9,408 research outputs found
Parity-violating coupling constant from the flavor-conserving effective weak chiral Lagrangian
We investigate the parity-violating pion-nucleon-nucleon coupling constant
, based on the chiral quark-soliton model. We employ an effective
weak Hamiltonian that takes into account the next-to-leading order corrections
from QCD to the weak interactions at the quark level. Using the gradient
expansion, we derive the leading-order effective weak chiral Lagrangian with
the low-energy constants determined. The effective weak chiral Lagrangian is
incorporated in the chiral quark-soliton model to calculate the
parity-violating constant . We obtain a value of about
at the leading order. The corrections from the next-to-leading order
reduce the leading order result by about 20~\%.Comment: 12 page
On Companion-Induced Off-Center Supernova-Like Explosions
We suggest that a neutron star with a strong magnetic field, spiraling into
the envelope of a companion star, can generate a ``companion induced SN-like
off-center explosion". The strongly magnetized neutron star ("magnetar") is
born in a supernova explosion before entering into an expanding envelope of a
supergiant companion. If the neutron star collapses into a black hole via the
hypercritical accretion during the spiral-in phase, a rapidly rotating black
hole with a strong magnetic field at the horizon results. The Blandford-Znajek
power is sufficient to power a supernova-like event with the center of
explosion displaced from the companion core. The companion core, after
explosion, evolves into a C/O-white dwarf or a neutron star with a second
explosion. The detection of highly eccentric black-hole, C/O-white dwarf
binaries or the double explosion structures in the supernova remnants could be
an evidence of the proposed scenario.Comment: 5 page
The knowledge base for physical education teacher education (PETE): a comparative study of university programmes in England and Korea
This study compares and explains the knowledge base (Kirk et al, 1997; Shulman, 1987) for teaching physical education in Physical Education Teacher Education (PETE) programmes in England and Korea from the 1960s to the present. In the USA (Siedentop, 1989), the UK (Kirk, 1992) and Australia (Macdonald et al, 1999), the erosion of time spent on content knowledge (CK) for sports and other physical activities has been noted as a matter of concern. The academicisation of the physical activity field and the marginalisation of PETE within it are major factors in the shift in the knowledge base.
Data was presented from a comparative study of four PETE programme in two countries in respect of social constructionism (Berger and Luckmann, 1966). The historical resources such as timetables, curricula and official documents were analysed using documentary methods and grounded theory. Grounded theory was also used to analyse interviews with previous and present teacher educators, student teachers, and teachers who graduated from each university.
I found that for universities in both countries, first, the hours of theoretical content knowledge (TCK) and practical content knowledge (PRACK) in PETE had been reduced over time. Time for units of physical activity had decreased significantly. Second, student teachers learnt physical activity to introductory levels only, and the spiral system for the physical activity curriculum, where students ideally move from introductory to advanced levels of knowledge, did not work well. In terms of differences between the countries, first, in England there were many sessions where PRACK was interrelated with pedagogical content knowledge (PCK) and knowledge of learners and their characteristics (KLC). However, this was less common in Korea. In particular, interrelationships between PRACK and PCK and KLC were very weak because the Korean system is based on the study of kinesiology. Second, many students and teachers in England requested sessions to assist them to teach at GCSE and A Level. In Korea, in contrast, the need for PCK and KLC was identified.
I conclude by confirming that CK forms only a small proportion of the knowledge base for teaching physical education confirming that there is a gap between the knowledge base in PETE and the knowledge requirements for teaching physical education in schools. I suggest developing special units in the PETE course based on models of learning, teaching and philosophy and being suitable for inclusion in the academic and scholarly culture of the university
Closed-Loop Identification of Unstable Systems in Time and Frequency Domains
This dissertation presents closed-loop identification algorithms of an unstable system in the time and frequency domains. In the time domain, the projection filter, which is a linear transformation which projects (transforms) a finite number of input-output data of a system into its current space, is used to relate the state-space model with a finite difference model. The method developed can take into account the effects of process noise as well as measurement noise and identify open-loop systems with unknown feedback dynamics in the closed-loop operation. Then the recursive relations between Markov parameters and the ARX model are derived to identify recursively the system, controller and Kalman filter Markov parameters, which are finally used to identify the system, controller and Kalman filter gains. The closed-loop test data demonstrate that the open-loop state-space model identified by using projection filters is fairly accurate in predicting the step responses while the analytical model has several deficiencies. In the frequency domain, the relation between the closed-loop system matrices and the frequency response function is derived to identify system parameters. Also a simulation model of uncertainty to design a robust controller is proposed by using the maximum singular value of unstructured uncertainties caused by underestimated modes and noise. The uncertainty model developed here can be tested and used for the design of a high-performance robust controller in the future. The NASA Large-Angle Magnetic Suspension Test Facility (LAMSTF) is used to validate the algorithms developed
Progressive evolution of tunneling characteristics of in-situ fabricated intrinsic Josephson junctions in Bi_2Sr_2CaCu_2O_{8+delta} single crystals
Stacks of a few intrinsic tunnel junctions were micro-fabricated on the
surface of Bi-2212 single crystals. The number of junctions in a stack was
tailored by progressively increasing the height of the stack by ion-beam
etching, while its tunneling characteristics were measured in-situ in a vacuum
chamber for temperatures down to ~13 K. Using this in-situ etching/measurements
technique in a single piece of crystal, we systematically excluded any spurious
effects arising from variations in the junction parameters and made clear
analysis on the following properties of the surface and inner conducting
planes. First, the tunneling resistance and the current-voltage curves are
scaled by the surface junction resistance. Second, we confirm that the
reduction in both the gap and the superconducting transition temperature of the
surface conducting plane in contact with a normal metal is not caused by the
variation in the doping level, but is caused by the proximity contact. Finally,
the main feature of a junction is not affected by the presence of other
junctions in a stack in a low bias region.Comment: 25 pages, 7 figures, submitted to Phys. Rev.
Synthesis and Characteristics of Carbon Nanofibers/Silicon Composites and Application to Anode Materials of Li Secondary Batteries
Among the various synthesizing technologies of carbon nanofibers (CNFs), chemical vapor deposition (CVD) technology, which uses hydrocarbon gas or carbon monoxide as a carbon source gas and pyrolyzes it to grow CNFs on transition metal catalysts, such as Ni, Fe, and Co, has been regarded as the most inexpensive and convenient method to produce CNFs for industrial use. Experimental variables for CVD are source gas, catalyst layers, temperature, and reaction time. Since the particle size of metal catalysts has an influence on the diameter of CNFs, it is possible to control the diameter of CNFs by varying particle sizes of the metal. As such, it is possible to synthesize CNFs selectively through the selective deposition of catalyst metals. In this study, CNFs were grown by CVD on C-fiber textiles, which had catalysts deposited via electrophoretic deposition. The CNFs were coated with a silica layer via hydrolysis of TEOS (tetraethyl orthosilicate), and the CNFs were oxidized by nitric acid. Due to oxidation, a hydroxyl group was created on the CNFs, which was then able to be used as an activation site for the SiO2. CNFs and the CNFs/SiO2 composite can be used in various applications, such as a composite material, electromagnetic wave shielding material, ultrathin display devices, carbon semiconductors, and anode materials of Li secondary batteries. In particular, there is an increasing demand for lightweight, small-scale, and high-capacity batteries for portable electronic devices, such as laptop computers or smart phones, along with the escalating concern of fossil energy depletion. Accordingly, CNFs and CNFs/SiO2 composites are receiving attention for their use as anode materials of Li secondary batteries, which are eco-friendly, lightweight, and high capacity. Therefore, the physicochemical properties and electrochemical performance data of synthesized CNFs and CNFs/SiO2 composite are described in this chapter
Preparation and Characterization of Carbon Nanofibers and its Composites by Chemical Vapor Deposition
Hydrocarbon gas or carbon monoxide was pyrolyzed by chemical vapor deposition (CVD), and carbon nanofiber (CNF) synthesis was performed using transition metals such as Ni, Fe, and Co as catalysts. When synthesizing carbon nanofibers using the CVD method, experimental variables are temperature, catalysts, source gas, etc. Especially, the particle size of the catalyst is the most important factor in determining the diameter of carbon nanofibers. Hydrocarbon gases, such as CH4, C2H4, benzene, and toluene are used as the carbon source, and in addition to these reaction gases, nonreactive gases such as H2, Ar, and N2 gases are used for transportation. Synthesis occurs at a synthesis temperature of 600–900°C, and catalyst metals such as Ni, Co, and Fe are definitely required when synthesizing CNFs. Therefore, it is possible to synthesize CNFs in selective areas through selective deposition of such catalyst metals. In this study, CNFs were synthesized by CVD. Ethylene gas was employed as the carbon source for synthesis of CNFs with H2 as the promoting gas and N2 as the balancing gas. Synthesized CNFs can be used in various applications, such as composite materials, electromagnetic wave shielding materials, ultrathin display devices, carbon semiconductors, and anode materials of Li secondary batteries. In particular, there is an increasing demand for light-weight, small-scale, and high-capacity batteries for portable electronic devices, such as notebook computers or smartphones along with the recent issue of fossil energy depletion. Accordingly, CNFs and their silicon-series composites are receiving attention for use as anode materials for lithium secondary batteries that are eco-friendly, light weight, and high capacity
Suppressed Superconductivity of the Surface Conduction Layer in BiSrCaCuO Single Crystals Probed by {\it c}-Axis Tunneling Measurements
We fabricated small-size stacks on the surface of
BiSrCaCuO (BSCCO-2212) single crystals with the bulk
transition temperature 90 K, each containing a few intrinsic
Josephson junctions. Below a critical temperature ( ), we have
observed a weakened Josephson coupling between the CuO superconducting
double layer at the crystal surface and the adjacent one located deeper inside
a stack. The quasiparticle branch in the data of the weakened Josephson
junction (WJJ) fits well to the tunneling characteristics of a d-wave
superconductor()/insulator/d-wave superconductor (DID) junction. Also,
the tunneling resistance in the range agrees well with the
tunneling in a normal metal/insulator/d-wave superconductor (NID) junction. In
spite of the suppressed superconductivity at the surface layer the symmetry of
the order parameter appears to remain unaffected.Comment: 13 pages, 6 figure
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