An inviscid dyadic model of turbulence: the fixed point and Onsager's conjecture

Properties of an infinite system of nonlinearly coupled ordinary differential equations are discussed. This system models some properties present in the equations of motion for an inviscid fluid such as the skew symmetry and the 3-dimensional scaling of the quadratic nonlinearity. It is proved that the system with forcing has a unique equilibrium and that every solution blows up in finite time in $H^{5/6}$-norm. Onsager's conjecture is confirmed for the model system

Influence of mechanical activation on functional properties of barium hexaferrite ceramics

Barium hexaferrite ceramics were prepared using mechanically activated mixtures of iron and barium titanate. The 60:40 mass% Fe:BaTiO3 powder mixtures were mechanically activated for different times (100-240 min) and sintered at 1100 and 1200 degrees C in order to determine the influence of mechanical activation of the precursor on the magnetic and dielectric properties of the resulting barium hexaferrite ceramics. The final product contained 84-89 mass% of Ba2Fe22.46O38Ti1.54 phase, with higher content corresponding to longer mechanical activation of the precursor. XRD and Raman measurements indicated that the remainder of the sample consists of leftover BaTiO3 and hematite, which was formed by the oxidation of iron during mechanical activation and sintering in air. Magnetic properties of samples sintered at 1200 degrees C are superior to those sintered at 1100 degrees C, which can be attributed to higher Ba2Fe22.46O38Ti1.54 phase content. The position of the Curie temperature in 350-420 degrees C temperature region is consistent with 0.8:1 ratio of Ti to Ba. Maximum magnetization was observed for samples activated for 120 min. Dielectric properties of samples sintered at 1200 degrees C showed a dependence on frequency, with a significant drop in relative permittivity with an increase in frequency in the low-frequency region, and relatively constant values of relative permittivity in the high-frequency region. The tangent loss showed a decrease with increase in frequency, where peaks corresponding to the resonance of the electron hopping frequency with the external field were observed in the samples corresponding to the longer mechanical activation. Dielectric properties showed relatively small changes for samples activated longer than 150 min

Analysis of the initial-stage sintering of mechanically activated SrTiO3

The initial-stage of sintering plays a significant role in determining the final microstructure that defines the main characteristics of electroceramics materials such as functional properties. In this article non-isothermal sintering of non-activated and mechanically activated SrTiO3 samples was investigated up to 1300 °C. Dilatometric curves indicate that mechanical activation leads to an earlier onset of sintering, suggesting that it should lead to a more homogenous and denser sintered product. Analysis of the initial stage of sintering reveals that the sintering process of all examinated samples consists of two or three overlapping single-step processes, with a change in the dominant mass transport mechanism. The values of apparent activation energy of the considered single-step process exhibit a significant decrease with an increase in mechanical activation time. The values of the density of samples after isothermal sintering indicate that the final stage of sintering has not been reached by 1300 °C

Influence of the phase composition of refractory materials on creep

In this paper, the relationship between the creeping effect and mineralogical characteristics of the applied binding phase for various refractory materials (high-alumina materials, with high or low impurity content, tar bonded either magnesite or dolomite materials and silicate bonded chrom-magnesite materials) is presented. The mechanism of creeping is analyzed and the activation energy for creep for each investigated material is obtained and discussed. All investigated materials are creep sensitive under investigated conditions and have similar activation energies for creep except high-alumina refractories with a low impurity content

Analysis of the Initial-Stage Sintering of Mechanically Activated SrTiO3

The initial-stage of sintering plays a significant role in determining the final microstructure that defines the main characteristics of electroceramics materials such as functional properties. In this article non-isothermal sintering of non-activated and mechanically activated SrTiO3 samples was investigated up to 1300 degrees C. Dilatometric curves indicate that mechanical activation leads to an earlier onset of sintering, suggesting that it should lead to a more homogenous and denser sintered product. Analysis of the initial stage of sintering reveals that the sintering process of all examinated samples consists of two or three overlapping single-step processes, with a change in the dominant mass transport mechanism. The values of apparent activation energy of the considered single-step process exhibit a significant decrease with an increase in mechanical activation time. The values of the density of samples after isothermal sintering indicate that the final stage of sintering has not been reached by 1300 degrees C

Ultrasound diagnostics of carotid and vertebral arteries

Stroke is the third leading cause of death and themain cause ofmajor disability worldwide.Each yearmore than 700,000 people experience a new or recurrent stroke and on average someone dies every 4min of a stroke (1). In Serbia stroke is the first cause of death among women and the second one among men. While the percentage of strokes attributed to carotid disease is relatively low, the overall social and economic burden is high (2). It is, therefore, important to identify and manage carotid atherosclerosis with the aim of stroke prevention. The presence of an atherosclerotic lesion in the carotid bulb or in the extracranial internal carotid artery (ICA) is associated with elevated stroke risk (3). Severalmechanisms are attributable to the increased risk of cerebrovascular events including decrease in the blood flow resulting from critical stenosis or occlusion, or the stenotic lesion can also be the source of thromboembolic events. In this article the authors are going to focus on some important aspects of ultrasound diagnostics of extracranial parts of brain arteries

Updated radio Σ−D\Sigma-D relation for Galactic supernova remnants

We present updated empirical radio surface-brightness-to-diameter ($\Sigma-D$) relation for supernova remnants (SNRs) in our Galaxy. Our original calibration sample of Galactic SNRs with independently determined distances (Pavlovic et al. 2013, hereafter Paper I) is reconsidered and updated with data which became available in the past two years. The orthogonal fitting procedure and probability-density-function-based (PDF) method are applied to the calibration sample in the $\log \Sigma - \log D$ plane. Orthogonal regression keeps $\Sigma-D$ and $D-\Sigma$ relations invariant. Our previous Monte Carlo simulations verified that the slopes of the empirical $\Sigma-D$ relation should be determined by using orthogonal regression. Updated calibration sample contains 65 shell SNRs. 6 new Galactic SNRs are added to the sample from Paper I, one is omitted and distances are changed for 10 SNRs. The slope derived here is slightly steeper ($\beta \approx 5.2$) than $\Sigma-D$ slope in Paper I ($\beta \approx 4.8$). The PDF method relies on data points density maps which can provide more reliable calibrations that preserve more information contained in the calibration sample. We estimate distances to five new faint Galactic SNRs discovered for the first time by Canadian Galactic Plane Survey and obtained distances of 2.3, 4.0, 1.3, 2.9 and 4.7 kiloparsecs for G108.5+11.0, G128.5+2.6, G149.5+3.2, G150.8+3.8 and G160.1$-$1.1, respectively. The updated empirical relation is used to estimate distances of 160 shell Galactic SNRs and new results change their distance scales up to 15 per cent, compared to results from Paper I. The PDF calculation can provide even few times higher or lower values in comparison with orthogonal fit, as it uses totally different approach. However, in average, this difference is 32, 24 and 18 per cent for mode, median and mean distances.Comment: 17 pages, 3 figures, Accepted for publication in Serbian Astronomical Journa