Mat Density Research Articles

Ecological characteristics influence farmer selection of on-farm plant density and bunch mass of low input East African highland banana (Musa spp.) cropping systems

East African highland bananas (Musa spp., AAA-EA group) are a primary food and cash crop for smallholders in Rwanda and much of the East African highlands. Their production generally declines over time due to poor farm management and declining soil fertility. Farmers believe that among the bunch mass maintaining factors, plant density management offers some prospect. They often decrease banana mat (i.e. a single mother plant with interconnected suckers) density in an effort to increase bunch size, but the effectiveness and profitability of this practice has not been studied. In addition, not much research has been executed on the influence of climatic and edaphic factors on variations in on-farm plant density. An on-farm survey was conducted in contrasting agro-ecological sites of Rwanda (Ruhengeri, Rusizi, Karongi, Butare, Ruhango, Kibungo and Bugesera) to determine existing densities and their relationship to bunch mass. A plant density assessment method was used that measures the average distance of five mats to their respective nearest four mats to calculate average mat spacing. Plant density positively correlated with surplus/deficit water supply (i.e. difference between rainfall and water demand by bananas) (r2=0.62), with highest plant densities (>1500matsha−1) found in high rainfall areas (>1200mmyr−1) with water surplus (218–508mmyr−1) and lowest plant densities (1000–1400matsha−1) found in lower rainfall areas (1000–1200mmyr−1) with water deficit (from −223 to −119mmyr−1). Heaviest bunches (18.1–20.8kgfreshmassplant−1) were found at lowest plant densities and medium sized bunches (14.7–15.5kg) at highest plant densities. Lower soil and banana leaf nutrient contents (especially N, K, Ca and Mg) were observed on weathered soils (Acrisols) and were associated with smaller bunch mass in comparison to fertile soils (Andosols, Nitisols). Farmers tended to reduce mat densities (i) if they wanted to intercrop bearing in mind site characteristics, and (ii) to increase bunch mass to adapt to market preferences. The plant densities generally recommended by extension bodies (3m×3m or 2m×3m; i.e. 1111 and 1666matsha−1, respectively) are seldom practiced by farmers, nor do they seem to be very appropriate, as higher densities seem productive in areas with high rainfall and relatively good soil fertility.

Simple methods influencing on properties of electrospun fibrous mats

AbstractIn many cases, potentially good electrospun materials are not satisfactory to the intended uses, but the use of the additional processing allows for an achievement of more suitable properties. Sometimes certain modifications of the spinning solutions are needed to improve its spinning ability and to properly carry out the electrospinning. For example an introducing of ionic and nonionic surfactants as Tebac or Triton X‐100 significantly improved spinning ability of PLA or chitosan solutions. In turn the annealing or the annealing under pressure has enhanced crystallinity, mechanical strength, and an apparent density of raw electrospun fibrous mats from various PLAs, making them more useful. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

High-Temperature Resistivity of Dense Mats of Single-Walled Carbon Nanotube Bundles

The resistivity of mats of single-walled carbon nanotube (SWCNT) bundles has been measured in the temperature range 286–1051 K under high vacuum. The apparent density of mats was close to 1 g cm–3 ...

Volatile Organic Compounds Emissions of Particleboards in Response to Processing Parameters

The purpose of this study is to reveal the concentration variations of VOC concentrations of larch particleboards with different processing parameters. The mat moisture content (MC), panel type and density were chosen as the influencing factors to investigate the VOC emissions after processing, and consequently provide basic guideline for the selection of processing parameters of particleboards to control the pollutants. 1m3 environmental chamber and portable VOC monitor were used for VOC sampling and analysis. The results showed that these factors had significant impact on VOC concentrations. The increase of MC, board panel and density had a positive effect on VOC emissions. With the MC and board density various in the ranges from 6%-14% and 0.60-0.80 g·cm-3, the TVOC concentrations increased 42.6% and 74.7% separately. The three layers particleboard had the higher concentration than the single layer particleboard.

Neural Network–Based Intelligent Compaction Analyzer for Estimating Compaction Quality of Hot Asphalt Mixes

Continuous real-time estimating of compaction quality during the construction of a hot mix asphalt (HMA) pavement is addressed in this paper. The densification of asphalt pavements during construction usually is accomplished by using vibratory compactors. During compaction, the compactor and the asphalt mat form a coupled system whose dynamics are influenced by the changing stiffness of the mat. The measured vibrations of the compactor along with process parameters such as lift thickness, mix type, mix temperature, and compaction pressure can be used to predict the asphalt mat density. Contrary to existing techniques in the literature in which a model is developed to fit experimental data and to predict mat density, a neural network-based approach is adopted that is model-free and uses pattern-recognition techniques to estimate density. The neural network is designed to read the entire frequency spectrum of roller vibrations and to classify these vibrations into different levels. The intelligent asphalt c...

An investigation of the relationship between sediment particles size and the development of green algal mats (Ulva prolifera) on the intertidal flats of Muan, Korea

The relationship between median grain size of sediments and the abundance in the wild of green algal mats (Ulva prolifera) on the intertidal flats of Muan, Korea, were investigated. The impact of substratum particle size on the growth and survival of germlings was examined in the laboratory. In the wild, the average annual density of algal mats was 7,950 ind m−2. The algal mats mainly occurred in sands and exhibited patchy distribution. Statistical analysis indicates significant spatial analysis differences and a significant relationship between density and the ratio of sands to silts, suggesting that the distribution and density of this species were related to particle size. In laboratory experiments, the survival rate of U. prolifera germlings was the lowest value (22%) on sediments with a median grain size of 63–125 μm. Laboratory experiments have generally shown a positive relationship between attachment or survival of the alga and substratum particles size. Our laboratory results indicate a clear link between germling settlement/survival and substratum particle size. These results explain the spatial differences in abundance observed in the field in relation to the distribution and ratio of sands to silt on the Muan flats.

Production gradients in smallholder banana (cv. Giant Cavendish) farms in Central Kenya

Banana is an increasingly demanded food and cash crop in sub-Saharan Africa. Reported yields in smallholder farms vary substantially. The importance and spread of yield constraints have not been properly quantified. A study was carried out in Central Kenya to (i) quantify the yield levels, the primary yield constraints, and the spatial production gradients in such systems (ii) explore how soil fertility gradients relate to gradients in soil fertility management, and whether this is a function of farmer resource availability. Data was collected on crop management aspects, pests and diseases, and soil and plant tissue samples analyzed for nutrient contents. Bunch yields were higher near homesteads (29.8 t ha −1 yr −1) than at mid-distance (26.8 t ha −1 yr −1), or far away 20.2 t ha −1 yr −1. Yields were much higher than previously reported (11–14 t ha −1 yr −1) in Kenya. Both soil and tissue K levels were higher near and mid-distance, than far from the homestead. Gradients of soil pH, total N, available P and Organic carbon were found, being higher near the homestead, while Mg and Ca were lowest near the homesteads. K was the most deficient nutrient, with tissue K index ( I K) decreasing when moving away from the homesteads. P and Ca deficiencies were also observed. Resource-poor farmers’ soils were higher in exchangeable K and Mg, pH, and total N, and supported higher mat densities compared to resource-endowed farmers’ farms. Soil quality problems were the biggest yield loss factors and not pests and diseases.

Three-dimensional modeling of the structure formation and consolidation of wood composites

Abstract A new three-dimensional (3D) computer simulation model is proposed to study structure development in wood composites, particularly strand or short fiber wood composites. The model takes into account the stochastic positioning and orientation of the strands within the mat. It also predicts the response of individual strands within the structure to the compressive and shear forces produced during mat consolidation. The model provides a complete description of mat structure in three dimensions, including spatial distribution of porosity, inter-strand contact, and density. Predictions for porosity obtained with the 3D model compare very well with those from an earlier two-dimensional analytical model. Mat structure is dictated by mat density in a two-step process: rapid removal of macrovoids before the mat density reaches the original wood density and asymptotic elimination of microvoids at higher mat densification. Other factors of importance include original wood density and strand dimensions, particularly strand thickness and width. Although known for its influence on mechanical properties, strand orientation seems to have little effect on mat porosity and strand contact.

Alternative biomaterials: Natural, non-woven, fibroin-based silk nanofibers of weaver ants ( Oecophylla smaragdina)

Silks of silkworms and spiders have been widely studied as biomaterials, however, none has been reported on silks produced by weaver ants ( Oecophylla smaragdina). This study is the first to report on some properties of natural silk fibers of weaver ants and their potential application as a cell matrix. Weaver ant fibrous mat contained non-woven mesh of fibers with diameters ranging from 266 to 3056 nm. The average diameter of fibers was 766 ± 326 nm. The thickness, mass, and apparent density of the fibrous mats were 39.0 ± 9.8 μm, 0.8 ± 0.1 mg/cm 2, and 0.22 ± 0.03 g/cm 3, respectively. Freshly made fibrous mats by weaver ants were highly hydrophilic as determined by water contact angle analysis, whereas older ones were quite hydrophobic. TG–DTA analysis revealed a major weight loss peak from 260 up to about 330 °C, similar to the decomposition peak of Bombyx mori fibroin. FT-IR spectrum showed amide I, amide II, amide III, C–H and C–O peaks, which were attributed to random coil and β-sheet conformation in the protein structure of the weaver ant fibers. The fibrous mat was slight toxic to the fibroblast NIH 3T3 cells (37.8% cell death), probably due to some toxic particles deposited on the fibers. Nevertheless, weaver ant fibrous mat served as a good matrix for cell adhesion. Results of this work provided evidence for the properties and a potential application of natural weaver ant fibers as an alternative, natural, fibroin-based matrix.

Longitudinal Joint Data Collection Efforts in Virginia between 2005 and 2009

Premature deterioration of asphalt concrete at longitudinal joints has been a problem for many transportation agencies for years. The primary cause of this deterioration is the lack of in-place density. To address this issue, the Virginia Department of Transportation (VDOT) and the Virginia Asphalt Association (VAA) formed an alliance to seek a solution to the problem. Instead of developing a new specification for longitudinal joint density and potentially increasing construction costs, the alliance developed a communication and training plan focused on proper joint compaction. This plan included a joint construction memorandum and a field training program. During the implementation year (2005), data collection revealed improved density values at the joints. In subsequent years (2006 and 2007) the joint densities began to decline. Therefore VDOT and VAA emphasized adherence to proper joint construction during the 2009 paving season. Results collected through July 2009 indicated a significant improvement in joint densities. A substantial improvement was noted in the SM-12.5 surface mixes. Average differences of less than 2% between mat and joint densities for the 12.5-mm mixes were obtained. Statistical results from analysis of variance and F-tests also confirmed this trend.

Assessment of Workability and Compactability of Warm-Mix Asphalt

One of the main benefits advertised about the use of warm-mix asphalt is the increased workability at conventional and lower compaction temperatures. From a field perspective, “workability” is commonly defined as the asphalt mixture property that describes the ease with which the asphalt mixture can be placed, worked by hand, and compacted to the desired mat density. Unfortunately, a laboratory property and test condition have yet to be developed to quantify these field characteristics. A research effort to evaluate the workability and compactability of different warm-mix additives preblended in a polymer-modified asphalt binder at varying percentages is summarized. Different test procedures, both asphalt binder related and asphalt mixture related, were evaluated and compared. Test results indicated that conventional mixing and compaction temperature asphalt binder tests were insensitive to the different warm-mix additives and dosage rates. Compaction data obtained with the gyratory compactor also indicated the device was generally insensitive to workability and compactability. Meanwhile, the University of Massachusetts workability device and the Marshall compaction hammer were found to rank the general workability and compactability of the mixtures in a rational order and compared favorably with one another. Not only was a promising new asphalt binder test, the lubricity test, sensitive to dosage rate and warm-mix additive, but the ranking compared favorably with mixture tests. The hope is that the information in this research effort can help in the selection and validation of warm-mix additives as a compaction aid.

A Gradient Microarray Electronic Nose Based on Percolating SnO2 Nanowire Sensing Elements

Fabrication, characterization, and tests of the practical gradient microarray electronic nose with SnO(2) nanowire gas-sensing elements are reported. This novel device has demonstrated an excellent performance as a gas sensor and e-nose system capable of promptly detecting and reliably discriminating between several reducing gases in air at a ppb level of concentration. It has been found that, in addition to the temperature gradient across the nanowire layer, the density and morphological inhomogeneities of nanowire mats define the discriminating power of the electronic nose.

Intrinsic growth rate: A new approach to evaluate the effects of temperature, photoperiod and phosphorus–nitrogen concentrations on duckweed growth under controlled eutrophication

A comprehensive model based on a new approach was developed to simulate the duckweed growth under controlled conditions. Contrary to other approaches which use the specific growth rate, this approach uses the intrinsic growth rate which permits to differentiate the effect of duckweed mat density from that of temperature, photoperiod and phosphorus–nitrogen concentrations. The model was calibrated using data from laboratory experiments carried out during the present study and validated using other data from two literature sources. In both cases, the results demonstrated that the model was capable of predicting duckweed growth with a reliability of 95%.

Macroalgal standing crop estimate – fast method using ultralight aircraft

A simple and low-cost method for monitoring macroalgal standing crops in shallow water consists of flying over and photographing the areas in an ultralight aircraft to determine the surface area of macroalgal mats. In the proposed method, photos are analysed by AUTOCAD software and mat density is then estimated in the field. Using mat density and bottom surface covered by mats, a rough estimate of the Standing Crop (SC) can be computed. Total of all estimated SCs in a given period is the Total Macroalgal Standing Crop (TMSC). The method was developed to support macroalgal harvesting operations in Orbetello lagoon. SC and TMSC values were needed to decide places and times of macroalgal harvesting and to estimate the boat work required. Applied to ecological studies, this method called Fast Valuation Method (FVM) and is compared with a more time-consuming Accurate Valuation Method (AVM), which calls for extensive sampling and statistical processing. The t-test did not show significant differences between the results provided by the two methods. The results were more similar in winter, when macroalgal growth is slow and wind concentrates the mats. The results may diverge in summer when floating macroalgae are more evenly distributed, with FVM tending to underestimate TMSC. FVM is in any case of potential interest for monitoring studies.

Comparisons of Contractor and State Transportation Agency Quality Assurance Test Results on Mat Density of Hot-Mix Asphalt Concrete

A typical component of highway construction quality assurance programs is the process by which highway construction elements are sampled and tested to ensure compliance with specifications and other project requirements. The results of contractor-performed tests on in-place properties of hot-mix asphalt are increasingly used in the acceptance decision in many states. Results of tests performed by contractors and state departments of transportation (DOTs) in North Carolina, Florida, and Kansas consistently indicate that differences between contractors and state DOT test results for hot-mix asphalt concrete mat density are statistically significant. Furthermore, these comparisons consistently indicate less variable and more favorable contractor test results, relative to specification limits, that give more favorable acceptance outcomes. Details of quality assurance processes (sampling and testing frequencies, test methods, verification procedures, and acceptance procedures) appear to have little if any effect on these comparisons. These findings provide information for state DOTs to consider in structuring their quality assurance programs, specifically the role of contractor-performed tests in acceptance decisions.

Design of a Continuous Type Dryer for the Drying Kinetics Study of Foamed and Non-Foamed Mango Pulps

A continuous type dryer was designed for drying of foamed mango pulp at 0.30 kg/h w.b. over the 0.40-m2 surface area of the dryer belt. The pulp contained 10% egg albumen as a foaming agent and 0.5% methyl cellulose as a stabilizing agent. The dryer was operated with air heated to 60C and one mm foam thickness. Batch studies using similar conditions demonstrated that the foamed mango pulp could be dried to 5.07 % w.b. in 40 min when the foam was spread to a mat density of 0.52 kg/m2 w.b. Similarly, non-foamed pulp could be dried to 6.03% w.b. in 100 min when the pulp was spread to a mat density of 1.01 kg/m2. When the dryer was operated in continuous mode at a residence time of 35 min and a mat density of 0.52 kg/m2 w.b., the foamed mango pulp dried rapidly compared to the batch conditions, giving a final moisture content of 5.02% w.b. Biochemical changes were less for foamed drying compared to non-foamed drying.

Calibration of Nonnuclear Density Gauge Data for Accurate In-Place Density Prediction

Hot-mix asphalt (HMA) density is an important acceptance quality characteristic, which involves in situ tests for quality control and assurance (QC/QA). Highway agencies have conventionally used nuclear density gauges or core samples for mat density. More recently, alternate nondestructive testing methods have been considered to replace current test methods. Nonnuclear density gauges offer rapid testing while eliminating safety risks and costs associated with radioactive license. Although agencies have evaluated them, they are not implemented in acceptance testing so far. Results are presented from a field evaluation of three nonnuclear density gauges—PaveTracker, PQI 300, and PQI 301—conducted on Wisconsin Department of Transportation (WisDOT) paving projects. The main goal was to evaluate the performance and effectiveness of non-nuclear gauges for use in QC/QA activities by WisDOT. The study involved field tests at 16 project sites and included 21 mix designs and a variety of mix design and pavement design parameters, such as aggregate type, nominal maximum aggregate size, layer thickness, design traffic, and base type. Density measurements were recorded at 30 test points at each site with one nuclear gauge and three nonnuclear gauges. Although the mean standard deviation values of the nonnuclear gauge data were less than those of the nuclear gauge measurements, a consistent bias was observed between the two data sets. This bias was adjusted by using a calibration factor to yield density predictions statistically the same as the nuclear gauge measurements. It is recommended that a calibration factor determined from 10 points by using a slope function be implemented for agency use. Further, daily calibration for each mix design is recommended when the project involves multiple paving days.

Comprehensive modeling of mat density effect on duckweed ( Lemna minor) growth under controlled eutrophication

The effect of mat density on duckweed (Lemna minor) growth was studied under controlled conditions: 12.5 h a day light exposure and 342 mol m −2 s −1 light intensity at 20 °C. The plant growth was carried out in Hoagland medium for 7 days without harvesting. The results revealed a maximal biomass growth rate of 88 g-dry m −2 (1470 g-wet m −2) at an optimal initial mat density of 45 g-dry m −2 (750 g-wet m −2), with removal rates for nitrogen (N) and phosphorus (P) of 483 mg-N m −2 d −1 and 128 mg-P m −2 d −1, respectively. A mathematical model that takes into account the mat density was developed in order to simulate the growth of Lemna minor under controlled eutrophication. Based on experiments carried out, the model exhibits a reliability of 89% . The model remains to be validated at the full-scale level.

Negative effects of an autogenic ecosystem engineer: interactions between coralline turf and an ephemeral green alga

Organisms that physically modify habitat by their own presence can either positively or negatively affect other species. The direction of the effect depends on how physical variables are modified and the response of species to these variables. In this study, we investigated the interactions between an intertidal turf-forming algae Corallina officinalis and the common sea lettuce Ulva lac- tuca. Field sampling showed that U. lactuca coverage and individual dry weight was less when coex- isting with coralline turf than when growing alone at the same tidal height. However, there was no difference in mat density between both growing conditions. Transplant experiments showed that coralline turfs affect the biomass of U. lactuca and that this effect is related to turf/desiccation inter- action. Surface was more irregular in zones with turf than in zones without turf, and transplant exper- iments showed that the effect of C. officinalis surface mimics on U. lactuca was similar to the effect of real turf. This example demonstrated that species' response to habitat modification by autogenic ecosystem engineers such as coralline algae is not necessarily positive.

Macroalgal-mediated transfers of water column nitrogen to intertidal sediments and salt marsh plants

In many temperate estuaries, mats of opportunistic macroalgae accumulate on intertidal flats and in lower elevations of salt marshes, perhaps playing a role in linking water column nitrogen (N) supply to these benthic habitats. Using a flow-through seawater system and tidal simulator, we varied densities (equivalent to 0, 1, 2, or 3 kg m −2 wet mass) of 15N-labelled macroalgae ( Enteromorpha intestinalis) on estuarine sediments in microcosms with/without pickleweed ( Salicornia virginica) to assess N transfers from algae. In the 6-week experiment, macroalgal biomass increased from initial levels in the lower density treatments but all algae lost N mass, probably through both leakage and decomposition. With all densities of algae added, sediments and pickleweed became enriched in 15N. With increasing mat density, losses of algal N mass increased, resulting in stepwise increases in 15N labeling of the deeper sediments and pickleweed. While we did not detect a growth response in pickleweed with macroalgal addition during the experiment, N losses from algal mats that persist over many months and/or recur each year could be important to the mineral nutrition of N-limited marsh plants. We conclude that N dynamics of intertidal sediments and lower salt marsh vegetation are linked to the N pools of co-occurring macroalgae and that further study is needed to assess the magnitude and importance of N transfers.