Structural behavior of uranium dioxide under pressure by LSDA+U calculations

The structural behavior of UO2 under high pressure up to 300GPa has been studied by first-principles calculations with LSDA+U approximation. The results show that a pressure-induced structural transition to the cotunnite-type (orthorhombic Pnma) phase occurs at 38GPa. It agrees well with the experimentally observed ~42 GPa. An isostructural transition following that is also predicted to take place from 80 to 130GPa, which has not yet been observed in experiments. Further high compression beyond 226GPa will result in a metallic and paramagnetic transition. It corresponds to a volume of 90A^3 per cell, in good agreement with a previous theoretical analysis in the reduction of volume required to delocalize 5f states.Comment: 10 pages, 8 figure

Magnetoroton scattering by phonons in the fractional quantum Hall regime

Motivated by recent phonon spectroscopy experiments in the fractional quantum Hall regime we consider processes in which thermally excited magnetoroton excitations are scattered by low energy phonons. We show that such scattering processes can never give rise to dissociation of magnetorotons into unbound charged quasiparticles as had been proposed previously. In addition we show that scattering of magnetorotons to longer wavelengths by phonon absorption is possible because of the shape of the magnetoroton dispersion curve and it is shown that there is a characteristic cross-over temperature above which the rate of energy transfer to the electron gas changes from an exponential (activated) to a power law dependence on the effective phonon temperature.Comment: LaTex document, 3 eps figures. submitted to Phys Rev

Two-phonon scattering of magnetorotons in fractional quantum Hall liquids

We study the phonon-assisted process of dissociation of a magnetoroton, in a fractional quantum Hall liquid, into an unbound pair of quasiparticles. Whilst the dissociation is forbidden to first order in the electron-phonon interaction, it can occur as a two-phonon process. Depending on the value of final separation between the quasiparticles, the dissociation is either a single event involving absorption of one phonon and emission of another phonon of similar energy, or a two-phonon diffusion of a quasiexciton in momentum space. The dependence of the magnetoroton dissociation time on the filling factor of the incompressible liquid is found.Comment: 4 pages, no figure

Sleep Pattern and Academic Performance of Undergraduate Students

There have been studies that demonstrate the impact of sleep on both implicit and explicit memory. Of particular interest is that sleep has been shown to aid memory consolidation. This holds some implication for students, most of whom sleep for considerably very little amount of time, whereas they require sufficient amount of sleep to consolidate memory for material learned during the day. This study was therefore designed to investigate the possible impact of sleep on the academic achievement of undergraduate students. The study participants were 300 undergraduate students drawn from about twenty Department of a private university in Nigeria. 152 of the participants were female and the rest were male. The School Sleep Survey Habit Scale previously validated in Nigeria by one of the authors (IDO) was used to measure sleep habit, while academic performance was measured as self-reported grade. The result of Analysis of variance using SPSS XX showed a significant effect of Sleepiness on Academic Performance F (8, 211)=3.73, P<.01, and on Cumulative Grade Point Average, F (4, 190) = 3.82, P<.005. The study also showed that stimulant intake significantly impacted on Sleep habit. It was concluded that to enhance student's academic achievement counseling centres should endeavour to include sleep in their orientation programme for students. Besides, it would be necessary not to cram up the programme in such a manner that would rob the students of adequate rest and sleep

Probing the quantum phase transition in the Dicke model through mechanical vibrations

This paper is concerned with quantum dynamics of a system coupled to a critical reservoir. In this context, we employ the Dicke model which is known to exhibit a super radiant quantum phase transition (QPT) and we allow one of the mirrors to move under a linear restoring force. The electromagnetic field couples to the movable mirror though radiation pressure just like in typical optomechanical setups. We show that, in the thermodynamical limit, the super-radiant phase induces a classical driving force on the mirror without causing decoherence.Comment: 6 pages, 3 figures, final versio