Critical Flaw Research Articles

Re-Thinking Trust in the News

This article argues that trust in journalism is a critical mechanism in social cohesion. However, trust research in journalism has a critical flaw, since trust is measured as news consumption, while journalists’ roles are considered via questions of authority. However, scholars have thought about trust in limited ways that have failed to address the relational nature of trust that includes journalists, audiences, sources, and other social actors such “objects of journalism.” The material turn in journalism is invoked as a way to move beyond this dichotomy. Via hard and soft objects of journalism, discussed here as news buildings, “raw materials” of journalism, and digital news products like software inspire new ways of thinking about trust.

The fracture toughness of inorganic glasses

AbstractMeasuring the fracture toughness (KIc) of glasses still remains a difficult task, raising experimental and theoretical problems as well. The available methods to estimate KIc are reviewed, with emphasis on their respective advantages and drawbacks. In view of our current understanding, this analysis gives precedence to the SEPB method. The ultimate glass strength, the critical flaw size, and the indentation load for the onset of crack initiation are discussed, in the light of the fundamentals of fracture mechanics and classical background regarding the mechanics of brittle materials. Analytical expressions were further proposed to predict the fracture energy and fracture toughness of glasses from different chemical systems from their nominal compositions. The theoretical values were compared with the experimental ones, as obtained by self‐consistent methods when available. The agreement observed in most cases suggests that measured KIc values correspond to the crack propagation regime (as opposed to the crack initiation threshold), and supports previous investigations in glasses and ceramics, which showed that a crack tip is nearly atomically sharp in these materials (but for metallic glasses). Some ideas to design tougher glasses are finally presented.

A Theoretical Model for Predicting Fracture Strength and Critical Flaw Size of the ZrB2-ZrC Composites at High Temperatures

This work shows a new rational theoretical model for quantitatively predicting fracture strength and critical flaw size of the ZrB2-ZrC composites at different temperatures, which is based on a new proposed temperature dependent fracture surface energy model and the Griffith criterion. The fracture model takes into account the combined effects of temperature and damage terms (surface flaws and internal flaws) with no any fitting parameters. The predictions of fracture strength and critical flaw size of the ZrB2-ZrC composites at high temperatures agree well with experimental data. Then using the theoretical method, the improvement and design of materials are proposed. The proposed model can be used to predict the fracture strength, find the critical flaw and study the effects of microstructures on the fracture mechanism of the ZrB2-ZrC composites at high temperatures, which thus could become a potential convenient, practical and economical technical means for predicting fracture properties and material design.

Determining fracture strength and critical flaw of the ZrB2–SiC composites on high temperature oxidation using theoretical method

Abstract In this work, based on the Griffith energy method and the sensitivities of the thermal-physical properties of materials to temperature, a theoretical method for studying the temperature dependent fracture strength and critical flaw size of the ZrB2–SiC composites on high temperature oxidation is proposed by using a temperature dependent fracture surface energy model. The combined effects of temperature, microstructure and oxidation damage are taken into account by this method. The method can be easily used to predict fracture strength of the composites and its key control mechanism by using some basic material parameters. The predictions are in good agreement with experimental reports. The theoretical method can become a potential convenient and practical technical means for determining temperature and oxidation dependent fracture strength and critical flaw of the ZrB2-SiC composites developed for aerospace applications related to hypersonic flight.

The strength of aged glass

Glass is known for its excellent durability, but the strength of glass is very sensitive to the characteristics of its surface, which is known to accumulate damage during its service life. There is however, a lack of strength data on weathered or aged glass, particularly on thermally or chemically treated glass. In this study a carefully calibrated sand trickling test is used to produce surface damage equivalent to erosive action of 20 years of natural weathering on different types of glass: soda-lime-silica annealed, soda-lime-silica fully toughened and aluminosilicate chemically toughened. The soda-lime-silica glass specimens are tested destructively in their as-received and artificially aged form in a conventional coaxial double ring set-up, while the alumino-silicate chemically toughened specimens are tested in an improved coaxial double ring set-up. Fractography is subsequently used to identify and measure the critical flaw size on each specimen. The strength data are analysed statistically and the design strengths for each glass type are obtained. It is found that all glasses suffer a loss in strength after artificial ageing, with fully toughened glass providing the best post-aged performance. It was also found that the degree of toughening in the glass affects the erosion resistance, with chemically toughened glass outperforming the other glasses in this respect.

Evaluation of Canister Weld Flaw Depth for Concrete Storage Cask

Domestically developed concrete storage casks include an internal canister to maintain the confinement integrity of radioactive materials. In this study, we analyzed the depth of flaws caused by loads that propagate canister weld cracks under normal, off-normal and accident conditions, and evaluated the maximum allowable weld flaw depth needed to secure the structural integrity of the canister weld and to reduce the welding time of the internal canister lid of the concrete storage cask. Structural analyses for normal, off-normal and accident conditions were performed using the general-purpose finite element analysis program ABAQUS; the allowable flaw depth was assessed according to ASME B&PV Code Section XI. Evaluation results revealed an allowable canister weld flaw depth of 18.75 mm for the concrete storage cask, which satisfies the critical flaw depth recommended in NUREG-1536.

Line-scan system for continuous hand authentication

An increasing number of heavy machinery and vehicles have come into service, giving rise to a significant concern over protecting these high-security systems from misuse. Conventionally, authentication performed merely at the initial login may not be sufficient for detecting intruders throughout the operating session. To address this critical security flaw, a line-scan continuous hand authentication system with the appearance of an operating rod is proposed. Given that the operating rod is occupied throughout the operating period, it can be a possible solution for unobtrusively recording the personal characteristics for continuous monitoring. The ergonomics in the physiological and psychological aspects are fully considered. Under the shape constraints, a highly integrated line-scan sensor, a controller unit, and a gear motor with encoder are utilized. This system is suitable for both the desktop and embedded platforms with a universal serial bus interface. The volume of the proposed system is smaller than 15% of current multispectral area-based camera systems. Based on experiments on a database with 4000 images from 200 volunteers, a competitive equal error rate of 0.1179% is achieved, which is far more accurate than the state-of-the-art continuous authentication systems using other modalities.

The Reaction of Thiyl Radical with Methyl Linoleate: Completing the Picture.

Cis lipids can be converted by thiols and free radicals into trans lipids, which are therefore a valuable tell-tale for free radical activity in the cell's lipidome. Our previous studies have shown that polyunsaturated lipids are isomerized by alkanethiyl radicals (S•) in a cycle propagated by reversible double-bond addition and terminated by radical H-abstraction from the lipid. A critical flaw in this picture has long been that the reported lipid abstraction rate from radiolysis studies is faster than addition-isomerization, implying that the "cycle" must be terminating faster than it is propagating! Herein, we resolved this longstanding puzzle by combining a detailed product analysis, with reinvestigation of the time-resolved kinetics, DFT calculations of the indicated pathways, and reformulation of the radical-stasis equations. We have determined thiol-coupled products in dilute solutions arise mainly from addition to the inside position of the bisallylic group, followed by rapid intramolecular H• transfer, yielding allylic radicals (LZZ + S• ⇄ SL• → SL'•) that are slowly reduced by thiol (SL'• + SH → SL'H + S•). The first-order grow-in rate of the L-H• signal (kexp280nm) may therefore be dominated by the addition-H-translocation rather than slower direct H•-abstraction. Steady-state kinetic analysis of the new mechanism is consistent with products and the rates and trends for polyunsaturated fatty acids (PUFAs), monounsaturated fatty acids (MUFAs), and mixtures, with and without physiological [O2]. Implications of this new paradigm for the thiol-ene reactivity fall in an interdisciplinary research area spanning from synthetic applications to metabolomics.

A high strength alumina-silicon carbide-boron carbide triplex ceramic

A ceramic particulate composite composed of oxide, and carbide ceramics was found to have high strength, hardness, and fracture toughness values. A composition consisting of Al2O3 with 15vol% SiC and 15vol% B4C additions was produced by hot-pressing at 1650°C for 30min, with full density reached after ~5min at temperature. Both WB and WB2 were observed, with the W source presumably an impurity from WC milling media, and Al18B4O33 was also detected following densification. Strength was ~880MPa, which is greater than values reported for comparable composites of Al2O3 containing 30vol% SiC or B4C. Vickers hardness was ~21GPa, and fracture toughness was ~4.5MPam½, comparable to values reported for the binary mixtures. The calculated critical flaw size of the material was similar to the size of the SiC/B4C clusters and microcracking at grain boundaries. The latter resulting from thermal expansion mismatch between the Al2O3 matrix and SiC/B4C reinforcing phases.

Fracture characteristics of laboratory-tested soda lime glass specimens

Static testing of glass plates has shown a pronounced distribution in the plate strength. The origin of fracture location along the plate span, the corresponding critical tensile stress, and the size of the critical flaw at the origin of fracture are failure characteristics of major importance. This paper provides data and insight into parameters influencing these failure characteristics through laboratory testing and analysis of soda lime glass, to find a rationale behind the observed disorder of their magnitudes and distributions. A recent stochastic model for glass plate analysis is implemented to predict the magnitudes and distributions of the failure characteristics, and to compare these with laboratory tests. The model provides good predictions of the distributions and magnitudes of the failure characteristics and sheds light on glass plate behaviour. It demonstrates that there are mechanics-based explanations to the wide scatter of experimental results and to the apparent disorder in glass behaviour.

Mechanical characterization of parts produced by ceramic on‐demand extrusion process

AbstractCeramic On‐Demand Extrusion (CODE) is an additive manufacturing process recently developed to produce dense three‐dimensional ceramic components. In this paper, the properties of parts produced using this freeform extrusion fabrication process are described. High solids loading (~60 vol%) alumina paste was prepared to fabricate parts and standard test methods were employed to examine their properties including the density, strength, Young's modulus, Weibull modulus, toughness, and hardness. Microstructural evaluation was also performed to measure the grain size and critical flaw size. The results indicate that the properties of parts surpass most other ceramic additive manufacturing processes and match conventional fabrication techniques.

Processing, microstructure, and mechanical properties of zirconium diboride-boron carbide ceramics

The processing, microstructure, and mechanical properties of zirconium diboride-boron carbide (ZrB2-B4C) ceramics were characterized. Ceramics containing nominally 5, 10, 20, 30, and 40vol% B4C were hot-pressed to full density at 1900°C. The ZrB2 grain size decreased from 4 to 2µm and B4C inclusion size increased from 3 to 5µm for B4C additions of 5 and 40vol% B4C, respectively. Elastic modulus decreased from 525 to 515GPa and Vickers hardness increased from 15 to 21GPa as the B4C content increased from 5 to 40vol%, respectively, following trends predicted using linear rules of mixtures. Flexure strength and fracture toughness both increased with increasing B4C content. Fracture toughness increased from 4.1MPam½ at 5vol% B4C to 5.3MPam½ at 40vol% B4C additions. Flexure strength was 450MPa with a 5vol% B4C addition, increasing to 590MPa for a 40vol% addition. The critical flaw size was calculated to be ~30µm for all compositions, and analysis of the fracture surfaces indicated that strength was controlled by edge flaws generated by machining induced sub-surface damage. Increasing amounts of B4C added to ZrB2 led to increasing hardness due to the higher hardness of B4C compared to ZrB2 and increased crack deflection. Additions of B4C also lead to increases in fracture toughness due to increased crack deflection and intergranular fracture.

Wireless’s “Critical Flaw”: The Marconi Company, Corporation Mentalities, and the Broadcasting Option

This article has a double aim: one empirical–historical and one theoretical. First, it analyzes how the idea of an “alternative” use of wireless (namely, broadcasting) emerged and was debated inside the British Marconi Company in the first two decades of the 20th century. This historical part, based on unpublished sources preserved in the Marconi Archives, shows that this idea was (rationally) opposed by the majority of company’s management. Second, this article aims to place private companies at the center of media historiography, and more in general media studies, through a multifocal approach.

Robust and Efficient Transfer Learning with Hidden Parameter Markov Decision Processes

An intriguing application of transfer learning emerges when tasks arise with similar, but not identical, dynamics. Hidden Parameter Markov Decision Processes (HiP-MDP) embed these tasks into a low-dimensional space; given the embedding parameters one can identify the MDP for a particular task. However, the original formulation of HiP-MDP had a critical flaw: the embedding uncertainty was modeled independently of the agent's state uncertainty, requiring an arduous training procedure. In this work, we apply a Gaussian Process latent variable model to jointly model the dynamics and the embedding, leading to a more elegant formulation, one that allows for better uncertainty quantification and thus more robust transfer.

Mechanical strength of ground WC-Co cemented carbides after coating deposition

Manufacturing of hardmetal tools often involves surface grinding, ion etching and final coating. Each stage throughout the manufacturing chain introduces surface integrity changes which may be critical for defining the final mechanical behavior of the coated tools. Within this context, an experimental test program has been developed to assess the influence of a coating (TiN) deposition on surface integrity and transverse rupture strength of a previously ground fine-grained WC-Co grade substrate. Four different substrate surface finish conditions (prior to ion etching and coating) were evaluated: as sintered (AS), ground (G), polished (P), and ground plus high temperature annealing (GTT). Surface integrity and fracture resistance characterization, complemented with a detailed fractographic analysis, were performed on both uncoated and coated samples. Results show that the surface integrity after grinding has been partly modified during the ion etching and film deposition processes, particularly in terms of a reduced compressive residual stress state at the substrate surface level. Consequently, the grinding induced strength enhancement in hardmetals is reduced for coated specimens. Main reason behind it is the change of nature, location and stress state acting on critical flaw: from processing defects existing at the subsurface (uncoated G specimens) to grinding-induced microcracks located close to the interface between coating and substrate, but within the subsurface of the latter (coated G specimens). This is not the case for AS and P conditions, where flexural strength does not change as a result of ion etching and coating. Finally, fracture resistance increases slightly for GTT specimens after coating process, possibly caused by a beneficial effect of the deposited film on the residual stress state at the surface.

Tight binding of heme to Staphylococcus aureus IsdG and IsdI precludes design of a competitive inhibitor.

The micromolar equilibrium constants for heme dissociation from IsdG and IsdI reported in the literature call into question whether these enzymes are actually members of the iron-regulated surface determinant system of Staphylococcus aureus, which harvests heme iron from a host during infection. In order to address this question, the heme dissociation constants for IsdG and IsdI were reevaluated using three approaches. The heme dissociation equilibrium constants were measured using a UV/Vis absorption-detected assay analyzed with an assumption-free model, and using a newly developed fluorescence-detected assay. The heme dissociation rate constants were estimated using apomyoglobin competition assays. Analyses of the UV/Vis absorption data revealed a critical flaw in the previous measurements; heme is 99.9% protein-bound at the micromolar concentrations needed for UV/Vis absorption spectroscopy, which renders accurate equilibrium constant measurement nearly impossible. However, fluorescence can be measured for more dilute samples, and analyses of these data resulted in dissociation equilibrium constants of 1.4 ± 0.6 nM and 12.9 ± 1.3 nM for IsdG and IsdI, respectively. Analyses of the kinetic data obtained from apomyoglobin competition assays estimated heme dissociation rate constants of 0.022 ± 0.002 s-1 for IsdG and 0.092 ± 0.008 s-1 for IsdI. Based upon these data, and what is known regarding the post-translational regulation of IsdG and IsdI, it is proposed that only IsdG is a member of the heme iron acquisition pathway and IsdI regulates heme homeostasis. Furthermore, the nanomolar dissociation constants mean that heme is bound tightly by IsdG and indicates that competitive inhibition of this protein will be difficult. Instead, uncompetitive inhibition based upon a detailed understanding of enzyme mechanism is a more promising antibiotic development strategy.

The logic of syntactic priming and acceptability judgments.

A critical flaw in Branigan & Pickering's (B&P's) advocacy of structural priming is the absence of a theory of priming. This undermines their claims about the value of priming as a methodology. In contrast, acceptability judgments enable clearer inferences about structure. It is important to engage thoroughly with the logic behind different structural diagnostics.

Design Considerations for Silica-Particle-Doped Nitric-Oxide-Releasing Polyurethane Glucose Biosensor Membranes.

Nitric oxide (NO)-releasing polymers have proven useful for improving the biocompatibility of in vivo glucose biosensors. Unfortunately, leaching of the NO donor from the polymer matrix remains a critical design flaw of NO-releasing membranes. Herein, a toolbox of NO-releasing silica nanoparticles (SNPs) was utilized to systematically evaluate SNP leaching from a diverse selection of biomedical-grade polyurethane sensor membranes. Glucose sensor analytical performance and NO-release kinetics from the sensor membranes were also evaluated as a function of particle and polyurethane (PU) chemistries. Particles modified with N-diazeniumdiolate NO donors were prone to leaching from PU membranes due to the zwitterionic nature of the NO donor modification. Leaching was minimized (<5% of the entrapped silica over 1 month) in low water uptake PUs. However, SNP modification with neutral S-nitrosothiol (RSNO) NO donors lead to biphasic leaching behavior. Particles with low alkanethiol content (<3.0 wt % sulfur) leached excessively from a hydrogel PU formulation (HP-93A-100 PU), while particles with greater degrees of thiol modification did not leach from any of the PUs tested. A functional glucose sensor was developed using an optimized HP-93A-100 PU membrane doped with RSNO-modified SNPs as the outer, glucose diffusion-limiting layer. The realized sensor design responded linearly to physiological concentrations of glucose (minimum 1-21 mM) over 2 weeks incubation in PBS and released NO at >0.8 pmol cm-2 s-1 for up to 6 days with no detectable (<0.6%) particle leaching.

HTTPAS: active authentication against HTTPS man‐in‐the‐middle attacks

Hypertext transfer protocol secure (HTTPS) relies on a group of pre-trusted certificate authorities (CAs) for authentication and hence can avoid man-in-the-middle attacks. However unfortunately, this authentication architecture can be completely subverted in case any one (usually the weakest one) of CAs has been compromised. To tackle this critical flaw, pioneer works such as notary-based systems and pre-shared secrets have been proposed. These state-of-the-art techniques can neither seek maximal protection from available CAs nor resist potential man-in-the-middle variants. In this study, the authors propose HTTPAS, a new HTTP Active Secure framework that can enhance the HTTPS authentication against man-in-the-middle attacks by actively utilising available CAs and exploiting Internet path diversity as much as possible. In particular, HTTPAS is designed with four practical solutions, each of which can make a unique trade-off among authentication capability, deployment difficulty and efficiency. They have implemented HTTPAS using the open secure sockets layer (SSL) suite, and also evaluated the implementation through experiments on several public certificate data sets and the Internet. Their results have successfully confirmed the authentication effectiveness of HTTPAS with only a few performance overheads and moderate deployment effort.

New test approach to determine the transverse tensile strength of CFRP with regard to the size effect

Abstract The subject of this work is the investigation of the size effect on transverse strength of CFRP. A new test approach uses the remaining parts of already tested specimens for a second transverse tensile test. With this method it is analysed, whether first failure is dominated by the most critical flaw inside the material or at a load that is equivalent to the maximum tensile strength of the matrix. Thickness of the specimens is varied to study the influence of specimen volume on transverse tensile strength. Test results show that strength follows the trend of defect distribution with increasing strength for decreasing volume. Second failure strength is higher than first failure strength, showing that first failure occurs at the most critical defect and gives no evidence of the maximum transverse tensile strength of the material. Stress at second failure showed less scatter, proving good applicability of the proposed test method.