Improved periodic spectral analysis with application to diesel vibration data

The purpose of this work is to begin the development of a comprehensive time/frequency spectral analysis approach that can be applied to complex signals associated with real world systems, such as rotating machinery. Rotating machinery operating at nominally constant speed comprise a large class of important real world systems that have received relatively little attention in terms of stochastic characterizations of any greater sophistication than those associated with wide sense stationary processes. In this work, a periodic-time/frequency characterization procedure is introduced in the context of vibration analysis associated with a diesel engine operating at nominally constant speed. This application highlights a number of difficulties, such as the need for accurate period estimation, accommodation of noninteger periods in relation to digital processing, and identification and separation of tonal components from the signature in order to arrive at a more parsimonious characterization. A theorem relating to the limiting influence of these difficulties is presented. These difficulties are addressed using advanced signal processing tools, such as a recently developed tone identification procedure and extended Kalman filtering, which to the authors\u27 knowledge have not been considered to date in such a setting. Results include a simple correction algorithm for noninteger periods, excellent separation of tonal components whose frequencies are slowly varying, and subsequently a modest improvement in the spectral characterization of the remainder of the process. These results have some significance in relation to diesel engine vibration, since they unambiguously identify tonal vibration components, in addition to a random structure which appears to include random excitation of resonances

Numerical renormalization group study of the correlation functions of the antiferromagnetic spin-12\frac{1}{2} Heisenberg chain

We use the density-matrix renormalization group technique developed by White \cite{white} to calculate the spin correlation functions $=(-1)^l \omega(l,N)$ for isotropic Heisenberg rings up to $N=70$ sites. The correlation functions for large $l$ and $N$ are found to obey the scaling relation $\omega(l,N)=\omega(l,\infty)f_{XY}^{\alpha} (l/N)$ proposed by Kaplan et al. \cite{horsch} , which is used to determine $\omega(l,\infty)$. The asymptotic correlation function $\omega(l,\infty)$ and the magnetic structure factor $S(q=\pi)$ show logarithmic corrections consistent with $\omega(l,\infty)\sim a\sqrt{\ln{cl}}/l$, where $c$ is related to the cut-off dependent coupling constant $g_{eff}(l_0)=1/\ln(cl_0)$, as predicted by field theoretical treatments.Comment: Accepted in Phys. Rev. B. 4 pages of text in Latex + 5 figures in uuencoded form containing the 5 postscripts (mailed separately

Characterizing mixed mode oscillations shaped by noise and bifurcation structure

Many neuronal systems and models display a certain class of mixed mode oscillations (MMOs) consisting of periods of small amplitude oscillations interspersed with spikes. Various models with different underlying mechanisms have been proposed to generate this type of behavior. Stochastic versions of these models can produce similarly looking time series, often with noise-driven mechanisms different from those of the deterministic models. We present a suite of measures which, when applied to the time series, serves to distinguish models and classify routes to producing MMOs, such as noise-induced oscillations or delay bifurcation. By focusing on the subthreshold oscillations, we analyze the interspike interval density, trends in the amplitude and a coherence measure. We develop these measures on a biophysical model for stellate cells and a phenomenological FitzHugh-Nagumo-type model and apply them on related models. The analysis highlights the influence of model parameters and reset and return mechanisms in the context of a novel approach using noise level to distinguish model types and MMO mechanisms. Ultimately, we indicate how the suite of measures can be applied to experimental time series to reveal the underlying dynamical structure, while exploiting either the intrinsic noise of the system or tunable extrinsic noise.Comment: 22 page

Tetracycline resistance genes in Salmonella from growing pigs and their relationship to antimicrobial use and resistance to other antimicrobials

The aim of this study was to describe the occurrence of three genes coding for tetracycline resistance in Salmonellae isolated from normal slaughter weight pigs, and to test for relationships between the occurrence of these genes, phenotypic resistance, and the use of antimicrobials in feed and water

Methods and considerations for the analysis and standardization of assessing muscle sympathetic nerve activity in humans.

The technique of microneurography and the assessment of muscle sympathetic nerve activity (MSNA) are used in laboratories throughout the world. The variables used to describe MSNA, and the criteria by which these variables are quantified from the integrated neurogram, vary among studies and laboratories and, therefore, can become confusing to those starting to learn the technique. Therefore, the purpose of this educational review is to discuss guidelines and standards for the assessment of sympathetic nervous activity through the collection and analysis of MSNA. This review will reiterate common practices in the collection of MSNA, but will also introduce considerations for the evaluation and physiological inference using MSNA

Methods and considerations for the analysis and standardization of assessing muscle sympathetic nerve activity in humans

© 2015 Elsevier B.V.. The technique of microneurography and the assessment of muscle sympathetic nerve activity (MSNA) are used in laboratories throughout the world. The variables used to describe MSNA, and the criteria by which these variables are quantified from the integrated neurogram, vary among studies and laboratories and, therefore, can become confusing to those starting to learn the technique. Therefore, the purpose of this educational review is to discuss guidelines and standards for the assessment of sympathetic nervous activity through the collection and analysis of MSNA. This review will reiterate common practices in the collection of MSNA, but will also introduce considerations for the evaluation and physiological inference using MSNA

Antioxidants Attenuate the Exercise Induced Resetting of the Arterial Baroreflex in Healthy Human Subjects: Implications for Exercise Induced Hypertension

Patients with Exercise-induced-Hypertension (EiHT) exhibit exaggerated increases in arterial pressure at the onset of exercise which may prevent EiHT patients from participating in exercise training programs. EiHT is thought to occur due to dysregulated resetting of the arterial baroreflex (ABR). Prior studies in animal models demonstrate that reactive oxygen species (ROS) generated in the brainstem scavenge the sympathoinhibitory function of central Nitric Oxide (NO) and, thereby enable ABR resetting of the operating point (OP) pressure and hypertension. We tested the hypothesis that a centrally and peripherally active antioxidant cocktail (CT; composed of Vitamin E and C with Co-Q10) will attenuate the exercise induced resetting of the ABR‘s centering point (CP) and OP pressures compared to the same exercise intensity performed with a vehicle placebo (PL). Seven healthy human subjects were recruited and performed 700 back-supported semi-recumbent dynamic leg exercise at moderate (HR at 120 beats per minute: e120) and heavy (HR at 150 beats per minute: e150) intensities. Mean arterial pressure (MAP) was continuously recorded using photoplethysmography at the finger, while HR was recorded via a three lead electrocardiogram (ECG). On experimental day 1, subjects were either given the CT or PL 1 hr. (time of peak plasma concentrations) prior to the start of exercise. On a separate experiment day 2, the subjects repeated the same exercise intensity protocol with the other test article (CT or PL) in a randomized repeated measures design. During exercise with the PL ingestion, the CP of the ABR was reset to higher MAPs from rest to e120 (100 ± 3 mm Hg to 121 ± 3 mm Hg, P\u3c0.02) but not e150 (113 ± 3 mm Hg, P=0.15). The absence of resetting at the higher work intensity was likely due to cardiovascular drift (decreasing MAP). Ingestion of the CT prior to the exercise protocols prevented the increase of the CP to higher MAPs from rest to e120 and e150 (rest: 97 ± 3 mm Hg, e120: 106 ± 3 mm Hg, e150: 106 ± 3 mm Hg, P \u3e0.21). Furthermore, the OP- pressure of the ABR was attenuated with CT ingestion compared to PL at e120 (placebo e120: 116 ± 0.8 mm Hg, CT e120: 111 ± 0.8 mm Hg, P = 0.04). These data: (a) confirm that centrally derived ROS contribute to exercise induced ABR resetting; and (b) indicate that EiHT could be treated by ingestion of an anti-oxidant cocktail prior to the start of exercise

Magnetic field diagnostics and spatio-temporal variability of the solar transition region

Magnetic field diagnostics of the transition region from the chromosphere to the corona faces us with the problem that one has to apply extreme UV spectro-polarimetry. While for coronal diagnostic techniques already exist through infrared coronagraphy above the limb and radio observations on the disk, for the transition region one has to investigate extreme UV observations. However, so far the success of such observations has been limited, but there are various projects to get spectro-polarimetric data in the extreme UV in the near future. Therefore it is timely to study the polarimetric signals we can expect for such observations through realistic forward modeling. We employ a 3D MHD forward model of the solar corona and synthesize the Stokes I and Stokes V profiles of C IV 1548 A. A signal well above 0.001 in Stokes V can be expected, even when integrating for several minutes in order to reach the required signal-to-noise ratio, despite the fact that the intensity in the model is rapidly changing (just as in observations). Often this variability of the intensity is used as an argument against transition region magnetic diagnostics which requires exposure times of minutes. However, the magnetic field is evolving much slower than the intensity, and thus when integrating in time the degree of (circular) polarization remains rather constant. Our study shows the feasibility to measure the transition region magnetic field, if a polarimetric accuracy on the order of 0.001 can be reached, which we can expect from planned instrumentation.Comment: Accepted for publication in Solar Physics (4.Mar.2013), 19 pages, 9 figure