Synthesis and antibacterial activity of metal complexes of ciprofloxacin

The interactions of ciprofloxacin (HCipro) with transition metals have been investigated. Two types of complexes, [M(Cipro)(OAc)(H₂O)₂] · 3H₂O (M = Mn^II, Co^II, Cu^II or Cd^II) and [M(Cipro)(OAc)] · 6H₂O (M = Ni^II or Zn^II), were obtained and characterized by physicochemical and spectroscopic methods. The i.r. spectra of the complexes suggest that the ciprofloxacin behaves as a monoanionic bidentate ligand. In vitro antibacterial activities of the HCipro and the complexes were tested.     

Critical behavior in earthquake energy dissipation

We explore bursty multiscale energy dissipation from earthquakes flanked by latitudes 29° S and 35.5° S, and longitudes 69.501° W and 73.944° W (in the Chilean central zone). Our work compares the predictions of a theory of nonequilibrium phase transitions with nonstandard statistical signatures of earthquake complex scaling behaviors. For temporal scales less than 84 hours, time development of earthquake radiated energy activity follows an algebraic arrangement consistent with estimates from the theory of nonequilibrium phase transitions. There are no characteristic scales for probability distributions of sizes and lifetimes of the activity bursts in the scaling region. The power-law exponents describing the probability distributions suggest that the main energy dissipation takes place due to largest bursts of activity, such as major earthquakes, as opposed to smaller activations which contribute less significantly though they have greater relative occurrence. The results obtained provide statistical evidence that earthquake energy dissipation mechanisms are essentially “scale-free”, displaying statistical and dynamical self-similarity. Our results provide some evidence that earthquake radiated energy and directed percolation belong to a similar universality class.     

Stabilization of solutions of the filtration equation with absorption and non-linear flux

This paper is primarily concerned with the large time behaviour of solutions of the initial boundary value problem $$\begin{gathered} u_t = \Delta \phi (u) - \varphi (x,u)in\Omega \times (0,\infty ) \hfill \\ - \frac{{\partial \phi (u)}}{{\partial \eta }} \in \beta (u)on\partial \Omega \times (0,\infty ) \hfill \\ u(x,0) = u_0 (x)in\Omega . \hfill \\ \end{gathered} $$ Problems of this sort arise in a number of areas of science; for instance, in models for gas or fluid flows in porous media and for the spread of certain biological populations.     

Vibration Analysis of Perforated Plates Using Time-Average Digital Speckle Pattern Interferometry

Digital Speckle Interferometry is a non invasive full-field coherent optical technique used in mechanical vibration measurement. In this research, it is used for tuning resonant frequencies of vibrating plates in order to investigate the dynamical behavior of perforated plates. The plate was excited to resonant vibration by a sinusoidal acoustic source. Fringe pattern produced during the time-average recording of the vibrating plate, for several resonant frequencies were registered. Results of plates fixed at one edge having internal holes and attached masses are presented. Experimental natural frequencies and modal shapes are compared to those obtained by an analytical approximate solution based on the Rayleigh–Ritz method with the use of orthogonal polynomials as coordinate function. A high degree of correlation between computational analysis and experimental results was observed, proving the potentiality of the optical technique as experimental validation of the numerical simulations.     

HOPS – Hamming-Oriented Partition Search for production planning in the spinning industry

In this paper, we investigate a two-stage lot-sizing and scheduling problem in a spinning industry. A new hybrid method called HOPS (Hamming-Oriented Partition Search), which is a branch-and-bound based procedure that incorporates a fix-and-optimize improvement method is proposed to solve the problem. An innovative partition choice for the fix-and-optimize is developed. The computational tests with generated instances based on real data show that HOPS is a good alternative for solving mixed integer problems with recognized partitions such as the lot-sizing and scheduling problem.     

A relax-and-fix-based algorithm for the vehicle-reservation assignment problem in a car rental company

Empty repositions are a major problem for car rental companies that deal with special types of vehicles whose number of units is small. In order to meet reservation requirements concerning time and location, companies are forced to transfer cars between rental stations, bearing significant costs and increasing the environmental impact of their activity due to the fuel consumption and CO₂${\text{CO}}_2$ emission. In this paper, this problem is tackled under a vehicle-reservation assignment framework as a network-flow model in which the profit is maximized. The reservations are allocated considering the initial and future availability of each car, interdependencies between rental groups, and different reservation priorities. To solve this model, a relax-and-fix heuristic procedure is proposed, including a constraint based on local branching that enables and controls modifications between iterations. Using real instances, the value of this approach is established and an improvement of 33% was achieved when compared to the company’s current practices.     

Behavior of oil well cement slurry systems aged in CO2-saturated water under high pressure and temperature

Journal of Thermal Analysis and Calorimetry - This paper aims at studying the effect of the exposure of hardened cement slurries, intended for oil wells, to carbon dioxide (CO2) in the state of...     

Sufficient conditions for total ill-posedness in linear semi-infinite optimization

This paper deals with the so-called total ill-posedness of linear optimization problems with an arbitrary (possibly infinite) number of constraints. We say that the nominal problem is totally ill-posed if it exhibits the highest unstability in the sense that arbitrarily small perturbations of the problem’s coefficients may provide both, consistent (with feasible solutions) and inconsistent problems, as well as bounded (with finite optimal value) and unbounded problems, and also solvable (with optimal solutions) and unsolvable problems. In this paper we provide sufficient conditions for the total ill-posedness property exclusively in terms of the coefficients of the nominal problem.     

Electrical field effects on dipole moment, structure and energetic of (H2O)n (2 n 15) cluster

The effect of an external electric field on water clusters of the (H₂O)_n type, with [1 n 15], in the ground state was analyzed at the B3LYP/cc-pVTZ level of theory. The calculations showed that an external electric field changes the number of hydrogen bonds, reduces the cluster sizes and increases the strength of the inter-cluster hydrogen bonds. The particular symmetry of the cluster and the null dipole moment in these specific configurations suggest that their stability can be associated with a perfect alignment of the water molecules, maximizing attractive electrostatic interactions caused by changes in the charge distribution of the clusters.     

Short-range forces between glass surfaces in aqueous solutions

We found that the force between glass surfaces measured with an atomic force microscope (AFM) has universal character in the short range, less than approximately 1 nm or about 3-4 water molecules, independent of solution conditions, that is, electrolyte ion size, charge and concentration and pH. Our results suggest that the excess DLVO force, obtained by subtracting the DLVO theory with a charge regulation model from the AFM force data, essentially does not change with the electrolytes Na, Ca, and Al, in the range of concentration from 10(-6) to 10(-2) M and the range of pH from 3.1 to 7.9. Single force curves for a glass-silica system in a 10-4 M aqueous NaCl solution at pH approximately 5.1 show oscillations with a period of about 0.25 nm, roughly the diameter of a water molecule. We postulate that the excess force between glass surfaces arises from a surface-induced solvent effect, from the creation of a hydrogen-bonding network at the surface level, rather than from a solvent-induced surface steric hindrance.