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A computationally efficient method to study the in-plane and out-of-plane dimensional instability of thin paper sheets under the influence of moisture changes is presented. The method explicitly resolves the bonded and the free segments of fibers in the sheet, capturing the effect of anisotropic hygroexpansion at the fiber level. The method is verified against a volumetric model. The importance of longitudinal fiber hygroexpansion is demonstrated in spite of the absolute value of longitudinal hygroexpansion being an order of magnitude lower than the transverse hygroexpansion component. Finally, the method is used to demonstrate the formation of macroscopic sheet curl due to a moisture gradient in structurally uniform sheets in the absence of viscoelastic or plastic constitutive behavior and through-thickness residual stress profiles. [ABSTRACT FROM AUTHOR]

Text processing tasks commonly grapple with the challenge of high dimensionality. One of the most effective solutions to this challenge is to preprocess text data through feature selection methods. Feature selection can select the most advantageous features for subsequent operations (e.g., classification) from the native feature space of the text. This process effectively trims the feature space's dimensionality, enhancing subsequent operations' efficiency and accuracy. This paper proposes a straightforward and efficient filter feature selection method based on document-term matrix unitization (DTMU) for text processing. Diverging from previous filter feature selection methods that concentrate on scoring criteria definition, our method achieves more optimal feature selection by unitizing each column of the document-term matrix. This approach mitigates feature-to-feature influence and reinforces the role of the weighting proportion within the features. Subsequently, our scoring criterion subtracts the sum of weights for negative samples from positive samples and takes the absolute value. We conduct numerical experiments to compare DTMU with four advanced filter feature selection methods: max–min ratio metric, proportional rough feature selector, least loss, and relative discrimination criterion, along with two classical filter feature selection methods: Chi-square and information gain. The experiments are performed on four ten-thousand-dimensional feature space datasets: b o o k , d v d , m u s i c , m o v i e and two thousand-dimensional feature space datasets: i m d b , a m a z o n _ c e l l s , sourced from Amazon product reviews and movie reviews. Experimental findings demonstrate that DTMU selects more advantageous features for subsequent operations and achieves a higher dimensionality reduction rate than those of the other six methods used for comparison. Moreover, DTMU exhibits robust generalization capabilities across various classifiers and dimensional datasets. Notably, the average CPU time for a single run of DTMU is measured at 1.455 s. • This paper offers DTMU, a filter feature selection method enhancing feature quality via unitization for improved properties. • DTMU is notably user-friendly, involving only two straightforward steps. • This paper substantiates, through numerical experiments, that DTMU stands as an advanced and effective method. [ABSTRACT FROM AUTHOR]

Cationic cellulose, despite its long history, has yet to find a place in the paper industry. However, recent research is evaluating the potential of its nanoscale forms. Likewise, the processes of Western manufacturers are optimized for wood pulps, relegating non-wood crops to specific products that, as also proposed by current research, could include nanocellulose. We combined these trends with the existing knowledge of the strong adsorption of poly(diallyldimethylammonium chloride) (polyDADMAC) on cellulosic fibers, which can be deemed a non-covalent kind of cationization. For that, polyDADMAC was first anchored to refined hemp pulps, under conditions that allowed the deprotonation of the primary hydroxyl groups of cellulose. The fiber surface remained positively-charged even after thoroughly washing the samples, owing not only to the small proportions of acidic hemicelluloses and lignin, but also to stable ion-dipole interactions. This non-covalent cationization was found to follow pseudo-second order kinetics, indicating that diffusion through the fiber was the rate-controlling step. PolyDADMAC-containing fibers were then fibrillated by high-pressure homogenization. The surface charge of cationic nanocellulose was greater than that of the starting fibers, as the specific surface area increased. Nonetheless, polyDADMAC caused agglomeration of fibrils to a certain extent. As a drawback, when applied in papermaking, cationic nanocellulose lowered air permeability to a lesser extent than non-cationized nanofibers. As an advantage, the tensile index increased by up to 57% in the absence of any retention agent. • Adsorption of polyDADMAC to hemp pulp fibers follows pseudo-second order kinetics. • Both refining and fibrillation increase the absolute value of the surface charge. • Strong binding of polyDADMAC: ionic in alkaline media, ion-dipole after neutralization. • The resulting nanofibers improve paper strength without the need of retention aids. [ABSTRACT FROM AUTHOR]

The spectral radius ρ (A) is the maximum absolute value of the eigenvalues of a matrix A. In this paper, we establish some relationship between the spectral radius of a symmetric matrix and its principal submatrices, i.e., if A is partitioned as a 2 × 2 block matrix A = ( 0 A 12 A 21 A 22 ) , then ρ (A) 2 ≤ ρ 2 2 + θ ⁎ , where θ ⁎ is the largest real root of the equation μ 2 = (x − ν) 2 (ρ 2 2 + x) and ρ 2 = ρ (A 22) , μ = ρ (A 12 A 22 A 21) , ν = ρ (A 12 A 21). Furthermore, the results are used to obtain several upper bounds of the spectral radius of graphs, which strengthen or improve some known results. [ABSTRACT FROM AUTHOR]

In this paper, Mg 2.3 Y 0.1 Ni + x wt.% graphene (x = 1, 3, 5, 7) composite hydrogen storage alloys were fabricated by mechanical ball milling of Mg 2.3 Y 0.1 Ni alloy powder and graphene. The experimental results show that the phases of the composite alloy consist mainly of Mg 2 Ni, Mg, MgNi 2 and Ni 3 Y phases, and graphene tends to be distributed at the edges of the alloy, increasing the phase boundary resulting from the contact between the C-boundary and the Mg 2.3 Y 0.1 Ni alloy, providing more channels for the diffusion of H 2. In which 7 wt.% of graphene is added, the gestation period of the composite alloy completely disappears. And the ball-milled alloy with 3 wt.% graphene at different temperatures has the highest hydrogen uptake in 2 min and the highest hydrogen release in 10 min. At 573 K, the composite alloy has a hydrogen absorption capacity of 3.251 wt.% H 2 in 2 min and reaches 90.21% of the maximum hydrogen absorption, while it is able to release 3.389 wt.% H 2 in 10 min and reaches 99.04% of the maximum hydrogen release. And the composite alloy with 3 wt.% graphene has the smallest dehydrogenation activation energy. The absolute value of the enthalpy change is reduced from 60.1 kJ/mol to 54.8 kJ/mol, and the desorption enthalpy change is reduced from 73.4 kJ/mol to 67.5 kJ/mol. • Addition of graphene increases the phase boundary of the composite alloy. • Graphene lowers the reaction barrier of the alloy with hydrogen. • Graphene improves the kinetics of hydrogen absorption/release of the alloy. • Graphene reduces the thermodynamic stability of composite alloys. [ABSTRACT FROM AUTHOR]

Let M n be the space of real matrices of order n. The sign-real spectral radius ξ : M n → R + , introduced in a 1997 paper by S.M. Rump, intervenes for instance in the problem of estimating the componentwise distance to singularity. The function ξ has also a bearing in the analysis of generalized absolute value equations and linear complementarity problems. Although ξ is not a norm, it is at least absolutely homogeneous and continuous. Furthermore, ξ is invariant under transposition, permutation similarity, and a few other linear isomorphisms on M n. A matrix A ∈ M n is called sign-real expansive if ξ (A) ≥ 1. Let Ω n be the set of such matrices. The purpose of this work is to discover new properties of the function ξ and to explore in detail the structure of the set Ω n. [ABSTRACT FROM AUTHOR]

Let G be a simple undirected graph. The Seidel energy of G , denoted by E s (G) , is the sum of absolute values of all Seidel eigenvalues of G. A complete r -partite graph with n vertices is called r -partite Turán graph, denoted by T (n , r) , if the number of vertices of each part is either ⌊ n r ⌋ or ⌈ n r ⌉. In 2021, Tian et al. proposed a problem that for any edge e of Turán graph T (n , r) with r ≥ 4 , does there exist a sufficiently large integer n 0 such that E s (T (n , r)) < E s (T (n , r) − e) whenever n ≥ n 0 . In this paper, we prove that the Seidel energy of T (n , 5) of order n ≥ 5 is always increased when an edge is deleted. [ABSTRACT FROM AUTHOR]

The energy of a graph is defined as the sum of absolute values of all eigenvalues of its adjacency matrix. For a nonempty graph G , S. Akbari, A. Alazemi, M. Andelić and M.A. Hosseinzadeh proposed a conjecture: The energy of the line graph of G is at least | E (G) | + Δ (G) − 3 , where E (G) is the edge set of G and Δ (G) is the maximum degree of G. In this paper, we give a proof confirming the conjecture, and present a lower bound and an upper bound for the energy of line graphs of regular graphs. [ABSTRACT FROM AUTHOR]

Strengthening environmental regulation (Reg) is an important measure to solve energy and environmental problems, then to realize the profit sustainable growth (Gro). Taking 116 listed renewable energy enterprises in China from 2010 to 2019 as samples, this paper uses FE and SYS-GMM models to examine the moderating effect of three types of Reg in the relationship of factor market distortions (Dist) and the Gro. The conclusions are as follows: For the direct impact, capital and labor market distortions (DistK and DistL) hinder the Gro. Specifically, the absolute value of the coefficient of DistK in state-owned enterprises (SOEs) is greater than that of the DistL, which indicates that the inhibitory effect of DistK in SOEs is more significant. For the indirect impact, the coefficients of economic and supervised environmental regulation (RegE and RegS) are positive and significant, and promote the Gro of SOEs and non-SOEs, while legal environmental regulation (RegL) is the opposite, which shows that Reg has significant "cost effect" and "rebound effect". Moreover, Reg has a positive moderating effect, which is mainly reflected in SOEs, and alleviates the inhibitory effect of DistK and DistL on Gro to a certain extent. Finally, this paper puts forward some targeted policy suggestions. [ABSTRACT FROM AUTHOR]

Process steam is an important product in the industrial sector but the traditional steam boiler will lead to tremendous fossil fuel consumption and carbon emissions. The non-concentrating solar collectors have a huge potential for process steam generation but their application potential has not been fully explored. In this paper, a high-efficient evacuated flat plate solar collector used for direct steam generation is proposed. Its thermal performance in both direct steam generation mode and pressurization water mode is presented via experiment test and a validated numerical model. The results indicate that the direct steam generation mode can obtain a 10% enhancement (absolute value) of the thermal efficiency compared with the pressurization water mode. The thermal radiant losses of the solar collector can be suppressed and the heat transfer coefficient of the working fluid can also be elevated. Furthermore, a dual-mode evacuated flat plate solar system is proposed to produce thermal energy for space heating in the heating season and generate steam in the non-heating season, thereby solving the solar seasonal mismatch problem for the traditional solar thermal heating system. The comparison with the state-of-the-art study manifests that the dual-mode system proposed in this paper has better performance all year round. [Display omitted] [ABSTRACT FROM AUTHOR]

The stress state of a fault plane influences the mode of sliding and characteristics of slide behaviour. Existing researchers have mainly focused on studying the effect of shear stiffness on fault behaviour under the constant normal load (CNL) boundary conditions. However, the impact of the normal stiffness effect of deep faults on fault sliding stability and seismic source parameters remains uncertain. Addressing the issue, this paper conducts friction tests on granite-simulated faults under the constant normal stiffness (CNS) boundary conditions. It analyzes the impact of normal stiffness on the mechanical behaviour of fault sliding. The results of this paper demonstrate the following findings: (1) Under both normal boundary conditions, various sliding modes occur, including creep-slip, chaotic stick-slip, regular inclusion chaotic stick-slip, and regular stick-slip. (2) The normal stiffness effect reduces the duration of creep-slip and chaotic stick-slip behaviour and decreases the frequency of regular inclusion chaotic stick-slip behaviour. (3) Shear stress and normal stress of the regular stick-slip mode exhibit periodic changes under the CNS boundary conditions. (4) Compared to the CNL boundary conditions, the CNS boundary conditions show a larger shear stress drop and a positive correlation between the normal stress drop and normal stiffness. (5) The CNS boundary conditions result in larger shear stiffness, the absolute value of stick-slip stiffness, characteristic sliding displacement, and fracture energy compared to the relevant seismic source parameters of the CNL boundary conditions. These parameters display positive correlations with normal stiffness. The stick-slip period and normal stiffness initially decrease and then increase, while the normal displacement drop and normal stiffness display a negative correlation trend. These analyses provide comprehensive insights into the mechanical characteristics of fault-slip behaviour and can contribute to improving models and predictions related to fault-sliding behaviour and seismic activity. • We discover a new fault-slip pattern known as regular inclusion chaotic stick-slip. • The normal stiffness effect shortens the duration of fault-slip behaviour. • Under CNS condition, the shear and normal stress exhibit synchronous changes. • The values of seismic source parameters tend to be larger for the CNS condition. [ABSTRACT FROM AUTHOR]

This paper proposes three novel accelerated inverse-free neurodynamic approaches to solve absolute value equations (AVEs). The first two are finite-time converging approaches and the third one is a fixed-time converging approach. It is shown that the proposed first two neurodynamic approaches converge to the solution of the concerned AVEs in a finite-time while, under some mild conditions, the third one converges to the solution in a fixed-time. It is also shown that the settling time for the proposed fixed-time converging approach has an uniform upper bound for all initial conditions, while the settling times for the proposed finite-time converging approaches are dependent on initial conditions. The proposed neurodynamic approaches have the advantage that they are all robust against bounded vanishing perturbations. The theoretical results are validated by means of a numerical example and an application in boundary value problems. [ABSTRACT FROM AUTHOR]

This paper is devoted to studying the global and finite convergence of the semi-smooth Newton method for solving a piecewise linear system that arises in cone-constrained quadratic programming problems and absolute value equations. We first provide a negative answer via a counterexample to a conjecture on the global and finite convergence of the Newton iteration for symmetric and positive definite matrices. Additionally, we discuss some surprising features of the semi-smooth Newton iteration in low dimensions and its behavior in higher dimensions. Secondly, we present two iterative schemes inspired by the classical Jacobi and Gauss-Seidel methods for linear systems of equations for finding a solution to the problem. We study sufficient conditions for the convergence of both proposed procedures, which are also sufficient for the existence and uniqueness of solutions to the problem. Lastly, we perform some computational experiments designed to illustrate the behavior (in terms of CPU time) of the proposed iterations versus the semi-smooth Newton method for dense and sparse large-scale problems. Moreover, we included the numerical solution of a discretization of the Boussinesq PDE modeling a two-dimensional flow in a homogeneous phreatic aquifer. [ABSTRACT FROM AUTHOR]

Robotic-Assisted Surgery (RAS) is beginning to unlock its potential. However, despite the latest advances in RAS, the steep learning curve of RAS devices remains a problem. A common teaching resource in surgery is the use of videos of previous procedures, which in RAS are almost always stereoscopic. It is important to be able to add virtual annotations onto these videos so that certain elements of the surgical process are tracked and highlighted during the teaching session. Including virtual annotations in stereoscopic videos turns them into Mixed Reality (MR) experiences, in which tissues, tools and procedures are better observed. However, an MR-based annotation of objects requires tracking and some kind of depth estimation. For this reason, this paper proposes a real-time hybrid tracking–matching method for performing virtual annotations on RAS videos. The proposed method is hybrid because it combines tracking and stereo matching, avoiding the need to calculate the real depth of the pixels. The method was tested with six different state-of-the-art trackers and assessed with videos of a sigmoidectomy of a sigma neoplasia, performed with a Da Vinci® X surgical system. Objective assessment metrics are proposed, presented and calculated for the different solutions. The results show that the method can successfully annotate RAS videos in real-time. Of all the trackers tested for the presented method, the CSRT (Channel and Spatial Reliability Tracking) tracker seems to be the most reliable and robust in terms of tracking capabilities. In addition, in the absence of an absolute ground truth, an assessment with a domain expert using a novel continuous-rating method with an Oculus Quest 2 Virtual Reality device was performed, showing that the depth perception of the virtual annotations is good, despite the fact that no absolute depth values are calculated. [Display omitted] • Enhancing videos of robotic surgery with virtual annotations is useful for training. • Tracking and depth estimation often required for annotation of stereoscopic videos. • A real-time tracking–matching framework is proposed; true pixel depth not necessary. • Validation with objective metrics and a domain expert using a continuous rating. • CSRT-based method provides suitable tracking and perception of virtual annotations. [ABSTRACT FROM AUTHOR]

• Temperature coefficients (TC) of PV modules were evaluated in different irradiances. • TC of V oc varies logarithmically with irradiance for c-Si PV modules. • A novel empirical function is derived to calculate the TC of V oc in any irradiance. • An improved description of PV module behavior under different irradiance is shown. In PV system performance models, the change in temperature coefficients (TC) as a function of solar irradiance (G) is usually not calculated. Although the variation of the TC of open circuit voltage (V oc) with G is predicted by solar cell theory, most performance models do not account for this behavior. Equations describing the variation of TCs with G are not readily available. The main objective of this paper is to experimentally evaluate the variation of TCs with G of crystalline silicon PV modules. Several I-V curves were measured, with G ranging from 100 to 1000 W/m2 and module temperature ranging from 25 to 65 °C. A matrix of 50 I-V curves was obtained for each PV module and TCs were calculated for different G values. The TC of the short-circuit current (I sc) is practically constant with G , except for two studied half-cell PV modules. The absolute value of TC of maximum power (P m) increases for lower irradiance values for most modules tested, but this trend is not seen for two recently manufactured PV modules where a negligible variation with G was obtained. The main result is a new logarithmic function that fits the experimental data and shows a well-defined increase in the modulus of the TC of V oc for low irradiance values. The equation proposed to describe this behavior is a novelty to improve PV device modeling. The results presented here contribute to a better understanding of TCs under varying irradiance, an important aspect of PV module performance. [ABSTRACT FROM AUTHOR]

The main purpose of this paper is to solve tensor absolute value equation by using preconditioned techniques and the inexact fixed point iteration method. For an existing preconditioner, we present a new inexact fixed point iteration method for solving tensor absolute value equation. Theoretically, we give the convergence of the proposed method. Numerically, we show the efficiency of the proposed method by two numerical examples. [ABSTRACT FROM AUTHOR]

Rapidly populating renewable energy sources and storage units at the distribution system, made it crucial to monitor the system in real-time. This necessity brings new challenges and business opportunities for the distribution system operator (DSO). DSO requires situational awareness on the system via several analyses, most of which rely on correct system topology. However, switch statuses of the distribution system may not be telemetered or transferred correctly to the DSO, despite having several switching actions daily. This paper proposes a state estimation based method for distribution systems with limited number of measurements to detect and identify topology error. The method is applicable with both conventional SCADA and/or PMU measurements. Weighted Least Absolute Values (WLAV) state estimator is employed because of its robustness against inaccurate measurements or bad data. The computational performance of the proposed method is comparable with that of the WLAV state estimator, and hence applicable in practical applications. • High performance algorithm for distribution system topology error detection. • Performing in the presence of limited number of field measurements. • Reduced uncertainty using the Weighted Least Absolute Value (WLAV) state estimator. [ABSTRACT FROM AUTHOR]

• A disturbance simulation model of tooth-flexible body residual film-soil based on DEM-MBD was established. • The flow characteristics of film-soil was studied using DEM-MBD simulation methods. • A film picking test bench was established to verify the reliability of the simulation model. • The cross-sectional shape of soil was used to verify the accuracy of DEM simulation models. • The mechanical properties and tensile performance of the residual film were analyzed. The residual film in the cotton cultivation layer will seriously affect cotton cultivation, and mechanized recycling of residual film is currently the best way to solve this problem. To improve the recovery effect of the chain tooth tillage layer residual film recovery machine, a bionic elastic tooth was designed in this paper. Furthermore, DEM-MBD coupling multibody dynamics was used as the research method to study the bionic elastic tooth-residual film-soil interactive disturbance. A DEM-MBD simulation model for predicting the film lifting effect of a film lifting device has been established. And the DEM-MBD simulation model was used to optimize the design parameters of the film lifting device by studying the film lifting effect of the elastic teeth. The absolute value of the maximum curvature at the tip of the elastic tooth (A), the angle between the midline of the power wheel and the ground plane (B), and the spacing of the elastic teeth (C) were used as the influencing factors. The optimal solution parameters (A = 0.03, B = 54°, C = 83 mm) were obtained. The field test's film picking and disturbance rate was 91.27 %, the error with the simulation results (89.69 %) was 1.8 %, which verified the accuracy of the simulation results and the superiority of the optimized parameters. The recovery rates of residual film under soil compaction conditions of 600 kPa, 800 kPa, and 1000 kPa were 91.25 %, 90.94 %, and 90.89 % (Verified the strong adaptability of the device). This study can provide a theoretical research basis and test methods for the design optimization of touching parts. [ABSTRACT FROM AUTHOR]

• A composite fringe pattern based on a spatial orthogonal frequency multiplexing is meticulously crafted, incorporating ample spatial and temporal information and providing neural network with the theoretical basis for learning the required mapping correspondence. • An end-to-end network is designed to achieve pixel-wise prediction of absolute phase values, utilizing a nested strategy and the concept of centralized information interaction. • A diverse dataset comprising numerous scenes is collected, wherein high-precision ground truths are computed using standard N -step phase-shifting and multi-frequency temporal phase unwrapping methods. • A seven-map training loss calculation strategy is adopted to instruct training process. • The first qualitative experiment proves the superiority of our method over alternative four methods. The second quantitative evaluation and respectively validates its capability in high dynamic range 3D measurement and in precise 3D measurement. The pursuit of precise and efficient 3D shape measurement has long been a focal point within the fringe projection profilometry (FPP) domain. However, achieving precise 3D reconstruction for isolated objects from a single fringe image remains a challenging task in the field. In this paper, a deep learning-based frequency-multiplexing (FM) composite-fringe projection profilometry (DFCP) is proposed, where an end-to-end absolute phase retrieval network (APR-Net) is trained to directly recover the absolute phase map from a FM composite fringe pattern. The obtained absolute phase map exhibits exceptional precision and is devoid of spectrum crosstalk or leakage disturbance typically encountered in traditional FM techniques. APR-Net is intricately crafted, incorporating a nested strategy along with the concept of centralized information interaction. A diverse dataset encompassing various scenarios and free from spectrum aliasing is assembled to guide the training process. A seven-map loss calculation scheme is employed to guide the training process, of which the efficacy is proved through ablation experiments. In the first qualitative experiment, DFCP demonstrates comparable phase accuracy to ground truths with 47 fewer projected images, outperforming other three methods with mean absolute phase errors of 0.0052 rad, 0.1761 rad, 0.0169 rad, and 0.0139 rad. The second qualitative experiment and the quantitative evaluation respectively prove DFCP's capability in high dynamic range 3D measurement and in precise 3D measurement, with sphere diameter errors of 0.0780 mm and 0.0726 mm, and a spherical centroid distance error of 0.0555 mm. [ABSTRACT FROM AUTHOR]

In order to enhance the texture and particle retention capabilities of the anti-abrasive seal layer, this paper focuses on the interlocking pattern between the seal and the particles of the pavement, and for the first time considers the base pavement texture, the particle size of the seal, and the amount of seal particles as design variables. The study investigates the relationship between these factor variables and response variables such as texture loss and mass loss. An optimization of the plan design was conducted using the I-optimization method in the mixture design of Design Expert software. The study involved a long-term wear test of 20,000 wear cycles on anti-abrasive seals. The response surfaces corresponding to each response variable were calculated using RSM (response surface method), thereby providing design solutions with high wear-resistant performance. Finally, the rationality and scientific nature of the optimized solutions were verified using three-dimensional texture indices, preliminarily elucidating the texture characteristics of the high wear-resistant performance. The results indicate that combinations of 0.7 kg/m² aggregate usage, 0.8 mm-1.0 mm texture depth, 0.6 mm-1.18 mm aggregate particle size, and 0.75 kg/m² aggregate usage, 1.2 mm-1.3 mm texture depth, 0.3 mm-0.6 mm aggregate particle size experienced the least quality and TD loss. The general texture characteristics of high wear-resistant seal layers include a small Sq value (Sq less than 1.8), a moderate Ssk value (Ssk approximately 0), and a slightly higher Sku value (Sku greater than 3). However, if Ssk is not close to zero (and the absolute value of Ssk is too large), even higher Sku values can result in increased large losses. • The durability of the seal layer is enhanced by improving the interlock between particles and aggregates. • RSM is used to optimize the design of sealing parameters such as aggregate size, aggregate amount, and base texture. • The height distribution of particles is assessed through the kurtosis and skewness measurements in three-dimensional texture analysis. • Recommendations are made regarding the appropriate matching of the base texture with the particle size and quantity. [ABSTRACT FROM AUTHOR]

In the paper, the mechanical properties of uniaxial tensile sintered nano-silver components were investigated by molecular dynamics method, and the effects of sintering pressure and temperature on them were analyzed. The sintered body was obtained by sintering three adjacent cubes, and the sintered nano-silver component under uniaxial tension was cut from the existing sintered body. The results show that the potential energy decreases while the kinetic energy has a jump. The higher the sintering pressure, the earlier the nano-silver sintering begins. Temperature has little effect on sintering time. When sintered nano-silver components are uniaxial tensile, the greater the sintering pressure, the greater the rising absolute value of the potential energy, and the greater the yield stress. When the sintering temperature is 250 °C, the variation of potential energy is large and the yield stress is high. The paper aims to supplement and guide the mechanical properties of sintered nano-silver. • The mechanical properties of sintered nano-silver components were simulated. • Uniaxial tension rather than sintering process is analyzed. • The influence of sintering pressure and temperature on it was investigated. • The greater the sintering pressure, the greater the yield stress. • When the sintering temperature is 250 °C, the yield stress is high. [ABSTRACT FROM AUTHOR]

• This paper presents a linearization interpolation method with high robustness and high accuracy for sinusoidal encoders. • The compensation coefficient is designed to amplify pseudo-linearized signal to approximate ideal linearized signal. • The estimation phase error reaches 0.007° over 360 signal period. • Due to its reasonable accuracy and simple implementation, it has been implemented on FPGA. This paper presents a linearization interpolation method with high robustness and high accuracy for sinusoidal encoders. Based on the pseudo-linearized signal constructed by the ratio of absolute values difference and absolute values sum of the sine and cosine signals, a compensation coefficient is designed to amplify pseudo-linearized signal to approximate ideal linearized signal for improving the linearity. The linearity is improved from 9.05% to 0.015%, which means that the linearized signal can be used to accurately determine the phase angle. This method is easy to implement, has high accuracy, and does not require the lookup tables (LUTs) or processors. The theoretical phase error is less than 0.007° over 0° ∼ 360°, corresponding to about 15-bit accuracy per signal period. In addition, the proposed method is implemented on the hardware platform with a field-programmable gate array (FPGA). Finally, the effectiveness of proposed method is demonstrated by experiments using simulated sinusoidal encoder. [ABSTRACT FROM AUTHOR]

This paper confirms a positive relationship between the aggressiveness of bids and the probability of renegotiating concession contracts. We use a database of 113 concessions awarded in Peru, finding that a 1% increase in bidding aggressiveness increases the probability of contract renegotiation by 2.4%–3%. This impact is higher for the transportation sector. Our results are robust to several econometric specifications. These results confirm the hypothesis that bidders will submit aggressive bids to renegotiate contract terms once the government and concessionaire are tied, and competition is no longer possible. • This paper is framed within those that study the economic and institutional determinants of concession contract renegotiations. Specifically, our objective is to study empirically how aggressive bids in concessions induce a higher number of renegotiations of such contracts. • There are few papers showing the impact of aggressive bids on concession contract renegotiations. For this reason, we have chosen to review separately two bodies of literature. First, we review the contributions on the institutional determinants of concession contract renegotiations. Second, we review the few studies that show the relationship between aggressive bids and the consequent renegotiations of such contracts. In this sense, aggressive bids become another explanatory variable among the determinants of renegotiations that have been studied more extensively. • With respect to aggressive bids, we understand in this work that they are those whose winning bid differs substantially from the estimates indicated by Proinversión, according to the value of the awarded bid. Mathematically, we define aggressiveness of a bid as the absolute value of the following formula: [ABSTRACT FROM AUTHOR]

It is well known that there are Q -linear discontinuous functions from R to R. Moreover, such functions have dense graph in the real plane. In this paper, we study the existence of linear spaces contained in the family of linear discontinuous functions in the generalized context of topological vector spaces and fields endowed with an absolute value. Furthermore, in the case of fields endowed with an absolute value, we study the algebraic genericity of the families of (1) linear discontinuous functions that are not everywhere surjective and (2) linear discontinuous functions that are strongly everywhere surjective. This extends a number of previous results of lineability theory. Generalizations of classical results of Q -linear discontinuous functions are also analyzed. [ABSTRACT FROM AUTHOR]

The energy of a graph G , E (G) , is defined as the sum of absolute values of the eigenvalues of its adjacency matrix. In Akbari and Hosseinzadeh (2020) [3] it was conjectured that for every graph G with maximum degree Δ (G) and minimum degree δ (G) whose adjacency matrix is non-singular, E (G) ≥ Δ (G) + δ (G) and the equality holds if and only if G is a complete graph. Let G be a connected graph with the edge set E (G). In this paper, first we show that E (L (G)) ≥ | E (G) | + Δ (G) − 5 , where L (G) denotes the line graph of G. Next, using this result, we prove the validity of the conjecture for the line of each connected graph of order at least 7. [ABSTRACT FROM AUTHOR]

Let G be a simple graph with vertex set V and edge set E , and let d i be the degree of the vertex v i ∈ V. If the vertices v i and v j are adjacent, we denote the respective edge by v i v j ∈ E. A vertex-degree-based topological index φ is defined as φ (G) = ∑ v i v j ∈ E φ d i , d j , where φ i , j is a function with the property φ i , j = φ j , i. The general extended adjacency matrix A φ is defined as [ A φ ] i j = φ d i , d j if v i v j ∈ E , and 0 otherwise. The energy associated to φ of G is the sum of the absolute values of the eigenvalues of A φ. In this paper we show that ρ (G) E φ (G) ≥ 2 φ (G) for all connected graphs G , where ρ (G) is the spectral radius of G and φ a , b ≠ 0 for all a , b ∈ N. We also characterize the graphs where equality holds. As a consequence, for any tree T with n vertices, E φ (T) ≥ 2 n − 1 φ 1 , (n − 1) , with equality holding if and only if T ≅ S n. [ABSTRACT FROM AUTHOR]

The influence of the main design parameters on the ablated mass bit (the mass ablated from the propellant in each discharge) of a coaxial ablative pulsed plasma thruster is analyzed in this paper. The analysis results show that the main influencing factor of the ablated mass bit in coaxial ablative pulsed plasma thrusters is the ablation energy from the arc. When the ablation energy is given, the shape and size of the propellant surface mainly affect the distribution of the ablated mass but have less influence on the ablated mass bit. Based on the analysis, a simple model that can be used to estimate the ablated mass bit of the coaxial ablative pulsed plasma thruster is established. To evaluate and complete the new model, a coaxial ablative pulsed plasma thruster is operated and tested under 10 different working conditions. The experimental results show that the ratio of the ablated mass bit to the absolute value integrals of the product of the electrode voltage and discharge current is approximately 0.38–0.49 μg / J. When the ratio is set to 0.44 μg / J, the maximum and average errors of the new model are 15.7% and 7.6%, respectively, for ablated mass bits under these 10 working conditions. The concept of the ablation direction is proposed in this paper. The experimental and simulation results show that the ablation direction has a great influence on the propellant surface profile change in coaxial ablative pulsed plasma thrusters, which also affects their performance and reliability. • A model is established for estimating the ablation mass of a coaxial APPT. • The average error of the new model is approximately 7.6%. • The concept of the ablation direction in APPTs is proposed. • The evolution process of the coaxial APPT propellant surface is analyzed. [ABSTRACT FROM AUTHOR]

This paper addresses mitigation measures against railway vibrations in soft soils by use of FE calculations. In order for calculation models to be used as design tools, it is essential that they are relatively easy to set up and have reasonably short computational times which would allow sensitivity and optimization analyses. It is therefore desirable to use two-dimensional (2D) models to the greatest possible extent. The focus of this paper is to investigate the advantages and limitation of using such models as engineering approach to study effect of countermeasures. The difference between 2D and three-dimensional (3D) calculation models, and the performance of absorbing boundary conditions are investigated. The study shows that 2D models provide satisfactory results as long as root mean square values are considered, the treated area is long compared to other relevant distances, and the results are primarily used to compare different mitigation measures. However, since geometrical attenuation is not correctly captured in 2D models, they should not be used to calculate absolute vibration values. In a presented case study, the effects of lime-cement columns under the track bed and as a vibration-reducing screen parallel to the track are calculated and compared. The study shows good effect of both mitigation measures in the low frequency range. To avoid structure-borne noise problems, it may be necessary to combine columns below track bed with mitigation measures effective at higher frequencies, such as rail pads or ballast mats. [ABSTRACT FROM AUTHOR]

Global warming has aroused the attention all over the world, because not only can it directly damage the living environment, but it can also impact on the social and economic development, of a region in an obvious and far-reaching way. In this paper, we builded a trans-log production function model incorporating variables, such as rainfall, labor force, technology and temperature to simulate how climate changes impacted on the regional economics. Time series data of the domestic economy of Nanjing, a city in the southeast China, between 1996 and 2017, were used to verify the production theory of trans-log production frontier. The results showed that: with the rainfall increased and the temperature declined, the climate impact on the economy and the absolute value of the output elasticity of the frontier diminished. In addtion, the climate change was also positively related to the capital investment. The larger variation of temperature negatively impacted on the economic development. • This paper builds a trans-log production function model. • Time series data are used to verify the production theory of trans-log production frontiers. • Analyzing the effect of climate change on the regional economy. • The larger variation of temperature negatively impacted on the economic development. [ABSTRACT FROM AUTHOR]

Many problems in scientific computing and engineering fields lead to the solution of generalized absolute value equations (GAVE). In this paper, by simultaneously splitting both coefficient matrices in the differential and non-differential parts of the GAVE, a modified Newton-based matrix splitting (MNMS) iteration method is proposed. The MNMS iteration method not only covers the well-known generalized Newton iteration method as well as the recent proposed modified Newton-based iteration method and the Newton-based matrix splitting iteration method for solving the GAVE, but also results in a series of relaxation versions that are very flexible in real applications. Convergence properties of the MNMS iteration method are studied in detail when the coefficient matrices are positive definite matrices and H + -matrices. Finally, three numerical examples are presented to show the feasibility and effectiveness of the proposed MNMS iteration method. [ABSTRACT FROM AUTHOR]

The current standard in China does not specify the standard test method for determining Poisson's ratio, and the Poisson's ratio used in pavement design is often roughly fixed, which can result in large errors in the calculations and analysis of road structure. In this paper, the research on different test methods for Poisson's ratio is carried out and the non-linear characteristics of tensile and compressive Poisson's ratio on pavement materials under different influencing factors are analyzed. The results indicate that the absolute value of the ratio between transverse rebound strain and longitudinal rebound strain under 50% of the maximum destructive load can objectively characterize the mechanical properties of Poisson's ratio, and it is the optimal measurement method for Poisson's ratio in asphalt pavement materials. The Poisson's ratio of two pavement materials both decreases with the increase of loading rate and gradually tends to a constant value. Cement dosage and temperature are the most significant factors affecting the tensile and compressive Poisson's ratio of cement stabilized crushed stone and asphalt mixture, respectively. Specifically, when cement dosage increases by 1%, the Poisson's ratio of cement stabilized crushed stone decreases by approximately 10%, and the temperature has a significant influence on the difference in tension and compression for Poisson's ratio of asphalt mixture (up to 40%). The asphalt content corresponding to the minimum Poisson's ratio is basically consistent with the optimal asphalt content obtained by the Marshall volume method. Based on these, a quantification value-taking model is established of the tensile and compressive Poisson's ratios of typical asphalt pavement materials varying with multiple factors. The research results can serve as a reference for the scientific value-taking of pavement structural design parameters considering the different mechanical characteristics of materials in tension and compression. • The scientific and reasonable measuring method of Poisson's ratio was established. • The quantitative model of Poisson's ratio affected by many factors was established. • The Poisson's ratio increases with loading speed and gradually tends to stabilize. • The optimum asphalt content mixture by Marshall method has minimum Poisson's ratio [ABSTRACT FROM AUTHOR]

Engine performance models are used in various fields, such as operation optimization, control, and diagnosis. In order to effectively apply an engine performance model in these fields, a high level of prediction accuracy is required. When improving the accuracy of an engine model through performance adaptation using measurement data, it is important to functionalize the component adaptation factors calculated at each measurement point to enable them to be utilized at other operating points. A method of curve fitting to find the adaptation factor for a single performance parameter was previously used to functionalize the component adaptation factor. In this paper, machine learning techniques are newly applied to functionalize component adaptation factors for several parameters, including engine operation characteristics, and their effectiveness is analyzed. The prediction accuracy of the adapted model for a two-spool mixed-flow turbofan engine is compared based on the fan exit total pressure, high-pressure compressor (HPC) exit static pressure, exhaust gas temperature (EGT), and high-pressure spool speed. For an engine model adapted using the existing functionalization method, the average absolute value of the relative errors in the fan exit total pressure, HPC exit static pressure, EGT, and high-pressure spool speed in the validation dataset were 2.91 %, 2.20 %, 5.32 %, and 1.84 %, respectively, whereas for an engine model adapted using the proposed machine learning-based functionalization method, these errors were 0.70 %, 1.00 %, 2.56 %, and 0.26 %, respectively, under the same conditions. As a result, it was confirmed that the performance prediction accuracy of the engine model adapted using the proposed method was improved compared to the existing method. [ABSTRACT FROM AUTHOR]

Precision current detection is essential in smart power switches. In this paper, a current-sensing amplifier with symmetric topology is presented, which adopts the chopping technique to improve sensing accuracy. This design offers four advantages at the same time. Firstly, the rail-to-rail complementary differential pairs are achieved to obtain a full input voltage swing, and the Class AB output stage is incorporated to increase the slew rate. Secondly, symmetric topology with the current shunt source provides moderate gain enhancement without extra power consumption and further increases the gain bandwidth product. Thirdly, the chopping technique is applied to achieve a significant reduction in the amplifier's input offset without an extra low pass filter. Fourthly, the constant G M -C biasing circuit is introduced to improve the robustness of system response and current sensing accuracy under process variations. The four advantages can be substantiated through the application of a 0.5-μm BCD technology process, with multiple simulation results, including frequency responses and current sensing accuracy in process corners and temperature variations. The mismatch Monte-Carlo and noise analyses are also conducted with the chopper on or off. Chip experimental results show that the current sensing error is within ±1.6 % from 0.01 A to 3 A load current. Furthermore, multiple tests have been conducted to determine the absolute values of the input offset voltages, ranging between 20 μV and 50 μV, which is a relatively small amount to vastly improve the sensing accuracy. [ABSTRACT FROM AUTHOR]

For layered models with a low-velocity half-space, Rayleigh waves can exhibit inversely dispersive patterns and thus are advantageous for providing useful information on the seismic properties of such structures. However, the calculation of dispersion curves usually encounters some difficulties such as root skipping or numerical instability due to the presence of leaky modes. The full-wavefield method and spectral element method can offer better solutions but at the cost of a significant computational effort. For practical applications, most researchers treat the zeros of the real part of the secular function as an approximation to the leaky modes, which may lead to relatively large errors that cannot be ignored. Instead, in this paper, we propose a simple and efficient method to approximate the leaky mode based on the local minima of the absolute value of the secular function. Compared with the dispersion curve generated from the real part of the secular function, the proposed method can provide a more accurate approximation. We further apply a new efficient Monte Carlo search technique to two synthetic datasets and a permafrost example. Results show that our forward and inverse methods are effective, efficient, and robust. Moreover, our numerical experiments indicate that the modified Thomson-Haskell method is more suitable for calculating leaky modes compared with the fast delta method and the generalized reflection/transmission method, and that the inversion results are less sensitive to the effect of the limited spread length on the measured dispersion curves. The present study emphasizes the high efficiency of the proposed method in imaging permafrost structures and foundation features of buildings or roads. • A fast solver for calculating the apparent modes due to a low-velocity half-space. • The modified Thomson-Haskell method is more suitable for calculating the leaky modes. • Application for imaging permafrost structures. [ABSTRACT FROM AUTHOR]

The matching energy of a graph G , denoted by M E (G) , is defined as the sum of absolute values of the zeros of the matching polynomial of G. In this paper, we would like to present some lower bounds for M E (G). For any connected graph G , it is proved that M E (G) ≥ 2 μ (G) , where μ (G) is the matching number of G. Also it is shown that if G has no perfect matching, then M E (G) ≥ 2 μ (G) + 1 , except for K 1 , 2. We characterize some class of graphs whose matching energy is at least equal to the number of vertices. It is shown that if G is a connected graph of order n , such that the multiplicity of 0 as a matching root is 1, then M E (G) > n , except for K 1 , 2. Also, it is proved that in a connected graph G of order n , if the multiplicity of 0 as a matching root is 2, then M E (G) > n with only four exceptions. [ABSTRACT FROM AUTHOR]

Lambda wing, as a commonly used configuration for modern combat aircraft, tend to reduce stability margin known as Pitch-Break before the wing completely stalls. This phenomenon greatly affected the safety of aircraft at high angles of attack. In this paper, the characteristics of Pitch-Break are clarified and it is found that the initial airflow separation position of the outer wing is the principal reason for generating nonlinear moment of lambda wing. The airflow separation position is generally affected by leading edge vortex and the trailing edge spanwise airflow. Furthermore, the following conclusions are obtained: 1. The distribution of the absolute value of the leading edge radius is a decisive parameter of the initial position of leading edge vortex at the beginning of Pitch-Break zone; 2. The difference of trailing edge pressure gradient brings difference of trailing edge spanwise airflow at the end of Pitch-Break zone. To solve the aerodynamic problem of Pitch-Break, this paper adopts an all moving wingtip (AMT) as auxiliary aileron which has minor fluctuations during the Pitch-Break zone compared with conventional aileron. The result shows the defect of the conventional aileron pitch control at high angle of attack and presents the engineering feasibility of the all moving wingtip auxiliary aileron. [ABSTRACT FROM AUTHOR]

In this paper, we analyze the existence of solutions of tensor absolute value equation (TAVE) and propose a SOR-type iteration algorithm for solving this equation. First, we introduce the interval tensor, which is the main tool for proving the unique solvability of TAVE. Then we present a sufficient condition for TAVE to have a unique solution. Furthermore, we propose a SOR-type iteration algorithm for solving TAVE. The convergence of the proposed algorithm is analysed under suitable assumptions. Finally, numerical experiments illustrate that our algorithm is feasible and effective. [ABSTRACT FROM AUTHOR]

Let G be a connected graph and let T be an acyclic set of edges of G. A partial orientation σ of G with respect to T is an orientation of the edges of G except those edges of T , the resulting graph associated with which is denoted by G T σ. In this paper we prove that there exists a partial orientation σ of G with respect to T such that the largest eigenvalue of the Hermitian adjacency matrix of G T σ is at most the largest absolute value of the roots of the matching polynomial of G. [ABSTRACT FROM AUTHOR]

• A simple and effective ridge valley point recognition method is present, which greatly reduces the number of potential feature points and improves the robustness of the recognition. • A freeform feature enhancement algorithm based on position and normal constraints is proposed. By different settings, several enhancement effects can be realized, such as preserving the original shape as much as possible, sharpen it or recovering a totally sharp edge. • A point cloud parameterization method based on feature line guidance is introduced to reduce the number of unknowns by 2/3 and eliminate the lateral sliding of points. [Display omitted] Ridge-valley features are important elements of a model. To recognize these features from point cloud, this paper introduces a new criterion named Extremal Point Distance (EPD) to greatly reduce the number of potential feature points and locate feature position more accurately. On this basis, a feature enhancement algorithm is proposed. The algorithm adjusts the coordinates of feature regions by minimizing a linear objective function consisting of expected position and normal, which can ensure the accurate sampling of feature position. We also present a parameterization method to eliminate the lateral sliding of feature points and reduce the number of unknowns in the objective function. Since the EPD criterion only depends on the changing trend, rather than the absolute value of the curvature, our algorithm can infer the expected position and normal with a large neighborhood radius, which makes it robust to noise. Experiments show that our algorithm can adjust the feature amplitude and sharpness freely, and achieve satisfactory results in feature recognition, feature enhancement and sharp feature restoration. [ABSTRACT FROM AUTHOR]

To assess the global sagittal balance of spine (GSBS) in asymptomatic controls. PubMed, Scopus, Cochrane library, and Web of Science searched up to July 2020. Studies were screened for the GSB parameters including T1 pelvic angle (TPA), spinosacral angle (SSA), sagittal vertical axis (SVA), C7/sacrofemoral distance ratio (Barrey index), odontoid hip axis (OD-HA), and Full Balance Index (FBI) as measured in asymptomatic participants. A meta-analysis was performed to synthesize pooled estimates. Heterogeneity and publication bias were assessed. Overall, 76 studies were identified including 12,169 participants (54.7% female) with mean age ranges from 12.0 to 72.9 years old. We used the Newcastle–Ottawa Scale (NOS) to evaluate the quality of studies included in this review. Begg's test did not indicate obvious publication bias. The pooled analysis reveals that the mean (standard deviation) normative values were: 1) age ˃18 years, SSA (°), 127.6 (0.89); SVA absolute value (millimeters), 13.1 (1.13); TPA (°), 9.8 (1.13); T1SPI (°), –4.3 (0.57); and Barrey index absolute value, 0.51 (0.3). The mean value of the OD-HA (°) was reported 2.9 (1.6), and the FBI average value was less than 5°. 2) Age ≤18 years, SSA (°), 132.1 (8.3); SVA absolute value (millimeters), 11.9 (2.0); and Barrey index, –0.7 (8.3). A significant difference was observed between the 2 age groups based on SVA and SSA. This paper presents normative data on TPA, SSA, SVA, Barrey index, OD-HA, and FBI as a reference for evaluating/measuring a GSB of spine in asymptomatic controls. [ABSTRACT FROM AUTHOR]

In this paper, a type of fractional-order quaternion-valued neural networks (FOQVNNs) with leakage and time-varying delays is established to simulate real-world situations, and the global Mittag-Leffler stability of the system is investigated by using the non-decomposition method. First, to avoid decomposing the system into two complex-valued systems or four real-valued systems, a new sign function for quaternion numbers is introduced based on the ones for real and complex numbers. And two novel lemmas for quaternion-valued sign function and Caputo fractional derivative are established in quaternion domain, which are used to investigate the stability of FOQVNNs. Second, a concise and flexible quaternion-valued state feedback controller is directly designed and a novel 1-norm Lyapunov function composed of the absolute values of real and imaginary parts is established. Then, based on the designed quaternion-valued state feedback controller and the proposed lemmas, some sufficient conditions are given to ensure the global Mittag-Leffler stability of the system. Finally, a numerical simulation is given to verify the theoretical results. [ABSTRACT FROM AUTHOR]

In this paper, an inverse-free dynamical system is built to solve the absolute value equations (AVEs), whose equilibrium points coincide with the solutions of the AVEs. Under proper assumptions, the equilibrium points of the dynamical system exist and could be (globally) asymptotically stable. In addition, with strongly monotone property, a global projection-type error bound is provided to estimate the distance between any trajectories and the unique equilibrium point. Compared with four existing dynamical systems for solving the AVEs, our method is inverse-free and is still valid even if 1 is an eigenvalue of the coefficient matrix. Some numerical simulations are given to show the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

To explore an air-fireable and economically functional phase for thick-film resistors, the crystal structure, microstructure, sintering, and resistive properties of LaCo 0·4 Ni 0.6−x Mg x O 3 (LCNM, x = 0.00–0.08) ceramics are studied in this paper, based on solid-state reaction experiments and theoretical calculations. With Mg-ion increase, the impurity phases of NiO and La 3 Ni 4 O 10 increased, the maximum shrinkage rate occurred at a higher temperature, and the microstructures became worse. The addition of the Mg ion increased the resistivity and decreased the temperature coefficient of resistivity (TCρ). The calculation results, including the bond population, electron density distribution, and density of states of the system agreed with the change in experimental resistivity. Relatively low resistivity and TCρ with a small absolute value could be achieved for specimens with x ≤ 0.02 sintered at 1200 °C and 1250 °C. Hence, the LCNM (x ≤ 0.02) ceramics are possible functional material for thick-film resistors. [ABSTRACT FROM AUTHOR]

The distribution of ranked heights of excursions of a Brownian bridge is given by Pitman and Yor (2001). In this work, we consider excursions of a Brownian excursion above a random level x , where x is the value of the excursion at an independent uniform time on [0,1]. We study the maximum heights of these excursions as Pitman and Yor did for excursions of a Brownian bridge. In particular, the probability functions and the moments of the sum of the j th highest maximum over an excursion above x and the absolute value of the k th lowest minimum over an excursion below x , including j = 1 and k = 2 , are computed in this paper. [ABSTRACT FROM AUTHOR]

The energy of a graph G , E (G) , is the sum of absolute values of the eigenvalues of its adjacency matrix. This concept was extended by Nikiforov to arbitrary complex matrices. Recall that the trace norm of a digraph D is defined as, N (D) = ∑ i = 1 n σ i , where σ 1 ≥ ⋯ ≥ σ n are the singular values of the adjacency matrix of D. In this paper we would like to present some lower and upper bounds for N (D). For any digraph D it is proved that N (D) ≥ rank (D) and the equality holds if and only if D is a disjoint union of directed cycles and directed paths. Finally, we present a lower bound on σ 1 and N (D) in terms of the size of digraph D. [ABSTRACT FROM AUTHOR]

The fusion of infrared (IR) and visible images should not only increase the brightness of the infrared targets, but also preserve more details in visible images. A fusion approach to infrared and visible images with Gabor filter and sigmoid function is proposed in this paper. In order to make targets prominent in the fused image, the IR image is normalized by the sigmoid function to get a mapping matrix W, and then the visible image is enhanced by the matrix W to obtain an enhanced visible image, so that the contrast between the target and the background in the visible image is enhanced. After the decomposition of the IR image, the visible image and the enhanced visible image with Gabor filter, the detail layers of the visible image and the enhanced visible image are fused using the "max-absolute" rule, and the base layers are fused using the rule of weighted summation, which greatly increases the amount of information in the visible image. The weighted summation is calculated for the basic layers of the infrared and fused visible image, and the absolute maximum value is calculated for their detail layers. Finally, the fused image is generated by a linear combination of the final detail layer and the final base layer. Nine existing algorithms with better performance and the algorithm proposed in this paper are tested on public datasets, and use six evaluation metrics such as average gradient (AG), cross entropy (CE), edge gradient (EI), information entropy (IE), peak signal-to-noise ratio (PSNR) and spatial frequency (SF) to evaluate the quality of the fused image. Experiments show that the new algorithm has achieved better visual effects, and most of the objective evaluation metrics are also better than other algorithms. In particular, the low-light image is enhanced by the sigmoid function and then fused, so that the fused image is clearer and the target is more prominent. The gradient information is retained in the fused image as much as possible. All these prove the advantage and effectiveness of the new algorithm. • The visible image is enhanced by a mapping matrix gotten from the IR image using the sigmoid function. • The base and detail layer of the image are generated by the real and imaginary parts of the Gabor filter. • Using the weighted sum rule to fuse base layers of the visible image and the enhanced visible image. • The base layers of the infrared image and the fused visible image are fused using the mapping matrix W. [ABSTRACT FROM AUTHOR]

In 2011, Haemers asked the following question: If S is the Seidel matrix of a graph of order n and S is singular, does there exist an eigenvector of S corresponding to 0 which has only ±1 elements? In this paper, we construct infinite families of graphs which give a negative answer to this question. One of our constructions implies that for every natural number N , there exists a graph whose Seidel matrix S is singular such that for any integer vector in the nullspace of S , the absolute value of any entry in this vector is more than N. We also derive some characteristics of vectors in the nullspace of Seidel matrices, which lead to some necessary conditions for the singularity of Seidel matrices. Finally, we obtain some properties of the graphs which affirm the above question. [ABSTRACT FROM AUTHOR]

Let X be a graph with adjacency matrix A. The continuous quantum walk on X is determined by the unitary matrices U (t) = exp ⁡ (i t A) (for t ∈ R). If X is the complete graph K n and a ∈ V (X) , then 1 − | U (t) a , a | ≤ 2 / n. Roughly speaking, this means that a quantum walk on a complete graph stays home with high probability. We say that a family of graphs is sedentary if there is a constant c such that 1 − | U (t) a , a | ≤ c / | V (X) | for all t. In this paper we investigate this condition, and produce further examples of sedentary graphs. A cone over a graph X is the graph we get by adjoining a new vertex and making it adjacent to each vertex of X. We prove that if X is the cone over an ℓ -regular graph on n vertices, then | U (t) a , a | ≤ ℓ 2 / (ℓ 2 + 4 n). It follows that if we choose ℓ and n such that n / ℓ 2 → 0 , then a continuous quantum walk starting on the "conical" vertex will remain there with probability close to 1. On the other hand, if ℓ ≤ 2 , we show there is a time t such that all entries in the a -column of U (t) e a have absolute value 1 / n. We show that there are large classes of strongly regular graphs such that 1 − | U (t) a , a | ≤ c / V (X) for some constant c. On the other hand, for Paley graphs on n vertices, we prove that if t = π / n , then | U (t) a , a | ≤ 1 / n. [ABSTRACT FROM AUTHOR]

In order to improve the reliability of precise time comparison, this paper takes advantage of long-term stability of TWSTFT (Two-Way Satellite Time and Frequency Transfer) and short-term stability of PPP (GPS Precise Point Positioning). Stability weighting, Vondrák-Čepek combined filtering, and Kalman filtering methods are applied to fuse the TWSTFT and GPS PPP time comparison between the NTSC (National Time Service Center) and PTB (Physikalisch-Technische Bundesanstalt). The results show that the three fusion methods all improve the diurnal variations in TWSTFT and the discontinuities in GPS PPP solution, and the absolute value of the DCD (Double Clock Difference) between fusion results and PPP solution is kept within the link calibration uncertainty. The 1 d time and frequency stability of the three methods can reach the order of sub-nanosecond and 10 − 15 , respectively. The Vondrák-Čepek fusion method has the highest stability within 1 d, which is suitable for the fusion of time comparison links with requirements for short stability. Stability weighting and Kalman filtering fusion have better fidelity, which are suitable for the fusion of time comparison links that require high accuracy. [ABSTRACT FROM AUTHOR]