2,423 research outputs found
Turbulence in nonabelian gauge theory
Kolmogorov wave turbulence plays an important role for the thermalization
process following plasma instabilities in nonabelian gauge theories. We show
that classical-statistical simulations in SU(2) gauge theory indicate a
Kolmogorov scaling exponent known from scalar models. In the range of validity
of resummed perturbation theory this result is shown to agree with analytical
estimates. We study the effect of classical-statistical versus quantum
corrections and demonstrate that the latter lead to the absence of turbulence
in the far ultraviolet.Comment: 13 pages, 4 figures. PLB version, improved statistics indicates
Kolmogorov exponent 4/
Territorial rights and open borders
Territorial rights consist of the right to jurisdiction, the right to resources and the right to exclude immigrants and are assumed to be essential to state sovereignty. Scholars who have discussed the justification of these rights have mostly focused on the right to jurisdiction. Few engage with the implications of such justification for the right to exclude immigrants. This paper argues that the justification for territorial rights cannot justify the right of states to exclude immigrants. Allowing immigrants to settle within the territory does not undermine any of the interests territorial rights are meant to protect. In addition, the interests of current inhabitants do not provide sufficient reasons to grant the state the right to exclude immigrants from the territory that everyone has equal right to in an original situation. State sovereignty is therefore seen as compatible with open borders
Structure and stability of a high-coverage (1x1) oxygen phase on Ru(0001)
The formation of chemisorbed O-phases on Ru(0001) by exposure to O_2 at low
pressures is apparently limited to coverages Theta <= 0.5. Using low-energy
electron diffraction and density functional theory we show that this
restriction is caused by kinetic hindering and that a dense O overlayer (Theta
= 1) can be formed with a (1x1) periodicity. The structural and energetic
properties of this new adsorbate phase are analyzed and discussed in view of
attempts to bridge the so-called "pressure gap" in heterogeneous catalysis. It
is argued that the identified system actuates the unusually high rate of
oxidizing reactions at Ru surfaces under high oxygen pressure conditions.Comment: RevTeX, 6 pages, 3 figures, to appear in Phys. Rev. Let
Beyond the Mandates of Pennsylvania Chapter 354: Supervising, Evaluating and Qualifying Urban Pre-Service Teachers with a Focus on Elementary Literacy Instruction
BEYOND THE MANDATES OF PENNSYLVANIA CHAPTER 354: SUPERVISING, EVALUATING, AND QUALIFYING URBAN PRE-SERVICE TEACHERS WITH A FOCUS ON ELEMENTARY LITERACY INSTRUCTION Patricia S. Scheffler, Ed.D.University of Pittsburgh, 2006This research was conducted using a case study analysis of four Elementary Education pre-service teachers. The participants were placed in urban school settings, and represented two graduate-level certification programs. All four of the participants were required, by the Pennsylvania Department of Education (PDE), to be evaluated for certification, according to the PDE 430 checklist. This research was grounded in Danielson's Framework for Professional Practice (1996) and measured against the Pennsylvania Department of Education or PDE 430 form. Three specific teacher behaviors were analyzed. They included student centered planning, student engagement, and reflective practice. As the University Supervisor of the participants, I used ethnographic methods to determine the extent to which they demonstrated these best practices. As a result of a review of related research and an analysis of data generated, I concluded that pre-service teachers in the study implemented these best practices at below or at basic levels when assessed within a constructivist framework while they earned scores above basic levels when state and local measures were used
Non-Adiabatic Potential-Energy Surfaces by Constrained Density-Functional Theory
Non-adiabatic effects play an important role in many chemical processes. In
order to study the underlying non-adiabatic potential-energy surfaces (PESs),
we present a locally-constrained density-functional theory approach, which
enables us to confine electrons to sub-spaces of the Hilbert space, e.g. to
selected atoms or groups of atoms. This allows to calculate non-adiabatic PESs
for defined charge and spin states of the chosen subsystems. The capability of
the method is demonstrated by calculating non-adiabatic PESs for the scattering
of a sodium and a chlorine atom, for the interaction of a chlorine molecule
with a small metal cluster, and for the dissociation of an oxygen molecule at
the Al(111) surface.Comment: 11 pages including 7 figures; related publications can be found at
http://www.fhi-berlin.mpg.de/th/th.htm
THz conductivity of SrCaRuO
We investigate the optical conductivity of SrCaRuO across the
ferromagnetic to paramagnetic transition that occurs at . The thin films
were grown by metalorganic aerosol deposition with onto
NdGaO substrates. We performed THz frequency domain spectroscopy in a
frequency range from 3~cm to 40~cm (100~GHz to 1.4~THz) and at
temperatures ranging from 5~K to 300~K, measuring transmittivity and phase
shift through the films. From this we obtained real and imaginary parts of the
optical conductivity. The end-members, ferromagnetic SrRuO and paramagnetic
CaRuO, show a strongly frequency-dependent metallic response at
temperatures below 20~K. Due to the high quality of these samples we can access
pronounced intrinsic electronic contributions to the optical scattering rate,
which at 1.4~THz exceeds the residual scattering rate by more than a factor of
three. Deviations from a Drude response start at about 0.7~THz for both
end-members in a remarkably similar way. For the intermediate members a higher
residual scattering originating in the compositional disorder leads to a
featureless optical response, instead. The relevance of low-lying interband
transitions is addressed by a calculation of the optical conductivity within
density functional theory in the local density approximation (LDA)
Shaping a superconducting dome: Enhanced Cooper-pairing versus suppressed phase coherence in coupled aluminum nanograins
Deterministic enhancement of the superconducting (SC) critical temperature
is a long-standing goal in material science. One strategy is engineering
a material at the nanometer scale such that quantum confinement strengthens the
electron pairing, thus increasing the superconducting energy gap , as
was observed for individual nanoparticles. A true phase-coherent SC condensate,
however, can exist only on larger scales and requires a finite phase stiffness
. In the case of coupled aluminium (Al) nanograins, can exceed that of
bulk Al by a factor of three, but despite several proposals the relevant
mechanism at play is not yet understood. Here we use optical spectroscopy on
granular Al to disentangle the evolution of the fundamental SC energy scales,
and , as a function of grain coupling. Starting from well-coupled
arrays, grows with progressive grain decoupling, causing the
increasing of . As the grain-coupling is further suppressed,
saturates while decreases, concomitantly with a sharp decline of .
This crossover to a phase-driven SC transition is accompanied by an optical gap
persisting above . These findings identify granular Al as an ideal
playground to test the basic mechanisms that enhance superconductivity by
nano-inhomogeneity.Comment: 6 + 6 pages (manuscript + supplementary material
Out of equilibrium dynamics of coherent non-abelian gauge fields
We study out-of-equilibrium dynamics of intense non-abelian gauge fields.
Generalizing the well-known Nielsen-Olesen instabilities for constant initial
color-magnetic fields, we investigate the impact of temporal modulations and
fluctuations in the initial conditions. This leads to a remarkable coexistence
of the original Nielsen-Olesen instability and the subdominant phenomenon of
parametric resonance. Taking into account that the fields may be correlated
only over a limited transverse size, we model characteristic aspects of the
dynamics of color flux tubes relevant in the context of heavy-ion collisions.Comment: 12 pages, 10 figures; PRD version, minor change
- …