Scale free networks from a Hamiltonian dynamics

Contrary to many recent models of growing networks, we present a model with fixed number of nodes and links, where it is introduced a dynamics favoring the formation of links between nodes with degree of connectivity as different as possible. By applying a local rewiring move, the network reaches equilibrium states assuming broad degree distributions, which have a power law form in an intermediate range of the parameters used. Interestingly, in the same range we find non-trivial hierarchical clustering.Comment: 4 pages, revtex4, 5 figures. v2: corrected statements about equilibriu

Switchgrass Biochar Effects Two Aridisols

The use of biochar has received growing attention with regards to improving the physico-chemical properties of highly weathered Ultisols and Oxisols, yet very little research has focused on effects in Aridisols. The objective of this study was to investigate the effect of either low or high temperature (250 or 500C) pyrolyzed switchgrass biochar on two Aridisols. In a pot study, biochar was added at 2% w/w to either a Declo loam (Xeric Haplocalcids) or a Warden very fine sandy loam (Xeric Haplocambids) and then incubated at 15% moisture content (by weight) for 127 days; a control (no biochar) was also included. Soils were leached with 1.2 to 1.3 pore volumes of deionized water on days 34, 62, 92, and 127, and cumulative leachate Ca, K, Mg, Na, P, Cu, Fe, Mn, Ni, Zn, NO3-N, NO2-N, and NH4-N concentrations were quantified. After the incubation experiment had terminated, soils were destructively sampled for extractable Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Zn, NO3-N, and NH4-N, total C, inorganic C, organic C, and pH. As compared to the 250C, the 500C pyrolysis temperature resulted in greater biochar surface area, elevated pH, higher ash content, and minimal total surface charge. For both soils, leachate Ca and Mg decreased with the 250C switchgrass biochar likely due to binding by biochar’s functional group sites. Both biochars caused an increase in leachate K, while the 500C biochar increased leachate P. The 500C biochar reduced leachate NO3-N concentrations as compared to the control; however, the 250C biochar reduced NO3-N concentrations to the greatest extent. Easily degradable C, associated with the 250C biochar’s structural make-up, likely stimulated microbial growth which caused NO3-N immobilization. Soil extractable K, P, and NO3-N followed a pattern similar to the leachate observations. Total soil C content increases were linked to an increase in organic C from the biochars. Cumulative results suggest that the use of switchgrass biochar prepared at 250C could improve environmental quality in calcareous soil systems by reducing nutrient leaching potential

Estimating ET using scintillometers and satellites in an irrigated vineyard in the Costa De Hermosillo, Sonora, Mexico

Observation techniques for surface energy balancecomponents on kilometer scale. Several methods have been proposed to estimate ET overlarge areas which combine Earth Observation Satellite datawith standard climate data. Here we use the Makkinkapproach where incoming solar radiation is obtained bycalculating exoatmospheric incoming solar radiation, usingvisible data from GOES West to estimate cloudiness and16-day composite MODIS Enhanced Vegetation Index data toestimate fractional vegetation cover. This methodology can beused operationally at a spatial resolution of 1 km2 butvalidation data are required at a similar spatial scale. LargeAperture Scintillometers transmit and receive near infraredradiation over distances of several kilometers and providemeasurements of the structure parameter for the refractiveindex of air which is related by Monin-Obukhov SimilarityTheory to the surface sensible heat flux (H), which requiresmeasurements of air temperature, pressure and wind speed.ET can then be obtained indirectly as the residual of theenergy balance, ET = Rn – G – H so that we need estimates ofNet Radiation (Rn) and Soil Heat Flux (G) as well. Ascintillometer (Scintec BLS-450) was installed over anirrigated vineyard with area of 72 hectares (1200m x 600m) inJune 6th 2009. Net Radiation was measured in the field andsoil heat flux was estimated using G = A * Rn, where theparameter A was obtained from 8-day composite MODIS LandSurface Temperature data. Comparison of ET derived fromsatellite and scintillometer for June 2009 showed considerablescatter with r2 = 0.81 and ETSAT = 1.12 * ETBLS. Thisapparent overestimation from the satellite-based ET is similarto that found in previous work. However, in these initialcalculations it was assumed that unstable conditions wouldprevail during the daytime but it appears that stableconditions often occur in the late afternoon. Secondly, theestimation of G needs to be carefully revised since this canhave a large effect on ET. These factors are being included inthe analysis of data over an entire growing season to assessthe seasonal behavior of the model

Social Cohesion, Structural Holes, and a Tale of Two Measures

EMBARGOED - author can archive pre-print or post-print on any open access repository after 12 months from publication. Publication date is May 2013 so embargoed until May 2014.This is an author’s accepted manuscript (deposited at arXiv arXiv:1211.0719v2 [physics.soc-ph] ), which was subsequently published in Journal of Statistical Physics May 2013, Volume 151, Issue 3-4, pp 745-764. The final publication is available at link.springer.com http://link.springer.com/article/10.1007/s10955-013-0722-

Tobacco Harm Reduction with Vaporised Nicotine (THRiVe): A Feasibility Trial of Nicotine Vaping Products for Smoking Cessation Among People Living with HIV

OnlinePublPeople living with HIV (PLHIV) have high rates of tobacco smoking. Nicotine vaping products (NVPs) may promote tobacco smoking cessation and/or harm reduction. This study aimed to trial the feasibility of NVPs for promoting tobacco smoking cessation among PLHIV. The Tobacco Harm Reduction with Vaporised Nicotine (THRiVe) study was a mixed-methods trial among 29 PLHIV who used tobacco daily. Participants trialled a 12-week intervention of NVPs. This study reports descriptive analyses of quantitative data on tobacco abstinence and associated adverse events. Short-term abstinence (7-day point prevalence; i.e., no tobacco use for 7 days) was achieved by 35% of participants at Week 12 and 31% reported shortterm abstinence at Week 24. Sustained medium-term abstinence (8 weeks’ abstinence) was achieved by 15% of participants at Week 12 and 31% at Week 24. Most adverse events were mild. NVPs may represent a feasible and potentially effective short-to-medium term tobacco smoking cessation aid and/or harm reduction strategy among PLHIV.Stephanie Edwards, Cheneal Puljević, Judith A. Dean, Charles Gilks, Mark A. Boyd, Peter Baker, Peter Watts, Chris Howard, Coral E. Gartne

Measurement of the Charged Multiplicities in b, c and Light Quark Events from Z0 Decays

Average charged multiplicities have been measured separately in $b$, $c$ and light quark ($u,d,s$) events from $Z^0$ decays measured in the SLD experiment. Impact parameters of charged tracks were used to select enriched samples of $b$ and light quark events, and reconstructed charmed mesons were used to select $c$ quark events. We measured the charged multiplicities: $\bar{n}_{uds} = 20.21 \pm 0.10 (\rm{stat.})\pm 0.22(\rm{syst.})$, $\bar{n}_{c} = 21.28 \pm 0.46(\rm{stat.}) ^{+0.41}_{-0.36}(\rm{syst.})$ $\bar{n}_{b} = 23.14 \pm 0.10(\rm{stat.}) ^{+0.38}_{-0.37}(\rm{syst.})$, from which we derived the differences between the total average charged multiplicities of $c$ or $b$ quark events and light quark events: $\Delta \bar{n}_c = 1.07 \pm 0.47(\rm{stat.})^{+0.36}_{-0.30}(\rm{syst.})$ and $\Delta \bar{n}_b = 2.93 \pm 0.14(\rm{stat.})^{+0.30}_{-0.29}(\rm{syst.})$. We compared these measurements with those at lower center-of-mass energies and with perturbative QCD predictions. These combined results are in agreement with the QCD expectations and disfavor the hypothesis of flavor-independent fragmentation.Comment: 19 pages LaTex, 4 EPS figures, to appear in Physics Letters

Biochars impact on soil moisture storage in an Ultisol and two Aridisols

Droughts associated with low or erratic rainfall distribution can cause detrimental crop moisture stress. This problem is exacerbated in the USA’s arid western and southeastern Coastal Plain due to poor rainfall distribution, poor soil water storage, or poorly-aggregated, subsurface hard layers that limit root penetration. We hypothesized that soil physical deficiencies may be improved by biochar applications. Research indicates a single biochar will not serve as a universal supplement to all soils; consequently, biochars may need to be designed with physico-chemical properties that can ameliorate specific soil physical deficiencies. We conducted a laboratory study that examined the effect of biochar on soil moisture retention and aggregate formation. Eight biochars were made from four feedstocks at two different pyrolysis temperature classes (500°C; 932°C) and were characterized for their physical and chemical properties. In addition, we included a biochar made using fast pyrolysis of hardwood wastes. All biochars were mixed at 2% w/w with either a Norfolk loamy sand (Fine-loamy, kaolinitic, thermic Typic Kandiudults), a Declo silt loam (Coarse-loamy, mixed, superactive, mesic xeric Haplocalcids), or a Warden silt loam (Coarse-silty, mixed, superactive, mesic xeric Haplocambids). Amended soils were laboratory incubated in pots for up to 127 days. About every 30 days, bulk density was measured and then each pot was leached with 1.2 to 1.3 pore volumes of deionized water. Gravimetric and volumetric soil moisture contents were determined after free drainage had ceased and again 2 and 6 days after leaching. The Norfolk-treated soils were later dry-sieved, and the sum by weight of their 0.5- to 1.0-mm aggregates was determined. In general, the biochar surface area and surface tension increased when produced under higher pyrolytic temperatures (>500°C). After leaching, Norfolk soils treated with switchgrass biochars had the most significant increase in soil moisture capacities. Similar increases were found in the Declo and Warden soils. Formation of 0.5- to 1.0-mm aggregates in the Norfolk loamy sand varied with biochar. Biochars enhanced the moisture storage capacity of the Ultisol and Aridisols thereby potentially reducing the on-set of crop moisture stress; however, the effect varied considerably with biochar feedstock and pyrolysis temperature

Fire as a fundamental ecological process: Research advances and frontiers

Fire is a powerful ecological and evolutionary force that regulates organismal traits, population sizes, species interactions, community composition, carbon and nutrient cycling and ecosystem function. It also presents a rapidly growing societal challenge, due to both increasingly destructive wildfires and fire exclusion in fire‐dependent ecosystems. As an ecological process, fire integrates complex feedbacks among biological, social and geophysical processes, requiring coordination across several fields and scales of study. Here, we describe the diversity of ways in which fire operates as a fundamental ecological and evolutionary process on Earth. We explore research priorities in six categories of fire ecology: (a) characteristics of fire regimes, (b) changing fire regimes, (c) fire effects on above‐ground ecology, (d) fire effects on below‐ground ecology, (e) fire behaviour and (f) fire ecology modelling. We identify three emergent themes: the need to study fire across temporal scales, to assess the mechanisms underlying a variety of ecological feedbacks involving fire and to improve representation of fire in a range of modelling contexts. Synthesis : As fire regimes and our relationships with fire continue to change, prioritizing these research areas will facilitate understanding of the ecological causes and consequences of future fires and rethinking fire management alternatives