bluuebunny/crossref_metadata_2025 huggingface dataset:
3D-printed torsional mechanism demonstrating fundamentals of free vibrations
Authors: Tekes Ayse
Published: May 2020

Commercially available turn-key systems are expensive and require substantial lab space, making it harder to accommodate many in vibrations laboratories. This study presents a low-cost, compact, and portable torsional mechanism incorporating multiple rotating disks and a long thin rod supported vertically with bearings and fixed supports at the top and bottom ends to study the modeling of systems using experimental data. The mechanism consisting of a rod, disks, bearing, and disk supports, and the base is built by 3D printing using thermoplastic PETG. The long, thin rod in this mechanism serves as a torsional spring. The equivalent stiffnesses of the 2 DOF system can be changed by adjusting the vertical position of the disks with respect to the ends, thereby shortening or lengthening the effective twist length of the thin rod. The overall dimensions of the mechanism are 6 inches in height, 5 inches in width, and 2 inches in depth, and the expected cost including the experimental setup is around USD$30 if an Arduino is used for data acquisition and $170 if equipped with a National Instruments external data acquisition card. Learning objectives of the lab course utilizing the proposed mechanism are identified. The free response data are collected for a single degree-of-freedom system using an external data acquisition card and potentiometer and unknown parameters of the system are determined by system identification. Mechanism unknown parameters are calculated using system identification and a theoretical model is compared with the experimental data.
Insertions of mitochondrial DNA into the nucleus—effects and role in cell evolution
Authors: Puertas María J. , González-Sánchez Mónica
Published: May 2020

We review the insertion of mitochondrial DNA (mtDNA) fragments into nuclear DNA (NUMTS) as a general and ongoing process that has occurred many times during genome evolution. Fragments of mtDNA are generated during the lifetime of organisms in both somatic and germinal cells, by the production of reactive oxygen species in the mitochondria. The fragments are inserted into the nucleus during the double-strand breaks repair via the non-homologous end-joining machinery, followed by genomic instability, giving rise to the high variability observed in NUMT patterns among species, populations, or genotypes. Some de novo produced mtDNA insertions show harmful effects, being involved in human diseases, carcinogenesis, and ageing. NUMT generation is a non-stop process overpassing the Mendelian transmission. This parasitic property ensures their survival even against their harmful effects. The accumulation of mtDNA fragments mainly at pericentromeric and subtelomeric regions is important to understand the transmission and integration of NUMTs into the genomes. The possible effect of female meiotic drive for mtDNA insertions at centromeres remains to be studied. In spite of the harmful feature of NUMTs, they are important in cell evolution, representing a major source of genomic variation.
Decay constant of $$B_s$$ and $$B^*_s$$ mesons from $$\mathrm{N_f}=2$$ lattice QCD
Authors: Balasubramamian Rahul , Blossier Benoît
Published: May 2020

We report on a two-flavor lattice QCD estimate of the$$B_s$$Bsand$$B^*_s$$Bs∗leptonic decays parameterized by the decay constants$$f_{B_s}$$fBsand$$f_{B^*_s}$$fBs∗. In addition to their relevance for phenomenology, their extraction has allowed us to investigate whether the “step scaling in mass” strategy is suitable with Wilson–Clover fermions to smoothly extrapolate quantities of the heavy-strange sector up to the bottom scale. From the central value of$$f_{D_s}$$fDsquoted by FLAG at$$N_f=2$$Nf=2and our ratio$$\frac{f_{B_s}}{f_{D_s}}$$fBsfDs, we obtain$$f_{B_s}=215(10)(2)(^{+2}_{-5})$$fBs=215(10)(2)(-5+2)MeV and$$f_{B^*_s}/f_{B_s}=1.02(2)(^{+2}_{-0})$$fBs∗/fBs=1.02(2)(-0+2).
Minimally deformed anisotropic dark stars in the framework of gravitational decoupling
Authors: Tello-Ortiz Francisco
Published: May 2020

In this work an analytic fluid sphere built on the well-known Tolman IV space–time is obtained. This toy model is sourced by an imperfect fluid distribution with a dark matter component. The anisotropic behavior is introduced into the system via gravitational decoupling by means of minimal geometric deformation. In this regard, the temporal component of the $$\theta $$θ-sector has been interpreted as the dark side of the matter distribution. To validate the feasibility of the salient model a detailed graphical analysis is performed, supported by real observational data corresponding to some strange star candidates. Besides, the impacts of minimal geometric deformation approach on the main macro physical observables ı.e, the total mass M, compactness factor u and surface gravitational red-shift $$z_{s}$$zs are discussed.
A New MIP Approach on the Least Distance Problem in DEA
Authors: Wang Xu , Lu Kuan , Shi Jianming , Hasuike Takashi
Published: May 2020

In this paper, we deal with the least distance problem (LDP) in Data Envelopment Analysis (DEA), which is to find a closest efficient target over the whole efficient frontier. To this end, we define the efficient frontier by a linear complementarity system and propose a mixed integer programming (MIP) approach to solve the LDP. Our proposed MIP approach: (1) can solve the LDP based on [Formula: see text]-norm ([Formula: see text]) by using a state-of-the-art solver and obtain the closest efficient target over the whole efficient frontier instead of a subset of it; (2) can be applied for computing the least distance DEA models satisfying the monotonicity; (3) is more user-friendly, because it allows a decision maker to improve the efficiency of a decision making unit (DMU) by setting the affordable input/output level under his/her circumstance. Thus, the efficient target provided by our approach may be more appropriate from the perspective of the decision makers of DMUs.
DOA Estimation of Noncircular Signals for Coprime Linear Array via Polynomial Root-Finding Technique
Authors: Zhai Hui , Li Zheng , Zhang Xiaofei
Published: May 2020

In this paper, we investigate the direction of arrival (DOA) estimation problem of noncircular signals for coprime linear array (CLA). From the perspective of the CLA as extracted from a filled uniform linear array (ULA), a noncircular root-MUSIC algorithm is proposed to estimate the DOA which can avoid the spectral peak search and lower the computational complexity. Due to the noncircular characteristic, the proposed algorithm enables to resolve more sources than sensors. Meanwhile, the proposed algorithm has better angle estimation performance than some conventional DOA estimation algorithms. Numerical simulation results illustrate the performance of the proposed method.
Nuclear binding energy predictions based on BP neural network
Authors: Jiao B. B.
Published: May 2020

Nuclear masses are of great importance in nuclear physics and astrophysics. Descriptive experimental data on nuclear masses and the prediction of unknown masses based on residual proton–neutron interactions are a focus in nuclear physics. The accuracy of the residual interaction determines the accuracy of the nuclear mass values, so the study of residual interactions is essential. Before we carry out this study, there are many papers using artificial neural networks in nuclear physics. But no one uses BP neural network to study residual interactions. In this paper, we obtained a description and prediction model for residual interactions based on BP neural network. By combining experimental values with residual interactions model, we successfully calculate the nuclear masses of [Formula: see text]. Results demonstrate that the differences between our calculated values and experimental values (AME2003, AME2012 and AME2016) show that the root-mean-squared deviations (RMSDs) are small (comparing with AME2003, the odd-A nuclei RMSD and the even-A nuclei RMSD are 112 and 128[Formula: see text]keV; comparing with AME2012, the odd-A nuclei RMSD and the even-A nuclei RMSD are 103 and 121[Formula: see text]keV; comparing with AME2016, the RMSD of odd-A nuclei and even-A nuclei are 106 and 122[Formula: see text]keV, respectively). In addition, we obtained some predicted masses based on AME2003 and AME2012, the predicted values have good accuracy and compared well with experimental values (AME2012 and AME2016). The results show that the study of residual interactions using the proposed BP neural network method is feasible and accurate. This method is helpful for analyzing and extracting useful information from a large number of experimental values and then providing a reference for discovering physical laws and support for physical experiments.
Digitalization-Based Innovation — A Case Study Framework
Authors: Apostolov Mico , Coco Nunzia
Published: May 2020

Small- and medium-sized enterprises (SMEs) have been leading innovation processes, where the upsurge of digital technology has overpowering implications on competitive positioning, firm’s value chains and overall business model. Value creation facilitated by emerging digital technologies alters costs, as well as process performance. Due to field research and in-depth interviews with owners and managers of SMEs in North-East Italy area, we combine and analyze evidence of the contingent challenges companies face while trying to redesign their business model. Our results point out that being able to accumulate and put into action external ideas can be vital in supplementing internal knowledge base and therefore crucial in escaping technological lock-ins; thus, imposing efforts toward digital transformation offers favorable outcoes.
Separating subgroups of mapping class groups in homological representations
Authors: Hadari Asaf
Published: May 2020

Let [Formula: see text] be either the mapping class group of a closed surface of genus [Formula: see text], or the automorphism group of a free group of rank [Formula: see text]. Given any homological representation [Formula: see text] of [Formula: see text] corresponding to a finite cover, and any term [Formula: see text] of the Johnson filtration, we show that [Formula: see text] has finite index in [Formula: see text], the Torelli subgroup of [Formula: see text]. Since [Formula: see text] for [Formula: see text], this implies for instance that no such representation is faithful.
Optical design and simulation of an integrated OCT and video rigid laryngoscope
Authors: Kang Jiajing , Li Xinyu , Wan Mingming , Wang Jiahui , Liang Shanshan , Zhang Jun
Published: May 2020

An integrated optical coherence tomography (OCT) and video rigid laryngoscope have been designed to acquire surface and subsurface tissue images of larynx simultaneously. The dual-modality system that is based on a common-path design with components as few as possible effectively maintains the light transmittance without compromising the imaging quality. In this paper, the field of view (FOV) of the system can reach [Formula: see text] by use of a gradient index (GRIN) lens as the relay element and a four-lens group as the distal objective, respectively. The simulation showed that the modulation transfer function (MTF) value in each FOV of the rigid video endoscope at 160[Formula: see text]lp/mm is greater than 0.1 while the root mean square (RMS) radii of the OCT beam in the center and edge of the FOV are 14.948[Formula: see text][Formula: see text]m and 73.609[Formula: see text][Formula: see text]m, respectively. The resolutions of both OCT and video endoscope meet the requirement of clinical application. In addition, all the components of the system are spherical, therefore the system can be of low cost and easy to assemble.
Scientific scripting in Java with JShellLab and application to deep learning using DeepLearning4j
Authors: Papadimitriou Stergios
Published: May 2020

JShellLab is an easy to use MATLAB-like environment for the Java Virtual Machine (JVM). It implements scientific scripting based on the JShell Application Programming Interface (API) of modern Java.

The paper illustrates that JShellLab can significantly facilitate and simplify the development of complex computational demanding scientific software at the JVM. The novelty at the JShellLab is that it completely hides the complexity and the intricate dependencies of optimized scientific software. As an example, the demanded field of deep learning is exploited. Specifically, the implementation of effective practical deep learning-based systems using the JShellLab environment and the Deeplearning4j Java library is considered.
The constant electric field effect on the radio absorption of crystals BaTiO3 and piezoceramics PCR-1
Authors: Sidorenko Eugeny , Ngoc Chan Thi Beat , Prikhodko Gennady , Natkhin Ivan , Shloma Alexander , Kharchenko Diana
Published: May 2020

The effect of a constant electric field ([Formula: see text]) on the absorption of microwave electromagnetic energy ([Formula: see text]) by BaTiO3 crystals and the highly sensitive PCR-1 piezoceramic was studied. The field dependence of the absorption value [Formula: see text] at the maximum of the spectrum [Formula: see text] has the form of a “butterfly”, and the dependence of the frequency shift of the maximum on the field strength [Formula: see text] has a hysteretic character. The PCR-1 [Formula: see text] absorption spectrum at high [Formula: see text] is modulated by pulses in a wide frequency range. It is assumed that the cause of the amplitude–frequency modulation of the spectrum may be the electromagnetic radiation of incomplete local discharges at the surface of piezoceramics. The change in the magnitude and position of the resonance maximum in the absorption spectra and the appearance of amplitude–frequency modulation [Formula: see text] when exposed to a constant field is interpreted from the point of view of changes in the parameters and concentration of the domains walls, as well as the [Formula: see text]- and [Formula: see text]-domain wedges of mechanical twins resonating in the electromagnetic field.
Computational Approaches for Unraveling the Effects of Variation in the Human Genome and Microbiome
Authors: Zhu Chengsheng , Miller Maximilian , Zeng Zishuo , Wang Yanran , Mahlich Yannick , Aptekmann Ariel , Bromberg Yana
Published: May 2020

The past two decades of analytical efforts have highlighted how much more remains to be learned about the human genome and, particularly, its complex involvement in promoting disease development and progression. While numerous computational tools exist for the assessment of the functional and pathogenic effects of genome variants, their precision is far from satisfactory, particularly for clinical use. Accumulating evidence also suggests that the human microbiome's interaction with the human genome plays a critical role in determining health and disease states. While numerous microbial taxonomic groups and molecular functions of the human microbiome have been associated with disease, the reproducibility of these findings is lacking. The human microbiome–genome interaction in healthy individuals is even less well understood. This review summarizes the available computational methods built to analyze the effect of variation in the human genome and microbiome. We address the applicability and precision of these methods across their possible uses. We also briefly discuss the exciting, necessary, and now possible integration of the two types of data to improve the understanding of pathogenicity mechanisms.
Recent Advances in Understanding the Genetic Architecture of Autism
Authors: Dias Caroline M. , Walsh Christopher A.
Published: May 2020

Recent advances in understanding the genetic architecture of autism spectrum disorder have allowed for unprecedented insight into its biological underpinnings. New studies have elucidated the contributions of a variety of forms of genetic variation to autism susceptibility. While the roles of de novo copy number variants and single-nucleotide variants—causing loss-of-function or missense changes—have been increasingly recognized and refined, mosaic single-nucleotide variants have been implicated more recently in some cases. Moreover, inherited variants (including common variants) and, more recently, rare recessive inherited variants have come into greater focus. Finally, noncoding variants—both inherited and de novo—have been implicated in the last few years. This work has revealed a convergence of diverse genetic drivers on common biological pathways and has highlighted the ongoing importance of increasing sample size and experimental innovation. Continuing to synthesize these genetic findings with functional and phenotypic evidence and translating these discoveries to clinical care remain considerable challenges for the field.
Corrosion-Induced Microstructural Variability Affects Transport-Kinetics Interaction in PEM Fuel Cell Catalyst Layers
Authors: Goswami Navneet , Mistry Aashutosh N. , Grunewald Jonathan B. , Fuller Thomas F. , Mukherjee Partha P.
Published: May 2020

The ionomer, which is responsible for proton transport, oxygen accessibility to reaction sites, and binding the carbon support particles, plays a central role in dictating the catalyst layer performance. In this work, we study the effect of ionomer distribution owing to the corrosion induced degradation mode in the catalyst layer based on a combined mesoscale modeling and experimental image-based data. It is observed that the coverage of the ionomer over the platinum-carbon interface is heterogeneous at the pore-scale which in turn can critically affect the electrode-scale performance. Further, an investigation of the response of the pristine as well as degraded microstructures that have been exposed to carbon support corrosion has been demonstrated to highlight the kinetic-transport underpinnings on the catalyst layer performance decay.
(Invited) Fluorescence and Sensing Applications of Graphene Oxide
Authors: Wu Nianqiang
Published: May 2020

This presentation describes the finger-printing fluorescence of functional groups in graphene oxide. In particular, this talk highlights the excitation wavelength-dependent fluorescence emission of graphene oxide. In addition, graphene oxide has been functionalized with aptamers for detection of heavy metals and cancer biomarkers.
Utilizing 2D Graphite Carbon Nitride for Industrial Applications – from Supercapacitors to Biosensors
Authors: Mandal Debabrata , Biswas Sudipta , Chowdhury Ananya , Chandra Amreesh
Published: May 2020

2D materials are slowly overcoming the critical drawbacks of stability, low conductivity, reproducibility and cost. Therefore, with their intrinsic advantages of: ultra-large specific surface areas, well-defined layered architecture, tuneable redox activity and material hybridization, many 2D materials beyond graphene are being discovered. Few such 2-D materials, which have been reported are WS2, MoS2, h-BN, etc. Recently, 2D nano-sized graphite carbon nitride (g-C3N4) has been reported, with prediction that it can become an excellent candidate for miniaturized energy storage and optoelectronic devices. Graphite carbon nitride is a 2-D layered structure, where the tris-triazine unit are connected with planner amino groups in each layer, and weak van der Waal force acts between the layers. The quantum size effect are quite prominent along the inplane direction, which leads to interesting modulations in electrical and chemical properties. The nitrogen functional groups-rich frame-work is also expected to synergistically contribute in enhancing the electrochemical response of the material. Large synthesis of this material has remained a challenging task.

In this paper, using a low-cost pyrolysis synthesis protocol, it is established that 2D nano-sized graphite carbon nitride can be produced in large quantities, with reproducible characteristics. The preliminary characterization of graphite carbon nitride was performed using XRD, SEM, TEM, Raman, FTIR, AFM, and BET techniques. The sizes of the nanosheets was found to be in the range of 200-300 nm, while the thickness of these sheets was ~90 nm. The performance of 2D nano-sized graphite carbon nitride in supercapacitors was investigated in detail. The electrochemical properties were investigated by cyclic voltammetry and charge-discharge measurements in 3 M KOH. The results clearly indicated improved cyclic stabilities up to 2500 cycles, with a specific capacitance of 84 F g-1 at 1 A g-1 current density. A typical charge-discharge profile (as a function of current density) for the synthesized g-C3N4 is shown in Fig. 1. A symmetric supercapacitor was also fabricated using this material as an active electrode, which showed ~ 11Wh Kg-1 energy and 500 W Kg-1 power density. The versatilaty of the material is established by extending its application to biosensing and catalytic applications. The results of electrochemical sensor for the detection of hydrogen peroxide is also presented in the paper. The result of cyclic voltammetry and chronoamperometric experiments showed that the linear response ranges are 0-80 nM, with a detection limit of 0.42 nM. The materials also shows excellent capability to catalytically reduce p-nitrophenol, which is a common pollutant in industrial waste water.

Figure 1
(Invited) Controlling Monolayer and Few-Layer MoS2 and WS2 Optoelectronic and Catalytic Properties
Authors: Miller Elisa M.
Published: May 2020

By functionalizing, doping, and changing phases, we can control the optoelectronic and catalytic properties of 2D transition metal dichalcogenides (TMDCs), specifically MoS2 and WS2. These 2D layered nanomaterials can be made via a top-down (exfoliation) or bottom-up (chemical vapor deposition) approach. The optoelectronic properties of monolayer TMDCs are strongly influenced by their surroundings and can be used as a humidity sensor, which we demonstrate with photoluminescence measurements. Furthermore, we quantify the stability of metallic, monolayer TMDCs when it is converted from the semiconducting to the metallic phase and functionalized, where comparisons are made to few-layer TMDCs. By controlling these optoelectronic properties, we can better understand the catalytic performance for hydrogen evolution.
(Invited) Controlling Defects and Oxidation at Molybdenum Disulfide Electrodes and the Impact on Capacitive Charging
Authors: Pope Michael A
Published: May 2020

Supercapacitors based on 1T-molybdenum disulfide (MoS2) have achieved record high volumetric capacitance due to a combination of high surface area, bulk density and the ability for ions to easily penetrate between restacked layers. While many promising MoS2-based devices have been demonstrated, few works have examined capacitive charging mechanisms at the MoS2/electrolyte interface and how defects and oxidation play a role. In fact, unlike similar materials like graphene and graphite, no fundamental studies on double-charging have ever been reported for this promising material. In this talk, I will first discuss recent work from my group which examines degradation mechanisms which act to rapidly and significantly oxidize MoS2 during aqueous processing. Light, oxygen and pH are found to play significant roles in the degradation mechanism and rate. In the second part of my talk, I will describe a model study of charging mechanisms at flat electrodes composed of various ratios of 2H and 1T MoS2 produced by chemical exfoliation and with various degrees of oxidation. Using this system we attempt to identify the intrinsic capacitance of the 1T and 2H phase, the mechanism of charging and the impact of defects and oxidation on double-layer charging and pseudocapacitance and relate these to the known theories of charging at the interface of semi-metals and semi-conductors. The intrinsic capacitance and theoretical surface area are used to discuss theoretical capacitance limits for MoS2 and MoS2-based heterostructures.
(Invited) Single Nanosheet Photoelectrochemistry: Probing Charge Recombination and Transport Pathways in Monolayer Transition Metal Dichalcogenide Photoelectrodes
Authors: Sambur Justin , Wang Li
Published: May 2020

Monolayer heterojunctions such as MoS2/WS2 are attractive for solar energy conversion applications because the interfacial electric field spatially separates charge carriers in less than 100 femtoseconds. Photoelectrochemical cells represent an intriguing platform to collect the spatially separated carriers. However, the recombination, transport, and interfacial charge transfer processes that take place following the ultrafast charge separation step have not been investigated. Here we demonstrate novel charge recombination and transport pathways in monolayer MoS2/WS2 photoelectrochemical cells by spatially resolving the net collection of carriers (i.e., the photocurrent) at the single nanosheet-level. We discovered an excitation wavelength-dependent recombination pathway that depends on the heterojunction stacking configuration and the carrier generation profile in the heterostructure. Photocurrent mapping measurements revealed that charge transport occurs parallel to the layers over micrometre-scale distances even though the indium tin oxide electrode and liquid electrolyte provide efficient charge extraction pathways via intimate electron- and hole-selective contacts. Our results reveal how composition heterogeneity influences the performance of bulk heterojunction electrodes made from randomly oriented nanosheets and provide critical insight into the design of efficient heterojunction photoelectrodes for solar energy conversion applications.

Figure 1
(Invited) 2D Materials for Backend Technology
Authors: Chen Zhihong , Lo Chun-Li , Zhang Shengjiao
Published: May 2020

Cu is used as the interconnect material in IC chips because of its superior conductivity. However, the diffusion of Cu into the dielectric between two interconnects can cause shorting and create chip failures, while the diffusion to transistors can introduce deep-level traps to Si and affect the transistor performance. Ta/TaN bilayer stacks have been used as diffusion barrier/liner materials to isolate Cu from surrounding intra/inter-layer dielectrics. Along with the scaling of VLSI, the dimensions of interconnects and vias need to be scaled as well. To maximize Cu volume for lower line resistance and reduce the via resistance, the thickness of the barrier/liner bilayer should be scaled accordingly. However, these materials lose their capability of blocking Cu diffusion as their thickness is extremely reduced. In this talk, I will show that the diffusion barrier and liner properties of several 2D materials are investigated by various characterization methods. We observe that the lifetime of the dielectrics surrounding Cu electrodes can be significantly extended with the presence of the tested 2D barriers, providing strong evidence for promising alternative barrier/liner solutions.
(Invited) Ferromagnetism and Exchange Coupling with Fe-Doped WSe2
Authors: Hinkle Christopher
Published: May 2020

The incorporation of magnetic dopants is a way to realize magnetism in semiconductors. The 2D material WSe2 is a semiconductor with a bandgap of 1.3 eV, and Fe-doped WSe2 is predicted to have room temperature, long-range ferromagnetism. Moreover, WSe2 has been extensively studied for applications in electronic devices, and can be prepared by deposition methods that are compatible with semiconductor fabrication processes. 2D magnetic films are particularly intriguing in technologies that rely on exchange coupling since the efficiency of the exchange with the magnet is inversely proportional to the magnet thickness 1/tFM. Chalcogenide-based TMD magnets can also have ideal interfaces with chalcogenide-based topological insulators (like Bi2Se3), enabling efficient spin torque devices and potentially realizing the quantum Hall effect without an external magnetic field.

In this work, we demonstrate the growth of Fe-doped WSe2 and report on its up to room temperature ferromagnetic properties. The evolution of Fe-doped WSe2 films under different doping levels indicates that strain from the impurity atom itself coupled with strain imparted by the substrate can drive phase separation at high Fe concentrations. We find that suppressing that film strain helps promote more Fe incorporation (and higher Curie temperatures).

Cr2O3 has only 0.2% lattice mismatch with WSe2 and is a magnetoelectric that can couple with ferromagnetic films. By using seed-layer techniques, we successfully prepared layered Fe-WSe2 on Cr2O3 and demonstrate magnetic coupling between the two, a potentially promising route toward realizing electric field control of 2D magnets. Magnetic measurements show a clear hysteresis loop at 100 K in a 2 Tesla cooling field, from which a large negative bias field of 600 Oe is resolved. The bias field vs temperature mesurements, where a negative bias field emerges below 250 K, indicates the existence of ferromagnetic exchange coupling in this heterostructure.

This work is supported in part by NEWLIMITS, a center in nCORE, a Semiconductor Research Corporation (SRC) program sponsored by NIST through award number 70NANB17H041. This work is also supported by the National Science Foundation under awards 1917025 and 1921818.
Production of High-Quality Graphene Using a Novel Electrochemical Intercalation-Exfoliation Approach
Authors: Singh Ashutosh Kumar , Perez-Page Maria , Yasri Nael , Holmes Stuart , Roberts Edward P.L.
Published: May 2020

Large scale production of graphene has recently received a great deal of attention because of its interesting properties and wide range of potential applications. Conventional chemical exfoliation approaches, such as Hummer’s method,provides cost-effective pathway for large scale production, however, the method suffers from several key challenges such as the usage of corrosive and toxic solution, high processing temperature, long duration, and the poor quality of graphene produced which severely affects its potential applications. Recently, electrochemical exfoliation of graphene has been proposed for a high production yield with better quality. The electrochemical method involves two steps: 1) intercalation of ionic species between the graphene layers, followed by 2) oxidation of these ionic species under an anodic voltage into gas molecule enabling exfoliation of graphene flakes from the graphite electrode.1 In this study we examine a new approach to the intercalation, using an intercalating ion that has received very little attention and has not been evaluated for electrochemical exfoliation. The intercalation was followed by exfoliation in (NH4)2SO4 solution leading to the production of graphene flakes. The resultant graphene was found to have less disrupted sp2 lattice structure, with a high yield of about 95 % of graphene, along with high electrical conductivity and a low oxidation level (with a C:O ratio of about 15, determined by XPS). In addition, the presence of nitrogen and sulfur moieties in the resulting graphene structure can act as an electrocatalyst2 for applications such as the oxygen reduction reaction. Thus, the as-prepared graphene could be used for a range of electrochemical applications.

References:

(1) Sharif, F.; Zeraati, A. S.; Ganjeh-Anzabi, P.; Yasri, N.; Perez-Page, M.; Holmes, S. M.; Sundararaj, U.; Trifkovic, M.; Roberts, E. P. L. Synthesis of a High-Temperature Stable Electrochemically Exfoliated Graphene. Carbon
2019.

(2) Singh, A.; Yasri, N.; Karan, K.; Roberts, E. P. L. Electrocatalytic Activity of Functionalized Carbon Paper Electrodes and Their Correlation to the Fermi Level Derived from Raman Spectra. ACS Appl. Energy Mater.
2019, acsaem.9b00180.
Advanced Single Cell Thermal Runaway Initiation Techniques
Authors: Lamb Joshua , Torres-Castro Loraine , Stanley June , Grosso Christopher
Published: May 2020

The evaluation of lithium ion battery safety has traditionally focused on the performance of single cells exposed to abusive conditions. As lithium ion batteries are fielded in increasingly large and complex systems, the system level safety performance is becoming of greater concern. Testing laboratories and battery end users have begun to consider the hazards associated with a localized thermal runaway event, a single cell or small group of cells, propagating to the bulk of a large battery system. Evaluating this propagating failure requires initiating thermal runaway of a single cell or group of cells and observing how that failure affects the surrounding system.

Ultimately, testing cell to cell propagation requires a method for initiating or simulating single cell runaway while adding a minimum of excess energy into the system. Traditionally single cell failure is initiated with standard battery abuse tests, such as overcharge, thermal ramp and nail penetration tests. However, nail penetration tests can be difficult to perform in fully developed battery systems while overcharge and thermal ramp add a significant amount of excess energy into the battery system. Recent work at Sandia has looked at non-traditional thermal runaway triggers that can be applied to off-the-shelf cells. Single cells were initiated using a fiber coupled laser to create a localized failure on a cell. The ability to initiate single cell failure in both pouch and cylindrical cells is in multiple orientations is demonstrated. Limited cell to cell propagation initiated by the laser is performed as well, demonstrating the technique as a low energy initiation source for propagation testing.

Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.
Estimation of the Entropy Coefficient of Lithium-Ion Batteries Via a Temperature and Open-Circuit Voltage Kernel Function
Authors: Widanage Widanalage Dhammika , Prosser Ryan , Paarmann Sabine , Queisser Oliver , Shahjalal Mohammad
Published: May 2020

Lithium-ion battery temperature is driven by two key heat source terms – irreversible and reversible heat. The reversible heat generation term is often neglected when characterising and simulating battery temperature. This is primarily due to the long experimental time (~20 hours) associated with the widely followed potentiometric technique used to quantify reversible heat. Reversible heat can however contribute to around 70% of the total heat generation, when a battery is subjected to low charge and discharge currents, and it is quantified via a coefficient termed as the entropy coefficient.

Robust techniques are therefore required that can significantly reduce the experimental time and quantify the entropy coefficient to improve battery temperature prediction and subsequent design of battery pack thermal management systems. In this abstract a bespoke experimental rig using a Peltier element is built that allows a user-defined thermal profile to be applied on to the surface of a coin cell (Figure 1). The applied temperature profile is designed in a manner that perturbs the cell open-circuit-voltage (OCV) to identify the underlying dynamics between the measured OCV response (at a given state-of-charge, SoC) and applied cell surface temperature profile. This dynamic relationship is characterised by a kernel function relating temperature and OCV. Using system identification techniques, the temperature profile can be designed to minimise the experimental time required to estimate the underlying open-circuit voltage and temperature kernel function and robustly determine the entropy coefficient at the particular cell SoC.

The approach is applied on a coin cell consisting of Kokam 5 Ah electrodes and the entropy coefficient, is estimated as -0.57 ± 0.02 mV/K (when at 30% SoC) within an experimental time interval of 8 hours. The initial results are encouraging and further work is in progress to compare and validate the procedure against the default potentiometric technique.

Figure 1: Experimental rig design for the thermal excitation and open-circuit voltage (OCV) measurement of the coin cell under test.

Figure 1
Fast Operando GCMS Gas Analysis for Monitoring Electrolyte Decomposition in Lithium Ion Batteries
Authors: Kahr Jürgen , Rezqita Arlavinda , Antoniadou Maria , Rosenberg Erwin , Fontana Daniela , Jahn Marcus
Published: May 2020

Lithium Ion Batteries (LIB) find not only wide use in portable devices and consumer electronics, but also attract increasing attention in stationary energy storage and the automotive sector. In this regard, LIBs play a significant role as intermediate energy storage due to their high volumetric and gravimetric energy, high power density, and long cycle life.

To achieve the required performance, the interaction of novel anode and cathode materials is of paramount interest. Particularly, the safety of cell operation must be assessed with respect to the formation of volatile and reactive species during cycling which can negatively alter cell components. Gas chromatography mass spectroscopy (GCMS) has proven to be a reliable tool for species detection. Unfortunately, conventional GC systems lack time resolution for in-situ gas analysis regarding fast processes, for example battery failure. Therefore, developing operando testing methods with improved time resolution is key to giving insight into electrolyte alterations during battery operation.

Here one of them, a novel multiplex injection method is presented as a monitoring technique for gas species arising from the decomposition of conventional LIB electrolytes. The combination of the multiplexing technique and GCMS allows the analysis of fast decomposition processes by 15 fold increase of time resolution compared to conventional gas chromatography. In addition, FTIR allows online monitoring of selected vibration bands. Commercially produced pouch cells were monitored with respect to evolving gas species during battery operation under overcharge conditions. For the decomposition of LiPF6 / organic carbonate- based electrolytes alkanes, alcohols, ethers, esters, aldehydes and also derivatives that appear in the presence of hydrofluoric acid such as fluorinated alkane species, have been evaluated.

The author gratefully acknowledges the FFG (Austrian Research Promotion Agency) for funding this research within project No. 858298.
3D Printable Ionogels with High Ionic Conductivity
Authors: Lange Alyna , Zehbe Kerstin
Published: May 2020

Hybrid materials based on ionic or polymer components are very useful in electrochemical devices like battery systems or fuel cells due to their unique properties like thermal and electrochemical stability and polarity. For all advances over the past, lithium ion based materials are still costly, limited and not very stable. Currently, solid-state polymer electrolytes (SPEs) and gel polymer electrolytes (GPEs) [1] have ion conductivities below 10-4 S/cm at room temperature.

Polymer electrolytes can be established by ionic liquids (ILs) which combine beneficial properties like high ionic conductivity, wide electrochemical potential window and high viscosity. These kinds of electrolytes can be very beneficial in solid-state batteries for example. This technology has garnered immense excitement from investors and large corporations. The main advantage of all-solid-state to liquid electrolyte-based batteries is that the size can be easily made smaller e.g. solid‐state electrolytes have a typical thickness of approximately 1.0 μm, whereas the separator in liquid electrolyte‐based cells typically has a thickness of 20 μm. Several investigators are exploring 3D architectures for thin-film rechargeable battery electrodes. Nevertheless additive manufacturing, also known as 3D printing, could revolutionize the structural properties of batteries. In addition, this technology could improve the adaptability of the electrolyte to the electrodes.

This scientific approach introduces the possibility to combine ionic liquids with a commercial photoreactive resin to realise a well-defined structure by using stereolithography (SLA). This provides, for the first time, access to ionogels (IGs) with complex 3D shapes (figure 1a) with potential application in battery or fuel cell technology. For first experiments new IGs were prepared by adding a series of sulfonate-based ionic liquids (ILs), 1-methyl-3-(4-sulfobutyl)imidazolium para-toluenesulfonate [BmimSO3H][pTS], 1-methyl-1-butylpiperidiniumsulfonate para-toluenesulfonate [BmpipSO3][pTS], and 1-methyl-3-(4-sulfobutyl) imidazolium methylsulfonate [BmimSO3H][MeSO3] with a clear photoreactive resin which were used in a Form 2 3D printer [2]. Moreover, the IGs are thermally stable up to about 200 °C and mechanically robust. In addition to this synthesized protic conductive IGs, sulfobataine, metal and lanthanides containing IGs were prepared and analysed. These IGs exhibit higher conductivities compared to the sulfonated based IGs in the range from 10-4 to 10-2 S/cm at room temperature. 3D Printable metal-lanthanide IGs could possibly be an adequate replacement for lithium-ion electrolytes.

Figure 1: a) Well-defined structures of IGs by SLA, b) Rhd battery cell for electrochemical measurements.

Literature:

[1] Stephan, A.M., Review on gel polymer electrolytes for lithium batteries. European polymer journal, 2006. 42(1): p. 21-42.

[2] Zehbe, K.; Lange,A.; Taubert, A., Stereolithography provides access to 3D printed ionogels with high ionic conductivity, Energy and Fuels, accepted.

Figure 1
Effects of Discharge Products on Zinc-Air Flow Cells
Authors: Fuchs David , Müller Christoph , Mahlendorf Falko , Heinzel Angelika
Published: May 2020

As one of the proposed post lithium-ion technologies, zinc-air batteries have received revived interest in the recent years, which is driven by the increased demand of high-performance, efficient, safe and environment-friendly energy storage solutions. These energy storage systems need to address variable power, capacity and profitability requests. Zinc-air flow batteries with higher specific energy density than lithium-ion and low-cost, highly available, eco-friendly active materials are suitable to fulfill these requirements. The energy density of most zinc-air flow batteries is limited by the low solubility of ZnO in the electrolyte. The use of a flow battery type with zinc-particles suspended in alkaline solution (zinc-slurry) in addition with high performance oxygen-reduction electrodes enables the development of high-power zinc-air batteries. This setup also enables the independent scaling of capacity and power.

The cooperative project, ZnMobil, funded by the Federal Ministry of Economic Affairs and Energy in Germany, combines the experience of industrial and academic partners (Covestro Deutschland AG; Grillo-Werke AG; VARTA Microbattery GmbH; Accurec Recycling GmbH; Technical University Freiberg, Gottfried Wilhelm Leibniz University Hannover; University of Duisburg-Essen; the fuel cell research center ZBT GmbH) to develop a high-performance and low-cost zinc-air flow battery.

The battery system consists of a 100 cm² copper plate as current collector for the zinc-suspension electrode and an oxygen reduction electrode with gas-diffusion layer (supplied by Covestro Deutschland AG). The zinc-slurry contains zinc particles (supplied by Grillo-Werke AG) suspended in alkaline solution (30 wt-% KOH) and stabilized with polyacrylic acid.

Here we present a systematic study regarding the effects of the discharge products on the cell performance. Depending on the state of discharge and operation parameters the discharge product ZnO causes several important effects. The solid ZnO limits the discharge capacity in several ways. At high current densities, passivation is the main topic. If passivation is avoided, e.g. with the help of additives, the solid ZnO causes a viscosity increase until the cell is blocked. For this study we evaluated parameters like cell voltage, cell resistance, slurry viscosity, ZnO concentration in the electrolyte and other parameters in correspondence to the state of discharge. The understanding of these effects is essential to build a hydraulically rechargeable battery with high zinc usage and therefore high energy densities.

Depending on parameters like current density and additive selection, it is possible to reach more than 70 % DOD, which corresponds to 287 mAh/gslurry or 574 mAh/gzinc. A demonstrator-cell was operated for more than 140 h. During this time it was successfully hydraulically recharged several times.
Pore-Scale Modeling of the Fuel Cell Catalyst Layer: The Role of Nafion Thin Films
Authors: Sadeghi Mohammad Amin , Agnaou Mehrez , Barralet Jake , Friscic Tomislav , Gostick Jeff T.
Published: May 2020

In this work, a multiphysics pore-scale model of electrochemical reactive transport inside a fuel cell catalyst layer (CL) is presented and is used to elucidate the role of Nafion thin films on the overall performance of the CL. One of the main challenges of modeling transport in CL is the hierarchy of length scales and the multiphysics nature of transport. Consequently, traditional continuum methods, in which volume-averaged quantities are used to encapsulate the microstructural features, cannot give a clear picture of the multiphysics transport processes inside the CL. Alternatively, pore-scale methods, which take into account the true geometry down to the pore level, are suited to capture these processes for such systems. Previously, researchers have mainly employed direct numerical simulation (DNS) techniques for pore-scale modeling of the CL. While these techniques are highly accurate, they are very computationally expensive. This limits the domain size that can be simulated in a reasonable time. In this work, pore network modeling, a computationally cheap technique to simulate pore-scale transport, is used to study transport in the CL. Using this approach, we were able to speed up the simulation runtime up to 20-50x compared to DNS. Consequently, simulation of much larger domains of the CL was made possible, leading to more representative results. Finally, the developed multiphysics pore-scale model was used to study the role of Nafion thin films on the overall performance of the CL. It is notable that the network approach was only applied to the void phase, and the Nafion region was resolved using DNS. Therefore, yet further speed up can potentially be obtained by applying the network approach to the Nafion phase.