Nanoassembly of a fractal polymer: a molecular "Sierpinski hexagonal gasket"

Mathematics and art converge in the fractal forms that also abound in nature. We used molecular self-assembly to create a synthetic, nanometer-scale, Sierpinski hexagonal gasket. This nondendritic, perfectly self-similar fractal macromolecule is composed of bis-terpyridine building blocks that are bound together by coordination to 36 Ru and 6 Fe ions to form a nearly planar array of increasingly larger hexagons around a hollow center.     

Old faithful: a physical model

The recent confirmation of a prediction that relates the duration of eruption to time between eruptions suggests a physical model of the internal cavity of Old Faithful.     

Discussion: moving food regimes forward: reflections on symposium essays

All authors in this symposium use a food regime perspective to ask questions about the present which—as these articles demonstrate—have several possible answers. History suggests a time perspective of 25–40 year cycles so far—a food regime 1870–1914, an experimental and chaotic era 1914–1947, and a food regime 1947–1973. It has been less than 40 years since 1973, when food regime analysts agree that a contested and experimental period began. There is no consensus on whether it has already ended or how it might issue into a new food regime. The conversation is more fruitful than the conclusions. I intend these comments as an invitation to join in.     

外浮顶油罐密封装置问题探讨

针对外浮顶油罐密封装置在生产运行中出现的密封不严或密封压缩过紧的现象进行了现场调查,分析了产生这一问题的原因,提出油罐基础沉降,罐壁的垂直度和椭圆度超差等是造成密封不严或密封压缩过紧的主要原因,提出了施工控制方法,特别是要加强油罐壁板预制质量控制,提高底圈壁板的安装质量,对第二圈以上壁板垂直度逐圈控制,把总体垂直度的控制误差分解到各圈壁板中,建议在大型储罐施工中,除提高技术水平外,还应加强人员质量     

Homeokinetics: a physical science for complex systems

A physical basis for reductionism is put forth in the form of five propositions that bridge levels of organization in natural phenomena. The outlook is that complex systems and processes all have to be traced back to physical law, which applies the only general scientific constraint on reality, but that out of physical law a hierarchy of organization emerges. The basic extension of normal physics in this homeokinetic field form is to complex systems. In such systems the repetitive units of concern are internally complex and exhibit elaborate internal time-delayed processes, for example, memory.     

Centimetre-precision guidance of moving implements in the open field: a simulation based on GPS measurements

High quality and sustainable agricultural production in the open field will be supported by centimetre-precision guidance of agricultural implements. In this paper, a complete guidance system is proposed and simulated using real sensor data obtained from a real time kinematic (RTK) differential global positioning system (DGPS). This type of the satellite navigation system became available commercially in 1997 and is claimed to reach cm accuracy. It uses real time kinematics to improve the accuracy of a position fix by phase comparison of the carrier signal. The simulation primarily aims to investigate the accuracy of the guidance system that can be obtained with RTK DGPS. Using real DGPS measurement errors the simulated system showed a tracking error less than 0.005 m when the PID-controller had settled.     

Earthquakes in the los angeles metropolitan region: a possible fractal distribution of rupture size

Although there is debate on the maximum size of earthquake that is possible on any of several known fault systems in the greater Los Angeles metropolitan region, it is reasonable to assume that the distribution of earthquakes will follow a fractal distribution of rupture areas. For this assumption and an overall slip-rate for the region of approximately 1 centimeter per year, roughly one magnitude 7.4 to 7.5 event is expected to occur every 245 to 325 years. A model in which the earthquake distribution is fractal predicts that, additionally, there should be approximately six events in the range of magnitude 6.6 in this same span of time, a higher rate than has occurred in the historic record.     

农田汇水河道水生植物原位净化工程处理效果分析

为了研究水生植物原位净化工程处理效果,于2017年5—11月,在江苏省泗洪县四河乡的农田汇水河道,利用水葫芦和绿狐尾藻构建组合生态浮床,沿着水流方向设置4个水质采样点,每月监测水体基本理化指标,主要包括水温(T)、酸碱度(pH)、溶解氧(DO)、总氮(TN)、总磷(TP)、化学需氧量(COD_(Cr))、悬浮物(SS),分析河段水质沿程变化;在试验开始时、每次采收时监测单位面积植物生物量,干物质含量与氮磷含量,计算植物氮磷富集量。结果显示:植物种养后,沿程各采样点数据对比,水体pH值逐渐趋于中性;各采样时间数据对比,水体DO浓度呈升高趋势。在植物旺盛生长期(7—10月),组合生态浮床对河段水体TN、TP、COD和SS的沿程总消减率分别为50.41%～78.00%、44.62%～73.33%、46.15%～57.82%和33.33%～52.38%,其中最高值出现在8月。按照有效试验周期180 d(5—10月)计算,水葫芦的氮、磷去除量分别约为0.76 g·m~(-2)·d~(-1)和0.09 g·m~(-2)·d~(-1);绿狐尾藻的氮、磷去除量分别约为1.17 g·m~(-2)·d~(-1)和0.08 g·m~(-2)·d~(-1)。除了植物自身的吸收作用,根系微生物降解作用在污染物净化过程中也发挥了重要作用。在农田汇水河道原位净化工程中,水葫芦与绿狐尾藻组合生态浮床大幅消减水体氮磷浓度,有效降解有机物及拦截颗粒物,对于缓解下游水域富营养化问题具有积极的意义。     

Milk-like fluid in a mammary adenocarcinoma: biochemical characterization

The milk-like accumulation in the R3230AC mammary adenocarcinoma that follows treatment with estrogen contains lactose, fatty acids, and proteins with electrophoretic properties similar to those of casein and whey of rat milk. This mammary tumor retains the biochemical capacity of the mammary gland in its lactational response to administration of hormone.     

Human synovial fluid: detection of a new component

A new component has been detected in synovial fluid by the agar double-diffusion technique. This component is closely related immunologically to the proteinpolysaccharides of cartilage, and is the first probable degradation product of the cartilage matrix to be consistently identified in human synovial fluid.     

Hooked trichomes: a physical plant barrier to a major agricultural pest

Hooked epidermal appendages (trichomes) on leaves of field bean cultivars effectively capture nymph and adult leafhoppers. Frequency of capture and capture mortality are highly correlated with trichome density. Hooked trichomes inserted at angles less than 30 degrees are ineffective in capture.     

Petroleum: tar quantities floating in the northwestern atlantic taken with a new quantitative neuston net

The neuston net has been modified to obtain quantitative samples of surface zooplankton. Petroleum lumps are commonly taken with these nets, and quantities of tar up to almost 0.1 gram (wet weight) per cubic meter of filtered surface water have been taken in the northwestern Atlantic. This information is used to estimate the quantity of tar lumps present in the North Atlantic and to indicate the probable limits of the degree of existing oil pollution in this region. It is suggested that previous estimates of ocean oil pollution may be too low.     

Nitrogen fixation by floating diatom mats: a source of new nitrogen to oligotrophic ocean waters

Nitrogen fixation, apparently by bacterial endosymbionts, is associated with intertwining chains of two species of the diatom Rhizosolenia. In situ fixation rates were enhanced by incubation in the dark, whereas concurrent shipboard experiments either underestimated or did not detect nitrogen fixation. This is the first example of nitrogen fixation associated with a bacteria-diatom symbiosis in the pelagic zone, and it indicates that these systems may contribute a significant amount of "new" nitrogen to oligotrophic waters.     

组合型生态浮床系统脱氮效果的周年变化

构建集挺水植物、沉水植物和微生物于一体的组合型生态浮床系统,并对其技术工艺周年运行效果进行探究。分析了组合型生态浮床对水中氨氮(NH_4~+-N)与总氮(TN)的去除动力学,不同介质对水体净化的贡献率及削减模型。实验结果表明,组合型生态浮床脱氮效果明显,其中浮床上层贡献率15.6%±1.2%,中层37.6%±2.2%,下层23.8%±1.8%,说明浮床系统中层介质对氨氮与总氮的降解能力占主导地位。实验组NH_4~+-N最高去除率为93.0%±3.4%,TN最高去除率达94.2%±0.9%,而上中下层兼具有的池5去除效果最显著(P0.10)。由各实验组消解NH_4~+-N和TN的去除动力学曲线得出其削减模型及不同程度的衰减指数曲线。初步探索了组合型生态浮床脱氮效果的周年变化,为其进一步推广应用提供了技术支撑。     

Density gradients in a rotating stratified fluid: experimental evidence for a new instability

Velocity gradients induced in a rapidly rotaiting, density-stratified saltwater solution by a slowly rotating disk produce sharp vertical gradients of density, which appear as regularly spaced, curved horizontal sheets when the ratio of angular velocities exceeds a critical value. The existence of the sheets is apparently a finite amplitude manifestationl of a recently proposed viscous instability.