Modelling multi-scale problems in the transmission line modelling method

Modern electromagnetic problems are becoming increasingly complex and their simulation must take into account geometrical features that are both large and small compared to the wavelength of interest. These multi-scale problems lead to a heavy computational burden in a discretised computational simulation approach since the small features require fine mesh to be used in the simulation, resulting in large run time and memory storage. To overcome such problems, this thesis presents an efficient and versatile method for embedding small features into an otherwise coarse mesh. The embedded model eliminates the need for discretising the small features and allows for a relative large mesh size to be used, thus saving the computational costs. The subject of the thesis is embedding a thin film as a small feature into the numerical Transmission Line Modelling (TLM) method, although any small feature with known analytical response can be implemented in practice. In the embedded model, the thin film is treated as a section of transmission line, whose admittance matrix is used to describe the frequency response of the thin film. The admittance matrix is manipulated by expanding the constituent cotangent and cosecant functions analytically, and then transforming them from the frequency domain to the time domain using the inverse Z transform and general digital filter theory. In this way the frequency responses of the thin film are successfully embedded into the TLM algorithm. The embedded thin film model can be applied to both single and multiple thin film layers. The embedded thin film model has been implemented in the one-dimensional (1D) and two-dimensional (2D) TLM method in the thesis. In the 1D TLM method, the embedded thin film model is used to investigate the reflection and transmission properties of lossy,anisotropic and lossless thin films, e.g. carbon fibre composite (CFC) panels, titanium panels, antireflection (AR) coatings and fibre Bragg gratings (FBG). The shielding performance of CFC panels is also discussed. In the 2D TLM method, the embedded thin film model is extended to model arbitrary excitations and curved thin films. The electromagnetic behaviour of infinitely long CFC panels with oblique incidence and a CFC panel of finite length with a point source excitation are studied using the embedded thin film model. The resonant effects of CFC circular and elliptical resonators and the shielding performance of a CFC airfoil with the profile of NACA2415 are investigated using the embedded curved thin film model. In addition, the effects of small gaps in the airfoil structure on the shielding performance are also reported. All the examples discussed in the thesis have validated the accuracy, stability, convergence and efficiency of the embedded thin film model developed. At the same time, the embedded thin film model has been proven to have the advantage of significantly saving computational overheads

Modelling multi-scale problems in the transmission line modelling method

Modern electromagnetic problems are becoming increasingly complex and their simulation must take into account geometrical features that are both large and small compared to the wavelength of interest. These multi-scale problems lead to a heavy computational burden in a discretised computational simulation approach since the small features require fine mesh to be used in the simulation, resulting in large run time and memory storage. To overcome such problems, this thesis presents an efficient and versatile method for embedding small features into an otherwise coarse mesh. The embedded model eliminates the need for discretising the small features and allows for a relative large mesh size to be used, thus saving the computational costs. The subject of the thesis is embedding a thin film as a small feature into the numerical Transmission Line Modelling (TLM) method, although any small feature with known analytical response can be implemented in practice. In the embedded model, the thin film is treated as a section of transmission line, whose admittance matrix is used to describe the frequency response of the thin film. The admittance matrix is manipulated by expanding the constituent cotangent and cosecant functions analytically, and then transforming them from the frequency domain to the time domain using the inverse Z transform and general digital filter theory. In this way the frequency responses of the thin film are successfully embedded into the TLM algorithm. The embedded thin film model can be applied to both single and multiple thin film layers. The embedded thin film model has been implemented in the one-dimensional (1D) and two-dimensional (2D) TLM method in the thesis. In the 1D TLM method, the embedded thin film model is used to investigate the reflection and transmission properties of lossy,anisotropic and lossless thin films, e.g. carbon fibre composite (CFC) panels, titanium panels, antireflection (AR) coatings and fibre Bragg gratings (FBG). The shielding performance of CFC panels is also discussed. In the 2D TLM method, the embedded thin film model is extended to model arbitrary excitations and curved thin films. The electromagnetic behaviour of infinitely long CFC panels with oblique incidence and a CFC panel of finite length with a point source excitation are studied using the embedded thin film model. The resonant effects of CFC circular and elliptical resonators and the shielding performance of a CFC airfoil with the profile of NACA2415 are investigated using the embedded curved thin film model. In addition, the effects of small gaps in the airfoil structure on the shielding performance are also reported. All the examples discussed in the thesis have validated the accuracy, stability, convergence and efficiency of the embedded thin film model developed. At the same time, the embedded thin film model has been proven to have the advantage of significantly saving computational overheads

Automatic Classification of Bug Reports Based on Multiple Text Information and Reports' Intention

With the rapid growth of software scale and complexity, a large number of bug reports are submitted to the bug tracking system. In order to speed up defect repair, these reports need to be accurately classified so that they can be sent to the appropriate developers. However, the existing classification methods only use the text information of the bug report, which leads to their low performance. To solve the above problems, this paper proposes a new automatic classification method for bug reports. The innovation is that when categorizing bug reports, in addition to using the text information of the report, the intention of the report (i.e. suggestion or explanation) is also considered, thereby improving the performance of the classification. First, we collect bug reports from four ecosystems (Apache, Eclipse, Gentoo, Mozilla) and manually annotate them to construct an experimental data set. Then, we use Natural Language Processing technology to preprocess the data. On this basis, BERT and TF-IDF are used to extract the features of the intention and the multiple text information. Finally, the features are used to train the classifiers. The experimental result on five classifiers (including K-Nearest Neighbor, Naive Bayes, Logistic Regression, Support Vector Machine, and Random Forest) show that our proposed method achieves better performance and its F-Measure achieves from 87.3% to 95.5%

Prognostic Outcomes and Risk Factors for Patients with Renal Cell Carcinoma and Venous Tumor Thrombus after Radical Nephrectomy and Thrombectomy: The Prognostic Significance of Venous Tumor Thrombus Level.

IntroductionTo evaluate the prognostic outcomes and risk factors for renal cell carcinoma (RCC) patients with venous tumor thrombus in China.Materials and methodsWe reviewed the clinical information of 169 patients who underwent radical nephrectomy and thrombectomy. Overall and cancer-specific survival rates were analyzed. Univariate and multivariate analyses were used to investigate the potential prognostic factors.ResultsThe median survival time was 63 months. The five-year overall survival and cancer-specific survival rate were 53.6% and 54.4% for all patients. For all patients, significant survival difference was only observed between early (below hepatic vein) and advanced (above hepatic vein) tumor thrombus. However, significant differences existed between both RV/IVC and early/advanced tumor thrombus groups in N0M0 patients. Multivariate analysis demonstrated that higher tumor thrombus level (p = 0.016, RR = 1.58), N (p = 0.013, RR = 2.60), and M (p < 0.001, RR = 4.14) stages and adrenal gland invasion (p = 0.001, RR = 4.91) were the most significant negative prognostic predictors.ConclusionsIn this study, we reported most cases of RCC patients with venous extension in China. We proved that patients with RCC and venous tumor thrombus may have relative promising long-term survival rate, especially those with early tumor thrombus

Installed antenna performance in airborne radomes of different profiles

In this paper, broadband interactions between an antenna and a radome are modelled using a full wave numerical solver. By accurately describing both the antenna and the radome geometry with a single numerical method, a comprehensive prediction of the performance of the coupled antenna and radome installation is provided. The paper compares how different airborne dielectric radome profiles affect the antenna performance, predicting effects not seen in uncoupled simulations

Experimental benchmarking of Unstructured Transmission Line Modelling (UTLM) method in modelling twisted wires

In this paper the Unstructured Transmission Line Modelling (UTLM) method based on a tetrahedral mesh has been applied to modelling of the coupling between a single wire and a twisted wire pair. The effects of wire twisting on the crosstalk and coupling between wires are modelled by explicitly meshing wire geometries; simulation results are compared with experimental ones. Excellent agreement between simulated and measured results validates the viability and accuracy of the UTLM method and indicates the potential of the UTLM method for modelling complex wire structures