Analysis of a heterodyne-detected transient-grating experiment on a molecular supercooled liquid. II. Application to m-toluidine

International audienceThis paper reports the first detailed analysis of a transient grating TG experiment on a supercooled molecular liquid, m-toluidine, from 330 K 1.75Tg to 190 K 1.01Tg based on the theoretical model presented in Paper I of this series. This method allows one to give a precise description, over a wide dynamical range, of the different physical phenomena giving rise to the signals. Disentangling the isotropic and the anisotropic parts of the TG response, a careful fitting analysis yields detailed information on the rotation-translation coupling function. We also extract the structural relaxation times related to the "longitudinal" viscosity over almost 10 decades in time and the corresponding stretching coefficient. The value of some other parameters and information on their thermal behavior is also reporte

Time-domain THz spectroscopy of the characteristics of hydroxyapatite provides a signature of heating in bone tissue

Because of the importance of bone in the biomedical, forensic and archaeological contexts, new investigation techniques are constantly required to better characterize bone ultrastructure. In the present paper, we provide an extended investigation of the vibrational features of bone tissue in the 0.1-3 THz frequency range by time-domain THz spectroscopy. Their assignment is supported by a combination of X-ray diffraction and DFT-normal modes calculations. We investigate the effect of heating on bone tissue and synthetic calcium-phosphates compounds with close structure and composition to bone mineral, including stoichiometric and non-stoichiometric hydroxyapatite (HA), tricalcium phosphate, calcium pyrophosphate and tetracalcium phosphate. We thus demonstrate that the narrow vibrational mode at 2.1 THz in bone samples exposed to thermal treatment above 750 °C arises from a lattice mode of stoichiometric HA. This feature is also observed in the other synthetic compounds, although weaker or broader, but is completely smeared out in the non-stoichiometric HA, close to natural bone mineral composition, or in synthetic poorly crystalline HA powder. The THz spectral range therefore provides a clear signature of the crystalline state of the investigated bone tissue and could, therefore be used to monitor or identify structural transitions occurring in bone upon heating

Does exist an anomalous sound dispersion in supercooled water?

International audienceAcoustic sound velocity of water in the supercooled regime shows a peculiar behaviour. Accordingly to the available data, sound velocity displays a complex behaviour below $-15$ $^\circ$C, here anomalous frequency dispersion phenomena seem to appear and need to be understood. In particular lower frequencies data at a few tens of KHz show leveling-off of the sound velocity value below -25 $^\circ$C, with a possible minimum around -30 $^\circ$C. Other data at higher frequencies, around 1 GHz, in comparison with the low frequency data, could instead suggest the existence of a "negative dispersion", yet other high frequency data show a normal dispersion behaviour. To get new insight into this topic, we made measurements of acoustic sound velocity in bulk water in the liquid and supercooled phase down to -29 $^\circ$C by means of a heterodyne detected transient grating (TG) experiment at an unexplored frequency value around 100 MHz