Transformational part-count in layered octahedral-tetrahedral truss configurations

The number of component part (nodes, struts and panels) termed part count, is an important factor in the design, manufacture, and assembly of modular space structures. Part count expressions are presented for a variety of profiles derived from the layered octahedral-tetrahedral truss configuration. Referred to as the tetrahedral truss in the NASA projects, this specific geometry has been used in several missions. The general expressions presented here transforms to others as one profile changes to another. Such transformational part count relations provide a measure of flexibility and generality, and may be useful when dealing with a wider range of geometric configurations

Comparative morphology of configurations with reduced part count derived from the octahedral-tetrahedral truss

Morphology (the study of structure and form) of the octahedral-tetrahedral (octet) truss is described. Both the geometry and symmetry of the octet truss are considered. Morphological techniques based on symmetry operations are presented which enable the derivation of reduced-part-count truss configurations from the octet truss by removing struts and nodes. These techniques are unique because their Morphological origination and they allow for the systematic generation and analysis of a large variety of structures. Methods for easily determining the part count and redundancy of infinite truss configurations are presented. Nine examples of truss configurations obtained by applying the derivation techniques are considered. These configurations are structurally stable while at the same time exhibiting significant reductions in part count. Some practical and analytical considerations, such as structural performance, regarding the example reduced-part-count truss geometries are briefly discussed

Impact of various heat treatments on the microstructure evolution and mechanical properties of hot forged 18CrNiMo7-6 steel

Carburizing is a method of enhancing the surface properties of components, primarily made from low to medium carbon steels, such as shafts, gears, bearings, etc. Carburized parts are generally quenched and tempered before being put into service; however, after quenching of carburized parts further annealing and hardening treatments can be employed before final tempering. This work analyses the impact of the two aforementioned heat treatment approaches on the development of subsequent microstructures and mechanical properties of hot forged 18CrNiMo7-6 steel. Moreover, this study aims to understand the impact of normalizing treatments prior to the two aforementioned heat treatment routes. Microstructural and mechanical tests were conducted on four as forged flat cylinder components that received a combination of the abovementioned heat treatments. In general, better microstructure refinement, in terms of prior austenite grain size (PAGS), was obtained for carburized parts that received the intermediate annealing and hardening treatments after quenching and prior to the final tempering. Additionally, further refinement of the martensitic pockets/blocks was observed for parts that did not receive a normalising treatment prior to carburisation. The studied heat treatments appear to have a negligible effect on the mechanical properties of the hot forged flat cylinder components

P109 The impact of tb nice guidance on resource capacity and contact screening outcomes: a retrospective, observational study within a central london tb centre

Introduction and objectives: Recently published NICE guidance has significantly expanded the approach to adult tuberculosis (TB) contact screening by recommending tuberculin skin testing (TST) for pulmonary and laryngeal contacts only, increasing the age threshold for screening and treatment to 65 years and defining a positive TST as induration ≥5 mm, regardless of BCG vaccination status. Interferon Gamma Release Assay (IGRA) is recommended only in situations where more evidence of infection is needed. Our institution has previously adopted an approach comprising a chest radiograph, TST and IGRA. The aim of our study was to evaluate the impact of NICE guidance on screening outcomes and resource capacity by applying the criteria to a well-defined historic cohort of TB contacts. Methods: This was a retrospective, observational study carried out at a central London teaching hospital. The study population comprised 593 consecutive, adult TB contacts screened between 1/1/2008 and 31/12/2010. Data was collected through a retrospective review of TST and IGRA tests. Results: Of the 593 contacts screened, 358 pulmonary contacts had TST and IGRA results. 56% had a TST ≥5 mm, regardless of BCG status, qualifying them for treatment as per the new NICE guidance. Of these, 61% were IGRA negative (discordant) and may therefore include false positive diagnoses, resulting in the potential for over treatment. In those with TST 5–14 mm, discordance rises to 84%. Conversely, 6% of those with TST < 5 mm are IGRA positive representing potentially missed cases. 16% of screened individuals were contacts of extra pulmonary TB. Not screening this group would reduce the demand for outpatient appointments by 151* in our cohort. In contrast, testing contacts > 35 years would require capacity for an additional 165* appointments. Furthermore, there were 162 additional LTBI cases in comparison to previous guidance requiring an additional 648* appointments. 72% of this group were IGRA negative. (*Approximate) Conclusions: Our results show the revised guidance will require increased resource capacity largely due to more patients being classified as having latent TB. In addition to workforce planning to meet these demands, further debate is needed to decide if this new approach truly reduces the incidence of active TB or results in unnecessary treatment