Derivation of exact master equation with stochastic description: Dissipative harmonic oscillator

A systematic procedure for deriving the master equation of a dissipative system is reported in the framework of stochastic description. For the Caldeira-Leggett model of the harmonic-oscillator bath, a detailed and elementary derivation of the bath-induced stochastic field is presented. The dynamics of the system is thereby fully described by a stochastic differential equation and the desired master equation would be acquired with statistical averaging. It is shown that the existence of a closed-form master equation depends on the specificity of the system as well as the feature of the dissipation characterized by the spectral density function. For a dissipative harmonic oscillator it is observed that the correlation between the stochastic field due to the bath and the system can be decoupled and the master equation naturally comes out. Such an equation possesses the Lindblad form in which time dependent coefficients are determined by a set of integral equations. It is proved that the obtained master equation is equivalent to the well-known Hu-Paz-Zhang equation based on the path integral technique. The procedure is also used to obtain the master equation of a dissipative harmonic oscillator in time-dependent fields.Comment: 24page

Fatigue resistant lead-free multilayer ceramic capacitors with ultrahigh energy density

The critical role of electrical homogeneity in optimising electric-field breakdown strength (BDS) and energy storage in high energy density (0.7 − x)BiFeO3–0.3BaTiO3–xBi(Li0.5Nb0.5)O3 (BF–BT–xBLN) lead-free capacitors is demonstrated. The high BDS for bulk ceramics and multilayers (dielectric layer thickness ∼ 8 μm) of ∼260 and ∼950 kV cm−1, respectively, gives rise to record-performance of recoverable energy density, Wrec = 13.8 J cm−3 and efficiency, η = 81%. Under an electric field of 400 kV cm−1, multilayers are temperature stable up to 100 °C, frequency independent in the range 10−2 to 102 Hz, have low strain (<0.03%) and are fatigue-resistant up to 104 cycles (Wrec variation < 10%). These properties show promise for practical use in pulsed power systems

Chemical characterisation of degraded nuclear fuel analogues simulating the Fukushima Daiichi nuclear accident

The Fukushima Daiichi accident generated degraded nuclear fuel material, mixed with other reactor components, known as molten core-concrete interaction (MCCI) material. Simulant MCCI material was synthesised, excluding highly radioactive fission products, containing depleted U, and incorporating Ce as a surrogate for Pu. Multi-modal µ-focus X-ray analysis revealed the presence of the expected suite of U-Zr-O containing minerals, in addition to crystalline silicate phases CaSiO3, SiO2-cristobalite and Ce-bearing percleveite, (Ce,Nd)2Si2O7. The formation of perclevite resulted from reaction between the U-Zr-O-depleted Ce-Nd-O melt and the silicate (SiO2) melt. It was determined that the majority of U was present as U4+, whereas Ce was observed to be present as Ce3+, consistent with the highly reducing synthesis conditions. A range of Fe-containing phases characterised by different average oxidation states were identified, and it is hypothesised that their formation induced heterogeneity in the local oxygen potential, influencing the oxidation state of Ce.</p