Fiber-Optic Ring-Down Spectroscopy Using a Tunable Picosecond Gain-Switched Diode Laser

Visible and near-infrared laser light pulses were coupled into two different types of optical fiber cavities. One cavity consisted of a short strand of fiber waveguide that contained two identical fiber Bragg gratings. Another cavity was made using a loop of optical fiber. In either cavity ∼ 40 ps laser pulses, which were generated using a custom-built gainswitched diode laser, circulated for a large number of round trips. The optical loss of either cavity was determined from the ring-down times. Cavity ring-down spectroscopy was performed on 200 pL volumes of liquid samples that were injected into the cavities using a 100 μm gap in the fiber loop. A detection limit of 20 ppm of methylene blue dye in aqueous solution, corresponding to a minimum absorptivity of εC < 6 cm−1, was realized.

A gain-of-function mutation in the HIF2A gene in familial erythrocytosis

Hypoxia-inducible factor (HIF) a, which has three isoforms, is central to the continuous balancing of the supply and demand of oxygen throughout the body. HIF-a is a transcription factor that modulates a wide range of processes, including erythropoiesis, angiogenesis, and cellular metabolism. We describe a family with erythrocytosis and a mutation in the HIF2A gene, which encodes the HIF-2a protein. Our functional studies indicate that this mutation leads to stabilization of the HIF-2a protein and suggest that wild-type HIF-2a regulates erythropoietin production in adults.

High-gain subwavelength resonant cavity antennas based on metamaterial ground planes

Planar metarnaterial Surfaces with negative reflection phase values are proposed as ground planes in a high-gain resonant cavity antenna configuration. The antenna is formed by the metarnaterial ground plane (MGP) and a superimposed metallodielectric electromagnetic band gap (MEBG) array that acts as a partially reflective surface (PRS). A single dipole positioned between the PRS and the ground IS utilised as the excitation. Ray analysis is employed to describe the functioning of the antennas and to qualitatively predict the effect of the MGP oil the antenna performance. By employing MGPs with negative reflection phase values, the planar antenna profile is reduced to subwavelength values (less than lambda/6) whilst maintaining high directivity. Full-wave simulations have been carried out with commercially available software (Microstripes (TM)). The effect of the finite PRS size on the antenna radiation performance (directivity and sidelobe level) is studied. A prototype has been fabricated and tested experimentally in order to validate the predictions.

Artificial magnetic conductor surfaces and their application to low-profile high-gain planar antennas

Planar periodic metallic arrays behave as artificial magnetic conductor (AMC) surfaces when placed on a grounded dielectric substrate and they introduce a zero degrees reflection phase shift to incident waves. In this paper the AMC operation of single-layer arrays without vias is studied using a resonant cavity model and a new application to high-gain printed antennas is presented. A ray analysis is employed in order to give physical insight into the performance of AMCs and derive design guidelines. The bandwidth and center frequency of AMC surfaces are investigated using full-wave analysis and the qualitative predictions of the ray model are validated. Planar AMC surfaces are used for the first time as the ground plane in a high-gain microstrip patch antenna with a partially reflective surface as superstrate. A significant reduction of the antenna profile is achieved. A ray theory approach is employed in order to describe the functioning of the antenna and to predict the existence of quarter wavelength resonant cavities.

Measurements of the XUV mass absorption coefficient of an overdense liquid metal

The increase in the XUV mass absorption coefficient of liquid aluminium, produced by high-power-laser shock-compression, is measured using XUV laser radiography. At a photon energy of 63 eV a change in the mass absorption coefficient by up to a factor of similar to2.2 is determined at densities close to twice that of solid and electron temperatures of the order of 1 eV. Comparison with hydrodynamic simulations indicate that the absorption coefficient scales with density as rho (1.3 +/-0.2).

Sampled-data gain scheduling of continuous LTV plants

This paper discusses the design of gain- scheduled sampled-data controllers for continuous-time polytopic linear parameter-varying systems. The scheduling variables are assumed to available only at the sampling instants, and a bound on the time-variation of the scheduling parameters is also assumed to be known. The resultant gain-scheduled controllers improve the maximum achieveable delay bound over previous constant-gain ones in the literature.

An assessment of the earth pressure coefficient in overconsolidated clays

The determination of the earth pressure coefficient K 0 in a natural clay deposit is a problem of considerable significance in geotechnical engineering. While the methods for evaluation of K 0 are reliable for normally consolidated soils, significant difficulties still exist in evaluating K 0 in overconsolidated clays, given that it is influenced by the stress history of the material, together with the age, structure, mineralogical composition and depositional environment. Indeed, some of these factors are responsible for the soil becoming anisotropic. The existing framework for prediction of K 0 in overconsolidated soils does not account for any influences caused by anisotropy. The work reported in this paper evaluates the validity of a revised relationship between K 0oc and OCR (overconsolidation ratio) using data obtained from laboratory investigations. The tests were performed on reconstituted and undisturbed samples of Belfast Upper Boulder Clay, London Clay and Gault Clay. Tests were also performed on reconstituted samples of kaolin. The values of K 0oc were determined using various approaches, including on-sample measurements. The results have confirmed that reliable predictions of K 0oc can be made using the proposed relationship.