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Pearce, J V,Edler, F,Elliott, C J,Greenen, A,Harris, P M,Izquierdo, C Garcia,Kim, Y-G,Martin, M J,Smith, I M,Tucker, D,Veltcheva, R I BUREAU INTERNATIONAL DES POIDS ET MESURES 2018 METROLOGIA -BERLIN- Vol.55 No.4
<P>By using a simple model to relate the electromotive force drift rate of Pt–Rh thermoelements to d<I>S</I>/d<I>c</I>, i.e. the sensitivity of the Seebeck coefficient, <I>S</I>, to rhodium mass fraction, <I>c</I>, the composition of the optimal pair of Pt–Rh wires that minimizes thermoelectric drift can be determined. The model has been applied to four multi-wire thermocouples each comprising 5 or 7 Pt–Rh wires of different composition. Two thermocouples were exposed to a temperature of around 1324 °C, one thermocouple to around 1492 °C, i.e. the melting points of the Co–C and Pd–C high temperature fixed points, respectively, and one thermocouple to a series of temperatures between 1315 °C and 1450 °C. The duration of exposure at each temperature was several thousand hours. By performing repeated calibrations <I>in situ</I> with the appropriate fixed point during the high temperature exposure, the drift performance has been quantified with high accuracy, entirely free from errors associated with thermoelectric homogeneity. By combining these results it is concluded that the Pt-40%Rh versus Pt-6%Rh is the most stable at the temperatures investigated. A preliminary reference function was determined and is presented.</P>
Kim, Yung-Kun,Hong, Yoon-Jee,Min, Mi-Sook,Kim, Kyung Seok,Kim, Young-Jun,Voloshina, Inna,Myslenkov, Alexander,Smith, Gavin J D,Cuong, Nguyen Dinh,Tho, Huynh Huu,Han, Sang-Hoon,Yang, Doo-Ha,Kim, Chang- published for the Association by Oxford University 2011 The Journal of heredity Vol.102 No.2
<P>The Asiatic black bear is one of the most endangered mammals in South Korea owing to population declines resulting from human exploitation and habitat fragmentation. To restore the black bear population in South Korea, 27 bear cubs from North Korea and Russian Far East (Primorsky Krai) were imported and released into Jirisan National Park, a reservoir of the largest wild population in South Korea, in 2004. To monitor the success of this reintroduction, the genetic diversity and population structure of the reintroduced black bears were measured using both mitochondrial and nuclear DNA markers. Mitochondrial D-loop region DNA sequences (615 bp) of 43 Japanese black bears from previous study and 14 Southeast Asian black bears in this study were employed to obtain phylogenetic inference of the reintroduced black bears. The mitochondrial phylogeny indicated Asiatic black bear populations from Russian Far East and North Korea form a single evolutionary unit distinct from populations from Japan and Southeast Asia. Mean expected heterozygosity (H(E)) across 16 microsatellite loci was 0.648 for Russian and 0.676 for North Korean populations. There was a moderate but significant level of microsatellite differentiation (F(ST) = 0.063) between black bears from the 2 source areas. In addition, genetic evidences revealed that 2 populations are represented as diverging groups, with lingering genetic admixture among individuals of 2 source populations. Relatedness analysis based on genetic markers indicated several discrepancies with the pedigree records. Implication of the phylogenetic and genetic evidences on long-term management of Asiatic black bears in South Korea is discussed.</P>
Coupled double-row formation in a quasi-1D wire
Smith, L.W.,Hew, W.K.,Thomas, K.J.,Pepper, M.,Farrer, I.,Anderson, D.,Jones, G.A.C.,Ritchie, D.A. North-Holland 2010 Physica E, Low-dimensional systems & nanostructure Vol.42 No.4
We investigate one-dimensional (1D) quantum wires in the weak confinement regime, where, at certain densities, the 1D system of electrons bifurcates into two rows. We show that the two rows are coupled, forming bonding and antibonding states, and that the coupling persists in magnetic fields from 0 to 16 T. In order for a double row to form, the Coulomb interactions in the channel must overcome the confining potential, which can be achieved by tuning the density and confinement. Using a split-gate device with a top gate and back gate, we observe a transition from single-row to double-row behaviour in the weak confinement regime. We further probe the characteristics of the coupled double row regime with dc source-drain bias measurements.
Excitons in Motion in CdTe, ZnTe and ZnSe
J. J. Davies,L. C. Smith,D. Wolverson,H. Boukari,R. T. Cox,H. Mariette,J. Cibert 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.5
We report remarkable changes in the magnetic properties of excitons as they acquire kinetic energy in wide (001) quantum wells of CdTe, ZnSe, ZnTe and GaAs. In particular, the magnetic moments (g-values) when magnetic fields are applied in the growth direction are shown to have a strong dependence on the translational wavevector Kz. The dependence is particularly marked when Kz is of the order of the inverse of the exciton Bohr radius or, equivalently, when the translational kinetic energy becomes comparable with the exciton Rydberg. The behaviour is ascribed to motionallyinduced mixing between the 1S hydrogenic exciton ground state and excited nP states and is describable by what appears to be a universal formula.
Modulation of Quantum Well Optical Properties by Illumination above the Barrier Bandgap
D. Wolverson,A. V. Koudinov,Yu. G. Kusrayev,L. C. Smith,J. J. Davies,M. Wiater,G. Karczewski,T. Wojtowicz 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.5
The spin flip Raman scattering signals associated with the Mn2+ 3d5 electrons in a range of CdTe-based dilute magnetic semiconductor quantum well structures is shown to be sensitive to even very weak above-barrier illumination, as are the quantum-well photoluminescence from exciton and trion recombination and acoustic phonon Raman scattering signals excited in resonance with the quantum well. This surprising degree of sensitivity is discussed in terms of the modulation of the carrier densities in the quantum wells, leading to a modulation of the resonant intermediate state for Raman scattering and, therefore, of the scattering cross section. Depending on the majority intrinsic carrier type in the quantum wells, we show that either enhancing or quenching of the Raman signals can result.
THE BRIGHTEST YOUNG STAR CLUSTERS IN NGC 5253
Calzetti, D.,Johnson, K. E.,Adamo, A.,Gallagher III, J. S.,Andrews, J. E.,Smith, L. J.,Clayton, G. C.,Lee, J. C.,Sabbi, E.,Ubeda, L.,Kim, H.,Ryon, J. E.,Thilker, D.,Bright, S. N.,Zackrisson, E.,Kennic IOP Publishing 2015 The Astrophysical journal Vol.811 No.2
<P>The nearby dwarf starburst galaxy NGC 5253 hosts a number of young, massive star clusters, the two youngest of which are centrally concentrated and surrounded by thermal radio emission (the 'radio nebula'). To investigate the role of these clusters in the starburst energetics, we combine new and archival Hubble Space Telescope images of NGC 5253 with wavelength coverage from 1500 angstrom 1.9 mu m in 13 filters. These include H alpha, P beta, and P alpha, and the imaging from the Hubble Treasury Program LEGUS (Legacy Extragalactic UV Survey). The extraordinarily well-sampled spectral energy distributions enable modeling with unprecedented accuracy the ages, masses, and extinctions of the nine optically brightest clusters (M-V < -8.8) and the two young radio nebula clusters. The clusters have ages similar to 1-15 Myr and masses similar to 1 x 10(4)-2.5 x 10(5) M-circle dot. The clusters' spatial location and ages indicate that star formation has become more concentrated toward the radio nebula over the last similar to 15 Myr. The most massive cluster is in the radio nebula; with a mass similar to 2.5 x 10(5) M-circle dot and an age similar to 1 Myr, it is 2-4 times less massive and younger than previously estimated. It is within a dust cloud with AV similar to 50 mag, and shows a clear near-IR excess, likely from hot dust. The second radio nebula cluster is also similar to 1 Myr old, confirming the extreme youth of the starburst region. These two clusters account for about half of the ionizing photon rate in the radio nebula, and will eventually supply about 2/3 of the mechanical energy in present-day shocks. Additional sources are required to supply the remaining ionizing radiation, and may include very massive stars.</P>
Two-Dimensional Nanosheets Produced by Liquid Exfoliation of Layered Materials
Coleman, J. N.,Lotya, M.,O'Neill, A.,Bergin, S. D.,King, P. J.,Khan, U.,Young, K.,Gaucher, A.,De, S.,Smith, R. J.,Shvets, I. V.,Arora, S. K.,Stanton, G.,Kim, H.-Y.,Lee, K.,Kim, G. T.,Duesberg, G. S.,H American Association for the Advancement of Scienc 2011 Science Vol.331 No.6017
<P>If they could be easily exfoliated, layered materials would become a diverse source of two-dimensional crystals whose properties would be useful in applications ranging from electronics to energy storage. We show that layered compounds such as MoS(2), WS(2), MoSe(2), MoTe(2), TaSe(2), NbSe(2), NiTe(2), BN, and Bi(2)Te(3) can be efficiently dispersed in common solvents and can be deposited as individual flakes or formed into films. Electron microscopy strongly suggests that the material is exfoliated into individual layers. By blending this material with suspensions of other nanomaterials or polymer solutions, we can prepare hybrid dispersions or composites, which can be cast into films. We show that WS(2) and MoS(2) effectively reinforce polymers, whereas WS(2)/carbon nanotube hybrid films have high conductivity, leading to promising thermoelectric properties.</P>
Searching for Resonances in the Unbound 6Be Nucleus by Using a Radioactive 7Be Beam
채경육,D. W. Bardayan,J. C. Blackmon,M. S. Smith,A. E. Champagne,J. J. Das,R. P. Fitzgerald,D. W. Visser,V. Guimaraes,K. L. Jones,S. D. Pain,J. S. Thomas,M. S. Johnson,R. L. Kozub,R. J. Livesay,Z. Ma,C. 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.11
Knowledge of the <sup>3</sup>He(<sup>3</sup>He,<sup>2</sup><i>p</i>)<sup>4</sup>He reaction is important for understanding stellar burning and solar neutrino production. Previous measurements have found a surprisingly large rise in the cross section at low energies that could be due to a low-energy resonance in the <sup>3</sup>He + <sup>3</sup>He (<sup>6</sup>Be) system or electron screening. In the <sup>6</sup>Be nucleus, however, no excited states have been observed above the first 2<sup>+</sup> state at <i>E<sub>x</sub></i> = 1.67 MeV up to 23 MeV, even though several are expected. The <sup>2</sup>H(<sup>7</sup>Be,<sup>3</sup>H)<sup>6</sup>Be reaction has been studied for the first time to search for resonances in the <sup>6</sup>Be nucleus that may affect our understanding of the <sup>3</sup>He(<sup>3</sup>He,<sup>2</sup><i>p,</i>)<sup>4</sup>He reaction. A 100-MeV radioactive <sup>7</sup>Be beam from the Holifield Radioactive Ion Beam Facility (HRIBF) was used to bombard CD<sub>2</sub> targets, and tritons were detected by using the silicon detector array (SIDAR). A combination of reaction mechanisms appears to be necessary to explain the observed triton energy spectrum.