No abstract

The dielectric, piezoelectric and elastic properties of 0.91(PbZn1/3Nb2/3)O3–0.09PbTiO3 single crystals have been investigated as functions of temperature and applied electric field. Two multiple phase transitions at 68°C and 178°C, the crystal changing from the rhombohedral ferroelectric phase to tetragonal ferroelectric and then to cubic paraelectric, have been observed. Both the transitions are of first-order, but both are slightly diffused. Significant increases in the dielectric, piezoelectric and elastic constants are observed at the lower transition point. In particular, the sample poled along the pseudo-cubic [001] axis reveals anomalously large piezoelectric and electro-mechanical coupling constants at room temperature in the rhombohedral phase (d [001]//=1500×10-12 C/N, k [001]//=0.92).

No abstract

No abstract

SynopsisThe interaction of water with collagenous tissue was investigated using dynamic mechanical spectroscopy and cryogenic X-ray techniques. The loss spectrum was found to be very sensitive to water which is highly associated with the macromolecule. Two water-sensitive loss peaks were observed below OOC: the 02 or "water dispersion" a t 150'K and the dl a t 200°K which is attributed to motion of polar side chains. Changes in peak temperature and intensity were not continuous with water content, but exhibited regimes in behavior which were associated with two types of nonfreezable water, structural and bound water. In cryogenic X-ray experiments, specimens which contained some freezable water exhibited reflections identified with the cubic form of ice. These ice crystals underwent an irreversible transition to the more common hexagonal form when warmed above 200°K. On the basis of these experiments, a model for the hydration of native collagenous tissue was proposed. INTRODUCTIONThe relation between water and biological macromolecules is one of the most important phenomena of all life processes. Connective tissue, for example, depends upon the association with water for the unique and specific mechanical properties. Here water is an important component of both the collagen fibers and the polysaccharide gel matrix which comprises the highly organized composite structure. Despite the obvious importance, many aspects of the structural protein-water interaction in the condensed native state remain a mystery. This is largely due to the complex chemical composition of the protein molecule and the equally complex hierarchies of structural organization which exist in connective tissue. A spectrum of interactions may be expected which differ as regards the energy of interaction and the effect on physical properties.Traditionally the water associated with proteins is divided into three types: structural, bound, and free water. High resolution X-ray diffraction data of protein crystals provide a description of the spatial arrangement of water molecules located within the crystal. The structural water associated with the crystal can be described by a specific stoichiometry much as the hydrates of inorganic salts. The term bound water is frequently used to describe protein-water interactions both in aqueous solution and the hydrated condensed state. The best definition remains an operational one in which the bound water is considered as that having properties measurably different from those of bulk water measured by the same technique. This definition includes considerably more water than the structural water.Although the actual value might be expected to vary considerably, different experimental techniques frequently give surprisingly similar values. For collagen, the amount of bound water is generally on the order of 0.35 glg. In addition, most collagenous tissue contains additional water in varying amounts which has essentially the properties of bulk water.In investigating the nature of water-collagen interactions we hav...