Buffer Standards for the Physiological pH of Zwitterionic Compounds,MOBS and TABS from 5 to 55°C

The values of the second dissociation constant, pK₂, and related thermodynamic quantities of 4-(N-morpholino)butanesulfonic acid (MOBS) and N-tris(hydroxymethyl)-4-aminobutanesulfonic acid (TABS) have already been reported over the temperature range 5–55°C including 37{°}C. This paper reports the pH values of twelve equimolal buffer solutions at designated pH (s) with the following compositions: (a) mixtures of MOBS (0.05 mol-kg^–1) + NaMOBS (0.05 mol-kg^–1); (b) MOBS (0.08 mol-kg^–1) + NaMOBS (0.08 mol-kg^–1); (c) MOBS (0.08 mol-kg^–1) + NaMOBS (0.08 mol-kg^–1) + NaCl (0.08 mol-kg^–1); (d) TABS (0.05 mol-kg^–1) + NaTABS (0.05 mol-kg^–1); and (e) TABS (0.08 mol-kg^–1) + NaTABS (0.08 mol-kg^–1); and (f) TABS (0.08 mol-kg^–1) + NaTABS (0.08 mol-kg^–1) + NaCl (0.08 mol-kg^–1). Two buffer solutions have ionic strengths I= 0.05 mol-kg^–1, another two have I=0.08 mol-kg^–1, and the remaining two buffer solutions have I= 0.16 mol-kg^–1, which is close to that of the clinical fluids (blood serum). These buffers have been recommended as a useful pH standard for the measurements of physiological solutions. Conventional pH values of all six buffer solutions from 5–55°C, as well as those obtained from the liquid junction potential correction at 25 and 37{°}C have been calculated. The flowing-junction calomel cell has been utilized to measure E_j, the liquid junction potential.     

Thermodynamics of the Second Dissociation Constant of N-tris[Hydroxymethyl]-4-amino-butanesulfonic Acid (TABS) from 5 to 55°C

N-tris[Hydroxymethyl]-4-aminobutanesulfonic acid (TABS) has been investigated for the determination of the values of the second dissociation constant, pK ₂, in water at 12 temperatures in the range 5–55°C, including 37°C. This zwitterionic compound is useful as a secondary pH standard in the range of pH (7–9) for physiological applications. The electromotive force (emf) measurements have been carried out using a hydrogen gas electrode and a silver–silver chloride electrode. The values of pK ₂ are fitted as a function of temperature with the following results: pK ₂ = 1671.305/T+14.8737–2.04383 ln T, where T is the thermodynamic temperature in Kelvins. The experimental values of pK ₂ are 8.834 ± 0.0005 and 8.539 ± 0.0004 at 25 and 37°C, respectively. The related thermodynamic quantities, G°, H°, S°, and C _p ° characterizing the dissociation process have been derived from the pK ₂ and its temperature coefficients.     

Photorecovery of nanoparticles from an organic solvent

Commercial silica nanoparticles were dispersed in toluene, stabilized by a mixture of sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and a photolyzable anionic surfactant sodium hexylphenylazosulfonate (C6PAS). Selective photolysis of the interfacial C6PAS component induces colloid instability, resulting in flocculation and eventual phase separation of the silica nanoparticles. UV-vis spectroscopy was used to follow the photochemical breakdown of C6PAS; diffusion coefficient measurements by dynamic light scattering were employed to monitor the photoinduced flocculation; and silica contents in the toluene, before and after UV light irradiation, were determined gravimetrically. The results show that light can be used to trigger separation and recovery of nanoparticles stabilized by photolabile interfacial layers.     

Controlled dispersion of polystyrene‐capped Au nanoparticles in P3HT:PC61BM and consequences upon active layer nanostructure

Numerous recent publications detail higher absorption and photovoltaic performance within organic photovoltaic (OPV) devices which are loaded with Au or Ag nanoparticles to leverage the light management properties of the localized surface plasmon resonance (LSPR). This report details the impact upon film morphology and polymer/nanoparticle interactions caused by incorporation of polystyrene‐coated Au nanoparticles (Au/PS) into the P3HT:PC₆₁BM bulk heterojunction film. Nanostructural analysis by transmission electron microscopy and X‐ray scattering reveals tunable Au/PS particle assembly that depends upon the choice of casting solvent, polymer chain length, film drying time, and Au/PS particle loading density. This Au/PS particle assembly has implications on the spectral position of the Au nanoparticle LSPR, which shifts from 535 nm for individually dispersed particles in toluene to 650 nm for particles arranged in large clusters within the P3HT:PC₆₁BM matrix. These results suggest a critical impact from PS/P3HT phase separation, which causes controlled assembly of a separate Au/PS phase in the nanoparticle/OPV composite; controlled Au/PS phase formation provides a blueprint for designing AuNP/OPV hybrid films that impart tunable optical behavior and potentially improve photovoltaic performance. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 709–720     

Visualisation of results from LES of combustion

We examine the role of visualisation in the context of LES simulations of premixed turbulent combustion. The physical processes involved in premixed turbulent combustion are extremely complex, and the modelling of both the turbulence (via LES) and the combustion (via flame-wrinkling models) is difficult. Appropriate visualisation is required to understand the behaviour of the models, and ultimately to understand better the flow processes which are important in many industrial applications. We examine visualisations of two specific cases; simple flame kernel growth in a box of turbulence, and combustion behind a backward-facing step. A number of visualisation techniques are used to produce results that are similar to experimentally determined Schlieren and Mie photography for the flame kernel. In addition, isosurfaces of the reaction regress variable coloured by the laminar flame speed and sub-grid wrinkling are also plotted in an attempt to gain deeper insight into the physics of turbulent combustion in the context of these particular cases. Finally we discuss the role of the WWW in the continuing development of scientific visualisation techniques.     

Reversible pH‐ and Photocontrollable Carbohydrate‐Based Surfactants

The parallel synthesis and properties of a library of photoswitchable surfactants comprising a hydrophobic butylazobenzene tail‐group and a hydrophilic carbohydrate head‐group, including the first surfactants to exhibit dual photo‐ and pH‐responsive behavior, is reported. This new generation of surfactants shows varying micelle morphologies, photocontrollable surface tension, and pH‐induced aggregation and adsorption.     

Applications of Inverse Limits to Extensions of Operators and Approximation of Lipschitz Functions

We consider extensions of linear operators from finite dimensional subspaces. As a corollary of Steenrod's theorem about inverse limits of topological spaces, we obtain new results concerning approximation in tensor product spaces and the stability of the Cauchy functional equation.     

On the division by R n

Summary In this paper we prove that, ifS ×R ⁿ is homeomorphic toR ^{n + 1}, thenS is homeomorphic toR.     

Expansivity and Cone-fields in Metric Spaces

Due to the results of Lewowicz and Tolosa expansivity can be characterized with the aid of Lyapunov function. In this paper we study a similar problem for uniform expansivity and show that it can be described using generalized cone-fields on metric spaces. We say that a function \(f:X\rightarrow X\) is uniformly expansive on a set \(\varLambda \subset X\) if there exist \(\varepsilon >0\) and \(\alpha \in (0,1)\) such that for any two orbits \(\hbox {x}:\{-N,\ldots ,N\} \rightarrow \varLambda \) , \(\hbox {v}:\{-N,\ldots ,N\} \rightarrow X\) of \(f\) we have $$\begin{aligned} \sup _{-N\le n\le N}d(\hbox {x}_n,\hbox {v}_n) \le \varepsilon \implies d(\hbox {x}_0,\hbox {v}_0) \le \alpha \sup _{-N\le n\le N}d(\hbox {x}_n,\hbox {v}_n). \end{aligned}$$ It occurs that a function is uniformly expansive iff there exists a generalized cone-field on \(X\) such that \(f\) is cone-hyperbolic.     

Imaging cytoplasmic cAMP in mouse brainstem neurons

Background  

cAMP is an ubiquitous second messenger mediating various neuronal functions, often as a consequence of increased intracellular Ca²⁺ levels. While imaging of calcium is commonly used in neuroscience applications, probing for cAMP levels has not yet been performed in living vertebrate neuronal tissue before.