The ability of both living and dry cells of Gloeothece magna, a non-toxic freshwater cyanobacterium, to adsorb cadmium and manganese is demonstrated in this study. Chlorophyll a content of living cells was not influenced by either cadmium or manganese concentrations, indicating that adsorption of both Cd2+ and Mn2+ by living cells of G. magna, was independent of the metabolic state of the organism. Moreover, the adsorption of both Cd2+ and Mn2+ to living cells and dry cells, was dependent on the metal concentrations, and fitted the Freundlich adsorption isotherm. However, dry cells had larger binding capacity for both Cd2+ (Kf=912.6) and Mn2+ (Kf=2398) than living cells (Kf=151.4 & 63, respectively). The role of the capsular polysaccharides, the main constituents of the cyanobacterial envelope, in binding these two metals was also studied. Polysaccharide extracts of this organism adsorbed high amounts of both Cd2+ (115–425 μg mg−1) and Mn2+ (473–906 μg mg−1). This study suggests that G. magna would probably be cultured in water bodies contaminated by heavy metals to ameliorate their toxicity. Also dry material of this cyanobacterium being a non-toxic species, could be used as a safe biofilter to remove toxic metals from drinking water. 相似文献
The synthesis of several S- and N-substituted derivatives of 5-[(5,6-diphenyl-1,2,4-triazin-3-yl)oxymethyl]-s-triazole-3-thiol, 2-[(5,6-diphenyl-1,2,4-triazin-3-yl)-oxymethyl]-5,6-dihydrothiazolo-[3,2-b]-s-briazole, 2-[(5,6-diphenyl-1, 2,4-triazin-3-yl)oxymethyl]-5H,6,7-dihydro-s-triazolo-[3,2-b]-1,3-thiazine, 2-[(5,6-diphenyl-1,2,4-triazin-3-yl)oxymethyl]-5,6-dihydrothiazolo-[3,2-b]-s-triazol-5-one and 2-[(5,6-diphenyl-1,2,4-triazin-3-yl)oxymethyl]-6-phenylthiazolo-[3,2-b]-s-triazole is reported. All the novel compounds have been screened for antimicrobial activity and one of them showed noteworthy activity. 相似文献
Gases may induce extensive and irreversible damage in elastomers when they are allowed to escape from the polymeric matrix. The damage is most evident as internal lacerations and also as an overall change in certain mechanical properties. The damage process, commonly termed explosive decompression failure, is really confined to gas-polymer systems which are initially equilibrated at high pneumatic stresses; greater than 107 Pa. Two interrelated facets of this phenomenon are described in the context of elastomeric composites with particular emphasis on the role of interfacial quality. The results of an optical examination of the internal cracks found during a typical gas-induced rupture cycle are described. The system is a commercial silicone elastomer-glass filler composite where the fillers have been surface modified in order to alter the adhesive strength of the interface. The data indicate that the filler particles significantly modify the stress fields in the elastomer during gas-induced rupture. Essentially, the fillers suppress the development of the characteristic large scale axially symmetrical stress fields in the composites. This visual assessment of the damage is then related to the deterioration in certain mechanical properties of this current system. 相似文献
To guarantee an industry standard of reliability in ICs, manufacturers incorporate special testing techniques into the circuit manufacturing process. For most electronic devices, the specific reliability required is quite high, often producing a lifespan of several years. Testing such devices for reliability under normal operating conditions would require a very long period of time to gather the data necessary for modeling the device's failure characteristics. Under this scenario, a device might become obsolete by the time the manufacturer could guarantee its reliability. High-voltage stress testing (HVST) is common in IC manufacturing, but publications comparing it with other test and burn-in methods are scarce. This article shows that the use of HVST can dramatically reduce the amount of required burn-in. 相似文献
This paper presents Gene-Expression Programming (GEP), which is an extension to the genetic programming (GP) approach to predict the total bed material load for three Malaysian rivers. The GEP is employed without any restriction to an extensive database compiled from measurements in the Muda, Langat, and Kurau rivers. The GEP approach demonstrated a superior performance compared to other traditional sediment load methods. The coefficient of determination, R2 (= 0.97) and the mean square error, MSE (= 0.057) of the GEP method are higher than those of the traditional method. The performance of the GEP method demonstrates its predictive capability and the possibility of the generalization of the model to nonlinear problems for river engineering applications. 相似文献
This paper reports the result of sewage pollution monitoring conducted in South and Southeast Asia during 1998-2003 using linear alkylbenzenes (LABs) as molecular tracers of sewage contamination. Eighty-nine water samples collected from Malaysia, Vietnam, and Japan (Tokyo), and 161 surface sediment samples collected from Tokyo, Thailand, Malaysia, Philippines, Vietnam, Cambodia, Indonesia, and India were analyzed for alkylbenzenes. The concentration range of SigmaLABs in river water particles in Southeast Asia (<0.005-0.913 microg/L) was comparable to or higher than those found in Tokyo (<0.005-0.638 microg/L). I/E ratios (a ratio of internal to external isomers of LABs) in tropical Asian waters were close to the value of LABs in raw sewage ( approximately 1) and much lower than those in secondary effluents (3-5). This suggests that untreated or inadequately treated sewage is discharged into the water. SigmaLABs concentrations in sediments from South and Southeast Asia ranged from <0.002-42.6 microg/g-dry with the highest concentration occurring at several populous cities. Low I/E ratios of the sediments with high SigmaLABs concentrations suggest a heavy load of untreated sewage. Clearly in view of the current data and evidence of the implications of sewage pollution, this paper highlights the necessity of the continuation of water treatment system improvement in tropical Asia. 相似文献
Insertion sites for cysteines with optimal stereochemistry forthe formation of unstrained disulfide bridges were identifiedin recombinant human interferon- (rhu-IFN-) by computer modelling.We have engineered two different disulfide cross-linked mutants,containing a pair of symmetry-related disulfide bonds, whichstabilize the N-termini of both monomers of the homodimenc protein.Mutations E7C and S69C allow the formation of an intramonomerdisuffide bond between helices A and D. In contrast, the A17Cand H111C mutations lead to a covalent cross-link between bothmonomers. The AB-loop is linked to helix F. The fluorescenceproperties of native and disulfide cross-linked proteins werestudied as a function of guanidine hydrochloride concentration.Melting temperatures (Tm) were calculated from the decreasein CD ellipticity at 220 nm. The induction of the antiviraleffect was measured using A549 fibroblast cells infected withencephalomyocarditis virus. The ability to induce the expressionof the HLA-DR antigen in Colo 205 cells was determined by fluorescence-activatedcell scanning analysis. The stability of both mutants was stronglyenhanced against temperature- and cosolvent-induced unfolding.The Tm of mutant IFN- E7C/S69C was 15°C. All measured biologicalactivities of this mutant were equal to wild type. In the caseof the other mutant IFN- A17C/H111C, the Tm value was 25°C.This mutation abolishes nearly the entire biological activity(<1%) with no detectable changes of secondary structure inthe CD spectrum. Our results illustrate the importance of theN-terminal helix A and the AB-loop for the unfolding pathwayand thermodynamic stability of rhu-IFN-. 相似文献
Summary: Polymer‐layered silicate nanocomposites (PLSN), based on polyamide 6 (PA6) and montmorillonite (MMT) modified with an octadecylammonium salt, were produced via melt compounding in a co‐rotating twin‐screw extruder. Wide angle X‐ray diffraction (WAXD) and TEM revealed a PLSN containing 3.3% by weight (wt.‐%) of MMT to exhibit a mixed exfoliated/intercalated morphology, consisting mainly of individual silicate lamellae together with some intercalated stacks, resulting in a mean value of 1.8 lamellae per particle. In contrast, a PLSN containing a higher level of 7.2 wt.‐% MMT exhibited a more ordered intercalated structure, consisting mainly of a distribution of lamellae stacks with a mean value of 3.8 lamellae per particle. The dispersion of MMT in the PLSN generated very large polymer–filler interfacial areas, resulting in significant increase in the volume of constrained PA6 chain segments. Consequently, significant changes in the ratio of α/γ crystallites and in the thermal behaviour of the matrix PA6 were observed during WAXD, DSC and dynamic‐mechanical thermal analysis (DMTA) studies of the PLSN. In particular, damping data from DMTA showed relaxations between Tg and Tm resulting from amorphous polymer chain segments constrained at the polymer–filler interface, indicating the formation of a continuous phase of constrained polymer. In contrast, a PA6 microcomposite formed using unmodified MMT generated much lower polymer–filler interfacial area, with most of the MMT residing within large, poorly wetted aggregates. Consequently, changes to the thermal behaviour of the matrix PA6 were much less significant than those induced in the PLSN.
This paper deals with the redox properties of Cu ions implanted in ZSM-5 and supported on Al2O3, catalysts active in the selective reduction of NO by hydrocarbons such as propane. Data on the reducibility of the Cu systems in various atmospheres (vacuum, CO, H2, O2) and on their DeNOx activity are presented. The methods used to obtain informations on the surface and bulk transformations (and their link with catalytic behaviour) are complementary: UV–visible diffuse reflectance spectroscopy being useful to detect the presence of Cu2+ and Cu0, while Cu+ is detected indirectly by the analysis of the IR spectrum of CO bound selectively to this cation.
The main contributions to the previous knowledge are the following: it is possible to distinguish CO bound to isolated and non-isolated Cu+ ions; the isolated Cu2+ ions are reducible under vacuum without participation of organic impurities; the more active solids for the NO reduction into N2 are characterized by the presence of isolated Cun+ ions beside the additional influence of the zeolitic framework; after the formation of Cu+ ions the redox cycles are reversible but, after the formation of Cu0, the reversibility or irreversibility of the redox cycles and the restoration of the SCR activity are function of the copper content; the activity decreases after agglomeration into bulk oxides; there is no formation of bulk CuO during the reaction and, with reducing and moderate oxidizing mixtures, part of the copper remains as cuprous ions. 相似文献