Showing 5 results for Repellent
Mahdieh Saeidi, Saeid Moharramipour,
Volume 2, Issue 1 (3-2013)
Abstract
The essential oils of aerial parts of three medicinal plants Artemisia khorassanica Podl., Rosmarinus officinalis L. and Mentha longifolia L. were isolated by hydrodistillation and investigated for their toxicity and repellency against Tribolium confusum Jacquelin du Val. at 27 ± 1 ºC and 60 ± 5% RH in darkness. The mortality of the adults increased with concentration from 185 to 1111 μl/l air and with exposure time from 9 to 24 h. A concentration of 185 μl/l air and exposure time of 24 h was sufficient to obtain nearly 100% kill of the adults in all of the three essential oils tested. At the highest concentration (1111 μl/l air) R. officinalis oil caused 15% mortality for an exposure time of 6-h. whilst, the oil of A. khorassanica resulted in 1% mortality at the same exposure time. The oil of A. khorassanica at 1111 μl/l air caused 81% mortality for 12-h exposure time. No significant differences were observed between the lethal time (LT50) values at essential oil concentrations of 741 and 1111 μl/l air. For 24-h exposure time, the LC50 values of A. khorassanica, R. officinalis and M. longifolia essential oils were estimated to be 22.45, 22.14 and 39.96 μl/l air respectively. Based on LC50 values, adults of T. confusum showed similar susceptibility to the A. khorassanica and R. officinalis oils, but M. longifolia oil proved to be less toxic. In contrast to their low fumigant properties, the essential oil of M. longifolia had significantly higher repellency to T. confusum adults than did the other two.
Volume 6, Issue 4 (11-2018)
Abstract
Introduction: Soil water repellency was first reported in the first half of the 20
th century for peat soils. Depending on the severity of water repellency, a water repellent soil will resist water penetration during seconds to hours or even days. This has detrimental effects on surface and subsurface flow processes such as increased runoff, erosion, and preferential flow. The present study was conducted with the aim of investigating the effects of Soil water repellency on hydrological and erosion processes in order to identify gaps in the existing investigations.
Conclusion: Major survey gaps remained, including the dissociation of the symptoms of water repellency on soil erosion such as the existence of a soil crust and little knowledge of the temporal patterns of water repellency and their hydrological outcomes. Understanding the mechanisms of water repellency is relevant to the separation of different causal chains as well as the adjust runoff coefficients in different water repellency areas. Soil water repellency can be caused by a variety of compounds and processes and generally occurs after a period of drying weather. Under such conditions, the soil can change from a wettable to a water-repellent state when dried below its critical soil water content. Soil water repellency is found to occur in different soils worldwide, ranging from coarse to fine-textured. Water repellency in soils can result in losses of plant-available water, reduced agricultural crop production, and deterioration of turf quality on sports fields.
Volume 9, Issue 0 (3-2010)
Abstract
The family of staphylinidae (rove beetles) includes 40000 species and has a world-wide distribution .
Many species of Paederus have been known for a long time as the causative agent of linear dermatitis. Paederus beetles are attracted to artificial lights in the evening during the hot and humid summer nights. Whenever they are crashed or smeared on the skin they release their toxin called Pederin from their haemolymph .
So far, various recommendation have been made to control paederus, but most of them were inefficient .
The aim of this study was to investigate the repellency effect of the neem oil (Azadirachta indica Juss), as a personal protection method against paederus beetles.
Neem oil was used in three different dosages (2.5 ,5 ,10 percent) on treated paper inside the ptri dishes. The results showed that protection percentage produced by Neem oil at 2.5 ,5 and 10 percent dose was 46.2 ,69.3 ,84.62 percente respectivly .
Volume 10, Issue 2 (4-2008)
Abstract
Fibers of poplar wood (Populus nigra L.) were prepared and oven dried. Afterwards, they were acetylated with acetic anhydride without a catalyst. Acetylation was carried out for different durations at 120ºC. Different weight percentage gains (WPGs) were achieved based on the operating conditions. Acetylated fibers were exposed to varying levels of relative humidity to determine equilibrium moisture contents (EMC). IR-spectra were also taken from the fibers to indicate substitution of the hydroxyl groups by the acetyl groups. Results showed that the acetylation decreased moisture absorption in the fibers. It was revealed that a WPG of about 10% had a proper moisture repellent effect on fibers. IR-spectra confirmed fully the substitution of the acetyl groups.
Volume 16, Issue 3 (10-2016)
Abstract
Spur dike is one of the river training structures that is considered to deviate the river from critical and erodible areas and the flow from the sides and towards the central axis. As a result of flow is developing a circular area with high turbulence around the spur dike. The hydraulic process results development of the scour hole on the upstream of the spur dike and settlement of sediment in the downstream and sides of the river. While scouring in spur dike structures results a serious threat to the river so it is needed to be researches in this field. This paper describes triplex repellent shielded spur dikes (directed to the upstream) with a distance of 3.5 times of the effective length of the spur dike in the outer bank of the channel. The first spur dike is located at 30 degree from the start of bend. The experimental channel is a 90º channel with rectangular section. The radius of curvature to the channel width is 2, which is classified as a sharp bend. Materials used are sands with uniform grains and its mean diameter is 1.28mm and its standard deviation coefficient is 1.3 and the relative density of sediment is 2.35. The results of flow field on flat bed and a scouring experiment are presented. Discharge was 25 l/s and All scour tests were done in 24 hours and in the moving threshold conditions (U/Uc =0.98) and clear water condition. Flow field is recorded using the Vectrino II velocimeter that can profile water in a 3cm column. It was found that in the levels upstream of the first spur dike in an adjacent to bed, stream lines are deviated to the inner bank. While in the middle levels, flow lines upstream of the spur dike is almost parallel to the channel walls and approached the spur dike, resulting deviation in the separation zone. In the scouring experiment it was obvious that at the beginning of the experiment, thus creating the down flow upstream of the spur dikes scouring initiates near the wing of each spur dike and it develops by the horse shoe vortex. But with the time sediment had been washed from upstream of the first spur dike, and moved to the foot of the spur dike until it reaches upstream of the former to the latter. Then scour hole upstream of the second spur dike starts to form. Results showed that the amount of scour upstream of second spur dike is 33 % and upstream of third spur dike is 81 % the maximum amount of scour that occurs upstream of the first spur dike. Mechanism causing scour and flows occurring within this range detailed in this paper.
