96 research outputs found

    Crack Growth from Naturally Occurring Material Discontinuities in Operational Aircraft

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    AbstractThis paper focuses on problems associated with aircraft sustainment related issues and illustrates how cracks that grow from small naturally occurring material discontinuities in operational aircraft behave. The example discussed in this paper, which is associated with crack growth under a representative maritime aircraft load spectrum, when taken in conjunction with previous studies into cracks growing under combat aircraft load spectra illustrates how for cracks that grow from naturally occurring material discontinuities under such operational load spectra there is generally little crack closure so that the crack growth history from its initial equivalent pre-crack size (EPS) through to final failure can be easily and accurately computed

    A Reference Dataset for Network Traffic Activity Based Intrusion Detection System

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    The network traffic dataset is a crucial part of anomaly based intrusion detection systems (IDSs). These IDSs train themselves to learn normal and anomalous activities. Properly labeled dataset is used for the training purpose. For the activities based IDSs, proper network traffic activity labeled dataset is the first requirement, however non-availability of such datasets is bottlenecked in the field of IDS research. In this experiment, a synthetic dataset "Panjab University - Intrusion Dataset (PU-IDS)" is created. The purpose of this study is to provide the researchers a reference dataset for the performance evaluation of network traffic activity based IDSs. University of New Brunswick Network Security Laboratory - Knowledge Disscovery in Databases (NSL-KDD) is a benchmark dataset for anomaly detection but it does not contain activity based labeling. So basic characteristics of this dataset are taken for the generation of the new synthetic dataset with various activities based labels. The dataset is first categorized as per protocol and service. Thereafter, as per minimum & maximum values of attributes, activity profiles are synthetically generated. This paper also discusses various statistical characteristics of PU-IDS. The total number of 198533 instances along with 273 of activity profiles are created. This dataset also contain different 98 protocol_service profiles

    Composite repairs to bridge steels demystified

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    This paper examines crack growth associated with carbon fibre reinforced plastic (CFRP) repairs to cracked bridge steels and boron epoxy composite and fibre metal patch repairs to cracked aluminium alloy structures. It is first shown that the da/dN versus ΔK curves associated with bridge steels is very similar to that seen in the high strength aerospace steel D6ac. The importance of 1st ply failure, which was first observed on a boron epoxy repair to the F-111 D6ac steel wing pivot fitting, and how to alleviate this failure mechanism is then discussed as is the common design approach whereby after patching the repair is designed to have a ΔK beneath the ASTM long crack threshold ΔKth. It is shown that crack growth in bridge steels repaired with CFRP patches and in aluminium alloy structures repaired with either boron epoxy or glare patches exhibit a near linear relationship between the log of the crack length and the number of cycles. We then show that crack growth in these repairs can be represented by the same simple master curve relationship that has been found to hold for cracks growing in both operational aircraft and full scale fatigue tests. These findings are important since they suggest that the methodology used by the Royal Australian Air Force to certify structural modifications to operational aircraft may also be applicable to composite repairs/modifications to steel bridges, which are generally experience significantly lower stresses

    Quantitative Analysis of Curing Mechanisms of Epoxy Resin by Mid- and Near- Fourier Transform Infra Red Spectroscopy

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    This article informs the essence of major work done by a number of researchers on the analysis of two-step curing mechanism of diglycidyl ether of bisphenol A (DGEBA) epoxy resin in presence of amine curing agents using near- and mid-IR technology. Various peaks used as a marker for resin formation are discussed and their implementation is comprehensively studied. In addition to this, a wide range of information about the importance of reference peaks in both near-IR (NIR) and mid-IR (MIR) regions are congregated and their accuracy is audited. Also discrepancies observed by researchers in epoxy conversion (α) in NIR and MIR regions are reviewed to highlight the comparative advantages of both regions, one over the other.Defence Science Journal, Vol. 64, No. 3, May 2014, pp. 314-321, DOI:http://dx.doi.org/10.14429/dsj.64.732

    Podophyllum hexandrum Offers Radioprotection by Modulating Free Radical Flux: Role of Aryl-Tetralin Lignans

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    We have evaluated the effect of variation in aryl-tetralin lignans on the radioprotective properties of Podophyllum hexandrum. Two fractionated fractions of P. hexandrum [methanolic (S1) and chloroform fractions (S2)], with varying aryl-tetralin lignan content were utilized for the present study. The peroxyl ion scavenging potentials of S1 and S2 were found to be comparable [i.e. 45.88% (S1) and 41% (S2)] after a 48 h interval in a time-dependent study, whereas in a 2 h study, S2 exhibited significant (P < 0.05) antioxidant activity in different metal ion + flux states. In the aqueous phase, S2 exhibited non-site-specific reactive oxygen species scavenging activity, i.e. 73.12% inhibition at 500 μg ml(−1). S1 exhibited 58.40 ± 0.8% inhibition (at 0.025 μg ml(−1)) of the formation of reactive nitrite radicals, comparable to S2 (52.45 ± 0.825%), and also showed 45.01% site-specific activity (1000 μg ml(−1)), along with significant (P < 0.05) electron donation potential (50–2000 μg ml(−1)) compared to S2. Such activities of S1 could be attributed to the significantly (P < 0.05) higher levels of podophyllotoxin β-d-glucopyranoside (16.5 times) and demethyl podophyllotoxin glucoside (2.9 times) compared with S2. Together, these findings clearly prove that aryl-tetralin lignan content influences the radiation protective potential of the Podophyllum fractions to a great extent

    Crack growth: Does microstructure play a role?

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    The experimental data presented in this paper reveals that even if the growth of long cracks in two materials, with different microstructures, have different da/dN versus ΔK curves the corresponding small crack curves can be similar. We also see that long cracks in a large range of steels with different microstructures, chemical compositions, and yield stresses can have similar crack growth rates. The materials science community is challenged to explain these observations. The experimental data also suggests that the threshold term ΔKthr in the Hartman-Schijve variant of the NASGRO crack growth equation appears to have the potential to quantify the way in which small cracks interact with the local microstructure. In this context it is also noted that the variability in the life of operational aircraft is controlled by the probability distribution associated with the size and nature of the material discontinuities in the airframe rather than the probability distribution associated with the scatter in the growth of small cracks with a fixed initial size

    SARS-CoV-2-specific nasal IgA wanes 9 months after hospitalisation with COVID-19 and is not induced by subsequent vaccination

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    BACKGROUND: Most studies of immunity to SARS-CoV-2 focus on circulating antibody, giving limited insights into mucosal defences that prevent viral replication and onward transmission. We studied nasal and plasma antibody responses one year after hospitalisation for COVID-19, including a period when SARS-CoV-2 vaccination was introduced. METHODS: In this follow up study, plasma and nasosorption samples were prospectively collected from 446 adults hospitalised for COVID-19 between February 2020 and March 2021 via the ISARIC4C and PHOSP-COVID consortia. IgA and IgG responses to NP and S of ancestral SARS-CoV-2, Delta and Omicron (BA.1) variants were measured by electrochemiluminescence and compared with plasma neutralisation data. FINDINGS: Strong and consistent nasal anti-NP and anti-S IgA responses were demonstrated, which remained elevated for nine months (p < 0.0001). Nasal and plasma anti-S IgG remained elevated for at least 12 months (p < 0.0001) with plasma neutralising titres that were raised against all variants compared to controls (p < 0.0001). Of 323 with complete data, 307 were vaccinated between 6 and 12 months; coinciding with rises in nasal and plasma IgA and IgG anti-S titres for all SARS-CoV-2 variants, although the change in nasal IgA was minimal (1.46-fold change after 10 months, p = 0.011) and the median remained below the positive threshold determined by pre-pandemic controls. Samples 12 months after admission showed no association between nasal IgA and plasma IgG anti-S responses (R = 0.05, p = 0.18), indicating that nasal IgA responses are distinct from those in plasma and minimally boosted by vaccination. INTERPRETATION: The decline in nasal IgA responses 9 months after infection and minimal impact of subsequent vaccination may explain the lack of long-lasting nasal defence against reinfection and the limited effects of vaccination on transmission. These findings highlight the need to develop vaccines that enhance nasal immunity. FUNDING: This study has been supported by ISARIC4C and PHOSP-COVID consortia. ISARIC4C is supported by grants from the National Institute for Health and Care Research and the Medical Research Council. Liverpool Experimental Cancer Medicine Centre provided infrastructure support for this research. The PHOSP-COVD study is jointly funded by UK Research and Innovation and National Institute of Health and Care Research. The funders were not involved in the study design, interpretation of data or the writing of this manuscript

    Large-scale phenotyping of patients with long COVID post-hospitalization reveals mechanistic subtypes of disease

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    One in ten severe acute respiratory syndrome coronavirus 2 infections result in prolonged symptoms termed long coronavirus disease (COVID), yet disease phenotypes and mechanisms are poorly understood1. Here we profiled 368 plasma proteins in 657 participants ≥3 months following hospitalization. Of these, 426 had at least one long COVID symptom and 233 had fully recovered. Elevated markers of myeloid inflammation and complement activation were associated with long COVID. IL-1R2, MATN2 and COLEC12 were associated with cardiorespiratory symptoms, fatigue and anxiety/depression; MATN2, CSF3 and C1QA were elevated in gastrointestinal symptoms and C1QA was elevated in cognitive impairment. Additional markers of alterations in nerve tissue repair (SPON-1 and NFASC) were elevated in those with cognitive impairment and SCG3, suggestive of brain–gut axis disturbance, was elevated in gastrointestinal symptoms. Severe acute respiratory syndrome coronavirus 2-specific immunoglobulin G (IgG) was persistently elevated in some individuals with long COVID, but virus was not detected in sputum. Analysis of inflammatory markers in nasal fluids showed no association with symptoms. Our study aimed to understand inflammatory processes that underlie long COVID and was not designed for biomarker discovery. Our findings suggest that specific inflammatory pathways related to tissue damage are implicated in subtypes of long COVID, which might be targeted in future therapeutic trials
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