Drawdown Ratio Research Articles

Estimating RESCON model parameters for efficient sediment flushing in a dam reservoir

In this study, we developed a parameter estimation method of a reservoir conservation model that was developed by the World Bank for efficient sediment flushing operation in dam reservoirs. The parameters for sediment flushing operation are flushing discharge, duration, frequency, and necessary reservoir drawdown. The parameter estimation method was applied to Shahpur Dam in Pakistan, in which sediment balance ratio and long-term capacity ratio were used as indicators of flushing efficiency. For efficient flushing of Shahpur Dam, we recommended that bottom outlets at the dam be retrofitted to achieve a flushing discharge of 7.5 m3/s. The reservoir water elevation should be drawn to a minimum level of 430 m, and the flushing operation should be performed annually over a 15-day span. Flushing using these parameters would result in 100% sediment balance, with 69% of original dam capacity recovered in the long term. We also assessed constraints on dam site for successful flushing. The drawdown ratio was 0.72, sediment balance ratio at full drawdown was 1.58, flushing width ratio was 0.88, and top width ratio was 1.23. For every increment of 0.5 m3/s in flushing discharge, the amount of sediment flushed increased by 0.020–0.025 million tonnes. This method can provide guidelines for implementation of sediment flushing operations for reservoir sediment management.

Shear Force Fiber Spinning: Process Parameter and Polymer Solution Property Considerations.

For application of polymer nanofibers (e.g., sensors, and scaffolds to study cell behavior) it is important to control the spatial orientation of the fibers. We compare the ability to align and pattern fibers using shear force fiber spinning, i.e. contacting a drop of polymer solution with a rotating collector to mechanically draw a fiber, with electrospinning onto a rotating drum. Using polystyrene as a model system, we observe that the fiber spacing using shear force fiber spinning was more uniform than electrospinning with the rotating drum with relative standard deviations of 18% and 39%, respectively. Importantly, the approaches are complementary as the fiber spacing achieved using electrospinning with the rotating drum was ~10 microns while fiber spacing achieved using shear force fiber spinning was ~250 microns. To expand to additional polymer systems, we use polymer entanglement and capillary number. Solution properties that favor large capillary numbers (>50) prevent droplet breakup to facilitate fiber formation. Draw-down ratio was useful for determining appropriate process conditions (flow rate, rotational speed of the collector) to achieve continuous formation of fibers. These rules of thumb for considering the polymer solution properties and process parameters are expected to expand use of this platform for creating hierarchical structures of multiple fiber layers for cell scaffolds and additional applications.

An experimental investigation on effect of drawdown rate and drawdown ratios on stability of cohesionless river bank and evaluation of factor of safety by total strength reduction method

ABSTRACTThis paper presents an experimental investigation on the stability of a model river bank composed of homogeneous cohesionless soil under rapid drawdown condition. The effects of major influencing parameters controlling Factor of Safety (FoS) of a river bank under depletion of water level have been considered in the present study. A series of laboratory model studies have been carried out to investigate the cases of drawdown rate and drawdown ratios rendering the bank to maximum damage. Moreover, the effect of water level drawdown on the response variables namely pore water pressure, deformation of the bank profile, and shear strength of bank material have been observed and analysed. Stability analysis of the experimental model banks under drawdown conditions was carried out by evaluating FoS using the principle of reduced shear strength methodology. The in-situ total shear strength after each drawdown was measured using a laboratory vane shear apparatus. The minimum shear strength among these values has been identified. Now the FoS against each drawdown ratio has been computed from the ratio of total shear strength obtained after drawdown for that particular drawdown ratio to the minimum shear strength as obtained. This experimental programme examined the optimum combination of drawdown rate and drawdown ratio causing mass failure of the bank. It was revealed from the variation of pore pressure after drawdown that changes of pressures at points close to the toe of the bank slope is strongly controlled by the stress-state induced by drawdown. From the failure observations it was found that the drawdown rate is the dominating cause of maximum deformation of the bank than that of drawdown ratio. The findings of the present research work may help in predicting the actual failure scenario and stability condition of prototype river under similar boundary conditions.

Optimum development options and strategies for water injection development of carbonate reservoirs in the Middle East

Abstract Through the research on several carbonate reservoirs developed in the Middle East, the basic characteristics of different types of carbonate reservoirs are determined, and a set of high-efficiency water injection development options and strategies are presented. Hidden baffles and barriers exist in carbonate reservoirs in the Middle East, so the reservoirs could be divided into different separated development units based on the baffles and barriers characteristics. Flexible and diverse profile control techniques such as high angle wells and simple and applicative zonal water injection have been introduced to improve the control and development degree of reservoirs. Three principal water injection development methods suitable for different carbonate reservoirs in the Middle East are proposed, including the combination of crestal gas injection and peripheral water injection, bottom interval injection and top interval production (buoyancy underpinning), and “weak point and strong plane” area well pattern. Based on the characteristics of very low shale content, fast and far pressure transmission in the Middle East carbonate reservoirs, a large well-spacing flood pattern is recommended, and reasonable development strategies have been made such as moderate water injection rate and maintaining reasonable production pressure drawdown and voidage replacement ratio, so as to maximize the recovery of reservoirs in the none or low water cut period.

A process-oriented scale-up/scale-down strategy for industrial blown film processes: Theory and experiments

To gain a competitive edge in developing innovative products, new multi-layer film manufacturers need to know whether laboratory-scale blown film line results reliably translate to large-scale production. This, however, is not always the case: Transferring process conditions and getting equal final film properties are not ensured. To address this problem, this paper presents a scale-independent scale-up/scale-down strategy to produce films with consistently similar properties regardless of a plant’s size and design. A second aim is to prove this strategy is applicable by comparing the reference and experimental film mechanical properties. Here, experimental scale-down runs were carried out based on a process-oriented scale-up/scale-down strategy for the blown film process. An industrial production process (>800 kg/h), successfully transferred to a laboratory-scale blown film line, was used as the reference. The introduced process-oriented scale-up/scale-down is based on geometric and dynamic similarity. In this context, blow-up ratio, draw-down ratio and process time have been identified as major scale-up/scale-down variables. Unlike existing scale-up strategies, the process-oriented approach is more flexible in practice. Film mechanical properties taken from the experimental runs were determined by tensile and puncture resistance tests. The compared results confirmed that process-oriented scale-up/scale-down is feasible for the applied material and under the existing plant-specific restrictions. The comparison indicated that most film properties produced on the laboratory-scale plant were comparable to those from the high-capacity blown film line.

Insights into Silk Formation Process: Correlation of Mechanical Properties and Structural Evolution during Artificial Spinning of Silk Fibers.

The extraordinary comprehensive mechanical properties of animal silk (especially spider and silkworm silk) have led to extensive research on the underlying mechanisms involved. Herein, we selected various regenerated silk fibroin (RSF) fibers by choosing different postdraw conditions in a wet-spinning process developed in this laboratory to study their structure-property relationship. We use synchrotron radiation infrared and X-ray diffraction techniques to monitor the structural differences in these RSF fibers and correlate them with their mechanical properties. The results show that with the increase of post draw-down ratio, the β-sheet content, crystallinity, and molecular orientation in these RSF fibers increase while the crystalline size decreases. The relationship between structural changes and the draw-down ratio reflects the corresponding variation in mechanical properties, namely, an increase in breaking stress with a decline in breaking strain in relation to increases in draw-down ratio. Therefore, these results provide solid and direct evidence on the evolution of structure during the artificial spinning process and on how structure determines the final mechanical performance of silk fibers. We believe this study provides a good background on the relationship between microscopic structure and macroscopic properties in polymer science and may prove useful in the production of high performance materials, not only for silk fibers but also for other natural and synthetic polymeric materials.

Bioactive trace metal time series during Austral summer in Ryder Bay, Western Antarctic Peninsula

The Western Antarctic Peninsula, one of the most productive regions of the Southern Ocean, is currently affected by the increasing of atmospheric and oceanic temperatures. For several decades, the Rothera Time Series (RaTS) site located in Ryder Bay has been monitored by the British Antarctic Survey and has shown long lasting phytoplankton summer blooms (over a month) that are likely driven by the length of the sea ice season. The dynamics of phytoplankton blooms in Ryder Bay may just as well be influenced by natural fertilization of iron and other bioactive trace metals due to the proximity of land, islands and glaciers. For the first time, temporal distributions in the surface layer (0–75m depth) of six bioactive trace metals (dissolved: Fe, Mn, Zn, Cd, Cu and dissolved labile Co) have been investigated with high temporal and spatial resolution at the RaTS site during a total of ~2 and 3.5 months respectively, over two consecutive summers. Most of the studied trace elements showed wide ranges of concentrations and this dynamics appears to be driven by phytoplankton uptake, remineralization and occasional vertical mixing associated with storm episodes. The biological uptake of DMn, DZn, DCd, DCoL and DCu was proportional to uptake of phosphate and silicate, which was associated with weak to strong linear relationships depending on which phytoplankton bloom events was considered. This further suggests that the surface water distributions of these studied bio-active trace metals were mainly driven by biological uptake and remineralization during austral spring and summer in Ryder Bay. Even though DFe did not show any strong relationship with phosphate, DFe decreasing concentrations during each bloom event suggest that Fe is a key essential element for phytoplankton in the area of study. The consistency of trace metals/nutrient ratios during two consecutive summers indicates that over-winter scavenging removal was slow relative to mixing. The increase of DCd/P and DCoL/P drawdown ratios during the two consecutive blooms monitored during the second season could reflect the substitution of DZn by trace metals DCd and DCoL due to lowered DZn concentrations after the first bloom. Relationships of trace elements versus silicate appear to be dominated by diatoms abundances which tend to vary both at the season and bloom time scale. Simultaneous short-term events of depletions of both nutrients and bio-active trace metals might induce stress in the growth of the phytoplankton assemblage.

SLOPE STABILITY AND DEFORMATION ANALYSIS UNDER DRAWDOWN CONDITIONS (CASE STUDY: RAMA 9 RESERVOIR)

The Rapid drawdown condition is one of the most dangerous conditions for earth slopes. The change of water level in reservoir always causes a slope failure. This paper presents an investigation on the slope stability of the Rama 9 Reservoir under different drawdown conditions depending on the drawdown ratio, the drawdown rate and the loading conditions. Finite element analysis program PLAXIS 2D 2012 were applied to define the displacement and the factor of safety for slopes at selected positions. The results shown that, in the rapid drawdown condition for the drawdown ratio of 0.75, the factor of safety is 1.16. In the slow drawdown condition for the drawdown ratio of 1.00, the factor of safety is 1.26. Both are less than the ratio of allowable security value of 1.3. For the Rama 9 Reservoir, the reduction of the water level should be controlled more carefully.

Electrical conductivity of melt-spun thermoplastic poly(hydroxy ether of bisphenol A) fibres containing multi-wall carbon nanotubes

Fibres spun from thermoplastic poly(hydroxy ether of bisphenol A) filled with weight fractions of 1, 3, 6, 8 and 12 wt.% of multi-wall carbon nanotubes (MWCNTs) were prepared at elevated process temperatures using a three-roll-mill for homogeneous dispersion of the MWCNTs and a twin-screw compounder with an attached winding roll for fibre spinning. Production caused fibre draw down ratios (DDR) from 1 to a maximum of 54 resulting in fibre diameters from 0.7 mm down to 0.07 mm were used. The state of dispersion of the MWCNTs was characterized by transmission electron microscopy (TEM). The electrical resistivity of the fibres and the percolation threshold were obtained as a function of weight fraction of MWCNTs and the fibre draw down ratio. The effect on resistivity of a subsequent heat treatment at 180 °C and on dissolution of the fibre’s outer layers were analysed when embedded in liquid epoxy resin. Percolation thresholds between 6 wt.% and 12 wt.% were estimated depending on the draw down ratio of the fibres. The observed lowest resistivity was about 5 Ωm for as spun fibres without drawing. It increases over several orders of magnitude to the limit of measurability with increasing the draw down ratio. It was further shown that the resistivity greatly reduced after heat treatment, as well as after embedding the fibres in epoxy resin due to the effect of near surface solubility of the thermoplastic fibre when in contact to the epoxy resin. A reduced percolation threshold of about 6 wt.% can be obtained after heat treatment. Thereby, the production related influence of fibre stretching is largely eliminated.

Strain sensing, electrical and mechanical properties of polycarbonate/multiwall carbon nanotube monofilament fibers fabricated by melt spinning

Polycarbonate (PC)/multiwall carbon nanotube (MWCNT)/composites were prepared by melt mixing and subsequently melt spun to monofilament fibers. Electrical, mechanical and piezoresistive (strain sensing) properties of the fibers were evaluated as a function of the MWCNT weight concentration, which was varied up to 6 wt%. After the incorporation of MWCNTs, a decrease in electrical resistivity of the fibers was found for MWCNT concentrations as low as 2 wt%. Furthermore, an important effect of the draw down ratio (DDR) on the electrical properties of the fibers was observed. While the electrical percolation threshold (φc) for the bulk material was <1 wt% and ∼1 wt% for the undrawn-extruded rods, for the melt-spun fibers φc was found to be highly dependent on the DDR. Stiffness and offset yield stress of the MWCNT/PC fibers were increased starting with the addition of 1 wt% of MWCNTs. However, decreased spinnability was observed for fibers with MWCNT concentrations above 4 wt%. The coefficient that relates the electrical resistance changes to the mechanical strain (strain gage factor SGF) was estimated for fibers with MWCNTs amounts that range from 3.5 to 6 wt%. The highest SGF ∼16 was found at 3.5 wt% and the lowest SGF ∼2.5 at 6 wt% MWCNT. Smart multifunctional textiles, made from such conductive fibers, have wide applications such as structural health monitoring, detection of gases and liquids, sensor arrays and flexible sensors.

The Blended Approach to Real Estate Allocations: Performance Implications of Combining an Exposure to German Spezialfonds with Global Listed Real Estate Securities

This paper seeks to increase the understanding of the performance implications for investors who choose to combine an unlisted real estate portfolio (in this case German Spezialfonds) with a (global) listed real estate element. We call this a “blended” approach to real estate allocations. For the avoidance of doubt, in this paper we are dealing purely with real estate equity (listed and unlisted) allocations, and do not incorporate real estate debt (listed or unlisted) or direct property into the process. A previous paper (Moss and Farrelly 2014) showed the benefits of the blended approach as it applied to UK Defined Contribution Pension Schemes. The catalyst for this paper has been the recent attention focused on German pension fund allocations, which have a relatively low (real estate) equity content, and a high bond content. We have used the MSCI Spezialfonds Index as a proxy for domestic German institutional real estate allocations, and the EPRA Global Developed Index as a proxy for a global listed real estate allocation. We also examine whether a rules based trading strategy, in this case Trend Following, can improve the risk adjusted returns above those of a simple buy and hold strategy for our sample period 2004-2015. Our findings are that by blending a 30% global listed portfolio with a 70% allocation (as opposed to a typical 100% weighting) to Spezialfonds, the real estate allocation returns increase from 2.88% p.a. to 5.42% pa. Volatility increases, but only to 6.53%., but there is a noticeable impact on maximum drawdown which increases to 19.4%. By using a Trend Following strategy raw returns are improved from 2.88% to 6.94% p.a. , The Sharpe Ratio increases from 1.05 to 1.49 and the Maximum Drawdown ratio is now only 1.83% compared to 19.4% using a buy and hold strategy . Finally, adding this (9%) real estate allocation to a mixed asset portfolio allocation typical for German pension funds there is an improvement in both the raw return (from 7.66% to 8.28%) and the Sharpe Ratio (from 0.91 to 0.98).

Production and characterization of melt-spun Poly(Ether Ether Ketone) fibers for biomedical applications

Melt-spun Poly (Ether Ether Ketone) (PEEK) fibers were produced on a custom built melt-spinning system. Fibers of two different grades were spun at two different draw-down ratios, with one of three possible post-spinning treatments: as-spun, annealed, or hot drawn. Fibers were characterized with SEM, DSC, WAXS, and tensile testing. Hot drawn fibers had the highest degree of crystalline orientation (S = 0.81). Modulus, strength, and yield stress, were found to be 1.7 GPa, 175 MPa, and 45 MPa, respectively for as-spun fibers. As-spun fibers had strains-to-failure as high as 215%, which decreased to about 25% after hot drawing. Annealed and drawn fibers had similar crystallinity and crystalline orientation, but drawn fibers had significantly higher moduli of 2.8 GPa and 5.2 GPa, and strength of 195 MPa and 480 MPa, respectively. Fiber properties were found to be tunable to a number of combinations, with potential for numerous applications as novel biomaterials.

Dynamics of dissolved iron and other bioactive trace metals (Mn, Ni, Cu, Zn) in the Amundsen Sea Polynya, Antarctica

Abstract The Amundsen Sea Polynya is experiencing large increases in glacial meltwater input and hosts an extremely productive and long-lasting summer phytoplankton bloom, suggesting a crucial role for natural Fe fertilization. Early summer distributions and dynamics of the dissolved bioactive metals Fe, Mn, Zn, Cu and Ni were investigated during a three week period in 2010–2011, using GEOTRACES-compliant methods. Dissolved Fe was very low (0.06–0.12 nmol kg−1) in the upper 20 m of the central polynya, suggesting that the sub-maximal rates of in situ primary productivity reported previously for this growth phase of the bloom are attributable to insufficient Fe availability. Weeks after the sampling period, phytoplankton biomass accumulated to peak bloom conditions, implying a continuous supply of bioavailable Fe to the euphotic zone. The dominant biologically-relevant Fe source was meltwater-enriched seawater flowing from the Dotson Ice Shelf cavity and delivering Fe at 0.7 nmol kg−1 to the broader polynya. The modest Fe content of Circumpolar Deep Water (CDW; 0.3 nmol kg−1), invading through cross-shelf troughs, was strongly augmented by benthic Fe inputs, which may combine with glacial meltwater dFe in the Dotson outflow. Sea ice melting provided a modest local Fe flux, insufficient to drive large annual blooms. Dissolved Mn was strongly reduced in surface waters, but displayed a subsurface maximum likely advected through the region from shallow coastal sediments. Nutrient-type elements Zn, Cu and Ni had large to small dynamic ranges, respectively, and increasing concentrations with depth, indicating uptake and remineralization within the polynya system. Surface water drawdown ratios of metals and nutrients provided novel estimates of metal quotas (metal/P) for the dominant bloom phytoplankton, Phaeocystis antarctica. At one unique mature bloom station, Zn and Cu were scavenged to low concentrations throughout the 350 m water column, a possible result of intense removal onto sinking Phaeocystis biodetritus. The Amundsen Sea appears to be a model region for studying the biogeochemical consequences of increased glacial meltwater inputs.

Optimal Betting Sizes for the Game of Blackjack

We develop the theory of Kelly and Thorp in analyzing the optimal bet sizes for blackjack by incorporating the practical considerations of players wherein only a finite number of plays shall occur as well as pursuing maximizing risk-adjusted returns. We show that the ratio of return to bet size is approximately proportional to the return / drawdown ratio and is a reasonable proxy for risk-adjusted returns. Thus, bet sizes that maximize this measure or its marginal increase are also reasonable choices. Both theoretical analysis and computer simulation show that these alternative choices of bet sizes are much more conservative compared to what the Kelly-Thorp theory suggests and makes sense in practice. In principle, the analysis and results here also apply to money management problems for investment as well as more generalized cumulative resource allocation considerations involving risk.

Sources and distributions of Mn, Fe, Co, Ni, Cu, Zn, and Cd relative to macronutrients along the central California coast during the spring and summer upwelling season

Coastal upwelling in the central California Current System (cCCS) delivers macro and micronutrients to the surface ocean that fuel biological productivity. Variations in upwelling strength and continental shelf width affect trace metal sources seasonally. The purpose of this study was to investigate various sources and distributions for a suite of dissolved trace metals (Mn, Fe, Co, Ni, Cu, Zn, and Cd) in the cCCS (34–41°N) as well as to determine the effects of biological uptake, physical advection, and mixing processes on trace metal concentrations during the spring and summer upwelling season. Continental shelf sediments did not substantially affect upwelled concentrations of Ni, Zn, and Cd — three typical nutrient-type trace metals. However, shelf sediments provided a significant external source for Mn, Fe, Co, and Cu — scavenged and hybrid-type trace metals. There was no clear seasonal trend in benthic boundary layer (BBL) Fe concentrations; however, higher concentrations of Mn and Co together with lower O2 concentrations were found in the BBL in the late summer compared to early spring. Conversely, there was a higher sedimentary Cu source to the BBL in the early spring before O2 concentrations dropped. Surface transect samples along the Big Sur Coast (May, 2010) and North Coast (August, 2011) demonstrated both mixing and biological assimilation of NO3− and trace metals. Iron and Zn showed accelerated drawdown relative to NO3− during both seasons suggesting an increased metal to nitrogen drawdown ratio at higher dissolved metal concentrations. Surface Mn and Co concentrations were higher in the late summer and both showed evidence for accelerated drawdown relative to NO3−. Cadmium and Ni were strongly correlated with NO3− indicating that both are affected by a combination of assimilation and regeneration at a constant rate relative to NO3−; however, Cd showed slightly increased drawdown in aged upwelled waters during the late summer when Zn and Fe concentrations were low. This study provides field trace metal and macronutrient data supporting past laboratory studies suggesting that complex biological interactions are a key control on trace metal distributions and marine biogeochemical cycles.

Creep-resistant behavior of MWCNT-polycarbonate melt spun nanocomposite fibers at elevated temperature

The influence of polymer chain orientation as well as multi-walled carbon nanotube (MWCNT) alignment on the creep-resistant behavior of nanocomposites has not been fully revealed yet. In this work, tensile and creep behaviors of MWCNT modified polycarbonate nanocomposite fibers produced by melt-spinning at different draw-down ratios have been studied at a temperature of 120 °C. For fibers with 2 wt.% MWCNTs, it was found that the Young's modulus and creep resistance show clear dependence on the orientation degree of the polymer chains and the alignment of the nanotubes. Parametric studies based on Burger's model and Weibull distribution function were employed to understand the reinforcing mechanisms. Polarized Raman spectroscopy was utilized to evaluate the orientation degree of nanotubes, and further to reveal the variation in alignment during creep deformation. The results show that Raman analysis was consistent with the creep results.

Orientated CNT-polypropylene nanocomposite films made from extruded monofilaments

In this study, a method for making an orientated polymer nanocomposite film was developed. Melt-drawn nanocomposite monofilaments of isotactic polypropylene and acicular nanofillers, i.e. carbon nanotubes (CNT) or vapor grown carbon nanofibers (VGCF), were prepared and characterized from the aspect of polymer chain orientation, mechanical properties, and overall morphology. A marked improvement in mechanical properties was observed as a function of the addition of CNT, increasing draw down ratio (DDR) and annealing. Nanocomposite films were prepared from drawn monofilaments by hot-pressing under low pressure in order to maintain the orientation of the monofilaments. Wide angle X-ray diffraction showed a high degree of residual orientation in the films. Electron microscopy (high-resolution scanning electron microscopy, transmission electron microscopy) unexpectedly revealed that the CNT-matrix interface is amorphous. However, differential scanning calorimetry found no measurable influence of the CNT on the overall crystallinity as determined by the enthalpy of melting of the matrix. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers

The effect of inorganic nitrogen speciation on primary production in the San Francisco Estuary

We describe the results of a series of 96-h enclosure experiments conducted using water from stations in the northern San Francisco Estuary (SFE) along a gradient in ammonium (NH4) and nitrate (NO3) concentrations. Using dual-labeled 13C/15N tracers, we followed the timing and sequence of primary (carbon, C) production and phytoplankton nitrogen (N) use during experimental phytoplankton blooms. Our results show that diatoms consistently drive the phytoplankton blooms in the enclosures. By tracing both C and N uptake we provide clear evidence that high rates of C uptake are linked to phytoplankton NO3, and not NH4, use. Results from kinetics experiments demonstrated higher specific uptake rates (VMAx) for NO3 compared to NH4 in the SFE. Finally, dissolved inorganic carbon and nutrient drawdown ratios in the enclosures from the chronically high NH4 regions of the SFE were substantially lower than predicted from the Redfield ratio, suggesting suppressed C uptake, in relation to other elemental uptake. Our conceptual model of the DIN interactions that lead to higher primary production and phytoplankton blooms in the SFE suggests that higher rates of primary production that accompany phytoplankton NO3 uptake are sufficient to outpace phytoplankton losses, leading to blooms, compared to the lower rates associated with NH4 uptake (only 20% of that based upon NO3). Historical changes in wastewater practices have increased the proportion of NH4 to the DIN pool in the SFE leading to reduced access to NO3 by phytoplankton. This may help to explain some of the reduced primary production and phytoplankton biomass observed there since the 1970s.

Effect of extrusion conditions on the surface quality, mechanical properties, and morphology of cellular wood flour/high-density polyethylene composite profiles

Wood-plastic composite (WPC) can be fine-cell processed to create a new class of low-weight composite material with improved mechanical properties that could broaden their applications. This study investigated the effects of a chemical blowing agent (CBA) and the drawdown ratio (DDR) on the surface quality, cell morphology, and mechanical properties of extruded foamed WPC profiles. The rectangular foamed WPC profiles were produced from high-density polyethylene and wood flour with different CBA contents and DDR values using a twin-screw extrusion line. The foam density, cell density, and their sizes and shapes were largely depended on the CBA content and the DDR. A foamed WPC profile with a 22% density reduction with cellular structure can be produced using an extrusion profile line.

Combined effects of hydrographic structure and iron and copper availability on the phytoplankton growth in Terra Nova Bay Polynya (Ross Sea, Antarctica)

Surface water (<100m) samples were collected from the Terra Nova Bay polynya region of the Ross Sea (Antarctica) in January 2006, with the aim of evaluating the individual and combined effects of hydrographic structure, iron and copper concentration and availability on the phytoplankton growth. The measurements were conducted within the framework of the Climatic Long Term Interaction for the Mass-balance in Antarctica (CLIMA) Project of the Programma Nazionale di Ricerca in Antartide activities. Dissolved oxygen, nutrients, phytoplankton pigments and concentration and complexation of dissolved trace metals were determined. Experimental data were elaborated by Principal Component Analysis (PCA). As a result of solar heating and freshwater inputs from melting sea-ice, the water column was strongly stratified with an Upper Mixed Layer 4–16m deep. The integrated Chl a in the layer 0–100m ranged from 60mgm−2 to 235mgm−2, with a mean value of 138mgm−2. The pigment analysis showed that diatoms dominated the phytoplankton assemblage. Major nutrients were generally high, with the lowest concentration at the surface and they were never fully depleted. The Si:N drawdown ratio was close to the expected value of 1 for Fe-replete diatoms. We evaluated both the total and the labile dissolved fraction of Fe and Cu. The labile fraction was operationally defined by employing the chelating resin Chelex-100, which retains free and loosely bound trace metal species. The total dissolved Fe ranged from 0.48 to 3.02nM, while the total dissolved Cu from 3.68 to 6.84nM. The dissolved labile Fe ranged from below the detection limit (0.15nM) to 1.22nM, and the dissolved labile Cu from 0.31 to 1.59nM, respectively. The labile fractions measured at 20m were significantly lower than values in 40–100m samples. As two stations were re-sampled 5 days later, we evaluated the short-term variability of the physical and biogeochemical properties. In particular, in a re-sampled station at 20m, the total dissolved Fe increased and the total dissolved Cu decreased, while their labile fraction was relatively steady. As a result of the increase in total Fe, the percentage of the labile Fe decreased. An increase of the Si:N, Si:P and Si:FUCO ratios was measured also in the re-sampled station. On this basis, we speculated that a switch from a Fe-replete to a Fe-deplete condition was occurring.