553 research outputs found
Lectures on curvature flow of networks
We present a collection of results on the evolution by curvature of networks of planar curves. We discuss in particular the existence of a solution and the analysis of singularities
Close-up of primary and secondary asteroseismic CoRoT targets and the ground-based follow-up observations
To optimise the science results of the asteroseismic part of the CoRoT
satellite mission a complementary simultaneous ground-based observational
campaign is organised for selected CoRoT targets. The observations include both
high-resolution spectroscopic and multi-colour photometric data. We present the
preliminary results of the analysis of the ground-based observations of three
targets. A line-profile analysis of 216 high-resolution FEROS spectra of the
delta Sct star HD 50844 reveals more than ten pulsation frequencies in the
frequency range 5-18 c/d, including possibly one radial fundamental mode (6.92
c/d). Based on more than 600 multi-colour photometric datapoints of the beta
Cep star HD180642, spanning about three years and obtained with different
telescopes and different instruments, we confirm the presence of a dominant
radial mode nu1=5.48695 c/d, and detect also its first two harmonics. We find
evidence for a second mode nu2=0.3017 c/d, possibly a g-mode, and indications
for two more frequencies in the 7-8 c/d domain. From Stromgren photometry we
find evidence for the hybrid delta Sct/gamma Dor character of the F0 star HD
44195, as frequencies near 3 c/d and 21 c/d are detected simultaneously in the
different filters.Comment: 7 pages, 6 figures, HELAS II International Conference
"Helioseismology, Asteroseismology and MHD Connections", 2008, J.Phys.: Conf.
Ser. 118, 01207
Mean curvature flow with triple junctions in higher space dimensions
We consider mean curvature flow of n-dimensional surface clusters. At
(n-1)-dimensional triple junctions an angle condition is required which in the
symmetric case reduces to the well-known 120 degree angle condition. Using a
novel parametrization of evolving surface clusters and a new existence and
regularity approach for parabolic equations on surface clusters we show local
well-posedness by a contraction argument in parabolic Hoelder spaces.Comment: 31 pages, 2 figure
ClC-1 chloride channels: state-of-the-art research and future challenges
The voltage-dependent ClC-1 chloride channel belongs to the CLC channel/transporter family. It is a homodimer comprising two individual pores which can operate independently or simultaneously according to two gating modes, the fast and the slow gate of the channel. ClC-1 is preferentially expressed in the skeletal muscle fibers where the presence of an efficient Cl(-) homeostasis is crucial for the correct membrane repolarization and propagation of action potential. As a consequence, mutations in the CLCN1 gene cause dominant and recessive forms of myotonia congenita (MC), a rare skeletal muscle channelopathy caused by abnormal membrane excitation, and clinically characterized by muscle stiffness and various degrees of transitory weakness. Elucidation of the mechanistic link between the genetic defects and the disease pathogenesis is still incomplete and, at this time, there is no specific treatment for MC. Still controversial is the subcellular localization pattern of ClC-1 channels in skeletal muscle as well as its modulation by some intracellular factors. The expression of ClC-1 in other tissues such as in brain and heart and the possible assembly of ClC-1/ClC-2 heterodimers further expand the physiological properties of ClC-1 and its involvement in diseases. A recent de novo CLCN1 truncation mutation in a patient with generalized epilepsy indeed postulates an unexpected role of this channel in the control of neuronal network excitability. This review summarizes the most relevant and state-of-the-art research on ClC-1 chloride channels physiology and associated diseases
N20 fluxes evaluation in pasture management system under different densities of babassu palms.
Spectroscopic Survey of {\gamma} Doradus Stars I. Comprehensive atmospheric parameters and abundance analysis of {\gamma} Doradus stars
We present a spectroscopic survey of known and candidate \,Doradus
stars. The high-resolution, high signal-to-noise spectra of 52 objects were
collected by five different spectrographs. The spectral classification,
atmospheric parameters (\teff, , ), and chemical
composition of the stars were derived. The stellar spectral and luminosity
classes were found between G0-A7 and IV-V, respectively. The initial values for
\teff\ and \logg\ were determined from the photometric indices and spectral
energy distribution. Those parameters were improved by the analysis of hydrogen
lines. The final values of \teff, \logg\ and were derived from the iron
lines analysis. The \teff\ values were found between 6000\,K and 7900\,K, while
\logg\,values range from 3.8 to 4.5\,dex. Chemical abundances and
values were derived by the spectrum synthesis method. The values were
found between 5 and 240\,km\,s. The chemical abundance pattern of
\,Doradus stars were compared with the pattern of non-pulsating stars.
It turned out that there is no significant difference in abundance patterns
between these two groups. Additionally, the relations between the atmospheric
parameters and the pulsation quantities were checked. A strong correlation
between the and the pulsation periods of \,Doradus variables
was obtained. The accurate positions of the analysed stars in the H-R diagram
have been shown. Most of our objects are located inside or close to the blue
edge of the theoretical instability strip of \,Doradus.Comment: 18 pages, 13 figure
The multiperiodicity of the Doradus stars HD 224945 and HD 224638 as detected from a multisite campaign
We discuss new photometric data collected on the gamma Dor variables HD
224945 and HD 224638. Multiperiodicity was detected in both stars, thanks to
the clear spectral window of a multisite campaign that involved five
observatories. HD 224945 shows the shortest period among the gamma Dor stars,
i.e., 0.3330 d. The pulsation behaviour is very different: HD 224945 displays a
set of frequencies spread over an interval much wider than that of HD 224638.
We clearly found evidence for amplitude variations in the excited modes by
comparing data from different years. HD 224945 and HD 224638 are among the best
examples of Dor stars that show multimode pulsations, which make them
very interesting from an asteroseismological point of view.Comment: 8 pages (in A&A style), 3 eps figures. Accepted for A&A Main Journa
Preparing the COROT space mission: new variable stars in the galactic Anticenter direction
The activities related to the preparation of the asteroseismic, photometric
space mission COROT are described. Photoelectric observations, wide--field CCD
photometry, uvbyB calibrations and further time--series have been obtained at
different observatories and telescopes. They have been planned to complete the
COROT programme in the direction of the galactic Anticenter. In addition to
suitable asteroseismic targets covering the different evolutionary stages
between ZAMS and TAMS, we discovered several other variable stars, both
pulsating and geometrical. We compared results on the incidence of variability
in the galactic Center and Anticenter directions. Physical parameters have been
obtained and evolutionary tracks fitting them have been calculated. The
peculiarities of some individual stars alre pointed out. Paper based on
observations collected at the San Pedro Martir, Sierra Nevada, Teide, La Silla,
Haute-Provence and Roque de Los Muchachos (Telescopio Nazionale Galileo and
Mercator telescopes) observatories.Comment: 13 pages, 9 figures. Accepted for The Astronomical Journal (2005 May
volume
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