ZnO micro and nanocrystals with enhanced visible light absorption

In this paper, we investigate the effect of the particle size and morphology on the optical properties of ZnO. A series of ZnO micro and nanocrystals were synthesized by the hydrothermal processing of zinc acetate dihydrate and sodium hydroxide as the starting materials, and polyvinylpyrrolidone (PVP) as the polymer surfactant. The particle size and morphology were tailored by adjusting the reactant molar ratios [Zn²⁺]/[OH⁻], while the reaction temperature and the time remained unchanged. X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and high-resolution TEM (HRTEM) have shown that the micro and nanocrystals have a high crystalline pure wurtzite-type hexagonal structure with nanosized crystallites. The size and morphology of the ZnO micro and nanocrystals were investigated by field emission scanning electron microscopy (FE-SEM), which showed a modification from micro-rods via hexagonal-faceted prismatic morphology to nanospheres, caused by simple adjustment of the reactant molar ratio [Zn²⁺]/[OH⁻] from 1:1 to 1:5. The optical properties of the ZnO micro and nanocrystals, as well as their dependence on the particle size and morphology were investigated by Raman and ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy (DRS). The UV–vis spectra showed that the modification of the particle size and morphology from nanospheres to micro-rods resulted in increased absorption, and a slight red-shift of the absorption edge (0.06 eV). Besides, the band gap energy of the synthesized ZnO micro and nanocrystals showed the red shift (∼0.20 eV) compared to bulk ZnO. According to the results of a Raman spectroscopy, the enhanced visible light absorption of the ZnO micro and nanocrystals is related to two phenomena: (1) the existence of lattice defects (oxygen vacancies and zinc interstitials), and (2) the particle surface sensitization by PVP.     

Reduction of fume and gas emissions using innovative gas metal arc welding variants

New environmental, health and safety legislation, both in the EU and in the USA, is driving the need for the study of new welding processes, and the selection of the operational procedures that will reduce fume emissions and will promote a healthier, safer and more productive work environment. Actually, there are a significant number of publications related with gas metal arc welding hazards. However, for the new gas metal arc welding hazards variants, especially cold metal transfer, there is no data available concerning fumes and gases emissions. This paper attempts to point out ways of reducing the harmful effects of gas metal arc welding processes using different filler materials, different shielding gases, different operational welding procedures and three welding processes: gas metal arc welding process and two variants, pulsed gas metal arc welding and cold metal transfer. The effect of nitrogen oxide addition to the shielding gas composition on the amount of welding fumes and gaseous emissions produced during welding is also analysed. The amount of fume and gases generated during welding was measured over a range of current intensity and arc voltages, using the standard procedures contained in EN ISO 15011-2 [1]. The data presented give a summary of the different gas metal arc welding variants and their relations to fume generation rates and gases emitted. The results obtained give indications on measures to be taken in order to reduce fume and gas emissions. In general, the minimisation of fume formation rate can be achieved by using lower energy gas metal arc welding variants, gas shielding with low CO₂ and O₂ contents and “green” wires.     

A novel system for on-farm fertility monitoring based on milk progesterone

Timely identification of a cow's reproduction status is essential to minimize fertility-related losses on dairy farms. This includes optimal estrus detection, pregnancy diagnosis, and the timely recognition of early embryonic death and ovarian problems. On-farm milk progesterone (P4) analysis can indicate all of these fertility events simultaneously. However, milk P4 measurements are subject to a large variability both in terms of measurement errors and absolute values between cycles. The objective of this paper is to present a newly developed methodology for detecting luteolysis preceding estrus and give an indication of its on-farm use. The innovative monitoring system presented is based on milk P4 using the principles of synergistic control. Instead of using filtering techniques and fixed thresholds, the present system employs an individually on-line updated model to describe the P4 profile, combined with a statistical process control chart to identify the cow's fertility status. The inputs for the latter are the residuals of the on-line updated model, corrected for the concentration-dependent variability that is typical for milk P4 measurements. To show its possible use, the system was validated on the P4 profiles of 38 dairy cows. The positive predictive value for luteolysis followed by estrus was 100%, meaning that the monitoring system picked up all estrous periods identified by the experts. Pregnancy or embryonic mortality was characterized by the absence or detection of luteolysis following an insemination, respectively. For 13 cows, no luteolysis was detected by the system within the 25 to 32 d after insemination, indicating pregnancy, which was confirmed later by rectal palpation. It was also shown that the system is able to cope with deviating P4 profiles having prolonged follicular or luteal phases, which may suggest the occurrence of cysts. Future research is recommended for optimizing sampling frequency, predicting the optimal insemination window, and establishing rules to detect problems based on deviating P4 patterns.     

Correlation between morphological properties and thermal conductivity of injection‐molded polyamide 46

The morphology and thermal conductivity of injection‐molded polyamide 46 (PA46) samples were investigated in this study. It was found that injection molding parameters had no influence on the thermal conductivity. This was attributed to the high crystallization speed and therefore imperfect crystal structure of PA46. By annealing of some samples at 260°C for 24 h the thermal conductivity was increased by 30%. Polarization light microscopy revealed only minor changes of the visible morphological structure for the as molded and annealed samples. For the investigation of the sample crystallinity via Raman spectroscopy an analysis method was established and the term “Raman crystallinity” is introduced as the intensity ratio of characteristic Raman bands. Via Raman crystallinity it was possible to distinguish between different mold temperatures and the annealed PA46 samples showed a significantly increased Raman crystallinity. Our results show that the thermal conductivity of PA46 primarily depends on the crystal structure on a length scale of crystallites. The size of the visible spherulite‐like structures did not correlate with the change in thermal conductivity. A correlation of the Raman crystallinity with the thermal conductivity of PA46 was shown. POLYM. ENG. SCI., 55:2231–2236, 2015. © 2015 Society of Plastics Engineers     

New fault detection method based on reduced kernel principal component analysis (RKPCA)

Remanufacturing is the only way for sustainable development of mechanical equipment manufacturing. For remanufacturing blanks containing cracks, the primary task is the prevention of crack propagation to ensure effectiveness of the manufacturing processes to follow. When pulsed current passes through a specimen, due to the existence of crack, the temperature around the crack tips rises sharply and may even climb above the fusion point of the material, which causes the crack tip to become blunt. In this work, with compressor rotor blade material FV520B as a specimen, the distributions of current density, temperature field, and stress field are calculated at the instant of discharge based on the thermo-electro-structure coupled theory. The crack arrest experiment is performed on high pulsed current discharge device of type HCPD-I. By making comparisons of morphology, microstructure, and size of fusion zone and heat-affected zone (HAZ) around the crack tip before and after energizing, the relationships between the sizes of fusion zone and the HAZ and the discharge energy and the current path are derived. The obvious partition and refined grains around the crack tip are prominent because of violent temperature change. The experimental and simulation results are found in fine agreement. The high current pulsed discharge can be used effectively to prevent a crack to further expand and show substantial potentials for application in remanufacturing domain.     

Simulating Biomolecular Folding and Function by Native-Structure-Based/Go-Type Models

The 2013 Nobel Prize in Chemistry highlights how crucial computer simulations have become for many scientific and engineering fields. Nowadays, scientific progress is not only driven by the interplay of new experimental measurements and increasingly sophisticated theoretical frameworks, but also by an incredible toolbox of complex computational models meeting ubiquitously available computing power and data storage facilities. Quantum mechanical (QM) calculations can be condensed into molecular mechanics (MM) force fields and coupled QM/MM calculations can derive atomic and molecular properties of biomolecular or materials science systems with high accuracy. Pure MM simulations driven by Monte Carlo or molecular dynamics algorithms are widely applied in biological chemistry/physics and can investigate large biomolecular systems, such as proteins, DNA, or RNA. One coarse-grained class of these models, native-structure-based or Go models, are based on energy landscape theory and the principle of minimal frustration. Herein, an ensemble of converging pathways guide protein folding on a funnel-like shape of the entire energy landscape towards the native state. Simulations based on these ideas have been tremendously successful in explaining protein folding and function. Their history and recent application highlights are reviewed.     

Significance of Nanopatterned and Clustered DLL1 for Hematopoietic Stem Cell Proliferation

Hematopoietic stem cells are the stem cells of the blood that are applied to treat hematological disorders by transplanting donor cells to a patient. Rarity of donors and low cell counts in alternative hematopoietic stem cell sources such as cord blood limit the clinical use of hematopoietic stem cells. Here, it is shown that bifunctional surfaces containing the adhesive RGD peptide together with the Notch‐activating Delta‐like 1 (DLL1)—provided in a nanopatterned or unpatterned manner in different densities—are able to enhance hematopoietic stem and progenitor cell proliferation. Nanopatterning allows determining the maximal distance between DLL1 molecules that results in efficient cell stimulation (40 nm). Applying unpatterned substrates with statistically distributed DLL1 shows that the elicited effects depend on ligand density and clustering (minimum 2 molecules/cluster). Thereby, the present study contributes to the development of cost‐efficient bioreactors for hematopoietic stem cell expansion and to deciphering how cells gain control over Notch signaling by DLL1 clustering.     

Conductivity and nanoscale morphology of thin films prepared from indolo[2,3-a]carbazole and 11,12-dioctylindolo[2,3-a]carbazole

A systematic study on the thin film morphology of heteroacenic derivatives such as indolo[2,3-a]carbazole and 11,12-dioctylindolo[2,3-a]carbazole has been carried out using scanning force microscopy and optical microscopy techniques. The investigation has comprised the preparation of a series of thin films by combining different solvents (dimethylformamide and tetrahydrofurane), substrates (glass, gold, silicon and aluminium) and deposition techniques (spin coating and thermal evaporation) we found a wide variety of self-assembled structures. In addition, conductivity measurements have been performed, showing a very large spread in conductivity values. Some of the samples give quite high conductivity while others conduct very poorly, even in the case of samples prepared with essentially the same conditions. These results indicate that morphology is very critical for the final conductivity of the thin films. In addition we conclude that for some of the films prepared the homogeneous thin film approximation must be revised otherwise obtained conductivity measurements lead to significant error.     

High rate UWB CMOS transceiver chipset for WBAN and biomedical applications

This work presents a high rate UWB transceiver chipset implemented in a 130 nm CMOS technology for WBAN and biomedical applications in the 3–5 GHz band. The transmitter architecture is based on a double-filter excitation technique that can generate high magnitude pulses and address bipolar modulations such as BPSK. Measurements show that bipolar pulses with a peak-to-peak voltage of 1.9 Vpp for a power consumption of 139 µW@100 kbps can be generated. The receiver is a non-coherent architecture based on LNA followed by an envelope detector. A BER of 10^?3 is achieved for a 3–5 GHz input peak-to-peak amplitude of 3.4 mVpp which corresponds to a ?89.3 dBm sensitivity at 100 kbps. The energy consumption of the receiver and of the transmitter is respectively 0.144 nJ/bit and 196 pJ/bit at 100 Mbps. To improve the budget link of our non-coherent based transceiver a Randomly Alternate OOK signaling is proposed which leads to an estimated communication range of 2.36 m in a free space propagation channel.     

An efficient algorithm for electromagnetic scattering by a set of perfect conducting cylindrical objects using the artificial neural network

In this article an efficient algorithm based on the wave concept iterative process is formulated and applied in order to investigate the electromagnetic scattering by a set of conducting arbitrarily shaped objects placed in the free space. In this approach, the cylindrical coordinates system is used as a modal base in order to develop the modal coefficients of the diffraction operator. This operator models the reaction of the environment expressing the electromagnetic coupling between each two pixels of the discretized surface. A study of electromagnetic coupling between two pixels positioned and oriented somehow in the free space is highlighted so as to determine the coupling operator for different positions and orientations of the emitted and received waves. Twelve coupling operators are developed. For a complex geometric shape structure, the determination of these characteristics involved the determination of interactions between each pixel and the others that constitute the discretized surface. This interaction involves the wave formulation already highlighted for each couple of pixels which implies a higher calculation time. In order to optimize the calculation time, the artificial neural networks are adopted with the feed‐forward architecture. The supervised learning has been chosen with the use of the resilient backpropagation algorithm.