ACTIVATION ENERGY OF DESORPTION OF DIBENZOFURAN ON ACTIVATED CARBONS

1. INTRODUCTION With the development of municipalization in China, more and more cities are challenged by the problem of how to dispose of the dramatically increased municipal waste. Generally, most of municipal solid waste is landfilled or dumped openly in the suburbs. It causes not only land waste, but also serious environment pollution. In order to solve efficiently the environment pollution caused by municipal solid waste, incineration technique was introduced in some big cities such…     

Studies of layered uranium(VI) compounds. III. Structural investigations of hydrogen uranyl phosphate and arsenate tetrahydrates below the respective transition temperatures of 274 and 301°K

The layered hydrates HUO₂PO₄·4H₂O (HUP), and HUO₂AsO₄·4H₂O (HUAs), which are protonconducting solid electrolytes above the conductivity transitions at 274 and 301°K, respectively, have been shown, using powder X-ray diffraction, to change from tetragonal to orthorhombic symmetry below these temperatures. For HUP the unit-cell dimensions were a = 6.985(5) and c = 17.45(1)Å at 290°K, and a = 6.966(5), b = 7.004(5), and c = 17.43(1)Å at 260°K. The values for HUAs were a = 7.150(2) and c = 17.608(5)Å, at 305°K, and a = 7.128(2), b = 7.168(2), and c = 17.613(5)Å at 293°K. The enthalpies of these displacive-type transitions were found from differential scanning calorimetry to be less than 0.5 kJ per mole of water for both compounds. Such a small value indicates that the rigid-like water lattices existing below the transitions do not become liquid-like above the transitions. The infrared spectra of HUP and HUAs both above the transitions, and down to 80°K, showed clear evidence of the presence of H₃O⁺ ions, showing that the conductivity transitions are not caused by a loss of carriers. Rather, the antiferroelectric ordering, known to exist for HUAs, would appear to cause the conductivity drop. Upon this indication of ordering within the water layers, two possible related H-bond ordered structures have been proposed which are consistent with the observed twinning behavior and cell symmetry. The same ordered structures are suggested for HUP from our observations of the twinning behavior.     

Laser-diode wavelength tuning based on butt coupling into an optical fiber

An extremely short external cavity that is realized when a Fabry-Perot laser diode is butt coupled to a waveguide or a fiber produces feedback that is effective for controlled wavelength tuning. We used butt coupling to tune a high-output-power laser diode over a wide range (as great as 15 nm) while maintaining constant driving current and temperature. Single-mode or multimode operation repeatedly occurred at specific points throughout the tuning range. An analytical model that includes the effect of multiple reflections from the external cavity, each attenuated by a modal overlap integral, and which is based on phenomenological principles, shows good agreement with the experimental results.     

Nitrile oxide cycloaddition routes to 2-(isoxazolyl)-benzoates and 2-(1,2,4-oxadiazol-3-yl)benzoates

Cycloaddition of aromatic nitrile oxides to methyl o-vinylbenzoate produced methyl 2-(3-aryl-2-isoxazolin-5-yl)benzoates; the isoxazolines were converted to methyl 2-(3-arylisoxazol-5-yl)benzoates. Reaction of the nitrile oxide from o-methoxycarbonylbenzohydroximinoyl chloride ( 11 ) with phenylacetylene, styrenes, and aromatic nitriles resulted in methyl 2-(5-phenylisoxazol-3-yl)benzoate, methyl 2-(5-aryl-2-isoxazolin-3-yl)-benzoates ( 15 ), and methyl 2-(5-aryl-1,2,4-oxadiazol-3-yl)benzoates, respectively. The isoxazolines 15 were converted to the corresponding isoxazoles 16 .     

Decreased surfactant activity coefficients in polymer-surfactant mixtures

The SDS unimer concentration in a series of mixed anionic/non-ionic surfactant solutions comprising sodium dodecylsulphate (SDS) and sugar-based dodecyl bis-N-methyl gluconamides (C₁₂BNMG) have been studied using an anionic surfactant selective electrode, both in the presence and absence of the polyampholyte gelatin. The activity of the SDS has been calculated at the critical micelle concentration (CMC) in the gelatin-free studies and at CMC(1) in the gelatin studies. From the known solution composition, the activity coefficients can be calculated; these show deviations from unity around a solution mole fraction (_SDS) of 0.95 SDS in both cases. The deviation is significantly greater in the presence of gelatin, to an extent that the SDS activity versus _SDS curve exhibits a maximum and a minimum in the region _SDS=0.8–1.0, consistent with the possibility of coexisting micelle types, in agreement with our earlier NMR study (Griffiths et al. (1998) J Chem Soc Chem Comm 1:53).     

The ultra-violet question in maximally supersymmetric field theories

We discuss various approaches to the problem of determining which supersymmetric invariants are permitted as counterterms in maximally supersymmetric super Yang–Mills and supergravity theories in various dimensions. We review the superspace non-renormalisation theorems based on conventional, light-cone, harmonic and certain non-Lorentz covariant superspaces, and we write down explicitly the relevant invariants. While the first two types of superspace admit the possibility of one-half BPS counterterms, of the form F ⁴ and R ⁴ respectively, the last two do not. This suggests that UV divergences begin with one-quarter BPS counterterms, i.e. d ² F ⁴ and d ⁴ R ⁴, and this is supported by an entirely different approach based on algebraic renormalisation. The algebraic formalism is discussed for non-renormalisable theories and it is shown how the allowable supersymmetric counterterms can be determined via cohomological methods. These results are in agreement with all the explicit computations that have been carried out to date. In particular, they suggest that maximal supergravity is likely to diverge at four loops in D = 5 and at five loops in D = 4, unless other infinity suppression mechanisms not involving supersymmetry or gauge invariance are at work.     

Phenazines as model low-midpoint potential electron shuttles for photosynthetic bioelectrochemical systems

Bioelectrochemical approaches for energy conversion rely on efficient wiring of natural electron transport chains to electrodes. However, state-of-the-art exogenous electron mediators give rise to significant energy losses and, in the case of living systems, long-term cytotoxicity. Here, we explored new selection criteria for exogenous electron mediation by examining phenazines as novel low-midpoint potential molecules for wiring the photosynthetic electron transport chain of the cyanobacterium Synechocystis sp. PCC 6803 to electrodes. We identified pyocyanin (PYO) as an effective cell-permeable phenazine that can harvest electrons from highly reducing points of photosynthesis. PYO-mediated photocurrents were observed to be 4-fold higher than mediator-free systems with an energetic gain of 200 mV compared to the common high-midpoint potential mediator 2,6-dichloro-1,4-benzoquinone (DCBQ). The low-midpoint potential of PYO led to O₂ reduction side-reactions, which competed significantly against photocurrent generation; the tuning of mediator concentration was important for outcompeting the side-reactions whilst avoiding acute cytotoxicity. DCBQ-mediated photocurrents were generally much higher but also decayed rapidly and were non-recoverable with fresh mediator addition. This suggests that the cells can acquire DCBQ-resistance over time. In contrast, PYO gave rise to steadier current enhancement despite the co-generation of undesirable reactive oxygen species, and PYO-exposed cells did not develop acquired resistance. Moreover, we demonstrated that the cyanobacteria can be genetically engineered to produce PYO endogenously to improve long-term prospects. Overall, this study established that energetic gains can be achieved via the use of low-potential phenazines in photosynthetic bioelectrochemical systems, and quantifies the factors and trade-offs that determine efficacious mediation in living bioelectrochemical systems.

Phenazines were explored as novel low-midpoint potential molecules for wiring cyanobacteria to electrodes.