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RISS 인기검색어
- 검색키워드
- 저자 : Zhbanov, Alexander I. (검색결과 7 건)
- 무료
- 기관 내 무료
- 유료
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Zhbanov, A.,Yang, S. The Royal Society of Chemistry 2018 Analytical methods Vol.10 No.2
<P>The study of erythrocyte aggregation and erythrocyte sedimentation rate (ESR) is very important both for basic research and medical applications. The duration of the Westergren ESR test is one hour which seems excessive. The hematocrit and conductivity of blood demonstrate high correlation. This makes it possible to evaluate the erythrocyte aggregation kinetics and ESR by measuring changes in the blood conductivity. We measured the time-dependent changes in conductivity at the bottom of the blood column during sedimentation. A digital camera is used to obtain the blood sedimentation curve and to determine the hematocrit profile. The effective conductivity of blood is calculated based on effective medium theory. Simple analytical expressions are derived to extrapolate changes in blood conductivity over time. We proposed an improved physical model of sedimentation which reveals additional information about the kinetics of blood sedimentation and erythrocyte aggregation. An explicit expression is obtained to characterize the rate of aggregate formation. A numerical model was developed to investigate these mechanisms, and it was tested by comparing simulation results with experimental data. Based on our model, the ESR, blood sedimentation curve and hematocrit profiles can be numerically restored using only the first 400 seconds of the recorded changes in blood conductivity. The proposed technique allows measuring the erythrocyte aggregation as well as the sedimentation kinetics. The changes in blood conductivity at the bottom of the blood column at the initial stage of sedimentation reliably reflect the erythrocyte aggregation kinetics and ESR over time.</P>
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Comment on ‘Model calculation of the scanned field enhancement factor of CNTs’
Zhbanov, A I,Lee, Yong-Gu,Pogorelov, E G,Chang, Yia-Chung IOP Pub 2010 Nanotechnology Vol.21 No.35
<P>The model proposed by Ahmad and Tripathi (2006 <I>Nanotechnology</I> <B>17</B> 3798) demonstrates that the field enhancement factor of carbon nanotubes (CNTs) reaches a maximum at a certain length. Here, we show that this behavior should not occur and suggest our correction to this model.</P>
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Zhbanov, A.,Yang, S. Royal Society of Chemistry 2017 Analytical methods Vol.9 No.22
<P>Electrochemical impedance spectroscopy (EIS) is a highly promising tool for the analysis of blood. The electrical properties of plasma and blood cells provide fundamental insights into the health status of patients. Nevertheless, the potential of EIS has not been fully exploited to date. In this study, a small chamber with two planar electrodes placed at the bottom is used for sensitive detection of blood hematocrit, sedimentation and dielectric properties of plasma and erythrocytes. The changes in the blood impedance spectrum were measured at frequencies between 40 Hz and 110 MHz for a few hours. An updated lumped-parameter circuit is proposed to describe the impedance in the measuring chamber filled with blood. This updated circuit model allows the correction of the polarization effect and exclusion of the stray capacitance from experimental data with a high accuracy. A theoretical approach based on the effective medium theory is developed for calculating the effective permittivity and conductivity of whole blood. An algorithm is proposed to extract the electrical properties of erythrocyte cytoplasm and membranes from the impedance spectrum. The EIS of blood samples reveals beta- and delta-dispersions. It is found that the electrical properties of membranes have a significant influence on the blood impedance at frequencies between 100 kHz and 10 MHz (beta-dispersion), while the cytoplasm has an effect at frequencies between 10 MHz and 1 GHz (delta-dispersion). The proposed method provides an estimation of hematocrit levels during blood sedimentation, which is important for blood tests.</P>
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Field enhancement factor and optimal emitter density in a nanowall array
Zhbanov, A.,Yang, S. Pergamon Press ; Elsevier Science Ltd 2014 Carbon Vol.75 No.-
The field emission from carbon nanowalls has excited the interest of researchers as a potential electron source for a variety of device applications. We derive an explicit analytical expression for the field enhancement factor of a nanowall placed in a nanowall array using the ''floating cylinder'' model. We show that if the thickness of the walls and the distance between them remain invariable while the height of walls becomes taller, the field enhancement factor increases monotonically but never exceeds a certain constant value. We propose an explicit algebraic formula for finding the optimal distance between the nanowalls at which the anode current reaches a maximum. The optimal emitter density depends only on the applied electric field and the work function of the material; it does not depend on the height of nanowalls. We analyze published experimental data and specify the resource to increase the total current.
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Kim, Byung Jun,Lee, Ye Sung,Zhbanov, Alexander,Yang, Sung The Royal Society of Chemistry 2019 The Analyst Vol.144 No.9
<P>In this study, a microfluidic-based physiometer capable of measuring whole blood viscosity, hematocrit, and red blood cell (RBC) deformability on a chip is introduced. The physiometer consists of two major parts: a hydrodynamic component for whole blood viscosity measurement and an electronic component for hematocrit and RBC deformability measurement. In the hydrodynamic component, the whole blood is infused with phosphate buffered saline as a reference fluid for estimation of the whole blood viscosity. At a given flow rate, ten sets of whole blood viscosity readings are successfully obtained over a wide range of shear rates; this is achieved <I>via</I> a series of geometrically optimized microchannel arrays. In the electronic component, analysis of the whole blood impedance spectrum under flowing conditions reveals the electrical characteristics of the blood: the cytoplasm resistance (<I>R</I>cytoplsm), plasma resistance (<I>R</I>plasma), and RBC membrane capacitance (constant phase element). The hematocrit is estimated from <I>R</I>cytoplsm and <I>R</I>plasma, while the RBC deformation index is determined from the membrane capacitance change of the RBC. Each unique function is experimentally demonstrated and compared to the corresponding gold standard method. The whole blood viscosity measured using the physiometer is 0.8 ± 1.4% in normalized difference compared to that using a rotational cone-and-plate viscometer. For the hematocrit measurement, the coefficient of variation for the physiometer ranges from 0.3 to 1.2% which is lower than the one obtained from centrifugation. In the deformability measurement, there is a strong linear correlation (<I>R</I><SUP>2</SUP> = 0.97) between the deformation index acquired by image processing and the change in the membrane capacitance acquired by using the physiometer. The effects of the hematocrit and RBC deformability on the whole blood viscosity are also demonstrated. For simultaneous and reliable measurement on a chip, a physiometer equipped with a temperature-control system is prepared. Lab-made software enables the measurement of the three target indices and the temperature control in an automated manner. By using this system, the temperature is controlled to 36.9 ± 0.2 °C which greatly matches with the target temperature (37.0 °C) and it is varied from 25 °C to 43 °C. The developed physiometer is potentially applicable for a comprehensive analysis of biophysical indices in whole blood.</P>
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