1,358 research outputs found
Conceptualizing Democracy as Preparation for Teaching for Democracy
In this essay, a broad spectrum of the work of influential educational scholars was examined in order to identify crucial components of teaching for democracy. Synthesizing the literature with their experiences as middle level teachers and teacher educators, the authors determined those conceptions that would be most fruitful for moving in-service teachers to enact the more “muscular” concepts that foster civic participation and social justice. This collaboration resulted in the identification of four democratic practices as a foundation for designing a course on teaching for democracy. These included amplification of the voices of historically marginalized people, recognition that those in power must work to meet the needs of those without power, recognition of the advantages of diversity even at the potential expense of efficiency, and collaboration in order to teach for democracy
The polymerisation of oligo(ethylene glycol methyl ether) methacrylate from a multifunctional poly(ethylene imine) derived amide: a stabiliser for the synthesis and dispersion of magnetite nanoparticles
A facile synthetic route to poly(ethylene imine)-graft-poly(oligo(ethylene glycol methyl ether)) (PEI-graft-POEGMA) functionalised superparamagnetic magnetite nanoparticles is described. The polymerisation of OEGMA from a model molecular amide demonstrated the feasibility of POEGMA synthesis under mild ATRP conditions (20 °C in ethanol) albeit with low initiator efficiencies. DFT studies suggest that the amide functionality is intrinsically of lower activity than ester functional monomers and initiators for atom transfer polymerisation (ATRP) as a consequence of higher bond dissociation energies and bond dissociation free energies (BDFE). However these studies further highlighted that use of an appropriate solvent could reduce the free energy of dissociation thereby reducing the relative difference in BDFE between the ester and amide groups. A commercial branched PEI sample was functionalised by reaction with 2-bromo-2-methylpropanoyl bromide giving an amide macroinitiator suitable for the atom transfer radical polymerisation (ATRP) of oligo(ethylene glycol methyl ether) methacrylate. The resulting PEI-graft-POEGMA copolymers were characterised by SEC, FT-IR and 1H and 13C NMR spectroscopy. PEI-graft-POEGMA coated magnetite nanoparticles were synthesised by a basic aqueous co-precipitation method and were characterised by transmission electron microscopy, thermogravimetric analysis and vibrating sample magnetometry and dynamic light scattering. These copolymer coated magnetite nanoparticles were demonstrated to be effectively stabilised in an aqueous medium. Overall the particle sizes and magnetic and physical properties of the coated samples were similar to those of uncoated samples
Dynamics of Bloch Oscillations in Disordered Lattice Potentials
We present a detailed analysis of the dynamics of Bloch oscillations of
Bose-Einstein condensates in disordered lattice potentials. Due to the disorder
and the interparticle interactions these oscillations undergo a dephasing,
reflected in a damping of the center of mass oscillations, which should be
observable under realistic experimental conditions. The interplay between
interactions and disorder is far from trivial, ranging from an
interaction-enhanced damping due to modulational instability for strong
interactions, to an interaction-reduced damping due to a dynamical screening of
the disorder potential
Radioactive Probes of the Supernova-Contaminated Solar Nebula: Evidence that the Sun was Born in a Cluster
We construct a simple model for radioisotopic enrichment of the protosolar
nebula by injection from a nearby supernova, based on the inverse square law
for ejecta dispersion. We find that the presolar radioisotopes abundances
(i.e., in solar masses) demand a nearby supernova: its distance can be no
larger than 66 times the size of the protosolar nebula, at a 90% confidence
level, assuming 1 solar mass of protosolar material. The relevant size of the
nebula depends on its state of evolution at the time of radioactivity
injection. In one scenario, a collection of low-mass stars, including our sun,
formed in a group or cluster with an intermediate- to high-mass star that ended
its life as a supernova while our sun was still a protostar, a starless core,
or perhaps a diffuse cloud. Using recent observations of protostars to estimate
the size of the protosolar nebula constrains the distance of the supernova at
0.02 to 1.6 pc. The supernova distance limit is consistent with the scales of
low-mass stars formation around one or more massive stars, but it is closer
than expected were the sun formed in an isolated, solitary state. Consequently,
if any presolar radioactivities originated via supernova injection, we must
conclude that our sun was a member of such a group or cluster that has since
dispersed, and thus that solar system formation should be understood in this
context. In addition, we show that the timescale from explosion to the creation
of small bodies was on the order of 1.8 Myr (formal 90% confidence range of 0
to 2.2 Myr), and thus the temporal choreography from supernova ejecta to
meteorites is important. Finally, we can not distinguish between progenitor
masses from 15 to 25 solar masses in the nucleosynthesis models; however, the
20 solar mass model is somewhat preferred.Comment: ApJ accepted, 19 pages, 3 figure
Spin-charge separation in two-component Bose-gases
We show that one of the key characteristics of interacting one-dimensional
electronic quantum systems, the separation of spin and charge, can be observed
in a two-component system of bosonic ultracold atoms even close to a competing
phase separation regime. To this purpose we determine the real-time evolution
of a single particle excitation and the single-particle spectral function using
density-matrix renormalization group techniques. Due to efficient bosonic
cooling and good tunability this setup exhibits very good conditions for
observing this strong correlation effect. In anticipation of experimental
realizations we calculate the velocities for spin and charge perturbations for
a wide range of parameters
Pressure Induced Quantum Critical Point and Non-Fermi-Liquid Behavior in BaVS3
The phase diagram of BaVS3 is studied under pressure using resistivity
measurements. The temperature of the metal to nonmagnetic Mott insulator
transition decreases under pressure, and vanishes at the quantum critical point
p_cr=20kbar. We find two kinds of anomalous conducting states. The
high-pressure metallic phase is a non-Fermi liquid described by Delta rho = T^n
where n=1.2-1.3 at 1K < T < 60K. At p<p_cr, the transition is preceded by a
wide precursor region with critically increasing resistivity which we ascribe
to the opening of a soft Coulomb gap.Comment: 4 pages, 5 eps figures, problem with figure correcte
Excitations in two-component Bose-gases
In this paper, we study a strongly correlated quantum system that has become
amenable to experiment by the advent of ultracold bosonic atoms in optical
lattices, a chain of two different bosonic constituents. Excitations in this
system are first considered within the framework of bosonization and Luttinger
liquid theory which are applicable if the Luttinger liquid parameters are
determined numerically. The occurrence of a bosonic counterpart of fermionic
spin-charge separation is signalled by a characteristic two-peak structure in
the spectral functions found by dynamical DMRG in good agreement with
analytical predictions. Experimentally, single-particle excitations as probed
by spectral functions are currently not accessible in cold atoms. We therefore
consider the modifications needed for current experiments, namely the
investigation of the real-time evolution of density perturbations instead of
single particle excitations, a slight inequivalence between the two
intraspecies interactions in actual experiments, and the presence of a
confining trap potential. Using time-dependent DMRG we show that only
quantitative modifications occur. With an eye to the simulation of strongly
correlated quantum systems far from equilibrium we detect a strong dependence
of the time-evolution of entanglement entropy on the initial perturbation,
signalling limitations to current reasonings on entanglement growth in
many-body systems
Extension of Darby\u27s Model of a Hydrophylic Gas Fed Porous Electrode
A model presented previously by one of the authors (1,2) is reviewed and extended. Aspects of this model which were not previously available in the open literature are considered, and the model is extended to include previously neglected terms in the governing differential equations, fractional reaction orders in the current density-overpotential expression, and mass-transfer coefficients to account for mass-transfer resistance of the reactants to the faces of the porous electrode. The model is used to predict quantities of interest for oxygen reduction in an acidic aqueous solution in a porous carbon electrode
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