Wyniki wyszukiwania - BazTech

1

Modelowanie i badanie impulsów HPM

Królikowski Rafał, Słobodzian Piotr

Przegląd Telekomunikacyjny + Wiadomości Telekomunikacyjne

|

2022

|

nr 4

587--590

PL

W artykule przedstawiono model analityczny typowego impulsu HPM uzyskiwanego za pomocą wirkatora (ang. Virtual Cathode Oscillator). Opisano również eksperymentalną weryfikację zaproponowanego modelu w oparciu o pomiary impulsów HPM wygenerowanych za pomocą generatora arbitralnego.

EN

This article presents an analytical model of a typical HPM impulse obtained with a vircator (Virtual Cathode Oscillator). An experimental verification of the proposed model based on measurements of HPM pulses generated by means of an arbitrary generator is also described.

2

Spectrum Aliasing Does Occur Only in Case of Non-ideal Signal Sampling

Borys Andrzej Marek

International Journal of Electronics and Telecommunications

|

2021

|

Vol. 67, No. 1

79--85

EN

In this paper, it has been shown that the spectrum aliasing and folding effects occur only in the case of non-ideal signal sampling. When the duration of the signal sampling is equal to zero, these effects do not occur at all. In other words, the absolutely necessary condition for their occurrence is just a nonzero value of this time. Periodicity of the sampling process plays a secondary role.

3

Spectrum Aliasing Does not Occur in Case of Ideal Signal Sampling

Borys Andrzej Marek

International Journal of Electronics and Telecommunications

|

2021

|

Vol. 67, No. 1

71--77

EN

A new model of ideal signal sampling operation is developed in this paper. This model does not use the Dirac comb in an analytical description of sampled signals in the continuous time domain. Instead, it utilizes functions of a continuous time variable, which are introduced in this paper: a basic Kronecker time function and a Kronecker comb (that exploits the first of them). But, a basic principle behind this model remains the same; that is it also a multiplier which multiplies a signal of a continuous time by a comb. Using a concept of a signal object (or utilizing equivalent arguments) presented elsewhere, it has been possible to find a correct expression describing the spectrum of a sampled signal so modelled. Moreover, the analysis of this expression showed that aliases and folding effects cannot occur in the sampled signal spectrum, provided that the signal sampling is performed ideally.

4

Functional Magnetic Resonance Imaging Signal Modelling and Contrasts : an Example of Manual Praxis Tasks

Buchwald M.

Computational Methods in Science and Technology

|

2021

|

Vol. 27, No. 4

159--167

EN

The goal of neuroscience as a discipline is to understand how the neural system is organized in the brain, giving rise to mental processes and the control of behavior. One of the most frequently utilized methods in neuroscientific studies is the functional magnetic resonance imaging (fMRI), which is a non-invasive technique for quantifying brain processes dynamics. In a standard fMRI procedure, the hypothesis of the correlation between a cognitive task and the observed physiological signal is tested. This way, a certain computational model of a given brain mechanism can be validated. The procedure of modelling fMRI signal time course will be explained in this article as exemplified by planning functional grasps of tools. Subsequently, the results of contrasting model parameter estimates will be presented for a different experiment on manual praxis skills, i.e., bimanual tool grasps and manipulations.

5

Using neural networks with data quantization for time series analysis in LHC superconducting magnets

Wielgosz Maciej, Skoczeń Andrzej

International Journal of Applied Mathematics and Computer Science

|

2019

|

Vol. 29, no. 3

503--515

EN

The aim of this paper is to present a model based on the recurrent neural network (RNN) architecture, the long short-term memory (LSTM) in particular, for modeling the work parameters of Large Hadron Collider (LHC) superconducting magnets. High-resolution data available in the post mortem database were used to train a set of models and compare their performance for various hyper-parameters such as input data quantization and the number of cells. A novel approach to signal level quantization allowed reducing the size of the model, simplifying the tuning of the magnet monitoring system and making the process scalable. The paper shows that an RNN such as the LSTM or a gated recurrent unit (GRU) can be used for modeling high-resolution signals with the accuracy of over 0.95 and a small number of parameters, ranging from 800 to 1200. This makes the solution suitable for hardware implementation, which is essential in the case of monitoring the performance critical and high-speed signal of LHC superconducting magnets.

6

Two-stage method of impulsive noise detection for audio signals

Cisowski K.

Poznan University of Technology Academic Journals. Electrical Engineering

|

2007

|

No 54

17-24

EN

The paper deals with problems of impulsive noise detection for audio signals. The two-stage method of noise detection, based on analysis of probability density function of a noise corrupted signal, is proposed. The algorithm for determining triggering levels of the threshold detector is described.

7

Modelling of non-invasively recorded maternal and fetal electrocardiographic signals

Matonia A., Jeżewski J., Kupka T., Wróbel J., Horoba K.

Biocybernetics and Biomedical Engineering

|

2005

|

Vol. 25, no. 2

27-39

EN

The fetal electrocardiogram (FECG) recorded from the maternaI abdominal wall, due to its low amplitude, is very sensitive to various interferences. Some of them, like the muscular interferences, are characterized by a wide range of shared frequencies and comparable amplitudes. The most dominant interference - maternaI electrocardiogram - many times exceeds the level of the useful signaI. Contrary to the classical adult's electrocardiography, in fetal electrocardiography, there are no established signal databases (AHA, MIT-BIH) enabling us to perform the testing of the systems and algorithms being under development. This paper presents a method of modelling of artificial signals corresponding to the waveforms recorded on the abdominal wall. The method enables generation of electrocardiographic signals, with strictly determined parameters, and allows us to control the type and level of the noise added. The proposed database with the pattern signals will enable us to test new signal processing the algorithms used in our KOMPOREL System for non-invasive FECG diagnostics.

8

Zakłócenia bierne modelowane rozkładem Suzuki

Jakubiak A., Chrustowski A.

Kwartalnik Elektroniki i Telekomunikacji

|

2004

|

Vol. 50, z. 2

251-260

PL

Zakłócenia bierne, powstające w wyniku przypadkowych odbić fali elektromagnetycznej w przestrzeni pomiędzy nadajnikiem a odbiornikiem, stanowią poważne utrudnienie w transmisji sygnałów drogą radiową. Zjawisko to występuje szczególnie intensywnie w obszarze zabudowy miejskiej, powodując istotne zakłócenia w systemach telefonii komórkowej, łączności radiowej służb specjalnych czy też w systemach radiolokacyjnych. Znalezienie właściwego modelu probabilistycznego (ze względu na losowy charakter zjawiska) pozwala między innymi na efektywne projektowanie układów eliminujących bądź minimalizujących wpływ tego typu zakłóceń. Opisany w artykule tak zwany model Suzuki jest jednym z najlepszych modeli, potwierdzonych empirycznie, tyle tylko, że ze względu na skomplikowaną postać analityczną trudny do aplikacji. Zaproponowany sposób symulacji komputerowej został przetestowany i pozwala na efektywne generowanie próbek zakłóceń Suzuki.

EN

Signal modelling plays an important role in analytic design studies and computer simulation of many systems, like mobile communications, radar etc. The construction of suitable signal models are commonly concentrated on finding a mathematical description of experimental data and on generation of artificial signal draws with assumed properties. The urban radio channel is essentially a multipath channel, due to reflections and scattering by bildings, commonly modeled as a linear filter. A mixture of Raleigh and lognormal distribution, called Suzuki distribution, appropriately describes local andd global spatial variations of a signal envelope and/or short-term and long-term temporal fluctuations of a signal envelope in fading-shadowing wireless channel. Suzuki probability density function f(x) and cumulative distribution function F(x) for different parameters are shown as well as the convergence of Suzuki pdf to Rayleigh and long-normal pdf. The Suzuki model of a signal envelope in fading-shadowing wireless channel has a complicated integral forms of probability density function and cumulative distribution. From this reason it is very difficult to generate pseudorandom Suzuki draws by using the most widely disseminated inverse distribution method. However it is not difficult to prove that if: R is a Ralyleigh distributed random variable, V is lognormal distributed random variable, R and V are statistical independent, than S = RV is Suzuki distributed. Thus an algorithm of generation is simple: 1. Generate a lognormal distributed sample v with assumed parameters ž and A. 2. Generate a Rayleigh distributed sample r with parameter o = v. 3. Multiply r and v. This algorithm was succesfully verified by Chi-square test for different parameters values. The proposed algorithm of Suzuki random samples generation is effective and permits design studies by using the computers simulation methods in order to avoid costly hardware tests of wireless communication systems.