Ultrasonic field modeling: a comparison of analytical, semi-analytical, and numerical techniques

Modeling ultrasonic fields in front of a transducer in the presence and absence of a scatterer is a fundamental problem that has been attempted by different techniques: analytical, semi-analytical, and numerical. However, a comprehensive comparison study among these techniques is currently missing in the literature. The objective of this paper is to make this comparison for different ultrasonic field modeling problems with various degrees of difficulty. Four fundamental problems are considered: a flat circular transducer, a flat square transducer, a circular concave transducer, and a point focused transducer (concave lens) in the presence of a cavity. The ultrasonic field in front of a finite-sized transducer can be obtained by Huygens-Fresnel superposition principle that integrates the contributions of several point sources distributed on the transducer face. This integral which is also known as the Rayleigh integral or Rayleigh-Sommerfeld integral (RSI) can be evaluated analytically for obtaining the pressure field variation along the central axis of the transducer for simple geometries, such as a flat circular transducer. The semi-analytical solution is a newly developed mesh-free technique called the distributed point source method (DPSM). The numerical solution is obtained from finite element analysis. Note that the first three problems study the effect of the transducer size and shape, whereas the fourth problem computes the field in presence of a scatterer.     

Converting date seed biomass into highly absorbing hydrogel

Converting biomass into value-added products has attracted great attention in recent years. In this paper, a facile approach for using date seed powder without delignification is introduced to convert date seed biomass into a water-absorbing polymer. The biomass of date seed as a source of polysaccharides was immersed in the emulsions of acrylic microgels with different chemical structures. Different polymer latexes based on acrylic acid (AA), sodium acrylate (SA), acrylamide (AM) and 2-acrylamide-2-methyl propane sulfonic acid (AMPS) were prepared using inverse emulsion polymerization. A chemical reaction was carried out between date seed and acrylic latex by heating, which caused the conversion of date seed into a semi-synthetic hydrogel with 60 % natural and 40 % synthetic components. The best modification of date seed to absorbing hydrogel was obtained with poly(AA–SA–AM–AMPS). The modified date seed with this latex had water absorbency of up to 71 g/g, while the unmodified date seed had only 0.2 g/g water absorbency. Date seed hydrogels were characterized by Fourier transform infrared spectroscopy (FTIR), dynamic mechanical thermal analysis (DMTA), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), rheometric analysis and swelling measurement. The effect of several modifications of parameters such as latex type, AMPS content in latex, aquatic–organic phase ratios of latex and modification temperature on the swelling properties of hydrogel was investigated. The obtained hybrid hydrogel based on date seed biomass contained a considerable amount of biomass in its structure as well as 71 g/g water absorbency, which can be a proper candidate for agricultural applications.     

Investigating microstructural evolution during homogenization of the equiatomic NiTi shape memory alloy produced by vacuum arc remelting

The vacuum arc remelting process is widely used for the commercial production of NiTi shape memory alloys. Due to the absence of electromagnetic forces in this method, several remelting and long-time homogenizing are required. In this work, a Ti-50 at.% Ni alloy was prepared using the non-consumable vacuum arc melting technique in a water-cooled copper crucible. After four times of remelting process, specimens were subjected to homogenization at 1000 °C. Micro/macrostructural changes during homogenization were investigated by optical microscope and SEM equipped with EDS analyzer. The results showed that the as-cast specimen consisted of mostly Ni₃Ti, Ti₂Ni and monoclinic (B1^9′) phases with high segregation. By increasing the holding time during the homogenization process at 1000 °C, the amount of austenite (B₂) phase was increased, while segregation and unfavorable phases, and accordingly, hardness were decreased. After 4 h of homogenization, austenite (B₂) was the only phase maintained in the microstructure of Ti-50 at.% Ni. In addition, macrostructure of the alloy was turned into polygonal structure after such a homogenization treatment.     

Heat Induced Damage Detection by Terahertz (THz) Radiation

Terahertz (THz) and sub-terahertz imaging and spectroscopy are becoming increasingly popular nondestructive evaluation techniques for damage detection and characterization of materials. THz radiation is being used for inspecting ceramic foam tiles used in TPS (Thermal Protection System), thick polymer composites and polymer tiles that are not good conductors of ultrasonic waves. Capability of THz electromagnetic waves in detecting heat induced damage in porous materials is investigated in this paper. Porous pumice stone blocks are subjected to long time heat exposures to produce heat induced damage in the block. The dielectric properties extracted from THz TDS (Time Domain Spectroscopy) measurements are compared for different levels of heat exposure. Experimental results show noticeable and consistent change in dielectric properties with increasing levels of heat exposure, well before its melting point.     

The interplay between formal and informal elements in analysing situations of role conflict among construction participants

The interplay of formal and informal factors in construction teams influences the enactment of roles and the individuals who fulfil those roles. With a specific focus on a phenomenon called role conflict, the aim is to explore if and how the interaction of formal and informal elements would lead to situations of role conflict. This phenomenon proved to lead to frustration, tension and employee burnout. An analytical model of role interaction was developed, which disentangles formal and informal elements that shape role interactions. Qualitative data was collected through semi-structured interviews, project documents and observations. Four cases of role conflict are presented here. Contract, as a formal element, and participant’s values and interests, as informal elements, appeared to be the most important factor shaping participants’ expectations and behaviours. The analysis in this study showed that if a participant who faces role conflict is able to influence the formal elements in favour of his or her informal elements, then he or she may experience less frustration. At a more general level, the results suggest that increasing formality can increase participants’ frustration, which then would decrease the likelihood of collaboration. As the theoretical contribution, this research extends organizational role theory to deal with informal and formal aspects. Taking into account formal sources enables the study of how roles are institutionally governed while including informal sources allows for the idea that some of the aspects of the role, even in the context of work role, are socially constructed.     

Alcohophilic gels: Polymeric organogels composing carboxylic and sulfonic acid groups

Polymeric organogels based on acrylic acid (AA) and sodium allyl sulfonate (SAS) were prepared through solution polymerization using a persulfate initiator and a polyethylene glycol diacrylate (PEGDA) crosslinker. FTIR spectroscopy, elemental, and rheological analyses were used for a preliminary characterization. Thermo‐mechanical analysis was also carried out for characterizing samples. Glass transition temperature (T_g) of copolymer was decreased after acid treatment which could be attributed to detachment of ion pairs during the post‐treatment. Due to counterion binding of Na⁺ to form ionomer, the poly(AA‐SAS) gels showed no polyelectrolyte behavior to have high swelling capacity in conventional alcohols, i.e., ethanol and methanol. It was postulated that modification via removing Na⁺ could help breaking ion pair aggregates which leads to swelling enhancement. Thus, poly(AA‐SAS) was treated with hydrochloric acid to remove (Na⁺) counterions. This modification led to the gel transform from ionomer regime to a polyelectrolyte regime in which free mobile ions were existed in the network. The gel swelling capacity was increased due to raise of mobile ions after the treatment. It was found that both of the acid concentration and treatment time had constructive influence on the gel alcohophilicity. The acid‐treated samples could imbibe ethanol and methanol as high as 25.8 and 39.5 g/g, respectively. They may be superior candidates for applications such as pharmaceuticals gels and fire starters. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and evaluation of novel aromatic acrylic monomers for optically clear adhesive with high refractive index

Conventional optical polymers have low refractive index; (RI <1.5) which limit their usage in the field of optoelectronics. Therefore, two types of aromatic monomers with high RI value were developed; that is, ionic monomer (PA.HEMA.NEt3.H⁺) with RI = 1.5150 and monomer (PA.BA.GMA) with RI = 1.5403. The monomers were then individually combined with a newly synthesized oligomer based on phthalic anhydride epoxy acrylate; that is, (EA.PA) with RI = 1.5567. The structures of the synthesized monomers and oligomer were confirmed by NMR and FTIR spectroscopy and the chemical titration of the structure end groups. Different combinations of the monomers with oligomer EA.PA were examined to develop a UV-curing adhesive with appropriate viscosity. According to TGA and DMTA test results, the composition containing oligomer EA.PA showed improved thermal degradation stability and high glass transition temperature. The lap shear adhesion test showed positive effect of oligomer EA.PA and PA.BA.GMA with an adhesion strength of up to 1.2 MPa. The RI value of the composition containing PA.BA.GMA and oligomer EA.PA was measured as 1.55 which is qualified for the most applications in optoelectronic. The improvement in RI value may be well attributed to the presence of aromatic rings in the polymer chain backbone. The high degree of aromaticity is in favor with the improved thermal stability in adhesive composition.     

Aqueous free-radical polymerization of PEGMEMA macromer: kinetic studies via an on-line 1H NMR technique

Free-radical polymerization of polyethylene glycol methyl ether methacrylate macromer (PEGMEMA) was studied in aqueous media and in the presence of potassium persulfate (KPS) as water soluble initiator. An on-line nuclear magnetic resonance (NMR) method was applied to record the reaction data and determine the monomer conversion at various times during the polymerization reaction progress. ¹H NMR spectrum of reaction mixture containing monomer, initiator and resultant polymer was continuously recorded in NMR instrument with the increase of reaction time. By processing the obtained data from NMR spectrum, the rate equation can be derived and reaction order can be determined with regard to monomer and initiator concentration. In other words, to determine the order of polymerization with regard to the concentration of reactants in free-radical polymerization of PEGMEMA, macromer samples with different amounts of monomer and KPS were prepared and polymerized at 50?°C. Orders of reaction with respect to monomer and initiator molar concentrations were equal to 1.025 and 0.480, respectively. The obtained values for reaction orders in this study were consistent with the classical kinetic rate equation in which the dependency of polymerization rate (R _p) on monomer and initiator concentrations was equal to 1 and 0.5, respectively. To measure polymerization activation energy (E _a), the effect of reaction temperature on the polymerization rate was investigated and E _a?=?37.08?kJ/mol was obtained at the temperature range of 40?C50?°C.     

Intercalating Electron Dyes for TEM Visualization of DNA at the Single-Molecule Level

Staining compounds containing heavy elements (electron dyes) can facilitate the visualization of DNA and related biomolecules by using TEM. However, research into the synthesis and utilization of alternative electron dyes has been limited. Here, we report the synthesis of a novel DNA intercalator molecule, bis-acridine uranyl (BAU). NMR spectroscopy and MS confirmed the validity of the synthetic strategy and gel electrophoresis verified the binding of BAU to DNA. For TEM imaging of DNA, two-dimensional DNA origami nanostructures were used as a robust microscopy test object. By using scanning transmission electron microscopy (STEM) imaging, which is favored over conventional wide-field TEM for improved contrast, and therefore, quantitative image analysis, it is found that the synthesized BAU intercalator can render DNA visible, even at the single-molecule scale. For comparison, other staining compounds with a purported affinity towards DNA, such as dichloroplatinum, cisplatin, osmium tetroxide, and uranyl acetate, have been evaluated. The STEM contrast is discussed in terms of the DNA–dye association constants, number of dye molecules bound per base pair, and the electron-scattering capacity of the metal-containing ligands. These findings pave the way for the future development of electron dyes with specific DNA-binding motifs for high-resolution TEM imaging.     

Semibatch emulsion copolymerization of butyl acrylate and glycidyl methacrylate: Effect of operating variables

Semibatch emulsion copolymerization was carried out to prepare poly(butyl acrylate‐co‐glycidyl methacrylate) latexes at 75°C, using potassium persulfate as an initiator, sodium dodecylbenzene sulfonate as an emulsifier and sodium bicarbonate as a buffer. The reaction was conducted in three stages; a further stage (called the steady stage, 2 h) was added to the traditionally stages (i.e., feed and seed stages) to improve considerably the monomer conversion. The monomer conversion and particle size distribution were studied by gravimetric and laser light scattering methods, respectively. The effects of variables such as agitation speed, emulsifier concentration, initiator concentration, feeding rate and comonomers ratio were fully investigated based on the monomer conversion‐time profiles and the particle size distribution to find the optimized copolymerization conditions. Increasing the agitation speed had a negative effect on the monomer conversion, but reduced coagulation of polymer particles. Monomer conversion could be improved by increasing the initiator or emulsifier contents. Feeding rate increased the polymer particle size sharply; however, it showed no significant effect on conversion. The final conversions were as high as 97–99% and they were recognized to be independent of the comonomers ratios employed. Morphological studies by scanning electron microscopy showed nano‐sized isolated particles which were partially aggregated. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010