MIT's interferometer CST testbed

The MIT Space Engineering Research Center (SERC) has developed a controlled structures technology (CST) testbed based on one design for a space-based optical interferometer. The role of the testbed is to provide a versatile platform for experimental investigation and discovery of CST approaches. In particular, it will serve as the focus for experimental verification of CSI methodologies and control strategies at SERC. The testbed program has an emphasis on experimental CST--incorporating a broad suite of actuators and sensors, active struts, system identification, passive damping, active mirror mounts, and precision component characterization. The SERC testbed represents a one-tenth scaled version of an optical interferometer concept based on an inherently rigid tetrahedral configuration with collecting apertures on one face. The testbed consists of six 3.5 meter long truss legs joined at four vertices and is suspended with attachment points at three vertices. Each aluminum leg has a 0.2 m by 0.2 m by 0.25 m triangular cross-section. The structure has a first flexible mode at 31 Hz and has over 50 global modes below 200 Hz. The stiff tetrahedral design differs from similar testbeds (such as the JPL Phase B) in that the structural topology is closed. The tetrahedral design minimizes structural deflections at the vertices (site of optical components for maximum baseline) resulting in reduced stroke requirements for isolation and pointing of optics. Typical total light path length stability goals are on the order of lambda/20, with a wavelength of light, lambda, of roughly 500 nanometers. It is expected that active structural control will be necessary to achieve this goal in the presence of disturbances

Alternative Finance Strategies for Small Business Sustainability and Growth

Many small business leaders lack alternative financing strategies to sustain and grow their businesses. Small business leaders are concerned with accessing financial capital to ensure sustainability. Grounded in Donaldson’s pecking order theory (POT), the purpose of this qualitative multiple case study was to explore alternative finance strategies some small business leaders use to sustain and grow their businesses. Participants comprised five small business leaders in Oakland, California, with successful experiences using alternative financing strategies to raise financial capital for their businesses. Data were collected from semistructured interviews, archival organizational documentation, and physical artifacts. Yin’s 5-step analysis process guided the data analysis. The following themes emerged: financing strategies of small business leaders, modification strategies used to improve financial effectiveness, strategies for overcoming financial constraints, and strategies to minimize the effects of the COVID-19 health crisis on small business sustainability. A key recommendation is for small business leaders to maintain accurate financial records to monitor the performance of their businesses. By improving their record-keeping systems, small business leaders may reduce costly consequences and promote financial sustainability. Implications for positive social change include the potential for business leaders to increase their ability to implement alternative finance strategies to generate revenues. Higher revenues may lead to more economic growth that entrepreneurs could use to create jobs in their local communities

Ramsey numbers of cycles versus general graphs

The Ramsey number $R(F,H)$ is the minimum number $N$ such that any $N$-vertex graph either contains a copy of $F$ or its complement contains $H$. Burr in 1981 proved a pleasingly general result that for any graph $H$, provided $n$ is sufficiently large, a natural lower bound construction gives the correct Ramsey number involving cycles: $R(C_n,H)=(n-1)(\chi(H)-1)+\sigma(H)$, where $\sigma(H)$ is the minimum possible size of a colour class in a $\chi(H)$-colouring of $H$. Allen, Brightwell and Skokan conjectured that the same should be true already when $n\geq |H|\chi(H)$. We improve this 40-year-old result of Burr by giving quantitative bounds of the form $n\geq C|H|\log^4\chi(H)$, which is optimal up to the logarithmic factor. In particular, this proves a strengthening of the Allen-Brightwell-Skokan conjecture for all graphs $H$ with large chromatic number.Comment: 20 pages, 3 figures. Final version to appear in Forum of Mathematics, Sigm

The norovirus NS3 protein is a dynamic lipid- and microtubule-associated protein involved in viral RNA replication

Norovirus (NoV) infections are a significant health burden to society, yet the lack of reliable tissue culture systems has hampered the development of appropriate antiviral therapies. Here we show that the NoV NS3 protein, derived from murine NoV (MNV), is intimately associated with the MNV replication complex and the viral replication intermediate double-stranded RNA (dsRNA). We observed that when expressed individually, MNV NS3 and NS3 encoded by human Norwalk virus (NV) induced the formation of distinct vesicle-like structures that did not colocalize with any particular protein markers to cellular organelles but localized to cellular membranes, in particular those with a high cholesterol content. Both proteins also showed some degree of colocalization with the cytoskeleton marker β-tubulin. Although the distribution of MNV and NV NS3s were similar, NV NS3 displayed a higher level of colocalization with the Golgi apparatus and the endoplasmic reticulum (ER). However, we observed that although both proteins colocalized in membranes counterstained with filipin, an indicator of cholesterol content, MNV NS3 displayed a greater association with flotillin and stomatin, proteins known to associate with sphingolipid- and cholesterol-rich microdomains. Utilizing time-lapse epifluorescence microscopy, we observed that the membrane-derived vesicular structures induced by MNV NS3 were highly motile and dynamic in nature, and their movement was dependent on intact microtubules. These results begin to interrogate the functions of NoV proteins during virus replication and highlight the conserved properties of the NoV NS3 proteins among the seven Norovirus genogroups

Effect of large deformation on creep property evaluation by small-specimen bending tests

For small-specimen bending creep tests, large deformation occurs inevitably when the specimen under a large load or a long creep time. In such a circumstance, the conventional method for creep property evaluation, which is based on the small deformation assumption, may fail to attain a sufficiently high accuracy. Three typical specimens including circular ring, three-point bending and cantilever-beam specimens, are therefore examined. Based on the limit load approach, a critical load method is proposed to control the large deformation effect. Analytical solutions of the critical loads of the specimens are derived. Finite element method is used to quantitatively assess the effect of large deformation. The results show that the predicted creep curves of all the three specimens are significantly affected by the large deformation. Creep properties can only be accurately regressed when the applied load is below the critical load. The critical loads calculated by finite element method agree well with the analytical solutions. Furthermore, the analytical solutions are validated by the experimental results. The effect of creep time on the critical load has also been discussed

Application of small punch creep testing to a thermally sprayed CoNiCrAlY bond coat

High velocity oxy-fuel thermal spraying was used to prepare free-standing CoNiCrAlY (Co–31.7% Ni–20.8% Cr–8.1% Al–0.5% Y (wt%)) bond coat alloy samples approximately 0.5 mm thick. Creep tests were conducted at 750 °C on these samples using a small punch (SP) creep test method. The samples were characterised before and after creep testing using scanning electron microscopy with electron backscatter diffraction (EBSD). EBSD revealed a two phase fcc γ-Ni and bcc B2 β-NiAl microstructure with grain sizes ~1–2 μm for both phases, which did not change significantly following testing. The constant temperature SP test data were characterised by a minimum creep strain rate, View the MathML source, and a total time to failure, tf, at different applied stresses. The data are fitted to conventional power law equations with a stress exponent for creep close to 8 in the Norton power law and between 7 and 10 in the Monkman–Grant creep rupture law. Creep rupture was predominantly due to creep cavitation voids nucleating at both the γ–β interphase boundaries and the γ–γ grain boundaries leading to final failure by void linkage. However, rupture life was influenced by the quantity of oxide entrained in the coating during the spray deposition process

Biogeochemical and Optical Analysis of Coastal DOM for Satellite Retrieval of Terrigenous DOM in the U.S. Middle Atlantic Bight

Estuaries and coastal ocean waters experience a high degree of variability in the composition and concentration of particulate and dissolved organic matter (DOM) as a consequence of riverine/estuarine fluxes of terrigenous DOM, sediments, detritus and nutrients into coastal waters and associated phytoplankton blooms. Our approach integrates biogeochemical measurements (elemental content, molecular analyses), optical properties (absorption) and remote sensing to examine terrestrial DOM contributions into the U.S. Middle Atlantic Bight (MAB). We measured lignin phenol composition, DOC and CDOM absorption within the Chesapeake and Delaware Bay mouths, plumes and adjacent coastal ocean waters to derive empirical relationships between CDOM and biogeochemical measurements for satellite remote sensing application. Lignin ranged from 0.03 to 6.6 ug/L between estuarine and outer shelf waters. Our results demonstrate that satellite-derived CDOM is useful as a tracer of terrigenous DOM in the coastal ocea

Outcomes of elective head and neck confirmed or suspected cancer surgery during the COVID-19 pandemic.

PURPOSE: To analyse the complication outcomes of COVID-19 negative patients undergoing elective head and neck surgery during the COVID-19 pandemic. METHODS: This was a retrospective case review of all patients undergoing elective head and neck surgery for confirmed or suspected head and neck cancer. RESULTS: There were no mortalities recorded in the cohort of patients analysed. At 30 days, pulmonary complications had occurred in 4 patients (9%). None of these were related to COVID infection. CONCLUSION: With careful pre-operative screening of patients for COVID-19 and post-operative care in a COVID-19 clean ward, head and neck surgery can proceed safely during the epidemic. This data could help to minimise delay in treatment by allowing a greater number of elective head and neck cancer operations to proceed

Modelling of a Grade 91 power plant pressurised header weldment under ultra super-critical creep conditions

This paper is concerned with the creep-damage modelling of a Grade 91 pressurised header, which was observed to undergo in-service cracking in the weldments. A multi-axial creep damage model of Kachanov type, with a single state damage variable, has been implemented into finite element analysis to study the creep damage responses of weldments and the sub-zones i.e. the base metal (BM), weld metal (WM) and heat-affected zone (HAZ). Material properties for each weld constituent were obtained from the results of accelerated creep tests on materials extracted from the header. Predictions of crack initiation were made for sections of the stub to header welds. This analysis was also used to estimate creep failure life of the header weldment under ultra-super-critical conditions. Further, creep crack growth behaviour was predicted based on time-dependent critical damage growth. The predicted damage distributions and failure mode of the cross-weld creep test specimens were in good agreement with the reported experimental observations. The predicted damage distributions and cracking in the header correlate reasonably well with the reported industrial observations