740 research outputs found
Interactions with a photonic crystal micro-cavity using AFM in contact or tapping mode operation
In this paper we show how the evanescent field of a localized mode in a photonic crystal micro-cavity can be perturbed by a nano-sized AFM tip. Due to the high field intensities in the cavity, we can see a significant change in output power when the tip is brought into the evanescent field in either contact or tapping mode operation. We find a 4 dB modulation, when using a tip and we show that the transmittance can be tuned from 0.32 to 0.8 by varying the average tapping height
Nano-mechanical tuning and imaging of a photonic crystal micro-cavity resonance
We show that nano-mechanical interaction using atomic force microscopy (AFM) can be used to map out mode-patterns of an optical micro-resonator with high spatial accuracy. Furthermore we demonstrate how the Q-factor and center wavelength of such resonances can be sensitively modified by both horizontal and vertical displacement of an AFM tip consisting of either Si3N4 or Si material. With a silicon tip we are able to tune the resonance wavelength by 2.3 nm, and to set Q between values of 615 and zero, by expedient positioning of the AFM tip. We find full on/off switching for less than 100 nm vertical, and for 500 nm lateral\ud
displacement at the strongest resonance antinode locations
Giant star-forming clumps?
With the spatial resolution of the Atacama Large Millimetre Array (ALMA),
dusty galaxies in the distant Universe typically appear as single, compact
blobs of dust emission, with a median half-light radius, 1 kpc.
Occasionally, strong gravitational lensing by foreground galaxies or galaxy
clusters has probed spatial scales 1-2 orders of magnitude smaller, often
revealing late-stage mergers, sometimes with tantalising hints of
sub-structure. One lensed galaxy in particular, the Cosmic Eyelash at 2.3,
has been cited extensively as an example of where the interstellar medium
exhibits obvious, pronounced clumps, on a spatial scale of 100 pc.
Seven orders of magnitude more luminous than giant molecular clouds in the
local Universe, these features are presented as circumstantial evidence that
the blue clumps observed in many 2-3 galaxies are important sites of
ongoing star formation, with significant masses of gas and stars. Here, we
present data from ALMA which reveal that the dust continuum of the Cosmic
Eyelash is in fact smooth and can be reproduced using two S\'ersic profiles
with effective radii, 1.2 and 4.4 kpc, with no evidence of significant
star-forming clumps down to a spatial scale of 80 pc and a
star-formation rate of 3 M yr.Comment: 5 pages; 3 figures; in press as a Letter to MNRA
Nationwide Outcome of Gastrectomy with En-Bloc Partial Pancreatectomy for Gastric Cancer
Background Radical gastrectomy is the cornerstone of the treatment of gastric cancer. For tumors invading the pancreas, en-bloc partial pancreatectomy may be needed for a radical resection. The aim of this study was to evaluate the outcome of gastrectomies with partial pancreatectomy for gastric cancer. Methods Patients who underwent gastrectomy with or without partial pancreatectomy for gastric or gastro-oesophageal junction cancer between 2011 and 2015 were selected from the Dutch Upper GI Cancer Audit (DUCA). Outcomes were resection margin (pR0) and Clavien-Dindo grade >= III postoperative complications and survival. The association between partial pancreatectomy and postoperative complications was analyzed with multivariable logistic regression. Overall survival of patients with partial pancreatectomy was estimated using the Kaplan-Meier method. Results Of 1966 patients that underwent gastrectomy, 55 patients (2.8%) underwent en-bloc partial pancreatectomy. A pR0 resection was achieved in 45 of 55 patients (82% versus 85% in the group without additional resection, P = 0.82). Clavien-Dindo grade = III complications occurred in 21 of 55 patients (38% versus 17%, P <0.001). Median overall survival [95% confidence interval] was 15 [6.8-23.2] months. For patients with and without perioperative systemic therapy, median survival was 20 [12.3-27.7] and 10 [5.7-14.3] months, and for patients with pR0 and pR1 resection, it was 20 [11.8-28.3] and 5 [2.4-7.6] months, respectively. Conclusions Gastrectomy with partial pancreatectomy is not only associated with a pR0 resection rate of 82% but also with increased postoperative morbidity. It should only be performed if a pR0 resection is feasible
Optical to near-infrared transit observations of super-Earth GJ1214b: water-world or mini-Neptune?
GJ1214b is thought to be either a mini-Neptune with a thick, hydrogen-rich
atmosphere, or a planet with a composition dominated by water. In the case of a
hydrogen-rich atmosphere, molecular absorption and scattering processes may
result in detectable radius variations as a function of wavelength. The aim of
this paper is to measure these variations. We have obtained observations of the
transit of GJ1214b in the r- and I-band with the INT, in the g, r, i and z
bands with the 2.2 meter MPI/ESO telescope, in the Ks-band with the NOT, and in
the Kc-band with the WHT. By comparing the transit depth between the the
different bands, which is a measure for the planet-to-star size ratio, the
atmosphere is investigated. We do not detect clearly significant variations in
the planet-to-star size ratio as function of wavelength. Although the ratio at
the shortest measured wavelength, in g-band, is 2sigma larger than in the other
bands. The uncertainties in the Ks and Kc bands are large, due to systematic
features in the light curves. The tentative increase in the planet-to-star size
ratio at the shortest wavelength could be a sign of an increase in the
effective planet-size due to Rayleigh scattering, which would require GJ1214b
to have a hydrogen-rich atmosphere. If true, then the atmosphere has to have
both clouds, to suppress planet-size variations at red optical wavelengths, as
well as a sub-solar metallicity, to suppress strong molecular features in the
near- and mid-infrared. However, star spots, which are known to be present on
the hoststar's surface, can (partly) cancel out the expected variations in
planet-to-star size ratio, due to the lower surface temperature of the spots .
A hypothetical spot-fraction of 10% would be able to raise the infrared points
sufficiently with respect to the optical measurements to be inconsistent with a
water-dominated atmosphere. [abridged]Comment: 13 pages, 8 figures. Accepted for publication in A&
Production of antihydrogen at reduced magnetic field for anti-atom trapping
We have demonstrated production of antihydrogen in a 1T solenoidal
magnetic field. This field strength is significantly smaller than that used in
the first generation experiments ATHENA (3T) and ATRAP (5T). The
motivation for using a smaller magnetic field is to facilitate trapping of
antihydrogen atoms in a neutral atom trap surrounding the production region. We
report the results of measurements with the ALPHA (Antihydrogen Laser PHysics
Apparatus) device, which can capture and cool antiprotons at 3T, and then
mix the antiprotons with positrons at 1T. We infer antihydrogen production
from the time structure of antiproton annihilations during mixing, using mixing
with heated positrons as the null experiment, as demonstrated in ATHENA.
Implications for antihydrogen trapping are discussed
A novel antiproton radial diagnostic based on octupole induced ballistic loss
We report results from a novel diagnostic that probes the outer radial
profile of trapped antiproton clouds. The diagnostic allows us to determine the
profile by monitoring the time-history of antiproton losses that occur as an
octupole field in the antiproton confinement region is increased. We show
several examples of how this diagnostic helps us to understand the radial
dynamics of antiprotons in normal and nested Penning-Malmberg traps. Better
understanding of these dynamics may aid current attempts to trap antihydrogen
atoms
Daily and 3-hourly variability in global fire emissions and consequences for atmospheric model predictions of carbon monoxide
Attribution of the causes of atmospheric trace gas and aerosol variability often requires the use of high resolution time series of anthropogenic and natural emissions inventories. Here we developed an approach for representing synoptic-and diurnal-scale temporal variability in fire emissions for the Global Fire Emissions Database version 3 (GFED3). We disaggregated monthly GFED3 emissions during 2003-2009 to a daily time step using Moderate Resolution Imaging Spectroradiometer (MODIS)-derived measurements of active fires from Terra and Aqua satellites. In parallel, mean diurnal cycles were constructed from Geostationary Operational Environmental Satellite (GOES) Wildfire Automated Biomass Burning Algorithm (WF_ABBA) active fire observations. Daily variability in fires varied considerably across different biomes, with short but intense periods of daily emissions in boreal ecosystems and lower intensity (but more continuous) periods of burning in savannas. These patterns were consistent with earlier field and modeling work characterizing fire behavior dynamics in different ecosystems. On diurnal timescales, our analysis of the GOES WF_ABBA active fires indicated that fires in savannas, grasslands, and croplands occurred earlier in the day as compared to fires in nearby forests. Comparison with Total Carbon Column Observing Network (TCCON) and Measurements of Pollution in the Troposphere (MOPITT) column CO observations provided evidence that including daily variability in emissions moderately improved atmospheric model simulations, particularly during the fire season and near regions with high levels of biomass burning. The high temporal resolution estimates of fire emissions developed here may ultimately reduce uncertainties related to fire contributions to atmospheric trace gases and aerosols. Important future directions include reconciling top-down and bottom up estimates of fire radiative power and integrating burned area and active fire time series from multiple satellite sensors to improve daily emissions estimates
Daily and 3-hourly variability in global fire emissions and consequences for atmospheric model predictions of carbon monoxide
Attribution of the causes of atmospheric trace gas and aerosol variability often requires the use of high resolution time series of anthropogenic and natural emissions inventories. Here we developed an approach for representing synoptic-and diurnal-scale temporal variability in fire emissions for the Global Fire Emissions Database version 3 (GFED3). We disaggregated monthly GFED3 emissions during 2003-2009 to a daily time step using Moderate Resolution Imaging Spectroradiometer (MODIS)-derived measurements of active fires from Terra and Aqua satellites. In parallel, mean diurnal cycles were constructed from Geostationary Operational Environmental Satellite (GOES) Wildfire Automated Biomass Burning Algorithm (WF_ABBA) active fire observations. Daily variability in fires varied considerably across different biomes, with short but intense periods of daily emissions in boreal ecosystems and lower intensity (but more continuous) periods of burning in savannas. These patterns were consistent with earlier field and modeling work characterizing fire behavior dynamics in different ecosystems. On diurnal timescales, our analysis of the GOES WF_ABBA active fires indicated that fires in savannas, grasslands, and croplands occurred earlier in the day as compared to fires in nearby forests. Comparison with Total Carbon Column Observing Network (TCCON) and Measurements of Pollution in the Troposphere (MOPITT) column CO observations provided evidence that including daily variability in emissions moderately improved atmospheric model simulations, particularly during the fire season and near regions with high levels of biomass burning. The high temporal resolution estimates of fire emissions developed here may ultimately reduce uncertainties related to fire contributions to atmospheric trace gases and aerosols. Important future directions include reconciling top-down and bottom up estimates of fire radiative power and integrating burned area and active fire time series from multiple satellite sensors to improve daily emissions estimates
Compression of Antiproton Clouds for Antihydrogen Trapping
Control of the radial profile of trapped antiproton clouds is critical to
trapping antihydrogen. We report the first detailed measurements of the radial
manipulation of antiproton clouds, including areal density compressions by
factors as large as ten, by manipulating spatially overlapped electron plasmas.
We show detailed measurements of the near-axis antiproton radial profile and
its relation to that of the electron plasma
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