54 research outputs found
The random phase property and the Lyapunov Spectrum for disordered multi-channel systems
A random phase property establishing in the weak coupling limit a link between quasi-one-dimensional random Schrödinger operators and full random matrix theory is advocated. Briefly summarized it states that the random transfer matrices placed into a normal system of coordinates act on the isotropic frames and lead to a Markov process with a unique invariant measure which is of geometric nature. On the elliptic part of the transfer matrices, this measure is invariant under the unitaries in the hermitian symplectic group of the universality class under study. While the random phase property can up to now only be proved in special models or in a restricted sense, we provide strong numerical evidence that it holds in the Anderson model of localization. A main outcome of the random phase property is a perturbative calculation of the Lyapunov exponents which shows that the Lyapunov spectrum is equidistant and that the localization lengths for large systems in the unitary, orthogonal and symplectic ensemble differ by a factor 2 each. In an Anderson-Ando model on a tubular geometry with magnetic field and spin-orbit coupling, the normal system of coordinates is calculated and this is used to derive explicit energy dependent formulas for the Lyapunov spectrum
Electric field and exciton structure in CdSe nanocrystals
Quantum Stark effect in semiconductor nanocrystals is theoretically
investigated, using the effective mass formalism within a
Baldereschi-Lipari Hamiltonian model for the hole states. General expressions
are reported for the hole eigenfunctions at zero electric field. Electron and
hole single particle energies as functions of the electric field
() are reported. Stark shift and binding energy of the
excitonic levels are obtained by full diagonalization of the correlated
electron-hole Hamiltonian in presence of the external field. Particularly, the
structure of the lower excitonic states and their symmetry properties in CdSe
nanocrystals are studied. It is found that the dependence of the exciton
binding energy upon the applied field is strongly reduced for small quantum dot
radius. Optical selection rules for absorption and luminescence are obtained.
The electric-field induced quenching of the optical spectra as a function of
is studied in terms of the exciton dipole matrix element. It
is predicted that photoluminescence spectra present anomalous field dependence
of the emission lines. These results agree in magnitude with experimental
observation and with the main features of photoluminescence experiments in
nanostructures.Comment: 9 pages, 7 figures, 1 tabl
Searching for Higgs : From LEP towards LHC
After a brief introduction to the theoretical basis of the Higgs mechanism
for generating the masses of elementary particles, the experimental searches
for Higgs particles will be summarized, from bounds at LEP to inferences for
LHC. The report will focus on the Standard Model, though some central results
on extended Higgs systems, as conjectured for example in supersymmetric
theories, will also be recapitulated. Alternative scenarios based on
spontaneous symmetry breaking by novel strong interactions are adumbrated at
the theoretical level.Comment: Added reference
Splenectomy for splenomegaly and secondary hypersplenism
Splenomegaly and secondary hypersplenism may be associated with acute and chronic infections, autoimmune states, portal hypertension or splenic vein thrombosis, and a number of infiltrative and neoplastic conditions involving the spleen. Our experience and that of others with these various conditions demonstrates that the decision to perform splenectomy should be based on well-defined and often strictly limited indications. Except for idiopathic splenomegaly, the presence and severity of secondary hypersplenism or severely symptomatic splenomegaly should be well documented. In each case, the potential for palliation and known mean duration of expected response must be weighed against the increased morbidity and mortality of splenectomy (as compared to operation for “primary” hypersplenism) . La splĂ©nomĂ©galie avec hypersplĂ©nisme secondaire relève de multiples causes: infection aigue ou chronique, Ă©tats autoimmunologiques, hypertension portale, thrombose de la veine splĂ©nique, lĂ©sions tumorales splĂ©niques. L'expĂ©rience de l'auteur qui rejoint celle de nombreux collègues lui permet d'affirmer que les indications de la splĂ©nectomie doivent ĂŞtre bien dĂ©finies et sont strictement limitĂ©es. A l'exception de la splĂ©nomĂ©galie idiopathique, l'existence et l'intensitĂ© de l'hypersplĂ©nisme, l'importance des symptomes provoquĂ©s par la splĂ©nomĂ©galie doivent ĂŞtre aprrĂ©ciĂ©es avec prĂ©cision. Dans chaque cas le potentiel de la rĂ©mission de l'affection et la durĂ©e de la rĂ©mission doivent ĂŞtre pris en considĂ©ration en fonction de l'Ă©ventuelle morbiditĂ© et de l'Ă©ventuelle mortalitĂ© de la splĂ©nectomie (par comparaison avec la splĂ©nectomie pour hypersplĂ©nisme primaire). Eplenomegalia e hiperesplenismo secundario pueden estar asociados con infecciones agudas y crĂłnicas, estados autoinmunes (sĂndrome de Felty, lupus eritematoso sistĂ©mico), “esplenomegalia congestiva” por hipertensiĂłn portal o trombosis de la vena esplĂ©nica y con una variedad de entidades de tipo infiltrativo y neoplásico que afectan al bazo (sarcoidosis, enfermedad de Gaucher, varios desĂłrdenes mieloproliferativos y linfomas). Nuestra experiencia, y aquella de otros autores, con tales condiciones demuestra que la decisiĂłn de realizar esplenectomĂa debe estar fundamentada en indicaciones bien definidas y estrictamente limitadas. Excepto en casos de esplenomegalia idiopática, la presencia y severidad del hiperesplenismo secundario o de esplenomegalia severamente sintomática debe ser bien documentada. En cada caso debe determinarse el potencial de paliaciĂłn y la duraciĂłn de la respuesta que se espera obtener frente a la incrementada morbilidad y mortalidad de la esplenectomĂa (en comparaciĂłn con la operaciĂłn que se realiza por hiperesplenismo “primario”).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41318/1/268_2005_Article_BF01655279.pd
Combining Hotel Promotions, Discount Packages, and Yield Management Systems: Make Sure It's Legal
The Two-Oscillator Circadian System of Tree Shrews (Tupaia belangeri) and Its Response to Light and Dark Pulses
- …