COMPARISON OF DIFFERENT METHODS FOR GENERATION AND ABSORPTION OF WATER WAVES

The knowledge of water wave characteristics (generation, propagation, transformation and breaking) is fundamental for hydrodynamic studies and the design of ocean, coastal and port structures. In addition to the small-scale experimental studies, the use of numerical models is also a very important tool in hydrodynamic studies. To have reliable numerical results a proper validation is required. The main objective of this paper is to compare different methods of wave generation and wave absorption in a numerical flume, and to find what is the most suited to simulate non-breaking regular wave propagation in a two-dimensional flume in deep water condition. The numerical simulations were made using the OpenFOAM® software package. Two solvers, waves2Foam and IHFoam/OlaFlow, the utility GroovyBC and a mesh stretching technique are compared. These numerical codes solve the transient Navier-Stokes equations and use a VoF (Volume of Fluid) method to identify the free surface. A solution dependence study with the methods of wave generation and wave absorption is presented. The results are also compared with the theoretical wave and experimental data. The results show that the different methods of generation produce waves similar to the theoretical and the experimental ones, only slightly differences were visible. The three method of wave dissipation considered produce very different results: IHFoam/OlaFlow is not able to dissipate the wave tested; the mesh stretching technique is able to dissipate the waves but produces a water level rise; the waves2Foam solver is able to dissipate properly the wave tested

Spatial sampling of the thermospheric vertical wind field at auroral latitudes

Results are presented from two nights of bistatic Doppler measurements of neutral thermospheric winds using Fabry!Perot spectrometers at Mawson and Davis stations in Antarctica. A scanning Doppler imager (SDI) at Mawson and a narrow-field Fabry-Perot spectrometer (FPS) at Davis have been used to estimate the vertical wind at three locations along the great circle joining the two stations, in addition to the vertical wind routinely observed above each station. These data were obtained from observations of the 630.0 nm airglow line of atomic oxygen, at a nominal altitude of 240 km. Low!resolution all-sky images produced by the Mawson SDI have been used to relate disturbances in the measured vertical wind field to auroral activity and divergence in the horizontal wind field. Correlated vertical wind responses were observed on a range of horizontal scales from ~150 to 480 km. In general, the behavior of the vertical wind was in agreement with earlier studies, with strong upward winds observed poleward of the optical aurora and sustained, though weak, downward winds observed early in the night. The relation between vertical wind and horizontal divergence was seen to follow the general trend predicted by Burnside et al. (1981), whereby upward vertical winds were associated with positive divergence and vice versa; however, a scale height approximately 3–4 times greater than that modeled by NRLMSISE-00 was required to best fit the data using this relation

Low substrate temperature deposition of amorphous and microcrystalline silicon films on plastic substrates by hot-wire chemical vapor deposition

Amorphous and microcrystalline silicon films were deposited by radio-frequency plasma enhanced chemical vapor deposition (rf-PECVD) and hot-wire chemical Vapor deposition (HW-CVD) on plastic (polyethylene terephthalate-PET) at 100 degrees C and 25 degrees C. Structural properties of these films were measured by Raman spectroscopy. Electronic properties were measured by dark conductivity and photoconductivity. For amorphous silicon films deposited by rf-PECVD on PET, photosensitivities > 10(5) were obtained at both 100 degrees C and 25 degrees C, For amorphous silicon films deposited by HW-CVD, a photosensitivity of > 10(5) was obtained at 100 degrees C. Microcrystalline silicon films deposited by HW-CVD at 95% hydrogen dilution had sigma(ph) similar to 10(-4) Omega(-1) cm(-1), while maintaining a photosensitivity of similar to 10(2) at both 100 degrees C and 15 degrees C. Microcrystalline silicon films with a large crystalline fraction (>50%) can be deposited by HW-CVD all the way down to room temperature. All the films had good adhesion and mechanical stability as neither adhesive nor cohesive failure was observed even when the substrates were bent elastically.Fundação para a Ciência e Tecnologia (FCT) Universidade do Minho (UM) Fundação Luso-Americana para o Desenvolvimento (FLAD

Doping of amorphous and microcrystalline silicon films deposited at low substrate temperatures by hot-wire chemical vapor deposition

The gas phase doping of amorphous (alpha -Si:H) and microcrystalline (muc-Si:H) silicon thin films deposited at substrate temperatures of 25 degreesC and 100 degreesC by hot-wire chemical vapor deposition is studied. Phosphine was used for n-type doping and diborane for p-type doping. The electronic and structural properties of the doped films are studied as functions of hydrogen dilution. Films were deposited on glass and polyethylene terephthalate. Similar dark conductivities, sigma (d), were obtained for the doped films deposited on either substrate. sigma (d) above 10(-6) Omega (-1) cm(-1) were obtained for a-Si:H films doped n-type at 25 degreesC and 100 degreesC (sigma (d)> 10(-4) Omega (-1) cm(-1)) and for alpha -Si:H doped p-type only at 100 degreesC. sigma (d), equal or above 10(-1) Omega (-1) cm(-1), were obtained for muc-Si:H doped p-type at 25 degreesC and 100 degreesC for Ac-Si:H doped n-type. only at 100 degreesC. Isochronal annealing at temperatures up to 200 degreesC reveals that, while the dopants are fully activated in microcrystalline samples, they are only partially activated in amorphous films deposited at a low substrate temperature.Fundação para a Ciência e Tecnologia (FCT) University of Minho (UM

Electronic and structural properties of doped amorphous and nanocrystalline silicon deposited at low substrate temperatures by radio-frequency plasma-enhanced chemical vapor deposition

The gas phase doping of hydrogenated amorphous silicon and hydrogenated nanocrystalline silicon thin films deposited on glass and on plastic (polyethylene terephthalate) substrates is reported. Two substrate temperatures were used during deposition: 25 degreesC and 100 degreesC. Films were deposited by radio-frequency plasma-enhanced chemical vapor deposition using phosphine or diborane for n- or p-type doping, respectively. Similar electronic and structural properties are obtained for the doped films deposited on either substrate. Hydrogen dilution of silane is used to improve the electronic and structural properties of the amorphous films and to obtain nanocrystalline films. The most conductive amorphous films have n-type dark conductivity at room temperature similar to10(-3) Omega(-1) cm(-1) and similar to10(-5) Omega(-1) cm(-1) when deposited at 100degreesC and 25degreesC, respectively, or p-type room-temperature dark conductivity similar to10(-7) Omega(-1) cm(-1) at both substrate temperatures. The most conductive nanocrystalline films deposited at 100 degreesC have n- and p-type dark conductivity at room temperature above 10(-2) Omega(-1) cm(-1) while nanocrystalline films deposited at 25 degreesC only have p-type conductivity higher than 10(-2) Omega(-1) cm(-1) at room temperature. Isochronal annealing at temperatures up to 300 degreesC showed that the dopants are fully activated at the deposition temperature in doped nanocrystalline samples and that they are only partially activated in amorphous films deposited at low substrate temperatures.Fundação para a Ciência e Tecnologia (FCT) Universidade do Minho (UM

The Kondo-Hubbard model at half-filling

We have analyzed the antiferromagnetic (J>0) Kondo-Hubbard lattice with the band at half-filling by means of a perturbative approach in the strong coupling limit, the small parameter is an arbitrary tight-binding band. The results are valid for any band shape and any dimension. We have obtained the energies of elementary charge and spin excitations as well as the magnetic correlations in order to elucidate the magnetic and charge behavior of the Kondo lattice at half-filling. Finally, we have briefly analyzed the ferromagnetic case (J<0), which is shown to be equivalent to an effective antiferromagnetic Heisenberg model.Comment: 4 pages, Proceedings of SCES98/Pari

Electronic transport in low-temperature silicon nitride

Perpendicular current transport through thin silicon nitride films deposited at 100 degreesC by radio frequency chemical vapor deposition (RF) is measured between patterned square contacts with side lengths between 5 and 200 mum. Hydrogen dilution, silane-to-ammonia ratio, and total gas flow were varied to achieve control of film properties. The dependence of the current on the applied field and measurement temperature are correlated to structural parameters such as the index of refraction, etching rate in buffered hydrofluoric acid and infrared vibrational band strengths. Using the appropriate deposition parameters, it is possible to prepare, at 100 degreesC, silicon nitride dielectric films with electronic properties compatible with use as gate dielectrics of thin-film transistors.Fundação para a Ciência e Tecnologia (FCT) Universidade do Minho (UM

CVD of CrO2 Thin Films: Influence of the Deposition Parameters on their Structural and Magnetic Properties

This work reports on the synthesis of CrO2 thin films by atmospheric pressure CVD using chromium trioxide (CrO3) and oxygen. Highly oriented (100) CrO2 films containing highly oriented (0001) Cr2O3 were grown onto Al2O3(0001) substrates. Films display a sharp magnetic transition at 375 K and a saturation magnetization of 1.92 Bohr magnetons per f.u., close to the bulk value of 2 Bohr magnetons per f.u. for the CrO2. Keywords: Chromium dioxide (CrO2), Atmospheric pressure CVD, Spintronics.Comment: 5 pages, 6 figure