Determining VtbV_{tb} at Electron-Positron Colliders

Verifying $V_{tb} \simeq 1$ is critical to test the three generation assumption of the Standard Model. So far our best knowledge of $V_{tb}$ is inferred either from the $3\times 3$ unitarity of CKM matrix or from single top-quark productions upon the assumption of universal weak couplings. The unitarity could be relaxed in new physics models with extra heavy quarks and the universality of weak couplings could also be broken if the $Wtb$ coupling is modified in new physics models. In this work we propose to measure $V_{tb}$ in the process of $e^+ e^- \to t\bar{t}$ without prior knowledge of the number of fermion generations or the strength of the $Wtb$ coupling. Using an effective Lagrangian approach, we perform a model-independent analysis of the interactions among electroweak gauge bosons and the third generation quarks, i.e. the $Wtb$, $Zt\bar{t}$ and $Zb\bar{b}$ couplings. The electroweak symmetry of the Standard Model specifies a pattern of deviations of the $Z$-$t_L$-$t_L$ and $W$-$t_L$-$b_L$ couplings after one imposes the known experimental constraint on the $Z$-$b_L$-$b_L$ coupling. We demonstrate that, making use of the predicted pattern and the accurate measurements of top-quark mass and width from the energy threshold scan experiments, one can determine $V_{tb}$ from the cross section and the forward-backward asymmetry of top-quark pair production at an {\it unpolarized} electron-positron collider.Comment: publish versio

Exploiting Problem Structure in Pathfinding

With a given map and a start and a goal position on the graph, a pathfinding algorithm typically searches on this graph from the start node and exploring its neighbour nodes until reaching the goal. It is closely related to the shortest path problem. A* is one of the best and most popular heuristic-guided algorithms used in pathfinding for video games. The algorithm always picks the node with the smallest f value and process this node. The f value is the sum of two parameters g (the actual cost from the start node to the current node) and h (estimated cost from the current node to the goal). At each step of the algorithm, the node with lowest f will be removed from an open list and its neighbour nodes with their f values would be updated in this list. The main cost of this algorithm is the frequent insertion and deleteMin operations of the open list. Typically, implementation of A* uses a priority queue or min-heap to implement the open list, which takes O(log n) for the operations in the worst case. But this is still expensive when using the algorithm in a large and complicated map with numerous nodes. We came up with a new data structure called multi-stack heap for the open list based on the 2D grid map and Manhattan distance, which only costs O(1) for insertion and deleteMin. It is very efficient especially when we have a considerable number of nodes to explore. Additionally, traditional A* requires checking whether the open list contains a duplicated of the being inserted node before every insertion, which takes O(n). We proposed a new implementation method based on admissible and consistent heuristic called “Check From Closed List”, it can reduce the time of this process to O(1)

High density semiconducting nanotube arrays for high-performance electronics

Single-walled carbon nanotubes are poised to replace silicon in high-performance microprocessor chips and are expected to offer a significant improvement in energy-delay product. However, one key challenge of realizing such a technology is to produce semiconducting nanotube arrays with both minuscule and uniform inter-tube pitch to provide sufficient packing density, power output, and performance homogeneity for each transistor. Here, we will review our latest progress on assembling pre-sorted high purity semiconducting nanotubes into densely packed arrays. In an example, double-layered arrays with full surface coverage and a tube density \u3e500 tubes/μm are assembled with Langmuir–Schaefer method. The nanotube pitch is self-limited by the tube diameter plus Van der Waals separation. In another example, submonolayered arrays with both tight and consistent pitch as small as 21 ± 6 nm are assembled using the fringing field formed between surface microelectrodes and the substrate. Effective screening of the fringing field by the deposition of nanotubes limits the pitch and prevents the formation of multilayer structures in a self-limited fashion as revealed by detailed experimental and theoretical studies. Field-effect transistors based on such arrays demonstrate exceptional performances, setting new benchmarks for nanotube devices

Translating 'Nation' in Late Qing China: The Discourse and Power of Nation in the Remaking of Chinese Society, 1895-1911

Nation as a translated concept must be understood within this backdrop of rapid, volatile and often violent changes around the turn of the 20th century in the last decade of the Qing Empire. There were two major phases of translation in late Qing, paralleling two waves of external conflicts. The first was the 1860–1900 period, in which a total of 555 books were translated—five times more than the first half of the century. The second phase of translation occurred during the last decade of the Qing Dynasty, from 1900 to the 1911 Xinhai Revolution. It is important to note the conceptual transfer from the West to China, however, is different from other Asian countries. Late Qing anti-establishment forces did not overlook the idea of guomin. Richter argues that the understanding of translation as intercultural communication is flawed by inequalities of power in colonial or semi-colonial settings

Enhancing Electronic Commerce by Implementing Agile Manufacturing: An Empirical Study in the Manufacturing Sector

Electronic commerce (EC) is emerging as a driving force in today’s economy. According to Forrester Research Institute (1997), the estimated sales in electronic commerce would rise from US$1 billion in 1995 to US$117 billion by the year 2006. EC activities are ranging from shopping to manufacturing (Shaw et al., 1997). This research is specifically focused on compatibility issues of operational strategies used in the manufacturing sector of electronic commerce. Electronic commerce is changing manufacturing systems from mass production to demand-driven and possibly customized, just-in-time manufacturing (Turban et al., 2000, Kalakota, R. et al., 1996). In electronic commerce, as product life cycle becomes shortened, high product quality becomes necessary for survival, markets become highly diversified and global, and continuous and unexpected change becomes the key factor for success. The ability to respond quickly and effectively to satisfy customers has become a defining characteristic of competitiveness for manufacturing companies in the electronic commerce era. Agile manufacturing is an emerging new manufacturing paradigm, which considers agility a key concept necessary to survive against competitors under an unexpectedly turbulent and changing environment (Goldman et al., 1995). Thus, agile manufacturing is a viable operational choice for the manufacturing companies in electronic commerce. As Shaw et al. (1997) point out that a key feature of electronic commerce research as a distinct discipline is its multidisciplinary perspective. This study is exploring electronic commerce research from both MIS and OM perspectives

Microstructure study of the rare-earth intermetallic compounds R5(SixGe1-x)4 and R5(SixGe1-x)3

The unique combination of magnetic properties and structural transitions exhibited by many members of the R5(SixGe1-x)4 family (R = rare earths, 0 ≤ x ≤1) presents numerous opportunities for these materials in advanced energy transformation applications. Past research has proven that the crystal structure and magnetic ordering of the R5(SixGe1-x)4 compounds can be altered by temperature, magnetic field, pressure and the Si/Ge ratio. Results of this thesis study on the crystal structure of the Er5Si4 compound have for the first time shown that the application of mechanical forces (i.e. shear stress introduced during the mechanical grinding) can also result in a structural transition from Gd5Si4-type orthorhombic to Gd5Si2Ge2-type monoclinic. This structural transition is reversible, moving in the opposite direction when the material is subjected to low-temperature annealing at 500 &^°C. Successful future utilization of the R5(SixGe1-x)4 family in novel devices depends on a fundamental understanding of the structure-property interplay on the nanoscale level, which makes a complete understanding of the microstructure of this family especially important. Past scanning electron microscopy (SEM) observation has shown that nanometer-thin plates exist in every R5(SixGe1-x)4 (“5:4”) phase studied, independent of initial parent crystal structure and composition. A comprehensive electron microscopy study including SEM, energy dispersive spectroscopy (EDS), selected area diffraction (SAD), and high resolution transmission electron microscopy (HRTEM) of a selected complex 5:4 compound based on Er rather than Gd, (Er0.9Lu0.1)5Si4, has produced data supporting the assumption that all the platelet-like features present in the R5(SixGe1-x)4 family are hexagonal R5(SixGe1-x)3 (“5:3”) phase and possess the same reported orientation relationship that exists for the Gd5Ge4 and Gd5Si2Ge2 compounds, i.e. [010](10-2)m || [10-10](1-211)p. Additionally, the phase identification in (Er0.9Lu0.1)5Si4 carried out using X-ray powder diffraction (XRD) techniques revealed that the low amount of 5:3 phase is undetectable in a conventional laboratory Cu Kαdiffractometer due to detection limitations, but that extremely low amounts of the 5:3 phase can be detected using high resolution powder diffraction (HRPD) employing a synchrotron source. These results suggest that use of synchrotron radiation for the study of R5(SixGe1-x)4 compounds should be favored over conventional XRD for future investigations. The phase stability of the thin 5:3 plates in a Gd5Ge4 sample was examined by performing long-term annealing at very high temperature. The experimental results indicate the plates are thermally unstable above 1200&^°C. While phase transformation of 5:3 to 5:4 occurs during the annealing, the phase transition is still fairly sluggish, being incomplete even after 24 hours annealing at this elevated temperature. Additional experiments using laser surface melting performed on the surface of a Ho5(Si0.8Ge0.2)4 sample showed that rapid cooling will suppress the precipitation of 5:3 plates. Bulk microstructure studies of polycrystalline and monocrystalline Gd5Ge3 compounds examined using optical microscopy, SEM and TEM also show a series of linear features present in the Gd5Ge3 matrix, similar in appearance in many ways to the 5:3 plates observed in R5(SixGe1-x)4 compounds. A systematic microscopy analysis of these linear features revealed they also are thin plates with a stoichiometric composition of Gd5Ge4 with an orthorhombic structure. The orientation relationship between the 5:3 matrix and the precipitate 5:4 thin plates was determined as [10-10] (1-211)m || [010] (10-2)p