Crack growth analysis in aluminium alloy plate (Al 2024 - T351) using finite element method

In this paper, an aluminium alloy (Al 2024 – T351) was discretized into four linear elements and crack growth rate analysis was carried out using the Finite Element Method (FEM). The overall results from these finite elements were finally assembled to represent the crack growth in the entire domain of the aluminium alloy. The results obtained from the finite element method shows that as the number of cycle increases, the crack growth also increases linearly. This was shown for different cycle from 0 to 4000 with an initial crack growth of 0.05mm. The result obtained from the FEM when compared with the result obtained from the exact differential equation method shows a strong agreement.Keywords: Crack, Priddle Model, Weak Formulation, Aluminium Allo

A review and investigations of some properties of foamed aerated concrete

The paper presents the results of investigation conducted on foamed aerated concrete a lightweight concrete - with a view to determining its potential as a construction material in Nigeria. The properties investigated on foamed aerated concrete having a designed density of 1600kg/m3 were: workability, density, compressive strength, tensile strength, and the water absorption capacity. The results showed that at the designed density adopted for this work, the material was workable and repeatable. Other results at 28 days of curing are: (i) compressive strength of 15. 43N/mm2, 13.89N/mm2 respectively for air-cured and water-cured specimens, (ii) modulus of rupture of 2.53N/mm2 (ii) splitting tensile strength of 1.63N/mm2, and (iv) the water absorption capacity of 1.03% The tensile strength to compressive strength ratio was more than 10%. These properties improved with time. It can be concluded that the foamed aerated concrete used for this work is repeatable, and of adequate strength for use as a construction material.Keywords: Aerated Concrete, Compressive Strength, Tensile Strength, Workabilit

Effect of heat on laterised concrete

This study presents the results of investigation of the effects of temperature variation on the compressive strength of laterised concrete. Cube specimens were cast, cured in water at ambient laboratory temperature and subjected to different temperature regimes before testing. A concrete mix ratio of 2:3:6 (cement: laterite/sand: granite) with water/cement ratio of 0.65 was adopted for this investigation. The laterite content in the fine aggregate was varied from 0 to 100% at 25% interval. Specimens cured for 7 and 28 days were subjected to uniaxial compressive loading tests at room and elevated temperatures of 250, 500 and 750oC. The results show that normal concrete cannot withstand appreciable load above 250oC while laterised concrete with 25% laterite in the fine aggregate is able to resist higher load with increase in age and at temperature up to 500oC. It is also observed that there is no appreciable increase in strength at higher temperatures. The peak compressive strength value of 30.44 N/mm2 is recorded for the mix with 25% laterite-75% sand at 500oC. This is an indication that the strength of laterised concrete is generally sufficient for use at elevated temperature not exceeding 500oC

ASSESSMENT OF THE MICRO-STRUCTURE OF COMPACTED SOILS USING VARIED COMPACTIVE EFFORTS: A CASE STUDY OF SOME SELECTED AREAS IN PORT HARCOURT, NIGERIA

This research studies the effects of varying British standard heavy and British standard light compactions on the resulting micro-structures of soils using digital microscope. Three soils classified as A-6, A-7-6, and A-2-7 using AASHTO classification system were analysed. The initial properties tests and moisture- dry density relationship were carried out in accordance to British standard 1377 of 1990. The liquid limits ranged from 50.5% to 34.7% using the Casagrande liquid limit apparatus, plasticity index ranged from 22.3% to 12.4% and natural moisture content ranged from 24.3% to 21.2%. The lower the plasticity index the higher the maximum dry density for both degrees of compactions. From the micro-structural analysis, there was evidence of lines of shear at the wet-side of optimum moisture for all compactions and that the presence of these lines is high for soils of lower plasticity index at low compaction energies. At higher compaction effort, there was closer inter-particle aggregation of grains than at lower compaction efforts. The voids at the optimum moisture are smaller compared to those at the extremes of optimum, with voids on the wet-side of optimum larger than those at the dry side of optimum moisture for both compactive efforts. Thus, the micro-structure of the compacted soil revealed that the degree of compaction influences the degree of compactness of gains, the average dimension of voids, and the occurrence of thin lines of shear in their structure

Experimental Research on the Shear Connectors in Foam Concrete

In order to improve the longitudinal shear resistance between foam concrete and C-Channels, an investigation is carried out on the shear connectors in foam concrete with cold-formed steel double C-Channels embedment. Twenty-four tests have been carried out in two groups. Two types of connectors: flange connectors and web connectors are installed using self-drilling screws for a rapid construction. The experimental results show that they can effectively improve the longitudinal shear-resist capacity of the concrete. After the experiment, the specimens are dismantled for an interior observation. Based on the observation, the form of damage, the failure mechanism was discovered, and the equation of longitudinal shear capacity was developed. It is concluded that the failure involves independent slippage between two C-Channels and the shear connection fractures. Since the composite structure requires sufficient slip between the two materials, these types of shear connectors will have good enhancement for this type of composite structures subjected to dynamic loads

Acute Lassa Virus Encephalitis with Lassa Virus in the Cerebrospinal Fluid but Absent in the Blood: A Case Report with a Positive Outcome

It is rare both to have the central nervous system (CNS) as the main focus in the acute phase of Lassa fever infection without associated bleeding, and to find Lassa virus (LAV) in the cerebrospinal fluid (CSF) but not in the serum. We report the case of a 38-year-old Nigerian woman with mainly CNS manifestation of Lassa fever. She was admitted twice within 11 days because of persistent fever. A clinical diagnosis of acute LAV encephalitis was made because of a high index of suspicion and CNS involvement confirmed by positive reverse transcriptase polymerase chain reaction (RT-PCR) for LAV in the CSF, while her blood was repeatedly negative for LAV by RT-PCR test. She recovered fully following supportive care coupled with treatment with an 18-day course of ribavirin, and suffered no long-term neurological complication or relapse. Post-treatment CSF examination by RT-PCR did not detect LAV

Most neutralizing human monoclonal antibodies target novel epitopes requiring both Lassa virus glycoprotein subunits

Lassa fever is a severe multisystem disease that often has haemorrhagic manifestations. The epitopes of the Lassa virus (LASV) surface glycoproteins recognized by naturally infected human hosts have not been identified or characterized. Here we have cloned 113 human monoclonal antibodies (mAbs) specific for LASV glycoproteins from memory B cells of Lassa fever survivors from West Africa. One-half bind the GP2 fusion subunit, one-fourth recognize the GP1 receptor-binding subunit and the remaining fourth are specific for the assembled glycoprotein complex, requiring both GP1 and GP2 subunits for recognition. Notably, of the 16 mAbs that neutralize LASV, 13 require the assembled glycoprotein complex for binding, while the remaining 3 require GP1 only. Compared with non-neutralizing mAbs, neutralizing mAbs have higher binding affinities and greater divergence from germline progenitors. Some mAbs potently neutralize all four LASV lineages. These insights from LASV human mAb characterization will guide strategies for immunotherapeutic development and vaccine design

Capturing sequence diversity in metagenomes with comprehensive and scalable probe design.

Metagenomic sequencing has the potential to transform microbial detection and characterization, but new tools are needed to improve its sensitivity. Here we present CATCH, a computational method to enhance nucleic acid capture for enrichment of diverse microbial taxa. CATCH designs optimal probe sets, with a specified number of oligonucleotides, that achieve full coverage of, and scale well with, known sequence diversity. We focus on applying CATCH to capture viral genomes in complex metagenomic samples. We design, synthesize, and validate multiple probe sets, including one that targets the whole genomes of the 356 viral species known to infect humans. Capture with these probe sets enriches unique viral content on average 18-fold, allowing us to assemble genomes that could not be recovered without enrichment, and accurately preserves within-sample diversity. We also use these probe sets to recover genomes from the 2018 Lassa fever outbreak in Nigeria and to improve detection of uncharacterized viral infections in human and mosquito samples. The results demonstrate that CATCH enables more sensitive and cost-effective metagenomic sequencing

Emergence and spread of two SARS-CoV-2 variants of interest in Nigeria.

Identifying the dissemination patterns and impacts of a virus of economic or health importance during a pandemic is crucial, as it informs the public on policies for containment in order to reduce the spread of the virus. In this study, we integrated genomic and travel data to investigate the emergence and spread of the SARS-CoV-2 B.1.1.318 and B.1.525 (Eta) variants of interest in Nigeria and the wider Africa region. By integrating travel data and phylogeographic reconstructions, we find that these two variants that arose during the second wave in Nigeria emerged from within Africa, with the B.1.525 from Nigeria, and then spread to other parts of the world. Data from this study show how regional connectivity of Nigeria drove the spread of these variants of interest to surrounding countries and those connected by air-traffic. Our findings demonstrate the power of genomic analysis when combined with mobility and epidemiological data to identify the drivers of transmission, as bidirectional transmission within and between African nations are grossly underestimated as seen in our import risk index estimates

Genome-wide association study identifies human genetic variants associated with fatal outcome from Lassa fever

Infection with Lassa virus (LASV) can cause Lassa fever, a haemorrhagic illness with an estimated fatality rate of 29.7%, but causes no or mild symptoms in many individuals. Here, to investigate whether human genetic variation underlies the heterogeneity of LASV infection, we carried out genome-wide association studies (GWAS) as well as seroprevalence surveys, human leukocyte antigen typing and high-throughput variant functional characterization assays. We analysed Lassa fever susceptibility and fatal outcomes in 533 cases of Lassa fever and 1,986 population controls recruited over a 7 year period in Nigeria and Sierra Leone. We detected genome-wide significant variant associations with Lassa fever fatal outcomes near GRM7 and LIF in the Nigerian cohort. We also show that a haplotype bearing signatures of positive selection and overlapping LARGE1, a required LASV entry factor, is associated with decreased risk of Lassa fever in the Nigerian cohort but not in the Sierra Leone cohort. Overall, we identified variants and genes that may impact the risk of severe Lassa fever, demonstrating how GWAS can provide insight into viral pathogenesis