982 research outputs found
Quantum Monte Carlo study of circular quantum dots in presence of Rashba interaction
We present the numerical Quantum Monte Carlo results for the ground state
energy of circular quantum dots in which Rashba spin-orbit iteraction is
present. Diffusion Monte Carlo with spin propagation is applied in order to
treat the spin-orbit interaction correctly, following previous work done in the
fieldof the two-dimensional electron gas. Together with ground state energies,
also numerical results for density and spin-density profiles are given
Spin-orbit excitations of quantum wells
Confinement asymmetry effects on the photoabsorption of a quantum well are
discussed by means of a sum-rules approach using a Hamiltonian including a
Rashba spin-orbt coupling. We show that while the strength of the excitation is
zero when the spin-orbit coupling is neglected, the inclusion of the spin-orbit
interaction gives rise to a non zero strength and mean excitation energy in the
far-infrared region. A simple expression for these quantities up to the second
order in the Rashba parameter was derived. The effect of two-body Coulomb
interaction is then studied by means of a Quantum Monte Carlo calculation,
showing that electron-electron correlations induce only a small deviation from
the independent particle model result
The Conformal Willmore Functional: a Perturbative Approach
The conformal Willmore functional (which is conformal invariant in general
Riemannian manifold ) is studied with a perturbative method: the
Lyapunov-Schmidt reduction. Existence of critical points is shown in ambient
manifolds -where is a metric close
and asymptotic to the euclidean one. With the same technique a non existence
result is proved in general Riemannian manifolds of dimension three.Comment: 34 pages; Journal of Geometric Analysis, on line first 23 September
201
Adsorption of rare-gas atoms on Cu(111) and Pb(111) surfaces by van der Waals-corrected Density Functional Theory
The DFT/vdW-WF method, recently developed to include the Van der Waals
interactions in Density Functional Theory (DFT) using the Maximally Localized
Wannier functions, is applied to the study of the adsorption of rare-gas atoms
(Ne, Ar, Kr, and Xe) on the Cu(111) and Pb(111) surfaces, at three
high-symmetry sites. We evaluate the equilibrium binding energies and
distances, and the induced work-function changes and dipole moments. We find
that, for Ne, Ar, and Kr on the Cu(111) surface the different adsorption
configurations are characterized by very similar binding energies, while the
favored adsorption site for Xe on Cu(111) is on top of a Cu atom, in agreement
with previous theoretical calculations and experimental findings, and in common
with other close-packed metal surfaces. Instead, the favored site is always the
hollow one on the Pb(111) surface, which therefore represents an interesting
system where the investigation of high-coordination sites is possible.
Moreover, the Pb(111) substrate is subject, upon rare-gas adsorption, to a
significantly smaller change in the work function (and to a correspondingly
smaller induced dipole moment) than Cu(111). The role of the chosen reference
DFT functional and of different Van der Waals corrections, and their dependence
on different rare-gas adatoms, are also discussed
Critical sets of nonlinear Sturm-Liouville operators of Ambrosetti-Prodi type
The critical set C of the operator F:H^2_D([0,pi]) -> L^2([0,pi]) defined by
F(u)=-u''+f(u) is studied. Here X:=H^2_D([0,pi]) stands for the set of
functions that satisfy the Dirichlet boundary conditions and whose derivatives
are in L^2([0,pi]). For generic nonlinearities f, C=\cup C_k decomposes into
manifolds of codimension 1 in X. If f''0, the set C_j is shown to be
non-empty if, and only if, -j^2 (the j-th eigenvalue of u -> u'') is in the
range of f'. The critical components C_k are (topological) hyperplanes.Comment: 6 pages, no figure
Direct electrification of Rh/Al2O3 washcoated SiSiC foams for methane steam reforming: An experimental and modelling study
Electrified methane steam reforming (eMSR) is a promising concept for low-carbon hydrogen production. We investigate an innovative eMSR reactor where SiSiC foams, coated with Rh/Al2O3 catalyst, act as electrical resistances to generate the reaction heat via the Joule effect. The novel system was studied at different temperatures, space velocities, operating pressures and catalyst loadings. Thanks to efficient heating, active catalyst and optimal substrate geometry, complete methane conversions were observed even at a high space velocity of 200000 Nl/h/kgcat. A specific energy demand as low as 1.24 kWh/Nm3H2, with an unprecedented energy efficiency of 81%, was achieved on a washcoated foam with catalyst density of 86.3 g/L (GHSV = 150000 Nl/h/kgcat, S/C = 4.1, ambient pressure). A mathematical model was validated against measured performance indicators and used to design an intensified eMSR unit for small scale H2 production.(c) 2023 The Authors. Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/)
Recurrent respiratory infections in Down syndrome and control subjects: a prospective study of bacterial adhesion.
Physical Adsorption at the Nanoscale: Towards Controllable Scaling of the Substrate-Adsorbate van der Waals Interaction
The Lifshitz-Zaremba-Kohn (LZK) theory is commonly considered as the correct
large-distance limit for the van der Waals (vdW) interaction of adsorbates
(atoms, molecules, or nanoparticles) with solid substrates. In the standard
approximate form, implicitly based on "local" dielectric functions, the LZK
approach predicts universal power laws for vdW interactions depending only on
the dimensionality of the interacting objects. However, recent experimental
findings are challenging the universality of this theoretical approach at
finite distances of relevance for nanoscale assembly. Here, we present a
combined analytical and numerical many-body study demonstrating that physical
adsorption can be significantly enhanced at the nanoscale. Regardless of the
band gap or the nature of the adsorbate specie, we find deviations from
conventional LZK power laws that extend to separation distances of up to 10--20
nanometers. Comparison with recent experimental observation of ultra
long-ranged vdW interactions in the delamination of graphene from a silicon
substrate reveals qualitative agreement with the present theory. The
sensitivity of vdW interactions to the substrate response and to the adsorbate
characteristic excitation frequency also suggests that adsorption strength can
be effectively tuned in experiments, paving the way to an improved control of
physical adsorption at the nanoscale
Action minimizing orbits in the n-body problem with simple choreography constraint
In 1999 Chenciner and Montgomery found a remarkably simple choreographic
motion for the planar 3-body problem (see \cite{CM}). In this solution 3 equal
masses travel on a eight shaped planar curve; this orbit is obtained minimizing
the action integral on the set of simple planar choreographies with some
special symmetry constraints. In this work our aim is to study the problem of
masses moving in \RR^d under an attractive force generated by a potential
of the kind , , with the only constraint to be a simple
choreography: if are the orbits then we impose the
existence of x \in H^1_{2 \pi}(\RR,\RR^d) such that q_i(t)=x(t+(i-1) \tau),
i=1,...,n, t \in \RR, where . In this setting, we first
prove that for every d,n \in \NN and , the lagrangian action
attains its absolute minimum on the planar circle. Next we deal with the
problem in a rotating frame and we show a reacher phenomenology: indeed while
for some values of the angular velocity minimizers are still circles, for
others the minima of the action are not anymore rigid motions.Comment: 24 pages; 4 figures; submitted to Nonlinearit
Positive Least Energy Solutions and Phase Separation for Coupled Schrodinger Equations with Critical Exponent: Higher Dimensional Case
We study the following nonlinear Schr\"{o}dinger system which is related to
Bose-Einstein condensate: {displaymath} {cases}-\Delta u +\la_1 u = \mu_1
u^{2^\ast-1}+\beta u^{\frac{2^\ast}{2}-1}v^{\frac{2^\ast}{2}}, \quad x\in
\Omega, -\Delta v +\la_2 v =\mu_2 v^{2^\ast-1}+\beta v^{\frac{2^\ast}{2}-1}
u^{\frac{2^\ast}{2}}, \quad x\in \om, u\ge 0, v\ge 0 \,\,\hbox{in \om},\quad
u=v=0 \,\,\hbox{on \partial\om}.{cases}{displaymath} Here \om\subset \R^N
is a smooth bounded domain, is the Sobolev critical
exponent, -\la_1(\om)0 and , where
\lambda_1(\om) is the first eigenvalue of with the Dirichlet
boundary condition. When \bb=0, this is just the well-known Brezis-Nirenberg
problem. The special case N=4 was studied by the authors in (Arch. Ration.
Mech. Anal. 205: 515-551, 2012). In this paper we consider {\it the higher
dimensional case }. It is interesting that we can prove the existence
of a positive least energy solution (u_\bb, v_\bb) {\it for any } (which can not hold in the special case N=4). We also study the limit
behavior of (u_\bb, v_\bb) as and phase separation is
expected. In particular, u_\bb-v_\bb will converge to {\it sign-changing
solutions} of the Brezis-Nirenberg problem, provided . In case
\la_1=\la_2, the classification of the least energy solutions is also
studied. It turns out that some quite different phenomena appear comparing to
the special case N=4.Comment: 48 pages. This is a revised version of arXiv:1209.2522v1 [math.AP
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