291 research outputs found
Comparison of the sidereal angular velocity of subphotospheric layers and small bright coronal structures during the declining phase of solar cycle 23
Context. We compare solar differential rotation of subphotospheric layers
derived from local helioseismology analysis of GONG++ dopplergrams and the one
derived from tracing small bright coronal structures (SBCS) using EIT/SOHO
images for the period August 2001 - December 2006, which correspond to the
declining phase of solar cycle 23. Aims. The study aims to find a relationship
between the rotation of the SBCS and the subphotospheric angular velocity. The
northsouth asymmetries of both rotation velocity measurements are also
investigated. Methods. Subphotospheric differential rotation was derived using
ring-diagram analysis of GONG++ full-disk dopplergrams of 1 min cadence. The
coronal rotation was derived by using an automatic method to identify and track
the small bright coronal structures in EIT full-disk images of 6 hours cadence.
Results. We find that the SBCS rotate faster than the considered upper
subphotospheric layer (3Mm) by about 0.5 deg/day at the equator. This result
joins the results of several other magnetic features (sunspots, plages,
faculae, etc.) with a higher rotation than the solar plasma. The rotation rate
latitudinal gradients of the SBCS and the subphotospheric layers are very
similar. The SBCS motion shows an acceleration of about 0.005 deg/day/month
during the declining phase of solar cycle 23, whereas the angular velocity of
subsurface layers does not display any evident variation with time, except for
the well known torsional oscillation pattern. Finally, both subphotospheric and
coronal rotations of the southern hemisphere are predominantly larger than
those of the northern hemisphere. At latitudes where the north-south asymmetry
of the angular velocity increases (decreases) with activity for the SBCS, it
decreases (increases) for subphotospheric layers.Comment: 6pages, 8 figures, Accepted for publication in Astronomy and
Astrophysic
Strategy for Dynamic Wisp Removal in James Webb Space Telescope NIRCam Images
The James Webb Space Telescope (JWST) near-infrared camera (NIRCam) has been
found to exhibit serious wisp-like structures in four of its eight
short-wavelength detectors. The exact structure and strength of these wisps is
highly variable with the position and orientation of JWST, so the use of static
templates is non-optimal. Here we investigate a dynamic strategy to mitigate
these wisps using long-wavelength reference images. Based on a suite of
experiments where we embed a worst-case scenario median-stacked wisp into
wisp-free images, we define suitable parameters for our wisp removal strategy.
Using this setup we re-process wisp-affected public Prime Extragalactic Areas
for Reionization and Lensing Science (PEARLS) data in the North Ecliptic Pole
Time Domain Field (NEP-TDF) field, resulting in significant visual improvement
in our detector frames and reduced noise in the final stacked images.Comment: 16 pages, 10 figures, submitted to PASP, comments welcom
Buoyancy-induced time delays in Babcock-Leighton flux-transport dynamo models
The Sun is a magnetic star whose cyclic activity is thought to be linked to
internal dynamo mechanisms. A combination of numerical modelling with various
levels of complexity is an efficient and accurate tool to investigate such
intricate dynamical processes. We investigate the role of the magnetic buoyancy
process in 2D Babcock-Leighton dynamo models, by modelling more accurately the
surface source term for poloidal field. Methods. To do so, we reintroduce in
mean-field models the results of full 3D MHD calculations of the non-linear
evolution of a rising flux tube in a convective shell. More specifically, the
Babcock-Leighton source term is modified to take into account the delay
introduced by the rise time of the toroidal structures from the base of the
convection zone to the solar surface. We find that the time delays introduced
in the equations produce large temporal modulation of the cycle amplitude even
when strong and thus rapidly rising flux tubes are considered. Aperiodic
modulations of the solar cycle appear after a sequence of period doubling
bifurcations typical of non-linear systems. The strong effects introduced even
by small delays is found to be due to the dependence of the delays on the
magnetic field strength at the base of the convection zone, the modulation
being much less when time delays remain constant. We do not find any
significant influence on the cycle period except when the delays are made
artificially strong. A possible new origin of the solar cycle variability is
here revealed. This modulated activity and the resulting butterfly diagram are
then more compatible with observations than what the standard Babcock-Leighton
model produces.Comment: 13 pages, 10 figures, accepted for publication in A&
Adenovirus Encoding Human Platelet-Derived Growth Factor-B Delivered to Alveolar Bone Defects Exhibits Safety and Biodistribution Profiles Favorable for Clinical Use
Abstract Platelet-derived growth factor (PDGF) gene therapy offers promise for tissue engineering of tooth-supporting alveolar bone defects. To date, limited information exists regarding the safety profile and systemic biodistribution of PDGF gene therapy vectors when delivered locally to periodontal osseous defects. The aim of this preclinical study was to determine the safety profile of adenovirus encoding the PDGF-B gene (AdPDGF-B) delivered in a collagen matrix to periodontal lesions. Standardized alveolar bone defects were created in rats, followed by delivery of matrix alone or containing AdPDGF-B at 5.5-108 or 5.5-109 plaque-forming units/ml. The regenerative response was confirmed histologically. Gross clinical observations, hematology, and blood chemistries were monitored to evaluate systemic involvement. Bioluminescence and quantitative polymerase chain reaction were used to assess vector biodistribution. No significant histopathological changes were noted during the investigation. Minor alterations in specific hematological and blood chemistries were seen; however, most parameters were within the normal range for all groups. Bioluminescence analysis revealed vector distribution at the axillary lymph nodes during the first 2 weeks with subsequent return to baseline levels. AdPDGF-B was well contained within the localized osseous defect area without viremia or distant organ involvement. These results indicate that AdPDGF-B delivered in a collagen matrix exhibits acceptable safety profiles for possible use in human clinical studies.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/78106/1/hum.2008.114.pd
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Pretreatment dietary intake is associated with tumor suppressor DNA methylation in head and neck squamous cell carcinomas
Diet is associated with cancer prognosis, including head and neck cancer (HNC), and has been hypothesized to influence epigenetic state by determining the availability of functional groups involved in the modification of DNA and histone proteins. The goal of this study was to describe the association between pretreatment diet and HNC tumor DNA methylation. Information on usual pretreatment food and nutrient intake was estimated via food frequency questionnaire (FFQ) on 49 HNC cases. Tumor DNA methylation patterns were assessed using the Illumina Goldengate Methylation Cancer Panel. First, a methylation score, the sum of individual hypermethylated tumor suppressor associated CpG sites, was calculated and associated with dietary intake of micronutrients involved in one-carbon metabolism and antioxidant activity, and food groups abundant in these nutrients. Second, gene specific analyses using linear modeling with empirical Bayesian variance estimation were conducted to identify if methylation at individual CpG sites was associated with diet. All models were controlled for age, sex, smoking, alcohol and HPV status. Individuals reporting in the highest quartile of folate, vitamin B12 and vitamin A intake, compared with those in the lowest quartile, showed significantly less tumor suppressor gene methylation, as did patients reporting the highest cruciferous vegetable intake. Gene specific analyses identified differential associations between DNA methylation and vitamin B12 and vitamin A intake when stratifying by HPV status. These preliminary results suggest that intake of folate, vitamin A and vitamin B12 may be associated with the tumor DNA methylation profile in HNC and enhance tumor suppression
Pretreatment dietary intake is associated with tumor suppressor DNA methylation in head and neck squamous cell carcinomas
Diet is associated with cancer prognosis, including head and neck cancer (HNC), and has been hypothesized to influence epigenetic state by determining the availability of functional groups involved in the modification of DNA and histone proteins. The goal of this study was to describe the association between pretreatment diet and HNC tumor DNA methylation. Information on usual pretreatment food and nutrient intake was estimated via food frequency questionnaire (FFQ) on 49 HNC cases. Tumor DNA methylation patterns were assessed using the Illumina Goldengate Methylation Cancer Panel. First, a methylation score, the sum of individual hypermethylated tumor suppressor associated CpG sites, was calculated and associated with dietary intake of micronutrients involved in one-carbon metabolism and antioxidant activity, and food groups abundant in these nutrients. Second, gene specific analyses using linear modeling with empirical Bayesian variance estimation were conducted to identify if methylation at individual CpG sites was associated with diet. All models were controlled for age, sex, smoking, alcohol and HPV status. Individuals reporting in the highest quartile of folate, vitamin B12 and vitamin A intake, compared with those in the lowest quartile, showed significantly less tumor suppressor gene methylation, as did patients reporting the highest cruciferous vegetable intake. Gene specific analyses identified differential associations between DNA methylation and vitamin B12 and vitamin A intake when stratifying by HPV status. These preliminary results suggest that intake of folate, vitamin A and vitamin B12 may be associated with the tumor DNA methylation profile in HNC and enhance tumor suppression
High-resolution mass spectrometry provides novel insights into products of human metabolism of organophosphate and brominated flame retardants
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