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In this work, the downconversion (DC) behaviour of Ho3+ ions doped in pure YVO 4 , YNbO 4 , YTaO 4 hosts and their intermixed (i.e. Ta/V, Ta/Nb and Nb/V) compositions have been investigated and compared. The samples were synthesized by solid-state reaction technique at 1473 K. The UV–Vis absorption and photoluminescence behaviour of 1 mol % Ho3+ doped YVO 4 , YNbO 4 and YTaO 4 as well as their intermixed compositions have been studied. The DS green emission of Ho3+ ion in vanadate host (λ exc = 326 nm) is 5 times stronger than in niobate host (λ exc = 262 nm) due to efficient energy transfer between [VO 4 ]3- and Ho3+ ion. The downshifting (DS) emissions are also investigated on direct excitation of Ho3+ ion in YVO 4 , YNbO 4 and YTaO 4 hosts on excitation with 450/456 nm (5I 8 →5G 6 transition of Ho3+ ion) wavelength. It is found that the overall DS emission intensity is dominant in YNbO 4 :Ho3+ phosphor due to low phonon frequency and larger particle size of YNbO 4. The Ho3+ doped in mixed hosts viz. YTa 1-x V x O 4 , YTa 1-y Nb y O 4 , YNb 1-z V z O 4 (where x, y and z = 0, 0.25, 0.50, 0.75 and 1.0) phosphors also emit intense green DS emission along with their violet-blue band emission on ultraviolet (UV) excitation. The mixing of Ta/V and Ta/Nb enhances the blue emission of host matrix on UV excitation. The green emission is found to increase with 'V' and 'Nb' concentrations in YTa 1-x V x O 4 :0.01Ho3+, YTa 1-y Nb y O 4 :0.01Ho3+, respectively. Further, we also investigated quantum cutting (QC) in YNb 1-z V z O 4 :5 mol% Yb3+ (where z = 0, 0.25, 0.50, 0.75, 1.0) phosphors on UV excitation (λ exc = 262 and 326 nm). The intensity of QC NIR emission is found to increase with the incorporation of 'V' in YNb 1-z V z O 4 phosphors. The strongest QC emission is observed in pure YVO 4 host as compared to pure YNbO 4 as well as other mixed matrices. The QC efficiency of NIR emission for YVO 4 :5 Yb has been calculated and found to 129%. Therefore, the prepared phosphor material is highly applicable to increase the efficiency of Si- solar cell by QC NIR emission. [ABSTRACT FROM AUTHOR]

Pore wettability plays a key role in controlling shale gas adsorption and flow in marine shales. To reveal the mechanism of shale gas adsorption and flow in pores with different wettability (hydrophobic or hydrophilic), molecular modelling is simulated using the molecular dynamics method. Three pore assemblages, namely, the quartz–illite (Q–I) pores, the quartz–organic matter (Q–OM) pores, and the illite–organic matter (I–OM) pores, are proposed and the adsorption and diffusion behavior in these pores are simulated under different conditions. The results show that matrix compositions in shale greatly affect pore wettability. Water molecules preferentially absorb on the junction of materials and result in more hydrophilicity at the junction than pores. Methane density simulations reveal that free methane molecules form clusters in the Q–I pores, with higher free methane density than adsorbed methane. Methane molecules in the Q–OM pores are primarily adsorbed on organic matter. Free methane molecules extensively exist in the I–OM pores, leading stronger density of free methane than adsorbed methane. The more the proportion of free methane, the larger the methane self‐diffusion coefficient. This study provides new insights to understanding of shale gas adsorption and diffusion behavior, which is important for the effective development of shale gas reservoirs. [ABSTRACT FROM AUTHOR]

An aqueous solution route has been developed to prepare calcium sodium borate compositions of the formula x B 2 O 3 ·(100– x)(0.5CaO·0.45Na 2 O·0.05P 2 O 5) (36.2 ≤ x ≤ 61.3 mol%). The effect of heat-treatment and melt-quenching on the structure and physical properties was investigated using differential thermal analysis, X-ray diffraction, FTIR spectroscopy, 11B MAS NMR and density. Dried powders were heat treated at temperatures 400–800 °C for 3h. XRD revealed formation of crystalline Na 2 B 4 O 7 ·5H 2 O, Ca 5 (PO 4) 3 OH, Na 3 B 5 O 9 H 2 O and CaB 3 O 5 (OH) in the samples treated up to 500 °C. Samples treated at higher temperature show the presence of CaNaB 5 O 9 , CaNa 3 B 5 O 10 and CaNaPO 4. Quenched solids obtained by melting powders are amorphous. It is deduced from FTIR spectra that CaO and Na 2 O modify the borate network forming BO 4 and BO 3 with non-bridging units, which depend on the molar ratio R =(Na 2 O+CaO)/B 2 O 3 and temperature. The fraction N 4 of four coordinated boron atoms changes with R and can be predicted by treating the compositions as if they are mixtures of Na 2 O–B 2 O 3 and CaO–B 2 O 3 matrices. N 4 values have been used to calculate the fraction of all units in the glass structure. The results are confirmed by 11B MAS NMR spectra that show the presence of symmetric and asymmetric trigonal BO 3 groups and splitting line shape of [4]B. The latter is assumed being related to different four-coordinated boron environments. Density and molar volume obtained by using mixed matrices concept agree well with the experimental data. • Crystalline B 2 O 3 –CaO–Na 2 O–P 2 O 5 powders could be obtained from solution route. • Related glasses have been prepared by melting the powders. • Glasses can be treated as being formed of borate and phosphate phases. • Each phase is composed of two matrices, modified by Na 2 O and CaO. • N 4 , D and V m can be calculated by applying the mixed matrices concept. [ABSTRACT FROM AUTHOR]

Recently, a new class of matrices, called mixed matrices, that unifies the Z-matrices and symmetric matrices has been identified. They share the property that when the leading principal minors are positive, all principal minors are positive. It is natural to ask what other properties of M-matrices and positive definite matrices are enjoyed by mixed matrices as well. Here, we show that mixed P-matrices satisfy a broad family of determinantal inequalities, the Koteljanskii inequalities, previously known for those two classes. In the process, other properties of mixed matrices are developed, and consequences of the Koteljanskii inequalities are given. [ABSTRACT FROM AUTHOR]

A technology has been developed for making carbon-ceramic composite refractories by combining carbon fibers as reinforcing component with a mixture matrix, which allows one to make refractory components of various sizes and geometry, including thin-walled large constructions. The heat resistance of these composite refractories increases with the bulk silicization during ceramic production on a carbon-carbon substrate. The degree of silicization is determined by the volume of the open microporosity of transport type, which is formed by pyrolysis of a polymer coke-forming matrix in the initial carbon plastic. The transport micropores are produced by a modification of the phenol-formaldehyde resin additive treatment, which does not give rise to coke on pyrolysis. As a result, the content of open pores in the carbon framework attains 55%, which enables one to make a silicized composite refractory of density up to 2.7 g/cm3 with a compressive strength of 250 – 300 MPa, bending strength 120 – 140, and tensile strength 60 – 80 MPa, elastic modulus 120 – 140 GPa, linear expansion coefficient 3.5 × 10–6 – 4.5 × 10–6 K–1, and thermal conductivity 6 – 8 W/(m ∙ K). These refractories are widely used in various branches of industry [ABSTRACT FROM AUTHOR]