63 research outputs found
Theoretical calculations for solid oxygen under high pressure
The crystal structure of solid oxygen at low temperatures and at pressures up
to 7 GPa is studied by theoretical calculations. In the calculations, the
adiabatic potential of the crystal is approximated by a superposition of
pair-potentials between oxygen molecules calculated by an ab-initio method. The
monoclinic alpha structure is stable up to 6 GPa and calculated lattice
parameters agree well with experiments. The origin of a distortion and that of
an anisotropic lattice compressibility of the basal plane of alpha-O2 are
clearly demonstrated. In the pressure range from 6 to 7 GPa, two kinds of
structures are proposed by X-ray diffraction experiments: the alpha and
orthorhombic delta structures. It is found that the energy difference between
these structures becomes very small in this pressure range. The relation
between this trend and the incompatible results of X-ray diffraction
experiments is discussed.Comment: 12 pages, 6 figure
Understanding and addressing institutionalized inequity: Disrupting pathways to juvenile justice for Black youth in Allegheny County
This report reveals that in Pittsburgh and Allegheny County, we are criminalizing our Black youth, manifested by disproportionately high arrest rates and referrals to juvenile justice. It presents information on two primary causes of the over-referral of Black youth to juvenile justice: 1) arrests and referrals made by school police and 2) summary citations. It concludes with recommendations for addressing these issues.
As you read this report, keep in mind that the behavior of Black youth is not worse in Pittsburgh and Allegheny County than in other places and does not in any way account for these high levels of arrests, citations, and juvenile justice referrals. In fact, this report reveals that many of the behaviors for which our Black youth are arrested and cited are developmentally normal teenage behaviors for which White youth are rarely arrested and cited.
This is a systems problem that demands reforms at the system level. It is incumbent on the adults running the systems criminalizing Black youth to address the systemic racism these patterns reveal
Meta-orbital Transition in Heavy-fermion Systems: Analysis by Dynamical Mean Field Theory and Self-consistent Renormalization Theory of Orbital Fluctuations
We investigate a two-orbital Anderson lattice model with Ising orbital
intersite exchange interactions by means of dynamical mean field theory
combined with the static mean field approximation of the intersite orbital
interactions. Focusing on Ce-based heavy-fermion compounds, we examine the
orbital crossover between the two orbital states, when the total f-electron
number per site n_f is n_f ~ 1. We show that a "meta-orbital" transition, at
which the occupancy of the two orbitals changes steeply, occurs when the
hybridization between the ground-state f-electron orbital and conduction
electrons are smaller than that between the excited f-electron orbital and
conduction electrons. Near the meta-orbital critical end point, the orbital
fluctuations are enhanced, and couple with the charge fluctuations. A critical
theory of the meta-orbital fluctuations is also developed by applying the
self-consistent renormalization theory of itinerant electron magnetism to the
orbital fluctuations. The critical end point, first-order transition and
crossover are described within Gaussian approximations of orbital fluctuations.
We discuss the relevance of our results to CeAl2, CeCu2Si2, CeCu2Ge2 and the
related compounds, which all have low-lying crystalline-electric-field excited
states.Comment: 11 pages, 6 figures, J. Phys. Soc. Jpn. 79, (2010) 11471
Coulomb effects in tunneling through a quantum dot stack
Tunneling through two vertically coupled quantum dots is studied by means of
a Pauli master equation model. The observation of double peaks in the
current-voltage characteristic in a recent experiment is analyzed in terms of
the tunnel coupling between the quantum dots and the coupling to the contacts.
Different regimes for the emitter chemical potential indicating different peak
scenarios in the tunneling current are discussed in detail. We show by
comparison with a density matrix approach that the interplay of coherent and
incoherent effects in the stationary current can be fully described by this
approach.Comment: 6 pages, 6 figure
Ferromagnetic Properties of ZrZn
The low Curie temperature (T_C approx 28K) and small ordered moment (M_0
approx 0.17 mu_B f.u.^-1) of ZrZn2 make it one of the few examples of a weak
itinerant ferromagnet. We report results of susceptibility, magnetization,
resistivity and specific heat measurements made on high-quality single crystals
of ZrZn2. From magnetization scaling in the vicinity of T_C
(0.001<|T-T_C|/T_C<0.08), we obtain the critical exponents beta=0.52+/-0.05 and
delta=3.20+/-0.08, and T_C=27.50+/-0.05K. Low-temperature magnetization
measurements show that the easy axis is [111]. Resistivity measurements reveal
an anomaly at T_C and a non-Fermi liquid temperature dependence
rho(T)=rho_0+AT^n, where n=1.67+/-0.02, for 1<T<14K. The specific heat
measurements show a mean-field-like anomaly at T_C. We compare our results to
various theoretical models.Comment: submitted to PR
Kinetic Energy, Condensation Energy, Optical Sum Rule and Pairing Mechanism in High-Tc Cuprates
The mechanism of high-Tc superconductivity is investigated with interests on
the microscopic aspects of the condensation energy. The theoretical analysis is
performed on the basis of the FLEX approximation which is a microscopic
description of the spin-fluctuation-induced-superconductivity. Most of phase
transitions in strongly correlated electron system arise from the correlation
energy which is copmetitive to the kinetic energy. However, we show that the
kinetic energy cooperatively induces the superconductivity in the underdoped
region. This unusual decrease of kinetic energy below T_c is induced by the
feedback effect. The feedback effect induces the magnetic resonance mode as
well as the kink in the electronic dispersion, and alters the properties of
quasi-particles, such as mass renormalization and lifetime. The crossover from
BCS behavior to this unusual behavior occurs for hole dopings. On the other
hand, the decrease of kinetic energy below T_c does not occur in the
electron-doped region. We discuss the relation to the recent obserbation of the
violation of optical sum rule
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