Investigation of the enhancing effects of sulfur and/or oxygen functional groups of nanoporous carbons on adsorption of dibenzothiophenes

Adsorption of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (DMDBT) from simulated diesel fuel with 20 ppmw total concentration of sulfur was investigated on polymer-derived carbon containing various amounts of oxygen and sulfur incorporated to the surface. Initial and exhausted carbons were characterized using adsorption of nitrogen, thermal analysis, potentiometric titration, XPS, mass spectroscopy and elemental analysis. Selectivities for DBT and DMDBT adsorption were calculated with reference to naphthalene. It was found that both the capacity and selectivity for DBT and DMDBT removal from model diesel fuel were affected by the content and arrangement of heteroatoms. Although both oxygen and sulfur containing groups enhance the capacity, the enhancing effects of surface chemistry were more pronounced on the carbon with sulfur incorporated to its matrix. This is linked to sulfur–sulfur interactions.     

Mechanical behavior and failure mechanisms of boron carbide based three-layered laminates with weak interfaces

The effect of weak interfaces on failure mechanisms of a three-layered composite was studied. Three-layered B₄C/B₄C–C_nanofibers laminates have been produced using a hot pressing technique. The laminates were designed with thick (∼2.6 mm) outer layers of B₄C and a thin (∼90 μm) center layer of B₄C–70 wt.% C_nanofibers. Based on the difference in coefficients of thermal expansion and Young's moduli of the pure B₄C and B₄C–70 wt.% C_nanofibers layers, it was estimated that low tensile thermal residual stress with a magnitude of 11.3 ± 2.5 MPa was developed in the thick B₄C outer layers, and compressive residual stress with a magnitude of 455.7 ± 5 MPa was developed in the thin central B₄C–70 wt.% C_nanofibers layer. The apparent fracture toughness of laminates was measured and based on the estimated fracture toughness values, a threshold stress was calculated.     

Ohmic heating of peaches in the wide range of frequencies (50 Hz to 1 MHz)

Abstract: The ohmic heating (OH) rate of peaches was studied at fixed electric field strength of 60 V.cm⁻¹, square-shaped instant reversal bipolar pulses, and frequencies varying within 50 Hz to 1 MHz. Thermal damage of tissue was evaluated from electrical admittivity. It showed that the time for half disruption (τ_T) of tissue was required more than 10 h at temperatures below 40 °C. However, cellular thermal disruption occurred almost instantly (τ_T < 1 s) at high temperatures (> 90 °C). Electrical conductivity σ_o and admittivity σ_o* of tissue at T_o= 0 °C and their temperature coefficients (m, m*) were calculated. For freeze–thawed tissues, σ and σ* as well as m and m* were nearly indifferent to the frequency. However, for the intact tissue, both σ_o, σ_o* and m, m* were frequency dependent. For freeze–thawed product, the power factor (P) was approximately equal to 1 and indifferent to the frequency and temperature. On the other hand, strong frequency dependence was observed for intact tissue with the minimum P approximately equal to 0.68 in the range of tens of kHz. The time required to reach a target temperature t_f was evaluated. The t_f increased with frequency up to the middle of the range of tens of kHz and thereafter continuously decreased. Samples exposed to the low-frequency electric field demonstrated faster electro-thermal damage rates. The textural relaxation data supported more intense damage kinetics at low-frequency OH. It has been demonstrated that a combination of high-frequency OH with pasteurization at moderate temperature followed by rapid cooling minimizes texture degradation of peach tissue. Practical Application: In this study, we investigated the electric field frequency effect on the rate of OH of peaches. It was shown that the time required for reaching the target temperature is strongly dependent upon the frequency. Samples exposed to low-frequency OH demonstrated higher electro-thermal damage rates. It has been shown that the combination of high-frequency OH with pasteurization at moderate temperature followed by rapid cooling minimizes texture degradation of peach tissue. Obtained results provide new information on the impact of electric field frequency on OH, which is useful for OH process design.     

Defects in Hybrid Perovskites: The Secret of Efficient Charge Transport

The interaction of free carriers with defects and some critical defect properties are still unclear in methylammonium lead halide perovskites (MHPs). Here, a multi-method approach is used to quantify and characterize defects in single crystal MAPbI₃, giving a cross-checked overview of their properties. Time of flight current waveform spectroscopy reveals the interaction of carriers with five shallow and deep defects. Photo-Hall and thermoelectric effect spectroscopy assess the defect density, cross-section, and relative (to the valence band) energy. The detailed reconstruction of free carrier relaxation through Monte Carlo simulation allows for quantifying the lifetime, mobility, and diffusion length of holes and electrons separately. Here, it is demonstrated that the dominant part of defects releases free carriers after trapping; this happens without non-radiative recombination with consequent positive effects on the photoconversion and charge transport properties. On the other hand, shallow traps decrease drift mobility sensibly. The results are the key for the optimization of the charge transport properties and defects in MHP and contribute to the research aiming to improve perovskite stability. This study paves the way for doping and defect control, enhancing the scalability of perovskite devices with large diffusion lengths and lifetimes.     

Simulation and optimization of the ohmic processing of highly viscous food product in chambers with sidewise parallel electrodes

Three dimensional numerical simulations of ohmic heating (OH) of highly viscous chicken chow mein sauce in typical and modified pilot scale ohmic heating chambers with sidewise parallel electrodes arrangement were undertaken. The fully coupled momentum, electrostatic and energy transfer partial differential equations were solved using commercial finite element modeling (FEM) software. The residence time (RT) of sauce in the OH treatment chambers was studied by solving the convection and diffusion equation for a tracer species injected in the system. The key parameters affecting the process, including electrical conductivity, σ, thermal conductivity, k, specific heat capacitance, C_p, density, ρ and viscosity, η, were measured experimentally. For the model validation, the predicted current delivered by each generator and temperatures in selected locations were compared with those obtained from trials performed under the same conditions. A good agreement was observed between experimental and simulated data with the coefficients of determination R² = 0.987.     

Mathematical Modeling and Microbiological Verification of Ohmic Heating of a Multicomponent Mixture of Particles in a Continuous Flow Ohmic Heater System with Electric Field Parallel to Flow

To accomplish continuous flow ohmic heating of a low‐acid food product, sufficient heat treatment needs to be delivered to the slowest‐heating particle at the outlet of the holding section. This research was aimed at developing mathematical models for sterilization of a multicomponent food in a pilot‐scale ohmic heater with electric‐field‐oriented parallel to the flow and validating microbial inactivation by inoculated particle methods. The model involved 2 sets of simulations, one for determination of fluid temperatures, and a second for evaluating the worst‐case scenario. A residence time distribution study was conducted using radio frequency identification methodology to determine the residence time of the fastest‐moving particle from a sample of at least 300 particles. Thermal verification of the mathematical model showed good agreement between calculated and experimental fluid temperatures (P > 0.05) at heater and holding tube exits, with a maximum error of 0.6 °C. To achieve a specified target lethal effect at the cold spot of the slowest‐heating particle, the length of holding tube required was predicted to be 22 m for a 139.6 °C process temperature with volumetric flow rate of 1.0 × 10^?4 m³/s and 0.05 m in diameter. To verify the model, a microbiological validation test was conducted using at least 299 chicken‐alginate particles inoculated with Clostridium sporogenes spores per run. The inoculated pack study indicated the absence of viable microorganisms at the target treatment and its presence for a subtarget treatment, thereby verifying model predictions.     

Tobacco waste/industrial sludge based desulfurization adsorbents: effect of phase interactions during pyrolysis on surface activity

Industrial waste derived adsorbents were obtained by pyrolysis of tobacco waste with either metal sludge or waste oil sludge from a shipyard. The materials were used as media to remove hydrogen sulfide at room temperature in the presence of moisture. The initial and exhausted adsorbents after the breakthrough tests were characterized using sorption of nitrogen, thermal analysis, XRD, elemental analysis, and surface pH measurements. It was found that mixing tobacco and industrial sludges results in a strong synergy, enhancing the catalytic properties of adsorbents. This synergy is observed in both surface chemistry and porosity. During pyrolysis, new mineral phases are formed as a result of solid-state reactions between the components of the sludges. They are highly dispersed on the surface of mesopores. A high volume of these pores is a result of activation of the carbon phase in the composite by alkaline earth metals and also by the release of water from the decomposition of an inorganic phase that is in the predominant quantity. A high temperature of pyrolysis is beneficial for the adsorbents due to the enhanced activation of the carbonaceous phase and the chemical stabilization of the inorganic phase. Samples obtained at low temperatures are sensitive to water, which deactivates their catalytic centers.     

Mössbauer spectroscopic investigation of iron species in coal

A series of Herrin No. 6 coal and three coal-derived samples have been examined by Mössbauer spectroscopy. It is established that Mössbauer spectroscopy can be used to identify multiple iron species in a whole coal or an autoclaved char sample without the need to concentrate the minerals to enhance resolution. Our results indicate that there may be an association between the pyrite in raw coal and the coal matrix. This association appears to be broken down when the coal is heated to temperatures as low as 175 °C. It is also apparent that the iron sulphide present in the whole coal is converted to pyrite at these low temperatures. For our samples, the total quantity of iron species in different coal lithotypes is about the same, but they differ in their distributions. The fusain has the least amount of Fe²⁺ species when compared to the vitrain or whole-coal sample used. At least two types of nonstoichiometric pyrrhotite are produced in the heat-treated samples. One of these pyrrhotites is unstable and contains dissolved sulphur which is apparently liberated as the temperature is increased.     

Efficient and effective training of sparse recurrent neural networks

Neural Computing and Applications - Recurrent neural networks (RNNs) have achieved state-of-the-art performances on various applications. However, RNNs are prone to be memory-bandwidth limited in...