Dams, increasingly common in riverine systems worldwide, are particularly prevalent on the Columbia River (CR) in the United States. Hydroelectric projects, including both storage and run‐of‐river (i.e., minimal storage) structures, on the mainstem CR highly manage water flow, often by releasing water over (rather than through) dams as “spill.” To test the effects of run‐of‐river dam spill on microplankton abundance and composition, we sampled above and below two dams in the lower CR before and during spill conditions in spring 2016 and during and after spill conditions in late summer 2007. We tested the effects of location (i.e., above vs. below dams), spill condition (i.e., before, during, and after spill), and their interaction on microplankton abundance. Generally, diatoms were most abundant during springtime, whereas cyanobacteria were most abundant in late summer. Most taxa were not significantly different in abundance above and below dams, regardless of spill status; although cyanobacteria abundance was marginally higher below dams in summer 2007 (p = .04). Abundances of all taxa were significantly different between pre‐spill and spill periods in spring 2016, whereas only diatom and flagellate abundances were significantly different between spill and post‐spill periods in summer 2007. We conclude that spill conditions may influence microplankton abundance, but are not likely to affect microplankton communities on either side of run‐of‐river dams on the CR. This is important information for dam managers concerned about ecosystem impacts of spill. 相似文献
Barriers to fish movement have been used to prevent the spread of invasive fishes but may also limit the movements of native fishes. We evaluated the potential consequences of a proposed barrier on the Illinois River Waterway, meant to inhibit the spread of silver and bighead carps, to the continued recovery of native fishes in the Des Plaines River following water quality improvements. We compared changes in upstream cumulative species richness and community structure from 1983 to 2013 in the DuPage River, an adjacent tributary with an impassable dam, to the area upstream of a newly proposed barrier on the Des Plaines River where fish can currently pass through a navigational lock. Fewer species displayed truncated distributions upstream of the passable lock and dam (n = 18) compared with the impassable dam (n = 23). Due to water quality improvements in the Illinois River as a whole, cumulative species richness downstream of both dams steadily increased over time. Richness also increased upstream of the passable dam but plateaued upstream of the impassable dam. Fifteen to 18 species accounted for differences in community structure between areas downstream and upstream of either dam. Most species (78–100%) were found in greater relative abundance downstream of the impassable dam, and only 53% were found in greater relative abundance downstream of the passable dam. The truncation in species richness and abundance at the impassable dam foreshadows the potential consequences of an indiscriminate barrier on native fishes and the continued recovery of native assemblages. 相似文献
Bi2Se3, as a Te‐free alternative of room‐temperature state‐of‐the‐art thermoelectric (TE) Bi2Te3, has attracted little attention due to its poor electrical transport properties and high thermal conductivity. Interestingly, BiSbSe3, a product of alloying 50% Sb on Bi sites, shows outstanding electron and phonon transports. BiSbSe3 possesses orthorhombic structure and exhibits multiple conduction bands, which can be activated when the carrier density is increased as high as ≈3.7 × 1020 cm?3 through heavily Br doping, resulting in simultaneously enhancing the electrical conductivities and Seebeck coefficients. Meanwhile, an extremely low thermal conductivity (≈0.6–0.4 W m?1 K?1 at 300–800 K) is found in BiSbSe3. Both first‐principles calculations and elastic properties measurements show the strong anharmonicity and support the ultra‐low thermal conductivity of BiSbSe3. Finally, a maximum dimensionless figure of merit ZT ～ 1.4 at 800 K is achieved in BiSb(Se0.94Br0.06)3, which is comparable to the most n‐type Te‐free TE materials. The present results indicate that BiSbSe3 is a new and a robust candidate for TE power generation in medium‐temperature range. 相似文献
2,5‐Disubstituted oxazoles are synthesized by oxidative gold catalysis. In contrast to a reported procedure that delivers 2,4‐disubstituted oxazoles starting from terminal alkynes, a switch in selectivity towards a 2,5‐disubstitution is achieved by the use of propynals as starting materials. In the new reaction, the key intermediate is formed by the nucleophilic attack of the carboxamide onto a gold carbenoid, and then condensates with the more electrophilic aldehyde moiety already present in the substrate and not with the ketone that is derived from the oxygen donor. This new cyclization mode introduces a new carbonyl moiety as substituent at the 2,5‐disubstituted oxazole, an attractive motive that can be found in bioactive compounds or be used for further derivatizations.
Quadruplex nucleic acids are promising targets for cancer therapy. In this study we used a fragment-based approach to create new flexible G-quadruplex (G4) DNA-interactive small molecules with good calculated oral drug-like properties, based on quinoline and triazole heterocycles. G4 melting temperature and polymerase chain reaction (PCR)-stop assays showed that two of these compounds are selective G4 ligands, as they were able to induce and stabilize G4s in a dose- and DNA sequence-dependent manner. Molecular docking studies have suggested plausible quadruplex binding to both the G-quartet and groove, with the quinoline module playing the major role. Compounds were screened for cytotoxicity against four cancer cell lines, where 4,4′-(4,4′-(1,3-phenylene)bis(1H-1,2,3-triazole-4,1-diyl))bis(1-methylquinolin-1-ium) ( 1 d ) showed the greater activity. Importantly, dose–response curves show that 1 d is cytotoxic in the human colon cancer HT-29 cell line enriched in cancer stem-like cells, a subpopulation of cells implicated in chemoresistance. Overall, this study identified a new small molecule as a promising lead for the development of drugs targeting G4 in cancer stem cells. 相似文献
Mg2Sn based solid solutions have attracted much research interest due to their high thermoelectric (TE) performance in the mid‐temperature region and abundant constituent elements. Further enhancement of the figure of merit zT lies in the effective reduction of the relatively high lattice thermal conductivity. It has been demonstrated that alloying high content of aliovalent Sb (>10%) in Mg2Si analogue can induce Mg vacancies and dense dislocations to greatly suppress the lattice thermal conductivity. In this work, the strategy is extended to the Sb alloyed Mg2Sn to enhance zT. Detailed microstructure investigations reveal the existence of high density of interstitial clusters. By introducing these nanostructures as the additional phonon scattering sources, the theoretical calculation well match the low experimental lattice thermal conductivity. Superior to the Sb alloyed Mg2Si, relatively high power factor is maintained in the Sb alloyed Mg2Sn and the maximum zT of 0.9 at 750 K is obtained. With simpler chemical composition though, the Mg2Sn1–xSbx (x > 0.1) has comparable TE performance with the Sb alloyed Mg2Si0.4Sn0.6 solid solutions, exhibiting promising potential for practical applications. The present work offers a comprehensive understanding of the effect of aliovalent alloying and concomitant complex microstructure in reducing thermal conductivity and enhancing zT. 相似文献
Owing to their ability to efficiently deliver biological cargo and sense the intracellular milieu, vertical arrays of high aspect ratio nanostructures, known as nanoneedles, are being developed as minimally invasive tools for cell manipulation. However, little is known of the mechanisms of cargo transfer across the cell membrane‐nanoneedle interface. In particular, the contributions of membrane piercing, modulation of membrane permeability and endocytosis to cargo transfer remain largely unexplored. Here, combining state‐of‐the‐art electron and scanning ion conductance microscopy with molecular biology techniques, it is shown that porous silicon nanoneedle arrays concurrently stimulate independent endocytic pathways which contribute to enhanced biomolecule delivery into human mesenchymal stem cells. Electron microscopy of the cell membrane at nanoneedle sites shows an intact lipid bilayer, accompanied by an accumulation of clathrin‐coated pits and caveolae. Nanoneedles enhance the internalization of biomolecular markers of endocytosis, highlighting the concurrent activation of caveolae‐ and clathrin‐mediated endocytosis, alongside macropinocytosis. These events contribute to the nanoneedle‐mediated delivery (nanoinjection) of nucleic acids into human stem cells, which distribute across the cytosol and the endolysosomal system. This data extends the understanding of how nanoneedles modulate biological processes to mediate interaction with the intracellular space, providing indications for the rational design of improved cell‐manipulation technologies. 相似文献
Doped networks of semiconducting single‐walled carbon nanotubes (s‐SWCNTs) have recently demonstrated high thermoelectric (TE) power factors and figures of merit. Efforts to further improve the TE performance of s‐SWCNT networks hinge upon deeper understanding of the mechanisms underlying charge transport. This study explores the dependence of conductivity, thermopower, and resulting TE power factor on carrier density and temperature in s‐SWCNT networks. Careful control of charge‐carrier density illustrates a distinct transition between transport that is limited by energetic barriers between nanotube bundles to an “intrinsic” regime where these barriers are small enough to reveal the intrinsic transport mechanism of the nanotubes. Transport is activated in the s‐SWCNT networks, although a critical survey of the literature demonstrates that the activation energies in s‐SWCNT networks are appreciably smaller than typical semiconducting polymers. At high conductivity, transport behavior is consistent with deformation potential scattering. The analysis demonstrates that mitigation of the “extrinsic” limitations to transport (e.g., inter‐nanotube junctions), and the concomitant reduction of conductivity activation energies, can lead to at least a doubling of the TE power factor. Further comparison to prototypical semiconducting polymers demonstrates that this strategy likely represents a general design principle for improving the TE performance of organic materials. 相似文献
Lead‐free 0.95(K0.48Na0.52)(Nb0.95Sb0.05)O3‐0.05Bi0.5(Na0.82K0.18)0.5ZrO3 (KNSN‐BNKZ0.05) piezoelectric films with preferred crystal orientation and enhanced thickness are fabricated on silicon substrates from a chemical solution approach. Adequate K excess is introduced to obtain a single perovskite phase in the resulting thicker films. The effects of thickness, crystal orientation, and structure of the films on the performance are investigated. Outstandingly large effective piezoelectric strain coefficient up to 250 pm V−1 is demonstrated over a macroscopic scale using a laser scanning vibrometer in the [100]‐KNSN‐BNKZ0.05 film with an enhanced thickness of 2.7 µm, competitive to the benchmark oriented lead zirconate titanate films on silicon. Atomically resolved electron microscopy reveals the coexistence of oriented ferroelectric rhombohedral (R) and tetragonal (T) phases at the nanometer scale with gradual polarization rotation, which can lower the domain wall energy and facilitate the large piezoelectric response. The increased film thickness reduces the in‐plane mechanical clamping to enable more free deformation in the thickness direction and improve domain wall mobility, both further contributing to enhanced piezoelectric response. 相似文献
