Temperature Dependence Of RH Research Articles

Characteristics of Soil Respiration and Its Components of a Mixed Dipterocarp Forest in China

Background: Although numerous studies have been carried out in recent decades, soil respiration remains one of the less understood elements in global carbon budget research. Tropical forests store a considerable amount of carbon, and a well-established knowledge of the patterns, components, and controls of soil respiration in these forests will be crucial in global change research. Methods: Soil respiration was separated into two components using the trenching method. Each component was measured at multiple temporal scales and in different microhabitats. A commercial soil efflux system (Li8100/8150) was used to accomplish soil respiration monitoring. Four commonly used models were compared that described the temperature dependence of soil heterotrophic respiration using nonlinear statistics. Results and Conclusions: Trenching has a limited effect on soil temperature but considerably affects soil water content due to the exclusion of water loss via tree transpiration. Soil respiration decreased gradually from 8 to 4 μmol·m−2·s−1 6 days after trenching. Soil autotrophic (Ra) and heterotrophic respiration (Rh) have contrasting diel patterns and different responses to temperature. Rh was negatively correlated with temperature but positively correlated with relative humidity. Both Ra and Rh varied dramatically among microhabitats. The Q10 value of Rh derived using the Q10 model was 2.54. The Kirschbaum–O’Connell model, which implied a strong decrease of Q10 with temperature, worked best in describing temperature dependence of Rh. Heterotrophic respiration accounted for nearly half of the total soil efflux. We found an unexpected diurnal pattern in soil heterotrophic respiration which might be related to diurnal moisture dynamics. Temperature, but not soil moisture, was the major controller of seasonal variation of soil respiration in both autotrophic and heterotrophic components. From a statistical perspective, the best model to describe the temperature sensitivity of soil respiration was the Kirschbaum–O’Connell model. Soil respiration varied strongly among the microhabitats and played a crucial role in stand-level ecosystem carbon balance assessment.

Oxygen isotope exchange in praseodymium nickelate

Oxygen surface exchange kinetics and diffusion were studied in Pr2NiO4 + δ (PNO) by the isotope exchange method with gas phase equilibration in the temperature range of 600–800 °C and oxygen pressure range of 0.33–1.62 kPa. The oxygen heterogeneous exchange rate (rH), oxygen diffusion coefficient (D), rates of oxygen dissociative adsorption (ra), and oxygen incorporation (ri) were calculated along with the apparent activation energies of oxygen surface exchange and diffusion processes. The temperature dependence of rH was found to benon-linear in Arrhenius coordinates. The apparent activation energy changed from 1.4 ± 0.2 eV at T > 700 °C to 2.0 ± 0.1 eV. This might be attributed to the change in the rate-determining stage of oxygen exchange for Pr2NiO4 + δ at T ~ 700 °C, because of a shift in the ratio between ra and ri caused by the difference in their activation energies. Possible reasons for the observed changes in the rate-determining stage are discussed.

Quantum interference effects in [Co/Bi]nthin films

Magnetoconductivity (MC), Δσ(Β), and Hall coefficient, RH (B), measurements have been performed in polycrystalline thin films of Bi(15nm), Bi(10nm)/Co(1nm)/Bi(10nm) trilayer and [Co(0.7nm)/Bi(2nm)]10 multilayer, grown by magnetron scattering. The temperature dependence of RH (B) curves reveal the existence of a second conduction channel below 250K, that can be assigned to surface states. MC measurements between ±0.4T show at 5K an interplay between weak-antilocalization (WAL) in Bi and Bi/Co/Bi films and weal-localization (WL) in [Co/Bi]10 multilayer.

Superconductivity Modulated by Binary Doping in Nd<sub>1-x</sub>Ba<sub>x</sub>FeAsO<sub>1-2x</sub>F<sub>2x</sub>

Binary doping effect is studied for the Fe-based superconductors of Nd1-xBaxFeAsO1-2xF2x(x = 0.02, 0.05, 0.1, 0.15, 0.2). The X-ray diffractions show that the c-axis lattice constant decreases monotonously with the doping content, in contrast to the little change in the a-axis. Temperature dependences of electric resistivity and magnetic susceptibility reveal that the superconductivity for the studied system emerges at x = 0.1, and enhances together with Hc2(0) as the doping content x increases further. In case of x = 0.2, the superconducting critical temperature reaches as high as 50 K, which is the first demonstration of superconductivity with a high fluorine-doping induced by both electron and hole doping in this family. Negative Hall coefficient (RH) indicates that electron-type carriers are dominated in the present samples. The complicated temperature dependence of RH, is believed to arise from a multiband effect together with a complicated scattering, especially at the tem-perature near the TC.

Transport properties of neptunium superconductor NpPd5Al2

We measured the electrical resistivity in the current J||[100] and [001] and the Hall coefficient for the magnetic field H||[010] and [001]. The resistivity is anisotropic for the current direction. The Hall coefficient Rh is also extremely anisotropic, revealing that RH for H||[010] and [001] possesses a positive maximum at 55 K for H||[010], and a negative minimum at 25 K for H||[001], respectively. The temperature dependence of RH is well explained by the skew scattering processes at high temperatures.

The semiconductor–metal transition of liquid tellurium–arsenic mixtures

The Hall coefficients, RH, conductivity, σ, and the EXAFS spectra of liquid As–Te mixtures containing 0–40 at.% As have been measured up to 600°C. There are three regimes: I (semiconducting state), II (strong scattering state) and III (metallic state) in the temperature dependence of RH. From EXAFS measurement it is found that the As–Te bonds break with increasing temperature, which coincides with a rapid decrease of RH in regime II, and consequently the network structure of liquid As–Te mixtures is transformed into a chain like structure around 500°C. The structural transformation induces the transition from a semiconductor to metal.

Scaling behavior of the Hall coefficient of Si:P at the metal-insulator transition

Measurements of the Hall coefficient RH(T, B) of Si:P with P concentration N between 3.54 and 7.0·1018 cm−3 are reported for the temperature range 0.04 K ≤ T ≤ 4K and in magnetic fields up to 7 T. Even far above the metal-insulator transition (MIT), a sign change of the temperature coefficient similar to the behavior of the conductivity σ(T) in moderate fields is not observed in RH(T). Field and temperature dependence of RH both increase as the MIT (at the critical concentration Nc = 3.52 · 1018 cm−3) is approached. A careful extrapolation to T → 0 and B → 0 indicates that RH−1 scales to zero as RH−1 ∼| N − NcμH with μH = (0.44 ± 0.04) in agreement with previous results.

The low-field galvanomagnetic properties of dilute lead alloys

The field dependences of the Hall coefficient and the transverse magnetoresistance of dilute Pb-In, Pb-Sn and Pb-Bi alloys were measured in the lower field regions at liquid-helium temperatures. The low-field-Hall coefficient (RH) was always found to change in the negative direction with respect to the positive value of pure lead measured at room temperature: RH=-1.15*10-110 m3 C-1 for Pb-In, -0.55*10-10 m3 C-1for Pb-Sn and -0.20*10-10 m3 C-1 for Pb-Bi. This means that the electrons on the second-zone hole surface are more strongly scattered by these impurities than those on the third-zone electron surface. The temperature dependence of RH was also measured for some selected specimens. The results were analysed on the basis of the electron charge distribution in real space computed from the 8 OPW wave function together with the semi-empirical two-carrier group formulae.

Concentration and temperature dependence of the Hall resistivity in FeZr glasses

Hall resistivity measurements are reported for amorphous FexZr1−x alloys near the critical concentration, xc =0.37, for the onset of ferromagnetism. At room temperature, the Hall coefficient RH is positive and grows systematically with Fe concentration as xc is approached from the paramagnetic side. The temperature dependence of RH follows a Curie-like variation whose coefficient diverges at xc. In the ferromagnetic regime, the spontaneous Hall coefficient is extremely large, leading to the conclusion that the side-jump mechanism is responsible for the magnetic contribution. Furthermore, the dependence of RH on susceptibility in the two regimes suggests that this same side-jump term is also responsible for the positive Hall coefficient in the nonmagnetic glasses.

Low-temperature hall coefficient for ?-U and some dilute U-Mo solid solutions

Measurements of the Hall coefficient R H have been made as a function of temperature between 4 and 100 K for single-crystal and polycrystal α-U and α-phase U-Mo alloys containing 0.6, 3, and 7 at % Mo. A strong temperature dependence for R H, leading to a change in its sign for the single-crystal sample, is found for the uranium below 45 K. Alloying with Mo reduces the temperature dependence of R H and that for the 7 at % Mo alloy is temperature independent. The anomalous transport behavior for the uranium is linked with the anomalies which have been observed in many of the physical properties of uranium around 45 K, and the possibility that these are due to a change in Fermi surface topology resulting from a periodic lattice distortion associated with charge density wave formation is discussed.