A control algorithm for improving the accuracy of five-axis machine tools

An algorithm for reducing the influence of geometrical, thermal, kinematic and stiffness errors in five-axis machine tool components on the desired tool position and orientation is given. This new algorithm is based on the calculation of the cutting tool error matrix for orthogonal machine tools. In the new model of this matrix, all angular errors of the machine links are considered as infinitesimal rotations. The error matrix is a function of the commanded machine component positions and the errors in these positions. To correct errors in the three translational and two angular tool positions, a matrix of commanded tool position and orientation is multiplied by the inverse error matrix in every period of the tool trajectory interpolation. This corrected matrix of the tool position and orientation provides the inverse kinematics used for calculation of the successive links positions required for achieving the given tool trajectory. The control algorithm for five-axis machine tools with the error compensation is implemented both in the CNC system and in the postprocessor. The proposed algorithm is applied on a vertical five-axis turning centre with two translational and three rotational axes. Twenty-four errors that could cause inaccurate machining are recognised on this machine. The machine links and their coordinate frames are denoted using the Denavit–Hartenberg parameters.     

Dependence of induced transmembrane potential on cell density,arrangement, and cell position inside a cell system

A nonuniform transmembrane potential (TMP) is induced on a cell membrane exposed to external electric field. If the induced TMP is above the threshold value, cell membrane becomes permeabilized in a reversible process called electropermeabilization. Studying electric potential distribution on the cell membrane gives us an insight into the effects of the electric field on cells and tissues. Since cells are always surrounded by other cells, we studied how their interactions influence the induced TMP. In the first part of our study, we studied dependence of potential distribution on cell arrangement and density in infinite cell suspensions where cells were organized into simple-cubic, body-centered cubic, and face-centered cubic lattice. In the second part of the study, we examined how induced TMP on a cell membrane is dependent on its position inside a three-dimensional cell cluster. Finally, the results for cells inside the cluster were compared to those in infinite lattice. We used numerical analysis for the study, specifically the finite-element method (FEM). The results for infinite cell suspensions show that the induced TMP depends on both: cell volume fraction and cell arrangement. We established from the results for finite volume cell clusters and layers, that there is no radial dependence of induced TMP for cells inside the cluster.     

Comparison procedure of predicting the time to default in behavioural scoring

The paper deals with the problem of predicting the time to default in credit behavioural scoring. This area opens a possibility of including a dynamic component in behavioural scoring modelling which enables making decisions related to limit, collection and recovery strategies, retention and attrition, as well as providing an insight into the profitability, pricing or term structure of the loan. In this paper, we compare survival analysis and neural networks in terms of modelling and results. The neural network architecture is designed such that its output is comparable to the survival analysis output. Six neural network models were created, one for each period of default. A radial basis neural network algorithm was used to test all six models. The survival model used a Cox modelling procedure. Further, different performance measures of all models were discussed since even in highly accurate scoring models, misclassification patterns appear. A systematic comparison ‘3 + 2 + 2’ procedure is suggested to find the most effective model for a bank. Additionally, the survival analysis model is compared to neural network models according to the relative importance of different variables in predicting the time to default. Although different models can have very similar performance measures they may consist of different variables. The dataset used for the research was collected from a Croatian bank and credit customers were observed during a 12-month period. The paper emphasizes the importance of conducting a detailed comparison procedure while selecting the best model that satisfies the users’ interest.     

Data envelopment analysis of AGV fleet sizing at a port container terminal

A decision-making approach based on Data Envelopment Analysis (DEA) for determining the efficient container handling processes (considering the number of employed Automated Guided Vehicles (AGVs)) at a port container terminal (PCT) is presented in this paper. Containers are unloaded from the ship by quay cranes and transported to the storage area by AGVs. We defined performance measures of proposed container handling processes and analysed the effects when changing the number of AGVs. The values of performance measures were collected and/or calculated from simulation. Container handling process, with a fixed number of quay cranes, when a different number of AGVs is used to transport containers from berth to assigned locations within storage area, represents a decision-making unit (DMU). We applied the basic CCR (Charnes, Cooper and Rhodes) DEA model with two inputs: average ship operating delay costs and average operating costs of employed equipment at a PCT, and two outputs: average number of handled import containers per ship and weighted average utilisation rate of equipment at a PCT. DEA method proved to be useful when testing different DMUs and when determining efficient DMUs for planning purposes. This study shows that efficiency evaluation of AGV fleet sizing and operations is useful for planning purposes at PCTs.     

Bilberry and blueberry anthocyanins act as powerful intracellular antioxidants in mammalian cells

Berry anthocyanins have pronounced health effects, even though they have a low bioavailability. The common mechanism underlying health protection is believed to relate to antioxidant activity. Berry extracts, chemically characterised for their phenolic content, were prepared from bilberries (Vaccinium myrtillus L.) and blueberries (Vaccinium corymbosum L.); the bilberry extract was further purified to obtain the anthocyanin fraction. The antioxidant activity of each extract was examined at the cellular level. For this purpose a specific assay, known as cellular antioxidant activity assay (CAA), was implemented in different cell lines: human colon cancer (Caco-2), human hepatocarcinoma (HepG2), human endothelial (EA.hy926) and rat vascular smooth muscle (A7r5). Here we show for the first time that anthocyanins had intracellular antioxidant activity if applied at very low concentrations (<1 μg/l; nM range), thereby providing a long-sought rationale for their health protecting effects in spite of their unfavorable pharmacokinetic properties.     

A survey of the lactic acid bacteria isolated from Serbian artisanal dairy product kajmak

Kajmak is an artisanal Serbian dairy product made by fermentation of milk fat. Overall, 374 bacterial isolates were collected from six kajmak samples of different ages produced in the households located in distinct regions of Serbia. In order to identify lactic acid bacteria present in chosen samples of kajmak, total 349 Gram-positive and catalase-negative isolates were analyzed. The recognition of isolates was performed by phenotypic characterization followed by molecular identification using (GTG)(5)-PCR and sequence analysis of 16S rRNA gene. Leuconostoc mesenteroides and Enterococcus faecium were the most frequently isolated species from kajmak samples. In contrast, leuconostocs and enterococci were found in BGMK3 and BGMK1 kajmak respectively, only after using enrichment technique for isolation suggesting they are present in low numbers in these kajmaks. Lactococcus lactis, Lactococcus raffinolactis and Lactococcus garvieae were also found in those samples but in lower proportion. Results showed that Lactobacillus plantarum, Lb. paracasei and Lb. kefiri were the most frequently isolated Lactobacillus species in analyzed kajmaks.     

Effects of Metformin on Spontaneous Ca2+ Signals in Cultured Microglia Cells under Normoxic and Hypoxic Conditions

Microglial functioning depends on Ca²⁺ signaling. By using Ca²⁺ sensitive fluorescence dye, we studied how inhibition of mitochondrial respiration changed spontaneous Ca²⁺ signals in soma of microglial cells from 5–7-day-old rats grown under normoxic and mild-hypoxic conditions. In microglia under normoxic conditions, metformin or rotenone elevated the rate and the amplitude of Ca²⁺ signals 10–15 min after drug application. Addition of cyclosporin A, a blocker of mitochondrial permeability transition pore (mPTP), antioxidant trolox, or inositol 1,4,5-trisphosphate receptor (IP3R) blocker caffeine in the presence of rotenone reduced the elevated rate and the amplitude of the signals implying sensitivity to reactive oxygen species (ROS), and involvement of mitochondrial mPTP together with IP3R. Microglial cells exposed to mild hypoxic conditions for 24 h showed elevated rate and increased amplitude of Ca²⁺ signals. Application of metformin or rotenone but not phenformin before mild hypoxia reduced this elevated rate. Thus, metformin and rotenone had the opposing fast action in normoxia after 10–15 min and the slow action during 24 h mild-hypoxia implying activation of different signaling pathways. The slow action of metformin through inhibition of complex I could stabilize Ca²⁺ homeostasis after mild hypoxia and could be important for reduction of ischemia-induced microglial activation.     

Copy-move forgery detection based on multifractals

Multimedia Tools and Applications - Digital images and video are the basic media for communication nowadays. They are used as authenticated proofs or corroboratory evidence in different areas like:...     

Microcell prediction model based on support vector machine algorithm

A new microcell prediction model for mobile radio environment is presented in this paper. The popular support vector machine algorithm is used as an optimizing tool to build a model. In order to validate the model quality, extensive electric field strength measurements were carried out in the city of Belgrade, for two different test transmitter locations. The analysis of the model has shown that proposed model is fast, accurate (on the order of the local mean measurements uncertainty), reliable, and suitable for computer implementation.     

New Apatite‐Type Oxide Ion Conductor,Bi2La8[(GeO4)6]O3: Structure,Properties, and Direct Imaging of Low‐Level Interstitial Oxygen Atoms Using Aberration‐Corrected Scanning Transmission Electron Microscopy

The new solid electrolyte Bi₂La₈[(GeO₄)₆]O₃ is prepared and characterized by variable‐temperature synchrotron X‐ray and neutron diffraction, aberration‐corrected scanning transmission electron microscopy, and physical property measurements (impedance spectroscopy and second harmonic generation). The material is a triclinic variant of the apatite structure type and owes its ionic conductivity to the presence of oxide ion interstitials. A combination of annular bright‐field scanning transmission electron microscopy experiments and frozen‐phonon multislice simulations enables direct imaging of the crucial interstitial oxygen atoms present at a level of 8 out of 1030 electrons per formula unit of the material, and crystallographically disordered, in the unit cell. Scanning transmission electron microscopy also leads to a direct observation of the local departures from the centrosymmetric average structure determined by diffraction. As no second harmonic generation signal is observed, these displacements are non‐cooperative on the longer length scales probed by optical methods.