Plateau Length Research Articles

Review of European design provisions for buckling of aluminium members with longitudinal welds – part 3

AbstractAs part of the ongoing revision of the Eurocodes, design provisions in EN 1999‐1‐1 on the buckling of longitudinally welded aluminium compression members have been subjected to a critical review. The numerical investigations described in part 1 of the paper were conducted because a need for improvement was identified. In part 2 the main observations were presented qualitatively. Part 3, the final part of the paper, presents the statistical evaluation of the numerical investigations and the determination of the buckling curves. Two different approaches are conceivable for these buckling curves: conventional buckling curves with explicitly specified imperfection factor and plateau length parameters, and a modified Ayrton‐Perry approach with interpolated parameters. Both approaches are compared with the results of the numerical investigations and with test results.

Dynamics of Lithium Stripping on Graphite Electrodes

As fast charging of lithium-ion batteries becomes a critical barrier to the widespread adoption of electric vehicles, development of facile methods of detection and quantification of lithium plating is a top priority. The voltage plateau observed during the rest or discharge phase ensuing a charge in which plating has occurred is a popular in-operando signature of lithium plating. Recent works have shown that the length of the stripping plateau is not a reliable metric for plating quantification, as was previously thought. An improved analytical method for relative quantification of lithium plating is presented herein. Furthermore, an in-situ method is developed for direct visualization of lithium stripping and graphite phase redistribution during the open circuit rest phase after charge. The dependence of lithium stripping dynamics on temperature and charge rate are comprehensively investigated. These techniques help in understanding the mechanistic underpinnings of the stripping processes occurring in the graphite electrode during relaxation after fast charging and enhance the capability to study lithium plating in a non-destructive manner.

Lüders strain of the fine-grained material under the electric current

The Hall-Petch-like relationship between the Lüders strain and the average grain size of an Al-5.16Zn-2.2Mg-1.46Cu alloy under the pulsed electric current is investigated. It is found that the Lüders strain increases as the average grain size decreases. In addition, when the average grain size is the same, the current parameter has a significant effect on the absolute value of the slope in the Hall-Petch-like relationship. Based on the characteristics of interaction between the solute atoms and dislocations during the Lüders strain, the competition between pinning behavior of solute atoms and depinning behavior of dislocations under the electric current is explored, and a relevant mathematical model is established. According to the new mathematical model, the difference of the above competitive behavior under two different current densities is analyzed. When the current density is 5 A/mm2, the pinning behavior of solute atoms is dominant in the competition, and the length of the yield plateau of each grain size becomes shorter; however, when the current density is 55 A/mm2, the dislocation depinning behavior dominants the competition and the Lüders strain of each grain size increases. It is found that the current density can affect the competition between the pinning of solute atoms and the depinning of dislocations, thus affecting the Lüders strain.

Spatio-temporal synchronization in complex ore-forming systems: Mesoscale case study in south China

Synchronization is an important current frontier area of nonlinear sciences. In order to explore the spatio-temporal evolution of ore-forming elements in complex system at mesoscale, the principles, promises, methods and procedures of a spatio-temporal synchronization method were defined.Based on the phase conversion equation, the phase data and the phase difference were calculated in two directions, and the phase difference constant was set as 0.1 as a critical value to extract the plateau length in two directions. After the plateau length in both directions was superimposed, we got the synchronization threshold. Through its spatio-temporal extension, the synchronized space-time domain was determined. Then, we utilized geostatistics and Kriging method to generate the map of synchronized space-time domain, which includes ore formation, time and space. Applying the developed method and using local stream sediment geochemical data in Dajishan tungsten deposit (China), we have carried out the research on the synchronization of pairwise matching elements between ore-forming and ore-transporting elements in two directions at mesoscale, besides pairwise matching elements between ore-forming elements.Results indicate that the mineralization time-space domains of W, Sn, Mo, Bi, Cu, Pb, Zn, Au, Ag, and Be elements in the study area and their isoconcentration contours show a good coincident correspondence. For pairwise matching elements of ore-forming element matching with ore-transporting element, the high synchronization threshold area appears on the edge of the element mineralization center in the map of space-time domain for synchronization (or mineralization), which reveals the onset of ore formation; For pairwise matching elements between ore-forming elements, it reveals the mechanism of ore formation. Furthermore, this theory and method can be also applied to other fields of geochemistry, such as environmental geochemistry.

Influence of sheet resistance and strip width on the detection efficiency saturation in micron-wide superconducting strips and large-area meanders

We report our study of detection efficiency (DE) saturation in wavelength range 400–1550 nm for the NbN superconducting microstrip single-photon detectors (SMSPDs) featuring the strip width up to 3 µm. We observe an expected decrease of the DE saturation plateau with the increase of photon wavelength and decrease of film sheet resistance. At 1.7 K temperature DE saturation can be clearly observed at 1550 nm wavelength in strip with the width up to 2 µm when sheet resistance of the film is above 630 Ω sq−1. In such strips the length of the saturation plateau almost does not depend on the strip width. We used these films to make meander-shaped detectors with the light sensitive area from 20 × 20 µm2 to a circle 50 µm in diameter. In the latter case, the detector with the strip width of 0.49 µm demonstrates saturation of DE up to 1064 nm wavelength. Although DE at 1310 and 1550 nm is not saturated, it is as high as 60%. The response time is limited by the kinetic inductance and equals to 20 ns (by 1/e decay), timing jitter is 44 ps. When coupled to multi-mode fibre large-area meanders demonstrate significantly higher dark count rate which we attribute to thermal background photons, thus advanced filtering technique would be required for practical applications.

Characterization of an anion-exchange membrane subjected to phosphate and sulfate separation by electrodialysis at overlimiting current density condition

The structural degradation of an anion-exchange membrane used on the separation of phosphate from sulfate ions at overlimiting current density conditions was investigated. To this, the chemical structure changes, apparent counterion transport number, limiting current density, the apparent fraction of surface conductive regions, degree of hydrophobicity, membrane resistance and conductivity, morphology and thermal degradation profile were studied for the original and used samples of the anion-exchange membrane. The results showed that the degradation of the membrane fixed ion groups and structural polymer backbone affected the ionic transport conditions, reducing its apparent permselectivity and fraction of conductive regions. Also, the increase in the hydrophobicity degree together with the formation of cavities observed in the membrane surface may be responsible for the alteration of membrane conductivity, leading to a higher limiting current density value and a decrease in the plateau length.

Proximodistal and caudocranial position of the insertion of the patellar ligament on the tibial tuberosity and patellar ligament length of normal stifles and stifles with grade II medial patellar luxation in small-breed dogs.

To assess the role of the proximodistal and caudocranial relative position of the patellar ligament insertion on the tibia and patellar ligament length-to-patellar length ratio (PLL:PL) in small-breed dogs with and without grade II medial patellar luxation (MPL). Retrospective study. Dogs weighing ≤15 kg, including 43 stifles with MPL and 34 control stifles. The proximodistal and caudocranial relative position of the patellar ligament insertion was determined as a ratio using the vertical (VTT) and horizontal distance (HTT) between the tibial tuberosity insertion and the tibial plateau divided by the tibial plateau length (TPL). In addition, PLL:PL and tibial plateau angle (TPA) were determined. The VTT:TPL ratio was lower in affected stifles (95% CI: 0.86-0.94) than in the control group (0.93-1.01; p=.01). No other difference was identified between affected and normal stifles. The only difference identified in this study consisted of a more proximal position of the patellar ligament insertion in the stifles of small-breed dogs with grade II MPL. The more proximal position of the patellar ligament insertion will result in a more proximal position of the patella in the trochlear groove and may contribute to the development of MPL. Potentially, this will also affect the risk of recurrence of MPL after surgical treatment.

A theoretical model for the estimate of plateau force for the crushing process of 3D auxetic anti-tetra chiral structures

Auxetic, anti-tetra-chiral structures designed as tubes subjected to axial quasi-static crushing were investigated in this research. Experimental work was carried on samples manufactured by laser cutting from a pipe. At the same time, numerical simulations were performed using a parametric numerical model of the structure. The experimental results analysis revealed that the crushing force presents a plateau region that extends up to the densification phase defined by the close contact between the ligaments joining the nodes. Subsequently, based on the representative unit's deformation characteristics, theoretical calculation models were established to estimate the plateau force. According to Bernoulli's beam model, the force calculation model was developed from the plastic hinge's structural design and theory. Sametime, the length or crushing distance with a constant force (plateau), can be estimated to provide the complete set of parameters for design activities. The analytical solution was validated against results obtained numerical simulation for various configurations. There is a good agreement between experimental, numerical, and theoretical results that proves the proposed model's reliability to estimate plateau force. Furthermore, individual parts were stacked to define graded structures. It was found that the crushing force displays successive stages according to each individual part. There is a possibility to reconstruct the response for stacked structure from the individual response using the analytical solution's results for force and length of individual plateau stages.The set of equations can design this structure when the capable load is one of the input parameters.

Parametric and experiment studies of 3D auxetic lattices based on hollow shell cuboctahedron

As a kind of mechanical metamaterials with negative Poisson’s ratio (NPR), auxetic lattices possess unusual mechanical responses such as higher sensitivity to strain and reversibility after large deformation. Therefore, they are regarded as a potential candidate to sensors, actuators, and optics. Here, we designed four types of auxetic lattices with long stress plateau based on the assembly of hollow shell cuboctahedron. To begin with, experiments along with finite element simulations were performed to probe their auxetic behaviors under uniaxial compression, which give an excellent qualitative and quantitative agreement. To establish design criteria on specific applications, we systematically investigated the mechanical properties of the four kinds of lattices with different volume fractions, including critical stresses, strain–stress curves, strain energy densities, strain-dependent Poisson’s ratios, and the length of stress plateau. The results demonstrate that these lattices can suffer from buckling with NPR in an extended range of volume fractions, and high reversibility was observed in several compressive loadings, which provides insight into energy absorption such as the body protection equipments and smart packaging material

Biodiversity of Edible, Medicinal, Mychorhizal, Poisonous and Wild Macrofungi in Chhattisgarh

A systematic study through extensive and repetitive was conducted across the length and breadth of Chhattisgarh plains, Bastar plateau and northern hill zones of Chhattisgarh to benchmark the diversity of macrofungi and characterize, collect, preserve, and evaluate their edibility and medicinal value. About 83 mushroom flora/fungal genera of edible, non-edible, medicinal, poisonous, mycorhyzal mushroom were collected from litter, soil, termite mounds, wood logs, live plants and rotten leaves across dense stretches of forests of Bastar, Amarkantak, Jagdalpur, Ambikapur to name a few and also from various market areas of different districts cutting across Chhattisgarh. All stages of Rhizopogon sps. and Termitomyces sps. (Kanki Futu) was observed in in-situ conditions. The market survey was also conducted and it was found that Termitomyces and Rhizopogon were sold in abundance at very high prices across Chhattisgarh. The other edible macrofungi collected and isolated from forests were Calocybe indica (milky mushroom), Volvariella volvaceae (Paddy straw mushroom), Pleurotus djamor, Pleurotus ostreatus, Pleurotus florida and Hypsizygous ulmarius. Few macrofungi as mycorrhizal partners, bioabsorbents, decomposers and storehouses of medicinal biomolecules were also collected, characterized and stored. However many issues relating to their taxonomy and phylogeny, ecology, and geographical distributions remain unclear. Keywords: Biodiversity, macrofungi, Pleurotus, Calocybe, Rhizopogon and Termitomyces

Improving the Geiger Muller Counter Characteristics by Optimizing the Anode and Cathode Radius Dimensions

This article considers the influence of the anode (r <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</sub> ) and cathode (r <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</sub> ) radius dimensions in the Geiger Muller counter chamber on its characteristics such as efficiency, measurement uncertainty, dead time, slope, plateau length, and aging. The article is of a theoretical and experimental nature. In the theoretical part of the article, the expression for the dependence of the electrical discharge parameters of a cylindrical electrode system is derived from various radius dimensions of the anode and cathode. For this purpose, the enlargement law of the probability was applied. The experimental part of the work was performed on the models of the Geiger Muller's chamber of different radius dimensions of the anode and cathode. The chamber models (and insulation gas) were made to maintain the geometrical similarity of the commercially applicable chamber. In the first experimental part of this article, the effect of radioactive radiation was simulated with a fast pulse voltage, while real radioactive elements were used in the second experimental part. The testing has shown that the synergy of the stochastic volume effect of the breakdown voltage of the Ruffer-Kuilling mechanism and the corona of the plasma can significantly improve all tested characteristics.

Strong-field ionization of homonuclear diatomic molecules using orthogonally polarized two-color laser fields

Using the improved molecular strong-field approximation we investigate high-order above-threshold ionization (HATI) of homonuclear diatomic molecules by an orthogonally polarized two-color (OTC) laser field. The OTC field components are linearly polarized, having the relative phase $\ensuremath{\varphi}$ and frequencies $r\ensuremath{\omega}$ and $s\ensuremath{\omega}$ ($r$ and $s$ are integers and $\ensuremath{\omega}$ is the fundamental frequency). The molecule is aligned in the laser-field polarization plane. We have found that for even values of $r+s$ the HATI spectra obey the ${C}_{2}$ rotational symmetry regardless of the relative phase, component intensities, and molecular orientation, while the spectra calculated for odd values of $r+s$ and for certain molecular orientations exhibit the reflection symmetry. We have also explored the symmetry transformations of the HATI spectra for a shift of the relative phase by ${180}^{\ensuremath{\circ}}$ and for various values of $r$ and $s$. These symmetries are illustrated by numerical examples of the HATI spectra of the ${\mathrm{N}}_{2}$ molecule. For particular values of the laser-field parameters, internuclear distance, and the electron emission angle we observed minima in the ionization yield as a function of the molecular orientation angle and the photoelectron energy. These minima are well fitted with the curve obtained using a condition for the destructive interference minima which we derived for an arbitrary laser field and applied to the OTC field. The relative phase between the OTC field components can be used to control the length and shape of the HATI plateau, as well as the appearance of these destructive interference minima.

Effects of magnetic fields on the Current-Voltage (I-V) characteristics of the chitosan membrane

This work aimed to study the effect of magnetic fields on the current-voltage (I-V) characteristics of a chitosan membrane. The study consists of the plateau length, limiting current density (LCD), and the ratio of resistance of region III (RIII) and region I (RI) (RIII/RI). The chitosan membranes were prepared by a casting method using chitosan as a matrix and acetic acid as a solvent. The chitosan membranes polymerized under a strong magnetic field of 1.5 mT applied along the membrane surface with various times i.e. 2, 4, 8, and 12 h. The I-V measurements were conducted using a cell model with two working electrodes made of platinum and two reference electrodes connected to a voltmeter. The electrolyte solutions used were HCl and CaCl2 with a concentration of 0.025 M. All experiments were carried out at a room temperature of 28.6 °C. The results showed that the plateau length, LCD and RIII/RI of the chitosan membrane is influenced by the magnetic field given during the membrane formation reaction. The magnitude of the impact depends on the length of exposure. These results can be used in tailoring the chitosan membrane according to the application needed.

Effect of the resin content in cation-exchange membranes on development of electroconvection

Comparative analysis of the effect of ion-exchanger content in heterogeneous sulfonated ion-exchange membranes Ralex CM Pes produced by MEGA a.s. (Czech Republic) on their microstructure, current-voltage characteristics and intensity of electroconvective instability was carried out. Using the SEM method, it has been found that with an increase in resin content from 45 to 70 wt%, fraction of the ion-exchanger on the surface of swollen membranes increases 1.8 times, and the distance between them is halved. At the cross-section of membranes, the growth of fraction of ion-exchange regions is 46%. An increase in the resin loading into the membrane causes a 1.7-fold and a twofold increase in the fraction of macropore on the surface and on the cross-section, respectively.With an increase in the ion-exchanger content in membranes, a decrease in the potential of the onset of the overlimiting state and a decrease in the plateau length of the limiting current on the current-voltage curve were revealed. It is shown that a change in resin/inert binder ratio determines the occurrence and development of heteroelectroconvection. Using laser interferometry and flicker noise spectroscopy, evidences of more intense electroconvective mixing of the solution at the boundary with the Ralex cation-exchange membrane with maximum resin loading were obtained.

The entry point of intramedullary tibia cutting guide should vary according to the individual tibia morphology in TKA.

In total knee arthroplasty (TKA) using the intramedullary tibial cutting guide (IMTCG), the positioning of the IMTCG is important for accurate tibial bone resection. The aim of this study was to evaluate the ideal entry point of IMTCG and affecting radiologic factors. From May 2017 to February 2018, 91 consecutive TKAs for osteoarthritis were included. From preoperative full-length radiographs, we measured the medial proximal tibia angle (MPTA), lateral distal tibia angle (LDTA), tibial bowing angle (TBA), medial to lateral width of the tibial plateau, tibial length, and ideal coronal entry point. In preoperative short knee lateral radiographs, we measured the anterior to posterior length of the tibial plateau, tibial posterior slope angle (TPSA), metaphysio-diaphyseal angle (MDA), and ideal sagittal entry point. The ideal coronal and sagittal entry points were defined as the points crossing the tibial plateau and tibial anatomical axis on the coronal and sagittal radiographs, respectively. The ideal entry point was 51.4 ± 4.3% (SD) from the medial margin and 27.0 ± 5.8% (SD) from the anterior margin of the tibial plateau. However, the range varied from 39.8 to 60.5% on the coronal plane and from 9.6 to 37.7% on the sagittal plane, respectively. As the MPTA (rho = -0.490) and TBA (rho = -0.433) were increased, the coronal entry point moved medially. As TPSA (rho = -0.761) and MDA (rho = -0.495) were increased, the sagittal entry point moved anteriorly. The ideal entry point of IMTCG should vary according to the individual tibial morphology.

Lateral location of the tibial tunnel increases lateral meniscal extrusion after anatomical single-bundle anterior cruciate ligament reconstruction

IntroductionThe tibial footprint of the anterior cruciate ligament (ACL) overlaps with the anterior lateral meniscal root (ALMR), and there is a possibility that an anatomical tibial tunnel reaming might damage the attachment of ALMR. The aim of this study was to investigate the relationship between tibial tunnel location and lateral meniscal extrusion (LME) after anatomical single-bundle ACL reconstruction.MethodsA prospectively collected database and associated intraoperative findings for 153 patients undergoing primary anatomical ACL reconstruction between October 2014 and July 2016 were investigated. Those cases with no meniscal injury seen at surgery and meeting the criteria (52/153) were included. Tibial plateau length (TPL), width (TPW), tibial tunnel location and LME were evaluated from postoperative high-resolution MRI. The location of the centre of the tibial tunnel was evaluated by the position relative to the medial tibial eminence with two measures, the medial–lateral distance (MLD) and anterior–posterior distance. These measures were expressed as a percentage of the TPW and TPL, respectively. The LME was also expressed as a percentage of TPW and correlated with tibial tunnel location.ResultsThere was a positive correlation between percentage of LME (%LME) and percentage of MLD (%MLD) (r=0.478; p<0.001). Applying receiver operating characteristic analysis, we determined that a cut-off value of 4 %MLD was significant. The mean percentage of LME was 1.20 for >4 %MLD, compared with 0.17 for ≤4 %MLD (p<0.001). No significant correlation was found between %LME and clinical outcomes at 1-year follow-up.ConclusionLateral location of the tibial tunnel increases the rate of LME after single-bundle ACL reconstruction.Level of evidenceLevel IV, Case series.

The Berkeley sample of Type II supernovae: BVRI light curves and spectroscopy of 55 SNe II

ABSTRACT In this work, BVRI light curves of 55 Type II supernovae (SNe II) from the Lick Observatory Supernova Search programme obtained with the Katzman Automatic Imaging Telescope and the 1 m Nickel telescope from 2006 to 2018 are presented. Additionally, more than 150 spectra gathered with the 3 m Shane telescope are published. We conduct an analyse of the peak absolute magnitudes, decline rates, and time durations of different phases of the light and colour curves. Typically, our light curves are sampled with a median cadence of 5.5 d for a total of 5093 photometric points. In average, V-band plateau declines with a rate of 1.29 mag (100 d)−1, which is consistent with previously published samples. For each band, the plateau slope correlates with the plateau length and the absolute peak magnitude: SNe II with steeper decline have shorter plateau duration and are brighter. A time-evolution analysis of spectral lines in term of velocities and pseudo-equivalent widths is also presented in this paper. Our spectroscopic sample ranges between 1 and 200 d post-explosion and has a median ejecta expansion velocity at 50 d post-explosion of 6500 km s−1 (H α line) and a standard dispersion of 2000 km s−1. Nebular spectra are in good agreement with theoretical models using a progenitor star having a mass &amp;lt;16M⊙. All the data are available to the community and will help to understand SN II diversity better, and therefore to improve their utility as cosmological distance indicators.

Correlation between the mid-substance cross-sectional anterior cruciate ligament size and the knee osseous morphology.

One of the final goals of anatomical anterior cruciate ligament (ACL) reconstruction is the restoration of native anatomy. It is essential to obtain more accurate predictors of mid-substance ACL size before surgery. However, to the best of our knowledge, no study has reported correlation between the mid-substance cross-sectional ACL size and the knee osseous morphology. The purpose of this study was to reveal correlation between the mid-substance cross-sectional ACL size and the knee osseous morphology. We used 39 non-paired formalin fixed Japanese cadaveric knees. All surrounding muscles, ligaments and soft tissues in the knee were resected. After soft tissue resection, the knee was flexed at 90°, and a tangential plane of the femoral posterior condyles was marked and cut the ACL. Femoral ACL footprint size, Blumensaat's line length, lateral wall of the femoral intercondylar notch size, lateral wall of the femoral intercondylar notch height, tibial ACL footprint size, tibia plateau size, the whole anterior-posterior (AP) length, the medial and the lateral AP length of the tibia plateau, and the medial-lateral (ML) length of the tibia plateau were measured. The Pearson's product movement correlation was calculated to reveal correlation between the mid-substance cross-sectional ACL size and the measured parameters of the knee osseous morphology. The measured mid-substance cross-sectional ACL size was 49.9 ± 16.3mm2. The tibial ACL footprint size, the tibia plateau size, the whole AP length of the tibia plateau, the lateral AP length of the tibia plateau and the ML length of the tibia plateau were significantly correlated with the mid-substance cross-sectional ACL size. For clinical relevance, some tibial sides of the knee osseous morphology were significantly correlated with the mid-substance cross-sectional ACL size. It might be possible to predict the mid-substance ACL size measuring these parameters.

Solubility and Stability of NaO2 in Diglyme-Based Na-O2 Batteries

Aprotic Na-O2 batteries have attracted extensive attention because of their relatively large theoretical energy density and low charge overpotential. Several discharge products have been reported, including NaO2,[1] Na2O2,[2] Na2O2·2H2O,[3] Na2CO3,[4] which adds in complexity to specify the chemistry and reaction mechanism of Na-O2 battery.[5] In ether-based electrolyte, NaO2 is recognized as the major discharge products and often appeared as NaO2 cubes with size of 1-50 μm. These NaO2 cubes is believed to form through a dissolution-precipitation process as previously reported by operando transmission electron microscope (operando TEM),[6] rotating ring-disk electrode (RRDE),[7] atomic force microscopy (AFM)[8] and two-working electrode electrochemical technique.[9] The solubility and stability of NaO2 in electrolyte are important factors which influence the dissolution-precipitation path and cycling performance respectively. However, direct measurement of NaO2 solubility in ether-based Na-O2 batteries is still not available[9] and the lack of investigation on NaO2 stability makes such system even more mysterious. The two-working electrode electrochemical technique shows great promise in measuring the solubility of NaO2 in cell conditions, because it can quantitatively detect dissolved NaO2. Herein, modified two-working electrode Na-O2 batteries (Figure a) are fabricated and galvanostatic method is applied to investigate the solubility of NaO2.[9] NaO2 is generated on one air electrode (WE1), dissolved in electrolyte and oxidized on the other air electrode (WE2). Based on the assumptions that all dissolved NaO2 can be oxidized and the oxidation rate of NaO2 is significantly larger than dissolution rate, the solubility of NaO2 in electrolyte can be estimated. As discharge time of WE1 increases, the length of charge plateau of dissolved NaO2 at ~2.3 V vs. Na/Na+ on WE2 firstly increases and gradually approach a maximum value (Figure b), implying saturation of NaO2 in electrolyte is reached. Substantial solubility of NaO2 (~1.4 mM) in diglyme-based electrolyte is obtained. Conventional two-electrode Na-O2 batteries consisting of a Na anode and a carbon cathode are also fabricated to investigate NaO2 stability. These Na-O2 batteries are discharge-(rest)-charge tested at 25 μA/cm2 for varied time (Figure c-e). The percentage of recovered NaO2 (ratio of charge capacity due to NaO2 to total discharge capacity) against discharge time is ploted in Figure f, the longest discharge time shows the highest recovery percentage of NaO2. The recovery results depend on the concentration of NaO2 in electrolyte, which is in turn governed by supersaturation and precipitation processes. The average degradation rate of NaO2 during rest for varied discharge time can also be calculated to evaluate cycling performance. Our research therefore provides additional insights to dissolution-precipitation mechanism and NaO2 stability. The authors acknowledge the financial support from National Natural Science Foundation of China (NSFC)/Research Grant council (RGC) of Hong Kong Joint Research Scheme N_HKU728/17. [1] P. Hartmann, C. L. Bender, M. Vračar, A. K. Dürr, A. Garsuch, J. Janek, P. Adelhelm, Nat. Mater. 2013, 12, 228. [2] Y. Hu, X. Han, Q. Zhao, J. Du, F. Cheng, J. Chen, J. Mater. Chem. A 2015, 3, 3320. [3] X. Bi, R. Wang, L. Ma, D. Zhang, K. Amine, J. Lu, Small Methods 2017, 1, 1700102. [4] J. Kim, H. D. Lim, H. Gwon, K. Kang, Phys. Chem. Chem. Phys. 2013, 15, 3623. [5] S. Zhao, B. Qin, K. Y. Chan, C. Y. V. Li, F. Li, Recent development of aprotic Na-O2 batteries, Batteries & Supercaps 2019, Under review. [6] L. Lutz, W. Dachraoui, A. Demortière, L. R. Johnson, P. G. Bruce, A. Grimaud, J. M. Tarascon, Nano Lett. 2018, 18, 1280. [7] C. Xia, R. Black, R. Fernandes, B. Adams, L. F. Nazar, Nature Chemistry 2015, 7, 496. [8] I. M. Aldous, L. J. Hardwick, Chem. Commun. 2018, 54, 3444. [9] P. Hartmann, M. Heinemann, C. L. Bender, K. Graf, R.-P. Baumann, P. Adelhelm, C. Heiliger, J. Janek, The Journal of Physical Chemistry C 2015, 119, 22778. Figure 1

Investigation of microfluidic co-flow effects on step emulsification: Wall contact angle and critical dimensions

We propose a co-flowing step emulsification strategy for the on-line control of micro-droplet generation. The effects of four parameters including wall contact angle, plateau length, channel distance and diameter are investigated numerically and experimentally in this study. The results indicate that the wall contact angle, whose applicable range can be expanded to 90°–180° by co-flow, is critical to droplet formation. The effect of the plateau length on droplet generation is reduced by the co-flow, and the droplet diameter is almost independent of the plateau length, which ranges from 0.7 to 1.5 mm. In addition, the droplet diameter increases significantly with increasing channel distance and diameter. Combining these results with those of our previous study, we derived an explicit equation for droplet diameter prediction. The predicted droplet diameter based on this equation has good agreement with the simulation and experimental results. Furthermore, we proposed a coefficient α as a function of physical and dimensional parameters to predict the regimes and modes in the co-flowing step emulsification process. The conclusion of this study not only provides an important reference for the design and improvement of step emulsification chips, but also offers a new idea and a scientific basis for tuneable monodisperse micro-droplet production.