Vision Stations: Addressing Corrective Vision Needs With Low-cost Technologies

Eyeglasses, required for functional vision by nearly half the world\u27s population, are still needed by more than a billion people. There are a number of constraints on the provision of eyeglasses: product cost, durability, and appearance; traditional approaches to evaluating refraction; and sustainably scaling potential distribution methods. We offer our experience with an immigrant population in a US urban setting using a Vision Station. The station allowed for immediate provision of adjustable glasses using self-refraction, ordering of custom lenses from a low-cost website, and referral to primary and eye care physicians for those with medical eye concerns. As with models in development by other groups, Vision Stations connect people with the life-changing provision of functional vision

Stratification of sunspot umbral dots from inversion of Stokes profiles recorded by Hinode

This work aims to constrain the physical nature of umbral dots (UDs) using high-resolution spectropolarimetry. Full Stokes spectra recorded by the spectropolarimeter on Hinode of 51 UDs in a sunspot close to the disk center are analyzed. The height dependence of the temperature, magnetic field vector, and line-of-sight velocity across each UD is obtained from an inversion of the Stokes vectors of the two FeI lines at 630 nm. No difference is found at higher altitudes (-3 <= log(tau) <= -2) between the UDs and the diffuse umbral background. Below that level the difference rapidly increases, so that at the continuum formation level (log(tau) = 0) we find on average a temperature enhancement of 570 K, a magnetic field weakening of 510 G, and upflows of 800 m/s for peripheral UDs, whereas central UDs display an excess temperature of on average 550 K, a field weakening of 480 G, and no significant upflows. The results for, in particular, the peripheral UDs, including cuts of magnetic vector and velocity through them, look remarkably similar to the output of recent radiation MHD simulations. They strongly suggest that UDs are produced by convective upwellings

Persistence and vertical movement of 2,4-dichlorophenoxyacetic acid in two subarctic soils

Thesis (M.S.) University of Alaska Fairbanks, 2009"The persistence of 2,4-dichlorophenoxyacetic acid (2,4-D) was studied in soils from two sub-arctic regions of Alaska. Study sites were established in Delta Junction, where the climate is cold and dry, and Valdez, a more temperate and humid climate. Soil samples were collected from three depth ranges (0-7.6 cm, 10-30 cm, and 36-60 cm) for roughly 360 days following the application of 2,4-D iso-octyl ester at both study sites. 2,4-D was extracted from the soil samples and analyzed using a gas chromatograph and mass selection detector (GC/MSD). Both study sites saw vertical movement of the herbicide, with 2,4-D concentrations detected to a depth of 60 cm in the soil column. The half-life calculated for the Delta Junction site during the growing season was comparable to those observed in studies conducted in temperate climates. However, 2,4-D exhibited longer persistence times at both study sites than the persistence observed in studies conducted in temperate climates, with 2,4-D concentrations present in surface soils one year after application"--Leaf ii

On the inversion of Stokes profiles with local stray-light contamination

Obtaining the magnetic properties of non-resolved structures in the solar photosphere is always challenging and problems arise because the inversion is carried out through the numerical minimization of a merit function that depends on the proposed model. We investigate the reliability of inversions in which the stray-light contamination is obtained from the same observations as a local average. In this case, we show that it is fundamental to include the covariance between the observed Stokes profiles and the stray-light contamination. The ensuing modified merit function of the inversion process penalizes large stray-light contaminations simply because of the presence of positive correlations between the observables and the stray-light, fundamentally produced by spatially variable systematics. We caution that using the wrong merit function, artificially large stray-light contaminations might be inferred. Since this effect disappears if the stray-light contamination is obtained as an average over the full field-of-view, we recommend to take into account stray-light contamination using a global approach.Comment: 5 pages, 3 figures, accepted for publication in Ap

Bovine oocytes in secondary follicles grow and acquire meiotic competence in severe combined immunodeficient mice

A rigorous methodology is developed that addresses numerical and statistical issues when developing group contribution (GC) based property models such as regression methods, optimization algorithms, performance statistics, outlier treatment, parameter identifiability, and uncertainty of the prediction. The methodology is evaluated through development of a GC method for the prediction of the heat of combustion (Δ<i>H</i>_c^o) for pure components. The results showed that robust regression lead to best performance statistics for parameter estimation. The bootstrap method is found to be a valid alternative to calculate parameter estimation errors when underlying distribution of residuals is unknown. Many parameters (first, second, third order group contributions) are found unidentifiable from the typically available data, with large estimation error bounds and significant correlation. Due to this poor parameter identifiability issues, reporting of the 95% confidence intervals of the predicted property values should be mandatory as opposed to reporting only single value prediction, currently the norm in literature. Moreover, inclusion of higher order groups (additional parameters) does not always lead to improved prediction accuracy for the GC-models; in some cases, it may even increase the prediction error (hence worse prediction accuracy). However, additional parameters do not affect calculated 95% confidence interval. Last but not least, the newly developed GC model of the heat of combustion (Δ<i>H</i>_c^o) shows predictions of great accuracy and quality (the most data falling within the 95% confidence intervals) and provides additional information on the uncertainty of each prediction compared to other Δ<i>H</i>_c^o models reported in literature

Bayesian inference of solar and stellar magnetic fields in the weak-field approximation

The weak-field approximation is one of the simplest models that allows us to relate the observed polarization induced by the Zeeman effect with the magnetic field vector present on the plasma of interest. It is usually applied for diagnosing magnetic fields in the solar and stellar atmospheres. A fully Bayesian approach to the inference of magnetic properties in unresolved structures is presented. The analytical expression for the marginal posterior distribution is obtained, from which we can obtain statistically relevant information about the model parameters. The role of a-priori information is discussed and a hierarchical procedure is presented that gives robust results that are almost insensitive to the precise election of the prior. The strength of the formalism is demonstrated through an application to IMaX data. Bayesian methods can optimally exploit data from filter-polarimeters given the scarcity of spectral information as compared with spectro-polarimeters. The effect of noise and how it degrades our ability to extract information from the Stokes profiles is analyzed in detail.Comment: 16 pages, 5 figures, accepted for publication in Ap

On detectability of Zeeman broadening in optical spectra of F- and G-dwarfs

We investigate the detectability of Zeeman broadening in optical Stokes I spectra of slowly rotating sun-like stars. To this end, we apply the LTE spectral line inversion package SPINOR to very-high quality CES data and explore how fit quality depends on the average magnetic field, Bf . One-component (OC) and two-component (TC) models are adopted. In OC models, the entire surface is assumed to be magnetic. Under this assumption, we determine formal 3{\sigma} upper limits on the average magnetic field of 200 G for the Sun, and 150 G for 61 Vir (G6V). Evidence for an average magnetic field of ~ 500 G is found for 59 Vir (G0V), and of ~ 1000 G for HD 68456 (F6V). A distinction between magnetic and non-magnetic regions is made in TC models, while assuming a homogeneous distribution of both components. In our TC inversions of 59 Vir, we investigate three cases: both components have equal temperatures; warm magnetic regions; cool magnetic regions. Our TC model with equal temperatures does not yield significant improvement over OC inversions for 59 Vir. The resulting Bf values are consistent for both. Fit quality is significantly improved, however, by using two components of different temperatures. The inversions for 59 Vir that assume different temperatures for the two components yield results consistent with 0 - 450 G at the formal 3{\sigma} confidence level. We thus find a model dependence of our analysis and demonstrate that the influence of an additional temperature component can dominate over the Zeeman broadening signature, at least in optical data. Previous comparable analyses that neglected effects due to multiple temperature components may be prone to the same ambiguities.Comment: 18 pages, 11 figures, accepted for publication in Astronomy & Astrophysic

Morphology of powerful suction organs from blepharicerid larvae living in raging torrents

BackgroundSuction organs provide powerful yet dynamic attachments for many aquatic animals, including octopus, squid, remora, and clingfish. While the functional morphology of suction organs from some cephalopods and fishes has been investigated in detail, there are only few studies on such attachment devices in insects. Here we characterise the morphology and ultrastructure of the suction attachment organs of net-winged midge larvae (genus Liponeura; Diptera: Blephariceridae) – aquatic insects that live on rocks in rapid alpine waterways where flow speeds can reach 3 m s− 1 – using scanning electron microscopy, confocal laser scanning microscopy, and X-ray computed micro-tomography (micro-CT). Furthermore, we study the function of these organs in vivo using interference reflection microscopy.ResultsWe identified structural adaptations important for the function of the suction attachment organs in L. cinerascens and L. cordata. First, a dense array of spine-like microtrichia covering each suction disc comes into contact with the substrate upon attachment, analogous to hairy structures on suction organs from octopus, clingfish, and remora fish. These spine-like microtrichia may contribute to the seal and provide increased shear force resistance in high-drag environments. Second, specialised rim microtrichia at the suction disc periphery were found to form a continuous ring in close contact and may serve as a seal on a variety of surfaces. Third, a V-shaped cut on the suction disc (“V-notch“) is actively opened via two cuticular apodemes inserting on its flanks. The apodemes are attached to dedicated V-notch opening muscles, thereby providing a unique detachment mechanism. The complex cuticular design of the suction organs, along with specialised muscles that attach to them, allows blepharicerid larvae to generate powerful attachments which can withstand strong hydrodynamic forces and quickly detach for locomotion.ConclusionThe suction organs from Liponeura are underwater attachment devices specialised for resisting extremely fast flows. Structural adaptations from these suction organs could translate into future bioinspired attachment systems that perform well on a wide range of surfaces

Nonlinear force-free modelling: influence of inaccuracies in the measured magnetic vector

Context: Solar magnetic fields are regularly extrapolated into the corona starting from photospheric magnetic measurements that can suffer from significant uncertainties. Aims: Here we study how inaccuracies introduced into the maps of the photospheric magnetic vector from the inversion of ideal and noisy Stokes parameters influence the extrapolation of nonlinear force-free magnetic fields. Methods: We compute nonlinear force-free magnetic fields based on simulated vector magnetograms, which have been produced by the inversion of Stokes profiles, computed froma 3-D radiation MHD simulation snapshot. These extrapolations are compared with extrapolations starting directly from the field in the MHD simulations, which is our reference. We investigate how line formation and instrumental effects such as noise, limited spatial resolution and the effect of employing a filter instrument influence the resulting magnetic field structure. The comparison is done qualitatively by visual inspection of the magnetic field distribution and quantitatively by different metrics. Results: The reconstructed field is most accurate if ideal Stokes data are inverted and becomes less accurate if instrumental effects and noise are included. The results demonstrate that the non-linear force-free field extrapolation method tested here is relatively insensitive to the effects of noise in measured polarization spectra at levels consistent with present-day instruments. Conclusions heading: Our results show that we can reconstruct the coronal magnetic field as a nonlinear force-free field from realistic photospheric measurements with an accuracy of a few percent, at least in the absence of sunspots.Comment: A&A, accepted, 9 Pages, 4 Figure

Modified p-modes in penumbral filaments?

Aims: The primary objective of this study is to search for and identify wave modes within a sunspot penumbra. Methods: Infrared spectropolarimetric time series data are inverted using a model comprising two atmospheric components in each spatial pixel. Fourier phase difference analysis is performed on the line-of-sight velocities retrieved from both components to determine time delays between the velocity signals. In addition, the vertical separation between the signals in the two components is calculated from the Stokes velocity response functions. Results: The inversion yields two atmospheric components, one permeated by a nearly horizontal magnetic field, the other with a less-inclined magnetic field. Time delays between the oscillations in the two components in the frequency range 2.5-4.5 mHz are combined with speeds of atmospheric wave modes to determine wave travel distances. These are compared to expected path lengths obtained from response functions of the observed spectral lines in the different atmospheric components. Fast-mode (i.e., modified p-mode) waves exhibit the best agreement with the observations when propagating toward the sunspot at an angle ~50 degrees to the vertical.Comment: 8 pages, 12 figures, accepted for publication in Astronomy & Astrophysic