Micromechanics of cyclic deformation in SSME turbopump blade materials

Current and candidate Space Shuttle Main Engine (SSME) turbopump blade materials are anisotropic, both in their elastic and plastic response. The major objective is to characterize the plastic deformation behavior of a typical single crystal nickel-base superalloy, PWA 1480, and to use this information to help guide the development of anisotropic constitutive models

Techniques for improving reliability of computers

Modular design techniques improve methods of error detection, diagnosis, and recovery. Theoretical computer (MARCS (Modular Architecture for Reliable Computer Systems)) study deals with postulated and modeled technology indigenous to 1975-1980. Study developments are discussed

Deformation modeling and constitutive modeling for anisotropic superalloys

A study of deformation mechanisms in the single crystal superalloy PWA 1480 was conducted. Monotonic and cyclic tests were conducted from 20 to 1093 C. Both (001) and near-(123) crystals were tested, at strain rates of 0.5 and 50 percent/minute. The deformation behavior could be grouped into two temperature regimes: low temperatures, below 760 C; and high temperatures, above 820 to 950 C depending on the strain rate. At low temperatures, the mechanical behavior was very anisotropic. An orientation dependent CRSS, a tension-compression asymmetry, and anisotropic strain hardening were all observed. The material was deformed by planar octahedral slip. The anisotropic properties were correlated with the ease of cube cross-slip, as well as the number of active slip systems. At high temperatures, the material was isotropic, and deformed by homogeneous gamma by-pass. It was found that the temperature dependence of the formation of superlattice-intrinsic stacking faults was responsible for the local minimum in the CRSS of this alloy at 400 C. It was proposed that the cube cross-slip process must be reversible. This was used to explain the reversible tension-compression asymmetry, and was used to study models of cross-slip. As a result, the cross-slip model proposed by Paidar, Pope and Vitek was found to be consistent with the proposed slip reversibility. The results were related to anisotropic viscoplastic constitutive models. The model proposed by Walter and Jordan was found to be capable of modeling all aspects of the material anisotropy. Temperature and strain rate boundaries for the model were proposed, and guidelines for numerical experiments were proposed

Deformation and fatigue behavior of SSME turbopump blade materials

Directionally solidified and single crystal superalloys which are intended for use as turbopump blade materials are anisotropic both elastically and plastically. Therefore, isotropic constitutive models must be modified. Several models which are now being developed are based on metallurgical theories of deformation in these types of alloys. However, these theories have not been fully justified, and the temperature and strain regimes over which they may be valid are poorly defined. The objective of this work is to study the deformation behavior of the alloys, in order to determine the validity of these models and to thereby support the ongoing research efforts in solid mechanics

Fe XI emission lines in a high resolution extreme ultraviolet spectrum obtained by SERTS

New calculations of radiative rates and electron impact excitation cross sections for Fe XI are used to derive emission line intensity ratios involving 3s^23p^4 - 3s^23p^33d transitions in the 180-223 A wavelength range. These ratios are subsequently compared with observations of a solar active region, obtained during the 1995 flight Solar EUV Research Telescope and Spectrograph (SERTS). The version of SERTS flown in 1995 incorporated a multilayer grating that enhanced the instrumental sensitivity for features in the 170 - 225 A wavelength range, observed in second-order between 340 and 450 A. This enhancement led to the detection of many emission lines not seen on previous SERTS flights, which were measured with the highest spectral resolution (0.03 A) ever achieved for spatially resolved active region spectra in this wavelength range. However, even at this high spectral resolution, several of the Fe XI lines are found to be blended, although the sources of the blends are identified in the majority of cases. The most useful Fe XI electron density diagnostic line intensity ratio is I(184.80 A)/I(188.21 A). This ratio involves lines close in wavelength and free from blends, and which varies by a factor of 11.7 between N_e = 10^9 and 10^11 cm^-3, yet shows little temperature sensitivity. An unknown line in the SERTS spectrum at 189.00 A is found to be due to Fe XI, the first time (to our knowledge) this feature has been identified in the solar spectrum. Similarly, there are new identifications of the Fe XI 192.88, 198.56 and 202.42 A features, although the latter two are blended with S VIII/Fe XII and Fe XIII, respectively.Comment: 21 pages, 9 gigures, accepted for publication in the Astrophysical Journa

Pleiotropic effects of Syntaxin16 identified by gene editing in cultured adipocytes

Adipocytes play multiple roles in the regulation of glucose metabolism which rely on the regulation of membrane traffic. These include secretion of adipokines and serving as an energy store. Central to their energy storing function is the ability to increase glucose uptake in response to insulin, mediated through translocation of the facilitative glucose transporter GLUT4 to the cell surface. The trans-Golgi reticulum localized SNARE protein syntaxin 16 (Sx16) has been identified as a key component of the secretory pathway required for insulin-regulated trafficking of GLUT4. We used CRISPR/Cas9 technology to generate 3T3-L1 adipocytes lacking Sx16 to understand the role of the secretory pathway on adipocyte function. GLUT4 mRNA and protein levels were reduced in Sx16 knockout adipocytes and insulin stimulated GLUT4 translocation to the cell surface was reduced. Strikingly, neither basal nor insulin-stimulated glucose transport were affected. By contrast, GLUT1 levels were upregulated in Sx16 knockout cells. Levels of sortilin and insulin regulated aminopeptidase were also increased in Sx16 knockout adipocytes which may indicate an upregulation of an alternative GLUT4 sorting pathway as a compensatory mechanism for the loss of Sx16. In response to chronic insulin stimulation, Sx16 knockout adipocytes exhibit elevated insulin-independent glucose transport and significant alterations in lactate metabolism. We further show that the adipokine secretory pathways are impaired in Sx16 knockout cells. Together this demonstrates a role for Sx16 in the control of glucose transport, the response to elevated insulin, cellular metabolic profiles and adipocytokine secretion. [Abstract copyright: Copyright © 2022 Bremner, Al Shammari, Milligan, Hudson, Sutherland, Bryant and Gould.

Multi-label classification using ensembles of pruned sets

This paper presents a Pruned Sets method (PS) for multi-label classification. It is centred on the concept of treating sets of labels as single labels. This allows the classification process to inherently take into account correlations between labels. By pruning these sets, PS focuses only on the most important correlations, which reduces complexity and improves accuracy. By combining pruned sets in an ensemble scheme (EPS), new label sets can be formed to adapt to irregular or complex data. The results from experimental evaluation on a variety of multi-label datasets show that [E]PS can achieve better performance and train much faster than other multi-label methods

Profiling of transcriptional and epigenetic changes during directed endothelial differentiation of human embryonic stem cells identifies FOXA2 as a marker of early mesoderm commitment

Introduction: Differentiation of vascular endothelial cells (ECs) in clinically relevant numbers for injection into ischaemic areas could offer therapeutic potential in the treatment of cardiovascular conditions, including myocardial infarction, peripheral vascular disease and stroke. While we and others have demonstrated successful generation of functional endothelial-like cells from human embryonic stem cells (hESCs), little is understood regarding the complex transcriptional and epigenetic changes that occur during differentiation, in particular during early commitment to a mesodermal lineage. Methods: We performed the first gene expression microarray study of hESCs undergoing directed differentiation to ECs using a monolayer-based, feeder-free and serum-free protocol. Microarray results were confirmed by quantitative RT-PCR and immunocytochemistry, and chromatin immunoprecipitation (ChIP)-PCR analysis was utilised to determine the bivalent status of differentially expressed genes. Results: We identified 22 transcription factors specific to early mesoderm commitment. Among these factors, FOXA2 was observed to be the most significantly differentially expressed at the hESC–EC day 2 timepoint. ChIP-PCR analysis revealed that the FOXA2 transcription start site is bivalently marked with histone modifications for both gene activation (H3K4me3) and repression (H3K27me3) in hESCs, suggesting the transcription factor may be a key regulator of hESC differentiation. Conclusion: This enhanced knowledge of the lineage commitment process will help improve the design of directed differentiation protocols, increasing the yield of endothelial-like cells for regenerative medicine therapies in cardiovascular disease