2,432 research outputs found
Modelling large-scale structures in the high-latitude ionosphere using 15 years of data from the EISCAT Svalbard Radar
The ionosphere is a highly complex plasma containing electron density structures with a wide range of spatial scale sizes. Large-scale structures with horizontal extents of tens to hundreds of km exhibit variation with time of day, season, solar cycle, geomagnetic activity, solar wind conditions, and location. Whilst the processes driving these large-scale structures are well understood, the relative importance of these driving processes is a fundamental, unanswered question. The large-scale structures can also cause smaller-scale irregularities that arise due to instability processes such as the gradient drift instability (GDI) and turbulence. These smaller scale structures can disrupt trans-ionospheric radio signals, including those used by Global Navigation Satellite Systems (GNSS). Statistical modelling techniques have been used to generate models of various measures of large-scale plasma structuring in the high-latitude ionosphere using 15 years of data gathered by the EISCAT Svalbard Radar. These models quantify the relative importance of the dominant driving processes in four time sectors (noon, dusk, midnight and dawn). In every sector the dominant process is the seasonal variation, and this difference is attributed to both the variation in the chemical composition of the atmosphere and the maintenance of the background ionosphere by photoionization in summer. Secondary processes vary with time sector, but include variations with the solar cycle, geomagnetic activity, and the strength, orientation and variation of the Interplanetary Magnetic Field. Geophysical variables are used as proxies for these physical processes. As data for the geophysical variables selected are available in real time, these models have the potential to make real time predictions of the amount of plasma structuring in the ionosphere for GNSS applications
Modulation of nightside polar patches by substorm activity
Results are presented from a multi-instrument study showing the influence of geomagnetic substorm activity on the spatial distribution of the high-latitude ionospheric plasma. Incoherent scatter radar and radio tomography measurements on 12 December 2001 were used to directly observe the remnants of polar patches in the nightside ionosphere and to investigate their characteristics. The patches occurred under conditions of IMF <I>B<sub>z</sub></I> negative and IMF <I>B<sub>y</sub></I> negative. They were attributed to dayside photoionisation transported by the high-latitude convection pattern across the polar cap and into the nighttime European sector. The patches on the nightside were separated by some 5&deg; latitude during substorm expansion, but this was reduced to some 2&deg; when the activity had subsided. The different patch separations resulted from the expansion and contraction of the high-latitude plasma convection pattern on the nightside in response to the substorm activity. The patches of larger separation occurred in the antisunward cross-polar flow as it entered the nightside sector. Those of smaller separation were also in antisunward flow, but close to the equatorward edge of the convection pattern, in the slower, diverging flow at the Harang discontinuity. A patch repetition time of some 10 to 30 min was estimated depending on the phase of the substorm
Multi-instrument observations of nightside plasma patches under conditions of IMF Bz positive
Results are presented from two multi-instrument case studies showing patches
of cold, long-lived plasma in the winter nightside ionosphere during times
when the z-component of the Interplanetary Magnetic Field (IMF Bz) was
positive. These enhancements were coincident with the antisunward convective
plasma drift, flowing from polar to nightside auroral latitudes. In the
first case, on 5 December 2005 with IMF By negative, two regions of
enhanced electron density were observed extended in MLT in the magnetic
midnight sector separated by lower densities near midnight. It is likely
that the earlier enhancement originated on the dayside near magnetic noon
and was transported to the nightside sector in the convective flow, whilst
the later feature originated in the morning magnetic sector. The lower
densities separating the two enhancements were a consequence of a pair of
lobe cells essentially blocking the direct antisunward cross polar flow from
the dayside. A second case study on 4 February 2006 with IMF By
positive revealed a single nightside enhancement likely to have originated
in the morning magnetic sector. These multi-instrument investigations,
incorporating observations by the EISCAT radar facility, the SuperDARN
network and radio tomography, reveal that plasma flowing from the dayside
can play a significant role in the nightside ionosphere under conditions of
IMF Bz positive. The observations are reinforced by simulations of
flux-tube transport and plasma decay
Fluidized Bed Polymer Particle ALD Process for Producing HDPE/Alumina Nanocomposites
Micron-sized High Density Polyethylene (HDPE) particles were coated with ultrathin alumina (Al2O3) films in a Fluidized Bed Reactor (FBR) by Atomic Layer Deposition (ALD) at 77 ºC. Al2O3 films on the HDPE particles were confirmed by different methods. These particles were extruded conventionally with the ceramic shells mixing intimately in the polymer matrix. The successful dispersion of the Al2O3 shells in the polymer matrix following extrusion was confirmed using cross sectional Transmission Electron Microscopy (TEM)
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Can the Heterosexual HIV Epidemic be Eliminated in South Africa Using Combination Prevention? A Modeling Analysis
Little is known about how combining efficacious HIV prevention interventions could lead to HIV elimination. We used an agent-based simulation model, the HIV Calibrated Dynamic Model (HIV-CDM), to assess the potential for HIV elimination in South Africa. We examined several scenarios (from continuation of current status quo to perfect targets) with differing combinations of male condoms, adult male circumcision, HIV testing, and early antiretroviral therapy (ART). We varied parameters including: proportion of adult males circumcised, frequency of condom use in sex acts, HIV test acceptance, linkage to care, ART initiation criteria, ART suppression rates, and loss to follow up. Maintaining current levels of combination prevention will lead to increasing HIV incidence and prevalence while the perfect combination scenario is projected to eliminate HIV on a 50-year time scale from 2013 to 2063. Perfecting testing and treatment, without changing condom use or circumcision rates, resulted in 89% incidence reduction but not elimination. Universal adult male circumcision alone resulted in a 21% incidence reduction within 20 years. Substantial decreases in HIV incidence are possible from sufficient uptake of both primary prevention and ART, but with continuation of the status quo, HIV elimination in South Africa is unlikely within a 50-year time scale
Sustainability appraisal: Jack of all trades, master of none?
Sustainable development is a commonly quoted goal for decision making and supports a large number of other discourses. Sustainability appraisal has a stated goal of supporting decision making for sustainable development. We suggest that the inherent flexibility of sustainability appraisal facilitates outcomes that often do not adhere to the three goals enshrined in most definitions of sustainable development: economic growth, environmental protection and enhancement, and the wellbeing of the human population. Current practice is for sustainable development to be disenfranchised through the interpretation of sustainability, whereby the best alternative is good enough even when unsustainable. Practitioners must carefully and transparently review the frameworks applied during sustainability appraisal to ensure that outcomes will meet the three goals, rather than focusing on a discourse that emphasises one or more goals at the expense of the other(s)
LSST Science Book, Version 2.0
A survey that can cover the sky in optical bands over wide fields to faint
magnitudes with a fast cadence will enable many of the exciting science
opportunities of the next decade. The Large Synoptic Survey Telescope (LSST)
will have an effective aperture of 6.7 meters and an imaging camera with field
of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over
20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with
fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a
total point-source depth of r~27.5. The LSST Science Book describes the basic
parameters of the LSST hardware, software, and observing plans. The book
discusses educational and outreach opportunities, then goes on to describe a
broad range of science that LSST will revolutionize: mapping the inner and
outer Solar System, stellar populations in the Milky Way and nearby galaxies,
the structure of the Milky Way disk and halo and other objects in the Local
Volume, transient and variable objects both at low and high redshift, and the
properties of normal and active galaxies at low and high redshift. It then
turns to far-field cosmological topics, exploring properties of supernovae to
z~1, strong and weak lensing, the large-scale distribution of galaxies and
baryon oscillations, and how these different probes may be combined to
constrain cosmological models and the physics of dark energy.Comment: 596 pages. Also available at full resolution at
http://www.lsst.org/lsst/sciboo
Broad targeting of resistance to apoptosis in cancer
Apoptosis or programmed cell death is natural way of removing aged cells from the body. Most of the anti-cancer therapies trigger apoptosis induction and related cell death networks to eliminate malignant cells. However, in cancer, de-regulated apoptotic signaling, particularly the activation of an anti-apoptotic systems, allows cancer cells to escape this program leading to uncontrolled proliferation resulting in tumor survival, therapeutic resistance and recurrence of cancer. This resistance is a complicated phenomenon that emanates from the interactions of various molecules and signaling pathways. In this comprehensive review we discuss the various factors contributing to apoptosis resistance in cancers. The key resistance targets that are discussed include (1) Bcl-2 and Mcl-1 proteins; (2) autophagy processes; (3) necrosis and necroptosis; (4) heat shock protein signaling; (5) the proteasome pathway; (6) epigenetic mechanisms; and (7) aberrant nuclear export signaling. The shortcomings of current therapeutic modalities are highlighted and a broad spectrum strategy using approaches including (a) gossypol; (b) epigallocatechin-3-gallate; (c) UMI-77 (d) triptolide and (e) selinexor that can be used to overcome cell death resistance is presented. This review provides a roadmap for the design of successful anti-cancer strategies that overcome resistance to apoptosis for better therapeutic outcome in patients with cancer
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