Actual Cycling Research Articles

Improving Cycling Behaviors of Dockless Bike-Sharing Users Based on an Extended Theory of Planned Behavior and Credit-Based Supervision Policies in China.

Motivating users’ civilized cycling plays a significant role in alleviating the troubles of dockless bike-sharing programs (DBSPs) and promoting the sustainable development of bike-sharing organizations. Based on the theory of planned behavior (TPB) and observed practices in China, this study develops a theoretical framework to examine how attitudes (ATT), subjective norms (SN), perceived behavioral control (PBC), and personal norms (PN) motivate users’ civilized cycling behavior through civilized cycling intentions. Furthermore, the moderating effect of perceived policy effectiveness (PPE) between users’ civilized cycling intention and their actual behavior is tested. Using structural equation model-multiple group analysis (SEM-MGA) for a sample of 874 valid questionnaire responses in Beijing and Shanghai, China, our results reveal that (1) ATT, PBC, and PN are positively related to both users’ civilized cycling intentions and their actual behavior, while SN positively affect users’ civilized cycling intention only; (2) users’ civilized cycling intentions mediate the relationship between the four influencing factors and their actual behavior; and (3) PPE plays a moderating role for the effect of users’ civilized cycling intentions on their actual civilized cycling behavior. Our results indicate that the four influencing factors can encourage users’ civilized cycling behavior, especially when civilized cycling intention exists. Policies like credit-based supervision mechanisms could promote users’ civilized-cycling intentions, which could then be transformed into actual behavior.

Effect of Thermal Cycling on Operational Characteristics and Lifetime Prediction of Space Pulse Tube Refrigerator

This paper presents the operation status and results of ground thermal cycling test of pulse tube refrigerators (PTRs) for space application. Firstly, a thermal cycling degradation model was proposed by considering two physical mechanisms: contamination and fatigue damage. Then, a thermal cycling test scheme of two types of PTRs was designed and performed to demonstrate their long lifetime and high thermal stability. Two type A PTRs with cooling capacity of 1W@60 K and two type B PTRs with cooling capacity of 5W@80 K were continuously operated for about two years in a simulated vacuum thermal cycling environment. Effects of heat rejection temperature variation on thermal stability and dynamic performance of the PTRs were investigated. Furthermore, the thermal cycling degradation model was validated with the actual thermal cycling test data. Finally, the predicted pseudo-failure lifetime was acquired via experimental data and degradation model. Moreover, the estimated reliability of PTRs was obtained through using the Weibull distribution. The proposed thermal cycling test scheme and innovative lifetime prediction and reliability estimation method provide a quick and accurate approach for the cooler manufacturer to assess the lifetime and reliability of the space PTRs.

Design of an isokinetic knee dynamometer for evaluation of functional electrical stimulation strategies

BackgroundThe limitations of functional electrical stimulation (FES) cycling directly affect the health benefits acquired from this technology and prevents its’ full potential to be realised. Experiments should be done on a test bed which can isolate and focus only on one muscle group, namely the quadriceps. The aim of this work was to design and develop an isokinetic robotic leg extension/flexion dynamometer which can mimic knee joint motion during actual cycling to be used for evaluation of novel functional electrical stimulation strategies. Although the main motivation for development of the dynamometer was for application in FES studies, it has the potential to be used for various different muscle physiology studies. MethodsA feedback control system with integrated electrical stimulation for isokinetic knee joint torque measurement has been developed and tested for safety and functionality. The leg extension/flexion device was modified and equipped with a DC motor drive system to imitate isokinetic knee joint motion during cycling when the hip joint remains fixed. Real-time bi-directional effective torque on the lever arm was measured by a magnetostrictive torque sensor and a load cell. Closed-loop motor control system was also designed to mimic the cyclical motion at desired angular velocity. ResultsA functional model of the robotic dynamometer was developed and evaluated. The dynamometer is capable of simulating the knee angle during cycling at a cadence of up to 70 rpm with range of motion of 72∘. The magnetostrictive torque sensor can measure torque values up to 75 Nm. The lever arm can be adjusted and the target knee angle was controlled with RMSE tracking error of less than 2.1∘ in tests with and without a test person, and with and without muscle stimulation. ConclusionsThe isokinetic knee joint torque measurement system was designed and validated in this work, and subsequently used to develop and evaluate novel muscle activation strategies. This is important for fundamental research on effective stimulation patterns and novel activation strategies. This will, in turn, enhance the efficiency of FES cycling exercise and has the potential to improve the health-beneficial effects.

Vertical variation of bulk and metabolically active prokaryotic community in sediment of a hypereutrophic freshwater lake.

This study was conducted to acquire novel insight into differences between bulk (16S rDNA) and metabolically active (16S rRNA) prokaryotic communities in the sediment of a hypereutrophic lake (Japan). In the bulk communities, the class Deltaproteobacteria and the order Methanomicrobiales were dominant among bacteria and methanogens. In the metabolically active communities, the class Alphaproteobacteria and the order Methanomicrobiales and the family Methanosaetaceae were frequently found among bacteria and methanogens. Unlike the bulk communities of prokaryotes, the composition of the metabolically active communities varied remarkably vertically, and their diversities greatly decreased in the lower 20cm of sediment. The metabolically active prokaryotic community in the sediment core was divided into three sections based on their similarity: 0-6cm (section 1), 9-18cm (section 2), and 21-42cm (section 3). This sectional distribution was consistent with the vertical pattern of the sedimentary stable carbon and nitrogen isotope ratios and oxidation-reduction potential in the porewater. These results suggest that vertical disturbance of the sediment may influence the communities and functions of metabolically active prokaryotes in freshwater lake sediments. Overall, our results indicate that rRNA analysis may be more effective than rDNA analysis for evaluation of relationships between actual microbial processes and material cycling in lake sediments.

Evaluati on of long-term start up costs impact on short-term price based operational optimization of a CCGT using MILP

An increasing share of the weather-dependent RES generation in the power system leads to the growing importance of flexibility of conventional power plants. They were usually designed for base load operation and it is a challenge to determine the actual long-term cycling costs, which account for an increase in maintenance and overhaul expenditures, increased forced outage rates and shortened life expectancy of the plant and components. In this paper, the overall impact of start up costs is evaluated by formulating and solving price based unit commitment problem (PBUC). The electricity spot market is considered as a measure for remunerating flexibility. This approach is applied to a real-life case study based on the 70 MWe PGE Gorzόw CCGT power plant. Different operation modes are calculated and results are used to derive a mixed integer linear programming (MILP) model to optimize the operation of the plant. The developed mathematical model is implemented in Python within the frame of the PuLP library and solved using GUROBI. Results of the application of the method to a numerical example are presented.

OA018] Improved absolute metabolite quantification by localized magnetic resonance spectroscopy simulations

Purpose Magnetic resonance spectroscopy (MRS) provides a non-invasive method for assessment of the in vivo abundance of metabolites and serves as a useful diagnostic tool for several pathologies. The most common method for quantification of metabolite abundance includes fitting a linear combination of individual a priori acquired metabolite spectra. The set of individual metabolite spectra (basis set) can either be acquired through phantom measurements or simulations. While simulation has recently become more popular, it is not clear at what complexity level the simulations have to be run. The aim of this work was to study the impact of simulation complexity on absolute concentration estimates. Specifically, results based on non-localized and localized simulations were compared. Methods The Braino phantom (General Electric) containing the most common brain metabolites was used in this study. It included choline (Cho, 3.0 mM), creatine (Cr, 10.0 mM), lactate (Lac, 5.0 mM), myoinositole (mI, 7.5 mM), glutamic acid (Glu, 12.5 mM) and N-acetylactic acid (NAA, 12.5 mM). MR spectra were acquired on a Philips Achieva 3 T scanner with the PRESS pulse sequence. Parameters: echo time 35 ms, repetition time 5000 ms, number of acquisitions 128, volume of interest size 20 × 20 × 20 mm3. Basis sets were generated in MATLAB with the same sequence timing as on the scanner both with a non-localized simulation (using ideal RF pulses) and with a localized simulation (using the actual RF pulses, gradient waveforms and phase cycling scheme as on the scanner) using full density matrix calculations. The acquired spectra were analyzed with LCModel. Metabolite concentrations were separately estimated based on the two basis sets. Results The estimated concentrations based on localized simulations were closer to true ones for all metabolites: Cho 3.6/3.5 mM, Cr 10.8/10.5 mM, Lac 3.8/5.3 mM, mI 6.5/6.9 mM, Glu 12.7/12.6 mM, NAA 13.3/13.1 mM (ideal/localized). A substantial gain in accuracy was especially seen for lactate which was underestimated by 24% with the non-localized simulation, but overestimated by only 6% by the localized simulation. Conclusions Metabolite quantification was improved by inclusion of actual RF pulses, gradient waveforms and phase cycling scheme. This was especially seen for lactate.

Differences in physical environmental characteristics between adolescents\u2019 actual and shortest cycling routes: a study using a Google Street View-based audit

BackgroundThe objective evaluation of the physical environmental characteristics (e.g. speed limit, cycling infrastructure) along adolescents’ actual cycling routes remains understudied, although it may provide important insights into why adolescents prefer one cycling route over another. The present study aims to gain insight into the physical environmental characteristics determining the route choice of adolescent cyclists by comparing differences in physical environmental characteristics between their actual cycling routes and the shortest possible cycling routes.MethodsAdolescents (n = 204; 46.5% boys; 14.4 ± 1.2 years) recruited at secondary schools in and around Ghent (city in Flanders, northern part of Belgium) were instructed to wear a Global Positioning System device in order to identify cycling trips. For all identified cycling trips, the shortest possible route that could have been taken was calculated. Actual cycling routes that were not the shortest possible cycling routes were divided into street segments. Segments were audited with a Google Street View-based tool to assess physical environmental characteristics along actual and shortest cycling routes.ResultsOut of 160 actual cycling trips, 73.1% did not differ from the shortest possible cycling route. For actual cycling routes that were not the shortest cycling route, a speed limit of 30 km/h, roads having few buildings with windows on the street side and roads without cycle lane were more frequently present compared to the shortest possible cycling routes. A mixed land use, roads with commercial destinations, arterial roads, cycle lanes separated from traffic by white lines, small cycle lanes and cycle lanes covered by lighting were less frequently present along actual cycling routes compared to the shortest possible cycling routes.ConclusionsResults showed that distance mainly determines the route along which adolescents cycle. In addition, adolescents cycled more along residential streets (even if no cycle lane was present) and less along busy, arterial roads. Local authorities should provide shortcuts free from motorised traffic to meet adolescents’ preference to cycle along the shortest route and to avoid cycling along arterial roads.

Modeling Solid-Electrolyte Interphase (SEI) Fracture: Coupled Mechanical/Chemical Degradation of the Lithium Ion Battery

In lithium ion batteries, intercalation and deintercalation of lithium may result in volume changes that induce stresses in the lithium-host electrode-material particles. At relatively high rates of charging or discharging, the host electrode particles may see large lithium concentration gradients which may result in fracture and pulverization due to large diffusion-induced stresses. Conversely, during low-rate charge/discharge operations, the lithium concentration gradients in the particle are minimal; in turn, the internal stresses to which the electrode particles are subjected are low. The electrode particle-cracking models fail to explain why cells exhibit higher coulombic capacity loss during low-rate cycling than during storage. The primary reason being that most of these models focus on understanding the host particle pulverization but fall short of recognizing the importance of possible mechanical degradation of the solid electrolyte interphase (SEI) layer. In this article, we develop a mathematical model to study stresses experienced by the SEI and demonstrate that stresses of large magnitude are exerted on the SEI layer during the expansion/contraction of an electrode particle which may fracture the SEI layer. With these stress calculations we also show that the larger the state-of-lithiation (SOL) change (or ‘swing’) during a lithiation event, the larger the possibility of SEI fracture. We propose that at lower discharge/charge rates of battery operation the SEI cracking and reforming, rather than the host particle fatigue, is a dominant mechanism of cell capacity loss. The capacity loss due to SEI cracking is shown to be proportional to the square of the SOL swing of the electrode particle during lithiation. An equation is derived to estimate battery capacity fade with SEI fracture and reformation as the main capacity-loss mechanism. The equation is used to estimate capacity fade during actual cell cycling experiments with satisfactory agreement between estimated and observed capacity fade with only one adjustable parameter.

Research and Application of Device for Simulation Sports Training based on Cycle Condition

The slope simulation method of the spiral mechanism, the rubbing transmission, the resistance simulation method of magnetic particle brake loading on the rear wheel is proposed by anglicizing the road sports conditions and resistance of the actual cycling. the structure design, loading design and control design of the road sports condition simulator is designed. the structure of putting the motor forward and forcing the big sprocket rotation through the chain transmission, and the method of the frequency converter regulates the rotational speed of the motor within the range of certain frequency, PLC programming the rotation rules is adopted. The complete device is applied to athletes sports training of the national bicycle team at ordinary times after debugging successfully.

Riding performance on a conventional bicycle and a pedelec in low speed exercises: Objective and subjective evaluation of middle-aged and older persons

This study investigated cycling performance of middle-aged (30–45yearsold; n=30) versus older (65+ years; n=31) participants during low-speed tasks for which stabilization skills are known to be important. Additionally, participants’ self-ratings of their cycling skills and performance were assessed. Participants rode once on a conventional bicycle and once on a pedelec, in counterbalanced order. Three standardized tasks were performed: (1) low-speed cycling, (2) acceleration from a standstill, and (3) shoulder check. During Tasks 1and3, the mean absolute steering angle (a measure of the cyclist’s steering activity) and the mean absolute roll rate (a measure of the amount of angular movement of the frame) were significantly greater for older participants than for middle-aged participants. These large lateral motions among older cyclists may indicate a difficulty to control the inherently unstable system. Comparing the conventional bicycle and the pedelec, participants reached a 16km/h threshold speed in Task 2 sooner on the pedelec, an effect that was most pronounced among the older participants. Correlations between skills assessed with the Cycling Skill Inventory and actual measures of cycling performance were mostly not statistically significant. This indicates that self-reported motor-tactical and safety skills are not strongly predictive of measures of actual cycling performance. Our findings add to the existing knowledge on self-assessment of cycling skills, and suggest that age-related changes in psychomotor and sensory functions pose hazards for cycling safety.

Pre-Lithiation of Li(Ni1-x-yMnxCoy)O2 Materials Enabling Enhancement of Performance for Li-Ion Battery.

Transition metal oxide materials Li(NixMnyCoz)O2 (NMCxyz) based on layered structure are potential cathode candidates for automotive Li-ion batteries because of their high specific capacities and operating potentials. However, the actual usable capacity, cycling stability, and first-cycle Coulombic efficiency remain far from practical. Previously, we reported a combined strategy consisting of depolarization with embedded carbon nanotube (CNT) and activation through pre-lithiation of the NMC host, which significantly improved the reversible capacity and cycling stability of NMC532-based material. In the present work we attempt to understand how pre-lithiation leads to these improvements on an atomic level with experimental investigation and ab initio calculations. By lithiating a series of NMC materials with varying chemical compositions prepared via a conventional approach, we identified the Ni in the NMC lattice as the component responsible for accommodating a double-layered Li structure. Specifically, much better improvements in the cycling stability and capacity can be achieved with the NMC lattices populated with Ni(3+) than those populated with only Ni(2+). Using the XRD we also found that the emergence of a double-layer Li structure is not only reversible during the pre-lithiation and the following delithiation, but also stable against elevated temperatures up to 320 °C. These new findings regarding the mechanism of pre-lithiation as well as how it affects the reversibility and stability of NMC-based cathode materials prepared by the conventional slurry approach will promote the possibility of their application in the future battery industry.

Children's route choice during active transportation to school: difference between shortest and actual route.

BackgroundThe purpose of this study is to increase our understanding of environmental correlates that are associated with route choice during active transportation to school (ATS) by comparing characteristics of actual walking and cycling routes between home and school with the shortest possible route to school.MethodsChildren (n = 184; 86 boys, 98 girls; age range: 8–12 years) from seven schools in suburban municipalities in the Netherlands participated in the study. Actual walking and cycling routes to school were measured with a GPS-device that children wore during an entire school week. Measurements were conducted in the period April–June 2014. Route characteristics for both actual and shortest routes between home and school were determined for a buffer of 25 m from the routes and divided into four categories: Land use (residential, commercial, recreational, traffic areas), Aesthetics (presence of greenery/natural water ways along route), Traffic (safety measures such as traffic lights, zebra crossings, speed bumps) and Type of street (pedestrian, cycling, residential streets, arterial roads). Comparison of characteristics of shortest and actual routes was performed with conditional logistic regression models.ResultsMedian distance of the actual walking routes was 390.1 m, whereas median distance of actual cycling routes was 673.9 m. Actual walking and cycling routes were not significantly longer than the shortest possible routes. Children mainly traveled through residential areas on their way to school (>80 % of the route). Traffic lights were found to be positively associated with route choice during ATS. Zebra crossings were less often present along the actual routes (walking: OR = 0.17, 95 % CI = 0.05–0.58; cycling: OR = 0.31, 95 % CI = 0.14–0.67), and streets with a high occurrence of accidents were less often used during cycling to school (OR = 0.57, 95 % CI = 0.43–0.76). Moreover, percentage of visible surface water along the actual route was higher compared to the shortest routes (walking: OR = 1.04, 95 % CI = 1.01–1.07; cycling: OR = 1.03, 95 % CI = 1.01–1.05).DiscussionThis study showed a novel approach to examine built environmental exposure during active transport to school. Most of the results of the study suggest that children avoid to walk or cycle along busy roads on their way to school.Electronic supplementary materialThe online version of this article (doi:10.1186/s12966-016-0373-y) contains supplementary material, which is available to authorized users.

A control-oriented cycle-life model for hybrid electric vehicle lithium-ion batteries

In this paper, a semi-empirical Lithium-iron phosphate-graphite battery aging model is identified over data mimicking actual cycling conditions that a hybrid electric vehicle battery encounters under real driving scenarios. The aging model is then used to construct the severity factor map, used to characterize relative aging of the battery under different operating conditions. This is used as a battery degradation criterion within a multi-objective optimization problem where battery aging minimization is to be achieved along with fuel consumption minimization. The method proposed is general and can be applied to other battery chemistry as well as different vehicular applications. Finally, simulations conducted using a hybrid electric vehicle simulator show how the two modeling tools developed in this paper, i.e., the severity factor map and the aging model, can be effectively used in a multi-objective optimization problem to predict and control battery degradation.

Defects, Entropy, and the Stabilization of Alternative Phase Boundary Orientations in Battery Electrode Particles

Using a novel statistical approach that efficiently explores the space of possible defect configurations, the present study investigates the chemomechanical coupling between interfacial structural defects and phase boundary alignments within phase‐separating electrode particles. Applied to the battery cathode material LiXFePO4 as an example, the theoretical analysis reveals that small, defect‐induced deviations from an ideal interface can lead to dramatic shifts in the orientations of phase boundaries between Li‐rich and Li‐lean phases, stabilizing otherwise unfavorable orientations. Significantly, this stabilization arises predominantly from configurational entropic factors associated with the presence of the interfacial defects rather than from absolute energetic considerations. The specific entropic factors pertain to the diversity of defect configurations and their contributions to rotational/orientational rigidity of phase boundaries. Comparison of the predictions with experimental observations indicates that the additional entropy contributions indeed play a dominant role under actual cycling conditions, leading to the conclusion that interfacial defects must be considered when analyzing the stability and evolution kinetics of the internal phase microstructure of strongly phase‐separating systems. Possible implications for tuning the kinetics of (de)lithiation based on selective defect incorporation are discussed. This understanding can be generalized to the chemomechanics of other defective solid phase boundaries.

Estimation of Handgrip Position Based on Force Measurement During Steady Pedaling

There have been many studies on pedaling skills (Bini et al., 2013) to improve cycling efficiency. Riding position of upper body as well as leg motion is very important for cycling because it has a substantial impact on air resistance and physical fatigue (Burke & Pruitt, 2003). Although camera-based motion capture systems are the most popular solution to measure riders’ position during cycling, they limit the range of motion and cannot be applied to actual outdoor cycling. In this study, we aim for developing a bike--mountable position estimation system. For this purpose, as a first step, we propose a method for estimation of handgrip position based on the force measurement during steady pedaling. Wattbike Trainer (Wattbike Ltd.) was used for our prototype system. A 6-- ‐ axis force/torque Sensor (BFS067XS102EU6S, Leptrino) was installed at an ahead- ‐ stem to measure the forces and torques loaded on the handlebar. According to the preliminary experiments, three parameters– 𝐹 ! , 𝐹 ! ,!–were chosen for the estimation. The proposed system classifies the observed data into three classes corresponding to the positions of handgrip, such as drops, hoods, and tops (Fig. 1) based on the SVM (Support Vector Machine) (Cortes & Vapnik, 1995), which is one of the most powerful machine learning techniques Experiments were conducted to verify the effectiveness of the proposed method. Four amateur male cyclists (mean 45.5 years old) participated in the experiments. The experiments consist of two phases, such as a learning phase and a test phase. To construct an SVM classifier, 60 seconds learning data for each handgrip position was collected at 100Hz for each participant in the learning phase. In the test phase, participants changed their handgrip positions every 30 seconds and steadily pedaled 6 minutes in total. Based on the individually learned SVM classifier, the system estimated the handgrip position at each sampling time. In both phases, the pedaling load and cadence were set according to each participant’s preference. Table 1 shows a confusion matrix of the experimental results. The proposed method achieves both high precision and recall. According to the experimental results, the proposed method can estimate the handgrip position with high reliability during steady pedaling. For future works, we will apply our system and estimation method to normal road bikes and develop a method to estimate positions of cyclists’ upper body.

Self-Propagating Catalysis: On the Comparison of ORR/Oer Mechanism in Li-O2 Battery with Fuel Cell

Li-O2 battery has attracted a great deal of attentions recently due to its high theoretical energy density.[1] Many studies were reported on the investigation of catalysts and cathode structures to the battery performance.[2] They revealed that the actual redox mechanism in Li-O2 battery could be significantly more complicated than originally thought. During the discharge-charge cycling, cathodic oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) occur in Li-O2 battery. Various catalysts were disclosed in attempts to promote ORR and OER processes at lower overpotentials therefore higher overall round-trip efficiency. However, little information is available on the catalytic mechanism. For example, it is commonly accepted that lithium peroxide, Li2O2, serves as a redox intermediate during cycling reactions. Li2O2 is nearly insoluble in the organic electrolytes and precipitates on the surface of the cathode once formed. How a solid-state catalyst could promote not only Li2O2 formation during ORR, but also its dissipation during OER is completely unclear. Such catalytic reactions would require a solid-solid interaction with limited or no mass-transport. How the catalytic transition intermediates can be formed under such condition remains a mystery. Without a better understanding of the catalytic mechanism, it is difficult to rationally design and improve the next generation Li-O2battery. At Argonne National Laboratory, our team has explored a low-cost, high surface area Fe/N/C composite as the cathode catalyst for Li-O2 battery application, inspired by the non-precious metal catalyst study for the proton exchange membrane fuel cell.[3] The catalyst demonstrated reduced ORR and OER overpotentials in the discharge-charge cycle and minimized the electrolyte decomposition. We also developed a holistic approach in studying electrochemical processes in Li-O2 battery using various characterization tools, such as SEM, TEM, FTIR, XRD, etc..[4] Particularly, we introduced a microfocused synchrotron X-ray diffraction (m-XRD) and a micro-tomographic techniques (µ-CT) for the spatiotemporal study on the phase and structural change in Li-O2 battery under actual cell cycling condition.[5] The m-XRD has a spatial resolution at micron level with the complete penetration and sampling from cell’s radial direction, rendering it possible to probe battery’s composition layer-by-layer under in situconditions. The data collection at any given position usually takes a few seconds, making the method particularly suitable to study the dynamic change inside the battery in real time. In this presentation, we will focus on our recent operando, spatiotemporal investigation on the catalytic processes at the Li-O2 battery cathode using the m-XRD technique. We prepared an in situ Li-O2 battery using the representative material and cell design and studied formation, dissipation and distribution of the lithium redox intermediate under the multiple discharge-charge cycling condition in the entire cathode region. We demonstrated, for the first time, the evolutions of the grain size, concentration and spatial distribution of lithium peroxide as the functions of ORR/OER potentials and capacity. A new “self-propagating” catalytic mechanism was derived from the experimental data and compared to the similar electrocatalytic processes in fuel cell. The new finding could clarify some of the on-going controversies on the redox mechanism. More importantly, it shed lights on the new structural and material research directions for better cycloability and durability of the Li-O2battery. Acknowledgement: The work performed at Argonne is supported by DOE under Contract No. DE-AC02-06CH11357 by UChicago Argonne, LLC.

In Operando Spatiotemporal Study of Li2O2 Grain Growth and its Distribution Inside Operating Li–O2 Batteries

Nanocrystalline lithium peroxide (Li2 O2 ) is considered to play a critical role in the redox chemistry during the discharge-charge cycling of the Li-O2 batteries. In this report, a spatially resolved, real-time synchrotron X-ray diffraction technique was applied to study the cyclic formation/decomposition of Li2 O2 crystallites in an operating Li-O2 cell. The evaluation of Li2 O2 grain size, concentration, and spatial distribution inside the cathode is demonstrated under the actual cycling conditions. The study not only unambiguously proved the reversibility of the Li2 O2 redox reaction during reduction and evolution of O2 , but also allowed for the concentration and dimension growths of the peroxide nanocrystallites to be accurately measured at different regions within the cathode. The results provide important insights for future investigation on mass and charge transport properties in Li2 O2 and improvement in cathode structure and material design.

Application of coupled electro-thermal and physics-of-failure-based analysis to the design of accelerated life tests for power modules

In the reliability theme a central activity is to investigate, characterize and understand the contributory wear-out and overstress mechanisms to meet through-life reliability targets. For power modules, it is critical to understand the response of typical wear-out mechanisms, for example wire-bond lifting and solder degradation, to in-service environmental and load-induced thermal cycling. This paper presents the use of a reduced-order thermal model coupled with physics-of-failure-based life models to quantify the wear-out rates and life consumption for the dominant failure mechanisms under prospective in-service and qualification test conditions. When applied in the design of accelerated life and qualification tests it can be used to design tests that separate the failure mechanisms (e.g. wire-bond and substrate-solder) and provide predictions of conditions that yield a minimum elapsed test time. The combined approach provides a useful tool for reliability assessment and estimation of remaining useful life which can be used at the design stage or in-service. An example case study shows that it is possible to determine the actual power cycling frequency for which failure occurs in the shortest elapsed time. The results demonstrate that bond-wire degradation is the dominant failure mechanism for all power cycling conditions whereas substrate-solder failure dominates for externally applied (ambient or passive) thermal cycling.

Nonlinear Regression Models for Determination of Nicotinamide Adenine Dinucleotide Content in Human Embryonic Stem Cells

Recent evidence suggests that energy metabolism contributes to molecular mechanisms controlling stem cell identity. For example, human embryonic stem cells (hESCs) receive their metabolic energy mostly via glycolysis rather than mitochondrial oxidative phosphorylation. This suggests a connection of metabolic homeostasis to stemness. Nicotinamide adenine dinucleotide (NAD) is an important cellular redox carrier and a cofactor for various metabolic pathways, including glycolysis. Therefore, accurate determination of NAD cellular levels and dynamics is of growing importance for understanding the physiology of stem cells. Conventional analytic methods for the determination of metabolite levels rely on linear calibration curves. However, in actual practice many two-enzyme cycling assays, such as the assay systems used in this work, display prominently nonlinear behavior. Here we present a diaphorase/lactate dehydrogenase NAD cycling assay optimized for hESCs, together with a mechanism-based, nonlinear regression models for the determination of NAD(+), NADH, and total NAD. We also present experimental data on metabolic homeostasis of hESC under various physiological conditions. We show that NAD(+)/NADH ratio varies considerably with time in culture after routine change of medium, while the total NAD content undergoes relatively minor changes. In addition, we show that the NAD(+)/NADH ratio, as well as the total NAD levels, vary between stem cells and their differentiated counterparts. Importantly, the NAD(+)/NADH ratio was found to be substantially higher in hESC-derived fibroblasts versus hESCs. Overall, our nonlinear mathematical model is applicable to other enzymatic amplification systems.

Follow-Based Forward Obstacle Detection Using Vision Insensitive Feature for Road Cycling

Paper proposes a method for detecting general obstacles on a road by subtracting present and past in road cycling camera images. The image-subtraction-based object detection approach can be applied to detect any kind of obstacles although the existing learning based methods detect only specific obstacles. To detect general obstacles, the proposed method first computes a frame-by-frame correspondence between the present and the past in-road cycling camera image sequences, and then registries road surfaces between the frames. Finally, obstacles are detected by applying image subtraction to the redistricted road surface regions with a vision insensitive feature for robust detection. Experiments were conducted by using several image sequences captured by an actual in-road cycling camera to confirm the effectiveness of the proposed method. The experimental results shows that the proposed method can detect general obstacles accurately at a distance enough to avoid them safely even with different situations.