Investigation of helicopter loading spectra variations on fatigue crack growth in titanium and aluminium alloys

An investigation has been made into the effect of omitting small, vibratory load cycles from a helicopter load spectrum on the fatigue crack growth rates of high strength titanium (Ti-lOV 2Fe 3A1) and aluminium (7010 T73651) alloys. The investigation is made in the light of new requirements for the damage tolerance design of transport helicopter structures that have normally been designed to safe life criteria. The work aims to improve the damage tolerance design of helicopter structures by understanding the contribution of the vibratory load cycles to fatigue crack growth damage. The experimental work consisted of two parts that considered fatigue crack growth under simple overload type loading and complex fatigue load sequences using compact tension specimens. Simple overload and underload tests were run under near-threshold, plane strain crack growth rates typical of those experienced in helicopter components. These were supplemented by crack closure measurements made using a strain gauge adhered close to the crack tip. Fatigue crack growth rate retardation was observed after an overload and this was reduced if a tensile underload was subsequently applied. The experimental evidence suggested that observed crack growth transient behaviour could be explained by a residual stress field mechanism ahead of the crack tip with closure only serving in a secondary role to modify the applied external loading. A fatigue load sequence was developed for a helicopter rotorhead component and included representations of manoeuvre loads superimposed with the high mean stress, vibratory load cycles. A technique of progressively omitting small load cycles of increasing range from this sequence was used to determine the effect of these cycles on the fatigue crack growth. It was found that the these cycles of 16% range caused up to 80% of the total crack length damage and that the observed crack growth rate of the cycles was three times greater than that predicted by a conservative fatigue crack growth model. These are significant observations because vibratory cycles are usually considered to be non-damaging under a safe life design to which most current transport helicopters have been certified to. It was proposed that the accelerated growth rate of these cycles was caused by frequent underloads in the rotorhead loading sequence. A residual stress field model was invoked to explain this behaviour. The results are used to provide guidance for damage tolerant design of helicopter structures.Ph

The Human Virome in Children and its Relationship to Febrile Illness

This study investigates the relationship of viruses to febrile illness in children. Subjects are normal children 2-36 months of age with fever along with normal children of the same age without fever, plus immunocompromised children with fever along with immunocompromised children without fever. Specimens obtained include blood, nasopharyngeal secretions, and feces. Specimens are analyzed using a panel of virus-specific PCR assays and also by high throughput sequencing using 454 and Illumina platforms

Conventional and regulatory CD4+ T cells that share identical TCRs are derived from common clones

Results from studies comparing the diversity and specificity of the TCR repertoires expressed by conventional (Tconv) and regulatory (Treg) CD4+ T cell have varied depending on the experimental system employed. We developed a new model in which T cells express a single fixed TCRα chain, randomly rearranged endogenous TCRβ chains, and a Foxp3-GFP reporter. We purified CD4+Foxp3- and CD4+Foxp3+ cells, then performed biased controlled multiplex PCR and high throughput sequencing of endogenous TCRβ chains. We identified >7,000 different TCRβ sequences in the periphery of 5 individual mice. On average, ~12% of TCR sequences were expressed by both conventional and regulatory populations within individual mice. The CD4+ T cells that expressed shared TCR sequences were present at higher frequencies compared to T cells expressing non-shared TCRs. Furthermore, nearly all (>90%) of the TCR sequences that were shared within mice were identical at the DNA sequence level, indicating that conventional and regulatory T cells that express shared TCRs are derived from common clones. Analysis of TCR repertoire overlap in the thymus reveals that a large proportion of Tconv and Treg sharing observed in the periphery is due to clonal expansion in the thymus. Together these data show that there are a limited number of TCR sequences shared between Tconv and Tregs. Also, Tconv and Tregs sharing identical TCRs are found at relatively high frequencies and are derived from common progenitors, of which a large portion are generated in the thymus

Development and evaluation of an enterovirus D68 real-time reverse transcriptase PCR assay

We have developed and evaluated a real-time reverse transcriptase PCR (RT-PCR) assay for the detection of human enterovirus D68 (EV-D68) in clinical specimens. This assay was developed in response to the unprecedented 2014 nationwide EV-D68 outbreak in the United States associated with severe respiratory illness. As part of our evaluation of the outbreak, we sequenced and published the genome sequence of the EV-D68 virus circulating in St. Louis, MO. This sequence, along with other GenBank sequences from past EV-D68 occurrences, was used to computationally select a region of EV-D68 appropriate for targeting in a strain-specific RT-PCR assay. The RT-PCR assay amplifies a segment of the VP1 gene, with an analytic limit of detection of 4 copies per reaction, and it was more sensitive than commercially available assays that detect enteroviruses and rhinoviruses without distinguishing between the two, including three multiplex respiratory panels approved for clinical use by the FDA. The assay did not detect any other enteroviruses or rhinoviruses tested and did detect divergent strains of EV-D68, including the first EV-D68 strain (Fermon) identified in California in 1962. This assay should be useful for identifying and studying current and future outbreaks of EV-D68 viruses

Long-range depth imaging using a single-photon detector array and non-local data fusion

The ability to measure and record high-resolution depth images at long stand-off distances is important for a wide range of applications, including connected and automotive vehicles, defense and security, and agriculture and mining. In LIDAR (light detection and ranging) applications, single-photon sensitive detection is an emerging approach, offering high sensitivity to light and picosecond temporal resolution, and consequently excellent surface-to-surface resolution. The use of large format CMOS (complementary metal-oxide semiconductor) single-photon detector arrays provides high spatial resolution and allows the timing information to be acquired simultaneously across many pixels. In this work, we combine state-of-the-art single-photon detector array technology with non-local data fusion to generate high resolution three-dimensional depth information of long-range targets. The system is based on a visible pulsed illumination system at a wavelength of 670 nm and a 240 × 320 array sensor, achieving sub-centimeter precision in all three spatial dimensions at a distance of 150 meters. The non-local data fusion combines information from an optical image with sparse sampling of the single-photon array data, providing accurate depth information at low signature regions of the target