468 research outputs found
Re-evaluation of the age model for North Atlantic Ocean Site 982 – arguments for a return to the original chronology
No full textRecently, the veracity of the published chronology for the Pliocene section of North Atlantic Ocean Drilling Program Site 982 was called into question. Here, we examine the robustness of the original age model as well as the proposed age model revision. The proposed revision is predicated on an apparent mis-identification of the depth to the Gauss-Matuyama (G/M) polarity chronozone reversal boundary (2.581 Ma) based on preliminary shipboard paleomagnetic data and offers a new chronology which includes a hiatus between ~3.2 and 3 Ma. However, an even more accurate shore-based, u-channel-derived polarity chronozone stratigraphy for the past ~2.7 Ma supports the shipboard composite stratigraphy and demonstrates that the original estimate of the depth of the G/M reversal in the Site 982 record is correct. Thus, the main justification forwarded to support the revised chronology no longer exists. We demonstrate that the proposed revision results in a pronounced anomaly in sedimentation rates proximal to the proposed hiatus, erroneous assignment of marine-isotope stages in the Site 982 Pliocene benthic stable oxygen isotope stratigraphy, and a markedly worse correlation of proxy records between this site and other regional paleoclimate data. We conclude that the original chronology for Site 982 is a far more accurate age-model than that which arises from the published revision. We strongly recommend the use of the original chronology for all future work at Site 982
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Dithiolane ligands for semiconductor quantum dots
No full textWe have investigated the potential of the dithiolane ring to anchor organic compounds on the surface of CdSe–ZnS core–shell quantum dots. In particular, we have synthesized three monomeric ligands, incorporating an azobenzene chromophore and a single dithiolane anchor in their molecular skeleton, as well as a polymeric ligand with multiple chromophoric labels and anchoring groups. All compounds co-adsorb on the surface of preformed quantum dots, together with their native tri-n-octylphosphine oxide surfactants, when chloroform dispersion of the organic ligands and the inorganic nanoparticles are heated under reflux for 24–72 h. The reaction time dictates the average number of azobenzene chromophores incorporated in the final assemblies, which can range from 6 up to 92. However, the modified quantum dots retain a substantial hydrophobic character and are not soluble in water, despite the presence of hydrophilic poly(ethylene glycol) chains in three of the four dithiolane ligands. The adsorbed azobenzene chromophores can be switched from trans to cis configurations with ultraviolet stimulations. The photochemical process is thermally reversibly and, in the case of the polymeric ligand, results in the photomodulation of the luminescence intensity of the nanostructured construc
Chiroptical switching based on the photoinduced proton transfer between homopolymers bearing side-chain spiropyran and azopyridine moieties
No full textA novel optically-active polymeric methacrylate, bearing the (S)-3-hydroxy pyrrolidinyl group linked through the nitrogen atom to an azopyridine chromophore, was synthesized and investigated in combination with a polymeric methacrylate incorporating the photoisomerizable spiropyran chromophore in the side-chain. In the presence of acid, this system can be operated in solution to modulate the protonation of the azopyridine moieties by photoisomerizing the spiropyran component. In addition to UV-vis spectroscopy, the proton transfer process occurring between the macromolecular components can be also followed by CD spectroscopy, thus behaving as a chiroptical switch
Pliocene shorelines and the epeirogenic motion of continental margins: a target dataset for dynamic topography models
No full textGlobal mean sea level during the mid-Pliocene epoch (∼3 Ma), when CO2 and temperatures were above present levels, was notably higher than today due to reduced global ice sheet coverage. Nevertheless, the extent to which ice sheets responded to Pliocene warmth remains in question owing to high levels of uncertainty in proxy-based sea level reconstructions as well as solid Earth dynamic models that have been used to evaluate a limited number of data constraints. Here, we present a global dataset of 10 wave-cut scarps that formed by successive Pliocene sea level oscillations and which are observed today at elevations ranging from ∼6 to 109 m above sea level. The present-day elevations of these features have been identified using a combination of high-resolution digital elevation models and field mapping. Using the MATLAB interface TerraceM, we extrapolate the cliff and platform surfaces to determine the elevation of the scarp toe, which in most settings is buried under meters of talus. We correct the scarp-toe elevations for glacial isostatic adjustment and find that this process alone cannot explain observed differences in Pliocene paleo-shoreline elevations around the globe. We next determine the signal associated with mantle dynamic topography by back-advecting the present-day three-dimensional buoyancy structure of the mantle and calculating the difference in radial surface stresses over the last 3 Myr using the convection code ASPECT. We include a wide range of present-day mantle structures (buoyancy and viscosity) constrained by seismic tomography models, geodynamic observations, and rock mechanics laboratory experiments. Finally, we identify preferred dynamic topography change predictions based on their agreement with scarp elevations and use our most confident result to estimate a Pliocene global mean sea level based on one scarp from De Hoop, South Africa. This inference (11.6 ± 5.2 m) is a downward revision and may imply that ice sheets were relatively resistant to warm Pliocene climate conditions. We also conclude, however, that more targeted model development is needed to more reliably infer mid-Pliocene global mean sea level based on all scarps mapped in this study
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Photochromic Polymers Based on the Photoinduced Opening and Thermal Closing of [1,3]Oxazine Rings
No full textTwo macromolecular constructs incorporating a single polymer backbone with multiple photochromic side chains are developed. Both systems are prepared from preformed photochromic [1,3]oxazines after the ring-opening polymerization of their norbornene appendages. In solution, UV illumination of these polymers opens the [1,3]oxazine rings in their side chains in less than 6 ns and with a quantum yield of 0.09 in both instances. The photogenerated species incorporate a 4-nitrophenolate chromophore, and hence, their formation is accompanied by the appearance of an intense band in the visible region of the
absorption spectrum. The photoproducts revert spontaneously to the original state with first-order kinetics inmicroseconds. Furthermore, both photochromic polymers tolerate hundreds of switching cycles with no sign of degradation, even in the presence of molecular oxygen. Thus, this design logic and choice of
functional building blocks can translate into the realization of innovative photoresponsive materials with excellent photochromic performance
Prompting sustainability in the citrus derivates industry: A case study
No full textA systemic approach was proposed to analyse a complex system such that of food value chains. Typical management methodologies were applied to a citrus derivatives industry and, based on the survey outcomes, a sustainable optimisation plan was formulated integrating the critical domains of the water-food-energy nexus. The overall process was mapped in detail. The SWOT analysis was applied to identify strengths, weaknesses, opportunities, and threats related to each step of the production chain of the citrus derived products. To prioritize its critical output factors, the Impact-Feasibility Map tool was defined. Critical issues characterised by the highest impact and easiest feasibility were the un-optimized fertilization and irrigation, non-objective human inspections, lack of production standardization and accumulation of organic waste. Structured interviews to the company managers were conducted to identify the most relevant company's needs. With a view on process and product sustainability, suggestions based on good manufacturing practices and on literature were scheduled within a 10-years industrial development plan accomplishing a circular economy scheme. The performed analysis is preliminary to optimisation actions in view of process sustainability that will be carried out according to the classic engineering approach. The present actual goal is to contextualize the engineering interventions in relation to the needs of the producers. Indeed, empirical contextualised research will be necessary to assess whether the sustainable actions and measures identified in this study can be validated in actual practice with conventional chemical engineering optimisation procedures
Synthesis and photoresponsive behavior of optically active methacrylic homopolymers containing side-chain spiropyran chromophores
No full textNovel optically-active methacrylic homopolymers bearing in the side chain one or more chiral groups of one single configuration (based on the L-lactic acid residue) linked to the spiropyran chromophore, have
been successfully synthesized and fully characterized.
These intrinsically chiral polymers exhibit remarkable thermal stability, with glass transition temperatures in the range 100–130 C and decomposition temperatures around 270 C. The chiroptical characterization indicates the occurrence of asymmetric induction on the electronic transitions of the side-chain chromophore related to the number of L-lactic acid residues interposed between the main
chain and the spiropyran chromophore.
In the presence of acid, these systems can be used to modulate the protonation of polymeric azopyridine moieties upon photoisomerization of the spiropyran group. In addition to UV–Vis spectroscopy, the
proton transfer process occurring between the macromolecular components can be also followed by CD spectroscopy, the system thus behaving as a chiroptical switch
Simple molecular-level machines. Interchange between different threads in pseudorotaxanes
No full textIn suitably designed supramolecular systems, composed of a macrocycle and two different thread-like compounds, it is possible to choose, by means of chemical inputs, which thread enters the macrocycle's cavity, and it is also possible to cause reversible interchange between the two threads. Two such systems are described. In one of them, the macrocyclic component is 1,5-dinaphtho-38-crown-10, the potential threads are 1,1′-dibenzyl-4,4′-bipyridinium and 2,7-dibenzyldiazapyrenium dications, and the chemical input used is amine/acid. In the other system, the macrocyclic component is the tetracationic cyclophane, cyclobis(paraquat-p-phenylene), the potential threads are tetrathiafulvalene and a 1,5-dioxynaphthalene derivative, and the input is reduction/oxidation. These systems are examples of chemically driven molecular-level mechanical machines
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Optical and Chiroptical Switches Based on Photoinduced Photon and Proton Transfer in Copolymers Containing Spiropyran and Azopyridine Chromophores in Their Side Chains
No full textNew methacrylic copolymers, bearing in the side chain spiropyran moieties and/or the optically-active (S)-3-hydroxy pyrrolidinyl group linked through the nitrogen atom to an azopyridine chromophore, along with an opportune molar content of methyl methacrylate co-units, have been prepared by radical polymerization of the corresponding monomers.
The resulting macromolecules have been fully characterized with particular attention to the study of their thermal stability, optical activity, chiroptical and photoinduced properties.
In the presence of acid, it is possible to modulate the protonation of the azopyridine groups by photo-isomerisation (with UV and/or Vis light) of the spiropyran component. The resulting signal communication between these macromolecular switches can be monitored by UV-VIS as well as CD spectroscopy and is completely reversible and reproducible.
The results are discussed in terms of copolymer composition and different cooperative behavior, which lead to a variation of interactions between spiropyran and azoaromatic chromophores and reveal that the best proton transfer is actually obtained in the random terpolymer with lower amounts of co-units of spiropyran and azopyridine chromophores in the side chain, which displays improved sensitivity to proton-transfer process and, in addition, exhibits good stability to repeated cycles of irradiation with UV and Vis light
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Structural Implications on the Electrochemical and Spectroscopic Signature of CdSe-ZnS Core-Shell Quantum Dots
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