Periodically rippled graphene: growth and spatially resolved electronic structure

We studied the growth of an epitaxial graphene monolayer on Ru(0001). The graphene monolayer covers uniformly the Ru substrate over lateral distances larger than several microns reproducing the structural defects of the Ru substrate. The graphene is rippled with a periodicity dictated by the difference in lattice parameter between C and Ru. The theoretical model predict inhomogeneities in the electronic structure. This is confirmed by measurements in real space by means of scanning tunnelling spectroscopy. We observe electron pockets at the higher parts of the ripples.Comment: 5 page

Carrier and Light Trapping in Graded Quantum Well Laser Structures

We investigated the carrier and light trapping in GaInAs/AlGaAs single quantum well laser structures by means of time resolved photoluminescence and Raman spectroscopy. The influence of the shape and depth of the confinement potential and of the cavity geometry was studied by using different AlGaAs/GaAs short-period superlattices as barriers. Our results show that grading the optical cavity improves considerably both carrier and light trapping in the quantum well, and that the trapping efficiency is enhanced by increasing the graded confining potential.Comment: PDF-format, 15 pages (including 4 figures), Applied Physics Letters (June 2000

Longer hospital stay, more complications, and increased mortality but substantially improved function after knee replacement in older patients

Background and purpose — Total knee replacement (TKR) is being increasingly performed in elderly patients, yet there is little information on specific requirements and complication rates encountered by this group. We assessed whether elderly patients undergoing TKR had different length of stay, requirements, complication rates, and functional outcomes compared to younger counterparts. Patients and methods — We analyzed prospectively gathered data on 3,144 consecutive primary TKRs (in 2,092 patients aged less than 75 years, 694 patients aged between 75 and 80 years, and 358 patients aged over 80 years at the time of surgery). Results — Incidence of blood transfusion, urinary catheterization, postoperative confusion, cardiac arrhythmia, and 1-year mortality increased with age, even after adjusting for confounding factors, whereas the incidences of chest infection and mortality at 1 month were highest in those aged 75–80. Rates of thromboembolism, prosthetic infection, and revision were similar in the 3 age groups. All groups showed similar substantial improvements in American Knee Society (AKS) knee scores, which were maintained at 5 years. Older patients had smaller improvements in AKS function score, which deteriorated between 3 and 5 years postoperatively, in contrast to the younger group. Interpretation — Elderly people stand to gain considerably from TKR, particularly in terms of pain relief, and they should not be denied surgery based solely on age. However, they should be warned that they can expect a longer length of stay, a higher requirement for blood transfusion and/or urinary catheterization, and more medical complications postoperatively. Mortality was also higher in the older age groups. The risks have been quantified to assist in perioperative counselling, informed consent, and healthcare planning.peer-reviewe

Breakdown of anomalous channeling with ion energy for accurate strain determination in gan-based heterostructures

The influence of the beam energy on the determination of strain state with ion channeling in GaN-based heterostructures (HSs) is addressed. Experimental results show that anomalous channeling may hinder an accurate analysis due to the steering effects at the HS interface, which are more intense at lower ion energies. The experimental angular scans have been well reproduced by Monte Carlo simulations, correlating the steering effects with the close encounter probability at the interface. Consequently, limitations in the determination of the strain state by ion channeling can be overcome by selecting the adequate beam energy

Effect of Finite Impurity Mass on the Anderson Orthogonality Catastrophe in One Dimension

A one-dimensional tight-binding Hamiltonian describes the evolution of a single impurity interacting locally with $N$ electrons. The impurity spectral function has a power-law singularity $A(\omega)\propto\mid\omega-\omega_0\mid^{-1+\beta}$ with the same exponent $\beta$ that characterizes the logarithmic decay of the quasiparticle weight $Z$ with the number of electrons $N$, $Z\propto N^{-\beta}$. The exponent $\beta$ is computed by (1) perturbation theory in the interaction strength and (2) numerical evaluations with exact results for small systems and variational results for larger systems. A nonanalytical behavior of $\beta$ is observed in the limit of infinite impurity mass. For large interaction strength, the exponent depends strongly on the mass of the impurity in contrast to the perturbative result.Comment: 26 pages, RevTeX, 7 figures included, to be published in Phys. Rev.

Método complexométrico para el análisis rápido del cemento portland

Not availableSe aborda en este trabajo el problema del análisis rápido del cemento y de los materiales silíceos por medios puramente químicos y sin la ayuda que pudieran prestar otras técnicas físicas. Se adopta un método volumétrico casi general, basado en la .complexometría, sin más excepción que la determinación gravimétrica acelerada de la sílice. Para la determinación del óxido férrico se mantiene el procedimiento dicromatométrico por su sencillez y precisión. Por complexometría se determinan con Complexona III 0,01 M la suma de alúmina y ácido férrico (la alúmina se calcula por diferencia), la suma de cal y magnesia y, aparte, la cal (la magnesia se calcula por diferencia) y el trióxido de azufre. El método se manifiesta tan preciso y reproducible como los clásicos l (dentro de las tolerancias de las Normas A. S. T. M.) y es mucho más rápido, puesto que permite efectuar el análisis completo del cemento en unas tres horas. Es también más sencillo, ya que ahorra pesadas y calcificaciones (gravimetrías) y no requiere el empleo de equipos especiales de colorimetría, fotometría, espectrometría de rayos X, si bien se conjuga bien con cualquiera de estas técnicas de naturaleza física. Es susceptible de sucesivas mejoras, y en tal sentido se continúa trabajando en el Departamento de Quimica del I.E.T.c.c

Growth and characterization of InGaN/GaN quantum dots for violet/blue applications

We report on plasma-assisted molecular beam epitaxy growth and characterization of InGaN/GaN quantum dots (QDs) for violet/blue applications