Limitations and improvements upon the two-level approximation for molecular nonlinear optics

When parametric nonlinear processes are employed in the cause of efficient optical frequency conversion, the media involved are generally subjected to substantially off-resonant input radiation. As such, it is usually only electronic ground states of the conversion material that are significantly populated; higher levels are engaged only in the capacity of virtual states, and it is frequently assumed that just one such state dominates in determining the response. Calculating the nonlinear optical susceptibilities of molecules on this basis, excluding all but the ground and one excited state in a sum-over-states formulation, signifies the adoption of a two-level model, a technique that is widely deployed in the calculation and analysis of nonlinear optical properties. The two-level model offers tractable and physically simple representations of molecular response, including wavelength dependence; it is also the origin of the widely applied 'push-pull' approach to designing optically nonlinear chromophores. By contrast, direct ab initio calculations of optical susceptibility are commonly frustrated by a complete failure to determine such dispersion features. However, caution is required; the two-level model can deliver potentially misleading results if it is applied without regard to the criteria for its validity, especially when molecular excited states are significantly populated. On the basis of a precise, quantum electrodynamical basis for the theory, we explore in detail why there are grounds for questioning the general validity of two-level calculations in nonlinear optics; we assess the criteria for high frequency conversion efficiency and provide a new graphical method to assist in determining the applicability of a two-level model for hyperpolarizability calculations. Lastly, this paper also explores the applicability and detailed conditions for the two-level model for electronically excited molecules, identifying problematic results and providing tractable methods for improving the accuracy of calculations on real molecule-photon interactions

Nonlinear optical techniques for improved data capture in fluorescence microscopy and imaging

Multiphoton fluorescence microscopy is now a well-established technique, currently attracting much interest across all fields of biophysics - especially with regard to enhanced focal resolution. The fundamental mechanism behind the technique, identified and understood through the application of quantum theory, reveals new optical polarization features that can be exploited to increase the information content of images from biological samples. In another development, based on a newly discovered, fundamentally related mechanism, it emerges the passage of off-resonant probe laser pulses may characteristically modify the intensity of single-photon fluorescence, and its associated optical polarization behavior. Here, the probe essentially confers optical nonlinearity on the decay transition, affording a means of optical control over the fluorescent emission. Compared to a catalogue of other laser-based techniques widely used in the life sciences, most suffer limitations reflecting the exploitation of specifically lifetime-associated features; the new optical control mechanism promises to be more generally applicable for the determination of kinetic data. Again, there is a prospect of improving spatial resolution, non-intrusively. It is anticipated that tight directionality can be imposed on single-photon fluorescence emission, expediting the development of new imaging applications. In addition, varying the optical frequency of the probe beam can add another dimension to the experimental parameter space. This affords a means of differentiating between molecular species with strongly overlapping fluorescence spectra, on the basis of their differential nonlinear optical properties. Such techniques significantly extend the scope and the precision of spatial and temporal information accessible from fluorescence studies

Method to Predict Crowding Effects by Postprocessing Molecular Dynamics Trajectories: Application to the Flap Dynamics of HIV-1 Protease.

The internal dynamics of proteins inside of cells may be affected by the crowded intracellular environments. Here, we test a novel approach to simulations of crowding, in which simulations in the absence of crowders are postprocessed to predict crowding effects, against the direct approach of simulations in the presence of crowders. The effects of crowding on the flap dynamics of HIV-1 protease predicted by the postprocessing approach are found to agree well with those calculated by the direct approach. The postprocessing approach presents distinct advantages over the direct approach in terms of accuracy and speed and is expected to have broad impact on atomistic simulations of macromolecular crowding

Optical control through light transmission

The simple action of passing laser light through an optically transparent system may enable researchers to control a number of mechanical and optoelectronic processes. These novel interactions of light present an array of useful applications in optical switching, optical binding and fluorescence imaging

Artificial Shelters And Survival Of Juvenile Caribbean Spiny Lobster Panulirus-Argus - Spatial, Habitat, And Lobster Size Effects

A principal mechanism underlying a production hypothesis that artifical reefs increase environmental carrying capacity and eventually the biomass of reef-associated organisms is that these structures reduce predation on reef residents. We tested this predation mechanism with a series of field experiments at two sites (inner-bay sand-seagrass flat, and outer-bay seagrass bed adjacent to coral reefs) in Bahia de la Ascension, Mexico. We examined survival of two size-classes of juvenile Caribbean spiny lobster Panulirus argus tethered in seagrass beds with and without access to artificial lobster shelters, and at different distances from the shelters. The artificial shelters were concrete structures (casitas) that simulate lobster dens. Large juvenile lobsters (56-65 mm CL) attained a relative size refuge when tethered 60 m away from casitas compared with smaller (46-55 mm CL) lobsters. Conversely, the small lobsters survived better beneath casitas than did large lobsters. Small juveniles also survived better at casitas or 30 m away from casitas than at 15 m or 70 m away. Observations indicated that the daytime predator guild, composed primarily of snappers (family Lutjanidae), seldom foraged more than 60 m from casitas and were typically within 15 m of casitas. There was also a significant positive correlation between predation-induced lobster mortality and numbers of snapper associated with casitas at the inner-bay site. Thus, tethering lobsters 70 m away from casitas appeared adequate to examine survival of lobsters in an environment uninfluenced by daytime predators aggregating to casitas. These results indicate that (1) the relative importance of a lobster-size refuge from predators varies according to shelter availability, and (2) that there is a nonlinear relationship between predation risk and distance from an artifical shelter. Our results demonstrate that casitas increase survival of small juvenile lobsters but reduce survival of larger juveniles. Small casitas scaled according to body size may enhance survival of large juvenile lobsters in nursery habitats where large conspecifics are removed from large casitas

The Prevalence of Intestinal Coccidian Parasites Burden in HIV/AIDS Patients on Antiretroviral Therapy in HIV Centers in Mubi, Nigeria

Background: Intestinal coccidia are group of protozoa which parasitize the epithelial cells of the intestinal tract of their hosts. Most infections usually produce mild, self-limiting infections in man, but they now constitute a serious public health problem, especially in developing countries with inadequate sanitary conditions coupled with widespread HIV/AIDS infection.Objective: To determine the Prevalence of intestinal coccidian parasites burden in HIV/AIDS patients on antiretroviral therapy in HIV Centers in Mubi, NigeriaMaterials and Methods: This was a hospital-based cross-sectional study in which stool specimens from  IV-positive patients on ART were examined for the presence ofoocysts of intestinal coccidian parasitesusing Modified Acid Fast Stain technique. In addition, patients’ blood samples were analyzed for CD4 count by flow cytometry and packed cell volume (PCV) through microhaematocrit centrifugation.Results A total of 305 specimens examined, 236(77.4%) were positive for Cryptosporidium parvum, Isospora belli and Microsporidium species. Patients within the age group of 21 – 30 were the most infected. Generally, the  duration of ART influenced the prevalence of the intestinal coccidian parasites. There was a highly significant  association between the CD4 count and prevalence coccidian parasites (p ˂ 0.05). There was a significant  negative correlation (r = -0.95) between the duration of the ART and the prevalence of coccidian presence.Conclusion: Routine screening of HIV-positive patients for intestinal parasites is advocated as standard operative procedure (SOP) before antiretroviral therapy (ART) is given. Construction of public health facilities, toilets and boreholes as well as public enlightenment campaign is recommended for more effective management of these patients.Keywords: intestinal coccidian parasites, antiretroviral therapy, Mubi Contexte: Les coccidies intestinales sont un groupe de protozoaires qui parasitent les cellules épithéliales du tube digestif de leurs hôtes. La plupart des infections humaines sont d'habitude peu sévères et autolimitées, mais elles constituent de nos jours un véritable problème de santé publique, particulièrement dans des pays en voie de développement où les conditions sanitaires sont inadéquates, et couplées à l'infection répanduedu VIH/SIDA.Objectif: Déterminer la fréquence de coccidies intestinales chezles patients atteints de VIH/SIDA sous traitement antirétroviral dans les Centres de contrôle de VIH de Mubi au Nigeria.Matérielset Méthodes: Il s’agissait d’une étude transversale dans laquelle les spécimens de selles des patients séropositifs au VIH et sous traitement antirétroviralétaient examinés en vue d’en dépister là la présence  d’oocystes de coccidies intestinales grâce à la technique de de coloration acido-résistante modifiée. De plus, les  prélèvements de sang des patients étaient analysés pour en déterminer le taux de CD4 et le taux demicro-hématocrite par les techniques de flux cytométrique et de centrifugation respectivement.Résultats: Untotal de 305 spécimens ont été examinés, 236 (77.4 %) étaient positifs pour le Cryptosporidiumparvum,le Isospora belli et les espèces de Microsporidie. Les patients dans la tranche d'âge de 21 – 30 ans étaient les plus infectés. Généralement, la durée du traitement antirétroviralinfluençait la fréquence des coccidies intestinales. Il y avait une association fortement significative entre le taux de CD4 et les infections(p< 0.05). Il existait une corrélation négative significative (r =-0.95) entre la durée detraitement antirétroviralet la fréquence de coccidies intestinales.Conclusion: Le dépistage de routine des patients séropositifs pour des parasites intestinaux est préconisé dans la procédure opératoire standard avant toute administration de thérapie antirétrovirale. La construction d'installations de santé publique, des toilettes et des puits de forage ainsi que des campagnes  d'éducationsanitaire sontfortement recommandées en vue d’une prise en charge effectivedes patients atteints de VIH.Mots-clés : coccidies intestinales, thérapie antirétrovirale, MubiArticle in English

Cx43 regulates mechanotransduction mechanisms in human preterm amniotic membrane defects

Objective: The effects of mechanical stimulation in preterm amniotic membrane (AM) defects were explored. Methods: Preterm AM was collected from women undergoing planned preterm caesarean section (CS) due to fetal growth restriction or emergency CS after spontaneous preterm prelabour rupture of the membranes (sPPROM). AM explants near the cervix or placenta were subjected to trauma and/or mechanical stimulation with the Cx43 antisense. Markers for nuclear morphology (DAPI), myofibroblasts (αSMA), migration (Cx43), inflammation (PGE2) and repair (collagen, elastin and transforming growth factor β [TGFβ1]) were examined by confocal microscopy, second harmonic generation, qPCR and biochemical assays. Results: In preterm AM defects, myofibroblast nuclei were highly deformed and contractile and expressed αSMA and Cx43. Mechanical stimulation increased collagen fibre polarisation and the effects on matrix markers were dependent on tissue region, disease state, gestational age and the number of fetuses. PGE2 levels were broadly similar but reduced after co-treatment with Cx43 antisense in late sPPROM AM defects. TGFβ1 and Cx43 gene expression were significantly increased after trauma and mechanical stimulation but this response dependent on gestational age. Conclusion: Mechanical stimulation affects Cx43 signalling and cell/collagen mechanics in preterm AM defects. Establishing how Cx43 regulates mechanosignalling could be an approach to repair tissue integrity after trauma

Cx43 regulates mechanotransduction mechanisms in human preterm amniotic membrane defects.

OBJECTIVE: The effects of mechanical stimulation in preterm amniotic membrane (AM) defects were explored. METHODS: Preterm AM was collected from women undergoing planned preterm caesarean section (CS) due to fetal growth restriction or emergency CS after spontaneous preterm prelabour rupture of the membranes (sPPROM). AM explants near the cervix or placenta were subjected to trauma and/or mechanical stimulation with the Cx43 antisense. Markers for nuclear morphology (DAPI), myofibroblasts (αSMA), migration (Cx43), inflammation (PGE2 ) and repair (collagen, elastin and transforming growth factor β [TGFβ1 ]) were examined by confocal microscopy, second harmonic generation, qPCR and biochemical assays. RESULTS: In preterm AM defects, myofibroblast nuclei were highly deformed and contractile and expressed αSMA and Cx43. Mechanical stimulation increased collagen fibre polarisation and the effects on matrix markers were dependent on tissue region, disease state, gestational age and the number of fetuses. PGE2 levels were broadly similar but reduced after co-treatment with Cx43 antisense in late sPPROM AM defects. TGFβ1 and Cx43 gene expression were significantly increased after trauma and mechanical stimulation but this response dependent on gestational age. CONCLUSION: Mechanical stimulation affects Cx43 signalling and cell/collagen mechanics in preterm AM defects. Establishing how Cx43 regulates mechanosignalling could be an approach to repair tissue integrity after trauma

Plant communities affect arbuscular mycorrhizal fungal diversity and community composition in grassland microcosms

The diversity of arbuscular mycorrhizal (AM) fungi was investigated in an unfertilized limestone grassland soil supporting different synthesized vascular plant assemblages that had developed for 3 yr. The experimental treatments comprised: bare soil; monocultures of the nonmycotrophic sedge Carex flacca; monocultures of the mycotrophic grass Festuca ovina; and a species-rich mixture of four forbs, four grasses and four sedges. The diversity of AM fungi was analysed in roots of Plantago lanceolata bioassay seedlings using terminal-restriction fragment length polymorphism (T-RFLP). The extent of AM colonization, shoot biomass and nitrogen and phosphorus concentrations were also measured. The AM diversity was affected significantly by the floristic composition of the microcosms and shoot phosphorus concentration was positively correlated with AM diversity. The diversity of AM fungi in P. lanceolata decreased in the order: bare soil > C. flacca > 12 species > F. ovina. The unexpectedly high diversity in the bare soil and sedge monoculture likely reflects differences in the modes of colonization and sources of inoculum in these treatments compared with the assemblages containing established AM-compatible plants