Analysis and parametric sensitivity of the behavior of overshoots in the concentration of a charged adsorbate in the adsorbed phase of charged adsorbent particles: practical implications for separations of charged solutes

In this work, an analysis of the parametric sensitivity of the overshoot in the concentration of the adsorbate in the adsorbed phase, which occurs under certain conditions during an ion-exchange adsorption process, is presented and used to suggest practical implications of the concentration overshoot phenomenon on operational policies and configurations of chromatographic columns and finite bath adsorption systems. The results presented in this work demonstrate and explain how the development of an overshoot in the concentration of the adsorbate in the adsorbed phase could be enhanced or suppressed by (i) varying the diffusion coefficient, D3, of the adsorbate relative to the diffusion coefficients, D1 and D2, of the cations and anions, respectively, of the background/buffer electrolyte, (ii) altering the initial surface charge density, delta0, of the charged adsorbent particles, (iii) varying the Debye length, lambda, and (iv) changing the initial concentration, Cd3(0), of the adsorbate in the bulk liquid of the finite bath. The influence of the pH and ionic strength, Iinfinity, of the liquid solution on the development of an overshoot in the concentration of the adsorbate in the adsorbed phase is also presented and discussed through the relationships of these parameters to delta0 and lambda, respectively. Furthermore, a detailed explanation of the effects of each parameter on the interplay between the diffusive and electrophoretic molar fluxes, as well as on the structure and functioning of the electrical double layer, which are responsible for the concentration overshoot phenomenon, is presented.     

Mechanically responsive films of variable hydrophobicity made of polyelectrolyte multilayers

Mechanically responsive surfaces that allow to switch reversibly from a hydrophobic to a hydrophilic substrate are reported. The surfaces are constituted of polyelectrolyte multilayers deposited on modified charged silicone sheets. n bilayers of poly(allylamine)-Nafion (PAH-Naf) and m bilayers of poly(allylamine)-poly(acrylic acid) (PAH-PAA) composed the multilayers. A (PAH-Naf)(n) film possesses a water contact angle of around 105 degrees, whereas the contact angle of a (PAH-Naf)(4)-(PAH-PAA)(m) multilayer is around 50 degrees. When such a film with m < 5 and terminated by PAA is stretched out, its water contact angle increases up to around 100 degrees. Successive elongation/retraction cycles allow the water contact angle to alternate reversibly between 100 and 57 degrees indicating the reversible mechanical responsive nature of the film.     

Dipping versus spraying: exploring the deposition conditions for speeding up layer-by-layer assembly

Polyelectrolyte film fabrication by successive spraying of polycation and polyanion solutions is described and compared to classic dipping. The poly(styrenesulfonate)/poly(allylamine) system is examined in detail. The influence of various parameters such as spraying time, polyelectrolyte concentration, and effect of film drying during multilayer construction is investigated. It is found that film deposition by spraying is easily controlled and very reliable. The thickness of the multilayers grows linearly with the number of deposition cycles similarly to what is observed when dipping substrates or when polyelectrolyte solutions flow over a surface. The assembly of films is very fast and leads to films with small surface roughness as estimated by atomic force microscopy and X-ray reflectometry. Spray deposition allows achieving regular multilayer growth even under conditions for which dipping fails to produce homogeneous films (e.g., extremely short contact times). Moreover, because drainage constantly removes a certain quantity of the excess material arriving at the surface, one can even skip the rinsing step and, thus, speed up even further the whole buildup process.     

Investigation of the reactivity of arylamines, organo-hydrazines and tolylisocyanate towards [PW12-xMxO40]n- Keggin anions

Reaction of K7[A,alpha-PW9Mo2O39] with Na2MoO4.2H2O in a mixture of water/dioxane/hydrochloric acid and further precipitation with (Bu4N)Br provided (Bu4N)3[A,alpha-PW9Mo3O40](3). Analogous reaction with K7-xNax[alpha-PW11O39] is an alternative to the synthesis of (Bu4N)3[alpha-PW11O39{MoVIO}]2. Multinuclear NMR and ESI mass spectrometry have been used to interpret the reaction of (Bu4N)x[alpha-PW11O39{ReO}](x=3 1; x=4 1I), (Bu4N)x[alpha-PW11O39{MoO}](x=3 2; x=4 2I) and (Bu4N)3[A,alpha-PW9Mo3O40]3 by organohydrazines, arylamines, tolylisocyanate and tetraphenylphosphine imide.     

Proton affinity of proline and modified prolines using the kinetic method: role of the conformation investigated by ab initio calculations

The proton affinities of proline, cis-3-methylproline and cis-3-ethylproline have been measured by the kinetic method using an ion trap instrument; the values obtained are 936, 940.5, and 943 kJ mol(-1), respectively. The experimental values are consistent with those obtained by high-level ab initio calculations (B3LYP/6-31+G*//B3LYP/6-31G* and B3P86/6-31+G*//B3LYP/6-31G*). Several conformations of neutral and protonated proline were considered, in particular the endo and exo ring structure and the position of the carboxyl group. These results show the importance of the position of the hydrogen atom of the carboxyl group in determining the most stable protonated proline structure.     

Defending and improving the ‘slotting fee’: how it can benefit all the stakeholders dealing with a newsvendor product with price and effort-dependent demand

‘Slotting fee’ (hereafter ‘SF’) is an upfront fee a ‘supplier’ is required to pay a retailer in order to have his product sold on the retailer's shelves. It is becoming increasingly common, but also widely reviled. This paper considers a newsvendor product whose expected demand is dependent on retail price and sales effort. The question we pose is: given that the Stackelberg-dominant retailer has to choose a pricing contract with which she transacts with the supplier, how would the supply-chain stakeholders fare when the retailer implements SF instead of another practical pricing contract? We show that, contradicting its negative public image, SF empowers the dominant retailer to specify contract terms that will benefit all the stakeholder-groups. That is, the supplier's and the retailer's profits are higher, the production workers are asked to produce more, and the consumers pay a lower retail price. We also propose a new ‘composite’ contract format that incorporates both the SF and ‘buyback’ features. This composite format empowers the retailer to provide even greater benefits to the supply-chain's stakeholders.

     

A dynamic programming algorithm for scheduling jobs in a two-machine open shop with an availability constraint

This paper studies a two-machine open shop scheduling problem with an availability constraint, ie we assume that a machine is not always available and that the processing of the interrupted job can be resumed when the machine becomes available again. We consider the makespan minimization as criterion. This problem is NP-hard. We develop a pseudo-polynomial time dynamic programming algorithm to solve the problem optimally when the machine is not available at time s>0. Then, we propose a mixed integer linear programming formulation, that allows to solve instances with up to 500 jobs optimally in less than 5?min with CPLEX solver. Finally, we show that any heuristic algorithm has a worst-case error bound of 1.     

Molecular junctions by joining single-walled carbon nanotubes

Crossing single-walled carbon nanotubes can be joined by electron beam welding to form molecular junctions. Stable junctions of various geometries are created in situ in a transmission electron microscope. Electron beam exposure at high temperatures induces structural defects which promote the joining of tubes via cross-linking of dangling bonds. The observations are supported by molecular dynamics simulations which show that the creation of vacancies and interstitials induces the formation of junctions involving seven- or eight-membered carbon rings at the surface between the tubes.     

Two-proton radioactivity of 45Fe

In an experiment at the SISSI-LISE3 facility of GANIL, the decay of the proton drip line nucleus 45Fe has been studied. Fragment-implantation events have been correlated with radioactive decay events in a 16x16 pixel silicon-strip detector. The decay-energy spectrum of 45Fe implants shows a distinct peak at (1.14+/-0.04) MeV with a half-life of T(1/2)=(4.7(+3.4)(-1.4)) ms. None of the events in this peak is in coincidence with beta particles. For a longer correlation interval, daughter decays of the two-proton daughter 43Cr can be observed after 45Fe implantation. The decay energy for 45Fe agrees nicely with several theoretical predictions for two-proton radioactivity.