Formänderungsgrößenverfahren mittig gedrückter dünnwandiger Stäbe mit einfach‐ und doppeltsymmetrischen offenen Querschnitten

Deformation method for centrically compressed thin‐walled bars with mono‐ and bisymmetrical open cross‐sections. In correspondence with the classic deformation method of warping torsion for thin‐walled bars [1], that method has been moved into the field of column stability. For the single cross‐sectional symmetry, the general solution of the fundamental system of equations has been found and its particular shapes for three basic kinds of column support presented. Thereby, the formulas or the boundary simplified for analysis of the bimoments have been settled. These relations have been simplified for the double cross‐sectional symmetry. An analysis of a bisymmetrical cross‐section has lead to the determination of the necessary boundary forces for the three kinds of column support considered. It has been shown that all the relations for torsion are similar to those for bending. A proposal for the calculations of the critical loads of torsional buckling in continuous columns has been formulated and a relevant numerical example given. The paper calls special attention to the related merits of Professor Kurt Klöppel , a graduate of the former Technischen Hochschule Danzig. Actually, already 100 years have passed since the foundation of TH Danzig. It is also the predecessor of the contemporary Politechnika Gdańska, with which the author is being connected since 1949.     

Results demonstrating techniques for enhancing electrochemical reactions involving iron oxide in slags and C in liquid iron

Two techniques are described for the enhancement of the kinetics of reduction of iron oxide from slags by carbon in molten iron. Laboratory experiments have shown that the rate of iron oxide reduction by carbon-saturated iron can be increased by 5 to 10 times when the reaction is carried out under a reduced-pressure atmosphere. This effect is thought to be the result of the increased volumetric gas evolution through the slag layer and the associated increase in slag stirring. A model is presented, which relates the mass-transfer coefficient for ferrous ions in the slag to its stirring that is controlled by varying the ambient pressure. Additional laboratory experiments examined the electrochemical nature of iron oxide reduction from slag by carbon in liquid iron. Results indicate that the reduction of iron oxide from slag is increased in the presence of an applied electric field. The external circuit allows for the separation of the half-cell reactions associated with iron oxide reduction and decarburization and increases the reaction area available for the individual reactions. These results have significant implications for several important slag metal reactions, which occur during ironmaking and steelmaking operations.     

Chalcogenide Glasses Based on Germanium Disulfide for Second Harmonic Generation

High second‐order susceptibilities are created by thermal poling in bulk germanium disulfide based chalcogenide glasses. Experimental conditions of the poling treatment (temperature, voltage, time) were optimized for each glass composition. The second‐order nonlinear signals were recorded by using the Maker fringes experiment and a second‐order coefficient χ⁽²⁾ up to 8 pm V^–1 was measured in the Ge₂₅Sb₁₀S₆₅ glass. This value is obtained using a simulation based on accurate knowledge of the thickness of the nonlinear layer. Two mechanisms are proposed to explain the creation of a nonlinear layer under the anode: the formation and the migration of charged defects towards the anode may mainly occur in Ge₂₀Ga₅Sb₁₀S₆₅ and Ge₂₅Ga₅S₇₀ glasses, whereas the migration of Na⁺ ions towards the cathode may be responsible for the accumulation of negative charges under the anode in Ge₃₃S₆₇ and Ge₂₅Sb₁₀S₆₅ glasses. Different electronic conductivity behaviors seem to be at the origin of the phenomenon. In parallel, the potential effect of the poling treatment on the structural and electronic properties is studied using Raman spectroscopy and secondary ion mass spectroscopy measurements.     

Machine Learning-Based Predictions of Customers’ Decisions in Car Insurance

Predicting customer decisions allows companies to obtain higher profits due to better resource management. The accuracy of those predictions can be currently boosted by the application of machine learning algorithms.

We propose a new method to predict a car driver’s decision about taking a replacement car after a vehicle accident happens. We use feature engineering to create attributes of high significance. The generated attributes are related to time (e.g., school holidays), place of collision (e.g., distance from home), time and conditions (e.g., weather), vehicles (e.g., vehicle value), addresses of both the victim and the perpetrator. Feature engineering involves external sources of data.

Five machine learning methods of classification are considered: decision trees, multi-layer perceptrons, AdaBoost, logistic regression and gradient boosting. Algorithms are tested on real data from a Polish insurance company. Over 80% accuracy of prediction is achieved. Significance of the attributes is calculated using the linear vector quantization method.

Presented work shows the applicability of machine learning in the car insurance market.     

Analysis of maintenance policies for finite life-cycle multi-state systems

Maintenance policies for multi-state systems (MSS) are often analyzed under infinite horizon assumptions. In practice, it is important to consider maintenance policies under a finite horizon because the life cycles of most systems are finite. In this paper, we consider a finite life-cycle MSS that is subject to both degradation and Poisson failures. We study two classes of maintenance policies – preventive replacements and corrective replacements, and their effectiveness in controlling the customer’s expected discounted maintenance cost (EDMC). For both policies, replacement decisions are modelled via two control parameters – a threshold on the current system state and a threshold on the residual life cycle, which is measured as the time span from present to the end of life cycle. We derive close-to-explicit forms of the cost models under each of the policy. Methodologies for optimizing the maintenance thresholds are further proposed. Computational results verify that preventive replacements outperform corrective replacements typically when the downtime cost per failure is relatively high compared to the repair cost.     

Scheduling Algorithms and Throughput Maximization for the Downlink of Packet-Data Cellular Systems with Multiple Antennas at the Base Station

The capacity-achieving coding scheme for the multiple-input multiple-output (MIMO) broadcast channel is dirty-paper coding. With this type of transmission scheme the optimal number of active users that receive data and the optimal power allocation strategy are highly dependent on the structure of the channel matrix and on the total transmit power available. In the context of packet-data access with adaptive transmission where mobile users are equipped with a single receive antenna and the base station has multiple transmit antennas, we study the optimal number of active users and the optimal power allocation. In the particular case of two transmit antennas, we prove that the optimal number of active users can be a non-monotonic function of the total transmit power. Thus not only the number of users that should optimally be served simultaneously depends on the user channel vectors but also on the power available at the base station transmitter. The expected complexity of optimal scheduling algorithms is thus very high. Yet we then prove that at most as many users as the number of transmit antennas are allocated a large amount of power asymptotically in the high-power region in order to achieve the sum-capacity. Simulations confirm that constraining the number of active users to be no more than the number of transmit antennas incurs only a marginal loss in spectral efficiency. Based on these observations, we propose low-complexity scheduling algorithms with sub-optimal transmission schemes that can approach the sum-capacity of the MIMO broadcast channel by taking advantage of multiuser diversity. The suitability of known antenna selection algorithms is also demonstrated. We consider the cases of complete and partial channel knowledge at the transmitter. We provide simulation results to illustrate our conclusions.     

Interaction of guided light in rib polymer waveguides with dielectrophoretically controlled nanoparticles

This work demonstrates an optofluidic system, where dielectrophoretically controlled suspended nanoparticles are used to manipulate the properties of an optical waveguide. This optofluidic device is composed of a multimode polymeric rib waveguide and a microfluidic channel as its upper cladding. This channel integrates dielectrophoretic (DEP) microelectrodes and is infiltrated with suspended silica and tungsten trioxide nanoparticles. By applying electrical signals with various intensities and frequencies to the DEP microelectrodes, the nanoparticles can be concentrated close to the waveguide surface significantly altering the optical properties in this region. Depending on the particle refractive indices, concentrations, positions and dimensions, the light remains confined or is scattered into the surrounding media in the microfluidic channel.     

On reliability of a certain elementary safety system

The paper deals with the determination of reliability of an elementary safety system which consists of two identical elements used simultaneously (hot reserve) whereas for correct system operation is enough when one out of it is good. The operation time is so short that is assumed it is of zero length. Knowing the reliability of element, reliability of system is found.     

Phase unwrapping for 2-D blind deconvolution of ultrasound images

In most approaches to the problem of two-dimensional homomorphic deconvolution of ultrasound images, the estimation of a corresponding point-spread function (PSF) is necessarily the first stage in the process of image restoration. This estimation is usually performed in the Fourier domain by either successive or simultaneous estimation of the amplitude and phase of the Fourier transform (FT) of the PSE This paper addresses the problem of recovering the FT-phase of the PSF, which is an important reconstruction problem by itself. The purpose of this paper is twofold. First, it provides a theoretical framework, establishing that the FT-phase of the PSF can be effectively estimated by a proper smoothing of the FT-phase of the appropriate radio-frequency (RF) image. Second, it presents a novel approach to the estimation of the FT-phase of the PSF, by solving a continuous Poisson equation over a predefined smooth subspace, in contrast to the discrete Poisson equation solver used for the classical least mean squares phase unwrapping algorithms, followed by a smoothing procedure. The proposed approach is possible due to the distinct properties of the FT-phases, among which the most important property is the availability of precise values of their partial derivatives. This property overcomes the main disadvantage of the discrete schemes, which routinely use wrapped (principal) values of the phase in order to approximate its partial derivatives. Since such an approximation is feasible subject to the restriction that the partial phase differences do not exceed pi in absolute value, the discrete schemes perform satisfactory only for few practical situations. The proposed approach is shown to be independent of this restriction and, thus, it performs for a wider class of the phases with significantly lower errors. The main advantages of the novel method over the algorithms based on discrete schemes are demonstrated in a series of computer simulations and for in vivo measurements.