13,945 research outputs found
Rotating Superconductors and the London Moment: Thermodynamics versus Microscopics
Comparing various microscopic theories of rotating superconductors to the
conclusions of thermodynamic considerations, we traced their marked difference
to the question of how some thermodynamic quantities (the electrostatic and
chemical potentials) are related to more microscopic ones: The electron's the
work function, mean-field potential and Fermi energy -- certainly a question of
general import.
After the correct identification is established, the relativistic correction
for the London Moment is shown to vanish, with the obvious contribution from
the Fermi velocity being compensated by other contributions such as
electrostatics and interactions.Comment: 23 pages 4 fi
The power of low-resolution spectroscopy: On the spectral classification of planet candidates in the ground-based CoRoT follow-up
Planetary transits detected by the CoRoT mission can be mimicked by a
low-mass star in orbit around a giant star. Spectral classification helps to
identify the giant stars and also early-type stars which are often excluded
from further follow-up.
We study the potential and the limitations of low-resolution spectroscopy to
improve the photometric spectral types of CoRoT candidates. In particular, we
want to study the influence of the signal-to-noise ratio (SNR) of the target
spectrum in a quantitative way. We built an own template library and
investigate whether a template library from the literature is able to reproduce
the classifications. Including previous photometric estimates, we show how the
additional spectroscopic information improves the constraints on spectral type.
Low-resolution spectroscopy (1000) of 42 CoRoT targets covering a
wide range in SNR (1-437) and of 149 templates was obtained in 2012-2013 with
the Nasmyth spectrograph at the Tautenburg 2m telescope. Spectral types have
been derived automatically by comparing with the observed template spectra. The
classification has been repeated with the external CFLIB library.
The spectral class obtained with the external library agrees within a few
sub-classes when the target spectrum has a SNR of about 100 at least. While the
photometric spectral type can deviate by an entire spectral class, the
photometric luminosity classification is as close as a spectroscopic
classification with the external library. A low SNR of the target spectrum
limits the attainable accuracy of classification more strongly than the use of
external templates or photometry. Furthermore we found that low-resolution
reconnaissance spectroscopy ensures that good planet candidates are kept that
would otherwise be discarded based on photometric spectral type alone.Comment: accepted for publication in Astronomische Nachrichten; 12 pages, 4
figures, 7 table
Nonlinear spin-polarized transport through a ferromagnetic domain wall
A domain wall separating two oppositely magnetized regions in a ferromagnetic
semiconductor exhibits, under appropriate conditions, strongly nonlinear I-V
characteristics similar to those of a p-n diode. We study these characteristics
as functions of wall width and temperature. As the width increases or the
temperature decreases, direct tunneling between the majority spin bands
decreases the effectiveness of the diode. This has important implications for
the zero-field quenched resistance of magnetic semiconductors and for the
design of a recently proposed spin transistor.Comment: 5 pages, 3 figure
Measurement Of Quasiparticle Transport In Aluminum Films Using Tungsten Transition-Edge Sensors
We report new experimental studies to understand the physics of phonon
sensors which utilize quasiparticle diffusion in thin aluminum films into
tungsten transition-edge-sensors (TESs) operated at 35 mK. We show that basic
TES physics and a simple physical model of the overlap region between the W and
Al films in our devices enables us to accurately reproduce the experimentally
observed pulse shapes from x-rays absorbed in the Al films. We further estimate
quasiparticle loss in Al films using a simple diffusion equation approach.Comment: 5 pages, 6 figures, PRA
Adjuvants : an essential component of neisseria vaccines
Adjuvants may be classified into delivery systems and immune potentiator or modulator molecules based on their mechanism of action. Neisseria vaccines containing traditional adjuvants such as aluminium salts have existed for long time, but meningitis caused by Neisseria meningitidis serogroups, particularly serogroup B, continues to be a global health problem. Novel strategies have applied in silico and recombinant technologies to develop "universal" antigens (e.g. proteins, peptides and plasmid DNA) for vaccines, but these antigens have been shown to be poorly immunogenic even when alum adjuvanted, implying a need for better vaccine design. In this work we review the use of natural, detoxified, or synthetic molecules in combination with antigens to activate the innate immune system and to modulate the adaptive immune responses. In the main, antigenic and imune potentiator signals are delivered using nano-, micro-particles, alum, or emulsions. The importance of interaction between adjuvants and antigens to activate and target dendritic cells, the bridge between the innate and adaptive immune systems, will be discussed. In addition, nasal vaccine strategies based on the development of mucosal adjuvants and Neisseria derivatives to eliminate the pathogen at the site of infection provide promising adjuvants effective not only against respiratory pathogens, but also against pathogens responsible for enteric and sexually transmitted diseases
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