the
phase transition point. The conjectured duality leads to definite predictions
for the scaling exponents of the gauge theory transition in the type II region,
and allows thus to be scrutinized empirically. We review these predictions, and
carry out numerical lattice Monte Carlo measurements to test them: a number of
exponents, characterising the two phases as well as the transition point, are
found to agree with expectations, supporting the conjecture. We explain why
some others, like the exponent characterising the photon correlation length,
appear to disagree with expectations, unless very large system sizes and the
extreme vicinity of the transition point are considered. Finally, we remark
that in the type I region the duality implies an interesting quantitative
relationship between a magnetic flux tube and a 2-dimensional non-topological
soliton.Comment: 27 pages. v2: reference and minor clarifications added, to appear in
Nucl.Phys.
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