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Accidental Peccei–Quinn symmetry from discrete flavour symmetry and Pati–Salam
Bjö,rkeroth, Fredrik,Chun, Eung Jin,King, Stephen F. North-Holland Pub. Co 2018 Physics letters. Section B Vol.777 No.-
<P><B>Abstract</B></P> <P>We show how an accidental U ( 1 ) Peccei–Quinn (PQ) symmetry can arise from a discrete <SUB> A 4 </SUB> family symmetry combined with a discrete flavour symmetry <SUB> Z 3 </SUB> × Z 5 2 , in a realistic Pati–Salam unified theory of flavour. Imposing only these discrete flavour symmetries, the axion solution to the strong <I>CP</I> problem is protected from PQ-breaking operators to the required degree. A QCD axion arises from a linear combination of <SUB> A 4 </SUB> triplet flavons, which are also responsible for fermion flavour structures due to their vacuum alignments. We find that the requirement of an accidental PQ symmetry arising from a discrete flavour symmetry constrains the form of the Yukawa matrices, providing a link between flavour and the strong <I>CP</I> problem. Our model predicts specific flavour-violating couplings of the flavourful axion and thus puts a strong limit on the axion scale from kaon decays.</P>
Irradiation testing of enhanced uranium oxide fuels
Insulander Bjö,rk, Klara,Kelly, Julian F.,Vitanza, Carlo,Drera, Saleem S.,Holcombe, Scott,Tverberg, Terje,Tuomisto, Harri,Wright, Jonathan,Sarsfield, Mark,Blench, Trevor,Yang, Jae Ho,Kim, Hyun-Gil Elsevier 2019 Annals of nuclear energy Vol.125 No.-
<P><B>Abstract</B></P> <P>Enhanced uranium oxide fuel types are being tested in the Halden Research Reactor in Norway with the aim is to assess the effect that these enhancements have on fuel performance. Fuel temperatures, rod pressures and dimensional changes are being monitored online and an extensive post-irradiation examination programme is planned. Preliminary data show that fuel centerline temperatures can be lowered by addition of ThO<SUB>2</SUB> to the fuel matrix, or by incorporating Cr or SiO<SUB>2</SUB>-TiO<SUB>2</SUB> as a network structure within the fuel. In parallel, two types of cladding coatings are tested in order to investigate their in-core properties. No abnormal behaviour has been noted during the first 100 days of irradiation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Irradiation testing of uranium oxide fuel enhanced with Cr, SiO<SUB>2</SUB>/TiO<SUB>2</SUB> and ThO<SUB>2</SUB>. </LI> <LI> Irradiation testing of cladding coated with (Fe,Cr,Al) and (Cr,Al) alloys. </LI> <LI> All tested materials perform as expected, or better. </LI> <LI> Lowered fuel temperatures observed for fuel enhanced with Cr microcell structure. </LI> <LI> Unexpectedly low temperatures observed for SiO<SUB>2</SUB>/TiO<SUB>2</SUB> and 40% ThO<SUB>2</SUB> enhanced fuel. </LI> </UL> </P>
Lin, Yao-Cheng,Wang, Jing,Delhomme, Nicolas,Schiffthaler, Bastian,Sundströ,m, Gö,rel,Zuccolo, Andrea,Nystedt, Bjö,rn,Hvidsten, Torgeir R.,de la Torre, Amanda,Cossu, Rosa M.,Hoeppner, Marc National Academy of Sciences 2018 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF Vol.115 No.46
<▼1><P><B>Significance</B></P><P>We performed de novo, full-genome sequence analysis of two <I>Populus</I> species, North American quaking and Eurasian trembling aspen, that contain striking levels of genetic variation. Our results showed that positive and negative selection broadly affects patterns of genomic variation, but to varying degrees across coding and noncoding regions. The strength of selection and rates of sequence divergence were strongly related to differences in gene expression and coexpression network connectivity. These results highlight the importance of both positive and negative selection in shaping genome-wide levels of genetic variation in an obligately outcrossing, perennial plant. The resources we present establish aspens as a powerful study system enabling future studies for understanding the genomic determinants of adaptive evolution.</P></▼1><▼2><P>The <I>Populus</I> genus is one of the major plant model systems, but genomic resources have thus far primarily been available for poplar species, and primarily <I>Populus trichocarpa</I> (Torr. & Gray), which was the first tree with a whole-genome assembly. To further advance evolutionary and functional genomic analyses in <I>Populus</I>, we produced genome assemblies and population genetics resources of two aspen species, <I>Populus tremula</I> L. and <I>Populus tremuloides</I> Michx. The two aspen species have distributions spanning the Northern Hemisphere, where they are keystone species supporting a wide variety of dependent communities and produce a diverse array of secondary metabolites. Our analyses show that the two aspens share a similar genome structure and a highly conserved gene content with <I>P. trichocarpa</I> but display substantially higher levels of heterozygosity. Based on population resequencing data, we observed widespread positive and negative selection acting on both coding and noncoding regions. Furthermore, patterns of genetic diversity and molecular evolution in aspen are influenced by a number of features, such as expression level, coexpression network connectivity, and regulatory variation. To maximize the community utility of these resources, we have integrated all presented data within the PopGenIE web resource (PopGenIE.org).</P></▼2>
Experimental characterization of quantum polarization of three-photon states
Kim, Yosep,Bjö,rk, Gunnar,Kim, Yoon-Ho American Physical Society 2017 Physical Review A Vol.96 No.3
<P>We experimentally investigate various quantum polarization features of three-photon quantum states, including product and entangled states with varying purity. The three-photon quantum states are categorized into six classes based on the rotation symmetry of mean, variance, and skewness of the polarization distribution. The representative three-photon quantum states in each category are prepared from double-pair emission from pulsed spontaneous parametric down-conversion and quantum interferometry. We demonstrate that the three-photon quantum states show interesting quantum polarization properties, such as maximum sum-uncertainty and hidden polarizations.</P>
First-principles investigation of two-dimensional trichalcogenide and sesquichalcogenide monolayers
Debbichi, L.,Kim, H.,Bjö,rkman, T.,Eriksson, O.,Lebè,gue, S. American Physical Society 2016 Physical Review B Vol.93 No.24
<P>We have used density functional theory to investigate the dynamical stability and the electronic structure of several new semiconducting two-dimensional single layers, with chemical compositions such as ABX(3) and A(2)X(3). The calculated interlayer binding energies and the absence of imaginary states in the phonon spectra indicate the possibility to isolate them in the form of a single layer. Also, the calculated band edges reveal that some of these two-dimensional materials are promising candidates for water-splitting applications.</P>
Gautam, Mukesh Kumar,Lee, Kwang-Sik,Berg, Bjö,rn,Song, Byeong-Yeol,Yeon, Jeh-Yeong Pergamon Press 2019 Chemosphere Vol. No.
<P><B>Abstract</B></P> <P>The decomposition dynamics of 34 different elements in four different litter types (foliar and woody litter) from <I>Pinus densiflora</I> (Korean red pine) and <I>Castanea crenata</I> (Korean chestnut) was investigated in a cool temperate ecosystem using the litterbag method. Two contrasting trends were observed in the dynamics of elements with accumulated mass loss of litter and carbon. Leaf litter of Korean chestnut, which was richer in elements, showed a general decrease in concentrations of elements with accumulated mass loss of litter and carbon on a dry mass basis during decomposition in the field. Other litter types, with initially lower concentrations of elements, exhibited an increase in concentration on a dry mass basis during field incubation. Highest relative increase in the concentration was noticed for the minor elements, and for the woody litters. Concentrations of major and minor elements increased by factors ranging from 1.07 for antimony (Sb) to 853.7 for vanadium (V). Rare earth elements (REE) concentrations increased by factors ranging from 1.04 for scandium (Sc) to 83.5 for thorium (Th). Our results suggest that litter type plays an important role for nutrient dynamics. Results from principal component analysis for major, minor, and rare earth elements showed grouping of elements and high correlation among them (<I>P</I> < 0.05), which suggests a common source. At both sites, element concentrations were high in the soil, especially for REE. This suggests that increase in element concentrations during field incubation probably was due to transfer of elements from soil to the overlying decomposing litter.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The dynamics of major, minor, and rare earth element was studied in decomposing forest litter. </LI> <LI> Angiosperm and gymnosperm leaf litter showed contrasting patterns of changes in concentrations of the studied elements. </LI> <LI> Rare earth elements showed identical pattern of accumulation in woody litters after one year of decomposition. </LI> </UL> </P>
EXOTIME: searching for planets around pulsating subdwarf B stars
Schuh, Sonja,Silvotti, Roberto,Lutz, Ronny,Loeptien, Bjö,rn,Green, Elizabeth M.,Østensen, Roy H.,Leccia, Silvio,Kim, Seung-Lee,Fontaine, Gilles,Charpinet, Sté,phane,Francœur, Myriam,Randall, Springer-Verlag 2010 Astrophysics and space science Vol. No.