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"Snyder, Alexander"
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Ranking the world : grading states as a tool of global governance
\"Over the last decade international rankings have emerged as a critical tool used by international actors engaged in global governance. State practices and performance are now judged by a number of high profile indexes, including assessments of their levels of corruption, quality of democracy, creditworthiness, media freedom, and business environment. However, these rankings always carry value judgments, methodological choices, and implicit political agendas. This volume expertly addresses the important analytical, normative and policy issues associated with the contemporary practice of 'grading states'. The chapters explore how rankings affect our perceptions about state performance, how states react to being ranked, why some rankings exert more global influence than others, and how states have come to strategize and respond to these public judgments. It also critically examines how treating state rankings like popular consumer choice indexes may actually lead policymakers to internalize questionable normative assumptions and lead to poorer, not improved, public policy outcomes\"-- Provided by publisher.
Book
Polymer-derived SiOC reinforced with core–shell nanophase structure of ZrB2/ZrO2 for excellent and stable high-temperature microwave absorption (up to 900 °C)
Microwave absorbing materials for high-temperature harsh environments are highly desirable for aerodynamically heated parts and engine combustion induced hot spots of aircrafts. This study reports ceramic composites with excellent and stable high-temperature microwave absorption in air, which are made of polymer-derived SiOC reinforced with core–shell nanophase structure of ZrB
2
/ZrO
2
. The fabricated ceramic composites have a crystallized t-ZrO
2
interface between ZrB
2
and SiOC domains. The ceramic composites exhibit stable dielectric properties, which are relatively insensitive to temperature change from room temperature to 900 °C. The return loss exceeds − 10 dB, especially between 28 and 40 GHz, at the elevated temperatures. The stable high-temperature electromagnetic (EM) absorption properties are attributed to the stable dielectric and electrical properties induced by the core–shell nanophase structure of ZrB
2
/ZrO
2
. Crystallized t-ZrO
2
serve as nanoscale dielectric interfaces between ZrB
2
and SiOC, which are favorable for EM wave introduction for enhancing polarization loss and absorption. Existence of t-ZrO
2
interface also changes the temperature-dependent DC conductivity of ZrB
2
/SiOC ceramic composites when compared to that of ZrB
2
and SiOC alone. Experimental results from thermomechanical, jet flow, thermal shock, and water vapor tests demonstrate that the developed ceramic composites have high stability in harsh environments, and can be used as high-temperature wide-band microwave absorbing structural materials.
Journal Article
Prolonged in situ self-healing in structural composites via thermo-reversible entanglement
Natural processes continuously degrade a material’s performance throughout its life cycle. An emerging class of synthetic self-healing polymers and composites possess property-retaining functions with the promise of longer lifetimes. But sustained in-service repair of structural fiber-reinforced composites remains unfulfilled due to material heterogeneity and thermodynamic barriers in commonly cross-linked polymer-matrix constituents. Overcoming these inherent challenges for mechanical self-recovery is vital to extend in-service operation and attain widespread adoption of such bioinspired structural materials. Here we transcend existing obstacles and report a fiber-composite capable of minute-scale and prolonged in situ healing — 100 cycles: an order of magnitude higher than prior studies. By 3D printing a mendable thermoplastic onto woven glass/carbon fiber reinforcement and co-laminating with electrically resistive heater interlayers, we achieve in situ thermal remending of internal delamination via dynamic bond re-association. Full fracture recovery occurs below the glass-transition temperature of the thermoset epoxy-matrix composite, thus preserving stiffness during and after repair. A discovery of chemically driven improvement in thermal remending of glass- over carbon-fiber composites is also revealed. The marked lifetime extension offered by this self-healing strategy mitigates costly maintenance, facilitates repair of difficult-to-access structures (e.g., wind-turbine blades), and reduces part replacement, thereby benefiting economy and environment.
Synthetic materials that can repeatedly self-repair, akin to biological systems, are vital to meeting the 21st century’s infrastructural demands. Here, authors develop fiber-reinforced composites with rapid and prolonged in situ self-healing while also preserving structural integrity.
Journal Article
Effect of Pore Defects on Uniaxial Mechanical Properties of Bulk Hexagonal Hydroxyapatite: A Molecular Dynamics Study
Hydroxyapatite (HAP) is a calcium apatite bioceramic used in various naturally-derived and synthetic forms for bone repair and regeneration. While useful for the regrowth of osseus tissue, the poor load-bearing capacity of this material relative to other biomaterials is worsened by the propensity for pore formation during the synthetic processing of scaffolds, blocks, and granules. Here we use molecular dynamics (MD) simulations to improve the current understanding of the defect-altered uniaxial mechanical response in hexagonal HAP single crystals relative to defect-free structures. The inclusion of a central spherical pore within a repeated lattice was found to reduce both the failure stress and failure strain in uniaxial tension and compression, with up to a 30% reduction in maximum stress at the point of failure compared to a perfect crystalline structure observed when a 30 Å diameter pore was included. The Z axis ([0 0 0 1] crystalline direction) was found to be the least susceptible to pore defects in tension but the most sensitive to pore inclusion in compression. The deformation mechanisms are discussed to explain the observed mechanical responses, for which charge imbalances and geometric stress concentration factor effects caused by pore inclusion play a significant role.
Journal Article
Tissue Engineering Strategies for Treating Avascular Necrosis of the Femoral Head
Avascular necrosis (AVN) of the femoral head commonly leads to symptomatic osteoarthritis of the hip. In older patients, hip replacement is a viable option that restores the hip biomechanics and improves pain but in pediatric, adolescent, and young adult patients hip replacements impose significant activity limitations and the need for multiple revision surgeries with increasing risk of complication. Early detection of AVN requires a high level of suspicion as diagnostic techniques such as X-rays are not sensitive in the early stages of the disease. There are multiple etiologies that can lead to this disease. In the pediatric and adolescent population, trauma is a commonly recognized cause of AVN. The understanding of the pathophysiology of the disease is limited, adding to the challenge of devising a clinically effective treatment strategy. Surgical techniques to prevent progression of the disease and avoid total hip replacement include core decompression, vascular grafts, and use of bone-marrow derived stem cells with or without adjuncts, such as bisphosphonates and bone morphogenetic protein (BMP), all of which are partially effective only in the very early stages of the disease. Further, these strategies often only improve pain and range of motion in the short-term in some patients and do not predictably prevent progression of the disease. Tissue engineering strategies with the combined use of biomaterials, stem cells and growth factors offer a potential strategy to avoid metallic implants and surgery. Structural, bioactive biomaterial platforms could help in stabilizing the femoral head while inducing osteogenic differentiation to regenerate bone and provide angiogenic cues to concomitantly recover vasculature in the femoral head. Moreover, injectable systems that can be delivered using a minimal invasive procedure and provide mechanical support the collapsing femoral head could potentially alleviate the need for surgical interventions in the future. The present review describes the limitations of existing surgical methods and the recent advances in tissue engineering that are leading in the direction of a clinically effective, translational solution for AVN in future.
Journal Article
Acquired resistance to immunotherapy and future challenges
Many patients have now received various types of immunotherapy, so we asked three scientists to give their views on whether acquired resistance to immunotherapy exists in patients and the future challenges posed by immunotherapy.
Advances in immunotherapy have resulted in remarkable clinical responses in some patients. However, one of the biggest challenges in cancer therapeutics is the development of resistant disease and disease progression on or after therapy. Given that many patients have now received various types of immunotherapy, we asked three scientists to give their views on the current evidence for whether acquired resistance to immunotherapy exists in patients and the future challenges posed by immunotherapy.
Journal Article
Diverse tsunamigenesis triggered by the Hunga Tonga-Hunga Ha’apai eruption
On the evening of 15 January 2022, the Hunga Tonga-Hunga Ha’apai volcano
1
unleashed a violent underwater eruption, blanketing the surrounding land masses in ash and debris
2
,
3
. The eruption generated tsunamis observed around the world. An event of this type last occurred in 1883 during the eruption of Krakatau
4
, and thus we have the first observations of a tsunami from a large emergent volcanic eruption captured with modern instrumentation. Here we show that the explosive eruption generated waves through multiple mechanisms, including: (1) air–sea coupling with the initial and powerful shock wave radiating out from the explosion in the immediate vicinity of the eruption; (2) collapse of the water cavity created by the underwater explosion; and (3) air–sea coupling with the air-pressure pulse that circled the Earth several times, leading to a global tsunami. In the near field, tsunami impacts are strongly controlled by the water-cavity source whereas the far-field tsunami, which was unusually persistent, can be largely described by the air-pressure pulse mechanism. Catastrophic damage in some harbours in the far field was averted by just tens of centimetres, implying that a modest sea level rise combined with a future, similar event would lead to a step-function increase in impacts on infrastructure. Piecing together the complexity of this event has broad implications for coastal hazards in similar geophysical settings, suggesting a currently neglected source of global tsunamis.
January 2022 saw the first observations of a tsunami resulting from a large emergent volcanic eruption (Hunga Tonga) captured using modern instrumentation, with broad implications for hazard management in similar geophysical settings.
Journal Article
The chemical defense of the Texas cave harvestman Chinquipellobunus madlae: first report on the family Stygnopsidae and on a North American troglobiont harvestman (Opilones: Gonyleptoidea)
The stygnopsid harvestman Chinquipellobunus madlae (Goodnight and Goodnight 1967) is known from numerous caves in eleven counties in Texas and is a highly adapted troglobiont (Cokendolpher 2004). Adult and juvenile specimens were extracted in methanol, and the major volatile component of their chemical defense secretion was identified as 2-methyl-5-ethylphenol; a minor component was 2, 5-dimethylphenol. Methylethyl phenols and dimethyl phenols have also been identified in other grassatorid Opiliones, but this is the first report of defensive chemistry from a member of the family Stygnopsidae and from a North American troglobiont harvestman.
Journal Article
Polymer-derived SiOC reinforced with core-shell nanophase structure of ZrB 2 /ZrO 2 for excellent and stable high-temperature microwave absorption (up to 900 °C)
Microwave absorbing materials for high-temperature harsh environments are highly desirable for aerodynamically heated parts and engine combustion induced hot spots of aircrafts. This study reports ceramic composites with excellent and stable high-temperature microwave absorption in air, which are made of polymer-derived SiOC reinforced with core-shell nanophase structure of ZrB
/ZrO
. The fabricated ceramic composites have a crystallized t-ZrO
interface between ZrB
and SiOC domains. The ceramic composites exhibit stable dielectric properties, which are relatively insensitive to temperature change from room temperature to 900 °C. The return loss exceeds - 10 dB, especially between 28 and 40 GHz, at the elevated temperatures. The stable high-temperature electromagnetic (EM) absorption properties are attributed to the stable dielectric and electrical properties induced by the core-shell nanophase structure of ZrB
/ZrO
. Crystallized t-ZrO
serve as nanoscale dielectric interfaces between ZrB
and SiOC, which are favorable for EM wave introduction for enhancing polarization loss and absorption. Existence of t-ZrO
interface also changes the temperature-dependent DC conductivity of ZrB
/SiOC ceramic composites when compared to that of ZrB
and SiOC alone. Experimental results from thermomechanical, jet flow, thermal shock, and water vapor tests demonstrate that the developed ceramic composites have high stability in harsh environments, and can be used as high-temperature wide-band microwave absorbing structural materials.
Journal Article
Nanoscale Deformation Mechanisms in Bulk Hexagonal Hydroxyapatite and Effect of Defects on Mechanical Properties
The use of hydroxyapatite (HAP) as a bioactive scaffold and implant coating material has grown with recent advances in tissue engineering and biomaterial design. It is known that computational material design via hierarchical structuring offers reduced cost and increased material performance. The goal of understanding of material behavior and underlying causes across multiple time and length scales offers distinct advantages over traditional experimental material processing and analysis at each scale. To date, no work has been performed which specifically addresses the nanoscale deformation mechanisms of bulk hydroxyapatite or the effects of common defects on its mechanical behavior. Molecular Dynamics (MD) simulations were conducted in LAMMS with OVITO for post processing to determine the involvement of bond species in different loading cases. The effects of strain rate, temperature, vacancy pairs, and porosity on the mechanical properties of the crystal were also qualified.
Dissertation