High Seebeck coefficient and ultra-low lattice thermal conductivity in Cs2InAgCl6

The elastic, electronic and thermoelectric properties of indium-based double-perovskite halide, Cs2InAgCl6 have been studied by first principles study. The Cs2InAgCl6 is found to be elastically stable, ductile, anisotropic and relatively low hard material. The calculated direct bandgap 3.67 eV by TB-mBJ functional fairly agrees with the experimentally measured value 3.3 eV but PBE functional underestimates the bandgap by 1.483 eV. The relaxation time and lattice thermal conductivity have been calculated by using relaxation time approximation (RTA) within the supercell approach. The lattice thermal conductivity (\k{appa}l) is quite low (0.2 Wm-1K-1). The quite low phonon group velocity in the large weighted phase space, and high anharmonicity (large phonon scattering) are responsible for small \k{appa}l. The room temperature Seebeck coefficient is 199 {\mu}VK-1. Such high Seebeck coefficient arises from the combination of the flat conduction band and large bandgap. We obtain power factors at 300K by using PBE and TB-mBJ potentials are ~29 and ~31 mWm-1K-2, respectively and the corresponding thermoelectric figure of merit of Cs2BiAgCl6 are 0.71 and 0.72. However, the maximum ZT value obtained at 700K is ~0.74 by TB-mBJ potential. The obtained results implies that Cs2InAgCl6 is a promising material for thermoelectric device applications.Comment: 19 pages. arXiv admin note: text overlap with arXiv:1801.0370

DFT based study on structural stability and transport properties of Sr3AsN: A potential thermoelectric material

Antiperovskite materials are well known for their high thermoelectric performance and gained huge research interest. Here, we report the structural stability and transport properties of Sr$_3$AsN from a precise first-principles study. The calculated equilibrium lattice parameters are in a good agreement with the available data. We find that Sr$_3$AsN is a mechanically, energetically and dynamically stable at ambient condition. Our calculated electronic structure indicates that it is a direct bandgap semiconductor, with a value ~1.2 eV. Sr-4d and N-2p orbitals mainly formulate the direct bandgap. This antiperovskite possesses a high Seebeck coefficient. Although its lattice thermal conductivity is comparatively low, electronic thermal conductivity is very high. The calculated maximum TE figure of merit is 0.75 at 700 K, indicating that it is a potential material for thermoelectric applications.Comment: 22 pages, 11 figure

Infant mortality and the decline of fertility in Bangladesh

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Flood frequency analysis : a case study for the Brisbane River catchment

Flood is the most common natural hazards around the globe that has notable negative effects on humans and environment. One of the examples is Queensland 2010-2011 flood, which is considered as one of the severest floods in recent history of Australia that claimed 31 human lives and caused direct damage costing over $5 billion. To reduce the flood damage, it is vital to understand properly the causes of major floods, their magnitudes and frequencies. Estimation of the magnitude of possible future floods (also called design floods) is an important task in hydrology. Most of the hydraulic structures and flood management tasks require an accurate estimation of design floods. For this reason, estimation of design flood is still an area of great interest in flood hydrology and is being researched worldwide. Frequent devastating floods in Australia have drawn attention at the state and national levels for more accurate flood estimation with reduced uncertainty. Many design floods estimation methods are being practiced around the world. This study focuses on the widely used design flood estimate techniques called “flood frequency analysis (FFA)”. The main objective of FFA is to find probability distribution model that best fits the measured flood data series at a given site. Although Australian Rainfall and Runoff ARR (Australian Rainfall and Runoff), 1987 recommended Log Pearson type III probability distribution to use for FFA in Australia, in ARR 2019, no specific probability distribution is recommended. There has been limited guideline in Australia to select probability distribution models for flood frequency analysis. Also, many users have limited understanding on the uncertainties involved in design flood estimates based on a given probability distribution. This study is devoted to fill this research gap and examines the selection of the most appropriate probability distributions and associated uncertainty in FFA. This study focuses on the Brisbane River catchment of Queensland, one of the worst flood-prone areas in Australia. In this research, a total of 26 streamflow gauging stations are selected from the Brisbane River catchment, with the lengths of recorded annual maximum flood (AMF) data series in the range of 20 years to 91 years

First-principles prediction of phonon-mediated superconductivity in XBC (X= Mg, Ca, Sr, Ba)

From first-principles calculations, we predict four new intercalated hexagonal $X$BC ($X$=Mg, Ca, Sr, Ba) compounds to be dynamically stable and phonon-mediated superconductors. These compounds form a LiBC like structure but are metallic. The calculated superconducting critical temperature, $T{_c}$, of MgBC is 51 K. The strong attractive interaction between $\sigma$-bonding electrons and the B${_{1g}}$ phonon mode gives rise to a larger electron-phonon coupling constant (1.135) and hence high $T_c$; notably, higher than that of MgB$_2$. The other compounds have a low superconducting critical temperature (4-17 K) due to the interaction between $\sigma$-bonding electrons and low energy phonons (E${_{2u}}$ modes). Due to their energetic and dynamic stability, we envisage that these compounds can be synthesized experimentally.Comment: 7 pages, 6 figure

First-principles prediction of extraordinary thermoelectric efficiency in superionic Li2SnX3(X=S,Se)

Thermoelectric materials create an electric potential when subject to a temperature gradient and vice versa hence they can be used to harvest waste heat into electricity and in thermal management applications. However, finding highly efficient thermoelectrics with high figures of merit, zT$\geq$1, is very challenging because the combination of high power factor and low thermal conductivity is rare in materials. Here, we use first-principles methods to analyze the thermoelectric properties of Li$_2$Sn$X_3$ ($X$=S,Se), a recently synthesized class of lithium fast-ion conductors presenting high thermal stability. In p-type Li$_2$Sn$X_3$, we estimate highly flat electronic valence bands that render high Seebeck coefficients exceeding 400 ${\mu}$VK$^{-1}$ at 700K. In n-type Li$_2$Sn$X_3$, the electronic conduction bands are slightly dispersive however the accompanying weak electron-acoustic phonon scattering induces high electrical conductivity. The combination of high Seebeck coefficient and electrical conductivity gives rise to high power factors, reaching a maximum of 4 mWm$^{-1}$K$^{-2}$ in p-type Li$_2$SnS$_3$ and 8 mWm$^{-1}$K$^{-2}$ in n-type Li$_2$SnSe$_3$ at 300 K. Likewise, the thermal conductivity in Li$_2$Sn$X_3$ is low as compared to conventional thermoelectric materials, 2-5 Wm$^{-1}$K$^{-1}$ at room temperature. As a result, we estimate a maximum zT = 1.05 in p-type Li$_2$SnS$_3$ at 700 K and an extraordinary 3.07 (1.5) in n-type Li$_2$SnSe$_3$ at the same temperature (300 K). Our findings of huge zT in Li$_2$Sn$X_3$ suggest that lithium fast-ion conductors, typically employed as electrolytes in solid-state batteries, hold exceptional promise as thermoelectric materials.Comment: 21 Page

Forecasting Volatility of Quality Assessment for High Energy Biscuits (HEB) with ARCH Model

The High Energy Biscuits (HEB) products-310 data were collected from Institute of Food Science and Technology (IFST), Bangladesh Council of Scientific and Industrial Research (BCSIR), Dhaka over the year 2007 to 2012 in the method of single stage cluster sampling. Volatility as a measure of risk plays an important role in many qualitative decisions in such a situations. The main purpose of this study is to examine the volatility of the quality of High Energy Biscuits (HEB) products and its related stylized facts using Auto-regressive Conditional Heteoskedastic (ARCH) models. The physiochemical analysis data was used to study the volatility in the quality of High Energy Biscuits (HEB) products over a 5 years period. The adequacy of selected model tested using Auto-regressive Conditional Heteoskedastic-Lagrange Multiplier (ARCH-LM) test. The study concludes that ARCH model explains volatility of the quality of High Energy Biscuits (HEB) products. Keywords: Volatility; ARCH models; ARCH-LM test; Quality of High Energy Biscuits (HEB) products; Single stage cluster sampling; Institute of Food Science and Technology (IFST). DOI: 10.7176/FSQM/121-05 Publication date: January 31st 202

Simultaneous heat and mass transfer on oscillatory free convection boundary layer flow

The problem of simultaneous heat and mass transfer in two-dimensional free convection from a semi-infinite vertical flat plate is investigated. An integral method is used to find a solution for zero wall velocity and for a mass transfer velocity at the wall with small-amplitude oscillatory wall temperature. Low- and high-frequency solutions are developed separately and are discussed graphically with the effects of the parameters Gr (the Grashof number for heat transfer), Gc (the Grashof number for mass transfer) and Sc (the Schmidt number) for Pr = 0–71 representing aid at 20°C