Influence of Cobalt Doping on the Physical Properties of Zn<Subscript>0.9</Subscript>Cd<Subscript>0.1</Subscript>S Nanoparticles

Zn_0.9Cd_0.1S nanoparticles doped with 0.005–0.24 M cobalt have been prepared by co-precipitation technique in ice bath at 280 K. For the cobalt concentration >0.18 M, XRD pattern shows unidentified phases along with Zn_0.9Cd_0.1S sphalerite phase. For low cobalt concentration (≤0.05 M) particle size, d _XRD is ~3.5 nm, while for high cobalt concentration (>0.05 M) particle size decreases abruptly (~2 nm) as detected by XRD. However, TEM analysis shows the similar particle size (~3.5 nm) irrespective of the cobalt concentration. Local strain in the alloyed nanoparticles with cobalt concentration of 0.18 M increases ~46% in comparison to that of 0.05 M. Direct to indirect energy band-gap transition is obtained when cobalt concentration goes beyond 0.05 M. A red shift in energy band gap is also observed for both the cases. Nanoparticles with low cobalt concentrations were found to have paramagnetic nature with no antiferromagnetic coupling. A negative Curie–Weiss temperature of −75 K with antiferromagnetic coupling was obtained for the high cobalt concentration.     

Some thermodynamic and kinetic properties of the system PETG-CO2, and morphological characteristics of the CO2-blown PETG foams

The solubility of CO₂ in PETG, a glycol-modified PET, was measured at different temperatures and over a broad pressure range, and diffusion coefficients were derived at the corresponding conditions. The solubility of CO₂ is quits high. For example, almost 15 wt% CO₂ can be dissolved in PETG at 35°C and 6.0 MPa. Consequently, CO₂ is good blowing agent for PETG. Cellular foams in the density range of about 0.04 to 1.2 g/cm³ and diameters in the range of about 10 to 150 µm were produced. The foam density and the cell size were found to depend on the foaming temperature and time, with larger cells obtained at higher temperatures or when the sample was foamed for a longer time. The foam density decreased with an increase in the foaming temperature to about 90°C, beyond which the density tended to increase slightly due to the cell collapse or coalescence. The density reduction also depended on the pressure at which the polymer was saturated with CO₂; the higher the saturating pressure at a given temperature, the greater the density reduction.     

Extracting Constitutive Stress–Strain Behavior of Microscopic Phases by Micropillar Compression

The macroscopic behavior of metallic materials is a complex function of microstructure. The size, morphology, volume fraction, crystallography, and distribution of a 2nd phase within a surrounding matrix all control the mechanical properties. Understanding the contributions of the individual microconstituents to the mechanical behavior of multiphase materials has proven difficult due to the inability to obtain accurate constitutive relationships of each individual constituent. In dual-phase steels, for example, the properties of martensite or ferrite in bulk form are not representative of their behavior at the microscale. In this study, micropillar compression was employed to determine the mechanical properties of individual microconstituents in metallic materials with “composite” microstructures, consisting of two distinct microconstituents: (I) a Mg–Al alloy with pure Mg dendrites and eutectic regions and (II) a powder metallurgy steel with ferrite and martensite constituents. The approach is first demonstrated in a Mg–Al directionally solidified alloy where the representative stress–strain behavior of the matrix and eutectic phases was obtained. The work is then extended to a dual-phase steel where the constitutive behavior of the ferrite and martensite were obtained. Here, the results were also incorporated into a modified rule-of-mixtures approach to predict the composite behavior of the steel. The constitutive behavior of the ferrite and martensite phases developed from micropillar compression was coupled with existing strength–porosity models from the literature to predict the ultimate tensile strength of the steel. Direct comparisons of the predictions with tensile tests of the bulk dual-phase steel were conducted and the correlations were quite good.     

Creep deformation behavior of Sn-3.5Ag solder at small length scales

To adequately characterize the behavior of solder spheres in electronic packaging, their mechanical behavior needs to be studied at small-length scales. The creep behavior of single Sn-3.5Ag solder spheres on a copper substrate was studied between 25°C and 130°C using a microforce testing system. In the low-stress regime, the creep stress exponent changed from 6 at lower temperatures to 4 at higher temperatures, indicating creep by dislocation climb. The activation energy for creep was also found to be temperature dependent, and correlated with values for dislocation core diffusion and lattice diffusion in pure tin. A change in the stress exponent with increasing stress was also observed and explained in terms of a threshold stress for dislocation motion, due to the presence of obstacles in the form of Ag₃Sn particles. For more information, contact N. Chawla, Arizona State University, Department of Chemical and Materials Engineering, Ira A. Fulton School of Engineering, Tempe, AZ 85287-6006; e-mail nchawla@asu.edu.     

Optimization of sintering temperature in CdZnS films using reflection spectroscopy

In the present investigation, the polycrystalline films of Cd _X Zn_1–X S were prepared using a sintering technique. We coated slurry consisting of CdS, ZnS in the desired proportion—CdCl₂ (as adhesive) and ethylene glycol (as binder)—onto the glass substrates. The films were sintered at a range of temperatures in air atmosphere for the optimization of sintering temperatures using reflection spectroscopy. It was noticed that below 500°C, CdS-dominated films were obtained, and above 500°C, ZnS-dominated films were obtained. The films of desired composition giving appropriate results are obtained at 500°C. The reason is easily understood through reflection spectroscopic studies. Thus, we found 500°C to be the optimum sintering temperature and 10 min was the proper sintering time.     

Modeling drop breakage using the full energy spectrum and a specific realization of turbulence anisotropy

The assumption of homogeneous isotropic turbulence when modeling drop breakage in industrially relevant geometries is questionable. We describe the development of an anisotropic breakage model, where the anisotropy is introduced via the inclusion of a perturbed turbulence spectrum. The selection of the perturbed spectrum is itself motivated by our previous large-eddy simulations of high-pressure homogenizers. The model redistributes energy from small to large scales, and assumes that the anisotropic part of the Reynolds stresses is confined to the energy-containing range. The second-order structure function arising from the perturbed spectrum is used in the standard framework of Coulaloglou and Tavlarides to calculate breakage frequency. While the base model exhibits non-monotonic behavior (by predicting a maximum value for a certain drop size), the effect of anisotropy is shown to increase breakage frequency in length scales larger than this peak, thereby reducing non-monotonicity. This effect is more pronounced for small turbulence Reynolds numbers.     

Metal and Metal Oxide Nanoparticle as a Novel Antibiotic Carrier for the Direct Delivery of Antibiotics

In addition to the benefits, increasing the constant need for antibiotics has resulted in the development of antibiotic bacterial resistance over time. Antibiotic tolerance mainly evolves in these bacteria through efflux pumps and biofilms. Leading to its modern and profitable uses, emerging nanotechnology is a significant field of research that is considered as the most important scientific breakthrough in recent years. Metal nanoparticles as nanocarriers are currently attracting a lot of interest from scientists, because of their wide range of applications and higher compatibility with bioactive components. As a consequence of their ability to inhibit the growth of bacteria, nanoparticles have been shown to have significant antibacterial, antifungal, antiviral, and antiparasitic efficacy in the battle against antibiotic resistance in microorganisms. As a result, this study covers bacterial tolerance to antibiotics, the antibacterial properties of various metal nanoparticles, their mechanisms, and the use of various metal and metal oxide nanoparticles as novel antibiotic carriers for direct antibiotic delivery.     

Physiological Imaging Methods for Evaluating Response to Immunotherapies in Glioblastomas

Glioblastoma (GBM) is the most malignant brain tumor in adults, with a dismal prognosis despite aggressive multi-modal therapy. Immunotherapy is currently being evaluated as an alternate treatment modality for recurrent GBMs in clinical trials. These immunotherapeutic approaches harness the patient’s immune response to fight and eliminate tumor cells. Standard MR imaging is not adequate for response assessment to immunotherapy in GBM patients even after using refined response assessment criteria secondary to amplified immune response. Thus, there is an urgent need for the development of effective and alternative neuroimaging techniques for accurate response assessment. To this end, some groups have reported the potential of diffusion and perfusion MR imaging and amino acid-based positron emission tomography techniques in evaluating treatment response to different immunotherapeutic regimens in GBMs. The main goal of these techniques is to provide definitive metrics of treatment response at earlier time points for making informed decisions on future therapeutic interventions. This review provides an overview of available immunotherapeutic approaches used to treat GBMs. It discusses the limitations of conventional imaging and potential utilities of physiologic imaging techniques in the response assessment to immunotherapies. It also describes challenges associated with these imaging methods and potential solutions to avoid them.     

Development and benchmarking of a mechanical model for GFR plate-type fuel

The reference fuel design currently being considered within the Generation-IV Gas-cooled Fast Reactor (GFR) project is a ceramic plate matrix with a honeycomb inner structure containing small fuel cylinders. The fuel is mixed plutonium–uranium carbide, while the matrix material is silicon carbide. The present paper describes the mechanical part of a thermal–mechanical model being developed for studying the transient behavior of this highly heterogeneous fuel type. Benchmarking has been carried out against detailed finite-elements modeling (FEM).The resultant thermal–mechanical model can provide reliable fuel and cladding (matrix) stress/strain conditions to evaluate temperatures and neutronic feedbacks. As such, it has been integrated into PSI’s coupled code system “FAST”, which aims at the comprehensive safety analysis of advanced fast reactor systems.The detailed FEM analysis of the GFR fuel has been useful not only for benchmarking the new model, but also for obtaining an in-depth understanding of fuel stress/strain characteristics, which cannot be reproduced with simplified models. Thereby, the range of applicability of the new model has clearly been defined. In particular, the 3D FEM analysis has revealed a concentration of stresses at the pellet corners during pellet/matrix contact, which could lead to fuel element failure. This effect is found to be mitigated considerably, if the fuel pellets are shaped in a manner which enhances the contact area.     

Oxidation Behavior of Rare-Earth-Containing Pb-Free Solders

We have previously shown that small additions of the rare-earth (RE) element La to Sn-Ag-Cu alloys significantly increases their ductility, without significant loss in the overall strength. However, due to the high reactivity of La with oxygen, oxidation of the La-containing phases can affect the mechanical performance of the solder. In this work, we have investigated the effect of the addition of 2 wt.% Ce, La and Y on the oxidation behavior of Sn-3.9Ag-0.7Cu. Oxidation kinetics were established by heating samples in ambient air to 60°C, 95°C or 130°C for up to 250 h. Microstructural characterization of the samples, before and after oxidation, was conducted in order to determine the influence of RE-containing phases on the oxidation kinetics. The oxidation mechanism, including the phenomenon of Sn whiskering during oxidation, is also discussed.