Granular circulation in a cylindrical pan: simulations of reversing radial and tangential flows

Granular flows due to simultaneous vertical and horizontal excitations of a flat-bottomed cylindrical pan are investigated using event-driven molecular dynamics simulations. In agreement with recent experimental results, we observe a transition from a solid-like state, to a fluidized state in which circulatory flow occurs simultaneously in the radial and tangential directions. By going beyond the range of conditions explored experimentally, we find that each of these circulations reverse their direction as a function of the control parameters of the motion. We numerically evaluate the dynamical phase diagram for this system and show, using a simple model, that the solid-fluid transition can be understood in terms of a critical value of the radial acceleration of the pan bottom; and that the circulation reversals are controlled by the phase shift relating the horizontal and vertical components of the vibrations. We also discuss the crucial role played by the geometry of the boundary conditions, and point out a relationship of the circulation observed here and the flows generated in vibratory conveyors.Comment: 10 pages, 8 figure

Nanocellulose-polypyrrole-coated paperboard for food packaging application

Currently, studies on packaging that improves the shelf life of perishable food while reducing the waste that is produced upon disposal are encouraged. Thus, exploration of the property improvement of paperboard (Pb) packaging is of interest since this type of packaging is biodegradable and recyclable. This work emphasizes the added value of (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl (TEMPO) oxidized cellulose nanofibres (TOCN) and polypyrrole (PPy) coating on such paperboard. The mechanical properties and reduced gas permeability of the coated paperboard (CPb) were significantly improved due to the dense network formed by TOCN and polypyrrole particles. These results suggest that surface coating by polypyrrole particles may be utilized for the manufacture of multilayer paperboard containers in industrial applications to reduce packaging waste generated by the often added conventional plastic. © 2018 Elsevier B.V

Effect of boundary conditions on diffusion in two-dimensional granular gases

We analyze the influence of boundary conditions on numerical simulations of the diffusive properties of a two dimensional granular gas. We show in particular that periodic boundary conditions introduce unphysical correlations in time which cause the coefficient of diffusion to be strongly dependent on the system size. On the other hand, in large enough systems with hard walls at the boundaries, diffusion is found to be independent of the system size. We compare the results obtained in this case with Langevin theory for an elastic gas. Good agreement is found. We then calculate the relaxation time and the influence of the mass for a particle of radius $R_s$ in a sea of particles of radius $R_b$. As granular gases are dissipative, we also study the influence of an external random force on the diffusion process in a forced dissipative system. In particular, we analyze differences in the mean square velocity and displacement between the elastic and inelastic cases.Comment: 15 figures eps figures, include

Conductive nanocomposites based on TEMPO-oxidized cellulose and poly(N-3-aminopropylpyrrole-co-pyrrole)

In this paper, conductive composite films were synthetized based on oxidized cellulosic nanofibres (CNFo), 1-(2-cyanoethyl)pyrrole and pyrrole. The 1-(2-cyanoethyl)pyrrole was reduced into N-(3-aminopropyl)pyrrole before being grafted on carboxyl groups of CNFo. Oxidative polymerization of polypyrrole (Ppy) was conducted in an iron(III) chloride (FeCl3) solution, onto the N-(3-aminopropyl)pyrrole grafted. The resulting composite films were characterized by FTIR-ATR Spectroscopy, scanning electron microscopy (SEM) equipped with energy-dispersive x-ray spectroscopy (EDX), tensile strength measurement, thermogravimetric analysis (TGA), wettability and electrical conductivity measurements. The grafting of 1-(2-cyanoethyl)pyrrole played a leading role in improving these properties by increasing potential connections between chains of conducting polymer and cellulose fibres. The outcomes show that the PPy nanoparticles coating on the grafted films increase a lot of characteristics of our composite such as wettability, mechanical properties, thermal protection and more importantly the electrical conductivity which was improved by a 10E5 factor in comparison to the uncoated films. In this condition, this nanostructure could be considered in the design of high-performance electrodes for supercapacitor, battery and sensor applications. © 2016 Elsevier B.V

Printed microwave frequency humidity sensor operating with phase shifting scheme

This paper investigates a shifting sensing scheme combining slots, transmission lines, and printing technologies. This sensing scheme translates the electrical sensitivity of a transmission line conductor to the insertion phase as a measurement variable. A coplanar waveguide (CPW) based structure was designed, screen-printed, and tested on relative humidity (RH) conditions ranging from 22.8-75.3 %RH. For the first time, a composite material made of poly-pyrrole and TEMPO Oxidized Cellulose Nanofibers (TOCN/PPy) was integrated to the structure and studied as a humidity sensitive conductor in microwave frequencies. The measured sensitivity was 0.154°/%RH at 5.870 GHz, while insertion losses decreased by 1.26 dB. The effects of sensing layers thickness as well as trade-off considerations between phase sensitivity and signal attenuation were analyzed by simulation. © 2001-2012 IEEE

Mechanical and antibacterial properties of a nanocellulose-polypyrrole multilayer composite

In this study, a composite film based on TEMPO-oxidized cellulose nanofibers (TOCN), polyvinyl alcohol (PVA) and polypyrrole (PPy) was synthesized in situ by a chemical polymerization, resulting in the induced absorption of PPy on the surface of the TOCN. The composite films were investigated with scanning electron microscopy, thermogravimetric analysis, contact angle measurements, mechanical tests, and evaluation of antibacterial properties. The developed composite has nearly identical Young modulus (3.4 GPa), elongation (2.6%) and tensile stress (about 51 MPa) to TOCN even if PPy, which as poor properties by itself, was incorporated. From the energy-dispersive X-ray spectroscopy (EDX) results, it was shown that PPy is mainly located on the composite surface. Results confirmed by an increase from 54.5 to 83° in contact angle, an increased heat protection (Thermogravimetric analysis) and a decrease in surface energy. The nanocomposites were also evaluated for antibacterial activity against bacteria occasionally found in food: Gram-positive Bacillus subtilis (B. subtilis) and Gram-negative bacteria Escherichia coli (E. coli). The results indicate that the nanocomposites are effective against all of the bacteria studied as shown by the decrease of 5.2 log colony forming units (CFU) for B. subtilis and 6.5 log CFU for E. coli. Resulting in the total destruction of the studied bacteria. The perfect match between the resulting inhibition zone and the composite surface area has demonstrated that our composite was contact active with a slight leaching of PPy. Our composite was successful as an active packaging on meat (liver) as bacteria were killed by contact, thereby preventing the spread of possible diseases. While it has not been tested on bacteria found in medicine, TOCN/PVA-PPy film may be able to act as an active sterile packaging for surgical instruments. © 2016 Elsevier B.V

Polypyrrole/nanocellulose composite for food preservation: barrier and antioxidant characterization

When food cannot be consumed immediately after production, food packaging must create a protective atmosphere around the food product. The packaging must improve the shelf life of perishable foods and protect the food from dirt, dust, oxygen, light, pathogenic microorganisms, and moisture by acting as an effective barrier to moisture, gases (CO2 and O2) or even by possessing antimicrobial properties. However, extending the shelf life and enhancing food quality while reducing packaging waste is encouraged. The exploration of new bio-based packaging materials, such as TEMPO-oxidize nanofibrillated cellulose (TOCN), has increased due to its biodegradable and renewable character. This work emphasizes the antioxidant activity and high barrier properties against the diffusion of oxygen, carbon dioxide and water vapor from a nanocomposite based on polypyrrole (PPy) and TOCN, as well as its biodegradability for food packaging applications. The preparation, characterization and application of the nanocomposite in food packaging are discussed. © 2017 Elsevier Lt

Environmentally-friendly cellulose nanofibre sheets for humidity sensing in microwave frequencies

This paper investigates environment friendly cellulose nanofibres (CNF) as new and sensitive material for humidity sensing in RF/microwave frequencies. CNF sheets were fabricated by sonocatalyzed TEMPO process and physically characterized. Humidity sensing investigation was performed with CNF sheets taped on the top of circuits in coplanar waveguide (CPW) technology. This investigation includes sensitivity and dynamic range analysis with reflected waves along the CPW circuit through resonant frequency shift, and transmitted waves through S21 phase shift. Moreover, sheets with various amounts of CNF were used to study the influence of CNF weight on humidity sensing performances. Regarding the resonant frequency shift, the best sensitivity was measured with the weightier CNF film (71 g/m2), that is 2.82 MHz/%RH from 55%RH to 100%RH. Regarding the phase shift, the same film sensitivity is 0.7°/%RH from 70%RH to 100%RH, with a figure of merit of 7.43°/dB as a phase shifter. © 2017 Elsevier B.V

TEMPO-oxidized cellulose nanofibre (TOCN) films and composites with PVOH as sensitive dielectrics for microwave humidity sensing

This paper investigates TEMPO oxidized cellulose nanofibers (so-called TOCN)films as sensitive dielectrics for humidity detection in microwave frequencies. TOCN is used either as a sensitive material or as a host-matrix enclosing polyvinyl alcohol (PVOH)to achieve highly sensitive humidity sensing. A resonator in coplanar waveguide grounded (CPWG)technology was designed and fabricated. TOCN and TOCN/PVOH gels were dropped in the area of the resonator where the analysis showed the electromagnetic field to be maximum at the resonance. Gels became thin films after drying. Experimental humidity tests were then conducted within the 21.9–89.3%RH range, using the resonant frequency and the transmission phase as measurement variables. The best sensitivity with TOCN was 2.67 MHz/%RH regarding the resonant frequency, and 0.523°/%RH regarding the transmission phase. The effects of PVOH were visible starting from 55%RH, where the sensitivity was raised to 6.000 MHz/%RH and 0.785°/%RH respectively. © 2019 Elsevier B.V

The UK prevalence of hereditary haemorrhagic telangiectasia and its association with sex, socioeconomic status and region of residence: a population-based study

Background Hereditary haemorrhagic telangiectasia (HHT) is an autosomal dominant genetic disorder of aberrant blood vessel development characterised by arteriovenous malformations. HHT is associated with significant morbidity due to complications including epistaxis, gastrointestinal bleeding and stroke. We explored the hypothesis that a diagnosis of HHT is associated with sex, socioeconomic status and geographical location.Methods We used The Health Improvement Network, a longitudinal, computerised general practice database covering 5% of the UK population to calculate prevalence estimates for HHT stratified by age, sex, socioeconomic status and geographical location.Results The 2010 UK point prevalence for HHT was 1.06/10 000 person years (95% CI 0.95 to 1.17) or 1 in 9400 individuals. The diagnosed prevalence of HHT was significantly higher in women compared with men (adjusted prevalence rate ratio (PRR) 1.53, 95% CI 1.24 to 1.88) and in those from the most affluent socioeconomic group compared with the least (adjusted PRR 1.74, 95% CI 1.14 to 2.64). The PRR varied between different regions of the UK, being highest in the South West and lowest in the West Midlands (adjusted PRR for former compared with latter 1.86, 95% CI 1.61 to 2.15).Conclusions HHT prevalence is more common in the UK population than previously demonstrated, though this updated figure is still likely to be an underestimate. HHT appears to be significantly under-diagnosed in men, which is likely to reflect their lower rates of consultation with primary care services. There is under-diagnosis in patients from lower socioeconomic groups and a marked variation in the prevalence of diagnosis between different geographical regions across the UK that requires further investigation