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We dispersed electrochemical etched Si into a colloid of ultrabright blue luminescent nanoparticles (1 nm in diameter) and reconstituted it into films or microcrystallites. When the film is excited by a near-infrared two-photon process at 780 nm, the emission exhibits a sharp threshold near 106 W/cm2, rising by many orders of magnitude, beyond which a low power dependence sets in. Under some conditions, spontaneous recrystallization forms crystals of smooth shape from which we observe collimated beam emission, pointing to very large gain coefficients. The results are discussed in terms of population inversion, produced by quantum tunneling or/and thermal activation, and stimulated emission in the quantum confinement-engineered Si-Si phase found only on ultrasmall Si nanoparticles. The Si-Si phase model provides gain coefficients as large as 103-105 cm-1. © 2001 American Institute of Physics.

We dispersed crystalline Si into a colloid of ultrasmall nano particles (∼1 nm), and reconstituted it into microcrystallites films on device-quality Si. The film is excited by near-infrared femtosecond two-photon process in the range 765-835 nm, with incident average power in the range 15-70 mW, focused to ∼1 μm. We have observed strong radiation at half the wavelength of the incident beam. The results are analyzed in terms of second-harmonic generation, a process that is not allowed in silicon due to the centrosymmetry. Ionic vibration of or/and excitonic self-trapping on novel radiative Si-Si dimer phase, found only in ultrasmall nanoparticles, are suggested as a basic mechanism for inducing anharmonicity that breaks the centrosymmetry. © 2000 American Institute of Physics.

We dispersed electrochemical etched Si into a colloid of ultrasmall blue luminescent nanoparticles, observable with the naked eye, in room light. We use two-photon near-infrared femtosecond excitation at 780 nm to record the fluctuating time series of the luminescence, and determine the number density, brightness, and size of diffusing fluorescent particles. The luminescence efficiency of particles is high enough such that we are able to detect a single particle, in a focal volume, of 1 pcm3. The measurements yield a particle size of 1 nm, consistent with direct imaging by transmission electron microscopy. They also yield an excitation efficiency under two-photon excitation two to threefold larger than that of fluorescein. Detection of single particles paves the way for their use as labels in biosensing applications. © 2000 American Institute of Physics.

Porous silicon is excited using near-infrared femtosecond pulsed and continuous wave radiation at an average intensity of ∼106 W/cm2 (8×1010 ;W/cm2 peak intensity in pulsed mode). Our results demonstrate the presence of micron-size regions for which the intensity of the photoluminescence has a highly nonlinear threshold, rising by several orders of magnitude near this incident intensity for both the pulsed and continuous wave cases. These results are discussed in terms of stimulated emission from quantum confinement engineered intrinsic Si-Si radiative traps in ultrasmall nanocrystallites, populated following two-photon absorption. © 1999 American Institute of Physics.

Analysis of carbon ([sup.13]C/[sup.12]C) and nitrogen ([sup.15]N/[sup.14]N) stable isotope ratios (hereafter [delta][sup.13]C and [delta][sup.15]N, respectively) in animal tissues is a powerful tool in food-web studies. However, isotopic ratios of prey are not transmitted directly to a consumer, as a diet-tissue discrimination factor (denoted A) occurs between sources and consumer's tissues. An accurate assessment of the diet of a consumer with stable isotopes thus requires that the [DELTA][sup.13]C and [DELTA][sup.15]N of the studied species are known. Our aim was to establish [DELTA][sup.13]C and [DELTA][sup.15]N values in the Snowy Owl (Bubo scandiacus (L., 1758)). Moreover, we assessed the potential effect of ethanol preservation of blood samples on [delta][sup.13]C and [delta][sup.15]N values. We kept four captive adult Snowy Owls on a pure diet of mice for [greater than or equal to] 6 weeks. We then collected mouse muscle and blood samples from the owls and analyzed their [delta][sup.13]C and [delta][sup.15]N values. [DELTA][sup.13]C and [DELTA][sup.15]N values (mean [+ or -] SE) for owl blood were +0.3 [per thousand] [+ or -] 0.2 [per thousand] and +1.9 [per thousand] [+ or -] 0.1 [per thousand], respectively. These values are the first discrimination factors ever reported in Strigiformes and are lower, for [DELTA][sup.15]N, than those obtained in terrestrial carnivores and other bird species, including falcons. Preservation in ethanol did not significantly affect [delta][sup.13]C and [delta][sup.15]N values. L'analyse des ratios isotopiques de carbone ([sup.13]C/[sup.12]C) et d'azote ([sup.15]N/[sup.14]N) (symbolises par [delta][sup.13]C et [delta][sup.15]N respectivement) dans les tissus animaux est un outil puissant pour l' etude des reseaux trophiques. Cependant, les ratios isotopiques des proies ne sont pas transmis directement au consommateur et un facteur de discrimination (note [DELTA]) est observe entre les ratios des sources et ceux du consommateur. La determination exacte du regime alimentaire d'un consommateur a l'aide des isotopes stables demande donc une connaissance des [DELTA][sup.13]C et [DELTA][sup.15]N chez l'espece a l'etude. Notre objectif etait de determiner les valeurs de [DELTA][sup.13]C et [DELTA][sup.15]N chez le harfang des neiges (Bubo scandiacus (L., 1758)). De plus, nous voulions determiner l'impact potentiel de la conservation d'echantillons sanguins dans une solution d'ethanol 70 % sur les valeurs de [delta][sup.13]Cet [delta][sup.15]N. Nous avons garde quatre harfangs des neiges en captivite, nourris exclusivement de souris pendant [greater than or equal to] 6 semaines. Nous avons ensuite recolte des echantillons sanguins des oiseaux et des muscles de souris et nous avons determine leur signature de [delta][sup.13]C et de [delta][sup.15]N. Les valeurs de [DELTA][sup.13]C et [DELTA][sup.15]N (moyenne [+ or -] ES) du sang chez le harfang des neiges sont de +0,3 [per thousand] [+ or -] 0,2 [per thousand] et +1,9 [per thousand] [+ or -] 0,1 [per thousand], respectivement. Ces valeurs de discrimination sont les premieres rapportees a ce jour chez les strigiformes et elles sont plus faibles, pour l'azote, que celles observees chez les carnivores terrestres et d'autres especes d'oiseaux, incluant les faucons. La conservation des echantillons sanguins dans une solution d'ethanol 70 % n'as pas affecte significativement les valeurs de [delta][sup.13]C et de [delta][sup.15]N., Introduction Naturally occurring stable isotopes of carbon ([sup.13]C, [sup.12]C) and nitrogen ([sup.15]N, [sup.14]N) are present in every living organism and they occur under specific ratios (denoted [delta][sup.13]C and [delta][sup.15]N, respectively) [...]

At the La Grande hydroelectric complex located in northern Quebec, Canada, mercury concentrations were measured in over 25 000 fish as part of an ongoing environmental effects monitoring program. Five fish species were monitored over a 30-year period: the non-piscivorous lake whitefish (Coregonus clupeaformis) and longnose sucker (Catostomus catostomus) and the piscivorous northern pike (Esox lucius), walleye (Sander vitreus) and lake trout (Salvelinus namaycush). Total mercury concentrations were measured by standard cold vapour atomic absorption spectrophotometry. Fish population characteristics, such as fishing yields, growth rates and condition factors were also monitored over a 20-year period. In reservoirs, mercury concentrations in all species increased rapidly after impoundment, peaking after 5 to 9 years in non-piscivorous fishes, and after 9 to 11 years in piscivorous species, at levels 3 to 6 times those measured in surrounding natural lakes, then significantly and gradually declined. Concentrations in most species have returned to levels typical of natural lakes, 10 to 30 years after flooding. Despite such increases, the monitored fish showed no mercury-related ill effects at the population level. For most species, increases were observed in fishing yields (by factors ranging from 2 to over 20), in growth rates and in condition factors (for more than a decade). The fishing yield increase was highest for northern pike of the Robert-Bourassa Reservoir, for which the highest average mercury concentrations were measured (3.28 μg g-1 (ww) for 700-mm fish). The biological boom usually observed after reservoir impoundment, resulting from increased nutrients, may have prevented potential mercury-related ill effects.

Predator–prey interactions can control population fluctuations of several terrestrial vertebrates and energy fluxes in food webs. Quantifying these interactions typically requires the number of prey consumed by predators to be known, but prey size is often ignored. We hypothesized that rodent mandibles, which are routinely found in predatory bird pellets and mammalian scats, could be used to accurately determine prey size and thus estimate biomass consumed by Arctic predators. We used 1863 lemmings and voles from museum and field specimens collected across the North American Arctic to relate three measurements of the dentary bone and one on the molar toothrow with individual body mass. When species and location of specimens are known, our results suggest that the body mass of small rodents can be estimated with high precision using the dentary bone measurements (average R2 ranging from 0.73 to 0.81), especially for lemmings and Microtus voles. Body mass can also be estimated with reasonable precision using the dentary bone measurements even when species or location was unknown (0.71 ≤ R2 ≤ 0.80). Equations to convert mandible size to body mass are provided for site‐ and species‐specific estimations. Geographic variations in the relationship between mandible size and body mass were found, suggesting potential effects of genetic isolation or interactions with the immediate environment on size. Using mandible measurements in prey remains allows more precise estimation of biomass consumed by predators, which is essential to quantify energy fluxes within ecosystems and examine resource partitioning among Arctic predators. [ABSTRACT FROM AUTHOR]

With its thick, leathery leaves, reticulate venation, and large sori, Polypodium scouleri, located in a narrow band along the Pacific coast of North America, is perhaps the most distinctive member of the cosmopolitan P. vulgare species complex. Although early studies based on morphology and chromosomes were able to develop hypotheses about the relationships among some elements of this complex, no close alliances to P. scouleri could be proposed. Combining data from rbcL and trnL DNA sequences with isozymic analyses suggests that P. scouleri is a recently evolved species that is closely allied to and sympatric with P. californicum and P. glycyrrhiza. Alternatively, because isozyme data indicate that P. scouleri is quite distinct from its sympatric neighbors, hybridization between these lineages may have led to chloroplast capture prior to range expansion of P. scouleri. Adding further intrigue is that P. scouleri contrasts strikingly with its congeners in having never been implicated in the origin of allotetraploid derivatives. As early as 1951, Manton suggested that P. scouleri could be forming hybrids with neighboring polypods, but she was sufficiently unsure of the morphology to request, 'a purer sample of P. scouleri,' before stating positively that hybrids had been discovered. Since that time, others have suggested that P. scouleri might be involved in hybridization, but no solid evidence has been obtained. Using isozyme techniques, we have detected little or no infraspecific variation across the range of the species. We have been able to confirm that P. scouleri is hybridizing with neighboring P. californicum and/or P. calirhiza. Individuals that appear to be intermediate in morphology contain isozyme marker alleles from two putative lineages. We are currently characterizing these hybrids further and studying the dynamics of this interesting population and species.

A valence isoelectronic and isostructural series of charged bis(N-heterocyclic carbene) pincer complexes [M(bC^N^bC)X]OTf and [M(bC^N^bC)CH3CN](OTf)2 (where M = Ni, Pd, and Pt, bC^N^bC = 1,1′-(pyridine-2,6-diylbis(methylene))bis(3-butylbenzo[d]imidazol-2-ylidene)) were synthesized, characterized, modelled by density functional theory calculations, and compared for their electrochemical properties and reactivity with CO2. Although the electrochemical response of each complex is altered by the presence of CO2, controlled potential electrolysis experiments demonstrated the superior ability of [Pd] to reduce CO2 to CO in faradaic efficiencies up to 58% in the presence of trifluoroacetic acid, compared to [Pt] and [Ni] which showed only marginal production of CO, giving the trend [Pd] > [Pt] ＞ [Ni] for this series. [ABSTRACT FROM AUTHOR]

Reasons for performing study: Skin trauma in horses often leads to the development of chronic nonhealing wounds that lack a keratinocyte cover, vital for healing. Reports in mouse and man confirm the possibility of generating functional keratinocytes from induced pluripotent stem cells (iPSC), thus presenting myriad potential applications for wound management or treatment of skin disease. Similarly, differentiation of equine iPSC (eiPSC) into a keratinocyte lineage should provide opportunities for the advancement of veterinary regenerative medicine. Objectives: The purpose of this study was to develop an efficient method for the differentiation of eiPSC into a keratinocyte lineage. It was hypothesised that eiPSC can form differentiated keratinocytes (eiPSC-KC) comparable with primary equine keratinocytes (PEK) in their morphological and functional characteristics. Study design: Experimental in vitro study. Methods: Equine iPSC established using a nonviral system were treated for 30 days with retinoic acid and bone morphogenetic protein-4 to induce directed differentiation into iPSC-KC. Temporospatial gene and protein expression by eiPSC-KC was measured at weekly intervals of differentiation and in response to calcium switch. Proliferative and migratory capacities of eiPSC-KC were compared with those of PEK. Results: Equine iPSC, upon directed differentiation, showed loss of pluripotency genes and progressive increase in pancytokeratin expression indicating ectodermal specification into keratinocytes. High differentiation efficiency was achieved, with 82.5% of eiPSC expressing keratin 14, a marker of epidermal-specific basal stem cells, after 30 days of directed differentiation. Moreover, the proliferative capacity of eiPSC-KC was superior, while the migratory capacity (measured as the ability to epithelise in vitro wounds) was comparable with that of PEK. Conclusions: This proof of concept study suggests that eiPSC can successfully be differentiated into equine keratinocytes (eiPSC-KC) with features that are promising to the development of a stem cell-based skin construct, with the potential to regenerate lost or damaged skin. [ABSTRACT FROM AUTHOR]