Signal Amplitude Ratio Research Articles

Spin Label Oximetry to Assess Extracellular Oxygen During Myocardial Ischemia

We describe real-time measurement of myocardial oxygen consumption during ischemia in the intact heart. Measurement of extracellular oxygen concentration during myocardial ischemia by spin label oximetry has been limited by ischemia-induced reduction of the neutral, water-soluble nitroxide TEMPONE. We have overcome this problem by encapsulating the nitroxides. Isolated immature (7–10 d old) rabbit hearts ( n = 8) were perfused aerobically within the cavity of a loop gap resonator with bicarbonate buffer containing an oxygen-sensitive, lipid-soluble nitroxide ( 14N-TEMPO laurate in FC-43 perfluorocarbon micelles) and a much less oxygen-sensitive and positively charged nitroxide ( 15N-TEMPO choline in multilamellar vesicles) as an internal standard. The ratio of the ESR signal amplitudes of these nitroxides was used as a sensitive index of oxygen concentration. Sequestration of the nitroxides decreased their reduction rate by ascorbate in comparison with nonsequestered nitroxides. Hearts were subjected to 60 min of global no-flow ischemia at 20°C. Extracellular oxygen content (mean ± SD) during aerobic perfusion was 1195 ± 55 μmol/liter. The electron spin resonance signal from TEMPO laurate increased with the onset and progression of ischemia, consistent with a decrease in extracellular oxygen, while the signal for TEMPO choline was relatively unchanged. Extracellular oxygen content after 40 and 60 min of ischemia was reduced to 393 ± 27 μmol/liter ( p < .05) and 61 ± 5 μmol/liter ( p < .05), respectively. We conclude that spin-label oximetry can directly and precisely measure myocardial oxygen consumption at constant temperature during ischemia in the intact heart. Copyright © 1996 Elsevier Science Inc.

Integrated optical-disk pickup that uses a focusing grating coupler with a high numerical aperture

An integrated optical-disk pickup that uses a focusing grating coupler with a numerical aperture of 0.45 (a focal length of 1.0 mm and an aperture of 1.0 mm × 0.8 mm) was developed, and the readout signal on an International Standards Organization (ISO) -formatted 90-mm optical disk was detected by the pickup. The signal-amplitude ratio of the minimum-limit data pattern to the maximum was 0.53 on the innermost track. It meets the requirement on the signal resolution for optical-disk storage devices.

Absolute quantitation of short TE brain 1H-MR spectra and spectroscopic imaging data.

A method for determining the concentrations of the materials that produce the well-resolved singlet signals in short TE brain 1H MR spectroscopic examinations is presented. Concentration determination is achieved by a water-referencing procedure. The ratios of the areas of the choline, total creatine, and N-acetyl signals to that of the water signal from the same volume of interest (VOI) are determined using acquisitions with and without water suppression. The tissue concentrations of the molecules producing the three signals can then be determined if the water concentration in the VOI can be found. This is done with a density-weighted MR study. The MR study provides the ratio of the mean MR signal amplitude from the VOI to that from an external standard containing a known water concentration. The method's flexibility is illustrated by using it with two different single-volume localization schemes and spectroscopic imaging. Preliminary evaluations of accuracy and reproducibility are made in phantom, animal, and limited human studies. The method's advantages and limitations are discussed.

Use of the trans-spectral-coherence technique to separate signals from noise

A new technique to separate signals from noise is proposed. This technique is specifically meant for signals that are wholly or partly generated through some nonlinear process. A signal processing technique is described, which is specifically aimed at such signals. As long as the underlying process can be assumed to be nonlinear, this technique can be beneficially used, even if the details of the generating mechanism are unknown. To accomplish this goal, three new concepts have been introduced. The first is the concept of the transphase. This is a generalization of the concept of phase, except that it applies to two different frequencies. The second concept is that of the trans-spectral coherence (TSC). This is the generalization of the concept of ordinary coherence and is once again valid for two signals at different frequencies. The third concept is that of the auto-trans-spectral coherence (ATSC), which applies to two signals that are duplicate copies of the same signal. It has been shown that these concepts can be used to detect the presence of minute signals (of a nonlinear origin) even when they are mixed with a random noise that exceeds the signal in magnitude. It is shown with a simulated signal that the presence of a signal could be detected when the ratio of signal amplitude to the standard deviation of the noise was 0.1.

The spacelab 2 XRT xenon-filled position-sensitive proportional counters

The dual coded-mask X-ray telescope flown on the Spacelab 2 mission utilised two position-sensitive proportional counters, the largest yet used in space for X-ray astronomy. Each had a geometric area of over 1000 cm 2 and a depth of 5.3 cm atmospheres of xenon-methane, providing useful sensitivity up to 30 keV. A novel position readout technique used a combination of delay line timing and measuring ratios of cathode signal amplitudes. Analysis of flight data indicates the performance was close to that obtained during ground calibration tests. The possibilities for developments for higher energies and larger areas are discussed.

Nasal consonants in esophageal speech.

Nasalization of nasal consonants was measured using the ratio of a nasal accelerometer signal amplitude to air-borne microphone signal amplitude. Utterances produced by 3 esophageal speakers were studied. Word position (and time following air injection) of the nasal consonants was varied. Degree of nasal resonance was dependent on word position, with significantly higher values for word-final than for word-initial position.

Measuring Tool-Chip Interface Temperatures

A two-color pyrometer was developed for monitoring the surface temperature of metal chips formed during high-speed machining processes. Optical access to the tool-chip interface was obtained by cementing a plastic light pipe into a 1/16-in. (1.6-mm) hole milled through the carbide tool insert. The light pipe serves to transmit radiation falling on the rake face of the insert to radiation detectors located elsewhere. Radiation captured by the light pipe is passed through a lens-beam splitter combination and imaged on two identical photodiode detectors. The diodes have integral operational amplifiers to achieve high detectivity and low-noise operation. Each photodiode is masked by an interference type narrow-band filter having spectral bandpass frequencies chosen to match the point where the emittance of several metals is constant for all temperatures. Thus, the temperature of the chip stream monitored by the diodes is a function of the intensity measured for each spectral band at the same instant in time. The functional relationship between true temperature and the ratio of signal amplitudes (the calibration curve) was established for pyrometer over the interval 1000–1750 K using standard laboratory methods.

Interference in Frequency-Locked Doppler Tracking Loops

The effects of interference on frequency-locked Doppler tracking loops are investigated. Conditions for jump from locking on the desired signal to locking on the interfering signal are established. Parasitic frequency modulation of the desired signal results when the other signal interferes with it. The index of this parasitic modulation as a function of the interference-to-desired signal amplitude ratio is computed. Both critical amplitude ratio and critical parasitic modulation index at the occurrence of jump are derived. Comparing frequency-locked loops with phase-locked loops with phase-locked loops in the presence of interference shows the former performs better for most cases of practical importance in Doppler tracking systems.

Diffraction of elastic waves by cracks: application to time-of-flight inspection

We obtain expressions for the angular variation of diffracted signal amplitude when infinite plane P or SV waves are incident on a semi-infinite crack. The importance of these calculations to non-destructive testing by the time-of-flight technique is discussed. We obtain the optimum angles to use for the case of a defect symmetrically placed with respect to transmitter and receiver. These angles are those for which the ratio of emitted signal amplitude to incident wave amplitude is a maximum. We compare two methods of obtaining the exact solution for the diffraction of elastic waves at a semi-infinite crack. Both methods involve the solution of a set of integral equations, the equations being different in the two methods. In the far-field approximation the results from these methods are shown to be equivalent.

Sources of loss processes in phonon generation and detection experiments with superconducting tunneling junctions

Observing the phonon yield, i.e. the ratio of the experimental phonon signal amplitude and the corresponding calculated value, phonon losses within the generation-detection system can be localized and determined quantitatively. With tin junctions on pure silicon substrates immersed in liquid helium the phonon yield is 3–5%. Under vacuum conditions the yield rises to 10–12% indicating strong phonon transmission to the helium bath. The experimental lifetime for 280 GHz phonons in the silicon substrate is longer than 65 µs indicating negligible volume losses and losses at the free substrate surface. It is further shown, that volume losses inside the phonon generator and detector are small compared to the total loss of about 90%. By phonon reverberation measurements we find evidence that the main sources for phonon losses are localized at the boundaries of the tunneling junctions to the substrate. This is supported by an increase of the phonon yield with improved polishing from about 9% (mechanical), 10% (chemical) to 12% (sputter etching). A SIMS analysis indicates the presence of carbonhydrates and probably of water in the boundaries. This layer of extraneous molecules together with the nonideal surface structure of the substrate and the evaporated films weakens the mechanical bonding between the tunnel junctions and the substrate and is possibly causing strong phonon splitting by anharmonic forces.

Principles and Application of Ultrasonic Spectroscopy in NDE of Adhesive Bonds

Ultrasonic spectroscopy utilizes the principle of construc- tive and destructive wave interferences to obtain information about ultrasound in the frequency domain. For applications in the nondes- tructive evaluation (NDE) of adhesive-bonded structures, destructive interference of the pulsed sound waves at the boundaries of the adhesive bond layer produces spectroscopic signals characteristic of the bond. The bondline thickness can be determined accurately from the fre- quency minima in the spectrum. The width of the antiresonance dips at half-power points and the amplitude of the dips are related to the acoustical properties at the interfaces of the adhesive layer. The amplitude ratio of the RF signals reflected from the boundary surfaces of the adhesive layer in the time domain is also affected by the acous- tic impedance mismatch at the boundaries. A combination of these measurements in the frequency and time domains characterize the adhesive properties between the adherend and the adhesive. The ex- perimental set-up consists of a wide-band pulser/receiver as an energy source, a highly damped piezoelectric sensor serving as the transmitting and receiving transducer, and a digital computer for waveform digitiza- tion and Fourier transform. Single lap-shear adhesive-bond specimens using three types of adhesive systems were used in a correlation study between bond strengul and NDE parameters from the ultrasonic spectroscopy method. An empirical bond strength/NDE parameters relationship established from the correlation study has been justified by analytical calculation. The experimental procedures, analytical derivations of the sound wave interactions in the layered media, and the statistically valid correlation of the bond strength with NDE parameters is presented. obtained by using the ultrasonic spectroscopy technique wlll be presented. The bondline thickness can be measured ac- curately by means of reflected spectra using a known value of the velocity of sound. An anlytical calculation of the sound wave interference in the bondline is presented. This calcula- tion takes into consideration the attenuation in the adhesive and relates the attenuation coefficients to the antiresonances in the frequency spectra. A brief presentation of the experi- mental setup precedes the results obtained on single lap-shear specimens. Discussions on the potentials of the ultrasonic spectroscopy technique and conclusions on the presentation are included. 11. ANALYTICAL CALCULATION For the normal incidence of compressive ultrasonic waves on an attenuating layer, the wave numbers in the media will, in general, be complex. The complex form of the wave numbers was presented by Brekhovskikh (5) as

Adaptive Delta Modulation

In this paper, design principles of a delta modulator are discussed to arrive at the design parameters. For a sampling rate of 25 K/bits and reference frequency of speech at 1·12 KHz, the maximum signal to quantization noise ratio is found to be around 24 db. The concept of reference frequency of speech spectrum is explained while deriving the design parameters. The parameter S/K, which is the ratio of signal amplitude to quantizing step, is then, used for discussing the principles of companding, keeping the signal to quantizing noise power ratio constant. Syllabic compandor and instantaneous compander are then discussed. Performance characteristics of a companded system is also given.

Hard limiting of three and four sinusoidal signals

An analysis of the effect of hard limiting on a sum of three or four sinusoidal signals has been performed. Analytic expressions are obtained for the output amplitudes for three input signals, two of equal amplitude, and for four signals, amplitudes equal in pairs. The results are compared with previous investigations that employ digital computer simulation, and excellent agreement is obtained. The signal suppression is investigated, and the "negative suppression" effect found numerically by other authors is shown to arise from logarithmic terms in the dependence of the output amplitude on the input signal amplitude ratio. These results should aid in understanding the interactions that occur when a limiting communications receiver is addressed by several signals.

Response of an FM Discriminator to a Digital FM Signal in Randomly Fading Channels

The calculation of the error rate resulting from the detection of a binary FSK signal using an FM discriminator-lowpass filter detector is described for an FM signal undergoing nonselective fading in additive Gaussian noise. The results extend the error rate calculations of Schilling et al. [1], [2] which were performed for a nonfading channel. While the technique employed is quite general, examples considering Rayleigh fading and an alternating mark-space sequence are given. Following a CCIR recommendation for Rayleigh fading, the percentage of time that the signal envelope is below a minimum level is ignored, since in this case the circuit would be completely cut off or switched to a better path. Thus, the results also depend on the depth of fade or ratio of the minimum signal amplitude squared to the average carrier power. The use of diversity is studied, and the error rate for a discriminator using predetection combining diversity is found. In this case the possibility of infinitely deep fades is considered. The analysis is based on the work of Nelson[9], [14], who considered signal-to-noise ratio performance of an FM discriminator with an analog FM signal undergoing nonselective fading. Experimental results are shown to verify the theory.

Use of amplitude ratios in phase correlation of seismic waves

A discussion concerning the probability of variation in the amplitude correlation of the seismic wave extrema under the action of random interferences is presented. In the process of choosing a correlation version with the use of amplitude criteria, it was possible to pass from one phase to another in the result of variation in the amplitude relations between the signal extremes (under the action of interferences). This phenomenon was called here "the amplitude inversion. It was proved analytically that the probability of the amplitude inversion depended not only on the interference dispersion and the ratio of signal amplitudes, but also on the width of the band occupied by the energy spectrum of the interference. The probability of the inversions (especially of the near one) increased with the increase in the width of the interference spectrum. The concept of the "amplitude domination" (for the axes of the synchronous phases) is introduced, and used for the choice of the correlation variant in a set of permissible axes. -- Petroleum Abstracts.

A possible source of nerve signal distortion arising in pulse rate encoding of signals

Biological receptors, some central neurons and some neurone models translate signals into a pulse-rate form. In a single-fibered system, the translation results in some signal loss. This paper is a theoretical examination of the effects on the signal of translation of that signal into a pulse-rate form with reference to a multichannel system. It is shown that even in a multichannel system, considerable signal distortion could result from the process of pulse-rate translation of a dynamic signal. The special case of the translation of sinusoidal wave forms is considered in some detail and it is shown that both signal phase, amplitude ratio and wave form are affected by the original signal amplitude, frequency and background tonic level in a predictable manner. It is shown that the magnitude of the signal-distorting effects in a system composed of multiple asynchronous pulse-rate channels depends primarily on the pulse rate in the individual channels, rather than on the sum of the pulse rates on all of the channels. Within the physiological range of signal and pulse-rate characteristics, both signal delays of as much as 100 msec and complete failure of signal transmission are possible consequences of one pulse-rate translation. Wherever the nervous system employs a pulse-rate representation of signal intensity, the translation from a continuous process to the pulse-rate form of signal should be recognized as a possible source of major signal modification.

Near and distant observations of the 1962 Johnston Island high-altitude nuclear tests

During the 1962 Johnston Island high-altitude nuclear tests, USAELDRL operated high-sensitivity, high-time-resolution magnetometers in the Pacific area and in the continental United States, Large loops of up to 100-km2 area, spin-resonance (metastable-helium) magnetometers, and telluric probes were used. Shot Starfish (the July 9, 1962, explosion of about 1½ megatons at 400-km altitude) produced very strong oscillatory signals of many minutes duration at all our stations (Hawaii, Samoa, Florida, South Carolina, New Jersey, and Maine). The signals consist of several physically different parts—a practically instantaneous broad-band pulse (observed clearly only in the Pacific area) containing mainly higher frequencies, a strong oscillatory signal starting 1.9 seconds later simultaneously at all stations, a complex part lasting several minutes which is probably a superposition of different hydromagnetic modes, and an extremely long-period disturbance (observed only in the Pacific area) carrying considerable energy (which we interpret as a hydrodynamic-gravitational mode). The maximum signal amplitude (occurring within 3 to 5 seconds after the shot), when plotted versus distance from Johnston Island, results in a smoothly decreasing curve. Of the four other high-altitude nuclear tests above Johnston Island between October 20 and November 4, 1962, which were at various heights but all considerably lower than Starfish, none gave magnetic signals clearly above the noise level at the mainland stations. Three of these events produced clear effects at Hawaii (about 1500 km to the magnetic ENE of Johnston) and at Samoa (about 3400 km magnetically south of Johnston). The signal-amplitude ratio (Samoa to Hawaii) becomes, for sufficiently low shot heights, a pronounced function of the explosion height, indicating that the magnetic-signal propagation becomes more and more confined to the north-south direction as the explosion height is lowered.

An Analysis of the Intermodulation Method of Distortion Measurement

Part A of this paper is an analysis of the intermodulation method of distortion measurement. Results obtained by its use are compared with those obtained by the harmonic-measurement method. Predicted values for the intermodulation distortion and harmonic distortion are given for several typical transfer characteristics. For single-ended and push-pull characteristics, which are representable by simple power series, general equations are derived for intermodulation and harmonic distortion. With the aid of equations for the former, the effects of the ratio of signal amplitudes used in intermodulation testing are studied. These equations also permit derivation of relatively fixed ratios of per cent intermodulation distortion to per cent harmonic distortion for an intermodulation test method, which is described. Predicted values for distortion and their ratios are supported by test results. Curves expressing the actual distortion ratios, plotted against harmonic distortion, summarize the results of this analysis. These curves are useful for correlating the results of the two methods of test. Possible meter types, usable for metering the carrier- and intermodulation-frequency components in the intermodulation test method, are reviewed. The choice of meter type is found to affect the readings obtained for these components, and hence will affect the per cent intermodulation distortion. In Part B, simple equations are given for approximate predetermination of per cent intermodulation distortion from three or five points on the transfer characteristic. For more accurate prediction, tables are given for calculation of the prominent intermodulation components from eleven points on the transfer characteristics.