A weight-function approach for determining watershed initial conditions for combustion waves

In many generic combustion models, one finds that a combustionwave will develop with a specific wave speed. However, thereare possible initial temperature profiles which do not evolveinto such waves, but rather die out to the ambient temperature.There can exist, in some models, a clear distinction betweenthose initial conditions that do evolve into combustion wavesand those that do not; this is sometimes referred to as thewatershed initial condition. When fuel consumption is consideredto be negligible, analytical methods can be used to obtain theexact watershed. In this paper, we consider the problem of determiningpseudo-watersheds and ascertaining the relationship betweenthese pseudo-watersheds and the exact watersheds. In the processa novel weight-function approach for infinite spatial domainsis developed.     

Self-powered sensors

One of the problems associated with miniaturization and portability of sensors is the power supply. Power supplies, such as batteries, are difficult to miniaturize and require a sensor design that allows for easy replacement or recharging. This review describes the field of self-powered sensing, where the sensor itself provides the power for the sensing device. Most self-powered-sensing strategies employ either nuclear energy conversion or electrochemical energy conversion. Nuclear energy conversion is employed for radioisotope or nuclear reactor sensing. Electrochemical energy conversion is employed for chemical and biological sensing. This review details the common strategies for self-powered nuclear, chemical, and biological sensing and discusses the future of the technology.     

Dual fluorescence from an isonido ReIII rhenacarborane phosphine complex, [7,10-mu-H-7-CO-7,7-(PPh3)2-isonido-7,8,9-ReC2B7H9

The complex [7,10-mu-H-7-CO-7,7-(PPh3)2-isonido-7,8,9-ReC2B7H9] has been synthesized by treatment of the complex salt [NHMe3][3,3-Cl2-3,3-(CO)2-closo-3,1,2-ReC2B9H11] with PPh3 in refluxing THF (tetrahydrofuran) and isolated as intensely colored orange-red microcrystals. Spectroscopic NMR and IR data have suggested that the product has a highly asymmetric structure with two inequivalent PPh3 ligands and a single CO ligand. Measurement of 11B NMR spectra in particular have indicated seven distinct boron vertexes, although the resulting cage degradation by removal of two BH vertexes was confirmed only following X-ray crystallographic analysis, which revealed the pentadecahedral isonido-7,8,9-ReC2B7 architecture. The 11B NMR resonances span an enormous chemical shift range (Deltadelta = 113), and this appears to be a direct consequence of the deshielding of the boron vertex directly opposite the quadrilateral |ReCCB| aperture. The new complex has been shown by electrochemical measurements to undergo a reversible one-electron oxidation. Digitally simulated cyclic voltammograms support a proposed square scheme (E(1/2) = 0.58, 0.69 V vs ferrocene) involving a reversible isonido-closo transition of the metallacarborane cage. Most unusually for a metallacarborane complex, ambient temperature solutions in CH2Cl2 and DMF have been shown to be intensely turquoise-blue fluorescent (lambda(em) = 442 nm, Phi = 0.012). Fluorescence spectroscopy measurements in MeTHF (2-methyltetrahydrofuran) glass at 77 K have indicated that the likely cause of such a broad emission is dual fluorescence (lambda(em) = 404, 505 nm), with both emissions displaying vibronic structure. Following excited-state lifetime decay analysis, the emissive behavior has been accredited to metal-perturbed 1IL states, with the lower energy emission arising from a slight geometric distortion of the initially excited complex.     

Nicotinamide Adenine Dinucleotide Oxidation Studies at Multiwalled Carbon Nanotube/Polymer Composite Modified Glassy Carbon Electrodes

NADH oxidation has previously been investigated at carbon nanotube surfaces, although studies into the effect of the polymer binders are needed to fully understand whether the polymer binder affects the electrochemistry. This work details NADH oxidation at glassy carbon electrodes modified with composites containing multiwalled carbon nanotubes and selected polymer binders. NADH is shown to be oxidized at a lower potential than at glassy carbon electrodes and the oxidation potential is a function of the polymer binder. Hydrophobically modified Nafion, Nafion, linear poly(ethylenimine) (LPEI), octyl‐modified LPEI, and poly(vinylpyridine) binders were studied. Experiments showed the peak current and electrochemically assessible electrode area are dependent on the polymer binder. Overall, this paper shows that polymer binders affect NADH oxidation potential at carbon nanotube modified electrodes.     

Electrocatalytic reductive dimerization of the 2,2′-bipyridyl tungsten alkylidyne complex [W(CC6H4NMe2-4)(NCMe)(CO)2{κ-2,2′-(NC5H4)2}]

Potentiometric measurements have shown that the cationic 2,2′-bipyridyl tungsten alkylidyne complex [W(CC₆H₄NMe₂-4)(NCMe)(CO)₂{κ²-2,2′-(NC₅H₄)₂}][PF₆] (2) is electroactive in MeCN solution with a reduction (E_pc ≈ −1.0 V vs. ferrocene) leading to complex dimerization, identified by a number of electrochemical markers. Multiple redox cycles have led to the partial deposition of the dimerized product on the electrode surface, which appears to electrocatalyze subsequent coupling cycles. Comparison with electrochemical measurements of related alkylidyne complexes, including the precursor complex [W(CC₆H₄NMe₂-4)(O₂CCF₃)(CO)₂{κ²-2,2′- (NC₅H₄)₂}] (1), has provided indirect evidence of intermolecular bond formation between κ²-2,2′-bipyridyl ligands. The cationic complex 2 has additionally been the subject of gamess computational analysis, revealing calculated ν_max(CO) stretching absorptions in good agreement with measured parameters. This study has also permitted a molecular orbital analysis, which has indicated an energy-accessible LUMO almost entirely located on the 2,2′-bipyridyl ligand of complex 2, the purported site for dimerization. It is believed that occupation of this orbital upon reduction of compound 2 leads to a short-lived metastable precursor to 2,2′-bipyridyl ring coupling. Furthermore, a very weak π-antibonding interaction of the metal-alkylidyne π-framework with the MeCN ligand in the occupied frontier molecular orbitals of complex 2 has been noted and compared with a surprisingly significant π interaction with the carboxylate group in complex 1.     

Electroenzymatic Nitrogen Fixation Using a MoFe Protein System Immobilized in an Organic Redox Polymer

We report an organic redox‐polymer‐based electroenzymatic nitrogen fixation system using a metal‐free redox polymer, namely neutral‐red‐modified poly(glycidyl methacrylate‐co‐methylmethacrylate‐co‐poly(ethyleneglycol)methacrylate) with a low redox potential of ?0.58 V vs. SCE. The stable and efficient electric wiring of nitrogenase within the redox polymer matrix enables mediated bioelectrocatalysis of N₃^?, NO₂^? and N₂ to NH₃ catalyzed by the MoFe protein via the polymer‐bound redox moieties distributed in the polymer matrix in the absence of the Fe protein. Bulk bioelectrosynthetic experiments produced 209±30 nmol NH₃ nmol MoFe^?1 h^?1 from N₂ reduction. ¹⁵N₂ labeling experiments and NMR analysis were performed to confirm biosynthetic N₂ reduction to NH₃.     

Characterization and Stability Study of Immobilized PQQ‐Dependent Aldose Dehydrogenase Bioanodes

In this paper, glucose oxidizing bioanodes employing immobilized PQQ‐dependent aldose dehydrogenase were prepared and characterized. The enzyme was immobilized on carbon paper in two different polymeric systems: tetrabutylammonium bromide (TBAB) modified Nafion and butanal modified chitosan. Characterization of the bioanodes included electron microscopy, electrochemical evaluation, as well as stability and leaching studies. Results indicate that the operational degradation was the same but the long term storage stability is better in the case of modified Nafion. The performance of the modified Nafion immobilized bioanodes stayed at 70 % of the initial value after 60 days of storing at 4 °C and 25 °C. Compared to TBAB modified Nafion immobilized bioanodes, butanal modified chitosan immobilized bioanodes showed 50 % activity after eight weeks storage at 4°C and one week storage at 25 °C. However, the electrochemical properties of modified chitosan were better.     

Enzymatic Electrosynthesis of Alkanes by Bioelectrocatalytic Decarbonylation of Fatty Aldehydes

An enzymatic electrosynthesis system was created by combining an aldehyde deformylating oxygenase (ADO) from cyanobacteria that catalyzes the decarbonylation of fatty aldehydes to alkanes and formic acid with an electrochemical interface. This system is able to produce a range of alkanes (octane to propane) from aldehydes and alcohols. The combination of this bioelectrochemical system with a hydrogenase bioanode yields a H₂/heptanal enzymatic fuel cell (EFC) able to simultaneously generate electrical energy with a maximum current density of 25 μA cm^?2 at 0.6 V and produce hexane with a faradaic efficiency of 24 %.     

Creating a Low‐Potential Redox Polymer for Efficient Electroenzymatic CO2 Reduction

Increasing greenhouse gas emissions have resulted in greater motivation to find novel carbon dioxide (CO₂) reduction technologies, where the reduction of CO₂ to valuable chemical commodities is desirable. Molybdenum‐dependent formate dehydrogenase (Mo‐FDH) from Escherichia coli is a metalloenzyme that is able to interconvert formate and CO₂. We describe a low‐potential redox polymer, synthesized by a facile method, that contains cobaltocene (grafted to poly(allylamine), Cc‐PAA) to simultaneously mediate electrons to Mo‐FDH and immobilize Mo‐FDH at the surface of a carbon electrode. The resulting bioelectrode reduces CO₂ to formate with a high Faradaic efficiency of 99±5 % at a mild applied potential of ?0.66 V vs. SHE.