共查询到20条相似文献，搜索用时 31 毫秒
1.
Large sharks (Carcharhinidae, Sphyrnidae), in their natural environment, were attracted to low-frequency (predominantly 20 to 60 cy/sec) pulsed sounds, but apparently not to higher frequency (400 to 600 cy/sec) pulsed sounds, or to low-frequency continuous sounds. The sharks apparently detected and oriented to the sounds in the acoustic far field. 相似文献
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针对LNG泄漏在地面上潜在危险的分析,需要对其在地面上扩散和蒸发速率的变化进行准确预测。基于液体扩散的动力学模型和热传递模型,采用微分方法建立了LNG在连续性泄漏情况下液池漫延半径、蒸发速率随时间变化的预测模型,克服了现有预测模型单纯依赖一维傅里叶导热方程的局限性。根据所建立的预测模型,LNG液池蒸发速率先随时间线性增加到最大值,随后随时间的延长而降低,即与时间的平方根成反比。以5m^3圆柱形LNG储罐为例,计算得到LNG泄漏的速率为19．92kg／s,泄漏完全所需时间为69S,液池半径达到最大的时间为33S,液池半径最大值为7m,0～33S时间内LNG蒸发速率先线性达到最大值19．92kg／s,34-69s时间内液池蒸发速率与时间平方根成反比,液池厚度由2．3mm逐渐增加到6mm。 相似文献
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J I Dalland 《Science (New York, N.Y.)》1965,150(700):1185-1186
Absolute hearing thresholds for two bats were determined by an operant conditioning technique. Pure tones rangingFrom 2.5 to 100 kilocycles per second were perceived by a single Eptesicus fuscus. Its maximum sensitivity was on the order of 68 decibles below 1 dyne per square centimeter and occurred at 20 kc/ sec. Maximum sensitivity for a single Myotis lucifugus was about 64 db below 1 dyne/ cm2 and occurred at 40 kc/ sec. The Myotis clearly heard a tone of120 kc/ sec but gave no evidence of hearing below 10 kc/ sec. 相似文献
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Ultrasonic vibrations can be perceived as audible sounds when a piezoelectric transducer is pressed against certain areas of the human body. In the range of frequencies investigated (20 to 108 kcy/sec), the threshold of perception seemed to lie near the threshold of feeling (about 10(-4) watt/cm(2)), and the perceived audible sound appeared to be between 8 and 9 kcy/sec, as judged by six test subjects. The threshold of perception and the perceived frequency appear to be dependent upon the hearing characteristics of the individual. 相似文献
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M. F. Gurbanov 《Russian Agricultural Sciences》2017,43(6):490-493
The drainage system designs and their function principles at the experimental production plot for the siphon- and vacuum-assisted drainage in the Mugan-Salyan massif characterized by the nongradient area have been described. The surveys are carried out in the natural environments during the vegetation period for the irrigation of cotton occupying the entire area of the experimental plot. A high efficiency of the siphonand vacuum-assisted drainage system has been calculated. In addition, the drain discharge and the discharge module are closely connected to the existing water pressure value in the interdrain. In the vegetation period, the maximum and minimum water discharges comprised 11.1 L/sec and 2.8 L/sec, respectively. The drainage module value varied from 0.14 to 0.55 L/sec hectare. It has been ascertained that the drainage system operation provides the opportunity to lower the depth of the groundwater table within the interdrain up to 250–280 cm (the initial depth is 120–150 cm). The possibilities of significant increases in the flushing intensity and the reduction of the terms of the regulated ameliorative activities within the certain hydrogeological regime have been proven. 相似文献
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寡核苷酸芯片检测兽医病原菌耐药性的研究 总被引：7，自引：0，他引：7
利用寡核苷酸芯片（oligonucleotide array）对兽医临床常见病原菌耐药性检测进行了初步研究。设计1对兼并引物扩增3种病原菌（E. coli、S. aureus、M. gallisepticum）的gyrA基因片段，并用cy5-dCTP标记荧光。设计一系列检测病原菌对氟喹诺酮类药物耐药的寡核苷酸探针，将探针固定在APS-PDC法制作的Microarray上，用标记的PCR产物与之杂交，置于Scanarrray4000中扫描，利用ImaGene3.0软件对杂交图像进行分析。研究结果表明，设计的兼并引物能很好地扩增出3种病原菌的gyrA基因片段，与Microarray杂交后在相应的位点出现可检测的杂交信号，样本O78S（禽大肠杆菌）、SS（金黄色葡萄球菌）、S6-10（鸡毒支原体）的ratio比值均≥2，说明这3株是敏感株；样本EDr（犬大肠杆菌）、ECr（猫大肠杆菌）与a1探针（检测GyrA第83位氨基酸发生突变的探针）的ratio比值≤0.5，说明这两株是耐药突变株，均与样本的实际情况相吻合。说明利用Oligonucleotide array能快速准确地检测出GyrA亚基第83、87位发生突变的耐药菌株，是可行、有效、快捷的抗菌药耐药性的监测方法。本研究为进一步研制和开发兽医临床常见病原菌耐药性检测芯片打下初步基础。 相似文献
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An x-ray survey of the Virgo region revealed signals from the directions of 3C 273 and M 87. Three other x-ray sources appear in the region scanned, but do not fit any known radio sources. The x-ray flux (1 to 10 angstroms) from the direction of 3C 273 is about 1000 times weaker than from the strongest x-ray source, Sco XR-1. If the source is located at the cosmological distance of 500 megaparsecs, the x-ray luminosity is 7.3 x 10(45) ergs per second. The x-ray luminosity of M87 is 1.5 x 10(43) ergs per second. 相似文献
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[目的]分析亚硝化单胞菌is79a3 Sec途径分泌装置及底物蛋白。[方法]从NCBI中选取亚硝化单胞菌is79a3菌株基因组注释的蛋白质氨基酸序列,采用Blast程序搜寻基因组中编码Sec途径分泌装置的蛋白,同时采用Signal P 4.0、Lipo P、TMHMM 2.0软件分析该菌株基因组中Sec途径的底物蛋白,同时采用COG功能数据库进行功能分析。[结果]通过分析发现亚硝化单胞菌is79a3菌株编码Sec途径分泌装置有关的蛋白15个,包含Sec途径分泌系统中12个转运蛋白编码基因,1个信号肽识别蛋白编码基因和2个信号肽酶蛋白编码基因;Sec途径底物蛋白分析结果显示366个含有Sec途径Spase I类肽酶识别的信号肽,36个蛋白只含有Spase II类肽酶识别的信号肽。402个Sec途径底物蛋白功能分析结果显示:有272个蛋白功能不清楚,130个蛋白有具体的功能注释。[结论]亚硝化单胞菌is79a3 Sec途径分泌装置完整,该菌株Sec途径底物蛋白大多数没有功能注释和功能未知,在有功能注释的蛋白中,主要参与细胞壁/细胞膜的生物合成、蛋白质翻译后修饰/蛋白更替、无机离子转运代谢、能源产生与转换。 相似文献
9.
9种药剂防治柑桔木虱成虫药效评价 总被引：2，自引：0，他引：2
为了筛选防治柑桔木虱成虫的有效药剂,试验采用一种新的方法,即将木虱饲养在九里香上,并用40目纱网套袋封口,然后进行9种农药防治柑桔木虱成虫药效试验。结果表明,48％毒死蜱EC480mg／L、10％吡虫啉WP100mg／L、25％吡虫啉WP250mg／L、20％甲氰菊酯EC200mg／L、20％哒虱威EC200mg／L、20％丁硫克百威EC 200mg／L、2．5％三氟氯氰菊酯EC25mg／L、药后24h对柑桔木虱成虫的防治效果达97．1％-100．0％,生产上可单独使用;而采用20％异丙威EC＋25％吡虫啉WP450mg／L药后24h对柑桔木虱成虫的防治效果比单独使用的效果好,防效达到100．0％,表明杀虫剂合理混用可提高对柑桔木虱成虫的防治效果。 相似文献
10.
A cell-cycle constraint on the regulation of gene expression by platelet-derived growth factor 总被引：7，自引：0，他引：7
In density-arrested monolayer cultures of Balb/c 3T3 cells, platelet-derived growth factor (PDGF) stimulates expression of the c-myc and c-fos proto-oncogenes, as well as the functionally uncharacterized genes, JE, KC, and JB. These genes are not coordinately regulated. Under ordinary conditions, c-fos, JE, KC, and JB respond to PDGF only when the cells are in a state of G0 growth arrest at the time of PDGF addition. The c-myc gene is regulated in opposition to the other genes, responding best to PDGF in cycling cultures. 相似文献
11.
Proton relaxation rates of water in brain and brain tumors 总被引：1，自引：0，他引：1
The distribution of relaxation rates of water in "normal" (autopsy) samples of canine and human brain shows considerable overlap with that for brain tumor samples. The following ranges of values for the spin-spin relaxation rates were observed: for normal brain gray matter, 8.6 to 11.3 sec(-1) (mean, 9.5 sec(-1)); for normal brain white matter, 13.3 to 15.7 sec(-1) (mean, 15.5 sec(-1)); for six types of malignant tumor, 4.8 to 13.4 sec(-1) (mean, 9.3 sec(-1)); for five types of benign tumor, 7.1 to 16.4 sec(-1) (mean, 11.5 sec(-1)). Spin-lattice relaxation rates showed a similar pattern. At least two nonexchanging water components with different relaxation rates were indicated by the analysis of the spin-spin relaxation measurements for the white matter samples. 相似文献
12.
The ultrasonic dosages given in W. J. Fry et al., "Ultrasonic lesions in the mammalian central nervous system" [Science 122, 517 (1955)] should be corrected as follows: For the lesion illusrated in Fig. 1, the dosage was 40 atm acoustic pressure amplitude and 3.9(10(2)) cm/sec acoustic particle velocity amplitude. For the lesions illustrated in Figs. 2 and 3, the dosage was 41 atm acoustic pressure amplitude and 4.0(10(2)) cm/sec acoustic particle velocity amplitude. 相似文献
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为评价莪术油/(麦芽糊精-Povacoat)微囊的质量,建立了硫酸香茅醛显色测定其载药量和包封率的方法。对莪术油乙醇溶液进行波长扫描,确定508nm为最大吸收波长,显色稳定性试验表明,反应液在150min内吸光度较稳定。莪术油检测浓度在0.199 2μg/mL~9.960μg/mL范围内线性关系良好(A=0.094 7C-0.001 2,r=0.999 3),微囊的载药量测定和包封率测定的方法回收率分别为99.6%和99.1%。经测定,3批微囊的载药量为51.5mg/g~53.2mg/g,包封率为88.2%~90.7%。 相似文献
17.
苦楝RAPD反应体系的优化 总被引：1，自引：0，他引：1
以苦楝叶片提取的基因组DNA为材料,通过单因素多水平梯度试验,筛选DNA模板,Mg^2＋,Taq DNA聚合酶,dNTPs和随机引物的浓度及用量,建立苦楝RAPD技术分析体系.结果表明：当基因组DNA浓度为60 ng/μL,镁离子浓度为3.0 mmol/L,dNTP浓度为0.25 mmol/L,引物浓度为0.30μmol/L,Taq DNA聚合酶用量为1 U/20μL,反应体系总体积20μL时,出现可辨认的清晰谱带.其扩增程序为：94℃预变性2 m in;然后38个循环（94℃变性30 s,37℃退火1 min,72℃延伸80 s）;最后72℃延伸8 min,4℃保存. 相似文献
18.
温尚昆 《山东农业大学学报(自然科学版)》2005,36(4):521-523
提取金黄色葡萄球菌px—1总DNA经酶切后,与载体质粒Puc18链接,并转化E.coli DH5α,从而构成金黄色葡萄球菌px—1的基因文库。用PCR方法扩增基因文库,所得PER产物点于芯片上,从而制各px—1DNA芯片。分别提取不同盐浓度培养的px—1的总RNA,把不同盐浓度培养的px—1的总RNA反转录为DNA,用Cy3,CY5分别标记反转录的DNA。通过杂交检测芯片,并获得杂交图像。 相似文献
19.
带式脱粒器的研究(初报) 总被引：1，自引：0，他引：1
蒋亦元 《东北农业大学学报》1981,(3)
带式脫粒器因喂入口较低有利于站杆脱粒穗幅差大的水稻,但它的带面振颤大影响脱粒器的工作平稳和使用寿命。为了探索解决这一问题提出了几种途径。研究表明,弓齿在纵向作更均匀的配置,对消除它在辊面转过时所产生的弦效应是减轻振颤、延长使用寿命的有效办法。研究中改进设计试验样机,把它的前进速度提高到1.2—1.38米/秒。结果表明,脱粒性能良好。在田间用电阻应度测量设备测定结果:带式脱粒器的单位喂入量(公斤/秒)的脱粒功率消耗明显低于传统的纹杆滚筒式和夹持半喂入式者。 相似文献
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纳米技术是在纳米尺度基础上研究物质的特性及相互作用,纳米为毫微米,既十亿分之一
米,利用纳米特性可解决实际生产中的多种问题。纳米技术在水产养殖工程中应用正处于初级阶段,
和发达国家还存在明显差异,故文章对纳米技术在水产养殖工程中的应用详细分析,旨在为实际水产
养殖开展提供理论参考。 相似文献