Rheological and Microscopic Properties of Fat Blends with Similar Solid Fat Content but Different Trans Composition

In this study, two different groups of fat samples were prepared in a way that samples of each group had different trans fatty acid (TFA) composition but similar solid fat content (SFC). Samples of the first group (named group A) had TFA between 0.0 and 56.23 %, while the samples of the second group (group B) contained trans isomers ranging from 0.0 to 44.4 %. A polarized microscope was used to monitor the differences between the samples in terms of crystal size and crystal number during isothermal crystallization. In general, increasing TFA resulted in formation of larger crystals in a shorter time. Similar findings were also observed when small deformation time and frequency sweep experiments were conducted. A higher TFA content led to higher complex modulus values during isothermal crystallization. On the other hand, when the samples were stored at 4 °C for 48 h, the samples with the lower trans isomer had higher hardness values.     

A Thienothiophene-Based Cation Treatment Allows Semitransparent Perovskite Solar Cells with Improved Efficiency and Stability

Perovskite surface treatment with additives has been reported to improve charge extraction, stability, and/or surface passivation. In this study, treatment of a 3D perovskite ((FAPbI₃)_1−x(MAPbBr₃)_x) layer with a thienothiophene-based organic cation (TTMAI), synthesized in this work, is investigated. Detailed analyses reveal that a 2D (n = 1) or quasi-2D layer does not form on the PbI₂-rich surface 3D perovskite. TTMAI-treated 3D perovskite solar cells (PSCs) fabricated in this study show improved fill factors, providing an increase in their power conversion efficiencies (PCEs) from 17% to over 20%. It is demonstrated that the enhancement is due to better hole extraction by drift-diffusion simulations. Furthermore, thanks to the hydrophobic nature of the TTMAI, PSC maintains 82% of its initial PCE under 15% humidity for over 380 h (the reference retains 38%). Additionally, semitransparent cells are demonstrated reaching 17.9% PCE with treated 3D perovskite, which is one of the highest reported efficiencies for double cationic 3D perovskites. Moreover, the semitransparent 3D PSC (TTMAI-treated) maintains 87% of its initial efficiency for six weeks (>1000 h) when kept in the dark at room temperature. These results clearly show that this study fills a critical void in perovskite research where highly efficient and stable semitransparent perovskite solar cells are scarce.     

Benchmarking grey particle approximations against nongrey particle radiation in circulating fluidized bed combustors

Investigation of the effect of grey/nongrey particle property models on radiative heat fluxes and source terms is performed in the dilute zone of the lignite-fired 150?kW Middle East Technical University circulating fluidized bed combustor test rig. Predictive accuracy and computational economy of several grey particle models, geometric optics approximation (GOA) with average particle reflectivity (GOA2), GOA with Fresnel solution for particle reflectivity (GOA3), and Planck mean particle properties from spectral Mie solution are tested by benchmarking their predictions against spectrally banded solution of radiative transfer equation (RTE). Comparisons reveal that all grey models lead to accurate and CPU efficient radiative heat flux predictions. On the other hand, only GOA3 and Planck mean properties are in favorable agreement with the benchmark solution for both incident fluxes and source terms. These findings indicate that grey particle approximation with GOA3 is a more practical choice in solution of RTE as it eliminates the need for spectral calculations.     

Fatigue fracture of SnAgCu solder joints by microstructural modeling

The ongoing miniaturization trend in the microelectronic industry enforces component sizes to approach the micron, or even the nano scale. At these scales, the underlying microstructural sizes and the geometrical dimensions are comparable. The increasing influence of microscopic entities on the overall mechanical properties makes conventional continuum material models more and more questionable. In this study, the thermomechanical reliability of lead-free BGA solder balls is investigated by microstructural modeling. Microstructural input is provided by orientation imaging microscopy (OIM), converted into a finite element framework. Blowholes in BGA solder balls are examined by optical microscopy and a statistical analysis on their size, position and frequency is conducted. Combining the microstructural data with the appropriate material models, three dimensional local models are created. The fatigue life of the package is determined through a critical solder ball. The thermomechanical reliability of the local models are predicted using cohesive zone based fatigue damage models. The simulation results are validated by statistical analyses provided by the industry.     

Electrical characterization of a-Si:H(n)/c-Si(p) structure

In this study, n-type hydrogenated amorphous silicon (a-Si:H) was fabricated on p-type crystalline silicon (c-Si) substrates to obtain heterojunction diodes. The amorphous films were obtained by the Plasma Enhanced Chemical Vapor Deposition (PECVD) technique. Temperature dependent current-voltage (I-V-T) measurements and investigation of the dc current injection mechanism of a-Si:H(n)/c-Si(p) device structure have been performed. The series resistance (4.6-8.2 Ω) values displayed nearly temperature independent behavior and the ideality factor varied between 2.7 and 1.6 in the temperature range 100-320 K. The forward bias I-V-T characteristics of c-Si/a-Si:H heterojunctions are found to behave like the Schottky junctions where carrier injection is especially influenced by the carrier generation-recombination in the junction interface formed on the amorphous side. The temperature dependent ideality factor behavior shows that tunneling enhanced recombination is valid rather than thermionic emission theory. In the frame of this model, characteristic tunneling energy and characteristic temperature are found to be 9 meV and 1900 K, respectively. It is concluded that fabricate n-type hydrogenated amorphous silicon is a preferable semiconductor material layer with low interface state density because the temperature dependent interface state density calculations give values of the order of 10¹⁴ eV⁻¹ cm⁻².     

A Unique Processable Green Polymer with a Transmissive Oxidized State for Realization of Potential RGB‐Based Electrochromic Device Applications

Realization of commercial RGB‐based polymer electrochromic‐device applications can only be achieved by processable materials that possess three complementary colors in the reduced state and are transparent in the oxidized state. This report highlights the synthesis of the first processable green polymer with a transmissive oxidized state. The polymer revealed superior optical contrast in the visible region with fast switching times and robust stability. Hence, this material is the outstanding candidate for completion of RGB color space through commercial polymeric electrochromics.     

Fast recovery of non‐fickian moisture absorption parameters for polymers and polymer composites

Moisture absorption is known to detrimentally affect the mechanical integrity and durability of polymeric materials. Consequently, accurately characterizing the moisture diffusion into these materials is critical when predicting their service life behavior. The hindered diffusion model (HDM), that is, Langmuir‐type absorption, has been widely used to successfully describe both Fickian and anomalous absorption behavior of polymeric materials. In this article, proper use of both exact and approximate solutions of the HDM model is illustrated on two material systems: nanoclay/epoxy composites and thin epoxy laminates. A parameter recovery technique, based on a modified version of the steepest descent search, is shown to accurately recover all absorption parameters simultaneously from experimental data. The absorption behavior predicted by the recovered parameters is then validated by long‐term absorption data not used in the recovery process. The errors induced by approximate solutions are observed to be material‐dependent and could be substantially larger compared to the exact solution. In addition, a novel method to computationally accelerate the recovery of the absorption parameters is proposed. The new technique uses the approximate absorption parameters as the initial guess. It is shown that this approach substantially reduces the computational effort by decreasing the number of iterations without compromising from accuracy. POLYM. ENG. SCI., 57:921–931, 2017. © 2016 Society of Plastics Engineers     

The impact of lot-sizing in multiple product environments with congestion

We present a production planning model for a multiple product single machine dynamic lot-sizing problem with congestion. Using queuing models, we develop a set of functions to capture the nonlinear relationship between the output, lot sizes and available work in process inventory levels of all products in the system. We then embed these functions in a nonlinear optimization model with continuous variables, and construct an approximate solution to the original problem by rounding the resulting fractional solution. Computational experiments show that our model with congestion provides significantly better flow time and inventory performance than a benchmark model that does not consider the effects of congestion. These advantages arise from the use of multiple smaller lots in a period instead of a single large lot as suggested by conventional fixed-charge models without congestion.