Application of Electromagnetic Braking to Minimize a Surface Wave in a Continuous Caster.

The turbulent flow in the mold region drastically influences the quality of steel produced during continuous casting. The flow itself can lead to surface defects or slag entrainment based on the formation. A high surface wave can lead to fluctuations and the instability compromises the quality of the steel produced, as well as entrain the slag. To regulate the flow, electromagnetic forces can be applied in the mold, dampening the local turbulent flow. As the electrically conductive molten steel interacts with the induced magnetic field, it reduces the velocity of the steel jet released from the ports of the submerged entry nozzle. Utilizing Star-CCM+, a simulation-based study is conducted modeling the impact of Electromagnetic braking (EMBr) on the flow formation and surface standing wave. Specifically, a parametric study is conducted investigating the impact of submergence entry nozzle (SEN) depth and mold width with applied EMBr. Per the simulation-based study conducted increasing the EMBr strength from 2975 G to 4350 G reduced the average surface wave height by 12.5% and volume of flux rate of decrease by 4.25%. Additionally, increasing the SEN depth from 110 mm to 350 mm increased the average wave height by 19% and volume of flux rate of decrease by 2.6%. Lastly, increasing the mold width from 1.067 m to 1.50 m increased average wave height by 8.71% and volume of flux rate of decrease by 0.9%.

Aptidão funcional e qualidade de vida de idosos praticantes de Lian Gong, Tai Chi e Qigong / Aptitud funcional y calidad de vida de adultos mayores que practican Lian Gong, Tai Chi y Qigong / Functional fitness and quality of life of elderly Lian Gong, Tai Chi and Qigong practitioners

Resumo Objetivo Comparar a aptidão funcional e as dimensões da qualidade de vida de idosos participantes e não participantes das práticas orientadas Lian Gong, Tai Chi e Qigong. Métodos Estudo caso-controle, desenvolvido no município de São Paulo - SP, Brasil, com 118 idosos, pareados por sexo e idade: 59 no grupo caso, participantes das práticas corporais, divididos em subgrupos por tempo de adesão:< 24 meses e ≥ 24 meses; e 59 no grupo controle, não participantes das práticas. Para a coleta de dados, aplicaram-se: questionário com variáveis sociodemográficas e de saúde, testes funcionais e o instrumento Medical Outcomes Study 36- Item Short-Form Health Survey (SF36). As análises estatísticas foram realizadas com o programa R versão 3.3.2. Os dados foram inicialmente analisados de forma descritiva e, em seguida, efetuou-se regressão logística univariada e o teste Kruskal Wallis. Os aspectos éticos da pesquisa com seres humanos foram obedecidos. Resultados Verificou-se que, no grupo caso, idosos com tempo de adesão às práticas ≥ 24 meses apresentaram resultado superior no teste funcional de levantar e sentar da cadeira (p=0,006), bem como melhor desempenho nos seguintes domínios da qualidade de vida: dor (p= 0,003), vitalidade (p=0,021), aspectos emocionais (p=0,034) e saúde mental (p=0,020). Conclusão A participação nas práticas corporais, orientadas, Lian Gong, Tai Chi e Qigong pode contribuir para a qualidade de vida e a aptidão funcional de idosos.

Resumen Objetivo Comparar la aptitud funcional y las dimensiones de la calidad de vida de adultos mayores que participan y que no participan en prácticas orientadas Lian Gong, Tai Chi y Qigong. Métodos Estudio caso-control, realizado en el municipio de São Paulo - estado de São Paulo, Brasil, con 118 adultos mayores, pareados por sexo y edad: 59 en el grupo caso, participantes de las prácticas corporales, divididos en subgrupos por tiempo de participación: < 24 meses y ≥ 24 meses; y 59 en el grupo control, no participantes de las prácticas. Para la recopilación de datos, se aplicó un cuestionario con variables sociodemográficas y de salud, pruebas funcionales y el instrumento Medical Outcomes Study 36- Item Short-Form Health Survey (SF36). Los análisis estadísticos se realizaron con el programa R versión 3.3.2. Los datos se analizaron inicialmente de forma descriptiva y, a continuación, se realizó regresión logística univariada y la prueba de Kruskal Wallis. Los aspectos éticos de la investigación con seres humanos fueron cumplidos. Resultados Se verificó que, en el grupo caso, los adultos mayores con tiempo de participación en las prácticas ≥ 24 meses presentaron un resultado superior a la prueba funcional de levantarse y sentarse en la silla (p=0,006), como también un mejor desempeño en los siguientes dominios de calidad de vida: dolor (p= 0,003), vitalidad (p=0,021), aspectos emocionales (p=0,034) y salud mental (p=0,020). Conclusión La participación en las prácticas corporales orientadas Lian Gong, Tai Chi y Qigong puede contribuir para la calidad de vida y para la aptitud funcional de adultos mayores.

Abstract Objective To compare functional fitness and quality of life dimensions of elderly participants and non-participants of Lian Gong, Tai Chi and Qigong guided practices. Methods This is a case-control study, carried out in the city of São Paulo, SP, Brazil, with 118 elderly people, matched by sex and age: 59 in the case group, participants in body practices, divided into subgroups by time of compliance: < 24 months and ≥ 24 months; and 59 in the control group, non-participants in body practices. For data collection, the following were applied: a questionnaire with sociodemographic and health variables, functional tests and the Medical Outcomes Study 36- Item Short-Form Health Survey (SF-36). Statistical analyzes were performed using R version 3.3.2. The data were initially analyzed in a descriptive way and, then, a univariate logistic regression and the Kruskal Wallis test were performed. The ethical aspects of research with human beings were obeyed. Results It was found that, in the case group, elderly people with a time of compliance with practices ≥ 24 months showed a superior result in the functional 30-second chair stand test (p=0.006), as well as better performance in the following quality of life domains: bodily pain (p=0.003); vitality (p=0.021); role emotional (p=0.034); and mental health (p=0.020). Conclusion Participation in guided body practices, Lian Gong, Tai Chi and Qigong, can contribute to elderly people's quality of life and functional fitness.

Tuning the electro-optical properties of nanowire networks.

Conductive and transparent metallic nanowire networks are regarded as promising alternatives to Indium-Tin-Oxides (ITOs) in emerging flexible next-generation technologies due to their prominent optoelectronic properties and low-cost fabrication. The performance of such systems closely relies on many geometrical, physical, and intrinsic properties of the nanowire materials as well as the device-layout. A comprehensive computational study is essential to model and quantify the device's optical and electrical responses prior to fabrication. Here, we present a computational toolkit that exploits the electro-optical specifications of distinct device-layouts, namely standard random nanowire network and transparent mesh pattern structures. The target materials for transparent conducting electrodes of this study are aluminium, gold, copper, and silver nanowires. We have examined a variety of tunable parameters including network area fraction, length to diameter aspect ratio, and nanowires angular orientations under different device designs. Moreover, the optical extinction efficiency factors of each material are estimated by two approaches: Mie light scattering theory and finite element method (FEM) algorithm implemented in COMSOL®Multiphysics software. We studied various nanowire network structures and calculated their respective figures of merit (optical transmittance versus sheet resistance) from which insights on the design of next-generation transparent conductor devices can be inferred.

The endoscopic endonasal eustachian tube anterolateral mobilization strategy: minimizing the cost of the extreme-medial approach.

OBJECTIVE: The ventral jugular foramen and the infrapetrous region are difficult to access through conventional lateral and posterolateral approaches. Endoscopic endonasal approaches to this region are obstructed by the eustachian tube (ET). This study presents a novel strategy for mobilizing the ET while preserving its integrity. Qualitative and quantitative comparisons with previous ET management paradigms are also presented. METHODS: Ten dry skulls were analyzed. Four ET management strategies were sequentially performed on a total of 6 sides of cadaveric head specimens. Four measurement groups were generated: in group A, the ET was intact and not mobilized; in group B, the ET was mobilized inferolaterally; in group C, the ET underwent anterolateral mobilization; and in group D, the ET was resected. ET range of mobilization, surgical exposure area, and surgical freedom were measured and compared among the groups. RESULTS: Wide exposure of the infrapetrous region and jugular foramen was achieved by removing the pterygoid process, unroofing the cartilaginous ET up to the level of the posterior aspect of the foramen ovale, and detaching the ET from the skull base and soft palate. Anterolateral mobilization of the ET facilitated significantly more retraction (a 126% increase) of the ET than inferolateral mobilization (mean ± SD: 20.8 ± 11.2 mm vs 9.2 ± 3.6 mm [p = 0.02]). Compared with group A, groups C and D had enhanced surgical exposure (142.5% [1176.9 ± 935.7 mm2] and 155.9% [1242.0 ± 1096.2 mm2], respectively, vs 485.4 ± 377.6 mm2 for group A [both p = 0.02]). Furthermore, group C had a significantly larger surgical exposure area than group B (p = 0.02). No statistically significant difference was found between the area of exposure obtained by ET removal and anterolateral mobilization. Anterolateral mobilization of the ET resulted in a 39.5% increase in surgical freedom toward the exocranial jugular foramen compared with that obtained through inferolateral mobilization of the ET (67.2° ± 20.5° vs 48.1° ± 6.7° [p = 0.047]) and a 65.4% increase compared with that afforded by an intact ET position (67.2° ± 20.5° vs 40.6° ± 14.3° [p = 0.03]). CONCLUSIONS: Anterolateral mobilization of the ET provides excellent access to the ventral jugular foramen and infrapetrous region. The surgical exposure obtained is superior to that achieved with other ET management strategies and is comparable to that obtained by ET resection.

Nonlinear ion drift-diffusion memristance description of TiO2 RRAM devices.

The nature and direction of the hysteresis in memristive devices is critical to device operation and performance and the ability to realise their potential in neuromorphic applications. TiO2 is a prototypical memristive device material and is known to show hysteresis loops with both clockwise switching and counter-clockwise switching and in many instances evidence of negative differential resistance (NDR) behaviour. Here we study the electrical response of a device composed of a single nanowire channel Au-Ti/TiO2/Ti-Au both in air and under vacuum and simulate the I-V characteristics in each case using the Schottky barrier and an ohmic-like transport memristive model which capture nonlinear diffusion and migration of ions within the wire. The dynamics of this complex charge conduction phenomenon is obtained by fitting the nonlinear ion-drift equations with the experimental data. Our experimental results support a nonlinear drift of oxygen vacancies acting as shallow donors under vacuum conditions. Simulations show that dopant diffusion under bias creates a depletion region along the channel which results in NDR behaviour, but it is overcome at higher applied bias due to oxygen vacancy generation at the anode. The model allows the motion of the charged dopants to be visualised during device operation in air and under vacuum and predicts the elimination of the NDR under low bias operation, in agreement with experiments.

The Electro-Optical Performance of Silver Nanowire Networks.

Networks of metallic nanowires have the potential to meet the needs of next-generation device technologies that require flexible transparent conductors. At present, there does not exist a first principles model capable of predicting the electro-optical performance of a nanowire network. Here we combine an electrical model derived from fundamental material properties and electrical equations with an optical model based on Mie theory scattering of light by small particles. This approach enables the generation of analogues for any nanowire network and then accurately predicts, without the use of fitting factors, the optical transmittance and sheet resistance of the transparent electrode. Predictions are validated using experimental data from the literature of networks comprised of a wide range of aspect ratios (nanowire length/diameter). The separation of the contributions of the material resistance and the junction resistance allows the effectiveness of post-deposition processing methods to be evaluated and provides a benchmark for the minimum attainable sheet resistance. The predictive power of this model enables a material-by-design approach, whereby suitable systems can be prescribed for targeted technology applications.

Time-resolved impurity-invisibility in graphene nanoribbons.

We investigate time-resolved charge transport through graphene nanoribbons supplemented with adsorbed impurity atoms. Depending on the location of the impurities with respect to the hexagonal carbon lattice, the transport properties of the system may become invisible to the impurity due to the symmetry properties of the binding mechanism. This motivates a chemical sensing device since dopants affecting the underlying sublattice symmetry of the pristine graphene nanoribbon introduce scattering. Using the time-dependent Landauer-Büttiker formalism, we extend the stationary current-voltage picture to the transient regime, where we observe how the impurity invisibility takes place at sub-picosecond time scales further motivating ultrafast sensor technology. We further characterize time-dependent local charge and current profiles within the nanoribbons, and we identify rearrangements of the current pathways through the nanoribbons due to the impurities. We finally study the behavior of the transients with ac driving which provides another way of identifying the lattice-symmetry breaking caused by the impurities.

PHYSICAL ACTIVITY PROGRAM FOR ELDERLY AND ECONOMY FOR THE HEALTH SYSTEM.

OBJECTIVE: To evaluate the impact of physical activity on the use of the health system and the quality of life in sedentary elderly. METHODS: A prospective interventional study was carried out between March 2010 and February 2011 with 100 subjects (60-90 years of age,) divided into active group (AG) and control group (CG). During this period, AG performed physical exercise twice a week in 60-minute sessions and the CG remained sedentary with observation of their activities. Before and after the study, all subjects were clinically evaluated and completed a quality of life questionnaire. RESULTS: Eighty-nine subjects (AG = 44; CG = 45) were analyzed. AG had fewer visits to emergency room (p = 0.0056), hospitalizations (p = 0.0011), length of hospital stay (p = 0.0012) and fewer subsidiary tests (p = 0.0236) compared to the CG. The quality of life score analyzed before and after physical activity increased in AG compared to CG (p < 0.0001) and among subjects in AG (p < 0.0001), with no change in the CG. CONCLUSION: The intervention of a physical activity program for sedentary elderly can contribute to reduce the use of the health system and improve the quality of life. Level of evidence II, Therapeutics Studies. Prospective comparative study.

OBJETIVO: Avaliar o impacto da atividade física sobre o uso do sistema de saúde e a qualidade de vida em idosos sedentários. MÉTODOS: Estudo prospectivo intervencionista (março/2010 a fevereiro/2011) com 100 indivíduos (mín. 60 e máx. 90 anos de idade), divididos em grupo ativo (GA) e grupo controle (GC). Nesse período, o GA realizou exercício físico duas vezes por semana, em sessões de 60 minutos e o GC permaneceu sedentário, com observação de suas atividades. Antes e depois do estudo, todos os indivíduos foram avaliados clinicamente e responderam a um questionário de qualidade de vida. RESULTADOS: Foram analisados 89 indivíduos (44 no GA, e 45 no GC). O GA teve menor número de visitas ao pronto-socorro (p = 0,0056), internações (p = 0,0011), tempo de internação (p = 0,0012) e de exames subsidiários realizados (p = 0,0236) comparado com o GC. O escore de qualidade de vida, analisado pré e pós-atividade física apresentou aumento no GA em comparação com o GC (p < 0,0001) e entre os indivíduos do próprio GA (p < 0,0001), não havendo alteração no GC. CONCLUSÃO: A intervenção de um programa de atividade física para idosos sedentários pode contribuir para reduzir a utilização do sistema de saúde e melhorar a qualidade de vida. Nível de Evidência II, Estudos terapêuticos. Estudo prospectivo comparativo.

Emergence of winner-takes-all connectivity paths in random nanowire networks.

Nanowire networks are promising memristive architectures for neuromorphic applications due to their connectivity and neurosynaptic-like behaviours. Here, we demonstrate a self-similar scaling of the conductance of networks and the junctions that comprise them. We show this behavior is an emergent property of any junction-dominated network. A particular class of junctions naturally leads to the emergence of conductance plateaus and a "winner-takes-all" conducting path that spans the entire network, and which we show corresponds to the lowest-energy connectivity path. The memory stored in the conductance state is distributed across the network but encoded in specific connectivity pathways, similar to that found in biological systems. These results are expected to have important implications for development of neuromorphic devices based on reservoir computing.

Human Placenta Simulator for Intracranial-Intracranial Bypass: Vascular Anatomy and 5 Bypass Techniques.

BACKGROUND: Intracranial-intracranial (IC-IC) bypass surgery involves the use of significant technical bimanual skills. Indications for this procedure are limited, so training in a simulator with brain vessels similarity could maintain microsurgical dexterity. Our goal is to describe the human placenta vascular anatomy to guide IC-IC bypasses apprenticeship. METHODS: Human placenta vascular anatomy was reported and validated with comparison to brain main vessels after studying the vascular tree of 100 placentas. Five simulated IC-IC bypasses (end to end, end to lateral, lateral to lateral, aneurysm bridge, and aneurysm exiting branch transposition) were developed and construct and concurrent validated. Statistical analysis using the t variance test was performed with a confidence interval of 0.95. RESULTS: A total of 1200 placenta vessels were used for test-retest validation with a reliability index of 0.95. All 100 human placentas were suitable to perform the 5 different bypasses. Construct validity showed a P < 0.005. Concurrent validity highlighted the technical differences among simulators. CONCLUSIONS: An ex vivo bypass model offers great similarity to main brain vessels with the possibility to practice a variety of IC-IC bypass techniques in a single simulator. Placenta vascular anatomy knowledge can improve laboratory microsurgical training.

Physical activity program for elderly and economy for the health system / Programa de atividade física para idosos e economia para o sistema de saúde

ABSTRACT Objective: To evaluate the impact of physical activity on the use of the health system and the quality of life in sedentary elderly. Methods: A prospective interventional study was carried out between March 2010 and February 2011 with 100 subjects (60-90 years of age,) divided into active group (AG) and control group (CG). During this period, AG performed physical exercise twice a week in 60-minute sessions and the CG remained sedentary with observation of their activities. Before and after the study, all subjects were clinically evaluated and completed a quality of life questionnaire. Results: Eighty-nine subjects (AG = 44; CG = 45) were analyzed. AG had fewer visits to emergency room (p = 0.0056), hospitalizations (p = 0.0011), length of hospital stay (p = 0.0012) and fewer subsidiary tests (p = 0.0236) compared to the CG. The quality of life score analyzed before and after physical activity increased in AG compared to CG (p < 0.0001) and among subjects in AG (p < 0.0001), with no change in the CG. Conclusion: The intervention of a physical activity program for sedentary elderly can contribute to reduce the use of the health system and improve the quality of life. Level of evidence II, Therapeutics Studies. Prospective comparative study.

RESUMO Objetivo: Avaliar o impacto da atividade física sobre o uso do sistema de saúde e a qualidade de vida em idosos sedentários. Métodos: Estudo prospectivo intervencionista (março/2010 a fevereiro/2011) com 100 indivíduos (mín. 60 e máx. 90 anos de idade), divididos em grupo ativo (GA) e grupo controle (GC). Nesse período, o GA realizou exercício físico duas vezes por semana, em sessões de 60 minutos e o GC permaneceu sedentário, com observação de suas atividades. Antes e depois do estudo, todos os indivíduos foram avaliados clinicamente e responderam a um questionário de qualidade de vida. Resultados: Foram analisados 89 indivíduos (44 no GA, e 45 no GC). O GA teve menor número de visitas ao pronto-socorro (p = 0,0056), internações (p = 0,0011), tempo de internação (p = 0,0012) e de exames subsidiários realizados (p = 0,0236) comparado com o GC. O escore de qualidade de vida, analisado pré e pós-atividade física apresentou aumento no GA em comparação com o GC (p < 0,0001) e entre os indivíduos do próprio GA (p < 0,0001), não havendo alteração no GC. Conclusão: A intervenção de um programa de atividade física para idosos sedentários pode contribuir para reduzir a utilização do sistema de saúde e melhorar a qualidade de vida. Nível de Evidência II, Estudos terapêuticos. Estudo prospectivo comparativo.

Oxide-mediated recovery of field-effect mobility in plasma-treated MoS2.

Precise tunability of electronic properties of two-dimensional (2D) nanomaterials is a key goal of current research in this field of materials science. Chemical modification of layered transition metal dichalcogenides leads to the creation of heterostructures of low-dimensional variants of these materials. In particular, the effect of oxygen-containing plasma treatment on molybdenum disulfide (MoS2) has long been thought to be detrimental to the electrical performance of the material. We show that the mobility and conductivity of MoS2 can be precisely controlled and improved by systematic exposure to oxygen/argon plasma and characterize the material using advanced spectroscopy and microscopy. Through complementary theoretical modeling, which confirms conductivity enhancement, we infer the role of a transient 2D substoichiometric phase of molybdenum trioxide (2D-MoO x ) in modulating the electronic behavior of the material. Deduction of the beneficial role of MoO x will serve to open the field to new approaches with regard to the tunability of 2D semiconductors by their low-dimensional oxides in nano-modified heterostructures.

Learning brain aneurysm microsurgical skills in a human placenta model: predictive validity.

OBJECTIVE Surgery for brain aneurysms is technically demanding. In recent years, the process to learn the technical skills necessary for these challenging procedures has been affected by a decrease in the number of surgical cases available and progressive restrictions on resident training hours. To overcome these limitations, surgical simulators such as cadaver heads and human placenta models have been developed. However, the effectiveness of these models in improving technical skills is unknown. This study assessed concurrent and predictive validity of brain aneurysm surgery simulation in a human placenta model compared with a "live" human brain cadaveric model. METHODS Two human cadaver heads and 30 human placentas were used. Twelve neurosurgeons participated in the concurrent validity part of this study, each operating on 1 human cadaver head aneurysm model and 1 human placenta model. Simulators were evaluated regarding their ability to simulate different surgical steps encountered during real surgery. The time to complete the entire aneurysm task in each simulator was analyzed. The predictive validity component of the study involved 9 neurosurgical residents divided into 3 groups to perform simulation exercises, each lasting 6 weeks. The training for the 3 groups consisted of educational video only (3 residents), human cadaver only (3 residents), and human placenta only (3 residents). All residents had equivalent microsurgical experience with superficial brain tumor surgery. After completing their practice training, residents in each of the 3 simulation groups performed surgery for an unruptured middle cerebral artery (MCA) aneurysm, and their performance was assessed by an experienced vascular neurosurgeon who watched the operative videos. RESULTS All human cadaver heads and human placentas were suitable to simulate brain aneurysm surgery. In the concurrent validity portion of the experiment, the placenta model required a longer time (p < 0.001) than cadavers to complete the task. The placenta model was considered more effective than the cadaver model in simulating sylvian fissure splitting, bipolar coagulation of oozing microvessels, and aneurysm neck and dome dissection. Both models were equally effective in simulating neck aneurysm clipping, while the cadaver model was considered superior for simulation of intraoperative rupture and for reproduction of real anatomy during simulation. In the predictive validity portion of the experiment, residents were evaluated for 4 tasks: sylvian fissure dissection, microvessel bipolar coagulation, aneurysm dissection, and aneurysm clipping. Residents trained in the human placenta simulator consistently had the highest overall performance scores when compared with those who had trained in the cadaver model and those who had simply watched operative videos (p < 0.001). CONCLUSIONS The human placenta biological simulator provides excellent simulation for some critical tasks of aneurysm surgery such as splitting of the sylvian fissure, dissection of the aneurysm neck and dome, and bipolar coagulation of surrounding microvessels. When performing surgery for an unruptured MCA aneurysm, residents who had trained in the human placenta model performed better than residents trained with other simulation scenarios/models. In this age of reduced exposure to aneurysm surgery and restrictions on resident working hours, the placenta model is a valid simulation for microneurosurgery with striking similarities with real surgery.

Automated Inclusion Microanalysis in Steel by Computer-Based Scanning Electron Microscopy: Accelerating Voltage, Backscattered Electron Image Quality, and Analysis Time.

Automated inclusion microanalysis in steel samples by computer-based scanning electron microscopy provides rapid quantitative information on micro-inclusion distribution, composition, size distribution, morphology, and concentration. Performing the analysis at a lower accelerating voltage (10 kV), rather than the generally used 20 kV, improves analysis accuracy and may improve spatial resolution, but at the cost of a smaller backscattered electron signal and potentially smaller rate of generation of characteristic X-rays. These effects were quantified by simulation and practical measurements.

Sensitive electromechanical sensors using viscoelastic graphene-polymer nanocomposites.

Despite its widespread use in nanocomposites, the effect of embedding graphene in highly viscoelastic polymer matrices is not well understood. We added graphene to a lightly cross-linked polysilicone, often encountered as Silly Putty, changing its electromechanical properties substantially. The resulting nanocomposites display unusual electromechanical behavior, such as postdeformation temporal relaxation of electrical resistance and nonmonotonic changes in resistivity with strain. These phenomena are associated with the mobility of the nanosheets in the low-viscosity polymer matrix. By considering both the connectivity and mobility of the nanosheets, we developed a quantitative model that completely describes the electromechanical properties. These nanocomposites are sensitive electromechanical sensors with gauge factors >500 that can measure pulse, blood pressure, and even the impact associated with the footsteps of a small spider.

Effective medium theory for the conductivity of disordered metallic nanowire networks.

Motivated by numerous technological applications, there is current interest in the study of the conductive properties of networks made of randomly dispersed nanowires. The sheet resistance of such networks is normally calculated by numerically evaluating the conductance of a system of resistors but due to disorder and with so many variables to account for, calculations of this type are computationally demanding and may lack mathematical transparency. Here we establish the equivalence between the sheet resistance of disordered networks and that of a regular ordered network. Rather than through a fitting scheme, we provide a recipe to find the effective medium network that captures how the resistance of a nanowire network depends on several different parameters such as wire density, electrode size and electrode separation. Furthermore, the effective medium approach provides a simple way to distinguish the sheet resistance contribution of the junctions from that of the nanowires themselves. The contrast between these two contributions determines the potential to optimize the network performance for a particular application.

The influence of Gaussian strain on sublattice selectivity of impurities in graphene.

Among the different strategies used to induce the opening of a band gap in graphene, one common practice is through chemical doping. While a gap may be opened in this way, disorder-induced scattering is an unwanted side-effect that impacts the electron mobility in the conductive regime of the system. However, this undesirable side effect is known to be minimised if dopants interact asymmetrically with the two sublattices of graphene. In this work we propose that mechanical strain can be used to introduce such a sublattice asymmetry in the doping process of graphene. We argue that a localised out-of-plane deformation applied to a graphene sheet can make one of the graphene sublattices more energetically favourable for impurity adsorption than the other and that this can be controlled by varying the strain parameters. Two complementary modelling schemes are used to describe the electronic structure of the flat and deformed graphene sheets: a tight-binding model and density functional theory. Our results indicate a novel way to select the doping process of graphene through strain engineering.

Face, Content, and Construct Validity of Brain Tumor Microsurgery Simulation Using a Human Placenta Model.

BACKGROUND: Brain tumors are complex 3-dimensional lesions. Their resection involves training and the use of the multiple microsurgical techniques available for removal. Simulation models, with haptic and visual realism, may be useful for improving the bimanual technical skills of neurosurgical residents and neurosurgeons, potentially decreasing surgical errors and thus improving patient outcomes. OBJECTIVE: To describe and assess an ex vivo placental model for brain tumor microsurgery using a simulation tool in neurosurgical psychomotor teaching and assessment. METHODS: Sixteen human placentas were used in this research project. Intravascular blood remnants were removed by continuous saline solution irrigation of the 2 placental arteries and placental vein. Brain tumors were simulated using silicone injections in the placental stroma. Eight neurosurgeons and 8 neurosurgical residents carried out the resection of simulated tumors using the same surgical instruments and bimanual microsurgical techniques used to perform human brain tumor operations. Face and content validity was assessed using a subjective evaluation based on a 5-point Likert scale. Construct validity was assessed by analyzing the surgical performance of the neurosurgeon and resident groups. RESULTS: The placenta model simulated brain tumor surgical procedures with high fidelity. Results showed face and content validity. Construct validity was demonstrated by statistically different surgical performances among the evaluated groups. CONCLUSION: Human placentas are useful haptic models to simulate brain tumor microsurgical removal. Results using this model demonstrate face, content, and construct validity.

Resistance of Single Ag Nanowire Junctions and Their Role in the Conductivity of Nanowire Networks.

Networks of silver nanowires appear set to replace expensive indium tin oxide as the transparent conducting electrode material in next generation devices. The success of this approach depends on optimizing the material conductivity, which until now has largely focused on minimizing the junction resistance between wires. However, there have been no detailed reports on what the junction resistance is, nor is there a known benchmark for the minimum attainable sheet resistance of an optimized network. In this paper, we present junction resistance measurements of individual silver nanowire junctions, producing for the first time a distribution of junction resistance values and conclusively demonstrating that the junction contribution to the overall resistance can be reduced beyond that of the wires through standard processing techniques. We find that this distribution shows the presence of a small percentage (6%) of high-resistance junctions, and we show how these may impact the performance of network-based materials. Finally, through combining experiment with a rigorous model, we demonstrate the important role played by the network skeleton and the specific connectivity of the network in determining network performance.

Ultimate conductivity performance in metallic nanowire networks.

In this work, we introduce a combined experimental and computational approach to describe the conductivity of metallic nanowire networks. Due to their highly disordered nature, these materials are typically described by simplified models in which network junctions control the overall conductivity. Here, we introduce a combined experimental and simulation approach that involves a wire-by-wire junction-by-junction simulation of an actual network. Rather than dealing with computer-generated networks, we use a computational approach that captures the precise spatial distribution of wires from an SEM analysis of a real network. In this way, we fully account for all geometric aspects of the network, i.e. for the properties of the junctions and wire segments. Our model predicts characteristic junction resistances that are smaller than those found by earlier simplified models. The model outputs characteristic values that depend on the detailed connectivity of the network, which can be used to compare the performance of different networks and to predict the optimum performance of any network and its scope for improvement.