Measuring the quantum efficiency of single radiating dipoles using a scanning mirror

Using scanning probe techniques, we show the controlled manipulation of the radiation from single dipoles. In one experiment we study the modification of the fluorescence lifetime of a single molecular dipole in front of a movable silver mirror. A second experiment demonstrates the changing plasmon spectrum of a gold nanoparticle in front of a dielectric mirror. Comparison of our data with theoretical models allows determination of the quantum efficiency of each radiating dipole.Comment: 4 pages, 4 figure

Non-resonant direct p- and d-wave neutron capture by 12C

Discrete gamma-rays from the neutron capture state of 13C to its low-lying bound states have been measured using pulsed neutrons at En = 550 keV. The partial capture cross sections have been determined to be 1.7+/-0.5, 24.2+/-1.0, 2.0+/-0.4 and 1.0+/-0.4 microb for the ground (1/2-), first (1/2+), second (3/2-) and third (5/2+) excited states, respectively. From a comparison with theoretical predictions based on the non-resonant direct radiative capture mechanism, we could determine the spectroscopic factor for the 1/2+ state to be 0.80 +/- 0.04, free from neutron-nucleus interaction ambiguities in the continuum. In addition we have detected the contribution of the non-resonant d-wave capture component in the partial cross sections for transitions leading to the 1/2- and 3/2- states. While the s-wave capture dominates at En < 100 keV, the d-wave component turns out to be very important at higher energies. From the present investigation the 12C(n,gamma)13C reaction rate is obtained for temperatures in the range 10E+7 - 10E+10 K.Comment: Accepted for publication in Phys. Rev. C. - 16 pages + 8 figure

The s Process: Nuclear Physics, Stellar Models, Observations

Nucleosynthesis in the s process takes place in the He burning layers of low mass AGB stars and during the He and C burning phases of massive stars. The s process contributes about half of the element abundances between Cu and Bi in solar system material. Depending on stellar mass and metallicity the resulting s-abundance patterns exhibit characteristic features, which provide comprehensive information for our understanding of the stellar life cycle and for the chemical evolution of galaxies. The rapidly growing body of detailed abundance observations, in particular for AGB and post-AGB stars, for objects in binary systems, and for the very faint metal-poor population represents exciting challenges and constraints for stellar model calculations. Based on updated and improved nuclear physics data for the s-process reaction network, current models are aiming at ab initio solution for the stellar physics related to convection and mixing processes. Progress in the intimately related areas of observations, nuclear and atomic physics, and stellar modeling is reviewed and the corresponding interplay is illustrated by the general abundance patterns of the elements beyond iron and by the effect of sensitive branching points along the s-process path. The strong variations of the s-process efficiency with metallicity bear also interesting consequences for Galactic chemical evolution.Comment: 53 pages, 20 figures, 3 tables; Reviews of Modern Physics, accepte

Dependence of direct neutron capture on nuclear-structure models

The prediction of cross sections for nuclei far off stability is crucial in the field of nuclear astrophysics. We calculate direct neutron capture on the even-even isotopes $^{124-145}$Sn and $^{208-238}$Pb with energy levels, masses, and nuclear density distributions taken from different nuclear-structure models. The utilized structure models are a Hartree-Fock-Bogoliubov model, a relativistic mean field theory, and a macroscopic-microscopic model based on the finite-range droplet model and a folded-Yukawa single-particle potential. Due to the differences in the resulting neutron separation and level energies, the investigated models yield capture cross sections sometimes differing by orders of magnitude. This may also lead to differences in the predicted astrophysical r-process paths. Astrophysical implications are discussed.Comment: 25 pages including 12 figures, RevTeX, to appear in Phys. Rev.

Correlated radio:X-ray emission in the hard states of Galactic microquasars

We present results of our study of correlated radio and X-ray emission in two black hole candidates and Galactic microquasars GRS 1915+105 and Cygnus X-1 in their steady long term hard states, along with Cygnus X-3 (using data obtained from RXTE-ASM, CGRO-BATSE and GBI). We detect a pivotal behavior in the X-ray spectrum of GRS 1915+105, correlated to the radio emission. Similar to the results obtained for Cygnus X-3, the flux of X-rays softer than the pivoting point correlates with the radio emission, while the corresponding harder X-ray flux anti-correlates with both the radio and the softer X-ray emission, in this state. We examine all the previously reported correlations of X-ray properties with the radio emission in Galactic microquasars and argue that these are consistent with a general picture where a spectral pivoting is a common feature in these sources with the shape of the spectrum determining the flux of radio emission, during the hard states. We also detect a general monotonic increase in the radio emission of these sources with the soft X-ray emission spanning about 5 orders of magnitude. We qualitatively explain these findings with a Two Component Advective Flow model where the location of a boundary layer between the thin disk and the Comptonizing region determines the spectral shape and also the amount of outflow.Comment: Minor typos corrected in matter as well as figures. 12 pages, 5 figures, to appear in ApJ, August 2003 (vol. 593

School performance in Australia: is there a role for quasi-markets?

Recent changes to the organisation of Australia's education system have raised the possibility of implementing wide-ranging market reforms. In this article we discuss the scope for introducing reforms similar to the United Kingdom's 'quasi-market' model. We discuss the role of school league tables in providing signals and incentives in a quasi-market. Specifically, we compare a range of unadjusted and model-based league tables of primary school performance in Queensland's public education system. These comparisons indicate that model-based tables which account for socio-economic status and student intake quality vary significantly from the unadjusted tables

AXIN2-related oligodontia-colorectal cancer syndrome with cleft palate as a possible new feature

Background: Pathogenic variants in AXIN2 have been associated with tooth agenesis, colon polyps, and colon cancer. Given the rare nature of this phenotype, we set out to collect additional genotypic and phenotypic information. Methods: Data were collected via a structured questionnaire. Sequencing was performed in these patients mostly due to diagnostic purpose. A little more than half of the AXIN2 variant carriers were identified by NGS; other six were family members. Results: Here, we report 13 individuals with a heterozygous AXIN2 pathogenic/likely pathogenic variant who have a variable expression of oligodontia-colorectal cancer syndrome (OMIM 608615) or oligodontia-cancer predisposition syndrome (ORPHA 300576). Three individuals from one family also had cleft palate, which might represent a new clinical feature of AXIN2 phenotype, also given the fact that AXIN2 polymorphisms have been found in association with oral clefting in population studies. AXIN2 has already been added to multigene cancer panel tests; further research should be conducted to determine whether it should be added to cleft lip/palate multigene panels. Conclusion: More clarity about oligodontia-colorectal cancer syndrome, about the variable expression, and associated cancer risks is needed to improve clinical management and to establish guidelines for surveillance. We collected information about the surveillance that was advised, which might support clinical management of these patients.</p

Multiscale modelling of vascular tumour growth in 3D: the roles of domain size & boundary condition

We investigate a three-dimensional multiscale model of vascular tumour growth, which couples blood flow, angiogenesis, vascular remodelling, nutrient/growth factor transport, movement of, and interactions between, normal and tumour cells, and nutrient-dependent cell cycle dynamics within each cell. In particular, we determine how the domain size, aspect ratio and initial vascular network influence the tumour's growth dynamics and its long-time composition. We establish whether it is possible to extrapolate simulation results obtained for small domains to larger ones, by constructing a large simulation domain from a number of identical subdomains, each subsystem initially comprising two parallel parent vessels, with associated cells and diffusible substances. We find that the subsystem is not representative of the full domain and conclude that, for this initial vessel geometry, interactions between adjacent subsystems contribute to the overall growth dynamics. We then show that extrapolation of results from a small subdomain to a larger domain can only be made if the subdomain is sufficiently large and is initialised with a sufficiently complex vascular network. Motivated by these results, we perform simulations to investigate the tumour's response to therapy and show that the probability of tumour elimination in a larger domain can be extrapolated from simulation results on a smaller domain. Finally, we demonstrate how our model may be combined with experimental data, to predict the spatio-temporal evolution of a vascular tumour

Changes in Floquet state structure at avoided crossings: delocalization and harmonic generation

Avoided crossings are common in the quasienergy spectra of strongly driven nonlinear quantum wells. In this paper we examine the sinusoidally driven particle in a square potential well to show that avoided crossings can alter the structure of Floquet states in this system. Two types of avoided crossings are identified: on type leads only to temporary changes (as a function of driving field strength) in Floquet state structure while the second type can lead to permanent delocalization of the Floquet states. Radiation spectra from these latter states show significant increase in high harmonic generation as the system passes through the avoided crossing.Comment: 8 pages with 10 figures submitted to Physical Review