3,620 research outputs found
Association of drusen deposition with choroidal intercapillary pillars in the aging human eye
PURPOSE. To determine the pattern of drusen accumulation with age and to investigate the initial sites of deposition and their relationship to choroidal capillaries in human donor eyes from the eye bank of Moorfields Eye Hospital.METHODS. Wholemounted, hydrated preparations of the choriocapillaris and Bruch's membrane from donor eyes ranging from 42 to 95 years, with or without retinal pigment epithelium (RPE), were examined by conventional and confocal microscopy. Drusen were visualized by their autofluorescence.RESULTS. In all age groups studied autofluorescent drusen were present at the equator but were not found centrally where the vascular architecture is different, being tubular rather than a honeycomb pattern. Autofluorescing drusen were strongly associated with the lateral walls of the choriocapillaris (an area commonly known as the intercapillary pillars of the choriocapillaris (P = 0.028; Wilcoxon signed ranks test). Nonfluorescing drusen were occasionally seen centrally, but were not easily identified, and because of their large size, their localization with respect to capillary walls was not possible.CONCLUSIONS. These results strongly support the notion that autofluorescent drusen are not randomly distributed and have a specific spatial relationship to choroidal vessel walls. That equatorial drusen fluoresce, whereas central drusen do not, suggests that they may have different chemical compositions at the two sites and possibly different significance in age-related macular disease
Herpetofaunal Inventories of the National Parks of South Florida and the Caribbean: Volume III. Big Cypress National Preserve
Amphibian declines and extinctions have been documented around the world, often in protected
natural areas. Concern for this trend has prompted the U.S. Geological Survey and the National Park
Service to document all species of amphibians that occur within U.S. National Parks and to search for any
signs that amphibians may be declining. This study, an inventory of amphibian species in Big Cypress
National Preserve, was conducted from 2002 to 2003. The goals of the project were to create a
georeferenced inventory of amphibian species, use new analytical techniques to estimate proportion of
sites occupied by each species, look for any signs of amphibian decline (missing species, disease, die-offs,
and so forth.), and to establish a protocol that could be used for future monitoring efforts.
Several sampling methods were used to accomplish these goals. Visual encounter surveys and
anuran vocalization surveys were conducted in all habitats throughout the park to estimate the proportion
of sites or proportion of area occupied (PAO) by each amphibian species in each habitat. Opportunistic
collections, as well as limited drift fence data, were used to augment the visual encounter methods for
highly aquatic or cryptic species. A total of 545 visits to 104 sites were conducted for standard sampling
alone, and 2,358 individual amphibians and 374 reptiles were encountered. Data analysis was conducted
in program PRESENCE to provide PAO estimates for each of the anuran species.
All of the amphibian species historically found in Big Cypress National Preserve were detected
during this project. At least one individual of each of the four salamander species was captured during
sampling. Each of the anuran species in the preserve was adequately sampled using standard
herpetological sampling methods, and PAO estimates were produced for each species of anuran by habitat.
This information serves as an indicator of habitat associations of the species and relative abundance of
sites occupied, but it will also be useful as a comparative baseline for future monitoring efforts.
In addition to sampling for amphibians, all encounters with reptiles were documented. The
sampling methods used for detecting amphibians are also appropriate for many reptile species. These
reptile locations are included in this report, but the number of reptile observations was not sufficient to
estimate PAO for reptile species. We encountered 35 of the 46 species of reptiles believed to be present in
Big Cypress National Preserve during this study, and evidence exists of the presence of four other reptile
species in the Preserve.
This study found no evidence of amphibian decline in Big Cypress National Preserve. Although no
evidence of decline was observed, several threats to amphibians were identified. Introduced species,
especially the Cuban treefrog (Osteopilus septentrionalis), are predators and competitors with several
native frog species. The recreational use of off-road vehicles has the potential to affect some amphibian
populations, and a study on those potential impacts is currently underway. Also, interference by humans
with the natural hydrologic cycle of south Florida has the potential to alter the amphibian community.
Continued monitoring of the amphibian species in Big Cypress National Preserve is recommended.
The methods used in this study were adequate to produce reliable estimates of the proportion of sites
occupied by most anuran species, and are a cost-effective means of determining the status of their
populations
Weeklong improved colour contrasts sensitivity after single 670 nm exposures associated with enhanced mitochondrial function
Mitochondrial decline in ageing robs cells of ATP. However, animal studies show that long wavelength exposure (650-900 nm) over weeks partially restores ATP and improves function. The likely mechanism is via long wavelengths reducing nanoscopic interfacial water viscosity around ATP rota pumps, improving their efficiency. Recently, repeated 670 nm exposures have been used on the aged human retina, which has high-energy demands and significant mitochondrial and functional decline, to improve vision. We show here that single 3 min 670 nm exposures, at much lower energies than previously used, are sufficient to significantly improve for 1 week cone mediated colour contrast thresholds (detection) in ageing populations (37-70 years) to levels associated with younger subjects. But light needs to be delivered at specific times. In environments with artificial lighting humans are rarely dark-adapted, hence cone function becomes critical. This intervention, demonstrated to improve aged mitochondrial function can be applied to enhance colour vision in old age
Diffusiophoretic Behavior of Polyelectrolyte-Coated Particles
Diffusiophoresis, the movement of particles under a solute concentration gradient, has practical implications in a number of applications, such as particle sorting, focusing, and sensing. For diffusiophoresis in an electrolyte solution, the particle velocity is described by the electrolyte relative concentration gradient and the diffusiophoretic mobility of the particle. The electrolyte concentration, which typically varies throughout the system in space and time, can also influence the zeta potential of particles in space and time. This variation affects the diffusiophoretic behavior, especially when the zeta potential is highly dependent on the electrolyte concentration. In this work, we show that adsorbing a single bilayer (or 4 bilayers) of a polyelectrolyte pair (PDADMAC/PSS) on the surface of microparticles resulted in effectively constant zeta potential values with respect to salt concentration throughout the experimental range of salt concentrations. This allowed a constant potential model for diffusiophoretic transport to describe the experimental observations, which was not the case for uncoated particles in the same electrolyte system. This work highlights the use of simple polyelectrolyte pairs to tune the zeta potential and maintain constant values for precise control of diffusiophoretic transport
Limitations in Predicting the Space Radiation Health Risk for Exploration Astronauts
Despite years of research, understanding of the space radiation environment
and the risk it poses to long-duration astronauts remains limited. There is a
disparity between research results and observed empirical effects seen in human
astronaut crews, likely due to the numerous factors that limit terrestrial
simulation of the complex space environment and extrapolation of human clinical
consequences from varied animal models. Given the intended future of human
spaceflight, with efforts now to rapidly expand capabilities for human missions
to the moon and Mars, there is a pressing need to improve upon the
understanding of the space radiation risk, predict likely clinical outcomes of
interplanetary radiation exposure, and develop appropriate and effective
mitigation strategies for future missions. To achieve this goal, the space
radiation and aerospace community must recognize the historical limitations of
radiation research and how such limitations could be addressed in future
research endeavors. We have sought to highlight the numerous factors that limit
understanding of the risk of space radiation for human crews and to identify
ways in which these limitations could be addressed for improved understanding
and appropriate risk posture regarding future human spaceflight.Comment: Accepted for publication by Nature Microgravity (2018
An analysis of ultraviolet spectra of Extreme Helium Stars and new clues to their origins
Abundances of about 18 elements including the heavy elements Y and Zr are
determined from Hubble Space Telescope Space Telescope Imaging Spectrograph
ultraviolet spectra of seven extreme helium stars (EHes): LSE 78, BD+10 2179,
V1920 Cyg, HD 124448, PV Tel, LS IV -1 2, and FQ Aqr. New optical spectra of
the three stars -- BD+10 2179, V1920 Cyg, and HD 124448 were analysed. The
abundance analyses is done using LTE line formation and LTE model atmospheres
especially constructed for these EHe stars. The stellar parameters derived from
an EHe's UV spectrum are in satisfactory agreement with those derived from its
optical spectrum. Adopted abundances for the seven EHes are from a combination
of the UV and optical analyses. Published results for an additional ten EHes
provide abundances obtained in a nearly uniform manner for a total of 17 EHes,
the largest sample on record. The initial metallicity of an EHe is indicated by
the abundance of elements from Al to Ni; Fe is adopted to be the representative
of initial metallicity. Iron abundances range from approximately solar to about
one-hundredth of solar. Clues to EHe evolution are contained within the H, He,
C, N, O, Y, and Zr abundances. Two novel results are (i) the O abundance for
some stars is close to the predicted initial abundance yet the N abundance
indicates almost complete conversion of initial C, N, and O to N by the
CNO-cycles; (ii) three of the seven stars with UV spectra show a strong
enhancement of Y and Zr attributable to an s-process. The observed compositions
are discussed in light of expectations from accretion of a He white dwarf by a
CO white dwarf.Comment: 126 pages, 15 figures, 20 Tables, accepted for publication in the Ap
Possible Stellar Metallicity Enhancements from the Accretion of Planets
A number of recently discovered extrasolar planet candidates have
surprisingly small orbits, which may indicate that considerable orbital
migration takes place in protoplanetary systems. A natural consequence of
orbital migration is for a series of planets to be accreted, destroyed, and
then thoroughly mixed into the convective envelope of the central star. We
study the ramifications of planet accretion for the final main sequence
metallicity of the star. If maximum disk lifetimes are on the order of 10 Myr,
stars with masses near 1 solar mass are predicted to have virtually no
metallicity enhancement. On the other hand, early F and late A type stars with
masses of 1.5--2.0 solar masses can experience significant metallicity
enhancements due to their considerably smaller convection zones during the
first 10 Myr of pre-main-sequence evolution. We show that the metallicities of
an aggregate of unevolved F stars are consistent with an average star accreting
about 2 Jupiter-mass planets from a protoplanetary disk having a 10 Myr
dispersal time.Comment: 14 pages, AAS LaTeX, 3 figures, accepted to ApJ Letter
Mitochondrial absorption of short wavelength light drives primate blue retinal cones into glycolysis which may increase their pace of aging
Photoreceptors have high energy demands and densely packed mitochondria through which light passes before phototransduction. Old world primates including humans have three cone photoreceptor types mediating color vision with short (S blue), medium (M green), and long (L red) wavelength sensitivities. However, S-cones are enigmatic. They comprise <10% of the total cone population, their responses saturate early, and they are susceptible in aging and disease. Here, we show that primate S-cones actually have few mitochondria and are fueled by glycolysis, not by mitochondrial respiration. Glycolysis has a limited ability to sustain activity, potentially explaining early S-cone saturation. Mitochondria act as optical filters showing reduced light transmission at 400–450 nm where S-cones are most sensitive (420 nm). This absorbance is likely to arise in a mitochondrial porphyrin that absorbs strongly in the Soret band. Hence, reducing mitochondria will improve S-cone sensitivity but result in increased glycolysis as an alternative energy source, potentially increasing diabetic vulnerability due to restricted glucose access. Further, glycolysis carries a price resulting in premature functional decline as seen in aged S-cones. Soret band absorption may also impact on mitochondrial rich M and L cones by reducing sensitivity at the lower end of their spectral sensitivity range resulting in increased differentiation from S-cone responses. These data add to the list of unique characteristic of S-cones and may also explain aspects of their vulnerability
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