Change In Oscillation Frequency Research Articles

Frequency, amplitude, and propagation velocity of spontaneous Ca++-dependent contractile waves in intact adult rat cardiac muscle and isolated myocytes.

Spontaneous contractile waves due to spontaneous calcium cycling by the sarcoplasmic reticulum occur in unstimulated bulk rat papillary muscle and single rat cardiac myocytes with intact sarcolemmal function. We used video analytic techniques to quantify the wave characteristics in both bulk muscle and myocytes; laser-light scattering techniques were also employed in muscle. In muscle bathed in physiological concentrations of calcium, the true periodicity of these waves was a fraction of 1 Hz and increased up to several hertz with increases in cell calcium. This was paralleled by an increase in the frequency of scattered laser light intensity fluctuations. In myocytes, a range of spontaneous contractile wave frequencies similar to that which occurred in the muscle was observed; it could be demonstrated that an increase in superfusate calcium concentrations (2-15 mM at 23 degrees C) increases the oscillation frequency but not amplitude. In both myocytes and muscle, low concentrations of caffeine (0.5 mM) and higher temperature increased the oscillation frequency but diminished their amplitude. However, the scattered light fluctuations did not change with temperature and decreased with caffeine. These results demonstrate that (1) the true frequency of spontaneous sarcoplasmic reticulum oscillations in the unstimulated rat muscle and single myocytes with intact sarcolemmal function is low, i.e., a fraction of a hertz; (2) with cell calcium loading, the oscillation frequency accelerates to those frequencies measured previously in the "calcium overload" state; (3) while scattered light fluctuations which sample myofilament motion are a sensitive, noninvasive method of detecting the oscillations in bulk muscle, they can be insensitive to the divergent changes in oscillation amplitude and frequency.

The oscillation frequency of a quartz resonator in contact with liquid

A simple relationship is derived which expresses the change in oscillation frequency of a quartz crystal in contact with a fluid in terms of material parameters of the fluid and the quartz. The relationship is Δ f = − f 3 2 0(η L ϱ L /πμ Qϱ Q) 1 2 , where f 0 is the oscillation frequency of the free (dry) crystal, η L and ϱ L are the absolute viscosity and density of the liquid, respectively, and μ Q and ϱ Q are the elastic modulus and density of the quartz. This relation is obtained from a simple physical model which couples the shear wave in the quartz to a damped shear wave in the fluid. Quantitative comparisons with two test cases, aqueous solutions of glucose and ethanol at various concentrations, demonstrate the accuracy of this model.

DC and pulse-light illuminated optical responses of microwave GaAs-MESFET oscillators

Experimental results of two kinds of optical effects, optical tuning and optical switching, of GaAs MESFET oscillators are presented. For optical tuning, the oscillation frequency decreases with optical illumination and the maximum tuning range depends principally on oscillator mode (common-source, common-drain or common-gate), with 3.8% and 1.9% being achieved at S band and X band, respectively, with an optical power density of 0.5 mW/mm2. The oscillator power output generally increases with optical illumination, the increase being around 1 to 2 dB at 0.5 mW/mm2 light intensity. For optical switching, power output switching from no oscillation to 7.5 mW was obtained at X band with illumination from a 2 mW laser diode. The optical response of microwave GaAs MESFET oscillators is attributed to the capture of holes by two kinds of hole traps in the Schottky-gate depletion region. The oscillation frequency and power output changes with optical illumination become appreciably reduced with increase of optical modulation rate, becoming 10% of the constant-illumination induced change at an optical modulation rate of 1 MHz and negligibly small at 10 MHz. The drain current bias still responds above 10 MHz, with a response amount about 0.5 mA attributed to the photoconductivity effect in the channel.

A frequency-modulated capacitance transducer for on-line measurement of two-component fluid flow

A capacitance instrument is described, which is capable of detecting and measuring the amount of undissolved gas in either oil or water flowing in a pipe. Experimental results are presented relating meter output to gas concentration at known water velocities. Sensing electrodes are formed into an insulated section of the conveyor and form a capacitor in which the dielectric consists of a section of the following medium. This capacitor is connected in parallel with an inductor to form a parallel tuned oscillator circuit. The frequency of oscillation varies with the concentration of the second component. The second component is not uniformly distributed throughout the water but may be visualised as an average concentration with superimposed fluctuations. These fluctuations arise due to the random distribution of the phases and the turbulence of the flow. They are termed flow noise, and the resultant changes in capacitance cause corresponding changes in oscillator frequency. The change in frequency is detected by a frequency demodulator which produces a fluctuating voltage. The rms value of the fluctuations varies as the concentration of the second component.

A D.C. biased, microwave operating SQUID

A device with two long overlap hysteretic Josephson tunnel junctions in parallel is analyzed by a mechanical analog. Two identical junctions incorporated in a superconducting ring in a suitable geometrical configuration behave as a single junction. A magnetic flux threading the ring introduces a phase discontinuity in the center of the junction. On the analog the introduction of the discontinuity gives rise to significant changes in the kink's oscillation frequency.

The Potentiostatic Current Oscillations at Iron/Sulfuric Acid Solution Interfaces

The regular oscillations of current at potentiostatically controlled (aq) interfaces are studied as a function of electrolyte concentration, hydrogen ion activity, stirring conditions, and temperature. The oscillation frequency changes according to well‐defined relationships among these parameters. The analysis of results indicates that various concurrent chemical and electrochemical reactions together with diffusional contributions participate to a different extent during each period.

Nonlinear behavior of the BARITT diode microwave oscillator

Nonlinear behavior of the free-running BARITT diode oscillator has been observed. Discontinuous changes in oscillation frequency and output power occur as the bias current changes. These non-linearities have been investigated in coaxial and waveguide oscillators and are caused by device and circuit interactions.

Aftereffects in IMPATT oscillators with transient ionizing radiation

Two types of aftereffects were observed in testing IMPATT diodes under ionizing radiation. The first type can be characterized by a 10-25-percent decrease in power and a 5-20-MHz change in oscillation frequency after the radiation pulse. The second type is characterized by a large change in oscillator performance (3-dB decrease in power and 1-GHz change in frequency) or irreversible diode failure, and occurred with two GaAs Schottky diodes. A strong cavity-RF load dependence has been demonstrated for the latter type of aftereffect.

Elastic properties of the lunar surface from Surveyor spacecraft data

Elastic properties of the upper few centimeters of the lunar surface material are estimated from frequency and decay rate of vertical oscillations of Surveyor spacecraft on landing. Data from tests using a duplicate spacecraft resting on a rigid surface and on test soils provided the elastic properties of the spacecraft and the expected changes in resonant frequency of oscillations when going from a rigid to a compliant surface. The surface stiffness is obtained by matching the output of an analog computer model with the test and lunar data. From the stiffness of the lunar material a range of possible seismic velocities is obtained. Compressional and shear velocities are estimated to be about 45 m/sec and 23 m/sec, respectively. These results appear to be consistent with data from the Apollo program.

The effect of lattice vibrations on the nature of order-disorder transitions the hydrogen halides

The effect of a change in oscillation frequency or barrier hindering rotation of molecules on an order-disorder transition is considered. To the order of approximation of Bragg and Williams it is shown that when the frequency of oscillation of the molecules is lowered by the transition, part of the transition becomes first order. Expressions for the thermodynamic quantities associated with the effect have been developed. The effect of isotopic substitution on the total enthalpy of transition of hydrogen chloride and hydrogen bromide has been calculated from the experimental data and from the spectroscopic data and used to justify the interpretation of the infrared spectra of hydrogen chloride and hydrogen bromide. Frequencies above and below the transition have been used to calculate the part of the enthalpy of transition that is involved in the second and first order parts of the transition respectively. The effect of a change in the Debye lattice frequencies is discussed and it is shown that this in itself does not introduce first order character into the transition. The entropy changes at the transitions have been calculated and it has been shown that these are affected by a change in oscillation frequency on transition. The nature of the transitions in plastic crystals has been discussed in the light of frequency changes of the oscillating molecules.

A super-regenerative microwave Doppler moving-target indicator

A reflex klystron oscillator is used as the microwave transmitter and superregenerative receiver in a Doppler radar designed to measure the relative speed of a moving target at distances of up to three hundred feet. It is shown that the klystron oscillation frequency must be kept within close limits, and the rate of oscillation decay must be suitably controlled, in order that the receiver sensitivity may be kept high. Experiments are described which further relate the sensitivity of the system to the change in oscillation frequency occurring during the quench cycle; in particular, by using a resonator quench, the effective power of the receiver is increased by over 50 dB above that obtained with a repeller quench. Road tests of the receiver have shown it to be of value as part of a collision-warning device for road vehicles.

Temperature Dependence of Surface Tension for Liquid Metals

The surface-tension temperature dependence is calculated for liquid metals. In this calculation the ion motion is taken as a harmonic oscillation and it is shown that the difference in oscillation frequencies for surface and inner ions is mainly responsible for the temperature dependence of the surface tension. There is, however, a second influence caused by the change of particle density due to thermal expansion. An expression for the surface tension is derived and comparison is made with experimental values. The change of oscillator frequency, the surface tension at zero temperature, and a characteristic temperature corresponding to the critical temperature are calculated.

Instrument for Continuous High Resolution Measurement of Changes in the Velocity of Ultrasound

The frequency of the ``reference'' oscillator in a coherent pulse echo apparatus is phase-locked to the spacing in time of the acoustic echoes. A change in echo spacing is thereby converted to the same fractional change of oscillator frequency, which is measured continuously. Echo spacing changes of 2 to 3 parts in 108 have been resolved at 12 Mc. The gated AFC circuit which controls the reference oscillator derives its error voltage from a phase-detected echo. The error voltage is zero when the echo is in quadrature with the reference. When the echo spacing changes, the AFC shifts the reference frequency to preserve the quadrature condition. The system is largely insensitive to changes of echo amplitude because such changes do not affect the quadrature condition. The attainable accuracy is set mainly by the temperature stability of the sample. There is a detailed discussion of circuitry, performance, and suggested refinements.

Dynamic mechanical properties of supported polymers. II. Application of the torsional braid technique to the study of the curing and stability of resins

AbstractTransformations, physical and chemical, which occur in polymeric systems are usually accompanied by changes in rigidity. In the present method, a modified torsional pendulum is employed such that the vertical specimen shaft consists of a fabric braid which is impregnated with the polymeric material under investigation. Therefore, in principle, any changes in the mechanical properties of the composite will be reflected by changes in frequency of free oscillation of the system. This dynamic mechanical technique provides a very sensitive tool for following nondestructively, the liquid to solid transitions accompanying the curing of polymers. In this communication the utility of the torsional braid technique in the study of heat resistant polymers is emphasized. Curing and thermal softening behavior, as well as pyrolytic and oxidative degradations are monitored with precision. A comparative study between three thermosetting resins, i.e., a phenolic, an unsaturated polyester and a phosphonitrilic, is presented.

Measurement of the dielectric constant of filament nylon in a transverse field

An instrument has been designed for measuring the dielectric constant of a material in the form of a single cylindrical filament, and experiments are described in which it is used for measurements on nylon. The filament is placed centrally between two silvered optical flats, which form a parallel-plate capacitor and serve as the tuning capacitor of a radio-frequency oscillator. According to an existing theory, the change in capacity due to the presence of the dielectric is given by: δC = ((b2H/2D2) tanh πB/2D)/(( + 1)/( - 1) - π2b2/3D2) (where b is the radius of the filament, H the length of the capacitor, B the width and D the distance between the plates) and δC can be determined from the corresponding change in oscillator frequency, if the electrical parameters of the circuit are known. The experimental observations confirmed the general form of the equation, but they were not sufficiently accurate to verify the second-order term π2b2/3D2. A value of 3.0 was found for the dielectric constant of nylon at 6 to 7 Mc/s, which is in reasonable agreement with values of 3.1 to 3.4 recorded by other workers for both filament and bulk nylon.

Characteristics of the Beam Type Maser I

Experimental investigation of the characteristics of the ammonia maser is given and compared with theory. Observed saturation characteristics agree fairly well with the theory descibed in the previous paper. The change of oscillation frequency shows the expected increase with focuser voltage which arises from unresolved hyperfine structure of the 3,3 line. Small discrepancies are explained by the velocity distribution and different saturation of each hyperfine component. Frequency pulling due to cavity detuning was measured in detail and compared with theory. Thus the velocity spread of the effective molecules in the cavity can be estimated as roughly ±30%. Tentative estimate of the center frequency on U T 2 is compared with other measurements.

An Automatic Frequency-Controlled Oscillator and Amplifier for Driving Mechanical Vibrators

An oscillator system has been developed for driving mechanical sound generators or other vibrating mechanical systems which require that the vibrating member be driven at its resonant frequency. The oscillator is a vacuum tube type in which an automatic frequency control, similar in principle to that employed in radio receivers, is used to keep the frequency at or very close to the resonant frequency of the vibrator. The change in phase of the vibrator motion relative to the driving force is used to supply a potential proportional to the difference between the driving frequency and the resonant frequency of the vibrating member, and having a polarity dependent on whether the driving frequency is less than or greater than the resonant frequency. This voltage is used to control a reactor tube which in turn controls the frequency of the oscillator circuit. The circuit is very effective, changes in either oscillator or vibrator frequency, or both, of approximately 500 cycles per second in 12 kilocycles, being followed automatically so that the oscillator frequency will not deviate from the resonant frequency of the vibrating member by more than 0.1 cycle per second.

A variable air condenser with adjustable compensation for temperature

The paper forms a natural continuation of an earlier investigation of the electrical stability of condensers and the development of satisfactory means of obtaining compensation for temperature variation. It has been shown in a previous paper that such compensation can readily be obtained for slow temperature-changes, but that great care is necessary in matching the thermal masses of the various parts if the temperature-changes are rapid. By applying the results of this previous analysis, a condenser of reasonable size has been developed which is compensated for temperature-changes as rapid as 7 deg. C. per minute.Special design features are introduced to produce this result, the most noticeable of which are the use of springloaded steel balls in place of plain bearings and the inversion of the normal electrical connections to rotor and stator, this latter alteration being adopted to eliminate difficulties which arise with an earthed screening case.Electrical tests of the performance under varying conditions of temperature-change show that the temperature coefficient of capacitance can be adjusted to have any value between the limits + 80 and − 80 parts in a million per deg. C. and therefore that the coefficient can be so adjusted as to compensate for the inductance coefficient of the associated inductance coil. The variation of the resultant frequency coefficient of the complete circuit with change of oscillation frequency is not large, and the transient variations do not exceed 10 parts in a million per deg. C. for temperaturechanges at a rate of 7 deg. C. per minute.

A variable air condenser with adjustable compensation for temperature

The paper forms a natural continuation of an earlier investigation of the electrical stability of condensers and the development of satisfactory means of obtaining compensation for temperature variation. It has been shown in a previous paper that such compensation can readily be obtained for slow temperature-changes, but that great care is necessary in matching the thermal masses of the various parts if the temperature-changes are rapid. By applying the results of this previous analysis, a condenser of reasonable size has been developed which is compensated for temperature-changes as rapid as 7 deg. C. per minute.Special design features are introduced to produce this result, the most noticeable of which are the use of springloaded steel balls in place of plain bearings and the inversion of the normal electrical connections to rotor and stator, this latter alteration being adopted to eliminate difficulties which arise with an earthed screening case.Electrical tests of the performance under varying conditions of temperature-change show that the temperature coefficient of capacitance can be adjusted to have any value between the limits + 80 and − 80 parts in a million per deg. C. and therefore that the coefficient can be so adjusted as to compensate for the inductance coefficient of the associated inductance coil. The variation of the resultant frequency coefficient of the complete circuit with change of oscillation frequency is not large, and the transient variations do not exceed 10 parts in a million per deg. C. for temperature changes at a rate of 7 deg. C. per minute.

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