Browsing by Author "Cetin H."

Now showing 1 - 4 of 4
  • No Thumbnail Available
    Item
    Soil-particle and pore orientations during drained and undrained shear of a cohesive sandy silt-clay soil
    (2004) Cetin H.; Söylemez M.
    The orientations of particles, pores, and other constituents of an artificially made cohesive sandy silt-clay soil were studied to investigate how they change during drained and undrained shear. The results show that the orientation pattern before shearing is nearly random, although there may be some degree of preferred orientation caused by the overburden pressure. The degree of preferred orientation increases as the shearing increases until failure in both the drained and undrained tests and increases towards the failure plane. After failure, the degree of preferred orientation does not change considerably near the failure plane but does continue to increase away from it. The number of oriented particles, pores, and other constituents increases, but their averages stay about the same as the shearing continues after failure in the drained tests. The differences between the degrees of preferred orientations 5 and 10 mm away from the failure planes at different shear (horizontal) displacements are much less in the drained tests than in the undrained tests, indicating formation of a wider deformation zone in the drained tests. This is probably because particles in the drained tests have enough time to respond to the applied shear stresses and change their orientation. This may explain why deformations occur in wide zones along tectonically active creeping (aseismic) faults, whose mechanisms are analogous to those of drained shear tests, and in narrow zones along seismic faults, whose mechanisms are analogous to those of undrained shear tests. © 2004 NRC.
  • No Thumbnail Available
    Item
    Soil structure changes during compaction of a cohesive soil
    (2007) Cetin H.; Fener M.; Söylemez M.; Günaydin O.
    Orientations of particles, pores and other constituents during compaction of an artificially made clayey soil were studied in order to investigate how soil structure, and in turn, engineering parameters such as dry unit weight, porosity, void ratio and compaction characteristics, change during compaction of a cohesive soil at different moisture contents on both the dry and wet sides of the optimum moisture content. The results show that the orientation pattern at the very dry stage of the compaction curve is nearly random. The overall degree of preferred orientation increases as the moisture content increases until the optimum moisture content is reached. Edge-edge contacts between the particles and/or domains at the very dry stage of the compaction curve first become mainly edge-face and then become face-face contacts near the optimum moisture content. Around the optimum moisture content, the overall degree of preferred orientation becomes the highest. From this point on, however, the overall degree of preferred orientation starts to decrease again indicating that further moisture content increase does not cause additional overall preferred orientation. The structure beyond the optimum moisture content is mainly characterised by long strings of differently oriented packets in the form of curved trajectories and mainly face-to-face contacts between the particles and/or domains in the packets. Though there is a high degree of preferred fabric orientation in each individual packet, the overall degree of preferred orientation decreases because the packets are themselves oriented in different directions. The results agree with previous studies showing that the soil fabric dry of optimum is randomly oriented but becomes increasingly oriented towards the optimum. However, as the moisture content increases on the wet side of optimum, the overall degree of preferred orientation decreases as opposed to the generally accepted view. © 2007 Elsevier B.V. All rights reserved.
  • No Thumbnail Available
    Item
    Fumigant toxicity of Satureja cuneifolia and Ziziphora clinopodioides essential oils on field collected sand flies (Diptera: Psychodidae: Phlebotomie)
    (Parlar Scientific Publications, 2018) Cetin H.; Ser O.; Arserim S.K.; Polnt Y.; Ozbek T.; Civil M.; Cinbilgel I.; Ozbel Y.
    Sand flies (Diptera: Psychodidae: Phlebotominae) are the vectors of Leishmania species. Since the larval control of the sand flies is very difficult and almost impossible, the fighting has mainly been carried out for the adults. In this research the fumigant toxicity of two plant essential oils obtained from Satureja cuneifolia Ten. and Ziziphora clinopodioides Lam. was evaluated against fieldcollected adult Phlebotomus sand flies under laboratory conditions. The fumigant activity was tested by exposing the sand flies to essential oil vapors at 10, 20, 50 and 100 μL/L air concentrations. Knock time 50 (KT50) values and the 95% confidence limits were calculated by using a probit analysis program. A decrease in the KT50 value is observed in S. cuneifolia and Z. clinopodioides essential oils in a concentration dependent manner. KT50 values at the highest concentration (100 μL/L air) are 9,3 and 11,6 min, respectively. After a 1 h exposure period, both test oils produced 100% mortality at all the concentrations tested. The results of the research suggest that essential oils from these two plants have a potential as control agents for sand flies. © by PSP.
  • No Thumbnail Available
    Item
    The Toxicity of Essential Oils From Three Origanum Species Against Head Louse, Pediculus humanus capitis
    (Springer Science and Business Media Deutschland GmbH, 2021) Arserim S.K.; Cetin H.; Yildirim A.; Limoncu M.E.; Cinbilgel I.; Kaya T.; Ozbel Y.; Balcioglu I.C.
    Purpose: Pediculosis caused by human head louse, Pediculus humanus capitis De Geer (Anoplura: Pediculidae) is a public health problem with a high prevalence, especially among children in school age. Different chemical pediculicides (insecticides) are used against lice but the repeated application of these pediculicides for the treatment of P. humanus capitis infestation in the past decades has resulted in the development of resistance. The plant essential oils have been used as alternative sources of lice treatment agents. Pediculicidal activity of the essential oils of three Origanum species (O. onites, O. majorana and O. minutiflorum) against P. humanus capitis adults was examined in this study. Methods: Essential oils from aerial parts of three Origanum species were obtained by hydrodistillation using a Clevenger-type apparatus. P. humanus capitis specimens used were obtained from infested children by combing method at primary schools. Adult lice were exposed to three dilutions (1%, 0.5% and 0.1% w/v) of tested oils for 5 min using the adult immersion test. Results: According to the results, all Origanum essential oils at 1% concentration have been shown to significantly decrease the rate of limb, bowel and abdomen movements, producing more than 90% mortality after 12 h. Conclusion: Our results indicated that Origanum essential oils can be used for the development of new pediculicides against head louse. © 2021, Witold Stefański Institute of Parasitology, Polish Academy of Sciences.