Bighorn Basin Coring Project (BBCP): a continental perspective on early Paleogene hyperthermals

During the summer of 2011, the Bighorn Basin Coring Project (BBCP) recovered over 900m of overlapping core from 3 different sites in late Paleocene to early Eocene fluvial deposits of northwestern Wyoming. BBCP cores are being used to develop high-resolution proxy records of the Paleocene–Eocene Thermal Maximum (PETM) and Eocene Thermal Maximum 2 (ETM2) hyperthermal events. These events are short-term, large magnitude global warming events associated with extreme perturbations to the earth’s carbon cycle. Although the PETM and ETM2 occurred ~55–52 million years ago, they are analogous in many ways to modern anthropogenic changes to the carbon cycle. By applying various sedimentological, geochemical, and palynological methods to the cores, we hope to better understand what caused these events, study the biogeochemical and ecological feedbacks that operated during them, and reveal precisely how they impacted continental environments. Core recovery was > 98% in all holes and most drilling was carried out without fluid additives, showing that continuous coring of continental smectitic deposits like these can be achieved with minimal risk of contamination to molecular biomarkers. Cores were processed in the Bremen Core Repository where the science team convened for 17 days to carry out data collection and sampling protocols similar to IODP projects. Initial results show that the weathered horizon extends to as much as ~30m below the surface and variations in magnetic susceptibility within the cores record an interplay between grain size and pedogenesis. Previous investigations of outcrops near the BBCP drill sites allow detailed evaluation of the effects of weathering on common proxy methods. Studies of lithofacies, organic geochemistry, stable isotope geochemistry, calibrated XRF core scanning, paleomagnetics, and palynology are underway and will represent the highest resolution and most integrated proxy records of the PETM from a continental setting yet known. An extensive outreach program is in place to capitalize on the educational value associated with the Bighorn Basin’s unusually complete record of Phanerozoic earth history

STARBENCH: the D-type expansion of an HII region

STARBENCH is a project focused on benchmarking and validating different star formation and stellar feedback codes. In this first STARBENCH paper we perform a comparison study of the D-type expansion of an H II region. The aim of this work is to understand the differences observed between the 12 participating numerical codes against the various analytical expressions examining the D-type phase of H II region expansion. To do this, we propose two well-defined tests which are tackled by 1D and 3D grid- and smoothed particle hydrodynamics-based codes. The first test examines the ‘early phase’ D-type scenario during which the mechanical pressure driving the expansion is significantly larger than the thermal pressure of the neutral medium. The second test examines the ‘late phase’ D-type scenario during which the system relaxes to pressure equilibrium with the external medium. Although they are mutually in excellent agreement, all 12 participating codes follow a modified expansion law that deviates significantly from the classical Spitzer solution in both scenarios. We present a semi-empirical formula combining the two different solutions appropriate to both early and late phases that agrees with high-resolution simulations to ≲ 2 per cent. This formula provides a much better benchmark solution for code validation than the Spitzer solution. The present comparison has validated the participating codes and through this project we provide a data set for calibrating the treatment of ionizing radiation hydrodynamics codes

Spatial and Temporal Patterns in Petrogenic Organic Carbon Mobilization During the Paleocene-Eocene Thermal Maximum

The Paleocene-Eocene Thermal Maximum (PETM) was a transient global warming event and is recognized in the geologic record by a prolonged negative carbon isotope excursion (CIE). The onset of the CIE was due to a rapid influx of 13C-depleted carbon into the ocean-atmosphere system. However, the mechanisms required to sustain the negative CIE remains unclear. Enhanced mobilization and oxidation of petrogenic organic carbon (OCpetro) has been invoked to explain elevated atmospheric carbon dioxide concentrations after the onset of the CIE. However, existing evidence is limited to the mid-latitudes and subtropics. Here, we determine whether: (a) enhanced mobilization and subsequent burial of OCpetro in marine sediments was a global phenomenon; and (b) whether it occurred throughout the PETM. To achieve this, we utilize a lipid biomarker approach to trace and quantify OCpetro burial in a global compilation of PETM-aged shallow marine sites (n = 7, including five new sites). Our results confirm that OCpetro mass accumulation rates (MARs) increased within the subtropics and mid-latitudes during the PETM, consistent with evidence of higher physical erosion rates and intense episodic rainfall events. High-latitude sites do not exhibit drastic changes in the source of organic carbon during the PETM and OCpetro MARs increase slightly or remain stable, perhaps due a more stable hydrological regime. Crucially, we also demonstrate that OCpetro MARs remained elevated during the recovery phase of the PETM. Although OCpetro oxidation was likely an important positive feedback mechanism throughout the PETM, we show that this feedback was both spatially and temporally variable

Mechanical Behavior and Microstructural Development of Low-Carbon Steel and Microcomposite Steel Reinforcement Bars Deformed under Quasi-Static and Dynamic Shear Loading

Reinforcement bars of microcomposite (MC) steel, composed of lath martensite and minor amounts of retained austenite, possess improved strength and corrosion characteristics over low-carbon (LC) steel rebar; however, their performance under shear loading has not previously been investigated at the microstructural level. In this study, LC and MC steel cylinders were compression tested, and specimens machined into a forced-shear geometry were subjected to quasi-static and dynamic shear loading to determine their shear behavior as a function of the strain and strain rate. The as-received and sheared microstructures were examined using optical microscopy (OM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD). Higher-resolution microstructural examinations were performed using transmission electron microscopy (TEM). The influence of the starting microstructure on the shear behavior was found to depend strongly on the strain rate; the MC steel exhibited not only greater strain-rate sensitivity than the LC steel but also a greater resistance to shear localization with load. In both steels, despite differences in the starting microstructure, post-mortem observations were consistent with a continuous mechanism operating within adiabatic shear bands (ASBs), in which subgrains rotated into highly misoriented grains containing a high density of dislocations

Evolution of microstructure and crystallographic texture during dissimilar friction stir welding of duplex stainless steel to low carbon-manganese structural steel

Electron backscattered diffraction (EBSD) was used to analyze the evolution of microstructure and crystallographic texture during friction stir welding of dissimilar type 2205 duplex stainless steel (DSS) to type S275 low carbon-manganese structural steel. The results of microstructural analyses show that the temperature in the center of stirred zone reached temperatures between Ac 1 and Ac 3 during welding, resulting in a minor ferrite-to-austenite phase transformation in the S275 steel, and no changes in the fractions of ferrite and austenite in the DSS. Temperatures in the thermomechanically affected and shoulder-affected zones of both materials, in particular toward the root of the weld, did not exceed the Ac 1 of S275 steel. The shear generated by the friction between the material and the rotating probe occurred in austenitic/ferritic phase field of the S275 and DSS. In the former, the transformed austenite regions of the microstructure were transformed to acicular ferrite, on cooling, while the dual-phase austenitic/ferritic structure of the latter was retained. Studying the development of crystallographic textures with regard to shear flow lines generated by the probe tool showed the dominance of simple shear components across the whole weld in both materials. The ferrite texture in S275 steel was dominated by D 1, D 2, E, E¯ , and F, where the fraction of acicular ferrite formed on cooling showed a negligible deviation from the texture for the ideal shear texture components of bcc metals. The ferrite texture in DSS was dominated by D 1, D 2, I, I¯ , and F, and that of austenite was dominated by the A, A¯ , B, and B¯ of the ideal shear texture components for bcc and fcc metals, respectively. While D 1, D 2, and F components of the ideal shear texture are common between the ferrite in S275 steel and that of dual-phase DSS, the preferential partitioning of strain into the ferrite phase of DSS led to the development of I and I¯ components in DSS, as opposed to E and E¯ in the S275 steel. The formations of fine and ultrafine equiaxed grains were observed in different regions of both materials that are believed to be due to strain-induced continuous dynamic recrystallization (CDRX) in ferrite of both DSS and S275 steel, and discontinuous dynamic recrystallization (DDRX) in austenite phase of DSS

Effect of Processing Schedules on Surface Roughening and Roping Behavior in Textured 6111 Aluminum Alloys

NRC publication: Ye

Temperature and hydration dependent protein dynamics in photosystem II of green plants studied by quasielastic neutron scattering

Protein dynamics in hydrated and vacuum dried photosystem II PS II membrane fragments from spinach has been investigated by quasielastic neutron scattering QENS in the temperature range between 5 and 300 K. Three distinct temperature ranges can be clearly distinguished by active type s of protein dynamics A At low temperatures T lt; 120 K , the protein dynamics of both dry and hydrated PS II is characterized by harmonic vibrational motions. B In the intermediate temperature range 120 lt; T lt; 240 K , the total mean square displacement u2 total slightly deviates from the predicted linear behavior. The QENS data indicate that this deviation, which is virtually independent of the extent of hydration, is due to a partial onset of diffusive protein motions. C At temperatures above 240 K, the protein flexibility drastically changes because of the onset of diffusive large amplitude protein motions. This dynamical transition is clearly hydration dependent since it is strongly suppressed in dry PS II. The thermally activated onset of protein flexibility as monitored by QENS is found to be strictly correlated with the temperaturedependent increase of the electron transport efficiency from QA to QB Garbers et al. 1998 Biochemistry 37, 11399 11404 . Analogously, the freezing of protein mobility by dehydration in dry PS II appears to be responsible for the blockage of QA reoxidation by QB at hydration values lower than 45 r.h. Kaminskaya et al. 2003 Biochemistry 42, 8119 8132 . Similar effects were observed for reactions of the water oxidizing complex as outlined in the Discussion sectio

PHYSICAL and VIRTUAL RECONSTRUCTION for AN INTEGRATED ARCHAEOLOGICAL MODEL: 3D PRINT and MAQUETTE

Museums perform various tasks such as collecting, cataloguing and preserving the cultural heritage (CH). In addition, they have an institutional task, which is to disseminate the heritage, discovering the most efficient tools to tell how a monument to the origin could have looked. In this process of knowledge and dissemination, digital technologies play an important role. In fact, they allow building a digital archive in which virtual copies of found objects are available to scholars for more or less in-depth analysis. Digital archives of this type also allow the dissemination of scientific data, constituting, if published, databases accessible everywhere. The role of the digital archive is also to preserve the characteristics of the finds, which are often already deteriorated, without worsening the situation through their continuous manipulation or movement. Of course, the construction of digital copies must be done in the most rigorous way so as to guarantee scholars the truthfulness of the data being analysed, and building procedures as standardized as possible to allow their use even by unskilled personnel. Moreover, museums have the very complex task of communicating the heritage, which envisages two steps: reconstruction and communication. The first phase, reconstruction, is a very complex operation, especially in the archaeological field, where there are few documents and the hypotheses are based on principles of similarity. Since no direct reference is available, the reconstruction takes place through comparison with similar objects from the same period, the same area and with the same function. Communication, then, has the task of disseminating the results and the hypotheses made, with the most appropriate tools. 3D printing allows to build three-dimensional models of reality, and therefore immediately comprehensible, even of complex forms, not always achievable with the traditional tools of modelling tools. This article describes this complex process, and its application to the funerary aediculae monument at the Museo Archeologico di Mantova, on the occasion of the refurbishment of the museum and its exhibits. In this experience, the use of new technologies is being investigated in combination with more traditional methods of representation, the maquette, but not less effective