Clustering in stable and unstable nuclei in pp-shell and sdsd-shell regions

According to microscopic calculations with antisymmetrized molecular dynamics, we studied cluster features in stable and unstable nuclei. A variety of structure was found in stable and unstable nuclei in the $p$-shell and $sd$-shell regions. The structure of excited states of $^{12}$Be was investigated, while in $sd$-shell nuclei we focused on molecular states and deformed states. The deformed states in $^{28}$Si and $^{40}$Ca were discussed in connection with the high-lying molecular states. Appealing molecular states in $^{36}$Ar and $^{24}$Mg were suggested. The results signified that both clustering of nucleons and mean-field formation are essential features in $sd$-shell nuclei as well as $p$-shell nuclei.Comment: 5 pages, 2 figs, proceedings of the 8th International conference on Clustering Aspects of Nuclear Structure and Dynamics, Nov. 2003, Nara, Japan, to be published in Nucl.Phys.

4He decay of excited states in 14C

A study of the 7Li(9Be,4He 10Be)2H reaction at E{beam}=70 MeV has been performed using resonant particle spectroscopy techniques and provides the first measurements of alpha-decaying states in 14C. Excited states are observed at 14.7, 15.5, 16.4, 18.5, 19.8, 20.6, 21.4, 22.4 and 24.0 MeV. The experimental technique was able to resolve decays to the various particle bound states in 10Be, and provides evidence for the preferential decay of the high energy excited states into states in 10Be at ~6 MeV. The decay processes are used to indicate the possible cluster structure of the 14C excited states.Comment: accepted for publication in PR

From the stable to the exotic: clustering in light nuclei

A great deal of research work has been undertaken in alpha-clustering study since the pioneering discovery of 12C+12C molecular resonances half a century ago. Our knowledge on physics of nuclear molecules has increased considerably and nuclear clustering remains one of the most fruitful domains of nuclear physics, facing some of the greatest challenges and opportunities in the years ahead. The occurrence of "exotic" shapes in light N=Z alpha-like nuclei is investigated. Various approaches of the superdeformed and hyperdeformed bands associated with quasimolecular resonant structures are presented. Evolution of clustering from stability to the drip-lines is examined: clustering aspects are, in particular, discussed for light exotic nuclei with large neutron excess such as neutron-rich Oxygen isotopes with their complete spectroscopy.Comment: 15 pages, 5 figures, Presented at the International Symposium on "New Horizons in Fundamental Physics - From Neutrons Nuclei via Superheavy Elements and Supercritical Fields to Neutron Stars and Cosmic Rays" held at Makutsi Safari Farm, South Africa, December 23-29, 2015. arXiv admin note: substantial text overlap with arXiv:1402.6590, arXiv:1303.0960, arXiv:1408.0684, arXiv:1011.342

Triaxial deformation in 10Be

The triaxial deformation in $^{10}$Be is investigated using a microscopic $\alpha+\alpha+n+n$ model. The states of two valence neutrons are classified based on the molecular-orbit (MO) model, and the $\pi$-orbit is introduced about the axis connecting the two $\alpha$-clusters for the description of the rotational bands. There appear two rotational bands comprised mainly of $K^\pi = 0^+$ and $K^\pi = 2^+$, respectively, at low excitation energy, where the two valence neutrons occupy $K^\pi = 3/2^-$ or $K^\pi = 1/2^-$ orbits. The triaxiality and the $K$-mixing are discussed in connection to the molecular structure, particularly, to the spin-orbit splitting. The extent of the triaxial deformation is evaluated in terms of the electro-magnetic transition matrix elements (Davydov-Filippov model, Q-invariant model), and density distribution in the intrinsic frame. The obtained values turned out to be $\gamma = 15^o \sim 20^o$.Comment: 15 pages, latex, 3 figure

Structure of excited states of Be-11 studied with Antisymmetrized Molecular Dynamics

The structures of the ground and excited states of Be-11 were studied with a microscopic method of antisymmetrized molecular dynamics. The theoretical results reproduce the abnormal parity of the ground state and predict various kinds of excited states. We suggest a new negative-parity band with a well-developed clustering structure which reaches high-spin states. Focusing on a $2\alpha$ clustering structure, we investigated structure of the ground and excited states. We point out that molecular orbits play important roles for the intruder ground state and the low-lying $2\hbar \omega$ states. The features of the breaking of $\alpha$ clusters were also studied with the help of data for Gamow-Teller transitions.Comment: 24 pages, 7 figures, to be submitted to Phys.Rev.

α\alpha-particle condensate states in 16^{16}O

The existence of a rotational band with the $\alpha$+$^{12}$C($0_2^+$) cluster structure, in which three $\alpha$ particles in $^{12}$C($0_2^+$) are locally condensed, is demonstrated near the four-$\alpha$ threshold of $^{16}$O in agreement with experiment. This is achieved by studying structure and scattering for the $\alpha$+$^{12}$C($0_2^+$) system in a unified way. A drastic reduction (quenching) of the moment of the inertia of the $0^+$ state at 15.1 MeV just above the four-$\alpha$ threshold in $^{16}$O suggests that it could be a candidate for the superfluid state in $\alpha$-particle condensation.Comment: 5 pages, 3 figure

Exotic clusters in the excited states of Be-12, Be-14 and B-15

The excited states of Be-12, Be-14 and B-15 were studied by an antisymmetrized molecular dynamics method. The theoretical results reproduced the energy levels of recently measured excited states of Be-12, and also predicted rotational bands with innovative clustering structures in Be-12, Be-14 and B-15. Clustering states with new exotic clusters (He-6, He-8 and Li-9) were theoretically suggested. One new aspect in very neutron-rich nuclei is a 6-nucleon correlation among 4 neutrons and 2 protons, which plays an important role in the formation of He-6 clusters during clustering: 8He + 6He of Be-14 and 9Li+6He of B-15.Comment: 8 pages, 3 figures. submitted to Phys.Rev.

Graphene/Strontium Titanate: Approaching Single Crystal–Like Charge Transport in Polycrystalline Oxide Perovskite Nanocomposites through Grain Boundary Engineering

Grain boundaries critically limit the electronic performance of oxide perovskites. These interfaces lower the carrier mobilities of polycrystalline materials by several orders of magnitude compared to single crystals. Despite extensive effort, improving the mobility of polycrystalline materials (to meet the performance of single crystals) is still a severe challenge. In this work, the grain boundary effect is eliminated in the perovskite strontium titanate by incorporating graphene into the polycrystalline microstructure. An effective mass model provides strong evidence that polycrystalline graphene/strontium titanate nanocomposites approach single crystal-like charge transport. This phenomenological model reduces the complexity of analyzing charge transport properties so that a quantitative comparison can be made between the nanocomposites and strontium titanate single crystals. In other related works, graphene composites also optimize the thermal transport properties of thermoelectric materials. Therefore, decorating grain boundaries with graphene appears to be a robust strategy to achieve “phonon glass–electron crystal” behavior in oxide perovskites.This work has received the funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie individual Fellowship programme No 800031. The authors gratefully acknowledge the support provided by the EPSRC (awards: EP/I036230/1, EP/L014068/1, EP/L017695/1). The authors would also like to acknowledge funding from the National Science Foundation (DMREF-1729487 and DMREF-1333335). As the Research Chair in Carbon Materials, IAK gratefully acknowledges support from Morgan Advanced Materials/ Royal Academy of Engineering. All research data supporting this publication are directly available within the publication

Helium Clustering in Neutron-Rich Be Isotopes

Measurements of the helium-cluster breakup and neutron removal cross sections for neutron-rich Be isotopes A=10-12,14 are presented. These have been studied in the 30 to 42 MeV/u energy range where reaction measurements are proposed to be sensitive to the cluster content of the ground-state wave-function. These measurements provide a comprehensive survey of the decay processes of the Be isotopes by which the valence neutrons are removed revealing the underlying alpha-alpha core-cluster structure. The measurements indicate that clustering in the Be isotopes remains important up to the drip-line nucleus 14^Be and that the dominant helium-cluster structure in the neutron-rich Be isotopes corresponds to alpha-Xn-alpha.Comment: 5 pages, 2 tables and 3 figure

Autoregressive Hidden Markov Models for the Early Detection of Neonatal Sepsis

Abstract—Late onset neonatal sepsis is one of the major clinical concerns when premature babies receive intensive care. Current practice relies on slow laboratory testing of blood cultures for diagnosis. A valuable research question is whether sepsis can be reliably detected before the blood sample is taken. This paper investigates the extent to which physiological events observed in the patient’s monitoring traces could be used for the early detec-tion of neonatal sepsis. We model the distribution of these events with an autoregressive hidden Markov model (AR-HMM).Both learning and inference carefully use domain knowledge to extract the baby’s true physiology from the monitoring data. Our model can produce real-time predictions about the onset of the infection and also handles missing data. We evaluate the effectiveness of the AR-HMM for sepsis detection on a dataset collected from the Neonatal Intensive Care Unit (NICU) at the Royal Infirmary of Edinburgh. Index Terms—neonatal sepsis, autoregressive hidden Markov model, real-time inference, intensive care. I