2,181 research outputs found
Harry\u27s Poetry Hour: Interview with Tony Barnstone & Mary Fitzpatrick
No full textTony Barnstone and Mary Fitzpatrick, both making their first appearances on Harry\u27s Poetry Hour, join Harry to read and discuss their poetry. Recorded Live September 27, 2022 Harry\u27s Poetry Hour is produced and Hosted by Harry E. Northup and is recorded weekly as a part of MPTF Studios\u27 Creative Chaos, a live broadcast of information and entertainment that was created to fight social isolation on the Wasserman Campus of the Motion Picture & Television Fund in the early days of the COVID-19 pandemic. Director & Executive Producer Jennifer Clymer MPTF Studios’ Creative Chaos Crew & Staff: Jennifer Esquivel, Michael Caiozzo, Kak Lee, Allegra Leedom, Jeff Mercer, Marijane Miller, Marcus Murrietta, Jody Schoffner, Joel Schroeder, Nikki Taylor, & Paige Thompson
Non 3-choosable bipartite graphs and the Fano plane
No full textIt is known that the smallest complete bipartite graph which is not 3-choosable has 14 vertices. We show that the extremal configuration is unique.PT: J; CR: BROWN E, 2002, MATH MAG, V75, P83 ERDOS P, 1979, CONGRESSUS NUMERANTI, V26, P155 FITZPATRICK SL, DMS854IR U VICT DEP HAUSON D, 1996, ARS COMBINATORIA, V44, P183 VIZING VG, 1976, DISKRET ANAL, V29, P3 WOODALL DR, 2001, LONDON MATH SOC LECT, V288, P269; NR: 6; TC: 0; J9: ARS COMB; PG: 15; GA: 948CQSource type: Electronic(1
Blown-powder direct-energy-deposition of titanium-diboride-strengthened IN718 Ni-base superalloy
Get PDFThis paper reports on the adoption of TiB2 as an inoculant to fabricate IN718 via the direct energy deposition (DED) process. Effective grain refinement and low texture were achieved in IN718/TiB2 using a TiB2 powder size of d90 = 10 μm and mass fraction of 1.5 wt%. The use of low linear energy density (33.08 J/mm) produced IN718/TiB2 deposits free from large grains (>300 μm), however at the cost of the formation of interlayer defects. By comparison, the large grains were present in deposits made with a linear energy density of 78.74 J/mm and also in deposits manufactured without an included inoculant. Production of deposits at lower energies without interlayer defects was possible by reducing the powder flow rate to 7 g/min. However, this caused a moderate increase in grain size. The TiB2 inoculant reduced the Laves phase network by replacing it with homogeneously distributed Cr-, Mo-, Nb-, and B-enriched needle-shaped precipitates. Tensile strength increased by 300–500 MPa with TiB2 addition, but at the cost of significant ductility drop, regardless of the deposition conditions. The IN718 deposit displayed many micro-cracks at the network of Laves phase during tensile loading, whereas micro-cracks in the IN718/TiB2 occurred at the interface between the needle-shaped precipitates and the matrix. The strength enhancement in IN718/TiB2 was by a combination of strengthening mechanisms: grain boundary, dislocation structure formation, Orowan-type and load transfer related to the needle-shaped precipitates.</p
Additive manufacturing-based repair of IN718 superalloy and high-cycle fatigue assessment of the joint
Get PDFRoom-temperature high-cycle fatigue (HCF) of IN718 repaired joint via laser direct energy deposition (DED) were studied with the fatigue axis perpendicular to the joint interface. Solution treated and aged (STA) were compared with directly aged (DA) conditions. The wrought IN718 substrate showed equiaxed grains with a size of ∼90 µm and a high fraction of annealing twins, whereas the DED deposit revealed a mixture of equiaxed and columnar grains with an average size of ∼20 µm. There was little difference between the STA and DA conditions in the grain length-scale. Micro-hardness results highlighted the need for the heat treatment as it can remove the heat-affected zone and hardness dip, creating a uniform hardness profile across the joint. Although the monolithic DED deposit had a similar tensile strength to the wrought substrate, the DED joint exhibited an overall decreased HCF performance, regardless of the heat treatment conditions. When the fatigue stress was low, the STA condition had a better HCF performance than the DA, however, the opposite trend appeared for the high stress, resulting in a cross-over point on the stress-life S-N plot. Interrupted fatigue tests, combined with microscopy and fractography, revealed that the fatigue failure occurred in the substrate for the DED joint in the DA condition, whilst in the deposit zone for the STA condition due to the distribution and fracture of the Laves and δ phases. Grain boundary cracking in the substrate near the substrate-to-deposit interface can occur in both cases, probably due to the Nb-rich liquid films.</p
Fatigue crack propagation in 15-5PH/316L bi-material steels fabricated by laser powder bed fusion
Get PDFMulti-material laser powder bed fusion (MM-LPBF) offers the possibility of components with material and compositional complexity, as well as the geometric complexity for which additive manufacturing is known. LPBF materials are susceptible to fatigue failures due to stress concentrating roughness and porosity defects. Understanding fatigue failure processes is therefore important to enable adoption of multi-material parts, and suitable combinations of materials may offer a strategy to enhance fatigue performance by resisting crack propagation. This study focused on fatigue crack propagation in 316L/15-5 precipitation hardened (PH) bi-material stainless steels (SS), and the effect of residual stress distribution and yield stress gradient on fatigue crack propagation through the interface. The expected yield stress gradient effect in bi-materials (soft to hard interface) was simulated using FE models, showing a slight shielding effect with a drop in J-integral value. Contour cutting measurements detected a residual stress distribution near the bi-material interface that was tensile in 316L layer and compressive in 15-5PH layer. Fatigue crack propagation rates in bi-materials deviated from those in the corresponding single-material specimens. A relatively small shielding effect due to the yield stress gradient was detected within a short distance of the crack tip from the interface. However, the effects of residual stress were more pronounced and inhibited the crack growth rate by up to 77.8 % in regions of 15-5PH SS under residual compression, which suggesting that MM-LPBF parts can be designed such that the compressive residual stress is positioned to intercept and suppress propagating cracks to improve damage tolerance
Probing the influence of steric bulk on anion binding by triarylboranes: comparative studies of FcB(o-Tol)2, FcB(o-Xyl)2 and FcBMes2.
No full textSteric crowding brought about on pyramidalization at boron has been predicted computationally to be of central importance to the strength and selectivity of anion binding by triarylboranes. The role of steric factors in systems containing a ferrocenyl reporter unit has been systematically probed in the current study by comparison of the F(-)/CN(-) binding properties of FcB(o-Tol)(2) (1, o-Tol = C(6)H(4)Me-2), FcB(o-Xyl)(2) (2, o-Xyl = C(6)H(3)Me(2)-2,6) and FcBMes(2) (3, Mes = C(6)H(2)Me(3)-2,4,6)), both in solution and in the solid state. Somewhat surprisingly, the inclusion of an extra ortho-methyl aryl substituent (e.g. for 2/3vs.1) is found to have a relatively small effect on the binding affinities of these boranes (e.g. log(10)K(CN) = 5.94(0.02), 4.73(0.01), 5.56(0.02), for 1, 2 and 3 respectively). Consistent with this observation, the degree of pyramidalization at boron determined for the cyanide adducts [1·CN](-), [2·CN](-) and [3·CN](-) in the solid state is also found to be essentially invariant (∠C(aryl)-B-C(aryl) = 338, 337, 337°, respectively), as are the B-CN and mean B-C(aryl) distances. In the solid state at least, it is apparent that the adverse steric effects potentially brought about by increasing ortho substitution are mitigated by a greater degree of synchronous rotation of the aryl substituents about the B-C(aryl) bonds. Thus a mean inter-plane angle of 71° is observed for [1·CN](-) while the corresponding values for [2·CN](-) and [3·CN](-) are 78° and 79°
Fatigue crack initiation and growth behavior within varying notch geometries in the low-cycle fatigue regime for FV566 turbine blade material
No full textPlain bend bars made from FV566 martensitic stainless steel were extracted from the root of ex-service power plant turbine blades and several industry-relevant notch geometries were introduced. Some of the samples were shot peened. The notched bend bars were loaded plastically in the low-cycle fatigue regime and finite element (FE) modeling carried out to investigate the effects of changing notch geometry, combined with shot peening, on fatigue behaviors such as crack initiation, short crack growth, and coalescence. Shot peening damaged the notch surface, accelerating initiation behaviors, but had a lifetime-extending effect by retarding short crack growth in all tested notch geometries. At a total strain range higher than 1.2%, the lifetime extension benefit from shot peening was diminished due to compressive residual stress relaxation in the notch stress field. Notch geometry (and the associated varying constraint levels and stress/strain gradients) was found to have no notable difference on fatigue life when tested at identical notch-root strain ranges.</p
Canyons, deltas and plains: towards a unified sculptural model of location-based hypertext
No full textWith the growing ubiquity of mobile devices, new ways of sensing context and the emergence of the mobile Web, digital storytelling is escaping the confines of the desktop and intertwinging in new and interesting ways with the physical world. Mobile, location aware, narrative systems are being applied to a range of areas including tour guides, educational tools and interactive fiction. Despite this there is little understanding of how these applications are related or how they link with existing hypertext models and theory.We argue that location aware narrative systems tend to follow three patterns (canyons, deltas and plains) and that it is possible to represent all of these patterns in a conceptual sculptural hypertext model. Our model builds on a general sculptural mechansim (of pre-conditions and behaviours) to include locality and narrative transitions as first class elements, opening the possibility of standardised viewers, formats, and hybrid stories. We show how existing structures can be mapped onto this conceptual sculptural model, and how narratives defined in the model can take advantage of open data sources and sensed contextual data. To demonstrate this we present the GeoYarn system, a prototype which implements the model to create interactive, location aware narratives, using all three patterns
Male-female relatedness and patterns of male reproductive investment in guppies
No full textInbreeding can cause reductions in fitness, driving the evolution of pre- and postcopulatory inbreeding avoidance mechanisms. There is now considerable evidence for such processes in females, but fewstudies have focused on males, particularly in the context of postcopulatory inbreeding avoidance. Here, we address this topic by exposing male guppies (Poecilia reticulata) to either full-sibling or unrelated females and determining whether they adjust investment in courtship and ejaculates. Our results revealed that males reduce their courtship but concomitantly exhibit short-term increases in ejaculate quality when paired with siblings. In conjunction with prior work reporting cryptic female preferences for unrelated sperm, our present findings reveal possible sexually antagonistic counter-adaptations that may offset postcopulatory inbreeding avoidance by females. © 2014 The Author(s)
Effect of postprocessing thermal treatments on electron- beam powder bed–fused Ti6Al4V
No full textElectron-beam powder-bed-fusion additive manufacturing was used to build Ti6Al4V blocks. Postfabrication thermal treatments were applied to modify the mechanical properties. The postfabrication treatments included hot isostatic pressing and solution treatment and ageing. The microstructure and mechani- cal properties of the as-built and postthermally treated material were characterised. The postfabrication treatments were found to be effective in homogenising the microstructure and reducing the number of defects/pores, which improved the material Charpy impact toughness and fatigue life with some reduction in the material's strength. Based on the present results, as well as data from previous literature studies, the reduction in material strength after the postthermal treatment is likely to be caused by the combined effect of α-lath coarsening and the low oxygen content of the powder feedstock
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