Stochastic contagion models without immunity: their long term behaviour and the optimal level of treatment

In this paper we analyze two stochastic versions of one of the simplest classes of contagion models, namely so-called SIS models. Several formulations of such models, based on stochastic differential equations, have been recently discussed in literature, mainly with a focus on the existence and uniqueness of stationary distributions. With applicability in view, the present paper uses the Fokker–Planck equations related to SIS stochastic differential equations, not only in order to derive basic facts, but also to derive explicit expressions for stationary densities and further characteristics related to the asymptotic behaviour. Two types of models are analyzed here: The first one is a version of the SIS model with external parameter noise and saturated incidence. The second one is based on the Kramers–Moyal approximation of the simple SIS Markov chain model, which leads to a model with scaled additive noise. In both cases we analyze the asymptotic behaviour, which leads to limiting stationary distributions in the first case and limiting quasistationary distributions in the second case. Finally, we use the derived properties for analyzing the decision problem of choosing the cost-optimal level of treatment intensity.

     

On Conservation and Balance Laws in Micromorphic Elastodynamics

In this paper, following Noether’s theorem we investigate the Lie point symmetries of linear micromorphic elastodynamics (linear elastodynamics with microstructure). Conservation and balance laws of linear, micromorphic elastodynamics are derived. We generalize the J, L and M integrals for this theory. In addition, we give the Eshelby stress tensor, pseudomomentum vector, field intensity vector, Hamiltonian, angular momentum tensor and scaling flux generalized to micromorphic elastodynamics.      

Theoretical study on the mechanism and kinetics of addition of hydroxyl radicals to fluorobenzene

Geometries, frequencies, reaction barriers, and reaction rates were calculated for the addition of OH radical to fluorobenzene using Möller–Plesset second‐order perturbation (MP2) and G3 methods. Four stationary points were found along each reaction path: reactants, prereaction complex, transition state, and product. A potential for association of OH radical and fluorobenzene into prereaction complex was calculated, and the associated transition state was determined for the first time. G3 calculations give higher reaction barriers than MP2, but also a significantly deeper prereaction complex minimum. The rate constants, calculated with Rice–Ramsperger–Kassel–Marcus (RRKM) theory using G3 energies, are much faster and in much better agreement with the experiment than those calculated with MP2 method, as the deeper well favors the formation of prereaction complex and also increases the final relative populations of adducts. The discrepancies between the experimental and calculated rate constants are attributed to the errors in calculated frequencies as well as to the overestimated G3 reaction barriers and underestimated prereaction complex well depth. It was possible to rectify those errors and to reproduce the experimental reaction rates in the temperature range 230–310 K by treating the relative translation of OH radical and fluorobenzene as a two‐dimensional particle‐in‐the‐box approximation and by downshifting the prereaction complex well and reaction barriers by 0.7 kcal mol^?1. The isomeric distribution of fluorohydroxycyclohexadienyl radicals is calculated from the reaction rates to be 30.9% ortho, 22.6% meta, 38.4% para, and 8.3% ipso. These results are in agreement with experiment that also shows dominance of ortho and para channels. © 2012 Wiley Periodicals, Inc.     

Thermal stability of new biologic active copper(II) complexes with 5,6-dimethylbenzimidazole

Three new coordinative compounds that contain mixed ligands (5,6-dimethylbenzimidazole and acrylato anion) were synthesized and characterized. The features of complexes have been assigned from microanalytical, IR, UV–Vis and EPR spectra as well as thermal analysis. IR data are in accordance with unidentate nature of 5,6-dimethylbenzimidazole while the acrilato ion acts as uni- or bidentate ligand. The electronic spectra display the characteristic pattern of square pyramidal or octahedral stereochemistry, which were confirmed by the EPR spectra. Antibacterial and antifungal activities of the complexes have been determined in vitro, against various Gram-negative and Gram-positive bacteria and fungi. The tested complexes exhibited different spectra of antimicrobial activity and inhibited the microbial ability to colonize the inert surfaces, acting as potential anti-adherence and biofilm-controlling agents. Thermal decomposition evidenced several well-defined steps as dehydration (complex 2), 5,6-dimethylbenzimidazole molecule release (all complexes) and the acrylate decomposition in carbonate (complex 3). The final residue is in all cases copper (II) oxide.     

Thermal, spectral, electrochemical and biologic characterization of new Pd(II) complexes with ligands bearing biguanide moieties

New complexes [Pd(HDMBG)₂]Cl₂·H₂O, [PdL¹]Cl₂·0.5H₂O and [PdL²]Cl₂·1.5H₂O (HDMBG: dimethylbiguanide, L¹ and L²: ligands resulted from HDMBG, ammonia/hydrazine and formaldehyde template condensation) were synthesized and characterized. The features of complexes have been assigned from microanalytical, IR, UV–Vis and cyclic voltammetry data. The thermal transformations are complex processes according to TG and DTA curves including water and hydrochloric acid elimination, thermolysis processes leading to paracyanide formation as well as PdO decomposition, final product being palladium. Complexes were screened for their antimicrobial properties against some pathogenic Gram-positive and Gram-negative bacterial as well as fungal Candida albicans strains. The complexes exhibit specific antibacterial and/or antifungal activity, depending on their structure and the tested microbial strains. All complexes inhibit the microbial biofilm development on the inert substratum. It was also observed that PdCl₂ complexation minimized their cytotoxic effect on the eukaryotic cells.     

Thermal study of new biologic active complexes with mixed ligands

Five new coordinative compounds that contain mixed ligands (4,4′-bipyridine and methacrylate anion) were synthesized and characterized (elemental analysis, IR and UV–Vis spectroscopy, and thermal studies). The complexes are of the type [M(4,4′-bipy)(C₄H₅O₂)₂]·nH₂O ((1) M:Mn, n = 0; (2) Co, n = 0.5; (3) M:Ni, n = 1.5; (4) M:Cu, n = 0.5; (5) M:Zn, n = 0.5; 4,4′-bipy: 4,4′-bipyridine; C₄H₅O₂: methacrylate anion). All the tested complexes exhibited very low MIC values against Escherichia coli strains and one compound against Staphylococcus aureus. Besides the specific antimicrobial spectrum, these compounds also inhibited the microbial ability to colonize the inert surfaces, acting as potential anti-adherence and biofilm-controlling agents. The thermal behavior provided confirmation of the complexes' compositions as well as the number and the nature of water molecules and the intervals of thermal stability.     

Evaluating the Thickness of Multivalent Glycopolymer Brushes for Lectin Binding

Electrochemical impedance spectroscopy (EIS) is applied for investigating binding of lectins to multivalent glycopolymer brushes grafted from interdigital gold microelectrodes. By variation of the measuring frequency, EIS allows simultaneous analysis of binding at different subnanometer distances from the sensor surfaces. In this way, the binding dynamics along the brushes are quantified, giving an idea about the motion of the lectin through the brush layer. Two different brush lengths are investigated, revealing distinct dynamics of lectin binding due to changing topology of the brushes. Moreover, very low K _D values in the nanomolar range are obtained. This unique platform may be used as sophisticated biosensor for detailed investigation of high‐affinity protein binding to poly­mer layers.

     

Mechanisms of Ceftazidime and Ciprofloxacin Transport through Porins in Multidrug-Resistance Developed by Extended-Spectrum Beta-Lactamase <Emphasis Type="Italic">E.coli</Emphasis> Strains

Resistance towards antibiotics stands out today as a major issue in the clinical act of treatment of bacterial-generated infections. This process was characterized in proteoliposomes reconstituted from an E.coli strain isolated from invasive infections (blood culture) occurred in patients with a cardio-vascular device admitted for surgery. Fluorescence spectroscopy and patch-clamp technique have been used. Two types of antibiotics have been targeted: ceftazidime and ciprofloxacin. Antibiotics addition in proteoliposomes suspension undergoes a quenching in tryptophan residues from outer membrane porins structure, probably due to the formation of a transient non-fluorescent porin-antibiotic complex. Patch-clamp recordings revealed strong ion current blockages for both antibiotics, reflecting antibiotic–channel interactions but with varying strength of interaction. The present study puts forward the mechanism of multidrug-resistance in extended-spectrum beta-lactamase E.coli strains, as being caused by alterations of the antibiotics transport across the porins of the outer bacterial membrane.