Abstract-The high resolution of recent sigma-delta analogue-todigital converters (ADCs) has made possible the direct acquisition of a wide range of biomedical data. Such ADCs allows creating universal systems as for medical research and for clinical practice. Keywords -Sigma-Delta, biomedical data acquisition systems INTRODUCTIONThe performance of biomedical data acquisition systems is generally limited by precision of the digital input data, which is achieved at the interface between analog and digital signals. The recent developments in digital VLSI technologies provide the practical means to implement the Sigma-Delta (Σ-∆) analogue-to-digital converters (ADCs). The increasing use of digital techniques in biomedical data acquisition systems has also contributed to the recent interest in cost effective high precision ADCs. Sigma-delta modulation based on analog-to-digital conversion technology is cost effective alternative for high resolution (greater than 14 bits) converts, which can be ultimately integrated on digital signal processor ICs [1]. METHODOLOGYElectrophysiological acquisition systems must extract and amplify the low -level signal (less than 200 µV in EEG and 10 mV in ECG) from a relatively high level (~ hundreds of mV) of common mode interference, electrode artefact etc. Traditional biomedical amplifiers front ends have been based on around instrumentation amplifiers.The high resolution of sigma-delta converters allows ECG or EEG signals to be acquired directly, without the use of instrumentation amplifiers. The large common mode signals can be digitized without saturation and the small differential signal can be recovered with resolutions comparable to convention methods [2,3,4]. One channel sigma-delta ADCs (Fig. 1) employ a negative feedback loop consist of an integrator, comparator and one-bit digital-to-analog converter (DAC). The input analogue signal is first integrated and compared with ground using a sampling comparator. Its output drives a one bit DAC that switches reference voltages to the summing node of the integrator, minimising the difference of signals. The loop operates at a high oversampling ratio. The output word is retrieved after digital low pass filter.One from the first sigma-delta ADC chip, prevalent in biomedical systems, was AD7716 of production Analog Devices. On it to a basis the systems for the ECG, EEG, IMG (impedance measure) are developed. On Fig.2 showed digital ECG system on AD7716 for registration standard lead. Devices consist of DC amplifiers (gain equals 4 for ECG and 19 for EEG), simply RC antialiasing filters, AD7716 and serial channel to PC. There are sampling rate 512kHz synchronously on all channel, high pass digital filtering and decimation. Output sampling rate may be programmable 1000, 500, 250, 125 Hz. Digital signals processingcorrection gain channels, leads calculation and filtration are made on the PC or microprocessor.The application sigma-delta ADC, intended for digital sound in majority of biomedical systems is poorly effective. As a rule, such A...

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The simulation results of the temperature distribution in the growth area of graphene layers obtained by the method of thermal decomposition of the silicon carbide surface substrates in setup with induction heating are presented. The heating parametrs of the setup elements are calculated using the commercial package COMSOL Multiphysics taking into account the electrical, thermal and magnetic properties of the materials from which the growth plant elements are made. A numerical estimate of the heating inhomogeneity of silicon carbide plates over its area during the growth of graphene layers at a given temperature is given. It is shown that the lateral temperature distribution over the area of the plate has radial symmetry with decreasing values towards the center. Keywords: graphene, silicon carbide, simulation, temperature distribution, sublimation growth.

Dimethyl 2-(1-bromocyclohexylcarbonyl)-, 2-(1-bromocyclopentylcarbonyl)-, and 2-(1-bromocyclobutylcarbonyl)-2-methylmalonates reacted with zinc and aromatic aldehydes to give the corresponding methyl 1-aryl-4-methyl-3,5-dioxo-2-oxaspiro[5.5]undecane-4-, 6-aryl-9-methyl-8,10-dioxo-7-oxaspiro[4.5]-decane-9-, and 5-aryl-8-methyl-7,9-dioxo-6-oxaspiro[3.5]nonane-8-carboxylates.I, IV, VII, X, XIII, n = 3; II, V, VIII, XI, XIV, n = 2; III, VI, IX, XII, XV, n = 1; X-XV, Ar = 4-BrC 6 H 4 (a), 4-ClC 6 H 4 (b); X, XIII, Ar = Ph (c), 4-MeOC 6 H 4 (d).We found previously [1] that dialkyl 2-(2-bromoisobutyryl)malonates react with zinc and aldehydes to give the corresponding alkyl 2,4-dioxotetrahydropyran-3-carboxylates [1]. In the present communication we report on the synthesis of analogous compounds having a spiro carbon atom. The reactions of dimethyl 2-bromo-2-methylmalonate with zinc and cyclohexane-, cyclopentane-, and cyclobutanecarbonyl chlorides gave dimethyl 2-cycloalkylcarbonyl-2-methylmalonates I-III which were subjected to bromination with molecular bromine to obtain bromo derivatives IV-VI. The latter reacted with zinc yielding zinc enolates VII-IX which added at the carbonyl group of aromatic aldehydes with formation of alkoxides X-XII. Intramolecular cyclization of X-XII with elimination of MeOBrZn resulted in the formation of methyl 1-aryl-4-methyl-3,5-dioxo-2-oxaspiro[5.5]undecane-4-carboxylates XIIIa-XIIId, methyl 6-aryl-9-methyl-8,10-dioxo-7-oxaspiro[4.5]decane-9-carboxylates XIVa and XIVb, and 5-aryl-8-methyl-7,9-dioxo-6-oxaspiro[3.5]nonane-8-carboxylates XVa and XVb (Scheme 1).The structure of the isolated compounds was confirmed by their elemental compositions and IR and 1 H NMR spectra. In the IR spectra of XIII-XV, absorption bands belonging to stretching vibrations of

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