Scaling of Coulomb pseudo-potential in s-wave narrow-band superconductors

The Coulomb pseudo-potential $\mu^*$ is extracted by fitting the numerically calculated transition temperature $T_c$ of the Eliashberg-Nambu equation which is extended to incorporate the narrow-band effects, that is, the vertex correction and the frequency dependence of the screened Coulomb interaction. It is shown that even for narrow-band superconductors, where the fermi energy $\epsilon_F$ is comparable with the phonon frequency $\omega_{ph}$, the Coulomb pseudo-potential is a pertinent parameter, and is still given by $\mu^* = \mu/[1+\mu \ln(\epsilon_F/\omega_{ph})]$, provided $\omega_{ph}$ is appropriately scaled.Comment: 5 pages, 3 figures, accepted for publication by Phys. Rev.

Nanogenerators in Korea

Fossil fuels leaded the 21st century industrial revolution but caused some critical problems such as exhaustion of resources and global warming. Also, current power plants require too much high cost and long time for establishment and facilities to provide electricity. Thus, developing new power production systems with environmental friendliness and low-cost is critical global needs. There are some emerging energy harvesting technologies such as thermoelectric, piezoelectric, and triboelectric nanogenerators, which have great advantages on eco-friendly low-cost materials, simple fabrication, and various operating sources. Since the introduction of various energy harvesting technologies, many novel designs and applications as power suppliers and physical sensors in the world have been demonstrated based on their unique advantages. In this Special Issue, we would like to address and share basic approaches, new designs, and industrial applications related to thermoelectric, piezoelectric, and triboelectric devices which are on-going in Korea. With this Special Issue, we aim to promote fundamental understanding and to find novel ways to achieve industrial product manufacturing for energy harvesters

Enhanced Piezoelectric Behavior of PVDF Nanocomposite by AC Dielectrophoresis Alignment of ZnO Nanowires

In contrast to commercial piezoelectric ceramics, lead-free materials such as ZnO and a polymer matrix are proper candidates for use in ecofriendly applications. In this article, the authors represent a technique using ZnO nanowires with a polyvinylidene fluoride (PVDF) matrix in a piezoelectric polymer composite. By aligning the nanowires in the matrix in a desired direction by AC dielectrophoresis, the piezoelectric behavior was enhanced. The dielectric constant of the composite was improved by increasing the concentration of the ZnO nanowires as well. Specifically, the resulting dielectric constant shows an improvement of 400% with aligned ZnO nanowires by increasing the poling effect compared to that of a randomly oriented nanowire composite without a poling process

Study of the Top-quark Pair Production in Association with a Bottom-quark Pair from Fast Simulations at the LHC

A large number of top quarks will be produced at the Large Hadron Collider (LHC) for Run II period. This will allow us to measure the rare processes from the top sector in great details. We present the study of the top-quark pair production in association with a bottom-quark pair (ttbb) from fast simulations for the Compact Muon Solenoid (CMS) experiment. The differential distributions of ttbb are compared with the top-quark pair production with two additional jets (ttjj) and with the production in association with the Higgs (ttH), where the Higgs decays to a bottom-quark pair. The significances of ttbb process in the dileptonic and semileptonic decay mode are calculated with the data corresponding to an integrated luminosity of 10 fb-1, which is foreseen to be collected in the early Run II period. This study will be an important input in searching for new physics beyond the standard model as well as in searching for ttH process where the Yukawa coupling with the top quark can be directly measured.Comment: 12 pages, 12 figure

A Modified Adaboost Algorithm to Reduce False Positives in Face Detection

We present a modified Adaboost algorithm in face detection, which aims at an accurate algorithm to reduce false-positive detection rates. We built a new Adaboost weighting system that considers the total error of weak classifiers and classification probability. The probability was determined by computing both positive and negative classification errors for each weak classifier. The new weighting system gives higher weights to weak classifiers with the best positive classifications, which reduces false positives during detection. Experimental results reveal that the original Adaboost and the proposed method have comparable face detection rate performances, and the false-positive results were reduced almost four times using the proposed method

Dynamical mean-field theory of Hubbard-Holstein model at half-filling: Zero temperature metal-insulator and insulator-insulator transitions

We study the Hubbard-Holstein model, which includes both the electron-electron and electron-phonon interactions characterized by $U$ and $g$, respectively, employing the dynamical mean-field theory combined with Wilson's numerical renormalization group technique. A zero temperature phase diagram of metal-insulator and insulator-insulator transitions at half-filling is mapped out which exhibits the interplay between $U$ and $g$. As $U$ ($g$) is increased, a metal to Mott-Hubbard insulator (bipolaron insulator) transition occurs, and the two insulating states are distinct and can not be adiabatically connected. The nature of and transitions between the three states are discussed.Comment: 5 pages, 4 figures. Submitted to Physical Review Letter

Outsourcing education services in South Korea, England and Hong Kong: a discursive institutionalist analysis

The outsourcing of education services has been widely adopted across international contexts as a ‘tested solution’ or panacea to meet various educational problems including school management, curriculum design, teaching and student discipline. Contracting third party providers, it is argued, enhances organisational goals such as efficiency, quality and school improvement. However, the outsourcing of education services has also impacted on established notions concerning the boundaries around teachers’ work. This paper deploys the framework of discursive institutionalism to offer insight into how the idea of outsourcing has been activated and circulated by discursive communities in three diverse international settings. Despite its problem-solution logic, the institutionalisation of outsourcing creates its own problems, not least the undermining of teacher professionalism, the ‘businessification’ of schools and a diminishing of their educational mission