Porous electrospun nanocomposite mats based on chitosan–cellulose nanocrystals for wound dressing: effect of surface characteristics of nanocrystals

Randomly oriented fiber mats of chitosan–polyethylene oxide matrix reinforced with cellulose nanocrystals (CNCs) were prepared by electrospinning technique. The cellulose nanocrystals used were isolated using hydrochloric acid (CNC_HCl) or sulphuric acid (\({\text{CNC}}_{{{\text{H}}_{ 2} {\text{SO}}_{ 4} }}\)) and the concentration of CNCs was 50 wt% in the electrospun mats. The surface characteristics of the nanocrystals were found to affect the dispersion, viscosity, conductivity and zeta-potential of the respective spinning solutions and resulted in better spinnability, homogeneity as well as crosslinking of CNC_HCl based nanocomposite fiber mats compared to \({\text{CNC}}_{{{\text{H}}_{ 2} {\text{SO}}_{ 4} }}\) ones. The microscopy studies showed that the diameter of the electrospun fibers decreased with the inclusion of both types of nanocrystals and that crosslinking decreased the porosity of the mats. The tensile strength and tensile modulus of the mats increased with the addition of nanocrystals and increased further for the CNC_HCl based mats (58 MPa, 3.1 GPa) after crosslinking. The as-spun CNC_HCl based mats had average pore diameters of 1.6 μm and porosity of 38 %. The water vapor permeability and the O₂/CO₂ transmission increased with the addition of CNC_HCl. The used nanocrystals as well as electrospun mats showed non-cytotoxic impact on adipose derived stem cells (ASCs), which was considered favorable for wound dressing.     

Effect of long fiber thermoplastic extrusion process on fiber dispersion and mechanical properties of viscose fiber/polypropylene composites

Viscose fiber reinforced polypropylene (PP/VF) composites were manufactured using long fiber thermoplastic (LFT) extrusion techniques with two different methods namely LFT‐l and LFT‐2. The compatibilizer [maleated polypropylene (MAPP)] and dispersing agent [stearic acid (SA)] were added to the PP/VF in order to improve the fiber dispersion and interfacial adhesion. The PP/VF composites manufactured using LFT‐2 showed better fiber dispersion with higher tensile and flexural properties compared to the composites manufactured using LFT‐1 method. Similarly, the impact strength and toughness of the LET‐2 composites showed an improvement of 36 and 20% than LFT‐1 whereas the average fiber length of composites was decreased from 6.9 mm to 4.4 mm because of the increase in shear energy as a result of residence time. Further, the addition of SA and MAPP to LFT‐2 process has significantly improved the fiber dispersion and mechanical performance. The fiber dispersion and fracture behavior of the LFT‐1 and LFT‐2 composites were studied using scanning electron microscopy analysis. The Fourier transformation infrared spectra were also studied to ascertain the existence of type of interfacial bonds. Copyright © 2015 John Wiley & Sons, Ltd.     

Electronic structure of MgO-supported Au clusters: quantum dots probed by scanning tunneling microscopy

We investigate via density functional theory (DFT) the appearance of small MgO-supported gold clusters with 8 to 20 atoms in a scanning tunneling microscope (STM) experiment. Comparison of simulations of ultrathin films on a metal support with a bulk MgO leads to similar results for the cluster properties relevant for STM. Simulated STM pictures show the delocalized states of the cluster rather than the atomic structure. This finding is due to the presence of s- derived delocalized states of the cluster near the Fermi energy. The properties of theses states can be understood from a jellium model for monovalent gold.     

Advanced glossmeters for industrial applications

In this paper, we present three new types of diffractive-optical-element (DOE)-based glossmeters (DOGs) that have been developed for both laboratory and online local specular gloss measurements of objects in industrial processes. The three are denoted as the handheld wireless glossmeter, μDOG two-dimensional (2D) and μDOG one-dimensional (1D), respectively. These glossmeters are designed to operate under conditions where gloss measurement with conventional glossmeters is impossible or difficult, or when fine structures of the gloss over a surface are an issue. Here, we show the applicability of the handheld glossmeter and μDOG 2D in the inspection of gloss from rough stainless steel plates finished by different machining methods. We also briefly introduce the concept of online gauge μDOG 1D for gloss assessment in industrial measurement environments.     

Meet and join matrices in the poset of exponential divisors

It is well-known that (ℤ₊, |) = (ℤ₊, GCD, LCM) is a lattice, where | is the usual divisibility relation and GCD and LCM stand for the greatest common divisor and the least common multiple of positive integers. The number $ d = \prod\nolimits_{k = 1}^r {p_k^{d^{(k)} } } $ d = \prod\nolimits_{k = 1}^r {p_k^{d^{(k)} } } is said to be an exponential divisor or an e-divisor of $ n = \prod\nolimits_{k = 1}^r {p_k^{n^{(k)} } } $ n = \prod\nolimits_{k = 1}^r {p_k^{n^{(k)} } } (n > 1), written as d | _e n, if d ^(k) for all prime divisors p _k of n. It is easy to see that (ℤ₊\{1}, | _e is a poset under the exponential divisibility relation but not a lattice, since the greatest common exponential divisor (GCED) and the least common exponential multiple (LCEM) do not always exist.     

Crosslinked fibrous composites based on cellulose nanofibers and collagen with in situ pH induced fibrillation

Collagen and cellulose nanofiber based composites were prepared by solution casting followed by pH induced in situ partial fibrillation of collagen phase and crosslinking of collagen phase using gluteraldehyde. Microscopy studies on the materials confirmed the presence of fibrous collagen and cellulose nanofibers embedded in the collagen matrix. The cellulose nanofiber addition as well as collagen crosslinking showed significant positive impact on the nanocomposite’s mechanical behaviour. The synergistic performance of the nanocomposites indicated stabilization and reinforcement through strong physical entanglement between collagen and cellulose fibres as well as chemical interaction between collagen matrix and collagen fibrils. The mechanical performance and stability in moist conditions showed the potential of these materials as implantable scaffolds in biomedical applications. The collagen-cellulose ratio, crosslinking agent and crosslinking level of collagen may be further optimised to tailor the mechanical properties and cytocompatibility of these composites for specific applications such as artificial ligament or tendon.     

Different aspects of the monotonicity of a function

In this paper, we investigate which aspects are overriding in the concept images of monotonicity of Finnish tertiary mathematics students, i.e., on which aspects of monotonicity they base their argument in different types of exercises related to that concept. Further, we examine the relationship between the quality of principal aspects and the success in solving monotonicity exercises and a few other standard problems in calculus. Our findings indicate that a mathematics student's conception about monotone functions is often restricted to continuous or differentiable functions and the algebraic aspect – the nearest one to the formal definition of monotonicity – is rare.     

A Class of Rational Arithmetical Functions with Combinatorial Meanings

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Evaluation of the fundamental sampling error in the sampling of particulate solids

Chemical analysis is a multi-stage process, which starts with primary sampling and ends with evaluation of the resuts. Especially in trace analysis and microanalysis of solid materials, sampling can far outweigh all other sources of error. For estimating the reliability of complete analytical procedures, a method is needed which can be used to estimate the errors made in the primary and the secondary sampling and sample preparation steps. Based on Gy's theory of sampling, a computer program (SAMPEX) was written for the solution of practical sampling problems. The method involves the estimation of the sampling constant, C. For well-characterized materials, C can be estimated from the material properties. If the necessary material properties are difficult to estimate, C can be evaluated experimentally. The program can be used to solve the following problems: minimum sample size for a tolerated relative standard deviation of the fundamental sampling error; relative size for a tolerated for a given sample size; maximum particle size of the material for a specified standard deviation and sample size; balanced design of a multi-stage sampling and sample-reduction process; and sampling for particle size determination.