Raman spectroscopy is experimentally widely available and relatively simple to perform at room temperature. Some difficulties nevertheless remain, as for instance separating some various ...contributions from the Raman spectrum, such as thermal emission for high temperature measurements or luminescence. Here, an optimized time‐resolved Raman spectroscopy system based on a gated detection and a nanosecond pulsed laser excitation (30 ns width, 532 nm wavelength) is described. The system allows contactless Raman measurements, at high temperatures, of some materials such as zirconia and yttria. An example of Raman spectra collected on yttria at very high temperature up to 2100 °C is provided. This optimized system may also be used to discriminate between Raman scattering and luminescence as demonstrated in zirconia material.
An optimized time‐resolved Raman spectroscopy system based on gated detection and a nanosecond pulsed laser excitation is described here. The system allows characterizing materials at high temperature by discriminating between Raman scattering and thermal emission. The optimized parameters were used to record in situ Raman data of polycrystalline c‐Y2O3 at high temperatures up to 2100 °C. In addition to high temperature, the process of photoluminescence has also been characterized by varying the couple delay time/opening (τ1/τ2) time of the ICCD.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Radopholus Similis
(
R. Similis
) or burrowing nematode, is one of the most damaging and widespread nematodes attacking bananas, causing toppling or blackhead disease. A mathematical model for the ...population dynamics of
R. Similis
is considered, with the aim of investigating the impact of climatic factors on the growth of
R. Similis
. In this paper, based on the life cycle of
R. Similis
, we first propose a mathematical model to study and control the population dynamics of this banana pest. We show also how control terms based on biological and chemical controls can be integrated to reduce the population of
R. Similis
within banana-plantain roots. Sensitivity analysis was performed to show the most important parameters of the model. We present the theoretical analysis of the model. More precisely, we derive a threshold parameter
N
0
, called the basic offspring number and show that the trivial equilibrium is globally asymptotically stable whenever
N
0
≤
1
, while when
N
0
>
1
, the non trivial equilibrium is globally asymptotically stable. After, we extend the proposed model by taking account climatic factors that influence the growth of this pest. Biological and chemical controls are now introduced through impulsive equations. Threshold and equilibria are obtained and global stabilities have been studied. The theoretical results are supported by numerical simulations. Numerical results of model with biological and chemical controls reveal that biological methods are more effective than chemical methods. We also found that the month February is the best time to apply these controls.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
This work reports the thermal degradation kinetics of five formulations of polyethylene terephthalate (PET) reinforced with 1, 5, 10, 15, and 20 % hemp fibers based on thermogravimetric ...investigations. Two consecutive degradation steps were observed between 573 and 773 K. Moreover, their kinetic triplets were determined by nonlinear curve fitting methods, with the Sestak–Berggren and the truncated Sestak–Berggren models, respectively. The resulting kinetic parameters varied with the fiber’s concentration in the following ranges: 1.8 ≤
A
≤ 5, 2.25 ≤
n
≤ 3.17, 7.05 ≤
m
≤ 12.74, and −2.21 ≤
p
≤ −1 for the first step; and 1.76 ≤
A
≤ 10, 1.37 ≤
n
≤ 2.49, and 0.77 ≤
m
≤ 2.35 for the second. This work further confirms the thermal stability of PET–hemp fiber composites and provides key information for the reaction mechanism, a crucial developmental step for bio-composite materials with high-melting thermoplastic matrices.
Full text
Available for:
DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The mechanical and structural properties of novel melt processed poly-ethylene terephthalate (PET)-hemp fiber composites for engineering applications were investigated. First, four reinforcement ...formulations were compared with the PET modified with poly-epsilon-caprolactone: hemp, Clay/hemp, pyromellitic dianhydride/hemp and glycidyl methacrylate/hemp. Next, the effect of hemp fibers concentration as well as the effect of heat treatment was analyzed. A significant difference was observed in the mechanical and structural properties of the composites. Moreover, we observed a good fiber–matrix interface without the use of a coupling agent, particularly in the absence of additives. Our data suggest that a careful trade-off between the additives, the hemp fiber concentration and the desired engineering applications is key requirement for the applications of high melting polymers-reinforced with natural fibers.
Full text
Available for:
NUK, OILJ, SAZU, UKNU, UL, UM, UPUK
6.
Effect of Hemp Fiber on PET/Hemp Composites Talla, Aimé Fotso S.; Erchiqui, Fouad; Kocaefe, Duygu ...
Journal of renewable materials,
12/2014, Volume:
2, Issue:
4
Journal Article
The properties of polyethylene terephthalate (PET) reinforced with 1, 5, 10, 15 and 20% (w/w) alkaline-treated hemp fibers were investigated following a series of processing stages. The fiber ...concentration significantly impacts the compounding process, yielding thermostable composites
below 300°C. Their elastic moduli varied logarithmically with fiber concentration, and were increased by up to 20% with respect to the nonreinforced formulation. Such reinforcement was, however, followed by a drastic decrease in the elongation at break, from more than 20 mm for the unreinforced
PET to as low as 2.5 mm. Other properties showed closer observations to the variations of the elastic moduli. An appreciably good fiber-matrix interface was also observed; however the actual processing method could not take advantage of the fiber's length. This work has a major impact in the
development of composite biomaterials, as it extends their application range to the subexploited area of high-melting thermoplastic matrices reinforced with natural fibers.
Background. Many empirical studies have assessed the effect of adults’ HIV infection on their livelihood. However, the effect of children’s HIV status on their educational outcomes during adolescence ...has not been adequately investigated. Objectives. The study aims to evaluate the effect of household members’ HIV infection and that of children on their educational outcomes (school enrolment and progression) during adolescence. Methods. Waves 1 to 4 of the South African National Income Dynamics Study panel data collected between 2008 and 2015 were used. Analytical samples contained data for 8 835 adolescents aged 10-19 years. Analysis involved the use of descriptive statistics, logistic and linear regression as well as Oaxaca and Ransom decomposition methods. Results. Of the study sample, 7 176 were currently in school and 636 were not. HIV infection had no effect on adolescent school enrolment. Adolescent HIV infection significantly reduced their school progress index by about 8.41. The explanatory variables explained 18% of the adolescents’ school progress gap associated with HIV infection. The unexplained gap might have been attributable to stigmatisation and/or unobserved morbidity associated with adolescents’ HIV infection. Conclusion. Adolescent HIV infection affects their school progression. Education support should be targeted directly at HIV-infected children instead of targeting families with infected parents only.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Alkaloid derivatives, oriciacridone A (
1) and B (
2), were isolated from the stems bark of
Oriciopsis glaberrima Engl., and their structures determined spectroscopically. The extract exhibited in ...vitro significant antimicrobial activity against a range of micro-organisms.
Two alkaloid derivative, oriciacridone A and B, were isolated from the stem bark of
Oriciopsis glaberrima (Rutaceae). The structures were elucidated by a detailed spectroscopic analysis. The extract exhibited in vitro significant antimicrobial activity against a range of micro-organisms.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A new flavone sulfonic acid 1 named niruriflavone was isolated from the 70% ethanolic extract of the whole plant of Phyllanthus niruri (Euphorbiaceae), together with 6,10,14-trimethyl-2- ...pentadecanone, hypophyllanthin, gallic acid, brevifolin carboxylic acid, methyl brevifolin carboxylate, isoquercetin, quercetin-3-O-β -D-glucopyranosyl(1→ 4)-α-rhamnopyranoside, corilagin, and isocorilagin, whose structures were determined by spectroscopic methods and comparison with published data. In an ABTS cation radical reduction assay, niruriflavone (1) exhibited potent radical scavenging properties. A biological test system based on bioluminescence of the dinoflagellate Lingulodinium polyedrum did not reveal any prooxidant properties of 1 at 50 μM.
