Realistic Temperature Dependence Research Articles

Temperature dependence of carrier scattering in polycrystalline bismuth

The dependence of the scattering process on temperatures ranging from 50 to 300 K was comprehensively investigated by measuring five transport coefficients (resistivity, magnetoresistivity, Seebeck coefficient, Hall coefficient, and Nernst coefficient) using polycrystalline bulk bismuth. The values of five physical properties (carrier density, electron and hole mobilities, and electron and hole Fermi energies) were calculated assuming that carrier scattering ranged from acoustic deformation potential scattering to ionized impurity scattering. The accompanying mean-free paths of carriers were also evaluated using the calculated Fermi energy and the effective mass tensor. The mean-free path and grain size (typically several micrometers) obtained from electron backscattered diffraction helped narrow the distribution range of the different scattering processes. Thus, the physical properties, including temperature dependence of the scattering processes, were recalculated, and realistic temperature dependence of the electron mobility was assumed. Quantitative and qualitative analyses showed that near room temperature, acoustic deformation potential scattering dominated, which changed to ionized impurity scattering when the estimated mean-free path exceeded 1 μm. This indicated that the scattering process of polycrystalline bulk bismuth depends on the grain size when the measurement results of the Nernst coefficient related to the scattering process are directly used. The bandgap energy of bismuth was also calculated, and the temperature dependence of the scattering process was estimated. The results showed that the temperature dependence tendency of bandgap energy is similar to that described in the literature. Finally, this study provides the temperature dependence of the physical properties of polycrystalline bismuth.

Second Breakdown and Robustness of Vertical and Lateral GaN Power Field‐Effect Transistors

Robustness of GaN power field‐effect transistors, including the vertical UMOSFET, vertical DMOSFET, and lateral p‐AlGaN gate HEMT is studied by analyzing their safe operating areas (SOA) using finite‐element‐analysis device simulation. At off‐state gate voltages, the devices are forced into high‐voltage, high‐current avalanche breakdown. Assuming isothermal conditions at 300 K, the simulated DMOSFET SOA exhibits high robustness, while the UMOSFET and the p‐AlGaN gate HEMT experiences current snapback. The simulated robustness of both the DMOSFET and the UMOSFET degrades when realistic temperature dependence is included in the non‐isothermal case, with current filamentation in high dissipation areas, leading to a more pronounced current snapback.

Rare temperature histories and cirrus ice number density in a parcel and a one-dimensional model

Abstract. A parcel and a one-dimensional model are used to investigate the temperature dependence of ice crystal number density. The number of ice crystals initially formed in a cold cirrus cloud is very sensitive to the nucleation mechanism and the detailed history of cooling rates during nucleation. A possible small spread in the homogeneous freezing threshold due to varying particle composition is identified as a sensitive nucleation parameter. In a parcel model, the slow growth rate of ice crystals at low temperatures inherently leads to a strong increase in ice number density at low temperatures. This temperature dependence is not observed. The model temperature dependence occurs for a wide range of assumptions and for either homogeneous or, less strongly, heterogeneous freezing. However, the parcel model also shows that random temperature fluctuations result in an extremely wide range of ice number densities. A one-dimensional model is used to show that the rare temperature trajectories resulting in the lowest number densities are disproportionately important. Low number density ice crystals sediment and influence a large volume of air. When such fall streaks are included, the ice number becomes less sensitive to the details of nucleation than it is in a parcel model. The one-dimensional simulations have a more realistic temperature dependence than the parcel mode. The one-dimensional model also produces layers with vertical dimensions of meters even if the temperature forcing has a much broader vertical wavelength. Unlike warm clouds, cirrus clouds are frequently surrounded by supersaturated air. Sedimentation through supersaturated air increases the importance of any process that produces small numbers of ice crystals. This paper emphasizes the relatively rare temperature trajectories that produce the fewest crystals. Other processes are heterogeneous nucleation, sedimentation from the very bottom of clouds, annealing of disordered to hexagonal ice, and entrainment.

Towards Subdaily Rainfall Disaggregation via Clausius–Clapeyron

AbstractTwo lines of research are combined in this study: first, the development of tools for the temporal disaggregation of precipitation, and second, some newer results on the exponential scaling of heavy short-term precipitation with temperature, roughly following the Clausius–Clapeyron (CC) relation. Having no extra temperature dependence, the traditional disaggregation schemes are shown to lack the crucial CC-type temperature dependence. The authors introduce a proof-of-concept adjustment of an existing disaggregation tool, the multiplicative cascade model of Olsson, and show that, in principal, it is possible to include temperature dependence in the disaggregation step, resulting in a fairly realistic temperature dependence of the CC type. They conclude by outlining the main calibration steps necessary to develop a full-fledged CC disaggregation scheme and discuss possible applications.

The H<sub>2</sub>O-O<sub>2</sub> water vapour complex in the Earth's atmosphere

Abstract. Until recently, abundance estimates for bound molecular complexes have been affected by uncertainties of a factor 10–100. This is due to the difficulty of accurately obtaining the equilibrium constant, either from laboratory experiments or by statistical thermodynamic calculations. In this paper, we firstly present laboratory experiments that we performed in order to determine the molecular structure of H2O-O2. We also derive global abundance estimates for H2O-O2 in the Earth's atmosphere. The equilibrium constant Kp evaluated using the "anharmonic oscillator approach" (AHOA) (Sabu et al., 2005) was employed: the AHOA explains well the structure of the complex obtained by the present experiment. The Kp calculated by this method shows a realistic temperature dependence. We used this Kp to derive global abundance estimates for H2O-O2 in the Earth's atmosphere. The distribution of H2-O2 follows that of water vapour in the troposphere and seems inversely proportional to temperature in the lower stratosphere. Preliminary estimates at the surface show amount of H2O-O2 is comparable to CO or N2O, ranking water vapour complexes among the ten most abundant species in the boundary layer.

Temperature Dependence of a Kelvin Model for Binary Nucleation

The temperature dependence of binary nucleation rates was studied using several different models for the cluster evaporation rates. The evaporation rates were found using the detailed balance relations in combination with three different models for the constrained equilibrium cluster concentrations: the classical Reiss model, the self-consistent classical model of Wilemski and Wyslouzil, and the new Kelvin model. The latter two models are modifications of the classical liquid droplet expression for the equilibrium cluster concentrations. The steady state binary kinetics equations were numerically solved using the technique of matrix inversion by patitioning. Numerous test calculations were made for the ideal ethanol−hexanol system. We found that the Kelvin model gave the most realistic temperature dependence of the three models examined. An analytical rate expression that accurately reproduces the numerical results is also presented.

A geometric and analytic approach to the process of vitrification. II. Kinetic treatment

The processes of evolution of the frozen non-equilibrium structure of a glass to the equilibrium state of an undercooled liquid are considered in terms of the thermodynamics of irreversible processes. An improved rate equation is derived which accounts for the non-symmetric course of the thermodynamic driving force of the stabilization process as well as for possible memory effects. An atomistic model of a simple single-component vitrifying liquid is employed in order to establish a realistic temperature dependence of the structural parameter, ξ, and of the time of molecular relaxation, τ( T). By using simple analytic considerations and geometric concepts, memory effects in the kinetics of vitrification are demonstrated and expressions for the kinetic stability of superheated and supercooled glasses are derived. An extended definition of the vitreous state, including supercooled and superheated glasses, is given.

A Mössbauer effect study of the electronic and structural properties of Fe9(PO4)O8

Fe9(PO4)O8 is a mixed valence compound with both layers of (FeO)6, which are similar to those in stoichiometric wustite, FeO, and layers of Fe3PO6, which are similar to those found in anhydrous iron(III) phosphate, FePO4. A detailed Mossbauer effect study between 232 and 850 K of the electronic and structural properties of Fe9(PO4)O8 has been undertaken for comparison purposes and to study any valence averaging electron delocalization or exchange that may be present. An earlier single crystal X-ray study has revealed that Fe9(PO4)O8 crystallizes with five distinct iron sites in the ratio of 1∶1∶2∶4∶1. The differently distorted octahedral Fe(1), Fe(3), and Fe(4) sites contain divalent iron, the tetrahedral Fe(5) site contains divalent iron, and the octahedral Fe(2) site contains trivalent iron. Because of the variety of iron sites, the paramagnetic Mossbauer spectra of Fe9(PO4)O8 are complex and exhibit many partially resolved lines. The logarithm of the Mossbauer spectral absorption area and the median isomer shift vary linearly with temperature and yield an effective Mossbauer temperature of 300 K for Fe9(PO4)O8. The temperature dependence of the median isomer shift indicates electron delocalization into an unspecified conduction band above 630 K. The differing site degeneracies, site symmetries, and site valencies make it possible to fit the Mossbauer spectra of Fe9(PO4)O8 with two different models, both of which yield a realistic temperature dependence of the hyperfine parameters, but which lead to different conclusions about the presence of valence averaging electron exchange. Hence, the Mossbauer spectra can not, unequivocally, demonstrate the presence of valence averaging in Fe9(PO4)O8. However, the spectra do indicate the presence of structural changes, both above and below 295 K, which are consistent with a monoclinic space group as suggested by the presence of the weak superlattice reflections reported earlier. The relative component spectral areas indicate, in agreement with the relative Wigner-Seitz cell volumes, that the iron(III) on the Fe(2) site has a relatively low recoil-free fraction, whereas the six-coordinate iron(II) on the Fe(1) site has a relatively high recoil-free fraction.