2,998 research outputs found
Beyond the c=1 Barrier in Two-Dimensional Quantum Gravity
We introduce a simple model of touching random surfaces, by adding a chemical
potential rho for ``minimal necks'', and study this model numerically coupled
to a Gaussian model in d-dimensions (for central charge c = d = 0, 1 and 2).
For c <= 1, this model has a phase transition to branched polymers, for
sufficiently large rho. For c = 2, however, the extensive simulations indicate
that this transition is replaced by a cross-over behavior on finite lattices
--- the model is always in the branched polymer phase. This supports recent
speculations that, in 2d-gravity, the behavior observe in simulations for , is dominated by finite size effects, which are exponentially enhanced
as c -> 1+.Comment: 5 pages, 6 eps-figure
4d Simplicial Quantum Gravity Interacting with Gauge Matter Fields
The effect of coupling non-compact gauge fields to four dimensional
simplicial quantum gravity is studied using strong coupling expansions and
Monte Carlo simulations. For one gauge field the back-reaction of the matter on
the geometry is weak. This changes, however, as more matter fields are
introduced. For more than two gauge fields the degeneracy of random manifolds
into branched polymers does not occur, and the branched polymer phase seems to
be replaced by a new phase with a negative string susceptibility exponent
and fractal dimension .Comment: latex2e, 10 pages incorporating 2 tables and 3 figures (using epsf
The Weak-Coupling Limit of 3D Simplicial Quantum Gravity
We investigate the weak-coupling limit, kappa going to infinity, of 3D
simplicial gravity using Monte Carlo simulations and a Strong Coupling
Expansion. With a suitable modification of the measure we observe a transition
from a branched polymer to a crinkled phase. However, the intrinsic geometry of
the latter appears similar to that of non-generic branched polymer, probable
excluding the existence of a sensible continuum limit in this phase.Comment: 3 pages 4 figs. LATTICE99(Gravity
Charge and spin state readout of a double quantum dot coupled to a resonator
State readout is a key requirement for a quantum computer. For
semiconductor-based qubit devices it is usually accomplished using a separate
mesoscopic electrometer. Here we demonstrate a simple detection scheme in which
a radio-frequency resonant circuit coupled to a semiconductor double quantum
dot is used to probe its charge and spin states. These results demonstrate a
new non-invasive technique for measuring charge and spin states in quantum dot
systems without requiring a separate mesoscopic detector
Discontinuity Theorem for First Order Phase Transitions. Implications for QCD
A first order phase transition leading to deconfinement and chiral
restoration is a likely possibility for QCD, at least in some region of the
temperature-density plane. A signal for a unique transition is that the order
parameters for such transitions (which can be understood in terms of symmetries
only in limiting situations of very massive or massless quarks) are both
discontinuous at the same critical temperature. We show that such a situation
can be understood on a precise thermodynamical basis because of a general
relation among discontinuities which holds for first order transitions. We
derive the result by a generalization of the Clausius-Clapeyron equation and
also through the effective action formalism. We illustrate the theorem in an
elementary example.Comment: 10 pages, LATEX, UGVA-DPT 1992/12/79
The Strong-Coupling Expansion in Simplicial Quantum Gravity
We construct the strong-coupling series in 4d simplicial quantum gravity up
to volume 38. It is used to calculate estimates for the string susceptibility
exponent gamma for various modifications of the theory. It provides a very
efficient way to get a first view of the phase structure of the models.Comment: LATTICE98(surfaces), 3 pages, 4 eps figure
Low incidence of toxoplasma infection during pregnancy and in newborns in Sweden
To estimate the burden of disease due to congenital toxoplasmosis in Sweden the incidence of primary infections during pregnancy and birth prevalence of congenital toxoplasmosis in 40978 children born in two regions in Sweden was determined. Women possibly infected during pregnancy were identified based on: 1, detection of specific IgG based on neonatal screening of the phenylketonuria (PKU) card blood spot followed by retrospective testing of stored prenatal samples to detect women who acquired infection during pregnancy and follow up of their children to 12 months; 2, detection of specific IgM on the PKU blood spot. The birth prevalence of congenital toxoplasmosis was 0·73/10000 (95% CI 0·15–2·14) (3/40978). The incidence of primary infection during pregnancy was 5·1/10000 (95% CI 2·6–8·9) susceptible pregnant women. The seroprevalence in the southern part was 25·7% and in the Stockholm area 14·0%. The incidence of infection during pregnancy was low, as the birth prevalence of congenital toxoplasmosis. Neonatal screening warrants consideration in view of the low cost and feasibility
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