Electroreflectance spectroscopy in self-assembled quantum dots: lens symmetry

Modulated electroreflectance spectroscopy $\Delta R/R$ of semiconductor self-assembled quantum dots is investigated. The structure is modeled as dots with lens shape geometry and circular cross section. A microscopic description of the electroreflectance spectrum and optical response in terms of an external electric field (${\bf F}$) and lens geometry have been considered. The field and lens symmetry dependence of all experimental parameters involved in the $\Delta R/R$ spectrum have been considered. Using the effective mass formalism the energies and the electronic states as a function of ${\bf F}$ and dot parameters are calculated. Also, in the framework of the strongly confined regime general expressions for the excitonic binding energies are reported. Optical selection rules are derived in the cases of the light wave vector perpendicular and parallel to $$. Detailed calculation of the Seraphin coefficients and electroreflectance spectrum are performed for the InAs and CdSe nanostructures. Calculations show good agreement with measurements recently performed on CdSe/ZnSe when statistical distribution on size is considered, explaining the main observed characteristic in the electroreflectance spectra

Blue flag with yellow tiger? Flags, authenticity and identity

The Flag of the Formosa Republic in the collection of the National Taiwan Museum is a national icon. It is a copy of one made in 1895 to mark the formation of a new Taiwanese republic; this replica, described in a contemporary newspaper account as an exact copy, was made in Japan in 1909. The painted flag was an intriguing puzzle. Instrumental analysis and a close study of the flag itself and of surviving historic photographs and records were used to try to establish whether what looked like later additions and repairs were actually part of the original construction. An international team of conservators and scientists from Taiwan, the UK, the USA and Germany carried out the investigation and the conservation treatment. Although dye analysis was inconclusive and it has not yet been possible to ascertain the original colour, it was felt that an addition in the upper right corner and some of the repairs could well be part of the original construction and these were left in situ though other repairs were removed. The paper lining was removed, revealing that the flag was painted on both sides. The fabric was cleaned using a vacuum suction table, while the paint surface was cleaned with swabs. The flag was supported using an adhesive treatment with Lascaux acrylic resin

The Electron Glass in a Switchable Mirror: Relaxation, Aging and Universality

The rare earth hydride YH$_{3-\delta}$ can be tuned through the metal-insulator transition both by changing $\delta$ and by illumination with ultraviolet light. The transition is dominated by strong electron-electron interactions, with transport in the insulator sensitive to both a Coulomb gap and persistent quantum fluctuations. Via a systematic variation of UV illumination time, photon flux, Coulomb gap depth, and temperature, we demonstrate that polycrystalline YH$_{3-\delta}$ serves as a model system for studying the properties of the interacting electron glass. Prominent among its features are logarithmic relaxation, aging, and universal scaling of the conductivity

Glassy behavior of electrons near metal-insulator transitions

The emergence of glassy behavior of electrons is investigated for systems close to the disorder and/or interaction-driven metal-insulator transitions. Our results indicate that Anderson localization effects strongly stabilize such glassy behavior, while Mott localization tends to suppress it. We predict the emergence of an intermediate metallic glassy phase separating the insulator from the normal metal. This effect is expected to be most pronounced for sufficiently disordered systems, in agreement with recent experimental observations.Comment: Final version as published in Physical Review Letter

Off-equilibrium dynamics of the two-dimensional Coulomb glass

The dynamics of the 2D Coulomb glass model is investigated by kinetic Monte Carlo simulation. An exponential divergence of the relaxation time signals a zero-temperature freezing transition. At low temperatures the dynamics of the system is glassy. The local charge correlations and the response to perturbations of the local potential show aging. The dynamics of formation of the Coulomb gap is slow and the density of states at the Fermi level decays in time as a power law. The relevance of these findings for recent transport experiments in Anderson-insulating films is pointed out.Comment: 7 pages, 7 figure

Complexes of Copper with a Flexible Bis-benzimidazole Ligand

The flexible bidentate ligand 1,3-bis(benzimidazol-2-yl)propane, L3, and its N-methylated derivative L4, form complexes with CUI and CUII. The X-ray crystal structure of [Cu(L4)(MeCN)] (PF6) (1) shows a trigonal coordination of the CuI with the eight-membered chelate ring adopting a half-chair conformation. With CuII in EtOH, L3 forms dimeric [(L3)Cu(μ-EtO)2Cu(L3)](ClO4)2 · 2EtOH (2) whose X-ray crystal structure shows CuII in a distorted square-planar environment with one bidentate ligand and two bridging ethoxides. The chelate ring now has a boat-chair conformation which forms a hydrophobic pocket around the metal

Universal Crossover between Efros-Shklovskii and Mott Variable-Range-Hopping Regimes

A universal scaling function, describing the crossover between the Mott and the Efros-Shklovskii hopping regimes, is derived, using the percolation picture of transport in strongly localized systems. This function is agrees very well with experimental data. Quantitative comparison with experiment allows for the possible determination of the role played by polarons in the transport.Comment: 7 pages + 1 figure, Revte

Non-Markovian Configurational Diffusion and Reaction Coordinates for Protein Folding

The non-Markovian nature of polymer motions is accounted for in folding kinetics, using frequency-dependent friction. Folding, like many other problems in the physics of disordered systems, involves barrier crossing on a correlated energy landscape. A variational transition state theory (VTST) that reduces to the usual Bryngelson-Wolynes Kramers approach when the non-Markovian aspects are neglected is used to obtain the rate, without making any assumptions regarding the size of the barrier, or the memory time of the friction. The transformation to collective variables dependent on the dynamics of the system allows the theory to address the controversial issue of what are ``good'' reaction coordinates for folding.Comment: 9 pages RevTeX, 3 eps-figures included, submitted to PR

Managed delay for coronary artery bypass graft surgery: The experience at one Canadian center

AbstractObjectives. This study sought to assess the impact of delaying coronary artery bypass surgery at one Canadian academic tertiary referral center.Background. Universal access to medical services in Canada comes at the expense of waiting lists whose impact has been incompletely assessed.Methods. A prospective, observational study of all residents of Nova Scotia and Prince Edward Island accepted for bypass surgery between 1 April 1992 and 31 October 1992 was undertaken to determine 1) whether triage guidelines were being followed; and 2) the incidence of cardiac death, nonfatal myocardial infarction and worsening symptoms associated with delayed operation. The analysis had 90% power to detect a mortality rate of ≥3% (alpha 0.05).Results. Of 423 patients referred, 35% were triaged as urgent, 9.7% as semiurgent A, 39% as semiurgent B and 16.3% as elective, with no age or gender bias identified. Operation occurred at ≤1 week in 25%, ≤1 month in 47%, and >6 months in 1.4%. There were no nonfatal myocardial infarctions, but five cardiac deaths occurred (1.2%). Of 275 patients not initially classified as urgent, 12.4% required reclassification to higher priorities because of worsening symptoms: none had perioperative myocardial infarction or died. One in four patients queued longer than target waiting times. Only 4% of patients considered prioritization on the basis of medical need unfair, but 64% experienced at least moderate anxiety.Conclusions. This triage system equitably stratified patients to a queue. Deaths were rare and could not be attributed to the triage process. Patients with worsening clinical status were safely accommodated with earlier waiting times, but concerns remain regarding excessive waiting times and patient anxiety