Multifragmentation of non-spherical nuclei : Analysis of central Xe + Sn collisions at 50 MeV/nucl

The influence of shape of expanding and rotating source on various characteristics of the multifragmentation process is studied. The analysis is based on the extension of the statistical microcanonical multifragmentation model. The comparison with the data is done for central Xe+Sn collisions at 50 A MeV as measured by INDRA Collaboration.Comment: 9 pages, 2 figures; Talk given at the XXVII International Workshop on Gross Properties of Nuclei and Nuclear Excitation, Hirschegg (Austria), January 17 - 23, 199

Complex Challenges in Policy Implementation

Efforts to improve education occur in complex landscapes, where policy, research, history, experiences, and communities shape practice in ways that have both intended and unintended outcomes. These landscapes change over time; however, there appear to be several core challenges that persist and which likely influence why it is difficult for policy to improve education in intended, effective and sustainable ways. Drawing on New Zealand and international research, this position paper identifies some of these key challenges and explores possible leverage points to navigate these. These include developing adaptive expertise, engaging key stakeholders in decision making, and developing a learning culture

Estimating Photometric Redshifts Using Support Vector Machines

We present a new approach to obtaining photometric redshifts using a kernel learning technique called Support Vector Machines (SVMs). Unlike traditional spectral energy distribution fitting, this technique requires a large and representative training set. When one is available, however, it is likely to produce results that are comparable to the best obtained using template fitting and artificial neural networks. Additional photometric parameters such as morphology, size and surface brightness can be easily incorporated. The technique is demonstrated using samples of galaxies from the Sloan Digital Sky Survey Data Release 2 and the hybrid galaxy formation code GalICS. The RMS error in redshift estimation is $<0.03$ for both samples. The strengths and limitations of the technique are assessed.Comment: 10 pages, 3 figures, to appear in the PASP, minor typos fixed to make consistent with published versio

Complex Challenges in Policy Implementation

Efforts to improve education occur in complex landscapes, where policy, research, history, experiences, and communities shape practice in ways that have both intended and unintended outcomes. These landscapes change over time; however, there appear to be several core challenges that persist and which likely influence why it is difficult for policy to improve education in intended, effective and sustainable ways. Drawing on New Zealand and international research, this position paper identifies some of these key challenges and explores possible leverage points to navigate these. These include developing adaptive expertise, engaging key stakeholders in decision making, and developing a learning culture

Shrinking a large dataset to identify variables associated with increased risk of Plasmodium falciparum infection in Western Kenya

Large datasets are often not amenable to analysis using traditional single-step approaches. Here, our general objective was to apply imputation techniques, principal component analysis (PCA), elastic net and generalized linear models to a large dataset in a systematic approach to extract the most meaningful predictors for a health outcome. We extracted predictors for Plasmodium falciparum infection, from a large covariate dataset while facing limited numbers of observations, using data from the People, Animals, and their Zoonoses (PAZ) project to demonstrate these techniques: data collected from 415 homesteads in western Kenya, contained over 1500 variables that describe the health, environment, and social factors of the humans, livestock, and the homesteads in which they reside. The wide, sparse dataset was simplified to 42 predictors of P. falciparum malaria infection and wealth rankings were produced for all homesteads. The 42 predictors make biological sense and are supported by previous studies. This systematic data-mining approach we used would make many large datasets more manageable and informative for decision-making processes and health policy prioritization

A search for gravitational lensing in 38 X-ray selected clusters of galaxies

We present the results of a CCD imaging survey for gravitational lensing in a sample of 38 X-ray-selected clusters of galaxies. Our sample consists of the most X-ray luminous (Lx>= 2x10^{44} erg s^{-1}) clusters selected from the Einstein Observatory Extended Medium Sensitivity Survey (EMSS) that are observable from Mauna Kea (dec > -40deg). The sample spans a redshift range of 0.15 0.5. CCD images of the clusters were obtained in excellent seeing. There is evidence of strong gravitational lensing in the form of giant arcs (length l > 8'', axis ratio l/w > 10) in 8 of the 38 clusters. Two additional clusters contain shorter arclets, and 6 more clusters contain candidate arcs that require follow-up observations to confirm their lensing origin. Since the survey does not have a uniform surface brightness limit we do not draw any conclusion based on the statistics of the arcs found. We note, however, that 60% (3 of 5) of the clusters with Lx > 10^{45} erg s^{-1}, and none of the 15 clusters with Lx < 4x10^{44} erg s^{-1} contain giant arcs, thereby confirming that high X-ray luminosity does identify the most massive systems, and thus X-ray selection is the preferred method for finding true, rich clusters at intermediate and high redshifts. The observed geometry of the arcs, most of which are thin, have large axis ratios (l/w > 10), and are aligned orthogonal to the optical major axes of the clusters, indicate the cluster core mass density profiles must be compact (steeper than isothermal). In several cases, however, there is also some evidence, in the form of possible radial arcs, for density profiles with finite core radii.Comment: Latex file, 17 pages, 7 jpeg figures, to be published in Astronomy and Astrophysics Supplement

Flow probe of symmetry energy in relativistic heavy-ion reactions

Flow observables in heavy-ion reactions at incident energies up to about 1 GeV per nucleon have been shown to be very useful for investigating the reaction dynamics and for determining the parameters of reaction models based on transport theory. In particular, the elliptic flow in collisions of neutron-rich heavy-ion systems emerges as an observable sensitive to the strength of the symmetry energy at supra-saturation densities. The comparison of ratios or differences of neutron and proton flows or neutron and hydrogen flows with predictions of transport models favors an approximately linear density dependence, consistent with ab-initio nuclear-matter theories. Extensive parameter searches have shown that the model dependence is comparable to the uncertainties of existing experimental data. Comprehensive new flow data of high accuracy, partly also through providing stronger constraints on model parameters, can thus be expected to improve our knowledge of the equation of state of asymmetric nuclear matter.Comment: 20 pages, 24 figures, review to appear in EPJA special volume on nuclear symmetry energ

Angle-resolved photoemission study of the role of nesting and orbital orderings in the antiferromagnetic phase of BaFe2As2

We present a detailed comparison of the electronic structure of BaFe2As2 in its paramagnetic and antiferromagnetic (AFM) phases, through angle-resolved photoemission studies. Using different experimental geometries, we resolve the full elliptic shape of the electron pockets, including parts of dxy symmetry along its major axis that are usually missing. This allows us to define precisely how the hole and electron pockets are nested and how the different orbitals evolve at the transition. We conclude that the imperfect nesting between hole and electron pockets explains rather well the formation of gaps and residual metallic droplets in the AFM phase, provided the relative parity of the different bands is taken into account. Beyond this nesting picture, we observe shifts and splittings of numerous bands at the transition. We show that the splittings are surface sensitive and probably not a reliable signature of the magnetic order. On the other hand, the shifts indicate a significant redistribution of the orbital occupations at the transition, especially within the dxz/dyz system, which we discuss