Achieving room temperature plasticity in brittle ceramics through elevated temperature preloading.

Ceramic materials with high strength and chemical inertness are widely used as engineering materials. However, the brittle nature limits their applications as fracture occurs before the onset of plastic yielding. There has been limited success despite extensive efforts to enhance the deformability of ceramics. Here we report a method for enhancing the room temperature plastic deformability of ceramics by artificially introducing abundant defects into the materials via preloading at elevated temperatures. After the preloading treatment, single crystal (SC) TiO2 exhibited a substantial increase in deformability, achieving 10% strain at room temperature. SC α-Al2O3 also showed plastic deformability, 6 to 7.5% strain, by using the preloading strategy. These preinjected defects enabled the plastic deformation process of the ceramics at room temperature. These findings suggest a great potential for defect engineering in achieving plasticity in ceramics at room temperature.

Performance benchmarks for open source porous electrode theory models.

The electrochemical response characteristics of existing and emerging porous electrode theory (PET) models was benchmarked to establish a common basis to assess their physical reaches, limitations, and accuracy. Three open source PET models: dualfoil, MPET, and LIONSIMBA were compared to simulate the discharge of a LiMn2O4-graphite cell against experimental data. For C-rates below 2C, the simulated discharge voltage curves matched the experimental data within 4% deviation for dualfoil, MPET, and LIONSIMBA, while for C-rates above 3C, dualfoil and MPET show smaller deviations, within 5%, against experiments. The electrochemical profiles of all three codes exhibit significant qualitative differences, despite showing the same macroscopic voltage response, leading the user to different conclusions regarding the battery performance and possible degradation mechanisms of the analyzed system.

Direct measurement of internal temperatures of commercially-available 18650 lithium-ion batteries.

Direct access to internal temperature readings in lithium-ion batteries provides the opportunity to infer physical information to study the effects of increased heating, degradation, and thermal runaway. In this context, a method to insert temperature sensors into commercial 18650 cells to determine the short- and long-term effects through characterization testing is developed. Results show that sensor insertion only causes a decrease in capacity of 0.5-2.3%, and an increase in DC resistance of approximately 15 mΩ. The temperatures of the modified cells are approximately 0.5 °C higher than the control cells, the difference between the internal and external temperature readings of the modified cells is approximately 0.4 °C, and the modified cells exhibit the same temperature behavior and trend during cycling as the control cells. The cells are able to operate and collect data for 100-150 cycles before their capacities fade and resistances increase beyond what is observed in the control cells. The results of the testing show that cells modified with internal temperature sensors provide useful internal temperature data for cells that have experienced little or no cyclic aging.

Artificial intelligence inferred microstructural properties from voltage-capacity curves.

The quantification of microstructural properties to optimize battery design and performance, to maintain product quality, or to track the degradation of LIBs remains expensive and slow when performed through currently used characterization approaches. In this paper, a convolution neural network-based deep learning approach (CNN) is reported to infer electrode microstructural properties from the inexpensive, easy to measure cell voltage versus capacity data. The developed framework combines two CNN models to balance the bias and variance of the overall predictions. As an example application, the method was demonstrated against porous electrode theory-generated voltage versus capacity plots. For the graphite|LiMn[Formula: see text]O[Formula: see text] chemistry, each voltage curve was parameterized as a function of the cathode microstructure tortuosity and area density, delivering CNN predictions of Bruggeman's exponent and shape factor with 0.97 [Formula: see text] score within 2 s each, enabling to distinguish between different types of particle morphologies, anisotropies, and particle alignments. The developed neural network model can readily accelerate the processing-properties-performance and degradation characteristics of the existing and emerging LIB chemistries.

Field-assisted growth of one-dimensional ZnO nanostructures with high defect density.

One-dimensional ZnO nanostructures have shown great potential in electronics, optoelectronics and electromechanical devices owing to their unique physical and chemical properties. Most of these nanostructures were grown by equilibrium processes where the defects density is controlled by thermodynamic equilibrium. In this work, flash sintering, a non-equilibrium field-assisted processing method, has been used to synthesize ZnO nanostructures. By applying a high electric field and limiting a low current flow, ZnO nanorods grew uniformly by a vapor-liquid-solid mechanism due to the extreme temperatures achieved near the hot spot. High density basal stacking faults in the nanorods along with ultraviolet excitonic emission and a red emission under room temperature demonstrate the potential of defect engineering in nanostructures via the field-assisted growth method.

Nanoscale stacking fault-assisted room temperature plasticity in flash-sintered TiO2.

Ceramic materials have been widely used for structural applications. However, most ceramics have rather limited plasticity at low temperatures and fracture well before the onset of plastic yielding. The brittle nature of ceramics arises from the lack of dislocation activity and the need for high stress to nucleate dislocations. Here, we have investigated the deformability of TiO2 prepared by a flash-sintering technique. Our in situ studies show that the flash-sintered TiO2 can be compressed to ~10% strain under room temperature without noticeable crack formation. The room temperature plasticity in flash-sintered TiO2 is attributed to the formation of nanoscale stacking faults and nanotwins, which may be assisted by the high-density preexisting defects and oxygen vacancies introduced by the flash-sintering process. Distinct deformation behaviors have been observed in flash-sintered TiO2 deformed at different testing temperatures, ranging from room temperature to 600°C. Potential mechanisms that may render ductile ceramic materials are discussed.

High temperature deformability of ductile flash-sintered ceramics via in-situ compression.

Flash sintering has attracted significant attention as its remarkably rapid densification process at low sintering furnace temperature leads to the retention of fine grains and enhanced dielectric properties. However, high-temperature mechanical behaviors of flash-sintered ceramics remain poorly understood. Here, we present high-temperature (up to 600 °C) in situ compression studies on flash-sintered yttria-stabilized zirconia (YSZ). Below 400 °C, the YSZ exhibits high ultimate compressive strength exceeding 3.5 GPa and high inelastic strain (~8%) due primarily to phase transformation toughening. At higher temperatures, crack nucleation and propagation are significantly retarded, and prominent plasticity arises mainly from dislocation activity. The high dislocation density induced in flash-sintered ceramics may have general implications for improving the plasticity of sintered ceramic materials.

Spheronization process particle kinematics determined by discrete element simulations and particle image velocimentry measurements.

UNLABELLED: Spheronization is an important pharmaceutical manufacturing technique to produce spherical agglomerates of 0.5-2mm diameter. These pellets have a narrow size distribution and a spherical shape. During the spheronization process, the extruded cylindrical strands break in short cylinders and evolve from a cylindrical to a spherical state by deformation and attrition/agglomeration mechanisms. Using the discrete element method, an integrated modeling-experimental framework is presented, that captures the particle motion during the spheronization process. Simulations were directly compared and validated against particle image velocimetry (PIV) experiments with monodisperse spherical and dry γ-Al2O3 particles. RESULT: demonstrate a characteristic torus like flow pattern, with particle velocities about three times slower than the rotation speed of the friction plate. Five characteristic zones controlling the spheronization process are identified: Zone I, where particles undergo shear forces that favors attrition and contributes material to the agglomeration process; Zone II, where the static wall contributes to the mass exchange between particles; Zone III, where gravitational forces combined with particle motion induce particles to collide with the moving plate and re-enter Zone I; Zone IV, where a subpopulation of particles are ejected into the air when in contact with the friction plate structure; and Zone V where the low poloidal velocity favors a stagnant particle population and is entirely controlled by the batch size. These new insights in to the particle motion are leading to deeper process understanding, e.g., the effect of load and rotation speed to the pellet formation kinetics. This could be beneficial for the optimization of a manufacturing process as well as for the development of new formulations.

Built-in electric field minimization in (In, Ga)N nanoheterostructures.

(In, Ga)N nanostructures show great promise as the basis for next generation LED lighting technology, for they offer the possibility of directly converting electrical energy into light of any visible wavelength without the use of down-converting phosphors. In this paper, three-dimensional computation of the spatial distribution of the mechanical and electrical equilibrium in nanoheterostructures of arbitrary topologies is used to elucidate the complex interactions between geometry, epitaxial strain, remnant polarization, and piezoelectric and dielectric contributions to the self-induced internal electric fields. For a specific geometry-nanorods with pyramidal caps-we demonstrate that by tuning the quantum well to cladding layer thickness ratio, h(w)/h(c), a minimal built-in electric field can be experimentally realized and canceled, in the limit of h(w)/h(c) = 1.28, for large h(c) values.

Dislocation filtering in GaN nanostructures.

Dislocation filtering in GaN by selective area growth through a nanoporous template is examined both by transmission electron microscopy and numerical modeling. These nanorods grow epitaxially from the (0001)-oriented GaN underlayer through the approximately 100 nm thick template and naturally terminate with hexagonal pyramid-shaped caps. It is demonstrated that for a certain window of geometric parameters a threading dislocation growing within a GaN nanorod is likely to be excluded by the strong image forces of the nearby free surfaces. Approximately 3000 nanorods were examined in cross-section, including growth through 50 and 80 nm diameter pores. The very few threading dislocations not filtered by the template turn toward a free surface within the nanorod, exiting less than 50 nm past the base of the template. The potential active region for light-emitting diode devices based on these nanorods would have been entirely free of threading dislocations for all samples examined. A greater than 2 orders of magnitude reduction in threading dislocation density can be surmised from a data set of this size. A finite element-based implementation of the eigenstrain model was employed to corroborate the experimentally observed data and examine a larger range of potential nanorod geometries, providing a simple map of the different regimes of dislocation filtering for this class of GaN nanorods. These results indicate that nanostructured semiconductor materials are effective at eliminating deleterious extended defects, as necessary to enhance the optoelectronic performance and device lifetimes compared to conventional planar heterostructures.

Application of a high throughput bioluminescence-based method and mathematical model for the quantitative comparison of polymer microbicide efficiency.

Quaternized poly(4-vinyl pyridine)-based copolymers are known to be effective against a wide range of bacteria and possess biocompatible properties. Extensive testing of a wide range of copolymers is necessary to further explore and enhance the biocidal properties. However, testing is hampered by labor-intensive bacteria testing techniques. The present paper presents a new testing method, based on bioluminescent reporter strains to enable fast evaluation of bactericidal properties. The reported method enables us to create real-time characterization of bacteria behavior with far less labor than required through traditional testing methods. A mathematical model was also developed to characterize the change in bacteria populations exposed to biocides and to enable the quantitative comparison of minimum bactericidal concentrations.

Ionic colloidal crystals: Ordered, multicomponent structures via controlled heterocoagulation.

We propose a new type of ordered colloid, the "ionic colloidal crystal" (ICC), which is stabilized by attractive electrostatic interactions analogous to those in atomic ionic materials. The rapid self-organization of colloids via this method should result in a diversity of orderings that are analogous to ionic compounds. Most of these complex structures would be difficult to produce by other methods. We use a Madelung summation approach to evaluate the conditions where ICC's are thermodynamically stable. Using this model, we compare the relative electrostatic energies of various structures showing that the regions of ICC stability are determined by two dimensionless parameters representing charge balance and the spatial extent of the electrostatic interactions. Parallels and distinctions between ICC's and classical ionic crystals are discussed. Monte Carlo simulations are utilized to examine the glass transition and melting temperatures, between which crystallization can occur, of a model system having the rocksalt structure. These tools allow us to make a first-order prediction of the experimentally accessible regions of surface charge, particle size, ionic strength, and temperature where ICC formation is probable.

Caracterización de los presuntos delitos sexuales evaluados por el Instituto Nacional de Medicina Legal y Ciencias Forences, Medellín, 1995-2000 / Characterization of presumed sexual crimes according to the evaluation of the National Institute of Legal Medicine and Forensic Sciences, Medellin, 1995-2000

Se caracterizan los presuntos delitos sexuales evaluados por el Instituto Nacional de Medicina Legal y Ciencias Forenses, según variables de persona, tiempo, lugar y circunstancia, entre los años 1995 y 2000, con base en 3.263 hojas de ruta sexológicas correspondientes a aquellas personas que denunciaron algún presunto delito sexual y cuyo reporte fue evaluado por el Instituto Nacional de Medicina Legal y Ciencias Forenses. La edad mediana de las víctimas fue de 11 años, con predominio del sexo femenino (86,2 por ciento ), al igual que aquellas con ocupación de estudiante (51,9 por ciento). El lugar donde más presuntas agresiones ocurrieron fue la casa de la víctima (60,3 por ciento), donde el acto sexual predominó especialmente en niños entre 3 meses y 7 años. El agresor más frecuente fue una persona conocida (65,7 por ciento), entre los que sobresalen el padre y el padrastro. El presunto delito más evaluado fue el acceso carnal (59,8 por ciento). Se encontró que por cada 100.000 habitantes, en el año 2000, se presentaron aproximadamente 161 presuntos delitos sexuales, en una relación de 6 en las mujeres por 1 en los hombres. Aquellas presuntas víctimas con 14 años o menos quintuplicaron las tasas de los mayores de 14 años. Se sugiere el mejoramiento de la calidad de la información institucional y estrategias de acción hacia la comunidad