bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation study of a pulsed DBD with an electrode containing charge injector parts
Authors: Pourali N. , Sarafraz M. M. , Hessel V. , Rebrov E. V.
Published: January 2021

By using a multispecies fluid model, the tunability and controllability of plasma parameters such as distributions of electron density, electron energy, ion density, and electric field in a microdielectric barrier discharge (DBD) with a charge injector electrode and driven by negatively polarized nanosecond pulsed voltage superimposed on a positive DC bias voltage are investigated. To this end, the effects of changing features of pulsed voltage like pulse rise time (10–20 ns), pulse peak width (10–15 ns), and pulse fall time (20–30 ns) on characteristics of argon plasma formed inside the reactor are studied. The results show that with the increase in pulse width and pulse rise time, the density of electron and ion increases, while fall time change does not significantly affect the plasma parameters. Generally, the results of this study explicitly prove the possibility of controlling plasma formed inside DBD reactors driven by negative pulse voltage combined with a positive DC voltage, which is very important in waste gas conversion applications.
Dense as diamond: Pn-C10, a superhard sp3 carbon allotrope
Authors: Li Shuaiqi , Zhang Jiawei , Wang Junpu , Guan Shixue , Li Yuanyuan
Published: January 2021

We introduce a carbon allotrope with rhombic symmetry and a high crystal density reached 3.56 g/cm3, named Pn-C10, which was found using an unbiased particle-swarm structural-searching technique. This fully sp3-bonded carbon phase is dynamically and mechanically stable in its ground state. Results from our calculations reveal the excellent mechanical nature of Pn-C10 with a claimed shear modulus and Vickers hardness of 484 GPa and 88.45 GPa, respectively, which also suggested its slight anisotropy in elasticity. The predicted electronic band structure indicates that Pn-C10 is an indirect-bandgap material with a bandgap of 5.05 eV. Natural tiling analysis and simulations of x-ray diffraction and Raman spectra were performed to provide insights for further studies into Pn-C10 and other carbon phases.
Shilnikov attractors in three-dimensional orientation-reversing maps
Authors: Karatetskaia Efrosiniia , Shykhmamedov Aikan , Kazakov Alexey
Published: January 2021

A Shilnikov homoclinic attractor of a three-dimensional diffeomorphism contains a saddle-focus fixed point with a two-dimensional unstable invariant manifold and homoclinic orbits to this saddle-focus. The orientation-reversing property of the diffeomorphism implies a symmetry between two branches of the one-dimensional stable manifold. This symmetry leads to a significant difference between Shilnikov attractors in the orientation-reversing and orientation-preserving cases. We consider the three-dimensional Mirá map x¯=y,y¯=z, and z¯=Bx+Cy+Az−y2 with the negative Jacobian (B<0) as a basic model demonstrating various types of Shilnikov attractors. We show that depending on values of parameters A,B, and C, such attractors can be of three possible types: hyperchaotic (with two positive and one negative Lyapunov exponent), flow-like (with one positive, one very close to zero, and one negative Lyapunov exponent), and strongly dissipative (with one positive and two negative Lyapunov exponents). We study scenarios of the formation of such attractors in one-parameter families.
Resolution of Reissner–Nordström singularities by higher-derivative corrections
Authors: Cano Pablo A , Murcia Ángel
Published: January 2021

We describe a non-minimal higher-derivative extension of Einstein–Maxwell theory in which electrically-charged black holes and point charges have globally regular gravitational and electromagnetic fields. We provide an exact static, spherically symmetric solution of this theory that reduces to the Reissner–Nordström one at weak coupling, but in which the singularity at r = 0 is regularized for arbitrary mass and (non-vanishing) charge. We discuss the properties of these solutions and comment on the physical significance of our results.
High-sensitivity liquid-metal-based contact lens sensor for continuous intraocular pressure monitoring
Authors: An Hongbin , Chen Liangzhou , Liu Xiaojun , Wang Xiangyang , Liu Yunfeng , Wu Zhigang , Zhao Bin , Zhang Hong
Published: January 2021

Intraocular pressure (IOP) is a crucial physiological indicator for the diagnosis and treatment of glaucoma. The current infrequent IOP measurement during an office visit is insufficient to characterize the symptoms. Here, an LC resonator strain sensor in a contact lens, composed of a stretchable inductance coil using liquid metal and a chip capacitor, was developed for real-time IOP monitoring. The lens sensor was operated on the basis of ‘mechanical-electrical’ principle. The rising IOP will increase the curvature radius of the cornea and stretch the inductance coils through the cornea and tear film, leading to a decrease in resonant frequency. The theoretical model of the whole process has been established and explored. The sensor has been scientifically designed and fabricated to be ultra-soft, comfortable, safe without leakage and has a stable signal. The sensor was calibrated on two silicone rubber model eyeballs, respectively, showing linear and stable responses. An experiment on porcine eyes in vitro was conducted. The sensor can track IOP changes and shows much higher sensitivity than the current mainstream lens sensors, which is even an order of magnitude higher than the existing inductive sensor. The high-sensitivity and ultra-flexible liquid-metal-based lens sensor is a promising approach for 24 h continuous IOP monitoring in clinics.
Visible light photocatalytic properties of one-step SnO2-templated grown SnO2/SnS2 heterostructure and SnS2 nanoflakes
Authors: Wang Chiu-Yen , Wu Yu-Kai , Tsai Liang-Feng , Lee Hou-Kuan , Hsu Ya-Chu
Published: January 2021

The nanoflakes of SnS2/SnO2 heterostructure and SnS2 were synthesized by a one-step SnO2-templated chemical vapor deposition method. The metal oxide-assisted growth mechanism of SnS2/SnO2 heterostructure and SnS2 nanoflakes were realized through investigating serial microstructures of products with varied growth time. Furthermore, the photocatalytic activity for MB dyes degradation of varied growth time products was used to explore the effect of product microstructure under the visible light irradiation. The SnO2/SnS2 heterostructure and the oxide vacancies of nanoflakes demonstrated an improved visible light photocatalytic performance for MB degradation, which was around twice of the pure SnS2 nanoflakes and better than P25. The results of different scavengers on the degradation efficiency for MB indicate the·O2
−, and ·OH are the main active species in the photodegradation reaction. The one-step growth mechanism of SnS2/SnO2 could prove a facile process to grow metal oxide-metal sulfide heterostructure.
MOF-derived porous carbon nanofibers wrapping Sn nanoparticles as flexible anodes for lithium/sodium ion batteries
Authors: Zhu Shaoqing , Huang Aoming , Wang Qian , Xu Ye
Published: January 2021

Facile synthesis of flexible electrodes with high reversible capacity plays a key role in meeting the ever-increasing demand for flexible batteries. Herein, we incorporated Sn-based metal-organic framework (Sn-MOF) templates into crosslinked one-dimensional carbon nanofibers (CNFs) using an electrospinning strategy and obtained a hierarchical porous film (Sn@C@CNF) after a carbothermal reduction reaction. Merits of this modification strategy and its mechanism in improving the electrochemical performance of Sn nanoparticles (NPs) were revealed. Electrospun CNFs substrate ensured a highly conductive skeleton and excellent mechanical toughness, making Sn@C@CNF a self-supported binder-free electrode. Serving as a self-sacrificing template, Sn-MOF provided Sn NPs and derived into porous structures on CNFs after pyrolysis. The hierarchical porous structure of the carbon substrate was beneficial to enhancing the Li+/Na+ storage of the active materials, and the carbon wrappings derived from polyacrylonitrile (PAN) nanofibers and the MOF skeleton could jointly accommodate the violent volume variation during cycling, enabling Sn@C@CNF to have excellent cycle stability. The Sn@C@CNF anode exhibited a stable discharge specific capacity of 610.8 mAh g−1 under 200 mA g−1 for 180 cycles in lithium ion batteries (LIBs) and 360.5 mAh g−1 under 100 mA g−1 after 100 cycles in sodium ion batteries (SIBs). As a flexible electrode, Sn@C@CNF demonstrated a stable electromechanical response to repeated ‘bending-releasing’ cycles and excellent electrochemical performance when assembled in a soft-pack half-LIB. This strategy provided promising candidates of active materials and fabrication methods for advanced flexible batteries.
Improved AlScN/GaN heterostructures grown by metal-organic chemical vapor deposition
Authors: Manz Christian , Leone Stefano , Kirste Lutz , Ligl Jana , Frei Kathrin , Fuchs Theodor , Prescher Mario , Waltereit Patrick , Verheijen Marcel A , Graff Andreas , Simon-Najasek Michél , Altmann Frank , Fiederle Michael , Ambacher Oliver
Published: January 2021

AlScN/GaN epitaxial heterostructures have raised much interest in recent years, because of the high potential of such structures for high-frequency and high-power electronic applications. Compared to conventional AlGaN/GaN heterostructures, the high spontaneous and piezoelectric polarization of AlScN can yield to a five-time increase in sheet carrier density of the two-dimensional electron gas formed at the AlScN/GaN heterointerface. Very promising radio-frequency device performance has been shown on samples deposited by molecular beam epitaxy. Recently, AlScN/GaN heterostructures have been demonstrated, which were processed by the more industrial compatible growth method metal-organic chemical vapor deposition (MOCVD). In this work, SiN
x
passivated MOCVD-grown AlScN/GaN heterostructures with improved structural quality have been developed. Analytical transmission electron microscopy, secondary ion mass spectrometry and high-resolution x-ray diffraction analysis indicate the presence of undefined interfaces between the epitaxial layers and an uneven distribution of Al and Sc in the AlScN layer. However, AlScN-based high-electron-mobility transistors (HEMT) have been fabricated and compared with AlN/GaN HEMTs. The device characteristics of the AlScN-based HEMT are promising, showing a transconductance close to 500 mS mm−1 and a drain current above 1700 mA mm−1.
Modelling of a soft multi-chambered climbing robot and experiments
Authors: Xu Fengyu , Quansheng Jiang , Lu Yuxuan , Jiang Guoping
Published: January 2021

Soft robots have wide potential applications prospects in unstructured environments owing to their being able to imitate forms of motion of creatures in climbing and creeping through small spaces. By utilising the high flexibility of soft materials, a pneumatic soft climbing robot was designed. At first, a model for soft climbing robots with a stiffness gradient was designed according to the drive mode of pneumatic networks in soft robots. Afterwards, the visco-mechanical properties of robots at the contact surface were analysed and also the deformation characteristics of cavities were discussed by using the method of minimum potential energy. Subsequently, through simulation and use of the finite element method, the optimal number of cavities in an actuator required by a climbing robot was calculated and also the climbing behaviours of the robot were analysed. Finally, by employing 3D printing and layer-by-layer casting, a prototype soft climbing robot was prepared to perform climbing experiments. The research is expected to provide a new method for monitoring complex unstructured environments.
Electrothermal shape memory behavior and recovery force of four-dimensional printed continuous carbon fiber/polylactic acid composite
Authors: Chen Haijia , Zhang Fenghua , Sun Ya , Sun Baozhong , Gu Bohong , Leng Jinsong , Zhang Wei
Published: January 2021

Four-dimensional (4D) printing technology provides new ideas for the preparation and structural design of multifunctional shape memory composites. Excellent electrothermal shape memory behavior and high shape recovery force are urgently demanded in practical applications. Herein, a continuous carbon fiber reinforced polylactic acid shape memory composite with high strength, high shape recovery force, low-voltage response and excellent electrothermal shape memory behavior was printed using a dual nozzle 3D printer. The effects of specimen thickness, carbon fiber content, and applied voltage on the electrothermal shape memory behavior and shape recovery force were investigated. The reinforcing effect of carbon fiber on 4D printed composite materials was characterized by dynamic mechanical analysis and 3-point bending test. Under electrical thermal stimulation, the shape recovery ratio of most specimens can reach 90%. The shape recovery force of different specimens was obtained by self-designed shape recovery force test system, and the maximum shape recovery force was about 7.38 N. The results show that the introduction of continuous carbon fiber not only significantly enhances the strength of 4D printed composite, but also improves the shape recovery force. The demonstrations of an electrothermal response shape memory deployable claw-device and load-bearing lifting device manifest the potential application in self-actuated intelligent structures.
Asymptotic analysis of the elephant random walk
Authors: Coletti Cristian F , Papageorgiou Ioannis
Published: January 2021

In this work we study asymptotic properties of a long range memory random walk known as elephant random walk. First we prove recurrence and positive recurrence for the elephant random walk. Then, we establish the transience regime of the model. Finally, under the Poisson hypothesis, we study the replica mean field limit for this random walk and we obtain an upper bound for the expected distance of the walker from the origin.
Two-Level Iterative Methods for Solving the Saddle Point Problems
Authors: Il’in V P
Published: January 2021

Iterative processes in the Krylov subspaces for solving large ill conditioned saddle-type SLAEs with sparse matrices arising in finite difference, finite volume, and finite element approximations of multidimensional boundary value problems with complex geometric and functional properties of the initial data, characteristic of many relevant applications are studied. Combined two-level iterative algorithms using efficient Chebyshev acceleration and variational the conjugate directions methods, as well as the Golub-Kahan bi-diagonalization algorithms in the Krylov subspaces are considered. Examples of two-dimensional and three-dimensional filtration problems are used to study the resource consumption and computational performance of the proposed algorithms, as well as their scalable parallization on the multiprocessor systems with distributed and hierarchical shared memory.
A modified algorithm of the latent semantic analysis for text processing in the Russian language
Authors: Ivanov A A , Holtzer S V
Published: January 2021

The paper presents a methodology for analyzing texts in the Russian language. The methodology is based on the Latent Semantic Analysis (LSA) algorithm. A number of disadvantages of the classical method are considered, and modification methods of extracting N-grams from the text are proposed. The modified method allows one to reduce a number of extracted N-grams and an increasing the meaningfulness of the retrieved collection in comparison with a standard method. The reduction of the collection size leads to a reduced dimension of the TF-IDF matrix and accelerated the execution of the SVD method. The advantages of the developed machine learning algorithm are demonstrated on simple sentences. Owing to discussed ideas it becomes possible to effectively parallelize the text processing at the lemmatization step.
The assessment of the atmospheric air quality in Tomsk with the use of a mesoscale photochemical model
Authors: Starchenko A V , Shelmina E A , Kizhner L I , Bart A A
Published: January 2021

The paper presents the results of studying the influence of the development of meteorological situation in clear weather with a weak wind on the level of atmospheric surface air pollution in the city of Tomsk (Russia). Mesoscale meteorological and photochemical models with a new kinetic scheme were applied to the analysis. The main local weather conditions were identified, in which numerical calculations show increased values of the air pollution index. The numerical predictions have confirmed an increase in the ground-level concentration of pollutants in the presence of temperature inversion or isothermy.
A new approach to estimating of the power of nitrogen oxides emissions from the anthropogenic source
Authors: Tikhonov N , Zakharova S , Davydova M
Published: January 2021

The paper presents a new approach to estimating of the power of nitrogen oxides emissions from the anthropogenic source. Authors created the model that describes the dynamics of the formation of a plume from the point anthropogenic source, coordinated in the complexity with the amount of the available data. Based on the proposed model, it is become possible to estimate the emission power by the satellite photographs obtained from the Resource-P series satellite. This estimate is the particular interest in the controlling emissions, which is the complex and non-trivial problem. Also authors determined the distribution of the height-integral amount of nitrogen dioxide over the Hebei Province, China, and compared it with the experimental data. The obtained estimates of the emission power can be used to integrate it into the complex chemical transport models.
New versions of the least-squares collocation method for solving differential and integral equations
Authors: Shapeev Vasily , Golushko Sergey , Belyaev Vasily , Bryndin Luka , Kirillov Pavel
Published: January 2021

This paper describes new versions of the least-squares collocation method for solving differential and integral equations. A p-version of the method has been proposed and implemented to solve nonlinear systems of partial differential equations. The stationary Navier-Stokes equations are used as an example. A hp-version of the method has been implemented for the numerical solution of the Fredholm integral equations of the second kind in the one-and two-dimensional cases. This paper shows that approximate solutions obtained by various versions of the least-squares collocation method converge with a high order and agree with analytical solutions of test problems with a high degree of accuracy.
On constructing the Riemannian metrics in refraction tomography problems
Authors: Yu Derevtsov E
Published: January 2021

A problem of the refraction tomography consists in reconstructing a function or tensor field by their attenuated ray transforms. Usually an absorption coefficient and refraction in the medium are assumed to be known. A solution to the refraction tomography problems can be obtained by approximate methods within the corresponding mathematical models, and the modeling of refraction is one of important elements of the model. We adduce summary data on the Riemannian metrics, suitable for the implementation in numerical tests, methods of their construction and main characteristics.
Fractional derivative order with respect to time for diffusion equation: an iterative method of determination
Authors: Kardashevsky A
Published: January 2021

The article proposes the iterative method for the inverse problem that determines an α-order of fractional derivative with respect to time for diffusion equation. The author presents the results obtained through numerical implementation of the method. The calculations were performed on model problems with exact solutions.
Identification of the energy system critical elements using the PARMONC library
Authors: Edelev A V , Marchenko M A , Yu Basharina O
Published: January 2021

In this paper, we presented a Monte Carlo-based approach for vulnerability analyse of energy systems. For high-performance Monte Carlo simulation the PARMONC software library was used. The PARMONC is implemented on high-performance clusters of the Siberian Supercomputer Center. The PARMONC effectively launches parallel stochastic simulation on supercomputers with different architectures. The proposed approach was applied was applied for the identification and ranking the most important elements of a real-world natural gas supply system.
A study of Hepatitis B virus infection using chi-square statistic
Authors: Odetunmibi Oluwole A , Adejumo Adebowale O , Anake Timothy A
Published: January 2021

Hepatitis B is caused by the hepatitis B virus (HBV) and it affects livers. It has been established that the disease is a serious medical condition caused by an overpowering immune response to infection. To this effect, there is a need for cross examination of records of patients on this disease to ascertain the factors that could be responsible for the survival or dying from this disease. Descriptive analysis of the data showed that sexually active age bracket (31 – 50) are greatly affected by the disease while female accounted for majority of those that are tested positive to the disease. Chi squared statistic was used to test for independence between age and gender of those who tested positive to disease between 2006 and 2015 in Lagos state, Nigeria. It was discovered that, both variables of age and gender are not independent which means there is association between the Age and Gender of HBV patients.
Radiological Hazard Assessment of Sharp-Sand from Ilorin-East, Kwara State, Nigeria
Authors: Orosun M. M. , Usikalu M. R. , Oyewumi K. J. , Oladapo O. F
Published: January 2021

Measurement of activity concentration of primordial radionuclides 40K, 232Th, 238U and the corresponding gamma dose rate over a major sharp-sand field in Ilorin, Nigeria, was carried out using Super Spec RS125 gamma ray spectrometer. The RS125 gamma spectrometer gives in-situ measurement of radioactivity concentration. Measurements were taken in 50 locations. The peak values of the measured activity concentrations of 40K, 238U, 232Th, the dose rate (D) and the resulting annual effective dose (AED) are 688.60, 48.17, 30.86 Bqkg−1, 49.50 nGyh−1 and 0.06 mSvy−1 respectively, while their corresponding lowest values are 31.30, 1.24, 0.41 Bqkg−1, 4.70 nGyh−1, and 0.01 mSvy−1 respectively. The estimated mean values of 40K, 232Th, 238U, the gamma dose rate (D) and AED are 454.48, 13.52, 11.63 Bqkg−1, 32.96 nGyh−1 and 0.04 mSvy−1 respectively. Consequently, the mean values of the measured radionuclides and the hazard parameters i.e. dose rate and annual effective dose are within the permissible levels. This follows that the risk of radiation exposure for this location is comparatively less, but the general public may not be safe from exposure to indoor ionizing radiation since no amount of radiation is safe for stochastic effects.
Geophysical investigation of road failure along Lagos-Badagry expressway using electrical resistivity imaging
Authors: Ogungbe Abiola S , Afolabi Timothy O , Onori Eugene O , Ogabi Cornelius O
Published: January 2021

Geophysical investigations of road failure using Two-dimensional (2D) electrical resistivity imaging was carried out along Lagos – Badagry expressway, Lagos State, Nigeria with a view to determining the subsurface geological structures that may pose a danger to the highway. The study was conducted on five worrisome parts of the highway, namely: Iyana Isashi, Iyana Era, Agbara, Magbon and Oko Afo, using Constant Separation Traversing (Wenner array) to obtain three (3) profiles at each location. ABEM Terrameter SAS 1000 was used for the survey which displays apparent resistivity values digitally. The data was processed with the aid of the RES2DINV software to produce 2D images of the study area. The subsurface images showed that the resistivity lies between 3.89 Ωm and 401 Ωm, indicating variation in soil matrix. It was found that the causes of road pavement collapse on the road examined were the result of a mixture of clay topsoil/subgrade soils with resistance varying from 3.79 m to 83.3 m, waterlogged sands. This is due to ingress with characteristically low resistance values and a thin pavement, thus unable to withstand the lane’s pressure.
Antimicrobial and antibiofilm activities of green synthesized silver nanoparticles for water treatment
Authors: Ismail A. O. , Ajayi S. O. , Alausa A. O. , Ogundile O. P. , Ademosun O. T.
Published: January 2021

Nanoparticles have found applications in wide areas due to their unique properties. Green synthesis of nanoparticles is an ecofriendly, safe and non-toxic approach that solve the problems associate with conventional methods. Waterborne pathogenic diseases have resulted in millions of deaths in humans especially children annually and infectious microorganism associated with water have all shown multiple resistance to conventional treatments. Bacteria biofilm accounts for majority of microbial infections and are more resistant to antimicrobial agents. The use of antibiotics is ineffective for treating biofilm-associated infections. Green synthesized silver nanoparticles (AgNps) have been reported to have important antimicrobial applications over a wide range of microorganisms, although many researchers have demonstrated in in vitro the antimicrobial activity of AgNps, few researches have been conducted on the exact mechanism of action of AgNps as antibiofilm, the possibility of infectious microbes to develop resistance and the toxicity limit of silver suitable for human consumption. This review discussed biocompatibility of green synthesis AgNps, the concept of biofilm formation, the impacts of AgNps water microbial environment, its mechanisms of action as antimicrobial agent in water treatment and the potential human toxicity.
PDTM for the solution of a time-fractional barrier option Black-Scholes model
Authors: Edeki S. O. , Jena R. M. , Ogundile O. P. , Chakraverty S.
Published: January 2021

This paper introduces the Fractional Projected Differential Transform Method (FPDTM) for the solution of the Time-fractional Barrier Option Black-Scholes Pricing Model (TFBOBSPM). The method seeks the solution using sufficient initial (transformed boundary conditions), without any discretization or restrictive assumptions. The efficiency and precision of the proposed methods are tested using illustrative examples. Thus, the FPDTM is suggested for strongly nonlinear differential models with financial applications.
Deforestation reshapes land-surface energy-flux partitioning
Authors: Yuan Kunxiaojia , Zhu Qing , Zheng Shiyu , Zhao Lei , Chen Min , Riley William J , Cai Xitian , Ma Hongxu , Li Fa , Wu Huayi , Chen Liang
Published: January 2021

Land-use and land-cover change significantly modify local land-surface characteristics and water/energy exchanges, which can lead to atmospheric circulation and regional climate changes. In particular, deforestation accounts for a large portion of global land-use changes, which transforms forests into other land cover types, such as croplands and grazing lands. Many previous efforts have focused on observing and modeling land–atmosphere–water/energy fluxes to investigate land–atmosphere coupling induced by deforestation. However, interpreting land–atmosphere–water/energy-flux responses to deforestation is often complicated by the concurrent impacts from shifts in land-surface properties versus background atmospheric forcings. In this study, we used 29 paired FLUXNET sites, to improve understanding of how deforested land surfaces drive changes in surface-energy-flux partitioning. Each paired sites included an intact forested and non-forested site that had similar background climate. We employed transfer entropy, a method based on information theory, to diagnose directional controls between coupling variables, and identify nonlinear cause–effect relationships. Transfer entropy is a powerful tool to detective causal relationships in nonlinear and asynchronous systems. The paired eddy covariance flux measurements showed consistent and strong information flows from vegetation activity (gross primary productivity (GPP)) and physical climate (e.g. shortwave radiation, air temperature) to evaporative fraction (EF) over both non-forested and forested land surfaces. More importantly, the information transfers from radiation, precipitation, and GPP to EF were significantly reduced at non-forested sites, compared to forested sites. We then applied these observationally constrained metrics as benchmarks to evaluate the Energy Exascale Earth System Model (E3SM) land model (ELM). ELM predicted vegetation controls on EF relatively well, but underpredicted climate factors on EF, indicating model deficiencies in describing the relationships between atmospheric state and surface fluxes. Moreover, changes in controls on surface energy flux partitioning due to deforestation were not detected in the model. We highlight the need for benchmarking model simulated surface-energy fluxes and the corresponding causal relationships against those of observations, to improve our understanding of model predictability on how deforestation reshapes land surface energy fluxes.
Species-specific climate–growth interactions determine tree species dynamics in mixed Central European mountain forests
Authors: Kašpar Jakub , Tumajer Jan , Šamonil Pavel , Vašíčková Ivana
Published: January 2021

Increasing growing season temperatures and the seasonal redistribution of precipitation due to climate change have recently been recorded across the globe. Simultaneously, increases of severe droughts and windstorm frequency have also been documented. However, the impacts of climate change on tree growth performance and fitness might largely differ among coexisting species. Consequently, ongoing temperature increases could lead to extensive changes in tree species compositions in many forest biomes including temperate mountain forests. In this study we used an extensive dataset of 2824 cored trees of three species from two sites, and parameterized a purely climate driven process-based model (Vaganov–Shaskin) to simulate the growth dynamics and climatic limitations of coexisting Picea abies, Fagus sylvatica and Abies alba in two of the oldest mountain forest reserves in Central Europe (the Boubín and Žofín Primeval Forests). We assumed that the species composition reflects climatic growth limitations, and considered between-site differences in mean temperature due to elevation as a model of future climate change effects on mountain forests. Our results show a complexity of site- and species-specific responses of Central European forests to climate change. Over the last 70 years, the proportion of F. sylvatica in Central European natural forests has increased at the expense of conifers. During the investigated period, we observed an increase in the growth rates of the studied species mainly at the higher elevation site, while for the lower elevation site there was increasing intensity of moisture limitation. Despite being the most moisture-limited species, P. abies showed the highest simulated growth rates. In contrast, A. alba was the least moisture limited of all considered species. Given its recent proportion in the forest species composition and intermediate drought resistance, we anticipate the future expansion of F. sylvatica in Central European mountain forests.
Exploring uncertainties in global crop yield projections in a large ensemble of crop models and CMIP5 and CMIP6 climate scenarios
Authors: Müller Christoph , Franke James , Jägermeyr Jonas , Ruane Alex C , Elliott Joshua , Moyer Elisabeth , Heinke Jens , Falloon Pete D , Folberth Christian , Francois Louis , Hank Tobias , Izaurralde R César , Jacquemin Ingrid , Liu Wenfeng , Olin Stefan , Pugh Thomas A M , Williams Karina , Zabel Florian
Published: January 2021

Concerns over climate change are motivated in large part because of their impact on human society. Assessing the effect of that uncertainty on specific potential impacts is demanding, since it requires a systematic survey over both climate and impacts models. We provide a comprehensive evaluation of uncertainty in projected crop yields for maize, spring and winter wheat, rice, and soybean, using a suite of nine crop models and up to 45 CMIP5 and 34 CMIP6 climate projections for three different forcing scenarios. To make this task computationally tractable, we use a new set of statistical crop model emulators. We find that climate and crop models contribute about equally to overall uncertainty. While the ranges of yield uncertainties under CMIP5 and CMIP6 projections are similar, median impact in aggregate total caloric production is typically more negative for the CMIP6 projections (+1% to −19%) than for CMIP5 (+5% to −13%). In the first half of the 21st century and for individual crops is the spread across crop models typically wider than that across climate models, but we find distinct differences between crops: globally, wheat and maize uncertainties are dominated by the crop models, but soybean and rice are more sensitive to the climate projections. Climate models with very similar global mean warming can lead to very different aggregate impacts so that climate model uncertainties remain a significant contributor to agricultural impacts uncertainty. These results show the utility of large-ensemble methods that allow comprehensively evaluating factors affecting crop yields or other impacts under climate change. The crop model ensemble used here is unbalanced and pulls the assumption that all projections are equally plausible into question. Better methods for consistent model testing, also at the level of individual processes, will have to be developed and applied by the crop modeling community.
CO2-plant effects do not account for the gap between dryness indices and projected dryness impacts in CMIP6 or CMIP5
Authors: Scheff Jacob , S Mankin Justin , Coats Sloan , Liu Haibo
Published: January 2021

Recent studies have found that terrestrial dryness indices like the Palmer Drought Severity Index (PDSI), Standardized Precipitation Evapotranspiration Index (SPEI), and Aridity Index calculated from future climate model projections are mostly negative, implying a drying land surface with warming. Yet, the same models’ future runoff and bulk soil moisture projections instead show regional signals of varying sign, and their vegetation projections show widespread greening, suggesting that the dryness indices could overstate climate change’s direct impacts. Most modeling studies have attributed this gap to the indices’ omission of CO2-driven stomatal closure. However, here we show that the index-impact gap is still wide even in future-like model experiments that switch off CO2 effects on plants. In these simulations, mean PDSI, Aridity Index, and SPEI still decline broadly with strong warming, while mean runoff, bulk soil moisture, and vegetation still respond more equivocally. This implies that CO2-plant effects are not the dominant or sole reason for the simulated index-impact gap. We discuss several alternative mechanisms that may explain it.
On the singularities of the discrete Korteweg–deVries equation
Authors: Um D , Ramani A , Grammaticos B , Willox R , Satsuma J
Published: January 2021

We study the structure of singularities in the discrete Korteweg–deVries (d-KdV) equation. Four different types of singularities are identified. The first type corresponds to localised, ‘confined’, singularities, the confinement constraints for which provide the integrability conditions for generalisations of d-KdV. Two other types of singularities are of infinite extent and consist of oblique lines of infinities, possibly alternating with lines of zeros. The fourth type of singularity corresponds to horizontal strips where the product of the values on vertically adjacent points is equal to 1. (A vertical version of this singularity with product equal to −1 on horizontally adjacent sites also exists). Due to its orientation this singularity can, in fact, interact with the other types. This leads to an extremely rich structure for the singularities of d-KdV, which is studied in detail in this paper. Given the important role played by the fourth type of singularity we decided to give it a special name: taishi (the origin of which is explained in the text). The taishi do not exist for nonintegrable extensions of d-KdV, which explains the relative paucity of singularity structures in the nonintegrable case: the second and third type of singularities that correspond to oblique lines still exist and the localised singularities of the integrable case now become unconfined, leading to semi-infinite lines of infinities alternating with zeros.
Complex systems approaches for Earth system data analysis
Authors: Boers Niklas , Kurths Jürgen , Marwan Norbert
Published: January 2021

Complex systems can, to a first approximation, be characterized by the fact that their dynamics emerging at the macroscopic level cannot be easily explained from the microscopic dynamics of the individual constituents of the system. This property of complex systems can be identified in virtually all natural systems surrounding us, but also in many social, economic, and technological systems. The defining characteristics of complex systems imply that their dynamics can often only be captured from the analysis of simulated or observed data. Here, we summarize recent advances in nonlinear data analysis of both simulated and real-world complex systems, with a focus on recurrence analysis for the investigation of individual or small sets of time series, and complex networks for the analysis of possibly very large, spatiotemporal datasets. We review and explain the recent success of these two key concepts of complexity science with an emphasis on applications for the analysis of geoscientific and in particular (palaeo-) climate data. In particular, we present several prominent examples where challenging problems in Earth system and climate science have been successfully addressed using recurrence analysis and complex networks. We outline several open questions for future lines of research in the direction of data-based complex system analysis, again with a focus on applications in the Earth sciences, and suggest possible combinations with suitable machine learning approaches. Beyond Earth system analysis, these methods have proven valuable also in many other scientific disciplines, such as neuroscience, physiology, epidemics, or engineering.
Performance of the Scheduled Relaxation Jacobi method in a geometric multilevel setting. I. Linear case
Authors: Bentivegna Eloisa
Published: January 2021

I investigate the suitability of the Scheduled-Relaxation-Jacobi method as a smoother within a geometric multilevel (ML) solver. Its performance in the solution of a linear elliptic equation is measured, based on two metrics: absolute performance (measured by the residual reduction in a fixed number of iterations), and parallel scalability. I discuss the theoretical expectations on the effect of this hybrid scheme on the solution iterate and, especially, the solution error, and confirm them numerically.
The finitistic dimension of an Artin algebra with radical square zero
Authors: Gélinas Vincent
Published: January 2021

We investigate the inequality

Findim
⁡

Λ

o
p

≤
dell
⁡
Λ

\operatorname {Findim} \Lambda ^{op} \leq \operatorname {dell} \Lambda

between the finitistic dimension and the delooping level of an Artin algebra

Λ
\Lambda

, and whether equality holds in general. We prove that equality

Findim
⁡

Λ

o
p

=
dell
⁡
Λ

\operatorname {Findim} \Lambda ^{op} = \operatorname {dell} \Lambda

always holds for Artin algebras with radical square zero.
A free boundary problem arising from branching Brownian motion with selection
Authors: Berestycki Julien , Brunet Éric , Nolen James , Penington Sarah
Published: January 2021

We study a free boundary problem for a parabolic partial differential equation in which the solution is coupled to the moving boundary through an integral constraint. The problem arises as the hydrodynamic limit of an interacting particle system involving branching Brownian motion with selection, the so-called Brownian bees model which is studied in the companion paper (see Julien Berestycki, Éric Brunet, James Nolen, and Sarah Penington [Brownian bees in the infinite swarm limit, 2020]). In this paper we prove existence and uniqueness of the solution to the free boundary problem, and we characterise the behaviour of the solution in the large time limit.
Genome-scale de novo assembly using ALGA
Authors: Swat Sylwester , Laskowski Artur , Badura Jan , Frohmberg Wojciech , Wojciechowski Pawel , Swiercz Aleksandra , Kasprzak Marta , Blazewicz Jacek
Published: January 2021

Motivation

There are very few methods for de novo genome assembly based on the overlap graph approach. It is considered as giving more exact results than the so-called de Bruijn graph approach but in much greater time and of much higher memory usage. It is not uncommon that assembly methods involving the overlap graph model are not able to successfully compute greater datasets, mainly due to memory limitation of a computer. This was the reason for developing in last decades mainly de Bruijn-based assembly methods, fast and fairly accurate. However, the latter methods can fail for longer or more repetitive genomes, as they decompose reads to shorter fragments and lose a part of information. An efficient assembler for processing big datasets and using the overlap graph model is still looked out.

Results

We propose a new genome-scale de novo assembler based on the overlap graph approach, designed for short-read sequencing data. The method, ALGA, incorporates several new ideas resulting in more exact contigs produced in short time. Among these ideas, we have creation of a sparse but quite informative graph, reduction of the graph including a procedure referring to the problem of minimum spanning tree of a local subgraph, and graph traversal connected with simultaneous analysis of contigs stored so far. What is rare in genome assembly, the algorithm is almost parameter-free, with only one optional parameter to be set by a user. ALGA was compared with nine state-of-the-art assemblers in tests on genome-scale sequencing data obtained from real experiments on six organisms, differing in size, coverage, GC content and repetition rate. ALGA produced best results in the sense of overall quality of genome reconstruction, understood as a good balance between genome coverage, accuracy and length of resulting sequences. The algorithm is one of tools involved in processing data in currently realized national project Genomic Map of Poland.

Availability and implementation

ALGA is available at http://alga.put.poznan.pl.

Supplementary information

Supplementary data are available at Bioinformatics online.
SWITCHES: Searchable Web Interface for Topologies of CHEmical Switches
Authors: HarshaRani G V , Moza S , Ramakrishnan N , Bhalla U S
Published: January 2021

Bistable biochemical switches are key motifs in cellular state decisions and long-term storage of cellular ‘memory’. There are a few known biological switches that have been well characterized, however, these examples are insufficient for systematic surveys of properties of these important systems. Here we present a resource of all possible bistable biochemical reaction networks with up to six reactions between three molecules, and three reactions between four molecules. Over 35 000 reaction topologies were constructed by identifying unique combinations of reactions between a fixed number of molecules. Then, these topologies were populated with rates within a biologically realistic range. The Searchable Web Interface for Topologies of CHEmical Switches (SWITCHES, https://switches.ncbs.res.in) provides a bistability and parameter analysis of over seven million models from this systematic survey of chemical reaction space. This database will be useful for theoreticians interested in analyzing stability in chemical systems and also experimentalists for creating robust synthetic biological switches.

Availability and implementation

Freely available on the web at https://switches.ncbs.res.in. Website implemented in PHP, MariaDB, Graphviz and Apache, with all major browsers supported.
Ten Years of Population-Level Genomic Escherichia coli and Klebsiella pneumoniae Serotype Surveillance Informs Vaccine Development for Invasive Infections
Authors: Lipworth Samuel , Vihta Karina-Doris , Chau Kevin K , Kavanagh James , Davies Timothy , George Sophie , Barker Leanne , Vaughan Ali , Andersson Monique , Jeffery Katie , Oakley Sarah , Morgan Marcus , Peto Timothy E A , Crook Derrick W , Walker A Sarah , Stoesser Nicole
Published: January 2021

Background

The incidence of bloodstream infections (BSIs) caused by Escherichia coli and Klebsiella pneumoniae is increasing, with substantial associated morbidity, mortality, and antimicrobial resistance. Unbiased serotyping studies to guide vaccine target selection are limited.

Methods

We conducted unselected, population-level genomic surveillance of bloodstream E. coli and Klebsiella pneumoniae isolates from 2008 to 2018 in Oxfordshire, United Kingdom. We supplemented this with an analysis of publicly available global sequencing data (n = 3678).

Results

We sequenced 3478 E. coli isolates (3278 passed quality control) and 556 K. pneumoniae isolates (535 [K-antigen] and 549 [O-antigen] passed quality control). The 4 most common E. coli O-antigens (O1/O2/O6/O25) were identified in 1499/3278 isolates; the incidence of these O-types increased over time (incidence rate ratio per year [IRRy] = 1.14, 95% confidence interval [CI]: 1.11–1.16). These O-types accounted for 616/1434 multidrug-resistant (MDR) and 173/256 extended-spectrum beta-lactamase (ESBL)-resistant isolates in Oxfordshire but only 19/90 carbapenem-resistant isolates across all studies. For Klebsiella pneumoniae, the most common O-antigens (O2v2/O1v1/O3b/O1v2) accounted for 410/549 isolates; the incidence of BSIs caused by these also increased annually (IRRy = 1.09; 95% CI: 1.05–1.12). These O-types accounted for 122/148 MDR and 106/123 ESBL isolates in Oxfordshire and 557/734 carbapenem-resistant isolates across all studies. Conversely we observed substantial capsular antigen diversity. Analysis of 3678 isolates from global studies demonstrated the generalizability of these findings. For E. coli, based on serotyping, the ExPEC4V and ExPEC10V vaccines under investigation would cover 46% and 72% of Oxfordshire isolates respectively, and 47% and 71% of MDR isolates.

Conclusions

O-antigen targeted vaccines may be useful in reducing the morbidity, mortality, and antimicrobial resistance associated with E. coli and K. pneumoniae BSIs.
Camilo Barcia Trelles on the Meaning of the Monroe Doctrine and the Legacy of Vitoria in the Americas
Authors: Scarfi Juan Pablo
Published: January 2021

This article explores three important dimensions of the work and trajectory of Camilo Barcia Trelles: his understanding of the Monroe Doctrine; his vision and contribution to the debates in Latin America and the United States over intervention and the codification of American international law; and how his own understanding of the intellectual legacy of Francisco de Vitoria shaped his views and approaches to these topics. The article argues that Barcia Trelles provided a Spanish Americanist version of international law in the Americas, according to which, following the Spanish conquest of America and Vitoria’s important contribution to international law, a irreversible division began to emerge between the two Americas, that is, the Latin American and US traditions of international law, especially since the US Declaration of Independence, the collapse of the Spanish Monarchy and the independence of the Spanish American republics.