19,009 research outputs found
Characteristics and Evolution of the Magnetic field and Chromospheric Emission in an Active Region Core Observed by Hinode
We describe the characteristics and evolution of the magnetic field and
chromospheric emission in an active region core observed by the Solar Optical
Telescope on Hinode. Consistent with previous studies, we find that the moss is
unipolar, the spatial distribution of magnetic flux evolves slowly, and the
magnetic field is only moderately inclined. We show that the field line
inclination and horizontal component are coherent, and that the magnetic field
is mostly sheared in the inter-moss regions where the highest magnetic flux
variability is seen. Using extrapolations from SP magnetograms we show that the
magnetic connectivity in the moss is different than in the quiet Sun because
most of the magnetic field extends to significant coronal heights. The magnetic
flux, field vector, and chromospheric emission in the moss also appear highly
dynamic, but actually show only small scale variations in magnitude on
time-scales longer than the cooling times for hydrodynamic loops computed from
our extrapolations, suggesting high-frequency (continuous) heating events. Some
evidence is found for flux (Ca 2 intensity) changes on the order of 100--200 G
(DN) on time-scales of 20--30 mins that could be taken as indicative of
low-frequency heating. We find, however, that only a small fraction (10%) of
our simulated loops would be expected to cool on these time-scales, and we find
no clear evidence that the flux changes consistently produce intensity changes
in the chromosphere. The magnetic flux and chromospheric intensity in most
individual SOT pixels in the moss vary by less than ~ 20% and ~ 10%,
respectively, on loop cooling time-scales. In view of the high energy
requirements of the chromosphere, we suggest that these variations could be
sufficient for the heating of `warm' EUV loops, but that the high basal levels
may be more important for powering the hot core loops rooted in the moss.Comment: Accepted by ApJ, 16 pages, 20 figures. Abridged abstract (original is
in PDF file). Figures 1 & 2 are reduced resolution to meet size limit
Evidence for Steady Heating: Observations of an Active Region Core with Hinode and TRACE
Previous observations have not been able to exclude the possibility that high
temperature active region loops are actually composed of many small scale
threads that are in various stages of heating and cooling and only appear to be
in equilibrium. With new observations from the EUV Imaging Spectrometer (EIS)
and X-ray Telescope (XRT) on \textit{Hinode} we have the ability to investigate
the properties of high temperature coronal plasma in extraordinary detail. We
examine the emission in the core of an active region and find three independent
lines of evidence for steady heating. We find that the emission observed in XRT
is generally steady for hours, with a fluctuation level of approximately 15% in
an individual pixel. Short-lived impulsive heating events are observed, but
they appear to be unrelated to the steady emission that dominates the active
region. Furthermore, we find no evidence for warm emission that is spatially
correlated with the hot emission, as would be expected if the high temperature
loops are the result of impulsive heating. Finally, we also find that
intensities in the "moss", the footpoints of high temperature loops, are
consistent with steady heating models provided that we account for the local
expansion of the loop from the base of the transition region to the corona. In
combination, these results provide strong evidence that the heating in the core
of an active region is effectively steady, that is, the time between heating
events is short relative to the relevant radiative and conductive cooling
times.Comment: Minor changes based on the final report from the referee; Movies are
available from the first autho
Constraints on dark and visible mass in galaxies from strong gravitational lensing
We give a non-exhaustive review of the use of strong gravitational lensing in
placing constraints on the quantity of dark and visible mass in galaxies. We
discuss development of the methodology and summarise some recent results.Comment: To appear in proceedings of IAU Symposium 244, 'Dark Galaxies and
Lost Baryons', 25th - 29th June 2007. Nine pages, five figures. Version 2
updates bibliograph
Continuous upflows and sporadic downflows observed in active regions
We present a study of the temporal evolution of coronal loops in active
regions and its implications for the dynamics in coronal loops. We analyzed
images of the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics
Observatory (SDO) at multiple temperatures to detect apparent motions in the
coronal loops. Quasi-periodic brightness fluctuations propagate upwards from
the loop footpoint in hot emission at 1MK, while sporadic downflows are seen in
cool emission below 1MK. The upward motion in hot emission increases just after
the cool downflows. The apparent propagating pattern suggests a hot upflow from
the loop footpoints, and is considered to supply hot plasma into the coronal
loop, but a wavelike phenomenon cannot be ruled out. Coronal condensation
occasionally happens in the coronal loop, and the cool material flows down to
the footpoint. Emission from cool plasma could have a significant contribution
to hot AIA channels in the event of coronal condensation.Comment: 5 pages, 6 figures, A&A in pres
Establishing a Connection Between Active Region Outflows and the Solar Wind: Abundance Measurements with EIS/Hinode
One of the most interesting discoveries of the X-ray Telescope and EUV
Imaging Spectrometer (EIS) on board the Hinode solar observatory is the
presence of persistent high temperature high speed outflows from the edges of
active regions. Measurements by EIS indicate that the outflows reach velocities
of 50 km/s with spectral line asymmetries approaching 200 km/s. It has been
suggested that these outflows may lie on open field lines that connect to the
heliosphere, and that they could potentially be a significant source of the
slow speed solar wind. A direct link has been difficult to establish, however.
In this letter, we use EIS measurements of spectral line intensities that are
sensitive to changes in the relative abundance of Si and S as a result of the
first ionization potential (FIP) effect, to measure the chemical composition in
the outflow regions of AR 10978 over a period of 5 days in December 2007. We
find that Si is always enhanced over S by a factor of 3--4. This is generally
consistent with the enhancement factor of low FIP elements measured in-situ in
the slow solar wind by non-spectroscopic methods. Plasma with a slow wind-like
composition was therefore flowing from the edge of the active region for at
least 5 days. Furthermore, on December 10--11, when the outflow from the
western side was favorably oriented in the Earth direction, the Si/S ratio was
found to match the value measured a few days later by ACE/SWICS. These results
provide strong observational evidence for a direct connection between the solar
wind, and the coronal plasma in the outflow regions.Comment: Version to be published in ApJ
Evidence of Impulsive Heating in Active Region Core Loops
Using a full spectral scan of an active region from the Extreme-Ultraviolet
Imaging Spectrometer (EIS) we have obtained Emission Measure EM
distributions in two different moss regions within the same active region. We
have compared these with theoretical transition region EMs derived for three
limiting cases, namely \textit{static equilibrium}, \textit{strong
condensation} and \textit{strong evaporation} from \cite{ebtel}. The EM
distributions in both the moss regions are strikingly similar and show a
monotonically increasing trend from . Using
photospheric abundances we obtain a consistent EM distribution for all ions.
Comparing the observed and theoretical EM distributions, we find that the
observed EM distribution is best explained by the \textit{strong condensation}
case (EM), suggesting that a downward enthalpy flux plays an important
and possibly dominant role in powering the transition region moss emission. The
downflows could be due to unresolved coronal plasma that is cooling and
draining after having been impulsively heated. This supports the idea that the
hot loops (with temperatures of 3{-}5 MK) seen in the core of active regions
are heated by nanoflares.Comment: 17 pages, 4 figures, Accepted for publication in The Astrophysical
Journa
The design, development and characterization of a self-replicating DNA expression technology
High quality T-cell immunogenicity can be an elusive type of immunity to generate and one that is often sought after by virologists, immunologists and cancer researchers alike. When T-cell immunity is generated using current methodologies the quality and magnitude of the immunological response achieved is often weak and unable to create protective immunity. Among current methods, DNA vaccines, generate highly specific T-cell immunity towards targeted antigens, and do not suffer from issues like misdirected vector targeted immunity, like viral based vectors. DNA vaccines, however, face a variety of their own weaknesses. These include, inefficient delivery, high biological loss inside the body, and the inability to counteract or avoid immediate innate cellular defence mechanisms, which limit their ability to persist inside a host cell. For these reasons, DNA vaccines are usually combined with more conventional viral vaccines in what is known as a DNA prime and viral boost regiment strategy. Combining them works well and results in improved immunity towards targeted antigens that is superior to what is obtained when either DNA or recombinant vaccines are used alone. To address many of the core issues faced by DNA vaccines, I report here on the design, development and characterization of a self-replication DNA gene expression technology. This novel DNA expression system employs a form of DNA replication (known as rolling circle replication) to generate a self-replicating DNA amplicon that can amplify its own copy number and the relative localised levels of antigen expression inside transfected mammalian cells in tissue culture and within Balb/cJ mice. These capabilities help effectively mitigate many of the core issues faced by DNA vaccines. The technology developed was shown to significantly increase gene expression for eGFP and Luciferase reporter genes, with an overall average increase in expression of approximately two-fold by 48 h post transfection in HeLa S3 cells. More specifically, an increase of at least two-fold in the absolute maximum level of the gene of interest per cell was also observed. Such localised doubling in antigen expression, at the cellular level, is believed to enhance innate immune activation and improve the overall immune response. Experimental results indicated that gene expression levels by this technology is non static in nature and appears to increase in magnitude within affected cells over time as was hypothesised. This provided strong evidence that the replication technology appears to be functioning as was expected and was able to demonstrate the ability to elevate antigen expression over time, potentially starting from extremely low and otherwise ineffective starting concentrations. This ability has potential to effectively mitigate many of the issues associated DNA vaccines such as low and ineffective delivery. This capability was observed in tissue culture as a steady increase in reporter gene expression levels across the entire range of DNA transfection levels. Furthermore, the increases in gene expression were observed to continue to amplify over time, eliminating the presence of weakly fluorescing cells in tissue culture. By 11 days post transfection, every observable cell transfected with the replication expression system, was observed to have extremely high levels of fluorescence. With recorded fluorescence levels being as bright or brighter than the highest levels obtained under normal transfections with no replicative plasmids (~48-72 h). Unique cellular responses to the presence of the replicating gene expression technology were also observed. These included an apparent slowdown in cellular metabolic activity and growth among cells transfected with replicating vectors. This was observed as a decrease in cellular division and total cell number by ~50%, by 48 h post transfection. This was accompanied by significant increases in cell size, internal cellular granularity, and gene-of-interest expression per cell. These changes were observed among all cells regardless of their relative DNA transfection level. This was demonstrated by assessment of the change in the range, mean, median, skewness and standard deviation of the cellular distribution curves for eGFP expression, cell size and internal cellular granularity. These observations provided further evidence of the dynamically changing and active nature of this technology. This also provided evidence that the replicating gene expression technology has a definitively different kind of cellular impact and effect on transfected cells compared to non-replicating DNA expression systems. Pilot studies to test the technology in Balb/cJ mice indicated, the technology appears to be functional within this animal model and was able to increase gene of interest (eGFP) expression levels compared to an equivalent non-replicating DNA expression vector control. Furthermore, these animal experiments also demonstrated significant increases in the maximum possible level of expression achieved within localised ‘hot spots' of muscle fibre bundles. This effect appeared to increase following transient addition of additional replication associated protein (Rep), giving further evidence this technology appears to be functional within the Balb/cJ animal model. Suggesting that the rate at which the replication amplification process occurs, may also be manipulated by adjusting Rep concentration. Finally, an antiviral response gene array was run to look for evidence that the replicating gene expression technology could increases antiviral response gene activation, to possibly improve T-cell activation and immunity. The array provided evidence improved antiviral response gene activation was occurring however the data was inconclusive in nature and further investigation is needed to verify these preliminary findings. The array also showed significant evidence of Rep induced Caspase 10 (CASP10), gene suppression. This suggests that Rep may play a role in the survival and virulence ofBFDV by acting as a suppressor of cellular apoptosis in a concentration-dependant manner and is worth investigating further
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Understanding the Effects of Lactose Hydrolysis Modeling on the Main Oligosaccharides in Goat Milk Whey Permeate.
Enzymatic hydrolysis of lactose is a crucial step to improve the efficiency and selectivity of membrane-based separations toward the recovery of milk oligosaccharides free from simple sugars. Response surface methodology was used to investigate the effects temperature (25.9 to 54.1 °C) and amount of enzyme (0.17 to 0.32% w/w) at 1, 2, and 4 h of reaction on the efficiency of lactose hydrolysis by Aspergillus oryzae β-galactosidase, preservation of major goat whey oligosaccharides, and on the de-novo formation of oligosaccharides. Lactose hydrolysis above 99% was achieved at 1, 2, and 4 h, not being significantly affected by temperature and amount of enzyme within the tested conditions. Formation of 4 Hexose (Hex) and 4 Hex 1 Hex and an increased de-novo formation of 2 Hex 1 N-Acetyl-Neuraminic Acid (NeuAc) and 2 Hex 1 N-Glycolylneuraminic acid (NeuGc) was observed in all treatments. Overall, processing conditions using temperatures ≤40 °C and enzyme concentration ≤0.25% resulted in higher preservation/formation of goat whey oligosaccharides
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