Linear Mode Of Operation Research Articles

A programmable log-linear amplifier for wide range nuclear power measuring channels

A programmable log-linear amplifier has been developed for nuclear channels. The amplifier can be programmed for logarithmic, linear or log-linear mode of operation. In the log-linear mode, the amplifier operates partially in log mode and automatically switches to linear mode at any preset point. The log-linear mode is used for wide range operation of nuclear channels and, hence, the amplifier will improve the fault finding capabilities of the nuclear channels used in power range. The amplifier is tested at nuclear reactor and the results are found in very good agreement with the designed specifications. This article presents design and construction of the amplifier and field test results.

A class-D vertical booster for CRT

Integrated vertical boosters for the cathodic tube (CRT) are in charge of the vertical scanning of the electron beam on the CRT. They are amplifiers, and their function is to apply a sawtooth current on their load, which is a deflection yoke. The value of the current to be considered is typically around 2 A peak to peak. For such circuits in linear operating mode, the power dissipation is around 6 W in the integrated circuit for 2 W supplied to the load. The following circuit in class-D operating mode allows to reduce drastically the power dissipated in the integrated circuit and consequently the power consumption of the application. The power saving is typically 4 W compared with a traditional class-AB application. Taking in account the main power supply efficiency the total power saving is around 5 W.

The design, fabrication, and measured acoustic performance of a 1-3 piezoelectric composite Navy calibration standard transducer.

The design, fabrication, and acoustic calibration of a new 1-3 piezoelectric composite-based U.S. Navy standard (USRD-F82) are presented. The F82 dual array/parametric mode projector may be used as a reciprocal linear transducer, or may be used to exploit the nonlinear properties of the water to produce highly directional acoustic beams (4 to 3 deg) at relatively low frequencies (5 to 50 kHz, respectively). As a result of its wide bandwidth, a broad range of primary as well as secondary frequencies of operation is possible. In the linear mode of operation the transducer provides two separate arrays to be addressed topside for either transmit or receive applications. The two circular apertures are centered on the acoustic axis and have active diameters of 22.8 cm (9 in.) and 5.1 cm (2 in.). The smaller array aperture could be used to obtain broader acoustic beams at relatively high frequencies. Due to the absence of air-filled pressure release components, the transducer will operate over most ocean pressures and temperatures. A general description of the 1-3 piezoelectric composite-based transducer configuration and measured performance is presented.

Simulation of circular array ultrasound transducers for intravascular applications.

The beam shape of a circular array transducer that is commonly used in intravascular ultrasound catheters was investigated in linear mode of operation. For this use, a simulation program which can simulate the radio frequency (rf)-response of a number of scatterers has been developed. The program is based on the impulse response method, which is implemented in the frequency domain. Due to the unusual geometry of the transducer, the far field gets peculiarly shaped for large apertures. Instead of having a far field with its maximum intensity in a single lobe on the acoustical axis, the far field splits up into a dual-lobe far field with maximum intensity in two lobes off the acoustical axis. A formula is derived that predicts the occurrence of these beam shapes.

Low Frequency Noise and Random Telegraph Signal in a Multiple Quantum Well Infrared Photodetector

AbstractCurrent-voltage, voltage-time, and noise measurements were taken on a three well, twenty period, InGaAs/A1GaAs quantum well infrared photodetector at low temperature and low constant current bias. Data from the voltage-time measurements exhibited random telegraph signal (RTS) which is a manifestation of a single electron capture/emission event. It thus contributes to generation-recombination noise of the device. A model is proposed that allows extraction of number of mobile carriers, continuum state electron mobility, electron emission times and trap activation energy from the RTS data. These parameters may then be utilized to predict the excess noise spectrum. Data from the noise spectral density measurements show 1/f like noise at frequencies below I kHz. It can be shown to be a sum of Lorenztian curves with various electron emission times.The model proposed predicts that the local number of mobile charge carriers in any barrier section is less than 5 (total in the device around 300), there is nearly ballistic electron transport (mobility values around 3×105cm2/Vs), and the traps causing the RTS are in the barriers of the device and there are two of them in the device tested. The model applies to the linear mode of operation and assumes that the well regions are electron reservoirs, i.e. contacts, for the resistive barrier regions. The device is thus divided into a number of resistive portions in series. Each resistive portion is statistically independent from the others at low temperatures since the time the electrons spend in the wells is long compared to intra-well scattering times. This allows the electrons to fully thermalize and lose any statistical information from their previous continuum state trajectory.

Simulation studies of 6 nm free electron laser at the TESLA test facility starting from noise

The paper presents simulation results of Self-Amplified Spontaneous Emission (SASE) FEL at the TESLA Test Facility (TTF) at DESY. One-dimensional, time-dependent program package FEL1D was used for simulations. When simulating linear mode of operation, we have used actual number of electrons in the beam, N ⋍ 6 × 10 9 , to calculate initial shot noise conditions at the undulator entrance. It was found that there is good agreement between simulation and analytical results. We also performed calculations of autocorrelation functions of the first and the second order, temporal and spectral characteristics of the output radiation of TTF FEL operating in linear and nonlinear SASE modes.

Matrix-assisted laser desorption/ionisation mass spectrometry of transfer ribonucleic acids isolated from yeast.

tRNATyr and tRNASer purified from bulk brewer's yeast tRNA were subjected to analysis by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry. Choosing a mixture of 2,4,6- and 2,3,4-trihydroxy-acetophenone and diammonium citrate as matrix a mass resolution of up to 220 (FWHM) was achieved in the linear mode of operation. Cation adduct suppression by addition of cation exchange beads and a chelating agent (CDTA) is shown to substantially improve mass resolution for this class of molecules.

Submicrochannel plate multipliers

A theoretical investigation of alumina micron and submicron multichannel electron amplifiers was carried out. The theoretical study was based on multiplier performance Monte-Carlo simulation and general concepts of secondary electron emission theory. The simulation was performed for multipliers for which the length-to-diameter ratio was varied from 40 to 60 and the bias voltage from 600 to 1400 V. Calculations were made for the linear mode of multiplier operation under single electron stimulus. The simulation showed that alumina plates of the considered configurations are expected to possess a high gain (> 1000 at applied voltages exceeding 1.2 kV). The simulation also demonstrated that submicrochannel multipliers have faster response (< 30 ps), better temporal resolution (< 10 ps) and higher tolerance to strong axial (parallel with respect to channel axis) magnetic fields (up to ∼ 4 T) than microchannel plates with the same length-to-diameter ratios. Anodic alumina submicrochannel plates with channel diameter 0.07–0.4 μm, length-to-diameter ratio up to 300 and an effective open area up to ∼ 50% have been produced.

Back and front interface related generation-recombination noise in buried-channel SOI pMOSFETs

This paper reports on a detailed study of generation-recombination (GR) noise in buried-channel silicon-on-insulator (SOI) pMOSFETs, occurring in the linear operation mode. In particular, the plateau amplitude and the corner frequency (relaxation time /spl tau/) of the Lorentzian are investigated as a function of the front (V/sub Gf/) and of the back gate bias (V/sub Gb/). It is shown that different cases can be distinguished, depending of the conduction mode of the device, i.e. for surface or buried channel operation. For surface channel operation the GR noise parameters are strongly influenced by the back gate bias and only weakly dependent on V/sub Gf/. The opposite is true when the front interface starts to deplete, thereby pushing the channel deeper into the Si film. As is shown, the relaxation time depends exponentially on either V/sub Gf/ or V/sub Gb/. A similar exponential gate-bias dependence is found for the Lorentzian amplitude. Based on the observations, it is concluded that the GR noise originates from the front or the back interface, depending on the operation mode. The effective density of front and back interface traps can be derived from the GR noise amplitude.

Information about previous phosphate fluctuations is stored via an adaptive response of the high-affinity phosphate uptake system of the cyanobacterium Anacystis nidulans

The high-affinity uptake system of phosphatelimited cyanobacterium Anacystis nidulans [Synechococcus leopoliensis (Raciborski) Komarek] is characterized by a threshold value below which uptake cannot occur. Here it is shown that, if phosphate-limited cyanobacteria are challenged with a short pulse of high phosphate concentration that appreciably exceeds this threshold value, the uptake system undergoes an adaptive response, leading to the attainment of new kinetic properties and a new threshold value. These new properties are maintained for several hours after the pulse. A notable characteristic of this new state is a wide linear dependence of the uptake rate on the external phosphate potential that is a function of the driving force of the uptake process. According to theoretical arguments it is shown that this “linear operation mode” can be explained by the simultaneous operation of several uptake systems with different, staggered threshold values and kinetic properties. Moreover, the new linear uptake properties, in turn, reflect the prehistory of phosphate supply experienced by the population. The consequences of this result with regard to environmental fluctuations of the phosphate concentration in lakes are discussed.

Efficiency of energy conversion in model biological pumps. Optimization by linear nonequilibrium thermodynamic relations.

Experimental investigations showed linear relations between flows and forces in some biological energy converters operating far from equilibrium. This observation cannot be understood on the basis of conventional nonequilibrium thermodynamics. Therefore, the efficiencies of a linear and a nonlinear mode of operation of an energy converter (a hypothetical redox-driven H+ pump) were compared. This comparison revealed that at physiological values of the forces and degrees of coupling (1) the force ratio permitting optimal efficiency was much higher in the linear than in the nonlinear mode and (2) the linear mode of operation was at least 10(6)-times more efficient that the nonlinear one. These observations suggest that the experimentally observed linear relations between flows and forces, particularly in the case of oxidative phosphorylation, may be due to a feedback regulation maintaining linear thermodynamic relations far from equilibrium. This regulation may have come about as the consequence of an evolutionary drive towards higher efficiency.

Linear and nonlinear excitation of a synchronous generator using a thyristor—magnetic amplifier regulator

This work introduces a new form of exciter—regulator for the dynamic control of a synchronous generator connected to a thyristor-controlled load. The method, called ‘linear and nonlinear excitation’, uses a combination of a thyristor bridge and a magnetic amplifier. The magnetic amplifier operates in either a linear or a nonlinear mode, associated with steady-state and dynamic generator operation, respectively. The linear mode of operation corresponds closely to operation of the conventional Goldington form of exciter system. The unique, nonlinear mode of operation of the proposed regulator gives greatly improved transient performance.

Switching-Type Servosystems in an Elementary Undergraduate Curriculum

The paper discusses how the concept of switchingtype servosystems can be introduced into an undergraduate curriculum without requiring a more advanced background in mathematics on the part of the student than is ordinarily expected. A differential equation approach is used to study the response of a second-order system which is excited with a step function input. The system starts to respond in a linear mode of operation with an over-all positive feedback and switches into a different linear mode with an over-all negative feedback at a predetermined instant. The system is designed so as to respond with no overshoot. The response time is shorter than that of a conventional critically-damped linear negative feedback system with the same major physical components. The results of a rigorous study by means of a phase-space representation are also given.