Recent Submissions

  • Chiral Helimagnetism and One-Dimensional Magnetic Solitons in a Cr-Intercalated Transition Metal Dichalcogenide

    Zhang, Chenhui; Zhang, Junwei; Liu, Chen; Zhang, Senfu; Yuan, Ye; Li, Peng; Wen, Yan; Jiang, Ze; Zhou, Bojian; Lei, Yongjiu; Zheng, Dongxing; Song, Chengkun; Hou, Zhipeng; Mi, Wenbo; Schwingenschlögl, Udo; Manchon, Aurélien; Qiu, Zi Qiang; Alshareef, Husam N.; Peng, Yong; Zhang, Xixiang (Advanced Materials, Wiley, 2021-07-24) [Article]
    Chiral magnets endowed with topological spin textures are expected to have promising applications in next-generation magnetic memories. In contrast to the well-studied 2D or 3D magnetic skyrmions, the authors report the discovery of 1D nontrivial magnetic solitons in a transition metal dichalcogenide 2H-TaS2 via precise intercalation of Cr elements. In the synthetic Cr1/3TaS2 (CTS) single crystal, the coupling of the strong spin–orbit interaction from TaS2 and the chiral arrangement of the magnetic Cr ions evoke a robust Dzyaloshinskii–Moriya interaction. A magnetic helix having a short spatial period of ≈25 nm is observed in CTS via Lorentz transmission electron microscopy. In a magnetic field perpendicular to the helical axis, the helical spin structure transforms into a chiral soliton lattice (CSL) with the spin structure evolution being consistent with the chiral sine-Gordon theory, which opens promising perspectives for the application of CSL to fast-speed nonvolatile magnetic memories. This work introduces a new paradigm to soliton physics and provides an effective strategy for seeking novel 2D magnets.
  • Landslide size matters: A new data-driven, spatial prototype

    Lombardo, Luigi; Tanyas, Hakan; Huser, Raphaël; Guzzetti, Fausto; Castro-Camilo, Daniela (Engineering Geology, Elsevier BV, 2021-07-24) [Article]
    The standard definition of landslide hazard requires the estimation of where, when (or how frequently) and how large a given landslide event may be. The geoscientific community involved in statistical models has addressed the component pertaining to how large a landslide event may be by introducing the concept of landslide-event magnitude scale. This scale, which depends on the planimetric area of the given population of landslides, in analogy to the earthquake magnitude, has been expressed with a single value per landslide event. As a result, the geographic or spatially-distributed estimation of how large a population of landslide may be when considered at the slope scale, has been disregarded in statistically-based landslide hazard studies. Conversely, the estimation of the landslide extent has been commonly part of physically-based applications, though their implementation is often limited to very small regions. In this work, we initially present a review of methods developed for landslide hazard assessment since its first conception decades ago. Subsequently, we introduce for the first time a statistically-based model able to estimate the planimetric area of landslides aggregated per slope units. More specifically, we implemented a Bayesian version of a Generalized Additive Model where the maximum landslide size per slope unit and the sum of all landslide sizes per slope unit are predicted via a Log-Gaussian model. These “max” and “sum” models capture the spatial distribution of (aggregated) landslide sizes. We tested these models on a global dataset expressing the distribution of co-seismic landslides due to 24 earthquakes across the globe. The two models we present are both evaluated on a suite of performance diagnostics that suggest our models suitably predict the aggregated landslide extent per slope unit. In addition to a complex procedure involving variable selection and a spatial uncertainty estimation, we built our model over slopes where landslides triggered in response to seismic shaking, and simulated the expected failing surface over slopes where the landslides did not occur in the past. What we achieved is the first statistically-based model in the literature able to provide information about the extent of the failed surface across a given landscape. This information is vital in landslide hazard studies and should be combined with the estimation of landslide occurrence locations. This could ensure that governmental and territorial agencies have a complete probabilistic overview of how a population of landslides could behave in response to a specific trigger. The predictive models we present are currently valid only for the 25 cases we tested. Statistically estimating landslide extents is still at its infancy stage. Many more applications should be successfully validated before considering such models in an operational way. For instance, the validity of our models should still be verified at the regional or catchment scale, as much as it needs to be tested for different landslide types and triggers. However, we envision that this new spatial predictive paradigm could be a breakthrough in the literature and, in time, could even become part of official landslide risk assessment protocols.
  • Natural processes dominate the pollution levels during COVID-19 lockdown over India.

    Madineni, Venkat Ratnam; Dasari, Hari Prasad; Karumuri, Ramakrishna; Viswanadhapalli, Yesubabu; Perumal, Prasad; Hoteit, Ibrahim (Scientific reports, Springer Science and Business Media LLC, 2021-07-24) [Article]
    The lockdown measures that were taken to combat the COVID-19 pandemic minimized anthropogenic activities and created natural laboratory conditions for studying air quality. Both observations and WRF-Chem simulations show a 20-50% reduction (compared to pre-lockdown and same period of previous year) in the concentrations of most aerosols and trace gases over Northwest India, the Indo Gangetic Plain (IGP), and the Northeast Indian regions. It is shown that this was mainly due to a 70-80% increase in the height of the boundary layer and the low emissions during lockdown. However, a 60-70% increase in the pollutants levels was observed over Central and South India including the Arabian sea and Bay of Bengal during this period, which is attributed to natural processes. Elevated (dust) aerosol layers are transported from the Middle East and Africa via long-range transport, and a decrease in the wind speed (20-40%) caused these aerosols to stagnate, enhancing the aerosol levels over Central and Southern India. A 40-60% increase in relative humidity further amplified aerosol concentrations. The results of this study suggest that besides emissions, natural processes including background meteorology and dynamics, play a crucial role in the pollution concentrations over the Indian sub-continent.
  • Aerial Swarms: Recent Applications and Challenges

    Abdelkader, Mohamed; Güler, Samet; Jaleel, Hassan; Shamma, Jeff S. (Current Robotics Reports, 2021-07-23) [Article]
    Purpose of Review Currently, there is a large body of research on multi-agent systems addressing their different system theoretic aspects. Aerial swarms as one type of multi-agent robotic systems have recently gained huge interest due to their potential applications. However, aerial robot groups are complex multi-disciplinary systems and usually research works focus on specific system aspects for particular applications. The purpose of this review is to provide an overview of the main motivating applications that drive the majority of research works in this field, and summarize fundamental and common algorithmic components required for their development. Recent Findings Most system demonstrations of current aerial swarms are based on simulations, some have shown experiments using few 10 s of robots in controlled indoor environment, and limited number of works have reported outdoor experiments with small number of autonomous aerial vehicles. This indicates scalability issues of current swarm systems in real world environments. This is mainly due to the limited confidence on the individual robot’s localization, swarm-level relative localization, and the rate of exchanged information between the robots that is required for planning safe coordinated motions. Summary This paper summarizes the main motivating aerial swarm applications and the associated research works. In addition, the main research findings of the core elements of any aerial swarm system, state estimation and mission planning, are also presented. Finally, this paper presents a proposed abstraction of an aerial swarm system architecture that can help developers understand the main required modules of such systems.
  • Two Phases of Monolayer Tantalum Sulfide on Au(111)

    Dombrowski, Daniela; Samad, Abdus; Murray, Clifford; Petrović, Marin; Ewen, Pascal; Michely, Thomas; Kralj, Marko; Schwingenschlögl, Udo; Busse, Carsten (ACS Nano, American Chemical Society (ACS), 2021-07-23) [Article]
    We prepared monolayers of tantalum sulfide on Au(111) by evaporation of Ta in a reactive background of H2S. Under sulfur-rich conditions, monolayers of 2H-TaS2 formed, whereas under sulfur-poor conditions TaS2–x with 0 ≤ x ≤ 1 were found. We identified this phase as TaS, a structure that can be derived from 2H-TaS2 by removal of the bottom S layer.
  • Pushing the Limits of Flexibility and Stretchability of Solar Cells: A Review

    Dauzon, Emilie; Sallenave, Xavier; Plesse, Cedric; Goubard, Fabrice; Amassian, Aram; Anthopoulos, Thomas D. (Advanced Materials, Wiley, 2021-07-23) [Article]
    Emerging forms of soft, flexible, and stretchable electronics promise to revolutionize the electronics industries of the future offering radically new products that combine multiple functionalities, including power generation, with arbitrary form factor. For example, skin-like electronics promise to transform the human-machine-interface, but the softness of the skin is incompatible with traditional electronic components. To address this issue, new strategies toward soft and wearable electronic systems are currently being pursued, which also include stretchable photovoltaics as self-powering systems for use in autonomous and stretchable electronics of the future. Here recent developments in the field of stretchable photovoltaics are reviewed and their potential for various emerging applications are examined. Emphasis is placed on the different strategies to induce stretchability including extrinsic and intrinsic approaches. In the former case, engineering and patterning of the materials and devices are key elements while intrinsically stretchable systems rely on mechanically compliant materials such as elastomers and organic conjugated polymers. The result is a review article that provides a comprehensive summary of the progress to date in the field of stretchable solar cells from the nanoscale to macroscopic functional devices. The article is concluded by discussing the emerging trends and future developments.
  • Ambiguities in solvation free energies from cluster-continuum quasichemical theory: lithium cation in protic and aprotic solvents.

    Itkis, Daniil; Cavallo, Luigi; Yashina, Lada V; Minenkov, Yury (Physical chemistry chemical physics : PCCP, Royal Society of Chemistry (RSC), 2021-07-22) [Article]
    Gibbs free energies for Li+ solvation in water, methanol, acetonitrile, DMSO, dimethylacetamide, dimethoxyethane, dimethylformamide, gamma-butyrolactone, pyridine, and sulfolane have been calculated using the cluster-continuum quasichemical theory. With n independent solvent molecules S initial state forming the "monomer" thermodynamic cycle, Li+ solvation free energies are found to be on average 14 kcal mol-1 more positive compared to those from the "cluster" thermodynamic cycle where the initial state is the cluster Sn. We ascribe the inconsistency between the "monomer" and "cluster" cycles mainly to the incorrectly predicted solvation free energies of solvent clusters Sn from the SMD and CPCM continuum solvation models, which is in line with the earlier study of Bryantsev et al., J. Phys. Chem. B, 2008, 112, 9709-9719. When experimental-based solvation free energies of individual solvent molecules and solvent clusters are employed, the "monomer" and "cluster" cycles result in identical numbers. The best overall agreement with experimental-based "bulk" scale lithium cation solvation free energies was obtained for the "monomer" scale, and we recommend this set of values. We expect that further progress in the field is possible if (i) consensus on the accuracy of experimental reference values is achieved; (ii) the most recent continuum solvation models are properly parameterized for all solute-solvent combinations and become widely accessible for testing.
  • Biomass as source for hydrochar and biochar production to recover phosphates from wastewater: A review on challenges, commercialization, and future perspectives.

    Shyam, Sivaprasad; Arun, Jayaseelan; Gopinath, Kannappan Panchamoorthy; Ribhu, Gautam; Ashish, Manandhar; Ajay, Shah (Chemosphere, Elsevier BV, 2021-07-22) [Article]
    Excessive phosphate run-off with total phosphorus concentration greater than 20 μg P L−1 triggers the growth of harmful algal species in waterbodies and potentially leads to eutrophication. This has severe negative implications on aquatic environment and impacts human health. The annual economic impact of harmful algal blooms is reported to be as high as $25 million for public health and commercial fishery sector, $29 million for recreation/tourism sector and $2 million for monitoring and management. Adsorption is widely considered as an effective and economic strategy to achieve extremely low concentration of phosphorus. The char produced by valorizing various waste biomasses have been gaining attention in phosphorus remediation owing to their availability, their ability to regenerate and reuse. This review paper exclusively focuses on utilizing hydrochar and biochar synthesized from waste biomass, respectively, through hydrothermal carbonization and slow pyrolysis to mitigate phosphorus concentration and potential strategies for handling the spent char. The key mechanisms involved in phosphate adsorption are electrostatic interaction, ion exchange and complexation. The maximum adsorption capacity of hydrochar and biochar ranges from 14–386 mg g−1 and 3–887 mg g−1, respectively. Hydrochar and biochar are cost-effective alternative to commercial activated carbon and spent char can be used for multiple adsorption cycles. Furthermore, extensive research studies on optimizing the feedstock, reaction and activation conditions coupled with technoeconomic analysis and life cycle assessment could pave way for commercialization of char-based adsorption technology.
  • Bayesian seismic inversion: A fast sampling Langevin dynamics Markov chain Monte Carlo method

    Izzatullah, Muhammad; van Leeuwen, Tristan; Peter, Daniel (Geophysical Journal International, Oxford University Press (OUP), 2021-07-22) [Article]
    Summary In this study, we aim to solve the seismic inversion in the Bayesian framework by generating samples from the posterior distribution. This distribution incorporates the uncertainties in the seismic data, forward model, and prior information about the subsurface model parameters; thus, we obtain more information through sampling than through a point estimate (e.g., Maximum a Posteriori method). Based on the numerical cost of solving the forward problem and the dimensions of the subsurface model parameters and observed data, sampling with Markov chain Monte Carlo (MCMC) algorithms can be prohibitively expensive. Herein, we consider the promising Langevin dynamics MCMC algorithm. However, this algorithm has two central challenges: (1) the step size requires prior tuning to achieve optimal performance, and (2) the Metropolis-Hastings acceptance step is computationally demanding. We approach these challenges by proposing an adaptive step-size rule and considering the suppression of the Metropolis-Hastings acceptance step. We highlight the proposed method’s potential through several numerical examples and rigorously validate it via qualitative and quantitative evaluation of the sample quality based on the kernelized Stein discrepancy (KSD) and other MCMC diagnostics such as trace and autocorrelation function (ACF) plots. We conclude that, by suppressing the Metropolis-Hastings step, the proposed method provides fast sampling at efficient computational costs for large-scale seismic Bayesian inference; however, this inflates the second statistical moment (variance) due to asymptotic bias. Nevertheless, the proposed method reliably recovers important aspects of the posterior, including means, variances, skewness, and one- and-twodimensional marginals. With larger computational budget, exact MCMC methods (i.e., with a Metropolis-Hastings step) should be favored. The results thus obtained can be considered a feasibility study for promoting the approximate Langevin dynamics MCMC method for Bayesian seismic inversion on limited computational resources.
  • Effects of Ecological Restoration Using Non-Native Mangrove Kandelia obovata to Replace Invasive Spartina alterniflora on Intertidal Macrobenthos Community in Maoyan Island (Zhejiang, China)

    Wang, Qiuxuan; Duarte, Carlos M.; Song, Li; Christakos, George; Agusti, Susana; Wu, Jiaping (Journal of Marine Science and Engineering, MDPI AG, 2021-07-22) [Article]
    Spartina alterniflora has extensively invaded the coastline of China, including in Maoyan Island of Zhejiang Province. Ecological restoration has been conducted using non-native mangrove Kandelia obovata to replace S. alterniflora in an attempt to restore the impacted intertidal zones. To illustrate the ecological effectiveness of the restoration projects, macrobenthos communities were studied among different habitats within the restored areas, including one non-restored S. alterniflora marsh (SA) and three differently-aged restored K. obovata stands planted in 2003, 2009, and 2011 respectively (KF14, KF8, and KF6). Besides, one unvegetated mudflat (MF) adjacent to the non-restored S. alterniflora marsh and one K. obovata forest transplanted in 2006 (RKF) at a previously barren mudflat without invasion history of S. alterniflora were set as reference sites. A total of 69 species of macrobenthos were collected from Maoyan Island, and the species richness was dominated by gastropoda (23 species), polychaeta (18 species), and malacostraca (16 species). There was no significant difference between the six sites in terms of the abundance of macrobenthos, with the average values of abundance peaking in KF6 (734.7 ind m−2) and being lowest in RKF (341.3 ind m−2). The six sites had significant differences in terms of the biomass of macrobenthos. The KF8 site contained the highest average biomass (168.3 g m−2), whereas the MF site had the lowest (54.3 g m−2). The Shannon-Wiener diversity index and Pielou’s evenness index of the macrobenthos did not exhibit significant differences among the six sites. However, the results of permutational multivariate analysis of variance (PERMANOVA) revealed significant spatial differences in the macrobenthos community structure between the sites. Since KF14 shared a similar macrobenthos community structure with RKF, while representing a strikingly different structure from SA, we infer that ecological restoration using K. obovata can restore the macrobenthos community to resemble to a normally planted K. obovata forest about 15 years after restoration.
  • Atomistic origin of compositional pulling effect in wurtzite (B, Al, In)xGa1−xN: A first-principles study

    Mizuseki, Hiroshi; Gueriba, Jessiel Siaron; Empizo, Melvin John F.; Sarukura, Nobuhiko; Kawazoe, Yoshiyuki; Ohkawa, Kazuhiro (Journal of Applied Physics, AIP Publishing, 2021-07-21) [Article]
    Some fluctuations in composition are commonly observed in epitaxial-grown III-V multinary alloys. These fluctuations are attributed to compositional pulling effects, and an insight into their atomistic origin is necessary to improve current epitaxial growth techniques. In addition, the crystallinity of III-V multinary alloys varies widely depending on the constituent atoms. Using first-principles calculations, we then investigated different geometric configurations of gallium nitride (GaN)-based ternary alloy, X0.125Ga0.875N where X is the minority atom which is boron (B), aluminum (Al), or indium (In). The minority atoms are presented as two atoms in the simulation cell, and the energetics of five geometric configurations are analyzed to estimate the most stable configuration. For the B0.125Ga0.875N alloy, the most stable configuration is the one where the minority atoms occupy gallium (Ga) sites in a collinear orientation along the c-axis. On the contrary, the configurations along the in-plane direction result in a higher energy state. In0.125Ga0.875N and Al0.125Ga0.875N also show the same trend with a small relative energy difference. These preferential sites of minority atoms are consistent with composition pulling effects in wurtzite nitride phases. Moreover, the degree of crystallinity for wurtzite nitride alloys can be well described by the order of calculated relative energy.
  • In Vitro and In Silico Approaches for the Antileishmanial Activity Evaluations of Actinomycins Isolated from Novel Streptomyces smyrnaeus Strain UKAQ_23

    Qureshi, Kamal A.; Al Nasr, Ibrahim; Koko, Waleed S.; Khan, Tariq A.; Fatmi, M. Qaiser; Imtiaz, Mahrukh; Khan, Riaz A.; Mohammed, Hamdoon A.; Jaremko, Mariusz; Emwas, Abdul-Hamid M.; Azam, Faizul; Bholay, Avinash D.; Elhassan, Gamal O.; Prajapati, Dinesh K. (Antibiotics, MDPI AG, 2021-07-21) [Article]
    Leishmaniasis, a Neglected Tropical Parasitic Disease (NTPD), is induced by several Leishmania species and is disseminated through sandfly (Lutzomyia longipalpis) bites. The parasite has developed resistance to currently prescribed antileishmanial drugs, and it has become pertinent to the search for new antileishmanial agents. The current study aimed to investigate the in vitro and in silico antileishmanial activity of two newly sourced actinomycins, X2 and D, produced by the novel Streptomyces smyrnaeus strain UKAQ_23. The antileishmanial activity conducted on promastigotes and amastigotes of Leishmania major showed actinomycin X2 having half-maximal effective concentrations (EC50), at 2.10 ± 0.10 μg/mL and 0.10 ± 0.0 μg/mL, and selectivity index (SI) values of 0.048 and 1, respectively, while the actinomycin D exhibited EC50 at 1.90 ± 0.10 μg/mL and 0.10 ± 0.0 μg/mL, and SI values of 0.052 and 1. The molecular docking studies demonstrated squalene synthase as the most favorable antileishmanial target protein for both the actinomycins X2 and D, while the xanthine phosphoribosyltransferase was the least favorable target protein. The molecular dynamics simulations confirmed that both the actinomycins remained stable in the binding pocket during the simulations. Furthermore, the MMPBSA (Molecular Mechanics Poisson-Boltzmann Surface Area) binding energy calculations established that the actinomycin X2 is a better binder than the actinomycin D. In conclusion, both actinomycins X2 and D from Streptomyces smyrnaeus strain UKAQ_23 are promising antileishmanial drug candidates and have strong potential to be used for treating the currently drug-resistant leishmaniasis.
  • Towards rainbow photo/electro-luminescence in copper(I) complexes with the versatile bridged bis-pyridyl ancillary ligand.

    Mahoro, Gilbert Umuhire; Fresta, Elisa; Elie, Margaux; di Nasso, Davide; Zhang, Qi; Lohier, Jean-François; Renaud, Jean-Luc; Linares, Mathieu; Wannemacher, Reinhold; Cabanillas-Gonzalez, Juan; Costa, Rubén D; Gaillard, Sylvain (Dalton transactions (Cambridge, England : 2003), Royal Society of Chemistry (RSC), 2021-07-21) [Article]
    The synthesis and characterization of a family of copper(i) complexes bearing a bridged bis-pyridyl ancillary ligand is reported, highlighting how the bridge nature impacts the photo- and electro-luminescent behaviours within the family. In particular, the phosphonium bridge led to copper(i) complexes featuring good electrochemical stability and high ionic conductivity, as well as a stark blue-to-orange luminescence shift compared to the others. This resulted in high performance light-emitting electrochemical cells reaching stabilities of 10 mJ at ca. 40 cd m-2 that are one order of magnitude higher than those of the other complexes. Overall, this work sheds light onto the crucial role of the bridge nature of the bis-pyridyl ancillary ligand on the photophysical features, film forming and, in turn, on the final device performances.
  • Re-infection with different SARS-CoV-2 clade and prolonged viral shedding in a patient with hematopoietic stem cell transplantation: SARS-CoV-2 Re-infection with different clade.

    Alshukairi, Abeer N; El-Kafrawy, Sherif A; Dada, Ashraf; Yasir, Mohamed; Yamani, Amani H; Saeedi, Mohammed F; Aljohaney, Ahmed; AlJohani, Naif I; Bahaudden, Husam A; Alam, Intikhab; Gojobori, Takashi; Radovanovic, Aleksandar; Alandijany, Thamir A; Othman, Norah A; Alsubhi, Tagreed L; Hassan, Ahmed M; Tolah, Ahmed M; Al-Tawfiq, Jaffar A; Zumla, Alimuddin; Azhar, Esam I (International journal of infectious diseases : IJID : official publication of the International Society for Infectious Diseases, Elsevier BV, 2021-07-21) [Article]
    Immunocompromised patients who have SARS-CoV-2 infection pose many clinical and public health challenges. We describe a patient with hematopoietic stem cell transplantation and lymphoma with protracted illness requiring 3 consecutive hospital admissions. Whole genome sequencing confirmed two different SARS-CoV-2 clades. Clinical management issues, and unanswered questions arising are discussed.
  • CRISPR-Based Crop Improvements: A Way Forward to Achieve Zero Hunger

    Ahmad, Shakeel; Tang, Liqun; Shahzad, Rahil; Mawia, Amos Musyoki; Rao, Gundra Sivakrishna; Jamil, Shakra; Wei, Chen; Sheng, Zhonghua; Shao, Gaoneng; Wei, Xiangjin; Hu, Peisong; Mahfouz, Magdy M.; Hu, Shikai; Tang, Shaoqing (Journal of Agricultural and Food Chemistry, American Chemical Society (ACS), 2021-07-21) [Article]
    Zero hunger is one of the sustainable development goals set by the United Nations in 2015 to achieve global food security by 2030. The current harvest of crops is insufficient; feeding the world's population and meeting the goal of zero hunger by 2030 will require larger and more consistent crop production. Clustered regularly interspaced short palindromic repeats-associated protein (CRISPR-Cas) technology is widely used for the plant genome editing. In this review, we consider this technology as a potential tool for achieving zero hunger. We provide a comprehensive overview of CRISPR-Cas technology and its most important applications for food crops' improvement. We also conferred current and potential technological breakthroughs that will help in breeding future crops to end global hunger. The regulatory aspects of deploying this technology in commercial sectors, bioethics, and the production of transgene-free plants are also discussed. We hope that the CRISPR-Cas system will accelerate the breeding of improved crop cultivars compared with conventional breeding and pave the way toward the zero hunger goal.
  • Surfactant-Emulating Amphiphilic Polycarbonates and Other Functional Polycarbonates through Metal-Free Copolymerization of CO2 with Ethylene Oxide

    Jia, Mingchen; Zhang, Dongyue; Gnanou, Yves; Feng, Xiaoshuang (ACS Sustainable Chemistry & Engineering, American Chemical Society (ACS), 2021-07-21) [Article]
    Three types of ethylene oxide-based and carbonate-containing copolymers were prepared through copolymerization of ethylene oxide (EO) with CO2 under metal-free conditions in the presence of triethylborane (TEB), using onium salts (OS) as initiator. Hydrophobic poly[(ethylene carbonate)x-co-(ethylene oxide)y] (PECEO) samples with carbonate contents above 90% (x ≫ y) were first prepared under a CO2 pressure of 10–30 bar with a ratio of [TEB] to [OS] of 1–1.2 equiv in tetrahydrofuran (THF) or in hexane. The above PECEO (carbonate > 91%) then served as a macroinitiator to grow two external poly(ethylene oxide) (PEO) blocks and generate in one-pot amphiphilic PEO-b-PECEO-b-PEO triblocks. Lastly, the copolymerization of EO under a low pressure of CO2 (1–2 bar) with a ratio of [TEB] to [OS] of 1.2–2.0 equiv afforded hydrophilic poly[(ethylene oxide)y-co-(ethylene carbonate)x] (PEOEC) random copolymers with carbonate contents below 10% (y ≫ x); allyl glycidyl ether (AGE) was also terpolymerized with EO and CO2 under the same conditions to introduce functional groups along the backbone of PEO chains. Critical micelle concentrations (CMC) and size of micelles were measured for amphiphilic PEO-b-PECEO-b-PEO samples and compared with the values of other nonionic surfactants. The properties of “PEO-like” hydrophilic PEOECs were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and wettability test; their degradation behavior was further investigated under different conditions.
  • Observation of Negative Photoconductivity in Lead-Free Cs3Bi2Br9Perovskite Single Crystal

    Tailor, Naveen Kumar; Maity, Partha; Satapathi, Soumitra (ACS Photonics, American Chemical Society (ACS), 2021-07-21) [Article]
    Light exposure usually causes an increase in photoconductivity in perovskite semiconductors. However, we report here light-induced negative photoconductivity, followed by slow dark self-recovery in a lead-free Cs3Bi2Br9 perovskite single crystal. Femtosecond transient reflection (fs-TR) spectroscopy studies further reveal hole self-trapping at the Vk center (Br2– dimer) in the midband states of this vacancy-ordered perovskite. Subsequently, these charged defect states (Vk) trap photogenerated charge carriers and produce an internal electrical field, which essentially opposes the externally applied field, leading to negative photoconductivity. A highly sensitive prototype photodetector was fabricated with figure of merits estimated as responsivity (6.42 mA/W), detectivity (2.51 × 1012 Jones), and current in a dark to light ratio (∼20). Our observation of this retrospective photocurrent in optically active perovskite materials can be applied for developing highly sensitive detectors.
  • The impact of COVID-19 lockdowns on surface urban heat island changes and air-quality improvements across 21 major cities in the Middle East.

    El Kenawy, Ahmed M; Lopez-Moreno, Juan I; McCabe, Matthew; Domínguez-Castro, Fernando; Peña-Angulo, Dhais; Gaber, Islam M; Alqasemi, Abduldaem S; Al Kindi, Khalifa M; Al-Awadhi, Talal; Hereher, Mohammed E; Robaa, Sayed M; Al Nasiri, Noura; Vicente-Serrano, Sergio M (Environmental pollution (Barking, Essex : 1987), Elsevier BV, 2021-07-20) [Article]
    This study investigates changes in air quality conditions during the restricted COVID-19 lockdown period in 2020 across 21 metropolitan areas in the Middle East and how these relate to surface urban heat island (SUHI) characteristics. Based on satellite observations of atmospheric gases from Sentinel-5, results indicate significant reductions in the levels of atmospheric pollutants, particularly nitrogen dioxide (NO2), sulfur dioxide (SO2), and carbon monoxide (CO). Air quality improved significantly during the middle phases of the lockdown (April and May), especially in small metropolitan cities like Amman, Beirut, and Jeddah, while it was less significant in “mega” cities like Cairo, Tehran, and Istanbul. For example, the concentrations of NO2 in Amman, Beirut, and Jeddah decreased by −56.6%, −43.4%, and −32.3%, respectively, during April 2020, compared to April 2019. Rather, there was a small decrease in NO2 levels in megacities like Tehran (−0.9%) and Cairo (−3.1%). Notably, during the lockdown period, there was a decrease in the mean intensity of nighttime SUHI, while the mean intensity of daytime SUHI experienced either an increase or a slight decrease across these locations. Together with the Gulf metropolitans (e.g. Kuwait, Dubai, and Muscat), the megacities (e.g. Tehran, Ankara, and Istanbul) exhibited anomalous increases in the intensity of daytime SUHI, which may exceed 2 °C. Statistical relationships were established to explore the association between changes in the mean intensity and the hotspot area in each metropolitan location during the lockdown. The findings indicate that the mean intensity of SUHI and the spatial extension of hotspot areas within each metropolitan had a statistically significant negative relationship, with Pearson's r values generally exceeding - 0.55, especially for daytime SUHI. This negative dependency was evident for both daytime and nighttime SUHI during all months of the lockdown. Our findings demonstrate that the decrease in primary pollutant levels during the lockdown contributed to the decrease in the intensity of nighttime SUHIs in the Middle East, especially in April and May. Changes in the characteristics of SUHIs during the lockdown period should be interpreted in the context of long-term climate change, rather than just the consequence of restrictive measures. This is simply because short-term air quality improvements were insufficient to generate meaningful changes in the region's urban climate.
  • CANITA: Faster Rates for Distributed Convex Optimization with Communication Compression

    Li, Zhize; Richtarik, Peter (arXiv, 2021-07-20) [Preprint]
    Due to the high communication cost in distributed and federated learning, methods relying on compressed communication are becoming increasingly popular. Besides, the best theoretically and practically performing gradient-type methods invariably rely on some form of acceleration/momentum to reduce the number of communications (faster convergence), e.g., Nesterov's accelerated gradient descent (Nesterov, 2004) and Adam (Kingma and Ba, 2014). In order to combine the benefits of communication compression and convergence acceleration, we propose a \emph{compressed and accelerated} gradient method for distributed optimization, which we call CANITA. Our CANITA achieves the \emph{first accelerated rate} $O\bigg(\sqrt{\Big(1+\sqrt{\frac{\omega^3}{n}}\Big)\frac{L}{\epsilon}} + \omega\big(\frac{1}{\epsilon}\big)^{\frac{1}{3}}\bigg)$, which improves upon the state-of-the-art non-accelerated rate $O\left((1+\frac{\omega}{n})\frac{L}{\epsilon} + \frac{\omega^2+n}{\omega+n}\frac{1}{\epsilon}\right)$ of DIANA (Khaled et al., 2020b) for distributed general convex problems, where $\epsilon$ is the target error, $L$ is the smooth parameter of the objective, $n$ is the number of machines/devices, and $\omega$ is the compression parameter (larger $\omega$ means more compression can be applied, and no compression implies $\omega=0$). Our results show that as long as the number of devices $n$ is large (often true in distributed/federated learning), or the compression $\omega$ is not very high, CANITA achieves the faster convergence rate $O\Big(\sqrt{\frac{L}{\epsilon}}\Big)$, i.e., the number of communication rounds is $O\Big(\sqrt{\frac{L}{\epsilon}}\Big)$ (vs. $O\big(\frac{L}{\epsilon}\big)$ achieved by previous works). As a result, CANITA enjoys the advantages of both compression (compressed communication in each round) and acceleration (much fewer communication rounds).
  • Decision trees based on 1-consequences

    Moshkov, Mikhail (Discrete Applied Mathematics, Elsevier BV, 2021-07-20) [Article]
    In this paper, we study arbitrary infinite binary information systems each of which consists of an infinite set of elements and an infinite set of two-valued non-constant functions (attributes) defined on the set of elements. We consider the notion of a problem over information system, which is described by a finite number of attributes: for a given element, we should determine values of these attributes. As algorithms for problem solving, we study decision trees that use arbitrary attributes from the considered infinite set of attributes and solve the problem based on 1-consequences. In such a tree, we take into account consequences each of which follows from one equation of the kind “attribute value” obtained during the decision tree work and ignore consequences that can be derived only from at least two equations. As time complexity, we study the depth of decision trees. We prove that in the worst case, with the growth of the number of attributes in the problem description, the minimum depth of decision trees based on 1-consequences grows either as a logarithm or linearly.

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