161 research outputs found
Local realizations of -Oscillators in Quantum Mechanics
Representations of the quantum q-oscillator algebra are studied with
particular attention to local Hamiltonian representations of the Schroedinger
type. In contrast to the standard harmonic oscillators such systems exhibit a
continuous spectrum. The general scheme of realization of the q-oscillator
algebra on the space of wave functions for a one-dimensional Schroedinger
Hamiltonian shows the existence of non-Fock irreducible representations
associated to the continuous part of the spectrum and directly related to the
deformation. An algorithm for the mapping of energy levels is described.Comment: 12 pages, LaTeX, Phys. Lett. A, to be publishe
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.
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
q-Supersymmetric Generalization of von Neumann's Theorem
Assuming that there exist operators which form an irreducible representation
of the q-superoscillator algebra, it is proved that any two such
representations are equivalent, related by a uniquely determined superunitary
transformation. This provides with a q-supersymmetric generalization of the
well-known uniqueness theorem of von Neumann for any finite number of degrees
of freedom.Comment: 10 pages, Latex, HU-TFT-93-2
Some remarks on the Gauss decomposition for quantum group GL_q(n)
In this letter some properties of the Gauss decomposition of quantum group
with application to q-bosonization are considered.Comment: 11 page
Molecular basis of FIR-mediated c-myc transcriptional control
The far upstream element (FUSE) regulatory system promotes a peak in the concentration of c-Myc during cell cycle. First, the FBP transcriptional activator binds to the FUSE DNA element upstream of the c-myc promoter. Then, FBP recruits its specific repressor (FIR), which acts as an on/off transcriptional switch. Here we describe the molecular basis of FIR recruitment, showing that the tandem RNA recognition motifs of FIR provide a platform for independent FUSE DNA and FBP protein binding and explaining the structural basis of the reversibility of the FBP-FIR interaction. We also show that the physical coupling between FBP and FIR is modulated by a flexible linker positioned sequentially to the recruiting element. Our data explain how the FUSE system precisely regulates c-myc transcription and suggest that a small change in FBP-FIR affinity leads to a substantial effect on c-Myc concentration.MRC Grant-in-aid U11757455
Field on Poincare group and quantum description of orientable objects
We propose an approach to the quantum-mechanical description of relativistic
orientable objects. It generalizes Wigner's ideas concerning the treatment of
nonrelativistic orientable objects (in particular, a nonrelativistic rotator)
with the help of two reference frames (space-fixed and body-fixed). A technical
realization of this generalization (for instance, in 3+1 dimensions) amounts to
introducing wave functions that depend on elements of the Poincare group . A
complete set of transformations that test the symmetries of an orientable
object and of the embedding space belongs to the group . All
such transformations can be studied by considering a generalized regular
representation of in the space of scalar functions on the group, ,
that depend on the Minkowski space points as well as on the
orientation variables given by the elements of a matrix .
In particular, the field is a generating function of usual spin-tensor
multicomponent fields. In the theory under consideration, there are four
different types of spinors, and an orientable object is characterized by ten
quantum numbers. We study the corresponding relativistic wave equations and
their symmetry properties.Comment: 46 page
Characterization and physical modeling of endurance in embedded non-volatile memory technology
Transient and endurance mechanisms in highperformance embedded non-volatile memory flash devices are investigated in detail. An extraction methodology combining measurements on equivalent transistors and flash cells is proposed to discriminate the effects of defects on program/erase (P/E) efficiencies and on DC characteristics. A semi-analytical multiphonon-assisted charge trapping model is used to investigate the role and the impact of trapped charges on channel hotelectron injection and Fowler-Nordheim efficiencies, threshold voltage variations and endurance characteristics. © 2011 IEEE
Realizations of Real Low-Dimensional Lie Algebras
Using a new powerful technique based on the notion of megaideal, we construct
a complete set of inequivalent realizations of real Lie algebras of dimension
no greater than four in vector fields on a space of an arbitrary (finite)
number of variables. Our classification amends and essentially generalizes
earlier works on the subject.
Known results on classification of low-dimensional real Lie algebras, their
automorphisms, differentiations, ideals, subalgebras and realizations are
reviewed.Comment: LaTeX2e, 39 pages. Essentially exetended version. Misprints in
Appendix are correcte
A formally verified compiler back-end
This article describes the development and formal verification (proof of
semantic preservation) of a compiler back-end from Cminor (a simple imperative
intermediate language) to PowerPC assembly code, using the Coq proof assistant
both for programming the compiler and for proving its correctness. Such a
verified compiler is useful in the context of formal methods applied to the
certification of critical software: the verification of the compiler guarantees
that the safety properties proved on the source code hold for the executable
compiled code as well
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