Retroarc Jurassic burial and exhumation of Barrovian metamorphic rocks dated by monazite petrochronology, Funeral Mountains, California

ABSTRACT In this study, we determined the timing of burial and subsequent exhumation of Barrovian metamorphic rocks from the Chloride Cliff area of the Funeral Mountains in southeastern California by constraining the ages of different portions of a pressure-temperature (P-T) path. Using a split-stream laser-ablation inductively coupled plasma–mass spectrometry (ICP-MS) system, we analyzed 192 domains from 35 grains of monazite within five samples with a spot size of 8 µm to determine U-Pb ages and trace-element abundances from the same samples (same polished sections) that were analyzed to produce the P-T paths. Changes that took place within individual monazite grains reflect localized equilibrium and captured the changes in heavy rare earth element (HREE) abundances in the matrix reservoir that occurred as garnet grew, resorbed, and then regrew, thus constraining ages on different portions of the P-T path. The results show that garnet began growing ca. 168 Ma, began resorbing ca. 160 Ma, began retrograde regrowth ca. 157 Ma, and continued to regrow at least through ca. 143 Ma. The early garnet growth corresponds to a period of pressure increase along the P-T path. The subsequent partial resorption corresponds to the prograde crossing of a garnet-consuming reaction during decompression, and the retrograde garnet regrowth occurred when this same reaction was recrossed in the retrograde sense during further decompression. These results are consistent with previously determined ages, which include a Lu-Hf garnet age of 167.3 ± 0.72 Ma for the early pressure-increase portion of the P-T path, and 40Ar/39Ar muscovite cooling ages of 153 and 146 Ma in the lower-grade Indian Pass area 10 km southeast of Chloride Cliff. The 40Ar/39Ar muscovite ages document cooling at the same time as retrograde garnet regrowth was taking place at Chloride Cliff. The oldest monazite age obtained in this study, 176 ± 5 Ma, suggests that southeast-directed thrusting within the Jurassic retroarc was ongoing by this time along the California portion of the western North American plate margin, as a consequence of east-dipping subduction and/or arc collision. The Funeral Mountains were likely located on the east side of the northern Sierra Nevada range in the Jurassic, taking into account dextral strike-slip displacement along the Cretaceous Mojave–Snow Lake fault. The Late Jurassic timing of burial in the Funeral Mountains and its Jurassic location suggest burial was associated with the East Sierran thrust system. The timing of prograde garnet resorption during exhumation (160–157 Ma) corresponds to a change from regional dextral transpression to sinistral transtension along the Jurassic plate margin inferred to have occurred ca. 157 Ma. The recorded exhumation was concurrent with intrusion of the 148 Ma Independence dike swarm in the eastern Sierra Nevada and Mojave regions, which developed within a regime of northeast-southwest extension.

Toward a definition of digital object reuse

Purpose The purpose of this paper is to present conceptual definitions for digital object use and reuse. Typically, assessment of digital repository content struggles to go beyond traditional usage metrics such as clicks, views or downloads. This is problematic for galleries, libraries, archives, museums and repositories (GLAMR) practitioners because use assessment does not tell a nuanced story of how users engage with digital content and objects. Design/methodology/approach This paper reviews prior research and literature aimed at defining use and reuse of digital content in GLAMR contexts and builds off of this group’s previous research to devise a new model for defining use and reuse called the use-reuse matrix. Findings This paper presents the use-reuse matrix, which visually represents eight categories and numerous examples of use and reuse. Additionally, the paper explores the concept of “permeability” and its bearing on the matrix. It concludes with the next steps for future research and application in the development of the Digital Content Reuse Assessment Framework Toolkit (D-CRAFT). Practical implications The authors developed this model and definitions to inform D-CRAFT, an Institute of Museum and Library Services National Leadership Grant project. This toolkit is being developed to help practitioners assess reuse at their own institutions. Originality/value To the best of the authors’ knowledge, this paper is one of the first to propose distinct definitions that describe and differentiate between digital object use and reuse in the context of assessing digital collections and data.

Study On Some Matrix Equations Involving The Weighted Geometric Mean and Their Application

In this paper we consider two matrix equations that involve the weighted geometric mean. We use the fixed point theorem in the cone of positive definite matrices to prove the existence of a unique positive definite solution. In addition, we study the multi-step stationary iterative method for those equations and prove the corresponding convergence. A fidelity measure for quantum states based on the matrix geometric mean is introduced as an application of matrix equation.

Adapting the CACAO model to support higher education STEM teaching reform

Background Efforts to achieve improved student outcomes in STEM are critically reliant on the success of reform efforts associated with teaching and learning. Reform efforts include the transformation of course-based practices, community values, and the institutional policies and structures associated with teaching and learning in higher education. Enacting change is a complex process that can be guided by change theories that describe how and why a desired change takes place. We analyzed the utility of a theory-based change model applied in a higher education setting. Our results provide guidance for change efforts at other institutions. Results Use of the CACAO model to guide the transformation of STEM instruction at a large public university resulted in changes to faculty teaching practices and department culture consistent with the vision defined for the project. Such changes varied across STEM departments in accordance with the emergent nature of project activities at the department level. Our application of the CACAO model demonstrates the importance of (1) creating a vision statement (statement of desired change or end-state); (2) attending to different levels of the organization (e.g., individuals, departments, and colleges); (3) working with change agents who are situated to be effective at different organizational levels; and (4) employing strategies to meet the needs and interests of faculty at different stages of adoption with respect to the desired change. Conclusion Our work, which demonstrates the utility of the CACAO model for change and captures its key elements in a matrix, provides a potential foundation for others considering how to frame and study change efforts. It reinforces the value of using change theories to inform change efforts and creates a structure that others can build on and modify, either by applying our CACAO matrix in their own setting or by using the matrix to identify elements that connect to other change theories. We contribute to the growing body of literature which seeks to understand how change theories can be useful and generalizable beyond a single project.

Mechanical and Conductive Properties of Cu Matrix Composites Reinforced by Oriented Carbon Nanotubes with Different Coatings

Because of the dilemma that the current industrial Cu enhancement methods lead to a significant decline in conductivity and ductility, Cu matrix composites reinforced by oriented multi-walled carbon nanotubes (MWCNTs) were prepared through sintering, hot extrusion, and cold drawing. Before sintering, Ni, Cu, and Ni&Cu coatings were electroless plated on MWCNTs as the intermediate transition layer, and then they were mixed with Cu powder through a nitrogen bubbling assisted ultrasonic process. By analyzing the composition, microstructure, and formation mechanism of the interface between MWCNTs and the matrix, the influence and mechanism of the interface on the mechanical properties, conductivity, and ductility of the composites were explored. The results indicated that MWCNTs maintained a highly dispersed and highly consistent orientation in the Cu matrix. The coating on Ni@CNT was the densest, continuous, and complete. The Ni@CNTs/Cu composite had the greatest effect, while the Cu composite reinforced by MWCNT without coating had the smallest reduction in elongation and conductivity. The comprehensive performance of the Cu@CNTs/Cu composite was the most balanced, with an ultimate tensile strength that reached 373 MPa, while the ductility and conductivity were not excessively reduced. The axial electrical and thermal conductivity were 79.9 IACS % (International Annealed Copper Standard) and 376 W/mK, respectively.

Corrosion Behavior and Mechanical Properties of 30CrMnSiA High-Strength Steel under an Indoor Accelerated Harsh Marine Atmospheric Environment

In this work, the corrosion behavior and mechanical properties of 30CrMnSiA high-strength steel under a harsh marine atmosphere environment were systematically studied using accelerated test technology, along with corrosion kinetic analysis, microstructure and phase composition analysis, electrochemical measurements, and mechanical property tests. The influence of corrosion time on corrosion kinetics was characterized by the weight loss method. The corrosion layer and its product evolution were analyzed by SEM, EDS, XRD, and XPS. The corrosion behavior of steel was studied by a potentiodynamic polarization curve and EIS. Finally, the influence of corrosion on mechanical properties was studied by tensile and fatigue tests. The results show that 30CrMnSiA high strength steel has good corrosion resistance in a harsh marine atmosphere environment. Its corrosion behavior is cyclical: the outer rust layer exfoliated, the inner rust layer became the outer rust layer, and the matrix became inner rust due to the attack by the corrosive medium. The rust layer had a great protective effect on the matrix. The mechanical properties of 30CrMnSiA high-strength steel were reduced under the corrosive environment, and corrosion had a significant effect on its fatigue resistance.

Electrochemical performance of composite electrodes based on rGO, Mn/Cu metal–organic frameworks, and PANI

Benzendicarboxylic acid (BDC)-based metal–organic frameworks (MOFs) have been widely utilized in various applications, including supercapacitor electrode materials. Manganese and copper have solid diamond frames formed with BDC linkers among transition metals chosen for MOF formation. They have shown the possibility to enlarge capacitance at different combinations of MOFs and polyaniline (PANI). Herein, reduced graphene oxide (rGO) was used as the matrix to fabricate electrochemical double-layer SCs. PANI and Mn/Cu-MOF's effect on the properties of electrode materials was investigated through electrochemical analysis. As a result, the highest specific capacitance of about 276 F/g at a current density of 0.5 A/g was obtained for rGO/Cu-MOF@PANI composite.

Handheld SERS coupled with QuEChERs for the sensitive analysis of multiple pesticides in basmati rice

Pesticides are a safety issue globally and cause serious concerns for the environment, wildlife and human health. The handheld detection of four pesticide residues widely used in Basmati rice production using surface-enhanced Raman spectroscopy (SERS) is reported. Different SERS substrates were synthesised and their plasmonic and Raman scattering properties evaluated. Using this approach, detection limits for pesticide residues were achieved within the range of 5 ppb-75 ppb, in solvent. Various extraction techniques were assessed to recover pesticide residues from spiked Basmati rice. Quick, Easy, Cheap, Effective, Rugged and Safe (QuEChERs) acetate extraction was applied and characteristic spectral data for each pesticide was obtained from the spiked matrix and analysed using handheld-SERS. This approach allowed detection limits within the matrix conditions to be markedly improved, due to the rapid aggregation of nanogold caused by the extraction medium. Thus, detection limits for three out of four pesticides were detectable below the Maximum Residue Limits (MRLs) of 10 ppb in Basmati rice. Furthermore, the multiplexing performance of handheld-SERS was assessed in solvent and matrix conditions. This study highlights the great potential of handheld-SERS for the rapid on-site detection of pesticide residues in rice and other commodities.