Chemistry, design, and processing of two-stage TRIP steel

A regular solution model was developed to calculate the chemical driving force for α-martensite formation, ΔGλ→ αChem. A model for the strain energy, ΔGλ→αstr, was formulated utilizing the Young’s modulus (E), lattice misfit squared (δ²), and molar volume (Ω) which opposed the chemical driving force for α-martensite formation. The MαS was determined at a temperature at which ΔGλ→αChem + ΔGλ→αstr = 0. In conjunction with a previously developed ε-martensite model, a means of predicting the volume fraction of λ-austenite was determined; and it was shown that for values of ΔMs \u3c 0, defined as Msε - Msα produced the greatest amounts of retained γ-austenite in the as quenched microstructure. These models were tested, and confirmed, with a new alloy formulated to produce a steel with chromium replacing the traditional aluminum to obtain a ΔMs = -100 C° that exhibited the two-stage TRIP behavior. From this substitution the dynamic strain aging response could be mitigated through M₂₃(C,N)₆ precipitation trapping carbon and nitrogen. The work hardening behavior of these steels was found to be due to the Stage II (ε→α) martensitic reaction and not the dynamic strain aging of the steels. Eight medium-Mn steels were processed and it was found that when the intrinsic stacking fault energy was less than 10.5 mJ/m² the two-stage TRIP response was activated. Empirical relationships for the strength and ductility were determined for the two-stage TRIP steels. The developed models have been used to optimize alloy composition and a designed steel with composition Fe-13.8Mn-1.0Si-3.0Cr-0.15C-0.003N (wt. pct.) is recommended for future investigation --Abstract, page iv

Bird Evolution: Convergence Fits the Bill

New fossils help pinpoint when some birds started relying on a seed-based diet and reveal that disparate bill shapes evolved repeatedly throughout bird evolutionary history

Fast and accurate prediction of numerical relativity waveforms from binary black hole coalescences using surrogate models

Simulating a binary black hole (BBH) coalescence by solving Einstein's equations is computationally expensive, requiring days to months of supercomputing time. Using reduced order modeling techniques, we construct an accurate surrogate model, which is evaluated in a millisecond to a second, for numerical relativity (NR) waveforms from non-spinning BBH coalescences with mass ratios in $[1, 10]$ and durations corresponding to about $15$ orbits before merger. We assess the model's uncertainty and show that our modeling strategy predicts NR waveforms {\em not} used for the surrogate's training with errors nearly as small as the numerical error of the NR code. Our model includes all spherical-harmonic ${}_{-2}Y_{\ell m}$ waveform modes resolved by the NR code up to $\ell=8.$ We compare our surrogate model to Effective One Body waveforms from $50$-$300 M_\odot$ for advanced LIGO detectors and find that the surrogate is always more faithful (by at least an order of magnitude in most cases).Comment: Updated to published version, which includes a section comparing the surrogate and effective-one-body models. The surrogate is publicly available for download at http://www.black-holes.org/surrogates/ . 6 pages, 6 figure

A Surrogate Model of Gravitational Waveforms from Numerical Relativity Simulations of Precessing Binary Black Hole Mergers

We present the first surrogate model for gravitational waveforms from the coalescence of precessing binary black holes. We call this surrogate model NRSur4d2s. Our methodology significantly extends recently introduced reduced-order and surrogate modeling techniques, and is capable of directly modeling numerical relativity waveforms without introducing phenomenological assumptions or approximations to general relativity. Motivated by GW150914, LIGO's first detection of gravitational waves from merging black holes, the model is built from a set of $276$ numerical relativity (NR) simulations with mass ratios $q \leq 2$, dimensionless spin magnitudes up to $0.8$, and the restriction that the initial spin of the smaller black hole lies along the axis of orbital angular momentum. It produces waveforms which begin $\sim 30$ gravitational wave cycles before merger and continue through ringdown, and which contain the effects of precession as well as all $\ell \in \{2, 3\}$ spin-weighted spherical-harmonic modes. We perform cross-validation studies to compare the model to NR waveforms \emph{not} used to build the model, and find a better agreement within the parameter range of the model than other, state-of-the-art precessing waveform models, with typical mismatches of $10^{-3}$. We also construct a frequency domain surrogate model (called NRSur4d2s_FDROM) which can be evaluated in $50\, \mathrm{ms}$ and is suitable for performing parameter estimation studies on gravitational wave detections similar to GW150914.Comment: 34 pages, 26 figure

Visible and Ultraviolet Laser Spectroscopy of ThF

The molecular ion ThF$^+$ is the species to be used in the next generation of search for the electron's Electric Dipole Moment (eEDM) at JILA. The measurement requires creating molecular ions in the eEDM sensitive state, the rovibronic ground state $^3\Delta_1$, $v^+=0$, $J^+=1$. Survey spectroscopy of neutral ThF is required to identify an appropriate intermediate state for a Resonance Enhanced Multi-Photon Ionization (REMPI) scheme that will create ions in the required state. We perform broadband survey spectroscopy (from 13000 to 44000~cm$^{-1}$) of ThF using both Laser Induced Fluorescence (LIF) and $1+1'$ REMPI spectroscopy. We observe and assign 345 previously unreported vibronic bands of ThF. We demonstrate 30\% efficiency in the production of ThF$^+$ ions in the eEDM sensitive state using the $\Omega = 3/2$ [32.85] intermediate state. In addition, we propose a method to increase the aforementioned efficiency to $\sim$100\% by using vibrational autoionization via core-nonpenetrating Rydberg states, and discuss theoretical and experimental challenges. Finally, we also report 83 vibronic bands of an impurity species, ThO.Comment: 49 pages, 7 figure

Wing Musculature Reconstruction in Extinct Flightless Auks (<i>Pinguinus</i> and <i>Mancalla</i>) Reveals Incomplete Convergence with Penguins (Spheniscidae) Due to Differing Ancestral States.

Despite longstanding interest in convergent evolution, factors that result in deviations from fully convergent phenotypes remain poorly understood. In birds, the evolution of flightless wing-propelled diving has emerged as a classic example of convergence, having arisen in disparate lineages including penguins (Sphenisciformes) and auks (Pan-Alcidae, Charadriiformes). Nevertheless, little is known about the functional anatomy of the wings of flightless auks because all such taxa are extinct, and their morphology is almost exclusively represented by skeletal remains. Here, in order to re-evaluate the extent of evolutionary convergence among flightless wing-propelled divers, wing muscles and ligaments were reconstructed in two extinct flightless auks, representing independent transitions to flightlessness: Pinguinus impennis (a crown-group alcid), and Mancalla (a stem-group alcid). Extensive anatomical data were gathered from dissections of 12 species of extant charadriiforms and 4 aequornithine waterbirds including a penguin. The results suggest that the wings of both flightless auk taxa were characterized by an increased mechanical advantage of wing elevator/retractor muscles, and decreased mobility of distal wing joints, both of which are likely advantageous for wing-propelled diving and parallel similar functional specializations in penguins. However, the conformations of individual muscles and ligaments underlying these specializations differ markedly between penguins and flightless auks, instead resembling those in each respective group's close relatives. Thus, the wings of these flightless wing-propelled divers can be described as convergent as overall functional units, but are incompletely convergent at lower levels of anatomical organization-a result of retaining differing conditions from each group's respective volant ancestors. Detailed investigations such as this one may indicate that, even in the face of similar functional demands, courses of phenotypic evolution are dictated to an important degree by ancestral starting points

The morphomolecular features of cholangiocarcinoma in the personalised era

Cholangiocarcinoma is a group of diverse invasive malignancies arising along the biliary tract. The outcomes for patients with cholangiocarcinoma remain poor but an understanding of molecular aberrations and subsequent targeted therapies to these have opened up new treatment prospects. This review describes the clinical and morphological features and classifications of intrahepatic and perihilar cholangiocarcinoma in addition to laying out the related landscape of the molecular pathology within cholangiocarcinoma. The importance of both a high index of suspicion of cholangiocarcinoma and preserving tissue whilst reporting to access molecular testing and personalised treatment pathways is emphasised

Performance Monitoring of a Bridge Abutment Spread Footing From Construction Through Service

The use of spread footings over compressible soils is becoming more common for Minnesota Department of Transportation bridges as technologies improve to better predict, mitigate, and evaluate settlement. In August of 2011 the north abutment of a new bridge crossing I-494 was constructed over compressible soils following a soil fill preload, designed to reduce the foundation settlement from several inches to less than one inch, to meet project requirements. Spread footing foundations are seldom outfitted with instrumentation; adequate performance is frequently assumed based on the decision to use shallow foundations. Here, a monitoring plan was developed to validate the preloading technique for mitigating otherwise unacceptable deformations, assess the efficacy of shallow foundation monitoring methods, and gain a better understanding of shallow foundation behavior with time. Instrumentation consisted of two earth pressure cells, a horizontal MEMS SAA deformation monitoring array, and four optical survey reflectors which were installed during the construction of the foundation and abutment wall. During the course of construction, portions of the abutment backfill soil volume were placed and removed to accommodate the construction of the bridge deck and the adjacent wall footings. The effect of the various loading and unloading conditions was observed on the sensors. The abutment foundation performance over the construction timeline is discussed, including apparent loading, deflection, and rotation. The data from the manually observed survey targets is compared to the automated data from the SAA and earth pressure cells