210 research outputs found
Genetic Basis for Thermal Tolerance in Two Different Strains of Rainbow Trout (Oncorhynchus mykiss): Case Western and Kamloops
This thesis examines the thermal tolerance based on how expression of Heat Shock Protein (HSP) 70 and HSP90 differ between two different strains of rainbow trout (Oncorhynchus mykiss), the Case Western strain and the Kamloops strain, and determines if cortisol levels affect HSP expression in red blood cells. The Case Western strain is considered the only warm water trout, only recently was any aspect of its thermal tolerance quantified. Porto (2012) determined critical thermal maxima (CTM) for the Case Western strain and found it to be about 0.15 °C higher than the Kamloops strain. This thesis is comprised of three chapters: (1) an introduction and literature review on the biological history of these two strains of rainbow trout, on studies related to HSPs expression as indicators of thermal tolerance, and studies on the relation between cortisol expression and HSPs expression; (2) an experimental study investigating the differences between HSP70 and HSP90 between the two strains, before and after a heat stress test and between individuals of different sizes; (3) an experimental study investigating the relation between the heat stress protein expression and cortisol levels pre- and post-stress. The results on the HSP70 and HSP90 relative expressions confirm that Case Western strain has higher thermal tolerance, highlighting the importance of this strain as a candidate to be cultured in aquaculture facilities as an answer to possible impacts of future climate changes. Earlier studies suggested HSP expression varied with age in rainbow trout, but failed to consider strain-specific differences. Our results show that age-specific HSPs expression is not species-specific in rainbow trout as it differs by strain. The results show that the plasma cortisol levels before and after thermal stress do not differ among strains, and that the physiological response to heat stress is species-specific. The variable that has the largest influence on the variance expressed among groups came from the HSP90 gene. We found the stressed Kamloops was the most diverse group, with less thermal tolerance, influenced mostly by the weight of the HSP90 on the total variance
X-ray flare modeling in the single giant HR 9024
We analyze a Chandra-HETGS observation of the single G-type giant HR 9024.
The high flux allows us to examine spectral line and continuum diagnostics at
high temporal resolution, to derive plasma parameters (thermal distribution,
abundances, temperature, ...). A time-dependent 1D hydrodynamic loop model with
semi-length 10cm (), and impulsive footpoint heating
triggering the flare, satisfactorily reproduces the observed evolution of
temperature and emission measure, derived from the analysis of the strong
continuum emission. The observed characteristics of the flare appear to be
common features in very large flares in active stars (also pre-main sequence
stars), possibly indicating some fundamental physics for these very dynamic and
extreme phenomena in stellar coronae.Comment: 2 pages, 4 figures. To be included in the proceedings of the 'X-ray
universe 2005 meeting' held in San Lorenzo de El Escorial (Spain), 26-30 Sep
200
Evidence of widespread hot plasma in a non-flaring coronal active region from Hinode/XRT
Nanoflares, short and intense heat pulses within spatially unresolved
magnetic strands, are now considered a leading candidate to solve the coronal
heating problem. However, the frequent occurrence of nanoflares requires that
flare-hot plasma be present in the corona at all times. Its detection has
proved elusive until now, in part because the intensities are predicted to be
very faint. Here we report on the analysis of an active region observed with
five filters by Hinode/XRT in November 2006. We have used the filter ratio
method to derive maps of temperature and emission measure both in soft and hard
ratios. These maps are approximate in that the plasma is assumed to be
isothermal along each line-of-sight. Nonetheless, the hardest available ratio
reveals the clear presence of plasma around 10 MK. To obtain more detailed
information about the plasma properties, we have performed Monte Carlo
simulations assuming a variety of non-isothermal emission measure distributions
along the lines-of-sight. We find that the observed filter ratios imply
bi-modal distributions consisting of a strong cool (log T ~ 6.3-6.5) component
and a weaker (few percent) and hotter (6.6 < log T < 7.2) component. The data
are consistent with bi-modal distributions along all lines of sight, i.e.,
throughout the active region. We also find that the isothermal temperature
inferred from a filter ratio depends sensitively on the precise temperature of
the cool component. A slight shift of this component can cause the hot
component to be obscured in a hard ratio measurement. Consequently, temperature
maps made in hard and soft ratios tend to be anti-correlated. We conclude that
this observation supports the presence of widespread nanoflaring activity in
the active region.Comment: 12 figures, accepted for publication on refereed journa
Comparison of Hinode/XRT and RHESSI detection of hot plasma in the non-flaring solar corona
We compare observations of the non-flaring solar corona made simultaneously
with Hinode/XRT and with RHESSI. The analyzed corona is dominated by a single
active region on 12 November 2006. The comparison is made on emission measures.
We derive emission measure distributions vs temperature of the entire active
region from multifilter XRT data. We check the compatibility with the total
emission measure values estimated from the flux measured with RHESSI if the
emission come from isothermal plasma. We find that RHESSI and XRT data analyses
consistently point to the presence of a minor emission measure component
peaking at log T ~ 6.8-6.9. The discrepancy between XRT and RHESSI results is
within a factor of a few and indicates an acceptable level of
cross-consistency.Comment: 12 pages, 3 figures, Letter accepted for publicatio
Spectroscopy of very hot plasma in non-flaring parts of a solar limb active region: spatial and temporal properties
In this work we investigate the thermal structure of an off-limb active
region in various non-flaring areas, as it provides key information on the way
these structures are heated. In particular, we concentrate in the very hot
component (>3 MK) as it is a crucial element to discriminate between different
heating mechanisms. We present an analysis using Fe and Ca emission lines from
both SOHO/SUMER and HINODE/EIS. A dataset covering all ionization stages from
Fe X to Fe XIX has been used for the thermal analysis (both DEM and EM). Ca XIV
is used for the SUMER-EIS radiometric cross-calibration.
We show how the very hot plasma is present and persistent almost everywhere
in the core of the limb AR. The off-limb AR is clearly structured in Fe XVIII.
Almost everywhere, the EM analysis reveals plasma at 10 MK (visible in Fe XIX
emission) which is down to 0.1% of EM of the main 3 MK plasma. We estimate the
power law index of the hot tail of the EM to be between -8.5 and -4.4. However,
we leave an open question on the possible existence of a small minor peak at
around 10 MK. The absence in some part of the AR of Fe XIX and Fe XXIII lines
(which fall into our spectral range) enables us to determine an upper limit on
the EM at such temperatures. Our results include a new Ca XIV 943.59 \AA~
atomic model
Temperature distribution of a non-flaring active region from simultaneous Hinode XRT and EIS observations
We analyze coordinated Hinode XRT and EIS observations of a non-flaring
active region to investigate the thermal properties of coronal plasma taking
advantage of the complementary diagnostics provided by the two instruments. In
particular we want to explore the presence of hot plasma in non-flaring
regions. Independent temperature analyses from the XRT multi-filter dataset,
and the EIS spectra, including the instrument entire wavelength range, provide
a cross-check of the different temperature diagnostics techniques applicable to
broad-band and spectral data respectively, and insights into cross-calibration
of the two instruments. The emission measure distribution, EM(T), we derive
from the two datasets have similar width and peak temperature, but show a
systematic shift of the absolute values, the EIS EM(T) being smaller than XRT
EM(T) by approximately a factor 2. We explore possible causes of this
discrepancy, and we discuss the influence of the assumptions for the plasma
element abundances. Specifically, we find that the disagreement between the
results from the two instruments is significantly mitigated by assuming
chemical composition closer to the solar photospheric composition rather than
the often adopted "coronal" composition (Feldman 1992). We find that the data
do not provide conclusive evidence on the high temperature (log T[K] >~ 6.5)
tail of the plasma temperature distribution, however, suggesting its presence
to a level in agreement with recent findings for other non-flaring regions.Comment: 14 pages, 15 figures. Accepted for publication in the Astrophysical
Journa
Reconnection nanojets in the solar corona
P.A. acknowledges STFC support from grant numbers ST/R004285/2 and ST/T000384/1 and support from the International Space Science Institute, Bern, Switzerland to the International Teams on ‘Implications for coronal heating and magnetic fields from coronal rain observations and modeling’ and ‘Observed Multi-Scale Variability of Coronal Loops as a Probe of Coronal Heating’. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 647214). P.T. was also supported by contracts 8100002705 and SP02H1701R from Lockheed-Martin to the Smithsonian Astrophysical Observatory (SAO), and NASA contract NNM07AB07C to the SAO.The solar corona is shaped and mysteriously heated to millions of degrees by the Sun’s magnetic field. It has long been hypothesized that the heating results from a myriad of tiny magnetic energy outbursts called nanoflares, driven by the fundamental process of magnetic reconnection. Misaligned magnetic field lines can break and reconnect, producing nanoflares in avalanche-like processes. However, no direct and unique observations of such nanoflares exist to date, and the lack of a smoking gun has cast doubt on the possibility of solving the coronal heating problem. From coordinated multi-band high-resolution observations, we report on the discovery of very fast and bursty nanojets, the telltale signature of reconnection-based nanoflares resulting in coronal heating. Using state-of-the-art numerical simulations, we demonstrate that the nanojet is a consequence of the slingshot effect from the magnetically tensed, curved magnetic field lines reconnecting at small angles. Nanojets are therefore the key signature of reconnection-based coronal heating in action.PostprintPeer reviewe
X-ray Flares of EV Lac: Statistics, Spectra, Diagnostics
We study the spectral and temporal behavior of X-ray flares from the active
M-dwarf EV Lac in 200 ks of exposure with the Chandra/HETGS. We derive flare
parameters by fitting an empirical function which characterizes the amplitude,
shape, and scale. The flares range from very short (<1 ks) to long (10 ks)
duration events with a range of shapes and amplitudes for all durations. We
extract spectra for composite flares to study their mean evolution and to
compare flares of different lengths. Evolution of spectral features in the
density-temperature plane shows probable sustained heating. The short flares
are significantly hotter than the longer flares. We determined an upper limit
to the Fe K fluorescent flux, the best fit value being close to what is
expected for compact loops.Comment: 9 pages; 9 figures; latex/emulateapj style; Submitted to The
Astrophysical Journa
Poly(ADP-ribosyl)ation is involved in the epigenetic control of TET1 gene transcription
TET enzymes are the epigenetic factors involved in the formation of the Sixth DNA base 5-hydroxymethylcytosine, whose deregulation has been associated with tumorigenesis. In particular, TET1 acts as tumor suppressor preventing cell proliferation and tumor metastasis and it has frequently been found down-regulated in cancer. Thus, considering the importance of a tight control of TET1 expression, the epigenetic mechanisms involved in the transcriptional regulation of TET1 gene are here investigated. The involvement of poly(ADP-ribosyl)ation in the control of DNA and histone methylation on TET1 gene was examined. PARP activity is able to positively regulate TET1 expression maintaining a permissive chromatin state characterized by DNA hypomethylation of TET1 CpG island as well as high levels of H3K4 trimethylation. These epigenetic modifications were affected by PAR depletion causing TET1 downregulation and in turn reduced recruitment of TET1 protein on HOXA9 target gene. In conclusion, this work shows that PARP activity is a transcriptional regulator of TET1 gene through the control of epigenetic events and it suggests that deregulation of these mechanisms could account for TET1 repression in cancer
Investigating the reliability of coronal emission measure distribution diagnostics using 3D radiative MHD simulations
Determining the temperature distribution of coronal plasmas can provide
stringent constraints on coronal heating. Current observations with the Extreme
ultraviolet Imaging Spectrograph onboard Hinode and the Atmospheric Imaging
Assembly onboard the Solar Dynamics Observatory provide diagnostics of the
emission measure distribution (EMD) of the coronal plasma.
Here we test the reliability of temperature diagnostics using 3D radiative
MHD simulations. We produce synthetic observables from the models, and apply
the Monte Carlo Markov chain EMD diagnostic. By comparing the derived EMDs with
the "true" distributions from the model we assess the limitations of the
diagnostics, as a function of the plasma parameters and of the signal-to-noise
of the data.
We find that EMDs derived from EIS synthetic data reproduce some general
characteristics of the true distributions, but usually show differences from
the true EMDs that are much larger than the estimated uncertainties suggest,
especially when structures with significantly different density overlap along
the line-of-sight. When using AIA synthetic data the derived EMDs reproduce the
true EMDs much less accurately, especially for broad EMDs. The differences
between the two instruments are due to the: (1) smaller number of constraints
provided by AIA data, (2) broad temperature response function of the AIA
channels which provide looser constraints to the temperature distribution.
Our results suggest that EMDs derived from current observatories may often
show significant discrepancies from the true EMDs, rendering their
interpretation fraught with uncertainty. These inherent limitations to the
method should be carefully considered when using these distributions to
constrain coronal heating.Comment: Accepted for publication on The Astrophysical Journal. 25 pages, 29
figures. Paper version with full resolution images and appendixes can be
found at: http://folk.uio.no/bdp/papers/3dEMD_ptesta.pd
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