A facile and green synthesis route to C@LaCO3OH core-shell microspheres using colloidal carbonaceous spheres as template and its by-products as carbon source

C@LaCO₃OH core-shell microspheres have been synthesized by a hydrothermal method using colloidal carbonaceous spheres (CCSs) as template and its by-products as reactant without any other precipitating agent added in the reaction system. The FT-IR and XRD results indicated the successful formation of the well-crystallized LaCO₃OH shell with hexagonal crystal structure on the CCSs’ surface. The morphology and qualitative elemental chemical analysis were characterized by SEM, TEM, and EDS. The effects of co-solvent on the crystallinity of the LaCO₃OH shell were also studied. In addition, PL result showed one emission band centered at 421 nm (λ_ex = 365 nm) of the C@LaCO₃OH microspheres. The UV–visible spectrum was also employed to investigate the optical property of the products. Further, a possible formation mechanism of the core-shell structure was proposed.     

The magnetic and electronic structure of vanadyl pyrophosphate from density functional theory

We have studied the magnetic structure of the high symmetry vanadyl pyrophosphate ((VO)(2)P(2)O(7), VOPO), focusing on the spin exchange couplings, using density functional theory (B3LYP) with the full three-dimensional periodicity. VOPO involves four distinct spin couplings: two larger couplings exist along the chain direction (a-axis), which we predict to be antiferromagnetic, J(OPO) = -156.8 K and J(O) = -68.6 K, and two weaker couplings appear along the c (between two layers) and b directions (between two chains in the same layer), which we calculate to be ferromagnetic, J(layer) = 19.2 K and J(chain) = 2.8 K. Based on the local density of states and the response of spin couplings to varying the cell parameter a, we found that J(OPO) originates from a super-exchange interaction through the bridging -O-P-O- unit. In contrast, J(O) results from a direct overlap of 3d(x(2)-y(2)) orbitals on two vanadium atoms in the same V(2)O(8) motif, making it very sensitive to structural fluctuations. Based on the variations in V-O bond length as a function of strain along a, we found that the V-O bonds of V-(OPO)(2)-V are covalent and rigid, whereas the bonds of V-(O)(2)-V are fragile and dative. These distinctions suggest that compression along the a-axis would have a dramatic impact on J(O), changing the magnetic structure and spin gap of VOPO. This result also suggests that assuming J(O) to be a constant over the range of 2-300 K whilst fitting couplings to the experimental magnetic susceptibility is an invalid method. Regarding its role as a catalyst, the bonding pattern suggests that O(2) can penetrate beyond the top layers of the VOPO surface, converting multiple V atoms from the +4 to +5 oxidation state, which seems crucial to explain the deep oxidation of n-butane to maleic anhydride.     

GEANT4 Monte Carlo simulation response of parallel plate avalanche counter for fast neutrons detection

In the present study, GEANT4 based Monte Carlo codes have been employed to evaluate parallel plate avalanche counter (PPAC) response for fast neutron detection. In order to detect fast neutrons, a thin polyethylene layer is coated on the surface of the electrode of the PPAC. Neutrons entering the converter produce protons which enter the counter and are detected. Fast neutrons in the energy range of 4.0 MeV–20.0 MeV have been transported onto the PPAC surface using GEANT4 MC code. The performance of the PPAC counter has been evaluated by means of simulation by employing QGSP_BERT_HP and QGSP_BIC_HP physics lists. The detection efficiencies of polyethylene-coated PPAC are 1.69 × 10^?2 and 1.86 × 10^?2 using converter thickness of 1 mm and 2 mm, respectively. The obtained results are discussed in detail.     

Regge behaviour of distribution functions and t and x-evolutions of gluon distribution function at low-x

In this paper, t and x-evolutions of gluon distribution function from Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) evolution equation in leading order (LO) at low-x are presented assuming the Regge behaviour of quarks and gluons at this limit. We compare our results of gluon distribution function with MRST 2001, MRST 2004 and GRV 1998 parametrizations and show the compatibility of Regge behaviour of quark and gluon distribution functions with perturbative quantum chromodynamics (PQCD) at low-x. We also discuss the limitations of Taylor series expansion method used earlier to solve DGLAP evolution equations in the Regge behaviour of distribution functions.      

High-speed visualisation of primary break-up of an annular liquid sheet

In this experimental study, a thin annular moving water sheet is placed between two annular co-flowing air streams. The shear at the interface gives rise to Kelvin–Helmholtz type instabilities and promotes development of a sinuous surface wave at the gas–liquid interface. The amplitude of the surface wave is amplified as it travels downstream of the nozzle exit until it ruptures forming spanwise and streamwise ligaments. The liquid sheet is illuminated with high-powered halogen lamps. High-speed imaging is used in this study to qualitatively visualise the structure of the spray—of particular interest is the evolution of the spray into a ligament structure during the primary break-up and the role the outer air stream plays in this process. Sequences of images with high temporal resolution (∼2,000 fps) are recorded for image processing and analysis of the surface waves and ligament formation. A preliminary analysis of the waveform of the outer gas–liquid interface of the annular liquid sheet over a range of conditions shows the sheet Strouhal number to increase with increasing gas to liquid momentum ratio. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Dirichlet-to-Neumann semigroup with respect to a general second order eigenvalue problem

In this paper we study a Dirichlet-to-Neumann operator with respect to a second order elliptic operator with measurable coefficients, including first order terms, namely, the operator on \(L^2(\partial \Omega )\) given by \(\varphi \mapsto \partial _{\nu }u\) where u is a weak solution of

$$\begin{aligned} \left\{ \begin{aligned}&-\mathrm{div}\, (a\nabla u) +b\cdot \nabla u -\mathrm{div}\, (cu)+du =\lambda u \ \ \text {on}\ \Omega ,\\&u|_{\partial \Omega } =\varphi . \end{aligned} \right. \end{aligned}$$

Under suitable assumptions on the matrix-valued function a, on the vector fields b and c, and on the function d, we investigate positivity, sub-Markovianity, irreducibility and domination properties of the associated Dirichlet-to-Neumann semigroups.