Glass-Like Heat Conduction in High-Mobility Crystalline Semiconductors

The thermal conductivity of polycrystalline semiconductors with type-I clathrate hydrate crystal structure is reported. Ge clathrates (doped with Sr and/or Eu) exhibit lattice thermal conductivities typical of amorphous materials. Remarkably, this behavior occurs in spite of the well-defined crystalline structure and relatively high electron mobility ($\sim 100 cm^2/Vs$). The dynamics of dopant ions and their interaction with the polyhedral cages of the structure are a likely source of the strong phonon scattering.Comment: 4 pages, 3 postscript figures, to be published, Phys. Rev. Let

Lattice thermal conductivity of disordered NiPd and NiPt alloys

Numerical calculations of lattice thermal conductivity are reported for the binary alloys NiPd and NiPt. The present work is a continuation of an earlier paper by us [PRB, 72, 214207 (2005)]which had developed a theoretical framework for the calculation of configuration-averaged lattice thermal conductivity and thermal diffusivity in disordered alloys. The formulation was based on the augmented space theorem combined with a scattering diagram technique. In this paper we shall show dependence of the lattice thermal conductivity on a series of variables like phonon frequency, temperature and alloy composition. The temperature dependence of $\kappa(T)$ and its realtion to the measured thermal conductivity is discussed. The concentration dependence of $\kappa$ appears to justify the notion of a minimum thermal conductivity as discussed by Kittel, Slack and others. We also study the frequency and composition dependence of the thermal diffusivity averaged over modes. A numerical estimate of this quantity gives an idea about the location of mobility edge and the fraction of states in the frequency spectrum which is delocalized.Comment: 23 pages, 18 figure

Thermoelectric transport in strained Si and Si/Ge heterostructures

The anisotropic thermoelectric transport properties of bulk silicon strained in [111]-direction were studied by detailed first-principles calculations focussing on a possible enhancement of the power factor. Electron as well as hole doping were examined in a broad doping and temperature range. At low temperature and low doping an enhancement of the power factor was obtained for compressive and tensile strain in the electron-doped case and for compressive strain in the hole-doped case. For the thermoelectrically more important high temperature and high doping regime a slight enhancement of the power factor was only found under small compressive strain with the power factor overall being robust against applied strain. To extend our findings the anisotropic thermoelectric transport of an [111]-oriented Si/Ge superlattice was investigated. Here, the cross-plane power factor under hole-doping was drastically suppressed due to quantum-well effects, while under electron-doping an enhanced power factor was found. With that, we state a figure of merit of ZT$=0.2$ and ZT$=1.4$ at T=\unit[300]{K} and T=\unit[900]{K} for the electron-doped [111]-oriented Si/Ge superlattice. All results are discussed in terms of band structure features

Heat transport in model jammed solids

We calculate numerically the normal modes of vibrations in 3D jammed packings of soft spheres as a function of the packing fraction and obtain the energy diffusivity, a spectral measure of transport that controls sound propagation and thermal conductivity. The crossover frequency between weak and strong phonon scattering is controlled by the coordination and shifts to zero as the system is decompressed towards the critical packing fraction at which rigidity is lost. Below the crossover, the diffusivity displays a power-law divergence with inverse frequency, which suggests that the vibrational modes are primarily transverse waves, weakly scattered by disorder. Above it, a large number of modes appear whose diffusivity plateaus at a nearly constant value independent of the inter-particle potential, before dropping to zero above the Anderson localization frequency. The thermal conductivity of a marginally jammed solid just above the rigidity threshold is calculated and related to the one measured experimentally at room temperature for most glasses.Comment: 15 pages, 7 figure

Characteristics and serotype distribution of childhood cases of invasive pneumococcal disease following pneumococcal conjugate vaccination in England and Wales, 2006-14

Background The 7-valent (PCV7) and 13-valent (PCV13) pneumococcal conjugate vaccines are highly effective in preventing invasive pneumococcal disease (IPD) caused by vaccine serotypes. Vaccine failure (vaccine-type IPD after age-appropriate immunisation) is rare. Little is known about the risk, clinical characteristics or outcomes of PCV13 compared to PCV7 vaccine failure. Methods Public Health England conducts IPD surveillance and provides a national reference service for serotyping pneumococcal isolates in England and Wales. We compared the epidemiology, rates, risk factors, serotype distribution, clinical characteristics, and outcomes of IPD in children with PCV13 and PCV7 vaccine failure. Results A total of 163 episodes of PCV failure were confirmed in 161 children over eight years (04 September 2006 to 03 September 2014) in ten birth cohorts. After three vaccine doses, PCV7 and PCV13 failure rates were 0.19/100,000 (95% CI, 0.10-0.33; 57 cases) and 0.66/100,000 (95% CI, 0.44-0.99; 104 cases) vaccinated person-years, respectively. Children with PCV13 failure were more likely to be healthy (87/105 [82.9%] vs. 37/56 [66.1%]; P=0.02), present with bacteremic lower respiratory tract infection (61/105 [58.1%] vs. 11/56 [19.6%]; P<0.001) and develop empyema (41/61 [67.2%] vs. 1/11 [9.1%]; P<0.001) compared to PCV7 failures. Serotypes 3 (n=38, 36.2%) and 19A (n=30, 28.6%) were responsible for most PCV13 failures. Five children died (3.1%; 95% CI, 1.0-7.1%), including four with co-morbidities. Conclusions PCV failure is rare and, compared to PCV7 serotypes, the additional PCV13 serotypes are more likely to cause bacteremic lower respiratory tract infection and empyema in healthy vaccinated children

Comparison of Positive and Negative Verbal Cueing on Muscular Endurance in College - Aged Females

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Comparison of a DNA Hybridization Probe and ELISA for the Detection of \u3ci\u3eClavibacter michiganensis\u3c/i\u3e subsp. \u3ci\u3esepedonicus\u3c/i\u3e in Field-Grown Potatoes

Clavibacter michiganensis subsp. sepedonicus, the causal agent of bacterial ring rot, was detected in field-grown potatoes using a 1.078-kb repeated C. m. sepedonicus sequence as a probe in DNA hybridizations. Stem and petiole samples from susceptible and tolerant cultivars (Russet Burbank and Belrus, respectively), inoculated with 10 mM phosphate buffer (pH 7.2) or 102 or 109 cfu of either an aggressive or a less aggressive C. m. sepedonicus strain, were processed by directly blotting cut tissue sections on nylon membranes, macerating frozen tissues, and applying xylem fluid collected by centrifugation to nylon membranes (stems only). The efficiency of detection was significantly influenced by sampling date, plant part, inoculum dose, and cultivar. The probe was compared with an enzyme-linked immunosorbent assay (ELISA) and showed 95-100% agreement when underground Russet Burbank stems inoculated with 109 cfu of aggressive C. m. sepedonicus strain SS43 were directly blotted. Although overall detection rates with stem sections were higher for ELISA (18.4% with ELISA vs. 11.3% with direct blotting), a high rate of false positives (53.9%) occurred with petiole tissues at 90 days after planting when ELISA was used, whereas none occurred with DNA hybridizations

Responsiveness of the order fulfilment process

This paper discusses evidence from field studies undertaken to investigate the responsiveness of the order fulfilment process in a number of companies. The evidence is analysed in the context of the literature on responsiveness and related areas such as time-based competition. Similarities and differences are analysed across a number of industrial sectors with respect to order fulfilment processes and the interpretation and significance of responsiveness. Generic factors that influence different types of companies are identified. Four components of responsiveness - stimuli, awareness, capabilities and goals - emerge from an analysis of the literature. The field and case study evidence allows the development of more precise definitions and descriptions of each of these components. The study also allows a generic responsiveness framework to be developed that incorporates both strategic and operational viewpoints. The need for more field studies on responsiveness is noted. More work is advocated on the assessment and measurement of responsiveness and on developing appropriate responsiveness interventions, particularly with respect to the order fulfilment process

Low thermal conductivity of the layered oxide (Na,Ca)Co_2O_4: Another example of a phonon glass and an electron crystal

The thermal conductivity of polycrystalline samples of (Na,Ca)Co_2O_4 is found to be unusually low, 20 mW/cmK at 280 K. On the assumption of the Wiedemann-Franz law, the lattice thermal conductivity is estimated to be 18 mW/cmK at 280 K, and it does not change appreciably with the substitution of Ca for Na. A quantitative analysis has revealed that the phonon mean free path is comparable with the lattice parameters, where the point-defect scattering plays an important role. Electronically the same samples show a metallic conduction down to 4.2 K, which strongly suggests that NaCo_2O_4 exhibits a glass-like poor thermal conduction together with a metal-like good electrical conduction. The present study further suggests that a strongly correlated system with layered structure can act as a material of a phonon glass and an electron crystal.Comment: 5 pages 3 figures, to be published in Phys. Rev.

Optical Properties of MFe_4P_12 filled skutterudites

Infrared reflectance spectroscopy measurements were made on four members of the MFe_4P_12 family of filled skutterudites, with M=La, Th, Ce and U. In progressing from M=La to U the system undergoes a metal-insulator transition. It is shown that, although the filling atom induces such dramatic changes in the transport properties of the system, it has only a small effect on lattice dynamics. We discuss this property of the compounds in the context of their possible thermoelectric applications.Comment: Manuscript in ReVTeX format, 7 figures in PostScirpt forma