Corner Defects Research Articles

Theoretical evidence for unexpected O-rich phases at corners of MgO surfaces

Realistic oxide materials are often semiconductors, in particular at elevated temperatures, and their surfaces contain undercoordinated atoms at structural defects such as steps and corners. Using hybrid density-functional theory and ab initio atomistic thermodynamics, we investigate the interplay of bond-making, bond-breaking, and charge-carrier trapping at the corner defects at the (100) surface of a $p$-doped MgO in thermodynamic equilibrium with an ${\mathrm{O}}_{2}$ atmosphere. We show that by manipulating the coordination of surface atoms, one can drastically change and even reverse the order of stability of reduced versus oxidized surface sites.

Aspect Ratio Evolution in Embedded, Surface, and Corner Cracks in Finite-Thickness Plates under Tensile Fatigue Loading

This article deals with the computational modelling of the fatigue crack aspect ratio evolution in embedded, surface, and corner cracks located in finite-thickness plates under tensile fatigue. The approach is based on the Paris law for fatigue propagation and an expression for the stress intensity factor (SIF) provided by Newman and Raju. Numerical results indicate that the crack path develops in such a manner that all flaws tend to reach similar aspect ratios, i.e., a preferential crack path does exist along which there is a one-to-one relationship between the aspect ratio and the relative crack depth (a sort of master curve in the matter of fatigue crack path evolution). Such a reference curve corresponds to that of a very superficial initial flaw with almost circular shape. The convergence (quicker or slower approach between fatigue crack paths starting from different initial defects) is higher for surface flaws than for corner cracks, and quicker for the latter than for embedded discontinuities. Corner defects increase their size faster than surface cracks, and the latter do the same quicker than the embedded ones.

Localised surface plasmon-like resonance generated by microwave electromagnetic waves in pipe defects

Localised surface plasmon (LSP)-like resonance phenomena were simulated in COMSOL Multiphysics™, and the electric field enhancement was evaluated in eight pipe defects using the microwave band from 1.80 to 3.00 GHz and analysed by finite element analysis (FEA). The simulation was carried out, in each defect case, on a pipe that has 762 mm length and 152.4 mm inner diameter, and 12.7 mm pipe wall thickness. Defects were positioned in the middle of the pipe and were named as follows; SD: Square Defect, FCD: fillet corner defect, FD: fillet defect, HCD: half circle defect, TCD: triangle corner defect, TD: triangle defect, ZD: zigzag defect, GD: gear defect. The LSP electric field, and scattering parametric (S21, and S11) waves were evaluated in all cases and found to be strongly dependent on the size and the shape of the defect rather than the pipe and or the medium materials.

Advanced Grading System for Quality Assurance of Ceramic Tiles based using Digital Image Processing

Objectives: To design an automated advanced grading system for maintaining quality assurance of ceramic tiles. Methods/ Statistical Analysis: We designed a machine that name is Upgraded Automated High Quality Maintaining Machine (UAHQMM). Customers required effect less and quality ceramic tiles. Findings: The block diagram of this research work presented three phases for automated quality Maintaining machine to maintain quality in ceramic tile industry. Application/Improvements: This automated machine is very useful for corner defect detection from different shapes of ceramic tile. In this research we discussed two shapes square and rectangle shapes. This modeled machine is very helpful for increasing production rate.

Preparation and characterization of expanded graphite/metal oxides for antimicrobial application

Composite materials based on expanded graphite (EG) and metal oxide (MO) particles was prepared by an explosive combustion and blending method. The objective of the study was to develop EG impregnated with metal oxide particulates (Ag2O, CuO and ZnO) and evaluate the level of protection the materials conferred against biological agents. The physical properties of the EG/MO composites were examined using SEM, EDX and XRD spectroscopy, and the results indicated that the MO particles were incorporated into the EG matrix after impregnation. The antimicrobial activities of the EG/MO composites against Gram-positive bacteria, Gram-negative bacteria and Bacillus anthracis were investigated using zone of inhibition, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and plate-counting methods. EG/Ag2O exhibited a stronger antibacterial activity than EG/CuO and EG/ZnO, with a MIC of 0.3mg/mL and a MBC of 0.5mg/mL. To the best of our knowledge, few studies have demonstrated that EG/MO composites can inhibit the growth of Bacillus anthracis-adhered cells, thus preventing the process of biofilm formation. Nanoscale metal oxides display enhanced reactive properties toward bacteria due to their high surface area, large number of highly reactive edges, corner defect sites and high surface to volume ratio.

Microstructure Examinations in Corners of the Low-Carbon Steel Slabs from Continuos Caster Machine

Abstract The exposed selvedge layers in slabs cast by the continuous process should be free from surface defects, which in most cases appear in the form of cracks on the casting surface and run to its interior. In addition to the parameters of the casting process, the occurrence of such defects depends on the chemical composition of cast steel, on the segregation of surface active elements and formation of the precipitates of carbides, nitrides and other phases. Due to the frequent occurrence of defects in corners of the slabs, non-destructive testing was performed on the mechanically cleaned surfaces of slabs. The test material was low-carbon API(American Petroleum Institute API 5L standard) steel micro alloyed with Nb and Ti designed for the production of pipes to handle gas, oil and other liquid and gaseous fuels. Despite the use of different methods of inspection, i.e. ultrasonic, magnetic particle and penetrant, cracks were not traced in the examined material. Then, from the corners of the examined slabs, specimens were cut out for metallographic examinations. The main purpose of these examinations was to disclose the presence of possible cracks and micro cracks on the surfaces transversal and longitudinal to the direction of casting. At the same time, studies were conducted to establish the number and morphology of non-metallic inclusions in selvedge layers of the slab corners and axis. Additionally, hardness of the slabs was measured. The conducted studies revealed only some minor differences in the slab hardness along its axis (130 ÷ 135 HB) and in selvedge layers (120 ÷ 123 HB).

Taming supersymmetric defects in 3d–3d correspondence

We study knots in 3d Chern–Simons theory with complex gauge group , in the context of its relation with 3d theory (the so-called 3d–3d correspondence). The defect has either co-dimension 2 or co-dimension 4 inside the 6d theory, which is compactified on a 3-manifold . We identify such defects in various corners of the 3d–3d correspondence, namely in 3d CS theory, in 3d theory, in 5d super Yang–Mills theory, and in the M-theory holographic dual. We can make quantitative checks of the 3d–3d correspondence by computing partition functions at each of these theories. This Letter is a companion to a longer paper [], which contains more details and more results.

Stress intensity factor calculation in sharp and beveled edge nozzle corners

This paper presents the work performed for the development of Stress Intensity Factor compendia for defects in nozzle corners. For that purpose, a large set Finite Element modeling were performed in order to cover the geometries, the defect sizes, the loading situations … encountered by large nuclear components. Then, based on that set of Finite Element modeling, an approximate solution relying on a fit of the stress field along the bisector line of the nozzle corner is proposed. This solution allows determining accurately the mean and maximum Stress Intensity Factor along the crack front for pressure loading and at the maximum of cold thermal shock loading. It is validated through a comparison to existing solutions or Finite Element modeling results.

Micromagnetic simulation of exploratory magnetic logic device with missing corner defect

Magnetic film nanostructures are attractive components of nonvolatile magnetoresistive memories and nanomagnet logic circuits. Recently, we studied switching properties (i.e., null logic preserving) of rectangle shape nanomagnet subjected to fabrication imperfections. Specifically, we presented typical missing corner material-related imperfections and adopted an isosceles triangle to model this defect for nanomagnets. Micromagnetic simulation shows that this kind of imperfections modeling method agrees well with previous experimental observations. Using the proposed defect modeling scheme, we investigate in detail the switching characteristics of different defective stand-alone and coupled nanomagnets. The results suggest that the state transition of defective nanomagnet element highly depends on defect type and device’s aspect ratio, and the defect type Bd needs the largest coercive field, while the defect type D requires the largest null field for switching. These findings can provide key technical parameters and guides for nanomagnet logic circuit design.

Herniation of cartilaginous endplates in the lumbar spine: MRI findings.

The purpose of this study was to determine reliable MRI findings suggesting disk herniation with cartilage endplate herniation in the lumbar spine. The records of 73 patients who underwent lumbar spinal MRI and lumbar microdiskectomy between March 2005 and January 2009 were searched to find those with the diagnosis of disk herniation with cartilage endplate herniation confirmed during surgery. The following morphologic features were assessed: posterior corners (posterior marginal nodes, dorsal corner defects, Modic changes, and posterior osteophytes), mid endplates (endplate irregularities, Modic changes), and heterogeneous low signal intensity of extruded material. The chi-square test and multiple logistic regression analysis with age, body mass index, and sex as covariates were used for the analysis. The ROC curve was obtained with scores of the statistically significant MRI findings. Posterior marginal nodes, posterior osteophytes, Modic changes in posterior corners, mid endplate irregularities, Modic changes in mid endplates, and heterogeneous low signal intensity of extruded material were significantly more frequent in patients with disk herniation with cartilage endplate herniation (0.000 < p < 0.009). The AUC for diagnosing disk herniation with cartilage endplate herniation with our scoring system of the six MRI findings (0-6) was 0.888. The presence of disk herniation with cartilage endplate herniation could be ascertained with the following MRI findings: posterior marginal nodes, posterior osteophytes, mid endplate irregularities, heterogeneous low signal intensity of extruded material, and Modic changes in posterior corners and mid endplates.

Application of a chamfered mold to improve corner defects of HSLA during slab continuous casting

Through the study of the slab continuous casting production process and laboratory simulation, the mechanism of transverse corner cracks on a micro-alloyed high-strength steel slab was explored. Then, a chamfered mold was developed and tested on the caster. The results show that on one hand, the chamfered mold could raise the temperature of the corner in the mold, and on the other hand, the higher temperature of the corner of the slab was an effective way to decrease the corner stress at the straightening point. The straightening deformation rate on the chamfered slab was lower than that on the square slab. Using the large chamfer mold technology, the optimization design of the foot roll structure and second cooling, the transverse corner crack was improved effectively. The hot transporting ratio was increased without the cutting angle.

Plasma Doping of InGaAs at Elevated Substrate Temperature for Reduced Sheet Resistance and Defect Formation

Plasma doping (PLAD), a high-throughput ion implantation technique capable of achieving ultrashallow junctions and conformal doping of 3-D structures such as fin field-effect transistors, is investigated as an alternative to conventional beam-line ion implantation for InGaAs at advanced technology nodes. The PLAD at an elevated substrate temperature (ET-PLAD) is studied and reported for InGaAs for the first time. The ET-PLAD can give lower sheet resistance than room-temperature PLAD due to enhanced dopant incorporation. More crucially, an ET can help to prevent amorphization. After dopant activation anneal, residual corner defects are observed in small fins that are amorphized during plasma ion implantation, whereas fins that remain crystalline during plasma ion implantation are free of corner defects.

Analysis of fatigue delamination growth in flip-chip package

An incremental crack extension procedure is implemented for simulating the growth of an interface defect in an electronic flip-chip device subjected to fatigue temperature cycling. The distributions of fracture mechanics parameters including the strain energy release rate, the stress intensity factors and phase angles along the curvilinear front of an embedded corner defect on the interface of silicon die and underfill are estimated and substituted into a subcritical crack growth model to predict the evolution of the defect under cyclic loading condition. It is observed from the analysis that the corner defect is under crack faces contact condition during temperature cycling, and consequently, the delamination growth is under mode-II and mode-III driving forces. In addition, the crack growth rate is highest in the middle of the crack front, and the corner crack evolves from an initially concave front to a quarter-circular front under temperature cycling.

Anatomy of Failure in Lumbar Disc Herniation. An in Vivo, Multimodal, Prospective Study of 181 Subjects

Study Design A prospective clinical study including radiological, serial postcontrast magnetic resonance imaging, intraoperative findings, and histopathological study. Objective The objective of this study is to document in vivo, the site of anatomical failure in lumbar disc herniation (LDH) in patients requiring disc excision surgery. Summary of Background Data In vitro mechanical disruption studies have demonstrated both the end plate junction (EPJ) and the annulus fibrosus (AF) as the site of failure in LDH depending upon the type of force used. However, corroborative studies in vivo to document the exact anatomy of failure have not been done in humans. Methods A total of 185 consecutive patients requiring microdiscectomy at a single level formed the study group. The status of the end plate and AF in the operated level (study discs) and the other discs (control) were evaluated by plain radiograph, thin slice computed tomographic scan, plain and contrast magnetic resonance imaging, intraoperative examination, and histopathological analysis. Results LDH due to EPJ failure (EPJF- type I herniation) was more common (117; 65%) than annulus fibrosis rupture. Herniated discs had a significantly higher incidence of EPJF than control discs ( p &lt; 0.0001) The EPJF was evident radiologically as vertebral corner defect in 30 patients, rim avulsion in 46, frank bony avulsions in 24, and avulsion at both upper and lower EP in 4. Thirteen discs with normal EP radiologically had cartilage or bone avulsion intraoperatively. Sixty-four discs (35%) had intact EP of which annular high intensity zone was found in 21 (11%) suggesting a disruption of AF (type II herniation). Postcontrast magnetic resonance image of 20 patients showed dye leak at the EPJ proving EPJF as main cause of LDH. Conclusion Our study is the first in vivo evidence that LDH in humans is more commonly the result of EPJF than AF rupture in patients requiring disc surgery. Our results offer clinical validation of previous in vitro mechanical disruption studies. Future research must focus on the EPJ as a primary area of interest in LDH. Disclosure of Interest None declared

ISSLS Prize Winner

A prospective multimodal study including clinical, radiological, serial postcontrast magnetic resonance imaging, intraoperative findings, and histopathological study. To document in vivo, the site of anatomical failure in lumbar disc herniation (LDH). Although in vitro mechanical disruption studies have implicated both the endplate junction (EPJ) and the annulus fibrosus (AF) as the site of failure in LDH, there are no in vivo human studies to document the exact anatomy of failure. One hundred eighty-one consecutive patients requiring microdiscectomy at a single level formed the study group. The status of the endplate and AF in the operated level (study discs) and the other discs (control) were evaluated by plain radiograph, thin slice computed tomographic scan, plain and contrast magnetic resonance imaging, intraoperative examination, and histopathological analysis. LDH due to EPJ failure (EPJF- type I herniation) was more common (117; 65%) than annulus fibrosis rupture. Herniated discs had a significantly higher incidence of EPJF than control discs (P < 0.0001). The EPJF was evident radiologically as vertebral corner defect in 30 patients, rim avulsion in 46, frank bony avulsions in 24, and avulsion at both upper and lower EP in 4. Thirteen discs with normal EP radiologically had cartilage or bone avulsion intraoperatively. Sixty-four discs (35%) had intact EP of which annular high intensity zone was found in 21 (11%), suggesting a disruption of AF (type II herniation). Postcontrast magnetic resonance image of 20 patients showed dye leak at the EPJ proving EPJF as main cause of LDH. Our study provides the first in vivo evidence that LDH in humans is more commonly the result of EPJF than AF rupture and offers clinical validation of previous in vitro mechanical disruption studies. Future research must focus on the EPJ as a primary area of interest in LDH. N/A.

Recent Advancements On Warfare Agents/metal Oxides Surface Chemistry And Their Simulation Study

Chemical warfare agents (CWA) have been used in the World Wars and in terrorist attacks, and hence there is an urgent need to find means of their decontamination. Metal oxides offer a rapid means of their disposal, since they contain reactive Lewis acid and basic sites, on which adsorption of the CWA, and subsequent hydrolysis, can take place. Destructive adsorption of CWA on metal oxides yields non-toxic products. Nanoscale metal oxides display enhanced reactive properties toward warfare agents due to their high surface area, large number of highly reactive edges, corner defect sites, unusual lattice planes and high surface to volume ratio. Both experimental and theoretical studies have established that decomposition of nerve agents is facilitated on nanoscale Al2O3, MgO, CaO, TiO2, ZnO and small edge and corner clay mineral fragments. Compared to sulfur mustard, nerve agents are more potent. We first briefly describe their mode of action. Many experimental and theoretical studies have been performed to study their decomposition on various metal oxide surfaces, such as MgO, CaO, Al2O3, TiO2, V2O5, and clay minerals. The results of these studies are reviewed here. Photochemical degradation on TiO2 nanosurfaces has also yielded promising results. Because of the toxicity and risk involved, experimental studies have been mostly confined to the benign simulants, whereas theoretical studies have attempted to compare the real agents with their mimics. These studies establish a qualitative correlation between the G-agents and their simulant DMMP, and, hence, decomposition on metal oxide surfaces can be analyzed by observing the surface chemistry of DMMP on a wide variety of metal oxide surfaces. This review attempts to compile the literature concerning CWA and their simulants. Copyright © 2013 VBRI press.

Хрящевая замыкательная пластинка и ее роль в дегенерации диска (аналитический обзор литературы)

В обзоре обобщены современные данные литературы о структуре и функции хрящевой замыкательной пластинки у человека и животных. Представлен возрастной аспект изменений хрящевой замыкательной пластинки и ее нарушения при дегенерации диска. Подчеркнута роль апоптоза хондроцитов замыкательной пластинки в инициации дегенерации межпозвоночного диска. Проанализированы экспериментальные модели повреждений хрящевой замыкательной пластинки и каскад следующих за ними патологических событий. Приведены клинические данные с привлечением аутопсийных наблюдений, свидетельствующие о том, что в грыжах диска разрывного типа на фоне выраженной дегенерации хрящевой замыкательной пластинки и наличия дорсального углового дефекта тела позвонка присутствует гиалиновая хрящевая ткань.

Director field in plastic crystals

The director field in a plastic crystal is calculated by particle-resolved Monte Carlo computer simulations of two-dimensional, slightly anisometric hard spherocylinders exposed to an external periodic substrate potential. We investigate the structure of the director field in the Wigner-Seitz cell and find a topological defect structure that can be controlled with the substrate potential. At zero potential we find a charge −1/2 defect at the corners besides the expected defect in the centre with unit topological charge. When switching the substrate potential on, the corner defects are surrounded by three satellite defects which bear charge −1/2, too. Additionally, we then find two charge +1/2 defects on each edge of the unit cell. Finally, within a simplified model, we obtain a qualitative explanation for this defect structure. Our predictions can in principle be verified by using particle-resolved experiments of colloidal plastic crystals.

Textures in Polygonal Arrangements of Square Nanoparticles in Nematic Liquid Crystal Matrices

A systematic analysis of defect textures in faceted nanoparticles with polygonal configurations embedded in a nematic matrix is performed using the Landau-de Gennes model, homeotropic strong anchoring in a square domain with uniform alignment in the outer boundaries. Defect and textures are analyzed as functions of temperature T, polygon size R, and polygon number N. For nematic nanocomposites, the texture satisfies a defect charge balance equation between bulk and surface (particle corner) charges. Upon decreasing the temperature, the central bulk defects split and together with other -1/2 bulk defects are absorbed by the nanoparticle's corners. Increasing the lattice size decreases confinement and eliminates bulk defects. Increasing the polygon number increases the central defect charge at high temperature and the number of surface defects at lower temperatures. The excess energy per particle is lower in even than in odd polygons, and it is minimized for a square particle arrangement. These discrete modeling results show for first time that, even under strong anchoring, defects are attached to particles as corner defects, leaving behind a low energy homogeneous orientation field that favors nanoparticle ordering in nematic matrices. These new insights are consistent with recent thermodynamic approaches to nematic nanocomposites that predict the existence of novel nematic/crystal phases and can be used to design nanocomposites with orientational and positional order.

CMOS-compatible dense arrays of Ge quantum dots on the Si(001) surface: hut cluster nucleation, atomic structure and array life cycle during UHV MBE growth.

We report a direct observation of Ge hut nucleation on Si(001) during UHV molecular beam epitaxy at 360°C. Nuclei of pyramids and wedges were observed on the wetting layer (WL) (M × N) patches starting from the coverage of 5.1 Å and found to have different structures. Atomic models of nuclei of both hut species have been built as well as models of the growing clusters. The growth of huts of each species has been demonstrated to follow generic scenarios. The formation of the second atomic layer of a wedge results in rearrangement of its first layer. Its ridge structure does not repeat the nucleus. A pyramid grows without phase transitions. A structure of its vertex copies the nucleus. Transitions between hut species turned out to be impossible. The wedges contain point defects in the upper corners of the triangular faces and have preferential growth directions along the ridges. The derived structure of the {105} facet follows the paired dimer model. Further growth of hut arrays results in domination of wedges, and the density of pyramids exponentially drops. The second generation of huts arises at coverages >10 Å; new huts occupy the whole WL at coverages ~14 Å. Nanocrystalline Ge 2D layer begins forming at coverages >14 Å.