共查询到20条相似文献，搜索用时 15 毫秒
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An investigation has been made of the development of the solarized latent image with p-amino-phenol, pyrogallol and hydroquinone developer without potassium bromide, and with a series of hydroquinone developers containing potassium bromide from 0.002N to 0.269N solution. These developers represent a series with different reduction potentials. The investigation was restricted to a pure silver bromide emulsion.It was shown by the application of the Bravais-Pearson method of determination of the correlation coefficient that A. H. Nietz' straight line proportionality between density and the logarithm of the potassium bromide concentration holds in general for normal exposures, but that in extreme cases of exposure and development, deviations from the straight line proportionality are detectable. This proportionality holds only in a limited way for the solarization region. At the threshold of the first reversal of the solarization there is no correlation at all.The criterion that a family of curves has, or has not, a tie-point was investigated by the determination of the correlation coefficient between density and gamma. It was shown that the tie-point of the solarization curves moves toward the origin of the distance/log E axes with increasing content of potassium bromide in the developer. 相似文献
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Xuan Zhao Yu Wang Yunli Da Xinxia Wang Tingting Wang Mingquan Xu Xiaoyun He Wu Zhou Yafei Li Jonathan N Coleman Yanguang Li 《国家科学评论(英文版)》2020,7(8):1360
The two-electron reduction of molecular oxygen represents an effective strategy to enable the green, mild and on-demand synthesis of hydrogen peroxide. Its practical viability, however, hinges on the development of advanced electrocatalysts, preferably composed of non-precious elements, to selectively expedite this reaction, particularly in acidic medium. Our study here introduces 2H-MoTe2 for the first time as the efficient non-precious-metal-based electrocatalyst for the electrochemical production of hydrogen peroxide in acids. We show that exfoliated 2H-MoTe2 nanoflakes have high activity (onset overpotential ∼140 mV and large mass activity of 27 A g−1 at 0.4 V versus reversible hydrogen electrode), great selectivity (H2O2 percentage up to 93%) and decent stability in 0.5 M H2SO4. Theoretical simulations evidence that the high activity and selectivity of 2H-MoTe2 arise from the proper binding energies of HOO* and O* at its zigzag edges that jointly favor the two-electron reduction instead of the four-electron reduction of molecular oxygen. 相似文献
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William J. Hooper 《Journal of The Franklin Institute》1926,201(3):311-331
The experiments of several previous investigators were repeated in substance with apparatus designed to make it possible to distinguish between ionization and certain spurious factors which have made questionable much of the existing evidence relating to ionization by positive-ion impact. A great many current-potential measurements and curves were obtained at different gas pressures and with a variety of electrical arrangements. The data and curves thus obtained present direct evidence (a) that the previously so-called “ionization current” is due to a secondary electron emission from the platinum walls of the ionization chamber, (b) that this secondary electron emission is produced by the impact of the positive ions with these metal walls, (c) that either there is no ionization in hydrogen gas by the impact of the positive ions accelerated by potential differences up to 925 volts, or that if this phenomenon exists, as is indicated by visual and spectroscopic evidence, its effects are so small at relatively low pressures (.012 mm.) that it is completely masked by secondary phenomena which make its detection by the ordinary direct methods problematic, and (d) that it seems possible that at relatively high gas pressures (considerably above .012 mm.), ionization by positive ions might be an important factor with accelerating potential differences between the ends of their M.F.P. well within this same range of voltages. 相似文献
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BackgroundThe development of a potential single culture that can co-produce hydrogen and ethanol is beneficial for industrial application. Strain improvement via molecular approach was proposed on hydrogen and ethanol co-producing bacterium, Escherichia coli SS1. Thus, the effect of additional copy of native hydrogenase gene hybC on hydrogen and ethanol co-production by E. coli SS1 was investigated.ResultsBoth E. coli SS1 and the recombinant hybC were subjected to fermentation using 10 g/L of glycerol at initial pH 7.5. Recombinant hybC had about 2-fold higher cell growth, 5.2-fold higher glycerol consumption rate and 3-fold higher ethanol productivity in comparison to wild-type SS1. Nevertheless, wild-type SS1 reported hydrogen yield of 0.57 mol/mol glycerol and ethanol yield of 0.88 mol/mol glycerol, which were 4- and 1.4-fold higher in comparison to recombinant hybC. Glucose fermentation was also conducted for comparison study. The performance of wild-type SS1 and recombinant hybC showed relatively similar results during glucose fermentation. Additional copy of hybC gene could manipulate the glycerol metabolic pathway of E. coli SS1 under slightly alkaline condition.ConclusionsHybC could improve glycerol consumption rate and ethanol productivity of E. coli despite lower hydrogen and ethanol yields. Higher glycerol consumption rate of recombinant hybC could be an advantage for bioconversion of glycerol into biofuels. This study could serve as a useful guidance for dissecting the role of hydrogenase in glycerol metabolism and future development of effective strain for biofuels production. 相似文献
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《Electronic Journal of Biotechnology》2014,17(3):122-125
BackgroundA biosurfactant produced by Pseudomonas aeruginosa cultivated in a low-cost medium formulated with 2.5% vegetable oil refinery residue and 2.5% corn steep liquor and distilled water was employed to stabilize silver nanoparticles in the liquid phase. The particles were initially synthesized using NaBH4 as reducing agent in biosurfactant reverse micelles and were extracted from the micellar solution to disperse in heptane.ResultsA silver particle size in the range of 1.13 nm was observed. The UV–vis absorption spectra proposed that silver nanoparticles could be formed in the reverse micelles and relatively stabilized for at least 3 months without passivator addition. The Transmission Electron Microscope (TEM) shows that the silver nanoparticles are of spherical form and relatively uniform.ConclusionsThis process provided a simpler route for nanoparticle synthesis compared to existing systems using whole organisms or partially purified biological extracts, showing that the low-cost biosurfactant can be used for nanoparticle synthesis as a non-toxic and biodegradable stabilizing agent. 相似文献
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BackgroundAn effective single culture with high glycerol consumption and hydrogen and ethanol coproduction yield is still in demand. A locally isolated glycerol-consuming Escherichia coli SS1 was found to produce lower hydrogen levels under optimized ethanol production conditions. Molecular approach was proposed to improve the hydrogen yield of E. coli SS1 while maintaining the ethanol yield, particularly in acidic conditions. Therefore, the effect of an additional copy of the native hydrogenase gene hycE and recombinant clostridial hydrogenase gene hydA on hydrogen production by E. coli SS1 at low pH was investigated.ResultsRecombinant E. coli with an additional copy of hycE or clostridial hydA was used for fermentation using 10 g/L (108.7 mmol/L) of glycerol with an initial pH of 5.8. The recombinant E. coli with hycE and recombinant E. coli with hydA showed 41% and 20% higher hydrogen yield than wild-type SS1 (0.46 ± 0.01 mol/mol glycerol), respectively. The ethanol yield of recombinant E. coli with hycE (0.50 ± 0.02 mol/mol glycerol) was approximately 30% lower than that of wild-type SS1, whereas the ethanol yield of recombinant E. coli with hydA (0.68 ± 0.09 mol/mol glycerol) was comparable to that of wild-type SS1.ConclusionsInsertion of either hycE or hydA can improve the hydrogen yield with an initial pH of 5.8. The recombinant E. coli with hydA could retain ethanol yield despite high hydrogen production, suggesting that clostridial hydA has an advantage over the hycE gene in hydrogen and ethanol coproduction under acidic conditions. This study could serve as a useful guidance for the future development of an effective strain coproducing hydrogen and ethanol. 相似文献
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BackgroundHelicobacter pylori is considered as the main risk factor in the development of gastric cancer. In the present study, we performed a detailed characterization of the probiotic properties and the anti-H. pylori activity of a previously isolated lactobacillus strain — Lactobacillus fermentum UCO-979C — obtained from human gut.ResultsThe strain tolerated pH 3.0; grew in the presence of 2% bile salts; produced lactic acid and hydrogen peroxide; aggregated in saline solution; showed high hydrophobicity; showed high adherence to glass; Caco-2 and gastric adenocarcinoma human cells (AGS) cells; showed an efficient colonization in Mongolian Gerbils; and potently inhibited the growth and urease activity of H. pylori strains. L. fermentum UCO-979C significantly inhibited H. pylori-induced IL-8 production in AGS cells and reduced the viability of H. pylori. With regard to innocuousness, the strain UCO-979C was susceptible to several antibiotics and did not produce histamine or beta-haemolysis in blood agar containing red blood cells from various origins.ConclusionThe results demonstrated that L. fermentum UCO-979C is a very good candidate as a probiotic for the protection of humans against H. pylori infections. 相似文献
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Yasir Hasan Siddique Tanveer Beg Mohammad Afzal 《Indian journal of clinical biochemistry : IJCB》2009,24(3):294-300
Hydrogen peroxide is one of the reactive oxygen species for cellular injury. It is overproduced during oxidative stress and
is known to damage proteins, nucleic acids and cell membranes. The present study was aimed to study the protective effect
of ascorbic acid against the toxic doses of hydrogen peroxide using lipid peroxidation and cytokinesis blocked micronucleus
assay. Hydrogen peroxide was studied at 50, 100 and 200μM and was found to increase a dose dependent increase in lipid peroxidation
and micronuclei frequency. The treatment of 100 and 200μM of hydrogen peroxide separately along with 20, 40 and 80μM of ascorbic
acid showed a dose dependent decrease in the lipid peroxidation and micronuclei frequency. The results suggest a protective
effect of ascorbic acid against the hydrogen peroxide induced oxidative damage in cultured human peripheral blood lymphocytes. 相似文献
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N. S. Nagane J. V. Ganu V. R. Bhagwat M. Subramanium 《Indian journal of clinical biochemistry : IJCB》2004,19(2):173-176
Thermal injury is associated with biochemical changes. The present study was undertaken to investigate relation of oxidative
free radical generation and related biochemical parameters in burn trauma. The specific aim was to compare the levels of serum
lipid peroxide, Ceruloplasmin and Uric Acid in burn patients during treatment with Silver Sulfadiazine Cream and honey therapy.
It is a single blind prospective controlled study involving comparison of biochemical changes after treatment with silver
sulfadiazine and honey treatment in burn injury. In burn trauma, there is excessive activity of free radicals at the site
of injury. This is reflected in elevated blood levels of Lipid peroxide, Ceruloplasmin & Uric Acid. Honey therapy was was
shown to decline the levels of serum Lipid peroxide, while there was mild increments in serum Ceruloplasmin levels whereas
there was no significant effect on serum Uric Acid levels as compared to silver sulfadiazine treatment. Honey therapy seems
to accelerate the process of healing. It has positive effect in reducing oxidative stressful state in burn trauma than the
silver sulfadiazine treatment that results in rapid wound healing. 相似文献
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A silver nitrate test is described for the quantitative determination of residual hypo in photographic prints. The hypo is converted in situ to silver sulfide, the transmission density of the sulfide determined, and the hypo content obtained by reference to a standard curve.The method used to establish the standard curve is outlined, the data being verified by quantitative analyses.A simplified procedure is suggested involving the application of a drop of silver nitrate to the back of the print and then matching the spot visually with a set of standards. 相似文献
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It is very difficult, if not impossible, to remove the last traces of hypo from photographic papers by any known procedure of washing. The sulfur in the residual hypo ultimately, and especially under abnormal conditions of temperature and humidity, combines with the silver image to form yellowish brown silver sulfide. This phenomenon is known as sulfiding or “fading” of the image. The various factors which affect the rate of fading of images and the washing out of hypo from films and papers are outlined.Chemical methods of hypo elimination have been proposed from time to time but the majority of these have not been satisfactory because they tend to leave substances such as thionates in the photographic material, which are equally as difficult to wash out as hypo and which also tend to sulfide or fade the silver image. A new hypo eliminator is recommended consisting of two volatile chemicals, hydrogen peroxide and ammonia. This eliminator oxidizes the hypo to sodium sulfate, which is inert and soluble in water, while any excess eliminator evaporates on drying.Two formulas and treatments are proposed: (1) Complete elimination of hypo for use by the professional, advanced amateur, and photofinisher who demand the highest standard of photographic quality in their prints.(2) Almost complete elimination of hypo (less than o.oi milligram per square inch).Since the conditions to which prints will be subjected are rarely known in advance, use of the “complete elimination treatment” is advised in all cases. 相似文献
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John D. Ball 《Journal of The Franklin Institute》1928,206(2):181-200
In this investigation the first series of tests consisted of obtaining zero flux in two varieties of steel from various maximum flux values and by three different methods. B-H curves were obtained after demagnetization by the three methods and from the maximum value of these B-H curves hysteresis loops were taken.One method of demagnetizing was that suggested by the U. S. Bureau of Standards, which consists of current reversals through a magnetizing winding, in which current values are gradually reduced to zero. The second method consisted of applying a negative current of such an amount that the resultant value of flux would be such that when the current was released the flux value would go to zero. The third method was substantially the same as the second except the zero flux was approached from the direction of opposite polarity.The resultant B-H curves proved to be different from each other and to depend upon not only their origin but the previous history of the material as regards methods of demagnetization.The areas between the curves were evaluated.It was found that in cases of two of the three typical B-H curves the B-log H curves gave straight lines for part of the range involved.A second series of tests consisted of taking a set of hysteresis loops and repeating the determinations, using a greater number of steps to find if by taking a greater number of steps there might be a greater indicated energy loss. The results of this group of tests were not sufficiently definite to warrant conclusions. 相似文献