Short-term Frequency Domain Research Articles

Risk spillover effect of the new energy market and its hedging effectiveness: New evidence from industry chain

During China’s industrial transformation, studying risk spillover effects and clarifying risk contagion pathways within the new energy industry chain is critical for promoting high-quality development in the new energy. The risk transmission mechanism of the new energy industry chain is explored by constructing a time–frequency index using a time-varying parameter vector autoregressive model in this paper. Additionally, we also further analyze the portfolio and hedging effectiveness of the new energy market. The findings reveal that, first, the downstream market serves as the primary risk source, propagating risk through the industry chain to the midstream and upstream sectors within the new energy industry chain contagion system. Second, the risk spillover effect of the new energy market has significant heterogeneity and time-varying due to the impact of short-term frequency domain drivers and extreme events. Third, the portfolio significantly reduces the investment risk of a single asset. With the extension of the investment horizon, investors’ portfolio weights in the upstream, midstream and downstream industries gradually tend to be even.

Digital enhancement of speech perception in noisy environments

If speech is reproduced in an acoustically disturbed environment via a loudspeaker, the perception in terms of intelligibility or listening effort may be impaired. Typical situations arise in connection with mobile phones or public address systems. The location of the listener is called the near-end while the speech signal is received from the far-end. Usually, the acoustical background noise cannot be influenced, but speech perception may be enhanced by digital pre-processing of the loudspeaker signal. This pre-processing technique is called Near-End Listening Enhancement (NELE). The received signal is filtered adaptively, by taking the instantaneous characteristics of the background noise into account and by exploiting psychoacoustic properties of the auditory system such as the masking threshold. The increase of the loudspeaker volume is often not allowed or very limited, to avoid injury of hearing or damages of the loudspeaker and because of the listening comfort. In this contribution, state-of-the-art NELE algorithms operating in the short-term frequency domain are reviewed and novel time domain approaches are presented. Furthermore, the differing NELE constraints of public address systems and mobile phones are discussed.

Cardiac autonomic modulation assessed by heart rate variability in children with asthma.

To assess cardiac autonomic modulation, measured by short-term frequency domain analysis of heart rate variability (HRV), in children with asthma. We conducted an observational study at a tertiary care teaching hospital. The sample consisted of 119 children aged 7 to 15 years with asthma and 56 age-matched healthy controls. Frequency domain HRV measures included low-frequency (LF; 0.04-0.15 Hz), high-frequency (HF; 0.15-0.4 Hz), and LF/HF ratio. The LF and HF components were expressed in both absolute values of power (ms2 ) and in normalized units (nu). Compared with healthy controls, asthmatic children had significantly higher value of HF (nu) (mean ± standard deviation: 45.9 ± 14.6 vs 40.7 ± 13.6; P = .02), and lower values of LF (nu) (54.1 ± 14.6 vs 59.3 ± 13.6; P = .02) and LF/HF ratio (median, interquartile range: 1.12, 0.82-1.88 vs 1.59, 1.02-2.08; P = .03). We did not find significant differences between children with persistent and intermittent asthma, and between children with well-controlled and partially-controlled or uncontrolled asthma, in terms of HRV measures. Children with stable chronic asthma may have a cardiac autonomic imbalance with a possible enhanced parasympathetic modulation, as assessed by short-term frequency domain analysis of HRV. Neither asthma severity nor asthma control was significantly associated with HRV measures, but the study did not have enough power to draw a firm conclusion on this point.

10 Autonomic Responses to Head Up Tilt in Patients with Syncope: The Influence of Ageing

Introduction Neurally mediated syncope is a common disorder but there remain large gaps in our understanding of its pathophysiology. Several groups have studied the role of the autonomic nervous system (ANS), baroreceptor sensitivity (BRS) and baroreceptor effectiveness (BEI) in syncope but have offered conflicting results. We hypothesised that patients who experience symptoms during head-up tilt testing (HUT) would have abnormal ANS and baroreceptor responses and that these changes may alter with advancing with age. Methods We analysed HUT data from tests performed at Ealing Hospital between 2004–2012. These were clinically indicated HUT for individuals who experienced either syncope or pre-syncope. The Italian protocol was used during HUT. Beat-to-beat heart rate and non-invasive plethysmographic blood pressure monitoring was employed throughout, using the Task Force Monitor® (CN Systems, Graz, Austria). The device calculates short-term frequency domain heart rate variability (HRV) using an autoregressive algorithm, BRS using the sequence method and cardiac output using impedance cardiography. Results HUT assessments in 298 patients were reviewed, there was no syncope in 187, 31 experienced syncope without GTN, 78 experienced syncope with GTN and 3 had carotid sinus syndrome (CSS). There was a bimodal age distribution for these HUT patients (Figure 1). CSS was found only in those > 60 years. There were differences across tertiles of age with respect to haemodynamics and ANS, BRS and BEI responses (Table 1). However, there were no differences, across tertiles of age, in the proportions of negative HUT, those positive without GTN and those positive with GTN (χ 2 , p = 0.445). For the different stages of HUT, there were no significant differences in HRV and BRS between individuals who experienced syncope (with or without GTN) and those that did not. Conclusions Autonomic nervous system variability and baroreceptor function at rest decline with age but this does not seem to influence the nature of syncope on HUT.

Efficient coding of high frequency signal information in a signal using a linear/non-linear prediction model based on a low pass baseband

An efficient coding scheme with higher audio bandwidth and/or better audio quality at lower bitrates, wherein the scheme eliminates long-term and short-term frequency domain correlation in a signal via frequency domain predictors. The coding scheme compresses information consisting of coded low frequency components as well as a parametric representation for the high frequency components based on a non-linear model. Additionally, by working on the frequency domain representations of the signal (such as the MDCT representation which is naturally available to a PAC encoder and decoder), low pass and high pass signal components are easily obtained by windowing the appropriate ranges of frequencies in the signal. Furthermore, the power functions of the signal are replaced by corresponding convolution functions of the same order.

Cardiac Autonomic Function in Patients Suffering from Primary Focal Hyperhidrosis

Cardiac autonomic function in patients (n = 63) with primary focal hyperhidrosis and healthy controls (n = 28) was investigated by short-term frequency domain power spectral analysis of heart rate variability. The power of the very-low-frequency band (0.01–0.05 Hz) was significantly lower in patients with axillary hyperhidrosis than in controls. No differences between groups could be observed at investigation of the low-frequency band (0.05–0.15 Hz), which was a surprising finding because this band represents also sympathetic cardiac innervation. At the high-frequency band (0.15–0.5 Hz), which represents parasympathetic cardiac innervation, an interaction of type and position influencing spectral power was detected. Our highly interesting findings indicate that primary focal hyperhidrosis is based on a much more complex autonomic dysfunction than generalised sympathetic overactivity and seems to involve the parasympathetic nervous system as well.