42,700 research outputs found
Analytical and experimental study of two concentric cylinders coupled by a fluid gap
From a structural point of view a liquid coolant type nuclear reactor consists of a heavy steel vessel containing the core and related mechanical components and filled with a hot fluid. This vessel is protected from the severe environment of the core by a shielding structure, the thermal liner, which is usually a relatively thin steel cylinder concentric with the reactor vessel and separated from it by a gap filled with the coolant fluid. This arrangement leads to a potential vibration problem if the fundamental frequency, or one of the higher natural vibration frequencies, of this liner system is close to the frequency of some vibration source present in the reactor vessel. The shell rigidly clamped at its base and free at the top was investigated since it is a better description of the conditions encountered in typical reactor designs
Competing topological and Kondo insulator phases on a honeycomb lattice
We investigate the competition between the spin-orbit interaction of
itinerant electrons and their Kondo coupling with local moments densely
distributed on the honeycomb lattice. We find that the model at half-filling
displays a quantum phase transition between topological and Kondo insulators at
a nonzero Kondo coupling. In the Kondo-screened case, tuning the electron
concentration can lead to a new topological insulator phase. The results
suggest that the heavy-fermion phase diagram contains a new regime with a
competition among topological, Kondo-coherent and magnetic states, and that the
regime may be especially relevant to Kondo lattice systems with -conduction
electrons. Finally, we discuss the implications of our results in the context
of the recent experiments on SmB implicating the surface states of a
topological insulator, as well as the existing experiments on the phase
transitions in SmB under pressure and in CeNiSn under chemical pressure.Comment: (v3) Published version including the main text (5 pages + 4 figures)
and a supplementary material discussing the effects of quantum fluctuations
of the slave bosons and antiferromagnetic ordering of the local moments on
the transitions among the Kondo, magnetic and topological state
Kondo effect in coupled quantum dots with RKKY interaction: Finite temperature and magnetic field effects
We study transport through two quantum dots coupled by an RKKY interaction as
a function of temperature and magnetic field. By applying the Numerical
Renormalization Group (NRG) method we obtain the transmission and the linear
conductance. At zero temperature and magnetic field, we observe a quantum phase
transition between the Kondo screened state and a local spin singlet as the
RKKY interaction is tuned. Above the critical RKKY coupling the Kondo peak is
split. However, we find that both finite temperature and magnetic field restore
the Kondo resonance. Our results agree well with recent transport experiments
on gold grain quantum dots in the presence of magnetic impurities.Comment: 4 pages, 5 figure
New Predictions for generalized spin polarizabilities from heavy baryon chiral perturbation theory
We extract the next-to-next-to-leading order results for spin-flip
generalized polarizabilities (GPs) of the nucleon from the spin-dependent
amplitudes for virtual Compton scattering (VCS) at in heavy
baryon chiral perturbation theory. At this order, no unknown low energy
constants enter the theory, allowing us to make absolute predictions for all
spin-flip GPs. Furthermore, by using constraint equations between the GPs due
to nucleon crossing combined with charge conjugation symmetry of the VCS
amplitudes, we get a next-to-next-to-next-to-leading order prediction for one
of the GPs. We provide estimates for forthcoming double polarization
experiments which allow to access these spin-flip GPs of the nucleon.Comment: 15 pages, 3 figure
Theory of ferromagnetism in (A,Mn)B semiconductors
A brief review of theory of ferromagnetism of dilute magnetic semiconductors
of the form (A,Mn)B based on the double exchange model is first given. A
systematic investigation of the phenomena extending the current theory is
outlined. We begin with an investigation of the regions of instability of the
nonmagnetic towards the ferromagnetic state of a system of Mn-atoms doped in
AB-type semiconductor. A self-consistent many-body theory of the ferromagnetic
state is then developed, going beyond the mean field approaches by including
fluctuations of the Mn-spins and the itinerant hole-gas. A functional theory
suitable for computation of system properties such as Curie temperature as a
function of hole and the Mn-concentration, spin-current, etc. is formulated.Comment: 16 page
The influence of the cluster environment on the star formation efficiency of 12 Virgo spiral galaxies
The influence of the environment on gas surface density and star formation
efficiency of cluster spiral galaxies is investigated. We extend previous work
on radial profiles by a pixel-to pixel analysis looking for asymmetries due to
environmental interactions. The star formation rate is derived from GALEX UV
and Spitzer total infrared data. As in field galaxies, the star formation rate
for most Virgo galaxies is approximately proportional to the molecular gas
mass. Except for NGC 4438, the cluster environment does not affect the star
formation efficiency with respect to the molecular gas. Gas truncation is not
associated with major changes in the total gas surface density distribution of
the inner disk of Virgo spiral galaxies. In three galaxies, possible increases
in the molecular fraction and the star formation efficiency with respect to the
total gas, of factors of 1.5 to 2, are observed on the windward side of the
galactic disk. A significant increase of the star formation efficiency with
respect to the molecular gas content on the windward side of ram
pressure-stripped galaxies is not observed. The ram-pressure stripped
extraplanar gas of 3 highly inclined spiral galaxies shows a depressed star
formation efficiency with respect to the total gas, and one of them (NGC 4438)
shows a depressed rate even with respect to the molecular gas. The
interpretation is that stripped gas loses the gravitational confinement and
associated pressure of the galactic disk, and the gas flow is diverging, so the
gas density decreases and the star formation rate drops. However, the stripped
extraplanar gas in one highly inclined galaxy (NGC 4569) shows a normal star
formation efficiency with respect to the total gas. We propose this galaxy is
different because it is observed long after peak pressure, and its extraplanar
gas is now in a converging flow as it resettles back into the disk.Comment: 34 pages, 24 figures, accepted for publication by A&
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