Measurement of thermophysical properties of YBa2Cu3O7−x thin film using picosecond thermoreflectance technique

Simultaneous determination of thermophysical properties of YBa₂Cu₃O_7?x thin film has been carried out using the optical pump–probe method. The thermal diffusivity and thermal effusivity were analyzed from the same picosecond thermoreflectance data. The thermal conductivity and specific heat were then derived from the measured values of the thermal diffusivity and effusivity. The thermal diffusivity, thermal effusivity and thermal conductivity obtained compared favorably with those reported in the literature.     

Pricing Variance Swaps in a Hybrid Model of Stochastic Volatility and Interest Rate with Regime-Switching

In this paper, we consider the problem of pricing discretely-sampled variance swaps based on a hybrid model of stochastic volatility and stochastic interest rate with regime-switching. Our modeling framework extends the Heston stochastic volatility model by including the Cox-Ingersoll-Ross (CIR) stochastic interest rate model. In addition, certain model parameters in our model switch according to a continuous-time observable Markov chain process. This enables our model to capture several macroeconomic issues such as alternating business cycles. A semi-closed form pricing formula for variance swaps is derived. The pricing formula is assessed through numerical implementation, where we validate our pricing formula against the Monte Carlo simulation. The impact of incorporating regime-switching for pricing variance swaps is also discussed, where variance swaps prices with and without regime-switching effects are examined in our model. We also explore the economic consequence for the prices of variance swaps by allowing the Heston-CIR model to switch across three different regimes.     

Tin stearate organometallic precursor prepared SnO2 quantum dots nanopowder for aqueous- and non-aqueous medium photocatalytic hydrogen gas evolution

Current study reports a rapid one-pot non-hydrolytic condition in the synthesis of Sn O₂ QDs nanopowder using tin（II） stearate（Sn（St）₂） as environmentally-benign organometallic precursor,which is an unprecedentedly employed-compound in preceding Sn O₂ nanopowder productions.The as-synthesized Sn O₂ QDs that are hydrophobic can be easily transferred from organic solvent to aqueous solution through a robust ligand exchange method.The stearate-capping ligands on the surface of QDs can be replaced by beta-cyclodextrin（β-CD） and eventually render the QDs highly water soluble,which ultimately make it exhibit bi-functionality for different liquid medium applications.Structural characterizations reveal that the bi-functional QDs are indeed well-matched with the standard rutile Sn O₂ cassiterite phase without the presence of any impurities.The QDs can be interchangeably used as photocatalyst for both aqueous and non-aqueous phase,where it shows significant enhancement of hydrogen gas production as compared to that of commercial Sn O₂ nanopowder.     

Magnetotransport properties of La<Subscript>0.67</Subscript>Ca<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript> with different grain sizes

The magnetotransport and magnetoresistive (MR) properties of manganese-based La_0.67Ca_0.33MnO₃ perovskite with different grain sizes are reported. The electrical resistivity was measured as a function of temperature in magnetic fields of 0.5 and 1 T. The insulator–metal transition temperature, T _IM, shifted to a higher temperature with the application of the magnetic field. In zero field, T _IM is almost constant (∼271 K) for all samples except for the sample with the largest grain size, where T _IM=265 K. The temperature dependence of resistivity was fitted with several equations in the metallic (ferromagnetic) region and the insulating (paramagnetic) region. The density of states at the Fermi level, N(E _F), and the activation energy of electron hopping were estimated by fitting the resistivity versus temperature curves. The ρ–T ² curves are nearly linear in the metallic regime, but the ρ–T ^2.5 curves exhibit a deviation from linearity. The variable range hopping model and small polaron hopping model fit the data well in the high-temperature region, indicating the existence of the Jahn–Teller distortion that localizes the charge carriers. MR was found to increase with an increase in the magnetic field, an effect which is attributed to the intergrain spin tunneling effect.     

On chromatic uniqueness of certain 5-partite graphs

Let P(G,λ) be the chromatic polynomial of a graph G. Two graphs G and H are said to be chromatically equivalent, denoted G～H, if P(G,λ)=P(H,λ). We write [G]={H∣H～G}. If [G]={G}, then G is said to be chromatically unique. In this paper, we first characterize certain complete 5-partite graphs with 5n+3 vertices according to the number of 6-independent partitions of G. Using these results, we investigate the chromaticity of G with certain star or matching deleted. As a by-product, many new families of chromatically unique complete 5-partite graphs with certain star or matching deleted are obtained.