It is shown that the lower bound on the maximum genus of a 3-edge connected loopless graph is at least one-third of its cycle rank. Moreover, this lower bound is tight. There are infinitely such graphs attaining the b...It is shown that the lower bound on the maximum genus of a 3-edge connected loopless graph is at least one-third of its cycle rank. Moreover, this lower bound is tight. There are infinitely such graphs attaining the bound.展开更多
We identified the antimony species present in a wide variety of plastic samples by X ray absorption spectroscopy(XAS)at the Sb L_(3)-edge.The samples contained different concentrations of antimony(Sb),ranging from PET...We identified the antimony species present in a wide variety of plastic samples by X ray absorption spectroscopy(XAS)at the Sb L_(3)-edge.The samples contained different concentrations of antimony(Sb),ranging from PET bottles in which Sb compounds are used as catalysts,with concentrations around 300 mg/kg,to electrical equipment in which the element is used as a flame retardant,with concentrations of several tens of thousands of mg/kg.Although the shape of the spectra at the L_(3)-edge is quite similar for all Sb reference materials,we were able to identify antimony glycolate or acetate in PET bottles,bound organic Sb in c-PET trays and senarmontite in electrical materials as themain Sb components.In samples with high Ca content(e.g.,electrical objects,some c-PET food trays and textiles)the Ca Ka emission line interferes with the Sb La line by introducing a high background which reduces the signal-to-noise ratio in the Sb XAS spectrum,resulting in noisy and distorted spectra.The element-resolved map on a PET bottle sample revealed both Sb and Ca hot spots of around 10-20 microns in size,with no correlation.展开更多
Rhenium is a very scarce element, occurring in the Earth's crust mainly carried by molybdenite (MoS2). Due to a very low availability comparative to actual industrial demand, rhenium is nowadays one of the most ex...Rhenium is a very scarce element, occurring in the Earth's crust mainly carried by molybdenite (MoS2). Due to a very low availability comparative to actual industrial demand, rhenium is nowadays one of the most expensive mineral commodities and an increased interest is focused on ex- ploring residues resulting from a long-term mining, particularly of sulphide ore deposits. It is therefore noteworthy to assign the presence of rhenium (in a concentration up to 3 ppm) in the waste materials from the old sulphur factory at the abandoned mine of Sao Domingos (Iberian Pyrite Belt, Southeast Portugal), exploited since the Roman occupation of Iberia. Aiming at a potential sustainable recovery of rhenium as a by-product, X-ray near-edge absorption spectroscopy (XANES) was applied to clarify the Re-binding and mode of occurrence by comparing Re L3-edge XANES spectra obtained from mine waste samples (previously fully characterized by X-ray laboratory techniques) with similar spectra collected from Re-rich molybdenites (Mo1-xRexS2) and from Re-O model compounds configuring various valences and coordination environments of rhenium ions. Obtained results are commented, ruling out a possible Re-S binding and rather conforming with the binding of rhenium to oxygen in the analysed mine waste materials.展开更多
文摘It is shown that the lower bound on the maximum genus of a 3-edge connected loopless graph is at least one-third of its cycle rank. Moreover, this lower bound is tight. There are infinitely such graphs attaining the bound.
文摘We identified the antimony species present in a wide variety of plastic samples by X ray absorption spectroscopy(XAS)at the Sb L_(3)-edge.The samples contained different concentrations of antimony(Sb),ranging from PET bottles in which Sb compounds are used as catalysts,with concentrations around 300 mg/kg,to electrical equipment in which the element is used as a flame retardant,with concentrations of several tens of thousands of mg/kg.Although the shape of the spectra at the L_(3)-edge is quite similar for all Sb reference materials,we were able to identify antimony glycolate or acetate in PET bottles,bound organic Sb in c-PET trays and senarmontite in electrical materials as themain Sb components.In samples with high Ca content(e.g.,electrical objects,some c-PET food trays and textiles)the Ca Ka emission line interferes with the Sb La line by introducing a high background which reduces the signal-to-noise ratio in the Sb XAS spectrum,resulting in noisy and distorted spectra.The element-resolved map on a PET bottle sample revealed both Sb and Ca hot spots of around 10-20 microns in size,with no correlation.
基金the project MinReMol(Ref.EXPL/AAG-REC/0978/2012),financed by FEDER Funds through the Operational Program on Competitive Factors(COMPETE:FCOMP-01-0124-FEDER-027516)by national funds through the Portuguese Foundation for Science and Technology(FCT-MCTES)support of FCT-MCTES through the Strategic Project LA25-2011-2012(ref.PEst-C/CTM/LA0025/2011).
文摘Rhenium is a very scarce element, occurring in the Earth's crust mainly carried by molybdenite (MoS2). Due to a very low availability comparative to actual industrial demand, rhenium is nowadays one of the most expensive mineral commodities and an increased interest is focused on ex- ploring residues resulting from a long-term mining, particularly of sulphide ore deposits. It is therefore noteworthy to assign the presence of rhenium (in a concentration up to 3 ppm) in the waste materials from the old sulphur factory at the abandoned mine of Sao Domingos (Iberian Pyrite Belt, Southeast Portugal), exploited since the Roman occupation of Iberia. Aiming at a potential sustainable recovery of rhenium as a by-product, X-ray near-edge absorption spectroscopy (XANES) was applied to clarify the Re-binding and mode of occurrence by comparing Re L3-edge XANES spectra obtained from mine waste samples (previously fully characterized by X-ray laboratory techniques) with similar spectra collected from Re-rich molybdenites (Mo1-xRexS2) and from Re-O model compounds configuring various valences and coordination environments of rhenium ions. Obtained results are commented, ruling out a possible Re-S binding and rather conforming with the binding of rhenium to oxygen in the analysed mine waste materials.
