7,997 research outputs found
Nesting properties and anomalous band effect in MgB2
First principle FLAPW band calculations of the new superconductor MgB2 were
performed and the polarization function P12(Q) between the two p-bands mainly
formed of boron pz-orbital was calculated. We found that P12(Q) is
substantially enhanced around Q=(0,0,p/c), which supports the two-band
mechanism of superconductivity for MgB2. P12(Q) peaks at Qz ~ 0.3(2p/c) and Qz
\~ 0.5(2p/c). These two peaks are related to the nesting of these Fermi
surfaces, but significantly deviates from the position expected from the
simplest tight-binding bands for the p-bands. From the calculations for
different lattice parameters, we have found significant dependences on the
isotopic species of B and on the pressure effect of the polarization function
in accordance with the respective changes of Tc in the above-mentioned
framework.Comment: 15 pages, 7 graphs. to be published in J. Phys. Soc. Jpn. 70_, No.
Sun-as-a-Star Spectrum Variations 1974-2006
We have observed selected Fraunhofer lines, both integrated over the Full
Disk and for a small circular region near the center of the solar disk, on
1,215 days for the past 30 years. Full Disk results: Ca II K 393 nm nicely
tracks the 11 year magnetic cycle based on sunspot number with a peak amplitude
in central intensity of ~37%. The wavelength of the mid-line core absorption
feature, called K3, referenced to nearby photospheric Fe, displays an activity
cycle variation with an amplitude of 3 milli-Angstroms. Other chromospheric
lines track Ca II K intensity with lower relative amplitudes. Low photosphere:
Temperature sensitive CI 5380 nm appears constant in intensity to 0.2%. High
photosphere: The cores of strong Fe I lines, Na D1 and D2, and the Mg I b
lines, present a puzzling signal perhaps indicating a role for the 22 y Hale
cycle. Solar minimum around 1985 was clearly seen, but the following minimum in
1996 was missing. This anomalous behavior is not seen in comparison atmospheric
O2. Center Disk results: Both Ca II K and C I 538 nm intensities are constant,
indicating that the basal quiet atmosphere is unaffected by cycle magnetism
within our observational error. A lower limit to the Ca II K central intensity
atmosphere is 0.040. The wavelength of Ca II K3 varies with the cycle by 6
milli-Angstroms, a factor of 2X over the full disk value. This may indicate the
predominance of radial motions at Center Disk. This is not an effect of motions
in plages since they are absent at Center Disk. This 11 y variation in the
center of chromospheric lines could complicate the radial velocity detection of
planets around solar-type stars. An appendix provides instructions for URL
access to both the raw and reduced data.Comment: 38 pages with 20 figures. Accepted for publication in The
Astrophysical Journa
Effective low-energy theory for correlated carbon nanotubes
The low-energy theory for single-wall carbon nanotubes including Coulomb
interactions is derived and analyzed. It describes two fermion chains without
interchain hopping but coupled in a specific way by the interaction. The
strong-coupling properties are studied by bosonization, and consequences for
experiments on single armchair nanotubes are discussed.Comment: 5 pages REVTeX, includes one figur
Wireless ion selective electrode autonomous sensing system
A paradigm shift in sensing methods and principles is required to meet the legislative demands for detecting hazardous substances in the molecular world. This will encompass the development of new sensing technologies capable of performing very selective and sensitive measurements at an acceptable cost, developed by multidisciplinary teams of chemists, engineers and computer scientists to harvest information from a multitude of molecular targets in health, food and the environment. In this study we present the successful implementation of a low-cost, wireless chemical sensing system that employs a minimum set of components for effective operation. Specifically, our efforts resulted in a wireless, tri-electrode, ISE pH sensor for use in environmental monitoring. Sensor calibration and validated insitu field trials have been carried out and are presented in this paper
The stability of a cubic fixed point in three dimensions from the renormalization group
The global structure of the renormalization-group flows of a model with
isotropic and cubic interactions is studied using the massive field theory
directly in three dimensions. The four-loop expansions of the \bt-functions
are calculated for arbitrary . The critical dimensionality and the stability matrix eigenvalues estimates obtained on the basis of
the generalized Pad-Borel-Leroy resummation technique are shown
to be in a good agreement with those found recently by exploiting the five-loop
\ve-expansions.Comment: 18 pages, LaTeX, 5 PostScript figure
- …