1,062 research outputs found
Variability of stellar granulation and convective blueshift with spectral type and magnetic activity. I. K and G main sequence stars
In solar-type stars, the attenuation of convective blueshift by stellar
magnetic activity dominates the RV variations over the low amplitude signal
induced by low mass planets. Models of stars that differ from the Sun will
require a good knowledge of the attenuation of the convective blueshift to
estimate its impact on the variations. It is therefore crucial to precisely
determine not only the amplitude of the convective blueshift for different
types of stars, but also the dependence of this convective blueshift on
magnetic activity, as these are key factors in our model producing the RV. We
studied a sample of main sequence stars with spectral types from G0 to K2 and
focused on their temporally averaged properties: the activity level and a
criterion allowing to characterise the amplitude of the convective blueshift.
We find the differential velocity shifts of spectral lines due to convection to
depend on the spectral type, the wavelength (this dependence is correlated with
the Teff and activity level), and on the activity level. This allows us to
quantify the dependence of granulation properties on magnetic activity for
stars other than the Sun. The attenuation factor of the convective blueshift
appears to be constant over the considered range of spectral types. We derive a
convective blueshift which decreases towards lower temperatures, with a trend
in close agreement with models for Teff lower than 5800 K, but with a
significantly larger global amplitude. We finally compare the observed RV
variation amplitudes with those that could be derived from our convective
blueshift using a simple law and find a general agreement on the amplitude. Our
results are consistent with previous results and provide, for the first time,
an estimation of the convective blueshift as a function of Teff, magnetic
activity, and wavelength, over a large sample of G and K main sequence stars
On the expressive power of read-once determinants
We introduce and study the notion of read- projections of the determinant:
a polynomial is called a {\it read-
projection of determinant} if , where entries of matrix are
either field elements or variables such that each variable appears at most
times in . A monomial set is said to be expressible as read-
projection of determinant if there is a read- projection of determinant
such that the monomial set of is equal to . We obtain basic results
relating read- determinantal projections to the well-studied notion of
determinantal complexity. We show that for sufficiently large , the permanent polynomial and the elementary symmetric
polynomials of degree on variables for are
not expressible as read-once projection of determinant, whereas
and are expressible as read-once projections of determinant. We
also give examples of monomial sets which are not expressible as read-once
projections of determinant
Aquilegia, Vol. 29 No. 4, September-October 2005: Newsletter of the Colorado Native Plant Society
https://epublications.regis.edu/aquilegia/1106/thumbnail.jp
Magnetic frustration in a stoichiometric spin-chain compound, CaCoIrO
The temperature dependent ac and dc magnetization and heat capacity data of
CaCoIrO, a spin-chain compound crystallizing in a KCdCl-derived
rhombohedral structure, show the features due to magnetic ordering of a
frustrated-type below about 30 K, however without exhibiting the signatures of
the so-called "partially disordered antiferromagnetic structure" encountered in
the isostructural compounds, CaCoO and CaCoRhO. This class
of compounds thus provides a variety for probing the consequences of magnetic
frustration due to topological reasons in stoichiometric spin-chain materials,
presumably arising from subtle differences in the interchain and intrachain
magnetic coupling strengths. This compound presents additional interesting
situations in the sense that, ac susceptibility exhibits a large frequency
dependence in the vicinity of 30 K uncharacteristic of conventional
spin-glasses, with this frustrated magnetic state being robust to the
application of external magnetic fields.Comment: Physical Review (Rapid Communications), in pres
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Downregulating Notch counteracts KrasG12D-induced ERK activation and oxidative phosphorylation in myeloproliferative neoplasm.
The Notch signaling pathway contributes to the pathogenesis of a wide spectrum of human cancers, including hematopoietic malignancies. Its functions are highly dependent on the specific cellular context. Gain-of-function NOTCH1 mutations are prevalent in human T-cell leukemia, while loss of Notch signaling is reported in myeloid leukemias. Here, we report a novel oncogenic function of Notch signaling in oncogenic Kras-induced myeloproliferative neoplasm (MPN). We find that downregulation of Notch signaling in hematopoietic cells via DNMAML expression or Pofut1 deletion significantly blocks MPN development in KrasG12D mice in a cell-autonomous manner. Further mechanistic studies indicate that inhibition of Notch signaling upregulates Dusp1, a dual phosphatase that inactivates p-ERK, and downregulates cytokine-evoked ERK activation in KrasG12D cells. Moreover, mitochondrial metabolism is greatly enhanced in KrasG12D cells but significantly reprogrammed by DNMAML close to that in control cells. Consequently, cell proliferation and expanded myeloid compartment in KrasG12D mice are significantly reduced. Consistent with these findings, combined inhibition of the MEK/ERK pathway and mitochondrial oxidative phosphorylation effectively inhibited the growth of human and mouse leukemia cells in vitro. Our study provides a strong rational to target both ERK signaling and aberrant metabolism in oncogenic Ras-driven myeloid leukemia
Caloric Restriction Alters Postprandial Responses of Essential Brain Metabolites in Young Adult Mice
Caloric restriction (CR) has been shown to extend longevity and protect brain function in aging. However, the effects of CR in young adult mice remain largely unexplored. In addition to the fundamental, long-term changes, recent studies demonstrate that CR has a significant impact on transient, postprandial metabolic flexibility and turnover compared to control groups. The goal of this study was to identify the brain metabolic changes at a transient (2 h) and steady (6 h) postprandial state in young mice (5–6 months of age) fed with CR or ad libitum (AL; free eating). Using metabolomics profiling, we show that CR mice had significantly higher levels of neurotransmitters (e.g., glutamate, N-acetylglutamate), neuronal integrity markers (e.g., NAA and NAAG), essential fatty acids (e.g., DHA and DPA), and biochemicals associated carnitine metabolism (related to reduced oxidative stress and inflammation) in the cerebral cortex and hippocampus at 2-h. These biochemicals remained at high levels at the 6-h postprandial time-point. The AL mice did not show the similar increases in essential fatty acid and carnitine metabolism until the 6-h time-point, and failed to show increases in neurotransmitters and neuronal integrity markers at any time-point. On the other hand, metabolites related to glucose utilization—glycolysis and pentose phosphate pathway (PPP)—were low in the CR mice throughout the 6-h period and significantly increased at the 6-h time-point in the AL mice. Our findings suggest that CR induces distinct postprandial responses in metabolites that are essential to maintain brain functions. CR mice produced higher levels of essential brain metabolites in a shorter period after a meal and sustained the levels for an extended period, while maintaining a lower level of glucose utilization. These early brain metabolism changes in the CR mice might play a critical role for neuroprotection in aging. Understanding the interplay between dietary intervention and postprandial metabolic responses from an early age may have profound implications for impeding brain aging and reducing risk for neurodegenerative disorders
Spin Gaps in High Temperature Superconductors
The phenomenology and theory of spin gap effects in high temperature
superconductors is summarized. It is argued that the spin gap behavior can only
be explained by a model of charge 0 spin 1/2 fermions which become paired into
singlets and that there are both theoretical and experimental reasons for
believing that the pairing is greatly enhanced in the bilayer structure of the
system.
This article will appear in the Proceedings of the Stanford Conference on
Spectroscopies in Novel Superconductors. To obtain postscript files containing
the figures send mail to [email protected]: 9 pages, revtex. To obtain figures contact [email protected]
Fast, broad-band magnetic resonance spectroscopy with diamond widefield relaxometry
We present an alternative to conventional Electron Paramagnetic Resonance
spectroscopy equipment. Avoiding the use of bulky magnets and magnetron
equipment, we use the photoluminescence of an ensemble of Nitrogen-Vacancy
centers at the surface of a diamond. Monitoring their relaxation time (or T1),
we detected their cross-relaxation with the compound of interest. In addition,
the EPR spectra is encoded through a localized magnetic field gradient. While
12 minutes was necessary to record each data point of the spectrum with
previous individual NV center's technics, we are able to reconstruct a full
spectrum at once in 3 seconds, over a range from 3 to 11 gauss. In term of
sensitivity, only 0.5 microliter of a hexaaquacopper (II) ion solution with 1
micromole per liter concentration was necessary.Comment: Main text (15 pages, 6 Figures) + Supplementary (6 Pages, 7 Figures
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