University of New Hampshire

About: University of New Hampshire is a education organization based out in Durham, New Hampshire, United States. It is known for research contribution in the topics: Population & Solar wind. The organization has 9379 authors who have published 24025 publications receiving 1020112 citations. The organization is also known as: UNH.

Multiple Type-B Response Regulators Mediate Cytokinin Signal Transduction in Arabidopsis

Abstract: Type-B Arabidopsis thaliana response regulators (ARRs) are transcription factors that function in the final step of two-component signaling systems. To characterize their role in plant growth and development, we isolated T-DNA insertions within six of the genes (ARR1, ARR2, ARR10, ARR11, ARR12, and ARR18) from the largest subfamily of type-B ARRs and also constructed various double and triple combinations of these mutations. Higher order mutants revealed progressively decreased sensitivity to cytokinin, including effects on root elongation, lateral root formation, callus induction and greening, and induction of cytokinin primary response genes. The triple mutant arr1,10,12 showed almost complete insensitivity to cytokinin under many of the assay conditions used. By contrast, no significant change in the sensitivity to ethylene was found among the mutants examined. These results indicate that there is functional overlap among the type-B ARRs and that they act as positive regulators of cytokinin signal transduction.

Phenology of a northern hardwood forest canopy

Abstract: While commonplace in other parts of the world, long-term and ongoing observations of the phenology of native tree species are rare in North America. We use 14 years of field survey data from the Hubbard Brook Experimental Forest to fit simple models of canopy phenology for three northern hardwood species, sugar maple (Acer saccharum), American beech (Fagus grandifolia), and yellow birch (Betula alleghaniensis). These models are then run with historical meteorological data to investigate potential climate change effects on phenology. Development and senescence are quantified using an index that ranges from 0 (dormant, no leaves) to 4 (full, green canopy). Sugar maple is the first species to leaf out in the spring, whereas American beech is the last species to drop its leaves in the fall. Across an elevational range from 250 to 825 m ASL, the onset of spring is delayed by 2.7±0.4 days for every 100 m increase in elevation, which is in reasonable agreement with Hopkin's law. More than 90% of the variation in spring canopy development, and just slightly less than 90% of the variation in autumn canopy senescence, is accounted for by a logistic model based on accumulated degree-days. However, degree-day based models fit to Hubbard Brook data appear to overestimate the rate at which spring development occurs at the more southerly Harvard Forest. Autumn senescence at the Harvard Forest can be predicted with reasonable accuracy in sugar maple but not American beech. Retrospective modeling using five decades (1957–2004) of Hubbard Brook daily mean temperature data suggests significant trends (P≤0.05) towards an earlier spring (e.g. sugar maple, rate of change=0.18 days earlier/yr), consistent with other studies documenting measurable climate change effects on the onset of spring in both North America and Europe. Our results also suggest that green canopy duration has increased by about 10 days (e.g. sugar maple, rate of change=0.21 days longer/yr) over the period of study.

Global atmospheric model for mercury including oxidation by bromine atoms

Abstract: . Global models of atmospheric mercury generally assume that gas-phase OH and ozone are the main oxidants converting Hg0 to HgII and thus driving mercury deposition to ecosystems. However, thermodynamic considerations argue against the importance of these reactions. We demonstrate here the viability of atomic bromine (Br) as an alternative Hg0 oxidant. We conduct a global 3-D simulation with the GEOS-Chem model assuming gas-phase Br to be the sole Hg0 oxidant (Hg + Br model) and compare to the previous version of the model with OH and ozone as the sole oxidants (Hg + OH/O3 model). We specify global 3-D Br concentration fields based on our best understanding of tropospheric and stratospheric Br chemistry. In both the Hg + Br and Hg + OH/O3 models, we add an aqueous photochemical reduction of HgII in cloud to impose a tropospheric lifetime for mercury of 6.5 months against deposition, as needed to reconcile observed total gaseous mercury (TGM) concentrations with current estimates of anthropogenic emissions. This added reduction would not be necessary in the Hg + Br model if we adjusted the Br oxidation kinetics downward within their range of uncertainty. We find that the Hg + Br and Hg + OH/O3 models are equally capable of reproducing the spatial distribution of TGM and its seasonal cycle at northern mid-latitudes. The Hg + Br model shows a steeper decline of TGM concentrations from the tropics to southern mid-latitudes. Only the Hg + Br model can reproduce the springtime depletion and summer rebound of TGM observed at polar sites; the snowpack component of GEOS-Chem suggests that 40% of HgII deposited to snow in the Arctic is transferred to the ocean and land reservoirs, amounting to a net deposition flux to the Arctic of 60 Mg a−1. Summertime events of depleted Hg0 at Antarctic sites due to subsidence are much better simulated by the Hg + Br model. Model comparisons to observed wet deposition fluxes of mercury in the US and Europe show general consistency. However the Hg + Br model does not capture the summer maximum over the southeast US because of low subtropical Br concentrations while the Hg + OH/O3 model does. Vertical profiles measured from aircraft show a decline of Hg0 above the tropopause that can be captured by both the Hg + Br and Hg + OH/O3 models, except in Arctic spring where the observed decline is much steeper than simulated by either model; we speculate that oxidation by Cl species might be responsible. The Hg + Br and Hg + OH/O3 models yield similar global budgets for the cycling of mercury between the atmosphere and surface reservoirs, but the Hg + Br model results in a much larger fraction of mercury deposited to the Southern Hemisphere oceans.

Unwanted and wanted exposure to online pornography in a national sample of youth Internet users.

Abstract: OBJECTIVE. The goal was to assess the extent of unwanted and wanted exposure to online pornography among youth Internet users and associated risk factors. METHODS. A telephone survey of a nationally representative sample of 1500 youth Internet users aged 10 to 17 years was conducted between March and June 2005. RESULTS. Forty-two percent of youth Internet users had been exposed to online pornography in the past year. Of those, 66% reported only unwanted exposure. Multinomial logistic regression analysis was used to compare youth with unwanted exposure only or any wanted exposure with those with no exposure. Unwanted exposure was related to only 1 Internet activity, namely, using file-sharing programs to download images. Filtering and blocking software reduced the risk of unwanted exposure, as did attending an Internet safety presentation by law enforcement personnel. Unwanted exposure rates were higher for teens, youth who reported being harassed or sexually solicited online or interpersonally victimized offline, and youth who scored in the borderline or clinically significant range on the Child Behavior Checklist subscale for depression. Wanted exposure rates were higher for teens, boys, and youth who used file-sharing programs to download images, talked online to unknown persons about sex, used the Internet at friends’ homes, or scored in the borderline or clinically significant range on the Child Behavior Checklist subscale for rule-breaking. Depression also could be a risk factor for some youth. Youth who used filtering and blocking software had lower odds of wanted exposure. CONCLUSIONS. More research concerning the potential impact of Internet pornography on youth is warranted, given the high rate of exposure, the fact that much exposure is unwanted, and the fact that youth with certain vulnerabilities, such as depression, interpersonal victimization, and delinquent tendencies, have more exposure.