Materials Engineering

Trion photoluminescence spectra were measured in undoped high-quality GaAs quantum wells. The lineshape is asymmetric with a temperature-dependent tail towards lower photon energies. We have solved numerically the trion Schrodinger equation in the quantum well and found good agreement for both the trion binding energy and the luminescence lineshape at different temperatures. To analyse the relative weight of trion and exciton emission, an equilibrium mass-action law for the respective densities is studied. Using calculated radiative lifetimes, the emission decay after pulsed excitation is found to deviate strongly from a single-exponential shape in case the trions are initially saturated.

Total ion concentrations of sodium, potassium, calcium and chloride have been measured reversibly by ion-selective optode membranes with comparable selectivity to potentiometric systems. The results of quality-control samples analysed by the selective optode membranes show a good agreement with the assigned values and a reasonable reproducibility, though for quantification of sodium and potassium the unknown concentrations are evaluated in a first trial by a standard addition method. All measurements are referred to a pair of blank membranes in a reference cell to compensate for interferences induced by the diluted plasma sample. The efficiency of the evaluated values with regard to the medical interpretation encompasses the performance standard of the analytical procedure as well as the intra-and interindividual variation of the subjects studied. The required performance characteristics of a sensor are constituted dilhzrently, depending on the mode of application and the medical question to be answered. The type of optodes described may be tailored to a large extent to adapt them to the required performance boundary conditions. This will bc discussed with respect to other optical sensor schemes.

The properties of optode membranes to be used for realizing miniature integrated optical sensors based on refractometry have been investigated theoretically and experimentally. In situ referencing by using optode and reference membranes on the same chip is a powerful means to discriminate against unspecific effects. The plasticized polymer membranes provide the function of selective extraction and chemical recognition of the analyte. In experiments performed for a pair of such membranes, refractive index differences ~3 x 10 3 per decade of molar Ca 2+ concentration in buffered aqueous solutions have been observed. With the characterized type of sensing pad implanted in a miniature integrated optical device, a typical overall resolution of 0.7 to 0.07% in units of Ca 2~ concentration was calculated.

The paper is focused on the structuring of glass wafers to obtain high aspect ratio glass columns with high vertical profile for Micro Electro Mechanical Systems (MEMS). The technique proposed is to pattern columns by mechanical sawing. The sawing parameters have been optimised to achieve a high yield. Different dimensions of the column have been tested and glass columns down to 150 m × 150 m of cross-section and 700 m height have been obtained. They present high aspect ratio (>100) and very good vertical profile (88-90 • ). Hoya SD-2 and Corning Pyrex #7740 glass wafers have been processed with similar results. Different cleaning procedures have been tested to improve the anodic bondability of the samples after sawing. Machined glass columns have also been structured by commercial sand blasting technique and the results are also compared to the sawed samples. The glass wafers with machined columns have been anodically bonded to silicon. Anodic bonding characterisation of glass columns of different sections is also presented. Pull tests confirmed the good bondability of the glass columns.

An X-ray absorption spectroscopy (XAS) study of the Fe local environment in natural amethyst (a variety of a-quartz, SiO 2 ) has been carried out. Room temperature measurements were performed at the Fe K-edge (7,112 eV), at both the X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) regions. Experimental results were then compared with DFT calculations. XANES experimental spectra suggest Fe to occur mainly in the trivalent state, although a fraction of Fe 2? is identified. EXAFS spectra, on the other hand, reveal an unusual short distance for the first coordination shell: \Fe-O[ = 1.78(2) A ˚, the coordination number being 2.7(5). These results allow to establish that Fe replaces Si in its tetrahedral site, and that numerous local distortions are occurring as a consequence of the presence of Fe 3? variably compensated by protons and/or alkaline ions, or uncompensated. The formal valence of Fe, on the basis of both experimental and DFT structural features, can be either 4? or 3?. Taking into account the XANES evidences, we suggest that Fe mainly occurs in the trivalent state, compensated by protons, and that a minor fraction of Fe 4? is stabilised by the favourable local structural arrangement.

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In this study nanostructured (grain size: 81 ± 31 nm) micron-sized pure copper powder was compacted in a die using a uniaxial force at room temperature and at pressures ranging from 0.25 to 1.00 GPa. The pressure range selected was based on an ability of the silicon wafer to withstand the pressure without experiencing mechanical damage. The as-compacted copper compacts were sintered at 200 • C for 2 h in an atmosphere of argon. The purpose of this research study was to optimize the compaction pressure to get properties in the compacted copper sample that makes it suitable for use as an electronic packaging material. The characterization studies revealed that an increase in compaction pressure followed by sintering at a low temperature had a minimal to no influence on grain size but a noticeable influence on both porosity and hardness of the compacted sample. The microhardness of the as-compacted samples was found to be superior to the values obtained for the samples synthesized using the techniques of inert gas deposition and in situ compaction, solution phase synthesis, and plasma pressure compaction. The influence of compaction pressure on hardness of the sintered samples is rationalized in light of its intrinsic influence on microstructural development and processing-related artifacts.

Ultra High Strength Concrete (UHSC) merupakan terobosan yang sedang dikembangkan dalam beberapa dekade terakhir ini. UHSC memiliki beberapa kelebihan dibandingkan Normal Strength Concrete (NSC), yaitu beton UHSC memiliki ketahanan yang lebih baik terhadap asam, kebakaran, maupun ketahanan jangka panjang. Pada tahun 2010, di Indonesia telah dapat dibuat beton UHSC dengan kekuatan mencapai 140 MPa dengan memanfaatkan material lokal dengan ukuran yang sangat halus walaupun masih di laboratorium. Dalam penelitian ini akan dicari mix design yang dapat mencapai kuat tekan UHSC, pengaruh steam curing, penambahan steel fibres, dan proses vacuum dalam pembuatan UHSC. Pencarian mix design dilakukan terebih dahulu sebelum melakukan penelitian yang lain. Kuat tekan maksimum yang dicapai adalah sebesar 115 MPa pada umur 28 hari. Perlakuan steam curing memberikan pengaruh pada kuat tekan awal dan dengan melakukan proses vacuum dalam proses pemadatan benda uji tidak memberikan pengaruh dalam kekuatan. Penambahan steel fibres memberikan pengaruh yang baik dari segi ketahan dalam mengatasi keruntuhan yang getas. KATA KUNCI: ultra high strength concrete, UHSC, steam curing, steel fibres, vacuum. Ultra High Strength Concrete (UHSC) merupakan terobosan yang sedang dikembangkan dalam beberapa dekade terakhir ini. UHSC memiliki beberapa kelebihan dibandingkan Normal Strength Concrete (NSC), yaitu beton UHSC memiliki durability yang lebih baik terhadap asam, kebakaran, maupun ketahanan jangka panjang. Penentuan komposisi yang optimum dari setiap material penyusun beton UHSC sangat diperlukan, baik dari aggregat halus, semen, supplementary cement material, air, dan metode-metode yang akan digunakan selama proses pembuatan.

Finite‐molecular‐mass homopolymers are modeled as binary random mixtures of high polymers and oligomers or chain ends, in proportions determined by the number‐average degree of polymerization. This leads directly to an entropic equation for the effect of molecular mass on Tq in terms of the glass‐transition temperatures and transition increments of heat capacity of these two components. Predictions of the theory are found to be in satisfactory agreement with calorimetric measurements of Tg over a wide range of molecular mass.

Previous luminescence and absorption experiments in Co-doped ZnO revealed two ionization and one intrashell transition of d(Co 2+ ) electrons. Those optical properties are analyzed within the generalized gradient approximation to the density functional theory. The two ionization channels involve electron excitations from the two Co 2+ gap states, the t 2↑ triplet and the e 2↓ doublet, to the conduction band. The third possible ionization channel, in which an electron is excited from the valence band to the Co 2+ level, requires energy in excess of 4 eV, and cannot lead to absorption below the ZnO band gap, contrary to earlier suggestions. We also consider two recombination channels, the direct recombination and a two-step process, in which a photoelectron is captured by Co 3+ and then recombines via the internal transition. Finally, the observed increase the band gap with the Co concentration is well reproduced by theory. The accurate description of ZnO:Co is achieved after including +U corrections to the relevant orbitals of Zn, O, and Co. The +U (Co) value was calculated by the linear response approach, and independently was obtained by fitting the calculated transition energies to the optical data. The respective values, 3.4 and 3.0 eV, agree well. Ionization of Co induces large energy shifts of the gap levels, driven by the varying Coulomb coupling between the d(Co) electrons, and by large lattice relaxations around Co ions. In turn, over ∼ 1 eV changes of Co 2+ levels induced by the internal transition are mainly caused by the occupation-dependent U (Co) corrections.

We report studies on the dc magnetization of YBCO thin ®lms in simultanously applied dc and ac ®elds. The eect of the ac ®elds is to decrease the irreversible magnetization drastically leading to complete collapse of the hysteresis loops for relatively small ac ®elds (25 Oe). The magnitude of the decrease depends on the component of the ac ®eld parallel to the c-axis. The decrease is non-linear with ac amplitude and is explained in the framework of the critical state response of ultrathin ®lms in perpendicular geometry. The ac ®elds increase the relaxation rapidly at short times while the long time response appears unaected.

We have investigated the hysteresis in the AC susceptibility of granular YBCO superconductors when the DC field is cycled. A crossover point is observed where the susceptibility X' in decreasing fields becomes more diamagnetic than for increasing fields, and this is investigated as a function of temperature, AC field amplitude and frequency. The behavior is consistent with the variation of the AC penetration depth with these variables and with a reduced flux density of the intergrain regions on field reversal. The zero field cooled behavior of the second harmonic X2 as well as the behavior of X' in field cooled conditions, are also reported. The DC field dependence of X' is analyzed using the low amplitude, linear response region approximations.

Highly microporous metal-MCM-41 ordered mesoporous structure catalysts having different metal/Si (V, Mo, Nb) atomic ratios and combinations of metal sources were hydrothermally synthesized. The structural properties estimated using different techniques were found to be in agreement with each other. Metals were successfully incorporated into MCM-41 without deteriorating the ordered hexagonal structure. The metal ions in the synthesis solutions probably settled on the hydrophilic end of the template hence the metal incorporation resulted improvements in the micropore structure. Low loading of metals caused an increase in the surface area and pore volume values of the catalysts. The highest total (1310 m 2 g -1 ) and micropore surface area values (1083 m 2 g -1 ) were obtained by Nb incorporation. The micro-and mesopore dimensions of MCM-41 increased from 0.5 to 1.1 nm and from 2.5 to 2.8 nm, respectively, with metal incorporation. Low V/Si ratios and presence of Nb in the starting solution enhanced narrow mesopore size distribution. The pore dimension and wall thickness values estimated from nitrogen adsorption and X-ray diffraction methods were consistent with the corresponding values obtained using transmission electron microscopy.

The localized corrosion behavior of Type 304L stainless steel (UNS S30400), Alloy 625 (UNS N06625), and three experimental NiCoCrMo multiprincipal element alloys (MPEA), exposed to methanol/lithium chloride solutions with different water contents, is examined in this paper. Cyclic potentiodynamic polarization tests indicated that water increased the pitting and repassivation potentials and the critical temperature at which localized corrosion occurred in chloride solutions. The effect of water on repassivation potential in methanol-chloride solution depended on the chloride concentration and alloy content. At lower chloride concentration and higher alloy content, water had a greater inhibiting effect on repassivation potential, suggesting a competitive reaction between chloride and water on the metal surface in the pit. The localized corrosion resistance of the MPEAs followed the same trend as that of commercial stainless steels and Ni-base alloys in terms of the effect of alloying ...

Advancements in data analytics techniques have enabled complex, disparate datasets to be leveraged for alloy design. Identifying outliers in a dataset can reduce noise, identify erroneous and/or anomalous records, prevent overfitting, and improve model assessment and optimization. In this work, two alloy datasets (9-12% Cr ferritic-martensitic steels, and austenitic stainless steels) have been assessed for outliers using unsupervised techniques and supplemented with domain knowledge. Principal component analysis and k-means clustering were applied to the data, and points were assessed as outliers based on their distance from other points in the cluster and from other points in the dataset. The outlier characteristics were investigated to determine both cluster-specific and overall trends in the properties of the outlier points. The approach demonstrated here is extensible to other alloy datasets for outlier identification and evaluation to improve the reliability of machine learning and modeling predictions for advanced alloy design.

Data analytics methods have been increasingly applied to understanding materials chemistry, processing due to the manufacturing approach, and uni-axial and cyclic property relationships in the highly complex space of alloy design. There are several benefits to applying data analytics to this space, including the ability to manage non-linearities in the responses of the alloy attributes and the resulting mechanical properties. However, key difficulties in applying and understanding the results of data analytics include the often lack of reported assumptions and data processing steps necessary to improve interpretation and reproducibility in derived results. In this work, the methods used to generate clustering and correlation analyses for experimental 9% Cr ferritic-martensitic steel data were investigated and the resulting implications for mechanical property predictions were assessed. This work uses principal component analysis, partitioning around medoids, t-SNE, and k-means clustering to investigate trends in composition, processing and microstructure information with creep and tensile properties, building on work done previously using a smaller version of the same dataset. The initial assumptions, preprocessing steps and methods are investigated and outlined in order to depict the fine level of detail required to convey the steps taken to process data and produce analytical results. The variations in the resulting analyses are explored due to the influence of new and more varied data.

Heritage data for the class of 9 to 12 wt pct Cr steels are studied using data science to quantify the statistically significant relationships among multiple processing/microstructure and performance variables. The effort is undertaken to find new martensitic steels for creep life of 10 5 hours or greater at 650 °C and 100 MPa using machine learning. Linear regression and lasso regression were utilized to identify alloying elements that contribute towards better creep strength. Visualization techniques such as t-distributed stochastic neighbor embedding and pair-wire element specific comparisons were utilized to explore information gaps that exist within the data and are in conflict with existing domain knowledge. Combining all results suggest that the next alloy design to be explored should be 9 wt pct Cr with high W (2 to 3 wt pct) and high Co (2 to 3 wt pct) for creep life of 10 5 hours or greater at 650 °C, 100 MPa.

The fatigue crack growth rates for nickel-based superalloy Haynes 282 were measured at 550, 650, and 750 °C using compact tension specimens with a load ratio of 0.1 and cyclic loading frequencies of 25 and 0.25 Hz. The crack path was observed to be primarily transgranular for all temperatures, and the observed effect of increasing temperature was to increase the fatigue crack growth rates. The activation energy associated with the increasing crack growth rates over these three temperatures was calculated less than 60 kJ/mol, which is significantly lower than typical creep or oxidation mechanisms; therefore, creep and oxidation cannot explain the increase in fatigue crack growth rates. Transmission electron microscopy was done on selected samples removed from the cyclic plastic zone, and a trend of decreasing dislocation density was observed with increasing temperature. Accordingly, the trend of increasing crack growth rates with increasing temperature was attributed to softening associated with thermally assisted cross slip and dislocation annihilation.

High-entropy alloys (HEAs) have generated interest in recent years due to their unique positioning within the alloy world. By incorporating a number of elements in high proportion, usually of equal atomic percent, they have high configurational entropy, and thus, they hold the promise of interesting and useful properties such as enhanced strength and alloy stability. The present study investigates the mechanical behavior, fracture characteristics, and microstructure of two single-phase FCC HEAs CoCrFeNi and CoCrFeNiMn with some detailed attention given to melting, homogenization, and thermo-mechanical processing. Ingots approaching 8 kg in mass were made by vacuum induction melting to avoid the extrinsic factors inherent to small-scale laboratory button samples. A computationally based homogenization heat treatment was given to both alloys in order to eliminate any solidification segregation. The alloys were then fabricated in the usual way (forging, followed by hot rolling) with typical thermo-mechanical processing parameters employed. Transmission electron microscopy was subsequently used to assess the single-phase nature of the alloys prior to mechanical testing. Tensile specimens (ASTM E8) were prepared with tensile mechanical properties obtained from room temperature through 800 °C. Material from the gage section of selected tensile specimens was extracted to document room and elevated temperature deformation within the HEAs. Fracture surfaces were also examined to note fracture failure modes. The tensile behavior and selected tensile properties were compared with results in the literature for similar alloys.

A two-step aging treatment is applied to nickel-base alloy 718 that has been previously surface-treated by mill finishing (MF) and machine hammer peening (MHP). As a result, a Cr-enriched oxide layer is formed along with a nano-precipitates layer that consists of high precipitate fractions of c 0 /c 00 on the top surface. Surface hardness increases after aging and the compressive residual stress is almost relaxed. The synergistic effects of MHP and aging on pitting corrosion behavior are studied. The results show that the corrosion resistance of the MHP specimens decreases after aging, although the corrosion resistance is still higher than the MF condition.

While extracorporeal membrane oxygenation (ECMO) is a valuable therapy for patients with lung or heart failure, clinical use of ECMO remains limited due to hemocompatibility concerns with pro-coagulatory hollow fiber membrane geometries. Previously, we demonstrated the feasibility of silicon nanopore (SNM) and micropore (SμM) membranes for transport between two liquidphase compartments in blood-contacting devices. Herein, we investigate various pore sizes of SNM and SμM membranesalone or with a polydimethylsiloxane (PDMS) protective coatingfor parameters that determine suitability for gas exchange. We characterized the bubble or rupture point of these membranes to determine sweep gas pressures at which gas emboli would form. The smallest pore size SNM and the SμM with PDMS coating could be pressurized in excess of 260 cmHg without rupture, which is comparable to hollow fiber sweep gas pressures. Oxygen flux for the SμM with and without PDMS was insignificantly different at 0.0306 ± 0.0028 and 0.0297 ± 0.0012 mL/min, respectively, while SNM flux was significantly lower at 0.0149 ± 0.0040 mL/min. However, the area-normalized mass transfer coefficient of the SNM was 338 ± 54 mL O 2 m -2 min -1 cmHg -1an order of magnitude higher than that of the SμM with and without PDMS (57.3 ± 5.5 and 55.6 ± 2.2 mL O 2 m -2 min -1 cmHg -1 ). Ultimately, we conclude that SμM-PDMS may make effective membranes for ECMO, since they are both mechanically robust and capable of high oxygen flux.

While extracorporeal membrane oxygenation (ECMO) is a valuable therapy for patients with lung or heart failure, clinical use of ECMO remains limited due to hemocompatibility concerns with pro-coagulatory hollow fiber membrane geometries. Previously, we demonstrated the feasibility of silicon nanopore (SNM) and micropore (SμM) membranes for transport between two liquidphase compartments in blood-contacting devices. Herein, we investigate various pore sizes of SNM and SμM membranesalone or with a polydimethylsiloxane (PDMS) protective coatingfor parameters that determine suitability for gas exchange. We characterized the bubble or rupture point of these membranes to determine sweep gas pressures at which gas emboli would form. The smallest pore size SNM and the SμM with PDMS coating could be pressurized in excess of 260 cmHg without rupture, which is comparable to hollow fiber sweep gas pressures. Oxygen flux for the SμM with and without PDMS was insignificantly different at 0.0306 ± 0.0028 and 0.0297 ± 0.0012 mL/min, respectively, while SNM flux was significantly lower at 0.0149 ± 0.0040 mL/min. However, the area-normalized mass transfer coefficient of the SNM was 338 ± 54 mL O 2 m -2 min -1 cmHg -1an order of magnitude higher than that of the SμM with and without PDMS (57.3 ± 5.5 and 55.6 ± 2.2 mL O 2 m -2 min -1 cmHg -1 ). Ultimately, we conclude that SμM-PDMS may make effective membranes for ECMO, since they are both mechanically robust and capable of high oxygen flux.

Growth of human connective tissue progenitor cells (CTPs) was characterized on smooth and microtextured polydimethylsiloxane (PDMS) surfaces. Human bone marrow derived cells were cultured for nine days under conditions promoting osteoblastic differentiation on Smooth PDMS and PDMS Channel microtextures (11 µm high, 45 µm wide channels, and separated by 5 µm wide ridges). Glass tissue culture dish surfaces were used

Any discussion concerning SiC as a material for MEMS first requires a basic understanding of these Silicon carbide (SiC) has recently attracted micromachining processes. attention as a wide bandgap semiconductor with great potential for microelectromechanical Bulk micromachining was developed in the 1970s systems (MEMS). SiC exhibits excellent electrical, as an extension of IC technology for the fabrication mechanical, and chemical properties, making it of three-dimensional structures.1 Bulk micromachinwell suited for harsh environment applications ing of silicon uses wet and dry etching techniques in where traditional MEMS are constrained by the conjunction with etch masks and etch stops to sculpt physical limitations of silicon (Si). This paper micromechanical devices from the Si substrate. There reviews the material properties, deposition are two key capabilities that make bulk micromachintechniques, micromachining processes, and other ing of Si a viable technology. First, the availability of issues regarding the fabrication of SiC-based anisotropic etchants of Si such as ethylene-diamine sensors and actuators. Special emphasis is placed pyrocatecol (EDP) and potassium hydroxide (KOH), on the properties that make SiC attractive for MEMS, and the Si-based processing techniques which preferentially etch single crystal Si along select that have been adapted to realise SiC MEMS crystal planes. Second, the availability of etch masks structures and devices. An introduction to and etch-stop techniques which can be used in conmicromachining is provided for readers not junction with silicon anisotropic etchants to prevent familiar with MEMS fabrication techniques.

Varying geometry and layout of microposts on a cell culture substrate provides an effective technique for applying mechanical stimuli to living cells. In the current study, the optimal geometry and arrangement of microposts on the polydimethylsiloxane (PDMS) surfaces to enhance cell growth behavior were investigated. Human bone marrow derived connective tissue progenitor cells were cultured on PDMS substrates comprising unpatterned smooth surfaces and cylindrical post microtextures that were 10 µm in diameter, 4 heights (5, 10, 20 and 40 µm) and 3 pitches (10, 20, and 40 µm). With the same 10 µm diameter, post heights ranging from 5 to 40 µm resulted in a more than 535000 fold range of rigidity from 0.011 nNµm -1 (40 µm height) up to 5888 nNµm -1 (5 µm height). Even though shorter microposts result in higher effective stiffness, decreasing post heights below the optimal value, 5 µm height micropost in this study decreased cell growth behavior. The maximum number of cells was observed on the post microtextures with 20 µm height and 10 µm inter-space, which exhibited a 675% increase relative to the smooth surfaces. The cells on all heights of post microtextures with 10 µm and 20 µm inter-spaces exhibited highly contoured morphology. Elucidating the cellular response to various external geometry cues enables us to better predict and control cellular behavior. In addition, knowledge of cell response to surface stimuli could lead to the incorporation of specific size post microtextures into surfaces of implants to achieve surface-textured scaffold materials for tissue engineering applications.

The aim of this work is to choose a miniaturized specimen version relevant for testing candidate fusion reactor materials including mechanical testing after combined neutron irradiation/plasma exposure in a fission reactor. The material examined was reactor pressure vessel type steel in irradiated and aged (unirradiated) conditions. Comparative standard impact, three point bend and small punch tests were conducted. It is established that there is a possibility of miniaturization of irradiated steel experimental specimens by means of proper specimens type choice with mass reducing from = 40 (Charpy) to 0.4 g (small plates).

Changes in the fine structure and mechanical properties of the base metal (BM) and weld metal (WM) of VVER-1000 pressure vessels during accumulation of neutron dose in the range of fluences $(3.2-15) Â 10 23 m À2 (E > 0.5 MeV) at 290 °C are studied using methods of transmission electron microscopy, fractographic analysis, and Auger electron spectroscopy. A correlation was found between the changes of mechanical properties and the micro-and nano-structures of the studied steels. Accumulation of neutron dose considerably raises the strength characteristics and transition temperature of VVER-1000 pressure vessel steels. The rate of changes in the mechanical properties of the weld metal is significantly higher than that of the base metal. The slower growth of strength characteristics and transition temperature shift of the base metal under irradiation as compared with the weld metal is due to the slower growth of the density of radiation defects and radiation-induced precipitates. The level of intergranular embrittlement under irradiation in the weld metal is not higher then in the base metal in spite of the higher content of nickel.

A high nickel VVER-1000 (15Kh2NMFAA) base metal (1.34 wt% Ni, 0.47% Mn, 0.29% Si and 0.05% Cu), and a high nickel (12Kh2N2MAA) weld metal (1.77 wt% Ni, 0.74% Mn, 0.26% Si and 0.07% Cu) have been characterized by atom probe tomography to determine the changes in the microstructure during neutron irradiation to high fluences. The base metal was studied in the unirradiated condition and after neutron irradiation to fluences between 2.4 and 14.9 Â 10 23 m À2 (E > 0.5 MeV), and the weld metal was studied in the unirradiated condition and after neutron irradiation to fluences between 2.4 and 11.5 Â 10 23 m À2 (E > 0.5 MeV). High number densities of $2-nm-diameter Ni-, Si-and Mn-enriched nanoclusters were found in the neutron irradiated base and weld metals. No significant copper enrichment was associated with these nanoclusters and no copper-enriched precipitates were observed. The number densities of these nanoclusters correlate with the shifts in the DT 41 J ductile-to-brittle transition temperature. These nanoclusters were present after a post irradiation anneal of 2 h at 450 °C, but had dissolved into the matrix after 24 h at 450 °C. Phosphorus, nickel, silicon and to a lesser extent manganese were found to be segregated to the dislocations.

Wood is traditionally modeled as an orthotropic material, with direction dependent transport properties, in this way homogenizing the specific structure of wood: a cellular material with growth rings, consisting of early wood and late wood layers. In this paper we present a mesoscopic model for vapor transport in wood, where earlywood and latewood are modeled as distinct materials. The sorption and vapor transport properties for early-and latewood are determined using a unit cell model with constant cell geometry. These properties are used in two-dimensional calculations of vapor transport in a piece of wood consisting of several growth rings. The mesoscopic results are compared to measurement results and to macroscopic results using homogenized orthotropic transport properties. For vapor transport in radial and tangential direction the difference between meso-and macro modeling of wood is negligible, justifying the vapor transport modeling with homogenized orthotropic transport properties.

Collagen is one of the most promising materials for 3D bioprinting because of its distinguished biocompatibility. Cell-laden constructs made of pure collagen with or without incorporated growth supplements support engineered constructs persistence in culture and are perfectly suitable for grafting. The limiting factor for direct 3D collagen printing was poor printability of collagen solutions, especially admixed with cells or tissue spheroids. In our study, we showed that concentrated solutions of native collagen branded Viscoll were effective as bioinks with high fidelity performance. Viscoll containing 20, 30, or 40 mg/ml collagen were used for direct extrusion 3D bioprinting to form scaffolds appropriate to support spatial arrangement of tissue spheroids into rigid patterns with resolution of 0.5 mm in details. Incorporated cells demonstrated sufficient viability. Associated rheological study showed that good printability of the collagen solutions correlates with their increased storage modulus value, notably exceeding the loss modulus value. The proper combination of these physical parameters could become technological criteria for manufacturing various collagen bioinks for 3D bioprinting.

The equilibrium charge storage characteristic of polyaniline films has been determined using step voltammetry technique. The step coulogram (plot of charge stored versus potential) consists of five distinct regions, which correspond to the different energy bands exhibited by the film, in keeping with Raman and ESR spectroscopy data. The coulogram is piecewise linear, with constant capacitance in each band. Effect of the type and concentration of the acid on the equilibrium capacitances of the bands has been studied. The polaron band has the highest capacitance, followed by the bipolaron band and then the polaron lattice band. The charge stored at a given potential is found to be proportional to film mass. The film needs to be polarized to a threshold charge before faradaic charging begins. This faradaic threshold is independent of the type and concentration of the acids. The step coulogram is compared with the sweep coulogram obtained from linear sweep voltammetry. At low sweep rates, the sweep coulogram also exhibits five distinct bands. However, with increase in the sweep rate, the bands progressively reduce in number. The capacitance of the polaron band decreases linearly with square root of sweep rate and attains the equilibrium capacitance at zero sweep rate.

Bioactive glasses are widely utilized to regenerate bone tissue and aid bonding of orthopedic implants. Forming composites of bioglass with bioactive polymers allow the mechanical properties and biological response to be tailored. Although several methods for creating bioglass–polymer composites exist, they require dissolution of the polymer, controlled phase separation, and appear to have an upper limit of ∼30 vol.% bioglass. Cold sintering is a novel technique for the densification of ceramics and glasses which utilizes a liquid phase and pressure to allow the production of components at reduced temperatures. We demonstrate that cold sintering (100°C) of Bioglass 45S5 powder produced via flame spray pyrolysis and the fabrication of Bioglass 45S5–polymer composites. Assessment of the in vitro response revealed that composites were not cytotoxic. Solid‐state 31P and 29Si MAS NMR studies of the silicon and phosphorus speciation in the glass powder, as‐received, wetted, and sintered s...

Both the pancake coiling and conductor on round core (CORC) cabling processes consist of winding second-generation high-temperature superconducting tape (REBCO) in a core. The contact behavior between the tape and the core during the winding process directly affects the critical current, cable flexibility, mechanical support and electrical contact resistance. Therefore, the winding process needs to be optimized to produce pancake coils and CORC cables with the desired electrical and mechanical properties. This paper comprehensively considers the role of the relaxation and Poisson effects. The theoretical model and the finite element model (FEM) for calculating the contact stress during the winding process are established, and a formula for the estimation of the contact force is proposed. The suitable winding pre-tension force, winding curvature radius of SCS2030 (2 mm width and 30 µm substrate thickness) and SCS4050 (4 mm width and 50 µm substrate thickness) of REBCO tapes are obtained and discussed by accounting for the relaxation effect and the critical current degradation limit. With consideration of the Poisson effect, the nonlinear contact behavior is investigated. In addition, the relaxation effect, Poisson effect and plasticity of the REBCO tape are taken into account in the FEM model. The results show that the axial strain in the REBCO layer during the winding process is related to the contact behavior. The greater the winding pre-tension force, the smaller the helical curvature radius, and the greater the contact force. The distribution of contact stress for several winding factors (winding pre-tension force, winding angle and the core radius) is divided into three contact types: the single-line contact, the double-line contact and the surface contact. The FEM model results are consistent with the theoretical evaluation and are more suitable for practical winding cases. This research is the basis for designing and optimizing pancake coils and CORC cables.

Diabetic patients with foot ulcer showed 150-fold increased risk of amputation, which is primarily caused by microbial infection. Silver ions are commonly incorporated into wound dressing to enhance the antimicrobial property. However, concerns have been expressed about the development of bacterial resistance to heavy metals. In this study, we evaluate the in vitro and in vivo efficacy of cellulose nanocrystal film to be used as antimicrobial drug delivery system in a diabetic wound dressing. Cellulose nanocrystals were successfully isolated from medical grade cotton fibers. We observe needle-like cellulose nanocrystals with an average length of 159 nm under transmission electron microscope. The developed film with curcumin shows a uniform yellow color, with a thickness of 0.4 mm. The film obtained is soft and flexible, based on the mechanical characterization study of the film. For the curcumin release test, the release reaches plateau condition at 36 h with a total release of 98.9% from the cellulose nanocrystal film. No burst release effect was detected during the test period. The film exhibited significant inhibitory activity on 3 Gram positive bacteria, 2 Gram negative bacteria and 1 yeast. On Hohenstein challenge test, all test microorganisms showed significant growth reduction, with the treatment of curcumin loaded film. 5 of 6 test microorganisms showed 99% of growth reduction relative to growth control. We also notice that the antimicrobial activity of the film sustained even after 15 washes. In the in vivo study using diabetic rat models, a significant reduction of wound size was observed from Day 7 with the topical application of curcumin loaded film. At the end of the study, the lesion was covered by epithelial tissue and the hair started to grow from the skin. A bacterial growth reduction of 99.99% was observed from the skin sample excised from the animal models. The histological examination of skin sample also showed that curcumin loaded film significantly improved the regeneration of hair follicles and sebaceous glands of the skin. Our results indicate that the curcumin load cellulose nanocrystal films can be used for diabetic wound healing applications.

An efficient simulation method for transmission-type radio-frequency single-electron transistors (RF-SETs) is developed. By introducing equivalent circuits of propagating microwaves through RF cables, we solve the master equation for RF-SETs self-consistently by using the conventional circuit simulator SPICE together with the SET current model. By examining transmitted waves from the transmission-type RF-SET, we show that the developed method successfully reproduces the numerical reference methods (calculated selfconsistently). We also show that our method provides simple and fast ways to simulate and analyze RF-SETs even under complicated circuit geometry and in high frequencies over GHz. Based on the developed simulation method, we introduce the modulation technique to estimate the charge sensitivity of the transmission-type RF-SET.

In this work, highly transparent La 2 O 3 -doped yttria ceramics were fabricated by a hot-pressing method. The effects of the La 2 O 3 doping concentration (0-17 at.%) on the optical transmittance, microstructures, microhardness, and thermal conductivity levels of the transparent yttria were investigated in an effort to develop a user's choice guide pertaining to the optical, mechanical, and thermal properties. The optimal La 2 O 3 doping concentration for the optical transmittance was found to be 12 at.%, leading to in-line transmittance levels of 68.9% at 400 nm and 81.9% at 1100 nm (2 mm thick).

The current study reports on the effect of the sintering temperature and secondary carbide (VC, Mo 2 C and TiC) and Mo additions on the NbC grain growth, microstructure evolution as well as concomitant Vickers hardness (HV 30 ) and fracture toughness of Ni-bonded NbC cermets. All cermets were prepared by pressureless sintering in vacuum. Detailed microstructural investigation was performed by electron backscatter diffraction (EBSD), electron probe microanalysis (EPMA) as well as X-ray diffraction (XRD) analysis. Sintering results indicated that the sintering temperature, especially secondary carbide additions had a significant effect on the properties of NbC-Ni cermets. Nickel pools and residual porosities were observed in the cermets sintered at temperatures ≤ 1340 °C. Increasing of the sintering temperature above 1380 °C resulted in fully densified NbC-Ni based cermets composed of homogeneous composition cubic NbC grains for the single carbide (VC or Mo/Mo 2 C) modified system, whereas core-rim structured NbC grains were observed with the addition of TiC + VC or TiC + Mo 2 C. The secondary carbide doped cermets with 5-10 vol% VC/Mo 2 C and 10 vol% TiC showed a clearly improved hardness and fracture toughness, as compared to the plain NbC-Ni cermets.

Hardmetal coatings prepared by high velocity oxy-fuel (HVOF) spraying represent an advanced solution for surface protection against wear. In the current systematic study the high-temperature oxidation and unidirectional sliding wear in dry and lubricated conditions were studied. Results for a series of experiments on self-mated pairs in dry conditions as part of that work are described in this paper. Coatings with nominal compositions WC-10%Co4%Cr, WC-(W,Cr) 2 C-7%Ni, Cr 3 C 2 -25%NiCr, (Ti,Mo)(C,N)-29%Ni and (Ti,Mo)(C,N)-29%Co were prepared with an ethylene-fuelled DJH 2700 HVOF spray gun. Electrolytic hard chromium (EHC) coatings and bulk (Ti,Mo)(C,N)-15%NiMo (TM10) hardmetal specimens were studied for comparison. The wear behaviour was investigated at room temperature, 400 and 600 • C. For the coatings sliding speeds were varied in the range 0.1-1 m/s for a wear distance of 5000 m and a normal force of 10 N. In some cases the WC-and (Ti,Mo)(C,N)-based coatings showed total wear rates (sum of wear rates of the rotating and stationary samples) of less than 10 -6 mm 3 /Nm, i.e., comparable to values typically measured under mixed/boundary conditions. Coefficients of friction above 0.4 were found for all test conditions. The P × V values as an engineering parameter for coating application are discussed. The microstructures and the sliding wear behaviour of the (Ti,Mo)(C,N)-based coatings and the (Ti,Mo)(C,N)-15%NiMo hardmetal are compared.

The intercritical annealing and isothermal bainitic processing response was studied for three Nb and V microalloyed Transformation-Induced Plasticity (TRIP)-assisted 980 MPa grade steels. Their mechanical and microstructural properties were compared to industrially produced TRIP 800 steel. Depending on the isothermal holding temperature and microalloying, the experimental steels reached properties comparable to the reference steel. The retained austenite content did not show direct correlation to elongation properties. Niobium was found to be more effective microalloying element than vanadium in increasing the elongation properties, which were investigated by measuring true fracture strain from tensile test specimens.