We systematically investigate ellipticity dependence of high-order harmonic generation of Ar and N2 in intense elliptically polarized laser fields. The experimental normalized ratios of low-order harmonic intensity to high-order harmonic intensity increase with ellipticity for both Ar and N2, and quantitatively depend on targets and trajectory paths. The experimental results are well reproduced by a nonadiabatic semiclassical simulation and explained by trajectory-based analysis. In addition, the influence of nuclear distance on the ratios is theoretically investigated. Our work reveals that the difference between atoms and molecules can be attributed to the influence of different ionic potentials, which depends on the molecular structure (internuclear distance) and alignment, on the evolution of the photoelectron.
Why are organizations sometimes so similar, and in other cases so different? For decades this question has been central to research on organizations, and two leading theories have answered the question very differently. Neo-institutional theory has pointed to the importance of mimetic isomorphism, where organizations imitate one another as they navigate decisions in the context of uncertainty over what is regarded as legitimate action. By contrast, ecological theory argues that competitive exclusion explains the differences we see around us, as organizations repel one another when they vie for the same resources. Decades of empirical work has tended to confirm one or the other theory, with scant effort being made to reconcile these conflicting predictions. Furthermore, much of the existing empirical work is limited to descriptive studies that make little or no attempt to empirically identify their findings, leaving the empirical record open to concerns over endogeneity. This paper conducts an identified empirical test, in a context where the two arguments make opposing predictions. In an analysis of auditor selection after the collapse of Arthur Andersen, we find evidence of competitive exclusion, but no evidence of mimetic isomorphism. Implications for the continued progress of organization theory are discussed.
Complex foam flows in series and parallel are investigated by means of a self-designed high-pressure high-temperature laboratory physical model. A total of twenty-two foam flow experiments were conducted in the porous media with a wide permeability range over two orders of magnitude. Specifically, fifteen single and seven dual foam flows in porous media with respective permeability range of 37−9705 mD and 41−7838 mD were performed to determine a series of physiochemical properties in terms of foam rheology, fluid profile and mobility control. For the foam flows in series, the overall gas saturation with process of foam injection is found to quickly increase within initial period but then tend to be stable. At the end of foam injection, the gas saturation curve could be clearly distinguished with permeability variances that a sharp rising range for permeability from 37 to 1233 mD while a quasi-stable range from 1233 to 9705 mD. Mobility reduction factor and apparent viscosity of the single flow cases are found to increase initially but in subsequent a decline with the permeability increase, whose maximum values were equal to 726.34 and 646.44 mPa•s at the permeability of 4386 mD. Moreover, the mobility curve basically performs as a U shape with three distinct periods: a sharp initial decrease period from 37 to 564 mD in subsequent of a second uniform mobility from 564 to 7309 and third increase period from 7309 to 9705 mD. On the other hand, for the foam flow in parallel, the profile control effect is determined to be favorable for a medium permeability ranging from 282 to 3855 mD but unfavorable for either lower- or higher-permeability cases. In the post-foam water injection period, the gas saturation for the single flow case monotonically decreases while for the flow in parallel, the gas and liquid production profiles perform oppositely to the profile control effect with respect to the permeability. Overall, gas and liquid mobilities are proven to be simultaneously controlled for foam flows in series and parallel through multiscale porous media, whereas a gas mobility is better controlled, particularly in porous media with lower permeability.
Nanopore structure development in shale is intimated with lithofacies that demonstrates a large variety in different formations. It is critical to differentiate and quantify the separate impact of lithological components (minerals and organic matter (OM)) on pore structure attributes associated with shale gas storage capacity. In this study, we classified shales into 12 lithofacies for compositional and petrophysical quantification. Parameters of our main target, the Goldwyer shales (argillaceous OM-poor, argillaceous OM-moderate, and argillaceous OM-rich lithofacies) were further compared with other shale lithofacies, pure clays and isolated kerogens, using XRD, Rock-Eval pyrolysis, Ar-SEM and low-pressure CO2/N2 gas adsorption techniques. Results show that argillaceous OM-rich lithofacies (TOC > 2% and illite-dominated clay contents > 50%) develop more interconnected pores with better hydrocarbon storage potential. The argillaceous lithofacies have large amounts of cleavage-sheet pores with large pore volumes; the accumulative pore volume of the pores in diameter from 2 to 17 nm constitutes the major amount of total pore volume that is associated with free gas. The OM-rich lithofacies develop more OM-pores (particularly in pore diameter <2 nm) that contain extraordinarily high specific surface area (SSA); the SSA of micropores makes up the major total surface area that is intimated with adsorbed gas. Further investigation on pure clays and isolated kerogens clarifies that illite mainly controls the pore sizes from 2 to 17 nm, resulting in large pore volumes in argillaceous shales. By contrast, isolated kerogen dominantly controls micropores in diameter <2 nm, leading to a larger surface area with higher adsorbed gas storage in organic-rich shales.
The invention relates to composite compositions including a carbonaceous material and a photocatalyst. The invention includes compositions and various methods, including methods for removing one or more contaminants from a substance such as air, soil, and water.
Abstract Climate and land-cover changes are major threats to biodiversity, and their impacts are expected to intensify in the future. Protected areas (PAs) are crucial for biodiversity conservation. However, their effectiveness under future climate and land-cover changes remains to be evaluated. Moreover, the impacts of climate and land-cover changes on multi-dimensions of biodiversity are rarely considered when expanding PAs. Using distributions of 8,732 woody species in China and species distribution models, we identified species that will be threatened by future climate and land-cover changes (i.e. species with significant projected loss of suitable habitats by the 2070s) under different dispersal scenarios. We then estimated the geographical patterns in species richness (SR) and phylogenetic diversity (PD) of threatened species, evaluated the effectiveness (i.e. the changes in SR and PD) of Chinese PAs and identified conservation priorities for future PA expansion. Approximately 12%–38% of woody species will be threatened under different scenarios. These species tend to be clustered in the tree of life, and their SR and PD show consistent spatial patterns, being highest at low latitudes. PAs currently protect 90% of threatened species. However, their SR and PD of threatened species within PAs will decrease by 30%–40% by the 2070s, which reduces the PA effectiveness, especially for PAs at low elevations and those with low topographic heterogeneity and high natural vegetation loss. The conservation priorities identified from the SR and PD of the threatened species are mainly in mountains in southern China, the Yunnan-Guizhou Plateau and Taiwan Island. PA expansion and ecological corridors in these regions are needed to conserve threatened species. Synthesis and applications. We present a systematic study of the impacts of future climate and land-cover changes on the conservation status of woody species and PA effectiveness in China. Our results suggest that future climate and land-cover changes will reduce PA effectiveness, and the spatial prioritization of biodiversity conservation should consider the influences of future global changes on biodiversity. These results shed new light on the conservation priorities for the post-2020 expansion of PAs in China.
Abstract Accelerated glacier-snow-permafrost erosion due to global warming amplifies the sediment availability in cold environments and affects the time-varying suspended sediment concentration (SSC) and discharge (Q) relationship. Here, the sediment-availability-transport (SAT) model is proposed to simulate dynamic SSC-Q relationships by integrating the sediment availability coupled by thermal processes, fluvial processes and long-term storage exhaustion into a sediment rating curve (SSC = a ? Qb with a and b as fitting parameters). In the SAT-model, increased sediment sources from glacier-snow-permafrost erosion are captured by changes in basin temperature, showing an exponential amplification of SSC when basin temperature increases. Enhanced fluvial erosion by the elevated water supply from rainfall and meltwater is captured by the factor of runoff surge, which results in a linear amplification of SSC. The SAT-model is validated for the permafrost-dominated Tuotuohe basin on Tibetan Plateau utilizing multi-decadal daily SSC/Q in-situ observations (1985?2017). Results show that sediment rating curves for Tuotuohe display significant inter-annual variations. The higher parameter-b in a warmer and wetter climate confirms the increased sediment availability due to the expanded erodible landscapes and gullying-enhanced connectivity between channels and slopes. Through capturing such time-varying sediment availability, the SAT-model can robustly reproduce the long-term evolution, seasonality, and various event-scale hysteresis of SSC, including clockwise, counter-clockwise, figure-eight, counter-figure-eight, and more complex hysteresis loops. Overall, the SAT-model can explain over 75% of long-term SSC variance with stable performance under hydroclimate abrupt changes, outperforming the conventional and static sediment rating curve approach by 20%. The SAT-model not only advances understanding of sediment transport mechanisms by integrating thermal- and fluvial-erosion processes, but also provides a model framework to simulate and project future sediment loads in other cold basins.
Iron hydroxides are important scavengers for dissolved chromium (Cr) via coprecipitation processes; however, the influences of organic matter (OM) on Cr sequestration in Fe/Cr-OM ternary systems and the stability of the coprecipitates are not well understood. Here, Fe/Cr-OM coprecipitation was conducted at pH 3, and Cr hydroxide was undersaturated. Acetic acid (HAc), poly(acrylic acid) (PAA), and Suwannee River natural organic matter (SRNOM) were selected as model OMs, which showed different complexation capabilities with Fe/Cr ions and Fe/Cr hydroxide particles. HAc had no significant effect on the coprecipitation, as the monodentate carboxyl ligand in HAc did not favor complexation with dissolved Fe/Cr ions or Fe/Cr hydroxide nanoparticles. Contrarily, PAA and SRNOM with polydentate carboxyl ligand had strong complexation with Fe/Cr ions and Fe/Cr hydroxide nanoparticles, leading to significant amounts of PAA/SRNOM sequestered in the coprecipitates, which caused the structural disorder and fast aggregation of the coprecipitates. In comparison with that of PAA, preferential complexation of Cr ions with SRNOM resulted in higher Cr/Fe ratios in the coprecipitates. This study advances the fundamental understanding of Fe/Cr-OM coprecipitation and mechanisms controlling the composition and stability of the coprecipitates, which is essential for successful Cr remediation and removal in both natural and engineered settings.
