1,216 research outputs found
Measuring snow cover using satellite imagery during 1973 and 1974 melt season: North Santiam, Boise, and Upper Snake Basins, phase 1
Measurements are examined of snow coverage during the snow-melt season in 1973 and 1974 from LANDSAT imagery for the three Columbia River Subbasins. Satellite derived snow cover inventories for the three test basins were obtained as an alternative to inventories performed with the current operational practice of using small aircraft flights over selected snow fields. The accuracy and precision versus cost for several different interactive image analysis procedures was investigated using a display device, the Electronic Satellite Image Analysis Console. Single-band radiance thresholding was the principal technique employed in the snow detection, although this technique was supplemented by an editing procedure involving reference to hand-generated elevation contours. For each data and view measured, a binary thematic map or "mask" depicting the snow cover was generated by a combination of objective and subjective procedures. Photographs of data analysis equipment (displays) are shown
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The Wolf-Rayet population of Westerlund 1
New NTT/SOFI near-IR narrow-band imaging and spectroscopy reveals an additional four Wolf-Rayet (WR) stars in the massive cluster Westerlund 1, bringing the total WR population to 24. Sixteen of the WR stars in Wd1 have been classified WN5–11, while eight are WC8–9. An observed WR to RSG/YHG ratio of ∼3 suggests an age of 4.5–5.0 Myr, with WR stars descended from 40–55MSolar progenitors. On the basis of dust and hard X-ray emission, we estimate that 40–65% are probable members of massive star binary systems
Mechanical properties of silicon nitride using RUS & C-Sphere methodology
Silicon Nitride is a type of engineering ceramics which has been used in ball bearing and other rolling contact applications due to its good fatigue life, high temperature strength and tribological performance. In this paper, the mechanical properties of Hot Isostatically Pressed (HIPed) and Sintered and Reaction Bonded Silion Nitride (SRBSN) have been studied. The elastic modulus and poisson’s ratio of three type of commerical grade HIPed silicon nitride, and groudn SRBSN with three surface condidtions were measured using a Resonance Ultrasound Spectroscopy (RUS). The RUS measurement reveals the variation of elastic properties across different types of HIPed silicon nitride specimens. The surface strength of silicon nitride are studied using a C-Sphere specimen, and the results show that different commercial grade HIPed silicon nitride show varying surface strength. The surface conditions of ground SRBSN have an effect on the surface strength of the specimens. The RUS and C-Sphere techniques can potentially be used to sample the quality and consistency of ball bearing elements
The influence of nonrandom extra-pair paternity on heritability estimates derived from wild pedigrees
Quantitative genetic analysis is often fundamental for understanding evolutionary processes in wild populations. Avian populations provide a model system due to the relative ease of inferring relatedness among individuals through observation. However, extra-pair paternity (EPP) creates erroneous links within the social pedigree. Previous work has suggested this causes minor underestimation of heritability if paternal misassignment is random and hence not influenced by the trait being studied. Nevertheless, much literature suggests numerous traits are associated with EPP and the accuracy of heritability estimates for such traits remains unexplored. We show analytically how nonrandom pedigree errors can influence heritability estimates. Then, combining empirical data from a large great tit (Parus major) pedigree with simulations, we assess how heritability estimates derived from social pedigrees change depending on the mode of the relationship between EPP and the focal trait. We show that the magnitude of the underestimation is typically small (<15%). Hence, our analyses suggest that quantitative genetic inference from pedigrees derived from observations of social relationships is relatively robust; our approach also provides a widely applicable method for assessing the consequences of nonrandom EPP
Long-distance entanglement-based quantum key distribution over optical fiber
We report the first entanglement-based quantum key distribution (QKD) experiment over a 100-km optical fiber. We used superconducting single photon detectors based on NbN nanowires that provide high-speed single photon detection for the 1.5-µm telecom band, an efficient entangled photon pair source that consists of a fiber coupled periodically poled lithium niobate waveguide and ultra low loss filters, and planar lightwave circuit Mach-Zehnder interferometers (MZIs) with ultra stable operation. These characteristics enabled us to perform an entanglement-based QKD experiment over a 100-km optical fiber. In the experiment, which lasted approximately 8 hours, we successfully generated a 16 kbit sifted key with a quantum bit error rate of 6.9 % at a rate of 0.59 bits per second, from which we were able to distill a 3.9 kbit secure key
Practical long-distance quantum key distribution system using decoy levels
Quantum key distribution (QKD) has the potential for widespread real-world
applications. To date no secure long-distance experiment has demonstrated the
truly practical operation needed to move QKD from the laboratory to the real
world due largely to limitations in synchronization and poor detector
performance. Here we report results obtained using a fully automated, robust
QKD system based on the Bennett Brassard 1984 protocol (BB84) with low-noise
superconducting nanowire single-photon detectors (SNSPDs) and decoy levels.
Secret key is produced with unconditional security over a record 144.3 km of
optical fibre, an increase of more than a factor of five compared to the
previous record for unconditionally secure key generation in a practical QKD
system.Comment: 9 page
A census of the Wolf-Rayet content in Westerlund 1 from near-infrared imaging and spectroscopy
New NTT/SOFI imaging and spectroscopy of the Wolf-Rayet population in
Westerlund 1 are presented. Narrow-band near-IR imaging together with follow up
spectroscopy reveals four new WR stars, of which three were independently
identified recently by Groh et al., bringing the confirmed WR content to 24 (23
excluding source S) [..] A quantitative near-IR spectral classification scheme
for WR stars is presented and applied to members of Westerlund 1. Late subtypes
are dominant, with no subtypes earlier than WN5 or WC8 for the nitrogen and
carbon sequences, respectively. A qualitative inspection of the WN stars
suggests that most (75%) are highly H-deficient. The WR binary fraction is high
(>62%), on the basis of dust emission from WC stars, in addition to a
significant WN binary fraction from hard X-ray detections according to Clark et
al. We exploit the large WN population of Westerlund 1 to reassess its distance
(~5.0kpc) and extinction (A_Ks ~ 0.96 mag), such that it is located at the edge
of the Galactic bar, [..]. The observed ratio of WR stars to red and yellow
hypergiants, N(WR)/N(RSG+YHG)~3, favours an age of 4.5-5.0 Myr, with individual
WR stars descended from progenitors of initial mass ~ 40-55 Msun. Qualitative
estimates of current masses for non-dusty, H-free WR stars are presented,
revealing 10-18 Msun, such that ~75% of the initial stellar mass has been
removed via stellar winds or close binary evolution. We present a revision to
the cluster turn-off mass for other Milky Way clusters in which WR stars are
known, based upon the latest temperature calibration for OB stars. Finally,
comparisons between the observed WR population and subtype distribution in
Westerlund 1 and instantaneous burst evolutionary synthesis models are
presented.Comment: 20 pages, 11 figures, accepted for MNRA
Levels of soluble fms-like tyrosine kinase one in first trimester and outcomes of pregnancy: a systematic review
Angiogenic factors are involved in formation of new blood vessels required for placental development and function; and critical for fetal growth and development. Soluble fms-like tyrosine kinase 1(sFlt-1) is an anti-angiogenic protein that inhibits formation of new blood vessels resulting in potential pregnancy complications. The objective of this study was to undertake a systematic review to assess levels of sFlt-1 in early pregnancy and association with adverse pregnancy outcomes. PubMed and Medline databases and reference lists were searched up to July 2010. Inclusion criteria were pregnant women, blood sample taken during first trimester and assessment/reporting of sFlt-1 concentrations and subsequent pregnancy complications. Twelve relevant studies were identified of 71 to 668 women. No pooling of results was undertaken due to variation in sFlt-1 concentrations (range, 166-6,349 pg/ml amongst controls), samples used (serum, plasma), different summary statistics (mean, median, odds ratio) and outcome definitions applied. Levels of sFlt-1 were generally higher among women who developed preeclampsia (11 studies) or gestational hypertension (two studies), but not significantly different to normotensive women in most studies. There was no consistent pattern in association between sFlt-1 concentrations and fetal growth restriction (4 studies); and levels were non-significantly higher for women with postpartum bleeding (1 study) and significantly lower for stillbirths (1 study).This review found no clear evidence of an association between sFlt-1 levels in first trimester and adverse pregnancy outcomes. However, findings were affected by methodological, biological and testing variations between studies; highlighting the need for consistent testing of new biomarkers and reporting of outcome measures
Anticancer phototherapy using activation of E-combretastatins by two-photon–induced isomerization
The photoisomerization of relatively nontoxic E-combretastatins to clinically active Z-isomers is
shown to occur in solution through both one- and two-photon excitations at 340 and 625 nm, respectively.
The photoisomerization is also demonstrated to induce mammalian cell death by a two-photon absorption process
at 625 nm. Unlike conventional photodynamic therapy (PDT), the mechanism of photoisomerization is oxygen-
independent and active in hypoxic environments such as in tumors. The use of red or near-infrared (NIR)
light for two-photon excitation allows greater tissue penetration than conventional UV one-photon excitation. The
results provide a baseline for the development of a novel phototherapy that overcomes nondiscriminative
systemic toxicity of Z-combretastatins and the limitations of PDT drugs that require the presence of oxygen
to promote their activity, with the added benefits of two-photon red or NIR excitation for deeper tissue penetration
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