Adsorption of four perfluorinated acids on non ion exchange polymer sorbents

Perfluorinated compounds (PFCs) have attracted global concern due to their ubiquitous distribution and properties of persistence, bio accumulation and toxicity. The process of adsorption has been identified as an effective technique to remove PFCs in water. Different non ion-exchange polymeric adsorbents were tested with regard to their sorption kinetics and isotherms at low PFCs concentrations. Selected PFCs were perfluorobutanoic acid (PFBA), perfluoroheptanoic acid (PFHpA), perfluorooctanoic acid (PFOA) and perfluorodecanoic acid (PFDA) and the tested polymers were three types of Dowex optopores (V-493, V503, and L493), Amberlite XAD-4, and Filtrasorb 400 (Granular Activated Carbon-GAC). We observed the selective adsorption of PFCs on synthetic polymers. For PFDA, Amberlite XAD-4 gave the Freundlich adsorption constant of 2,965 (microg PFCs/g sorbent)(microg PFCs/L)(-n), which was higher than that of GAC (121.89 (microg PFCs/g sorbent) (microg PFCS/L)(-n)). In the case of PFBA, GAC showed better performance (13.36) (microg PFCs/g sorbent) microg PFCS/L)(-n) than synthetic polymers (0.62-5.23) (microg PFCs/g sorbent) (microg PFCS/L)(-n). Adsorption kinetics of all adsorbents were well described (R2 = 0.85-1) by pseudo-second order kinetic model. Sorption capacity was influenced by initial PFCs concentration for all adsorbents. GAC reached the equilibrium concentration within 4 hours, Amberlite XAD 4 reached it within 10 hours and other polymers took more than 70 hours.     

Minimum entropy-neural network approach to turbulent-image reconstruction

We investigate a neural net-based algorithm for enhanced imaging through atmospheric turbulence. The concept is based on a standard model of optical turbulence, according to which a short-exposure point-spread function is a random superposition of speckles. This leads to a new method of image processing called the Fourier division approach. The latter requires the taking of two short-exposure images in rapid succession, which are picked up by an image-plane array, divided in Fourier space, and then processed by a minimum entropy-neural net approach. The main task of the processing is to estimate the two short-exposure point-spread functions that characterize the two images. Given these estimates, the two images may now be inverse filtered to produce two sharp object-scene estimates. These have most of the turbulence degradation removed, and are averaged to produce a single output image. The approach shows promise, in computer simulations, of removing nearly all of the turbulence degradation very quickly (currently tens of seconds). A further benefit arises from knowledge of the twoshort-exposure point-spread functions. These should permit identification of the state of turbulence along the imaging line of sight and, in particular, the presence of wind shear.     

Theoretical relationships of receptor and delivery sensitivities and measurable parameters in in vivo neuroreceptor-radioligand interactions

In vivo quantification of neuroreceptors in human brains by PET or SPECT is complicated by the fact that a number of variables other than receptor concentration may influence the observed radioactivity in a brain region. This consideration has led the authors to formulate rigorous mathematical definitions of the concepts of receptor and delivery sensitivities. It has been speculated that a neuroreceptor-radioligand system having a high (low) receptor sensitivity would have a low (high) delivery sensitivity, and that the receptor sensitivity of a neuroreceptor-radioligand system can be determined by observing the time-course of the brain radioligand concentration following injection of no carrier added (nca) radioligand. Computer simulation studies of the characteristics of a simple model for in vivo neuroreceptor-radioligand interaction show that, under a set of realistic restrictions, there is a unique and intuitively satisfying relationship between receptor and delivery sensitivities: receptor sensitivity+delivery sensitivity approximately 1. In addition, the receptor sensitivity can be computed as a function of the observable parameters of the nca radioligand time course. These straightforward relationships are surprising in light of the complexity of the analytical solutions.