Investigation of electrochemical properties of sodium ion intercalation into Fe2V4O13

The necessity of large-scale energy storage systems (ESS) have become vigorously issued in energy conversion research field. Especially, rechargeable sodium ion batteries have the benefits of low material cost and earth abundant. However, since the size of Na+ ion is larger than the Li+ ion does, it is challenge to find host materials with large enough interstitial site. In effort to overcome this challenge, we approach of searching for wide tunnel structure with controlling the size of materials. Submicron sized crystalline Diiron(III) Tetravanadate(V), Fe2V4O13, is prepared by the liquid precipitation synthesis technique and characterized by X-ray diffraction (XRD), Rietveld refinement, and scanning electron microscope (SEM). It was found that Fe2V4O13 has the monoclinic system which has ellipse shape like fairly large tunnel, compare to other cathode host materials. Although many other cathode battery storage systems have been researched such as sodium ion batteries, lithium ion batteries, or several multivalent ion batteries, studies on the Fe2V4O13 is insufficient. Herein, by using the Fe2V4O13 as a host material for Na-ion batteries, the X-ray diffraction pattern changes of NaxFe2V4O13 (0≤x≤1.0) upon insertion/extraction of Na-ion into/from host-framework analyzed through using ex-situ powder X-ray diffraction. ⓒ 2016 DGIST1.Introduction 1 -- 1.1 The ubiquitous issue: Developing energy storage system (ESS) 1 -- 1.2 A pioneer discover for ESS: Rechargeable battery system 4 -- 1.3 Alternative energy source: Sodium-ion batteries 6 -- 1.4 Theoretical background 8 -- 1.4.1 Electrolyte 8 -- 1.4.2 Solid electrolyte interphase (SEI) layer 8 -- 1.5 Important studies have been achieved on electrode material for SIBs 9 -- 1.5.1 Positive sodium ion electrode materials 9 -- 1.5.1.1 Layered structure base 10 -- 1.5.1.2 NASICON-type material 11 -- 1.5.1.3 Olivine type structure base 12 -- 1.5.1.4 Sodium vanadium fluorophosphates base 13 -- 1.6 1-Dimensional structure of Fe2V4O13 14 -- 2. Experiments 16 -- 2.1 Preparation of submicron size crystalline Fe2V4O13 16 -- 2.1.1 Wet chemical process 16 -- 2.1.2 Filtration 16 -- 2.1.3 Amorphous to crystallization: Calcination 16 -- 2.2 Physiochemical and electrochemical characterization 18 -- 2.2.1 Electrode preparation with hand-made beaker type cell 18 -- 2.2.2 Electrochemical operational mechanisms of the sodium ion capacitor 21 -- 2.3 Electrochemical characterization 24 -- 3. Results and Discussion 25 -- 3.1 Morphology and XRD study of Fe2V4O13 25 -- 3.2 Electrochemical properties 30 -- 3.2.1 Cyclic voltammetry and galvanostatic cycle profiles 30 -- 3.2.2 C-rate performance profiles 32 -- 3.2.3 Ex-situ XRD and unit cell parameters 33 -- 3.2.4 EDX element analysis of Fe2V4O13 35 -- 4. Conclusions 38 --드론, 휴대폰, 노트북 PC 등 휴대용 전자기기의 경량화 및 고기능화가 진행됨에 따라, 그 구동용 전원으로서 사용되는 전지의 고용량화, 고에너지 밀도화에 대한 연구가 이루어지고 있다. 리튬 전지는 기존의 납축전지, 니켈-카드뮴전지, 니켈수소전지, 니켈아연전지 등과 비교하여 단위 중량당 에너지 밀도가 3배 정도 높고 급속 충전이 가능하기 때문에 상업용으로 많이 사용되고 있다. 그러나 리튬 전지는 리튬의 높은 반응성으로 인해 안전성에 문제가 있으며, 또한 리튬원소는 고가이다. 반면, 나트륨 전지는 리튬 전지와 비교하여 친환경적이고, 가격경쟁력이 우수하며, 에너지 저장 특성이 높기 때문에 전력 저장용 및 전기자동차용 등 중대형전지 용도로 활발히 연구되고 있다. 나트륨 전지의 전극 활물질로서 Mn, Fe, Ni, Co, V, Cr 등의 전이 금속을 포함하는 나트륨 전이 금속 산화물이 사용될 수 있다. 상기 나트륨 전이 금속 산화물은 인산염(phosphate), 불화인산염(fluorophosphate) 등의 다가 음이온을 포함하는 인산화물에 비해 이론용량이 크고 결정 구조 내에 충분한 나트륨 이온의 이동 통로를 확보하고 있다는 구조적 이점이 있다. 그러나 나트륨 전이 금속 산화물은 충방전시 중심 금속 산화수의 변화에 따른 결정 구조의 전이에 의하여 전극이 급속히 열화되어 수명 특성이 부진하며, 결정 구조 내에 비활성 나트륨의 함량이 높아 방전 용량이 부진 하다는 단점이 있다. 따라서 수명 특성 및 방전 용량이 향상된 나트륨 전지를 제공할 수 있는 전극 활물질 개발이 여전히 요구되어 다양한 활물질을 연구한 결과 Fe2V4O13에 대한 연구를 진행하였다. 본 연구는 소듐 전지용 전극 활물질, 이의 제조 방법, 이를 포함하는 전극, 및 상기 전극을 포함하는 소듐 전지에 관한 것으로서, 소듐 이온을 가역적으로 탈/삽입 시킬 수 있어 소듐 전지용 전극 활물질로 사용될 수 있는가에 관한 것이다. 이 결과는 cyclic voltammetry, galvatnostatic cycle, x-ray diffraction, electron scanning microscopy, energy dispersive x-ray spectroscopy를 통해 얻을 수 있었다. 합성된 Fe2V4O13 물질은 XRD와 GSAS를 통한 Rietveld refinemnet로 확인했다. 마그네슘 이온의 Fe2V4O13 물질로의 탈/삽입은 XRD, EDX를 이용해 증명하고 구조가 가역적인 것을 확인하였다. 결과적으로 Fe2V4O13 물질은 이미 연구가 되어있는 활물질 보다 전기화학적 특성이 특출 나지 않았다. 비록 방전 용량 및 수명 특성 향상이 이루어 지지는 않았지만 새로운 소듐 전지용 전극 활물질을 발견했다는 것에 의의를 두고 있다. ⓒ 2016 DGISTMasterdCollectio

Risk factors for delayed and non-union following transfibular ankle arthrodesis

Background: This study was to identify risk factors associated with delayed union and non-union in patients who underwent transfibular ankle arthrodesis.Methods: This study included 43 patients who underwent ankle arthrodesis using transfibular approach between January 2012 and September 2018 and were followed up for more than 12 months. The patients were divided into two groups according to delayed union or non-union. Group A included patients who had delayed union or non-union and Group B included patients without these complications. Variables that could contribute to non-union including etiologies, age, chronic renal failure, hypertension, diabetes, smoking, pre-operative talus bone quality, pre-operative angulation of the talus and fixation methods were evaluated.Results: The mean time to bone union was 12.7±7.25 weeks. Group A included 12 patients with 5 cases of non-union and 7 cases of delayed union and group B included 31 patients. Infection of the ankle joint (OR, 1.73; p=0.041) was risk factor for non-union and delayed union on the basis of multivariate analysis.Conclusions: We concluded that infection of the ankle joint is the most significant risk factor for delayed union and nonunion in our study. Careful attention should be paid preoperatively, intraoperatively and postoperatively to patients who have this risk factor to obtain a satisfactory surgical outcome

Frequency-Based Decentralized Conservation Voltage Reduction Incorporated Into Voltage-Current Droop Control for an Inverter-Based Islanded Microgrid

Conservation voltage reduction (CVR) aims to decrease load demands by regulating bus voltages at a low level. This paper proposes a new strategy for decentralized CVR (DCVR), incorporated into the current-based droop control of inverter-interfaced distributed energy resources (IDERs), to improve the operational reliability of an islanded microgrid. An $I_{dq}$ controller is developed as an outer feedback controller for each IDER, consisting of $I_{d}$ $V$ controllers for the DCVR and $I_{d}$ $\omega$ and $I_{q}$ $V$ controllers for power sharing. In particular, the $I_{d}$ $V$ controllers adjust the output voltages of the IDERs in proportion to the frequency variation determined by the $I_{d}$ $\omega$ controllers. This enables the output voltages to be reduced by the same amount, without communication between the IDERs. The $I_{q}$ $V$ controllers are responsible for reactive power sharing by adjusting the voltages while taking into account the $I_{d}$ $V$ controllers. Small-signal analysis is used to verify the performance of the proposed DCVR with variation in the $I_{d}$ $\omega$ and $I_{q}$ $V$ droop gains. Case studies are also carried out to demonstrate that the DCVR effectively mitigates an increase in the load demand, improving the operational reliability, under various load conditions determined by power factors and load compositions.11Ysciescopu

Automating Reinforcement Learning with Example-based Resets

Deep reinforcement learning has enabled robots to learn motor skills from environmental interactions with minimal to no prior knowledge. However, existing reinforcement learning algorithms assume an episodic setting, in which the agent resets to a fixed initial state distribution at the end of each episode, to successfully train the agents from repeated trials. Such reset mechanism, while trivial for simulated tasks, can be challenging to provide for real-world robotics tasks. Resets in robotic systems often require extensive human supervision and task-specific workarounds, which contradicts the goal of autonomous robot learning. In this paper, we propose an extension to conventional reinforcement learning towards greater autonomy by introducing an additional agent that learns to reset in a self-supervised manner. The reset agent preemptively triggers a reset to prevent manual resets and implicitly imposes a curriculum for the forward agent. We apply our method to learn from scratch on a suite of simulated and real-world continuous control tasks and demonstrate that the reset agent successfully learns to reduce manual resets whilst also allowing the forward policy to improve gradually over time.Comment: 8 pages, 6 figures; accepted for publication in the IEEE Robotics and Automation Letters (RA-L); source code available at https://github.com/jigangkim/autoreset_rl ; supplementary video available at https://youtu.be/himd0Z5b64

Self-Supervised Visual Learning by Variable Playback Speeds Prediction of a Video

We propose a self-supervised visual learning method by predicting the variable playback speeds of a video. Without semantic labels, we learn the spatio-temporal visual representation of the video by leveraging the variations in the visual appearance according to different playback speeds under the assumption of temporal coherence. To learn the spatio-temporal visual variations in the entire video, we have not only predicted a single playback speed but also generated clips of various playback speeds and directions with randomized starting points. Hence the visual representation can be successfully learned from the meta information (playback speeds and directions) of the video. We also propose a new layer dependable temporal group normalization method that can be applied to 3D convolutional networks to improve the representation learning performance where we divide the temporal features into several groups and normalize each one using the different corresponding parameters. We validate the effectiveness of our method by fine-tuning it to the action recognition and video retrieval tasks on UCF-101 and HMDB-51.Comment: Accepted by IEEE Access on May 19, 202

VALIDATION OF OPTIMALLY DESIGNED STATOR-PROPELLER SYSTEM BY EFD AND CFD

The development of energy-saving devices to lower the energy efficiency design index (EEDI) of ships has been actively researched worldwide. One such device is an asymmetric pre-swirl stator, which helps to improve the propulsion efficiency by recovering the rotational energy generated during propeller rotation. Determining the pitch angle is the most important factor in the design of an efficient asymmetric pre-swirl stator. To optimize the pitch angle of an asymmetric pre-swirl stator, this study deals with potential-flow, computational fluid dynamics, and model tests. The model delivered power at a design speed of 24 kt was compared by changing the pitch angle by ±2° with respect to the reference angle designed using a potential-flow program. The commercial code Star-CCM+ was used for the numerical analysis, and the model was also tested in a towing tank at Pusan National University. This study proposes an effective method for determining and verifying the optimal pitch angle of an asymmetric pre-swirl stator

St. John’s Wort Regulates Proliferation and Apoptosis in MCF-7 Human Breast Cancer Cells by Inhibiting AMPK/mTOR and Activating the Mitochondrial Pathway

St. John’s Wort (SJW) has been used as an estrogen agonist in the systems affected by menopause. Also, hypericin, a bioactive compound of SJW, has been used as a photosensitizer in photodynamic therapy. In the present study, we investigate the anti-proliferative and pro-apoptotic effects of SJWto demonstrate the chemo-preventive effect in human breast cancer cells. MCF-7 cellswere culturedwith DMSO or various concentrations of SJWethanol extract (SJWE). Cell viability, proliferation, apoptosis, the expression of proteins involved in cell growth and apoptosis, and caspase-3/7 activity were examined. SJWE dose-dependently suppressed cell growth and induced apoptosis ofMCF-7 cells. Mechanistically, SJWE enhanced the phosphorylation of AMP-activated protein kinase (AMPK) and decreased the expression of p-mammalian target of rapamycin (p-mTOR) and p-eukaryotic translation initiation factor 4E (eIF4E)-binding protein 1 (4E-BP1). Also, SJWE inhibited the phosphorylation of protein kinase B (Akt) and showed increases in the expression of pro-apoptotic proteins Bax and Bad with decreases in the expression of anti-apoptotic proteins including B-cell lymphoma 2 (Bcl-2), B-cell lymphoma-extra large (Bcl-xL), and p-Bcl-2-associated death promoter (p-Bad). SJWE at 50 µg/mL showed markedly enhanced caspase-7 activation. Taken together, our results provide evidence that SJWE shows anti-proliferative and pro-apoptotic effects via inhibition of AMPK/mTOR and activation of a mitochondrial pathway. Therefore, SJWE can be used as a chemo-preventive agent without photo-activation

Retrospective Analysis of Methotrexate Elimination When Coadministered With Levetiracetam

Background: Delayed elimination of methotrexate was previously reported in 2 patients receiving concomitant levetiracetam. Objective: To explore the potential interaction between methotrexate and levetiracetam in patients receiving high-dose methotrexate. Methods: This retrospective study reviewed the records of 81 adults receiving 280 cycles of methotrexate to determine the effects of levetiracetam on methotrexate elimination. Institutional review board approval was obtained. Results: Levetiracetam was administered in 33 (12%) cycles of methotrexate. Patients receiving levetiracetam had significantly lower 24-hour methotrexate concentrations compared with those not receiving levetiracetam (2.91 vs 7.37 µmol/L, P = 0.005). Despite this difference, concentrations at 48 and 72 hours were similar between groups. Times to nontoxic methotrexate concentration (\u3c0.1 µmol/L) were the same regardless of the presence of levetiracetam. The frequency of delayed elimination at 24, 48, and 72 hours was similar in both groups as was the frequency of delayed elimination at any time point. Cox regression demonstrated that levetiracetam was not a significant predictor of time to nontoxic methotrexate concentration (P = 0.796; HR = 1.058; 95% CI = 0.692-1.617), and logistic regression demonstrated that levetiracetam was not a significant predictor of delayed elimination at any time point. Levetiracetam use was similar between groups when comparing patients experiencing delayed elimination at any time point with those without delayed elimination (13% vs 10%, respectively, P = 0.527). Conclusion: This study does not support the previous reports of a significant interaction between levetiracetam and methotrexate. A clinically significant interaction is unlikely in those without additional risk factors for delayed elimination

Small-scale spatial genetic structure of Asarum sieboldii metapopulation in a valley

Background Asarum sieboldii Miq., a species of forest understory vegetation, is an herbaceous perennial belonging to the family Aristolochiaceae. The metapopulation of A. sieboldii is distributed sparsely and has a short seed dispersal distance by ants as their seed distributor. It is known that many flowers of A. sieboldii depend on self-fertilization. Because these characteristics can affect negatively in genetic structure, investigating habitat structure and assessment of genetic structure is needed. A total of 27 individuals in a valley were sampled for measuring genetic diversity, genetic distance, and genetic differentiation by RAPD-PCR. Results The habitat areas of A. sieboldii metapopulation were relatively small (3.78~33.60 m2) and population density was very low (five to seven individuals in 20×20 m quadrat). The habitat of A. sieboldii was a very shady (relative light intensity = 0.9%) and mature forest with a high evenness value (J = 0.81~0.99) and a low dominance value (D = 0.19~0.28). The total genetic diversity of A. sieboldii was quite high (h = 0.338, I = 0.506). A total of 33 band loci were observed in five selected primers, and 31 band loci (94%) were polymorphic. However, genetic differentiation along the valley was highly progressed (Gst = 0.548, Nm = 0.412). The average genetic distance between subpopulations was 0.387. The results of AMOVA showed 52.77% of variance occurs among populations, which is evidence of population structuring. Conclusions It is expected that a small-scale founder effect had occurred, an individual spread far from the original subpopulation formed a new subpopulation. However, geographical distance between individuals would have been far and genetic flow occurred only within each subpopulation because of the low density of population. This made significant genetic distance between the original and new population by distance. Although genetic diversity of A. sieboldii metapopulation is not as low as concerned, the subpopulation of A. sieboldii can disappear by stochastic events due to small subpopulation size and low density of population. To prevent genetic isolation and to enhance the stable population size, conservative efforts such as increasing the size of each subpopulation or the connection between subpopulations are needed.This work was supported by a grant (NRF-2018R1A2B2002267) of the National Research Foundation (NRF) funded by the Ministry of Science, ICT and Future Planning (MSIT), Republic of Korea, and R&E program of Siheung Education Institute for Gifted