Performance of ocean hydrate-based engine for ocean thermal energy conversion system

Papers presented to the 11th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 20-23 July 2015.The performance of a theoretical thermodynamic cycle using clathrate hydrate as the working fluid (later we call it the hydrate cycle) is analyzed with emphasis on the application to “Ocean Thermal Energy Conversion (OTEC)” after organizing the processes in this cycle thermodynamically. OTEC is an electric power generation system utilizing a temperature difference of about 15 K to 25 K between the top and the bottom layers in the ocean. The organic Rankine cycle with fluorocarbons, ammonia or propane is considered to be one of the most effective methods for OTEC. There is, however, a growing tendency to avoid fluorocarbons in industries since they are powerful greenhouse gases. Ammonia is also improper because of not only its corrosion to metals but being a source of acid rain. This research proposes that the hydrate cycle may be an alternative to the above cycles for OTEC. In this cycle hydrate is formed at low temperature and dissociated at high temperature. Energy is generated through the alternate repetition of hydrate formation and dissociation. Various guest substances, neither corrosive nor influential in the environment like noble gases can form hydrates. When the hydrate cycle is operated with the high and low reservoirs at 280 K and 295 K, assuming the use in a temperate climate, the thermal efficiency of the hydrate cycle is 2.15 % for Kr hydrate and 2.58 % for Xe hydrate, which are comparable to that of the organic Rankine cycle: 2.24 % for CH2F2, 3.31 % for C2H3F3, 3.34 % for C3H8. These results indicate the prospects of the hydrate cycle for OTEC as more environment-friendly than the organic Rankine cycle.am201

Rate- and State-Dependent Friction Law and Statistical Properties of Earthquakes

In order to clarify how the statistical properties of earthquakes depend on the constitutive law characterizing the stick-slip dynamics, we make an extensive numerical simulation of the one-dimensional spring-block model with the rate- and state-dependent friction law. Both the magnitude distribution and the recurrence-time distribution are studied with varying the constitutive parameters characterizing the model. While a continuous spectrum of seismic events from smaller to larger magnitudes is obtained, earthquakes described by this model turn out to possess pronounced ``characteristic'' features.Comment: Minor revisions are made in the text and in the figures. Accepted for publication in Europhys. Letter

Superconducting and structural properties of the type-I superconductor PdTe₂ under high pressure

The transition metal dichalcogenide PdTe$_2$ has attractive features based on its classification as a type-II Dirac semimetal and the occurrence of type-I superconductivity, providing a platform for discussion of a topological superconductor. Our recent work revealed that type-I superconductivity persists up to pressures of $\sim2.5$ GPa and the superconducting transition temperature $T_{\rm c}$ reaches a maximum at around 1 GPa, which is inconsistent with the theoretical prediction. To understand its non-monotonic variation and investigate superconductivity at higher pressures, we performed structural analysis by x-ray diffraction at room temperature below 8 GPa and electrical resistivity measurements at low temperatures from 1 to 8 GPa. With regard to the superconductivity beyond 1 GPa, the monotonic decrease in $T_{\rm c}$ is reproduced without any noticeable anomalies; $T_{\rm c}$ changes from 1.8 K at 1 GPa to 0.82 K at 5.5 GPa with $dT_{\rm c}/dP\sim-0.22$ K/GPa. The crystal structure with spacegroup $P$\={3}$m$1 is stable in the pressure range we examined. On the other hand, the normalized pressure-strain analysis (finite strain analysis) indicates that the compressibility changes around 1 GPa, suggesting that a Lifshitz transition occurs. We here discuss the effect of pressure on the superconducting and structural properties based on the comparison of these experimental results

Asymptotic displaced charge round impurities in metal crystals with and without surfaces

The displaced charge Δρ at distance r from a localized perturbation V in an inhomogeneous degenerate electron gas may be written in a linear response framework as Δϱ(r) = ∝V(r′)F(rr′)dr′. The response function F is expressed in terms of the Green function of the unperturbed system and attention is then focussed on two cases: * 1. o| * 2. (i) A perfect periodic metal crystal, perturbed by V. * 3. (ii) A metal lattice with a surface in which V is embedded. A full discussion is given of the influence of Fermi surface topology on the anisotropy of Δϱ in the asymptotic region far from the defect. Provided V(r) has certain reasonable properties, it is shown that Δϱ ~ r−nx oscillatory function. For the bulk metal, n can take values between 1 and 5 in different directions for Fermi surfaces with particular topologies. Possible experiments which bear on this anisotropy are briefly referred to. For a planar surface, the displaced charge is shorter range for V embedded in the surface than for the bulk metal, in most, but not all cases. For a closed Fermi surface with non-zero curvature, n = 5 for the parallel configuration

Dynamics of earthquake nucleation process represented by the Burridge-Knopoff model

Dynamics of earthquake nucleation process is studied on the basis of the one-dimensional Burridge-Knopoff (BK) model obeying the rate- and state-dependent friction (RSF) law. We investigate the properties of the model at each stage of the nucleation process, including the quasi-static initial phase, the unstable acceleration phase and the high-speed rupture phase or a mainshock. Two kinds of nucleation lengths L_sc and L_c are identified and investigated. The nucleation length L_sc and the initial phase exist only for a weak frictional instability regime, while the nucleation length L_c and the acceleration phase exist for both weak and strong instability regimes. Both L_sc and L_c are found to be determined by the model parameters, the frictional weakening parameter and the elastic stiffness parameter, hardly dependent on the size of an ensuing mainshock. The sliding velocity is extremely slow in the initial phase up to L_sc, of order the pulling speed of the plate, while it reaches a detectable level at a certain stage of the acceleration phase. The continuum limits of the results are discussed. The continuum limit of the BK model lies in the weak frictional instability regime so that a mature homogeneous fault under the RSF law always accompanies the quasi-static nucleation process. Duration times of each stage of the nucleation process are examined. The relation to the elastic continuum model and implications to real seismicity are discussed.Comment: Title changed. Changes mainly in abstract and in section 1. To appear in European Physical Journal

An Excellent Monitoring System for Surface Ubiquitination-Induced Internalization in Mammals

Background. At present, it is difficult to visualize the internalization of surface receptors induced by ubiquitination that is taken place at the plasma membrane in mammals. This problem makes it difficult to reveal molecular basis for ubiquitinationmediated internalization in mammals. Methodology/Principle Findings. In order to overcome it, we have generated T-REx-c-MIR, a novel mammalian Tet-on B cell line using a constitutively active E3 ubiquitin ligase, c-MIR, and its artificial target molecule. By applying the surface biotinylation method to T-REx-c-MIR, we succeeded to monitor the fate of surface target molecules after initiation of ubiquitination process by doxycycline (Dox)-induced c-MIR expression. Target molecules that preexisted at the plasma membrane before induction of c-MIR expression were oligo-ubiquitinated and degraded by Dox-induced c-MIR expression. Dox-induced c-MIR expression initiated rapid internalization of surface target molecules, and blockage of the internalization induced the accumulation of the surface target molecules that were newly ubiquitinated by c-MIR. Inhibition of the surface ubiquitination by down-regulating ubiquitin conjugating enzyme E2 impaired the internalization of target molecules. Finally, a complex of c-MIR and target molecule was detected at the plasma membrane. Conclusions/ Significances. These results demonstrate that in T-REx-c-MIR, surface target molecule is ubiquitinated at the plasma membrane and followed by being internalized from the plasma membrane. Thus, T-REx-c-MIR is a useful experimental tool t