The addition of a current-controlled current source and a linear combination of two reference voltages in a typical biasing system to an electron source allows one to ground the cathode, anode and reference voltage sources, thereby improving the operation of the whole system. When a negative feedback loop is closed and the system works as a stabilizer, the first reference voltage, V ref1 , controls the electron emission current, while a voltage that is directly proportional to a linear combination of two reference voltages, V ref1 and V ref2 , controls the electron accelerating voltage. Consequently, this voltage is independent of the electron emission current and vice versa, which is particularly important for a mass spectrometer. The standard deviation of the electron emission current is smaller than 0.03% over the whole range of its intensity. When the negative feedback loop is open, the system is highly suitable for use in studying the static, dynamic and stochastic properties of an electron source by means of a simple and convenient use of a computer, because the reference voltage sources are grounded.
Electron sources with a hot cathode operating in consumption or generation modes are widely used in many vacuum devices as gas ion sources, thermionic energy converters. The main aim of this work is to get information how dynamic properties of the electron source changes within full range of work, therefore the identification of a hot cathode electron source using the step signal and the time domain approach to know dynamic parameters (DC incremental transconductance, time constant, delay time) of the electron source in full range of its operation is made. In the first part, an open-loop system identification using step response method was conducted. For the electron source with a thoriated tungsten cathode (d=0.1 mm, l=45 mm) operating in the range 1 μA to 1 mA, the time constant T varies from 0.71 s to 0.35 s, the delay time T0 from 0.04 s to 0.01 s and the DC incremental transconductance g0 from 0 to 0.0056 S, respectively. In the next step, an approximation of obtained characteristics is made and ultimate gains of thermionic emission current automatic control system for each fixed operating point are estimated. The results of similar investigations for electron sources with an yttrium oxide coated iridium cathode and a tungsten cathode have also been shown. Presented system identification approach can be successfully applied to other types of the hot cathode electron sources.
Despite the number of studies focused on sense-antisense transcription, the key question of whether such organization evolved as a regulator of gene expression or if this is only a byproduct of other regulatory processes has not been elucidated to date. In this study, protein-coding sense-antisense gene pairs were analyzed with a particular focus on pairs overlapping at their 5’ ends. Analyses were performed in 73 human transcription start site libraries. The results of our studies showed that the overlap between genes is not a stable feature and depends on which TSSs are utilized in a given cell type. An analysis of gene expression did not confirm that overlap between genes causes downregulation of their expression. This observation contradicts earlier findings. In addition, we showed that the switch from one promoter to another, leading to genes overlap, may occur in response to changing environment of a cell or tissue. We also demonstrated that in transfected and cancerous cells genes overlap is observed more often in comparison with normal tissues. Moreover, utilization of overlapping promoters depends on particular state of a cell and, at least in some groups of genes, is not merely coincidental.
The addition of another loop in a typical DC electron emission controller between (a) the filament supply point and (b) the inverting input of the operational amplifier improves the work of the whole system. If this loop consists of a diode directed from point a to point b and a capacitor connected in parallel to the diode the system has the following new features: (1) it enables a gradual heating of the filament for its outgassing when the system is turned on, (2) the filament is protected in the case when the main feedback loop having external parts is accidentally broken, (3) the capacitor eliminates the generation of any AC current in the filament circuit. The last property notably extends the lifetime of the filaments working in a strong magnetic field, e.g. in mass spectrometers.
The implementation of a non-linear combination of two reference voltages to control the anode voltage in the previously described biasing system of an electron source with a hot cathode allows elimination of the correlation between the emission current and the accelerating voltage. The presented system is highly suitable for applications in electron-impact mass spectrometers, ionization gauges and other instruments (for example, electron microscopes).
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