In most terahertz (THz) systems, the propagation of THz signals relies on metal or dielectric waveguides which suffer from high conductivity losses caused by the skin effect or dielectric losses resulted from the material absorption. Due to this reason, we propose and demonstrate a simple low-loss air-core tube strucutre for THz waveguiding. The simulation method we utilized is the finite-difference frequency-domain (FDFD) method with the perfectly matched layers (PMLs). The modal indices and propagation losses of the guided core modes on the THz tube waveguide are successfully obtained. The simulation results show that the guiding mechanism of the hollow tube waveguide is based on the antiresonant reflecting optical waveguide (ARROW) model. We also utilize a Fabry-Perot resonantor model to find out the resonance frequencies of the dielectric layer, which match well with the results of the FDFD method. By varying the core size, it is observed that the propagation losses are reduced when the core size is increased. The propagation losses can be reduced from 10-3 cm-1 (0.0043 dB/cm) to 10-4 cm-1 (4.34¡Ñ10-4 dB/cm). In addition, we can use the thin dielectric layer to provide a broad transmission band with £Gf = 0.13THz. We also propose a novel tube THz waveguide sensor. The influence of the thickness and material of the dielectric layer 2 are investigated. We can observe that the shift of the propagation loss peak is inversely proportional to the thickness of dielectric layer 2, which can be used as a thickness sensor with the sensing sensitivity being 0.125 GHz/£gm. On the other hand, the index of the dielectric layer 2 and the position of the propagation loss peak are in an exponential relationship. These properties of the tube waveguide can be applied in the dielectric-film sensing.

Die surface shape may improve the flow of materials, reduce stress concentration of the products, and decrease the processing load to extend the life of die. The objective of this paper is to show that how to design the die surface shape of T-shape protrusion hydroforming with different diameters. A finite element code DEFORM 3D is used to simulate the process of THF, including adaptive simulation to predict the internal pressurization in the tube, and utilize flow net distribution to predict the axial feeding stroke and counter punch (CP) movement. After the amendment to the loading path, the flowability and appearance of the product quality will achieve the best results. Experiments of T-shape warm hydroforming of magnesium alloy AZ61 tubes are. The forming temperature is set as 250¢J. The simulated loading paths are used. From the comparisons of product shape, thickness distribution between analytical and experimental values, the validity of this analytical model is verified.. Keywords: Tube hydroforming, Finite element simulation, Die surface design.

The success in fabrication of Cr-doped fibers (CDFs) with fluorescence of Cr3+ by powder-in-tube (PIT) method equipped with drawing-tower process is demonstrated for the first time. The fluorescence intensity of CDFs by fabricated RIT method is weak because the concentration of Cr-ion in Cr:YAG rod is low. However, the fabrication with powder-in-tube (PIT) provides a better solution to improve the concentration of Cr-ion to enhance the fluorescence of CDFs. The Cr-doped powder was composed of CaO-Al2O3-BaCO3-MgO-Cr2O3 as the material of core and then it was poured into the silica tube with outer diameter of 20 mm and inner diameter of 7 mm (20/7) to yield the perform. The CDFs had a 17.5 £gm core and a 125 £gm cladding. The transmission loss was 0.74 dB/cm at 1550 nm. And the fluorescence intensity of Cr3+ between 800~1200 nm was 50 nW/nm. To reduce transmission loss further, we used multi-tubes to raise the ratio of cladding to core. According to the principle of conservation of mass, the core diameter of CDFs was 5 £gm. The transmission loss was improved more than 50% and it reached to 0.135 dB/cm at 1550 nm. Moreover, a single-mode characteristic of CDF was observed when the propagation wavelengths were longer than 1260 nm. The CDFs were successfully fabricated by using a fiber drawing-tower technique with PIT method. The demonstration of CDFs makes it possible as a new generation broadband fiber amplifier, a tunable NIR fiber laser for sensor applications, and a broadband source for high resolution OCT.

Neural tube defects (NTDs) are malformations affecting about 2.6/1000 births worldwide, and 1/1000 in the United States. Their etiology remains unknown, and is likely due to interaction of genetic susceptibility factors with environmental exposure. Of the many environmental agents considered to potentially contribute to NTD risk, arsenic is one that is surrounded in controversy. We have developed a model system utilizing maternal intraperitoneal (I.P.) exposure on E7.5 and E8.5 to As 9.6 mg/kg (as sodium arsenate) in a normal inbred mouse strain, LM/Bc/Fnn, that is sensitive to arsenate-induced exencephaly. We investigated arsenate induced gene expression changes using DNA microarrays of embryonic anterior neural tube tissue, as well as monitoring of metabolic function in conjunction with the administration of select compounds to rescue the normal phenotype. Finally, to address questions concerning the importance of route of administration and potential maternal toxicity, a teratology study was performed using three arsenate doses administered orally. Regarding the gene expression study, we identified several candidate genes and ontology groups that may be responsible for arsenate’s teratogenicity. Genes include: engrailed 1 (En-1), platelet derived growth factor receptor alpha (Pdgfrα) and ephrinA7 (EphA7). Gene ontology groups identified include oxidative phosphorylation, redox response, and regulation of I-kappaB kinase/NF-kappaB cascade. Acute arsenate exposure induced disruption of mitochondrial function and dependent glucose homeostasis: subsequent hyperglycemia was teratogenic. Maternal treatment with insulin or n-acetyl cysteine, an antioxidant and precursor of glutathione synthesis, proved highly successful in rescuing both the normal phenotype, and to differing degree, the maternal hyperglycemia. Maternal oral arsenate administration also resulted in exencephaly, with exposed embryos exhibiting a positive linear trend with arsenate dosage. There were also linear trends in the relationships between arsenate dose and anomalies involving several components of the axial skeleton: the vertebrae and calvarium. There was no evidence of maternal toxicity as shown by lack of differences in maternal body weight gain, liver, and kidney weights. In conclusion, maternal arsenate exposure (regardless of exposure route) was teratogenic in our model, primarily causing NTDs. Responsible mechanisms may involve disruption of redox and glucose homeostasis as well as expression of established NTD candidate genes.

A new shock tube targeting low temperature, high pressure, and long test times was designed and installed at the Turbomachinery Laboratory in December of 2008. The single-pulse shock tube uses either lexan diaphragms or die-scored aluminum disks of up to 4 mm in thickness. The modular design of the tube allows for optimum operation over a large range of thermodynamic conditions from 1 to 100 atm and between 600-4000 K behind the reflected shock wave. The new facility allows for ignition delay time, chemical kinetics, high-temperature spectroscopy, vaporization, atomization, and solid particulate experiments. An example series of ignition delay time experiments was made on mixtures of CH4/C2H6/O2/Ar at pressures from 1 to 30.7 atm, intermediate temperatures from 1082 to 2248 K, varying dilutions (between 75 and 98% diluent), and equivalence ratios ranging from fuel lean (0.5) to fuel rich (2.0) in this new facility. The percentage by volume variation and equivalence ratios for the mixtures studied were chosen to cover a wide parameter space not previously well studied. Results are then used to validate and improve a detailed kinetics mechanism which models the oxidation and ignition of methane and other higher order hydrocarbons, through C4, with interest in further developing reactions important to methane- and ethane-related chemistry.

The tube hydroforming (THF) technology has been widely used in manufacturing the lightweight and high strength components. The success of THF is largely dependent on the selection of the loading paths: internal pressure vs. time and axial feeding vs. time. The Finite element method is used to simulate the forming result of different loading paths and reduce the cost of die-testing. T-shape tube hydroforming is investigated adaptive simulation by combining FEM code LS-DYNA with fuzzy logic controller subroutine is proposed. During the simulation process, subroutines can adjust the loading paths according to the values of the minimum tube thickness and its variance. Then, the purpose of better thickness distribution of the formed tube at the side branch is achieved. Comparing with other linear loading paths, this adaptive control method got better results. In experiments, the validity of LS-DYNA applied in THF process is verified and the experimental results by adaptive simulation are better than those by the linear loading paths.

The microstructures and mechanical properties of the AZ31 Mg tubes fabricated by one-pass forward piercing tube extrusion operated at 250-400oC and 10-2-100 s-1 are examined. The grain size is refined from the initial ~75

Tube hydroforming process is a relatively new technology compared to conventional manufacturing via stamping and welding. However there is not much knowledge available for the product or process designers. The objective of this study will determine the flow stress and forming limit diagram of tubular materials to discuss the formability of tubes. Firstly, a mathematical model is proposed to examine the plastic deformation behavior of a thin-walled tube at different process parameters during the bulge hydroforming process without axial feeding. In the formulation of this mathematical model, an ellipsoidal surface and non-uniform thinning in the free bulged region and sticking friction between the tube and die are assumed. In the sticking friction mode, the elements after contact with the die do not move or slide. The effects of various forming parameters, such as the die entry radius, the bulge length, anisotropy, the initial thickness of the tube, etc., upon the forming pressures are discussed systematically. Secondly, an analytical model combined with hydraulic bulge tests is proposed to evaluate the properties of tubular materials considering anisotropy effect. Annealed AA6011 aluminum tubes and SUS409 stainless steel tubes are used for the bulge test. The tube thickness and radius at the pole and the internal forming pressure are measured simultaneously during the bulge test. The anisotropic values are obtained from tensile tests. From above experimental data, the effective stress - effective strain relations can be derived by this analytical model. The finite element method is used to conduct the simulations of hydraulic bulge forming with the flow stresses obtained by the above-mentioned model. The analytical forming pressures versus bulge heights are compared with the experimental results to validate the approach proposed in this study. Finally, this study also establishes the Forming Limit Diagram (FLD) of aluminum tubular material. An experimental system of tube hydroforming in which axial feed is applied to carry out the hydraulic bulge-forming test of the annealed aluminum alloy tubes. Furthermore, Hill¡¦s new yield criterion is also used to predict the Forming Limit Curves of sheets. The predicted forming limit diagrams are compared with the experimental data. The results of this study can provide useful knowledge for process design. In addition, the process parameters of flow stress and forming limit diagram obtained can improve the accuracy of the simulation results in industrial and academic fields.

The tube hydro-forming (THF) is an innovative manufacturing process which is used to manufacture many industrial components widely. The success of THF is largely dependent on the selection of the loading paths: internal pressure versus time, axial feeding versus time and counter punch (CP) versus time. The finite element analysis is used to simulate the forming result of different loading paths and reduce the cost of die-testing. This paper presents the forming of T-branches and T-branches components with CP. These paper has developed an adaptive simulation algorithm by combining FEM code LS-DYNA 3D with controller subroutine to get ideal bulging height and uniform thickness of the formed tube with multi-stages. Discuss influence under different parameters of process. The results are compared with experimental results to validate accuracy by this adaptive control methods.

The purpose of this thesis is aimed to predict that what kind of adhesive bonded joint of composite tube the can obtain more efficient structure. APC-2 sixteen-layer laminates of AS-4/PEEK were used as adherends, including cross-ply [0/90]4S and quasi-isotropic [0/45/90/-45]2S laminates. And we use two different kinds of adhesive bonded joints, including stepped lap joint and scarf lap joint. On the aspect of numerical analysis, we employ finite element method incorporate with the software of ANSYS 5.5.1 to obtain the distribution of stress on adhesive bonded joint. In this thesis, there are two kinds of geometrical shape on stepped lap joint. The bonded layer height h that is vertical to the axis of the composite tube is 2mm and 5mm. There are also two kinds of the geometrical shape on scarf lap joint. The angle £\ between the bonded layer and the axis of the composite tube is 30¢Xand 45¢X.The boundary condition on one side of the composite tube is assumed to be fixed. The other side of the composite tube is due to torsion. According to the numerical result, the stepped lap joint with h=5mm and quasi-isotropic [0/45/90/-45] occurs minimum von Mises stress, and we predict this kind of joint can sustain the maximum external load and obtain better efficiency. In this thesis, the geometrical shape, size and the direction of laminates of the joint will effect the distribution of stress.