Operando unraveling photothermal-promoted dynamic active-sites generation in NiFe2O4 for markedly enhanced oxygen evolution.

The ability to develop highly active and low-cost electrocatalysts represents an important endeavor toward accelerating sluggish water-oxidation kinetics. Herein, we report the implementation and unraveling of the photothermal effect of spinel nanoparticles (NPs) on promoting dynamic active-sites generation to markedly enhance their oxygen evolution reaction (OER) activity via an integrated operando Raman and density functional theory (DFT) study. Specifically, NiFe2O4 (NFO) NPs are first synthesized by capitalizing on amphiphilic star-like diblock copolymers as nanoreactors. Upon the near-infrared light irradiation, the photothermal heating of the NFO-based electrode progressively raises the temperature, accompanied by a marked decrease of overpotential. Accordingly, only an overpotential of 309 mV is required to yield a high current density of 100 mA cm-2, greatly lower than recently reported earth-abundant electrocatalysts. More importantly, the photothermal effect of NFO NPs facilitates surface reconstruction into high-active oxyhydroxides at lower potential (1.36 V) under OER conditions, as revealed by operando Raman spectroelectrochemistry. The DFT calculation corroborates that these reconstructed (Ni,Fe)oxyhydroxides are electrocatalytically active sites as the kinetics barrier is largely reduced over pure NFO without surface reconstruction. Given the diversity of materials (metal oxides, sulfides, phosphides, etc.) possessing the photo-to-thermal conversion, this effect may thus provide a unique and robust platform to boost highly active surface species in nanomaterials for a fundamental understanding of enhanced performance that may underpin future advances in electrocatalysis, photocatalysis, solar-energy conversion, and renewable-energy production.

Recent advances in activating surface reconstruction for the high-efficiency oxygen evolution reaction.

A climax in the development of cost-effective and high-efficiency transition metal-based electrocatalysts has been witnessed recently for sustainable energy and related conversion technologies. In this regard, structure-activity relationships based on several descriptors have already been proposed to rationally design electrocatalysts. However, the dynamic reconstruction of the surface structures and compositions of catalysts during electrocatalytic water oxidation, especially during the anodic oxygen evolution reaction (OER), complicate the streamlined prediction of the catalytic activity. With the achievements in operando and in situ techniques, it has been found that electrocatalysts undergo surface reconstruction to form the actual active species in situ accompanied with an increase in their oxidation state during OER in alkaline solution. Accordingly, a thorough understanding of the surface reconstruction process plays a critical role in establishing unambiguous structure-composition-property relationships in pursuit of high-efficiency electrocatalysts. However, several issues still need to be explored before high electrocatalytic activities can be realized, as follows: (1) the identification of initiators and pathways for surface reconstruction, (2) establishing the relationships between structure, composition, and electrocatalytic activity, and (3) the rational manipulation of in situ catalyst surface reconstruction. In this review, the recent progress in the surface reconstruction of transition metal-based OER catalysts including oxides, non-oxides, hydroxides and alloys is summarized, emphasizing the fundamental understanding of reconstruction behavior from the original precatalysts to the actual catalysts based on operando analysis and theoretical calculations. The state-of-the-art strategies to tailor the surface reconstruction such as substituting/doping with metals, introducing anions, incorporating oxygen vacancies, tuning morphologies and exploiting plasmonic/thermal/photothermal effects are then introduced. Notably, comprehensive operando/in situ characterization together with computational calculations are responsible for unveiling the improvement mechanism for OER. By delivering the progress, strategies, insights, techniques, and perspectives, this review will provide a comprehensive understanding of the surface reconstruction in transition metal-based OER catalysts and future guidelines for their rational development.

Lithium-Conducting Branched Polymers: New Paradigm of Solid-State Electrolytes for Batteries.

The past decades have witnessed rapid development of lithium-based batteries. Significant research efforts have been progressively diverted from electrodes to electrolytes, particularly polymer electrolytes (PEs), to tackle the safety concern and promote the energy storage capability of batteries. To further increase the ionic conductivity of PEs, various branched polymers (BPs) have been rationally designed and synthesized. Compared with linear polymers, branched architectures effectively increase polymer segmental mobility, restrain crystallization, and reduce chain entanglement, thereby rendering BPs with greatly enhanced lithium transport. In this Mini Review, a diversity of BPs for PEs is summarized by scrutinizing their unique topologies and properties. Subsequently, the design principles for enhancing the physical properties, mechanical properties, and electrochemical performance of BP-based PEs (BP-PEs) are provided in which the ionic conduction is particularly examined in light of the Li+ transport mechanism. Finally, the challenges and future prospects of BP-PEs in this rapidly evolving field are outlined.

Metal-Organic Frameworks for Ion Conduction.

Solid-state ionic conductors are compelling alternatives to liquid electrolytes in clean energy-harvesting and -storage technologies. The development of novel ionic conducting materials is one of the most critical challenges for next-generation energy technologies. Several advancements in design strategies, synthetic approaches, conducting properties, and underlying mechanisms for ionic conducting metal-organic frameworks (MOFs) have been made over the past five years; however, despite the recent, considerable expansion of related research fields, there remains a lack of systematic overviews. Here, an extensive introduction to ionic conducting performance for MOFs with different design strategies is provided, focusing primarily on ion mobility with the aid of hydrogen-bonding networks or solvated ionic charge. Furthermore, current theories on ion conducting mechanisms in different regimes are comprehensively summarized to provide an understanding of the underlying working principles in complex, realistic systems. Finally, challenges and future research directions at the forefront of ionic conducting MOF technologies are outlined.

Recent Advances in Silicon-Based Electrodes: From Fundamental Research toward Practical Applications.

The increasing demand for higher-energy-density batteries driven by advancements in electric vehicles, hybrid electric vehicles, and portable electronic devices necessitates the development of alternative anode materials with a specific capacity beyond that of traditional graphite anodes. Here, the state-of-the-art developments made in the rational design of Si-based electrodes and their progression toward practical application are presented. First, a comprehensive overview of fundamental electrochemistry and selected critical challenges is given, including their large volume expansion, unstable solid electrolyte interface (SEI) growth, low initial Coulombic efficiency, low areal capacity, and safety issues. Second, the principles of potential solutions including nanoarchitectured construction, surface/interface engineering, novel binder and electrolyte design, and designing the whole electrode for stability are discussed in detail. Third, applications for Si-based anodes beyond LIBs are highlighted, specifically noting their promise in configurations of Li-S batteries and all-solid-state batteries. Fourth, the electrochemical reaction process, structural evolution, and degradation mechanisms are systematically investigated by advanced in situ and operando characterizations. Finally, the future trends and perspectives with an emphasis on commercialization of Si-based electrodes are provided. Si-based anode materials will be key in helping keep up with the demands for higher energy density in the coming decades.

Scalable Contour Tree Computation by Data Parallel Peak Pruning.

As data sets grow to exascale, automated data analysis and visualization are increasingly important, to intermediate human understanding and to reduce demands on disk storage via in situ analysis. Trends in architecture of high performance computing systems necessitate analysis algorithms to make effective use of combinations of massively multicore and distributed systems. One of the principal analytic tools is the contour tree, which analyses relationships between contours to identify features of more than local importance. Unfortunately, the predominant algorithms for computing the contour tree are explicitly serial, and founded on serial metaphors, which has limited the scalability of this form of analysis. While there is some work on distributed contour tree computation, and separately on hybrid GPU-CPU computation, there is no efficient algorithm with strong formal guarantees on performance allied with fast practical performance. We report the first shared SMP algorithm for fully parallel contour tree computation, with formal guarantees of O(lg V lg t) parallel steps and O(V lg V) work for data with V samples and t contour tree supernodes, and implementations with more than 30× parallel speed up on both CPU using TBB and GPU using Thrust and up 70× speed up compared to the serial sweep and merge algorithm.

Providing metrics and performance feedback in a surgical simulator.

One of the most important advantages of computer simulators for surgical training is the opportunity they afford for independent learning. However, if the simulator does not provide useful instructional feedback to the user, this advantage is significantly blunted by the need for an instructor to supervise and tutor the trainee while using the simulator. Thus, the incorporation of relevant, intuitive metrics is essential to the development of efficient simulators. Equally as important is the presentation of such metrics to the user in such a way so as to provide constructive feedback that facilitates independent learning and improvement. This paper presents a number of novel metrics for the automated evaluation of surgical technique. The general approach was to take criteria that are intuitive to surgeons and develop ways to quantify them in a simulator. Although many of the concepts behind these metrics have wide application throughout surgery, they have been implemented specifically in the context of a simulation of mastoidectomy. First, the visuohaptic simulator itself is described, followed by the details of a wide variety of metrics designed to assess the user's performance. We present mechanisms for presenting visualizations and other feedback based on these metrics during a virtual procedure. We further describe a novel performance evaluation console that displays metric-based information during an automated debriefing session. Finally, the results of several user studies are reported, providing some preliminary validation of the simulator, the metrics, and the feedback mechanisms. Several machine learning algorithms, including Hidden Markov Models and a Naïve Bayes Classifier, are applied to our simulator data to automatically differentiate users' expertise levels.

Representing fluid with smoothed particle hydrodynamics in a cranial base simulator.

We describe the implementation of irrigation and blood simulation using Smoothed Particle Hydrodynamics (SPH) in a cranial base surgical simulator. Graphical accuracy of virtual surgery is a significant goal for improving the realism and immersive experience of computerized training environments. For temporal bone micro-surgery fluids contribute not only to the visual integrity of the surgical field but provide relevant anatomic cues as well. The skill of 3-D sensory and navigation has become increasingly viable in surgery with the rising popularity of laparoscopic, catheter angiography and other minimally invasive approaches. The introduction of realistic simulated blood and irrigation enables the practice and coordination of two-handed microdissection techniques and the timing needed for safe bone removal and cautery.

Evaluating drilling and suctioning technique in a mastoidectomy simulator.

This paper presents several new metrics related to bone removal and suctioning technique in the context of a mastoidectomy simulator. The expertise with which decisions as to which regions of bone to remove and which to leave intact is evaluated by building a Naïve Bayes classifier using training data from known experts and novices. Since the bone voxel mesh is very large, and many voxels are always either removed or not removed regardless of expertise, the mutual information was calculated for each voxel and only the most informative voxels used for the classifier. Leave-out-one cross validation showed a high correlation of calculated expert probabilities with scores assigned by instructors. Additional metrics described in this paper include those for assessing smoothness of drill strokes, proper drill burr selection, sufficiency of suctioning, two-handed tool coordination, and application of appropriate force and velocity magnitudes as functions of distance from critical structures.

Validating metrics for a mastoidectomy simulator.

One of the primary barriers to the acceptance of surgical simulators is that most simulators still require a significant amount of an instructing surgeon's time to evaluate and provide feedback to the students using them. Thus, an important area of research in this field is the development of metrics that can enable a simulator to be an essentially self-contained teaching tool, capable of identifying and explaining the user's weaknesses. However, it is essential that these metrics be validated in able to ensure that the evaluations provided by the "virtual instructor" match those that the real instructor would provide were he/she present. We have previously proposed a number of algorithms for providing automated feedback in the context of a mastoidectomy simulator. In this paper, we present the results of a user study in which we attempted to establish construct validity (with inter-rater reliability) for our simulator itself and to validate our metrics. Fifteen subjects (8 experts, 7 novices) were asked to perform two virtual mastoidectomies. Each virtual procedure was recorded, and two experienced instructing surgeons assigned global scores that were correlated with subjects' experience levels. We then validated our metrics by correlating the scores generated by our algorithms with the instructors' global ratings, as well as with metric-specific sub-scores assigned by one of the instructors.

Achieving proper exposure in surgical simulation.

One important technique common throughout surgery is achieving proper exposure of critical anatomic structures so that their shapes, which may vary somewhat among patients, can be confidently established and avoided. In this paper, we present an algorithm for determining which regions of selected structures are properly exposed in the context of a mastoidectomy simulation. Furthermore, our algorithm then finds and displays all other points along the surface of the structure that lie along a sufficiently short and straight path from an exposed portion such that their locations can be safely inferred. Finally, we present an algorithm for providing realistic visual cues about underlying structures with view-dependent shading of the bone.

VTK-m: Accelerating the Visualization Toolkit for Massively Threaded Architectures.

One of the most critical challenges for high-performance computing (HPC) scientific visualization is execution on massively threaded processors. Of the many fundamental changes we are seeing in HPC systems, one of the most profound is a reliance on new processor types optimized for execution bandwidth over latency hiding. Our current production scientific visualization software is not designed for these new types of architectures. To address this issue, the VTK-m framework serves as a container for algorithms, provides flexible data representation, and simplifies the design of visualization algorithms on new and future computer architecture.

Quantifying risky behavior in surgical simulation.

Evaluating a trainee's performance on a simulated procedure involves determining whether a specified objective was met while avoiding certain "injurious" actions that damage vulnerable structures. However, it is also important to teach the stylistic behaviors that minimize overall risk to the patient, even though these criteria may be more difficult to explicitly specify and detect. In this paper, we address the development of metrics that evaluate the risk in a trainee's behavior while performing a simulated mastoidectomy. Specifically, we measure the trainee's ability to maintain an appropriate field of view so as to avoid drilling bone that is hidden from view, as well as to consistently apply appropriate forces and velocities. Models of the maximum safe force and velocity magnitudes as functions of distances from key vulnerable structures are learned from model procedures performed by an expert surgeon on the simulator. In addition to quantitatively scoring the trainee's performance, these metrics allow for interactive 3D visualization of the performance by distinctive coloring of regions in which excessive forces or velocities were applied or insufficient visibility was maintained, enabling the trainee to pinpoint his/her mistakes and how to correct them. Although these risky behaviors relate to a mastoidectomy simulator, the objectives of maintaining visibility and applying safe forces and velocities are common in surgery, so it may be possible to extend much of this methodology to other procedures.

Anxiety and the neural processing of threat in faces.

This study examined the relationship between social anxiety and the neural processing of threat in faces. Twenty-one adults with different levels of society anxiety were tested for their event-related potential responses to unattended threatening and nonthreatening faces, presented upright and upside-down, at three points in time: 160-210 ms (vertex positive potential), 300-350 ms (N3) and 440-500 ms (P3). Social anxiety was significantly correlated with the size of P3 to upright angry faces but not happy faces. This supports the theory that anxiety diverts attention towards goal-irrelevant threat cues, and suggests that this threat-related shift in attention starts to affect the processing of faces at 440-500 ms.

Visuohaptic simulation of bone surgery for training and evaluation.

Visual and haptic simulation of bone surgery can support and extend current surgical training techniques. The authors present a system for simulating surgeries involving bone manipulation, such as temporal bone surgery and mandibular surgery, and discuss the automatic computation of surgical performance metrics. Experimental results confirm the system's construct validity.

Reduction and methyl transfer kinetics of the alpha subunit from acetyl coenzyme a synthase.

Stopped-flow was used to evaluate the methylation and reduction kinetics of the isolated alpha subunit of acetyl-Coenzyme A synthase from Moorella thermoacetica. This catalytically active subunit contains a novel Ni-X-Fe4S4 cluster and a putative unidentified n = 2 redox site called D. The D-site must be reduced for a methyl group to transfer from a corrinoid-iron-sulfur protein, a key step in the catalytic synthesis of acetyl-CoA. The Fe4S4 component of this cluster is also redox active, raising the possibility that it is the D-site or a portion thereof. Results presented demonstrate that the D-site reduces far faster than the Fe4S4 component, effectively eliminating this possibility. Rather, this component may alter catalytically important properties of the Ni center. The D-site is reduced through a pathway that probably does not involve the Fe4S4 component of this active-site cluster.

Stopped-Flow Kinetics of Methyl Group Transfer between the Corrinoid-Iron-Sulfur Protein and Acetyl-Coenzyme A Synthase from Clostridium thermoaceticum.

Kinetics of methyl group transfer between the Ni-Fe-S-containing acetyl-CoA synthase (ACS) and the corrinoid protein (CoFeSP) from Clostridium thermoaceticum were investigated using the stopped-flow method at 390 nm. Rates of the reaction CH(3)-Co(3+)FeSP + ACS(red) <==> Co(1+)FeSP + CH(3)-ACS(ox) in both forward and reverse directions were determined using various protein and reductant concentrations. Ti(3+)citrate, dithionite, and CO were used to reductively activate ACS (forming ACS(red)). The simplest mechanism that adequately fit the data involved formation of a [CH(3)-Co(3+)FeSP]:[ACS(red)] complex, methyl group transfer (forming [Co(1+)FeSP]:[CH(3)-ACS(ox)]), product dissociation (forming Co(1+)FeSP + CH(3)-ACS(ox)), and CO binding yielding a nonproductive enzyme state (ACS(red) + CO <==> ACS(red)-CO). Best-fit rate constants were obtained. CO inhibited methyl group transfer by binding ACS(red) in accordance with K(D) = 180 +/- 90 microM. Fits were unimproved when >1 CO was assumed to bind. Ti(3+)citrate and dithionite inhibited the reverse methyl group transfer reaction, probably by reducing the D-site of CH(3)-ACS(ox). This redox site is oxidized by 2e(-) when the methyl cation is transferred from CH(3)-Co(3+)FeSP to ACS(red), and is reduced during the reverse reaction. Best-fit K(D) values for pre- and post-methyl-transfer complexes were 0.12 +/- 0.06 and 0.3 +/- 0.2 microM, respectively. Intracomplex methyl group transfer was reversible with K(eq) = 2.3 +/- 0.9 (k(f)/k(r) = 6.9 s(-1)/3.0 s(-1)). The nucleophilicity of the [Ni(2+)D(red)] unit appears comparable to that of Co(1+) cobalamins. Reduction of the D-site may cause the Ni(2+) of the A-cluster to behave like the Ni of an organometallic Ni(0) complex.

Analysis of protein homeostatic regulatory mechanisms in perturbed environments at steady state.

Nine different protein homeostatic regulatory mechanisms were analysed for their ability to maintain a generic protein P within a specified range of a set-point steady-state concentration while perturbed by external processes that altered the rates at which P was produced and/or consumed. Steady state regulatory effectiveness was defined by the area within a rectangular region of "perturbation space", where axes correspond to rates of positive and negative perturbations. The size of this region differed in accordance with the regulatory elements composing the homeostatic mechanism. Such elements included basic negative feedback control of transcription (in which P, at some high concentration relative to its set-point value, binds to the gene G that encodes it, thereby inhibiting transcription), multiple sequential binding of a feedback effector (two P's bind sequentially to G), and dimerization of a feedback effector (a P(2) dimer binds to G). Two homeostatic mechanisms included a cascade structure, one with and one without translational feedback control. Another mechanism included feedback control of P degradation. Finally, two mechanisms illustrated the limits of regulatory systems. One lacked all regulatory elements (and included only an invariant rate of P synthesis and degradation) while the other assumed perfect (Boolean) regulation, in which transcription is completely inhibited at [P]>[P](sp) and is fully active at [P]<[P](sp). All of the systems evaluated are known, but the analytical expressions developed here allow quantitative comparisons between them. These expressions were evaluated at values typical of the average protein in Escherichia coli. A method for building regulatory networks by linking semi-independent regulatory modules is discussed.