Numerical prediction of ship resistance and squat in confined waters

Accurate prediction of hydrodynamic forces opposing a ship displacement in restricted waterways is necessary in order to improve energy efficiency of inland transport. When a ship moves in restricted waterways, a significant increase in ship squat (combination of sinkage and trim) and resistance occurs compared to a movement in open waters. In this paper, a 3D numerical model based on fluid-structure coupling is presented and used to investigate the effect of limited water depth and channel width on ship resistance and squat

Fabrication methods for a quantum cascade photonic crystal surface emitting laser

Conventional quantum cascade (QC) lasers are intrinsically edge-emitting devices with mode confinement achieved via a standard mesa stripe configuration. Surface emission in edge emitting QC lasers has therefore necessitated redirecting the waveguided laser emission using a second order grating. This paper describes the methods used to fabricate a 2D photonic crystal (PC) structure with or without a central defect superimposed on an electrically pumped QC laser structure with the goal of achieving direct surface emission. A successful systematic study of PC hole radius and spacing was performed using e-beam lithography. This PC method offers the promise of a number of interesting applications, including miniaturization and integration of QC lasers

Quantum cascade photonic crystal surface emitting injection laser

A surface emitting quantum cascade injection laser is presented. Direct surface emission is obtained by using a 2D photonic-band-gap structure that simultaneously acts as a microcavity. The approach may allow miniaturization and on-chip-integration of the devices

Impact of spin-orbit coupling on quantum Hall nematic phases

Anisotropic charge transport is observed in a two-dimensional (2D) hole system in a perpendicular magnetic field at filling factors nu=7/2, nu=11/2, and nu=13/2 at low temperature. In stark contrast, the transport at nu=9/2 is isotropic for all temperatures. Isotropic hole transport at nu=7/2 is restored for sufficiently low 2D densities or an asymmetric confining potential. The density and symmetry dependences of the observed anisotropies suggest that strong spin-orbit coupling in the hole system contributes to the unusual transport behavior.Comment: 4 pages, 4 figure

Evaluation of different methods in quantification of manufacturing defects

In the context of manufacturing defects, our interest is the calculation methodologies that are used to quantify these defects. The manufacturing defects can be divided into two categories: machining defects and positioning defects. A double measurement method is principally used to quantify separately machining and positioning defect. The first measurement is operated inside a machine tool just after the final cutting step. The second measurement is realised outside of the machine tool (e.g. on a coordinate measuring machine - CMM). However, data processing method and precision between two different machines are different. Consequently, the measurement results obtained from these machines may be not comparable to quantify precisely the manufacturing defects. Several solutions are proposed and analysed in this paper to estimate comparable capability of the measurement results obtained by the two different measurement mean

Far-infrared surface-plasmon quantum-cascade lasers at 21.5 mu m and 24 mu m wavelengths

Quantum-cascade lasers operating above 20 mum (at lambda similar to 21.5 mum and lambda similar to 24 mum) wavelength are reported. Pulsed operation was obtained up to 140 K and with a peak power of a few milliwatts at cryogenic temperatures. Laser action originates from interminiband transitions in "chirped" superlattice active regions. The waveguides are based on surface-plasmon modes confined at a metal-semiconductor interface. The wavelengths were chosen in order to avoid major phonon absorption bands, which are particularly strong at energies just above the reststrahlen band. We also report on a 21.5-mum-wavelength laser based on a two-sided interface-plasmon waveguide. (C) 2001 American Institute of Physics

Quantum Cascade Surface-Emitting Photonic Crystal Laser

We combine photonic and electronic band structure engineering to create a surface-emitting quantum cascade microcavity laser. A high-index contrast two-dimensional photonic crystal is used to form a micro-resonator that simultaneously provides feedback for laser action and diffracts light vertically from the surface of the semiconductor surface. A top metallic contact allows electrical current injection and provides vertical optical confinement through a bound surface plasmon wave. The miniaturization and tailorable emission properties of this design are potentially important for sensing applications, while electrical pumping can allow new studies of photonic crystal and surface plasmon structures in nonlinear and near-field optics

Worldwide food recall patterns over an eleven month period: A country perspective.

<p>Abstract</p> <p>Background</p> <p>Following the World Health Organization Forum in November 2007, the Beijing Declaration recognized the importance of food safety along with the rights of all individuals to a safe and adequate diet. The aim of this study is to retrospectively analyze the patterns in food alert and recall by countries to identify the principal hazard generators and gatekeepers of food safety in the eleven months leading up to the Declaration.</p> <p>Methods</p> <p>The food recall data set was collected by the Laboratory of the Government Chemist (LGC, UK) over the period from January to November 2007. Statistics were computed with the focus reporting patterns by the 117 countries. The complexity of the recorded interrelations was depicted as a network constructed from structural properties contained in the data. The analysed network properties included degrees, weighted degrees, modularity and <it>k</it>-core decomposition. Network analyses of the reports, based on 'country making report' (<it>detector</it>) and 'country reported on' (<it>transgressor</it>), revealed that the network is organized around a dominant core.</p> <p>Results</p> <p>Ten countries were reported for sixty per cent of all faulty products marketed, with the top 5 countries having received between 100 to 281 reports. Further analysis of the dominant core revealed that out of the top five transgressors three made no reports (in the order China > Turkey > Iran). The top ten detectors account for three quarters of reports with three > 300 (Italy: 406, Germany: 340, United Kingdom: 322).</p> <p>Conclusion</p> <p>Of the 117 countries studied, the vast majority of food reports are made by 10 countries, with EU countries predominating. The majority of the faulty foodstuffs originate in ten countries with four major producers making no reports. This pattern is very distant from that proposed by the Beijing Declaration which urges all countries to take responsibility for the provision of safe and adequate diets for their nationals.</p

Quantum cascade photonic-crystal microlasers

We describe the realization of Quantum Cascade photonic-crystal microlasers. Photonic and electronic bandstructure engineering are combined to create a novel Quantum Cascade microcavity laser source. A high-index contrast two-dimensional photonic crystal forms a micro-resonator that provides feedback for laser action and diffracts light vertically from the surface of the semiconductor chip. A top metallic contact is used to form both a conductive path for current injection as well as to provide vertical optical confinement to the active region through a bound surface plasmon state at the metal-semiconductor interface. The device is miniaturized compared to standard Quantum Cascade technology, and the emission properties can in principle be engineered by design of the photonic crystal lattice. The combination of size reduction, vertical emission, and lithographic tailorability of the emission properties enabled by the use of a high-index contrast photonic crystal resonant cavity makes possible a number of active sensing applications in the mid- and far-infrared. In addition, the use of electrical pumping in these devices opens up another dimension of control for fundamental studies of photonic crystal and surface plasmon structures in linear, non-linear, and near-field optics