Laser surface cladding of steel

Imperial Users onl

Effect of the nearby levels on the resonance fluorescence spectrum of the atom-field interaction

We study the resonance fluorescence in the Jaynes-Cummings model when nearby levels are taking into account. We show that the Stark shift produced by such levels generates a displacement of the peaks of the resonance fluorescence due to an induced effective detuning and also induces an asymmetry. Specific results are presented assuming a coherent and a thermal fields

From circular paths to elliptic orbits: A geometric approach to Kepler's motion

The hodograph, i.e. the path traced by a body in velocity space, was introduced by Hamilton in 1846 as an alternative for studying certain dynamical problems. The hodograph of the Kepler problem was then investigated and shown to be a circle, it was next used to investigate some other properties of the motion. We here propose a new method for tracing the hodograph and the corresponding configuration space orbit in Kepler's problem starting from the initial conditions given and trying to use no more than the methods of synthetic geometry in a sort of Newtonian approach. All of our geometric constructions require straight edge and compass only.Comment: 9 pages, 4 figure

Fast on-wafer electrical, mechanical, and electromechanical characterization of piezoresistive cantilever force sensors

Validation of a technological process requires an intensive characterization of the performance of the resulting devices, circuits, or systems. The technology for the fabrication of micro and nanoelectromechanical systems (MEMS and NEMS) is evolving rapidly, with new kind of device concepts for applications like sensing or harvesting are being proposed and demonstrated. However, the characterization tools and methods for these new devices are still not fully developed. Here, we present an on-wafer, highly precise, and rapid characterization method to measure the mechanical, electrical, and electromechanical properties of piezoresistive cantilevers. The setup is based on a combination of probe-card and atomic force microscopy technology, it allows accessing many devices across a wafer and it can be applied to a broad range of MEMS and NEMS. Using this setup we have characterized the performance of multiple submicron thick piezoresistive cantilever force sensors. For the best design we have obtained a force sensitivity ℜ_F = 158μV/nN, a noise of 5.8 μV (1 Hz–1 kHz) and a minimum detectable force of 37 pN with a relative standard deviation of σ_r ≈ 8%. This small value of σr, together with a high fabrication yield >95%, validates our fabrication technology. These devices are intended to be used as bio-molecular detectors for the measurement of intermolecular forces between ligand and receptor molecule pairs

Efecto de los recubrimientos de pintura sobre la resistividad al vapor de yesos - Effect of paint on vapour resistivity in plaster

Se estudia el fenómeno de la resistividad al vapor de los de yeso y el efecto impermeabilizante que producen los recubrimientos de pintura sobre diversos tipos de yeso y escayola. Para ello, se ensayan probetas desnudas y recubiertas con distintos tipos de pintura, así como coloreados en masa. Se obtienen valores experimentales de la difusividad o permeabilidad al vapor o su inverso la resistividad al vapor de agua. Los datos obtenidos son muy útiles para valorar el fenómeno del intercambio de humedad entre el yeso y el ambiente, tanto durante el proceso de su secado inicial, como en el transcurso de su vida. Así como para disponer soluciones adecuadas para la evacuación del vapor de agua a través de los cerramientos, para utilizar la capacidad de regulación de la humedad, que proporciona el entramado poroso de los productos de yeso, o para impedir el paso del vapor de agua y evitar condensaciones. Como resumen de la investigación, se puede decir que la coloración en masa y las pinturas al agua, así como los hidrofugantes de silicona aumentan muy poco la resistencia al vapor. Por el contrario las pinturas plásticas y en mayor medida los esmaltes y las lacas aumentan un promedio de 5, 10 y 20 veces respectivamente esta resistividad al vapor. - The vapour resistivity of plaster coatings such as paint and their effectiveness as water repellents were studied in several types of plaster. To this end, painted, unpainted and pigmented specimens were tested. Experimental values were collected on diffusion and vapour permeability, or its inverse, water vapour resistivity. The data obtained were very useful for evaluating moisture exchange between plaster and the surrounding air, both during initial drying and throughout the life of the material. They likewise served as a basis for ensuring the proper evacuation of water vapour in walls, and use of the capacity of the porous network in plaster products to regulate moisture content or serve as a water vapour barrier to avoid condensation. Briefly, the research showed that pigments, water-based paints and silicon-based water repellents scantly raised vapour resistance. Plastic paints, enamels and lacquers, however, respectively induced five-, ten- and twenty-fold increases in vapour resistivity, on average

The Importance of Recess in the Lives of Children

Current research suggests that when children get the chance to play outdoors, they reap the benefits. However, in today’s society children aren’t outdoors very often. Children also don’t have very much time to play outdoors during recess time while in a school setting. The purpose of this project was to educate and inform elementary school principals about the importance and benefits that recess has on children, as well as help them become an advocate for recess. A video was created that focused on the benefits of outdoor play for children, the importance of recess for children, as well as ways in which principals can help to improve the recess experience for young children. The initial and post questionnaires indicated that the video did help the principals gain knowledge about not only the importance of recess for children, but the importance administrator involvement in advocating for recess. Overall, the video did complete the desired result of principals learning and understanding more about outdoor recess. Future research may consider having a larger group of participants from different regions and creating a collaborative in person group in which principals and administrators could be in the same room exchanging ideas

Stress-Induced Variations in the Stiffness of Micro- and Nanocantilever Beams

The effect of surface stress on the stiffness of cantilever beams remains an outstanding problem in the physical sciences. While numerous experimental studies report significant stiffness change due to surface stress, theoretical predictions are unable to rigorously and quantitatively reconcile these observations. In this Letter, we present the first controlled measurements of stress-induced change in cantilever stiffness with commensurate theoretical quantification. Simultaneous measurements are also performed on equivalent clamped-clamped beams. All experimental results are quantitatively and accurately predicted using elasticity theory. We also present conclusive experimental evidence for invalidity of the longstanding and unphysical axial force model, which has been widely applied to interpret measurements using cantilever beams. Our findings will be of value in the development of micro- and nanoscale resonant mechanical sensors