Closed trajectories of a particle model on null curves in anti-de Sitter 3-space

We study the existence of closed trajectories of a particle model on null curves in anti-de Sitter 3-space defined by a functional which is linear in the curvature of the particle path. Explicit expressions for the trajectories are found and the existence of infinitely many closed trajectories is proved.Comment: 12 pages, 1 figur

Semiconductor-metal nanoparticle molecules: hybrid excitons and non-linear Fano effect

Modern nanotechnology opens the possibility of combining nanocrystals of various materials with very different characteristics in one superstructure. The resultant superstructure may provide new physical properties not encountered in homogeneous systems. Here we study theoretically the optical properties of hybrid molecules composed of semiconductor and metal nanoparticles. Excitons and plasmons in such a hybrid molecule become strongly coupled and demonstrate novel properties. At low incident light intensity, the exciton peak in the absorption spectrum is broadened and shifted due to incoherent and coherent interactions between metal and semiconductor nanoparticles. At high light intensity, the absorption spectrum demonstrates a surprising, strongly asymmetric shape. This shape originates from the coherent inter-nanoparticle Coulomb interaction and can be viewed as a non-linear Fano effect which is quite different from the usual linear Fano resonance.Comment: 5 pages, 5 figures, submitted to Phys. Rev. Let

Extending health insurance in Ghana: effects of the National Health Insurance Scheme on maternity care

Background There is considerable interest in exploring the potential of social health insurance in Africa where a number of countries are currently experimenting with different approaches. Since these schemes have been introduced recently and are continuously evolving, it is important to evaluate their effectiveness in the enhancement of health care utilization and reduction of out-of-pocket expenses for potential policy suggestions. Objective To investigate how the National Health Insurance Schemes (NHIS) in Ghana affects the utilization of maternal health care services and medical out-of-pocket expenses. Methods We used nationally-representative household data from the Ghana Demographic and Health Survey (GDHS). We analyzed the 2014 GDHS focusing on four outcome variables, i.e. antenatal check up, delivery in a health facility, delivery assisted by a trained person and out-of-pocket expenditure. We estimated probit and bivariate probit models to take into account the issue of self selection into the health insurance schemes. Results The results suggest that, also taking into account the issue of self selection into the health insurance schemes, the NHIS enrollment positively affects the probability of formal antenatal check-ups before delivery, the probability of delivery in an institution and the probability of being assisted during delivery by a trained person. On the contrary, we find that, once the issue of self-selection is taken into account, the NHIS enrollment does not have a significant effect on out-of-pocket expenditure at the extensive margin. Conclusion Since a greater utilization of health-care services has a strong positive effect on the current and future health status of women and their children, the health-care authorities in Ghana should make every effort to extend this coverage. In particular, since the results of the first step of the bivariate probit regressions suggest that the educational attainment of women is a strong determinant of enrollment, and those with low education and unable to read are less likely to enroll, information on the NHIS should be disseminated in ways that reach those with little or no education. Moreover, the availability of government health facilities in a region is associated with higher likelihood of enrollment in the NHIS. Accordingly, extending geographical access is an important strategy for expanding NHIS membership and improving access to health-care

Geomagnetic activity forcing of the Northern Annular Mode via the stratosphere

We consider various aspects of the link between solar-modulated geomagnetic activity and the Northern Annular Mode (NAM). Our results indicate that the geomagnetic forcing of atmospheric circulation in the Northern Hemisphere is temporally and seasonally restricted, modulated by the Quasi-Biennial Oscillation (QBO), and reliant on stratosphere-troposphere coupling. When the data are restricted to January values after 1965, for years in which the January QBO is eastwards, the correlation coefficient between the geomagnetic AA index and the NAM is 0.85. These results can account for many of the enigmatic features of Northern Hemisphere circulation.<br><br> <b>Key words.</b> Meterology and atmospheric dynamics (general circulation, climatology

Modified Debye-Huckel Electron Shielding and Penetration Factor

Screened potential, modified by non standard electron cloud distributions responsible for the shielding effect on fusion of reacting nuclei in astrophysical plasmas, is derived. The case of clouds with depleted tails in space coordinates is discussed. The modified screened potential is obtained both from statistical mechanics arguments based on fluctuations of the inverse of the Debye-Huckel radius and from the solution of a Bernoulli equation used in generalized statistical mechanics. Plots and tables useful in evaluating penetration probability at any energy are provided.Comment: 9 pages, 3 figures, 3 table

PHYCOERYTHROCYANINS FROM Westiellopsis prolifica AND Nostoc rivulare: CHARACTERIZATION OF THE PHYCOVIOLOBILIN CHROMOPHORE IN BOTH STATES

Phycoerythrocyanin or fractions enriched in it have been isolated from the filamentous cyanobacteria, Westiellopsis prolifica ARM 365 and Nostoc rivulare ARM 212. Both show the photoreversible photochromism (difference maxima at 503 and 570 nm) characteristic of this pigment, which is related to the phycoviolobilin chromophore on the α-subunit. Native phycoerythrocyanin and its β-subunit show little if any reversible photochemistry in the 600–620 nm region, where the phycocyanobilin chromophores absorb maximally. Instead the phycocyanobilin chromophores are bleached irreversibly. At the same time, the data show that reversible photochemistry is a useful analytical tool to detect phycoerythrocyanin in cyanobacterial extracts. Fluorescence measurements indicate that: (i) the 510 nm absorbing isomer of the violobilin chromophore has only little fluorescence; and (ii) the energy transfer from the violobilin chromophores to the cyanin chromophores is efficient only in the 570 nm form

Calibrated Sub-Bundles in Non-Compact Manifolds of Special Holonomy

This paper is a continuation of math.DG/0408005. We first construct special Lagrangian submanifolds of the Ricci-flat Stenzel metric (of holonomy SU(n)) on the cotangent bundle of S^n by looking at the conormal bundle of appropriate submanifolds of S^n. We find that the condition for the conormal bundle to be special Lagrangian is the same as that discovered by Harvey-Lawson for submanifolds in R^n in their pioneering paper. We also construct calibrated submanifolds in complete metrics with special holonomy G_2 and Spin(7) discovered by Bryant and Salamon on the total spaces of appropriate bundles over self-dual Einstein four manifolds. The submanifolds are constructed as certain subbundles over immersed surfaces. We show that this construction requires the surface to be minimal in the associative and Cayley cases, and to be (properly oriented) real isotropic in the coassociative case. We also make some remarks about using these constructions as a possible local model for the intersection of compact calibrated submanifolds in a compact manifold with special holonomy.Comment: 20 pages; for Revised Version: Minor cosmetic changes, some paragraphs rewritten for improved clarit