260 research outputs found
High spectral resolution of GaAs/AlAs phononic cavities by subharmonic resonant pump-probe excitation
We present here precise measurement of the resonance frequency, lifetime and
shape of confined acoustic modes in the tens of GHz regime in GaAs/AlAs
superlattice planar and micropillar cavities at low temperature (). The subharmonic resonant pump-probe technique, where the
repetition rate of the pump laser is tuned to a subharmonic of the cavity
resonance to maximize the amplitude of the acoustic resonance, in combination
with a Sagnac interferometer technique for high sensitivity () to the surface displacement, has been used. The cavity
fundamental mode at and the higher order cavity
harmonics up to have been clearly resolved. Mechanical
Q-values up to have been measured in a planar superlattice,
and direct spatial mapping of confined acoustic modes in a superlattice cavity
micropillar has been demonstrated. The Q-frequency product obtained is demonstrating the suitability of these superlattice cavities
for optomechanical applications.Comment: 5 pages, 4 figure
Distributional issues in natural capital accounting: an application to land ownership and ecosystem services in Scotland
Accounting for ecosystems is increasingly central to natural capital accounting. What is missing from this, however, is an answer to questions about how natural capital is distributed. That is, who consumes ecosystem services and who owns or manages the underlying asset(s) that give rise to ecosystem services. In this paper, we examine the significance of the ownership of land on which ecosystem assets (or ecosystem types) is located in the context of natural capital accounting. We illustrate this in an empirical application to two ecosystem services and a range of ecosystem types and land ownership in Scotland, a context in which land reform debates are longstanding. Our results indicate the relative importance of private land in ecosystem service supply, rather than land held by the public sector. We find relative concentration of ownership for land providing comparatively high amounts of carbon sequestration. For air pollution removal, however, the role of smaller to medium sized, mostly privately owned, land holdings closer to urban settlements becomes more prominent. The contributions in this paper, we argue, represent important first steps in anticipating distributional impacts of natural capital (and related) policy in natural capital accounts as well as connecting these frameworks to broader concerns about wealth disparities across and within countries
Enhancing the optical excitation efficiency of a single self-assembled quantum dot with a plasmonic nanoantenna
We demonstrate how the controlled positioning of a plasmonic nanoparticle
modifies the photoluminescence of a single epitaxial GaAs quantum dot. The
antenna particle leads to an increase of the luminescence intensity by about a
factor of eight. Spectrally and temporally resolved photoluminescence
measurements prove an increase of the quantum dot's excitation rate. The
combination of stable epitaxial quantum emitters and plasmonic nanostructures
promises to be highly beneficial for nanoscience and quantum optics.Comment: 5 pages, 4 figure
Spin-Orbit induced phase-shift in BiSe Josephson junctions
The transmission of Cooper pairs between two weakly coupled superconductors
produces a superfluid current and a phase difference; the celebrated Josephson
effect. Because of time-reversal and parity symmetries, there is no Josephson
current without a phase difference between two superconductors. Reciprocally,
when those two symmetries are broken, an anomalous supercurrent can exist in
the absence of phase bias or, equivalently, an anomalous phase shift
can exist in the absence of a superfluid current. We report on the
observation of an anomalous phase shift in hybrid Josephson
junctions fabricated with the topological insulator BiSe submitted to
an in-plane magnetic field. This anomalous phase shift is observed
directly through measurements of the current-phase relationship in a Josephson
interferometer. This result provides a direct measurement of the spin-orbit
coupling strength and open new possibilities for phase-controlled Josephson
devices made from materials with strong spin-orbit coupling
Improved fidelity of triggered entangled photons from single quantum dots
We demonstrate the on-demand emission of polarisation-entangled photon pairs
from the biexciton cascade of a single InAs quantum dot embedded in a GaAs/AlAs
planar microcavity. Improvements in the sample design blue shifts the wetting
layer to reduce the contribution of background light in the measurements.
Results presented show that >70% of the detected photon pairs are entangled.
The high fidelity of the (|HxxHx>+|VxxVx>)/2^0.5 state that we determine is
sufficient to satisfy numerous tests for entanglement. The improved quality of
entanglement represents a significant step towards the realisation of a
practical quantum dot source compatible with applications in quantum
information.Comment: 9 pages. Paper is available free of charge at
http://www.iop.org/EJ/abstract/1367-2630/8/2/029/, see also 'A semiconductor
source of triggered entangled photon pairs', R. M. Stevenson et al., Nature
439, 179 (2006
Statistical and Proactive Analysis of an Inter-Laboratory Comparison: The Radiocarbon Dating of the Shroud of Turin.
We review the sampling and results of the radiocarbon dating of the archaeological cloth known as the Shroud of Turin, in the light of recent statistical analyses of both published and raw data. The statistical analyses highlight an inter-laboratory heterogeneity of the means and a monotone spatial variation of the ages of subsamples that suggest the presence of contaminants unevenly removed by the cleaning pretreatments. We consider the significance and overall impact of the statistical analyses on assessing the reliability of the dating results and the design of correct sampling. These analyses suggest that the 1988 radiocarbon dating does not match the current accuracy requirements. Should this be the case, it would be interesting to know the accurate age of the Shroud of Turin. Taking into account the whole body of scientific data, we discuss whether it makes sense to date the Shroud again
Effect of gallium termination on InGaAs wetting layer properties in droplet epitaxy InGaAs quantum dots
Self-assembled quantum dots based on III-V semiconductors have excellent
properties for applications in quantum optics. However, the presence of a 2D
wetting layer which forms during the Stranski-Krastanov growth of quantum dots
can limit their performance. Here, we investigate wetting layer formation
during quantum dot growth by the alternative droplet epitaxy technique. We use
a combination of photoluminescence excitation spectroscopy, lifetime
measurements, and transmission electron microscopy to identify the presence of
an InGaAs wetting layer in these droplet epitaxy quantum dots, even in the
absence of distinguishable wetting layer photoluminescence. We observe that
increasing the amount of Ga deposited on a GaAs (100) surface prior to the
growth of InGaAs quantum dots leads to a significant reduction in the emission
wavelength of the wetting layer to the point where it can no longer be
distinguished from the GaAs acceptor peak emission in photoluminescence
measurements
Heating cancer stem cells to reduce tumor relapse
Tumour relapse is believed to be caused by rare cancer-cells with stem-cell properties (cancer stem cells) that are intrinsically resistant to available treatments. The identification of novel strategies to increase their sensitivity has major clinical implications. Latest clinical trials have shown a positive antitumoral effect of hyperthermia in combination with chemotherapy or radiotherapy. In a recent paper, the combination of increased temperature at the tumour site, generated by laser treatment of intravenously-injected gold nanoshells, and ionizing radiations enhances radiosensitivity of cancer stem cells and tumor response. At the root of the success of hyperthermia in enhancing radio-sensitization of cancer stem cells is the inhibition of their capacity to repair DNA damage, affecting the survival rate of these cells
Predicting the effects of biochar on volatile petroleum hydrocarbon biodegradation and emanation from soil: a bacterial community finger-print analysis inferred modelling approach
We investigated the response of the dominant bacterial taxa in gravelly sand to the addition of biochar and/or mixtures of volatile petroleum hydrocarbons (VPHs) using denaturing gradient gel electrophoresis (DGGE) and sequencing of cut bands. Biochar addition alone had only weak effects on the soil bacterial community composition in batch study samples, while VPH addition had strong effects. Indirect effects of biochar on soil bacterial communities were apparent in column study samples, where biochar-enhanced sorption affected VPH spreading. Following VPH addition, cell abundance increased by no more than a factor of 2 and several Pseudomonas spp. became dominant in soil with and without biochar. We present a VPH fate model that considers soil bacterial biomass dynamics and a nutrient limited soil biomass carrying capacity. The model simulates an apparent lag phase before the onset of a brief period of intensive VPH biodegradation and biomass growth, which is followed by substantially slower VPH biodegradation, when nitrogen needs to be recycled between decaying and newly formed biomass. If biomass growth is limited by a factor other than the organic pollutant bioavailability, biochar amendment may enhance VPH attenuation in between a VPH source below ground and the atmosphere by reducing the risk of overloading the soil's biodegradation capacity
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