4,349 research outputs found
Photoresponsive Cellulose Nanocrystals Regular Paper
In this communication a method for the creation of fluorescent cellulose nanoparticles using click chemistry and subsequent photodimerization of the installed side-chains is demonstrated. In the first step, the primary hydroxyl groups on the surface of the CNCs were converted to carboxylic acids by using TEMPO-mediated hypohalite oxidation. The alkyne groups, essential for the click reaction, were introduced into the surface of TEMPO-oxidized CNCs via carbodiimide-mediated formation of an amide linkage between monomers carrying an amine functionality and carboxylic acid groups on the surface of the TEMPO-oxidized CNCs. Finally, the reaction of surface-modified TEMPO-oxidized cellulose nanocrystals and azido-bearing coumarin and anthracene monomers were carried out by means of a click chemistry, i.e., Copper(I))-catalyzed Azide-Alkyne Cycloaddition (CuAAC) to produce highly photo-responsive and fluorescent cellulose nanoparticles. Most significantly, the installed coumarin and/or anthracene side-chains were shown to undergo UV-induced [2+2] and [4+4] cycloaddition reactions, bringing and locking the cellulose nanocrystals together. This effort paves the way towards creating, cellulosic photo responsive nano-arrays with the potential of photo reversibility since these reactions are known to be reversible at varying wavelengths.Peer reviewe
Detection of velocity in high temperature liquid metals
Various efforts have been made to measure velocity in liquid metals. All of these efforts, however, share the same inherent limitation, namely, not being operative at the high temperatures required by liquid metals and liquid slags in an industrial application. In this paper, the current methods used were reviewed, and a new technique was presented for the measurement of velocity in high temperature liquid metals. In using this technique there are two stages. Starting with the calibration stage and then moving to the actual measurement stage by making use of the data obtained from calibration stage. Calibration proceeds in the following manner. Metallic spheres moving with a specific velocity are immersed in liquid metal held under isothermal conditions and at specific temperature. Their melting times are determined very accurately with a novel technique. These measurements are repeated for different metal bath temperatures and for different velocities of metallic spheres. In this manner it is possible to calculate the correlation between velocity and melting times for each metal bath temperature. During the actual measurement stage, when the metal bath temperature is known and its velocity is unknown, the magnitude of the unknown liquid metal velocity can be derived as follows: metallic spheres are immersed into the moving liquid metal and their melting times are determined. Using the above mentioned correlations, it will be shown that the magnitude of the unknown velocity in liquid metal can be deduced. This new technique was applied to high temperature liquid aluminum and liquid steel and these results were presented. The potential applicability of this technique in other liquid metals and liquid slags will also be discussed
Enhanced nonlinear optical effects in drift-biased nonreciprocal graphene plasmonics
Nonlinear light-matter interactions are typically enhanced by increasing the
local field and its interaction time with matter. Conventional methods to
achieve these goals are based on resonances or slow-light effects. However,
these methods suffer from various issues, including narrow operational
bandwidths, large footprints, and material absorption. An interesting
alternative approach to enhance the local field is offered by nonreciprocal
systems: by blocking the path of a unidirectional wave in a terminated
nonreciprocal waveguiding structure, broadband electromagnetic fields can be
drastically enhanced and localized near the termination. This approach was
previously studied only in three-dimensional gyrotropic material platforms
where the need for external magnets and bulky materials make it less practical.
Here, instead, we employ a magnet-free mechanism to break reciprocity in 2D
plasmonic materials, e.g., graphene. Specifically, we employ high-speed
drifting electrons on a voltage-biased graphene sheet to lift the
forward/backward degeneracy of the surface plasmon-polariton dispersion,
creating modes with different propagation properties parallel and antiparallel
to the current. We show that controllable, asymmetric, and intense field
hot-spots are generated at the edges of a suitably terminated graphene
metasurface. We then theoretically demonstrate that such asymmetric field
hot-spots offer an effective solution to enhance third-order nonlinear optical
effects. As an example, we predict that, using realistic values of drift
velocity, high third-harmonic conversion efficiencies of up to 0.3 percent are
achievable around the plasmon resonance frequencies
An efficient and stereoselective dearylation of asarinin and sesamin tetrahydrofurofuran lignans to acuminatolide by methyltrioxorhenium/H2O2 and UHP systems
The synthesis of stereoisomers of acuminatolide is rare and requires complex and time-consuming multistep procedures. Asarinin (1) and sesamin (2), two diasteromeric tetrahydrofurofuran lignans, are efficiently mono-dearylated by methyltrioxorhenium (MTO, I) and hydrogen peroxide (H2O2) or urea hydrogen peroxide adduct (UHP) as primary oxidant to give (-)-(7R,8'R,8R)-acuminatolide (3A) and (+)-(7S,8R,8'R)-acuminatolide (3B), respectively, in high yield and diastereoselectivity (de > 98%). The oxidation of 1 was also performed with novel heterogeneous catalysts based on the heterogenation of MTO on poly(4-vinylpyridine) and polystyrene resins. In these latter cases 3A was obtained with a different yield and selectivity depending on the physical-chemical properties of the support. Cytotoxic effects of 3A and 3B in mammalian cell lines in vitro are also reported
Collider searches for dark matter through the higgs lens
Despite the fact that dark matter constitutes one of the cornerstones of the
standard cosmological paradigm, its existence has so far only been inferred
from astronomical observations and its microscopic nature remains elusive.
Theoretical arguments suggest that dark matter might be connected to the
symmetry-breaking mechanism of the electroweak interactions or of other
symmetries extending the Standard Model of particle physics. The resulting
Higgs bosons, including the spin-0 particle discovered
recently at the Large Hadron Collider therefore represent a unique tool to
search for dark matter candidates at collider experiments. This article reviews
some of the relevant theoretical models as well as the results from the
searches for dark matter in signatures that involve a Higgs-like particle at
the Large Hadron Collider
Hypertonicity: Pathophysiologic Concept and Experimental Studies
Disturbances in tonicity (effective osmolarity) are the major clinical disorders affecting cell volume. Cell shrinking secondary to hypertonicity causes severe clinical manifestations and even death. Quantitative management of hypertonic disorders is based on formulas computing the volume of hypotonic fluids required to correct a given level of hypertonicity. These formulas have limitations. The major limitation of the predictive formulas is that they represent closed system calculations and have been tested in anuric animals. Consequently, the formulas do not account for ongoing fluid losses during development or treatment of the hypertonic disorders. In addition, early comparisons of serum osmolality changes predicted by these formulas and observed in animals infused with hypertonic solutions clearly demonstrated that hypertonicity creates new intracellular solutes causing rises in serum osmolality higher than those predicted by the formulas. The mechanisms and types of intracellular solutes generated by hypertonicity and the effects of the solutes have been studied extensively in recent times. The solutes accumulated intracellularly in hypertonic states have potentially major adverse effects on the outcomes of treatment of these states. When hypertonicity was produced by the infusion of hypertonic sodium chloride solutions, the predicted and observed changes in serum sodium concentration were equal. This finding justifies the use of the predictive formulas in the management of hypernatremic states
Electrochemical characterization of organic coatings for protection of historic steel artefacts
Figuras en el archivo zipElectrochemical techniques are mainly known in the field of cultural heritage conservation as a
tool for the elimination of corrosion layers or the removal of chlorides. However, these techniques are also
a valuable tool for assessing the anti-corrosive efficiency of protective coatings. The aim of this study was
to evaluate the performance of different coatings for their use in metallic heritage conservation using
polarization resistance (Rp) and electrochemical impedance spectroscopy (EIS). Carbon steel samples were
prepared to simulate the surface composition and morphology of historic steel artefacts, and coated by a
conservator-restorer following the common practices in conservation treatments. Three commercial organic
coatings have been studied: a microcrystalline wax (RenaissanceTM) and a methyl acrylate/ethyl
methacrylate copolymer resin (ParaloidTM B-72) dissolved in acetone –both them commonly used in
conservation and restoration treatments– and a ethylene copolymer wax emulsion in water (PoligenTM ES-
91009), that has not been used so far for this purposes. Four commercial corrosion inhibitor additives were
added to the ParaloidTM B-72 resin and PoligenTM ES-91009 wax. The additives were commercial
preparations with the following known active components: a blend of triazoles (M435), an ammonium salt
of tricarboxylic acid (M370), a calcium sulphonate (M109), and a bis-oxazoline (Alkaterge-TTM). Rp and
EIS results showed that the best protection of the steel specimens was afforded by PoligenTM ES-91009
when applied in thick layers. None of the additives have shown a clear improvement of the protection
properties of the coatings, and one of them impaired the barrier effect of the coating.Acknowledgements The authors express their gratitude to the Sixth
Framework Programme of the European Commission for financial
support of PROMET Project (Contract 509126). D.M. Bastidas
expresses his gratitude to the CSIC of Spain for his contract under
the I3P Programme, co-financed by the European Social Fund.Peer reviewe
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