Swollen and collapsed lyotropic lamellar rheology

We have investigated linear rheological properties and the structure-flow relationship of the swollen (Lam(1)) and collapsed (Lam(2)) lamellar phases, formed on didodecyldimethylammonium bromide (DDAB)/lecithin/water ternary system at 25 degrees C. Both lamellar phases behaved like Bingham fluids and showed remarkable yield stresses. At rest the Lam(1) phase, which is characterized by densely packed vesicles whose sizes increase as the water content decreases in accordance to evolution of (2)H NMR spectral profiles of D(2)O, resulted in a strong elastic gel-like response. On the other hand, the Lam(2) phase, formed at high surfactant concentrations, showed a weak-gel viscoelasticity and (2)H NMR spectral patterns which are typical of planar bilayered structures. The increase of the quadrupole splitting as the water content decreases was assumed as a strong evidence of size increasing of the lamellar domains. We have demonstrated that by using dynamic rheology and the derived relaxation time spectra, along with (2)H NMR spectra of D(2)O, it is possible to differentiate between equilibrium lamellar structures occurring in a broad interval of total surfactant concentration. In addition, a shear-thickening regime, observed at intermediate shear-rate values, highlighted the onset of out-equilibrium lamellar structures which were present both on Lam(1) and Lam(2) phases.     

Chitosan-DNA Particles for DNA Delivery: Effect of Chitosan Molecular Weight on Formation and Release Characteristics

Novel DNA-chitosan particles were prepared based on associative phase separation and interfacial diffusion. These particles formed at water/water emulsion type interfaces were characterized with respect to several properties including stability, DNA conformational state, and entrapment and release of DNA. In particular it was found that the chitosan molecular weight is a good controlling parameter.     

Aspects of electronic transport in YBaCo4O7+δ pellets

YBaCo₄O_7+δ powders were obtained by standard solid state reaction und their structural, morphological and electrical properties carefully analyzed. The X-ray powder diffraction patterns showed reflexes corresponding to a pure hexagonal structure (space group P6₃mc). The lattice parameters resulted to be very close to those reported in the literature for high-quality samples. Raman spectra at room temperature allowed for identifying bands associated with vibrating modes of CoO₄ and Y₂O₆ in tetrahedral and octahedral coordination, respectively. Additional bands, which seemed to stem from CoO in octahedral coordination, were also clearly identified. The dependence of the resistivity on temperature showed a semiconducting-like behavior and no indication of structural phase transition was observed up to temperatures as low as 20 K. The electronic transport mechanism in this material was analyzed within the framework of standard models as thermal activation, polaronic-type conductivity or Mott variable-range hopping. Contrary to some reports in the literature in which thermal activation was reported to be the main transport mechanism, careful analysis of the obtained resistivity data (this work) favored the variable-range hopping conduction model. Certainly, the experimental data recorded in a wide temperature range were well described by the function ρ(T) = ρ₀exp[(T^*/T)^1/4]. The fit procedure yielded a temperature scale T^* ～ 10⁶ K, similar to that found in other transition metal oxides. This parameter, in turn, allowed for estimating the density of states at the Fermi level N(E_F) for this compound.     

Polynomial time solutions for scheduling problems on a proportionate flowshop with two competing agents

In scheduling problems with two competing agents, each one of the agents has his own set of jobs and his own objective function, but both share the same processor. The goal is to minimize the value of the objective function of one agent, subject to an upper bound on the value of the objective function of the second agent. In this paper we study two-agent scheduling problems on a proportionate flowshop. Three objective functions of the first agent are considered: minimum maximum cost of all the jobs, minimum total completion time, and minimum number of tardy jobs. For the second agent, an upper bound on the maximum allowable cost is assumed. We introduce efficient polynomial time solution algorithms for all cases.     

Delay asymptotics and bounds for multitask parallel jobs

Queueing Systems - We study delay of jobs that consist of multiple parallel tasks, which is a critical performance metric in a wide range of applications such as data file retrieval in coded...     

Projected gradient methods for linearly constrained problems

The aim of this paper is to study the convergence properties of the gradient projection method and to apply these results to algorithms for linearly constrained problems. The main convergence result is obtained by defining a projected gradient, and proving that the gradient projection method forces the sequence of projected gradients to zero. A consequence of this result is that if the gradient projection method converges to a nondegenerate point of a linearly constrained problem, then the active and binding constraints are identified in a finite number of iterations. As an application of our theory, we develop quadratic programming algorithms that iteratively explore a subspace defined by the active constraints. These algorithms are able to drop and add many constraints from the active set, and can either compute an accurate minimizer by a direct method, or an approximate minimizer by an iterative method of the conjugate gradient type. Thus, these algorithms are attractive for large scale problems. We show that it is possible to develop a finite terminating quadratic programming algorithm without non-degeneracy assumptions. Work supported in part by the Applied Mathematical Sciences subprogram of the Office of Energy Research of the U.S. Department of Energy under Contract W-31-109-Eng-38. Work supported in part by the Applied Mathematical Sciences subprogram of the Office of Energy Research of the U.S. Department of Energy under Contract W-31-109-Eng-38.     

Electronic theory for the metal-non-metal transition in simple metal alloys

The metal-non-metal transition in liquid alloys such as Cs_1–x Au _x and Li_1–x Pb _x is explained as resulting from concentration dependent electron charge transfer causing short range atomic order and a change from metallic to ionic bonds. Numerical results for the electronic density of states, the electron charge transfer, the free energy of mixing and the volume change are given.     

Synthesis of Biaryl‐Bridged Cyclic Peptides via Catalytic Oxidative Cross‐Coupling Reactions

Biaryl‐bridged cyclic peptides comprise an intriguing class of structurally diverse natural products with significant biological activity. Especially noteworthy are the antibiotics arylomycin and its synthetic analogue G0775, which exhibits potent activity against Gram‐negative bacteria. Herein, we present a simple, flexible, and reliable strategy based on activating‐group‐assisted catalytic oxidative coupling for assembling biaryl‐bridged cyclic peptides from natural amino acids. The synthetic approach was utilized for preparing a number of natural and unnatural biaryl‐bridged cyclic peptides, including arylomycin/G0775 and RP 66453 cyclic cores.     

Application of thermal analysis for evaluating the digestion of microwave pre-treated sewage sludge

The effect of microwave pre-treatment (MwP) on anaerobic digestion of sewage sludge was studied by means of thermal analysis and evolved gas analysis. The effect of the pre-treatment at low energy input (<1000 kJ L^?1) on sludge solubilisation was studied with the aid of response surface methodology. The pre-treatment process was subsequently studied at energies of 488–2700 kJ L^?1 to evaluate the improvement in biogas production under mesophilic conditions. Organic matter modifications were studied using a Setaram TGA92 analyser at atmospheric pressure coupled to an MSC200 quadrupole mass spectrometer from Balzers. Particle size analysis was carried out using a Laser Diffraction Particle Size Analyser LS 13 320 Beckmann Coulter for evaluating the effect of MwP on sludge particles. Results showed an increase in organic matter solubilisation with the increase in the energy applied. Modifications in the specific surface area of the organic matter due to the MwP resulted in increments in methane yields. However, an accumulation of complex compounds was observed in thermal profiles at the maximum energy input (2700 kJ L^?1). Semi-continuous digestion experiments were evaluated using as substrate pre-treated sludge at the optimum energy value (975 kJ L^?1). Results showed a significant increase in methane yield (43 %) when evaluating the process at hydraulic retention times (HRTs) of 25–10 days.