220 research outputs found
Quantum calculations of the carrier mobility in thin films: Methodology, Matthiessen's rule and comparison with semi-classical approaches
We discuss the calculation of the carrier mobility in silicon films within
the quantum Non-Equilibrium Green's Functions (NEGF) framework. We introduce a
new method for the extraction of the carrier mobility that is free from contact
resistance contamination, and provides accurate mobilities at a reasonable
cost, with minimal needs for ensemble averages. We then introduce a new
paradigm for the definition of the partial mobility associated with a
given elastic scattering mechanism "M", taking phonons (PH) as a reference
(). We argue that this definition
makes better sense in a quantum transport framework as it is free from long
range interference effects that can appear in purely ballistic calculations. As
a matter of fact, these mobilities satisfy Matthiessen's rule for three
mechanisms [surface roughness (SR), remote Coulomb scattering (RCS) and
phonons] much better than the usual, single mechanism calculations. We also
discuss the problems raised by the long range spatial correlations in the RCS
disorder. Finally, we compare semi-classical Kubo-Greenwood (KG) and quantum
NEGF calculations. We show that KG and NEGF are in reasonable agreement for
phonon and RCS, yet not for SR. We point to possible deficiencies in the
treatment of SR scattering in KG, opening the way for further improvements.Comment: Submitted to Journal of Applied Physic
Contact resistances in trigate and FinFET devices in a Non-Equilibrium Green's Functions approach
We compute the contact resistances in trigate and FinFET devices
with widths and heights in the 4 to 24 nm range using a Non-Equilibrium Green's
Functions approach. Electron-phonon, surface roughness and Coulomb scattering
are taken into account. We show that represents a significant part
of the total resistance of devices with sub-30 nm gate lengths. The analysis of
the quasi-Fermi level profile reveals that the spacers between the heavily
doped source/drain and the gate are major contributors to the contact
resistance. The conductance is indeed limited by the poor electrostatic control
over the carrier density under the spacers. We then disentangle the ballistic
and diffusive components of , and analyze the impact of different
design parameters (cross section and doping profile in the contacts) on the
electrical performances of the devices. The contact resistance and variability
rapidly increase when the cross sectional area of the channel goes below
nm. We also highlight the role of the charges trapped at the
interface between silicon and the spacer material.Comment: 16 pages, 15 figure
Model for the on-site matrix elements of the tight-binding hamiltonian of a strained crystal: Application to silicon, germanium and their alloys
We discuss a model for the on-site matrix elements of the sp3d5s*
tight-binding hamiltonian of a strained diamond or zinc-blende crystal or
nanostructure. This model features on-site, off-diagonal couplings between the
s, p and d orbitals, and is able to reproduce the effects of arbitrary strains
on the band energies and effective masses in the full Brillouin zone. It
introduces only a few additional parameters and is free from any ambiguities
that might arise from the definition of the macroscopic strains as a function
of the atomic positions. We apply this model to silicon, germanium and their
alloys as an illustration. In particular, we make a detailed comparison of
tight-binding and ab initio data on strained Si, Ge and SiGe.Comment: Submitted to Phys. Rev.
Localized Endomorphisms of the Chiral Ising Model
Based on the treatment of the chiral Ising model by Mack and Schomerus, we
present examples of localized endomorphisms and
. It is shown that they lead to the same
superselection sectors as the global ones in the sense that unitary equivalence
and holds. Araki's formalism of the selfdual CAR algebra is
used for the proof. We prove local normality and extend representations and
localized endomorphisms to a global algebra of observables which is generated
by local von Neumann algebras on the punctured circle. In this framework, we
manifestly prove fusion rules and derive statistics operators.Comment: 41 pages, latex2
Generalized q-Oscillators and their Hopf Structures
We study the relationships among the various forms of the oscillator
algebra and consider the conditions under which it supports a Hopf structure.
We also present a generalization of this algebra together with its
corresponding Hopf structure. Its multimode extensions are also considered.Comment: 14 page
I-21 Current therapeutic guidelines in Duchenne Muscular Dystrophy to prolong life
Duchenne's myopathy is an X-linked disease with well defined evolutionary phases, characterized by degradation of the walking function, development of evolutive scoliosis and progressive decline of the respiratory function leading patients to premature death.
In 1985 Y. Rideau in France carried out a new global therapeutic strategy for treatment of lower limb deformities, scoliosis deformity and progressive restrictive syndrome.
The indication for surgery at the lower limbs is made very early, at the onset of the first signs of disease. The procedures are carried out at the same time and always bilaterally; they include: (i) hip section of superficial flexors; (ii) iliotibial band resection; (iii) subcutaneous tenotomy of semitendineous and gracilis; (iv) subcutaneous lengthening of Achilles tendons.
In the post-operative period, the patient begins exercises of active and passive mobility in few days and after three weeks recovers his performances; ambulation will remain almost normal for several years. A comparison of two groups of patients, the first precociously operated on the lower limbs, the other one not operated, shows better performances in the operated group.
The indications for surgical treatment of Duchenne scoliosis must be made after the loss of ambulation and not too late, to avoid the concurrent respiratory restrictive syndrome makes the patient inoperable. Over ten years ago, in Poitiers, a specific instrumentation for Duchenne scoliosis was created, providing for cylindrical rods fixed by peduncular screws at the sacro-lumbar level. On the dorso-lumbar level, the rod becomes flat to allow more flexibility of the trunk. The complications observed in a group of 55 patients operated for scoliosis, consisted in 2 cases of breaking of rods and 1 superficial infection. The surgery approach in DMD has the double aim to prolong the time of the autonomous ambulation and to avoid the evolution of scoliosis, limiting the harmful effects of the scoliosis on the respiratory function.
However, the surgery alone is unable to prolong the life expectancy in these patients, without treating the restrictive respiratory syndrome, first by nasal ventilation and then by elective tracheotomy, essential for the survival of the patient
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