Coarse-Grained Model for Prediction of Hole Mobility in Polyethylene

Electrical conductivity measurements of polyethylene indicate that the semicrystalline structure and morphology influence the conductivity. To include this effect in atomistic charge transport simulations, models that explicitly or implicitly take morphology into account are required. In the literature, charge transport simulations of amorphous polyethylene have been successfully performed using short oligomers to represent the polymer. However, a more realistic representation of the polymer structure is desired, requiring the development of fast and efficient charge transport algorithms that can handle large molecular systems through coarse-graining. Here, such a model for charge transport simulations in polyethylene is presented. Quantum chemistry calculations were used to define six segmentation rules on how to divide a polymer chain into shorter segments representing localized molecular orbitals. Applying the rules to amorphous systems yields distributions of segments with mode and median segment lengths relatively close to the persistence length of polyethylene. In an initial test, the segments of an amorphous polyethylene were used as hopping sites in kinetic Monte Carlo (KMC) simulations, which yielded simulated hole mobilities that were within the experimental range. The activation energy of the simulated system was lower compared to the experimental values reported in the literature. A conclusion may be that the experimental result can only be explained by a model containing chemical defects that generate deep traps.

Large-scale synthesis of 2D-silica (SiOx) nanosheets using graphene oxide (GO) as a template material

Graphene oxide (GO) was used in this study as a template to successfully synthesize silicon oxide (SiOx) based 2D-nanomaterials, adapting the same morphological features as the GO sheets. By performing a controlled condensation reaction using low concentrations of GO (<0.5 wt%), the study shows how to obtain 2D-nanoflakes, consisting of GO-flakes coated with a silica precursor that were ca. 500 nm in lateral diameter and ca. 1.5 nm in thickness. XPS revealed that the silanes had linked covalently with the GO sheets at the expense of the oxygen groups present on the GO surface. The GO template was shown to be fully removable through thermal treatment without affecting the nanoflake morphology of the pure SiOx-material, providing a methodology for large-scale preparation of SiOx-based 2D nanosheets with nearly identical dimensions as the GO template. The formation of SiOx sheets using a GO template was investigated for two different silane precursors, (3-aminopropyl) triethoxysilane (APTES) and tetraethyl orthosilicate (TEOS), showing that both precursors were capable of accurately templating the graphene oxide template. Molecular modeling revealed that the choice of silane affected the number of layers coated on the GO sheets. Furthermore, rheological measurements showed that the relative viscosity was significantly affected by the specific surface area of the synthesized particles. The protocol used showed the ability to synthesize these types of nanoparticles using a common aqueous alcohol solvent, and yield larger amounts (∼1 g) of SiOx-sheets than what has been previously reported.

Electric Resistance of Elastic Strain Sensors-Fundamental Mechanisms and Experimental Validation

Elastic strain sensor nanocomposites are emerging materials of high scientific and commercial interest. This study analyzes the major factors influencing the electrical behavior of elastic strain sensor nanocomposites. The sensor mechanisms were described for nanocomposites with conductive nanofillers, either dispersed inside the polymer matrix or coated onto the polymer surface. The purely geometrical contributions to the change in resistance were also assessed. The theoretical predictions indicated that maximum Gauge values are achieved for mixture composites with filler fractions slightly above the electrical percolation threshold, especially for nanocomposites with a very rapid conductivity increase around the threshold. PDMS/CB and PDMS/CNT mixture nanocomposites with 0-5.5 vol.% fillers were therefore manufactured and analyzed with resistivity measurements. In agreement with the predictions, the PDMS/CB with 2.0 vol.% CB gave very high Gauge values of around 20,000. The findings in this study will thus facilitate the development of highly optimized conductive polymer composites for strain sensor applications.

Molecular Dynamics Simulations of Cellulose and Dialcohol Cellulose under Dry and Moist Conditions

The development of wood-based thermoplastic polymers that can replace synthetic plastics is of high environmental importance, and previous studies have indicated that cellulose-rich fiber containing dialcohol cellulose (ring-opened cellulose) is a very promising candidate material. In this study, molecular dynamics simulations, complemented with experiments, were used to investigate how and why the degree of ring opening influences the properties of dialcohol cellulose, and how temperature and presence of water affect the material properties. Mechanical tensile properties, diffusion/mobility-related properties, densities, glass-transition temperatures, potential energies, hydrogen bonds, and free volumes were simulated for amorphous cellulosic materials with 0-100% ring opening, at ambient and high (150 °C) temperatures, with and without water. The simulations showed that the impact of ring openings, with respect to providing molecular mobility, was higher at high temperatures. This was also observed experimentally. Hence, the ring opening had the strongest beneficial effect on "processability" (reduced stiffness and strength) above the glass-transition temperature and in wet conditions. It also had the effect of lowering the glass-transition temperature. The results here showed that molecular dynamics is a valuable tool in the development of wood-based materials with optimal thermoplastic properties.

Excitonic Insulators and Superfluidity in Two-Dimensional Bilayers without External Fields

We explore a new platform for realizing excitonic insulators, namely van der Waals (vdW) bilayers comprising two-dimensional Janus materials. In previous studies, type II heterobilayers have been brought to the excitonic insulating regime by tuning the band alignment using external gates. In contrast, the Janus bilayers presented here represent intrinsic excitonic insulators. We first conduct ab initio calculations to obtain the quasiparticle band structures, screened Coulomb interaction, and interlayer exciton binding energies of the bilayers. These ab initio-derived quantities are then used to construct a BCS-like Hamiltonian of the exciton condensate. By solving the mean-field gap equation, we identify 16 vdW Janus bilayers with insulating ground states and superfluid properties. Our calculations expose a new class of advanced materials that are likely to exhibit novel excitonic phases at low temperatures and highlight the subtle competition between interlayer hybridization, spin-orbit coupling, and dielectric screening that governs their properties.

Sustainable Wheat Protein Biofoams: Dry Upscalable Extrusion at Low Temperature

Glycerol-plasticized wheat gluten was explored for producing soft high-density biofoams using dry upscalable extrusion (avoiding purposely added water). The largest pore size was obtained when using the food grade ammonium bicarbonate (ABC) as blowing agent, also resulting in the highest saline liquid uptake. Foams were, however, also obtained without adding a blowing agent, possibly due to a rapid moisture uptake by the dried protein powder when fed to the extruder. ABC's low decomposition temperature enabled extrusion of the material at a temperature as low as 70 °C, well below the protein aggregation temperature. Sodium bicarbonate (SBC), the most common food-grade blowing agent, did not yield the same high foam qualities. SBC's alkalinity, and the need to use a higher processing temperature (120 °C), resulted in high protein cross-linking and aggregation. The results show the potential of an energy-efficient and industrially upscalable low-temperature foam extrusion process for competitive production of sustainable biofoams using inexpensive and readily available protein obtained from industrial biomass (wheat gluten).

Highly insulating thermoplastic nanocomposites based on a polyolefin ternary blend for high-voltage direct current power cables

Octyl-silane-coated Al₂O₃ nanoparticles are found to be a promising conductivity-reducing additive for thermoplastic ternary blends comprising low-density polyethylene (LDPE), isotactic polypropylene and a styrenic copolymer. The ternary blend nanocomposites were prepared by compounding the blend components together with an LDPE-based masterbatch that contained the nanoparticles. The nanoparticles did not affect the superior stiffness of the ternary blends, compared to neat LDPE, between the melting temperatures of the two polyolefins. As a result, ternary blend nanocomposites comprising 38 wt% polypropylene displayed a storage modulus of more than 10 MPa up to at least 150 °C, independent of the chosen processing conditions. Moreover, the ternary blend nanocomposites featured a low direct-current electrical conductivity of about 3 × 10^-15 S m^-1 at 70 °C and an electric field of 30 kV mm^-1, which could only be achieved through the presence of both polypropylene and Al₂O₃ nanoparticles. This synergistic conductivity-reducing effect may facilitate the design of more resistive thermoplastic insulation materials for high-voltage direct current (HVDC) power cables.

Microplastics Originating from Polymer Blends: An Emerging Threat?

No one can have missed the growing global environmental problems with plastics ending up as microplastics in food, water, and soil, and the associated effects on nature, wildlife, and humans. A hitherto not specifically investigated source of microplastics is polymer blends. A 1 g polymer blend can contain millions to billions of micrometer-sized species of the dispersed phase and therefore aging-induced fragmentation of the polymer blends can lead to the release of an enormous amount of microplastics. Especially if the stability of the dispersed material is higher than that of the surrounding matrix, the risk of microplastic migration is notable, for instance, if the matrix material is biodegradable and the dispersed material is not. The release can also be much faster if the matrix polymer is biodegradable. The purpose of writing this feature article is to arise public and academic attention to the large microplastic risk from polymer blends during their development, production, use, and waste handling.

Starch/Alkane Diol Materials: Unexpected Ultraporous Surfaces, Near-Isoporous Cores, and Films Moving on Water

The aim of this study was to find alternative starch plasticizers to glycerol that yielded a less tacky material in high-moisture conditions without leading to starch crystallization. A range of glycerol films containing different potential plasticizers (linear alkane diols) were therefore produced, and it was shown that 1,3-propanediol, in combination with glycerol, was a possible solution to the problem. Several additional interesting features of the starch films were however also revealed. The larger diols, instead of showing plasticizing features, yielded a variety of unexpected structures and film properties. Films with 1,6-hexanediol and 1,7-heptanediol showed an ultraporous film surface and near-isoporous core. The most striking feature was that starch films with these two diols moved/rotated over the surface when placed on water, with no other stimulus than the interaction with water. Films with 1,8-octanediol and 1,10-decanediol did not show these features, but there was clear evidence of a structure with phase-separated crystallized diol in a starch matrix, as observed in high-resolution scanning electron microscopy (SEM) images.

Biocompatible, Flexible Strain Sensor Fabricated with Polydopamine-Coated Nanocomposites of Nitrile Rubber and Carbon Black

A flexible, biocompatible, nitrile butadiene rubber (NBR)-based strain sensor with high stretchability, good sensitivity, and excellent repeatability is presented for the first time. Carbon black (CB) particles were embedded into an NBR matrix via a dissolving-coating technique, and the obtained NBR/CB composite was coated with polydopamine (PDA) to preserve the CB layer. The mechanical properties of the NBR films were found to be significantly improved with the addition of CB and PDA, and the produced composite films were noncytotoxic and highly biocompatible. Strain-sensing tests showed that the uncoated CB/NBR films possess a high sensing range (strain of ∼550%) and good sensitivity (gauge factor of 52.2), whereas the PDA/NBR/CB films show a somewhat reduced sensing range (strain of ∼180%) but significantly improved sensitivity (gauge factor of 346). The hysteresis curves obtained from cyclic strain-sensing tests demonstrate the prominent robustness of the sensor material. Three novel equations were developed to accurately describe the uniaxial and cyclic strain-sensing behavior observed for the investigated strain sensors. Gloves and knee/elbow covers were produced from the films, revealing that the signals generated by different finger, elbow, and knee movements are easily distinguishable, thus confirming that the PDA/NBR/CB composite films can be used in a wide range of wearable strain sensor applications.

Surgical treatment of basal cell carcinoma: a case series on factors influencing the risk of an incomplete primary excision

BACKGROUND

Basal cell carcinoma (BCC) is the most common skin cancer form, and one first-line treatment is surgical excision. Complete excision is vital to minimize risk of recurrence. Studies on occurrence of incomplete excisions have given diverse results and seldom include large populations from a dermatological setting.

OBJECTIVES

The rate of positive surgical margins in primary surgery of BCC at a tertiary dermatology clinic is studied. Factors associated with an incomplete primary excision are analysed.

METHODS

Patients scheduled for standard excision, without perioperative margin control, of BCC during the years 2008-2015 were prospectively enrolled in the study. Tumour-specific factors, including histopathologic subtype, as well as postoperative outcome were registered. Incomplete excisions were analysed in relation to patient- and tumour-related factors.

RESULTS

In total, 4.6% of 3911 BCC tumours were incompletely excised. The rate of incomplete excisions was higher for facial tumours and among tumours with an aggressive histological subtype. Morpheiform BCC on the nose or ear had the highest rate of an incomplete excision, 61.5% and 50%, respectively.

CONCLUSIONS

Most BCCs, irrespective of subtype, were completely excised during the primary excision. Tumour sites nose and ears were associated with the highest rate of positive primary surgical margins, especially for infiltrative or morpheiform BCCs. Surgery with perioperative examination of margins is strongly recommended for these tumours.

Lamellae-controlled electrical properties of polyethylene - morphology, oxidation and effects of antioxidant on the DC conductivity

Destruction of the spherulite structure in low-density polyethylene (LDPE) is shown to result in a more insulating material at low temperatures, while the reverse effect is observed at high temperatures. On average, the change in morphology reduced the conductivity by a factor of 4, but this morphology-related decrease in conductivity was relatively small compared with the conductivity drop of more than 2 decades that was observed after slight oxidation of the LDPE (at 25 °C and 30 kV mm^-1). The conductivity of LDPE was measured at different temperatures (25-60 °C) and at different electrical field strengths (3.3-30 kV mm^-1) for multiple samples with a total crystalline content of 51 wt%. The transformation from a 5 μm coherent structure of spherulites in the LDPE to an evenly dispersed random lamellar phase (with retained crystallinity) was achieved by extrusion melt processing. The addition of 50 ppm commercial phenolic antioxidant to the LDPE matrix (e.g. for the long-term use of polyethylene in high voltage direct current (HVDC) cables) gave a conductivity ca. 3 times higher than that of the same material without antioxidants at 60 °C (the operating temperature for the cables). For larger amounts of antioxidant up to 1000 ppm, the DC conductivity remained stable at ca. 1 × 10^-14 S m^-1. Finite element modeling (FEM) simulations were carried out to model the phenomena observed, and the results suggested that the higher conductivity of the spherulite-containing LDPE stems from the displacement and increased presence of polymeric irregularities (formed during crystallization) in the border regions of the spherulite structures.

Electrical conductivity of anisotropic PMMA composite filaments with aligned carbon fibers - predicting the influence of measurement direction

In order to study the electrical conductivity of anisotropic PMMA/carbon fiber (CF) composites, cylindrical PMMA/CF filaments were extruded through a capillary rheometer, resulting in an induced CF orientation along the extrusion direction. The aspect ratios of the CFs in the filaments were accurately regulated using a two-step melt mixing process. By measuring the vertical and horizontal resistances of filaments where the outermost layer was successively peeled off, the anisotropic conductivities could be calculated. This was done using a novel analytical model where each cylindrical composite filament was defined as a structure consisting of three concentric cylinders with potentially different conductivities and CF orientations. The electrical conductivity increased with the degree of fiber orientation along the voltage direction and the effects of anisotropy and measurement direction were incorporated into the (isotropic) McLachlan equation. The required distance for electrical contact between the CFs was calculated to be 16 nm. Finite element (FEM) simulations were successfully utilized to confirm the data.

Revealed logarithm longitude electrical conductivity σ_∥ and transverse electrical conductivity σ_⊥ of PMMA/CF composite filaments.

Understanding and modelling the diffusion process of low molecular weight substances in polyethylene pipes

Peroxides are widely used as crosslinkers in polyethylene (PE) drinking water pipes. Cross-linked polyethylene (PEX) has better mechanical properties than PE, but peroxide decomposition by-products can migrate from PEX water pipes into the drinking water unless sufficient preventive actions are undertaken. This work systematically examines the migration of tert-Butyl methyl ether (MTBE), a dominating crosslinking by-product from PEX water pipes, into tap water by utilizing both experimental techniques and finite element (FEM) diffusion modeling. The effects of pipe geometry, tap water temperature (23-80 °C), boundary conditions (air or water interface) and degasing (at 180 °C) were considered. The MTBE diffusivity increased strongly with increasing temperature and it was concluded that a desired water quality can be achieved with proper degasing of the PEX pipes. As the FEM simulations were in excellent agreement with the experimental results, the model can accurately predict the MTBE concentration as a function of time, water temperature and PEX pipe geometry, and enable the pipe manufacturers to aid in ensuring desirable drinking water quality.

Novel definition of the synergistic effect between carbon nanotubes and carbon black for electrical conductivity

Anisotropic ternary composites comprising poly(methy-methacrylate) (PMMA), carbon black (CB), and carbon nanotubes (CNTs) were extruded using a capillary rheometer and the electrical conductivities of the composites were measured and presented in a detailed contour plot covering a large range of filler fractions (up to 30 vol% CNTs, 20 vol% CB). A recent generic conductivity model for ternary composites was successfully validated using the conductivity measurements. When analyzing the conductivity measurements using four traditional definitions of 'synergy' between two conductive fillers, no clear synergetic effect was observed between CB and CNT. Also, when all the conductivity data for ternary CNT/CB composites from the existing literature was carefully gathered and analyzed, the number of confirmed occurrences of strong and convincing CNT/CB synergies was surprisingly low. Finally, a novel definition of synergy based on the physical aspect, in particular, its maximum, the 'synergasm', was defined in order to obtain a more precise instrument for revealing regions of potential synergy.

Characterization of Reduced and Surface-Modified Graphene Oxide in Poly(Ethylene-co-Butyl Acrylate) Composites for Electrical Applications

Promising electrical field grading materials (FGMs) for high-voltage direct-current (HVDC) applications have been designed by dispersing reduced graphene oxide (rGO) grafted with relatively short chains of poly (n-butyl methacrylate) (PBMA) in a poly(ethylene-co-butyl acrylate) (EBA) matrix. All rGO-PBMA composites with a filler fraction above 3 vol.% exhibited a distinct non-linear resistivity with increasing electric field; and it was confirmed that the resistivity could be tailored by changing the PBMA graft length or the rGO filler fraction. A combined image analysis- and Monte-Carlo simulation strategy revealed that the addition of PBMA grafts improved the enthalpic solubility of rGO in EBA; resulting in improved particle dispersion and more controlled flake-to-flake distances. The addition of rGO and rGO-PBMAs increased the modulus of the materials up to 200% and the strain did not vary significantly as compared to that of the reference matrix for the rGO-PBMA-2 vol.% composites; indicating that the interphase between the rGO and EBA was subsequently improved. The new composites have comparable electrical properties as today's commercial FGMs; but are lighter and less brittle due to a lower filler fraction of semi-conductive particles (3 vol.% instead of 30-40 vol.%).

Is dissolved COD a suitable design parameter for ozone oxidation of organic micropollutants in wastewater?

Ozone oxidation of organic micropollutants in biologically treated wastewater was investigated in pilot-scale after a high- and a low loaded activated sludge process. Higher ozone doses were required to remove organic micropollutants in the effluent wastewater from the high loaded activated sludge process. Further comparison of the micropollutant removal was based on normalized ozone doses, expressed as g O₃/g DOC and g O₃/g soluble COD (sCOD). A clear difference was noted for the two effluents when the micropollutant removal was normalized by DOC. This difference disappeared almost completely when the removal was linked to ozone doses normalized by sCOD. The dose-response curves for the organic micropollutants were practically linear in the removal range up to 95%. A linear prediction model was developed and compared with literature values to test the transferability of the obtained results. Results from this comparison indicated that the slope of the dose-response functions could be used to predict the removal efficiency of organic micropollutants at a third plant with an average uncertainty of 10%. The modeled ozone requirements were then set in relation to the COD concentrations in the discharged water from approximately 90 Swedish activated sludge treatment plants with and without nitrogen removal. This comparison highlighted the need for a well-functioning biological treatment for an effective ozone oxidation of organic micropollutants. The results in this study suggest that soluble COD should be further explored for design and modeling of ozone oxidation of organic micropollutants in biologically treated wastewater.

Abstract P3-03-12: SentiDose interim analysis. A dose optimizing study with a super paramagnetic iron oxide for sentinel node detection

Background

Superparamagnetic iron oxide nanoparticles (SPIO) is a novel tracer for axillary mapping in breast cancer with comparable performance to the dual standard of isotope and blue dye. The earlier SPIO (Sienna+®) required 2 ml of SPIO diluted in 3 ml NaCl and was injected retro-areolarly. This was considered to be associated with the discoloration observed in 40% of breast conservation cases. Subsequently, a new form was developed (SiennaXPTM) in a volume of 2 ml without dilution. The aim of the ongoing SentiDose study is to compare smaller doses of SiennaXPTM injected in different time-frames (1.5 ml periareolarly on the operation day vs 1 ml peritumourally 1-7 days preoperatively) and compare it to the performance of the original SPIO (Sienna+®). A background mapping with isotope and blue dye was performed for assessment of concordance.

Method

In all, 330 patients will be recruited from six sites in Sweden, divided in two isonumerical cohorts injected as described above. Results from the 1.5 ml cohort are presented and compared on a patient-level analysis to the SentiMag Nordic trial that used Sienna+®, on a 2-sided non-inferiority margin of 5%. Study endpoints are detection rate per patient, number of sentinel nodes (SN) retrieved and discoloration at 3 weeks postoperatively.

Results

Detection rate for SiennaXPTM, 1.5 ml, was comparable with Sienna+® (96.9 vs 97.6%, p=0.76), even in multivariate analysis adjusting for age and metastasis rate (Exp(B)=0.68; 95% CI; 0.18-2.60, p=0.58). with a high concordance between isotope and SiennaXPTM. The number of SNs were similar (1.91 vs. 1.83, p=0.08) for Sienna+® and SiennaXPTM. Discoloration rate was lower for SiennaXPTM compared to Sienna+® (14.3% vs. 38.2%, p&lt;0.001) after breast conserving surgery. Furthermore, two patients were excluded in the SentiDose cohort due to protocol violation.

Demographics and outcomes are illustrated in

Table 1 Nordic SentiMag Trial (n=206)SentiDose 1.5ml Cohort (n=163)p-valueAge (yrs)61.864.30.03BMI (kg/m2)26.927.20.84Size (mm)19.220.00.64Type of Surgery (BCS/Mx)154 (74.8%) / 52 (25.2%)130 (79.8%) / 33 (20.2%)0.26SPIO Detection Rate (per patient)97.6%96.9%0.76SPIO-Tc Concordance97.5%97.5%0.42Mean SPIO detected SN1,831,910.08Metastasis Rate26.2%16.0%0.01SPIO nodal rate in malignancy91.2%81.6%0.21Discoloration in BCS38.2%14.3%&lt;0.001

Conclusion

The periareolar injection of 1.5 ml SiennaXPTM on the day of the operation provides comparable detection rates with much less skin discoloration, providing effectivity and flexibility. The completion of the SentiDose study will allow for more definitive results on the dose, timeframe and injection site of SPIO.

Citation Format: Hersi A-F, Obondo C, Pistioli L, Abdsaleh S, Nilsson F, Mohammed I, Eriksson S, Wärnberg F, Karakatsanis A. SentiDose interim analysis. A dose optimizing study with a super paramagnetic iron oxide for sentinel node detection [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P3-03-12.

Critical considerations on load-to-failure test for monolithic zirconia molar crowns

Application of monolithic zirconia crowns (MZCs) with reduced thickness to the molar region has been proposed, but potential complications have yet to be fully evaluated in laboratory tests. The present study aimed to develop a clinically relevant load-to-failure test in combination with fatigue treatments involving thermal and mechanical cycling (TC and MC) to evaluate the fracture resistance of molar MZCs. MZCs with a minimal thickness of 0.5 mm were bonded to dies made of resin-based composite (RBC), epoxy resin (EP), or polyoxymethylene-copolymer (POM-C). The samples were either untreated (UT) or subjected to TC (5-55 °C for 1 × 10⁵ cycles) and MC (300 N for 2.4 × 10⁶ cycles). The stress generated by TC and MC was simulated by finite element modeling. The load-to-failure test was performed using an inverse V-shaped two-plane indenter and was followed by fractographic analysis. The median values of fracture load for MZC/RBC and MZC/EP in the TC group were significantly lower than those in the UT group. MC also decreased the median value of fracture load for MZC/RBC significantly, but not that for MZC/EP and MZC/POM-C. Fractography revealed that the fracture started in the cervical area in all groups, which is similar to clinically failed crowns. The simulation confirmed stress concentration at the cervical area in both TC and MC groups. The present study suggests that the load-to-failure test using a two-plane indenter could induce clinically relevant fracture of MZCs, the vulnerability of the MZCs depends largely on the die material employed, and MZCs are more likely to be damaged by thermal fatigue than mechanical fatigue.

First-principle simulations of electronic structure in semicrystalline polyethylene

In order to increase our fundamental knowledge about high-voltage cable insulation materials, realistic polyethylene (PE) structures, generated with a novel molecular modeling strategy, have been analyzed using first principle electronic structure simulations. The PE structures were constructed by first generating atomistic PE configurations with an off-lattice Monte Carlo method and then equilibrating the structures at the desired temperature and pressure using molecular dynamics simulations. Semicrystalline, fully crystalline and fully amorphous PE, in some cases including crosslinks and short-chain branches, were analyzed. The modeled PE had a structure in agreement with established experimental data. Linear-scaling density functional theory (LS-DFT) was used to examine the electronic structure (e.g., spatial distribution of molecular orbitals, bandgaps and mobility edges) on all the materials, whereas conventional DFT was used to validate the LS-DFT results on small systems. When hybrid functionals were used, the simulated bandgaps were close to the experimental values. The localization of valence and conduction band states was demonstrated. The localized states in the conduction band were primarily found in the free volume (result of gauche conformations) present in the amorphous regions. For branched and crosslinked structures, the localized electronic states closest to the valence band edge were positioned at branches and crosslinks, respectively. At 0 K, the activation energy for transport was lower for holes than for electrons. However, at room temperature, the effective activation energy was very low (∼0.1 eV) for both holes and electrons, which indicates that the mobility will be relatively high even below the mobility edges and suggests that charge carriers can be hot carriers above the mobility edges in the presence of a high electrical field.

Three-Dimensional Nanometer Features of Direct Current Electrical Trees in Low-Density Polyethylene

Electrical trees are one reason for the breakdown of insulating materials in electrical power systems. An understanding of the growth of electrical trees plays a crucial role in the development of reliable high voltage direct current (HVDC) power grid systems with transmission voltages up to 1 MV. A section that contained an electrical tree in low-density polyethylene (LDPE) has been visualized in three dimensions (3D) with a resolution of 92 nm by X-ray ptychographic tomography. The 3D imaging revealed prechannel-formations with a lower density with the width of a couple of hundred nanometers formed around the main branch of the electrical tree. The prechannel structures were partially connected with the main tree via paths through material with a lower density, proving that the tree had grown in a step-by-step manner via the prestep structures formed in front of the main channels. All the prechannel structures had a size well below the limit of the Paschen law and were thus not formed by partial discharges. Instead, it is suggested that the prechannel structures were formed by electro-mechanical stress and impact ionization, where the former was confirmed by simulations to be a potential explanation with electro-mechanical stress tensors being almost of the same order of magnitude as the short-term modulus of low-density polyethylene.

Conductive biofoams of wheat gluten containing carbon nanotubes, carbon black or reduced graphene oxide

Conductive biofoams made from glycerol-plasticized wheat gluten (WGG) are presented as a potential substitute in electrical applications for conductive polymer foams from crude oil.

Population-based cohort study of variation in the use of emergency cholecystectomy for benign gallbladder diseases

Background

The aims of this prospective population-based cohort study were to identify the patient and hospital characteristics associated with emergency cholecystectomy, and the influences of these in determining variations between hospitals.

Methods

Data were collected for consecutive patients undergoing cholecystectomy in acute UK and Irish hospitals between 1 March and 1 May 2014. Potential explanatory variables influencing the performance of emergency cholecystectomy were analysed by means of multilevel, multivariable logistic regression modelling using a two-level hierarchical structure with patients (level 1) nested within hospitals (level 2).

Results

Data were collected on 4744 cholecystectomies from 165 hospitals. Increasing age, lower ASA fitness grade, biliary colic, the need for further imaging (magnetic retrograde cholangiopancreatography), endoscopic interventions (endoscopic retrograde cholangiopancreatography) and admission to a non-biliary centre significantly reduced the likelihood of an emergency cholecystectomy being performed. The multilevel model was used to calculate the probability of receiving an emergency cholecystectomy for a woman aged 40 years or over with an ASA grade of I or II and a BMI of at least 25·0 kg/m2, who presented with acute cholecystitis with an ultrasound scan showing a thick-walled gallbladder and a normal common bile duct. The mean predicted probability of receiving an emergency cholecystectomy was 0·52 (95 per cent c.i. 0·45 to 0·57). The predicted probabilities ranged from 0·02 to 0·95 across the 165 hospitals, demonstrating significant variation between hospitals.

Conclusion

Patients with similar characteristics presenting to different hospitals with acute gallbladder pathology do not receive comparable care.

Hydrophobic matrix-free graphene-oxide composites with isotropic and nematic states

We demonstrate a novel route to synthesise hydrophobic matrix-free composites of polymer-grafted graphene oxide (GO) showing isotropic or nematic alignment and shape-memory effects. For the first time, a cationic macroinitiator (MI) has been immobilised on anionic GO and subsequently grafted with hydrophobic polymer grafts. Dense grafts of PBA, PBMA and PMMA with a wide range of average graft lengths (MW: 1-440 kDa) were polymerised by surface-initiated controlled radical precipitation polymerisation from the statistical MI. The surface modification is designed similarly to bimodal graft systems, where the cationic MI generates nanoparticle repulsion, similar to dense short grafts, while the long grafts offer miscibility in non-polar environments and cohesion. The state-of-the-art dispersions of grafted GO were in the isotropic state. Transparent and translucent matrix-free GO-composites could be melt-processed directly using only grafted GO. After processing, birefringence due to nematic alignment of grafted GO was observed as a single giant Maltese cross, 3.4 cm across. Permeability models for composites containing aligned 2D-fillers were developed, which were compared with the experimental oxygen permeability data and found to be consistent with isotropic or nematic states. The storage modulus of the matrix-free GO-composites increased with GO content (50% increase at 0.67 wt%), while the significant increases in the thermal stability (up to 130 °C) and the glass transition temperature (up to 17 °C) were dependent on graft length. The tuneable matrix-free GO-composites with rapid thermo-responsive shape-memory effects are promising candidates for a vast range of applications, especially selective membranes and sensors.

Correction: Hydrophobic matrix-free graphene-oxide composites with isotropic and nematic states

Correction for 'Hydrophobic matrix-free graphene-oxide composites with isotropic and nematic states' by Martin Wåhlander, et al., Nanoscale, 2016, DOI: 10.1039/c6nr01502f.

Preoperative prediction of histopathological outcome in basal cell carcinoma: flat surface and multiple small erosions predict superficial basal cell carcinoma in lighter skin types

BACKGROUND

Prediction of the histopathological subtype of basal cell carcinoma (BCC) is important for tailoring optimal treatment, especially in patients with suspected superficial BCC (sBCC).

OBJECTIVES

To assess the accuracy of the preoperative prediction of subtypes of BCC in clinical practice, to evaluate whether dermoscopic examination enhances accuracy and to find dermoscopic criteria for discriminating sBCC from other subtypes.

MATERIALS AND METHODS

The main presurgical diagnosis was compared with the histopathological, postoperative diagnosis of routinely excised skin tumours in a predominantly fair-skinned patient cohort of northern Europe during a study period of 3 years (2011-13). The study period was split in two: during period 1, dermoscopy was optional (850 cases with a pre- or postoperative diagnosis of BCC), while during period 2 (after an educational dermoscopic update) dermoscopy was mandatory (651 cases). A classification tree based on clinical and dermoscopic features for prediction of sBCC was applied.

RESULTS

For a total of 3544 excised skin tumours, the sensitivity for the diagnosis of BCC (any subtype) was 93·3%, specificity 91·8%, and the positive predictive value (PPV) 89·0%. The diagnostic accuracy as well as the PPV and the positive likelihood ratio for sBCC were significantly higher when dermoscopy was mandatory. A flat surface and multiple small erosions predicted sBCC.

CONCLUSIONS

The study shows a high accuracy for an overall diagnosis of BCC and increased accuracy in prediction of sBCC for the period when dermoscopy was applied in all cases. The most discriminating findings for sBCC, based on clinical and dermoscopic features in this fair-skinned population, were a flat surface and multiple small erosions.

Safety of Etoricoxib, Celecoxib, and Nonselective Nonsteroidal Antiinflammatory Drugs in Ankylosing Spondylitis and Other Spondyloarthritis Patients: A Swedish National Population-Based Cohort Study

OBJECTIVE

Safety data regarding the use of etoricoxib and other nonsteroidal antiinflammatory drugs (NSAIDs) in ankylosing spondylitis (AS) and other spondyloarthritis (SpA) patients are rather limited. Our objective was to estimate and compare rates of gastrointestinal, renovascular, and cardiovascular adverse events in patients exposed to etoricoxib, celecoxib, or nonselective NSAIDs or totally unexposed to NSAIDs.

METHODS

We performed a national register-based cohort study on patients with AS or SpA (n = 21,872) identified in the Swedish national patient register from 1987-2009. Treatment exposure was assessed time dependently based on the prescription drug register from 2006-2009, adjusting for sociodemographics and comorbidities derived from national population-based registers.

RESULTS

Exposure to etoricoxib, celecoxib, and nonselective NSAIDs was 7.6%, 3.9%, and 71.2%, respectively. No major risk differences for serious cardiovascular, gastrointestinal, or renal adverse events were seen among the 3 exposure groups. Patients unexposed to NSAIDs had more baseline comorbidities and an increased relative risk for congestive heart failure events during the study period (2.0, 95% confidence interval [95% CI] 1.3-3.2). The relative risk for atherosclerotic events was nonsignificant when compared to the nonselective NSAID group (1.0, 95% CI 0.7-1.5), while the relative risk for gastrointestinal events was lower for unexposed patients (0.5, 95% CI 0.4-0.7).

CONCLUSION

Overall, serious adverse events related to nonselective NSAIDs, etoricoxib, and celecoxib were similar and in the range of what would be expected in a group of SpA patients. Patients unexposed to NSAIDs had considerably more baseline comorbidities and increased risk for congestive heart failure, reflecting a selection of patients being prescribed NSAIDs in clinical practice.

Budesonide inhaler device switch patterns in an asthma population in Swedish clinical practice (ASSURE)

BACKGROUND

Dry powder inhaler (DPI) device switch in asthma treatment could potentially increase with the entrance of new devices. We examined the switch patterns of budesonide (BUD) DPI analogues available in Sweden.

METHODS

This observational real-life study linked primary healthcare medical records data from the Västra Götaland region to national Swedish registries, and included asthma patients (ICD-10-CM J45) prescribed BUD in a multidose DPI. Index date: first dispense of BUD DPI. Switch date: prescription of another BUD DPI device. Study outcomes (switch vs. non-switch) were exacerbations and prescription of short-acting β2 -agonists. Study period was 1 July 2005 to 31 October 2013.

RESULTS

Overall, 15,169 asthma patients were on treatment with BUD DPI; 1178 (7.35%) switched to another BUD DPI during the study. Pair-wise 1:1 matching of switchers vs. non-switchers resulted in two groups of 463 patients each (mean age 36 years, 55% female patients). A 25% higher exacerbation rate was seen postswitch (0.40 vs. 0.32; p = 0.047). Switchers were 4.5 year younger and had lower medication possession rate than non-switchers. Switch without primary healthcare visit did not differ between groups regarding consultations and exacerbations (no visit 4.96 and 0.90; visit 4.29 and 0.77, respectively). However, patients without primary healthcare visit at switch had significantly more outpatient hospital visits (2.01 vs. 0.81; p < 0.001).

CONCLUSIONS

Considering the low switch rate, asthma patients and physicians in Swedish general practice seem reluctant to switch to another BUD DPI device. Switch, especially without primary healthcare visit, was associated with decreased asthma control resulting in higher exacerbation rate and more outpatient hospital visits.

A prospective, multicenter validation study of a prognostic index composed of S-phase fraction, progesterone receptor status, and tumour size predicts survival in node-negative breast cancer patients: NNBC, the node-negative breast cancer trial

BACKGROUND

In a retrospective study on node-negative breast cancer, a prognostic index consisting of a proliferation factor, S-phase fraction (SPF), progesterone receptor status (PR), and tumour size identified one-third of patients as high risk, with a sixfold increased risk of breast cancer death. This prospective multicenter cohort study was set up to validate the index.

PATIENTS AND METHODS

In 576 T1-2N0 patients <60 years, prospective analyses of PR and SPF were carried out. High risk was defined as ≥2 of the following: size >20 mm, PR-negativity, and high SPF (in the absence of SPF, Bloom-Richardson grade 3). Median follow-up was 17.8 years.

RESULTS

Thirty-one percent were high risk. In univariate analysis, the index was prognostic for breast cancer-specific survival after 5 years [hazard ratio (HR) = 4.7, 95% confidence interval (95% CI) 2.5-8.9], 10 years (HR = 2.2, 95% CI 1.5-3.3), and 15 years (HR = 1.7, 95% CI 1.2-2.5), and remained significant after adjustment for adjuvant medical treatment and age. In the 37% of patients with no risk factors, only one patient died of breast cancer the first 5 years.

CONCLUSIONS

This prospective study validates a prognostic index consisting of a proliferation factor, PR-status, and tumour size. The index may be helpful for prognostic considerations and for selection of patients in need of adjuvant therapy.

Thermal conductivity and combustion properties of wheat gluten foams

Freeze-dried wheat gluten foams were evaluated with respect to their thermal and fire-retardant properties, which are important for insulation applications. The thermal properties were assessed by differential scanning calorimetry, the laser flash method and a hot plate method. The unplasticised foam showed a similar specific heat capacity, a lower thermal diffusivity and a slightly higher thermal conductivity than conventional rigid polystyrene and polyurethane insulation foams. Interestingly, the thermal conductivity was similar to that of closed cell polyethylene and glass-wool insulation materials. Cone calorimetry showed that, compared to a polyurethane foam, both unplasticised and glycerol-plasticised foams had a significantly longer time to ignition, a lower effective heat of combustion and a higher char content. Overall, the unplasticised foam showed better fire-proof properties than the plasticized foam. The UL 94 test revealed that the unplasticised foam did not drip (form droplets of low viscous material) and, although the burning times varied, self-extinguished after flame removal. To conclude both the insulation and fire-retardant properties were very promising for the wheat gluten foam.