ARTICLE | doi:10.20944/preprints202002.0169.v1
Subject: Life Sciences, Other Keywords: bark stripping; wallabies; supplementary food; radiata pine plantations
Online: 13 February 2020 (12:35:44 CET)
Bark stripping by the Bennett’s wallaby (Macropus rufogriseus rufogriseus) from the lower stems of 3–6-year-old radiata pine (Pinus radiata) causes significant damage in Tasmanian plantations. The usual diet of this generalist herbivore is mainly grasses and broadleaved forbs. As the factors that attract wallabies to supplement its diet by eating the bark of plantation pine trees are currently not elucidated, the present study aimed to determine how the incidence and severity of bark damage in 12 Tasmanian radiata pine plantations was influenced by various inter-site factors such as the floristic composition of the surrounding forest and by various intra-site factors such as the height and circumference of individual trees, the number of branches in the first two whorls at the base of the tree, and their internode lengths. Site differences in the observed percentage of bark stripping were found to be related to ‘ease of access’ variables such as bare ground, bracken, and moss, ‘hindrance to access’ variables such as rock and woody debris, and the percentage of grass, the wallaby’s main food source, present in the five plots at each site. The difference between the mean minimum soil and air temperatures in spring, a driving force for carbohydrate production that occurs with tree growth in spring or early summer, was the only meteorological observation at the sites that was found to be statistically significant. Nevertheless, there was no direct evidence that it was the movement of sugars in the phloem tissue accompanying tree growth which provided wallabies with a supplementary food source.
REVIEW | doi:10.20944/preprints202301.0429.v1
Subject: Engineering, Construction Keywords: supplementary cementitious materials; fly ash; pozzolan; binder; Portland cement; geopolymers; concrete; cement
Online: 24 January 2023 (10:25:08 CET)
This paper discusses the use of fly ash in concrete construction industry. Fly ash is incorporated as a supplementary cementitious material (SCM) in ordinary Portland cement (OPC) concrete in partial replacement of cement, and is recently used as a geopolymer cement in the development of geopolymer concrete (GPC) mixes. Class C and Class F fly ash high aluminosilicate content, and fine granular size contributes to concrete improved workability, lower permeability, and reduced heat of cement hydration. Due to its chemical properties, the use of fly ash in producing OPC and GPC results in increased compressive strength, higher tensile strength evaluated by measuring hardened concrete modulus of rupture (MOR), and higher modulus of elasticity (MOE). The fine size of fly ash particles increases the concrete mix packing order, and reduce the ingress of moisture, and mitigates the impact of aggressive environmental attacks through the reduction of sulfates and chlorides rate of concrete penetration. Thus, fly ash improves concrete resistivity to alkali-aggregate reactions (AAR), and reduces the corrosion of reinforcing steel, and prestressing strands. Fly ash as an economic byproduct of coal industry results in reduced material cost, increased durability, and a higher sustainability of concrete construction projects.
ARTICLE | doi:10.20944/preprints201805.0239.v1
Subject: Engineering, Civil Engineering Keywords: microstructural modeling; cement hydration; Avrami constants; hydration kinetics; glass cullet; supplementary cementitious material (SCM)
Online: 17 May 2018 (08:07:24 CEST)
Finely ground glass has the potential for pozzolanic reactivity and can serve as a supplementary cementitious material (SCM). Glass reaction kinetics depends on both temperature and glass composition. Microstructural modeling is a helpful approach to get better understanding of cement hydration and microstructure development. Mechanical and performance properties of concrete are directly related to the development of concrete microstructure, which is the consequence of progress in cement hydration. This study initially provides a comprehensive background about cement hydration process and microstructural modeling of the hydration. It then utilizes results of experimental studies, i.e. isothermal calorimetry and thermogravimetric analysis, to find kinetics equation parameters called “Avrami Constants”. For the first time, these constants were found for three main components of cement, i.e. C3S, C2S, and C3A, and also for glass particles smaller than 25 µm. Although modeling of cement hydration and cementitious systems containing single glass particles showed promising results, simulations of combined glass types and sizes showed that more work on microstructural models is needed to properly model the reactivity of mixed glass particle systems.
ARTICLE | doi:10.20944/preprints202102.0138.v1
Subject: Mathematics & Computer Science, Probability And Statistics Keywords: Mean time to failure; Poisson shock; Steady-state availability; Steady-state frequency; Supplementary variable technique.
Online: 4 February 2021 (13:07:59 CET)
This article examines the impact of some system parameters on an industrial system composed of two dissimilar parallel units with one repairman. The active unit may fail due to essential factors like aging or deteriorating, or exterior phenomena such as Poisson shocks that occur at various time periods. Whenever the value of a shock is larger than the specified threshold of the active unit, the active unit will fail. The article assumes that the repairman has the right to take any of two decisions at the beginning of the system operation: either a takes a vacation if the two units work in a normal way, or stay in the system to monitor the system until the first system failure. In case of having a failure in any of the two units during the absence of the repairman, the failing unit will have to wait until the repairman is called back to work. We suppose that the value of every shock is assumed to be i.i.d. with some known distribution. The length of the repairman’s vacation, repair time, and recall time are arbitrary distributions. Various reliability measures have been calculated by the supplementary variable technique and the Markov’s vector process theory. At last, numerical computation and graphical analysis have been given for a particular case to validate the derived indices.
ARTICLE | doi:10.20944/preprints201806.0017.v1
Subject: Medicine & Pharmacology, Pediatrics Keywords: childhood malnutrition; community-based management of acute malnutrition–CMAM; moderate acute malnutrition–MAM; supplementary feeding programs–SFP; Zambia
Online: 1 June 2018 (12:04:50 CEST)
Background: Evaluation of nutrition programs is essential to guarantee the effectiveness of community-based management of acute malnutrition (CMAM). Methods: The Rainbow Project Supplementary Feeding Programs (SFPs) in Zambia were evaluated between years 2015-17, following implementation of new recommendations based on previous evaluations (years 2012-14). Outcomes of the program were compared with International Standards and with those of 2012-14. Cox proportional risk regression analysis was performed to identify predictors of mortality and defaulting. Results: Data for 900 under age 5 years malnourished children (48.8% male; mean age 19.7months ±9.9) were analyzed. Rainbow 2015-17 program outcomes met International Standards, for general malnutrition or stratified moderate acute malnutrition (MAM) and severe acute malnutrition (SAM). When comparing with 2012-14 outcomes, better performance was noted: mortality rates were reduced by half (5.6% vs 3.1%, p = 0.01; for SAM: 12.4% vs 6.7%, p = 0.006), with significant improvement in average weight gain and mean length of stay (p<0.001), and increased awareness of HIV status (+30%; p < 0.001). HIV infection (5.5; 1.9–15.9), WAZ < −3 at baseline (4.6; 1.3–16.1) and kwashiorkor (3.5; 1.2–9.5) remained the major predictors of mortality. Conclusion: The effectiveness of the Rainbow SFPs for child malnutrition treatment and prevention in Zambia has significantly improved after evaluation and implementation activities, with impressive outcomes which resulted in a 50% reduction in mortality.