共查询到20条相似文献，搜索用时 140 毫秒
1.
Muijres FT Johansson LC Barfield R Wolf M Spedding GR Hedenström A 《Science (New York, N.Y.)》2008,319(5867):1250-1253
Staying aloft when hovering and flying slowly is demanding. According to quasi-steady-state aerodynamic theory, slow-flying vertebrates should not be able to generate enough lift to remain aloft. Therefore, unsteady aerodynamic mechanisms to enhance lift production have been proposed. Using digital particle image velocimetry, we showed that a small nectar-feeding bat is able to increase lift by as much as 40% using attached leading-edge vortices (LEVs) during slow forward flight, resulting in a maximum lift coefficient of 4.8. The airflow passing over the LEV reattaches behind the LEV smoothly to the wing, despite the exceptionally large local angles of attack and wing camber. Our results show that the use of unsteady aerodynamic mechanisms in flapping flight is not limited to insects but is also used by larger and heavier animals. 相似文献
2.
The aerodynamics of free-flight maneuvers in Drosophila 总被引：2，自引：0，他引：2
Using three-dimensional infrared high-speed video, we captured the wing and body kinematics of free-flying fruit flies as they performed rapid flight maneuvers. We then "replayed" the wing kinematics on a dynamically scaled robotic model to measure the aerodynamic forces produced by the wings. The results show that a fly generates rapid turns with surprisingly subtle modifications in wing motion, which nonetheless generate sufficient torque for the fly to rotate its body through each turn. The magnitude and time course of the torque and body motion during rapid turns indicate that inertia, not friction, dominates the flight dynamics of insects. 相似文献
3.
Studies of insect flight have revealed novel mechanisms of production of aerodynamic lift. In the present study, large lift forces were measured during flight episodes elicited from dragonflies tethered to a force balance. Simultaneously, stroboscopic photographs provided stop-action views of wing motion and the flowfield structure surrounding the insect. Wing kinematics were correlated with both instantaneous lift generation and vortex-dominated flow fields. The large lift forces appear to be produced by unsteady flow-wing interactions. This successful utilization of unsteady separated flows by insects may signal the existence of a whole new class of fluid dynamic uses that remain to be explored. 相似文献
4.
Bennett L 《Science (New York, N.Y.)》1970,167(3915):177-179
Large changes in lift output result when a simulated insect wing, undergoing a downstroke, is subjected to a dynamic change of incidence. Given a large positive rate of change of incidence, transient lift values several times those realized in steady-state operation at the same angle of incidence are obtained. Thus a means exists by which insects achieve several times the lift expected by conventional quasi-steady considerations. 相似文献
5.
Hedenström A Johansson LC Wolf M von Busse R Winter Y Spedding GR 《Science (New York, N.Y.)》2007,316(5826):894-897
The flapping flight of animals generates an aerodynamic footprint as a time-varying vortex wake in which the rate of momentum change represents the aerodynamic force. We showed that the wakes of a small bat species differ from those of birds in some important respects. In our bats, each wing generated its own vortex loop. Also, at moderate and high flight speeds, the circulation on the outer (hand) wing and the arm wing differed in sign during the upstroke, resulting in negative lift on the hand wing and positive lift on the arm wing. Our interpretations of the unsteady aerodynamic performance and function of membranous-winged, flapping flight should change modeling strategies for the study of equivalent natural and engineered flying devices. 相似文献
6.
为了研究岐江河水生昆虫群落分布特征与水环境因子的相关性,在2009年6～7月和9～10月分季在岐江河上分设4个采样点,对水生昆虫和水质采样检测。结果共检测到水生昆虫750头,分属11科9属14种。简单相关分析与复相关分析都表明,氮浓度、磷浓度、生化需氧量与水生昆虫密度呈极显著正相关(P0.01),与水生昆虫的种数呈极显著负相关(P0.01)。水生昆虫组主要目为蜉蝣目和襀翅目,环境因子组主要因子为氮浓度、磷浓度、生化需氧量。由此得出,即使在低污染、低营养程度的水环境下,水生昆虫与环境因子也表现出群体的显著相关性,环境因子对EPT昆虫有重要影响。 相似文献
7.
中国水产品区域供求平衡能力预测 总被引：2，自引：0，他引：2
本文利用1990-2005年全国和各省、市、自治区水产品产量和消费量数据,运用聚类分析方法将全国划分为7个区,其中东部沿海区和长江流域区是我国水产品的主产区,两区域水产品产量之和占全国水产品总产量的90%左右;之后进一步分析了各区域水产品产量和消费量在过去十几年间的变化趋势,7个区域产量和消费量变化具有相似性,各区域产量和消费量占全国比例趋于稳定;最后使用时间序列分析方法预测了全国和各区域在2010年和2020年的水产品产量和消费量,2010年、2020年全国水产品预测产量分别为5900.44万t和7192.37万t. 相似文献
8.
为优化浮性水产饲料挤压膨化加工参数,以膨化度、容积密度、吸水性和溶失率作为饲料加工品质评价指标,采用响应面分析法研究了螺杆转速、出料段机筒温度和物料含水率对饲料加工品质的影响,并利用扫面电镜观测了饲料微观形貌。结果表明：适中的螺杆转速、出料段机筒温度以及低物料含水率,有利于形成较高的饲料膨化度;高螺杆转速与高出料段机筒温度有利于形成较低的饲料容积密度、吸水性以及溶失率;优化后的浮性水产饲料膨化加工参数为螺杆转速130 r·min-1,出料段机筒温度150 ℃,物料含水率10%,其加工后的饲料膨化度、容积密度、吸水性和溶失率分别为1.223、0.398 g·mL-1、214.803%、4.297%;优化后的浮性水产饲料微观表面相对光滑圆润,物料的熔融效果较好,结构质密,饲料膨化加工综合质量较好。 相似文献
9.
为优化浮性水产饲料挤压膨化加工参数,以膨化度、容积密度、吸水性和溶失率作为饲料加工品质评价指标,采用响应面分析法研究了螺杆转速、出料段机筒温度和物料含水率对饲料加工品质的影响,并利用扫面电镜观测了饲料微观形貌。结果表明：适中的螺杆转速、出料段机筒温度以及低物料含水率,有利于形成较高的饲料膨化度;高螺杆转速与高出料段机筒温度有利于形成较低的饲料容积密度、吸水性以及溶失率;优化后的浮性水产饲料膨化加工参数为螺杆转速130 r·min-1,出料段机筒温度150 ℃,物料含水率10%,其加工后的饲料膨化度、容积密度、吸水性和溶失率分别为1.223、0.398 g·mL-1、214.803%、4.297%;优化后的浮性水产饲料微观表面相对光滑圆润,物料的熔融效果较好,结构质密,饲料膨化加工综合质量较好。 相似文献
10.
Thermoregulation in endothermic insects 总被引：2，自引：0，他引：2
B Heinrich 《Science (New York, N.Y.)》1974,185(153):747-756
On the basis of body weight, most flying insects have higher rates of metabolism, and hence heat production, than other animals. However, rapid rates of cooling because of small body size in most cases precludes appreciable endothermy. The body temperature of small flies in flight is probably close to ambient temperature, and that of flying butterflies and locusts is 5 degrees to 10 degrees C above ambient temperature. Many moths and bumblebees are insulated with scales and hair, and their metabolism during flight can cause the temperature of the flight muscles to increase 20 degrees to 30 degrees C above ambient temperature. Curiously, those insects which (because of size, insulation) retain the most heat in the thorax during flight, also require the highest muscle temperature in order to maintain sufficient power output to continue flight. The minimum muscle temperature for flight varies widely between different species, while the maximum temperature varies over the relatively narrow range of 40 degrees to 45 degrees C. As a consequence, those insects that necessarily generate high muscle temperatures during flight must maintain their thoracic temperature within a relatively narrow range during flight. Active heat loss from the thorax to the abdomen prevents overheating of the flight motor and allows some large moths to be active over a wide range of ambient temperatures. Bumblebees similarly transfer heat from the flight musculature into the abdomen while incubating their brood by abdominal contact. Many of the larger insects would remain grounded if they did not actively increase the temperature of their flight muscles prior to flight. Male tettigoniid grasshoppers elevate their thoracic temperature prior to singing. In addition, some of the social Hymenoptera activate the "flight" muscles specifically to produce heat not only prior to flight but also during nest temperature regulation. During this "shivering" the "flight" muscles are often activated in patterns different from those during flight. The muscles contract primarily against each other rather than on the wings. However, the rate of heat production during shivering and flight is primarily a function of the action potential frequency rather than of the patterns of activation. Thermoregulation is a key factor in the energetics of foraging of some of the flower-visiting insects. The higher their muscle temperature the more flowers they can visit per unit time. When food supplies are ample, bees may invest relatively large amounts of energy for thermoregulation. While shivering to maintain high body temperatures during the short intervals they are perched on flowers (as well as while in the nest), bumblebees often expend energy at rates similar to the rates of energy expenditure in flight. Unlike vertebrates, which usually regulate their body temperature at specific set points, the body temperature of insects is labile. It often appears to be maintained near the lower temperature at which the muscles are able to perform the function at hand. The insects' thermal adaptations may not differ as much from those of vertebrates as previously supposed when size, anatomy, and energy requirements are taken into account. 相似文献
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12.
Implantable electrode assemblies that become penetrated by regenerating axons were used to record signals from single sensory and motor nerve fibers associated with leg movement in unrestrained amphibians (Xenopus laevis). Such neuroimplants may provide a means for establishing the roles of various muscle afferents and efferents in posture and locomotion, and have potential clinical applications. 相似文献
13.
Clarke JA Ksepka DT Salas-Gismondi R Altamirano AJ Shawkey MD D'Alba L Vinther J DeVries TJ Baby P 《Science (New York, N.Y.)》2010,330(6006):954-957
Penguin feathers are highly modified in form and function, but there have been no fossils to inform their evolution. A giant penguin with feathers was recovered from the late Eocene (~36 million years ago) of Peru. The fossil reveals that key feathering features, including undifferentiated primary wing feathers and broad body contour feather shafts, evolved early in the penguin lineage. Analyses of fossilized color-imparting melanosomes reveal that their dimensions were similar to those of non-penguin avian taxa and that the feathering may have been predominantly gray and reddish-brown. In contrast, the dark black-brown color of extant penguin feathers is generated by large, ellipsoidal melanosomes previously unknown for birds. The nanostructure of penguin feathers was thus modified after earlier macrostructural modifications of feather shape linked to aquatic flight. 相似文献
14.
Cuticular protein gene LmACP8 is involved in wing morphogenesis in the migratory locust,Locusta migratoria 
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下载免费PDF全文 Cuticular proteins(CPs) are major components of the insect cuticle-associated organs such as integument and wings, although the importance of CPs for wing development and function in hemimetabolous insects remains understudied. In the present study, a wing cuticular protein LmACP8 was identified from Locusta migratoria, which belongs to the RR-2 subfamily of cuticular protein RR consensus(CPR) chitin-binding proteins. LmACP8 was mainly expressed in the wing pads and showed high expression levels before ecdysis of third-, fourth-, and fifth-instar nymphs, with its encoded protein located in the procuticle of wing pads and adult wings. Depletion of LmACP8 by RNA interference markedly reduced the amount of its protein, which consequently caused abnormal wing morphogenesis in the transition from nymph to adult of L. migratoria. We further demonstrated that the abnormal morphogenesis was caused by severe damage of the endocuticle in the wings. LmACP8 was suppressed by 20-hydroxyecdysone(20 E) in vivo, however, its expression was significantly up-regulated after knocking down the hormone receptor gene LmHR39. Thus, the LmACP8 that is negatively regulated by the LmHR39-mediated 20 E signaling pathway is involved in wing development during the nymph to adult transition. 相似文献
15.
Goodyear CP 《Science (New York, N.Y.)》1970,168(3931):603-605
Starhead topminnows from various shores of a small woodland pond were displaced to unfamiliar surroundings, and their orientation was tested in aquatic and terrestrial arenas. These fish used a sun compass to move in a direction which, at the location of their capture, would have returned them to the land-water interface. The fish accomplished directional terrestrial locomotion by using the position of the sun to align its body for each jump. On heavily overcast days many fish were unable to orient their bodies in a consistent direction from, jump to jump; this inability to orient resulted in random rather than linear movement. There was considerable individual variation in terrestrial locomotor ability. 相似文献
16.
Adult body size and fecundity of a number of hemimetabolous aquatic insects depend largely on thermal conditions during the larval period. Small adults and reduced fecundity result when temperatures are either warmed or cooled with respect to more optimal thermal conditions. Temperature apparently affects adult size by altering the larval growth rate and the timing and rate of adult tissue development for each larva. The data suggest a new interpretation for the geographic distribution of aquatic insects. 相似文献
17.
At low temperatures, the reduction in mechanical power output of the aerobic muscle forces cold-blooded animals, such as carp, to recruit their rapidly fatiguing anaerobic fibers at relatively slow swimming speeds. Previous experimental data have suggested that changes in the biochemistry and morphology of the aerobic muscle during cold acclimation might increase its output of mechanical power. The present experiments show that, because of these changes, carp can swim faster at low temperature using only their aerobic muscle, which results in an increase in their sustainable swimming speed. By modifying their musculature, cold-blooded animals can achieve some independence from the effects of seasonal changes in environmental temperature. 相似文献
18.
果实蝇属昆虫危害水果和蔬菜,造成产量下降,影响对外贸易,对其识别是检疫工作中的重要部分,现有的人工辨识方法受时间、知识等因素影响不能准确、有效辨识。提出了一种基于BP神经网络模型的果实蝇分类方法,采用几何形态测量学中的标记点法对果蝇翅进行特征提取,通过方差分析确定了用于果蝇鉴定的11个主特征,建立3层BP神经网络模型,结合Levenberg-Marquardt BP训练函数对数据集进行训练,得到完整的可用于果实蝇分类的BP神经网络。实验表明,该方法能够对实蝇进行有效的辨识,对桔小实蝇、瓜实蝇、具条实蝇和南亚果实蝇等高风险果实蝇辨识的准确率分别是90.0%、93.3%、90.0%和96.7%,总体准确率为92.5%,具有良好的应用前景。 相似文献
19.
为优化设计森林防火小型无人机的机身,降低机身质量,减少空气阻力,以双尾撑固定翼无人机为基础,利用SolidWorks建立机身模型进行结构设计,并利用ANSYS-FLUENT对机身进行数值模拟。采用ANSYS ICEM CFD 网格生成器生成PRISM网格结构进行网格划分,对机身进行气动分析。通过FLUENT仿真对设计进行改进,分析改进前后的流体场、阻力和质量差异。结果表明:可以采用ANSYS-FLUENT软件对森林防火小型无人机机身进行气动外形优化。机身的气动外形优化对减少阻力有明显的影响,改进后机身所受空气阻力减少了45.9%,机身质量减轻了27.8%。 相似文献
20.
Denny M 《Science (New York, N.Y.)》1980,208(4449):1288-1290
The power of locomotion of a terrestrial slug rises linearly with crawling speed. The metabolic cost of movement is 904 joules per kilogram per meter, considerably more than that reported for other forms of locomotion. This high cost is primarily attributable to the production of the pedal mucus by which the slug adheres to the substratum. 相似文献