Silica final lens performance in laser fusion facilities: HiPER and LIFE

Nowadays, the projects LIFE (Laser Inertial Fusion Energy) in USA and HiPER (High Power Laser Energy Research) in Europe are the most advanced ones to demonstrate laser fusion energy viability. One of the main points of concern to properly achieve ignition is the performance of the final optics (lenses) under the severe irradiation conditions that take place in fusion facilities. In this paper, we calculate the radiation fluxes and doses as well as the radiation-induced temperature enhancement and colour centre formation in final lenses assuming realistic geometrical configurations for HiPER and LIFE. On these bases, the mechanical stresses generated by the established temperature gradients are evaluated showing that from a mechanical point of view lenses only fulfil specifications if ions resulting from the imploding target are mitigated. The absorption coefficient of the lenses is calculated during reactor startup and steady-state operation. The obtained results reveal the necessity of new solutions to tackle ignition problems during the startup process for HiPER. Finally, we evaluate the effect of temperature gradients on focal length changes and lens surface deformations. In summary, we discuss the capabilities and weak points of silica lenses and propose alternatives to overcome predictable problems

Magnetic resonance imaging based signal intensity mapping predicts appropriate therapies after prophylactic ventricular tachycardia substrate ablation in patients with previous myocardial infarction and secondary prevention implantable cardioverter-defibrillator implantation

The aim of this study was to determine the capability of ceMRI based signal intensity (SI) mapping to predict appropriate ICD therapies after PVTSA.

A novel scanning lens instrument for evaluating Fresnel lens performance: equipment development and initial results

A system dedicated to the optical transmittance characterization of Fresnel lenses has been developed at NREL, in collaboration with the UPM. The system quantifies the optical efficiency of the lens by generating a performance map. The shape of the focused spot may also be analyzed to understand change in the lens performance. The primary instrument components (lasers and CCD detector) have been characterized to confirm their capability for performing optical transmittance measurements. Measurements performed on SoG and PMMA lenses subject to a variety of indoor conditions (e.g., UV and damp heat) identified differences in the optical efficiency of the evaluated lenses, demonstrating the ability of the Scanning Lens Instrument (SLI) to distinguish between the aged lenses.

9-fold Fresnel-Kohler concentrator with Fresnel lens of variable focal point

Non-uniform irradiance patterns over Multi-Junction Cells gives rise to power losses, especially when considering spectral irradiance distributions over different junctions. Thermal effects on Silicone-on-Glass lenses affect spectral irradiance distributions. A new Photovoltaic Concentrator (CPV), formed by nine optical channels, each one with a Köhler configuration, has been designed to overcome these effects at high concentrations for a large acceptance angle. A Fresnel Lens with a Variable Focal Point is proposed to prevent optical crosstalk in multichannel systems. When integrated into the concentrator, improves the acceptance angle. These designs are designed to fulfill the expected requirements of four junction CPV systems.

Flooding through the lens of mobile phone activity

Natural disasters affect hundreds of millions of people worldwide every year. Emergency response efforts depend upon the availability of timely information, such as information concerning the movements of affected populations. The analysis of aggregated and anonymized Call Detail Records (CDR) captured from the mobile phone infrastructure provides new possibilities to characterize human behavior during critical events. In this work, we investigate the viability of using CDR data combined with other sources of information to characterize the floods that occurred in Tabasco, Mexico in 2009. An impact map has been reconstructed using Landsat-7 images to identify the floods. Within this frame, the underlying communication activity signals in the CDR data have been analyzed and compared against rainfall levels extracted from data of the NASA-TRMM project. The variations in the number of active phones connected to each cell tower reveal abnormal activity patterns in the most affected locations during and after the floods that could be used as signatures of the floods - both in terms of infrastructure impact assessment and population information awareness. The epresentativeness of the analysis has been assessed using census data and civil protection records. While a more extensive validation is required, these early results suggest high potential in using cell tower activity information to improve early warning and emergency management mechanisms.

Flooding through the lens of mobile phone activity

Natural disasters affect hundreds of millions of people worldwide every year. Emergency response efforts depend upon the availability of timely information, such as information concerning the movements of affected populations. The analysis of aggregated and anonymized Call Detail Records (CDR) captured from the mobile phone infrastructure provides new possibilities to characterize human behavior during critical events. In this work, we investigate the viability of using CDR data combined with other sources of information to characterize the floods that occurred in Tabasco, Mexico in 2009. An impact map has been reconstructed using Landsat-7 images to identify the floods. Within this frame, the underlying communication activity signals in the CDR data have been analyzed and compared against rainfall levels extracted from data of the NASA-TRMM project. The variations in the number of active phones connected to each cell tower reveal abnormal activity patterns in the most affected locations during and after the floods that could be used as signatures of the floods - both in terms of infrastructure impact assessment and population information awareness. The representativeness of the analysis has been assessed using census data and civil protection records. While a more extensive validation is required, these early results suggest high potential in using cell tower activity information to improve early warning and emergency management mechanisms.

Requirement for the c-Maf transcription factor in crystallin gene regulation and lens development

The vertebrate lens is a tissue composed of terminally differentiated fiber cells and anterior lens epithelial cells. The abundant, preferential expression of the soluble proteins called crystallins creates a transparent, refractive index gradient in the lens. Several transcription factors such as Pax6, Sox1, and L-Maf have been shown to regulate lens development. Here we show that mice lacking the transcription factor c-Maf are microphthalmic secondary to defective lens formation, specifically from the failure of posterior lens fiber elongation. The marked impairment of crystallin gene expression observed is likely explained by the ability of c-Maf to transactivate the crystallin gene promoter. Thus, c-Maf is required for the differentiation of the vertebrate lens.

Conservation of fibroblast growth factor function in lens regeneration

In urodele amphibians, lens induction during development and regeneration occurs through different pathways. During development, the lens is induced from the mutual interaction of the ectoderm and the optic vesicle, whereas after lentectomy the lens is regenerated through the transdifferentiation of the iris-pigmented epithelial cells. Given the known role of fibroblast growth factors (FGFs) during lens development, we examined whether or not the expression and the effects of exogenous FGF during urodele lens regeneration were conserved. In this paper, we describe expression of FGF-1 and its receptors, FGFR-2 (KGFR and bek variants) and FGFR-3, in newts during lens regeneration. Expression of these genes was readily observed in the dedifferentiating pigmented epithelial cells, and the levels of expression were high in the lens epithelium and the differentiating fibers and lower in the retina. These patterns of expression implied involvement of FGFs in lens regeneration. To further elucidate this function, we examined the effects of exogenous FGF-1 and FGF-4 during lens regeneration. FGF-1 or FGF-4 treatment in lentectomized eyes resulted in the induction of abnormalities reminiscent to the ones induced during lens development in transgenic mice. Effects included transformation of epithelial cells to fiber cells, double lens regeneration, and lenses with abnormal polarity. These results establish that FGF molecules are key factors in fiber differentiation, polarity, and morphogenesis of the lens during regeneration even though the regenerating lens is induced by a different mechanism than in lens development. In this sense, FGF function in lens regeneration and development should be regarded as conserved. Such conservation should help elucidate the mechanisms of lens regeneration in urodeles and its absence in higher vertebrates.

Tissue spreading on implantable substrates is a competitive outcome of cell–cell vs. cell–substratum adhesivity

While the interactions of cells with polymeric substrata are widely studied, the influence of cell–cell cohesivity on tissue spreading has not been rigorously investigated. Here we demonstrate that the rate of tissue spreading over a two-dimensional substratum reflects a competition or “tug-of-war” between cell–cell and cell–substratum adhesions. We have generated both a “library” of structurally related copolymeric substrata varying in their adhesivity to cells and a library of genetically engineered cell populations varying only in cohesivity. Cell–substratum adhesivity was varied through the poly(ethylene glycol) content of a series of copolymeric substrata, whereas cell–cell cohesivity was varied through the expression of the homophilic cohesion molecules N- and R-cadherin by otherwise noncohesive L929 cells. In the key experiment, multicellular aggregates containing about 600 cells were allowed to spread onto copolymeric surfaces. We compared the spreading behavior of aggregates having different levels of cell–cell cohesivity on a series of copolymeric substrata having different levels of cell–substratum adhesivity. In these experiments, cell–cell cohesivity was measured by tissue surface tensiometry, and cell–substratum adhesivity was assessed by a distractive method. Tissue spreading was assayed by confocal microscopy as the rate of cell emigration from similar-sized, fluorescence-labeled, multicellular aggregates deposited on each of the substrata. We demonstrate that either decreasing substratum adhesivity or increasing cell–cell cohesivity dramatically slowed the spreading rate of cell aggregates.

Direct observation of iron-induced conformational changes of mitochondrial DNA by high-resolution field-emission in-lens scanning electron microscopy.

When respiring rat liver mitochondria are incubated in the presence of Fe(III) gluconate, their DNA (mtDNA) relaxes from the supercoiled to the open circular form dependent on the iron dose. Anaerobiosis or antioxidants fail to completely inhibit the unwinding. High-resolution field-emission in-lens scanning electron microscopy imaging, in concert with backscattered electron detection, pinpoints nanometer-range iron colloids bound to mtDNA isolated from iron-exposed mitochondria. High-resolution field-emission in-lens scanning electron microscopy with backscattered electron detection imaging permits simultaneous detailed visual analysis of DNA topology, iron dose-dependent mtDNA unwinding, and assessment of iron colloid formation on mtDNA strands.

Heteromeric connexons in lens gap junction channels.

Gap junction channels are formed by paired oligomeric membrane hemichannels called connexons, which are composed of proteins of the connexin family. Experiments with transfected cell lines and paired Xenopus oocytes have demonstrated that heterotypic intercellular channels which are formed by two connexons, each composed of a different connexin, can selectively occur. Studies by Stauffer [Stauffer, K. A. (1995) J. Biol. Chem. 270, 6768-6772] have shown that recombinant Cx26 and Cx32 coinfected into insect cells may form heteromeric connexons. By solubilizing and subfractionating individual connexons from ovine lenses, we show by immunoprecipitation that connexons can contain two different connexins forming heteromeric assemblies in vivo.

Lens complementation system for the genetic analysis of growth, differentiation, and apoptosis in vivo.

A genetic approach has been established that combines the advantages of blastocyst complementation with the experimental attributes of the developing lens for the functional analysis of genes governing cellular proliferation, terminal differentiation, and apoptosis. This lens complementation system (LCS) makes use of a mutant mouse strain, aphakia (ak), homozygotes of which fail to develop an ocular lens. We demonstrate that microinjection of wild-type embryonic stem (ES) cells into ak/ak blastocysts produces chimeras with normal ES-cell-derived lenses and that microinjection of Rb-/- ES cells generates an aberrant lens phenotype identical to that obtained through conventional gene targeting methodology. Our determination that a cell autonomous defect underlies the aphakia condition assures that lenses generated through LCS are necessarily ES-cell-derived. LCS provides for the rapid phenotypic analysis of loss-of-function mutations, circumvents the need for germ-line transmission of null alleles, and, most significantly, facilitates the study of essential genes whose inactivation is associated with early lethal phenotypes.

Phase separation in aqueous solutions of lens gamma-crystallins: special role of gamma s.

We have studied liquid-liquid phase separation in aqueous ternary solutions of calf lens gamma-crystallin proteins. Specifically, we have examined two ternary systems containing gamma s--namely, gamma IVa with gamma s in water and gamma II with gamma s in water. For each system, the phase-separation temperatures (Tph (phi)) alpha as a function of the overall protein volume fraction phi at various fixed compositions alpha (the "cloud-point curves") were measured. For the gamma IVa, gamma s, and water ternary solution, a binodal curve composed of pairs of coexisting points, (phi I, alpha 1) and (phi II, alpha II), at a fixed temperature (20 degrees C) was also determined. We observe that on the cloud-point curve the critical point is at a higher volume fraction than the maximum phase-separation temperature point. We also find that typically the difference in composition between the coexisting phases is at least as significant as the difference in volume fraction. We show that the asymmetric shape of the cloud-point curve is a consequence of this significant composition difference. Our observation that the phase-separation temperature of the mixtures in the high volume fraction region is strongly suppressed suggests that gamma s-crystallin may play an important role in maintaining the transparency of the lens.

An apoptotic defect in lens differentiation caused by human p53 is rescued by a mutant allele.

If deprived of wild-type p53 function, the body loses a guardian that protects against cancer. Restoration of p53 function has, therefore, been proposed as a means of counteracting oncogenesis. This concept of therapy requires prior knowledge with regard to proper balance of p53 function in a given target tissue. We have addressed this problem by targeting expression of the wild-type human p53 gene to the lens, a tissue entirely composed of epithelial cells that differentiate into elongated fiber cells. Transgenic mice expressing wild-type human p53 develop microphthalmia as a result of a defect in fiber formation that sets in shortly after birth. We see apoptotic cells that fail to undergo proper differentiation. In an effort to directly link the observed lens phenotype to the activity of the wild-type human p53 transgene, we also generated mice expressing a mutant human p53 allele that lacks wild-type function. A normal lens phenotype is restored in double transgenic animals that carry both wild-type and mutant human p53 alleles. Our study highlights the difficulties that can arise if p53 levels are improperly balanced in a differentiating tissue.