Effect of sodium bicarbonate ingestion on exhaustive resistance exercise performance

Six weight trained males were studied prior to, during, and in recovery from exhaustive resistance exercise, 105 min after ingesting 300 mg.kg-1 of either a placebo or NaHCO3. The exercise test consisted of four sets of 12 repetitions with a fifth set to volitional fatigue on a Universal leg press machine at a resistance equaling approximately 70% of the subjects 1-repetition maximum. Arterialized venous blood was analyzed for lactate concentration, blood gas, and acid-base parameters. The ingestion of NaHCO3 produced a significant increase in resting pH (7.39 to 7.46), HCO3- (22.9 to 28.3 mEq.l-1), and oxygenated base excess (-1.3 to 4.4 mEq.l-1). With the completion of each exercise set, a progressive decline in the acid-base status of both groups was observed (pH set 1-5: NaHCO3, 7.40 to 7.31; placebo, 7.34 to 7.25; HCO3- set 1-5: NaHCO3, 25.3 to 17.9; placebo, 21.7 to 15.3 mEq.l-1; base excess set 1-5: NaHCO3, 3.7 to -7.1; placebo, -1.4 to -10.7 mEq.l-1); however, the NaHCO3 condition was significantly more alkaline than the placebo condition. Blood lactate concentration [La] progressively increased with the completion of each exercise set ([La] set 1-5: NaHCO3, 1.37 to 11.15; placebo, 1.31 to 9.81 mM); but were not significantly different between treatments. Repetitions performed in the final exercise set were not significantly different between groups (NaHCO3: 19.6 +/- 1.6, placebo: 18.2 +/- 1.1 repetitions).(ABSTRACT TRUNCATED AT 250 WORDS)     

The use of THz time-domain reflection measurements to investigate solvent diffusion in polymers

Solvent diffusion into polymers is central to their performance, for example as controlled delivery pharmaceutical products. In this work, we present the novel application of terahertz (THz) time-domain reflectance spectroscopy to quantify the ingress of acetone into various polymer materials. Reflections from the top and bottom surfaces of the discs are temporally resolved, as is a reflection from the interface between acetone-wet polymer and dry polymer. These reflections enable both the polymer swelling and more importantly the position of the liquid diffusion front to be quantified as a function of time. Verification of these measurements is provided by equivalent magnetic resonance imaging (MRI) measurements, with which there is excellent agreement.     

Oscillations in gas-fluidized beds: Ultra-fast magnetic resonance imaging and pressure sensor measurements

Ultra-fast Magnetic Resonance Imaging (MRI) and pressure sensor measurements have been applied to study: (i) pressure fluctuations, (ii) the eruption of bubbles at the top of a bed and (iii) the formation of bubbles in a gas-fluidized bed. Ultra-fast MRI has been applied for the first time to study the formation and eruption of bubbles; the technique is non-intrusive and provides measurements with good temporal and spatial resolutions. The MRI measurements revealed that bubbles are formed periodically, rather than randomly at a distributor, which in this case was a perforated plate. The frequency at which bubbles erupted from the top of the bed matched the frequency of the pressure fluctuations measured just above the distributor, where the measured pressure is predicted very well for the case of slug flow by Kehoe and Davidson's [P.W.K. Kehoe, J.F. Davidson, Pressure fluctuations in slugging fluidized beds, AIChE Symp. Ser. 128 (69) (1973) 34-40] correlation, originally developed for locations high up a bed. Both findings lead to the conclusion that the passage and eruption of bubbles at the top of a bed are the dominant cause of the pressure fluctuations, which are subsequently propagated downwards through the bed. Two new correlations are proposed for predicting the frequency of pressure fluctuations in a bubbling bed; both correlations agree well with experimental measurements. A modification of Baeyens and Geldart's [J. Baeyens, D. Geldart, An investigation into slugging fluidized beds, Chem. Eng. Sci. 29 (1974) 255-265] correlation predicts the frequency of pressure fluctuations when slugs are formed, but are not fully developed. The frequency of bubble formation, as measured by MRI, is equal to or higher than both the frequency of bubble eruption at the top of the bed and the frequency of pressure fluctuations, depending on the depth of the bed. The frequency of bubble formation is significantly lower than predicted by Davidson and Schüler's [J.F. Davidson, B.O.G. Schüler, Bubble formation at an orifice in an inviscid liquid, Trans. Inst. Chem. Eng. 38 (1960) 335-342] equation, originally developed for gas-liquid systems.     

Granular temperature: Comparison of Magnetic Resonance measurements with Discrete Element Model simulations

The Discrete Element Model (DEM) is a very promising modelling strategy for two-phase granular systems. However, owing to a lack of experimental measurements, validation of numerical simulations of two-phase granular systems is still an important issue. In this study, a small two-dimensional gas-fluidized bed was simulated using a Discrete Element Model. The dimensions of the simulated bed were 44 × 10 × 120 mm and the fluidized particles had a diameter d_p = 1.2 mm and density ρ_p = 1000 kg m^− 3. The influence of different drag-force correlations was investigated. Preliminary numerical experiments were also performed to study the effects of (i) the coefficient of restitution and (ii) the modelled transverse thickness of the two-dimensional bed. Experimental measurements were made using Magnetic Resonance (MR), with the comparisons between DEM simulations and experimental measurements performed on the basis of the time-averaged velocity and granular temperature profiles of the particles. It was found that the DEM simulations of the time-averaged vertical velocity of the particles agreed well with the MR measurements. The drag-force correlation proposed by [R. Beetstra, M.A. van der Hoef and J.A.M. Kuipers, Drag force of intermediate Reynolds number flow past mono- and bidispersed arrays of spheres. AIChE Journal, 53, 489-501 (2007).] showed the best agreement with the experimental data. Fair agreement was found if the granular temperature calculated by the DEM simulations was compared with MR measurements. At lower fluidization velocities and closer to the distributor the DEM simulations under-predicted both the velocity and the granular temperature measurements using MR.     

Magnetic resonance imaging of fluidized beds: Recent advances

Recent developments in magnetic resonance (MR) imaging techniques give measurements of particle velocities and voidage fractions in a bubbling fluidized bed, with a spatial resolution of approximately 0.6 mm and a time resolution of approximately 2 ms. The particles contained liquid, whose mobile molecules have more favorable relaxation times (T₁, T₂ and T₂^*), than for solids, facilitating rapid MR measurements. Seeds 0.5–2 mm in diameter containing oil and hollow, plastic spheres 1–10 mm in diameter filled with water were used. Published in Russian in Teoreticheskie Osnovy Khimicheskoi Tekhnologii, 2008, Vol. 42, No. 5, pp. 483–493. The text was submitted by the authors in English.     

Characterisation of fluid flow through porous media using three-dimensional microimaging and pulsed gradient stimulated echo NMR

Pulsed gradient stimulated echo (PGSTE) and microimaging nuclear magnetic resonance (NMR) are used to probe correlations between structure and flow in the void space of a model porous system formed from a packing of 1-mm diameter glass spheres. The pulsed gradient stimulated echo data determine the average propagator and permit the dispersion of the flow to be studied as a function of delay time. Microimaging yields structural information and, specifically, a reduced radial distribution function (rdf) for the structure of the void space. Transition to fully developed dispersive flow is shown to occur on a scale size for which no further correlations in the structure of the void space are observed.     

The role of surface vanadia species in butane dehydrogenation over VOx/Al2O3

A series of θ-Al₂O₃ supported VO_x catalysts, of different vanadium loadings, have been characterised and employed for the selective dehydrogenation of n-butane. Characterisation of the unreacted catalysts has been carried out by solid-state NMR (⁵¹V MAS NMR, ²⁷Al MAS NMR and ²⁷Al 3Q-MAS NMR), and FT-IR spectroscopies, with reference to previously acquired Raman and UV–vis spectroscopy data. As vanadium loading increases, so does the domain size of the supported vanadate units with significant quantities of V₂O₅ observed at the highest loadings. The influence of calcination, pre-reduction, reaction and regeneration on the structure of the catalysts has been studied by NMR, FT-IR, EPR, microanalysis and TEOM. Calcination disperses crystalline vanadate units, and at high loadings AlVO₄ formation is observed. Pre-reduction reduces the vanadium oxidation state from 5+ to 3+, while regeneration results in the formation of highly crystalline V⁵⁺ species. From these data it is possible to determine structure–activity relationships, with polymeric vanadia clusters favouring the formation of butenes and butadienes, while more isolated species are highly active towards the formation of polynuclear aromatic hydrocarbons retained on the catalyst surface post-reaction. These large polynuclear aromatic hydrocarbons are however not the principle cause of catalyst deactivation in this reaction.