Electromagnetic transition rates of ¹²C and ¹⁶O in rotational-vibrational models

We develop a formalism to calculate electromagnetic (EM) transition rates for rotational-vibrational models of nuclei. The formalism is applied to recently proposed models of ¹²C and ¹⁶O which are inspired by nuclear dynamics in the Skyrme model. We compare the results to experimental data as well as other nuclear models. The results for ¹²C are in good agreement with the data across all models, making it difficult to differentiate the models. More experimental data is needed to do this, and we suggest which transitions would be most interesting to measure. The models of ¹⁶O are less successful in describing the data, and we suggest some possible improvements to our approximations which may help

Oxygen-16 spectrum from tetrahedral vibrations and their rotational excitations

A reinterpretation of the complete energy spectrum of the Oxygen-16 nucleus up to 20MeV, and partly beyond, is proposed. The underlying intrinsic shape of the nucleus is tetrahedral, as in the naive alpha-particle model and other cluster models, and A-, E- and F-vibrational phonons are included. The A- and F-phonons are treated in the harmonic approximation, but the E-vibrations are extended into a two-dimensional E-manifold of D2-symmetric, four-alpha-particle configurations, following earlier works. This allows for the underlying tetrahedral configuration to tunnel through a square configuration into the dual tetrahedron, with the associated breaking of parity doubling. The frequency of an E-phonon is lower than in other models, and the first-excited 0+ state at 6.05MeV is modeled as a state with two E-phonons; this allows a good fit of the lowest 2+ and 2- states as excitations with one E-phonon. Rotational excitations of the vibrational states are analyzed as in the classic works of Dennison, Robson and others, with centrifugal corrections to the rotational energy included. States with F-phonons require Coriolis corrections, and the Coriolis parameter ζ is chosen positive to ensure the right splitting of the 3+ and 3- states near 11MeV. Altogether, about 80 states with isospin zero are predicted below 20MeV, and these match rather well the more than 60 experimentally tabulated states. Several high-spin states are predicted, up to spin 9 and energy 30MeV, and these match some of the observed high-spin, natural-parity states in this energy range. The model proposed here is mainly phenomenological but it receives some input from analysis of skyrmions with baryon number 16

Dynamical α-cluster model of ¹⁶O

We calculate the low-lying spectrum of the ¹⁶O nucleus using an α-cluster model which includes the important tetrahedral and square configurations. Our approach is motivated by the dynamics of α-particle scattering in the Skyrme model. We are able to replicate the large energy splitting that is observed between states of identical spin but opposite parities. We also provide a novel interpretation of the first excited state of ¹⁶O and make predictions for the energies of 6¯ states that have yet to be observed experimentally

Quantized Skyrmions from SU(4) weight diagrams

Starting from solutions of the lightly-bound Skyrme model, we construct many new Skyrmion solutions of the standard Skyrme model with tetrahedral or octahedral symmetry. These solutions are closely related to weight diagrams of the group SU(4), which enables us to systematically derive some geometric and energetic properties of the Skyrmions, up to baryon number 85. We discuss the rigid body quantization of these Skyrmions, and compare the results with properties of a selection of observed nuclei

Effect of the Coulomb energy on Skyrmions

The Coulomb effect, an essential ingredient in nuclear systems, is quantitatively investigated for certain Skyrmions with charge greater than 1. This is the first time such a calculation has been done. To do this we calculate the Coulomb energy from numerically generated multi-Skyrmions and, simultaneously, introduce an effective alpha-like particle approximation for large Skyrmions with baryon number B, where B is a multiple of 4. The calculated Coulomb energies and the corresponding fitted curve from this approximation match well with the results from the numerical method, as well as the behavior of the Coulomb energy in the semiempirical mass formula. The Skyrme model correctly reproduces the well known results for the Coulomb energy of nuclei. This suggests that the alpha particles can be used as the fundamental degrees of freedom in the Skyrme model, like the proposals in many other models. The Coulomb effect on the binding energy of the Skyrmions increases with baryon number but has a small effect overall. However, the effect could be significantly more pronounced for loosely bound Skyrme models

Like mother, like child : investigating perinatal and maternal health stress in post-medieval London.

Post-Medieval London (sixteenth-nineteenth centuries) was a stressful environment for the poor. Overcrowded and squalid housing, physically demanding and risky working conditions, air and water pollution, inadequate diet and exposure to infectious diseases created high levels of morbidity and low life expectancy. All of these factors pressed with particular severity on the lowest members of the social strata, with burgeoning disparities in health between the richest and poorest. Foetal, perinatal and infant skeletal remains provide the most sensitive source of bioarchaeological information regarding past population health and in particular maternal well-being. This chapter examined the evidence for chronic growth and health disruption in 136 foetal, perinatal and infant skeletons from four low-status cemetery samples in post-medieval London. The aim of this study was to consider the impact of poverty on the maternal-infant nexus, through an analysis of evidence of growth disruption and pathological lesions. The results highlight the dire consequences of poverty in London during this period from the very earliest moments of life

The dominant Anopheles vectors of human malaria in Africa, Europe and the Middle East: occurrence data, distribution maps and bionomic précis

<p>Abstract</p> <p>Background</p> <p>This is the second in a series of three articles documenting the geographical distribution of 41 dominant vector species (DVS) of human malaria. The first paper addressed the DVS of the Americas and the third will consider those of the Asian Pacific Region. Here, the DVS of Africa, Europe and the Middle East are discussed. The continent of Africa experiences the bulk of the global malaria burden due in part to the presence of the <it>An. gambiae </it>complex. <it>Anopheles gambiae </it>is one of four DVS within the <it>An. gambiae </it>complex, the others being <it>An. arabiensis </it>and the coastal <it>An. merus </it>and <it>An. melas</it>. There are a further three, highly anthropophilic DVS in Africa, <it>An. funestus</it>, <it>An. moucheti </it>and <it>An. nili</it>. Conversely, across Europe and the Middle East, malaria transmission is low and frequently absent, despite the presence of six DVS. To help control malaria in Africa and the Middle East, or to identify the risk of its re-emergence in Europe, the contemporary distribution and bionomics of the relevant DVS are needed.</p> <p>Results</p> <p>A contemporary database of occurrence data, compiled from the formal literature and other relevant resources, resulted in the collation of information for seven DVS from 44 countries in Africa containing 4234 geo-referenced, independent sites. In Europe and the Middle East, six DVS were identified from 2784 geo-referenced sites across 49 countries. These occurrence data were combined with expert opinion ranges and a suite of environmental and climatic variables of relevance to anopheline ecology to produce predictive distribution maps using the Boosted Regression Tree (BRT) method.</p> <p>Conclusions</p> <p>The predicted geographic extent for the following DVS (or species/suspected species complex*) is provided for Africa: <it>Anopheles </it>(<it>Cellia</it>) <it>arabiensis</it>, <it>An. </it>(<it>Cel.</it>) <it>funestus*</it>, <it>An. </it>(<it>Cel.</it>) <it>gambiae</it>, <it>An. </it>(<it>Cel.</it>) <it>melas</it>, <it>An. </it>(<it>Cel.</it>) <it>merus</it>, <it>An. </it>(<it>Cel.</it>) <it>moucheti </it>and <it>An. </it>(<it>Cel.</it>) <it>nili*</it>, and in the European and Middle Eastern Region: <it>An. </it>(<it>Anopheles</it>) <it>atroparvus</it>, <it>An. </it>(<it>Ano.</it>) <it>labranchiae</it>, <it>An. </it>(<it>Ano.</it>) <it>messeae</it>, <it>An. </it>(<it>Ano.</it>) <it>sacharovi</it>, <it>An. </it>(<it>Cel.</it>) <it>sergentii </it>and <it>An. </it>(<it>Cel.</it>) <it>superpictus*</it>. These maps are presented alongside a bionomics summary for each species relevant to its control.</p