Hypothetical Defect Research Articles

Accelerating defect predictions in semiconductors using graph neural networks

First-principles computations reliably predict the energetics of point defects in semiconductors but are constrained by the expense of using large supercells and advanced levels of theory. Machine learning models trained on computational data, especially ones that sufficiently encode defect coordination environments, can be used to accelerate defect predictions. Here, we develop a framework for the prediction and screening of native defects and functional impurities in a chemical space of group IV, III–V, and II–VI zinc blende semiconductors, powered by crystal Graph-based Neural Networks (GNNs) trained on high-throughput density functional theory (DFT) data. Using an innovative approach of sampling partially optimized defect configurations from DFT calculations, we generate one of the largest computational defect datasets to date, containing many types of vacancies, self-interstitials, anti-site substitutions, impurity interstitials and substitutions, as well as some defect complexes. We applied three types of established GNN techniques, namely crystal graph convolutional neural network, materials graph network, and Atomistic Line Graph Neural Network (ALIGNN), to rigorously train models for predicting defect formation energy (DFE) in multiple charge states and chemical potential conditions. We find that ALIGNN yields the best DFE predictions with root mean square errors around 0.3 eV, which represents a prediction accuracy of 98% given the range of values within the dataset, improving significantly on the state-of-the-art. We further show that GNN-based defective structure optimization can take us close to DFT-optimized geometries at a fraction of the cost of full DFT. The current models are based on the semi-local generalized gradient approximation-Perdew–Burke–Ernzerhof (PBE) functional but are highly promising because of the correlation of computed energetics and defect levels with higher levels of theory and experimental data, the accuracy and necessity of discovering novel metastable and low energy defect structures at the PBE level of theory before advanced methods could be applied, and the ability to train multi-fidelity models in the future with new data from non-local functionals. The DFT-GNN models enable prediction and screening across thousands of hypothetical defects based on both unoptimized and partially optimized defective structures, helping identify electronically active defects in technologically important semiconductors.

The grand canonical Monte Carlo simulation of hydrogen adsorption in single-walled carbon nanotubes

The grand canonical Monte Carlo (GCMC) simulation is adopted to study the hydrogen adsorption in armchair single-walled carbon nanotubes (SWCNTs) with diameters 1.4 and 2.7 nm at different temperatures and pressures. The effect of hypothetical defects existing in a SWCNT is also considered. The calculated results indicate that the effect of temperature on the hydrogen storage capacity is significant. At room temperature (280 K), hydrogen storage capacity of SWCNTs with diameters 1.4 and 2.7 nm all are low (<0.3%). The effect of pressure is obvious, but the hypothetical defects are insensitive. At low temperature (77 K), the hydrogen storage capacity is relatively high, where the DOE goal for 2020 can be reached by the larger diameter. The effect of pressure is insensitive, while the hypothetical defects have distinctly effect on gravimetric capacity. Moreover, there is a way to improve the gravimetric capacity by increasing defects in SWCNTs at low temperature.

Uncertainty measurement in the homogenization and sample reduction in the physical classification of rice and beans

ABSTRACT: The study aimed to i) quantify the measurement uncertainty in the physical tests of rice and beans for a hypothetical defect, ii) verify whether homogenization and sample reduction in the physical classification tests of rice and beans is effective to reduce the measurement uncertainty of the process and iii) determine whether the increase in size of beans sample increases accuracy and reduces measurement uncertainty in a significant way. Hypothetical defects in rice and beans with different damage levels were simulated according to the testing methodology determined by the Normative Ruling of each product. The homogenization and sample reduction in the physical classification of rice and beans are not effective, transferring to the final test result a high measurement uncertainty. The sample size indicated by the Normative Ruling did not allow an appropriate homogenization and should be increased.

Effect of Lüders Plateau on Fracture Response and Toughness of Pipelines Subject to Extreme Plastic Bending

The reeling technique presents an economical pipeline installation method for offshore oil and gas applications, especially for thick-wall (low D/t) pipelines. During reeling, the pipe is subjected to large plastic bending strains up to 3%. In thick-wall pipes, the tensile fracture response of the pipeline/girth weld would normally be the governing limit state. Seamless line pipes are preferred for the reeling applications in which the Lüders plateau is often exhibited in materials stress-strain response. In this paper, the fracture response of such pipelines is investigated from a continuum perspective using a nonlinear 3D finite element analysis. A typical pipeline with a hypothetical defect is considered, with the material having a range of Lüders strains and strain hardening indices. Results show that the Lüders plateau modifies the shape of the moment-strain response curves of the pipe, as well as the J-integral fracture response. It is observed that the response is always bounded between two limiting material models, which are (i) the elastic-perfectly plastic stress-strain response and (ii) the conventional elastic-strain hardening plasticity response, without a Lüders plateau. Also, the Lüders plateau was observed to decrease the crack opening stress ahead of the crack tip and thus the crack tip constraint. On the other hand, the presence of a Lüders plateau elevates the near tip plastic strain and stress triaxiality fields, thus promoting ductile fracture. A micromechanical damage integral model coupled with a modified boundary layer analysis was incorporated to study this aspect. Based on the findings of this study, it is believed that the presence of Lüders plateau could significantly alter the fracture response and toughness of pipes subject to relatively high strains.

Galeal Flap Based on Superficial Temporal Vessels for Oral Cavity and Pharynx Reconstruction – An Anatomical Study

Despite the advances in microvascular free tissue transfer for intraoral reconstruction, this surgery is not recommended for all patients. In specific cases, the pedicled temporoparietal galeal flap may be an option for reconstructive procedures in the head and neck regions. The objective of this paper is to present the anatomical aspects of a galeal flap based on the superficial temporal vessels and to test its potential for reconstructing diverse sites of the oral cavity and pharynx. We performed 40 dissections on 34 fresh adult cadavers. The flap vascular anatomy was studied by injecting latex into the superficial temporal vessels. A standardized square-shape flap measuring 10 x 10 cm(2), pedicled on the superficial temporal vessels, was raised. Oral cavity and oropharynx reconstruction simulations were performed after flap transposition into the mouth by passing it under the zygomatic arch. Hypopharyngeal reconstruction was tested by transposing the flap to the neck under the facial nerve. After latex injection, a rich vascular network over the temporoparietal galea was observed directly from the superficial temporal artery, and a well-vascularized flap based on this vessel was raised. In the reconstruction simulations, the flap was shown to be suitable for the coverage of hypothetical defects in most oral cavity and pharyngeal sites, mainly the retromolar trigone, tonsil area, and buccal mucosa. A galeal flap based on the superficial temporal vessels presents favorable anatomical characteristics for oral cavity and pharyngeal reconstruction.

Pattern recognition in the automatic inspection of aluminium castings

∑ Image Formation: The images are obtained by X-ray irradiation of the test-piece. The X-rays are then converted to a visible image by means of an image amplifier or a flat-panel detector that are sensitive to X-rays. The sensor is bi-dimensional (or unidimensional in motion) in order to capture the two dimensions of the image. An A/D converter turns the electrical signal into binary code that can be interpreted by a computer to form a digital image of the study object. ∑ Pre-processing: This stage is devoted to improving the quality of the image in order to better recognise flaws. Some of the techniques used in this stage are elimination of noise by means of digital filters or integration, improvement of contrast, and restoration. ∑ Segmentation: The segmentation process divides the digital image into disjoint regions with the purpose of separating the parts of interest from the rest of the scene. Over the last few decades, diverse segmentation techniques have been developed. These can largely be divided into three groups: pixel, edge and region orientated techniques. The present investigation uses the segmentation process oriented towards the detection of edges by employing the LoG filter (Mery and Filbert, 2002b). As can be seen in Figure 2, this technique searches for changes in the grey values of the image (edges), thus identifying zones delimited by edges that indicate flaws. ∑ Feature extraction: In the inspection of cast pieces, segmentation detects regions that are denominated as ‘hypothetical defects’, which may be flaws or structural features of the object. Subsequently the feature extraction is centred principally around

The Classification of Sample Defects in Electromagnetic Non Destructive Testing

Abstract An adaptive estimation technique is proposed for the automatic classification of defects in metal tubes during a high speed eddy current inspection process. The technique makes use of a bank of Kalman filters with each filter being matched to a specific hypothetical defect and the residual behaviour of each filter monitored via a simple nonlinear calculation to determine a best fit to actual measurements from the inspection coils. A lumped parameter model of the eddy current test phenomenon is presented which is amenable to state variable presentation and which matches an exact system performance based on solutions to the classical Helmholtz equations. This model has a unique property of accurately representing specific fault conditions within a sample volume and also enables a rigorous analytical investigation to be undertaken of the effects of a range of excitation waveforms of arbitrary complexity.

Theories of classical thermal hopping of a defect

The vineyard and the dynamical theories of classical hopping are tested by comparing their predictions of the hopping rate for a simple hypothetical defect in a crystal with the results of computer simulations. An extension of these theories is proposed.

A kinetic model for the intramolecular distribution of 15N in uric acid in patients with primary gout fed 15N-glycine

The concept of an abnormality of glutamine metabolism in primary gout was first proposed on the basis of isotope data: when 15N-glycine was administered to gouty subjects, there was disproportionately great enrichment of N-(3+9) of uric acid, which derive from the amide-N of glutamine. An unduly high concentration of 15N in glutamine was postulated, and attributed to a hypothetical defect in the catabolism of glutamine. Excess glutamine was proposed as the driving force of uric acid overproduction. We have reexamined this proposition in four gouty and three control subjects. In three of the gouty subjects the driving force of excessive purine biosynthesis was a known surplus of α-5-phosphoribosyl-1-pyrophosphate. The precursor glycine and glutamine pools were sampled by isolation of urinary hippurate and phenylacetylglutamine. Enrichment values of hippurate and of phenacetylglutamine were normal in all of the gouty subjects studied. However, the time course of 15N enrichment of hippurate differed from that of the amide-N of glutamine. A kenetic model was constructed, and experimentally derived data were used to drive the model. It was found that disproportionate labeling of N-(3+9) could be produced from the model when appropriate constraints were used. Thus, preferential enrichment of N-(3+9) in gouty overproducers given 15N-glycine does not necessarily reflect a specific abnormality of glutamine metabolism, but rather appears to be a kinetic phenomenon associated with accelerated purine biosynthesis per se.

The Kinetics of Intramolecular Distribution of 15N in Uric Acid after Administration of [15N]Glycine A REAPPRAISAL OF THE SIGNIFICANCE OF PREFERENTIAL LABELING OF N-(3 + 9) OF URIC ACID IN PRIMARY GOUT

THE CONCEPT OF AN ABNORMALITY OF GLUTAMINE METABOLISM IN PRIMARY GOUT WAS FIRST PROPOSED ON THE BASIS OF ISOTOPE DATA: when [(15)N]glycine was administered to gouty subjects, there was disproportionately great enrichment of N-(3 + 9) of uric acid, which derive from the amide-N of glutamine. An unduly high concentration of (15)N in glutamine was postulated, and attributed to a hypothetical defect in catabolism of glutamine. Excess glutamine was proposed as the driving force of uric acid overproduction. WE HAVE REEXAMINED THIS PROPOSITION IN FOUR GOUTY SUBJECTS: one mild overproducer of uric acid with "idiopathic gout," one marked overproducer with high-grade but "partial" hypoxanthine-guanine phosphoribosyl-transferase deficiency, and two extraordinary overproducers with superactive phosphoribosylpyrophosphate synthetases. In the last three, the driving force of excessive purine biosynthesis is a known surplus of alpha-5-phosphoribosyl-1-pyrophosphate. Disproportionately high labeling of N-(3 + 9) was present in all four gouty subjects, most marked in the most flamboyant overproducers. The precursor glucine pool was sampled by periodic administration of benzoic acid and isolation of urinary hippuric acid. Similarly, the precursor glutamine pool was sampled by periodic administration of phenylacetic acid and isolation of the amide-N of urinary phenylacetylglutamine. The time course of (15)N enrichment of hippurate differed from that of the amide-N of glutamine. Whereas initial enrichment values of hippurate were very high, those of glutamine-amide-N were low, increasing to a maximum at about 3 h, and then declining less rapidly than those of hippurate. However, enrichment values of hippurate and of phenacetyl glutamine were normal in all of the gouty subjects studied. Thus, preferential enrichment of N-(3 + 9) in gouty overproducers given [(15)N]glycine does not necessarily reflect a specific abnormality of glutamine metabolism, but rather appears to be a kinetic phenomenon associated with accelerated purine biosynthesis per se.In addition, greater enrichment of N-9 than of N-3 on days 1 and 2 provided suggestive evidence for a second pathway for synthesis of the initial precursor of purine biosynthesis, phosphoribosylamine, perhaps utilizing ammonia rather than the amide-N of glutamine as nitrogen donor. In this limited study, the activity of this potential second pathway did not appear to be selectively increased in gout.

Current developments in the theory of the vibrational properties of point defects (and their diffusion)

The main features of the response function technique in defect lattice dynamics are outlined. Applications to such problems as the calculations of recoilless fractions in the Mossbauer effect are illustrated by considering a simple hypothetical defect consisting of a substitutional atom which differs from a host atom in mass and in being subject to an extra potential which is a function of only one component of its displacement. It is also shown how the Vineyard theory of diffusion can be turned into a practical computational technique by response function methods and the same defect, with the extra potential chosen to give two positions of equilibrium, is used to illustrate the procedure. A method is proposed for simplifying computer simulation studies of diffusion by an application of the response function idea.

Biochemical study of muscle in progressive muscular dystrophy.

Current concepts of progressive muscular dystrophy hold that it is a disease in which, through genetic error, there are intrinsic defects in muscle metabolism, although the nature of these hypothetical defects remains unrecognized. It is the purpose of this report to describe one approach to the problem and to show that there are defects in the metabolism of isolated muscle from patients with progressive muscular dystrophy.