Whitney Museum of American Art

Single crystal (SX) nickel-based superalloys represent a critical advancement in the aerospace industry, enabling the manufacture of turbine airfoils capable of withstanding the extreme conditions of modern high-pressure turbine engines. Due to the elimination of grain boundaries, SX airfoils exhibit superior high-temperature properties compared to their polycrystalline counterparts. Consequently, the onset of recrystallization (RX) constitutes the introduction of high angle grain boundaries (HAGBs) into the single crystal lattice, compromising the fatigue and creep performance of the airfoil under operational conditions. RX in SX nickel-based superalloys is primarily driven by the stresses introduced during the investment casting manufacturing process. These stresses create localized regions of strain with associated stored energy within the material, which can trigger the nucleation of RX grains during subsequent solution heat treatment. However, the appearance of RX displays stochastic characteristics, the underlying causes of which are not fully understood. This uncertainty, coupled with the connection between geometry and residual strain evolution, constrains the complexity possible in the geometric features of the airfoil and internal cooling channel, and thus imposes an upper limit on the performance and efficiency gains possible in turbine blade design. Herein, the present review systematically examines the physical fundamentals of RX in SX nickel-based superalloys and provides a critical synthesis of the state of the art in nickel superalloy RX research. Focus is placed on the evolution of microstructure and defects during solidification and subsequent heat treatments, and the interplay between these factors and the spatial distribution of stored energy. From this investigation, the dominant factors affecting the driving force for RX are identified, and potential strategies to mitigate the presence of HAGBs in SX nickel-based superalloy turbine airfoils are proposed

Abstract Sandwich panels with truss cores (SPTCs) are widely used in crashworthiness and impact-related applications due to their light weight, high load-carrying capacity, and excellent energy dissipation performance. However, most existing design optimization methods for SPTCs are limited to size and shape optimization of the truss bars and often focus solely on linear elastic behavior. In this study, a topology optimization framework to design the core of SPTCs is proposed using the geometry projection method, aiming to maximize plastic energy absorption and minimize deflection under quasi-static loading, while constraining material usage. An elasto-plastic constitutive model is employed to capture the nonlinear material behavior, and an element removal strategy is used to avoid severe mesh distortion and ensure a robust analysis. Design sensitivities are computed using a finite difference scheme, leveraging the relatively low number of design variables describing the bars and circumventing the need for analytical derivatives. The proposed approach is demonstrated through numerical examples, with the optimized designs evaluated against conventional pyramidal truss-core panels. The results confirm the practical applicability and effectiveness of the method for designing protective structures.

Abstract The Wetland Reserve Easement (WRE/WRP) programs, administered by the United States Department of Agriculture, restore freshwater wetlands in agricultural areas to reestablish critical ecosystem functions. While these wetlands provide valuable services such as wildlife habitat and carbon sequestration, the potential loss of carbon through greenhouse gas emissions—specifically carbon dioxide (CO₂) and methane (CH₄)—has not been thoroughly evaluated. This study examined carbon cycling across ten seasonal wetland sites located on the Archbold Reserve and Buck Island Ranch, an operating cattle ranch in south-central Florida, both managed by the Archbold Biological Station. Sites had one of three treatment types: grazed-restored, ungrazed-restored, and grazed-unrestored (control). Over the course of the study, CO₂ and CH₄ fluxes were measured every two to three months using a LI-7810 LI-COR CO₂/CH₄/H₂O trace gas analyzer. Groundwater and surface water levels were monitored, and soil and plant samples were analyzed for total carbon, nitrogen, and phosphorus to assess nutrient storage. Results indicate that hydrology, water residence time, and grazing are key determinants of carbon storage and greenhouse gas emissions. Well-drained ephemeral wetlands primarily lost carbon through CO₂ emissions, while more poorly drained wetlands supported CH₄ production due to lower oxygen concentrations. Grazing was found to further increase soil methane emissions. Although wetlands remain effective carbon sinks overall, restoration and management strategies that consider hydrologic regime and inundation duration could enhance carbon capture and minimize seasonal greenhouse gas losses.

The oldest known pterosaurs lived approximately 220 million years ago1 and were already animals capable of powered flight,2 an ability that later evolved independently among paravian dinosaurs, the group that includes living birds and their closest non-avian relatives.3 Flight is a complex locomotory mode that requires physiological adaptations4 and a dramatic transformation of the body plan, including changes in body proportions, specialized integument, and acquisition of novel neurosensory capabilities.5 Although pterosaurs and birds developed distinct skeletal and integumentary adaptations for flight, they are hypothesized to share neuroanatomical traits linked to aerial locomotion.6,7,8,9 Here, we use geometric morphometrics and phylogenetically informed analyses to assess the origin and evolution of brain shape and size in pterosaurs, tracing the transformation from their non-volant closest relatives (lagerpetids), and compare their trajectory with that in the dinosaur-bird transition. Pterosaurs have globular brains with moderately enlarged hemispheres, more closely resembling non-avian paravians such as troodontids and Archaeopteryx lithographica than living birds. Whereas birds inherited their basic brain structure from their dinosaurian ancestors,10,11,12,13,14,15,16,17 pterosaurs share only the ventrolateralization of the optic lobe with their closest non-volant relatives, the lagerpetids. This suggests that, in contrast to the bird-line archosaurs, where exaptation may have played a central role in the stepwise assembly of the avian brain configuration, brain evolution in pterosaurs seems to have unfolded rapidly at the origin of flight.

Paleogeography of the Ediacaran Period has remained poorly understood because of paleomagnetic studies commonly yielding perplexing or conflicting data. Here, we report new magnetostratigraphic data from the Ediacaran Ouarzazate Group in the Anti-Atlas Mountains of Morocco, which have primary magnetizations supported by a positive conglomerate test and stratigraphically consistent directions within volcanic units across multiple localities. Comprehensive magnetostratigraphic sampling shows highly variable directions, consistent with a rapidly changing geomagnetic field along a longitudinally preferred band. High-precision geochronology constrains the geomagnetic variability to ~568 to 562 million years and suggests rates that are likely too rapid for true polar wander or plate tectonic interpretations. Comparison of igneous- and sedimentary-derived data, using a new statistical approach combining Bingham and Fisher distributions, indicates a high-inclination paleomagnetic direction that is compatible with independent evidence for regional glaciation. Our analysis produces a late Ediacaran paleogeographic reconstruction that is consistent with paleomagnetic and geologic constraints.

Elevated triglyceride levels have been associated with an elevated risk of cardiovascular disease, even when triglyceride levels are below common guidelines. This elevated risk of cardiovascular disease exists independent of total cholesterol or low-density lipoprotein cholesterol levels. Genetic analyses have demonstrated that elevated remnant lipoprotein, a product of triglyceride-rich lipoprotein, is a factor for coronary heart disease, indicating that the association between elevated triglyceride levels and elevated cardiovascular disease risk is causal rather than correlated. Despite this correlation between triglyceride levels and cardiovascular disease risk, treatments targeted at lowering triglyceride levels in patients receiving statin therapy, such as niacin or fibrates, have not demonstrated reduction in cardiovascular disease risk despite lowering triglyceride levels. In addition, omega-3 fatty acids containing a combination of docosahexaenoic acid plus eicosapentaenoic acid failed to demonstrate significant reductions in cardiovascular events in similar patients. Triglyceride-lowering therapies in development include monoclonal antibodies targeted against angiopoietin-like 3 (ANGPTL3); however, these newer ANGPTL3-targeted agents have not yet demonstrated a reduction in cardiovascular disease risk. In contrast, the landmark REDUCE-IT trial demonstrated significant cardiovascular protective effects for icosapent ethyl (IPE) in high cardiovascular risk patients with hypertriglyceridemia despite statin therapy. The protective effects of IPE may be due to unique mechanisms affecting the metabolism of E-series resolvins that may reduce atherosclerotic plaque. IPE also exhibits antiplatelet, antithrombotic, anti-inflammatory, and anti-oxidant effects, all of which contribute to an overall anti-atherosclerotic effect and an overall reduction in cardiovascular disease risk. As a result, treatment guidelines in the United States, China, and other countries recommend IPE for patients with hypertriglyceridemia that persists despite statin therapy.

Abstract A new deposition cooling facility was designed and constructed to examine the time-evolution of dust deposition and its effect on the cooling effectiveness of internal cooling circuits typical of gas turbine hot sections. The facility utilizes representative gas turbine engine cooling geometries and operates at relevant coolant and hot gas flow temperatures (650K and 1300K respectively). A combustion chamber is used to create a high speed (180m/s) 2cm diameter jet that impinges at a 26° angle (from the horizontal) onto a pre-oxidized flat plate made from a nickel-based alloy. The backside of this plate is cooled by an array of 0.5mm diameter impingement cooling jets with a 1.03 pressure ratio relative to the hot jet discharge pressure. An infrared camera is used to record the surface temperature of the flat plate as airborne dust is delivered through the cooling circuit. The dust delivered to the test article is 0–5micron Arizona Road Dust. Deposit evolution and cooling effectiveness trends were observed by performing successive tests with varying dust delivery period while maintaining constant dust loading (concentration). Observable patterns in the deposit behavior corroborate quantitative measurements of changes in local cooling effectiveness as measured by the IR camera. A limited test series at lower coolant and jet temperatures highlights the role of temperature in the deposition process.

Abstract This paper describes the aeromechanical aspects of multi-row forced response in embedded compressor rotors building upon previous research by the authors. Forced response in turbomachinery compressor is one of the grand challenge topics and has received a lot of attention in literature recently. The current paper fills a gap in literature by the authors. Previously, the multi-row analysis presented by the authors utilized the time transformation (TT) method within ANSYS CFX to reduce the number of passages in each row to a specific count. This enabled significant savings in computational resources but did not capture the rotor-rotor interaction accurately in computational space. The current paper fills that gap and models full wheel domains which indeed does capture the wave reflection, circumferential variation in pressure field, rotor-rotor interaction and its impact on mistuned forced response. The paper provides a new approach to analyzing and predicting forced response in turbomachinery which includes rotor-rotor interaction, and it provides a validation study by comparing simulations to experimental data. Mistuning in this paper is modeled from a random mistuning standpoint—because of frequency variations due to manufacturing. The computational results are validated with data from the Purdue 3.5stage compressor rig. The first part talks briefly about the unsteady CFD computational approach utilized to obtain the modal force values for each of the multirow cases. These modal forces were utilized to obtain the mistuned forced response predictions. The second part describes in detail the method used to quantify blade responses and goes onto account for a few discrepancies in the mistuned forced response predictions. The last part addresses the cause for these discrepancies and the authors conduct sensitivity studies to justify the anomaly. Some of the conclusions drawn from this study were 1) The rotor-rotor interaction was captured well by numerical methods and in-line with system identification data 2) The response was more localized at the -11ND computationally as against experimental data, which included significant responses at other ND’s although the -11ND content dominated. 3)Including the sidebands in the mistuning model from CFD predictions helped improve the mistuned blade response predictions significantly, in-line with data.

Encapsulating fibroblasts in alginate hydrogels is a promising strategy to promote wound healing. However, improving the cell function within the alginate matrix remains a challenge. In this study, we engineer an injectable hydrogel through mixing alginate function with collagen and fibronectin, creating a better microenvironment for enhancing fibroblast function and cytokine secretion. We systematically analyze microstructure, mechanical properties, and fibroblast behavior of the developed hydrogel and compare it to alginate control. Our results demonstrate that inclusion collagen and fibronectin lead to the formation of fibrils on macroporous structures with pore sizes ranging from 100 to 500 μm. Compared to collagen hydrogel, the composite hydrogel shows approximately 12-fold increase in storage modulus. After encapsulating fibroblasts into the modified hydrogels, we observed increased fibroblast spreading, proliferation, and cytokine secretion when compared to neat alginate hydrogel. In addition, VEGF secretion of encapsulated fibroblasts is upregulated, indicating its pro-angiogenic potential. These findings suggest that the alginate/collagen/fibronectin hydrogel-encapsulated fibroblasts might serve as a promising therapeutic approach for wound healing.