Signal Amplitude Variations Research Articles

Dynamic characteristics of blood glucose time series during the course of critical illness: Effects of intensive insulin therapy and relative association with mortality*

To assess the effect of intensive insulin therapy on blood glucose amplitude variation and pattern irregularity in critically ill patients. To assess the association of these blood glucose signal characteristics with hospital mortality, independent of blood glucose level. Retrospective analysis of the databases of two previously published randomized controlled trials. University hospital, 56-bed adult surgical intensive care unit and 17-bed medical intensive care unit. One thousand five-hundred forty-eight surgical intensive care unit patients, admitted between February 2000 and January 2001, and 1200 medical intensive care unit patients, admitted between March 2002 and May 2005. In the two randomized controlled trials, patients were randomized to receive either intensive insulin therapy (targeting normoglycemia, between 4.4 and 6.1 mmol/L) or conventional insulin therapy (infusing insulin when blood glucose levels were >12 mmol/L and stopping at 10 mmol/L). Intensive insulin therapy significantly lowered mean blood glucose (5.8 vs. 8.4 mmol/L), hyperglycemic index (0.8 vs. 3.2 mmol/L), and glycemic penalty index (26 vs. 53), but it increased the mean daily difference between minimum and maximum blood glucose (mean daily delta blood glucose; 4.0 vs. 3.3 mmol/L). There was no significant effect on the standard deviation of the blood glucose measurements or on jack-knifed approximate entropy. In multivariable logistic regression analysis, corrected for baseline risk factors, blood glucose levels outside the normoglycemic range, higher mean daily delta blood glucose, higher standard deviation blood glucose, and higher jack-knifed approximate entropy were independently associated with hospital mortality. The Leuven intensive insulin therapy strategy increased mean daily delta blood glucose while not affecting standard deviation blood glucose and jack-knifed approximate entropy. Increased blood glucose amplitude variation and pattern irregularity were associated with mortality, irrespective of blood glucose level. The reduced mortality observed with intensive insulin therapy in the Leuven trials cannot be attributed to an effect on blood glucose amplitude variation or entropy. Reducing amplitude variation and entropy of the blood glucose signal, irrespective of blood glucose concentration, may produce clinical benefits.

Comparison between different Photothermal Deflection methods to determine thermal properties of bulk semiconductor samples

In this study we will describe and compare different methods based on the Photothermal Deflection Technique (PTD) which permits the determination of thermal diffusivity for bulk semiconductors. The two first methods proposed here consist in drawing the experimental amplitude and phase variation of the photothermal signal versus square root modulation frequency. The sample placed in air is heated thanks to a modulated uniform light beam. The difference between these two methods is that in the second one the sample is covered by a thin graphite layer. We notice that the first method is only sensitive to the thermal diffusivity however the second method is sensitive for both thermal diffusivity and thermal conductivity. Finally the third method which is a spectroscopic one and where the sample is immersed in a CCl4 filled cell consists to draw the phase variation of the photothermal signal versus wavelength at a fixed modulation frequency. The phase difference between the two saturated zone (high and low absorption coefficient) is sensitive to the thermal diffusivity.

Amplitude and frequency variations of coherent radio signals during probing of the daytime Venusian ionosphere

A new procedure for analyzing the data obtained during radio probing of the Venusian ionosphere is proposed. The experimental results of the two-frequency probing with the use of the “Venera 15” and “Venera 16” orbiters that provide evidence that the daytime Venusian ionosphere has a layered structure are presented. It is shown that there exists a lower part of the daytime ionosphere at altitudes of 80 to 120 km.

Analog automatic lock-in amplifier for very low gas concentration detection

A novel automatic analog lock-in amplifier for low quantity detection of gas is here presented. When compared to similar commercial apparatus in the literature, the proposed scheme shows the self-alignment of the relative phase between input and reference signals, both at power-on and for any variation of the input noisy signal phase and amplitude during the working time, so allowing to detect, in a continuous way, the mean value of the input signal (buried into noise). The circuit has been optimized to operate at a specified reference frequency (77 Hz), whose value is suitable for gas sensor application, avoiding any kind of interferences at 50 Hz net frequency and its harmonics. Experimental results have confirmed the correct functionality of the system, tested for 10, 20 and 30 ppm of CO concentrations. With respect to the simple resistive gas sensor interface implemented by a resistive voltage divider, the sensitivity improvement given by the proposed lock-in amplifier is of a factor of about 80, while the resolution, starting from about 5ppm, has been enhanced to a theoretical value of about 0.05ppm.

Quasi-parabolic reflecting bottom surfaces of the Drygalski Antarctic floating ice tongue

Very high frequency deep radio sounding systems for ice thickness measurements are practically the only useful apparatuses for large scale radar flight surveys in polar regions. The morphology of the bottom surface of an Antarctic floating ice tongue, in the Ross Sea area, East Antarctica, was studied using the arrival times of signal echoes of the radio sounding system. The amplitude variations of radar signals from the reflecting surface were analyzed to determine the gain or the loss of the reflectors. Such surfaces show quasi-parabolic geometrical shapes at the ice/water interface with both concave and convex faces towards the sounding system. Electromagnetic analysis performed on radar echoes indicates that amplitude variations detected by the antenna are focusing or defocusing effects only due to the reflector's shape. A factor in the radar equation that represents the surface shape when coherent reflectors are involved is introduced. This factor allows us to determine more precisely the morphology and electromagnetic characteristics of the interface between the media investigated by means of radio echo sounding.

Multiple Vector Impedance Measurements During Biventricular Pacing: Feasibility and Possible Implications for Hemodynamic Monitoring

Intracardiac impedance (ICZ) has been known to reflect contractile capacity of the heart, and a strong relationship has been documented between stroke volume and ICZ. In this pilot study, conducted in heart failure patients during implantation of a biventricular device, we investigated acute changes in multiple vector ICZ signals during different pacing modes, and whether ICZ can be used to monitor hemodynamic variations. Z1 and Z2 impedance signals were recorded in the right ventricle (RV), and between the left ventricle (LV) and RV, respectively, in 12 patients during four programming modes. ICZ signals were analyzed with respect to average and peak-to-peak (p2p) amplitude and systolic slope, and correlated with noninvasive hemodynamic and echocardiographic variables. ICZ p2p amplitude decreased during LV stimulation both in Z1 and in Z2 configuration (P = 0.021 and P = 0.022 vs intrinsic conduction, respectively). No significant variations in average amplitude or systolic slope were observed. ICZ variables correlated directly with hemodynamic measures (r = 0.48, P < 0.05, between Z2 p2p amplitude and pulse pressure), LV ejection fraction (r = 0.32, P < 0.05, for Z1 average amplitude), RV ejection fraction (r = 0.75, P < 0.05, for Z1 p2p amplitude), and inversely with ventricular volumes. Variations in ICZ may be observed during different pacing modes and seem to correlate with hemodynamic and echocardiographic variables. Multiple vector ICZ measurement may be a feasible tool for hemodynamic assessment in patients treated with biventricular pacing.

Non performance estimation of a microwave communication link due to rain during the monsoon months of 2006 over Kolkata

The non performance of a microwave communication link located over Kolkata due to heavy rain in the monsoon months of 2006 has been investigated by monitoring the amplitude variation of signal on twenty hour basis. It has been seen that the link did not serve any purpose for 4% during the monsoon period of 2006 while the signal level was less than −78 dBm. Infact the study revealed that the link performance started deteriorating when the signal was of the order of −73 dBm.

Numerical and experimental simulation of the effect of long bone fracture healing stages on ultrasound transmission across an idealized fracture

The effect of various stages of fracture healing on the amplitude of 200 kHz ultrasonic waves propagating along cortical bone plates and across an idealized fracture has been modeled numerically and experimentally. A simple, water-filled, transverse fracture was used to simulate the inflammatory stage. Next, a symmetric external callus was added to represent the repair stage, while a callus of reducing size was used to simulate the remodeling stage. The variation in the first arrival signal amplitude across the fracture site was calculated and compared with data for an intact plate in order to calculate the fracture transmission loss (FTL) in decibels. The inclusion of the callus reduced the fracture loss. The most significant changes were calculated to occur from the initial inflammatory phase to the formation of a callus (with the FTL reducing from 6.3 to between 5.5 and 3.5 dB, depending on the properties of the callus) and in the remodeling phase where, after a 50% reduction in the size of the callus, the FTL reduced to between 2.0 and 1.3 dB. Qualitatively, the experimental results follow the model predictions. The change in signal amplitude with callus geometry and elastic properties could potentially be used to monitor the healing process.

Applied digital signal processing systems for vortex flowmeter with digital signal processing

The spectral analysis is combined with digital filter to process the vortex sensor signal for reducing the effect of disturbance at low frequency from pipe vibrations and increasing the turndown ratio. Using digital signal processing chip, two kinds of digital signal processing systems are developed to implement these algorithms. One is an integrative system, and the other is a separated system. A limiting amplifier is designed in the input analog condition circuit to adapt large amplitude variation of sensor signal. Some technique measures are taken to improve the accuracy of the output pulse, speed up the response time of the meter, and reduce the fluctuation of the output signal. The experimental results demonstrate the validity of the digital signal processing systems.

Simultaneous Characterization of Optical and Rheological Properties of Carotid Arteries via Bimodal Spectroscopy: Experimental and Simulation Results

This study aimed at identifying potential correlations between rheological and optical properties of carotid artery rings before and after cryopreservation at different mechanical deformations using experimental and simulation results. Therefore, a uniaxial mechanical test bench was coupled to fibered optical spectroscopes measuring 410 nm excited autofluorescence and 650-850 nm elastically backscattered intensity spectra. Furthermore, we developed a statistical simulation program of light transport and fluorescence adapted to our specific experimental configuration. Both spectroscopies gave intensity spectra with higher amplitude for the cryopreserved samples. These observations are to be related to histological modifications affecting the arterial wall of postcryopreserved samples. We also observed significant spectral amplitude variations (increasing autofluorescence intensity and decreasing diffuse reflectance) as a function of the circumferential strains (0%-60%). Due to simulation, we identified values of absorption, diffusion, and anisotropy coefficients, and their variations as a function of state (fresh-cryopreserved), strains (0, 30%, 60%), and wavelengths (700, 740, 780 nm). The media and the adventice are, respectively, less and more absorbing for postcryopreserved rings, and it is the opposite for the fresh ones at higher wavelengths. Absorption and diffusion coefficients are slightly higher, whatever the wavelengths and strains, for the fresh than for the cryopreserved samples.

Baseline blood oxygenation modulates response amplitude: Physiologic basis for intersubject variations in functional MRI signals

Although BOLD functional MRI (fMRI) provides a useful tool for probing neuronal activities, large intersubject variations in signal amplitude are commonly observed. Understanding the physiologic basis for these variations will have a significant impact on many fMRI studies. First, the physiologic modulator can be used as a regressor to reduce variations across subjects, thereby improving statistical power for detecting group differences. Second, if a pathologic condition or a drug treatment is shown to change fMRI responses, monitoring this modulatory parameter is useful in correctly interpreting the fMRI changes to neuronal deficits/recruitments. Here we present evidence that the task-evoked fMRI signals are modulated by baseline blood oxygenation. To measure global blood oxygenation, we used a recently developed technique, T(2) relaxation under spin-tagging (TRUST) MRI, which yielded baseline oxygenation of 63.7% +/- 7.2% in the sagittal sinus with an estimation error of 1.3%. It was found that individuals with higher baseline oxygenation tend to have a smaller fMRI signal, and vice versa. For every 10% difference in baseline oxygenation across subjects, BOLD and cerebral blood flow (CBF) signals differ by -0.4% and -30.0%, respectively, when using visual stimulation. TRUST MRI is a useful measurement for fMRI studies to control for the modulatory effects of baseline oxygenation that are unique to each subject.

Characterization of the gas pulse frequency, amplitude and velocity in non-steady dense phase pneumatic conveying of powders

Current modelling techniques for the prediction of conveying line pressure drop in low velocity dense phase pneumatic conveying are largely based on steady state analyses. Work in this area has been on-going for many years with only marginal improvements in the accuracy of prediction being achieved. Experimental and theoretical investigations undertaken by the authors suggest that the flow mechanisms involved in dense phase conveying are dominated by transient effects rather than those of steady state and are possibly the principal reasons for the limited improvement in accuracy. This paper reports on investigations on the pressure fluctuation behaviour in dense phase pneumatic conveying of powders. The pressure behaviour of the gas flow in the top section of the pipeline was found to exhibit pulsatile oscillations. In particular, the pulse velocity showed variation in magnitude while the frequency of the oscillations rarely exceeded 5 Hz. A wavelet analysis using the Daubechie 4 wavelet found that the amplitude of the oscillations increased along the pipeline. Furthermore, there was significant variation in gas pulse amplitude for different types of particulate material.

A global climatology of ionospheric irregularities derived from GPS radio occultation

GPS radio occultation measurements from CHAMP, GRACE‐A and FORMOSAT‐3/COSMIC are used to derive global information on small‐scale ionospheric irregularities such as sporadic E layers between January 2002 and December 2007. The investigations are based on the analysis of amplitude variations of the GPS radio occultation signals. The global distribution of ionospheric irregularities shows strong seasonal variations with highest occurrence rates during summer in the middle latitudes. The long‐term data set of CHAMP allows for first climatological studies, while the data coverage increases significantly with the combination of CHAMP, GRACE and FORMOSAT‐3/COSMIC measurements. This allows for global maps of sporadic E occurrence rates of very high spatial resolution where the influence of the Earth's magnetic field becomes visible in global sporadic E maps for the first time.

Microchannels as Axonal Amplifiers

An implantable neural interface capable of reliable long-term high-resolution recording from peripheral nerves has yet to be developed. Device design is challenging because extracellular axonal signals are very small, decay rapidly with distance from the axon, and in myelinated fibres are concentrated close to nodes of Ranvier, which are around 1 mum long and spaced several hundred micrometers apart. We present a finite element model examining the electrical behavior of axons in microchannels, and demonstrate that confining axons in such channels substantially amplifies the extracellular signal. For example, housing a 10-microm myelinated axon in a 1-cm-long channel with a 1000-microm(2) cross section is predicted to generate a peak extracellular voltage of over 10 mV. Furthermore, there is little radial signal decay within the channel, and a smooth axial variation of signal amplitude along the channel, irrespective of node location. Additional benefits include a greater extracellular voltage generated by large myelinated fibres compared to small unmyelinated axons, and the reduction of gain to unity at the end of the channel which ensures that there can be no crosstalk with electrodes in other channels nearby. A microchannel architecture seems well suited to the requirements of a peripheral nerve interface.

ON THE DETERMINATION OF LOWER IONOSPHERIC PERTURBATIONS DETECTED AS FAST AMPLITUDE VARIATIONS OF VLF SIGNALS

Normal 0 21 false false false MicrosoftInternetExplorer4 We analyze the occurrence of very low frequency (VLF) events and their association with geomagnetic activity. VLF events are detected as fast amplitude variations of VLF signals from Hawaii (NPM Navy transmitter) and received at Comandante Ferraz Brazilian Antarctic Station (EACF) in the period from September through November 2003. The results show VLF events occurring predominantly during the recovering phase of geomagnetic storms produced by high speed solar wind streams (HSSWSs), and by coronal mass ejections (CMEs) which were accompanied by HSSWSs impacts before returning to quiet geomagnetic level. Based on these results, and upon the good association of VLF events with enhancements in the energetic electron flux of the radiation belts, we suggest they might be the ionospheric response to the energetic electrons precipitated from the radiation belts which were predominantly scattered by whistler-mode waves generated by the electrons injected in the magnetosphere during geomagnetic activity produced by HSSWSs.

Mechanics of Single Cells: Rheology, Time Dependence, and Fluctuations

The results of mechanical measurements on single cultured epithelial cells using both magnetic twisting cytometry (MTC) and laser tracking microrheology (LTM) are described. Our unique approach uses laser deflection for high-performance tracking of cell-adhered magnetic beads either in response to an oscillatory magnetic torque (MTC) or due to random Brownian or ATP-dependent forces (LTM). This approach is well suited for accurately determining the rheology of single cells, the study of temporal and cell-to-cell variations in the MTC signal amplitude, and assessing the statistical character of the tracers’ random motion in detail. The temporal variation of the MTC rocking amplitude is surprisingly large and manifests as a frequency-independent multiplicative factor having a 1/ f spectrum in living cells, which disappears upon ATP depletion. In the epithelial cells we study, random bead position fluctuations are Gaussian to the limits of detection both in the Brownian and ATP-dependent cases, unlike earlier studies on other cell types.

Observation evidences of atmospheric Gravity Waves induced by seismic activity from analysis of subionospheric LF signal spectra

Abstract. We analyze variations of the LF subionospheric signal amplitude and phase from JJY transmitter in Japan (F=40 kHz) received in Petropavlovsk-Kamchatsky station during seismically quiet and active periods including also periods of magnetic storms. After 20 s averaging, the frequency range of the analysis is 0.28–15 mHz that corresponds to the period range from 1 to 60 min. Changes in spectra of the LF signal perturbations are found several days before and after three large earthquakes, which happened in November 2004 (M=7.1), August 2005 (M=7.2) and November 2006 (M=8.2) inside the Fresnel zone of the Japan-Kamchatka wavepath. Comparing the perturbed and background spectra we have found the evident increase in spectral range 10–25 min that is in the compliance with theoretical estimations on lithosphere-ionosphere coupling by the Atmospheric Gravity Waves (T&gt;6 min). Similar changes are not found for the periods of magnetic storms.

Earthquake effects along paths of VLF radio noise and impulsive signals as observed at Yakutsk

An analysis of amplitude variations in the noise and storm-induced impulsive VLF electromagnetic signals recorded at Yakutsk along paths above earthquakes is reported. It is shown that amplitude characteristics of storm-induced VLF signals can usefully supplement signals of radio stations as used in the radio monitoring of regions above earthquakes. The effect on these signals due to earthquakes of magnitude greater than 5 is observed as an amplitude increase within the three days following an earthquake. The pre-seismic variations in the storm-induced signal amplitude which can be regarded as precursors are generally observed as increased amplitudes (within 10 days before the earthquake) with a subsequent minimum.

Technical Considerations for Dominant Frequency Analysis

Dominant frequency (DF) analysis of atrial electrograms has been used to characterize atrial fibrillation (AF). The aim of this study was to explore technical issues that may affect the estimation of local activation rate during AF using DF analysis. Epicardial atrial electrograms recorded during AF from 10 dogs were used to evaluate the effects of unipolar versus bipolar recordings, bipolar electrode spacing, postrecording processing, far field ventricular depolarizations, ventricular template subtraction, and signal duration on DF analysis. Simulated electrograms were used to evaluate the effect of far field ventricular depolarizations and signal-to-noise ratio. DFs were compared with activation rates obtained by manual marking and the reproducibility of the DFs was evaluated. Bipolar electrograms were found to be preferable to unipolar electrograms. Preprocessing was a necessary step for bipolar signals, but also aided analysis of unipolar recordings. Ventricular far field depolarizations significantly affected DFs. Ventricular template subtraction helped DF analysis in signals with both minimal and significant ventricular components. A recording duration above 2 seconds was required for reliable DF measurements. Signal-to-noise ratios below 13 dB could also affect DF, particularly for signals with significant amplitude and frequency variation. Various factors affect DF analysis. Proper interpretation of DF analysis requires careful evaluation of the AF signals and robust processing techniques.

Comparison Between Intramuscular and Perimuscular Injections of Botulinum Toxin Type A

Botulinum toxin type A (BTX-A) must be injected in the intramuscular area to exert its paralytic effect. The durability of the BTX-A effect varies in different patients, and this fact can result from different locations of the drug injection, for example, the muscle peripheral area (perimuscular). This study aimed to evaluate whether a difference exists in the effect duration of the muscle paralysis between intramuscular and perimuscular injections of BTX-A. This study used 18 male New Zealand rabbits divided into two groups (A and B) based on the location of the BTX-A injection. The group A animals received 10 units of BTX-A diluted with 0.1 ml of normal saline injected perimuscularly. The group B animals received the same dosage injected in the intramuscular area of the left masseter muscle. An electroneurophysiologic study was performed 1 week before the experiment for all the animals, then repeated 1, 4, and 8 weeks after the toxin injection. The amplitude values recorded in the masseter muscle were significantly lower in both groups throughout the study than the physiologic amplitude. The comparison between groups A and B did not show any statistically significant amplitude variations throughout the 8 weeks. No significant difference in the neuromuscular blockade induced by botulinum toxin type A was observed between injections into the muscle peripheral area and intramuscular injections.