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The system SDS/decanol/water is investigated by polarized optical microscopy. A reported biaxial island is here confirmed by conoscopy, in the temperature interval 20°C to 26°C. Coexistence regions of the two uniaxial nematic phases (discotic ND+ cylindrical NC) are also confirmed, in different temperature intervals. While the biaxial phase is stable for at least 10 hours, in a reproducible way, along the same time the coexistence region evolves with time, and drops of the discotic phase grow immersed in a NCmatrix. Results are explained in terms of recent theories dealing with stabilization of mixtures of cylinders and discs. [ABSTRACT FROM AUTHOR]

Measurements of optical refractive indices (ordinary and extraordinary), as a function of temperature, are reported for the heavy water / SDS molar ratio Mw= 36, with a decanol / SDS molar ratio Md= 0.324. The nematic biaxial phase emerges from the crystal phase (which occurs below 18°C) into a coexistence region with two uniaxial nematic phases (discoticNDand cylindricalNC), before entrance in theNCphase. The transitions are discontinuous, and the biaxial phase differs from the coexistence regionND+NC. Results indicate changes of the micellar object with temperature, and at the phase transitions. [ABSTRACT FROM AUTHOR]

The optical characterization of uniaxial nematic liquid crystals gives basic information on its birefringence and on the shape anisotropy of micelles in nematic lyotropic phases. In this work, these optical parameters were determined as a function of temperature along the sequence discotic nematic (ND) - coexistence (ND + NC) - calamitic nematic (NC) - isotropic (I) in a lyotropic mixture of the sodium dodecyl (lauryl) sulphate (SDS) - decanol (DeOH) and D2O for a specific concentration. Results for the uniaxial phases agree with previous assignments. Results in the coexistence region indicate an inhomogeneous mixture of the two uniaxial phases. [ABSTRACT FROM AUTHOR]

The paper by Yu and Saupe on the first biaxial nematic phase created excitement for a number of reasons. Some theories of biaxial phases already existed, but experimental observation was still lacking. The phase was discovered in a lyotropic system with three components, which in theory is difficult. Lyotropic liquid crystals are composed of supramolecular assemblies of amphiphilic molecules, which may change shape and size as a function of concentration and temperature. The experimental phase diagram of the lyotropic biaxial phase was rather complex, with the biaxial region inserted between nematic cylindrical and nematic discotic phases via second-order transitions. In addition, re-entrant behaviour was evident. Saupe investigated further systems experimentally, observing that the biaxial phase might be absent in cases where a direct transition between the cylindrical and discotic phases occurred. He provided a range of theoretical and experimental contributions on the properties of these lyotropics, but was very cautious regarding the detailed amphiphilic assemblies involved. The present paper reviews this area, focusing on proposals for the structure of the micellar assemblies. Emphasis is placed on recent papers which indicate a transformation of the two uniaxial shapes, in mixing conditions, both from the theoretical and the experimental point of view, and to questions still requiring further study. [ABSTRACT FROM AUTHOR]

Lyotropic nematics consisting of surfactant-cosurfactant water solutions may present a biaxial phase or direct U(+)↔U(-) transitions, in different regions of the temperature-relative concentration phase diagram, for different systems and compositions. We propose that these may be related to changes of uniaxial micellar form, which may occur either smoothly or abruptly. Smooth change of cylinder-like into disc-like shapes requires a distribution of Maier-Saupe interaction constants and we consider two limiting cases for the distribution of forms: a single Gaussian and a double Gaussian. Alternatively, an abrupt change of form is described by a discontinuous distribution of interaction constants. Our results show that the dispersive distributions yield a biaxial phase, while an abrupt change of shape leads to coexistence of uniaxial phases. Fitting the theory to the experiment for the ternary system KL/decanol/D2O leads to transition lines in very good agreement with experimental results. In order to rationalise the results of the comparison, we analyse temperature and concentration form dependence, which connects micellar and experimental macroscopic parameters. Physically consistent variations of micellar asymmetry, amphiphile partitioning and volume are obtained. To the best of the authors' knowledge, this is the first truly statistical microscopic approach that is able to model experimentally observed lyotropic biaxial nematic phases. [ABSTRACT FROM AUTHOR]

Ion-beam-assisted phase transformation in the Fe-N system has been studied in Fe samples implanted with N. By bombarding with Ar ions at temperatures in the 140oC < T < 420oC range, the epsilon-Fe2N -> epsilon-Fe2+xN + epsilon-Fe3.2N and epsilon-Fe3.2N + gamma-Fe4N phase transformations were induced. The ion-assisted phase transformations were studied as a function of firstly the temperature of the substrate, secondly the initial N concentration and thirdly the irradiation time. The results of the experiments show that the concomitant use of ion bombardment and temperature induces a given phase transformation at a temperature that is typically 40-50oC lower than that required for thermal annealing alone. [ABSTRACT FROM AUTHOR]

In this opening introductory paper, we discuss the possibility that scaleinvariant correlations may be a feature of biological and possibly even social systems. We illustrate this possibility by reviewing recent work at Boston University. Specifically, we focus first on the apparent scale-invariant correlations in non-coding deoxyribonucleic acid (DNA) and show that this feature can be used to distinguish coding and non-coding DNA. We argue that the inflating a degassed lung is characterized by a cascade of avalanches, as the airways successively open, and that distribution functions characterizing this cascade are scale invariant. Moving from the lung to the heart, we find that the sequence of interbeat intervals is characterized by scale-invariant correlations in health, but not in disease. Moving from individual organs to entire organisms, we discuss recent experimental evidence that the foraging behaviour of the wandering albatross is governed by a scale-invariant Levy distribution. Finally, we enquire whether scale invariance describes not only animal behaviour but also human behaviour. To this end, we analyse data on urban growth patterns, on finance and on economics. For all cases, we find empirical evidence of scaling behaviour. We conclude by asking why such complex systems might display scale invariance. [ABSTRACT FROM AUTHOR]