Change of Acoustic Emission Characteristics during Temperature Induced Transition from Twinning to Dislocation Slip under Compression in Polycrystalline SN

In this study, acoustic emission (AE) measurements on polycrystalline tin as a function of temperature at different driving rates under compression were carried out. It is shown that there is a definite difference between the acoustic emission characteristics belonging to twinning (low temperatures) as well as to dislocation slip (high temperatures). The stress averaged values of the exponents of the energy probability density functions decreased from = 1.45 ± 0.05 (−60 °C) to = 1.20 ± 0.15 (50 °C) at a driving rate of , and the total acoustic energy decreased by three orders of magnitude with increasing temperature. In addition, the exponent γ in the scaling relation SAE~DAEγ (SAE is the area and DAEis the duration) also shows similar temperature dependence (changing from γ = 1.78 ± 0.08 to γ = 1.35 ± 0.05), illustrating that the avalanche statistics belong to two different microscopic deformation mechanisms. The power law scaling relations were also analyzed, taking into account that the detected signal is always the convolution of the source signal and the transfer function of the system. It was obtained that approximate values of the power exponents can be obtained from the parts of the above functions, belonging to large values of parameters. At short duration times, the attenuation effect of the AE detection system dominates the time dependence, from which the characteristic attenuation time, τa, was determined as τa≅ 70 μs.

Long-Term Statistics of Riming in Nonconvective Clouds Derived from Ground-Based Doppler Cloud Radar Observations

Riming is an efficient process of converting liquid cloud water into ice and plays an important role in the formation of precipitation in cold clouds. Due to the rapid increase in ice particle mass, riming enhances the particle’s terminal velocity, which can be detected by ground-based vertically pointing cloud radars if the effect of vertical air motions can be sufficiently mitigated. In our study, we first revisit a previously published approach to relate the radar mean Doppler velocity (MDV) to rime mass fraction (FR) using a large ground-based in situ dataset. This relation is then applied to multiyear datasets of cloud radar observations collected at four European sites covering polluted central European, clean maritime, and Arctic climatic conditions. We find that riming occurs in 1%–8% of the nonconvective ice containing clouds with median FR between 0.5 and 0.6. Both the frequency of riming and FR reveal relatively small variations for different seasons. In contrast to previous studies, which suggested enhanced riming for clean environments, our statistics indicate the opposite; however, the differences between the locations are overall small. We find a very strong relation between the frequency of riming and temperature. While riming is rare at temperatures lower than −12°C, it strongly increases toward 0°C. Previous studies found a very similar temperature dependence for the amount and droplet size of supercooled liquid water, which might be closely connected to the riming signature found in this study. In contrast to riming frequency, we find almost no temperature dependence for FR.

Structural, Mechanical, and Dynamical Properties of Amorphous Li2CO3 from Molecular Dynamics Simulations

Structural, mechanical, and transport properties of amorphous Li2CO3 were studied using molecular dynamics (MD) simulations and a hybrid MD-Monte Carlo (MC) scheme. A many-body polarizable force field (APPLE&P) was employed in all simulations. Dynamic and mechanical properties of Dilithium carbonate, Li2CO3, in amorphous liquid and glassy phases were calculated over a wide temperature range. At higher temperatures, both anion and cation diffusion coefficients showed similar temperature dependence. However, below the glass transition temperature (T < 450 K) the anions formed a glassy matrix, while Li+ continued to be mobile, showing decoupling of cation and anion diffusion. The conductivity of Li+ at room temperature was estimated to be on the order of 10−6 S/cm. Mechanical analysis revealed that at room temperature the amorphous phase had a shear modulus of about 8 GPa, which was high enough to suppress Li metal dendrite growth on an electrode surface.

Seasonal variation of secondary organic aerosol in Nam Co, Central Tibetan Plateau

Secondary organic aerosol (SOA) affects the earth's radiation balance and global climate. High-elevation areas are sensitive to global climate change. However, at present, SOA origins and seasonal variations are understudied in remote high-elevation areas. In this study, particulate samples were collected from July 2012 to July 2013 at the remote Nam Co (NC) site, Central Tibetan Plateau and analyzed for SOA tracers from biogenic (isoprene, monoterpenes and β-caryophyllene) and anthropogenic (aromatics) precursors. Among these compounds, isoprene SOA (SOAI) tracers represented the majority (26.6 ± 44.2 ng m−3), followed by monoterpene SOA (SOAM) tracers (0.97 ± 0.57 ng m−3), aromatic SOA (SOAA) tracer (2,3-dihydroxy-4-oxopentanoic acid, DHOPA, 0.25 ± 0.18 ng m−3) and β-caryophyllene SOA tracer (β-caryophyllenic acid, 0.09 ± 0.10 ng m−3). SOAI tracers exhibited high concentrations in the summer and low levels in the winter. The similar temperature dependence of SOAI tracers and isoprene emission suggested that the seasonal variation of SOAI at the NC site was mainly influenced by isoprene emission. The ratio of high-NOx to low-NOx products of isoprene (2-methylglyceric acid to 2-methyltetrols) was the highest in the winter and the lowest in the summer, due to the influence of temperature and relative humidity. The seasonal variation of SOAM tracers was impacted by monoterpenes emission and tracers partitioning. The similar temperature dependence of SOAM tracers and monoterpenes emission was only observed during winter to spring. SOAM tracer levels did not elevate with increased temperature in the summer, probably resulting from the counteraction of temperature effects on gas/particle partitioning and monoterpenes emission. The concentrations of DHOPA were 1–2 orders of magnitude lower than those reported in the urban regions of the world. Due to the transport of air pollutants from the adjacent Bangladesh and the eastern India, DHOPA presented relatively higher levels in the summer. In the winter when air masses mainly came from the northwestern India, mass fractions of DHOPA in total tracers increased, although its concentrations declined. The SOA-tracer method was applied to estimated secondary organic carbon (SOC) from these four precursors. The annual average of SOC was 0.22 ± 0.29 μg C m−3, with the biogenic SOC (sum of isoprene, monoterpenes and β-caryophyllene) accounting for 75%. In the summer, isoprene was the major precursor with its SOC contributions of 81%. In the winter when the emission of biogenic precursors largely dropped, the contributions of aromatic SOC increased. Our study implies that anthropogenic pollutants emitted in the Indian subcontinent could transport to the TP and have impact on SOC over the remote NC.

Epoxidised Natural Rubber Based Polymer Electrolyte Systems for Electrochemical Device Applications

Epoxidized Natural Rubber (ENR50), lithium imide salt, [LiN(SO2CF3)2] with and without solvent were prepared by solvent casting technique. Non solvated polymer electrolyte showed modest ionic conductivity at ambient temperature. To further enhance ionic conductivity a mixed solvent of ethylene carbonate/propylene carbonate was added into the system. Thermal characterization showed that single transition glass temperature (Tg) for all systems and amorphous phase is dominant. DSC traces of non solvated samples have shown Tg values increased whereas addition of mixed EC/PC solvent into the electrolyte system reduced their values respectively. Impedance measurements for the solvated epoxidized natural rubber (ENR) based electrolyte systems have shown optimal ionic conductivity 10-4 S cm-1 whereas 10-6 S cm-1 for a non solvated one. ENR electrolyte systems showed similar temperature dependence, which suggests that the conductivity is thermally activated.

A COMPARABLE STUDY ON STRUCTURAL AND OPTICAL PROPERTIES OF Cu2ZnSnS4 AND Cu2ZnSnSe4 NANOCRYSTALLINES

In this study, single-kesterite-phase Cu 2 ZnSnS 4 (CZTS) and Cu 2 ZnSnSe 4 (CZTSe) nanocrystallines have been synthesized by a simple solvothermal route. Scanning electron microscopy (SEM), X-ray diffraction (XRD), ultraviolet-visible (UV-vis) absorbance and Raman scattering spectroscopy were used to characterize the optical and micro-structure properties of the as-synthesized samples. The bandgap of CZTS could be tuned in a large range by incorporating a few Se atoms. Both the CZTS and CZTSe exhibited the similar temperature dependence of the Raman "A" modes, including a monotonic redshift in peak position and an irregular variation in peak linewidth. Such a behavior might be due to the cumulative effect of thermal expansion and small crystalline sizes.

MAGNETORESISTANCE IN TOPOLOGICAL INSULATOR MnxBi2-xSe3 CRYSTALS

The transport properties of magnetic-atoms doped Mn x Bi 2-x Se 3 single crystals are studied. The samples exhibit approximately similar temperature dependence of resistivity behavior under various applied magnetic fields from zero to 9 T. Magnetoresistance (MR) is modified significantly by high concentration of Mn dopants. The scatterings mechanism between the magnetic impurities and electrons plays an important role in both transport properties and MR effect.

Probing the Locally Generated Even and Odd Order Nonlinearity in Y–Ba–Cu–O and Tl–Ba–Ca–Cu–O (2212) Microwave Resonators Around <img src="/images/tex/19586.gif" alt="T_{\rm C}">

Spatial scanning of the synchronously generated second- and third-order intermodulation distortion in superconducting resonators uncovers local nonlinearity hot spots, and possible time reversal symmetry breaking, using a simple probe fashioned from coaxial cable. It is clear that even and odd order nonlinearity in these samples do not share the same physical origins, because their temperature and static magnetic field dependences are quite different. 2nd order intermodulation distortion remains strong in these measurements as the temperature continues to drop belowTCto 77 K even though the 3rd order peaks nearTCand becomes smaller at lower temperature as predicted by the nonlinear Meissner effect. Both YBa2Cu3O7and Tl2Ba2CaCu2O8resonators of the same structure exhibit similar temperature dependence in the second order with second order remaining high at lower temperature. The YBa2Cu3O7sample has lower third-order intermodulation distortion with a pronounced peak atTC.

Thermoelectric properties of doped and undoped mixed phase hydrogenated amorphous/nanocrystalline silicon thin films

The Seebeck coefficient and dark conductivity for undoped, and n-type doped thin film hydrogenated amorphous silicon (a-Si:H), and mixed-phase films with silicon nanocrystalline inclusions (a/nc-Si:H) are reported. For both undoped a-Si:H and undoped a/nc-Si:H films, the dark conductivity is enhanced by the addition of silicon nanocrystals. The thermopower of the undoped a/nc-Si:H has a lower Seebeck coefficient, and similar temperature dependence, to that observed for undoped a-Si:H. In contrast, the addition of nanoparticles in doped a/nc-Si:H thin films leads to a negative Seebeck coefficient (consistent with n-type doping) with a positive temperature dependence, that is, the Seebeck coefficient becomes larger at higher temperatures. The temperature dependence of the thermopower of the doped a/nc-Si:H is similar to that observed in unhydrogenated a-Si grown by sputtering or following high-temperature annealing of a-Si:H, suggesting that charge transport may occur via hopping in these materials.

Electrical Properties of β-FeSi2 Thin Films on Insulating Substrates

ABSTRACTIron silicide thin films were prepared on insulating substrates using RF magnetron sputtering method. Amorphous, polycrystalline and epitaxial β-FeSi2 were obtained on MgO(001), Al2O3(110) and Al2O3(001) substrates, respectively. Electrical conductivities of these films showed similar temperature dependence. Intrinsic band conduction and hopping conduction mechanism were predominant above and below 600K, respectively. The localized ordering in the polycrystalline and epitaxial films that controled the movement of carriers were as low as in the amorphous film. For the epitaxial β-FeSi2 film, electrical conductivity below 600K were affected by atomic ratio of silicon to iron (Si/Fe) in the films, because the localized ordering in the films decreased as Si/Fe atomic ratio decreased.