Results 1 - 10 of 43747
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[en] Polygonum perfoliatum L. is a Mn-tolerant plant as considered having the potential to revegetate in manganese mine wasteland. The glasshouse experiments were carried out to evaluate its tolerance and physiological response in different Mn concentrations (5, 500, 1000, 2000, 5000, and 10,000 μmol L−1). Absorption bands of P. perfoliatum differed greatly in lipids, proteins, and carbohydrates. With elevated levels of Mn (5–2000 μmol L−1), absorbance changed little, which demonstrated that lower Mn concentrations had negligible influence on transport functions. As Mn concentrations in excess of 2000 μmol L−1, absorbance increased slightly but eventually decreased. Furthermore, a hydroponic culture was carried out in order to study its changes of ultrastructure with the increasing Mn concentrations (5, 1000, and 10,000 μmol L−1). Lower Mn levels with 5 and 1000 μmol L−1 had no breakage function to the ultrastructure of P. perfoliatum. However, as Mn concentration was up to 10,000 μmol L−1, visible damages began to appear, the quantity of mitochondria in root cells increased, and the granum lamellae of leaf cell chloroplasts presented a disordered state. In comparison with the controls, black agglomerations were found in the cells of P. perfoliatum under the controlling concentration of Mn with 1000 and 10,000 μmol L−1 for 30 days, which became obvious at higher Mn concentrations. As Mn concentration was 10,000 μmol L−1, a kind of new acicular substance was developed in leaf cells and intercellular spaces, possibly indicating a resistance mechanism in P. perfoliatum. These results confirm that P. perfoliatum shows potential for the revegetation of abandoned manganese tailings.
[en] This paper studies linear Fresnel mirrors (LFMs) with flat facets. A model and a program for calculating the parameters and concentration of LFMs with flat facets have been developed. It is shown that LFMs can provide in increased concentration by up to 30 times at a number of facets of about 50 while ensuring the high uniformity of the concentrated radiation at the receiver. (author)
[en] A novel experimental technique was used to quantify the motion of E. coli to varying serine concentrations and gradients so as to capture the spatial and temporal variation of the chemotactic response. The average run speed and the cell diffusivity are found to be dependent on the serine concentration. The measured diffusivities were in the range of 1.2–2.5 × 10 −10 m2 s−1. The study revealed that the rotational diffusivity of the cells, induced by the extracellular environment, also varies with the serine concentration. The drift velocity increased with serine gradients reaching a maximum value of ∼5.5 µm s−1 at 1.6 µM µm−1 after which it decreased. Experimental analysis demonstrated the interdependence of run speed, rotational diffusivity and drift velocity that characterizes the motion. Further, the motion was found to critically depend on the oxygen concentration and energy level of the cells
[en] In this work, the performances of two optimized reflective secondary optics elements a CPC (Compound Parabolic Concentrator) and a Cone for use in a CPV concentrator system are studied using ray-tracing simulation for the same primary optical element: a Fresnel lens. These optical elements are compared in terms of concentration, acceptance angle, exit angle and output light distribution. Our results show that the power distribution at the end of the concentrator is more uniform in the case of the cone. The optical efficiency is higher when the secondary element is placed at a distance with f the focal length; R the input radius of the secondary optical element and θ the acceptance angle of the secondary optical element. Also, we found that the length and the input radius of each optical element decrease when the Fresnel lens diameter increases but the input radius of the CPC stills the larger. Finally, our calculation show that the CPC is longer than the cone while the Fresnel lens diameter is less than 200 mm and beyond this value both the cone and the CPC mostly present the same length. (paper)
[en] The description of the plasma torches for the analyzer of the atomic composition of liquid, solid and gaseous substances is given. The filamentary RF discharge, which is created in the torches with the aid of two continuous RF generators with a frequency of 13.56 MHz and a power of up to 350 W, is atomizer. The results of the measurements of the concentrations of harmful atomic admixtures in the water at the level of the maximum permissible concentrations (MPC) according to the sanitary standards are given. The possibility is shown of designing the universal analyzer of the composition of substances, in which on one platform the torches for liquids, gases and solids are combined
[en] The present study discusses a prime cause of fluctuating protein concentrations, which play a significant role in generating phenotypic diversity in bacteria. A genetic circuit integrated in a bacterial genome was used to evaluate the cell-to-cell variation in protein concentration. A simple dynamic model, comprising terms for synthesis and dilution, was used to elucidate the contributions of distinct noises to the fluctuation in cell protein concentration. Experimental and theoretical results demonstrated that noise in the rate of increase in cell volume (cell growth rate) serves as a source of extrinsic noise that accounts for dozens of percent of the total noise, whereas intrinsic noise in protein synthesis makes only a moderate contribution to the fluctuation in protein concentration. This suggests that such external noise in the cell growth rate has a global effect on cellular components, resulting in a large fluctuation in protein concentration in bacterial cells
[en] Highlights: • Development of an analytical model for assessing the well-mixing length of a tracer in a duct airflow. • Validation on data from in situ experiments. • Model simplification for proposing correlations more suitable for the industrial issue. - Abstract: The aim of this study is to propose an analytical model for assessing the well-mixing length of a tracer in a ventilation duct. The first part of the article is devoted to describe an experimental bench developed for validating the proposed model. This bench allows to follow the evolution of a tracer injected at a source point in the center of a duct by using an original optical measurement technique. In a second part, an analytical model for the spatial evolution of a tracer concentration in a circular duct is developed, taking into account an eddy viscosity model. The difficulty for applying this model to industrial cases led us to propose a simplified version that can be used for a non-dimensional distance greater than 20 diameters. The latter was then inverted in order to access to two criteria: the coefficient of variation in the duct section and the difference between the local measured concentration and the expected homogeneous concentration. Each one has its interest depending on whether a global information on the duct section or a local information (on the axis for example) at a given distance is required.
[en] We have analyzed the transport regimes and the asymptotic forms of the impurity concentration in a randomly inhomogeneous fractal medium in the case when an impurity source is surrounded by a weakly permeable degrading barrier. The systematization of transport regimes depends on the relation between the time t0 of emergence of impurity from the barrier and time t* corresponding to the beginning of degradation. For t0 < t*, degradation processes are immaterial. In the opposite situation, when t0 > t*, the results on time intervals t < t* can be formally reduced to the problem with a stationary barrier. The characteristics of regimes with t* < t < t0 depend on the scenario of barrier degradation. For an exponentially fast scenario, the interval t* < t < t0 is very narrow, and the transport regime occurring over time intervals t < t* passes almost jumpwise to the regime of the problem without a barrier. In the slow power-law scenario, the transport over long time interval t* < t < t0 occurs in a new regime, which is faster as compared to the problem with a stationary barrier, but slower than in the problem without a barrier. The asymptotic form of the concentration at large distances from the source over time intervals t < t0 has two steps, while for t > t0, it has only one step. The more remote step for t < t0 and the single step for t > t0 coincide with the asymptotic form in the problem without a barrier.
[en] Using the closed-can technique, radon exhalation rate, radon concentration and effective radium content have been carried out for soil samples collected from triple-junction of the North Anatolian Fault System and East Anatolian Fault System. The measured maximum values of the exhalation rate and radon concentration in the system were 400.7 (mBqm-2 h-1) and 8.10 Bqkg-1, respectively. However, effective radium concentration in soil samples has been found to vary from 0.02 to 0.80 Bqkg-1. Linear correlation was observed between soil-gas radon concentration, effective radium content and radon exhalation rate. The linear correlation coefficient between radium content and radon concentration was found to be 0.91. Nevertheless, it was found that there is a linear correlation (R2=0.99) between the radon concentration and exhalation rate
[en] The aim of this study was to survey the radon concentrations at 21 elementary schools in Gyeongju, Republic of Korea, to identify those schools with high radon concentrations. Considering their geological characteristics and the preliminary survey results, three schools were finally placed under close scrutiny. For these three schools, continuous measurements over 48 h were taken at the principal's and administration office. The radon concentrations at one school, Naenam, exceeded the action level (148 Bq/m3) established by the U.S. EPA, while those at the other two schools were below that level. - Highlights: • Preliminary measurements of the indoor radon concentrations were performed at the auditoriums in 23 elementary schools in Gyeongju. • Considering the geological characteristics and preliminary survey results, three elementary schools were screened for closer scrutiny. • For the three schools, continuous measurements were made at their principal's and administration offices over 48-h period. • The scrutiny revealed one elementary school of high radon concentration much higher than the U.S. EPA action level