NUMERICAL EXPERIMENTS ON NATURAL CONVECTION IN A STABLY STRATIFIED FLUID DUE TO SIDE-WALL HEATING

Numerical experiments were conducted to study the natural convection in a stably stratified salt water solution with lateral heating in a square rectangular enclosure. The method of investigation employed is the finite-difference solution of the basic conservation equations for a two-dimensional, laminar, unsteady double-diffusive convection, and calculation is made for 1.0 × 10⁵ ≤ Ra_T ≤ 1.0 × l0⁶ and ≤ N ≤ 15. Four distinct flow regimes are observed depending on the magnitude of solutal stratification relative to thermal buoyancy N; unicell flow regime for N - 1, fully developed flow regime for N - 3, layered flow regime with the stagnant core for N - 5, and stagnant flow regime for N - 7. Formation of layered flow structure with time and the corresponding temperature and concentration distributions are examined. Due to the double-diffusive nature of heat and salt, interesting temperature and concentration profiles are obtained in each flow regime.     

3D optical vortices generated by micro-optical elements and its novel applications

In this paper we report on recent development in the areas of optical vortices generated by micro-optical elements and applications of optical vortices, including optical manipulation, radial polarization and secure free space optical communi- cation     

Gemeinsame österreichisch-ungarische Sedimentforschung im Rahmen des EFRE-Projektes SEDDON

The multiple uses of the Danube River for navigation, hydropower production and as a drinking water supply influence its ecological quality. Flow restrictions due to regulation as well as impacts on the sediment regime such as retention in the catchment area and interruption of the sediment continuum result in changes of the hydromorphological structures and can produce major problems in the context of sediment management. In light of these facts, cross-border investigations of sediment transport at the Danube River are called for. As there are no uniform research approaches shared by Austria and Hungary, the EU-funded project SEDDON (Sediment Research and Management at the Danube River) aims to compare different monitoring and modeling techniques used to determine sediment transport, and to develop mutual solutions. Further, the laboratory equipment currently used for hydraulic model experiments is evaluated and a research channel with a free flowing discharge of up to 10 m³/s without pumping will be constructed, allowing large-scale joint laboratory tests concerning sediment to be performed.     

Theoretical model for calculation of breakdown voltage of implanted p-n junctions

Avalanche breakdown voltage (ABV) of an implanted planar p-n junction was calculated taking the junction curvature into consideration. Curvature was determined from the two-dimensional form of LSS-profiles incorporating lateral spread of implanted ions. Supposing a one-sided abrupt junction, theoretical ABVs are compared with experimental values. The junctions were produced by 20–80 keV boron implantation into 〈111〉 oriented, 1·5 ohmcm silicon. The structure was gate-controlled to set the surface into flat-band condition. The model satisfactorily describes the ABVs of fully annealed implanted planar junctions. For partially annealed diodes, the increase in ABV was attributed to effective curvature due to the depth-dependence of the electrically active portion.     

Influence of precursor solution coating parameters on structural and dielectric properties of PZT thick films

Ferroelectric PZT(70/30) thick films were fabricated by the hybrid technique adding the sol-coating process to the normal screen-printing process to obtain a good densification. The screen-printing procedure was repeated four times to form PZT(70/30) thick films, and then PZT(30/70) precursor solution was spin-coated on the PZT thick films. All PZT thick films showed the typical XRD patterns of a perovskite polycrystalline structure. The thickness of all thick films was approximately 75–80 μm. The relative dielectric constant and dielectric loss of the PZT-6 thick film were 656 and 1.2%, respectively. The remanent polarization increased and coercive field decreased with increasing the number of sol coatings and the values of the PZT-6 thick films were 28.3 μC/cm² and 13.1 kV/cm, respectively. Leakage current density of PZT-6 thick films was 2.4 × 10⁻⁹ A/cm² at 100 kV/cm.     

A DSP Architecture for High‐Speed FFT in OFDM Systems

This paper presents digital signal processor (DSP) instructions and their data processing unit (DPU) architecture for high‐speed fast Fourier transforms (FFTs) in orthogonal frequency division multiplexing (OFDM) systems. The proposed instructions jointly perform new operation flows that are more efficient than the operation flow of the multiply and accumulate (MAC) instruction on which existing DSP chips heavily depend. We further propose a DPU architecture that fully supports the instructions and show that the architecture is two times faster than existing DSP chips for FFTs. We simulated the proposed model with a Verilog HDL, performed a logic synthesis using the 0.35 µm standard cell library, and then verified the functions thoroughly.     

The effect of thermal contact resistance on the solidification process of a pure metal

The role of thermal contact resistance between a casting and a metal mold, as well as the effect of natural convection in the melt during solidification of a pure metal, is numerically studied. Numerical simulation is performed for a two-dimensional rectangular cavity using the coordinate transformation by boundary-fitted coordinate, and pure aluminum is used as the phase-change material. The influ-ences of thermal contact resistance on the interface shape and position, solidified volume fraction, streamlines, temperature field, and the local heat transfer are investigated.     

Zebra mussels and Eurasian watermilfoil reporting patterns in Minnesota

Recognizing common reporting patterns of aquatic invasive Zebra mussels (Dreissena polymorpha, ZM) and Eurasian watermilfoil (Myriophyllum spicatum, EWM) helps to better understand invasions. We hypothesize that confirmed invasions may be confounded by human population density, leading to overrepresentation of invasions in highly populated areas and underrepresentation in less populated areas. Here we recognize dispersal patterns of confirmed ZM and EWM invasions in Minnesota, USA, using spatial clustering and directionality tests, while adjusting for human density. By 2015, 125 (0.68%) and 304 (1.65%) of 18,411 Minnesota waterbodies were reported to have ZM and EWM, respectively. A multivariate multinomial model of the scan test was used to identify clustering of invasions. The resulting 23 clusters included 13 with either or both ZM and EWM, and most clusters (11/13) occurred in areas with >10 people per square kilometer. Whereas, among the 10 clusters without invasion, nine were from less populated areas. The standard deviation ellipse and the spatiotemporal directionality tests indicated a northwestern trend of invasions, which is in the same direction as the I-94 interstate highway connecting urban centers. Results suggested that confirmed ZM and EWM invasions are potentially confounded by human densities, which is explained by varying human impact on either or both dispersal and reporting of invasions. Considering this impact of human density, we suggest that a combination of passive and targeted surveillance, where the magnitude of efforts are stratified by the human densities, may provide insight into the true invasion status and its progression in the Great Lakes region.     

A multifractal edge detector

Multimedia Tools and Applications - Significant research has been conducted into image edge detection, usually focusing on gradient and higher order derivative approaches. Recent development in the...