5,156 research outputs found
Applicability of self-consistent mean-field theory
Within the constrained Hartree-Fock (CHF) theory, an analytic condition is
derived to estimate whether a concept of the self-consistent mean field is
realized or not in level repulsive region. The derived condition states that an
iterative calculation of CHF equation does not converge when the quantum
fluctuations coming from two-body residual interaction and quadrupole
deformation become larger than a single-particle energy difference between two
avoided crossing orbits. By means of the numerical calculation, it is shown
that the analytic condition works well for a realistic case.Comment: 11 pages, 8 figure
Application of photodiodes to the detection of electromagnetic bursts
A new type of photodiode + scintillator (1 m2 x 1 cm) detector is developed to detect the large electro-magnetic burst under an EX-chamber. The threshold burst size is found to be 4.3 x 10 the 5 particles at the center of the scintillator. Therefore a gamma-ray family of 10 TeV is detectable by it, when it is set under 14 r.1. of iron. In addition, a very fast (2.4 nsec width) and very bright (correspond to 10 to the 6 particles) scintillation pulse has become avarable for this study
A comparison of measured and calculated thermal stresses in a hybrid metal matrix composite spar cap element
A hybrid spar of titanium with an integrally brazed composite, consisting of an aluminum matrix reinforced with boron-carbide-coated fibers, was heated in an oven and the resulting thermal stresses were measured. Uniform heating of the spar in an oven resulted in thermal stresses arising from the effects of dissimilar materials and anisotropy of the metal matrix composite. Thermal stresses were calculated from a finite element structural model using anisotropic material properties deduced from constituent properties and rules of mixtures. Comparisons of calculated thermal stresses with measured thermal stresses on the spar are presented. It was shown that failure to account for anisotropy in the metal matrix composite elements would result in large errors in correlating measured and calculated thermal stresses. It was concluded that very strong material characterization efforts are required to predict accurate thermal stresses in anisotropic composite structures
Electromagnon and phonon excitations in multiferroic TbMnO3
We have performed Raman measurements on TbMnO3 single crystal under magnetic
field along the three crystallographic directions. The flip of the spin spiral
plane creates an electromagnon excitation. In addition to the electromagnons
induced by the Heisenberg coupling, we have detected the electromagnon created
by the Dzyaloshinskii-Moriya interaction along the c axis. We have identified
all the vibrational modes of TbMnO3. Their temperature dependences show that
only one phonon observed along the polarization axis is sensitive to the
ferroelectric transition. This mode is tied to the Tb3+ ion displacements that
contribute to the ferroelectric polarization
The development of air shower in the iron absorber
The iron open-sandwich experiments to observe one dimensional development of individual air showers were carried out at Akeno Observatory. One dimensional energy flow, incident energy and production height of shower is estimated using the data of size and age obtained from the above experiment and simple calculation
Magneto-electric excitations in multiferroic TbMnO3 by Raman scattering
Low energy excitations in the multiferroic material TbMnO3 have been
investigated by Raman spectroscopy. Our observations reveal the existence of
two peaks at 30 cm-1 and 60 cm-1. They are observed in the cycloidal phase
below the Curie temperature but not in the sinusoidal phase, suggesting their
magnetoelectric origin. While the peak energies coincide with the frequencies
of electromagnons measured previously by transmission spectroscopy, they show
surprisingly different selection rules, with the 30 cm-1 excitation enhanced by
the electric field of light along the spontaneous polarization. The origins of
the modes are discussed under Raman and infrared selection rules
considerations
Statistical Mechanics of Dictionary Learning
Finding a basis matrix (dictionary) by which objective signals are
represented sparsely is of major relevance in various scientific and
technological fields. We consider a problem to learn a dictionary from a set of
training signals. We employ techniques of statistical mechanics of disordered
systems to evaluate the size of the training set necessary to typically succeed
in the dictionary learning. The results indicate that the necessary size is
much smaller than previously estimated, which theoretically supports and/or
encourages the use of dictionary learning in practical situations.Comment: 6 pages, 4 figure
Pedagogy and History: Ujamaa and Learner-Centered Pedagogy in Tanzania
Social issues of today are rooted in history, and the study of contemporary issues would thus benefit from tracing their history. In Tanzania, Nyerere’s ujamaa philosophy and the accompanying education for self-reliance (ESR) policy offer a criterion relevant today in pedagogical analysis. Tanzania is currently implementing learner-centered pedagogy (LCP). This article considers the logic of ujamaa, which ostensibly appears to be compatible with LCP principles, and explores through empirical evidence the consistencies and inconsistencies between ujamaa/ESR, LCP, and the pedagogical approaches valued by present-day teachers. The teachers espoused the idea of self-reliance promoted through ujamaa, implying that pedagogies similar to LCP will produce self-reliant graduates. Instead of forcibly transmitting a universal form of ideal pedagogy, the cultural and historical connection between ujamaa and LCP could suggest appropriate forms of teaching and learning in the Tanzanian context
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