3,869 research outputs found
Design considerations for a HE-3 refrigerator for space applications
The low temperature provided by He-3 refrigerators (0.3 to 3 K) have useful space applications. However, the low temperatures and the low surface tension of He-3 require special design considerations. The considerations include the need for small pores to contain the liquid in a matrix; the effects of bubble nucleation and growth; and the effects of the thermal conductivity within the matrix. These design considerations are discussed and a possible confinement system is analyzed
Hopping and clustering of oxygen vacancies in SrTiO3 by anelastic relaxation
The complex elastic compliance s11(w,T) of SrTiO3-d has been measured as a
function of the O deficiency d < 0.01. The two main relaxation peaks in the
absorption are identified with hopping of isolated O vacancies over a barrier
of 0.60 eV and reorientation of pairs of vacancies involving a barrier of 1 eV.
The pair binding energy is ~0.2 eV and indications for additional clustering,
possibly into chains, is found already at d ~0.004. The anistropic component of
the elastic dipole of an O vacancy is Deltalambda = 0.026.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Let
Fast mode of rotating atoms in one-dimensional lattice rings
We study the rotation of atoms in one-dimensional lattice rings. In
particular, the "fast mode", where the ground state atoms rotate faster than
the stirring rotating the atoms, is studied both analytically and numerically.
The conditions for the transition to the fast mode are found to be very
different from that in continuum rings. We argue that these transition
frequencies remain unchanged for bosonic condensates described in a mean field.
We show that Fermionic interaction and filling factor have a significant effect
on the transition to the fast mode, and Pauli principle may suppress it
altogether.Comment: 4 pages, 5 figure
Dirac electrons in a Kronig-Penney potential: dispersion relation and transmission periodic in the strength of the barriers
The transmission T and conductance G through one or multiple one-dimensional,
delta-function barriers of two-dimensional fermions with a linear energy
spectrum are studied. T and G are periodic functions of the strength P of the
delta-function barrier V(x,y) / hbar v_F = P delta(x). The dispersion relation
of a Kronig-Penney (KP) model of a superlattice is also a periodic function of
P and causes collimation of an incident electron beam for P = 2 pi n and n
integer. For a KP superlattice with alternating sign of the height of the
barriers the Dirac point becomes a Dirac line for P = (n + 1/2) pi.Comment: 5 pages, 6 figure
On the RKKY range function of a one dimensional non interacting electron gas
We show that the pitfalls encountered in earlier calculations of the RKKY
range function for a non interacting one dimensional electron gas at zero
temperature can be unraveled and successfully dealt with through a proper
handling of the impurity potential.Comment: to appear in Phys. Re
Spatial search in a honeycomb network
The spatial search problem consists in minimizing the number of steps
required to find a given site in a network, under the restriction that only
oracle queries or translations to neighboring sites are allowed. In this paper,
a quantum algorithm for the spatial search problem on a honeycomb lattice with
sites and torus-like boundary conditions. The search algorithm is based on
a modified quantum walk on a hexagonal lattice and the general framework
proposed by Ambainis, Kempe and Rivosh is used to show that the time complexity
of this quantum search algorithm is .Comment: 10 pages, 2 figures; Minor typos corrected, one Reference added.
accepted in Math. Structures in Computer Science, special volume on Quantum
Computin
Heavy Neutrinos and Lepton Flavour Violation in Left-Right Symmetric Models at the LHC
We discuss lepton flavour violating processes induced in the production and
decay of heavy right-handed neutrinos at the LHC. Such particles appear in
left-right symmetrical extensions of the Standard Model as the messengers of
neutrino mass generation, and can have masses at the TeV scale. We determine
the expected sensitivity on the right-handed neutrino mixing matrix, as well as
on the right-handed gauge boson and heavy neutrino masses. By comparing the
sensitivity of the LHC with that of searches for low energy LFV processes, we
identify favourable areas of the parameter space to explore the complementarity
between LFV at low and high energies.Comment: 34 pages, 16 figures, PRD versio
Renormalization of the spin-wave spectrum in three-dimentional ferromagnets with dipolar interaction
Renormalization of the spin-wave spectrum is discussed in a cubic ferromagnet
with dipolar forces at . First 1/S-corrections are considered in
detail to the bare spectrum , where is the spin-wave stiffness,
is the angle between and the magnetization and
is the characteristic dipolar energy. In accordance with previous
results we obtain the thermal renormalization of constants and
in the expression for the bare spectrum. Besides, a number of previously
unknown features are revealed. We observe terms which depend on azimuthal angle
of the momentum . It is obtained an isotropic term proportional to
which makes the spectrum linear rather than quadratic when and . In particular a spin-wave gap proportional to
is observed. Essentially, thermal contribution from the
Hartree-Fock diagram to the isotropic correction as well as to the spin-wave
gap are proportional to the demagnetizing factor in the direction of domain
magnetization. This nontrivial behavior is attributed to the long-range nature
of the dipolar interaction. It is shown that the gap screens infrared
singularities of the first 1/S-corrections to the spin-wave stiffness and
longitudinal dynamical spin susceptibility (LDSS) obtained before. We
demonstrate that higher order 1/S-corrections to these quantities are small at
. However the analysis of the entire perturbation series is still
required to derive the spectrum and LDSS when .Comment: 11 pages, 1 figur
Bose Einstein Condensation of incommensurate solid 4He
It is pointed out that simulation computation of energy performed so far
cannot be used to decide if the ground state of solid 4He has the number of
lattice sites equal to the number of atoms (commensurate state) or if it is
different (incommensurate state). The best variational wave function, a shadow
wave function, gives an incommensurate state but the equilibrium concentration
of vacancies remains to be determined. In order to investigate the presence of
a supersolid phase we have computed the one--body density matrix in solid 4He
for the incommensurate state by means of the exact Shadow Path Integral Ground
State projector method. We find a vacancy induced Bose Einstein condensation of
about 0.23 atoms per vacancy at a pressure of 54 bar. This means that bulk
solid 4He is supersolid at low enough temperature if the exact ground state is
incommensurate.Comment: 5 pages, 2 figure
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