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81.
G Bachour K Failing S Georgii I Elmadfa H Brunn 《Canadian Metallurgical Quarterly》1998,35(4):666-673
According to previous experimental results, PCBs are deposited in muscle fat in animals and in humans, although they also reach the brain, the liver, and the lungs. The aim of the present study was to determine the concentrations of the so-called "indicator PCBs" (PCB nos. 28, 52, 101, 138, 153, 180), as described by the German ordinance for maximum concentrations of contaminants in foodstuffs, in muscle tissue, liver, and brain of four different species: fish, fox, roe deer, and humans, all exposed to PCBs directly in their environment. Potential target organs for the accumulation of these congeners were also to be identified. Furthermore, the organs or tissues were to be identified in which PCBs are accumulated, and unusual patterns of accumulation or breakdown of particular PCBs, for example the "dioxin-like PCBs" (coplanar PCBs) determined. For humans, the lungs were also included in these studies. Statistical comparison of PCB concentrations in samples from wild animals and humans showed that in spite of its relatively high fat concentration, brain tissue in all of the species examined (with the exception of fish) appeared to be better protected against accumulation of PCB than liver or muscle tissue. This protection may be the result of the blood-brain barrier, as witnessed by the relatively uniform concentration of PCBs throughout the various organs of fish, since the blood-brain barrier of fish is considerably less efficient than that of mammals. No peculiarities were found in regard to distribution of the coplanar PCBs over the other congeners in this study. This applies to the brain and other organs or tissues of the four species that were examined. Accumulations of PCBs and coplanar PCBs in the liver were only found in fox and roe deer. In contrast, humans were found to have accumulations of the high-chlorinated biphenyls studied here as well as PCB no. 118 in muscle tissue fat and not in the liver. Unexpectedly, low-chlorinated biphenyls were found to accumulate in the human lung. The results of this study show that the lung represents a target organ for the accumulation of potentially metabolically activated low-chlorinated biphenyls, indicating that the possible biological effects of PCBs on the lungs will need to receive more attention in the future. 相似文献
82.
Cherepanov V Zubkov E Junker H Korte S Blab M Coenen P Voigtländer B 《The Review of scientific instruments》2012,83(3):033707
We present a multitip scanning tunneling microscope (STM) where four independent STM units are integrated on a diameter of 50 mm. The coarse positioning of the tips is done under the control of an optical microscope or scanning electron microscopy in vacuum. The heart of this STM is a new type of piezoelectric coarse approach called KoalaDrive. The compactness of the KoalaDrive allows building a four-tip STM as small as a single-tip STM with a drift of less than 0.2 nm/min at room temperature and lowest resonance frequencies of 2.5 kHz (xy) and 5.5 kHz (z). We present as examples of the performance of the multitip STM four point measurements of silicide nanowires and graphene. 相似文献
83.
Bi Zhang Jun‐Wei Wang Lu‐Yuan Hao Xin Xu Simeon Agathopoulos Liang‐Jun Yin Cheng‐Ming Wang Hubertus T. Hintzen 《Journal of the American Ceramic Society》2017,100(1):257-264
One of the biggest problems in white light‐emitting diodes (WLEDs) is the moisture‐induced degradation of phosphors. This paper proposes a simple and feasible surface modification method to solve it, whereby a hydrophobic surface layer is developed on the surface of the phosphors. The particular case of orange‐red‐emitting Sr2Si5N8:Eu2+ (SSN) phosphor was investigated. The mechanism to develop the hydrophobic layer involves hydrolysis and polymerization of tetraethylorthosilicate (TEOS) and polydimethylsiloxane (PDMS). The experimental results showed that the surface layer of SSN phosphor was successfully modified to a hydrophobic nanolayer (8 nm) of amorphous silicon dioxide that contains CH3 groups in the surface. This hydrophobic surface layer gives the modified phosphor superior stability in high‐pressure water steam conditions at 150°C. 相似文献
84.
Synthesis,Crystal Structure,and Luminescence Properties of Y4Si2O7N2: Eu2+ Oxynitride Phosphors 下载免费PDF全文
Guozhang Chen Liang‐Jun Yin Jun‐Tao Dong Yan‐Yu Feng Yang Gao Weidong He Yu Jia Xin Xu Hubertus T. Hintzen 《Journal of the American Ceramic Society》2016,99(1):183-190
Y4Si2O7N2: Eu2+ phosphor has been prepared by a pretreatment method. Reduction in Eu3+ ions into Eu2+ by the use of hydrogen iodide (HI) is verified by X‐ray absorption near‐edge structure (XANES) and electrode potential analysis. Y4Si2O7N2: Eu2+ phosphor has a broad emission band in the range of 400–500 nm. Furthermore, the effect of Zr doping on the structure and luminescence properties of Y4Si2O7N2: Eu2+ phosphor is researched. It found that the Zr doping leads to an emission blueshift, and improves the luminescence intensity and thermal quenching behavior of Y4Si2O7N2: Eu2+ phosphors. Prospectively, the pretreatment approach could be extended to develop other Eu2+‐doped compounds. 相似文献
85.
Performance of non-porous graphite and titanium-based anodes in microbial fuel cells 总被引:1,自引:0,他引:1
Annemiek ter Heijne Hubertus V.M. Hamelers Michel Saakes Cees J.N. Buisman 《Electrochimica acta》2008,53(18):5697-5703
Four non-porous materials were compared for their suitability as bio-anode in microbial fuel cells (MFCs). These materials were flat graphite, roughened graphite, Pt-coated titanium, and uncoated titanium. The materials were placed in four identical MFCs, of which the anode compartments were hydraulically connected in series, as well as the cathode compartments. The MFCs were operated with four resistors. The anode kinetics at these electrode materials were studied by means of dc-voltammetry and electrochemical impedance spectroscopy (EIS). Both techniques were compared and showed that the bio-anode performance decreased in the order roughened graphite > Pt-coated titanium > flat graphite > uncoated titanium. Uncoated titanium was unsuitable as anode material. For the other three materials, specific surface area was not the single variable explaining the differences in current density for the different materials. All polarization curves showed a clear limiting current. This limit could not be attributed to mass transfer of the substrate and reflected the maximum biomass activity. The current density of the non-porous bio-anodes, except for the uncoated titanium anode, was comparable to the reported current densities of porous materials when normalized to the projected surface area. The high current densities that were recorded by dc-voltammetry, however, could not be maintained in a stable way for a longer period. This shows that polarization curves of MFCs should be evaluated critically. 相似文献
86.
Low pH buffer capacity of waste streams limits further development of bioelectrochemical systems (BES) because accumulation of protons potentially leads to acidification of the anodic biofilm. Here we introduce a system that makes it possible to recover alkalinity in an extra recovery compartment. The system consisted of this extra compartment which was located between anode and cathode compartment. The compartment was separated from the anode by a cation exchange membrane and from the cathode by an anion exchange membrane, which made clean hydrogen production possible. To compensate for the charge movement as a result of the flow of electrons, both cations and hydroxyl ions moved into the new recovery compartment. When a synthetic waste stream was fed through this recovery compartment, both pH and conductivity increased. When this stream is then fed to the anode of the BES, no additional buffer was required to produce the same current (3.5 A/m(2)) at an applied voltage of 1 V. 相似文献
87.
Phailaung Phohomsiri Firdaus E. Udwadia Hubertus F. von Bremen 《Canadian Metallurgical Quarterly》2006,132(6):690-703
In this paper we present and propose a design methodology that uses intentional time delays for the active control of structures. We use here positive velocity-feedback, time-delayed control and show that its performance is, in general, superior to the previously developed methodology of using time delayed, negative velocity-feedback control. A detailed study carried out in this paper of the nonsystem poles and their interaction with the system poles reveals the reasons for this. Analytical results related to performance and stability of the new method are presented. We apply the time delayed positive velocity feedback active control methodology to a multidegree-of-freedom system subjected to the S00E component of ground acceleration recorded during the El Centro 1940 earthquake. The excellent behavior in terms of stability, performance, and control efficiency that is demonstrated by our time-delayed control design as well as its facile implementation makes it attractive for earthquake hazard mitigation in a practical sense. 相似文献
88.
Using RDF to describe networks 总被引:1,自引:0,他引:1
Jeroen J. Freek Franco Hubertus M.A. Cees T.A.M. 《Future Generation Computer Systems》2006,22(8):862-867
89.
Tom H.J.A. Sleutels Hubertus V.M. Hamelers René A. Rozendal Cees J.N. Buisman 《International Journal of Hydrogen Energy》2009,34(9):3612-3620
Previous studies have shown that Microbial Electrolysis Cells (MECs) perform better when an anion exchange membrane (AEM) than when a cation exchange membrane (CEM) separates the electrode chambers. Here, we have further studied this phenomenon by comparing two analysis methods for bio-electrochemical systems, based on potential losses and partial system resistances. Our study reconfirmed the large difference in performance between the AEM configuration (2.1 m3 H2 m?3 d?1) and CEM configuration (0.4 m3 H2 m?3 d?1) at 1 V. This better performance was caused mainly by the much lower internal resistance of the AEM configuration (192 mΩ m2) compared to the CEM configuration (435 mΩ m2). This lower internal resistance could be attributed to the lower transport resistance of ions through the AEM compared to the CEM caused by the properties of both membranes. By analyzing the changes in resistances the limitations in an MEC can be identified which can lead to improved cell design and higher hydrogen production rates. 相似文献
90.
Tom H.J.A. Sleutels Rob Lodder Hubertus V.M. Hamelers Cees J.N. Buisman 《International Journal of Hydrogen Energy》2009
To create an efficient MEC high current densities and high coulombic efficiencies are required. The aim of this study was to increase current densities and coulombic efficiencies by influencing mass and charge transport in porous electrodes by: (i) introduction of a forced flow through the anode to see the effect of enhanced mass transport of substrate, buffer and protons inside the porous anode and (ii) the use of different concentrations of buffer solution to study the effect of enhanced proton transport near the biofilm. A combination of both strategies led to a high current density of 16.4 A m−2 and a hydrogen production rate of 5.6 m3 m−3 d−1 at an applied voltage of 1 V. This current density is 228% higher than the current density without forced flow and high buffer concentration. Furthermore the combination of the anode and transport resistance was reduced from 36 mΩm2 to 20 mΩm2. Because of this reduced resistance the coulombic efficiency reached values of over 60% in this continuous system. 相似文献