A Simple Algorithm for Optimal Search Trees with Two-way Comparisons

We present a simple O(n 4 ) -time algorithm for computing optimal search trees with two-way comparisons. The only previous solution to this problem, by Anderson et al., has the same running time but is significantly more complicated and is restricted to the variant where only successful queries are allowed. Our algorithm extends directly to solve the standard full variant of the problem, which also allows unsuccessful queries and for which no polynomial-time algorithm was previously known. The correctness proof of our algorithm relies on a new structural theorem for two-way-comparison search trees.

A position control-based approach to haptic rendering of stiff objects using piece-wise linear model

In traditional force rendering approaches, it is quite popular to model a virtual stiff wall as a spring-damper system to compute the interaction force, which can easily lead to unstable behavior. In this paper, we present an approach to ensure no penetration into the wall by position control. The approach approximates the nonlinear model of a 6-DOF parallel-structure haptic device by a piece-wise linear model to improve the performance compared with a controller designed from a one-point linearized model in haptic rendering. A simulation-based performance comparison study shows that the new controller can render higher stiffness than the previous solution.

LinGAN: an Advanced Model for Code Generating based on Linformer

Parsing natural language to corresponding programming language attracts much attention in recent years. Natural Language to SQL(NL2SQL) widely appears in numerous practical Internet applications. Previous solution was to convert the input as a heterogeneous graph which failed to learn good word representation in question utterance. In this paper, we propose a Relation-Aware framework named LinGAN, which has powerful semantic parsing abilities and can jointly encode the question utterance and syntax information of the object language. We also propose the pre-norm residual shrinkage unit to solve the problem of deep degradation of Linformer. Experiments show that LinGAN achieves excellent performance on multiple code generation tasks.

Solitons in a PT -symmetric grating-assisted co-directional coupler

We explore a co-directional coupling arrangement between two waveguides mediated by a PT-symmetric sinusoidal grating characterized by an index-modulation parameter κ and a gain/loss parameter g. We show that the device supports soliton-like solutions for both the PT -conserving regime g < κ and the PT -broken regime g > κ. In the first case the coupler exhibits a gap in wave-number k and the solitons can be regarded as an extension of a previous solution found for pure index modulation. In the second case the coupler exhibits a gap in frequency ω and the solutions are entirely new.

Food web reconstruction through phylogenetic transfer of low-rank network representation

Despite their importance in many ecological processes, collecting data and information on ecological interactions, and therefore species interaction networks, is an exceedingly challenging task. For this reason, large parts of the world have a deficit of data of which species interact, and what we can expect the network structure of these interactions to be. As data collection alone is unlikely to be sufficient at filling these global gaps, community ecologists must adopt predictive methods. In this contribution we develop such a method, relying on graph embedding (the extraction of explanatory latent variables from known graph structures) and transfer learning (the application of previous solution to novel problems with limited predictors overlap) in order to assemble a predicted list of trophic interactions between mammals of Canada. This interaction list is derived from extensive knowledge of the mammalian food web of Europe, despite the fact that there are fewer than 5% of common species between the two locations. We provide guidance on how this method can be adapted by substituting some approaches or predictors in order to make it more generally applicable to a broad family of ecological problems.

Optimized location of light sources to cover a rectangular region

The problem we considered was proposed by an industrial partner. The aim is to locate light sources around a rectangular field such that the areas these illuminate cover the whole field. We assume these illuminated areas to be rectangular as well, parallel to the field. Covering an area with multiple lights is allowed. There are several types of light sources, priced differently with different sizes of their illuminated area. We aim to minimize the cost of the cover. We propose a constraint generation approach for solving this covering problem. We formulate a MIP model to locate the light sources such that a finite number of predetermined points have to be covered. The result does not necessarily solve the original problem, i.e. it does not cover the whole field. Therefore, a constraint generation model is built to calculate a non-covered point such that the first model has to improve its previous solution to cover this new point as well. If no uncovered point is found, the result is an optimal covering, thus we stop. We have also designed some set of additional constraints to exclude symmetrical solutions, to speed up the algorithm. We analyze the efficiency of the additional constraints and report some computational results in realistic settings.

A simple and effective algorithm for the maximum happy vertices problem

In a recent paper, a solution approach to the Maximum Happy Vertices Problem has been proposed. The approach is based on a constructive heuristic improved by a matheuristic local search phase. We propose a new procedure able to outperform the previous solution algorithm both in terms of solution quality and computational time. Our approach is based on simple ingredients implying as starting solution generator an approximation algorithm and as an improving phase a new matheuristic local search. The procedure is then extended to a multi-start configuration, able to further improve the solution quality at the cost of an acceptable increase in computational time.

Contact stress in helical bevel gears

Helical bevel gears have inclined or twisted teeth on a conical surface and the common types are skew, spiral, zerol, and hypoid bevel gears. However, this study does not include hypoid bevel gears. Due to the geometric complexities of bevel gears, commonly used methods in their design are based on the concept of equivalent or virtual spur gear. The approach in this paper is based on the following assumptions, a) the helix angle of helical bevel gears is equal to mean spiral angle, b) the pitch diameter at the backend is defined as that of a helical gear, and c) the Tredgold's approximation is applied to the helical gear. Upon these premises, the contact stress capacity of helical bevel gears is formulated in explicit design parameters. The new contact stress capacity model is used to estimate the contact stress in three gear systems for three application examples and compared with previous solutions. Differences between the new estimated results and the previous solutions vary from -3% and -11%, with the new estimates being consistently but marginally or slightly lower than the previous solution values. Though the differences appear to be small, they are significant because the durability of gears is strongly influenced by the contact stress. For example, a 5% reduction in contact stress may result in almost 50% increase in durability in some steel materials. The equations developed do not apply to bevel crown gears.

EDGE PRESERVING CNN SAR DESPECKLING ALGORITHM

SAR despeckling is a key tool for Earth Observation. Interpretation of SAR images are impaired by speckle, a multiplicative noise related to interference of backscattering from the illuminated scene towards the sensor. Reducing the noise is a crucial task for the understanding of the scene. Based on the results of our previous solution KL-DNN, in this work we define a new cost function for training a convolutional neural network for despeckling. The aim is to control the edge preservation and to better filter man-made structures and urban areas that are very challenging for KL-DNN. The results show a very good improvement on the not homogeneous areas keeping the good results in the homogeneous ones. Result on both simulated and real data are shown in the paper.

Electrochemical study of carbon steel protection with a superhydrophobic coating under conditions of 100% humidity and the presence of corrosion stimulants in the air

100% humidity and the presence in the air of such corrosion stimulants as CO2, NH3 and H2S are characteristic of livestock buildings. Under these conditions, a surface phase film of moisture is formed on the surface of the metals in which the indicated micro-mixtures of air are dissolved and hydrated almost completely with the formation of NH4OH and acids H2CO3 and H2S. The potentiodynamic polarization method was used to study the corrosion and kinetics of electrode processes on steel with a superhydrophobic coating in a NaCl background solution (used to provide sufficient electrical conductivity) saturated in pairs with CO2 and NH3, NH3 and H2S. Similar studies were conducted with uncoated electrodes. Superhydrophobic coating was obtained on the basis of laser texturing of the surface with subsequent hydrophobization with fluoroxysilane (wetting angle 165±2°, rolling angle 3±1°). The influence of the duration of the exposure of the electrodes in solution (0,25…168 h) on the kinetics of electrode processes and the corrosion rate of steel is considered. In the presence of CO2 and NH3 dissolution products, the corrosion rate of an electrode with a superhydrophobic coating on the second and third days of exposure is about an order of magnitude, and on the fourth and seventh days it is more than an order of magnitude lower than without coating. During the entire time the electrodes are in solution, the anode process on the superhydrophobic electrode is inhibited compared to an unprotected electrode. The medium containing the dissolution products of NH3 and H2S is more aggressive than the previous solution. Therefore, the corrosion rate of the electrodes without coating and with a coating here is higher than in the latter one. The corrosion rate of electrodes with superhydrophobic coating in the study period is only 1,5…2,5 times lower than that of uncoated electrodes. During the first day of exposure, the anode process is inhibited, and in the next 144 hours, on the contrary, it is facilitated in comparison with an unprotected electrode. Taking into account the corrosivity of the chloride solution, the possible effect of the dissolution products of aggressive air micro-impurities in the absence of background salt was analyzed.