Polysaccharide films built by simultaneous or alternate spray: a rapid way to engineer biomaterial surfaces

We investigated polysaccharide films obtained by simultaneous and alternate spraying of a chitosan (CHI) solution as polycation and hyaluronic acid (HA), alginate (ALG), and chondroitin sulfate (CS) solutions as polyanions. For simultaneous spraying, the film thickness increases linearly with the cumulative spraying time and passes through a maximum for polyanion/CHI molar charge ratios lying between 0.6 and 1.2. The size of polyanion/CHI complexes formed in solution was compared with the simultaneously sprayed film growth rate as a function of the polyanion/CHI molar charge ratio. A good correlation was found. This suggests the importance of polyanion/polycation complexation in the simultaneous spraying process. Depending on the system, the film topography is either liquid-like or granular. Film biocompatibility was evaluated using human gingival fibroblasts. A small or no difference is observed in cell viability and adhesion between the two deposition processes. The CHI/HA system appears to be the best for cell adhesion inducing the clustering of CD44, a cell surface HA receptor, at the membrane of cells. Simultaneous or alternate spraying of CHI/HA appears thus to be a convenient and fast procedure for biomaterial surface modifications.     

Atomic structure of highly strained BiFeO3 thin films

We determine the atomic structure of the pseudotetragonal T phase and the pseudorhombohedral R phase in highly strained multiferroic BiFeO(3) thin films by using a combination of atomic-resolution scanning transmission electron microscopy and electron energy-loss spectroscopy. The coordination of the Fe atoms and their displacement relative to the O and Bi positions are assessed by direct imaging. These observations allow us to interpret the electronic structure data derived from electron energy-loss spectroscopy and provide evidence for the giant spontaneous polarization in strained BiFeO(3) thin films.     

Electrochemical properties of sputtered iridium oxide films

Iridium oxide films previously used in association with WO₃ and a proton conducting electrolyte in electrochromic devices, have been directly sputtered on both sides of an anhydrous membrane of a new proton conducting polymer electrolyte (nylon 6–10, 2H₃PO₄). Charge-discharge experiments show that this symmetric cell works reversibly in the “rocking chair” mode owing to the presence of roughly equal amounts of Ir³⁺ and Ir⁴⁺ in the as-deposited films. Impedance spectroscopy has been applied to the bare and sputtered polymer in order to characterize the main elements of the equivalent circuits for the two systems. Paper presented at the 2nd Euroconference in Funchal, Madeira, Portugal. Sept. 10–16, 1995     

Parity conservation and polarization of differential cross sections in complex-forming chemical reactions

For complex-forming chemical reactions, such as atom-diatom insertion reactions, quantum scattering and quantum statistical calculations usually predict sharp forward/backward peaks in the Differential Cross Sections (DCS). Conversely, the corresponding classical calculations are unable to reproduce these peaks. We show here that the basic reason for such an intriguing failure is that parity conservation is ignored in classical mechanics. A by-product of the analysis is a simple parity-restoring approximation that might significantly increase the ability of classical mechanics to describe DCSs over the whole angular range for the title processes.     

Cost analysis of the M/M/R machine repair problem with balking,reneging, and server breakdowns

We consider the machine repair problem in which failed machines balk (do not enter) with a constant probability (1 – b) and renege (leave the queue after entering) according to a negative exponential distribution. A group of identical automatic machines are maintained by R servers which themselves are subject to breakdowns. Failure and service times of the machines, and breakdown and repair times of the servers, are assumed to follow a negative exponential distribution. Each server is subject to breakdown even if no failed machines are in the system. This paper presents a matrix geometric method for deriving the steady-state probabilities, using which various system performance measures that can be obtained. A cost model is developed to determine the optimum number of servers. The minimum expected cost, the optimal number of servers, and various system performance measures are provided based on assumed numerical values given to the system parameters. Also the sensitivity analysis is investigated.     

Cost analysis of the unloader queueing system with a single unloader subject to breakdowns

In this paper, we deal with an unloader queueing model in which N identical trailers are unloaded by a single unloader. We consider two different types of a single unloader, which are subject to breakdowns. In type 1, the unloader can break down only when there is at least one trailer in the system, while in type 2, the unloader can break down even if no trailers are in the system. Analytic closed-form solutions of the unloader queueing system are derived. A cost model is developed in order to determine the optimal value of the number of trailers to be assigned to the unloader for both types. Under the optimal operating condition, numerical results are presented in which several system performance measures are evaluated based on assumed numerical values given to the system parameters. Sensitivity analysis is also investigated.     

Proton affinity ladder for uridine and analogs: influence of the hydroxyl group on the sugar ring conformation

A ladder of relative proton affinities (PA) for a series of modified uridines (e.g. araU, ddU, 5BrU, 5BrdU and 5IU) was established from competitive dissociations of proton-bound heterodimers using Cooks and co-workers' kinetic method. The studied heterodimers are constituted of a modified nucleoside and either an amino acid or a nucleoside with known PA value. These non-covalent heterodimers were prepared under electrospray conditions to be selected and dissociated into the ion-trap analyzer. These results allowed our PA ladder of uridine and deoxyuridine analogs substituted at the C-5 position in the uracil ring to be extended. From this scale, it was showed that the substitution of hydrogen atom at the C-2' position in the sugar ring by a hydroxyl group involves a decrease of about 7 kJ mol(-1). The experimental values for U, 5MeU, dU, 5MedU, ddU and araU are consistent with those obtained by DFT calculations (B3P86/6-31+G//B3LYP/6-31G(.)). Several neutral and protonated conformations of these compounds were considered, in particular the ring conformation of furanose and the orientation of the base with respect to the sugar ring. These calculated results showed the influence of sugar substituent on the conformation of the neutral form of theses nucleosides. However, the most stable protonated structure is the same for all the studied nucleosides except for araU, where the position of the anti 2'-OH group imposes a specific conformation.     

Submillimeter laser action of CW optically pumped CF2Cl2 (Fluorocarbon 12)

Eleven new CW far infrared (FIR) laser lines have been observed in the 600 m–1200 m range from the CF₂Cl₂ (Fluorocarbon 12) molecule optically pumped by a CO₂ laser. A 510^–4–10^–3 accuracy is achieved in the measurement of the FIR wavelengths.The frequency offset between the CO₂ pump center and the absorption line centers are measured using the transferred Lamb dip technique. Owing to a recent spectroscopic study of the CF₂ ³⁵Cl₂ molecule three lines may be assigned with great confidence as rotational transitions in thev ₆ vibrational band 923 cm^–1 of this main isotope.