2,171 research outputs found
Percolation Transition in the random antiferromagnetic spin-1 chain
We give a physical description in terms of percolation theory of the phase
transition that occurs when the disorder increases in the random
antiferromagnetic spin-1 chain between a gapless phase with topological order
and a random singlet phase. We study the statistical properties of the
percolation clusters by numerical simulations, and we compute exact exponents
characterizing the transition by a real-space renormalization group
calculation.Comment: 9 pages, 4 encapsulated Postscript figures, REVTeX 3.
Chain-Boundary Excitations in the Haldane Phase of 1D Systems
The chain-boundary excitations occurring in the Haldane phaseof
antiferromagnetic spin chains are investigated. The bilinear-biquadratic
hamiltonian is used to study these excitations as a function of the strength of
the biquadratic term, , between . At the AKLT point,
, we show explicitly that these excitations are localized at the
boundaries of the chain on a length scale equal to the correlation length
, and that the on-site magnetization for the first site is
. Applying the density matrixrenormalization group we show that
the chain-boundaryexcitations remain localized at the boundaries for
. As the two critical points are approached the
size of the objects diverges and their amplitude vanishes.Comment: 4 Pages, 4 eps figures. Uses RevTeX 3.0. Submitted to PR
Beta-decay branching ratios of 62Ga
Beta-decay branching ratios of 62Ga have been measured at the IGISOL facility
of the Accelerator Laboratory of the University of Jyvaskyla. 62Ga is one of
the heavier Tz = 0, 0+ -> 0+ beta-emitting nuclides used to determine the
vector coupling constant of the weak interaction and the Vud quark-mixing
matrix element. For part of the experimental studies presented here, the
JYFLTRAP facility has been employed to prepare isotopically pure beams of 62Ga.
The branching ratio obtained, BR= 99.893(24)%, for the super-allowed branch is
in agreement with previous measurements and allows to determine the ft value
and the universal Ft value for the super-allowed beta decay of 62Ga
Determinants of the Use of a Diabetes Risk-Screening Test
A study was designed to investigate why people do or do not make use of a diabetes risk test developed to facilitate the timely diagnosis of diabetes. Data were collected using a web-based questionnaire, which was based on the Health Belief Model, the Theory of Planned Behavior, and the Threatening Medical Situations Inventory. People who had and had not used the risk test were recruited to complete the survey. The sample consisted of 205 respondents: 44% who had used the test and 56% who had not. The hypothesized relationships between the dependent variable (diabetes risk test use) and the determinants used in this study were tested using logistic regression analysis. Only two significant predictors of diabetes risk test use were found: gender and barriers. More women than men use the test. Furthermore, people who experience more barriers will be less inclined to use the test. The contribution of diabetes screening tests fully depends on peopleâs willingness to use them. To optimize the usage of such test, it is especially important to address the barriers as perceived by the public. Two types of barriers must be addressed: practical barriers (time to take the test, fear of complexity of the test), and consequential barriers (fear of the disease and treatment, uncertainties about where to go in the case of an increased risk of diabetes)
8.4GHz VLBI observations of SN2004et in NGC6946
We report on 8.4GHz Very Long Baseline Interferometry (VLBI) observations of
the type II-P supernova SN2004et in the spiral galaxy NGC 6946, made on 20
February 2005 (151 days after explosion). The Very Large Array (VLA) flux
density was 1.230.07 mJy, corresponding to an isotropic luminosity at
8.4GHz of (4.450.3) erg s Hz and a brightness
temperature of (1.30.3) K. We also provide an improved
source position, accurate to about 0.5 mas in each coordinate. The VLBI image
shows a clear asymmetry. From model fitting of the size of the radio emission,
we estimate a minimum expansion velocity of 15,7002,000 km s. This
velocity is more than twice the expected mean expansion velocity estimated from
a synchrotron self-absorbed emission model, thus suggesting that synchrotron
self-absorption is not relevant for this supernova. With the benefit of an
optical spectrum obtained 12 days after explosion, we favor an emission model
which consists of two hot spots on an underlying expanding shell of width
comparable to that of SN 1993J.Comment: Accepted for publication in A&A (22/05/07
Nonequilibrium dynamics of random field Ising spin chains: exact results via real space RG
Non-equilibrium dynamics of classical random Ising spin chains are studied
using asymptotically exact real space renormalization group. Specifically the
random field Ising model with and without an applied field (and the Ising spin
glass (SG) in a field), in the universal regime of a large Imry Ma length so
that coarsening of domains after a quench occurs over large scales. Two types
of domain walls diffuse in opposite Sinai random potentials and mutually
annihilate. The domain walls converge rapidly to a set of system-specific
time-dependent positions {\it independent of the initial conditions}. We obtain
the time dependent energy, magnetization and domain size distribution
(statistically independent). The equilibrium limits agree with known exact
results. We obtain exact scaling forms for two-point equal time correlation and
two-time autocorrelations. We also compute the persistence properties of a
single spin, of local magnetization, and of domains. The analogous quantities
for the spin glass are obtained. We compute the two-point two-time correlation
which can be measured by experiments on spin-glass like systems. Thermal
fluctuations are found to be dominated by rare events; all moments of truncated
correlations are computed. The response to a small field applied after waiting
time , as measured in aging experiments, and the fluctuation-dissipation
ratio are computed. For ,
, it equals its equilibrium value X=1, though time
translational invariance fails. It exhibits for aging regime
with non-trivial , different from mean field.Comment: 55 pages, 9 figures, revte
Schooling for violence and peace : how does peace education differ from ânormalâ schooling?
This article reviews literature on the roles of schooling in both reproducing and actively perpetrating violence, and sets out an historical explanation of why schools are socially constructed in such a way as to make these roles possible. It then discusses notions of peace education in relation to one particular project in England before using empirical data from research on the project to examine contrasts between peace education approaches and ânormalâ schooling from the viewpoints of project workers, pupils and teachers. It concludes that such contrasts and tensions do indeed exist and that this raises serious questions about the compatibility of peace education and formal schooling
Q-value of the superallowed beta decay of Ga-62
Masses of the radioactive isotopes 62Ga, 62Zn and 62Cu have been measured at
the JYFLTRAP facility with a relative precision of better than 18 ppb. A Q_EC
value of (9181.07 +- 0.54) keV for the superallowed decay of 62Ga is obtained
from the measured cyclotron frequency ratios of 62Ga-62Zn, 62Ga-62Ni and
62Zn-62Ni ions. The resulting Ft-value supports the validity of the conserved
vector current hypothesis (CVC). The mass excess values measured were (-51986.5
+-1.0) keV for 62Ga, (-61167.9 +- 0.9) keV for 62Zn and (-62787.2 +- 0.9) keV
for 62Cu.Comment: 12 pages, 3 figures, 2 tables, submitted to Phys. Lett. B. v2: added
acknowledgement
A mega-analysis of memory reports from eight peer-reviewed false memory implantation studies
Understanding that suggestive practices can promote false beliefs and false memories forchildhood events is important in many settings (e.g., psychotherapeutic, medical, legal). The generalizability of findings from memory implantation studies has been questioned due to variability in estimates across studies. Such variability is partly due to false memories having been operationalized differently across studies and to differences in memory induction techniques. We explored ways of defining false memory based on memory science and developed a reliable coding system that we applied to reports from eight published implantation studies (N=423). Independent raters coded transcripts using seven criteria: accepting the suggestion, elaboration beyond the suggestion, imagery, coherence, emotion, memory statements, and not rejecting the suggestion. Using this scheme, 30.4% of cases were classified as false memories and another 23% were classified as having accepted the event to some degree. When the suggestion included self-relevant information, an imagination procedure, and was not
accompanied by a photo depicting the event, the memory formation rate was 46.1%. Our research demonstrates a useful procedure for systematically combining data that are not amenable to meta-analysis, and provides the most valid estimate of false memory formation and
associated moderating factors within the implantation literature to date
Bond-randomness-induced Neel order in weakly coupled antiferromagnetic spin chains
Quasi-one-dimensional antiferromagnetic (AF) quantum spin systems show a wide
range of interesting phenomena such as the spin-Peierls transition and disorder
driven long range ordering. While there is no magnetic long range order in
strictly one-dimensional systems, in real systems some amount of interchain
coupling is always present and AF long range order may appear below a Neel
ordering temperature T_N. We study the effect of bond randomness on Neel
ordering in weakly coupled random AF S=1/2 chains both with and without
dimerization (or spin-Peierls order). We use the real space renormalization
group method to tackle the intrachain couplings, and a mean-field approximation
to treat the interchain coupling. We show that in the non-dimerized chain,
disorder (represented by bond randomness) enhances the Neel order parameter; in
the dimerized chain which shows no magnetic ordering in the weak interchain
coupling limit without randomness, disorder can actually lead to long range
order. Thus disorder is shown to lead to, or enhance the tendency toward long
range order, providing another example of the order-by-disorder phenomenon. We
make a qualitative comparison of our results with the observed phenomenon of
doping induced long range ordering in quasi-one-dimensional spin systems such
as CuGeO_3.Comment: 8 pages, 4 figure
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