Cylindrical functionally graded shell model based on the first order shear deformation nonlocal strain gradient elasticity theory

Microsystem Technologies - In this article, a cylindrical functionally graded shell model is developed in the framework of nonlocal strain gradient theory for the first time. For this purpose, the...     

4D Printing of Polyvinyl Chloride (PVC): A Detailed Analysis of Microstructure,Programming, and Shape Memory Performance

In this research, polyvinyl chloride (PVC) with excellent shape-memory effects is 4D printed via fused deposition modeling (FDM) technology. An experimental procedure for successful 3D printing of lab-made filament from PVC granules is introduced. Macro- and microstructural features of 3D printed PVC are investigated by means of wide-angle X-ray scattering (WAXS), differential scanning calorimetry (DSC), and dynamic mechanical thermal analysis (DMTA) techniques. A promising shape-memory feature of PVC is hypothesized from the presence of small close imperfect thermodynamically stable crystallites as physical crosslinks, which are further reinforced by mesomorphs and possibly molecular entanglement. A detailed analysis of shape fixity and shape recovery performance of 3D printed PVC is carried out considering three programming scenarios of cold (T_g −45 °C), warm (T_g −15 °C), and hot (T_g +15 °C) and two load holding times of 0 s, and 600 s under three-point bending and compression modes. Extensive insightful discussions are presented, and in conclusion, shape-memory effects are promising,ranging from 83.24% to 100%. Due to the absence of similar results in the specialized literature, this paper is likely to fill a gap in the state-of-the-art shape-memory materials library for 4D printing, and provide pertinent results that are instrumental in the 3D printing of shape-memory PVC-based structures.     

Numerical study of blowing and suction slot geometry optimization on NACA 0012 airfoil

The effects of jet width on blowing and suction flow control were evaluated for a NACA 0012 airfoil. RANS equations were employed in conjunction with a Menter’s shear stress turbulent model. Tangential and perpendicular blowing at the trailing edge and perpendicular suction at the leading edge were applied on the airfoil upper surface. The jet widths were varied from 1.5% to 4% of the chord length, and the jet velocity was 0.3 and 0.5 of the free-stream velocity. Results of this study demonstrated that when the blowing jet width increases, the lift-to-drag ratio rises continuously in tangential blowing and decreases quasi-linearly in perpendicular blowing. The jet widths of 3.5% and 4% of the chord length are the most effective amounts for tangential blowing, and smaller jet widths are more effective for perpendicular blowing. The lift-to-drag ratio improves when the suction jet width increases and reaches its maximum value at 2.5% of the chord length.     

A concept of microfluidic electronic tongue

The information obtained by monitoring the diffusion progress rates of ionic species in liquid-filled microfluidic channels is used for their identification. The diffusion rates of five different analytes, HCl, KI, KCl, NaCl, and LiCl, through pure water-filled channels of different diameters are experimentally investigated by recording the temporal variation of the channel conductance. The results are described based on a modified diffusion equation which, along with the diffusivity of the ionic species, accounts for the rates of their physical adsorption to the channel walls. The addition of two scalar analyte-related parameters, other than the analyte diffusivity in the liquid medium, facilitates fitting of the theoretically predicted process rates to those measured in different microfluidic channels. It is shown that combining the data extracted from the temporal conductance variation in two appropriately designed channels facilitates recognition of an unknown electrolyte among HCl, KI, KCl, NaCl, and LiCl solutions in distilled water regardless of their concentrations. The two-channel device fabricated based on the presented concept is a low-cost disposable electronic tongue which can discriminate between ??sour?? and ??salty?? electrolytes. The ion discrimination power of the device can be enhanced by the addition of channels made of, or coated with, different materials.     

Graphene vanadic acid (GVA) as a novel heterogeneous catalyst for highly selective benzene hydroxylation under mild conditions

In the present study, Graphene Vanadic Acid (GVA) is introduced as a novel catalyst for high-efficiency hydroxylation of benzene to phenol using hydrogen peroxide at ambient conditions. Graphene oxide as a famous carbon support has converted to a high-performance catalyst through the functionalization using vanadium oxytrichloride (VOCl₃). This new carbon compound is regarded as the efficient catalyst due to the prominent advantages such as high-recativity and reusability, facile preparation, active Lewis and Bronsted acid sites, high potential for development of various oxidation reactions, and high thermal, chemical, and physical stability due to the regular carbon structure. GVA progressed the benzene oxidation toward the phenol formation as a useful raw material. Cause of the considerable reactivity of the synthesized catalyst, a minimum amount of hydrogen peroxide was required and the benzene oxidation carried out using an equimolar ratio of benzene/H₂O₂, and phenol obtained with a remarkable yield (28.2%) as the sole product.     

Nisin‐loaded alginate‐high methoxy pectin microparticles: preparation and physicochemical characterisation

The bacteriocin nisin has been extensively used as potential natural preservative in the food industry. However, antimicrobial activity of nisin due to its binding with food components and inactivation by enzymatic degradation is reduced when it is applied in food. Encapsulation of nisin is an efficient approach to overcome the problems related to the direct application of this antimicrobial peptide in foods. In this study, nisin was encapsulated in alginate‐high methoxy pectin (HMP) microparticles, and its release studies were performed in water to determine the diffusion and the kinetic behaviour of the matrix. Results showed that the nisin content had a significant influence on encapsulation efficiency (EE), loading capacity (LC) and microparticles size. The values of EE, LC and particle mean diameter were about 47–54%, 16–21% and 57–131 μm, respectively. The nisin‐loaded microparticles showed nearly spherical structure with fold on the surface, as displayed by scanning electron micrograph. Interaction between alginate and HMP was confirmed by the changes in the intensity and wave number of the stretching vibrations of the hydroxyl and carboxyl groups in alginate‐HMP microparticles FTIR spectra. Furthermore, the addition of nisin resulted in a markedly increase in intensity of carboxylic peak at 1620 cm^?1, indicating the presence of nisin inside of the microparticles. The in vitro nisin release from these microparticles followed a sustained release profile consistent with a Fickian diffusion mechanism.     

Effects of Chlorella vulgaris and Arthrospira platensis addition on viability of probiotic bacteria in yogurt and its biochemical properties

It is a practice to add microalgae into plain and probiotic fermented milks in order to promote the functionality of these products via their direct health effects as well as the enhancing impact on viability of probiotic microorganisms in product and in gastrointestinal tract. In this study, the effects of addition of two species of microalgae including Arthrospira platensis and Chlorella vulgaris (seven yogurt treatments containing three concentrations for each microalgae—0.25, 0.50, and 1.00?%—and a control without microalgae) on pH, titrable acidity, and redox potential changes as well as on the viability of probiotic bacteria during fermentation and during a 28-day refrigerated storage period (5?°C) were investigated in yogurt. Also, the amounts of lactic and acetic acids at the end of fermentation were assessed. The culture composition of yogurt was ABY type, containing Lactobacillus acidophilus LA-5, Bifidobacterium lactis BB-12, Lactobacillus delbrueckii ssp. bulgaricus, and Stresptococcus themophilus. The addition of microalgae significantly (p?<?0.05) increased the viability of L. acidophilus and bifdobacteria at the end of fermentation and during the storage period. Treatments containing A. platensis had slower pH decline, faster acidity increase, longer incubation time, and greater final titrable acidity than those containing C. vulgaris and control. In treatments containing 0.5 or 1?% microalgae, the viability was almost higher than 10⁷ cfu/mL until the end of refrigerated storage.     

Numerical Study of Reinforced Soil Segmental Walls Using Three Different Constitutive Soil Models

A numerical finite-difference method (FLAC) model was used to investigate the influence of constitutive soil model on predicted response of two full-scale reinforced soil walls during construction and surcharge loading. One wall was reinforced with a relatively extensible polymeric geogrid and the other with a relatively stiff welded wire mesh. The backfill sand was modeled using three different constitutive soil models varying as follows with respect to increasing complexity: linear elastic-plastic Mohr-Coulomb, modified Duncan-Chang hyperbolic model, and Lade’s single hardening model. Calculated results were compared against toe footing loads, foundation pressures, facing displacements, connection loads, and reinforcement strains. In general, predictions were within measurement accuracy for the end-of-construction and surcharge load levels corresponding to working stress conditions. However, the modified Duncan-Chang model which explicitly considers plane strain boundary conditions is a good compromise between prediction accuracy and availability of parameters from conventional triaxial compression testing. The results of this investigation give confidence that numerical FLAC models using this simple soil constitutive model are adequate to predict the performance of reinforced soil walls under typical operational conditions provided that the soil reinforcement, interfaces, boundaries, construction sequence, and soil compaction are modeled correctly. Further improvement of predictions using more sophisticated soil models is not guaranteed.     

The effects of extremes and temporal scale on multifractal properties of river flow time series

For accurate forecasting of extreme events in rivers, streamflow time series with sub‐daily temporal resolution (1–6 hour) are preferable, but discharge time series for long rivers are usually available at daily or monthly resolution. In this study, the scaling properties of hourly and daily streamflow time series were measured. As an innovation, the effects of extreme values on the multifractal behavior of these series were evaluated. Interestingly, both hourly and daily discharge records led to nearly identical scaling trends and identical crossover times. Daily and hourly discharge time series appeared to be non‐stationary when the timescale ranged from 75 to 366 days. Otherwise, the signals may be considered stationary time series. In addition, the results indicated that the extreme values strongly contribute to the multifractality of the series. The width of singularity spectra decreased considerably when the extreme events were removed from both hourly and daily discharge records.