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Giant modulation of the electronic band gap of carbon nanotubes by dielectric screening
Get PDFIon pairs and solubility related to ion-pairing in water influence many processes in nature and in synthesis including efficient drug delivery, contaminant transport in the environment, and self-assembly of materials in water. Ion pairs are difficult to observe spectroscopically because they generally do not persist unless extreme solution conditions are applied. Here we demonstrate two advanced techniques coupled with computational studies that quantify the persistence of ion pairs in simple solutions and offer explanations for observed solubility trends. The system of study, ([(CH₃)₄N]+,Cs)₈[M6O₁₉] (M = Nb,Ta), is a set of unique polyoxometalate salts whose water solubility increases with increasing ion-pairing, contrary to most ionic salts. The techniques employed to characterize Cs+ association with [M₆O₁₉]⁸⁻ and related clusters in simple aqueous media are ¹³³Cs NMR (nuclear magnetic resonance) quadrupolar relaxation rate and PDF (pair distribution function) from X-ray scattering. The NMR measurements consistently showed more extensive ion-pairing of Cs+ with the Ta-analogue than the Nb-analogue, although the electrostatics of the ions should be identical. Computational studies also ascertained more persistent Cs+–[Ta₆O₁₉] ion pairs than Cs+–[Nb₆O₁₉] ion pairs, and bond energy decomposition analyses determined relativistic effects to be the differentiating factor between the two. These distinctions are likely responsible for many of the unexplained differences between aqueous Nb and Ta chemistry, while they are so similar in the solid state. The X-ray scattering studies show atomic level detail of this ion association that has not been prior observed, enabling confidence in our structures for calculations of Cs-cluster association energies. Moreover, detailed NMR studies allow quantification of the number of Cs+ associated with a single [Nb₆O₁₉]⁸⁻ or [Ta₆O₁₉]⁸⁻ anion which agrees with the PDF analyses
The tissue-specific lncRNA Fendrr is an essential regulator of heart and body wall development in the mouse
Get PDFThe histone modifying complexes PRC2 and TrxG/MLL play pivotal roles in determining the activation state of genes controlling pluripotency, lineage commitment, and cell differentiation. Long non-coding RNAs (lncRNAs) can bind to either complex, and some have been shown to act as modulators of PRC2 or TrxG/MLL activity. Here we show that the lateral mesoderm-specific lncRNA Fendrr is essential for proper heart and body wall development in the mouse. Embryos lacking Fendrr displayed upregulation of several transcription factors controlling lateral plate or cardiac mesoderm differentiation, accompanied by a drastic reduction in PRC2 occupancy along with decreased H3K27 trimethylation and/or an increase in H3K4 trimethylation at their promoters. Fendrr binds to both the PRC2 and TrxG/MLL complexes, suggesting that it acts as modulator of chromatin signatures that define gene activity. Thus, our work identifies a lncRNA that plays an essential role in fine-tuning the regulatory networks which control the fate of lateral mesoderm derivatives
CreasonAllisonBotanyPlantPathologyAnalysisGenomeSequences.pdf
No full textMembers of Gram-positive Actinobacteria cause economically important diseases to plants. Within the Rhodococcus genus,
some members can cause growth deformities and persist as pathogens on a wide range of host plants. The current model
predicts that phytopathogenic isolates require a cluster of three loci present on a linear plasmid, with the fas operon central
to virulence. The Fas proteins synthesize, modify, and activate a mixture of growth regulating cytokinins, which cause a
hormonal imbalance in plants, resulting in abnormal growth. We sequenced and compared the genomes of 20 isolates of
Rhodococcus to gain insights into the mechanisms and evolution of virulence in these bacteria. Horizontal gene transfer was
identified as critical but limited in the scale of virulence evolution, as few loci are conserved and exclusive to
phytopathogenic isolates. Although the fas operon is present in most phytopathogenic isolates, it is absent from
phytopathogenic isolate A21d2. Instead, this isolate has a horizontally acquired gene chimera that encodes a novel fusion
protein with isopentyltransferase and phosphoribohydrolase domains, predicted to be capable of catalyzing and activating
cytokinins, respectively. Cytokinin profiling of the archetypal D188 isolate revealed only one activate cytokinin type that was
specifically synthesized in a fas-dependent manner. These results suggest that only the isopentenyladenine cytokinin type is
synthesized and necessary for Rhodococcus phytopathogenicity, which is not consistent with the extant model stating that a
mixture of cytokinins is necessary for Rhodococcus to cause leafy gall symptoms. In all, data indicate that only four
horizontally acquired functions are sufficient to confer the trait of phytopathogenicity to members of the genetically diverse
clade of Rhodococcus
The relative contribution of climate to changes in lesser prairie-chicken abundance
Get PDFManaging for species using current weather patterns fails to incorporate the uncertainty associated with future climatic conditions; without incorporating potential changes in climate into conservation strategies, management and conservation efforts may fall short or waste valuable resources. Understanding the effects of climate change on species in the Great Plains of North America is especially important, as this region is projected to experience an increased magnitude of climate change. Of particular ecological and conservation interest is the lesser prairie-chicken (Tympanuchus pallidicinctus), which was listed as “threatened” under the U.S. Endangered Species Act in May 2014. We used Bayesian hierarchical models to quantify the effects of extreme climatic events (extreme values of the Palmer Drought Severity Index [PDSI]) relative to intermediate (changes in El Niño Southern Oscillation) and long-term climate variability (changes in the Pacific Decadal Oscillation) on trends in lesser prairie-chicken abundance from 1981 to 2014. Our results indicate that lesser prairie-chicken abundance on leks responded to environmental conditions of the year previous by positively responding to wet springs (high PDSI) and negatively to years with hot, dry summers (low PDSI), but had little response to variation in the El Niño Southern Oscillation and the Pacific Decadal Oscillation. Additionally, greater variation in abundance on leks was explained by variation in site relative to broad-scale climatic indices. Consequently, lesser prairie-chicken abundance on leks in Kansas is more strongly influenced by extreme drought events during summer than other climatic conditions, which may have negative consequences for the population as drought conditions intensify throughout the Great Plains
A Systematic Review of Physical Activity among People with Disabilities in Mainland China : From 1992 to 2013
Get PDFContext: Regular physical activity has increasingly been recommended to promote human health and wellbeing. However, information on participation in physical activities by people with disabilities is relatively scarce. The aim of this article is to conduct a systematically review of studies on physical activity among people with disabilities in mainland China from 1992 to 2013. Evidence acquisition: In 2015, a search of three major Chinese electronic databases (CNKI, WANGFAN DATA, and VIP) was conducted for studies that examined physical activity among people with disabilities. The search included studies dating from January 1992 to December 2013. After applying inclusion criteria, 31 studies, all cross-sectional in design, were included in this review. Evidence synthesis: The 31 studies included some self-reports of physical activity by people with disabilities (N=5,982). The results from 9 of the 31 studies indicated that 12.7% of the participants in those studies (N=760) had physical activity levels that met the standards recommended by national physical activity guidelines for China. Levels of physical activity among people with disabilities varied by gender, income, and education. Men and people with higher education and income levels were more physically active compared to women and those with lower education and income levels. In addition, people living in urban areas were more active than those living in rural areas. Conclusions: Relatively low levels of physical activity were found among people with disabilities in mainland China. Further research on this special population is needed. Studies that employ rigorous standards for design and methodologies, including the use of objective physical activity measures, are recommended.Keywords: Exercise, disabilities, cross-sectional design, physical activity recommendations, healthy lifestyles
Mixing and the dynamics of the deep chlorophyll maximum in Lake Tahoe
Get PDFChlorophyll-temperature profiles were measured across Lake Tahoe about every 10 days from April through July 1980. Analysis of the 123 profiles and associated productivity and nutrient data identified three important processes in the formation and dynamics of the deep chlorophyll maximum (DCM): turbulent diffusion, nutrient supply rate, and light availability. Seasonal variation in these three processes resulted in three regimes: a diffusion-dominated regime with a weak DCM, a variable-mixing regime with a pronounced, nutrient supply-dominated DCM, and a stable regime with a deep, moderate light availability-dominated DCM. The transition between the first two regimes occurred in about 10 days, the transition between the last two more gradually over about 3 weeks. The degree of spatial variability of the DCM was highest in the second regime and lowest in the third. These data indicate that the DCM in Lake Tahoe is constant in neither time nor space
Comment on "Do geochemical estimates of sediment focusing pass the sediment test in the equatorial Pacific?" by M. Lyle et al.
Get PDFAccurately estimating the vertical flux of material reaching the seafloor from the overlying surface waters is essential for the paleoceanographic reconstruction of a wide variety of oceanic processes. Two approaches are currently being used. One consists of estimating mass accumulation rates (MAR) between dated horizons as the product of linear sedimentation rates, sediment dry bulk densities, and concentrations. One pitfall with this approach is that sediments can be redistributed on the seafloor by bottom currents, and their accumulation may not necessarily reflect the true vertical rain rate originating from the overlying water column. To address this problem, the method of ²³⁰Th normalization was developed [Bacon, 1984]. This method is based on the assumption that the rapid scavenging of ²³⁰Th produced in the water column by decay of dissolved uranium results in its flux to the seafloor always being close to its known rate of production. To the extent that this assumption is correct, scavenged ²³⁰Th can be used as a reference to estimate the settling flux of other sedimentary constituents and to correct for sediment redistribution on the seafloor [Henderson and Anderson, 2003; Francois et al., 2004]
The variation in the inherent optical properties of phytoplankton near an absorption peak as determined by various models of cell structure
Get PDFOptical oceanography models of attenuation and scattering properties often contain simple spectral relationships. Electromagnetic theory, however, predicts fluctuations in the spectra of the attenuation coefficients and scattering properties of substances at wavelengths near an absorption peak. We have modeled these effects for phytoplankton using homogeneous, two‐layered, and three‐layered sphere models of cell structure and using a wide range of plausible particle size distributions. The magnitude of the scattering in backward directions is affected the most. The effect on the beam attenuation spectra is relatively small compared with the effect on the absorption and scattering coefficients. The backscattering coefficient shows large variability, varying by almost a factor of 3 for some models. The results suggest that beam attenuation at any wavelength in the red shorter than the wavelength of the chlorophyll absorption peak will be insensitive to the chlorophyll content of the particles. Increases in the pigment content per unit volume of phytoplankton will increase the index of refraction in the infrared and therefore increase the attenuation and scattering coefficients there
An asymptotic closure theory for irradiance in the sea and its inversion to obtain the inherent optical properties
Get PDFAn expression is derived for the rate at which the diffuse attenuation coefficient for vector irradiance approaches its asymptotic value in a homogeneous medium. The asymptotic approach rate is shown to be a function of boundary conditions at the surface and the asymptotic diffuse attenuation coefficient which is an inherent optical property. The asymptotic approach rate is then used to derive the vertical structure of the vector and scalar irradiances, the vector and scalar diffuse attenuation coefficients, the average cosine of the light field, and the remotely sensed reflectance at the surface, based only on the surface values of the vector and scalar irradiances and the vector and scalar diffuse attenuation coefficients. This theory is inverted and combined with previously derived radiative transfer relations to show that in principle the vertical structure of the absorption, scattering, attenuation, and backscattering coefficients can be derived from the vertical structure of the scalar and vector irradiances and the nadir radiance. An example for the western North Atlantic Ocean is provided
Evidence for atmospheric control of sea-ice motion through Nares Strait
Get PDFSatellite observations of ice motion are combined with model estimates of low‐level winds and surface wind stress to provide evidence for atmospheric control of sea‐ice motion through Nares Strait, between Ellesmere Island and Greenland, during two periods in 2004. The results suggest that ice flux through the strait, and its shutdown through the formation of a landfast ice mass in the strait, can be controlled by wind stress and atmospheric cooling. Analysis of the model results during these two periods also suggest that the intense, low‐level, along‐strait winds are strongly ageostrophic, and may be usefully estimated from pressure differences along the Strait