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An external electric field has great effects on the sensitivity of cocrystal energetic materials. In order to find out the relationship between the external electric field

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It is a significant challenge to develop nanoscale magnetic resonance imaging (MRI) contrast agents with high performance of relaxation. In this work, Gd-doped CaF-based core-shell nanoparticles (CaF:Yb,Er@CaF:Gd) of sub-10 nm size were controllably synthesized by a facile sequential growth method. The as-prepared hydrophilic CaF:Yb,Er@CaF:Gd nanoparticles modified using PEG-PAA di-block copolymer benefited from the presence of Gd only in the outer CaF layer of the nanoparticles, which exhibited r as high as 21.86 mM s under 3.0 T, seven times as high as that of commercially used gadopentetate dimeglumine (Gd-DTPA). Low cytotoxicity, no hemolysis phenomenon and no potential gadolinium ion leakage phenomenon of the hydrophilic CaF:Yb,Er@CaF:Gd nanoparticles have been observed and confirmed. Clear vascular details can be observed in magnetic resonance angiography and obvious MR signal of 4T1 tumor area could be significantly improved by intravenous injection of the hydrophilic CaF:Yb,Er@CaF:Gd nanoparticles at a low dosage in mice. A series of in vivo biological safety evaluations confirmed the good biocompatibility of the hydrophilic CaF:Yb,Er@CaF:Gd nanoparticles, which might be employed in clinical blood pool imaging and tumor diagnosis as a safe and efficient MRI probe.

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A series of bridged pyridine-based energetic compounds were designed and their geometrical/electronic structures, ΔHf, detonation properties, thermal stabilities, thermodynamic properties and electrostatic potential were fully investigated using DFT.

Forty nitramines by incorporating −CO, −NH2, −N3, −NF2, −NHNO2, −NHNH2, −NO2, −ONO2, −C­(NO2)3, and −CH­(NO2)2 groups based on a 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX) framework were designed. Their electronic structures, heats of formation (HOFs), detonation properties, thermal stabilities, electrostatic potential, and thermodynamic properties were systematically investigated by density functional theory. The comprehensive relationships between the structures and performance of different substituents were studied. Results indicate that −C­(NO2)3 has the greatest effect on improvement of HOFs among the whole substituted groups. Thermodynamic parameters, such as standard molar heat capacity (C p,m θ), standard molar entropy (S m θ), and standard molar enthalpy (H m θ), of all designed compounds increase with the increasing number of energetic groups, and the volumes of energetic groups have a great influence on standard molar enthalpy. Except for −NH2(R1), −NHNH2(R5), and B3, all of the designed compounds have higher detonation velocities and pressures than HMX. Among them, E7 exhibits an extraordinarily high detonation performance (D = 10.89 km s–1, P = 57.3 GPa), E1 exhibits a relatively poor detonation performance (D = 8.93 km s–1, P = 35.5 GPa), and −NF2 and −C­(NO2)3 are the best ones in increasing the density by more or less 12%.