Landau Theory of the Reentrant Nematic-Smectic A Phase Transition

The reentrant, nematic to smectic A phase transition is shown to follow from the Landau theory if one assumes the existence of an optimum density for smectic ordering. The shape of the coexistence line in the P-T plane is fit exactly by this theory. The effects of concentration on reentrant behaviour are also explained.Engineering and Applied Science

Dislocation and Impurity Effects in Smectic-A Liquid Crystals

The effects of dislocations and impurities on the macroscopic elastic properties of smectic‐A liquid crystals are discussed. The first conclusion is that smectics behave like linear elastic media only so long as the stresses are smaller than some critical value that is analogous to the critical velocity of a superfluid. Below the critical stress, smectics can store elastic energy without flowing and consequently without any dissipative processes in analogy with the fact that, below a critical velocity, superfluids store kinetic energy without any dissipation. For most practical samples the critical smectic stress is that value for which pinned dislocation will grow unstable; however, for ideal samples, initially free of dislocations, the critical value is determined by the condition of unstable growth of thermally generated dislocation loops. In the linear elastic region both dislocations and impurities modify the macroscopic elastic properties such that the effective elastic constant is smaller than the value for an ideal sample. This is a sort of diaelasticity and can be discussed in the same way as diamagnetism. Impurities are shown to act as sources of stress fields analogous to the way magnetic dipoles and magnetic monopoles are sources of magnetic fields. The result is to predict long‐range elastic interactions between impurities in smectic systems. Since biological systems like chloroplasts and retinal rods have lamellarlike structures that are similar to the smectic structure, there is the possibility that long‐range elastic interactions may play some role in biological function.Engineering and Applied Science

Flexoelectricity in Nematic and Smectic-A Liquid Crystals

Flexoelectric effects are observed in both the nematic and smectic‐A phases of p‐butoxybenzal‐p‐($\beta$‐methylbutyl) aniline (BBMBA) and p‐cyano‐benzylidine‐p‐octyloxyaniline (CBOOA). This is the first reported observation of flexoelectricity in smectic phases. The use of a symmetric interdigital electrode in the homeotropic geometry facilitated the unambiguous separation of linear and quadratic electro‐optic effects. Both the interdigital electrodes and those liquid‐crystal deformations that are quadratic in the voltage act as optical diffraction gratings with a spacing that corresponds to the repeat distance d for adjacent electrodes. In contrast linear electro‐optic effects give rise to diffraction gratings with twice this spacing since adjacent electrodes have opposite voltages. Diffraction maxima due to the linear effects are halfway between the maxima due to the other effects. Using optical heterodyne detection, the intensity of the diffraction maxima believed to arise from the linear effect are indeed observed to be linear in the applied voltage $V (\omega)$. With homodyne detection the diffracted intensity is proportional to $V (\omega)^2$. Although previous discussions of flexoelectricity in nematics have been in terms of two flexoelectric coefficients $e_{11}$ and $e_{33}$, we present theoretical arguments that as long as $\nabla \times E=0$ there is only one true volume coefficient and that the other constant can always be included in surface effects. Our measurements of the volume coefficient $f=e_{11}+e_{33}$ are an order of magnitude larger than previously obtained values for $e_{11}$ and $e_{33}$. Measured values of f are also nearly independent of temperature, in contrast to previous theoretical models, and of similar magnitude in the smectic and nematic phases. Measurements of flexoelectric signals versus the frequency of the driving voltage obtain relaxation times for splaylike nematic fluctuations and undulation‐type smectic fluctuations.Engineering and Applied Science

Classroom, club or collective? Three types of community-based group intervention and why they matter for health

Interventions involving groups of laywomen, men and adolescents to promote health are increasingly popular, but past research has rarely distinguished between different types of intervention with groups. We introduce a simple typology that distinguishes three ideal types: classrooms, clubs and collectives. Classrooms treat groups as a platform for reaching a population with didactic behaviour change strategies. Clubs seek to build, strengthen and leverage relationships between group members to promote health. Collectives engage whole communities in assuming ownership over a health problem and taking action to address it. We argue that this distinction goes a long way towards explaining differences in achievable health outcomes using interventions with groups. First, classrooms and clubs are appropriate when policymakers primarily care about improving the health of group members, but collectives are better placed to achieve population-level impact. Second, classroom interventions implicitly assume bottleneck behaviours preventing a health outcome from being achieved can be reliably identified by experts, whereas collectives make use of local knowledge, skill and creativity to tackle complexity. Third, classroom interventions assume individual participants can address health issues largely on their own, while clubs and collectives are required to engender collective action in support of health. We invite public health researchers and policymakers to use our framework to align their own and communities’ ambitions with appropriate group-based interventions to test and implement for their context. We caution that our typology is meant to apply to groups of laypeople rather than professionalised groups such as whole civil society organisations

Factors Responsible for the Stability and the Existence of a Clean Energy Gap of a Silicon Nanocluster

We present a critical theoretical study of electronic properties of silicon nanoclusters, in particular the roles played by symmetry, relaxation, and hydrogen passivation on the the stability, the gap states and the energy gap of the system using the order-N [O(N)] non-orthogonal tight-binding molecular dynamics and the local analysis of electronic structure.Comment: 26 pages including figure

Cancer: repositioned to kill stem cells

Chemotherapy-resistant cancer stem cells make it hard to cure many forms of the disease. Repositioning an existing drug to tackle this problem could significantly improve treatment for one form of leukaemia

Nonequilibrium Fluctuations, Travelling Waves, and Instabilities in Active Membranes

The stability of a flexible fluid membrane containing a distribution of mobile, active proteins (e.g. proton pumps) is shown to depend on the structure and functional asymmetry of the proteins. A stable active membrane is in a nonequilibrium steady state with height fluctuations whose statistical properties are governed by the protein activity. Disturbances are predicted to travel as waves at sufficiently long wavelength, with speed set by the normal velocity of the pumps. The unstable case involves a spontaneous, pump-driven undulation of the membrane, with clumping of the proteins in regions of high activity.Comment: 4 two-column pages, two .eps figures included, revtex, uses eps

The role of psycho-education in improving outcome at a general hospital psychiatry clinic in Uganda

Objective: While psychoeducation has been shown to positively affect outcomes in psychiatric disorders, its utility has been little studied in developing countries. The current study sought to examine the role of psychoeducation at a general psychiatric outpatient clinic in Kampala, Uganda in improving clinic attendance, treatment adherence, and clinical outcomes. Method: A prospective casecontrol study using a quasi-experimental design was conducted in 117 patients suffering various psychiatric disorders. Participants were recruited for two months and then followed for a further three months after recruitment ended. Participants in the intervention group received formalized psychoeducation sessions at each clinic visit in addition to the usual psychiatric evaluation and care. Participants in the control group received the usual clinical care. Measured outcomes were knowledge of mental illness, compliance with medications and follow-up, and Clinical Global Impression (CGI). Results: The groups did not differ with respect to sociodemographiccharacteristics or attendance at scheduled follow-up visits. Both groups significantly improved on the CGI, but with no significant difference between the groups. However, the intervention group was more likely to adhere to medication, and their knowledge of mental illness was significantly higher at follow-up. Conclusion: These data suggest that psychoeducation is a beneficial mental health intervention in a developing country that may increase compliance with medication and result in greater knowledge of mental illness. However, other factors such as distance from a centralized clinic or cost of treatment may impact outcomes, including attendance at scheduled follow-up visits.Keywords: Low and middle income countries; Outpatient treatment; Psychosocial interventions; Transcultural Psychiatry; Africa;  Psychoeducatio