An Image Segmentation Technique with Statistical Strategies for Pesticide Efficacy Assessment

Image analysis is a useful technique to evaluate the efficacy of a treatment for weed control. In this study, we address two practical challenges in the image analysis. First, it is challenging to accurately quantify the efficacy of a treatment when an entire experimental unit is not affected by the treatment. Second, RGB codes, which can be used to identify weed growth in the image analysis, may not be stable due to various surrounding factors, human errors, and unknown reasons. To address the former challenge, the technique of image segmentation is considered. To address the latter challenge, the proportion of weed area is adjusted under a beta regression model. The beta regression is a useful statistical method when the outcome variable (proportion) ranges between zero and one. In this study, we attempt to accurately evaluate the efficacy of a 35% hydrogen peroxide (HP). The image segmentation was applied to separate two zones, where the HP was directly applied (gray zone) and its surroundings (nongray zone). The weed growth was monitored for five days after the treatment, and the beta regression was implemented to compare the weed growth between the gray zone and the control group and between the nongray zone and the control group. The estimated treatment effect was substantially different after the implementation of image segmentation and the adjustment of green area

Optical absorption in graphene integrated on silicon waveguides

To fully utilize graphene's remarkable optical properties for optoelectronic applications, it needs to be integrated in planar photonic systems. Here, we demonstrate integration of graphene on silicon photonic circuits and precise measurement of the optical absorption coefficient in a graphene/waveguide hybrid structure. A method based on Mach-Zehnder interferometry is employed to achieve high measurement precision and consistency, yielding a maximal value of absorption coefficient of 0.2 dB/{\mu}m when graphene is located directly on top of the waveguide. The results agree with theoretical model utilizing the universal ac conductivity in graphene. Our work provides an important guide for the design and optimization of integrated graphene optoelectronic devices.Comment: 14 pages, 4 figure

Reionization and the large-scale 21 cm-cosmic microwave background cross correlation

Of the many probes of reionization, the 21 cm line and the cosmic microwave background (CMB) are among the most effective. We examine how the cross-correlation of the 21 cm brightness and the CMB Doppler fluctuations on large angular scales can be used to study this epoch. We employ a new model of the growth of large scale fluctuations of the ionized fraction as reionization proceeds. We take into account the peculiar velocity field of baryons and show that its effect on the cross correlation can be interpreted as a mixing of Fourier modes. We find that the cross-correlation signal is strongly peaked toward the end of reionization and that the sign of the correlation should be positive because of the inhomogeneity inherent to reionization. The signal peaks at degree scales (l~100) and comes almost entirely from large physical scales (k~0.01 Mpc). Since many of the foregrounds and noise that plague low frequency radio observations will not correlate with CMB measurements, the cross correlation might appear to provide a robust diagnostic of the cosmological origin of the 21 cm radiation around the epoch of reionization. Unfortunately, we show that these signals are actually only weakly correlated and that cosmic variance dominates the error budget of any attempted detection. We conclude that the detection of a cross-correlation peak at degree-size angular scales is unlikely even with ideal experiments.Comment: 15 pages, 4 figures, submitted to MNRA

A Novel HDL-Mimetic Peptide HM-10/10 Protects RPE and Photoreceptors in Murine Models of Retinal Degeneration.

Age-related macular degeneration (AMD) is a leading cause of blindness in the developed world. The retinal pigment epithelium (RPE) is a critical site of pathology in AMD. Oxidative stress plays a key role in the development of AMD. We generated a chimeric high-density lipoprotein (HDL), mimetic peptide named HM-10/10, with anti-oxidant properties and investigated its potential for the treatment of retinal disease using cell culture and animal models of RPE and photoreceptor (PR) degeneration. Treatment with HM-10/10 peptide prevented human fetal RPE cell death caused by tert-Butyl hydroperoxide (tBH)-induced oxidative stress and sodium iodate (NaIO3), which causes RPE atrophy and is a model of geographic atrophy in mice. We also show that HM-10/10 peptide ameliorated photoreceptor cell death and significantly improved retinal function in a mouse model of N-methyl-N-nitrosourea (MNU)-induced PR degeneration. Our results demonstrate that HM-10/10 protects RPE and retina from oxidant injury and can serve as a potential therapeutic agent for the treatment of retinal degeneration

Is Double Reionization Physically Plausible?

Recent observations of z~6 quasars and the cosmic microwave background imply a complex history to cosmic reionization. Such a history requires some form of feedback to extend reionization over a long time interval, but the nature of the feedback and how rapidly it operates remain highly uncertain. Here we focus on one aspect of this complexity: which physical processes can cause the global ionized fraction to evolve non-monotonically with cosmic time? We consider a range of mechanisms and conclude that double reionization is much less likely than a long, but still monotonic, ionization history. We first examine how galactic winds affect the transition from metal-free to normal star formation. Because the transition is actually spatially inhomogeneous and temporally extended, this mechanism cannot be responsible for double reionization given plausible parameters for the winds. We next consider photoheating, which causes the cosmological Jeans mass to increase in ionized regions and hence suppresses galaxy formation there. In this case, double reionization requires that small halos form stars efficiently, that the suppression from photoheating is strong relative to current expectations, and that ionizing photons are preferentially produced outside of previously ionized regions. Finally, we consider H_2 photodissociation, in which the buildup of a soft ultraviolet background suppresses star formation in small halos. This can in principle cause the ionized fraction to temporarily decrease, but only during the earliest stages of reionization. Finally, we briefly consider the effects of some of these feedback mechanisms on the topology of reionization.Comment: 13 pages, 5 figures, in press at ApJ (reorganized significantly but major conclusions unchanged

Efficient Simulations of Early Structure Formation and Reionization

We present a method to construct semi-numerical ``simulations'', which can efficiently generate realizations of halo distributions and ionization maps at high redshifts. Our procedure combines an excursion-set approach with first-order Lagrangian perturbation theory and operates directly on the linear density and velocity fields. As such, the achievable dynamic range with our algorithm surpasses the current practical limit of N-body codes by orders of magnitude. This is particularly significant in studies of reionization, where the dynamic range is the principal limiting factor. We test our halo-finding and HII bubble-finding algorithms independently against N-body simulations with radiative transfer and obtain excellent agreement. We compute the size distributions of ionized and neutral regions in our maps. We find even larger ionized bubbles than do purely analytic models at the same volume-weighted mean hydrogen neutral fraction. We also generate maps and power spectra of 21-cm brightness temperature fluctuations, which for the first time include corrections due to gas bulk velocities. We find that velocities widen the tails of the temperature distributions and increase small-scale power, though these effects quickly diminish as reionization progresses. We also include some preliminary results from a simulation run with the largest dynamic range to date: a 250 Mpc box that resolves halos with masses M >~ 2.2 x10^8 M_sun. We show that accurately modeling the late stages of reionization requires such large scales. The speed and dynamic range provided by our semi-numerical approach will be extremely useful in the modeling of early structure formation and reionization.Comment: 13 pages, 10 figures; ApJ submitte