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[en] This thesis consists of an introduction, four chapters, a discussion and an appendix. The introduction provides the background to the work covered in this thesis, as well as an outline of the structure of the thesis. Chapter 1 presents a study related to fermion zero modes. The aim is to prove the existence of a zero mode that Klinkhamer and Lee observed in their study of a fermion doublet coupled to a chiral SU(2) gauge field. The proof comprises analytical and numerical analysis on the stability of the solutions obtained in the study of the Dirac equation of the fermion. Chapter 2 sketches a new mechanism for deriving a discrete and bounded fermion mass spectrum, based on the work of Klinkhamer and the present author. The model theory used consists of two fermion fields interacting with a Higgs-like scalar field. An open extra dimension is introduced to this theory so that a set of explicit classical solutions to the equations of motion is obtained. When the wave functions are required to be normalizable in the extra dimension, the masses of the four-dimensional fermions naturally become bounded and discrete. Chapter 3 consists of an investigation of a theory on the gauged Lorentz group. In Minkowskian space-time, the pure Yang-Mills theory of this group, with spherical symmetry imposed on the gauge field, reduces to a new theory in a two-dimensional space-time. The reduced theory has a scalar field with four degrees of freedom and a quartic potential, and two abelian gauge fields. A problem that remains to be solved, however, is that the potential of the scalar field is not bounded from below. In Chapter 4, a method for deriving a set of identities of the correlation functions in quantum field theories is presented. It can be used to obtain a variational equation (resembling a differential equation) for the generating functional of a given theory. When the generating functional is expanded into a Taylor series in terms of the source field(s), the variational equation makes it possible to relate the correlation functions of different processes to one another. The calculation here is non-perturbative. One of the identities derived for the λ - φ"4 theory is tested and verified. The thesis ends with a discussion in order to address the questions left unanswered in the previous chapters. Some reflections and ideas are given here, in hope that they can stimulate interest in future research.
[en] A thin layer of nanoparticle titanium dioxide was immobilized on polyamide 6 (PA6) fiber using titanium sulfate and urea at low temperature hydrothermal condition. The titanium dioxide loaded fabric was characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry and thermal gravimetry techniques. The optical and mechanical properties, water absorption and degradation of methylene blue dye under ultraviolet (UV) irradiation of the PA6 fabric before and after treatments were also examined. It was found that when PA6 fabric was treated in titanium sulfate and urea aqueous solution, anatase nanocrystalline titanium dioxide was synthesized and simultaneously adhered onto the fiber surface. The average crystal size of titanium dioxide nanoparticles was about 13.2 nm. The thermal behavior of PA6 fiber distinctly changed and the onset decomposition temperature decreased. As compared with the untreated fabric, the protection against UV radiation was improved. The water absorbency increased slightly. As the fabric dimensions were reduced in warp and weft directions, the breaking load and tensile strain increased to some extent. The titanium dioxide coated fabric could degradate methylene blue dye under UV irradiation. - Highlights: ► We employed a method to immobilize TiO2 nanoparticle on polyamide fiber. ► We fabricated the TiO2-coated polyamide fabric with the photocatalytic activity. ► The modification method may be suitable for the potential applications.
[en] We investigate the quantum Riemannian metric and the Euler characteristic number of the Bloch states manifold in a two-band lattice model, where a topological phase transition from the normal to the Chern insulator occurs. We derive the topological Euler number of the band from the Gauss–Bonnet theorem on the closed Bloch states manifold in the first Brillouin zone, where the Riemannian metric of the states manifold is established by the real part of the quantum geometric tensor in the 2D quasi-momentum space. Meanwhile, we show that the imaginary part of the geometric tensor corresponds to the Berry curvature which leads to the Chern number characterization of the band insulator. We discuss the topological numbers induced by the geometric tensor analytically in the case of two-band Hamiltonian and characteristic the zero-temperature phase diagram by the Euler number and first Chern number, respectively
[en] Highlights: • Ag@Ag_2MoO_4–AgBr composite is synthesized by in-situ exchange and photo depositio nmethod. • Compared with pure Ag_2MoO_4 crystal, the photocatalytic activity of Ag@Ag_2MoO_4–AgBr composite was increased by 348.4%. • Silver particles act as electron trap to enhance electron–hole separation. • This composite has the promising application to degrade organic wastewater. - Abstract: The Ag_2MoO_4-AgBr composite was prepared by a facile in-situ anion-exchange method, then the Ag nanoparticles were coated on this composite through photodeposition route to form a novel Ag@Ag_2MoO_4–AgBr composite. The in-situ Br"− replacement in a crystal lattice node position of Ag_2MoO_4 crystal allows for overcoming the resistance of electron transition effectively. Meanwhile silver nano-particles on the surface of Ag@Ag_2MoO_4–AgBr composite could act as electron traps to intensify the photogeneration electron-hole separation and the subsequent transfer of the trapped electron to the adsorbed O_2 as an electron acceptor. As an efficient visible light catalyst, the Ag@Ag_2MoO_4–AgBr composite exhibited superior photocatalytic activity for the degradation of various organic dyes. The experimental results demonstrated superior photocatalytic rate of Ag@Ag_2MoO_4–AgBr composite compared to pure AgBr and Ag_2MoO_4 crystals (37.6% and 348.4% enhancement respectively). The Ag@Ag_2MoO_4–AgBr composite cloud degraded Rhodamin B, bromophenol blue, and amino black 10b completed in 7 min.
[en] As the generalization of the well-known Cayley-Menger algebra, the general relation among points, hyperplanes and hyperspheres in En is proposed. A series of examples are given to show its applications. This study would be greatly helpful to symbolic computation in geometry, including computer-aided geometric reasoning. (author). 9 refs
[en] It is shown that Wu's non-degenerate condition which plays an important role in Wu's theory on algebraic system and automated theorem proving can be replaced with a much weaker one, so the characteristic-set-based method is extensively valid except for very few trivial instances. (author). 6 refs
[en] Nickel-based alloys have been extensively used as critical components in aerospace industry, especially in the key section of aero engine. In general, these sections are manufactured by milling process because most of them have complex forms. However, surface defects appear frequently in milling due to periodic impact force, which leads to the deterioration of the fatigue life. We conducted milling experiments under different cutting conditions and found that four kinds of defects, i.e., tear, cavity, build up edge (BUE) and groove, commonly appear on the machined surface. Based on the observed results, the morphology and generation regime of these defects are analyzed and the carbide particle cracking is discussed to explain the appearance of the nickel alloy defects. To study the effect of the cutting parameters on the severity of these surface defects, two qualitative indicators, which are named as average number of the defects per field and average area ratio of the defects per field, are presented and the influence laws are summarized based on the results correspondingly. This study is helpful for understanding the generation mechanism of the surface defects during milling process of nickel based super alloy.
[en] EPDM was procured by electron beam (EB) irradiation. The sensitizing efficiency of trimethylopropane trimethylacrylacrylate (TMPTMA) was studied. The compression set, water absorption, mechanical properties and surface of EPDM foam were compared at different absorbed doses. The results show that the closed cell property and mechanical properties of EPDM foam are heightened at 5-15 kGy. (authors)
[en] Handhold nuclear spectrometer is necessary in radiation location, nuclear security and homeland security, Which can fast find, identify and measure intensity for the exceptional nuclide. Also can provide accurate γ dose rate in advance. It is made up of digital spectrometry probe and handle PDA. Probe include NaI scintillator, photomultiplier tube, amplifier, multichannel analyzer, high voltage power, blue tooth and Li battery. Spectrometry acquire and analyse software are loaded in PDA, Which can show and analyse the data, nuclide identification, display measure information etc. Specifications: energy resolution 7.5% (137Cs), sensitivity 100 cps corresponding to 0.1 μSv/h, Spectrometry resolution 1024 channel. (authors)