Solute mixing in open channel flow

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Understory Growth Dynamics and Mensuration Techniques in Uneven-Aged, Mixed-Species Northern Conifer Stands

Managing uneven-aged, mixed-species stands requires balancing the need for high leaf area allocation in the overstory where it is most efficient versus the need to allow for sufficient growth of younger cohorts in the understory. To help forest managers make informed decisions to maintain this balance, the understory growth dynamics of northern conifer species in stands managed under uneven-aged silvicultural systems were studied. Sapling height growth of Picea rubens Sarg., Abies balsamea (L.) Mill, and Tsuga canadensis (L.) Carr. were modeled as a function of overstory canopy openness (gap fraction) using regression analysis. Research was conducted in four uneven-aged northern conifer stands on the Penobscot Experimental Forest in eastern Maine; two replicates each of selection cutting on five- and ten-year cycles. Gap fraction estimates were obtained directly above 167 sample trees between 0.5-6.0 m in height, using a LI- COR LAI-2000 plant canopy analyzer. These estimates were tested in several model forms along with initial tree height to predict sapling height growth. The effect of different vertical distributions of foliage on sapling height growth was also explored using analysis of covariance. Using cluster analysis, plots were grouped into one of three categories based on similar vertical leaf area structure. Species-specific height growth was then compared between groups of similar vertical structure using initial tree height as a covariate. An innovative method employing vertical point sampling was used to obtain leaf area estimates to quantify plot-level vertical leaf area structure. To validate the use of vertical point sampling, plot-level leaf area index (LAI) and basal area (BA) estimates based on vertical point sampling were compared with conventional horizontal point sampling using a 2 m2/ha basal area factor (BAF) prism. Tree-level LA1 estimates were replaced with specieslspecific constants based on projected leaf area (PLA)-height squared and PLA-DBH\u27 linear regression coefficients in an effort to develop a quick and accurate method to estimate LA1 in the field using both vertical point sampling and prism sampling. Leaf area index measurements, BA, and tree tallies from vertical point sampling were also related to gap fraction measurements to determine if an efficient method for in-the-field gap fraction estimation could also be developed. Regression modeling demonstrated that sapling height growth of all three species followed a monotonically increasing pattern with respect to decreasing canopy closure. Abies balsamea appeared to be the most aggressive competitor demonstrating the greatest response to changes in gap fraction while Tsuga canadensis appeared to be the least responsive to changes in gap fraction. Although total plot-level LA1 was not significant in predicting height growth in these complex stands, the vertical distribution of leaf area was. While height growth of Abies balsamea and Tsuga canadensis were not significantly different between vertical leaf area structures, height growth of Picea rubens was significantly higher in plots with well-developed understories with high LAI, regardless of overstory LAI. Vertical point sampling showed strong promise in providing LA1 estimates, and in particular facilitating in-the-field LA1 estimation with the use of species-specific tree- level LA1 constants that remove the need for individual tree measurements. More field- testing of this technique needs to be done. Simple vertical point sample measures were not successful in accurately predicting gap fraction

Palaeoenvironmental investigations of Holocene landscapes in the North Tyne basin, northern England

PhD ThesisThe vegetation history of the North Tyne basin, northern England, is presented for an extended Holocene period, dating back to ca. 8000 cal. BC. This study focuses upon vegetation histories from two types of site, which record changes at differing spatial scales. The regional vegetation of the area is recorded within three radiocarbon-dated pollen diagrams from upland sites at Drowning Flow, Bloody Moss and Sells Bum. These sites provide a different perspective of regional vegetation history in comparison to existing published accounts from the region. This work also fills a spatial gap in current knowledge, by providing records from the area between Hadrian's Wall in the south and the Cheviots to the north for which only one previous site exists (Steng Moss: Davies and Turner, 1979). These regional records are complemented by the reconstruction of local, valley floor vegetation derived from organic-rich palaeochannel fills at Brownchesters Farm, Redesdale and Snabdaugh Farm, North Tynedale. These sites demonstrate how patterns of vegetation at local scales can provide valuable additional insights into former landscapes, valley floor land-use and human activity. Perceived problems of the usage of alluvial sediments for palynological investigation are discussed, while methodologies to overcome these difficulties are developed and the potential benefits of these contexts for vegetation reconstruction outlined. The unusually long and readily dateable alluvial record has also facilitated a new perspective on the timing and controls of Holocene fluvial activity in the North Tyne basin. The close integration of archaeological evidence with the results from this study has contributed to a number of debates concerning former human activity in the area. Palynological results suggest that the impact of Mesolithic and Neolithic societies upon the landscape has been underestimated; that postulated alterations in upland / lowland settlement patterns during the Bronze Age are a consequence of a fragmentary archaeological record rather than a response to changing environmental conditions; that Iron Age (and earlier) agricultural activity has been underestimated and that forest clearance was a gradual phenomenon with its origins in the Late Mesolithic and not primarily a result of activity associated with invading Roman forces.Northumberland National Park The Bill Bishop Memorial Fun

Methane from UV-irradiated carbonaceous chondrites under simulated Martian conditions

A UV photolytic process was studied for the production of methane from carbonaceous chondrites under simulated Martian conditions. Methane evolution rates from carbonaceous chondrites were found to be positively correlated to temperature (−80 to 20°C) and the concentration of carbon in the chondrites (0.2 to 1.69 wt%); and decreased over time with Murchison samples exposed to Martian conditions. The amount of evolved methane (EM) per unit of UV energy was 7.9 × 10−13 mol J−1 for UV irradiation of Murchison (1.69 wt%) samples tested under Martian conditions (6.9 mbar and 20°C). Using a previously described Mars UV model (Moores et al., 2007), and the EM given above, an annual interplanetary dust particle (IDP) accreted mass of 2.4 × 105 kg carbon per year yields methane abundances between 2.2 to 11 ppbv for model scenarios in which 20 to 100% of the accreted carbon is converted to methane, respectively. The UV/CH4 model for accreted IDPs can explain a portion of the globally averaged methane abundance on Mars, but cannot easily explain seasonal, temporal, diurnal, or plume fluctuations of methane. Several impact processes were modeled to determine if periodic emplacement of organics from carbonaceous bolides could be invoked to explain the occurrence of methane plumes produced by the UV/CH4process. Modeling of surface impacts of high-density bolides, single airbursts of low-density bolides, and multiple airbursts of a cascading breakup of a low-density rubble-pile comet were all unable to reproduce a methane plume of 45 ppbv, as reported by Mumma et al

Design and construction of the Boscombe multi-purpose reef

The Boscombe Reef is a multipurpose reef structure designed primarily for the enhancement of surfing amenity at Boscombe, Poole Bay, England. The reef was designed to maximise the small and generally poor-quality surfing wave climate of the eastern English Channel coast. The reef was constructed from 54 large, sand filledgeotextile containers ranging in size from 1 to 5 m diameters and 15 to 70 m long with a total volume of approximately 13,000m3. Construction of the reef began in the summer of 2008, was suspended during the following winter and was completed in the late summer of 2009. The reef is now in service and provides a high intensity right hand surfing ride of up to 70 m and a shorter left hand ride of up to 30 m. Although the reef was not designed as a coastal protection structure, monitoring of the morphological response supports that the reef promotes shore protection through the formation of an inshore salie

Mitotic phosphorylation by NEK6 and NEK7 reduces the microtubule affinity of EML4 to promote chromosome congression

EML4 is a microtubule-associated protein that promotes microtubule stability. We investigated its regulation across the cell cycle and found that EML4 was distributed as punctate foci along the microtubule lattice in interphase but exhibited reduced association with spindle microtubules in mitosis. Microtubule sedimentation and cryo–electron microscopy with 3D reconstruction revealed that the basic N-terminal domain of EML4 mediated its binding to the acidic C-terminal tails of α- and β-tubulin on the microtubule surface. The mitotic kinases NEK6 and NEK7 phosphorylated the EML4 N-terminal domain at Ser144 and Ser146 in vitro, and depletion of these kinases in cells led to increased EML4 binding to microtubules in mitosis. An S144A-S146A double mutant not only bound inappropriately to mitotic microtubules but also increased their stability and interfered with chromosome congression. In addition, constitutive activation of NEK6 or NEK7 reduced the association of EML4 with interphase microtubules. Together, these data support a model in which NEK6- and NEK7-dependent phosphorylation promotes the dissociation of EML4 from microtubules in mitosis in a manner that is required for efficient chromosome congression

Geometric Properties of Water-ice Clouds as Observed from Jezero Crater in the First 600 sols with the NavCam Instrument On Board the Mars2020 Rover, Perseverance

In the first 600 sols of the Mars2020 mission, LS 5.6o – 316.8o, 46 cloud movies and 145 cloud surveys were collected to observe clouds at Jezero Crater, the landing site of the Perseverance Rover. Cloud movies were processed using the Mean-Frame Subtraction (MFS) method for revealing cloud structures, which were subsequently analyzed using digital-image processing. Two-dimensional Fast Fourier Transforms (2D-FFT) were used to compute cloud structure sizes ranging from 2.90 to 15.25 km for clouds between 30 and 50 km altitude, based on coincident Mars Climate Sounder vertical profiles of atmospheric water-ice. Same-value thresholding was used to detect the cloud structures in MFS-processed and projected cloud movies. The resolution dependence that was needed to resolve these structures over various thresholds was examined to find multifractal scaling of Mars clouds for resolutions between 0.1 and 1.6 km. We characterize the multiscaling observed in the images and its implications for the design of cloud-tracking cameras from the surface as well as for cloud-resolving models

The Methane Diurnal Variation and Microseepage Flux at Gale Crater, Mars as Constrained by the ExoMars Trace Gas Orbiter and Curiosity Observations

The upper bound of 50 parts per trillion by volume for Mars methane above 5 km established by the ExoMars Trace Gas Orbiter, substantially lower than the 410 parts per trillion by volume average measured overnight by the Curiosity Rover, places a strong constraint on the daytime methane flux at the Gale crater. We propose that these measurements may be largely reconciled by the inhibition of mixing near the surface overnight, whereby methane emitted from the subsurface accumulates within meters of the surface before being mixed below detection limits at dawn. A model of this scenario allows the first precise calculation of microseepage fluxes at Gale to be derived, consistent with a constant 1.5 à 10â 10 kg·mâ 2·solâ 1 (5.4 à 10â 5 tonnes·kmâ 2·yearâ 1) source at depth. Under this scenario, only 2.7 à 104 km2 of Mars’s surface may be emitting methane, unless a fast destruction mechanism exists.Plain Language SummaryThe ExoMars Trace Gas Orbiter and the Curiosity Rover have recorded different amounts of methane in the atmosphere on Mars. The Trace Gas Orbiter measured very little methane (<50 parts per trillion by volume) above 5 km in the sunlit atmosphere, while Curiosity measured substantially more (410 parts per trillion by volume) near the surface at night. In this paper we describe a framework which explains both measurements by suggesting that a small amount of methane seeps out of the ground constantly. During the day, this small amount of methane is rapidly mixed and diluted by vigorous convection, leading to low overall levels within the atmosphere. During the night, convection lessens, allowing methane to build up near the surface. At dawn, convection intensifies and the nearâ surface methane is mixed and diluted with much more atmosphere. Using this model and methane concentrations from both approaches, we are ableâ for the first timeâ to place a single number on the rate of seepage of methane at Gale crater which we find equivalent to 2.8 kg per Martian day. Future spacecraft measuring methane near the surface of Mars could determine how much methane seeps out of the ground in different locations, providing insight into what processes create that methane in the subsurface.Key PointsNighttime SAMâ TLS seasonal cycle enrichment measurements and TGO sunset/sunrise measurements are not in oppositionMicroseepage fluxes must be local to Gale, range from 0.82 to 4.6 kg/sol, and are consistent with a constant source at depthLittle of Mars experiences microseepage unless a fast destruction mechanism exists or Gale is very unusualPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151840/1/grl59471-sup-0001-2019GL083800-SI.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151840/2/grl59471_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151840/3/grl59471.pd