306 research outputs found
Phosphatidylinositol 3-kinase regulation of fluid phase endocytosis
AbstractEndocytosis of the fluid phase marker, horse radish peroxidase, into baby hamster kidney cells is inhibited by treatment of cells with the fungal metabolite wortmannin. The IC50 of approximately 5 nM is consistent with the well-described action of wortmannin upon phosphatidylinositol (PI) 3-kinase. Analysis of the kinetics of uptake indicates a > 50% decrease in the initial rate of marker internalisation, a concomitant decrease in the volume of the early endosome and an increased efficiency of recycling of that marker which is internalised. As PI 3-kinase binds to activated growth factor receptors our data suggest that receptor activation can be coupled to receptor internalisation (down regulation) by localising PI 3-kinase stimulation of endocytosis
ImageNet Large Scale Visual Recognition Challenge
The ImageNet Large Scale Visual Recognition Challenge is a benchmark in
object category classification and detection on hundreds of object categories
and millions of images. The challenge has been run annually from 2010 to
present, attracting participation from more than fifty institutions.
This paper describes the creation of this benchmark dataset and the advances
in object recognition that have been possible as a result. We discuss the
challenges of collecting large-scale ground truth annotation, highlight key
breakthroughs in categorical object recognition, provide a detailed analysis of
the current state of the field of large-scale image classification and object
detection, and compare the state-of-the-art computer vision accuracy with human
accuracy. We conclude with lessons learned in the five years of the challenge,
and propose future directions and improvements.Comment: 43 pages, 16 figures. v3 includes additional comparisons with PASCAL
VOC (per-category comparisons in Table 3, distribution of localization
difficulty in Fig 16), a list of queries used for obtaining object detection
images (Appendix C), and some additional reference
Frequency-stabilization to 6x10^-16 via spectral-hole burning
We demonstrate two-stage laser stabilization based on a combination of Fabry-
Perot and spectral-hole burning techniques. The laser is first pre-stabilized
by the Fabry-Perot cavity to a fractional-frequency stability of sigma_y(tau) <
10^-13. A pattern of spectral holes written in the absorption spectrum of
Eu3+:Y2SiO5 serves to further stabilize the laser to sigma_y(tau) = 6x10^-16
for 2 s < tau < 8 s. Measurements characterizing the frequency sensitivity of
Eu3+:Y2SiO5 spectral holes to environmental perturbations suggest that they can
be more frequency stable than Fabry-Perot cavities
Apoptosis at Inflection Point in Liquid Culture of Budding Yeasts
Budding yeasts are highly suitable for aging studies, because the number of bud
scars (stage) proportionally correlates with age. Its maximum stages are known
to reach at 20–30 stages on an isolated agar medium. However, their stage
dynamics in a liquid culture is virtually unknown. We investigate the population
dynamics by counting scars in each cell. Here one cell division produces one new
cell and one bud scar. This simple rule leads to a conservation law: “The
total number of bud scars is equal to the total number of cells.” We find
a large discrepancy: extremely fewer cells with over 5 scars than expected.
Almost all cells with 6 or more scars disappear within a short period of time in
the late log phase (corresponds to the inflection point). This discrepancy is
confirmed directly by the microscopic observations of broken cells. This finding
implies apoptosis in older cells (6 scars or more)
More questions than answers to the diagnosis and management of cauda equina syndrome-Authors' reply
No abstract available
Methane emissions from underground gas storage in California
Accurate and timely detection, quantification, and attribution of methane emissions from Underground Gas Storage (UGS) facilities is essential for improving confidence in greenhouse gas inventories, enabling emission mitigation by facility operators, and supporting efforts to assess facility integrity and safety. We conducted multiple airborne surveys of the 12 active UGS facilities in California between January 2016 and November 2017 using advanced remote sensing and in situ observations of near-surface atmospheric methane (CH₄). These measurements where combined with wind data to derive spatially and temporally resolved methane emission estimates for California UGS facilities and key components with spatial resolutions as small as 1–3 m and revisit intervals ranging from minutes to months. The study spanned normal operations, malfunctions, and maintenance activity from multiple facilities including the active phase of the Aliso Canyon blowout incident in 2016 and subsequent return to injection operations in summer 2017. We estimate that the net annual methane emissions from the UGS sector in California averaged between 11.0 ± 3.8 GgCH₄ yr⁻¹ (remote sensing) and 12.3 ± 3.8 GgCH₄ yr⁻¹ (in situ). Net annual methane emissions for the 7 facilities that reported emissions in 2016 were estimated between 9.0 ± 3.2 GgCH₄ yr⁻¹ (remote sensing) and 9.5 ± 3.2 GgCH₄ yr⁻¹ (in situ), in both cases around 5 times higher than reported. The majority of methane emissions from UGS facilities in this study are likely dominated by anomalous activity: higher than expected compressor loss and leaking bypass isolation valves. Significant variability was observed at different time-scales: daily compressor duty-cycles and infrequent but large emissions from compressor station blow-downs. This observed variability made comparison of remote sensing and in situ observations challenging given measurements were derived largely at different times, however, improved agreement occurred when comparing simultaneous measurements. Temporal variability in emissions remains one of the most challenging aspects of UGS emissions quantification, underscoring the need for more systematic and persistent methane monitoring
California’s methane super-emitters
Methane is a powerful greenhouse gas and is targeted for emissions mitigation by the US state of California and other jurisdictions worldwide. Unique opportunities for mitigation are presented by point-source emitters—surface features or infrastructure components that are typically less than 10 metres in diameter and emit plumes of highly concentrated methane. However, data on point-source emissions are sparse and typically lack sufficient spatial and temporal resolution to guide their mitigation and to accurately assess their magnitude4. Here we survey more than 272,000 infrastructure elements in California using an airborne imaging spectrometer that can rapidly map methane plumes. We conduct five campaigns over several months from 2016 to 2018, spanning the oil and gas, manure-management and waste-management sectors, resulting in the detection, geolocation and quantification of emissions from 564 strong methane point sources. Our remote sensing approach enables the rapid and repeated assessment of large areas at high spatial resolution for a poorly characterized population of methane emitters that often appear intermittently and stochastically. We estimate net methane point-source emissions in California to be 0.618 teragrams per year (95 per cent confidence interval 0.523–0.725), equivalent to 34–46 per cent of the state’s methane inventory for 2016. Methane ‘super-emitter’ activity occurs in every sector surveyed, with 10 per cent of point sources contributing roughly 60 per cent of point-source emissions—consistent with a study of the US Four Corners region that had a different sectoral mix. The largest methane emitters in California are a subset of landfills, which exhibit persistent anomalous activity. Methane point-source emissions in California are dominated by landfills (41 per cent), followed by dairies (26 per cent) and the oil and gas sector (26 per cent). Our data have enabled the identification of the 0.2 per cent of California’s infrastructure that is responsible for these emissions. Sharing these data with collaborating infrastructure operators has led to the mitigation of anomalous methane-emission activity
Spatiotemporal Patterns in Nest Box Occupancy by Tree Swallows Across North America
Data from the North American Breeding Bird Survey (BBS) suggest that populations of aerial insectivorous birds are declining, particularly in northeastern regions of the continent, and particularly since the mid-1980s. Species that use nest boxes, such as Tree Swallows (Tachycineta bicolor), may provide researchers with large data sets that better reveal finer-scale geographical patterns in population trends. We analyzed trends in occupancy rates for ca. 40,000 Tree Swallow nest-box-years from 16 sites across North America. The earliest site has been studied intensively since 1969 and the latest site since 2004. Nest box occupancy rates declined significantly at five of six (83%) sites east of -78° W longitude, whereas occupancy rates increased significantly at four of ten sites (40%) west of -78° W longitude. Decreasing box occupancy trends from the northeast were broadly consistent with aspects of a previous analysis of BBS data for Tree Swallows, but our finding of instances of increases in other parts of the continent are novel. Several questions remain, particularly with respect to causes of these broad-scale geographic changes in population densities of Tree Swallows. The broad geographic patterns are consistent with a hypothesis of widespread changes in climate on wintering, migratory, or breeding areas that in turn may differentially affect populations of aerial insects, but other explanations are possible. It is also unclear whether these changes in occupancy rates reflect an increase or decrease in overall populations of Tree Swallows. Regardless, important conservation steps will be to unravel causes of changing populations of aerial insectivores in North America
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