Contact-active antimicrobial and potentially self-polishing coatings based on cellulose

A contact-active antimicrobial coating is described that is only degraded in the presence of cellulase, which is an extracellular enzyme of numerous microbial strains. Antimicrobial DDA was grafted to a cellulose backbone via a polymeric spacer. The antimicrobial activity of the coatings, their biodegradability and their self-polishing potential were investigated. It was found that all coatings were antimicrobially active against Staphylococcus aureus. Coatings with high DS and long polymeric spacers degraded in water, while coatings with low DS and short spacers were not hydrolyzed even in the presence of cellulase. One coating was found to be selectively degradable by cellulase and recovered most of its antimicrobial activity after overloading and subsequent treatment with cellulase.     

All-numerical noise filtering of fluorescence signals for achieving ultra-low limit of detection in biomedical applications

We present an all-numerical method for post-processing of the fluorescent signal as obtained from labeled molecules by capillary electrophoresis (CE) in an optofluidic chip, on the basis of data filtering in the Fourier domain. It is shown that the method outperforms the well-known lock-in amplification during experiments in the reduction of noise by a factor of (square root)2. The method is illustrated using experimental data obtained during CE separation of molecules from a commercial DNA ladder with 17 fluorescently labeled molecules having different base-pair sizes. An improvement in signal-to-noise ratio by a factor of ～10 is achieved, resulting in a record-low limit of detection of 210 fM.     

On the extremal distance between two convex bodies

We consider the following modified version of the Banach-Mazur distance of convex bodies in \(\mathbb{R}^n :d\left( {K,L} \right) = \inf \left\{ {\left| \lambda \right|:\lambda \in \mathbb{R},\tilde K \subset \tilde L \subset \lambda \tilde K} \right\}\), where the infimum is taken over all non-degenerate affine images \(\tilde K\) and \(\tilde L\) of K and L. Gordon, Litvak, Meyer and Pajor in 2004 showed that for any two convex bodies d(K,L) ≤ n, moreover, if K is a simplex and L = ?L then d(K,L) = n. The following question arises naturally: Is equality only attained when one of the sets is a simplex? Leichtweiss in 1959, and later Palmon in 1992 proved that if d(K,B ₂ ⁿ ) = n, where B ₂ ⁿ is the Euclidean ball, then K is the simplex. We prove the affirmative answer to the question in the case when one of the bodies is strictly convex or smooth, thus obtaining a generalization of the result of Leichtweiss and Palmon.     

Universal approach for mesofluidic handling of bead suspensions in lab-on-valve format

In the present report, new protocols are introduced for automatic mesofluidic handling of irregularly shaped and non-uniformly sized bead materials for renewable micro-solid phase extraction (μSPE) under the lab-on-valve (LOV) format. To this end, two alternative strategies were studied comprising either (i) the direct aspiration of bead suspension placed at a container attached to LOV device or (ii) the aspiration of beads after a resuspension step, allowing the formation of a fluidized bed inside the beads’ container. Suspensions with homogeneously dispersed beads were also tested in the first strategy above, as prepared by increasing the viscosity of the suspension milieu with 75:15:10 glycerol/MeOH/H₂O (in wt). The bead injection protocols were applied to four commercial reversed-phase sorbent materials with different sorptive surfaces: Oasis HLB, SupelMIP β-receptors, Lichrolut EN and Discovery DSC-MCAX, and the mass of sorbent packed in each microcolumn was assessed. Direct aspiration of methanolic suspensions gave rise to bead stacking and clogging of the LOV microconduits, resulting in a source of results with poor precision (RSD: 3.8-67.6%). The use of glycerolic suspensions was merely effective for repeatable sampling and packing of Oasis HLB and SupelMIP β-receptor beads without sorbent settlement along time. The resuspension strategy was able to handle all the materials tested with acceptable precision (RSD: 1.6-13.8%). Enhanced precision was attained (RSD <4.1%) when the sorbent bed was physically restricted to the volume of the LOV microchannel cavity. Different volumes of suspension aiming at a target mass of sorbent of 10 mg were successfully handled (RSD: 3.1-13.8%), showing the reliability of the bead resuspension approach for varied nominal bead sampling volumes. The proposed bead handling protocols were applied to μSPE of propranolol taken as a model of β-blocker from aqueous solutions by SupelMIP β-receptors and Discovery DSC-MCAX beads with high repeatability (RSD <6%) and absolute recoveries between 69 and 74% in a bead-injection mode.     

Equivalence of Haar Bases Associated with Different Dyadic Systems

In this note we give sufficient conditions on two dyadic systems on a space of homogeneous type in order to obtain the equivalence of corresponding Haar systems on Lebesgue spaces. The main tool is the vector-valued Fefferman–Stein inequality for the Hardy–Littlewood maximal operator.     

Pants Decompositions of Random Surfaces

Our goal is to show, in two different contexts, that “random” surfaces have large pants decompositions. First we show that there are hyperbolic surfaces of genus g for which any pants decomposition requires curves of total length at least g ^7/6−ε . Moreover, we prove that this bound holds for most metrics in the moduli space of hyperbolic metrics equipped with the Weil–Petersson volume form. We then consider surfaces obtained by randomly gluing euclidean triangles (with unit side length) together and show that these surfaces have the same property.     

Measuring the level sets of anisotropic homogeneous functions

In this note we investigate some basic properties of the level sets of functions which are homogeneous with respect to nonisotropic dilations. In particular we obtain a formula for the volume of the level sets in terms of the area on the level surfaces. We relate the results to some well known mean value formulas for solutions of PDE’s.     

Four-terminal resistance of an interacting quantum wire with weakly invasive contacts

We analyze the behavior of the four-terminal resistance, relative to the two-terminal resistance of an interacting quantum wire with an impurity, taking into account the invasiveness of the voltage probes. We consider a one-dimensional Luttinger model of spinless fermions for the wire. We treat the coupling to the voltage probes perturbatively, within the framework of non-equilibrium Green function techniques. Our investigation unveils the combined effect of impurities, electron-electron interactions and invasiveness of the probes on the possible occurrence of negative resistance.     

Mechanochemical Synthesis and Nitrogenation of the Nd1.1Fe10CoTi Alloy for Permanent Magnet

In this work, the mechanochemical synthesis method was used for the first time to produce powders of the nanocrystalline Nd_1.1Fe₁₀CoTi compound from Nd₂O₃, Fe₂O₃, Co and TiO₂. High-energy-milled powders were heat treated at 1000 °C for 10 min to obtain the ThMn₁₂-type structure. Volume fraction of the 1:12 phase was found to be as high as 95.7% with 4.3% of a bcc phase also present. The nitrogenation process of the sample was carried out at 350 °C during 3, 6, 9 and 12 h using a static pressure of 80 kPa of N₂. The magnetic properties M_r, µ₀H_c, and (BH)_max were enhanced after nitrogenation, despite finding some residual nitrogen-free 1:12 phase. The magnetic values of a nitrogenated sample after 3 h were M_r = 75 Am² kg^–1, µ₀H_c = 0.500 T and (BH)_max = 58 kJ·m^–3. Samples were aligned under an applied field of 2 T after washing and were measured in a direction parallel to the applied field. The best value of (BH)_max ~ 114 kJ·m^–3 was obtained for 3 h and the highest µ₀H_c = 0.518 T for 6 h nitrogenation. SEM characterization revealed that the particles have a mean particle size around 360 nm and a rounded shape.