1,171 research outputs found
Calculation of ionization equilibria for oxygen, neon, silicon, and iron
Ionization equilibria for iron, neon, oxygen, and silico
Molecular architecture of softwood revealed by solid-state NMR
Economically important softwood from conifers is mainly composed of the polysaccharides cellulose, galactoglucomannan and xylan, and the phenolic polymer, lignin. The interactions between these polymers lead to wood mechanical strength and must be overcome in biorefining. Here, we use 13C multidimensional solid-state NMR to analyse the polymer interactions in never-dried cell walls of the softwood, spruce. In contrast to some earlier softwood cell wall models, most of the xylan binds to cellulose in the two-fold screw conformation. Moreover, galactoglucomannan alters its conformation by intimately binding to the surface of cellulose microfibrils in a semi-crystalline fashion. Some galactoglucomannan and xylan bind to the same cellulose microfibrils, and lignin is associated with both of these cellulose-bound polysaccharides. We propose a model of softwood molecular architecture which explains the origin of the different cellulose environments observed in the NMR experiments. Our model will assist strategies for improving wood usage in a sustainable bioeconomy
A Tale of Two Systems: Principals’ Concerns with NCLB Testing and School Resource Availability
This study examined the patterns, and discrepancies regarding concerns of principals with NCLB annual testing and school resource availability. An ethnographic approach was used to determine the attitudes of eight middle school principals from high resource availability, average resource availability, and low resource availability. From the responses of the participants, one of the themes that emerged was concerns with NCLB testing. The patterns which emerged for concerns with NCLB testing were: stress, finances, and content. Principals from all resource groups other than high resources spoke in detail about the stress that they felt NCLB testing was creating within their schools. Principals from high resource schools spoke about the financial impact that NCLB testing brought upon their budgets. Principals from high and low resource schools spoke from different perspectives about their concerns with the content of annual state tests
Discovery of long-period variable stars in the very-metal-poor globular cluster M15
We present a search for long-period variable (LPV) stars among giant branch
stars in M15 which, at [Fe/H] ~ -2.3, is one of the most metal-poor Galactic
globular clusters. We use multi-colour optical photometry from the 0.6-m Keele
Thornton and 2-m Liverpool Telescopes. Variability of delta-V ~ 0.15 mag is
detected in K757 and K825 over unusually-long timescales of nearly a year,
making them the most metal-poor LPVs found in a Galactic globular cluster. K825
is placed on the long secondary period sequence, identified for metal-rich
LPVs, though no primary period is detectable. We discuss this variability in
the context of dust production and stellar evolution at low metallicity, using
additional spectra from the 6.5-m Magellan (Las Campanas) telescope. A lack of
dust production, despite the presence of gaseous mass loss raises questions
about the production of dust and the intra-cluster medium of this cluster.Comment: 13 pages, 9 figures, accepted by MNRA
Soft X-ray coronal spectra at low activity levels observed by RESIK
The quiet-Sun X-ray emission is important for deducing coronal heating
mechanisms, but it has not been studied in detail since the Orbiting Solar
Observatory (OSO) spacecraft era. Bragg crystal spectrometer X-ray observations
have generally concentrated on flares and active regions. The high sensitivity
of the RESIK (REntgenovsky Spectrometer s Izognutymi Kristalami) instrument on
the CORONAS-F solar mission has enabled the X-ray emission from the quiet
corona to be studied in a systematic way for the first time. Our aim is to
deduce the physical conditions of the non-flaring corona from RESIK line
intensities in several spectral ranges using both isothermal and multithermal
assumptions. We selected and analyzed spectra in 312 quiet-Sun intervals in
January and February 2003, sorting them into 5 groups according to activity
level. For each group, the fluxes in selected spectral bands have been used to
calculate values parameters for the best-fit that lead to a intensities
characteristic of each group. We used both isothermal and multitemperature
assumptions, the latter described by differential emission measure (DEM)
distributions. RESIK spectra cover the wavelength range (3.3-6.1 A). This
includes emission lines of highly ionized Si, S, Cl, Ar, and K, which are
suitable for evaluating temperature and emission measure, were used. The RESIK
spectra during these intervals of very low solar activity for the first time
provide information on the temperature structure of the quiet corona. Although
most of the emission seems to arise from plasma with a temperature between 2MK
and 3MK, there is also evidence of a hotter plasma (T approx. 10MK) with an
emission measure 3 orders smaller than the cooler component. Neither coronal
nor photospheric element abundances appear to describe the observed spectra
satisfactorily.Comment: Submitting 1 Latex and 7 figure file
Acute neuroinflammation induces AIS structural plasticity in a NOX2-dependent manner
Background Chronic microglia-mediated inflammation and oxidative stress are well-characterized underlying factors in neurodegenerative disease, whereby reactive inflammatory microglia enhance ROS production and impact neuronal integrity. Recently, it has been shown that during chronic inflammation, neuronal integrity is compromised through targeted disruption of the axon initial segment (AIS), the axonal domain critical for action potential initiation. AIS disruption was associated with contact by reactive inflammatory microglia which wrap around the AIS, increasing association with disease progression. While it is clear that chronic microglial inflammation and enhanced ROS production impact neuronal integrity, little is known about how acute microglial inflammation influences AIS stability. Here, we demonstrate that acute neuroinflammation induces AIS structural plasticity in a ROS-mediated and calpain-dependent manner. Methods C57BL/6J and NOX2−/− mice were given a single injection of lipopolysaccharide (LPS; 5 mg/kg) or vehicle (0.9% saline, 10 mL/kg) and analyzed at 6 h–2 weeks post-injection. Anti-inflammatory Didox (250 mg/kg) or vehicle (0.9% saline, 10 mL/kg) was administered beginning 24 h post-LPS injection and continued for 5 days; animals were analyzed 1 week post-injection. Microglial inflammation was assessed using immunohistochemistry (IHC) and RT-qPCR, and AIS integrity was quantitatively analyzed using ankyrinG immunolabeling. Data were statistically compared by one-way or two-way ANOVA where mean differences were significant as assessed using Tukey’s post hoc analysis. Results LPS-induced neuroinflammation, characterized by enhanced microglial inflammation and increased expression of ROS-producing enzymes, altered AIS protein clustering. Importantly, inflammation-induced AIS changes were reversed following resolution of microglial inflammation. Modulation of the inflammatory response using anti-inflammatory Didox, even after significant AIS disruption occurred, increased the rate of AIS recovery. qPCR and IHC analysis revealed that expression of microglial NOX2, a ROS-producing enzyme, was significantly increased correlating with AIS disruption. Furthermore, ablation of NOX2 prevented inflammation-induced AIS plasticity, suggesting that ROS drive AIS structural plasticity. Conclusions In the presence of acute microglial inflammation, the AIS undergoes an adaptive change that is capable of spontaneous recovery. Moreover, recovery can be therapeutically accelerated. Together, these findings underscore the dynamic capabilities of this domain in the presence of a pathological insult and provide evidence that the AIS is a viable therapeutic target
Active cool stars and He I 10830 \AA: the coronal connection
The mechanism of formation of the He I 10830 A triplet in cool stars has been
subject of debate for the last 30 years. A relation between the X-ray
luminosity and the He I 10830 A flux was found in cool stars, but the dominant
mechanism of formation in these stars (photoionization by coronal radiation
followed by recombination and cascade, or collisional excitation in the
chromosphere), has not yet been established. We use modern instrumentation
(NOT/SOFIN) and a direct measurement of the EUV flux, which photoionizes He I,
to investigate the formation mechanism of the line for the most active stars
which are frequently excluded from analysis. We have observed with an
unprecedented resolution (R~170,000) the He I 10830 A triplet in a set of 15
stars that were also observed with the Extreme Ultraviolet Explorer (EUVE) in
order to compare the line strengths with their EUV and X-ray fluxes. Active
dwarf and subgiant stars do not exhibit a relation between the EUV flux and the
equivalent width of the He I 10830 A line. Giant stars however, show a positive
correlation between the strength of the He I 10830 A absorption and the EUV and
X-ray fluxes. The strength of the C IV 1550 A emission does not correlate with
coronal fluxes in this sample of 15 stars. Active dwarf stars may have high
chromospheric densities thus allowing collisional excitation to dominate
photoionization/recombination processes in forming the He I 10830 A line.
Active giant stars possess lower gravities, and lower chromospheric densities
than dwarfs, allowing for photoexcitation processes to become important.
Moreover, their extended chromospheres allowfor scattering of infrared
continuum radiation, producing strong absorption in He I and tracing wind
dynamics.Comment: 9 pages, 12 figures. Accepted by A&A (June 2008
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