5,534 research outputs found
Electron polarizability of crystalline solids in quantizing magnetic fields and topological gap numbers
A theory of the static electron polarizability of crystals whose energy
spectrum is modified by quantizing magnetic fields is presented. It is argued
that The polarizability is strongly affected by non-dissipative Hall currents
induced by the presence of crossed electric and magnetic fields: these can even
change its sign. Results are illustrated in detail for a two dimensional square
lattice. The polarizability and the Hall conductivity are respectively linked
to the two topological quantum numbers entering the so--called Diophantine
equation. These numbers could in principle be detected in actual experiments
Entropy estimates for a class of schemes for the euler equations
In this paper, we derive entropy estimates for a class of schemes for the
Euler equations which present the following features: they are based on the
internal energy equation (eventually with a positive corrective term at the
righ-hand-side so as to ensure consistency) and the possible upwinding is
performed with respect to the material velocity only. The implicit-in-time
first-order upwind scheme satisfies a local entropy inequality. A
generalization of the convection term is then introduced, which allows to limit
the scheme diffusion while ensuring a weaker property: the entropy inequality
is satisfied up to a remainder term which is shown to tend to zero with the
space and time steps, if the discrete solution is controlled in L and
BV norms. The explicit upwind variant also satisfies such a weaker property, at
the price of an estimate for the velocity which could be derived from the
introduction of a new stabilization term in the momentum balance. Still for the
explicit scheme, with the above-mentioned generalization of the convection
operator, the same result only holds if the ratio of the time to the space step
tends to zero
Extension of the osp(m|n)~ so(m-n) Correspondence to the Infinite-Dimensional Chiral Spinors and Self Dual Tensors
The spinor representations of the orthosymplectic Lie superalgebras osp(m|n)
are considered and constructed. These are infinite-dimensional irreducible
representations, of which the superdimension coincides with the dimension of
the spinor representation of so(m-n). Next, we consider the self dual tensor
representations of osp(m|n) and their generalizations: these are also
infinite-dimensional and correspond to the highest irreducible component of the
power of the spinor representation. We determine the character of
these representations, and deduce a superdimension formula. From this, it
follows that also for these representations the osp(m|n)~ so(m-n)
correspondence holds
Ro-vibrational relaxation of HCN in collisions with He: Rigid bender treatment of the bending-rotation interaction
We present a new theoretical method to treat atom-rigid bender inelastic
collisions at the Close Coupling level (RBCC) in the space fixed frame. The
coupling between rotation and bending is treated exactly within the rigid
bender approximation and we obtain the cross section for the rotational
transition between levels belonging to different bending levels. The results of
this approach are compared with those obtained when using the rigid bender
averaged approximation (RBAA) introduced in our previous work dedicated to this
system. We discuss the validity of this approximation and of the previous
studies based on rigid linear HCN
Symmetry breaking in (gravitating) scalar field models describing interacting boson stars and Q-balls
We investigate the properties of interacting Q-balls and boson stars that sit
on top of each other in great detail. The model that describes these solutions
is essentially a (gravitating) two-scalar field model where both scalar fields
are complex. We construct interacting Q-balls or boson stars with arbitrarily
small charges but finite mass. We observe that in the interacting case - where
the interaction can be either due to the potential or due to gravity - two
types of solutions exist for equal frequencies: one for which the two scalar
fields are equal, but also one for which the two scalar fields differ. This
constitutes a symmetry breaking in the model. While for Q-balls asymmetric
solutions have always corresponding symmetric solutions and are thus likely
unstable to decay to symmetric solutions with lower energy, there exists a
parameter regime for interacting boson stars, where only asymmetric solutions
exist. We present the domain of existence for two interacting non-rotating
solutions as well as for solutions describing the interaction between rotating
and non-rotating Q-balls and boson stars, respectively.Comment: 33 pages including 21 figures; v2: version considerably extended: 6
new figures added, equations of motion added, discussion on varying
gravitational coupling added, references adde
U-duality in three and four dimensions
Using generalised geometry we study the action of U-duality acting in three
and four dimensions on the bosonic fields of eleven dimensional supergravity.
We compare the U-duality symmetry with the T-duality symmetry of double field
theory and see how the and SL(5) U-duality groups reduce
to the SO(2,2) and SO(3,3) T-duality symmetry groups of the type IIA theory. As
examples we dualise M2-branes, both black and extreme. We find that uncharged
black M2-branes become charged under U-duality, generalising the Harrison
transformation, while extreme M2-branes will become new extreme M2-branes. The
resulting tension and charges are quantised appropriately if we use the
discrete U-duality group .Comment: v1: 35 pages; v2: minor corrections in section 4.1.2, many references
added; v3: further discussion added on the conformal factor of the
generalised metric in section 2 and on the Wick-rotation used to construct
examples in section
Quantum Non-Equilibrium Steady States Induced by Repeated Interactions
We study the steady state of a finite XX chain coupled at its boundaries to
quantum reservoirs made of free spins that interact one after the other with
the chain. The two-point correlations are calculated exactly and it is shown
that the steady state is completely characterized by the magnetization profile
and the associated current. Except at the boundary sites, the magnetization is
given by the average of the reservoirs' magnetizations. The steady state
current, proportional to the difference in the reservoirs' magnetizations,
shows a non-monotonous behavior with respect to the system-reservoir coupling
strength, with an optimal current state for a finite value of the coupling.
Moreover, we show that the steady state can be described by a generalized Gibbs
state.Comment: to appear in Phys. Rev. Let
Foreword
This work reports on the performances of ohmic contacts fabricated on highly p-type doped 4H-SiC epitaxial layer selectively grown by vapor-liquid-solid transport. Due to the very high doping level obtained, the contacts have an ohmic behavior even without any annealing process. Upon variation of annealing temperatures, it was shown that both 500 and 800 °C annealing temperature lead to a minimum value of the Specific Contact Resistance (SCR) down to 1.3×10−6 Ω⋅cm2. However, a large variation of the minimum SCR values has been observed (up to 4×10−4 Ω⋅cm2). Possible sources of this fluctuation have been also discussed in this paper
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