Publications

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Physisorption in porous materials is a promising approach for meeting H2 storage requirements for the transportation industry, because it is both fully reversible and fast at mild conditions. However, most current candidates lead to H2 binding energies that are too weak (leading to volumetric capacity at 298 K of <10 g/L compared to the DOE 2015 Target of 40 g/L). Using accurate quantum mechanical (QM) methods, we studied the H2 binding energy to 48 compounds based on various metalated analogues of five common linkers for covalent organic frameworks (COFs). Considering the first transition row metals (Sc though Cu) plus Pd and Pt, we find that the new COF-301-PdCl2 reaches 60 g total H2/L at 100 bar, which is 1.5 times the DOE 2015 target of 40 g/L and close to the ultimate (2050) target of 70 g/L. The best current materials, MOF-200 and MOF-177, are predicted to store 7.6 g/L (0.54 wt % excess) and 9.6 g/L (0.87 wt % excess), respectively, at 298 K and 100 bar compared with 60 g/L (4.2 wt % excess) for COF-301-PdCl2.

Single crystals of germanium-substituted Fe2O3 have been grown using chemical vapour transport with tellurium tetrachloride and their crystallographic, electrical, magnetic and photoelectronic properties have been studied. Germanium-substituted Fe2O3 crystallized with the corundum structure and is an extrinsic n-type semiconductor with a room-temperature resistivity of ca. 5 Ω cm and an impurity ionization energy of 0.12 eV. Low-temperature susceptibility measurements suggest that insertion of GeIV leads to reduction of FeIII to FeII without spinel-phase inclusion. Photoelectrochemical measurements and determinations of the flatband potential by different techniques suggest that the behaviour of Fe2O3 photoanodes may be influenced by energy levels in the bandgap near the conduction band.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

In article number 1906146, Robert O. Ritchie, Ashwin J. Shahani, and co-workers investigate the origins of certain eutectics that grow into spiral geometry. The spiral formation follows a two-step process, wherein the first step is mediated by the low solid–liquid interfacial energy of a precursor phase, and the second step by crystallographic defects on the precursor. The cover features a computed X-ray nano-tomography image of spiral eutectics in Mg-Zn alloy showing multiple spiral eutectic colonies with the eutectic MgZn2 and Zn phases shown in dark and light false colors (image courtesy of H. Bale).

Foreign-object damage associated with the ingestion of debris into aircraft turbine engines can lead to a marked degradation in the high-cycle fatigue (HCF) life of turbine components. This degradation is generally considered to be associated with the premature initiation of fatigue cracks at or near the damage sites; this is suspected to be due to, at least in part, the impact-induced residual stress state, which can be strongly tensile in these locations. However, recent experimental studies have shown the unexpected propensity for impact-induced fatigue crack formation at locations of compressive residual stress in the vicinity of the impact site. To address this issue, in situ and ex situ spatially-resolved X-ray diffraction and numerical modeling are utilized to show that the initial residual stress state can be strongly relaxed during the fatigue loading process. The magnitude and rate of relaxation is strongly dependent on the applied loads. For a Ti–6Al–4V turbine blade alloy, little relaxation was observed for an applied maximum stress of 325 MPa (0.35σ y , where σ y is the yield stress), and cracks tended to form in subsurface zones of tensile residual stress away from the damage sites. In contrast, at an applied maximum stress of 500 MPa (0.54σ y ), equal to the smooth-bar 107-cycle endurance strength, cracks tended to form at the damage sites in zones of high stress concentration that had initially been in strong compression, but had relaxed during the fatigue loading.

Current trends in Machine Learning~(ML) inference on hardware accelerated devices (e.g., GPUs, TPUs) point to alarmingly low utilization. As ML inference is increasingly time-bounded by tight latency SLOs, increasing data parallelism is not an option. The need for better efficiency motivates GPU multiplexing. Furthermore, existing GPU programming abstractions force programmers to micro-manage GPU resources in an early-binding, context-free fashion. We propose a VLIW-inspired Out-of-Order (OoO) Just-in-Time (JIT) compiler that coalesces and reorders execution kernels at runtime for throughput-optimal device utilization while satisfying latency SLOs. We quantify the inefficiencies of space-only and time-only multiplexing alternatives and demonstrate an achievable 7.7x opportunity gap through spatial coalescing.

A recently developed As2S3 chemical treatment was used to passivate the perimeters of self-aligned heterojunction bipolar transistors (HBTs). The As2S3 chemical treatment significantly lowered the base current resulting in a two order of magnitude reduction in the collector current density at which dc current gain was observed (β=1). No degradation with time has been observed in the electrical characteristics of the chemically treated HBTs. This absence of degradation is attributed to the impermeability to oxygen of the As2S3 glass which coats the perimeter of the HBT after chemical treatment.