Meta-Analysis: Contrast-Enhanced Ultrasound Versus Conventional Ultrasound for Differentiation of Benign and Malignant Breast Lesions

This meta-analysis aimed to compare the diagnostic performance of contrast-enhanced ultrasound (CEUS), conventional ultrasound (US) combined with CEUS (US + CEUS) and US for distinguishing breast lesions. From thorough literature research, studies that compared the diagnostic performance of CEUS versus US or US + CEUS versus US, using pathology results as the gold standard, were included. A total of 10 studies were included, of which 9 compared the diagnostic performance of CEUS and US, and 5 studies compared US + CEUS and US. In those comparing CEUS versus US, the pooled sensitivity was 0.93 (95% CI: 0.91–0.95) versus 0.87 (95% CI: 0.85–0.90) and pooled specificity was 0.86 (95% CI: 0.84–0.88) versus 0.72 (95% CI: 0.69–0.75). In studies comparing US + CEUS versus US, the pooled sensitivity was 0.94 (95% CI: 0.92–0.96) versus 0.87 (95% CI: 0.84–0.90) and pooled specificity was 0.86 (95% CI: 0.82–0.89) versus 0.80 (95% CI: 0.76–0.84). In terms of diagnosing breast malignancy, areas under the curve of the summary receiver operating characteristic (of both CEUS (p = 0.003) and US + CEUS (p = 0.000) were statistically higher than that of US. Both CEUS alone and US + CEUS had better diagnostic performance than US in differentiation of breast lesions, and US + CEUS also had low negative likelihood ratio

Scanning tunneling microscopy study of the possible topological surface states in BiTeCl

Recently, the non-centrosymmetric bismuth tellurohalides such as BiTeCl are being studied as possible candidates of topological insulators. While some photoemission studies showed that BiTeCl is an inversion asymmetric topological insulator, others showed that it is a normal semiconductor with Rashba splitting. Meanwhile, first-principle calculationsfailed to confirm the existence of topological surface states in BiTeCl so far. Therefore, the topological nature of BiTeCl requires further investigation. Here we report low temperature scanning tunneling microscopy study on the surface states of BiTeCl single crystals. On the tellurium-terminated surfaces with low defect density, strong evidences for topological surface states are found in the quasi-particle interference patterns generated by the scattering of these states, both in the anisotropy of the scattering vectors and the fast decay of the interference near step edges. Meanwhile, on samples with much higher defect densities, we observed surface states that behave differently. Our results help to resolve the current controversy on the topological nature of BiTeCl.Comment: 13pages,4figure

Enhanced superconductivity in TiO epitaxial thin films

Titanium oxides have many fascinating optical and electrical properties, such as the superconductivity at 2 K in cubic titanium monoxide (TiO) polycrystalline bulk. However, the lack of TiO single crystals or epitaxial films has prevented systematic investigations on its superconductivity. Here, we report the basic superconductivity characterizations of cubic TiO films epitaxially grown on (0001)-oriented α-Al2O3 substrates. The magnetic and electronic transport measurements confirmed that TiO is a type-II superconductor and the recorded high Tc is about 7.4 K. The lower critical field (Hc1) at 1.9 K, the extrapolated upper critical field Hc2(0), and coherence length are about 18 Oe, 13.7 T, and 4.9 nm, respectively. With increasing pressure, the value of Tc shifts to lower temperature while the normal state resistivity increases. Our results on the superconducting TiO films confirm the strategy to achieve higher Tc in the epitaxial films, which may be helpful for finding more superconducting materials in various related systems

Informative scene decomposition for crowd analysis, comparison and simulation guidance

Crowd simulation is a central topic in several fields including graphics. To achieve high-fidelity simulations, data has been increasingly relied upon for analysis and simulation guidance. However, the information in real-world data is often noisy, mixed and unstructured, making it difficult for effective analysis, therefore has not been fully utilized. With the fast-growing volume of crowd data, such a bottleneck needs to be addressed. In this paper, we propose a new framework which comprehensively tackles this problem. It centers at an unsupervised method for analysis. The method takes as input raw and noisy data with highly mixed multi-dimensional (space, time and dynamics) information, and automatically structure it by learning the correlations among these dimensions. The dimensions together with their correlations fully describe the scene semantics which consists of recurring activity patterns in a scene, manifested as space flows with temporal and dynamics profiles. The effectiveness and robustness of the analysis have been tested on datasets with great variations in volume, duration, environment and crowd dynamics. Based on the analysis, new methods for data visualization, simulation evaluation and simulation guidance are also proposed. Together, our framework establishes a highly automated pipeline from raw data to crowd analysis, comparison and simulation guidance. Extensive experiments and evaluations have been conducted to show the flexibility, versatility and intuitiveness of our framework

Quantum Transport on Topological Matter

Topological matter is a new state of matter which is characterized by topological nontrivial electronic structure. It not only has fundamental physical importance but also has practical applications. In this thesis, quantum transport measurement is used to study electronic structure and transport properties of various topological matter. In Chapter 3, we report a magneto-transport study on single crystals of the topological insulator BiSbTe3. Besides Shubnikov-de Haas oscillations and weak anti-localization (WAL) from the topological surface state, we also observed a crossover from the weak anti-localization to weak localization (WL) with increasing magnetic field, which is temperature dependent and exhibits two-dimensional features. The crossover is proposed to be the transport manifestation of the coexistence of the topological surface state and two-dimensional electron gas on the surface of TIs. In Chapter 4, we use Shubnikov-de Haas oscillations to investigate the electronic structure of the bulk conduction band of BiTeCl single crystals with different carrier densities. We observe the topological transition of the Fermi surface (FS) from a spindle-torus to a torus. The Landau level fan diagram reveals the expected non-trivial π Berry phase for both the inner and outer FSs. Angle-dependent oscillation measurements reveal threedimensional FS topology when the Fermi level lies in the vicinity of the Dirac point. All the observations are consistent with large Rashba spin-orbit splitting in the bulk conduction band..

Study of pinning and supercurrent enhancement in doped MgB2

MgB2 is one candidate of the superconductors for practical application. Most of the applications require the high critical current density (Jc) which means high performance and cost-effective. However the Jc of pristine MgB2 is far from the theoretical depairing current density because of the weak flux pinning and poor grain connectivity. In the work of this Master degree by research, several dopants were tried to enhance the Jc, meanwhile their corresponding flux pinning mechanism were studied. The first three chapters of this thesis give the introduction, literature review and experimental methods. They cover the research motivation, basic superconducting properties of MgB2, status quo of MgB2 research on enhancement of upper critical field Hc2 and Jc, and various experimental methods which are employed in this work. The last two chapters, chapter 4 and chapter 5, present the main experimental works of this thesis. In chapter 4, the effect of graphene oxide (GO) doping on improvement of Jc in MgB2 was systematically studied with emphasis on flux pinning mechanism. It was confirmed that both of low field Jc and high field Jc could be enhanced by GO doping, and the high field Jc was further improved by optimized doping level. The low field and high field Jc improvement are due to the improved the grain connectivity and enhanced flux pinning, respectively. To understand the superior performance of GO doped MgB2, the flux pinning mechanism was studied systematically. In the framework of the collective pinning theory, a B-T phase diagram has been constructed and in the single vortex regime, the transformation of pinning mechanism from transition temperature fluctuation induced pinning (δTc pinning) to mean free path fluctuation induced pinning (δl pinning) is observed in MgB2 by adjusting the GO doping level. Furthermore, in terms of the thermally activated flux flow model the pinning potential in high field (B \u3e 5 T) is enhanced by GO doping. In chapter 5, Based on the overall improvement of Jc in GO doped MgB2 and excellent high field Jc for nano-SiC doping, the effect of GO and nano-SiC co-doping effect on the superconductivity of MgB2 was systematically examined by powder xray diffraction, transport and magnetization measurement. By co-doping impurity phases Mg2Si and SiC appeared and a axis decreased and c axis remained unchanged. Compared with the un-doped samples, Jc was improved at high field for both of 5 K and 20 K. Compared with the 2wt % GO doped sample, at 20 K the Jc was further enhanced by co-doping but at 5 K the Jc improvement was not obvious as at 20 K. At 20 K, the normalized pinning force showed enhancement at high field compared with un-doped one but decrease compared with 2wt% GO doped ones. According to the thermally activated flux flow model, the pinning potentials of codoped samples were further enhanced at high field