Aims
: Adiponectin and leptin are adipocytokines associated with insulin resistance. The objective of this study was to evaluate the performance of the adiponectin-leptin ratio as a measure of ...insulin resistance in comparison with other surrogate measures of insulin resistance based on fasting insulin and glucose levels homeostasis model assessment (HOMA), quantitative insulin sensitivity check index (QUICKI), fasting glucose/insulin ratio and with measures based on fasting insulin and triglyceride levels (McAuley index) in Caucasian patients with Type 2 diabetes (T2D).
Methods
: In 70 patients included in DEMAND (delapril and manidipine for nephroprotection in diabetes) study, fasting samples of plasma insulin and adiponectin were determined by a radioimmunoassay, whereas plasma leptin was determined by an enzyme-linked immunosorbent assay. Insulin resistance estimates were derived by the established equations and compared with the direct measurement of insulin resistance obtained with the euglycemic hyperinsulinemic clamp. Insulin resistance estimates and the clamp derived sensitivity index were compared by correlation analysis.
Results
: The adiponectin-leptin ratio correlated best with the clamp derived sensitivity index (r=0.553,
p
<0.001) compared to other surrogate measures of insulin resistance. In multiple linear regression models including different surrogate measures of insulin resistance as independent predictors of the sensitivity index, the model with the adiponectin-leptin ratio accounted for the highest variability of the sensitivity index (
r
2
=0.336,
p
<0.001).
Conclusions
: The adiponectin-leptin ratio is associated with insulin resistance, measured with the euglycemic hyperinsulinemic clamp, in Caucasians with T2D. The association with clamp derived sensitivity index is even stronger than that of HOMA, QUICKI, fasting glucose/insulin ratio or McAuley index and is independent of body mass index or glycemic control. The adiponectin-leptin ratio promises to become a new laboratory marker of insulin resistance in T2D.
AIMSAdiponectin and leptin are adipocytokines associated with insulin resistance. The objective of this study was to evaluate the performance of the adiponectin-leptin ratio as a measure of insulin ...resistance in comparison with other surrogate measures of insulin resistance based on fasting insulin and glucose levels homeostasis model assessment (HOMA), quantitative insulin sensitivity check index (QUICKI), fasting glucose/insulin ratio and with measures based on fasting insulin and triglyceride levels (McAuley index) in Caucasian patients with Type 2 diabetes (T2D). METHODSIn 70 patients included in DEMAND (delapril and manidipine for nephroprotection in diabetes) study, fasting samples of plasma insulin and adiponectin were determined by a radioimmunoassay, whereas plasma leptin was determined by an enzyme-linked immunosorbent assay. Insulin resistance estimates were derived by the established equations and compared with the direct measurement of insulin resistance obtained with the euglycemic hyperinsulinemic clamp. Insulin resistance estimates and the clamp derived sensitivity index were compared by correlation analysis. RESULTSThe adiponectin-leptin ratio correlated best with the clamp derived sensitivity index (r=0.553, p<0.001) compared to other surrogate measures of insulin resistance. In multiple linear regression models including different surrogate measures of insulin resistance as independent predictors of the sensitivity index, the model with the adiponectin-leptin ratio accounted for the highest variability of the sensitivity index (r2=0.336, p<0.001). CONCLUSIONSThe adiponectin-leptin ratio is associated with insulin resistance, measured with the euglycemic hyperinsulinemic clamp, in Caucasians with T2D. The association with clamp derived sensitivity index is even stronger than that of HOMA, QUICKI, fasting glucose/insulin ratio or McAuley index and is independent of body mass index or glycemic control. The adiponectin-leptin ratio promises to become a new laboratory marker of insulin resistance in T2D.
On acoustic very near field measurements Prezelj, J.; Lipar, P.; Belšak, A. ...
Mechanical systems and signal processing,
October 2013, 2013-10-00, 20131001, Volume:
40, Issue:
1
Journal Article
Peer reviewed
Information about vibration modes is needed during the planning of noise control measures on different parts of machinery. A visualization of vibration modes is a starting point and different methods ...can be used to visualize vibration modes. Some methods which incorporate an inverse calculation of surface velocity from the sound pressure on some boundary have already been proposed, among others. A direct inverse method based on the discretized Rayleigh integral was used in our work, to demonstrate that microphones should be placed close to the vibrating structure to provide an acoustic transfer matrix with a low condition number. It is demonstrated, that there is practically no need for the calculation of the inverse matrix if microphones are placed in a very near field of the vibrating structure. A single microphone placed in a very near field together with a reference vibration sensor provides sufficient information for producing the images of vibration modes. Analytical results, numerical results, FEM simulations and measurement results were used to prove that properties of the sound pressure in a very near field permit a cost effective visualization of the vibration modes.
•Experimental, numerical and analytical investigations of possibility for measurements in a very near field.•Analysis of the very near field in front of the vibrating surface with nodes and antinodes.•Vibration modes visualization using a microphone scanning in a very near field.•Numerical stability of the Inverse Numerical Acoustic used for the vibration mode visualization.
Simple model of liquid piston compressor Cerkovnik, N; Čurović, L; Prezelj, J
Journal of physics. Conference series,
05/2024, Volume:
2766, Issue:
1
Journal Article
Peer reviewed
Open access
Abstract The study proposes a new 0D thermodynamic model for the fast and simple evaluation of Liquid Piston compressors whose geometry and operation are determined by large number of parameters. ...With the proposed model, the evaluation of the parameters becomes easier, more dependencies are found and the understanding of the influences of parameter changes is deepened. Therefore, optimal designs for the mentioned machines can be created and tested experimentally. During the study, the model was validated with experimental and CFD data, and the results showed good agreement. It was found that evaluation criteria need to be defined for each set of geometric and operational parameters in order to compare the designs.
Display omitted
•Proposed method can be used for evaluation of the Poisson's ratio of polymers, wood, and composites.•Sound in a Very Near Field has been analysed for determination of the vibration ...mode wavelength.•10% error of the Poisson's ratio estimate, results in a 2.4% reconstruction error of the Young's modulus.
During the evaluation of Young’s modulus by vibroacoustic methods, it is usually assumed that the Poisson's ratio is known. This assumption is based on a reasonable tolerance of the vibroacoustic methods to an inadequate estimate of Poisson's ratio. However, most studies do not consider the influence of the Poisson's ratio error in the estimation of the Young's modulus error. Moreover, the evaluation of the total error typically does not include any parametric analysis at all. Therefore, a new vibroacoustic method is proposed that provides a simple and reciprocal determination of the Young's modulus and Poisson's ratio. The method is based on measurements of the natural vibration modes of elongated plates using a scanning microphone in the very near field. The results of the sound pressure scanning are interpolated with a quadratic harmonic function to improve the spatial resolution in locating the vibration nodes. The advantage of this method is that the Poisson's ratio can be calculated directly by measuring the wavelength of the bending wave. Poisson's ratio is otherwise much more difficult to measure than Young's modulus. Therefore, this method can be used to determine the Poisson's ratio of various polymers, wood, and composites. The parametric analysis of the proposed method is compared with the parametric analysis of the standardised ASTM 1875 method “Standard Test Method for Dynamic Young's Modulus, Shear Modulus, and Poisson's Ratio by Sonic Resonance”. The results show that the accuracy of the Poisson's ratio determination is mainly influenced by the accuracy of the material density and the accuracy of the measured sample thickness. The accuracy of these two parameters also has a dominant influence on the accuracy of the determination of the Young's modulus. The proposed method and its accuracy are demonstrated on three different plates: aluminium, steel and soft plexiglass. The results of the proposed method for aluminium were compared with those obtained by the standardised ASTM method. The proposed method provides smaller error for given experimental conditions.
In this paper sound generated during the gas-metal arc welding process was studded. Experimental analyses of the acoustic signals have shown that there are two main noise-generating mechanisms, first ...having impulse form is arc extinction and arc ignition; the second is the arc itself acting as an ionization sound source. The sound signal is used for assessing and monitoring of the welding process, and for prediction of welding process stability and quality. A new algorithm based on the measured welding current was established for the calculation of emitted sound during the welding process. The comparisons have shown that the calculated values are in good agreement with the measured values.
The purpose of controlling the quenching process of an orange-hot steel workpiece is to ensure its required surface hardness. A sound in a cooling liquid generated by the quenching process was ...experimentally analyzed. It contains sufficient information about the ongoing process for its quantification, and it can be used in real time. Traditionally, the quenching and the resultant hardening can be controlled by selecting different process parameters, like, for example the characteristics of the cooling liquid, the velocity of the cooling liquid flow, its temperature, the temperature of the work-piece, and many others. The possibility of controlling the quenching process by using acoustic cavitation is considered in this article.
Display omitted
•The noise immission vector is defined with the length (the value of SPL) and the angle of noise event arrival.•Sub-windowing in time domain enables calculations of noise event ...arrival angle in time intervals shorter than 1 ms.•Immission directivity pattern is obtained with averaging of noise immission vectors.•Immission directivity pattern maintains traceability to calibrated sound pressure level.
This article brings a breakthrough in understanding the computation of direction of arrival (DOA) of sound waves and represents an important step in the further introduction of spatial domain into environmental noise and acoustics measurements in general. Instead of improving the accuracy of beamforming, it makes more sense to increase the number of DOA calculations in the time domain and to use the statistical properties of environmental noise to localise the noise sources. We know from experience that two noise sources never have the same frequency characteristics, operating times, and spatial locations. This is the foundation on which the presented research stands and is validated with experiments. The high frequency sampling of 192 kHz allows a subwindow approach to time domain beamforming and the subdivision of microphone signals into time intervals of less than one millisecond. This allows statistical analysis of the immission directivity during the typically used time constant of 125 ms. The calculation of DOA in the subwindows shortens the time needed to evaluate the contribution of each noise source to the total sound pressure level. This leads to more data points (immission vectors) and lower statistical error in environmental noise measurements. In this paper, we propose associating the temporal dominant direction with the temporal sound pressure level within the subwindow and integrating the results to determine the immission directivity. Numerical simulations, experiments and practical application of the sub-windowing differential beamforming algorithm (SubW-DBA) method provided promising results.
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