To investigate the tropical Atlantic response to the remote El Nino-Southern Oscillation (ENSO) forcing, a Reduced Physics – Coupled Global Circulation Model (RP-CGCM) is developed, and four experiments are carried out. The results show that the RP-CGCM is capable of capturing the major features of Tropical Atlantic Variability (TAV) and its response to ENSO forcing. The SST response to the remote influence of ENSO may be divided into two stages. In stage one, the ENSO influences the tropical Atlantic SST primarily through the Troposphere Temperature (TT) mechanism, which predicts a uniform warming in the tropical Atlantic following the mature phase of El Nino. In the north tropical Atlantic (NTA), the Walker mechanism and the Pacific-North-American (PNA) mechanism work in concert with the TT-induced warming, giving rise to a robust SST response during the boreal spring in this region. In the south tropical Atlantic (STA), the southeasterly wind anomaly and increased stratus clouds work against the TT-induced warming, resulting in a much weaker SST response in this region. At this stage, the response can be largely explained by the ocean mixed layer response to changes in surface heat fluxes induced by ENSO. In stage two, ocean dynamics play a more active role in determining the evolution of SST. The cross-equatorial wind anomaly in the western to central equatorial Atlantic can change the SST in the eastern equatorial Atlantic through Bjerknes feedback and the SST in the central equatorial Atlantic through Ekman feedback. These feedback result in a cooling of SST in the equatorial south Atlantic (ESA) region which is so overwhelming that it cancels the warming effect induced by the TT mechanism and reverses the sign of the warm SST anomaly that is formed during stage one in this region. In general, the horizontal advection of heat plays a secondary role in the SST response to the remote influence of ENSO, except in the regions where the North Equatorial Countercurrent (NECC) dominates and the SST variability is strong. Entrainment is particularly important in maintaining the correct SST structure during boreal summer.

Research is performed to assess the potential of surface moisture evaporative cooling from composite plates as a means of reducing the external temperature of military aircraft. To assess the feasibility of evaporative cooling for this application, a simplified theoretical model of the phenomenon is formulated. The model consists of a flat composite plate at an initial uniform temperature, T0. The plate also possesses an initial moisture (molecular water) content, M0. The plate is oriented vertically and at t=0 s, one surface is exposed to a free stream of air at an elevated temperature. The other surface is exposed to stagnant air at the same temperature as the plate’s initial temperature. The equations associated with energy and mass transport for the model are developed from the conservation laws per the continuum mechanics hypothesis. Constitutive equations and assumptions are introduced to express the two nonlinear partial differential equations in terms of the temperature, T, and the partial density of molecular water, ρw. These equations are approximated using a weak form Galerkin finite element formulation and the α–family of time approximation. An algorithm and accompanying computer program written in the Matlab programming language are presented for solving the nonlinear algebraic equations at successive time steps. The Matlab program is used to generate results for plates possessing a variety of initial moisture concentrations, M0, and diffusion coefficients, D. Surface temperature profiles, over time, of moisture bearing specimens are compared with the temperature profiles of dry composite plates. It is evident from the results that M0 and D affect the surface temperature of a moist plate. Surface temperature profiles are shown to decrease with increasing M0 and/or D. In particular, dry and moist specimens are shown to differ in final temperatures by as much as 30°C over a 900 s interval when M0 = 30% and D is on the order of 10–8m2/s (T0 = 25°C, h = 60 W/m2°C, T∞ = 90°C).

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The purpose of this thesis is to find out carrier concentration in nitride semiconductors by micro Raman measurements. We focus on the Raman measurements of two different III-nitride semiconductors doped with Si. First series is narrow band gap InN films with varying carrier concentration (ne). The highest (ne) in this series is 1.9 X 1019 cm-3. The second series is wide band gap GaN films, with highest (ne) of 8.0 X 1019 cm-3.From the room temperature Ramam measurements ,it is observed that the L- LOPCM (lower branch of longitudinal-optical phonon-plasmon coupled modes) depends on the carrier concentration. We focus the further analysis of this result and try to extract the carrier concentration and compare with electrical measurements.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: digital x-ray imaging; pixel size; scintillator. Includes bibliographical references (p. 57-59).

Title from PDF of title page (University of Missouri--Columbia, viewed on Mar. 15, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Dissertation advisor: Dr. J. David Robertson. Vita. Includes bibliographical references.

Numerical modeling of shallow microtidal semi-enclosed estuaries requires the effective simulation of physical processes with a wide range of temporal and spatial scales. In theory, application of sufficient grid resolution in both the horizontal and vertical should result in a reasonable simulation. However, in practice, this is not the case. Fully resolving the finest scales can be computationally prohibitive, and various algorithmic assumptions can break down at fine resolutions, leading to spurious oscillations in the solution. One method of simulating inherently cross-scale phenomena is to use multimodel approaches in which domain decomposition is used to divide the region into multiple subregions, each modeled by different submodels. These submodels are coupled to simulate the entire system efficiently. In general, the different models may involve different physics, they may be dimensionally heterogeneous or they may be both physically and dimensionally heterogeneous. A reduction in computational expense is obtained by using simpler physics and/or a reduced dimension model in the submodels. In this research, we look at the particular case of modeling shallow bays containing narrow, deep ship channels. In order to accurately model bay circulation, a model should capture the effect of these spatially localized navigational channels. Our research shows that modeling techniques currently used to simulate such systems using 2 dimensional or coarse resolution 3 dimensional estuary models misrepresent wind driven surface circulation in the shallow bay and tide driven volume fluxes through the channel. Fully resolving the geometry of the ship channel is impractical on all but large parallel computing clusters. We propose a more efficient method using the multimodel approach. This approach splits the estuary into a shallow bay region and a subsurface ship channel region. By separating the physical domain into two parts in this way, simpler models can be used that are targeted at the different physical processes and geometries dominant in each region. By using a low resolution 3D model (SELFE) in the shallow bay region, coupled through appropriate interface conditions with a 2D laterally averaged model, the effects of the ship channel on bay circulation are accurately represented at a fraction of the computational expense. In this research, this coupled model was developed and applied to an ideal shallow bay- ship channel system. The coupled model approach is found to be an effective strategy for modeling this type of system. / text

This work focuses on the development of a reliable numerical model for investigating the bone-conduction of sound in the human head. The main challenge of the problem is the lack of fundamental knowledge regarding the transmission of acoustic energy through non-airborne pathways to the cochlea. I employed a fully coupled model based on the acoustic/elastic interaction problem with a detailed resolution of the cochlea region and its interface with the skull and the air pathways. The problem was simulated via hp-finite element approximation, employing a hybrid mesh (tetrahedral, prismatic and pyramidal elements) to better capture the geometrical features of the head. The numerical results thus obtained provide an insight into this fundamental, long standing research problem. / text

Simulation, optimization, and implementation of a capacitor-loaded wireless power transfer structure at 6.78 MHz for a target transfer distance of one meter are presented. First, an investigation into the operating principles behind a capacitor-loaded coupled loop structure is carried out via simulation. By adjusting the structural design parameters, it is found that an optimal configuration for this structure is coplanar. A prototype constructed using thin 18 AWG wire for the loops and a variable capacitor for tuning is used to verify simulation. To reduce losses in the wire, thick 9 AWG wire is implemented and measured. Thick wire is necessary for high efficiency yet undesirable for planarization. Since current flows only on the surface of the wire, ‘unwrapping’ that portion yields copper strips that reduce loss by increasing only the width. Thus, by replacing thick wires with copper strips, a planarized structure can be obtained that can reduce ohmic losses without sacrificing its form factor. Next, additional advantages of a capacitor-loaded system, which include reduced electric near-field and the possibility of resonant frequency tuning, are investigated. It is shown by simulation that the capacitor-loaded structure is not strongly affected by nearby dielectric materials since the stored electric energy is significantly lower than the stored magnetic energy in air at resonance. Finally, further optimizations of the structure are considered along with the analytical expressions for maximum efficiency. / text

Nondestructive testing (NDT) plays a more important role today in evaluating structural integrity of civil infrastructure. Impact-echo method (IE) is an effective stress wave based NDT method for locating defects in concrete structures. However, the contact requirement between sensor and concrete surface significantly limits the test speed and wide application of this method to large-scale structures such as bridges. Recent studies show the feasibility of air-coupled sensing, which eliminates the contact requirement and thus accelerates IE test. To further improve the test speed, a fully non-contact IE test using air-coupled sensing and excitation is investigated in this dissertation. This dissertation provides the theoretical basis required for developing an effective air-coupled IE method. For air-coupled sensing, 2D numerical simulations are first conducted to study the wave propagation in the air-solid system during IE tests. Visualized wavefield indicates that parabolic reflectors can effectively enhance the IE signal strength by focusing airborne IE waves to an air-coupled sensor. To maximize signal amplification, an analytical solution for the focused axial pressure response of a parabolic reflector with incident plane waves is derived. This solution is used to determine the reflector geometry that gives the highest focusing gain. For air-coupled excitation, a focused spark source with an ellipsoidal reflector is employed to excite stress waves in concrete. Numerical simulations and available nonlinear computer code (KZKTexas) are employed to investigate the reflector geometry that gives the highest stress wave excitation in solids. An acoustical muffler that works with the focused spark source is proposed to decrease the spark-induced noise level. The effect of source receiver spacing on received IE signals is studied. Simulated wavefield demonstrates that the mode shape of IE surface displacement distribution along the radial direction matches the Bessel function of the first kind (J0). Numerical 3D simulation results show the relation between focused IE signals and source receiver spacings, and indicate the spacing should be minimized to obtain better focused IE signal strength. Air-coupled IE test using through transmission setup is also investigated. / text