Low temperature silicon epitaxy on hydrogen terminated Si(100) surfaces

Si deposition on H terminated Si(100)-2x1 and 3x1 surfaces at temperatures 300-530 K is studied by scanning tunneling microscopy. Hydrogen apparently hinders Si adatom diffusion and enhances surface roughening. The post-growth annealing effect is analyzed. Hydrogen is shown to remain on the growth front up to at least 10 ML. The dihydride units on the 3x1 surfaces further suppress the Si adatom diffusion and increase surface roughness.Comment: 26 pages, 9 figure

Moving Beyond Dichotomies: How the Intersection of Race, Class and Place Impacts High School Graduation Rates for African American Students

Over thirty years ago, William Julius Wilson declared that class trumped race as the more significant determinant of social mobility and economic opportunity. Despite the acclaim and scrutiny for Wilson\u27s work, the United States has grown increasingly divided by intersecting factors of race, class and other demographic factors such as place (Massey, 2007). These divisions are especially evident in the public education system. We analyze how race, class and place interact to predict high school graduation rates in a national sample of schools and students. Results confirm that a singular focus on race, class, or locale is insufficient to explain high school graduation rates. However, a more contextualized focus on the interactions between multiple determinants of inequality (e.g. race, class and place) can yield a more nuanced understanding of the indicators driving educational inequalities. Scholars and practitioners need to focus on the manner in which multiple positionalities influence the academic achievement of African American children and young adults

Repression of Proinflammatory Gene Expression by Lipid Extract of \u3ci\u3eNostoc commune\u3c/i\u3e var \u3ci\u3esphaeroides\u3c/i\u3e Kützing, a Blue-green Alga, via Inhibition of Nuclear Factor-κB in RAW 264.7 Macrophages

We investigated whether lipid extract from a blue-green alga, N. commune, modulates proinflammatory gene expression in RAW 264.7 macrophages. The cells were incubated with N. commune lipid extract (0–100 μg/mL) and subsequently activated by LPS (100 ng/mL). Quantitative real-time PCR analysis showed that mRNA abundance of proinflammatory mediators, including TNF-α, COX-2, IL-1β, IL-6, and iNOS, was significantly reduced by N. commune lipid extract in a dose-dependent manner. Secretion of TNF-α and IL-1β into cell culture medium was also significantly decreased by N. commune lipid extract. Thin-layer chromatography-densitometry analysis showed that N. commune lipid extract contained approximately 15% of fatty acids. To determine whether the inhibition of proinflammatory mediator production by N. commune lipid extract is primarily conferred by fatty acids in the lipid extract, macrophages were incubated with 100 μg/mL of N. commune lipid extract or 15 μg/mL of a fatty acid mixture, which was formulated to reflect the fatty acid composition of N. commune lipid extract. The fatty acid mixture significantly reduced RNA abundance of TNF-α and COX-2, but to a lesser extent than did the N. commune lipid extract, suggesting the presence of additional bioactive compounds with an anti-inflammatory property in the lipid extract. As NF-κB is a major regulator for the proinflammatory gene expression, we measured its DNA-binding activity. DNA-binding activity of NF-κB was significantly reduced by N. commune lipid extract. In conclusion, our study suggests that N. commune lipid extract represses the expression of proinflammatory genes in RAW 264.7 macrophages, at least in part, by inhibiting the activation of NF-κB pathway

mHealth hyperspectral learning for instantaneous spatiospectral imaging of hemodynamics

Hyperspectral imaging acquires data in both the spatial and frequency domains to offer abundant physical or biological information. However, conventional hyperspectral imaging has intrinsic limitations of bulky instruments, slow data acquisition rate, and spatiospectral tradeoff. Here we introduce hyperspectral learning for snapshot hyperspectral imaging in which sampled hyperspectral data in a small subarea are incorporated into a learning algorithm to recover the hypercube. Hyperspectral learning exploits the idea that a photograph is more than merely a picture and contains detailed spectral information. A small sampling of hyperspectral data enables spectrally informed learning to recover a hypercube from an RGB image. Hyperspectral learning is capable of recovering full spectroscopic resolution in the hypercube, comparable to high spectral resolutions of scientific spectrometers. Hyperspectral learning also enables ultrafast dynamic imaging, leveraging ultraslow video recording in an off-the-shelf smartphone, given that a video comprises a time series of multiple RGB images. To demonstrate its versatility, an experimental model of vascular development is used to extract hemodynamic parameters via statistical and deep-learning approaches. Subsequently, the hemodynamics of peripheral microcirculation is assessed at an ultrafast temporal resolution up to a millisecond, using a conventional smartphone camera. This spectrally informed learning method is analogous to compressed sensing; however, it further allows for reliable hypercube recovery and key feature extractions with a transparent learning algorithm. This learning-powered snapshot hyperspectral imaging method yields high spectral and temporal resolutions and eliminates the spatiospectral tradeoff, offering simple hardware requirements and potential applications of various machine-learning techniques.Comment: This paper will appear in PNAS Nexu

Dual function of Yap in the regulation of lens progenitor cells and cellular polarity

AbstractHippo-Yap signaling has been implicated in organ size determination via its regulation of cell proliferation, growth and apoptosis (Pan, 2007). The vertebrate lens comprises only two major cell types, lens progenitors and differentiated fiber cells, thereby providing a relatively simple system for studying size-controlling mechanisms. In order to investigate the role of Hippo-Yap signaling in lens size regulation, we conditionally ablated Yap in the developing mouse lens. Lens progenitor-specific deletion of Yap led to near obliteration of the lens primarily due to hypocellularity in the lens epithelium (LE) and accompanying lens fiber (LF) defects. A significantly reduced LE progenitor pool resulted mainly from failed self-renewal and increased apoptosis. Additionally, Yap-deficient lens progenitor cells precociously exited the cell cycle and expressed the LF marker, β-Crystallin. The mutant progenitor cells also exhibited multiple cellular and subcellular alterations including cell and nuclear shape change, organellar polarity disruption, and disorganized apical polarity complex and junction proteins such as Crumbs, Pals1, Par3 and ZO-1. Yap-deficient LF cells failed to anchor to the overlying LE layer, impairing their normal elongation and packaging. Furthermore, our localization study results suggest that, in the developing LE, Yap participates in the cell context-dependent transition from the proliferative to differentiation-competent state by integrating cell density information. Taken together, our results shed new light on Yap's indispensable and novel organizing role in mammalian organ size control by coordinating multiple events including cell proliferation, differentiation, and polarity

Hybrid type-I InAs/GaAs and type-II GaSb/GaAs quantum dot structure with enhanced photoluminescence

We investigate the photoluminescence (PL) properties of a hybrid type-I InAs/GaAs and type-II GaSb/GaAs quantum dot (QD) structure grown in a GaAs matrix by molecular beam epitaxy. This hybrid QD structure exhibits more intense PL with a broader spectral range, compared with control samples that contain only InAs or GaSb QDs. This enhanced PL performance is attributed to additional electron and hole injection from the type-I InAs QDs into the adjacent type-II GaSb QDs. We confirm this mechanism using time-resolved and power-dependent PL. These hybrid QD structures show potential for high efficiency QD solar cell applications