Coupled analysis of nonlinear structural motion and fluid sloshing

Fluid sloshing in containers is modeled using a finite element formulation previously proposed by the authors for problems with moderate motions [1], extending in this work its application to arbitrarily large rotations and small deformations relative to a floating frame of reference moving with the fluid. This novel approach is used to investigate the coupling effects originated by the incidence of environmental sea waves on rigid floating vessels with internal flexible structural parts and fluids oscillating inside rigid or flexible tanks

Inverse mass matrix via the method of localized lagrange multipliers

An efficient method for generating the mass matrix inverse is presented, which can be tailored to improve the accuracy of target frequency ranges and/or wave contents. The present method bypasses the use of biorthogonal construction of a kernel inverse mass matrix that requires special procedures for boundary conditions and free edges or surfaces, and constructs the free-free inverse mass matrix employing the standard FEM procedure. The various boundary conditions are realized by the method of localized Lagrange multipliers. Numerical experiments with the proposed inverse mass matrix method are carried out to validate the effectiveness proposed technique when applied to vibration analysis of bars and beams. A perfect agreement is found between the exact inverse of the mass matrix and its direct inverse computed through biorthogonal basis functions

Extreme waves generated by Typhoon Bolaven (201215) in Southern Korean waters

Unusual extreme waves were generated by Typhoon Bolaven (201215) in the Southern Korean Waters\ud (SKW) and gave destructive damages to the breakwaters of Seogwipo Harbor at Jeju Island. The waves were far\ud exceeding the design wave height (Hs50yrs 9.3m) and their duration was 14hours. The duration is a very significant\ud factor as much as the design wave height for breakwater armor stability in terms of cumulative damages. A significant\ud increase in strong typhoon intensity and duration in North West Pacific (NWP) due to global warming has been reported\ud and also in landfall typhoons on Korea/Japan in a recent decade. The frequency of typhoon passed SKW region had an\ud inter-annual and also a decadal variation and decreased in recent years, but several strong typhoons were occurred.\ud Bolaven was affected by high pressure distribution located above the warm eddy region to track toward NNW rather\ud than NE as usual in August. The extreme waves were analyzed with respect to typhoon genesis, evolution of the waves\ud through extensive measured data and model simulation. Numerical models of TC96 for the wind fields and WAM4.5.2\ud for the waves were used after calibration with measured data and correction of Cd in wave growth term. They produced\ud reasonably good results. It was found that the extreme waves were evolved by combination of distant large swell and\ud strong wind seas generated by consistent strong winds from front right quadrant of typhoon track for such a long time.\ud The variation of those waves was relatively small as 1-2m, which might be due to limitation of wave growth for\ud U>30m/s and bottom energy dissipation of long period waves in the region. It is essential to hindcast accurately the\ud extreme waves for design of the breakwaters and also for assessment of coastal flooding and coastal erosion in a\ud warming climate

Stoichiometry control of magnetron sputtered Bi2_2Sr2_2Ca1−x_{1-x}Yx_xCu2_2Oy_y (0≤\lex≤\le0.5) thin film, composition spread libraries: Substrate bias and gas density factors

A magnetron sputtering method for the production of thin-film libraries with a spatially varying composition, x, in Bi2Sr2Ca1-xYxCu2Oy (0<=x<=0.5) has been developed. Two targets with a composition of Bi2Sr2YCu2O_{8.5 + \delta} and Bi_2Sr_2CaCu_2O_{8 + \delta} are co-sputtered with appropriate masks. The target masks produce a linear variation in opposite, but co-linear radial direction, and the rotation speed of the substrate table is sufficient to intimately mix the atoms. EDS/WDS composition studies of the films show a depletion of Sr and Bi that is due to oxygen anion resputtering. The depletion is most pronounced at the centre of the film (i.e. on-axis with the target) and falls off symmetrically to either side of the 75 mm substrate. At either edge of the film the stoichiometry matches the desired ratios. Using a 12 mTorr process gas of argon and oxygen in a 2:1 ratio, the strontium depletion is corrected. The bismuth depletion is eliminated by employing a rotating carbon brush apparatus which supplies a -20 V DC bias to the sample substrate. The negative substrate bias has been used successfully with an increased chamber pressure to eliminate the resputtering effect across the film. The result is a thin film composition spread library with the desired stoichiometry.Comment: 16 pages, 12 figures, 4 tables, submitted to Physica C - Superconductivity (April 15, 2005), elsart.st

Growth of vertically aligned arrays of carbon nanotubes for high field emission

International audienceVertically aligned multi-walled carbon nanotubes have been grown on Ni-coated silicon substrates, by using either direct current diode or triode plasma-enhanced chemical vapor deposition at low temperature (around 620 °C). Acetylene gas has been used as the carbon source while ammonia and hydrogen have been used for etching. However densely packed (∼ 109 cm− 2) CNTs were obtained when the pressure was ∼ 100 Pa. The alignment of nanotubes is a necessary, but not a sufficient condition in order to get an efficient electron emission: the growth of nanotubes should be controlled along regular arrays, in order to minimize the electrostatic interactions between them. So a three dimensional numerical simulation has been developed to calculate the local electric field in the vicinity of the tips for a finite square array of nanotubes and thus to calculate the maximum of the electron emission current density as a function of the spacing between nanotubes. Finally the triode plasma- enhanced process combined with pre-patterned catalyst films (using different lithography techniques) has been chosen in order to grow regular arrays of aligned CNTs with different pitches in the micrometer range. The comparison between the experimental and the simulation data permits to define the most efficient CNT-based electron field emitter

Defect reduction of Ge on Si by selective epitaxy and hydrogen annealing

We demonstrate a promising approach for the monolithic integration of Ge-based nanoelectronics and nanophotonics with S-ilicon: the selective deposition of Ge on Si by Multiple Hydrogen Annealing for Heteroepitaxy (MHAH). Very high quality Ge layers can be selectively integrated on Si CMOS platform with this technique. We confirm the reduction of dislocation density in Ge layers using AFM surface morphology study. In addition, in situ doping of Ge layers is achieved and MOS capacitor structures are studied. ©The Electrochemical Society

Selective-area high-quality germanium growth for monolithic integrated optoelectronics

Selective-area germanium (Ge) layer on silicon (Si) is desired to realize the advanced Ge devices integrated with Si very-large-scale-integration (VLSI) components. We demonstrate the area-dependent high-quality Ge growth on Si substrate through SiO 2 windows. The combination of area-dependent growth and multistep deposition/hydrogen annealing cycles has effectively reduced the surface roughness and the threading dislocation density. Low root-mean-square surface roughness of 0.6 nm is confirmed by atomic-force-microscope analysis. Low defect density in the area-dependent grown Ge layer is measured to be as low as 1 × 10 7cm -2 by plan-view transmission-electron-miscroscope analysis. In addition, the excellent metal-semiconductor-metal photodiode characteristics are shown on the grown Ge layer to open up a possibility to merge Ge optoelectronics with Si VLSI. © 2012 IEEE

Stabilized electron emission from silicon coated carbon nanotubes for a high-performance electron source

The authors show that carbon nanotubes (CNTs) coated with an amorphous silicon layer around their periphery show enhanced and stable electron emission. The CNT-field emitter array was grown on silicon substrate through a resist-assisted patterning process. The CNTs become coated with silicon from the substrate, which is etched and redeposited onto the CNTs. The authors obtained enhanced and stabilized electron emission from the silicon coated CNTs with a turn-on field of 2 V/μm at an emission current density of 1 μA/ cm 2. The structure and electron emission properties of the functionalized emitters are discussed

Carrier-mediated ferromagnetic ordering in Mn ion-implanted p+GaAs:C

Highly p-type GaAs:C was ion-implanted with Mn at differing doses to produce Mn concentrations in the 1 - 5 at.% range. In comparison to LT-GaAs and n+GaAs:Si samples implanted under the same conditions, transport and magnetic properties show marked differences. Transport measurements show anomalies, consistent with observed magnetic properties and with epi- LT-(Ga,Mn)As, as well as the extraordinary Hall Effect up to the observed magnetic ordering temperature (T_C). Mn ion-implanted p+GaAs:C with as-grown carrier concentrations > 10^20 cm^-3 show remanent magnetization up to 280 K