Molecular biogeography of planktonic and benthic diatoms in the Yangtze River

Background: Diatoms are of great significance to primary productivity in oceans, yet little is known about their biogeographic distribution in oligotrophic rivers. Results: With the help of metabarcoding analysis of 279 samples from the Yangtze River, we provided the first integral biogeographic pattern of planktonic and benthic diatoms over a 6030 km continuum along the world's third largest river. Our study revealed spatial dissimilarity of diatoms under varying landforms, including plateau, mountain, foothill, basin, foothill-mountain, and plain regions, from the river source to the estuary. Environmental drivers of diatom communities were interpreted in terms of photosynthetically active radiation, temperature, channel slope and nutrients, and human interference. Typical benthic diatoms, such as Pinnularia, Paralia, and Aulacoseira, experienced considerable reduction in relative abundance downstream of the Three Gorges Dam and the Xiluodu Dam, two of the world's largest dams. Conclusions: Our study revealed that benthic diatoms are of particular significance in characterizing motile guild in riverine environments, which provides insights into diatom biogeography and biogeochemical cycles in large river ecosystems

Sustainable Construction and Design 2011 NOVEL CYLINDER POSITIONING SYSTEM REALISED BY USING SOLENOID VALVES

Abstract This paper presents a novel control design, developed to realise fast and accurate position control of a pneumatic actuator using inexpensive on/off solenoid valves. In contrast to conventional control methods, the proposed control method operates chatter free, based on air compression. The control principle was developed by investigating the dynamics of a pneumatic actuator with an identified mathematical model. This new approach is applied to a pneumatic double acting cylinder, controlled by a pair of 5/3 way directional single solenoid valves. The described closed-loop circuit copes with the discontinuities associated with the valve's switching dynamics, and relatively long response time. The experimental apparatus uses an analogue displacement encoder for metering the piston's position and velocity, and doesn't incorporate pressure sensors thus ensuring a low cost system design. The results of experiments with various step responses show that the proposed control method performs well. The measured steady-state position errors are equal to the used potentiometer's travel resolution, which is 0,01 mm. Therefore this novel control and the related pneumatic system design could be a cost effective alternative to the servo-pneumatic positioning systems. Keywords: Position Control, Solenoid Valve, Pneumatic Cylinder, Control Method, Actuator INTRODUCTION In order to achieve linear motion, pneumatic, electromagnetic and hydraulic actuators are typically used. Due to their advantageous characteristics in position control applications the latter two are more widespread. Though using hydraulic actuators high velocity and great force is achievable, and their position control can also be relatively easily solved, a handicap is that the leaking of hydraulic fluids might contaminate the workpiece. Electromagnetic actuators on the other hand are clean and reliable in their operation but often require a mechanical transmission, both to convert high speed and low torque to a more useful combination and to convert rotary motion to linear motion. While linear motors overcome the need for transmission, they can be expensive Pneumatic actuators have several advantages: they are fast, cheap, have an outstanding power-to-weight ratio, are easily maintainable and they don't contaminate the work piece. The challenge to the use of pneumatic drives is that due to piston friction and the characteristics of compressed gas flow their behaviour is non-linear. As a result their industrial use is only widespread in applications which require linear motions between end positions. In the last decade such industrial controllers became available which have adequate computing capacity for real-time usage. Thus there is now opportunity to develop pneumatic systems which don't require costly proportional valves for positioning and hence the usage of the more cost-efficient solenoid valves became possible A review of the papers on the topic is given i

Species-specific markers provide molecular genetic evidence for natural introgression of bullhead catfishes in Hungary

Since three bullhead catfish species were introduced to Europe in the late 19th century, they have spread to most European countries. In Hungary, the brown bullhead (Ameiurus nebulosus) was more widespread in the 1970s–1980s, but the black bullhead (Ameiurus melas) has gradually supplanted since their second introduction in 1980. The introgressive hybridization of the two species has been presumed based on morphological examinations, but it has not previously been supported by genetic evidence. In this study, 11 different Hungarian habitats were screened with a new species-specific nuclear genetic, duplex PCR based, marker system to distinguish the introduced catfish species, Ameiurus nebulosus, Ameiurus melas, and Ameiurus natalis, as well as the hybrids of the first two. More than 460 specimens were analyzed using the above markers and additional mitochondrial sequence analyses were also conducted on >25% of the individuals from each habitat sampled. The results showed that only 7.9% of the specimens from two habitats belonged to Ameiurus nebulosus, and 92.1% were classified as Ameiurus melas of all habitats, whereas the presence of Ameiurus natalis was not detected. Two specimens (>0.4%) showed the presence of both nuclear genomes and they were identified as hybrids of Ameiurus melas and Ameiurus nebulosus. An additional two individuals showed contradicting results from the nuclear and mitochondrial assays as a sign of a possible footprint of introgressive hybridization that might have happened two or more generations before. Surprisingly, the level of hybridization was much smaller than expected based on the analyses of the North American continent’s indigenous stock from the hybrid zones. This phenomenon has been observed in several invasive fish species and it is regarded as an added level of complexity in the management of their rapid adaptation