Brno University of Technology

About: Brno University of Technology is a education organization based out in Brno, Czechia. It is known for research contribution in the topics: Computer science & Fracture mechanics. The organization has 6339 authors who have published 15226 publications receiving 194088 citations. The organization is also known as: Vysoké učení technické v Brně & BUT.

The Parallel Bayesian Optimization Algorithm

Abstract: In the last few years there has been a growing interest in the field of Estimation of Distribution Algorithms (EDAs), where crossover and mutation genetic operators are replaced by probability estimation and sampling techniques. The Bayesian Optimization Algorithm incorporates methods for learning Bayesian networks and uses these to model the promising solutions and generate new ones. The aim of this paper is to propose the parallel version of this algorithm, where the optimization time decreases linearly with the number of processors. During the parallel construction of network, the explicit topological ordering of variables is used to keep the model acyclic. The performance of the optimization process seems to be not affected by this constraint and our version of algorithm was successfully tested for the discrete combinatorial problem represented by graph partitioning as well as for deceptive functions.

Symmetrical current?voltage characteristic of a metal?semiconductor?metal structure of Schottky contacts and parameter retrieval of a CdTe structure

Abstract: Symmetrical, non-linear and current–voltage (I–V) characteristics of a metal–semiconductor–metal (M-S-M) structure of two metallic Schottky contacts fabricated to a p-type semiconductor were modeled by treating the semiconductor as a resistor sandwiched between two identical head-to-head Schottky barriers. The voltage distributions along the M-S-M structure were numerically determined and found that the voltage drop across the reverse-biased Schottky barrier is dominating at the low bias voltage, and the dominant range depends on the value of the resistor of the semiconductor bulk. The field dependence of barrier height due to the image force was proposed to be the mechanism for the current through the M-S-M structure when the voltage drop across the reverse-biased barrier is dominating. The proposed model was applied to the I–V curves measured at different temperatures on low-resistivity p-type CdTe with Au contacts and the density of the effective acceptors calculated, and the zero-field Schottky barrier height and the Richardson constant were extracted using the activation energy method. The extracted parameters fitted well with that published for the same material structure.

Semi-supervised bootstrapping approach for neural network feature extractor training

Abstract: This paper presents bootstrapping approach for neural network training The neural networks serve as bottle-neck feature extractor for subsequent GMM-HMM recognizer The recognizer is also used for transcription and confidence assignment of untranscribed data Based on the confidence, segments are selected and mixed with supervised data and new NNs are trained With this approach, it is possible to recover 40-55% of the difference between partially and fully transcribed data (3 to 5% absolute improvement over NN trained on supervised data only) Using 70-85% of automatically transcribed segments with the highest confidence was found optimal to achieve this result

Incremental Block Cholesky Factorization for Nonlinear Least Squares in Robotics

Abstract: Efficiently solving nonlinear least squares (NLS) problems is crucial for many applications in robotics. In online applications, solving the associated nolinear systems every step may become very expensive. This paper introduces online, incremental solutions, which take full advantage of the sparseblock structure of the problems in robotics. In general, the solution of the nonlinear system is approximated by incrementally solving a series of linearized problems. The most computationally demanding part is to assemble and solve the linearized system at each iteration. In our solution, this is mitigated by incrementally updating the factorized form of the linear system and changing the linearization point only if needed. The incremental updates are done using a resumed factorization only on the parts affected by the new information added to the system at every step. The sparsity of the factorized form directly affects the efficiency. In order to obtain an incremental factorization with persistent reduced fill-in, a new incremental ordering scheme is proposed. Furthermore, the implementation exploits the block structure of the problems and offers efficient solutions to manipulate block matrices, including a highly efficient Cholesky factorization on sparse block matrices. In this work, we focus our efforts on testing the method on SLAM applications, but the applicability of the technique remains general. The experimental results show that our implementation outperforms the state of the art SLAM implementations on all the tested datasets.

Removal of ammonium from municipal wastewater with powdered and granulated metakaolin geopolymer

Abstract: Ammonium removal from municipal wastewater poses challenges with the commonly used biological processes. Especially at low wastewater temperatures, the process is frequently ineffective and difficult to control. One alternative is to use ion-exchange. In the present study, a novel ion-exchanger, metakaolin geopolymer (MK-GP), was prepared, characterised, and tested. Batch experiments with powdered MK-GP indicated that the maximum exchange capacities were 31.79, 28.77, and 17.75 mg/g in synthetic, screened, and pre-sedimented municipal wastewater, respectively, according to the Sips isotherm (R2 ≥ 0.91). Kinetics followed the pseudo-second-order rate equation in all cases (kp2 = 0.04–0.24 g mg−1 min−1, R2 ≥ 0.97) and the equilibrium was reached within 30–90 min. Granulated MK-GP proved to be suitable for a continuous column mode use. Granules were high-strength, porous at the surface and could be regenerated multiple times with NaCl/NaOH. A bench-scale pilot test further confirmed the feasibility o...