Four buoyant plumes were produced within a laboratory convectively mixed layer from a source height of about z[subscript s] = 0.15 h, where h is the height of the convectively mixed layer. The projected images of these plumes in the X-Z plane were analyzed using a densitometer (photomultiplier tube) to calculate dimensionless crosswind integrated concentration values. These values were examined at regular intervals of non-dimensionalized heights and downwind distances to calculate center-of-mass heights, approximate plume limits, and touchdown distances. The plume buoyancy values were expressed in dimensionless terms as the parameter F[subscript *]. The touchdown distances are greatest and the surface integrated crosswind concentrations are smallest for the three most buoyant plumes. The highest center-of-mass and plume limit positions are also associated with the most buoyant plumes. The surface crosswind integrated concentration values for even the least buoyant plumes are much smaller than for non-buoyant plumes from previous studies. Touchdown distances for buoyant plumes from this data set agree with data from Willis and Deardorff (1983); however, the centerline and lower plume limits are at greater heights for this study. Vertical profiles of crosswind integrated concentration values indicate that the least buoyant plume has a bimodal distribution near the stack then becomes uniform at greater distances. The vertical profiles for the three most buoyant plumes show the highest concentration values are present in the upper part of the mixed layer at most downwind distances examined in this study. This distribution of effluent is also indicated by the vertical center-of- mass heights being larger than the plume centerline calculated from the average of the lower and upper plume limits. / Graduation date: 1985

No description available.

According to the literature, the choice of the material, the device structure and the morphology of the active layer play an important role in the performance of the organic solar cell. For instance, many groups insert buffer layer between cathode and active layer to improve device efficiency. Otherwise, the tandem structure have attracted much attention due to different absorbing spectra of the top and bottom cells which can improve the device efficiency. In this study, we select TiOPc as the interlayer material because it can both extend the device absorption spectra and improve device performance. In our results, the thickness of 1 nm TiOPc has the best device efficiency based on the device structure ITO(1750 Å)/PEDOT:PSS(500 Å)/ P3HT:PCBM(800 Å)/TiOPc(10 Å)/Al(2000 Å) and the device area of 0.16 cm2, the performance increase from 0.97 % to 1.77 % compared to standard device under AM1.5 simulation light before post annealing. (which is 82.4 % improved). This consequence can be attributed to a increase open voltage from 0.40 V to 0.56 V, a short increas current density from 5.62 mA/cm2 to 6.16 mA/cm2 and fill factor increased from 0.428 to 0.511. After post annealing at 140 ¢XC, the power efficiency increase for 45.2 % contrast to standard post annealing.

On-going efforts to reduce aircraft drag through transition delay focus on understanding the process of boundary-layer transition from a physics-based perspective. For swept-wings subject to transition dominated by a stationary crossflow instability, one of the remaining challenges is understanding how freestream disturbances and surface features such as surface roughness create the initial amplitudes for unstable waves. These waves grow, modify the mean flow and create conditions for secondary instabilities to occur, which in turn ultimately lead to transition. Computational methods that model the primary and secondary instability growth can accurately model disturbance evolution as long as appropriate initial conditions are supplied. Additionally, transition delay using discrete roughness arrays that exploit known sensitivities to surface roughness has been demonstrated in flight and wind tunnel testing; however, inconsistencies in performance from the two test platforms indicate further testing is required. This study uses detailed hotwire boundary-layer velocity scans to quantify the relationship between roughness height and initial disturbance amplitude. Naphthalene flow visualization provides insight into how transition changes as a result of roughness height and spacing. Micron-sized, circular roughness elements were applied near the leading edge of the ASU(67)-0315 model installed at an angle of attack of -2.9 degrees in the Klebanoff-Saric Wind Tunnel. Extensive flow quality measurements show turbulence intensities less than 0.02% over the speed range of interest. A survey of multiple roughness heights for the most unstable and control wavelengths and Reynolds numbers of 2.4 x 10⁶ 2.8 x 10⁶ and 3.2 x 10⁶ was completed for chord locations of 10%, 15% and 20%. When care was taken to measure in the region of linear stability, it was found that the disturbance amplitude varies almost linearly with roughness height. Naphthalene flow visualization indicates that moderate changes in already-low freestream turbulence levels can have a significant impact on transition behavior.

This dissertation analyzes the effect of periodic roughness elements on the stability of a flat plate boundary layer. Receptivity data is extracted from direct numerical simulations and experimental data and the results are compared to theoretical predictions. This analysis shows that flow in the immediate vicinity of roughness elements is non-linear; however, the evolution of roughness-induced perturbations is a linear phenomena. New techniques are developed to calculate receptivity information for cases where direct numerical simulations are not yet possible. Additionally, the stability behavior of the roughness wake is analyzed. New instability modes are found, and the effect of boundary layer complexity, perturbation amplitude and other factors are examined. It is shown that the wake is much less stable than optimal perturbation theory predicts, and highlights the importance of receptivity studies. The implication of these results on transition-to-turbulence is discussed, and future work is proposed. T

The materials based on GaN have successfully developed on short-wavelength laser diodes (LDs), light-emitting diodes (LEDs) and ultraviolet photodetector. In this study, GaN epitaxial layers have been successfully grown on sapphire substrates. We used several methods including the growth temperature and time of amorphous nucleation layer before growing epilayer and the growth temperature of GaN epilayer to study it. From the results of the photoluminescence (PL) measured at 77K, the X-Ray diffraction measurement, SEM cross sectional views to realize the characteristic and we get a better qualities of GaN epilayers after using the foregoing methods. In this study, the re-crystallization of the amorphous nucleation layer would occur while temperature re-rise to high temperature, and the phenomenon have different crystallinity under the different growth conditions of nucleation layer, which influence the quality and morphology of GaN epilayers seriously. According to the results of the experiments, we study the mechanisms of yellows luminescence and donor-acceptor pair.

The first-principles calculation method has been used to obtain electronic and structural properties of few-layer-graphenes (FLG), the layer spacing for N = 2, 3, 4, 5, 6, 7 and 8 AB stacked FLG¡¦s are calculated. It is found that the AB stacking is more favorable than the AA stacking and the layer spacing for the two-layer FLG is only 2.725Å, which is substantially reduced from that of the graphite. The average layer spacing for 3-, 4-, 5-, 6-, 7-, and 8-layer AB stacked FLG¡¦s are 3.389Å, 3.331Å, 3.317Å, 3.192Å, 3.220Å, and 3.220Å, respectively, which show that the average layer spacing approaches the bulk value when the number of layers is increased. For all 2- to 8-layer AB stacked FLG¡¦s energy bands overlap near EF and near K, which show that FLG¡¦s are semi-metallic.

The materials based on GaN have successfully developed on short-wavelength laser diodes (LDs), light-emitting diodes (LEDs) and ultraviolet photodetector. In this study, GaN epitaxial layers have been successfully grown on sapphire substrates. We used several methods including the nitridation temperature for substrates before growing epilayer, the growth temperature and time of buffer layer and the growth temperature of GaN epilayer to study it. From the results of the photoluminescence (PL) measured at 77K, the X-Ray diffraction measurement, SEM cross sectional views to realize the characteristic and we get a better qualities of GaN epilayers after using the foregoing methods. In this study, the re-crystallization of the buffer layer would occur while temperature re-rise to high temperature, and the phenomenon of conglomeration influence the quality and morphology of GaN epilayers. According to the results of the experiments, we study the mechanisms of yellows luminescence and donor-acceptor pair.

Electrode is where electricity is generated. Its quality is important to the entire battery performance. In this study, we are going to establish a stable and automatic process for making electrodes as well as required equipment. By this way, the instability in the electrode process can be improved. Electrospray technology is developed to spray the catalyst and reduce the agglomeration. It is shown that the electrode performance is 37% better than before after electrospray is adopted for producing catalyst layer. If we check the catalyst grains by AFM and TEM, we can find that the electrospray does scatter the polymers containing Nafion effectively. Under SEM, the catalyst grains are small and well proportioned on the carbon cloth. Obviously, catalysts are better utilized. All of the above can be used to explain the performance boost.

Thesis (Ph. D.)--Lehigh University, 2000. / Includes vita. Includes bibliographical references (leaves 179-183).