Go-Science

1st Impressions

2006-08-03T20:47:00.000-07:00

It's these sorts of sentences that make you want to dive right in:

"The rigorous analytical solution for the fluxes from a mixture of 1:1 metal complexes toward an active surface under steady-state planar diffusion in a finite domain and excess ligand conditions allows for the computation of the globabl degree of lability of the system as well as particular degrees of lability of each complex in the mixture."

Woo! [/sarcasm]

Salvador etal. Lability of a Mixture of Metal Complexes under Steady-State Planar Diffusion in a Finite Domain.J.Phys.Chem. B, 110:13661. 2006.

2006-03-01T16:07:00.000-08:00

I've signed my self to another 3 years of fun (fun!) via a phd as of yesterday, which means more... stuff.
Continuing with the DGT philosophy and general outlook on life we have some modelling for you today:

"By making S a function of z but not distance from the DGT device, x, we are assuming that the sediment is horzontally uniform. The precise nature of the dependance of S on z could be varied, but we arbitrarily chose a Gaussian shaped distribution of S with vertical distance:

S(z, σ) = k exp (-z² / 2σ²) (11)

Where z is the vertical distance above the source maximum (z=0), σ is a dispersion coefficient analogous to the standard deviation in a normal distribution and k is a constant."

I really just wanted to put the last line in there. Plus today you get a free one:

"In the sediment, the particles increase the diffusional path length (the tortuosity) between two points, and the effective diffusion coefficient, D_s, is reduced below D₀ according to the relationship propsed by Berner (1980; Equation (13)):

D_s = D₀/Θ², Θ² = 1 - ln(Φ²), (13)

where Θ² is the tortuosity, Φ is the porosity, and the relationship between these is the one proposed by Bourdreau (1996). We have assumed D₀ = 5 x 10^-6 cm²s^-1 and a porosity of 0.9, giving a value for D_s of 4.13 x 10^-6 cm²s^-1. As with kinetic rate constants, there will exist in practice a distribution of diffusion coefficients depending on speciation, for example metals bound to slowly diffusing colloids."

Man, that theta looks like junk in this font. Not literally.

Harper, M.P., Davidson, W. and Tych, W. Estimation of Pore Water Concentrations from DGT Profiles: A Modelling Approach. Aquatic Geochemistry 5: 337-355. 1999.

Sounds Sci Fi

2005-10-18T21:15:00.000-07:00

Decidely more understandable this post (or is that because I've been reading this paper all year?), but still sounds funky.

"Sampling rates of PCBs by the PISCES sampling sytem comprising a polyethylene enclosed hexane receiveing phase have been quoted to vary between 0.41 l day^-1 at 10°c and 0.92 l day^-1 at 20°c. Arrhenius relatioships have also been evaluated for halogenated ether compounds in a system with XAD resin as receiving phase and a polycarbonate membrane."

Kingston, J.K., Greenwood, R. Mills, G.A., Morrison G.M. and Persson, L.b. "Development of a novel passive samplling system for the time-averaged measurement of a range of organic pollutants in aquatic environments" J. Envrion. Monit. 2: 492. 2000.

Go Diffusion!

2005-10-16T16:10:00.000-07:00

From the immortal advice of Meares, P. -

"The diffusion coefficient of the solvent measured with respect to the polymer as stationary reference D_s is related to its intrinsic diffusion coefficient ð_s, defined relative to a plane of zero mass flow, by

D_s = ð_s(1-v_s)³ = ð_sv³_p "

Dear god, why couldn't it have been linear?

Meares, P. "The influence of penetrant concentration on the diffusion and permeation of small molecules in polymers above T_g" European Polymer 29 2/3: 238. 1993.