Diets of Atlantic Sharpnose Shark (Rhizoprionodon terraenovae) and Bonnethead (Sphyrna tiburo) in the northern Gulf of Mexico

Diets of two coastal sharks, Atlantic Sharpnose Shark (Rhizoprionodon terraenovae) and Bonnethead (Sphyrna tiburo), were examined along the Texas and Alabama coasts in the northern Gulf of Mexico (GOM). Atlantic Sharpnose Sharks were collected from the northwest (n= 209) and northcentral (n= 245) GOM regions while Bonnetheads were collected from two locations within the northwest GOM (Galveston, Texas, n= 164; Matagorda, Texas, n= 79). Dietary analysis was conducted using stomach contents identified to the lowest taxonomic level, which were quantified using the index of relative importance (IRI) and non-parametric statistical analyses. Atlantic Sharpnose Sharks were revealed to be primarily piscivorous, with an overall %IRI of 79.76% for teleost fishes. Bonnetheads were shown to prey primarily on crustaceans (90.94% IRI), mainly crabs (22.06% IRI). Diets for Atlantic Sharpnose Sharks and Bonnetheads were evaluated by region and ontogeny, where variations by ontogeny were examined based on length at 50% maturity (L50) values, delineating mature from immature individuals. Atlantic Sharpnose Sharks and Bonnetheads showed a decrease in dietary prey species richness from juveniles to adults using %IRI. Regional dietary differences existed with Atlantic Sharpnose Sharks from the northwest GOM consuming more crustaceans than conspecifics from the northcentral GOM. Bonnetheads collected from Galveston, TX consumed more crab than Bonnetheads from Matagorda, TX, while Bonnetheads from Matagorda, TX displayed a diet with higher prey species richness. Our results highlight differences in diets of two common shark species at both local and regional spatial scales

Discovery of high-entropy ceramics via machine learning

AbstractAlthough high-entropy materials are attracting considerable interest due to a combination of useful properties and promising applications, predicting their formation remains a hindrance for rational discovery of new systems. Experimental approaches are based on physical intuition and/or expensive trial and error strategies. Most computational methods rely on the availability of sufficient experimental data and computational power. Machine learning (ML) applied to materials science can accelerate development and reduce costs. In this study, we propose an ML method, leveraging thermodynamic and compositional attributes of a given material for predicting the synthesizability (i.e., entropy-forming ability) of disordered metal carbides. The relative importance of the thermodynamic and compositional features for the predictions are then explored. The approach’s suitability is demonstrated by comparing values calculated with density functional theory to ML predictions. Finally, the model is employed to predict the entropy-forming ability of 70 new compositions; several predictions are validated by additional density functional theory calculations and experimental synthesis, corroborating the effectiveness in exploring vast compositional spaces in a high-throughput manner. Importantly, seven compositions are selected specifically, because they contain all three of the Group VI elements (Cr, Mo, and W), which do not form room temperature-stable rock-salt monocarbides. Incorporating the Group VI elements into the rock-salt structure provides further opportunity for tuning the electronic structure and potentially material performance

Suturing Workshop for Third-Year Medical Students: A Modern Educational Approach

Background: This study sought to determine if developing suturing workshops based on modern educational theory would lead to a significant increase in third-year medical students’ confidence and preparedness as compared to before the workshop. Methods: A group of pre-clinical, third-year medical students (n = 20) were voluntarily recruited. The workshop consisted of an interactive didactic session, a hands-on suturing session, and a question-answer session with surgeons. The nine-point Likert scale surveys were given pre-and post-workshop to 17 participants. Total scores of “confidence” and “preparedness” were analyzed using the Student t-test. Results of Q-Q plot and normality tests were used to validate the normality assumption. All analysis was conducted using SAS Software 9.4 (Cary, North Carolina). Results: A statistically significant increase in both confidence and preparedness was found between results of pre- and post-workshop surveys. Average total scores in confidence increased by 19.7 points, from 19.3 to 39 (95% CI: 15.0-24.4; P value \u3c 0.001). For scores in preparedness, the total score increased by an average of 18.4 points, from 22.8 to 41.2 (95% CI: 14.1-22.8; P value \u3c 0.001). Conclusions: These findings suggest that a structured course based on modern educational theory can increase both the confidence and preparedness of third-year medical students who are matriculating into their hospitalbased clerkships

Building visualization skills through investigating the Journal of the Medical Library Association coauthorship network from 2006–2017

Objective: The primary objective of this study was to explore different dimensions of Journal of the Medical Library Association (JMLA) authorship from 2006-2017. Dimensions that were evaluated using coauthorship networks and affiliation data included collaboration, geographical reach, and relationship between Medical Library Association (MLA) member and nonmember authors. A secondary objective was to analyze the practice and practical application of data science skills. Methods: A team of librarians who attended the 2017 Data Science and Visualization Institute used JMLA bibliographic metadata extracted from Scopus, together with select MLA membership data from 2006-2017. Data cleaning, anonymization, analysis, and visualization were done collaboratively by the team members to meet their learning objectives and to produce insights about the nature of collaborative authorship at JMLA. Results: Sixty-nine percent of the 1,351 JMLA authors from 2006-2017 were not MLA members. MLA members were more productive and collaborative, and tended to author articles together. The majority of the authoring institutions in JMLA are based in the United States. Global reach outside of the United States and Canada shows higher authorship in English-speaking countries (e.g., Australia, United Kingdom), as well as in Western Europe and Japan. Conclusions: MLA support of JMLA may benefit a wider network of health information specialists and medical professionals than is reflected in MLA membership. Conducting coauthorship network analyses can create opportunities for health sciences librarians to practice applying emerging data science and data visualization skills

First principles computational descriptor for entropy forming ability

Entropy stabilized materials [1], where the mixing of the components is driven by configurational entropy rather than formation enthalpy, are potential candidates for ultra-high temperature applications. The prediction of which compositions will form entropy stabilized materials is difficult since calculating the entropic contribution to the free energy from first principles is computationally expensive. Therefore, we have formulated a descriptor for the synthesizability of disordered materials based on the energy distribution of the thermodynamic density of states (TDOS) for an ensemble of ordered configurations generated using the AFLOW (Automatic FLOW) partial occupation (AFLOW-POCC) methodology [2,3] and calculated with DFT. This descriptor has been used to successfully predict which refractory metal carbide compositions can be experimentally synthesized as single-phase entropy stabilized materials [4]. This work is supported by the U.S. Office of Naval Research MURI program (grant No. N00014-15- 1-2863). [1] C. M. Rost, E. Sachet, T. Borman, A. Moballegh, E. C. Dickey, D. Hou, J. L. Jones, S. Curtarolo, and J.-P. Maria, Entropy Stabilized Oxides, Nat. Commun. 6, 8485 (2015). [2] S. Curtarolo, W. Setyawan, G. L. W. Hart, M. Jahnatek, R. V. Chepulskii, R. H. Taylor, S. Wang, J. Xue, K. Yang, O. Levy, M. J. Mehl, H. T. Stokes, D. O. Demchenko, and D. Morgan, AFLOW: an automatic framework for high-throughput materials discovery, Comput. Mater. Sci. 58, 218-226 (2012). [3] K. Yang, C. Oses, and S. Curtarolo, Modeling off-stoichiometry materials with a high-throughput ab-initio approach, Chem. Mater. 28, 6484-6492 (2016). [4] P. Sarker, T. Harrington, C. Toher, K. Vecchio, and S. Curtarolo, First principles materials design using a spectral descriptor for entropy forming ability, in preparation (2017)

Modelling and synthesis of high-entropy refractory carbides, nitrides and carbonitrides

It has been well demonstrated that, through entropic stabilization, many equiatomic multicomponent metallic compositions will form single-phase, complex solid solutions, often called high-entropy alloys. It is known for metallic systems that one can take advantage of the inherent favorable properties of these materials, including increased thermal stability and solid solution strengthening. In order to extend the field of high-entropy alloys into the ultra-high temperature realm, we investigate novel equiatomic, hexanery (5-metal + anion), high-entropy refractory carbides, nitrides, and carbonitrides of group IV, V, and VI transition metals via modeling and experimental synthesis routes. The CALPHAD technique enabled rapid screening of a vast number of material systems to find likely candidates for formation of truly single-phase high-entropy ultra-high temperature ceramics (UHTCs). Compositions that exhibited broad, single-phase solubility across a large temperature region were selected, making processing possible at reasonable temperatures (≤2500°C). For further screening of compositions, a novel, first-principles materials design method was developed. The theory follows that for low temperature single-phase formation, the different configurations should have similar energies to increase the number of thermodynamically accessible states. A partial occupation method was implemented within AFLOW to automate the generation and calculation of the different configurations. The energy distributions were then used to construct a descriptor to predict the formation of high-entropy materials. Following model predictions, bulk samples were synthesized using a combination of high-energy ball milling (HEBM), spark plasma sintering (SPS) at 2200°C, and hot press (HP) annealing at 2500°C. Phase determination was done via x-ray diffraction techniques as well as TEM microscopy, while chemistry was evaluated via energy dispersive x-ray spectroscopy and STEM-EDS. Many of the carbide compositions, including (Hf0.2Nb0.2Ta0.2Ti0.2Zr0.2)C, (Hf0.2Nb0.2Ta0.2Ti0.2V0.2)C, (Hf0.2Nb0.2Ta0.2Ti0.2W0.2)C, and (Nb0.2Ta0.2Ti0.2V0.2W0.2)C demonstrated virtually single-phase, solid-solution compounds and were sintered to greater than 95% theoretical density. Figure 1 shows the experimental X-ray diffraction patterns for a sample of composition (Hf0.2Nb0.2Ta0.2Ti0.2V0.2)C following each processing step. The material progresses into the desired single cubic NaCl structure following complete processing. Work on single-phase determination in nitride and carbonitride systems is ongoing. This work demonstrates the extension of entropic-stabilization principles into refractory interstitial ceramics and development of new classes of high-entropy ceramic materials for high-temperature applications Please click Additional Files below to see the full abstract

Modelling and synthesis of high-entropy refractory carbides

Bulk samples of equiatomic, hexanery (5-metal), high-entropy refractory carbides were fabricated using a combination of high-energy ball milling (HEBM), spark plasma sintering (SPS), and hot pressing (HP) annealing. To select candidate composition that are likely to form single phase high-entropy materials at lower processing temperatures (\u3c2500°C), a novel, first-principles materials design method was developed. The theory follows that for low temperature single phase formation, the different configurations should have similar energies to increase the number of thermodynamically accessible states. A partial occupation method was implemented within AFLOW to automate the generation and calculation of the different configurations. The energy distributions were then used to construct a descriptor of Entropy Forming Ability (EFA) to predict the formation of high-entropy materials. CALPHAD results were found to agree with the configuration energy range descriptor for each composition, and these carbides exhibited broad, single-phase solubility across each system, making processing possible at reasonable temperatures. Many of the complex carbide compositions, including (Hf0.2Nb0.2Ta0.2Ti0.2Zr0.2)C, (Hf0.2Nb0.2Ta0.2Ti0.2V0.2)C, (Hf0.2Nb0.2Ta0.2Ti0.2W0.2)C, and (Nb0.2Ta0.2Ti0.2V0.2W0.2)C demonstrated virtually single-phase, solid-solution compounds with the NaCl crystal structure as determined by x-ray diffraction (XRD) and energy dispersive x-ray spectroscopy (EDS), while some compositions, including (Hf0.2Mo 0.2Ta0.2W0.2Zr0.2)C and (Hf0.2Mo0.2V0.2W0.2Zr0.2)C, exhibited multiple phases. Results were found to be in good agreement with the ab initio based formulation of entropic stability, where the compositions with the highest EFA values were found to form a single rocksalt structure and compositions with the lower EFA values were found to exhibit multiple phases. Further, among the systems that were found to form single phase materials at 2500°C, artificial segregation was introduced via lower processing temperatures. In these artificially segregated samples, the extent of mixing was analyzed via peak broadening in XRD according to the formulation of Williamson and Hall [1] and compositional mapping in EDS. Results of artificially segregated samples provide continued support for the viability of the EFA formulation, where broadening was found to be more pronounced (i.e. more chemical segregation) in samples that were determined to have a lower EFA value. This work demonstrates the extension of entropic-stabilization into refractory interstitial carbides, paving the way for development of an entirely new class of UHTCs. This work is supported by the U.S. Office of Naval Research MURI program (Grant No. N00014-15- 1-2863). [1] G.. Williamson, W.. Hall, X-ray line broadening from filed aluminium and wolfram, Acta Metall. 1 (1953) 22–31. doi:10.1016/0001-6160(53)90006-6

Fabrication of high-entropy nitrides and carbonitrides

In high-entropy alloys, the use of multiple principle alloying elements is known to entropically stabilize the material. Refractory nitrides and carbides of transition metals are widely known for their ultra high-temperature stability and their high hardness, properties that make them valuable materials for extreme environments, such as coating the exterior of hypersonic flight vehicles and the interior of nuclear reactors. By creating entropy-stabilized complex solid solutions of nitrides and carbides, one can take advantage of the inherent favorable properties of these materials, as well as increased thermal stability and solid solution strengthening. Five-metal systems are chosen using first-principles calculations to describe the energetic distribution of possible atomic configurations, in order to identify systems that are likely to form an entropy-stabilized solid solution. Bulk samples of equiatomic, hexanery (5-metal), high-entropy refractory nitrides and carbonitrides were then fabricated to demonstrate this concept, by using a combination of high-energy ball milling, spark plasma sintering, and hot pressing. The uniformity of the microstructures is characterized, and single-phase solid solutions are achieved, thus demonstrating the ability to entropically stabilize multi-component random mixtures of refractory carbides and nitrides. This work is supported by the U.S. Office of Naval Research MURI program (Grant No. N00014-15- 1-2863