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  • Bioprospecting of Novel Extremozymes From Prokaryotes-The Advent of Culture-Independent Methods.

    Sysoev, Maksim; Grötzinger, Stefan W.; Renn, Dominik; Eppinger, Jörg; Rueping, Magnus; Karan, Ram (Frontiers in microbiology, Frontiers Media SA, 2021-03-01) [Article]
    Extremophiles are remarkable organisms that thrive in the harshest environments on Earth, such as hydrothermal vents, hypersaline lakes and pools, alkaline soda lakes, deserts, cold oceans, and volcanic areas. These organisms have developed several strategies to overcome environmental stress and nutrient limitations. Thus, they are among the best model organisms to study adaptive mechanisms that lead to stress tolerance. Genetic and structural information derived from extremophiles and extremozymes can be used for bioengineering other nontolerant enzymes. Furthermore, extremophiles can be a valuable resource for novel biotechnological and biomedical products due to their biosynthetic properties. However, understanding life under extreme conditions is challenging due to the difficulties of in vitro cultivation and observation since > 99% of organisms cannot be cultivated. Consequently, only a minor percentage of the potential extremophiles on Earth have been discovered and characterized. Herein, we present a review of culture-independent methods, sequence-based metagenomics (SBM), and single amplified genomes (SAGs) for studying enzymes from extremophiles, with a focus on prokaryotic (archaea and bacteria) microorganisms. Additionally, we provide a comprehensive list of extremozymes discovered via metagenomics and SAGs.
  • The Importance of Thermal Treatment on Wet-Kneaded Silica–Magnesia Catalyst and Lebedev Ethanol-to-Butadiene Process

    Chung, Sang-Ho; Galilea, Adrian; Shoinkhorova, Tuiana; Mukhambetov, Ildar; Abou-Hamad, Edy; Telalovic, Selevedin; Gascon, Jorge; Ruiz-Martinez, Javier (Nanomaterials, MDPI AG, 2021-02-26) [Article]
    The Lebedev process, in which ethanol is catalytically converted into 1,3-butadiene, is an alternative process for the production of this commodity chemical. Silica–magnesia (SiO2–MgO) is a benchmark catalyst for the Lebedev process. Among the different preparation methods, the SiO2–MgO catalysts prepared by wet-kneading typically perform best owing to the surface magnesium silicates formed during wet-kneading. Although the thermal treatment is of pivotal importance as a last step in the catalyst preparation, the effect of the calcination temperature of the wet-kneaded SiO2–MgO on the Lebedev process has not been clarified yet. Here, we prepared and characterized in detail a series of wet-kneaded SiO2–MgO catalysts using varying calcination temperatures. We find that the thermal treatment largely influences the type of magnesium silicates, which have different catalytic properties. Our results suggest that the structurally ill-defined amorphous magnesium silicates and lizardite are responsible for the production of ethylene. Further, we argue that forsterite, which has been conventionally considered detrimental for the formation of ethylene, favors the formation of butadiene, especially when combined with stevensite.
  • Superconductivity and High-Pressure Performance of 2D Mo2C Crystals

    Zhang, Junli; Cao, Zhen; He, Xin; Liu, Wenhao; Wen, Yan; Cavallo, Luigi; Ren, Wencai; Cheng, Huiming; Zhang, Xixiang (The Journal of Physical Chemistry Letters, American Chemical Society (ACS), 2021-02-26) [Article]
    Two-dimensional (2D) materials have attracted significant attention for their ability to support novel magneto-electrical transport and their optical and magnetic properties, of which their superconductivity is particularly of interest. Here we report on the behavior of superconductivity in 2D Mo2C crystals when hydrostatic pressure is applied, which has not yet been described in the literature. We found that the localization of boundary atoms disorder-induced Cooper pairs can suppress the superconducting transition temperature (Tc) as effectively as a magnetic field and current. We observed that the Tc initially decreased as the pressure increased to 1.75 GPa but then began to increase as the pressure increased further to 2.5 GPa. Our density functional theory calculations revealed that this behavior was linked to the modulation of the strength of the electron-phonon coupling and the electron property, which was triggered by compression of the lattice under high pressure. We attributed the inflection point in the hydrostatic pressure-dependent Tc curve to the structural phase transition of Mo2C from a hexagonal to an orthorhombic structure. This work presents a new avenue for the study of the superconductivity of Mo2C, which can be extended to apply to other 2D superconductors to modulate their electronic states.
  • Layer number dependent ferroelasticity in 2D Ruddlesden–Popper organic-inorganic hybrid perovskites

    Xiao, Xun; Zhou, Jian; Song, Kepeng; Zhao, Jingjing; Zhou, Yu; Rudd, Peter Neil; Han, Yu; Li, Ju; Huang, Jinsong (Nature Communications, Springer Science and Business Media LLC, 2021-02-26) [Article]
    AbstractFerroelasticity represents material domains possessing spontaneous strain that can be switched by external stress. Three-dimensional perovskites like methylammonium lead iodide are determined to be ferroelastic. Layered perovskites have been applied in optoelectronic devices with outstanding performance. However, the understanding of lattice strain and ferroelasticity in layered perovskites is still lacking. Here, using the in-situ observation of switching domains in layered perovskite single crystals under external strain, we discover the evidence of ferroelasticity in layered perovskites with layer number more than one, while the perovskites with single octahedra layer do not show ferroelasticity. Density functional theory calculation shows that ferroelasticity in layered perovskites originates from the distortion of inorganic octahedra resulting from the rotation of aspherical methylammonium cations. The absence of methylammonium cations in single layer perovskite accounts for the lack of ferroelasticity. These ferroelastic domains do not induce non-radiative recombination or reduce the photoluminescence quantum yield.
  • All-Solution-Processed Quantum Dot Electrical Double-Layer Transistors Enhanced by Surface Charges of Ti3C2Tx MXene Contacts

    Kim, Hyunho; Nugraha, Mohamad Insan; Guan, Xinwei; Wang,Zhenwei; Hota, Mrinal Kanti; Xu, Xiangming; Wu, Tao; Baran, Derya; Anthopoulos, Thomas D.; Alshareef, Husam N. (ACS Nano, American Chemical Society (ACS), 2021-02-26) [Article]
    Fully solution-processed, large-area, electrical double-layer transistors (EDLTs) are presented by employing lead sulfide (PbS) colloidal quantum dots (CQDs) as active channels and Ti3C2Tx MXene as electrical contacts (including gate, source, and drain). The MXene contacts are successfully patterned by standard photolithography and plasma-etch techniques and integrated with CQD films. The large surface area of CQD film channels is effectively gated by ionic gel, resulting in high performance EDLT devices. A large electron saturation mobility of 3.32 cm2 V-1 s-1 and current modulation of 1.87 × 104 operating at low driving gate voltage range of 1.25 V with negligible hysteresis are achieved. The relatively low work function of Ti3C2Tx MXene (4.42 eV) compared to vacuum-evaporated noble metals such as Au and Pt makes them a suitable contact material for n-type transport in iodide-capped PbS CQD films with a LUMO level of ∼4.14 eV. Moreover, we demonstrate that the negative surface charges of MXene enhance the accumulation of cations at lower gate bias, achieving a threshold voltage as low as 0.36 V. The current results suggest a promising potential of MXene electrical contacts by exploiting their negative surface charges.
  • Surrogate formulation and molecular characterization of sulfur species in vacuum residues using APPI and ESI FT-ICR mass spectrometry

    Abdul Jameel, Abdul Gani; Alquaity, Awad B.S.; Campuzano, Felipe; Emwas, Abdul-Hamid M.; Saxena, Saumitra; Sarathy, Mani; Roberts, William L. (Fuel, Elsevier BV, 2021-02-26) [Article]
    Vacuum residues (VR) are the bottom of the barrel products left after vacuum distillation of crude oils. VR are primarily used as feedstock for production of syn-gas and hydrogen via gasification; and heavy fuel oil (HFO) for use as fuel in power generation and shipping. However, VR contain relatively large amounts of sulfur (upto 8% by mass) and require the removal of varying amounts depending on the emission norms (eg. International Maritime Organization 2020 sulfur regulations). Understanding the fuel molecular structure and, in particular, the structure of sulfur species enables the adoption and optimization of suitable desulfurization strategies. In the present work, detailed molecular characterization of the sulfur species in VR was performed using positive ion atmospheric pressure photoionization (APPI) and electrospray ionization (ESI) coupled to Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry (MS). Ions possessing mass to charge (m/z) in the range of 100 to 1200 were detected using the ultra-high resolution instrument and were resolved into unique chemical formulas (CcHhSsNnOo). The assigned masses were then divided into molecular classes based on the presence of heteroatoms, and plots of carbon number versus double bond equivalency (DBE) were made for each molecular class. The molecular classes were further sub-divided based on the presence of sulfur families like sulfides (Su), thiophenes (Th), benzothiophenes (BT), dibenzothiophenes (DBT) and benzonaphthothiophene (BNT) and their derivatives. A single surrogate molecule that represents the average structure of the VR sample was then designed based on the average molecular parameters (AMP) obtained from APPI and ESI FT-ICR MS. Plausible core skeletal structures of VR were drawn from the average DBE value, and then a symmetrical, alkylated, polyaromatic sulfur heterocycles (PASH) molecule was formulated as the VR surrogate. A number of physical and thermo-chemical properties of the VR surrogate were then predicted using quantitative structure property relationships (QSPR). The VR surrogate proposed here will enable high-fidelity computational studies, including chemical kinetic modeling, property estimation, and emissions modeling.
  • Effect of Zinc-doping on the Reduction of the Hot-carrier Cooling Rate in Halide Perovskites

    Xing, Guichuan; WEI, Qi; Yin, Jun; Bakr, Osman; Wang, Ze; Wang, Chenhao; Mohammed, Omar F.; Li, Mingjie (Angewandte Chemie, Wiley, 2021-02-25) [Article]
    Fast hot-carrier cooling process in the solar-absorbers fundamentally limits the photon-energy conversion efficiencies. It is highly desirable to develop the solar absorber with long-lived hot-carriers at sun-illumination level, which can be used to develop the hot-carrier solar cells with enhanced efficiency. Herein, we reveal that zinc-doped (0.34%) halide perovskites have the slower hot-carrier cooling compared with the pristine sample through the transient absorption spectroscopy measurements and theoretical calculations. The hot-carrier energy loss rate at the low photoexcitation level of 10 17 cm -3 is found to be ~3 times smaller than that of un-doped perovskites for 500-K hot carriers, and up to ten times when the hot-carrier temperature approaching the lattice temperature. The incorporation of zinc-dopant into perovskites can reduce the nonadiabatic couplings between conduction bands, which retards the photogenerated hot-carriers relaxation process. Our findings present a practical strategy to slow down the hot-carrier cooling in perovskites at low carrier densities, which are valuable for the further development of practical perovskite hot-carrier photovoltaics .
  • Toward Electrically Pumped Organic Lasers: A Review and Outlook on Material Developments and Resonator Architectures

    Zhang, Qi; Tao, Wenwen; Huang, Jingsong; Xia, Ruidong; Cabanillas-Gonzalez, Juan (Advanced Photonics Research, Wiley, 2021-02-25) [Article]
    Organic lasers have undergone decades of development. A myriad of materials with excellent optical gain properties, including small molecules, dendrimers, and polymers, have been demonstrated. Various resonator geometries have also been applied. While sharing the advantages of the solution processability and mechanical flexibility features of organic materials, organic optical gain media also offer interesting optical properties, such as emission tunability through chemical functionalization and inherent large optical gain coefficients. They offer prospects for different applications in the fields of bioimaging, medicine, chemo- and biosensing, anticounterfeit applications, or displays. However, the realization of electrically pumped organic lasers still remains a challenge due to the inherent drawbacks of organic semiconductors, e.g., modest carrier mobility, long-lived excited-state absorption, and extra losses which originate in the device (e.g., absorption from metal electrodes). Herein, the past developments of organic lasers are discussed, highlighting the importance of materials and cavities with regard to the goal of electrically pumped organic lasers. The latest progress and the possible ways to address the challenge are discussed.
  • One-step conversion of crude oil to light olefins using a multi-zone reactor

    Alabdullah, Mohammed A.; Rodriguez Gomez, Alberto; Shoinkhorova, Tuiana; Dikhtiarenko, Alla; Chowdhury, Abhishek Dutta; Hita, Idoia; Kulkarni, Shekhar Rajabhau; Vittenet, Jullian; Sarathy, Mani; Castaño, Pedro; Bendjeriou-Sedjerari, Anissa; Abou-Hamad, Edy; Zhang, Wen; Ali, Ola S.; Morales-Osorio, Isidoro; Xu, Wei; Gascon, Jorge (Nature Catalysis, Springer Science and Business Media LLC, 2021-02-25) [Article]
    With the demand for gasoline and diesel expected to decline in the near future, crude-to-chemicals technologies have the potential to become the most important processes in the petrochemical industry. This trend has triggered intense research to maximize the production of light olefins and aromatics at the expense of fuels, which calls for disruptive processes able to transform crude oil to chemicals in an efficient and environmentally friendly way. Here we propose a catalytic reactor concept consisting of a multi-zone fluidized bed that is able to perform several refining steps in a single reactor vessel. This configuration allows for in situ catalyst stripping and regeneration, while the incorporation of silicon carbide in the catalyst confers it with improved physical, mechanical and heat-transport properties. As a result, this reactor–catalyst combination has shown stable conversion of untreated Arabian Light crude into light olefins with yields per pass of over 30 wt% with a minimum production of dry gas.
  • Towards Detecting Red Palm Weevil Using Machine Learning and Fiber Optic Distributed Acoustic Sensing

    Wang, Biwei; Mao, Yuan; Ashry, Islam; Al-Fehaid, Yousef; Al-Shawaf, Abdulmoneim; Ng, Tien Khee; Yu, Changyuan; Ooi, Boon S. (Sensors, MDPI AG, 2021-02-25) [Article]
    Red palm weevil (RPW) is a detrimental pest, which has wiped out many palm tree farms worldwide. Early detection of RPW is challenging, especially in large-scale farms. Here, we introduce the combination of machine learning and fiber optic distributed acoustic sensing (DAS) techniques as a solution for the early detection of RPW in vast farms. Within the laboratory environment, we reconstructed the conditions of a farm that includes an infested tree with ∼12 day old weevil larvae and another healthy tree. Meanwhile, some noise sources are introduced, including wind and bird sounds around the trees. After training with the experimental time- and frequency-domain data provided by the fiber optic DAS system, a fully-connected artificial neural network (ANN) and a convolutional neural network (CNN) can efficiently recognize the healthy and infested trees with high classification accuracy values (99.9% by ANN with temporal data and 99.7% by CNN with spectral data, in reasonable noise conditions). This work paves the way for deploying the high efficiency and cost-effective fiber optic DAS to monitor RPW in open-air and large-scale farms containing thousands of trees.
  • Evidence of Carrier Localization in AlGaN/GaN based Ultraviolet Multiple Quantum Wells with Opposite Polarity Domains Provided by Nanoscale Imaging

    Cui, Mei; Guo, Wei; Xu, Houqiang; Jiang, Jie'an; Chen, Li; Mitra, Somak; Roqan, Iman S.; Jiang, Haibo; Li, Xiaohang; Ye, Jichun (physica status solidi (RRL) – Rapid Research Letters, Wiley, 2021-02-25) [Article]
    AlGaN based multiple-quantum-wells (MQWs) incorporating opposite polarity domains was grown by MOCVD. A direct demonstration of carrier localization effect was provided by a combination analysis of space-resolved luminescence peak position and Ga/Al composition distribution. Furthermore, through Raman spectroscopy, it is found that compressive strain plays a key role in improving the optical properties of UV-MQWs despite of the inferior crystalline quality in the N-polar domains. This suggests that incorporating sub-micrometer scale polarity domains in the MQWs is a promising perspective for the development of efficient UV emitters.
  • Reporting Device Performance of Emerging Photovoltaic Materials (Version 1)

    Almora, Osbel; Baran, Derya; Bazan, Guillermo C; Cabrera, Carlos I; Catchpole, Kylie R; Erten-Ela, Sule; Guo, Fei; Hauch, Jens; Ho-Baillie, Anita W Y; Jacobsson, T Jesper; Janssen, Rene A J; Kirchartz, Thomas; Kopidakis, Nikos; Li, Yongfang; Loi, Maria A; Lunt, Richard R; Mathew, Xavier; Mcgehee, Michael D; Min, Jie; Mitzi, David B; Nazeeruddin, Mohammad K; Nelson, Jenny; Nogueira, Ana F; Paetzold, Ulrich W; Park, Nam-Gyu; Rand, Barry P; Rau, Uwe; Snaith, Henry J; Unger, Eva; Vaillant-Roca, Lídice; Yip, Hin-Lap; Brabec, Christoph J (Advanced Energy Materials, Authorea, Inc., 2021-02-24) [Preprint]
    Emerging photovoltaics (PVs), focuses on a variety of applications complementing large scale electricity generation. For instance, organic, dye-sensitized and some perovskite solar cells are considered in building integration, greenhouses, wearable and indoors, thereby motivating research on flexible, transparent, semitransparent, and multi-junction PVs. Nevertheless, it can be very time consuming to find or develop an up-to-date overview over the state-of-the-art performance for these systems and applications. Two important resources for record research cells efficiencies are the National Renewable Energy Laboratory chart and the efficiency tables compiled biannually by Martin Green and colleagues. Both publications provide an effective coverage over the established technologies, bridging research and industry. An alternative approach is proposed here summarizing the best reports in the diverse research subjects for emerging PVs. Best performance parameters are provided as a function of the photovoltaic bandgap energy for each technology and application, and are put into perspective using, e.g., the Shockley-Queisser limit. In all cases, the reported data correspond to published and/or properly described certified results, with enough details provided for prospective data reproduction. Additionally, the stability test energy yield (STEY) is included as an analysis parameter among state-of-the-art emerging PVs.
  • AniGAN: Style-Guided Generative Adversarial Networks for Unsupervised Anime Face Generation

    Li, Bing; Zhu, Yuanlue; Wang, Yitong; Lin, Chia-Wen; Ghanem, Bernard; Shen, Linlin (arXiv, 2021-02-24) [Preprint]
    In this paper, we propose a novel framework to translate a portrait photo-face into an anime appearance. Our aim is to synthesize anime-faces which are style-consistent with a given reference anime-face. However, unlike typical translation tasks, such anime-face translation is challenging due to complex variations of appearances among anime-faces. Existing methods often fail to transfer the styles of reference anime-faces, or introduce noticeable artifacts/distortions in the local shapes of their generated faces. We propose Ani- GAN, a novel GAN-based translator that synthesizes highquality anime-faces. Specifically, a new generator architecture is proposed to simultaneously transfer color/texture styles and transform local facial shapes into anime-like counterparts based on the style of a reference anime-face, while preserving the global structure of the source photoface. We propose a double-branch discriminator to learn both domain-specific distributions and domain-shared distributions, helping generate visually pleasing anime-faces and effectively mitigate artifacts. Extensive experiments qualitatively and quantitatively demonstrate the superiority of our method over state-of-the-art methods.
  • Single-Crystalline Ultrathin 2D Porous Nanosheets of Chiral Metal–Organic Frameworks

    Liu, Yuhao; Liu, L. M.; Chen, Xu; Liu, Yan; Han, Yu; Cui, Yong (Journal of the American Chemical Society, American Chemical Society (ACS), 2021-02-23) [Article]
    Two-dimensional (2D) materials with highly ordered in-plane nanopores are crucial for numerous applications, but their rational synthesis and local structural characterization remain two grand challenges. We illustrate here that single-crystalline ultrathin 2D MOF nanosheets (MONs) with intrinsic porosity can be prepared by exfoliating layered metal-organic frameworks (MOFs), whose layers are stabilized by sterically bulky groups. As a result, three three-dimensional (3D) isostructural lanthanide MOFs possessing porous layer structures are constructed by coordinating metal ions with an angular dicarboxylate linker derived from chiral 1,1'-biphenyl phosphoric acid with pendant mesityl groups. The Eu-MOF is readily ultrasonic exfoliated into single-crystalline nanosheets with a thickness of ca. 6.0 nm (2 layers) and a lateral size of 1.5 × 3.0 μm2. The detailed structural information, i.e., the pore channels and individual organic and inorganic building units in the framework, is clearly visualized by a low-dose high-resolution transmission electron microscopy (HRTEM) technique. Benefiting from their ultrathin feature, the nanosheets are well embedded into the polymer matrix to form free-standing mixed-matrix membranes. In both the solution and membrane phase, the fluorescence of the MONs can be effectively quenched by a total of 17 chiral terpenes and terpenoids through supramolecular interactions with uncoordinated chiral phosphoric acids, leading to a chiral optical sensor for detecting vapor enantiomers, which is among the most challenging molecular recognition tasks.
  • The performance limits of hexagonal boron nitride as an insulator for scaled CMOS devices based on two-dimensional materials

    Knobloch, Theresia; Illarionov, Yury Yu.; Ducry, Fabian; Schleich, Christian; Wachter, Stefan; Watanabe, Kenji; Taniguchi, Takashi; Mueller, Thomas; Waltl, Michael; Lanza, Mario; Vexler, Mikhail I.; Luisier, Mathieu; Grasser, Tibor (Nature Electronics, Springer Science and Business Media LLC, 2021-02-23) [Article]
    Complementary metal–oxide–semiconductor (CMOS) logic circuits at their ultimate scaling limits place extreme demands on the properties of all materials involved. The requirements for semiconductors are well explored and could possibly be satisfied by a number of layered two-dimensional (2D) materials, such as transition metal dichalcogenides or black phosphorus. The requirements for gate insulators are arguably even more challenging. At present, hexagonal boron nitride (hBN) is the most common 2D insulator and is widely considered to be the most promising gate insulator in 2D material-based transistors. Here we assess the material parameters and performance limits of hBN. We compare experimental and theoretical tunnel currents through ultrathin layers (equivalent oxide thickness of less than 1 nm) of hBN and other 2D gate insulators, including the ideal case of defect-free hBN. Though its properties make hBN a candidate for many applications in 2D nanoelectronics, excessive leakage currents lead us to conclude that hBN is unlikely to be suitable for use as a gate insulator in ultrascaled CMOS devices.
  • Replacing Thymine with a Strongly Pairing Fifth Base: a Combined Quantum Mechanics and Molecular Dynamics Study

    Chawla, Mohit; Gorle, Suresh; Shaikh, Abdul Rajjak; Oliva, Romina; Cavallo, Luigi (Computational and Structural Biotechnology Journal, Elsevier BV, 2021-02-23) [Article]
    The non-natural ethynylmethylpyridone C-nucleoside (W), a thymidine (T) analogue that can be incorporated in oligonucleotides by automated synthesis, has recently been reported to form a high fidelity base pair with adenosine (A) and to be well accommodated in B-DNA duplexes. The enhanced binding affinity for A of W, as compared to T, makes it an ideal modification for biotechnological applications, such as efficient probe hybridization for the parallel detection of multiple DNA strands. In order to complement the experimental study and rationalize the impact of the non-natural W nucleoside on the structure, stability and dynamics of DNA structures, we performed quantum mechanics (QM) calculations along with molecular dynamics (MD) simulations. Consistently with the experimental study, our QM calculations show that the A:W base pair has an increased stability as compared to the natural A:T pair, due to an additional CH-π interaction. Furthermore, we show that mispairing between W and guanine (G) causes a distortion in the planarity of the base pair, thus explaining the destabilization of DNA duplexes featuring a G:W pair. MD simulations show that incorporation of single or multiple consecutive A:W pairs in DNA duplexes causes minor changes to the intra- and inter-base geometrical parameters, while a moderate widening/shrinking of the major/minor groove of the duplexes is observed. QM calculations applied to selected stacks from the MD simulations also show an increased stacking energy for W, over T, with the neighboring bases.
  • A Unified, One Fluid Model for the Drag of Fluid and Solid Dispersals by Permeate Flux Towards a Membrane Surface

    Salama, Amgad; Sun, Shuyu; Zhang, Tao (Membranes, MDPI AG, 2021-02-22) [Article]
    The drag of dispersals towards a membrane surface is a consequence of the filtration process. It also represents the first step towards the development of the problem of fouling. In order to combat membrane fouling, it is important to understand such drag mechanisms and provide a modeling framework. In this work, a new modeling and numerical approach is introduced that is based on a one-domain model in which both the dispersals and the surrounding fluid are dealt with as a fluid with heterogeneous property fields. Furthermore, because of the fact that the geometry of the object assumes axial symmetry and the configuration remains fixed, the location of the interface may be calculated using geometrical relationships. This alleviates the need to define an indicator function and solve a hyperbolic equation to update the configuration. Furthermore, this approach simplifies the calculations and significantly reduces the computational burden required otherwise if one incorporates a hyperbolic equation to track the interface. To simplify the calculations, we consider the motion of an extended cylindrical object. This allows a reduction in the dimensions of the problem to two, thereby reducing the computational burden without a loss of generality. Furthermore, for this particular case there exists an approximate analytical solution that accounts for the effects of the confining boundaries that usually exist in real systems. We use such a setup to provide the benchmarking of the different averaging techniques for the calculations of properties at the cell faces and center, particularly in the cells involving the interface.
  • Numerical investigation of pressure effects on soot formation in laminar coflow ethylene/air diffusion flames

    Guo, Junjun; Tang, Yihao; Raman, Venkat; Im, Hong G. (Fuel, Elsevier BV, 2021-02-21) [Article]
    This study aims to provide fundamental understandings of the pressure effects on the soot formation and compare the performances of different soot aerosol models. Numerical simulations are performed in laminar coflow diffusion flames at pressures ranging from 1 to 16 bar. Two soot aerosol models are considered: the acetylene-based semi-empirical (SE) model and polycyclic aromatic hydrocarbons (PAH) based hybrid method of moment (HMOM). To study the effect of large-sized PAH species, a detailed reaction mechanism is used with PAH pathways up to coronene. Results show that the SE model provides good predictions of pressure scaling of peak soot mass with a deviation of 7%, while HMOM obtains better soot predictions on the flame centerline. Due to the shifting of PAH position towards the burner with increasing pressure, the nascent soot is formed earlier. The increase in the particle residence time is found to be an additional factor that further promotes the increased soot formation with pressure, apart from the increase in density, temperature, and PAH concentration. The residence time at 8 bar case is 2.5 times and 3.0 times longer than those at 1 bar case on the flame centerline and flame wings, respectively. Moreover, the pressure effects on the PAH contribution to the nucleation process are studied. Although small-sized PAH species (A2 and A2R5) dominate the nucleation process, the contribution of large-sized PAH species (larger than A4) increases from 5% to 20% of the total on the flame wings, when the pressure increases from 1 bar to 8 bar.
  • Numerical Analysis of a Continuous Vulcanization Line to Enhance CH4 Reduction in XLPE-Insulated Cables

    Ruslan, Mohd Fuad Anwari Che; Youn, Dong Joon; Aarons, Roshan; Sun, Yabin; Sun, Shuyu (Materials, MDPI AG, 2021-02-21) [Article]
    Herein, we apply a computational diffusion model based on Fick’s law to study the manner in which a cable production line and its operating conditions can be enhanced to effectively reduce the CH4 concentration in cables insulated with cross-linked polyethylene (XLPE). Thus, we quantitatively analyze the effect of the conductor temperature, curing tube temperature distribution, transition zone length, and online relaxation on CH4 generation and transport during the production of 132 kV cables with an insulation thickness of 16.3 mm. Results show that the conductor temperature, which is initially controlled by a preheater, and the curing tube temperature distribution considerably affect the CH4 concentration in the cable because of their direct impact on the insulation temperature. The simulation results show 2.7% less CH4 remaining in the cable when the preheater is set at 160 C compared with that when no preheater is used. To study the curing tube temperature distribution, we consider three distribution patterns across the curing tube: constant temperature and linear incremental and decremental temperature. The amount of CH4 remaining in the cable when the temperature was linearly increased from 300 to 400 C was 1.6% and 3.7% lower than in the cases with a constant temperature at 350 C and a linear temperature decrease from 400 to 300 C, respectively. In addition, simulations demonstrate that the amount of CH4 removal from the cable can be increased up to 9.7% by applying an elongated and insulated transition zone, which extends the residence time for CH4 removal and decelerates the decrease in cable temperature. Finally, simulations show that the addition of the online relaxation section can reduce the CH4 concentration in the cable because the high cable temperature in this section facilitates CH4 removal up to 2.2%, and this effect becomes greater at low production speeds.
  • Design of 3–5 GHz tunable memristor-based OOK-UWB transmitter

    Barraj, Imen; Bahloul, Mohamed; Masmoudi, Mohamed (AEU - International Journal of Electronics and Communications, Elsevier BV, 2021-02-21) [Article]
    This paper presents the design of a tunable memristor-based On-off keying (OOK) impulse-radio ultrawideband (IR-UWB) transmitter (TX), operating within the 3–5 GHz band. The proposed TX contains a CMOS-Memristor-based Ring Oscillator, an OOK modulator, a control signals circuit, and a pulse shape filter. The linear programming of the memristor device offers a smooth linear frequency variation of the ring oscillator. Accordingly, in the proposed circuit, two external control signals Vctrl and Vtune are used to tune the memristance value and the output pulse width, respectively, allowing adjusting the power spectral density (PSD) bandwidth and its central frequency. The IR-UWB TX is suitable for OOK modulation schema. It is designed and simulated using TSMC CMOS 0.18 µm technology with a 1.8 V supply voltage. The simulation results show that the proposed TX can cover both narrowband and wideband UWB PSD, depending on the number of oscillations per emitted pulse. The TX output swing is 483mVpp, and the pulse duration is 0.8 ns for narrowband and 1.74 ns for wideband. For a pulse repetition frequency of 10 MHz, the pulse generator consumes 94.8 µW and accomplishes an energy efficiency of 23.4%, while the total energy consumption is 9.48 pJ/pulse.

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