Towards ultra-responsive biodegradable polysaccharide humidity sensors

Sodium alginate is a biodegradable natural polymer that is derived from algae and is water soluble. Upon immersion in a CaCl₂ solution, a sodium alginate water solution is cross-linked to form water-insoluble calcium alginate. When the sodium alginate water solution is immersed in the CaCl₂ bath via a syringe pump, calcium alginate fibers are produced. By changing the CaCl₂ concentration, calcium alginate fibers with different degrees of cross-linking can be produced. Such fibers were found to differ in mechanical and morphological properties, and more interestingly, were found to possess humidity sensing and conductive properties. Interestingly, the higher the CaCl₂ concentration, the lower the degree of cross-linking, which produced softer fibers with better humidity sensing and conductive properties. The fibers were able to trap water in their structures, and a higher water content increased the conductivity due to the presence of an electrolyte salt in the fiber and due to the polyelectrolyte nature of the fiber itself. The cross-linking and percent shrinking degree, morphology and mechanical properties of the fibers were found to create significant changes in the conductivity and humidity sensing properties of the fibers. High humidity environments led to an increase in the conductivity of the fibers, whereas dry environments led to a decrease in the conductivity. The fibers, especially those with the highest CaCl₂ concentration, were determined to be ultra-responsive to humidity changes and exhibited very good repetition in humidity cycles. These tailored fibers are proposed as novel biodegradable conductive materials for various humidity sensing, robotic and bio-robotic applications.     

Optimal investment in markets with over and under-reaction to information

In this paper we introduce a jump-diffusion model of shot-noise type for stock prices, taking into account over and under-reaction of the market to incoming news. We work in a partial information setting, by supposing that standard investors do not have access to the market direction, the drift, (modeled via a random variable) after a jump. We focus on the expected (logarithmic) utility maximization problem by providing the optimal investment strategy in explicit form, both under full (i.e., from the insider point of view, aware of the right kind of market reaction at any time) and under partial information (i.e., from the standard investor viewpoint, who needs to infer the kind of market reaction from data). We test our results on market data relative to Enron and Ahold. The three main contributions of this paper are: the introduction of a new market model dealing with over and under-reaction to news, the explicit computation of the optimal filter dynamics using an original approach combining enlargement of filtrations with Innovation Theory and the application of the optimal portfolio allocation rule to market data.     

Local search algorithms for finding the Hamiltonian completion number of line graphs

Given a graph G=(V,E), the Hamiltonian completion number of G, HCN(G), is the minimum number of edges to be added to G to make it Hamiltonian. This problem is known to be -hard even when G is a line graph. In this paper, local search algorithms for finding HCN(G) when G is a line graph are proposed. The adopted approach is mainly based on finding a set of edge-disjoint trails that dominates all the edges of the root graph of G. Extensive computational experiments conducted on a wide set of instances allow to point out the behavior of the proposed algorithms with respect to both the quality of the solutions and the computation time.     

Effects of mutational (Lys to Ala) surface charge changes on the redox properties of electrode-immobilized cytochrome c

Untrimethylated yeast iso-1-cytochrome c (cytc) and its single and multiple Lys to Ala variants at the surface lysines 72, 73, and 79 were adsorbed on carboxyalkanethiol self-assembled monolayers (SAMs) on gold, and the thermodynamics and kinetics of the heterogeneous protein-electrode electron-transfer (ET) reaction were determined by voltammetry. The reaction thermodynamics were also measured for the same species freely diffusing in solution. The selected lysine residues surround the heme group and contribute to the positively charged domain of cytc involved in the binding to redox partners and to carboxyl-terminated SAM-coated surfaces. The E degrees' (standard reduction potential) values for the proteins immobilized on SAMs made of 11-mercapto-1-undecanoic acid and 11-mercapto-1-undecanol on gold were found to be lower than those for the corresponding diffusing species owing to the stabilization of the ferric state by the negatively charged SAM. For the immobilized proteins, Lys to Ala substitution(s) do not affect the surface coverage, but induce significant changes in the E degrees' values, which do not simply follow the Coulomb law. The results suggest that the species-dependent orientation of the protein (and thereby of the heme group) toward the negatively charged SAM influences the electrostatic interaction and the resulting E degree' change. Moreover, these charge suppressions moderately affect the kinetics of the heterogeneous ET acting on the reorganization energy and the donor-acceptor distance. The kinetic data suggest that none of the studied lysines belong to the interfacial ET pathway.     

Optical properties of emeraldine salt polymers from ab initio calculations: comparison with recent experimental data

We present the absorption coefficient alpha(omega), the transverse dielectric function epsilon(omega), the optical conductivity sigma(omega), and the reflectance R(omega) calculated for an emeraldine salt conducting polymer in its crystalline 3D polaronic structure. We utilize Kohn-Sham density functional theory (DFT) electronic wavefunctions and energies implemented in the expression of the macroscopic transverse dielectric function in the framework of the band theory without the electron-hole interaction. Contributions of intra-band transitions are taken into account by adding a Drude-like term to the dielectric function calculated ab initio. Comparison with optical properties, recently measured on high-quality emeraldine salts (Lee, K.; Cho, S.; Park, S. H.; Heeger, A. J.; Lee, C.-W.; Lee, S. H. Nature 2006, 441, 65), and with optical absorption spectra, recorded on other emeraldine salts, is very satisfactory. The calculated spectra are discussed in terms of energy-band structure, density of states, inter- and intra-band transitions, and transverse dielectric function.     

Relative stereochemistry of a diterpene from Salvia cinnabarina

The relative stereochemistry of 3,4-secoisopimara-4(18),7,15-triene-3-oic acid, a diterpenoid with antispasmodic, hypotensive and antibacterial activities isolated from Salvia cinnabarina, was determined by an X-ray diffraction analysis of a single crystal of a suitable crystalline derivative.     

Theory, measurements, and modeling of OH and HO2 formation in the reaction of cyclohexyl radicals with O2

The production of OH and HO(2) in Cl-initiated oxidation of cyclohexane has been measured using pulsed-laser photolytic initiation and continuous-laser absorption detection. The experimental data are modeled by master equation calculations that employ new G2(MP2)-like ab initio characterizations of important stationary points on the cyclo-C(6)H(11)O(2) surface. These ab initio calculations are a substantial expansion on previously published characterizations, including explicit consideration of conformational changes (chair-boat, axial-equatorial) and torsional potentials. The rate constants for the decomposition and ring-opening of cyclohexyl radical are also computed with ab initio based transition state theory calculations. Comparison of kinetic simulations based on the master equation results with the present experimental data and with literature determinations of branching fractions suggests adjustment of several transition state energies below their ab initio values. Simulations with the adjusted values agree well with the body of experimental data. The results once again emphasize the importance of both direct and indirect components of the kinetics for the production of both HO(2) and OH in radical + O(2) reactions.     

Reactivity of Ti(IV) species hosted in TS-1 towards H2O2-H2O solutions investigated by ab initio cluster and periodic approaches combined with experimental XANES and EXAFS data: a review and new highlights

This work is intended to underline how the most-advanced experimental and theoretical physical chemistry tools must be used synergistically to understand the reactivity of Ti-silicalite-1 (TS-1) in an important number of low-temperature oxidation reactions with aqueous H(2)O(2) as the oxidant. Literature results are carefully reviewed and accompanied with new, unpublished highlights of both experimental and computational origin. The first part of this work is devoted to a discussion of the defective nature of the material and to the synergic role played by Si vacancies and Ti insertion in the framework. A summary of the experimental Ti-K-edge EXAFS and XANES literature concerning the activated material in vacuo conditions is then presented and compared to the corresponding Ti geometries obtained by ab initio calculations. From such a comparison, the excellent agreement between experiment and theory is evident. A very good agreement is also obtained for the interaction with water and ammonia. For both H(2)O and NH(3), the agreement is due to the possibility to perform experiments in which the probe molecule is dosed from the gas phase, thus allowing to reach the 1 : 1 (or 1 : 2) ratio between the adsorbing Ti sites and the adsorbed molecule. Then, interaction with hydrogen peroxide is discussed, underlining the problems faced in reaching a common view between experimental and theoretical results, owing to the difficulties both in performing experiments where anhydrous H(2)O(2) is dosed on TS-1, and in taking into account the role played by the aqueous medium in the reactivity of Ti(iv) centres toward H(2)O(2) using ab initio calculations. Only once such difficulties have been overcome, by increasing the complexities of both experiments and ab initio models, is a joint-view finally obtained. Where needed, comparison with other experimental results (X-ray and neutron diffraction, NMR, IR, Raman, UV-vis and resonant Raman) is made.     

Magnetic structures produced by the small-scale dynamo

Small-scale dynamo action has been obtained for a flow previously used to model fluid turbulence, where the sensitivity of the magnetic field parameters to the kinetic energy spectrum can be explored. We apply quantitative morphology diagnostics, based on the Minkowski functionals, to magnetic fields produced by the kinematic small-scale dynamo to show that magnetic structures are predominantly filamentary rather than sheetlike. Our results suggest that the thickness, width, and length of the structures scale differently with magnetic Reynolds number as R(m)(-2/(1-s)) and R(m)(-0.55} for the former two, whereas the latter is independent of R(m), with s the slope of the energy spectrum.     

Surface heterogeneity study of some reference Cu–Ag alloys using laser‐induced breakdown spectroscopy

Investigation of the chemical composition, surface structure, metallurgical features, corrosion mechanism, and surface modification techniques of archeological metallic artifacts from Romans and pre‐Roman times aimed to simulate the most commonly used Cu‐based and Ag‐based alloys. These simulated reference alloys will be used as sacrificial materials to study the most appropriate conservation materials and procedures. In the present work, laser‐induced breakdown spectroscopy (LIBS) is introduced as a new validated surface mapping technique to study the micro‐chemical distribution of elements in binary reference copper–silver alloy samples. Using different techniques for surface and bulk analysis, such as SEM coupled with energy‐dispersive X‐ray spectroscopy and X‐ray diffraction, it has been proven that LIBS is a simple, sensitive, and direct technique in the determination of heterogeneity of the sample's surface. By changing the laser wavelength (λ/nm) and focal length of the used focusing lens (f/cm), different spot sizes can be obtained. It was possible to control the spatial resolution in mapping the investigated samples' surface and to achieve local chemical information. In the present work, Q‐switched neodymium‐doped yttrium aluminum garnet laser has been used at its fundamental wavelength 1064 nm and its second harmonic 532 nm. The studied samples were specially manufactured heterogeneous copper–silver alloys with known grain size as studied via SEM investigation. The obtained LIBS results are in good agreement with those by other analytical techniques and extend the applicability of the surface techniques to study metallic ancient objects. Copyright © 2015 John Wiley & Sons, Ltd.