The condemnations of black slavery were not common before the mid-18th century,and they were mostly based on Christian egalitarianism.Around the American Revolution,with the spread of the theory of natural rights,many social elites believed that slavery deprived blacks of their natural rights and violated the principle of equality in a democratic republic.Anti-slavery gradually became the mainstream public opinion.However,since slaves were private property of many politicians,the abolition of slavery would act against the interests of white elites,and the ideology of racial confrontation between blacks and whites provided an identity to the white community.Therefore,slavery was reserved from the founding period.In the mid-19th century,various social reforms arose.Humanitarianism was deeply rooted in elites'minds,and the idea that blacks have the general attributes of human beings is gradually accepted by educated white people.The sense of dignity of work in the North constituted a different value from the South and became another theoretical basis for public voice to criticize slavery.However,for the sake of party unity and the national interest,the abolition were not put into practice until the Civil War broke out.By the middle of the 19th century,although the public opinion of anti-slavery was formed in the North,the upper class elites held the position of realpolitik while balancing the morality of abolition and the economic and political interests.
Taking inspiration from beautiful colors in nature,structural colors produced from nanostructured metasurfaces have shown great promise as a platform for bright,highly saturated,and high-resolution colors.Both plasmonic and dielectric materials have been employed to produce static colors that fulfil the required criteria for high-performance color printing,however,for practical applications in dynamic situations,a form of tunability is desirable.Combinations of the additive color palette of red,green,and blue enable the expression of further colors beyond the three primary colors,while the simultaneous intensity modulation allows access to the full color gamut.Here,we demonstrate an electrically tunable metasurface that can represent saturated red,green,and blue pixels that can be dynamically and continuously controlled between on and off states using liquid crystals.We use this to experimentally realize ultrahigh-resolution color printing,active multicolor cryptographic applications,and tunable pixels toward high-performance full-color reflective displays.
Ores of infiltration sandstone-hosted uranium deposits in the sedimentary cover are ubiquitous composed of dispersed soot powder mineralization of black,brownish-black colour.Longterm studies of such loose U-ores by analytical transmission electron microscopy(ATEM)proved their polymineral nature.Uranium blacks are composed by at least three different U-mineral forms:oxide(uraninite),silicate(coffinite)and phosphate(ningyoite)which are present in various proportions of ore compositions.Such high dispersed friable uranium formations are difficult to diagnose by traditional mineralogical methods(optical,XRD,IR and X-ray spectroscopy,etc.)which analyze total sample composition(phases mixture);their results characterize the dominant sample phase,omitting both sharply subordinate and X-ray amorphous phases.All research results are based on ATEM methods(SAED+EDS),which are optimal for crystallochemical diagnostics in the mineralogical study of such uranium ores.The article presents the diagnostic characteristics under electron microscope(EM)of uranous minerals from different sandstone deposits with their origin being discussed.
The synthesis of ultrasmall metal nanoclusters(NCs) with high catalytic activities is of great importance for the development of clean and renewable energy technologies but remains a challenge. Here we report a facile wet-chemical method to prepare ~1.0 nm Au Pd NCs supported on amine-functionalized carbon blacks. The Au Pd NCs exhibit a specific activity of 5.98 mA cm_(AuPd)^(-2)and mass activity of 5.25 A mg_(auPd)^(-1) for ethanol electrooxidation, which are far better than those of commercial Pd/C catalysts(1.74 mAcm_(AuPd)^(-2) and 0.54 A mg_(Pd)^(-1) ). For formic acid dehydrogenation, the Au Pd NCs have an initial turn over frequency of 49339 h^(-1) at 298 K without any additive, which is much higher than those obtained for most of reported Au Pd catalysts. The reported synthesis may represent a facile and low-cost approach to prepare other ultrasmall metal NCs with high catalytic activities for various applications.