Nowadays, the bevel gears are widely applied in the industry for the intersected-axial transmission system. But the applications of the bevel gears are mostly limited to the usage of involute bevel gears. In this thesis, the bevel gear with circular-arc tooth profiles is derived by using general theorem of conjugate surfaces, coordinate transformation, constrained meshing equation, and spherical trigonometry. According to the bevel gears with circular-arc tooth profile derived above, the analyses and discussions of the interference are proposed. The interference situation is detected by applying the phase lead-lag concept while circular-arc curve is moving on the spherical cross-section. Furthermore, the ideal conditions to avoid occurrence of interference are proposed. Design charts for the maximum values of tooth profile angle are also constructed as a reference for designers. The 3D solid models of the bevel gear with circular-arc tooth profiles are constructed by using the computer software (Pro/E). Finally, the transmission ability is verified through the computer animation using CAE software (Visual Nastran). It is believed that the mathematical models and design method developed in the thesis will provide a useful foundation for the further studies.

In recent years there has been a growing demand for reduced mass, small launch volume, and, at the same time, high-gain large-aperture antenna systems in modern space-borne applications. This dissertation introduces new techniques for dual-band reflectarray antennas to meet these requirements. A series of developments is presented to show the dual-band capability of the reflectarray. A novel microstrip ring structure has been developed to achieve circular polarization (CP). A C/Ka dual-band front-fed reflectarray antenna has been designed to demonstrate the dual-band circular polarized operation. The proposed ring structure provides many advantages of compact size, more freedom in the selection of element spacing, less blockage between circuit layers, and broader CP bandwidth as compared to the patches. An X/Ka dual-band offset-fed reflectarray is made of thin membranes, with their thickness equal to 0.0508 mm in both layers. Several degrading effects of thin substrates are discussed. To overcome these problems, a new configuration is developed by inserting empty spaces of the proper thickness below both the X and Ka band membranes. More than 50 % efficiencies are achieved at both frequency ranges, and the proposed scheme is expected to be a good candidate to meet the demand for future inflatable antenna systems. An X/Ka dual-band microstrip reflectarray with circular polarization has also been constructed using thin membranes and a Cassegrain offset-fed configuration. It is believed that this is the first Cassegrain reflectarray ever developed. This antenna has a 0.75-meter-diameter aperture and uses a metallic sub-reflector and angular-rotated annular ring elements. It achieved a measured 3 dB gain bandwidth of 700 MHz at Xband and 1.5 GHz at Ka-band, as well as a CP bandwidth (3 dB axial ratio) of more than 700 MHz at X-band and more than 2 GHz at Ka-band. The measured peak efficiencies are 49.8 % at X-band and 48. 2 % at Ka-band. In summary, this dissertation presents a series of new research developments to support the dual-band operation of the reflectarray antenna. The results of this work are currently being implemented onto a 3-meter reflectarray with inflatable structures at the Jet Propulsion Laboratory and are planned for other applications such as an 8-meter inflatable reflectarray in the near future.

The study aims to explore flow-induced vibration of shear flow past a circular cylinder. The major parameters in the experiment are the natural frequency of the cylinder, and the velocity and velocity gradient of the shear flow approaching the cylinder. The vibration of the cylinder in a water tunnel were measured by two accelerometers to simultaneously obtain the vibration amplitudes in both the streamwise and cross-stream directions. The experimental results show that in the shear flow the cylinder tends of vibrate the orbits of the cylinder vibration become in the streamwise direction while in uniform flow the cylinder vibrates in all directions in the X-Y plane the tendency is obvious for the cylinder with high natural frequency (13Hz). The orbits of the cylinder with low natural frequency (9Hz) are basically similar in shear flow and in uniform flow.

The present study developes a mixed finite element formulation for the analysis of piezoelectric circular and annular plates. This formulation combines the conventional displacement-electric potential type variational principle and the piezoelectric Reissner`s principle with a weighting factor which represents ratio of weights imposed on the above two variational principles, and which can be adjusted by comparing with experiment results. With this formulation, stresses and electric displacements, like displacements and electric potential, are primary variables and are continuous across elements and element interfaces. Also, all displacement, stress, electric displacement, and electric potential boundary conditions can be easily and exactly imposed. Static deformations and vibration frequencies of some typical piezoelectric circular and annular plates are then obtained with the present approach and are compared with those by other methods. Based on experiment results in the literature, it is found that better results could be obtained in general by the present mixed finite element formulation than the others when 1 is chosen as the weighting factor.

Dragon grouper nervous necrosis virus (DGNNV), a betanodavirus, is the causative agent of viral nervous necrosis (VNN) in dragon grouper (Epinephelus lanceolatus). In our study, capsid protein of DGNNV was expressed in Escherichia coli. We mutated arginines at N-termini capsid protein to investigate the role of arginines at 29-31th position. When capsid protein lost 25 amino acids at N-termini VLPs form, mutation in any two arginines at 29-31 position to alanine could the prohibit VLPs formation. Another extending three arginines at 23-25 position wouldn¡¦t increase the RNA encapsulation into VLPs. Furthermore, N-termini mutated VLPs were all RNase resistance like wt-VLPs, but the yield was distinctly less than wt-VLPs. In the single point alanine mutations, the VLPs yield of R29A was apparently higher than others (R30A and R31A). Using circular dichroism to observe the thermal denature process and thermal stability of DGNNV VLPs, we found the Tm about 60¢J of VLPs wouldn¡¦t alter even if arginines at 23-31 position were mutated. The findings suggested the VLPs of mutated arginines at 23-31 position wouldn¡¦t affect RNase resistance and thermal stability, but the yield were lower. Another, the arginines at the 30 and 31 position is more important than at 29 position for formation of VLPs.

The observation of ferromagnetism of (Ga,Mn)As by Ohno in 1998 has inspired great interest in diluted magnetic semiconductors (DMS). DMS’s features combining ferromagnetism and semiconducting make them of great potential for conceptual spintronic devices, which is a promising field of research for the emerging electronics. The practical application of DMS requires a Curie temperature well above room temperature and an intrinsic ferromagnetism. There are several types of DMS materials. The typical ones are transition-metal (TM) doped GaAs, GaN and ZnO. The TM-doped ZnO has drawn particular attention due to the observation of room temperature ferromagnetism in this system including cobalt-doped ZnO.But the origin of ferromagnetic TM-doped ZnO is still unknown after a decade’s theoretical and experimental effort on this material. In this thesis, we do the magnetic circular dichroism(MCD) and Hall measurement of high quality Cobalt-doped ZnO thin films grown by molecular beam epitaxy (MBE). Room temperature ferromagnetism is observed in these samples. Combining the data from MCD and Hall measurement, we attribute the room temperature ferromagnetism in this system to the impurity band of the doped Cobalt cations. / published_or_final_version / Physics / Master / Master of Philosophy

published_or_final_version / abstract / toc / Medicine / Doctoral / Doctor of Philosophy

No description available.

No description available.

Mimicking the structure and even the function of an ??-peptide with artificial chainmolecules such as ??-peptides, ??-peptides and other unnatural oligomers has shown early success.The structural similarities between natural peptides and oligoureas lead to the belief that C2-symmetric oligoureas could be a good candidate for peptidomimicry. Molecular modelingindicates that both homochiral (all monomers have the same absolute configuration) andalternate chiral (absolute configuration of the residues alternate) C2-symmetric oligoureas canform helix- and sheet-like structures in solution conditionally.Several C2-symmetric 1,2-diamines were chosen as the building blocks for the synthesisof chiral oligoureas, and all diamines except for one were prepared in lab. Homochiral andheterochiral oligoureas based on the same diamine or mixed diamines were synthesized in thesolution phase, growing a chain by adding one unit at a time to one terminus or two units at atime to both termini with 4-nitrophenoxycarbonyl (PNP)- activated and t-butoxycarbonyl (Boc)- protected diamines as the intermediates. All the chiral oligoureas were purified by eitherrecrystallization and /or column chromatography and/ or HPLC and characterized by NMR andMALDI-MS. For some oligoureas, crystal structures were obtained. Fragment condensation wasattempted to improve the efficiency of the synthesis, but this approach led to cyclized oligoureasinstead of the desired concatenated residues.Conformational studies of chiral oligoureas were done in both the solid state and thesolution state. The crystal structures of some homochiral oligoureas and some alternate chiraloligoureas indicate that both helix-like structures and extended structures exist for these C2-symmetric oligoureas. NMR and Circular Dichroism (CD) were used to study the conformationof oligoureas in solution, but the conformational study by NMR was not conclusive. CD studyshowed that these oligoureas have multiple conformations in solution and that some of theconformations are sensitive to solvents and temperature. Also, short homochiral and alternatechiral oligoureas based on trans-1,2-diaminocyclohexane (DACH) exhibit signs of cooperativebehavior in solution as gauged by a series of experiments.