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Target site insensitivity because of mutations in the voltage‐sensitive sodium channel gene (Vssc) is a major mechanism of resistance to pyrethroid insecticides in the house fly, Musca domestica. There are three known Vssc alleles that confer resistance to pyrethroids in the house fly: knock down resistance (kdr; L1014F), super‐kdr (M918T + L1014F) and kdr‐his (L1014H), but there has been no side‐by‐side comparison of the resistance levels that they confer. We compared the levels of resistance conferred by the three Vssc alleles in congenic strains to 19 structurally diverse pyrethroids, and compared the full‐length Vssc cDNA sequences from each strain. Generally, the levels of resistance conferred were kdr‐his < kdr < super‐kdr. However, there was significant variation in this pattern, especially for super‐kdr, for which both high and low resistance ratios were observed for several pyrethroids. We also examined the levels of resistance in heterozygotes. Resistance in each of the hybrids was generally inherited as an incompletely recessive trait, except for the kdr‐his/kdr hybrids, which showed incompletely to completely dominant resistance (ie had resistance levels comparable to kdr homozygotes). The importance of these results to understanding the frequencies of these resistance alleles in natural populations, the evolution of insecticide resistance and resistance management strategies are discussed. 相似文献
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Albertine J. Oldehinkel 《Journal of child psychology and psychiatry, and allied disciplines》2017,58(8):863-864
Sex refers to biological differences and gender to socioculturally delineated masculine and feminine roles. Sex or gender are included as a covariate or effect modifier in the majority of child psychology and psychiatry studies, and differences found between boys and girls have inspired many researchers to postulate underlying mechanisms. Empirical tests of whether including these proposed explanatory variables actually reduces the variance explained by gender are lagging behind somewhat. That is a pity, because a lot can be gained from a greater focus on the active agents of specific gender differences. As opposed to biological sex as such, some of the processes explaining why a specific outcome shows gender differences may be changeable and so possible prevention targets. Moreover, while the sex binary may be reasonable adequate as a classification variable, the gender binary is far from perfect. Gender is a multidimensional, partly context-dependent factor, and the dichotomy generally used in research does not do justice to the diversity existing within boys and girls. 相似文献
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E.L. Powers 《International journal of radiation biology》2013,89(6):983-993
SummaryAs an extension of results obtained from radiation studies on caffeine both in other laboratories and more recently in this laboratory using the bacterial spore as the test system, six compounds with chemical structures closely resembling that of caffeine were tested as radiation modifiers. Of these compounds, purine, adenine and hypoxanthine resembled caffeine in sensitizing spores to radiation, while theobromine, xanthine and theophylline did not. These responses are discussed in relation to the electron sequestration hypothesis of cellular sensitization to high-energy radiation. 相似文献
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Alligator is a well-adapted living fossil covered with dorsal armor. This dermal shield consists of bony plates, called osteoderms, interconnected by sutures and non-mineralized collagen fibers, providing a dual function of protection and flexibility. Osteoderm features a sandwich structure, combining an inner porous core and an outer dense cortex, to offer enhancements for stiffness and energy absorbance. In this study, we investigated the multi-scale structure and mechanical behaviors of the American alligator (Alligator mississippiensis) osteoderm. Microcomputed tomography was applied to reveal the complex neurovascular network. Through the observation under optical and scanning electron microscopes, the osteoderm was found to consist of woven bone in the dorsal region and lamellar-zonal bone in the ventral region. Nanoindentation and compressive tests were performed to evaluate the mechanical properties of osteoderms. The varying mineral contents and porosity result in a graded mechanical property: a hard and stiff dorsal cortex gradually transform to a more compliant ventral base. Three protective mechanisms optimized for alligator osteoderms were proposed and elucidated. 相似文献
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目的 研究发现微塑料(粒径小于5 μm的塑料颗粒)在低等生物和哺乳动物中均可诱导生殖毒性和胚胎发育毒性。本文对微塑料在生殖和胚胎中的毒性效应和作用机制进行综述,可为预防和控制微塑料所致生殖毒性提供理论基础和科学依据。方法 以微塑料、暴露途径、毒性机制、生殖毒性、胚胎毒性为关键词在中国知网、PubMed 等数据库检索相关文献,并对国内外相关文献进行归纳与总结。结果 综述微塑料暴露途径及其转运和代谢分布、全面系统地概述微塑料生殖和胚胎发育毒性效应及毒性机制。结论 研究发现微塑料在低等生物和哺乳动物中均可诱导生殖毒性和胚胎发育毒性,但微塑料所致生殖毒性主要局限在表型研究,目前仍缺乏针对微塑料生殖毒性作用机制的系统研究,同时需在人群层面进一步研究。 相似文献
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The effect of denture installation at mandibular rest position on unsteady motion of the centre of pressure in postural sway
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Wearing dentures has been believed to decrease the instability of the postural sway using the total length of centre of pressure (CoP) trajectory or the magnitude of its variability. However, the physical aspects of the postural sway have not been taken into account while evaluating the CoP in patients who wear dentures. The CoP fluctuations are found to show a random walk process. Therefore, changes in the random movement of CoP caused by wearing dentures should be examined by nonlinear dynamics that enables analysis of the characteristics found in the random movement. We evaluated the effect of complete denture installation on CoP sway for twenty‐six edentulous patients by performing the following steps. First, we excluded subjects who did not show crossover in spectral analyses. Then, we evaluated the spectral characteristics and phase shifts of the velocities of CoP sway for the subjects who showed crossover. We found that wearing complete dentures decreased the fluctuations in the high‐frequency part of the power spectral density (PSD) and the phase shift in the mediolateral direction. On the other hand, we also found that the use of complete dentures decreased the fluctuations of PSD amplitude in the anteroposterior direction. From the point of view of the kinetic energy of the musculoskeletal system, we suggested that the use of complete dentures could reduce the energy consumption for the standing posture. 相似文献