11,363 research outputs found
Geiger-Mode Avalanche Photodiodes in Particle Detection
It is well known that avalanche photodiodes operated in the Geiger mode above
the breakdown voltage offer a virtually infinite sensitivity and time accuracy
in the picosecond range that can be used for single photon detection. However,
their performance in particle detection remains still unexplored. In this
contribution, we are going to expose the different steps that we have taken in
order to prove the efficiency of Geiger mode avalanche photodiodes in the
aforementioned field. In particular, we will present an array of pixels of
1mmx1mm fabricated with a standard CMOS technology for characterization in a
test beam.Comment: 7 pages, 2 figures, Proceedings of LCWS1
Probing the Lewis acidity and catalytic activity of the metal-organic framework [Cu-3(btc)(2)] (BTC = benzene-1,3,5-tricarboxylate)
Scattering Lens Resolves sub-100 nm Structures with Visible Light
The smallest structures that conventional lenses are able to optically
resolve are of the order of 200 nm. We introduce a new type of lens that
exploits multiple scattering of light to generate a scanning nano-sized optical
focus. With an experimental realization of this lens in gallium phosphide we
have succeeded to image gold nanoparticles at 97 nm optical resolution. Our
work is the first lens that provides a resolution in the nanometer regime at
visible wavelengths.Comment: 4 pages, 3 figure
Inhibited spontaneous emission of quantum dots observed in a 3D photonic band gap
We present time-resolved emission experiments of semiconductor quantum dots
in silicon 3D inverse-woodpile photonic band gap crystals. A systematic study
is made of crystals with a range of pore radii to tune the band gap relative to
the emission frequency. The decay rates averaged over all dipole orientations
are inhibited by a factor of 10 in the photonic band gap and enhanced up to 2?
outside the gap, in agreement with theory. We discuss the effects of spatial
inhomogeneity, nonradiative decay, and transition dipole orientations on the
observed inhibition in the band gap.Comment: 5 figures, update author lis
Observation of sub-Bragg diffraction of waves in crystals
We investigate the diffraction conditions and associated formation of
stopgaps for waves in crystals with different Bravais lattices. We identify a
prominent stopgap in high-symmetry directions that occurs at a frequency below
the ubiquitous first-order Bragg condition. This sub-Bragg diffraction
condition is demonstrated by reflectance spectroscopy on two-dimensional
photonic crystals with a centred rectangular lattice, revealing prominent
diffraction peaks for both the sub-Bragg and first-order Bragg condition. These
results have implications for wave propagation in 2 of the 5 two-dimensional
Bravais lattices and 7 out of 14 three-dimensional Bravais lattices, such as
centred rectangular, triangular, hexagonal and body-centred cubic
Controlling the quality factor of a tuning-fork resonance between 9 K and 300 K for scanning-probe microscopy
We study the dynamic response of a mechanical quartz tuning fork in the
temperature range from 9 K to 300 K. Since the quality factor Q of the
resonance strongly depends on temperature, we implement a procedure to control
the quality factor of the resonance. We show that we are able to dynamically
change the quality factor and keep it constant over the whole temperature
range. This procedure is suitable for applications in scanning probe
microscopy.Comment: 5 pages, 6 figure
Deterministic and controllable photonic scattering media via direct laser writing
Photonic scattering materials, such as biological tissue and white paper, are
made of randomly positioned nanoscale inhomogeneities in refractive index that
lead to multiple scattering of light. Typically these materials, both
naturally-occurring or man-made, are formed through self assembly of the
scattering inhomogeneities, which imposes challenges in tailoring the disorder
and hence the optical properties. Here, We report on the nanofabrication of
photonic scattering media using direct laser writing with deterministic design.
These deterministic scattering media consist of submicron thick polymer
nanorods that are randomly oriented within a cubic volume. We study the total
transmission of light as a function of the number density of rods and of the
sample thickness to extract the scattering and transport mean free paths using
radiative transfer theory. Such photonic scattering media with deterministic
and controllable properties are model systems for fundamental light scattering
in particular with strong anisotropy and offer new applications in solid-state
lighting and photovoltaics.Comment: 18 pages, 9 figure
A Reappraisal of Near-Tropical Ice Stability on Mars
Two arguments have suggested the presence of subsurface water ice at
latitudes lower than 30\textdegree~on Mars. First, the absence of CO2 frost on
pole-facing slopes was explained by the presence of subsurface ice. Second,
models suggested that subsurface ice could be stable underneath these slopes.
We revisit these arguments with a new slope microclimate model. Our model shows
that below 30{\deg} latitude, slopes are warmer than previously estimated as
the air above is heated by warm surrounding plains. This additional heat
prevents the formation of CO2 and subsurface water ice for most slopes. Higher
than 30{\deg}S, our model suggests the presence of subsurface water ice. In
sparse cases (steep dusty slopes), subsurface ice may exist down to 25{\deg}S.
While hypothetical unstable ice deposits cannot be excluded by our model, our
results suggest that water ice is rarer than previously thought in the +-
30{\deg} latitude range considered for human exploration
Looking for signatures of the Left-Right Twin Higgs model with the ATLAS detector at the LHC
The twin Higgs mechanism has recently been proposed to solve the little hierarchy problem. The phenomenology of this model is presented, and the possibility to observe some of the signatures predicted by this model using the ATLAS detector at the LHC is discussed
Assessment of Swedish snus for tobacco harm reduction: an epidemiological modelling study
BACKGROUND: Swedish snus is a smokeless tobacco product that has been suggested as a tobacco harm reduction product. Our aim was to assess the potential population health effects of snus. METHODS: We assessed the potential population health effects of snus in Australia with multistate life tables to estimate the difference in health-adjusted life expectancy between people who have never been smokers and various trajectories of tobacco use, including switching from smoking to snus use; and the potential for net population-level harm given different rates of snus uptake by current smokers, ex-smokers, and people who have never smoked. FINDINGS: There was little difference in health-adjusted life expectancy between smokers who quit all tobacco and smokers who switch to snus (difference of 0.1-0.3 years for men and 0.1-0.4 years for women). For net harm to occur, 14-25 ex-smokers would have to start using snus to offset the health gain from every smoker who switched to snus rather than continuing to smoke. Likewise, 14-25 people who have never smoked would need to start using snus to offset the health gain from every new tobacco user who used snus rather than smoking. INTERPRETATION: Current smokers who switch to using snus rather than continuing to smoke can realise substantial health gains. Snus could produce a net benefit to health at the population level if it is adopted in sufficient numbers by inveterate smokers. Relaxing current restrictions on the sale of snus is more likely to produce a net benefit than harm, with the size of the benefit dependent on how many inveterate smokers switch to snus
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