Variations In Material Composition Research Articles

Investigation towards the optimum of power capability, ageing stability and costs effectiveness on thick film resistor pastes for AlN ceramics

Abstract The focus of this work was the optimization of a 10 Ω/□ thick film resistor (TFR) paste composition to obtain increased power capability, aging stability and minimum use of ruthenium oxide for cost savings without changing the defined narrow sheet resistance (R□) and temperature coefficient of resistance (TCR) specifications. In times of highly fluctuating precious metal costs, the use of a minimum of the precious metal ruthenium respectively ruthenium dioxide is one essential part for cost-effectiveness. The thick film paste formulation consists of the electrically conducting phase ruthenium dioxide, a lead-free glass phase and two inorganic additives for tuning thermo-mechanical and electrical properties of the formed films. A phthalate free organic vehicle with ethyl cellulose polymer was used to formulate a screen printable ceramic thick film paste. For this paper, RuO2 powders with various specific surface area values (BET) were prepared by thermal annealing of a precipitated fine ruthenium dioxide powder. All other solid and liquid components of the paste were the same as used for IKTS 10 Ω/□ TFR paste FK9611 for AlN substrates. Furthermore, the content of ruthenium dioxide in the paste compositions was changed systematically around an assumed target content to achieve the desired sheet resistivity. Concurrent to the variation of the ruthenium dioxide content the inorganic additives had to be adapted too. The influence of the variations of raw material and paste composition on the film properties were investigated by screen printing 24 resistors of 2 mm × 1 mm dimension on an 1” × 1” AlN substrate, firing at 850 °C for 10 minutes in air atmosphere and subsequently measuring R□, TCR, the stability of resistance ΔR/R0 effected by artificial aging of the resistors (stored 100 up to 1000 hours @ 200°C) and the maximum rated power dissipation (MRPD) as well as short term overload voltage (STOL). The results are discussed in regard to find an optimum between all demands of the most important electrical film properties.

EFFECT OF VARIATION OF MIXTURE LEACHATE WITH FLUID IN CATTLE RUMEN FORMATION OF BIOGAS

Abstract Composting in addition to producing fertilizers also produce leachate containing organic material, the leachate can pollute the environment if not managed properly. This study uses leachate as the main substance of biogas, mixed with cattle rumen fluid as the biostarter. This study aims to determine the optimal composition of biogas and to determine the effect of variations in the raw material mixture to the volume of biogas, volatile solid, temperature, pH, and flame. The study was conducted over 43 days using three types of batch digester with a capacity of 27 L. Comparison of a mixture consisting of leachate composting organic waste with cattle rumen fluid in each digester with variations in material composition of the mixture of 70%: 30%, 50%: 50%, 100%: 0%. During the study was observed it the volume of biogas daily, daily pH, temperature daily, weekly flame test and volatile solid test every 10 days. The volume of biogas using the principle of cylinder volume and volatile solid test using USEPA 1684 method. The results show the variation of 70%:30%, which resulted in a final volume of 2.78 L of gas, as well as a decrease in the volatile solid 23.29%, 12.82% increase in the pH. In a variation of 50%:50% produces a final volume of gas that is 0.537 L, as well as a decrease in volatile solid 42.35%, 12.82% increase in the pH. Variations 100%:0% produces a final volume of gas that is 1,247 L, a decrease in volatile solid 21.83%, 5.19% increase in the pH. All three digesters are at mesophilic temperatures and produce blue flame. Based on the results of this study concluded that the composition of the mixture that are in the most optimal is composition of 70%:30%. Keywords : biogas, rumen fluid beef, lindi organic waste composting

A framework for clinical commissioning of 3D-printed patient support or immobilization devices in photon radiotherapy.

PurposeThe objective of this work is to outline a framework for dosimetric characterization that will comprehensively detail the clinical commissioning steps for 3D‐printed materials applied as patient support or immobilization devices in photon radiotherapy. The complex nature of 3D‐printed materials with application to patient‐specific configurations requires careful consideration. The framework presented is generalizable to any 3D‐printed object where the infill and shell combinations are unknown.MethodsA representative cylinder and wedge were used as test objects to characterize devices that may be printed of unknown, patient‐specific dimensions. A case study of a 3D‐printed CSI immobilization board was presented as an example of an object of known, but adaptable dimensions and proprietary material composition. A series of measurements were performed to characterize the material's kV radiologic properties, MV attenuation measurements and calculations, energy spectrum water equivalency, and surface dose measurements. These measurements complement the recommendations of the AAPM's TG176 to characterize the additional complexity of 3D‐printed materials for use in a clinical radiotherapy environment.ResultsThe dosimetric characterization of 3D‐printed test objects and a case study device informed the development of a step‐by‐step template that can easily be followed by clinicians to accurately and safely utilize 3D‐printed materials as patient‐specific support or immobilization devices.ConclusionsA series of steps is outlined to provide a formulaic approach to clinically commission 3D‐printed materials that may possess varying material composition, infill patterns, and patient‐specific dimensions.

Automatic Toolpath Generation for Heterogeneous Objects Manufactured by Directed Energy Deposition Additive Manufacturing Process

A heterogeneous object (HO) refers to a solid component consisting of two or more material primitives distributed either continuously or discontinuously within the object. HOs are commonly divided into three categories. The first category has distinct material domains separating the different materials. The second, called functionally graded materials (FGMs), has continuous variation of material composition that produces gradient in material properties. The third category allows for any combinations of the first two categories within the same part. Modeling and manufacturing of HOs has recently generated more interest due to the advent of additive manufacturing (AM) technology that makes it possible to build such parts. Directed energy deposition (DED) processes have the potential for depositing multiple powdered materials in various compositions in the process of creating a single layer of material. To make this possible, tool paths that provide proper positioning of the deposition head and proper control over the material composition are required. This paper presents an approach for automatically generating the toolpath for any type of HO considering the material composition changes that are required on each layer. The toolpath generation takes into account the physical limitations of the machine associated with powder delivery and ability to continually grade the materials. Simulation results using the toolpath generation methodology are demonstrated by several example parts.

Application of linear least squares to the analysis of Auger electron spectroscopy depth profiles of plutonium oxides

Application of the linear least squares (LLS) methodology allows for quantitative determination of variation in material composition with depth. LLS fits were applied to decompose and enhance the interpretation of spectra obtained by Auger electron spectroscopy during depth profiles of oxidized plutonium surfaces. By means of the LLS algorithm, chemical state assignments of the Pu P1VV/O45VV, O KLL, and C KLL Auger transitions were determined and the existence of a subsurface oxycarbide layer was identified, with confirmation of the oxide and metal components provided from comparison to previous measurements of standard samples.

Dynamic analysis of a thick hollow cylinder made of two-dimensional functionally graded material using time-domain spectral element method

ABSTRACTIn this paper, the time-domain dynamic response of a thick hollow cylinder made of two-dimensional functionally graded material is studied. An axisymmetric solid spectral finite element model is proposed for the analysis of elastic wave propagation in the cylinder. The effectiveness of the proposed model is verified by comparing with the conventional finite element method. The effect of material grading pattern is analyzed. The results demonstrate the effectiveness of the present method for the analysis of elastic wave propagation in functionally graded solids with axial symmetry and the material composition variation has an important effect on structural wave propagation behavior.

Experimental damage evaluation of honeycomb sandwich structures with Al/B4C FGM face plates under high velocity impact loads

In this experimental study, high velocity impact behavior of honeycomb sandwich structures with Al6061/B4C FGM face plates subjected to 0.30 caliber fragment simulating projectile impact was investigated via a single-stage gas gun. The material composition of the FGM face plates was represented according to a power-law variation through the plate thickness. The specimens were produced for six types of face plates, Al6061 and five different FGM face plates from metal-rich to ceramic-rich composition. Impact test results of the specimens were evaluated in terms of their damage and deformation mechanisms. The test results stated that the material composition variation of the FGM face plates was a highly influential parameter for damage modes, energy absorbing capacity, and impact resistance of the sandwich structure, and the honeycomb core contributed to the energy absorbing capacity of the sandwich structure with the plastic buckling of the cell walls and lateral crushing deformations.

Experimental Study on the Influence of Raw Materials to Concrete Compressive Strength

Through compressive strength test, the influence rule of material composition variation to the compressive strength of concrete had been studied. And the importance degree that different raw materials affected the compressive strength of concrete had been analyzed. Researches show that the importance degree that different raw materials affected the compressive strength of concrete could make a list, water cement ratio>aggregate grading> sand ratio>fly ash>blast furnace slag. The research results could be referenced for optimal design of concrete.

Influence of sugarcane bagasse variability on sugar recovery for cellulosic ethanol production

In the context of cellulosic ethanol production, special attention must be given to the raw material, as it affects final product yield. As observed for sugarcane, bagasse variations may derive from several elements, for instance edaphoclimatic factors, seasonality, maturation stage and harvesting techniques. Therefore, in the present work, to investigate the impact of raw material characteristics on process performance, sugarcane bagasse from four harvests from October/2010 to October/2011 was pretreated by steam explosion and had its soluble and insoluble solids contents measured, following enzymatic hydrolysis to assess glucan conversion. As confirmed by ANOVA, glucose concentration was related to the solids content in the reactor, whereas glucan conversion was related to the enzymatic load. Variations in raw material composition were indeed observed to significantly interfere in the final sugar recovery, probably due to the increase in the impurities observed as a result of the type of harvest performed in 2011.

Thermal stress analysis of one- and two-dimensional functionally graded plates subjected to in-plane heat fluxes

This study addresses the thermal stress analysis of one- and two-dimensional functionally graded plates subjected to in-plane heat fluxes. The material composition variation is assumed in-plane, not through the plate thickness according to a power-law distribution in terms of the volume fraction of the constituents. The mathematical model considers the spatial derivatives of local mechanical and thermal properties. The heat transfer and Navier equations of the two-dimensional thermo-elastic model were discretized using the finite difference method, and the set of linear equations were solved using the pseudo singular value method. The performance of both one- and two-dimensional functionally gradient material plates was investigated under two types of in-plane fluxes: one-edge and two-edges. For each type of heat fluxes, one- and two-dimensional functionally gradient material plates exhibited different displacement, stress and strain distributions. The temperature levels and distributions were affected with increasing ceramic constituent in the composition variation of the plate. One-dimensional functionally gradient material plate was more suitable for an one-edge heat flux along the direction of material composition variation, whereas two-dimensional functionally gradient material plate was more effective on the relieving the thermal stresses for a two-edges heat flux.

Strength of WC-Co hard metals as a function of the effectively loaded volume

WC-Co hard metals show defect-controlled fracture behaviour. This means that the fracture stress under tensile loading conditions is directly related to the size of the largest defect within the loaded volume. The size distribution of these defects relevant to failure under static and cyclic loading conditions can be quantitatively described by Weibull statistics.Prior studies on the fracture behaviour of hard metals and the nature and size of material inhomogeneities, i.e. defects, do not attain their data from one single batch of material. To avoid uncertainties from possible variations in material composition the current work studies the fracture behaviour of a single material batch as a function of the effectively loaded volume Veff. A variety of specimen geometries and loading arrangements was applied in order to vary Veff over five orders of magnitude. Fracture stress values are found to increase from about 1500MPa to 4200MPa while decreasing the effectively loaded volume from about 100mm3 down to about 0.01mm3. The observed volume effect of strength shows the expected qualitative trends with quantitative deviations from Weibull-like strength behaviour. The presence of two different kinds of defects in the form of pores and single enlarged WC grains on the attained fracture surfaces, as found by a fractographic analysis in the SEM, is a possible explanation for this observation. Information provided by the current study is the basis for the judgment of the relevance of volume defects regarding the failure of tools or structural components made of WC-Co hard metals under certain loading conditions.

A hybrid approach to define and represent material distribution in heterogeneous objects

ABSTRACTA hybrid representation is proposed to overcome the current limitations in modeling heterogeneous objects. The representation is based on the idea of decomposing the geometry such that the existing class of material functions (distance based function) can be used to define desired material variation in heterogeneous objects. This representation is supported by Medial Axis Transform (MAT), which defines and represents the material variation from inside to outside for heterogeneous objects. Local symmetry inherent in the MAT and the relationship between the object boundary and the MAT point has been used to achieve intuitive variations of material composition, local control over the same and a compact data structure. A material evaluation scheme has been proposed to evaluate the material composition at any given location in the object. Heterogeneous objects modeled with this scheme are shown in results depicting the material distribution varying from inside to outside and vice versa. This representa...

Parameters determining the portion of energy radiated during dynamic unloading of a section of rock massif

Presented are the main results of laboratory experiments aimed at studing the regularities of transition of the cumulated deformation energy to the kinetic one when a block exhibits stick-slip along model fracture filled with geomaterials with different properties. It was shown that even a small variation of material composition of the fault principal slip zone may result in a significant variation of the portion of seismic energy radiated during dynamic unloading of the enclosing rock massif.

Luminescence selective output characteristics tuned by laser pulse width in Tm3+ doped NaYF4 nanorods

The variations in material composition, phase and structure can provide a useful tool for tuning emission colour, but the controlling of the emission colour in a material, with a composition fixed, remains to be a daunting challenge. In this work, we systematically study the luminescence selective output characteristics of Tm3+ doped NaYF4 nanorods, and also the dependences of fluerecence output on pulse duration, excitation wavelength, pump power, and ambient temperature. The results show that the color of output light is strongly dependent on laser pulse duration compared with other factors. The temperature dependent luminescence of the nanorods shows very different behaviors with short-pulse laser excitation from those of continuous wave (CW) laser. When the pulse laser at 656 nm is employed, the emission spectra from NaYF4:0.5 mol% Tm3+ nanorods at the different temperatures are dominated by near-infrared (NIR) luminescence about 800 nm accompanied with weak blue luminescence, giving rise to nearly spectrally-pure NIR emissions at 20 K. When the pulse laser is replaced by CW laser, blue double emissions at 453 and 478 nm with the same order of magnitude of NIR luminescence can be clearly detected at room temperature. The key mechanism responsible for colour-tunable emission can be explained in terms of the population process of luminescence level, in which the different luminescence level populations need different time intervals. Considering excited-state absorption (ESA) for a particular 1D2 energy level, there needs an extra step of 3F2, 33H4 multiphonon nonradiation relaxation process to populate the 3H4 state and subsequently pump its 1D2 state for blue emission. Therefore, the pulse width should be longer than nonradiation relaxation time of 3F2, 33H4 to comply with the ESA, while the nonradiation relaxation time can further be tuned by controlling ambient temperature. We show that the variation of the excitation power leads to interesting change in the upconversion (UC) decay curve. We focus our attention on the excitation wavelength dependences of 3H4 and 1D2 emission lifetimes in order to validate the population mechanism of luminescence level. We demonstrate that the 3H4 luminescence time depends on excitation wavelength, while 1D2 emission lifetime nearly keeps constant when varying the excitation wavelength. Based on multi-phonon relaxation theory and time-resolved photoluminescence studies, it is indicated that the UC luminescence under short-pulse laser excitation mainly originates from the ions at/near the surface, while downconversion is mainly from the ions in the core for NaYF4:Tm3+ nanorods. The single-band NIR luminescence output by changing the pulse width and excitation wavelength provides an insight into the controlling of the population processes of luminescent levels and offers a versatile approach to tuning the spectral output.

Workshop 5 – Cross Section, Nuclear Data, and Uncertainties

The Cross Section, Nuclear Data, and Uncertainties Workshop met with 30 participants. There was a lively discussion that covered several different topics. Some of the topics had resonance with topics brought up in other workshop at this symposium. One major issue was how to assign an a priori uncertainty to the trial spectrum used in spectrum adjustment techniques, or, more specifically, the need for a more rigorous and automated coupling of uncertainties into the radiation transport codes that are used to generate the a priori (trial) spectrum that is used in neutron spectrum adjustment approaches. Approaches based on discrete ordinate transport provide a means of generating sensitivity coefficients for specific variations, but fall short of the required task. While some Monte Carlo-based radiation transport codes permit the user to vary the cross sections for specific reactions or to vary material densities, a more universal and automated variation of all relevant inputs to the radiation transport code is required. One approach mentioned was a Total Monte Carlo (TMC) approach provided by a coupling into radiation transport codes of the recently generated statistical sample of random ENDF nuclear data evaluations produced by the TALYS code and incorporated into the TENDL library (for some isotopes). This would provide a set of self-consistent nuclear data files that can be sampled in a transport calculation. This variation of nuclear data would need to be coupled with a variation in material composition, density, and spatial dimensions. Another discussion topic was the need for the community to revisit the consistency of current approaches to spectrum unfolds/adjustment, i.e. a new round of the older REAL-84 and REAL-88 exercises to assess our status. While the dosimetry community has made great strides with the IRDFF library in establishing an international community consensus for dosimetry cross sections and associated nuclear data, the differences within the community in the treatment of the uncertainty in the trial spectrum and the availability of new spectrum adjustment techniques, such as Maximum Entropy codes like MAXED and the use of genetic algorithms, warrant a revisit of these international exercises to assess the current consistency (within stated uncertainty bonds) of approaches within the community to the characterization of neutron spectra and towards expressing the uncertainty in integral metrics based on these spectrum uncertainties. Since the IAEA/NDS has done such a good job in coordinating an international consensus in dosimetry cross sections and nuclear data, and since they coordinated the older REAL-8X exercises, we look to them to coordinate a new international assessment of our consistency in treating spectrum adjustments and characterizing the resulting uncertainties.

Geographic, environmental and biotic sources of variation in the nutrient relations of tropical montane forests

Abstract:Tropical montane forests (TMF) are associated with a widely observed suite of characteristics encompassing forest structure, plant traits and biogeochemistry. With respect to nutrient relations, montane forests are characterized by slow decomposition of organic matter, high investment in below-ground biomass and poor litter quality, relative to tropical lowland forests. However, within TMF there is considerable variation in substrate age, parent material, disturbance and species composition. Here we emphasize that many TMFs are likely to be co-limited by multiple nutrients, and that feedback among soil properties, species traits, microbial communities and environmental conditions drive forest productivity and soil carbon storage. To date, studies of the biogeochemistry of montane forests have been restricted to a few, mostly neotropical, sites and focused mainly on trees while ignoring mycorrhizas, epiphytes and microbial community structure. Incorporating the geographic, environmental and biotic variability in TMF will lead to a greater recognition of plant–soil feedbacks that are critical to understanding constraints on productivity, both under present conditions and under future climate, nitrogen-deposition and land-use scenarios.

Growth parameter design for homogeneous material composition in ternary GaxIn1−xP nanowires

Ternary nanowires (NWs) often exhibit varying material composition along the NW growth axis because of different diffusion properties of the precursor molecules. This constitutes a problem for optoelectronic devices for which a homogeneous material composition is most often of importance. Especially, ternary GaInP NWs grown under a constant Ga–In precursor ratio typically show inhomogeneous material composition along the length of the NW due to the complexity of low temperature precursor pyrolysis and relative rates of growth species from gas phase diffusion and surface diffusion that contribute to synthesis of particle-assisted growth. Here, we present the results of a method to overcome this challenge by in situ tuning of the trimethylindium molar fraction during growth of ternary Zn-doped GaInP NWs. The NW material compositions were determined by use of x-ray diffraction, scanning transmission electron microscopy and energy dispersive x-ray spectroscopy and the optical properties by photoluminescence spectroscopy.

The effect of the variation in material composition on the heterogeneous pore structure of high-maturity shale of the Silurian Longmaxi formation in the southeastern Sichuan Basin, China

Studying complex pore structures is the key to understanding the mechanism of shale gas accumulation. The effect of the variation in material composition on the heterogeneous pore structure of high-maturity shale of the Silurian Longmaxi formation was analyzed based on fractal geometry using field emission scanning electron microscopy (FE-SEM), low-pressure N2 adsorption, and high-pressure mercury intrusion porosimetry (MIP). The results show that abundant micro- and nano-scale pores were distributed in all shale samples, with the majority of pores composed of ink-bottle-shaped organic pores and slit-shaped mineral matrix pores. Samples with different total organic carbon (TOC) contents and mineral compositions showed distinct differences in pore structure. Organic matter and clay mineral primarily affected the mesopore structure, and the heterogeneity of the mesopore structure increased with the clay mineral content. Plastic minerals, such as quartz and carbonate, primarily affected the macropore structure. The increase in the quartz content could reduce the heterogeneity of the macropore structure, and an increase in the carbonate mineral content could increase the heterogeneity of the macropore structure. Finally, organic matter could strengthen the heterogeneity of the macropore structure only when the TOC content was greater than 1.1 wt. %.

Adaptive Tetrahedral Mesh Generation of 3D Heterogeneous Objects

ABSTRACTIn this paper, a step-wise tetrahedral mesh generation method is introduced to solve the adaptive meshing problems of 3D heterogeneous objects, in which both the material heterogeneity and the geometric complexity have to be taken into account. In light of that, the proposed meshing strategy embraces three steps: initial mesh generation, material-oriented refinement, and geometry-oriented refinement. In the material-oriented refinement, a global refinement algorithm based on optimal Delaunay triangulation (ODT) is designed to control the mesh adaptation in terms of the material distribution. Compared to the refinement strategies based on local modifications, the global refinement algorithm takes full advantages of the material heterogeneity information and distributes the material composition variation over elements as equally as possible. As a result, the number of elements is reduced to a great extent regarding a given material threshold. Implementations show that the proposed approach guarantee...

Design and fabrication of biomimetic multiphased scaffolds for ligament-to-bone fixation

Conventional ligament grafts with single material composition cannot effectively integrate with the host bones due to mismatched properties and eventually affect their long-term function in vivo. Here we presented a multi-material strategy to design and fabricate composite scaffolds including ligament, interface and bone multiphased regions. The interface region consists of triphasic layers with varying material composition and porous structure to mimic native ligament-to-bone interface while the bone region contains polycaprolactone (PCL) anchor and microchanneled ceramic scaffolds to potentially provide combined mechanical and biological implant-bone fixation. Finite element analysis (FEA) demonstrated that the multiphased scaffolds with interference value smaller than 0.5 mm could avoid the fracture of ceramic scaffold during the implantation process, which was validated by in-vitro implanting the multiphased scaffolds into porcine joint bones. Pull-out experiment showed that the initial fixation between the multiphased scaffolds with 0.47 mm interference and the host bones could withstand the maximum force of 360.31±97.51 N, which can be improved by reinforcing the ceramic scaffolds with biopolymers. It is envisioned that the multiphased scaffold could potentially induce the regeneration of a new bone as well as interfacial tissue with the gradual degradation of the scaffold and subsequently realize long-term biological fixation of the implant with the host bone.