Shear Form (United States)

Abstract Temperature reshapes organismal performance and species interactions, yet competition models rarely treat the declining warm side of thermal performance curves explicitly, even though that regime is likely to become increasingly important under climate warming. We develop a density-dependent generalized Lotka–Volterra framework for pairwise exploitative competition in which effective competition coefficients depend on relative temperature-dependent consumption, and we analyse coexistence using the structural feasibility domain. Within this model class, one result is robust: pairwise structural coexistence is maximized when competitors have equal effective consumption, so with symmetric overlap the temperature of maximal coexistence is the temperature at which their consumption thermal performance curves intersect. Stronger ecological predictions are parameter dependent. In particular, whether coexistence declines more steeply under warming than under cooling, and whether the coexistence maximum for species with different thermal optima is shifted toward the lower optimum, depend on thermal-curve shape, relative peak heights, baseline competition, resource overlap, and any temperature dependence in carrying capacities. For the illustrative asymmetric unimodal curves analysed here, shared optima produce maximal coexistence near the optimum and a steeper decline under warming than under cooling, whereas different optima produce an intermediate coexistence peak biased toward the lower optimum. A qualitative comparison with classic Drosophila pairwise competition experiments at 19°C and 25°C is consistent with these expectations. Because the empirical comparison relies on broad thermal categories, unequal species groups, and binary pairwise outcomes, it should be interpreted as a proof of concept rather than a definitive quantitative test. More generally, our results clarify which aspects of temperature-dependent pairwise coexistence are robust consequences of thermal asymmetry and which are contingent on parameterization.

Metallic composites that remain stiff and retain their shape even though their majority phase is liquid are presented. Using X‐ray computed tomography, it is demonstrated that the solid minority phase forms a system‐spanning, load‐bearing skeleton: a behavior commonly observed in gels. Therefore, these novel composites are called “metallic gels.” To demonstrate their potential utility in liquid metal batteries (LMBs), galvanic cells are assembled with majority calcium (Ca) and bismuth (Bi) composite electrodes and iron (Fe) as the minority phase. At the operating temperature of these cells the majority phase is liquid, while the iron is solid. Conventional LMBs rely on gravitational segregation and low mutual solubility to maintain the arrangement of their electrodes and electrolyte. As a result, they cannot be reoriented, since that may cause layers to mix and short circuit. Unlike conventional LMBs, the cells can operate in a horizontal orientation without forming short circuits. Thus, metallic gel electrodes may circumvent the limitations of all‐liquid cells while retaining many of their benefits.

Tantalum (Ta) diffusion barriers used in Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn superconductors deform nonuniformly during wire drawing. A strategy sometimes used to mitigate this problem is to place a sacrificial layer of niobium (Nb) next to the Ta to act as a mechanical transition zone between the softer Cu-Nb composite and the harder Ta. This approach can promote more uniform co-deformation of the Ta layer enabling thinner Ta layers and a reduced chance of layer rupture, and has the added benefit of providing additional Nb for conversion to Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn. A thinner Ta layer translates to less Ta volume and less cost. In the current work the authors find that a layer of Nb adjacent to a Ta layer embedded in Cu significantly increases the composite wire strain to fracture, and appears to decrease the Ta layer interface roughness.

The mechanical properties of commercial polycrystalline pure niobium sheet used for superconducting radiofrequency cavities are known to provide inconsistent yield, springback and surface smoothness characteristics when plastically formed into a radiofrequency cavity. These inconsistent properties lead to significant variations in cavity geometry and thus superconducting cavity performance. One approach to reduce these problems is to refine the microstructure so that its properties are more uniform. Microstructural refinement of Nb sheet for RF cavities using multi-axis severe plastic deformation via equal channel angular extrusion (ECAE) was examined. ECAE was performed on 25 mm square cross-section bars of Reactor Grade Nb in a right angle die at room temperature following different extrusion routes to true strains above nine. This heavily worked material was rolled to 4 mm thick sheet and recrystallized. Measurements of hardness, springback, texture, and microstructural uniformity are reported and compared to those of commercial RRR Grade Nb sheet. Preliminary results show noteworthy promise for bulk Nb processed via severe plastic deformation prior to sheet rolling.

PurposeTo provide guidance to investment companies on document retention policies based on Section 802 of the Sarbanes‐Oxley Act of 2002, codified as Section 1519 of the United States Code.Design/methodology/approachReviews the conviction of Arthur Andersen for obstruction of justice based on the way the firm implemented its document retention/destruction policy as Enron was collapsing, and the Supreme Court reversal of that conviction. Explains why the Supreme Court decision should no longer guide an investment company's document retention/destruction policy in light of more recently enacted Section 1519, which imposes stiff penalties on anyone who knowingly alters, destroys, mutilates, conceals, or covers up any record or document with the intent to impede, obstruct, or influence any federal investigation, or in contemplation of such a proceeding.FindingsSuggests a few straightforward rules for an investment company's document retention/destruction policy with a warning to err on the side of caution.Originality/valueIn light of Section 1519, every investment company needs to review its document retention/destruction policy. This article provides useful guidelines for doing so.