Natural convection heat transfer in a nanofluid filled semi-annulus enclosure

To investigate natural convection heat transfer in a semi-annulus enclosure filled with nanofluid, the Control Volume based Finite Element Method (CVFEM) is used. The fluid in the enclosure is Cu–water nanofluid. The inner and outer semi circular walls are maintained at constant temperatures while the two other walls are thermally insulated. The Navier Stokes equations in their vorticity-stream function form are used to simulate the flow pattern and isotherms. The numerical investigation is carried out for different governing parameters namely; the Rayleigh number, nanoparticle volume fraction and the angle of turn for the enclosure. The effective thermal conductivity and viscosity of nanofluid are calculated using the Maxwell–Garnetts (MG) and Brinkman models, respectively. The results reveal that there is an optimum angle of turn in which the average Nusselt number is maximum for each Rayleigh number. Moreover, the angle of turn has an important effect on the streamlines, isotherms and maximum or minimum values of local Nusselt number.     

Facile synthesis of silver nanoparticles using Tribulus longipetalus extract and their antioxidant and antibacterial activities

In this study, the preparation of silver nanoparticles (Ag NPs) using Tribulus longipetalus Viv. leaf extract was evaluated. Additionally, the in vitro antioxidant and antibacterial activities of the extract were evaluated. The antioxidant activity was assessed by two different approaches based on 2,2-diphenyl-1-picryl-hydrazyl and reducing power assay. The antibacterial activity of the extract, on the other hand, was determined against gram positive and gram negative microorganisms. The AgNPs prepared under the optimal conditions were found to be 15 nm in size and were characterized by ultraviolet–visible spectroscopy, dynamic light scattering, X-ray diffraction and transmission electron microscopy.     

Effect of different precooking methods on chemical composition and lipid damage of silver carp (Hypophthalmichthys molitrix) muscle

The influence of three precooking methods (steaming, oven‐baking and microwave‐cooking) on the chemical composition and lipid quality of silver carp fillets was evaluated. The changes in protein, fat and moisture were found to be significant for all the treatments (P ≤ 0.05). The iron content in the samples subjected to steam‐cooking increased; however, the other precooking methods did not change the mineral contents (P ≥ 0.05). The free fatty acid content of the fillets did not change by the different precooking methods, while thiobarbituric acid (TBA) values increased for oven‐ and microwave‐cooked fillets and remained constant in the steam‐cooked samples. Conjugated diene and browning colour formation levels significantly increased in the oven‐baked fillets. Oven‐baking and microwave‐cooking marginally affected the fatty acid composition of the silver carp. On comparing the raw and precooked fillets, steam‐cooking was found to be the best precooking method on retaining nutritional constituents.     

Flexural free vibration as a non-destructive test for evaluation of viscoelastic properties of polymeric composites in bending direction

In many applications, viscoelastic properties of reinforced composites need to be determined prior to their real service life. Such properties can be assured by destructive and non-destructive tests. In this paper, a novel non-destructive test (NDT) method based on flexural free vibration is introduced to investigate the viscoelastic properties of fiber-reinforced composites. Three different types of industrial fibers (carbon, glass, and hemp) and an unsaturated polyester resin were selected to produce bar-shaped composites via pultrusion technique. These composite bars were used in a simple NDT method which just required a wooden hammer, two elastic jaws, a microphone and a recorder software program to perform the experiment. The composite bars were mounted on elastic jaws and hit by a wooden hammer at one end of the specimen as a perpendicular impulse. The produced sound at the other side of the bars was recorded. By analyzing the recorded sounds by means of fast Fourier transform (FFT), viscoelastic properties such as flexural elastic modulus and the loss parameter (Tan δ) were calculated for the fiber-reinforced composites. For determination of flexural elastic modulus, the first three modes of vibration in FFT graphs were analyzed using Temuschenco theory. Also, Tan δ was determined by analyzing the drop in the intensity of vibrational energy as a function of time. Although there was a slight discrepancy between the calculated values from the NDT method and the actual data from dynamic mechanical thermal analysis (DMTA) approach, a good agreement was achieved between NDT and DMTA results.     

Tuning the curing behavior of fluoroelastomer (FKM) by incorporation of nitrogen doped graphene nanoribbons (CNx-GNRs)

Graphene nanoribbons (GNRs), obtained by different methods from carbon nanotubes (CNTs) or graphene, are attractive materials for polymer nanocomposites due to their considerably high interfacial area, as compared to CNTs. Consequently, a better adhesion with a polymer matrix is anticipated for GNRs. Also, surface modification of these nanofillers, such as nitrogen doping, is known to be an efficient method to improve their properties. In this work, fluoroelastomers (FKM) were used as the polymer matrix to host GNRs. Undoped and nitrogen doped GNRs were synthesized from the parent multiwall carbon nanotubes (MWCNTs). MWCNT/FKM and GNR/FKM nanocomposites were prepared via a solution mixing/melt mixing protocol.     

Simultaneous transmission and absorption photometry of carbon-black absorption from drop-cast particle-laden filters

Simultaneous transmissivity and absorptivity measurements were carried out in the visible at a laser wavelength of 532?nm on drop-cast, carbon-black-laden filters under ambient (laboratory) conditions. The focus of this investigation was to establish the feasibility of this approach to estimate the mass absorption coefficient of the isolated particles and compare results to earlier work with the same carbon-black source. Transmissivity measurements were carried out with a laser probe beam positioned normal to the particle-laden filter surface. Absorptivity measurements were carried out using a laser-heating approach to record in time the sample temperature rise to steady-state and decay back to the ambient temperature. The sample temperature was recorded using a fine-wire thermocouple that was integrated into the transmission arrangement by placing the thermocouple flush with the filter back surface. The advantage of this approach is that the sample absorptivity can be determined directly (using laser heating) instead of resolving the difference between reflectivity (filter surface scattering) and transmissivity. The current approach also provides the filter optical characteristics, as well as an estimate of filter effects on the absorption coefficient due to particle absorption enhancement or shadowing. The approach may also be incorporated into other filter-based techniques, like the particle/soot absorption photometer, with the simple addition of a thermocouple to the commercial instrument. For this investigation, measurements were carried out with several blank uncoated quartz filters. A range of solution concentrations was prepared with a well-characterized carbon black in deionized water (i.e., a water-soluble carbonaceous material referred to as a surrogate black carbon or ‘carbon black’). The solution was then drop cast using a calibrated syringe onto blank filters to vary particle loading. After evaporation of the water, the measurements were repeated with the coated filters. The measurement repeatability (95% confidence level) was better than 0.3?K for temperature and 3?×?10^?5 mW for laser power. From the measurements with both the blank and coated filters, the absorption coefficient was determined for the isolated particles. The results were then compared with an earlier investigation by You et al. and Zangmeister and Radney, who used the same carbon-black material. The measurements were also compared with Lorenz–Mie computations for a polydispersion of spherical particles dispersed throughout a volume representative of the actual particles. The mass absorption coefficient for the polydispersion of carbon-black particles was estimated to be about 7.7?±?1.4?m² g^?1, which was consistent with the results expected for these carbon black particles.     

Divided-wall distillation column design using molecular tracking

Divided-wall column (DWC) is an intensified separation process and so far developing a simple procedure for designing these units has been challenging. In this work, the concept of molecular tracking has been integrated with conventional methods to build a simple and easy-to-use methodology for designing DWCs for multicomponent separations. Application of the proposed approach is highlighted through several three- and four-component mixtures. The configuration obtained using molecular tracking gives a design with lower energy demands for the column reboiler, compared to other design methodology, which directly impacts the OPEX of the system.     

Microscale 3D Printing of Nanotwinned Copper

Nanotwinned (nt)‐metals exhibit superior mechanical and electrical properties compared to their coarse‐grained and nanograined counterparts. nt‐metals in film and bulk forms are obtained using physical and chemical processes including pulsed electrodeposition (PED), plastic deformation, recrystallization, phase transformation, and sputter deposition. However, currently, there is no process for 3D printing (additive manufacturing) of nt‐metals. Microscale 3D printing of nt‐Cu is demonstrated with high density of coherent twin boundaries using a new room temperature process based on localized PED (L‐PED). The 3D printed nt‐Cu is fully dense, with low to none impurities, and low microstructural defects, and without obvious interface between printed layers, which overall result in good mechanical and electrical properties, without any postprocessing steps. The L‐PED process enables direct 3D printing of layer‐by‐layer and complex 3D microscale nt‐Cu structures, which may find applications for fabrication of metamaterials, sensors, plasmonics, and micro/nanoelectromechanical systems.     

Performance evaluation of EWMA and CUSUM control charts to detect anomalies in social networks using average and standard deviation of degree measures

Detection of communication outbreak among members of a network or a subgroup of a network has been a topic of interest in the literature of social network analysis. One approach to monitoring changes in a social network is to monitor graph measures related to the network representation in each period and detecting anomalies by applying a control chart. In this paper, we compare the performance of average degree and standard deviation of degree measures of a network for detecting outbreaks on a weighted undirected network using exponentially weighted moving average and cumulative sum control charts. Evaluation results indicate that average degree measure is better in detecting small changes than standard deviation of degree measure. Whereas for greater changes and outbreaks consisting of more members of the network, the opposite is true. In addition, exponentially weighted moving average control charts perform better than cumulative sum in detecting smaller changes and outbreaks consisting of less members of the network.     

A hybrid fuzzy multiple criteria group decision making approach for sustainable project selection

In this paper, a new hybrid fuzzy multiple criteria group decision making (FMCGDM) approach has been proposed for sustainable project selection. First, a comprehensive framework, including economic, social, and environmental effects of an investment, strategic alliance, organizational readiness, and risk of investment has been proposed for sustainable project selection. As the relative importance of the criteria of the proposed framework are hard to find through several conflictive preferences of a group of Decision Makers (DMs) so, a goal programming (GP) has been supplied to this aim considering multiplicative and fuzzy preference relation. Then, a fuzzy TOPSIS method has been developed to assess the fitness of investment chances. It is based on Preference Ratio (PR), which is known as an efficient ranking method for fuzzy numbers, and a fuzzy distance measurement. The properties of proposed hybrid approach make it robust for modeling real case of uncertain group decision making problems. The FMCGDM has been developed through a linkage between Lingo 11.0, MS-Excel 12.0, and Visual Basic 6.0. The proposed hybrid approach has been applied in a real case study called Iranian financial and credit institute for sustainable project selection.