Transmission parameters estimated for Salmonella typhimurium in swine using susceptible-infectious-resistant models and a Bayesian approach.

This is a freely-available open access publication. Please cite the published version which is available via the DOI link in this record.BACKGROUND: Transmission models can aid understanding of disease dynamics and are useful in testing the efficiency of control measures. The aim of this study was to formulate an appropriate stochastic Susceptible-Infectious-Resistant/Carrier (SIR) model for Salmonella Typhimurium in pigs and thus estimate the transmission parameters between states. RESULTS: The transmission parameters were estimated using data from a longitudinal study of three Danish farrow-to-finish pig herds known to be infected. A Bayesian model framework was proposed, which comprised Binomial components for the transition from susceptible to infectious and from infectious to carrier; and a Poisson component for carrier to infectious. Cohort random effects were incorporated into these models to allow for unobserved cohort-specific variables as well as unobserved sources of transmission, thus enabling a more realistic estimation of the transmission parameters. In the case of the transition from susceptible to infectious, the cohort random effects were also time varying. The number of infectious pigs not detected by the parallel testing was treated as unknown, and the probability of non-detection was estimated using information about the sensitivity and specificity of the bacteriological and serological tests. The estimate of the transmission rate from susceptible to infectious was 0.33 [0.06, 1.52], from infectious to carrier was 0.18 [0.14, 0.23] and from carrier to infectious was 0.01 [0.0001, 0.04]. The estimate for the basic reproduction ration (R0) was 1.91 [0.78, 5.24]. The probability of non-detection was estimated to be 0.18 [0.12, 0.25]. CONCLUSIONS: The proposed framework for stochastic SIR models was successfully implemented to estimate transmission rate parameters for Salmonella Typhimurium in swine field data. R0 was 1.91, implying that there was dissemination of the infection within pigs of the same cohort. There was significant temporal-cohort variability, especially at the susceptible to infectious stage. The model adequately fitted the data, allowing for both observed and unobserved sources of uncertainty (cohort effects, diagnostic test sensitivity), so leading to more reliable estimates of transmission parameters.FC

Subtle Roles of Sb and S in Regulating the Thermoelectric Properties of Nâ Type PbTe to High Performance

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138238/1/aenm201700099.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/138238/2/aenm201700099-sup-0001-S1.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/138238/3/aenm201700099_am.pd

High Thermoelectric Performance in Supersaturated Solid Solutions and Nanostructured nâ Type PbTeâ GeTe

Sbâ doped and GeTeâ alloyed nâ type thermoelectric materials that show an excellent figure of merit ZT in the intermediate temperature range (400â 800 K) are reported. The synergistic effect of favorable changes to the band structure resulting in high Seebeck coefficient and enhanced phonon scattering by point defects and nanoscale precipitates resulting in reduction of thermal conductivity are demonstrated. The samples can be tuned as singleâ phase solid solution (SS) or twoâ phase system with nanoscale precipitates (Nano) based on the annealing processes. The GeTe alloying results in band structure modification by widening the bandgap and increasing the densityâ ofâ states effective mass of PbTe, resulting in significantly enhanced Seebeck coefficients. The nanoscale precipitates can improve the power factor in the low temperature range and further reduce the lattice thermal conductivity (κlat). Specifically, the Seebeck coefficient of Pb0.988Sb0.012Teâ 13%GeTeâ Nano approaches â 280 µV Kâ 1 at 673 K with a low κlat of 0.56 W mâ 1 Kâ 1 at 573 K. Consequently, a peak ZT value of 1.38 is achieved at 623 K. Moreover, a high average ZTavg value of â 1.04 is obtained in the temperature range from 300 to 773 K for nâ type Pb0.988Sb0.012Teâ 13%GeTeâ Nano.Both supersaturated solid solutions and nanostructured nâ type Pb1â xGexTe systems with excellent thermoelectric performance can be prepared via a nonequilibrium process. The nanostructured sample enhances the figure of merit ZT via reducing the lattice thermal conductivity. A ZTavg of â 1.04 is obtained, which is among the highest ZTavg values for nâ type PbTe materials reported so far.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/145314/1/adfm201801617-sup-0001-S1.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/145314/2/adfm201801617.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/145314/3/adfm201801617_am.pd

Engineering Temperature‐Dependent Carrier Concentration in Bulk Composite Materials via Temperature‐Dependent Fermi Level Offset

Precise control of carrier concentration in both bulk and thin‐film materials is crucial for many solid‐state devices, including photovoltaic cells, superconductors, and high mobility transistors. For applications that span a wide temperature range (thermoelectric power generation being a prime example) the optimal carrier concentration varies as a function of temperature. This work presents a modified modulation doping method to engineer the temperature dependence of the carrier concentration by incorporating a nanosize secondary phase that controls the temperature‐dependent doping in the bulk matrix. This study demonstrates this technique by de‐doping the heavily defect‐doped degenerate semiconductor GeTe, thereby enhancing its average power factor by 100% at low temperatures, with no deterioration at high temperatures. This can be a general method to improve the average thermoelectric performance of many other materials.Temperature‐dependent modulation doping is demonstrated in a GeTe–CuInTe2 composite material. Temperature‐dependent carrier concentration is achieved by controlling the temperature‐dependent Fermi level offset between the GeTe matrix and CuInTe2 inclusions. An enhanced average power factor over a wide temperature range is demonstrated.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141881/1/aenm201701623.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/141881/2/aenm201701623-sup-0001-S1.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/141881/3/aenm201701623_am.pd

High Thermoelectric Performance in PbSe–NaSbSe2 Alloys from Valence Band Convergence and Low Thermal Conductivity

PbSe is an attractive thermoelectric material due to its favorable electronic structure, high melting point, and lower cost compared to PbTe. Herein, the hitherto unexplored alloys of PbSe with NaSbSe2 (NaPbmSbSem+2) are described and the most promising p‐type PbSe‐based thermoelectrics are found among them. Surprisingly, it is observed that below 500 K, NaPbmSbSem+2 exhibits unorthodox semiconducting‐like electrical conductivity, despite possessing degenerate carrier densities of ≈1020 cm−3. It is shown that the peculiar behavior derives from carrier scattering by the grain boundaries. It is further demonstrated that the high solubility of NaSbSe2 in PbSe augments both the thermoelectric properties while maintaining a rock salt structure. Namely, density functional theory calculations and photoemission spectroscopy demonstrate that introduction of NaSbSe2 lowers the energy separation between the L‐ and Σ‐valence bands and enhances the power factors under 700 K. The crystallographic disorder of Na+, Pb2+, and Sb3+ moreover provides exceptionally strong point defect phonon scattering yielding low lattice thermal conductivities of 1–0.55 W m‐1 K‐1 between 400 and 873 K without nanostructures. As a consequence, NaPb10SbSe12 achieves maximum ZT ≈1.4 near 900 K when optimally doped. More importantly, NaPb10SbSe12 maintains high ZT across a broad temperature range, giving an estimated record ZTavg of ≈0.64 between 400 and 873 K, a significant improvement over existing p‐type PbSe thermoelectrics.The high solubility of NaSbSe2 in PbSe is exploited to facilitate convergence of L‐ and Σ‐valence bands and to produce strong point defect phonon scattering. These processes yield enhanced power factors and low lattice thermal conductivity over ≈300–700 K, which together give NaPb10SbSe12 outstanding thermoelectric performance with a maximum ZT ≈ 1.4 at 873 K and ZTavg ≈0.64 over 400–873 K.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151353/1/aenm201901377.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151353/2/aenm201901377-sup-0001-S1.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151353/3/aenm201901377_am.pd

Weak Electron Phonon Coupling and Deep Level Impurity for High Thermoelectric Performance Pb1â xGaxTe

High ZT of 1.34 at 766 K and a record high average ZT above 1 in the temperature range of 300â 864 K are attained in nâ type PbTe by engineering the temperatureâ dependent carrier concentration and weakening electronâ phonon coupling upon Ga doping. The experimental studies and first principles band structure calculations show that doping with Ga introduces a shallow level impurity contributing extrinsic carriers and imparts a deeper impurity level that ionizes at higher temperatures. This adjusts the carrier concentration closer to the temperatureâ dependent optimum and thus maximizes the power factor in a wide temperature range. The maximum power factor of 35 µW cmâ 1 Kâ 2 is achieved for the Pb0.98Ga0.02Te compound, and is maintained over 20 µWcmâ 1 Kâ 2 from 300 to 767 K. Band structure calculations and Xâ ray photoelectron spectroscopy corroborate the amphoteric role of Ga in PbTe as the origin of shallow and deep levels. Additionally, Ga doping weakens the electronâ phonon coupling, leading to high carrier mobilities in excess of 1200 cm2 Vâ 1 sâ 1. Enhanced point defect phonon scattering yields a reduced lattice thermal conductivity. This work provides a new avenue, beyond the conventional shallow level doping, for further improving the average ZT in thermoelectric materials.Ga doping in PbTe not only induces a shallow level impurity but also imparts a deeper impurity level that ionizes at higher temperatures, facilitating the engineering of the temperatureâ dependent carrier concentration, maximizing the power factor over a wider temperature range. This work provides a new avenue, beyond the conventional shallow level doping, for further improving the average ZT in thermoelectric materials.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/145409/1/aenm201800659.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/145409/2/aenm201800659_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/145409/3/aenm201800659-sup-0001-S1.pd

CO₂ drawdown following the middle Miocene expansion of the Antarctic Ice Sheet

The development of a permanent, stable ice sheet in East Antarctica happened during the middle Miocene, about 14 Myr (million years) ago. The middle Miocene therefore represents one of the distinct phases of rapid change in the transition from the “greenhouse” of the early Eocene to the “icehouse” of the present day. Carbonate carbon isotope records of the period immediately following the main stage of ice sheet development reveal a major perturbation in the carbon system, represented by the positive δ13C excursion known as carbon maximum 6 (“CM6”), which has traditionally been interpreted as reflecting increased burial of organic matter and atmospheric pCO2 drawdown. More recently, it has been suggested that the δ13C excursion records a negative feedback resulting from the reduction of silicate weathering and an increase in atmospheric pCO2. Here we present high-resolution multi-proxy (alkenone carbon and foraminiferal boron isotope) records of atmospheric carbon dioxide and sea surface temperature across CM6. Similar to previously published records spanning this interval, our records document a world of generally low (~300 ppm) atmospheric pCO2 at a time generally accepted to be much warmer than today. Crucially, they also reveal a pCO2 decrease with associated cooling, which demonstrates that the carbon burial hypothesis for CM6 is feasible and could have acted as a positive feedback on global cooling.</p

Discovery of δ Scuti Pulsations in the Young Hybrid Debris Disk Star HD 156623

The bRing robotic observatory network was built to search for circumplanetary material within the transiting Hill sphere of the exoplanet β Pic b across its bright host star β Pic. During the bRing survey of β Pic, it simultaneously monitored the brightnesses of thousands of bright stars in the southern sky (V ; 4–8, δ −30°). In this work, we announce the discovery of δ Scuti pulsations in the A-type star HD 156623 using bRing data. HD 156623 is notable as it is a well-studied young star with a dusty and gas-rich debris disk, previously detected using ALMA. We present the observational results on the pulsation periods and amplitudes for HD 156623, discuss its evolutionary status, and provide further constraints on its nature and age. We find strong evidence of frequency regularity and grouping. We do not find evidence of frequency, amplitude, or phase modulation for any of the frequencies over the course of the observations. We show that HD 156623 is consistent with other hot and highfrequency pre-main sequence and early zero-age main sequence (ZAMS) δ Scutis as predicted by theoretical models and corresponding evolutionary tracks, although we observe that HD 156623 lies hotter than the theoretical blue edge of the classical instability strip. This, coupled with our characterization and Sco–Cen membership analyses, suggests that the star is most likely an outlying ZAMS member of the ∼16 Myr Upper Centaurus-Lupus subgroup of the Sco–Cen associatio