329 research outputs found
On the Geometric Interpretation of N = 2 Superconformal Theories
We clarify certain important issues relevant for the geometric interpretation
of a large class of N = 2 superconformal theories. By fully exploiting the
phase structure of these theories (discovered in earlier works) we are able to
clearly identify their geometric content. One application is to present a
simple and natural resolution to the question of what constitutes the mirror of
a rigid Calabi-Yau manifold. We also discuss some other models with unusual
phase diagrams that highlight some subtle features regarding the geometric
content of conformal theories.Comment: 25 pages, note adde
Modifiable lifestyle factors associated with risk of sessile serrated polyps, conventional adenomas, and hyperplastic polyps
ObjectiveTo identify modifiable factors associated with sessile serrated polyps (SSPs) and compare the association of these factors with conventional adenomas (ADs) and hyperplastic polyps (HPs).DesignWe used data from the Tennessee Colorectal Polyp Study, a colonoscopy-based case–control study. Included were 214 SSP cases, 1779 AD cases, 560 HP cases and 3851 polyp-free controls.ResultsCigarette smoking was associated with increased risk for all polyps and was stronger for SSPs than for ADs (OR 1.74, 95% CI 1.16 to 2.62, for current vs never, ptrend=0.008). Current regular use of non-steroidal anti-inflammatory drugs was associated with a 40% reduction in SSP risk in comparison with never users (OR 0.68, 95% CI 0.48 to 0.96, ptrend=0.03), similar to the association with AD. Red meat intake was strongly associated with SSP risk (OR 2.59, 95% CI 1.41 to 4.74 for highest vs lowest intake, ptrend<0.001) and the association with SSP was stronger than with AD (ptrend=0.003). Obesity, folate intake, fibre intake and fat intake were not associated with SSP risk after adjustment for other factors. Exercise, alcohol use and calcium intake were not associated with risk for SSPs.ConclusionsSSPs share some modifiable risk factors for ADs, some of which are more strongly associated with SSPs than ADs. Thus, preventive efforts to reduce risk for ADs may also be applicable to SSPs. Additionally, SSPs have some distinctive risk factors. Future studies should evaluate the preventive strategies for these factors. The findings from this study also contribute to an understanding of the aetiology and biology of SSPs.</jats:sec
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Magnesium, vitamin D status and mortality: results from US National Health and Nutrition Examination Survey (NHANES) 2001 to 2006 and NHANES III
Background: Magnesium plays an essential role in the synthesis and metabolism of vitamin D and magnesium supplementation substantially reversed the resistance to vitamin D treatment in patients with magnesium-dependent vitamin-D-resistant rickets. We hypothesized that dietary magnesium alone, particularly its interaction with vitamin D intake, contributes to serum 25-hydroxyvitamin D (25(OH)D) levels, and the associations between serum 25(OH)D and risk of mortality may be modified by magnesium intake level. Methods: We tested these novel hypotheses utilizing data from the National Health and Nutrition Examination Survey (NHANES) 2001 to 2006, a population-based cross-sectional study, and the NHANES III cohort, a population-based cohort study. Serum 25(OH)D was used to define vitamin D status. Mortality outcomes in the NHANES III cohort were determined by using probabilistic linkage with the National Death Index (NDI). Results: High intake of total, dietary or supplemental magnesium was independently associated with significantly reduced risks of vitamin D deficiency and insufficiency respectively. Intake of magnesium significantly interacted with intake of vitamin D in relation to risk of both vitamin D deficiency and insufficiency. Additionally, the inverse association between total magnesium intake and vitamin D insufficiency primarily appeared among populations at high risk of vitamin D insufficiency. Furthermore, the associations of serum 25(OH)D with mortality, particularly due to cardiovascular disease (CVD) and colorectal cancer, were modified by magnesium intake, and the inverse associations were primarily present among those with magnesium intake above the median. Conclusions: Our preliminary findings indicate it is possible that magnesium intake alone or its interaction with vitamin D intake may contribute to vitamin D status. The associations between serum 25(OH)D and risk of mortality may be modified by the intake level of magnesium. Future studies, including cohort studies and clinical trials, are necessary to confirm the findings
Comparison of Biomarker Expression between Proximal and Distal Colorectal Adenomas: The Tennessee-Indiana Adenoma Recurrence Study
It is unclear if proximal and distal traditional adenomas present with differences in molecular events which contribute to cancer heterogeneity by tumor anatomical subsite. Participants from a colonoscopy-based study (n=380) were divided into subgroups based on the location of their most advanced adenoma: proximal, distal, or “equivalent both sides”. Eight biomarkers in the most advanced adenomas were evaluated by immunohistochemistry (Ki-67, COX-2, TGFβRII, EGFR, β-catenin, cyclin D1, c-Myc) or TUNEL (apoptosis). After an adjustment for pathological features, there were no significant differences between proximal and distal adenomas for any biomarker. Conversely, expression levels did vary by other features, such as their size, villous component, and synchronousness. Large adenomas had higher expression levels of Ki-67(P<0.001), TGFβRII (P<0.0001), c-Myc (P<0.001), and cyclin D1 (P<0.001) in comparison to small adenomas, and tubulovillous/villous adenomas also were more likely to have similar higher expression levels in comparison to tubular adenomas. Adenoma location is not a major determinant of the expression of these biomarkers outside of other pathological features. This study suggests similarly important roles of Wnt/β-catenin and TGF-β pathways in carcinogenesis in both the proximal and distal colorectum
Multi-wavelength observations of Proxima Centauri
We report simultaneous observations of the nearby flare star Proxima Centauri
with VLT/UVES and XMM-Newton over three nights in March 2009. Our optical and
X-ray observations cover the star's quiescent state, as well as its flaring
activity and allow us to probe the stellar atmospheric conditions from the
photosphere into the chromosphere, and then the corona during its different
activity stages. Using the X-ray data, we investigate variations in coronal
densities and abundances and infer loop properties for an intermediate-sized
flare. The optical data are used to investigate the magnetic field and its
possible variability, to construct an emission line list for the chromosphere,
and use certain emission lines to construct physical models of Proxima
Centauri's chromosphere.
We report the discovery of a weak optical forbidden Fe xiii line at 3388 AA
during the more active states of Proxima Centauri. For the intermediate flare,
we find two secondary flare events that may originate in neighbouring loops,
and discuss the line asymmetries observed during this flare in H i, He i, and
Ca ii lines. The high time-resolution in the H alpha line highlights strong
temporal variations in the observed line asymmetries, which re-appear during a
secondary flare event. We also present theoretical modelling with the stellar
atmosphere code PHOENIX to construct flaring chromospheric models.Comment: 19 pages, 22 figures, accepted by A&
Multiwavelength observations of a giant flare on CN Leonis I. The chromosphere as seen in the optical spectra
Flares on dM stars contain plasmas at very different temperatures and thus
affect a wide wavelength range in the electromagnetic spectrum. While the
coronal properties of flares are studied best in X-rays, the chromosphere of
the star is observed best in the optical and ultraviolet ranges. Therefore,
multiwavelength observations are essential to study flare properties throughout
the atmosphere of a star. We analysed simultaneous observations with UVES/VLT
and XMM-Newton of the active M5.5 dwarf CN Leo (Gl 406) exhibiting a major
flare. The optical data cover the wavelength range from 3000 to 10000 Angstrom.
From our optical data, we find an enormous wealth of chromospheric emission
lines occurring throughout the spectrum. We identify a total of 1143 emission
lines, out of which 154 are located in the red arm, increasing the number of
observed emission lines in this red wavelength range by about a factor of 10.
Here we present an emission line list and a spectral atlas. We also find line
asymmetries for H I, He I, and Ca II lines. For the last, this is the first
observation of asymmetries due to a stellar flare. During the flare onset,
there is additional flux found in the blue wing, while in the decay phase,
additional flux is found in the red wing. We interpret both features as caused
by mass motions. In addition to the lines, the flare manifests itself in the
enhancement of the continuum throughout the whole spectrum, inverting the
normal slope for the net flare spectrum.Comment: 15 pages, accepted by A&
MAXI J1659-152: The shortest orbital period black-hole transient in outburst
MAXI J1659-152 is a bright X-ray transient black-hole candidate binary system
discovered in September 2010. We report here on MAXI, RXTE, Swift, and
XMM-Newton observations during its 2010/2011 outburst. We find that during the
first one and a half week of the outburst the X-ray light curves display drops
in intensity at regular intervals, which we interpret as absorption dips. About
three weeks into the outbursts, again drops in intensity are seen. These dips
have, however, a spectral behaviour opposite to that of the absorption dips,
and are related to fast spectral state changes (hence referred to as transition
dips). The absorption dips recur with a period of 2.414+/-0.005 hrs, which we
interpret as the orbital period of the system. This implies that MAXI J1659-152
is the shortest period black-hole candidate binary known to date. The
inclination of the accretion disk with respect to the line of sight is
estimated to be 65-80 degrees. We propose the companion to the black-hole
candidate to be close to an M5 dwarf star, with a mass and radius of about
0.15-0.25 M_sun and 0.2-0.25 R_sun, respectively. We derive that the companion
had an initial mass of about 1.5 M_sun, which evolved to its current mass in
about 5-6 billion years. The system is rather compact (orbital separation of
larger than ~1.33 R_sun), and is located at a distance of 8.6+/-3.7 kpc, with a
height above the Galactic plane of 2.4+/-1.0 kpc. The characteristics of short
orbital period and high Galactic scale height are shared with two other
transient black-hole candidate X-ray binaries, i.e., XTE J1118+480 and Swift
J1735.5-0127. We suggest that all three are kicked out of the Galactic plane
into the halo, rather than being formed in a globular cluster.Comment: 20 pages, 14 figures, accepted for publication in A&
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