Fifteen recumbent young health volunteers underwent 24-h beat-to-beat blood pressure (BP) and interbeat interval (IBI) recordings to explore the effects of wake and polygraphically recorded sleep on the nyctohemeral variations in the spectral frequency components of BP and IBI and in the arterial baroreflex sensitivity (BRS), independent of the confounding effects of changes in posture and physical activity. Spectral analysis of BP and IBI provided markers of sympathetic and vagal controls and of arterial BRS. When falling asleep, the low-frequency (LF) BP and IBI components showed a marked decrease while there was a clear-cut increase in the high-frequency (HF) IBI component. In contrast, only a slight nighttime rapid eye movement-related arterial BRS increase was observed. The final morning awakening induced a pronounced decrease in arterial BRS and the HF IBI component while there was a marked rise in the LF BP component. Hence, a clear 24-h variation in sympathetic and vagal tone but not in arterial BRS persists, independent of changes in activity and position.

We prove that if the average of the degrees of the irreducible characters of a finite group G is less than 16 5 , then G is solvable. This solves a conjecture of I. M. Isaacs, M. Loukaki and the first author. We discuss related questions.

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Early identification of failures in rolling element bearings is an important research issue in mechanical systems. In this study, a reliable methodology for bearing fault detection is proposed, which is based on an optimal sub-band selection scheme using the discrete wavelet packet transform (DWPT) and envelope power analysis techniques. A DWPT-based decomposition is first performed to extract the characteristic defect features from the acquired acoustic emission (AE) signals. The envelope power spectrum (EPS) of each sub-band signal is then calculated to detect the characteristic defect frequencies to reveal abnormal symptoms in bearings. The selection of an appropriate sub-band is essential for effective fault diagnosis, as it can reveal intrinsically explicit information about different types of bearing faults. To address this issue, we propose a Gaussian distribution model-based health-related index (HI) that is a powerful quantitative parameter to accurately estimate the severity of bearing defects. The most optimal sub-band for fault detection is determined using two dimensional (2D) visualization analysis. The efficiency of the proposed approach is validated using several experiments in which different defect conditions are identified under variable, and low operational speeds.

The authors introduce the synthetic process and the evaluation results for surfactant/polymer inorganic nanocomposite specially designed for the enhanced oil recovery (EOR) process in the high temperature and high brine-hardness offshore reservoirs. The SiO 2 nanoparticles (NPs) were introduced to the polymer matrix through the core-shell encapsulation-polymerization. New core-shell NPs were blended with surfactants in different ratios. The monodisperse particles, with the size of 50nm to 100nm identified by transmission electron microscopy (TEM), were investigated on their properties and morphology by IR spectroscopy, and thermal degradation (TGA). The blends of NPs and surfactants in brine were aged in one month in Dragon Southeast reservoir conditions to evaluate on the capacity as EOR agent. The results show that the nanocomposites produced IFT reduction and viscosity enhancement at critical concentration, high thermostability and salt-tolerance. These improved properties of core/shell NPs were suitable for producing high sweep volume and increasing crude oil displacement efficiency. The core flooding experiment was performed at 92 o C on the fractured-granite core model and brine blend of 800 ppm of surfactants and 200 ppm of core-shell NPs was injected in 0.25 PV. After water flooding, the oil saturation was reduced into 30% and by the core-shell NPs injection, the oil was displaced in 6.2% additionally. The obtained results shown the capacity of using the core-shell NPs as a really good EOR agent for HTHP offshore reservoirs.