Characterizing the universal rigidity of generic frameworks

A framework is a graph and a map from its vertices to E^d (for some d). A framework is universally rigid if any framework in any dimension with the same graph and edge lengths is a Euclidean image of it. We show that a generic universally rigid framework has a positive semi-definite stress matrix of maximal rank. Connelly showed that the existence of such a positive semi-definite stress matrix is sufficient for universal rigidity, so this provides a characterization of universal rigidity for generic frameworks. We also extend our argument to give a new result on the genericity of strict complementarity in semidefinite programming.Comment: 18 pages, v2: updates throughout; v3: published versio

Direct Observation of Electrostatically Driven Band Gap Renormalization in a Degenerate Perovskite Transparent Conducting Oxide

We have directly measured the band gap renormalization associated with the Moss-Burstein shift in the perovskite transparent conducting oxide (TCO), La-doped BaSnO_{3}, using hard x-ray photoelectron spectroscopy. We determine that the band gap renormalization is almost entirely associated with the evolution of the conduction band. Our experimental results are supported by hybrid density functional theory supercell calculations. We determine that unlike conventional TCOs where interactions with the dopant orbitals are important, the band gap renormalization in La-BaSnO_{3} is driven purely by electrostatic interactions

The influence of soil communities on the temperature sensitivity of soil respiration

Soil respiration represents a major carbon flux between terrestrial ecosystems and the atmosphere, and is expected to accelerate under climate warming. Despite its importance in climate change forecasts, however, our understanding of the effects of temperature on soil respiration (RS) is incomplete. Using a metabolic ecology approach we link soil biota metabolism, community composition and heterotrophic activity, to predict RS rates across five biomes. We find that accounting for the ecological mechanisms underpinning decomposition processes predicts climatological RS variations observed in an independent dataset (n = 312). The importance of community composition is evident because without it RS is substantially underestimated. With increasing temperature, we predict a latitudinal increase in RS temperature sensitivity, with Q10 values ranging between 2.33 ±0.01 in tropical forests to 2.72 ±0.03 in tundra. This global trend has been widely observed, but has not previously been linked to soil communities

Modifying Effects of the HFE Polymorphisms on the Association between Lead Burden and Cognitive Decline

Background: As iron and lead promote oxidative damage, and hemochromatosis (HFE) gene polymorphisms increase body iron burden, HFE variant alleles may modify the lead burden and cognitive decline relationship. Objective: Our goal was to assess the modifying effects of HFE variants on the lead burden and cognitive decline relation in older adults. Methods: We measured tibia and patella lead using K-X-ray fluorescence (1991–1999) among participants of the Normative Aging Study, a longitudinal study of community-dwelling men from greater Boston. We assessed cognitive function with the Mini-Mental State Examination (MMSE) twice (1993–1998 and 1995–2000) and genotyped participants for HFE polymorphisms. We estimated the adjusted mean differences in lead-associated annual cognitive decline across HFE genotype groups (n = 358). Results: Higher tibia lead was associated with steeper cognitive decline among participants with at least one HFE variant allele compared with men with only wild-type alleles (p interaction = 0.03), such that a 15 μg/g increase in tibia lead was associated with a 0.2 point annual decrement in MMSE score among HFE variant allele carriers. This difference in scores among men with at least one variant allele was comparable to the difference in baseline MMSE scores that we observed among men who were 4 years apart in age. Moreover, the deleterious association between tibia lead and cognitive decline appeared progressively worse in participants with increasingly more copies of HFE variant alleles (p-trend = 0.008). Results for patella lead were similar. Conclusion: Our findings suggest that HFE polymorphisms greatly enhance susceptibility to lead-related cognitive impairment in a pattern consistent with allelelic dose

p150 ADAR1 isoform involved in maintenance of HeLa cell proliferation

BACKGROUND: RNA-specific adenosine deaminase ADAR1 is ubiquitously expressed in a variety of mammalian cells and tissues. Although its physiological importance in non-nervous tissues has been confirmed by analysis of null mutation phenotypes, few endogenous editing substrates have been identified in numerous peripheral tissues and biological function of ADAR1 has not been fully understood. METHODS: A conditional site-specific, ribozyme-based gene knock-down strategy was utilized to study the function of full-length isoform of ADAR1 (p150 protein) in HeLa cell. Double-stable HeLa cell lines were developed by transfecting HeLa Tet-On cells with a pTRE-derived plasmid that can express a hammerhead ribozyme against mRNA of p150 ADAR1 isoform under induction condition. Semi-quantitative RT-PCR and Western blotting were performed to measure the expression of p150 in selected cell clones. Cell proliferation was evaluated by means of MTT assay and growth curve analysis. Cellular morphological changes were observed under light microscope. Flow Cytometry was used for cell cycle analysis. Growth rate of cell transplants in BALB/c nude mice was also investigated. RESULTS: Both HeLa cell proliferation in vitro and the growth rate of transplanted HeLa cell-derived tumors in nude mice in vivo were significantly inhibited due to reduced expression of ADAR1 p150. Additionally, cell cycle analysis showed that cell progression from G1 phase to S phase was retarded in the ADAR1 p150 suppressed cells. CONCLUSION: Our results suggest that normal expression and functioning of p150 ADAR1 is essential for the maintenance of proper cell growth. The mechanisms underlying ADAR1's action might include both editing of currently unknown double-stranded RNAs and interacting with other cellular dsRNA-related processes

Testing Nelder-Mead based repulsion algorithms for multiple roots of nonlinear systems via a two-level factorial design of experiments

This paper addresses the challenging task of computing multiple roots of a system of nonlinear equations. A repulsion algorithm that invokes the Nelder-Mead (N-M) local search method and uses a penalty-type merit function based on the error function, known as 'erf', is presented. In the N-M algorithm context, different strategies are proposed to enhance the quality of the solutions and improve the overall efficiency. The main goal of this paper is to use a two-level factorial design of experiments to analyze the statistical significance of the observed differences in selected performance criteria produced when testing different strategies in the N-M based repulsion algorithm. The main goal of this paper is to use a two-level factorial design of experiments to analyze the statistical significance of the observed differences in selected performance criteria produced when testing different strategies in the N-M based repulsion algorithm.Fundação para a Ciência e Tecnologia (FCT

Reversible Integration of Microfluidic Devices with Microelectrode Arrays for Neurobiological Applications

The majority of current state-of-the-art microfluidic devices are fabricated via replica molding of the fluidic channels into PDMS elastomer and then permanently bonding it to a Pyrex surface using plasma oxidation. This method presents a number of problems associated with the bond strengths, versatility, applicability to alternative substrates, and practicality. Thus, the aim of this study was to investigate a more practical method of integrating microfluidics which is superior in terms of bond strengths, reversible, and applicable to a larger variety of substrates, including microfabricated devices. To achieve the above aims, a modular microfluidic system, capable of reversible microfluidic device integration, simultaneous surface patterning and multichannel fluidic perfusion, was built. To demonstrate the system’s potential, the ability to control the distribution of A549 cells inside a microfluidic channel was tested. Then, the system was integrated with a chemically patterned microelectrode array, and used it to culture primary, rat embryo spinal cord neurons in a dynamic fluidic environment. The results of this study showed that this system has the potential to be a cost effective and importantly, a practical means of integrating microfluidics. The system’s robustness and the ability to withstand extensive manual handling have the additional benefit of reducing the workload. It also has the potential to be easily integrated with alternative substrates such as stainless steel or gold without extensive chemical modifications. The results of this study are of significant relevance to research involving neurobiological applications, where primary cell cultures on microelectrode arrays require this type of flexible integrated solution

Bitter Taste Receptors Influence Glucose Homeostasis

TAS1R- and TAS2R-type taste receptors are expressed in the gustatory system, where they detect sweet- and bitter-tasting stimuli, respectively. These receptors are also expressed in subsets of cells within the mammalian gastrointestinal tract, where they mediate nutrient assimilation and endocrine responses. For example, sweeteners stimulate taste receptors on the surface of gut enteroendocrine L cells to elicit an increase in intracellular Ca2+ and secretion of the incretin hormone glucagon-like peptide-1 (GLP-1), an important modulator of insulin biosynthesis and secretion. Because of the importance of taste receptors in the regulation of food intake and the alimentary responses to chemostimuli, we hypothesized that differences in taste receptor efficacy may impact glucose homeostasis. To address this issue, we initiated a candidate gene study within the Amish Family Diabetes Study and assessed the association of taste receptor variants with indicators of glucose dysregulation, including a diagnosis of type 2 diabetes mellitus and high levels of blood glucose and insulin during an oral glucose tolerance test. We report that a TAS2R haplotype is associated with altered glucose and insulin homeostasis. We also found that one SNP within this haplotype disrupts normal responses of a single receptor, TAS2R9, to its cognate ligands ofloxacin, procainamide and pirenzapine. Together, these findings suggest that a functionally compromised TAS2R receptor negatively impacts glucose homeostasis, providing an important link between alimentary chemosensation and metabolic disease

Measurement of the Bottom-Strange Meson Mixing Phase in the Full CDF Data Set

We report a measurement of the bottom-strange meson mixing phase \beta_s using the time evolution of B0_s -> J/\psi (->\mu+\mu-) \phi (-> K+ K-) decays in which the quark-flavor content of the bottom-strange meson is identified at production. This measurement uses the full data set of proton-antiproton collisions at sqrt(s)= 1.96 TeV collected by the Collider Detector experiment at the Fermilab Tevatron, corresponding to 9.6 fb-1 of integrated luminosity. We report confidence regions in the two-dimensional space of \beta_s and the B0_s decay-width difference \Delta\Gamma_s, and measure \beta_s in [-\pi/2, -1.51] U [-0.06, 0.30] U [1.26, \pi/2] at the 68% confidence level, in agreement with the standard model expectation. Assuming the standard model value of \beta_s, we also determine \Delta\Gamma_s = 0.068 +- 0.026 (stat) +- 0.009 (syst) ps-1 and the mean B0_s lifetime, \tau_s = 1.528 +- 0.019 (stat) +- 0.009 (syst) ps, which are consistent and competitive with determinations by other experiments.Comment: 8 pages, 2 figures, Phys. Rev. Lett 109, 171802 (2012

Water-Driven Assembly of Laser Ablation-Induced Au Condensates as Mesomorphic Nano- and Micro-Tubes

Reddish Au condensates, predominant atom clusters and minor amount of multiply twinned particles and fcc nanoparticles with internal compressive stress, were produced by pulsed laser ablation on gold target in de-ionized water under a very high power density. Such condensates were self-assembled as lamellae and then nano- to micro-diameter tubes with multiple walls when aged at room temperature in water for up to 40 days. The nano- and micro-tubes have a lamellar- and relaxed fcc-type wall, respectively, both following partial epitaxial relationship with the co-existing multiply twinned nanoparticles. The entangled tubes, being mesomorphic with a large extent of bifurcation, flexibility, opaqueness, and surface-enhanced Raman scattering, may have potential encapsulated and catalytic/label applications in biomedical systems