Non-layered InSe nanocrystalline bulk materials with ultra-low thermal conductivity

Exploring new prototypes for a given chemical composition is of great importance and interest to several disciplines.As a famous semiconducting binary compound,InSe usually exhibits a two-dimensional layered structure with decent physical and mechanical properties.However,it is less noticed that InSe can also adopt a monoclinic structure,denoted as mcl-InSe.The synthesis of such a phase usually re-quires high-pressure conditions,and the knowledge is quite scarce on its chemical bonding,lattice dynamics,and thermal transport.Here in this work,by developing a facile method combining me-chanical alloying and spark plasma sintering,we successfully synthesize mcl-InSe bulks with well-crystallized nanograins.The chemical bonding of mcl-InSe is understood as compared with layered InSe via charge analysis.Low cut-off frequencies of acoustic phonons and several low-lying optical modes are demonstrated.Noticeably,mcl-InSe exhibits a low room-temperature thermal conductivity of 0.6 W·m^(-1)·K^(-1),which is smaller than that of other materials in the IneSe system and many other selenides.Low-temperature thermal analyses corroborate the role of nanograin boundaries and low-frequency optical phonons in scattering acoustic phonons.This work provides new insights into the non-common prototype of the InSe binary compound with potential applications in thermoelectrics or thermal insulation.

Effect of protein molecular weight on the mass transfer in protein mixing

The mixing of protein solutions with that of precipitating agents is very important in protein crystallization experiments. In this work, the interferometry images were recorded during the mixing of two proteins with different molecular weights： lysozyme of -14.6 kDa, trypsin of -23.3 kDa and pepsin of -34.8 kDa were placed in a Mach-Zehnder interferometer. The protein mo- lecular weight dependence on the competition of the transport process and kinetics at the interface was studied. The concentra- tion profiles of protein solutions were calculated to analyze the mass transfer during the mixing process. It was observed that the mass transfer process is more efficient during the mixing of proteins with higher molecular weights. In addition, the more rapid concentration changes above the interface suggest that convection may dominate the diffusion. The phenomenon of con- vection is higher in the protein solutions with higher molecular weight.

The influence of lunar surface position on irradiance of moonbased earth radiation observation

As a platform for longer-term continuous moon-based earth radiation observation(MERO)which includes reflected solar short-wave(SW)radiation and long-wave infrared(LW)radiation,the huge lunar surface space can provide multiple location choices.It is important to analyze the influence of lunar surface position on irradiance which is the aim of the present work based on a radiation heat transfer model.To compare the differences caused by positions,the site of 0°E 0°N was selected as the reference site and a good agreement of the calculation results was verified by the comparison with the NISTAR’s actual detected data.By analyzing the spatial characteristics of the irradiance,the results showed that the irradiance on the lunar surface was of circular distribution and the instrument that was placed in the region of 65°W-65°E and 65°S-65°N could detect the irradiance most effectively.The relative deviation between the reference site and the marginal area(region of>65°S or 65°N or>65°W or 65°E)was less than 0.9 mW∙m^(-2) and the small regional differences make a small-scale network conducive to radiometric calibration between instruments.To achieve accurate measurement of the irradiance,the sensitivity design goal of the MERO instrument should be better than 1 mW∙m^(-2) in a future actual design.Because the lunar polar region is the priority region for future exploration,the irradiance at the poles has also been analyzed.The results show that the irradiance changes periodically and exhibits complementary characteristics of time.The variation range of irradiance for short-wave radiation is greater than longwave radiation and the irradiance of SW reaches the maximum at different times.The MERO at the polar region will provide valuable practical experiment for the followup study of the moon-based earth observation in low latitudes.

Soft-mode dynamics in the ferroelectric phase transition of GeTe

GeTe that exhibits a strong anharmonicity and a ferroelectric phase transition between the rhombohedral and cubic structures has emerged as one of the leading thermoelectric materials.Herein,combining molecular dynamics simulations and inelastic neutron scattering measurements,the lattice dynamics in GeTe have been investigated to reveal the soft-mode mechanisms across the phase transition.We have constructed a first-principles-based machine-learning interatomic potential,which successfully captures the dynamical ferroelectric phase transition of GeTe by adopting the neural network technique.Although the low-energy acoustic phonons remain relatively unaffected at elevated temperatures,the high-energy optical,and longitudinal acoustic phonons demonstrate strong renormalizations as evidenced from the vibrational phonon spectra,which are attributed to the large anharmonicity accompanying the phase transition.Furthermore,our results reveal a nonmonotonic temperature dependence of the soft-modes beyond the perturbative regime.The insight provided by this work into the soft-modes may pave the way for further phonon engineering of GeTe and the related thermoelectrics.