Hyperbaric storage at and above room temperature of a highly perishable food

Hyperbaric storage at naturally variable room temperature (RT) conditions (18–21 °C) and above (30 °C) was evaluated as a possible new food preservation method, regardless of temperature. Preservation of watermelon juice (used as a case study of a highly perishable food) at RT and 5 °C at atmospheric pressure was compared to preservation under 100 MPa at RT. After 8 h of hyperbaric storage at 100 MPa, the initial microbial loads of the watermelon juice were reduced by 1 log unit for total aerobic mesophiles, and 1–2 log units for Enterobacteriaceae and yeasts and moulds, to levels of about 3 log units for the former and below the detection limit for the latter, and remained thereafter unchanged up to 60 h. Similar results were obtained at 30 °C at 100 MPa after 8 h. At atmospheric pressure at RT (24 h) and 30 °C (8 h), microbial levels were already above quantification limits and unacceptable for consumption. Furthermore, pressure attenuated the increase in titratable acidity verified at atmospheric pressure, but caused higher colour changes, especially a higher lightness and a lower browning degree. Post-hyperbaric storage at 5 °C revealed an extended shelf life, as an additional benefit of hyperbaric storage. These results show that hyperbaric storage is a very promising food preservation methodology.     

A Low-Power Wakeup Radio for Application in WSN-Based Indoor Location Systems

This paper presents a low-power wakeup radio (WUR) for application in indoor location systems. The presented radio has a better performance than the state-of-the-art radios, since it has low-power consumption, only 10 μW and it is perfectly integrated into a wireless sensor network based on ZigBee, which is used for location purposes. This performance was achieved due to an optimised radio frequency design of the WUR, which was embedded with a low-cost/low-power processor, and due to an enhanced control algorithm. Moreover, a software defined radio approach has been used to implement the WUR protocol. The WUR was designed and integrated in an existing WSN-based indoor location system which was originally based on a periodic sleep-wake up duty-cycled protocol. In the WUR protocol the location sensor is kept in deep sleep mode until it receives an external wake-up order. According to estimates, with this scheme, the battery lifetime can be increased from 200 days (using conventional duty-cycle protocol) up to almost 8000 days (sensor waken-up few times per day).     

An accurate method to determine the through-plane electrical conductivity and to study transport properties in film samples

The through-plane conductivity of a film sample is critically important because it largely affects the performance of batteries, capacitors, and thermoelectric devices. In this study, we developed a modified four-probe through-plane electrical conductivity measurement method using a coaxial structure. This method is general and works for free-standing film samples. We studied different samples including a steel sheet, highly oriented pyrolytic graphite, and conducting polymers. We confirmed metallic transportation in the steel sheet and hopping transportation in graphite in the through-plane direction by conducting low temperature measurements at 100 K. In the case of a conducting polymer poly(3,4-ethylenedioxythiophene)/polystyrene sulfonate, the conductivity anisotropic ratio decreases with increasing in-plane conductivity. Temperature dependent measurements show two distinct activation energy regimes in the through-plane direction in PEDOT/PSS but almost no change in the in-plane electrical conductivity activation energy. This could be due to additional carrier paths that occur through the more disordered region (the PSS-rich region) in the through-plane direction. We also examined the Meyer–Neldel rule in PEDOT/PSS and concluded that PEDOT/PSS follows the anti-Meyer–Neldel rule, likely due to the high carrier density in the film.     

On the influence of shape and material used for the femoral component pegs in knee prostheses for reducing the problem of aseptic loosening

The integration of materials selection and design are essential to the success of new product development, especially when applied to biomedical devices. The knee prosthesis, like any other implant, is a product that still lacks satisfactory design solutions for solving the problem of aseptic loosening. Stress shielding is one of the main causes of aseptic loosening that is intimately related to the overall design of the knee prosthesis. The design of the location pegs in the femoral component of the knee prosthesis is seen to have a critical effect on the stress shielding. In this study, therefore, different combinations of location peg geometries and material designs were assessed using finite element analyses in conjunction with a design of experiments procedure. The materials considered were Co–Cr alloy (as reference material) and functionally graded material (FGM) for the main body of the femoral component, and various porous materials for the pegs (as promising new materials). The performance outputs (responses) were stress levels in the femoral bone to assess the stress shielding effect, and stress levels in the pegs to assess adequate peg strength. The result revealed conflicts in satisfying the design objectives. Therefore, a multi-objective optimization was carried out to find the optimal geometries of the pegs for the femoral component. Based on the findings of the optimization process, a set of candidate designs was generated and a multi-criteria decision making approach used to obtain the final ranking of candidate designs. The ranking order demonstrated the superiority of using a FGM femoral component with porous material pegs of conical geometry. By comparing the results with the standard Co–Cr design, it was shown that the new design of pegs can significantly increase the magnitude of stresses seen at the distal femur; hence reduce the stress shielding effect, without over compromising on the strength of the pegs.     

COSMO-RS-PDHS: A new predictive model for aqueous electrolytes solutions

This work introduces a new tool able to predict water activities and activity coefficients of electrolytes in binary {water–electrolyte} systems. In mixtures containing electrolytes, the system is characterized by the presence of both molecular and ionic species, resulting in three different types of interactions: ion–ion, molecule–molecule and ion–molecule.Ion–ion interactions are governed by electrostatic forces between ions that have a much longer range than other intermolecular forces. The long range interactions between ions are taken in account by the Pitzer term based on the Debye–Hückel theory.Molecule–molecule and ion–molecule interaction forces are known to be short-range in nature. To determine short range mean activity coefficients of salts in {water–electrolyte} binary mixtures, a chemical treatment of ions solvation is combined with the predictive power of the COSMO-RS model. The main originality of this work resides in this chemical treatment model that provides the thermodynamic relations which enable to determine the equilibrium properties of the real solution {water–salt}, knowing those of a hypothetical mixture containing water and hydrated clusters.The resulting model called “COSMO-RS-PDHS” predicts results that are in good agreement with experimental data.     

Photoluminescence study of GaAs thin films and nanowires grown on Si(111)

Mg-doped GaAs nanowires have been grown by molecular beam epitaxy on a partially Au-coated Si(111) substrate by the vapor–liquid–solid mechanism. Outside the coated areas, a thin film of GaAs was grown epitaxially at the same time. The optical properties in both parts of the sample were investigated by photoluminescence spectroscopy, as a function of temperature. A structured emission in the range ～1.25–1.55 eV was observed at 10 K and the resemblances in both cases were identified. The radiative transitions are discussed with relevance to known defect centers in the GaAs thin films and to their possible relation with the zinc-blende and wurtzite phases in the nanowires. The presence of both crystalline phases in the nanowires was confirmed by μ-Raman spectroscopy.     

Magnetic and specific heat studies of the frustrated Er2Mn2O7 compound

A new Er2Mn2O7 compound was synthesized by the ceramic method and its crystal structure was characterized using powder X-ray diffraction (XRD) and observed by scanning electron microscopy (SEM). The magnetic properties were investigated using a BS2 magnetometer and the heat capacity was studied using a quantum design (PPMS). The structural study revealed that this compound was monophasic and crystallized in the monoclinic system with the P2/M space group. Magnetization measurements were carried out in the temperature range of 1.8-200 K under an applied magnetic field of 0.05 T. A crossover from a room temperature paramagnetic phase to an antiferromagnetic one at low temperature was detected from the magnetic study. The magnetic susceptibility, in the paramagnetic region above 40 K, was found to present a simple Curie-Weiss type behavior. From the specific heat (CP) measurements in magnetic fields up to 5 T, we noted the presence of a wide peak characteristic of a second order mag-neto-structural transition.     

Fabrication of Si3N4 ceramics by post-reaction sintering using Si–Y2O3–Al2O3 nanocomposite particles prepared by mechanical treatment

Post-reaction sintering of a powder compact of Si and sintering aids is a useful technique for fabricating silicon nitride (Si₃N₄) ceramics at low costs. In order to inhibit the inhomogeneous and uncontrollable exothermic nitridation of Si in the powder compact, Si–Y₂O₃–Al₂O₃ nanocomposite particles are designed as an aid for post-reaction sintering. These Si–Y₂O₃–Al₂O₃ nanocomposite particles are prepared via mechanical treatment applying high shear stress. Scanning electron microscopy (SEM) observations show that Y₂O₃ and Al₂O₃ particles are homogenously dispersed, and fixed to the Si particles. A green compact prepared using the Si–Y₂O₃–Al₂O₃ nanocomposite particles results in lower electrical resistivity than that prepared using a powder mixed by wet ball-milling, which suggests that Si particles in the green compact prepared using the nanocomposite particles are isolated by Y₂O₃ and Al₂O₃ particles. The isolation of Si particles by the sintering aids successfully prevents the Si particles from melting and agglomerating during the nitridation process, resulting in a higher nitridation ratio and higher α-Si₃N₄ phase content due to the inhibition of rapid heat transfer caused by the exothermic reaction. The nitridation ratio also increases with the applied power during mechanical treatment. As a result of firing the homogeneously nitrided powder compacts at high temperatures, Si₃N₄ ceramics with homogeneous microstructure and improved density are successfully fabricated in this manner.     

Role of oxygen vacancies on the energy storage performance of battery-type NiO electrodes

In this study, the influence of the surface oxygen vacancies on the energy storage performance of electrodes based on nickel oxide (NiO) nanoparticles was investigated. NiO samples were synthesized by three facile and low-cost syntheses routes: nitrate calcination, citrate, and combustion methods. The concentration of surface defects in NiO powders was determined using XPS analyses, which showed a higher amount of oxygen vacancies for the sample obtained by nitrate calcination. According to the cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) curves, NiO-based electrodes were classified as battery-like. CV results suggest that redox reactions are diffusion-controlled processes with a faster diffusion rate for the sample obtained by the nitrate calcination method. This is in accordance with the GCD and electrochemical impedance spectroscopy (EIS) results, with higher specific capacity and higher electrical conductivity (lower equivalent series resistance) for the sample obtained by nitrate calcination. The results indicate that oxygen vacancies play an important role in the electrochemical performance of battery-type NiO electrodes.     

Development of a processing route for carbon allotrope-based TiC porous nanocomposites

Ti-foils are currently used as a spallation target material to produce radioisotopes for physics research at the ISOLDE facility at CERN. However, radioisotope production rates often decrease over time due to material degradation from high operation temperatures. Due to enhanced release rates, porous nanomaterials are being studied as spallation target materials for isotope production. TiC is a material with a very high melting point making it an interesting material to replace the Ti-foils. However, in its nanometric form it sinters readily at high temperatures. To overcome this, a new processing route was developed where TiC was co-milled with graphite, carbon black or multi-wall carbon nanotubes in order to hinder the sintering of TiC. The obtained nanocomposite particle sizes, density, specific surface area and porosity were characterized and compared using ANOVA. All carbon allotropes mixed with the TiC, were able to successfully stabilize the nanometric TiC, hindering its sintering up to 1500 °C for 10 h.