25,701 research outputs found
Reenergising professional creativity from a CHAT perspective: Seeing knowledge and history in practice
This is the author's accepted manuscript. The final published article is available from the link below. Copyright @ 2011 Regents of the University of California.This article offers a critical examination of aspects of a practice- and theory-developing intervention in the teacher education setting in England designed as a variation of Developmental Work Research. A positive case is argued for the distinctiveness of such cultural-historical activity theory [CHAT-] informed interventions and some points of contrast are drawn with the British tradition of educational action research. In describing the practice-developing intervention, the twin focus on seeing knowledge and history in human activity systems is advanced as two dimensions of CHAT's distinctive approach, with the goal of stimulating and studying the emergence of professional creativity. Creativity under this interpretation is defined as the perception and analysis of opportunities for learning within the social situation of development and the production of new conceptual tools and approaches to the social organisation of work. Professional creativity is advanced as a much needed capacity among teachers in industrial workplaces influenced by the techniques of New Public Management. Common ground between CHAT and action research approaches is seen in their optimistic and modernist commitments to progress, and CHAT-framed interventions, like action research approaches, are presented as part of an evolving intellectual project
Quantum Decoherence in a D-Foam Background
Within the general framework of Liouville string theory, we construct a model
for quantum D-brane fluctuations in the space-time background through which
light closed-string states propagate. The model is based on monopole and vortex
defects on the world sheet, which have been discussed previously in a treatment
of 1+1-dimensional black-hole fluctuations in the space-time background, and
makes use of a T-duality transformation to relate formulations with Neumann and
Dirichlet boundary conditions. In accordance with previous general arguments,
we derive an open quantum-mechanical description of this D-brane foam which
embodies momentum and energy conservation and small mean energy fluctuations.
Quantum decoherence effects appear at a rate consistent with previous
estimates.Comment: 16 pages, Latex, two eps figures include
Flipped Cryptons and the UHECRs
Cryptons are metastable bound states of fractionally-charged particles that
arise generically in the hidden sectors of models derived from heterotic
string. We study their properties and decay modes in a specific flipped SU(5)
model with long-lived four-particle spin-zero bound states called {\it
tetrons}. We show that the neutral tetrons are metastable, and exhibit the
tenth-order non-renormalizable superpotential operators responsible for their
dominant decays. By analogy with QCD, we expect charged tetrons to be somewhat
heavier, and to decay relatively rapidly via lower-order interactions that we
also exhibit. The expected masses and lifetimes of the neutral tetrons make
them good candidates for cold dark matter (CDM), and a potential source of the
ultra-high energy cosmic rays (UHECRs) which have been observed, whereas the
charged tetrons would have decayed in the early Universe.Comment: 8 Pages RevTex. New version with expanded introduction to flipped
SU(5). Accepted for publication in PR
Institutional conceptualisations of teacher education as academic work in England
This is the post-print version of the final paper published in Teaching and Teacher Education. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2012 Elsevier B.V.Through an analysis of job recruitment texts, and interviews with academic leaders, this article shows how the university-based teacher educator is produced as a category of academic worker in England. Focussing on the discursive processes of categorisation provides insights into how English universities conceptualise teacher education. Variations in conceptualisations are noted within and between institutions, with the teacher educator produced as a hybrid or exceptional category. Often, variations are produced around a practitioner/researcher contradiction. The article concludes by asking whether such variations and potential lack of coherence matter, in the context of national policy and funding constraints, and internationally
Photoproduction of mesons in ultraperipheral heavy ion collisions at energies available at the BNL Relativistic Heavy Ion Collider (RHIC) and CERN Large Hadron Collider (LHC)
We investigate the photoproduction of mesons in ultraperipheral heavy
ion collisions at RHIC and LHC energies in the dipole approach and within two
phenomenological models based on the the Color Glass Condensate (CGC)
formalism. We estimate the integrated cross section and rapidity distribution
for meson production and compare our predictions with the data from the STAR
collaboration. In particular, we demonstrate that the total cross section at
RHIC is strongly dependent on the energy behavior of the dipole-target cross
section at low energies, which is not well determined in the dipole approach.
In contrast, the predictions at midrapidities at RHIC and in the full rapidity
at LHC are under theoretical control and can be used to test the QCD dynamics
at high energies.Comment: 6 pages, 5 figures, 1 table. Improved version to be published in
Physical Review
Baryon Exotics in the Quark Model, the Skyrme Model and QCD
We identify the quantum numbers of baryon exotics in the Quark Model, the
Skyrme Model and QCD, and show that they agree for arbitrary colors and
flavors. We define exoticness, E, which can be used to classify the states. The
exotic baryons include the recently discovered qqqq qbar pentaquarks (E=1), as
well as exotic baryons with additional q qbar pairs (E >=1). The mass formula
for non-exotic and exotic baryons is given as an expansion in 1/N, and allows
one to relate the moment of inertia of the Skyrme soliton to the mass of a
constituent quark
Intrinsic Polarized Strangeness and Lambda Polarization in Deep-Inelastic Production
We propose a model for the longitudinal polarization of Lambda baryons
produced in deep-inelastic lepton scattering at any xF, based on static SU(6)
quark-diquark wave functions and polarized intrinsic strangeness in the nucleon
associated with individual valence quarks. Free parameters of the model are
fixed by fitting NOMAD data on the longitudinal polarization of Lambda hyperons
in neutrino collisions. Our model correctly reproduces the observed dependences
of Lambda polarization on the kinematic variables. Within the context of our
model, the NOMAD data imply that the intrinsic strangeness associated with a
valence quark has anticorrelated polarization. We also compare our model
predictions with results from the HERMES and E665 experiments using charged
leptons. Predictions of our model for the COMPASS experiment are also
presented
Estimate of the Three-Loop MS bar Contribution to sigma(W_L^+ W_L^- --> Z_L Z_L)
The three-loop contribution to the MS bar single-Higgs-doublet standard-model
cross-section at s = (5M_H)^2 is estimated
via least-squares matching of the asymptotic Pade-approximant prediction of the
next order term, a procedure that has been previously applied to QCD
corrections to correlation functions and decay amplitudes. In contrast to these
prior applications, the expansion parameter for the W_L^+ W_L^- \to Z_L Z_L
process is the non-asymptotically-free quartic scalar-field coupling of the
standard model, suggesting that the least-squares matching be performed over
the "infrared" mu^2 <= s region of the scale parameter. All three coefficients
of logarithms within the three-loop term obtained by such matching are found to
be within 6.6% relative error of their true values, as determined via
renormalization-group methods. Surprisingly, almost identical results are
obtained by performing the least squares matching over the mu^2 >= s region.Comment: 9 pages, LaTeX, 3 figures adde
Elements of F-ast Proton Decay
Gauge coupling unification in the Minimal Supersymmetric Standard Model
(MSSM) strongly suggests the existence of a Grand Unified Theory (GUT), which
could be probed by the observation of proton decay. Proton lifetime in the p
\to (e+|mu+) pi0 dimension six mode is proportional in the fourth power to the
GUT mass scale, and inversely proportional in the fourth power to the GUT
coupling. We provide an updated dictionary of solutions for the relevant
unification parameters with generic beta-function coefficients, significantly
upgrading the level of detail with which second order effects are treated, and
correcting subtle published errors. F-lipped SU(5) with strict MSSM field
content is known to survive existing null detection limits for proton decay
approaching 10^34 years, and indeed, the lifetime predicted by prior studies
can be so long that successful detection is not currently plausible. Recently
studied classes of F-theory derived GUT models postulate additional vector-like
multiplets at the TeV scale which modify the renormalization group to yield a
substantial increase in the SU(3)_C X SU(2)_L unified coupling. We find the
conjunction of these models with the F-resh analysis employed to be
comparatively F-ast proton decay, only narrowly evading existing detection
limits, and likely falling within the observable range of proposed next
generation detectors such as DUSEL and Hyper-Kamiokande. The TeV-scale vector
multiplets are themselves suitable for cross correlation by the Large Hadron
Collider. Their presence moreover magnifies the gap between the dual mass
scales of Flipped SU(5), allowing for an elongated second stage
renormalization, pushing grand unification to the doorstep of the reduced
Planck mass.Comment: V2, As published in Nuclear Physics B; 57 pages, 7 figures, 12 table
Search for Quantum Gravity
A satisfactory theory of quantum gravity may necessitate a drastic
modification of our perception of space-time, by giving it a foamy structure at
distances comparable to the Planck length. It is argued in this essay that the
experimental detection of such structures may be a realistic possibility in the
foreseeable future. After a brief review of different theoretical approaches to
quantum gravity and the relationships between them, we discuss various possible
experimental tests of the quantum nature of space-time. Observations of photons
from distant astrophysical sources such as Gamma-Ray Bursters and laboratory
experiments on neutral kaon decays may be sensitive to quantum-gravitational
effects if they are only minimally suppressed. Experimental limits from the
Whipple Observatory and the CPLEAR Collaboration are already probing close to
the Planck scale, and significant increases in sensitivity are feasible.Comment: 7 pages LATEX, no figures, Awarded First Prize in the Gravity
Research Foundation Essay Competition for 199
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