9,021 research outputs found
Correlation between fracture surface morphology and toughness in Zr-based bulk metallic glasses
Fracture surfaces of Zr-based bulk metallic glasses of various compositions tested in the as-cast and annealed conditions were analyzed using scanning electron microscopy. The tougher samples have shown highly jagged patterns at the beginning stage of crack propagation, and the length and roughness of this jagged pattern correlate well with the measured fracture toughness values. These jagged patterns, the main source of energy dissipation in the sample, are attributed to the formation of shear bands inside the sample. This observation provides strong evidence of significant “plastic zone” screening at the crack tip
The distribution of Polychlorinated Biphenyls (PCBs) in the River Thames Catchment under the scenarios of climate change
Measurements have shown low levels of PCBs in water but relatively high concentrations in the resident fish of the River Thames (UK). To better understand the distribution and behaviour of PCBs in the Thames river basin and their potential risks, a level III fugacity model was applied to selected PCB congeners (PCB 52, PCB 118 and PCB 153). The modelling results indicated that fish and sediments represent environmental compartments with the highest PCB concentrations; but the greatest mass of PCBs (over 70%) is likely to remain in the soil. As emissions decline, soil could then act as a significant secondary source of PCBs with the river bed-sediment functioning as a long-term reservoir of PCBs. The predicted changes in temperature and rainfall forecast in the UK Climate Projections 2009 (UKCP09) over the next 80 years had only a modest influence on PCB fate in the model. The most significant result was a tendency for climate change to enhance the evaporation of PCBs from soil to air in the Thames catchment. (C) 2015 Elsevier B.V. All rights reserved
Retired A Stars and Their Companions: Exoplanets Orbiting Three Intermediate-Mass Subgiants
We report precision Doppler measurements of three intermediate-mass subgiants
from Lick and Keck Observatories. All three stars show variability in their
radial velocities consistent with planet-mass companions in Keplerian orbits.
We find a planet with a minimum mass of 2.5 Mjup in a 351.5 day orbit around HD
192699, a planet with a minimum mass of 2.0 Mjup in a 341.1 day orbit around HD
210702, and a planet with a minimum mass of 0.61 Mjup in a 297.3 day orbit
around HD 175541. Stellar mass estimates from evolutionary models indicate that
all of these stars were formerly A-type dwarfs with masses ranging from 1.65 to
1.85 Msun. These three long-period planets would not have been detectable
during their stars' main-sequence phases due to the large rotational velocities
and stellar jitter exhibited by early-type dwarfs. There are now 9 "retired"
(evolved) A-type stars (Mstar > 1.6 Msun) with known planets. All 9 planets
orbit at distances a \geq 0.78 AU, which is significantly different than the
semimajor axis distribution of planets around lower-mass stars. We examine the
possibility that the observed lack of close-in planets is due to engulfment by
their expanding host stars, but we find that this explanation is inadequate
given the relatively small stellar radii of K giants (Rstar < 32 Rsun = 0.15
AU) and subgiants (Rstar < 7 Rsun = 0.03 AU). Instead, we conclude that planets
around intermediate-mass stars reside preferentially beyond ~0.8 AU, which may
be a reflection of different formation and migration histories of planets
around A-type stars.Comment: 31 pages, 9 figures, 6 tables, ApJ accepted, corrected minor typo
Oxidation of tertiary amine-derivatized surfaces to control protein adhesion
Selective oxidation of omega-tertiary amine self-assembled thiol monolayers to tertiary amine N-oxides is shown to transform the adhesion of model proteins lysozyme and fibrinogen upon them. Efficient preparation of both secondary and tertiary linker amides as judged by X-ray photoelectron spectroscopy (XPS) and water droplet contact angle was achieved with an improved amide bond formation on gold quartz crystal microbalance (QCM) sensors using 2-(1H-7-azabenzotriazol-1-yl)-1,1,3,3-tetramethyl hexafluorophosphate methanaminium uronium (HATU). Oxidation with hydrogen peroxide was similarly assessed, and adhesion of lysozyme and fibrinogen from phosphate buffered saline was then assayed by QCM and imaged by AFM. Tertiary amine-functionalized sensors adsorbed multilayers of aggregated lysozyme, whereas tertiary amine N-oxides and triethylene glycol-terminated monolayers are consistent with small protein aggregates. The surface containing a dimethylamine N-oxide headgroup and ethyl secondary amide linker showed the largest difference in adsorption of both proteins. Oxidation of tertiary amine decorated surfaces therefore holds the potential for selective deposition of proteins and cells through masking and other patterning techniques
Prototype finline-coupled TES bolometers for CLOVER
CLOVER is an experiment which aims to detect the signature of gravitational
waves from inflation by measuring the B-mode polarization of the cosmic
microwave background. CLOVER consists of three telescopes operating at 97, 150,
and 220 GHz. The 97-GHz telescope has 160 feedhorns in its focal plane while
the 150 and 220-GHz telescopes have 256 horns each. The horns are arranged in a
hexagonal array and feed a polarimeter which uses finline-coupled TES
bolometers as detectors. To detect the two polarizations the 97-GHz telescope
has 320 detectors while the 150 and 220-GHz telescopes have 512 detectors each.
To achieve the target NEPs (1.5, 2.5, and 4.5x10^-17 W/rtHz) the detectors are
cooled to 100 mK for the 97 and 150-GHz polarimeters and 230 mK for the 220-GHz
polarimeter. Each detector is fabricated as a single chip to ensure a 100%
operational focal plane. The detectors are contained in linear modules made of
copper which form split-block waveguides. The detector modules contain 16 or 20
detectors each for compatibility with the hexagonal arrays of horns in the
telescopes' focal planes. Each detector module contains a time-division SQUID
multiplexer to read out the detectors. Further amplification of the multiplexed
signals is provided by SQUID series arrays. The first prototype detectors for
CLOVER operate with a bath temperature of 230 mK and are used to validate the
detector design as well as the polarimeter technology. We describe the design
of the CLOVER detectors, detector blocks, and readout, and present preliminary
measurements of the prototype detectors performance.Comment: 4 pages, 6 figures; to appear in the Proceedings of the 17th
International Symposium on Space Terahertz Technology, held 10-12 May 2006 in
Pari
Development and evaluation of mosquito-electrocuting traps as alternatives to the human landing catch technique for sampling host-seeking malaria vectors
Background
The human landing catch (HLC) is the gold standard method for sampling host-seeking malaria vectors. However, the HLC is ethically questionable because it requires exposure of humans to potentially infectious mosquito bites.
Methods
Two exposure-free methods for sampling host-seeking mosquitoes were evaluated using electrocuting surfaces as potential replacements for HLC: (1) a previously evaluated, commercially available electrocuting grid (CA-EG) designed for killing flies, and (2) a custom-made mosquito electrocuting trap (MET) designed to kill African malaria vectors. The MET and the CA-EG were evaluated relative to the HLC in a Latin Square experiment conducted in the Kilombero Valley, Tanzania. The sampling consistency of the traps across the night and at varying mosquito densities was investigated. Estimates of the proportion of mosquitoes caught indoors (P i ), proportion of human exposure occurring indoors (π i ), and proportion of mosquitoes caught when most people are likely to be indoors (P fl ) were compared for all traps.
Results
Whereas the CA-EG performed poorly (<10 % of catch of HLC), sampling efficiency of the MET for sampling Anopheles funestus s.l. was indistinguishable from HLC indoors and outdoors. For Anopheles gambiae s.l., sampling sensitivity of MET was 20.9 % (95 % CI 10.3–42.2) indoors and 58.5 % (95 % CI 32.2–106.2) outdoors relative to HLC. There was no evidence of density-dependent sampling by the MET or CA-EG. Similar estimates of P i were obtained for An. gambiae s.l. and An. funestus s.l. from all trapping methods. The proportion of mosquitoes caught when people are usually indoors (P fl ) was underestimated by the CA-EG and MET for An. gambiae s.l., but similar to the HLC for An. funestus. Estimates of the proportion of human exposure occurring indoors (π i ) obtained from the CA-EG and MET were similar to the HLC for An. gambiae s.l., but overestimated for An. funestus.
Conclusions
The MET showed promise as an outdoor sampling tool for malaria vectors where it achieved >50 % sampling sensitivity relative to the HLC. The CA-EG had poor sampling sensitivity outdoors and inside. With further modification, the MET could provide an efficient and safer alternative to the HLC for the surveillance of mosquito vectors outdoors.
Keywords: Mosquito electrocuting trap; Human landing catch; Mosquito behaviour; Vector sampling tools; Outdoor biting; Malaria; Anopheles arabiensis ; Anopheles gambiae s.l.; Anopheles funestus s.l
Bayesian Accretion Modeling: Axisymmetric Equatorial Emission in the Kerr Spacetime
The Event Horizon Telescope (EHT) has produced images of two supermassive
black holes, Messier~87* (M 87*) and Sagittarius~A* (Sgr A*). The EHT
collaboration used these images to indirectly constrain black hole parameters
by calibrating measurements of the sky-plane emission morphology to images of
general relativistic magnetohydrodynamic (GRMHD) simulations. Here, we develop
a model for directly constraining the black hole mass, spin, and inclination
through signatures of lensing, redshift, and frame dragging, while
simultaneously marginalizing over the unknown accretion and emission
properties. By assuming optically thin, axisymmetric, equatorial emission near
the black hole, our model gains orders of magnitude in speed over similar
approaches that require radiative transfer. Using 2017 EHT M 87* baseline
coverage, we use fits of the model to itself to show that the data are
insufficient to demonstrate existence of the photon ring. We then survey
time-averaged GRMHD simulations fitting EHT-like data, and find that our model
is best-suited to fitting magnetically arrested disks, which are the favored
class of simulations for both M 87* and Sgr A*. For these simulations, the
best-fit model parameters are within of the true mass and within
for inclination. With 2017 EHT coverage and 1\% fractional
uncertainty on amplitudes, spin is unconstrained. Accurate inference of spin
axis position angle depends strongly on spin and electron temperature. Our
results show the promise of directly constraining black hole spacetimes with
interferometric data, but they also show that nearly identical images permit
large differences in black hole properties, highlighting degeneracies between
the plasma properties, spacetime, and most crucially, the unknown emission
geometry when studying lensed accretion flow images at a single frequency.Comment: Accepted to ApJ, 16 pages, 10 figure
Aspects of Type IIB Theory on ALE Spaces
D-brane technology and strong/weak coupling duality supplement traditional
orbifold techniques by making certain background geometries more accessible. In
this spirit, we consider some of the geometric properties of the type IIB
theory on R^6 \times M where M is an `Asymptotically Locally Euclidean (ALE)'
gravitational instanton. Given the self-duality of the theory, we can extract
the geometry (both singular and resolved) seen by the weakly coupled IIB string
by studying the physics of a D1-brane probe. The construction is both amusing
and instructive, as the physics of the probe completely captures the
mathematics of the construction of ALE instantons via `HyperKahler Quotients',
as presented by Kronheimer. This relation has been noted by Douglas and Moore
for the A-series. We extend the explicit construction to the case of the D- and
E-series -- uncovering a quite beautiful structure -- and highlight how all of
the elements of the mathematical construction find their counterparts in the
physics of the type IIB D-string. We discuss the explicit ALE metrics which may
be obtained using these techniques, and comment on the role duality plays in
relating gauged linear sigma models to conformal field theories.Comment: 27 pages, three figures. Uses harvmac.tex and epsf.tex (sentences
corrected on pages 13+14, reference added, small addition to final remarks
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