11,572 research outputs found
Promoting independent learning skills using video on digital language laboratories
This is the author's PDF version of an article published in Computer assisted language learning ©2006. The definitive version is available at http://www.informaworld.com/The article discusses the potential for developing independent learning skills using the digital language laboratory with particular reference to exploiting the increasingly available resource of digital video. It investigates the potential for recording and editing video clips from online sources and digitalising clips from analogue recordings and reflects on the current status quo regarding the complex copyright regulations in this area. It describes two pilot self-access programmes based on video clips which were undertaken with University College Chester undergraduates and reflects on the value of the experience for students in developing a wide range of language skills as well as independent learning skills using their feedback on the experience
Violation of the Wiedemann-Franz Law in a Large-N Solution of the t-J Model
We show that the Wiedemann-Franz law, which holds for Landau Fermi liquids,
breaks down in a large-n treatment of the t-J model. The calculated ratio of
the in-plane thermal and electrical conductivities agrees quantitatively with
experiments on the normal state of the electron-doped Pr_{2-x}Ce_xCuO_4 (x =
0.15) cuprate superconductor. The violation of the Wiedemann-Franz law in the
uniform phase contrasts with other properties of the phase that are Fermi
liquid like.Comment: 4 pages, 2 figures. Typos corrected, one added reference, revised
discussion of experiment on 214 cuprate material (x = 0.06
Focus Points and Naturalness in Supersymmetry
We analyze focus points in supersymmetric theories, where a parameter's
renormalization group trajectories meet for a family of ultraviolet boundary
conditions. We show that in a class of models including minimal supergravity,
the up-type Higgs mass has a focus point at the weak scale, where its value is
highly insensitive to the universal scalar mass. As a result, scalar masses as
large as 2 to 3 TeV are consistent with naturalness, and {\em all} squarks,
sleptons and heavy Higgs scalars may be beyond the discovery reaches of the
Large Hadron Collider and proposed linear colliders. Gaugino and Higgsino
masses are, however, still constrained to be near the weak scale. The focus
point behavior is remarkably robust, holding for both moderate and large
\tan\beta, any weak scale gaugino masses and A parameters, variations in the
top quark mass within experimental bounds, and for large variations in the
boundary condition scale.Comment: 30 pages, 17 figure
Towards Spectral Classification of L and T Dwarfs: Infrared and Optical Spectroscopy and Analysis
We present 0.6-2.5um, R~400 spectra of twenty-seven cool, low luminosity
stars and substellar objects. Based on these and previously published spectra
we develop a preliminary spectral classification system for L and T dwarfs. For
late L and T types the classification system is based entirely on four spectral
indices in the 1-2.5um interval. Two of these indices are derived from water
absorption bands at 1.15um and 1.4um, the latter of which shows a smooth
increase in depth through the L and T sequences and can be used to classify
both spectral types. The other two indices make use of methane absorption
features in the H and K bands, with the K band index also applicable to mid to
late L dwarfs. Continuum indices shortward of 1um used by previous authors to
classify L dwarfs are found to be useful only through mid L subclasses. We
employ the 1.5um water index and the 2.2um methane index to complete the L
classification through L9.5 and to link the new system with a modified version
of the 2MASS ``Color-d'' index. By correlating the depths of the methane and
water absorption features, we establish a T spectral sequence from types T0 to
T8, based on all four indices, which is a smooth continuation of the L
sequence. We reclassify two 2MASS L8 dwarfs as L9 and L9.5 and identify one
SDSS object as L9. In the proposed system methane absorption appears in the K
band approximately at L8, two subclasses earlier than its appearance in the H
band. The L and T spectral classes are distinguished by the absence and
presence, respectively, of H band methane absorption.Comment: 40 pages, 14 figures, to be published in Ap.J., Jan 1, 200
Asymmetric total synthesis of (+)-virosine a via sequential nucleophilic cyclizations onto an activated formamide
Abstract: The first synthesis of tetracyclic alkaloid virosine A is reported. The natural alkaloid was prepared in only 13 steps, in an enantioenriched form. The azabicyclo[2.2.2]octane core was efficiently assembled using a key Vilsmeier–Haack and Mannich cyclizations sequence performed in one pot
Effect of gauge boson mass on chiral symmetry breaking in QED
In three-dimensional quantum electrodynamics (QED) with massive gauge
boson, we investigate the Dyson-Schwinger equation for the fermion self-energy
in the Landau gauge and find that chiral symmetry breaking (CSB) occurs when
the gauge boson mass is smaller than a finite critical value
but is suppressed when . We further show that the critical
value does not qualitatively change after considering higher order
corrections from the wave function renormalization and vertex function. Based
on the relation between CSB and the gauge boson mass , we give a field
theoretical description of the competing antiferromagnetic and superconducting
orders and, in particular, the coexistence of these two orders in high
temperature superconductors. When the gauge boson mass is generated via
instanton effect in a compact QED of massless fermions, our result shows
that CSB coexists with instanton effect in a wide region of , which can be
used to study the confinement-deconfinement phase transition.Comment: 34 pagess, 2 figure
Independent freezing of charge and spin dynamics in La1.5Sr0.5CoO4
We present elastic and quasielastic neutron scattering measurements
characterizing peculiar short-range charge-orbital and spin order in the
layered perovskite material La1.5Sr0.5CoO4. We find that below Tc~750 K holes
introduced by Sr doping lose mobility and enter a statically ordered {\it
charge glass} phase with loosely correlated checkerboard arrangement of empty
and occupied d{3z2-r2} orbitals (Co3+ and Co2+). The dynamics of the resultant
mixed spin system is governed by the anisotropic nature of the crystal-field
Hamiltonian and the peculiar exchange pattern produced by the orbital order. It
undergoes a {\it spin freezing} transition at much a lower temperature, Ts~30
K.Comment: 4 pages, 3 figures, Latex. Submitted to PR
Universality, limits and predictability of gold-medal performances at the Olympic Games
Inspired by the Games held in ancient Greece, modern Olympics represent the
world's largest pageant of athletic skill and competitive spirit. Performances
of athletes at the Olympic Games mirror, since 1896, human potentialities in
sports, and thus provide an optimal source of information for studying the
evolution of sport achievements and predicting the limits that athletes can
reach. Unfortunately, the models introduced so far for the description of
athlete performances at the Olympics are either sophisticated or unrealistic,
and more importantly, do not provide a unified theory for sport performances.
Here, we address this issue by showing that relative performance improvements
of medal winners at the Olympics are normally distributed, implying that the
evolution of performance values can be described in good approximation as an
exponential approach to an a priori unknown limiting performance value. This
law holds for all specialties in athletics-including running, jumping, and
throwing-and swimming. We present a self-consistent method, based on normality
hypothesis testing, able to predict limiting performance values in all
specialties. We further quantify the most likely years in which athletes will
breach challenging performance walls in running, jumping, throwing, and
swimming events, as well as the probability that new world records will be
established at the next edition of the Olympic Games.Comment: 8 pages, 3 figures, 1 table. Supporting information files and data
are available at filrad.homelinux.or
Predictive fermion mass matrix ansatzes in non-supersymmetric SO(10) grand unification
We investigate the status of predictive fermion mass ansatzes which make use
of the grand unification scale conditions , , and in non-supersymmetric SO(10) grand unification.
The gauge symmetry below an intermediate symmetry breaking scale is
assumed to be that of the standard model with either one Higgs doublet or two
Higgs doublets . We find in both cases that a maximum of 5 standard model
parameters may be predicted within experimental ranges. We find that
the standard model scenario predicts the low energy to be in
a range which includes its experimental mid-value 0.044 and which for a large
top mass can extend to lower values than the range resulting in the
supersymmetric case. In the two Higgs standard model case, we identify the
regions of parameter space for which unification of the bottom quark and tau
lepton Yukawa couplings is possible at grand unification scale. In fact, we
find that unification of the top, bottom and tau Yukawa couplings is possible
with the running b-quark mass within the preferred range provided is near the low end of its allowed
range. In this case, one may make 6 predictions which include
within its confidence limits. However unless the running mass , third generation Yukawa coupling unification requires the top mass to be
greater thanComment: 30 pages, 8 figures available on request from
[email protected], Late
Physical activity attitudes, intentions and behaviour among 18-25 year olds: a mixed method study
Peer reviewedPublisher PD
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