Preamplifier for biological signals processing

Práce se zabývá problematikou návrhu a optimalizace zesilovačů v technologii CMOS s nízkým napájecím napětím a nízkou spotřebou. Hlavním zaměřením práce je navrhnout zesilovač pro zesílení biologických signálu. V první části práce je stručný úvod do teorie biologických signálů. Dále práce obsahuje stručný popis metod zpracování biologických signálů a jejich vlastnosti. Důležitou částí práce je popis metod pro snížení napájecí napětí zesilovače. Praktická část této práce je zaměřena na návrh zesilovače s nízkým napájecím napětím a s nízkou spotřebou. Všechny aktivní prvky a příklady aplikací byly ověřeny pomocí PSpice simulací s využitím parametrů technologie 0,18 µm TSMC CMOS. Pro ilustraci chování struktur je v diplomové práci zahrnuty simulační výsledky.The work deals with the design and optimization of amplifiers in CMOS technology with low supply voltage and low power consumption. The main aim is to design an amplifier to amplify the biological signal. The first part is a brief introduction to the theory of biological signals. The work also contains a brief description of the biological signal processing methods and their properties. The important part is the description of the methods to reduce the supply voltage of the amplifier. The practical part of this thesis focuses on the design amplifiers with low supply voltage and low power consumption. All active elements and application examples have been verified by PSpice simulator using the 0.18 µm TSMC CMOS parameters. Simulated plots are included in this thesis to illustrate behavior of structures.

Cyclotron line formation in the magnetized atmospheres of compact stars: I. The transfer equations for polarized radiation

We find the forms of the transfer equations for polarized cyclotron radiation in the atmospheres of compact stars, which are simple enough to allow practical implementation and still preserve all important physical effects. We take into account a frequency redistribution of radiation within the cyclotron line as well as the relativistic and quantum-electrodynamic effects. Our analysis is valid for the magnetic fields up to $10^{13}$G and for temperatures well below 500keV.} We present and compare two forms of the radiation transfer equations. The first form, for the intensities of ordinary and extraordinary modes, is applicable for the compact stars with a moderate magnetic field strength up to $10^{11}$G for typical neutron star and up to $10^9$G for magnetic white dwarfs. The second form, for the Stokes parameters, is more complex, but applicable even if a linear mode coupling takes place somewhere in the scattering-dominated atmosphere. Analysing dispersion properties of a magnetized plasma {in the latter case, we describe a range of parameters where the linear mode coupling is possible and essential.Comment: 12 pages, 3 figures, MNRA

Off-axis emission from relativistic plasma flows

We show that there is no universal law describing how the spectra and luminosity of synchrotron and inverse Compton radiation from relativistic jets change with increasing observation angle. Instead, the physics of particle acceleration leaves pronounced imprints in the observed spectra and allows for a freedom in numerous modifications of them. The impact of these effects is the largest for high-energy radiation and depends on the details of particle acceleration mechanism(s), what can be used to discriminate between different models. Generally, the beam patterns of relativistic jets in GeV-TeV spectral domain are much wider than the inverse Lorentz factor. The off-axis emission in this energy range appear to be brighter, have much harder spectra and a much higher cut-off frequency compared to the values derived from Doppler boosting considerations alone. The implications include the possibility to explain high-latitude unidentified EGRET sources as off-axis but otherwise typical relativistic-jet sources, such as blazars, and the prediction of GeV-TeV afterglow from transient jet sources, such as Gamma-Ray Bursts. We also discuss the phenomenon of beam-pattern broadening in application to neutrino emission.Comment: Submitted to the Astrophysical Journa

High-energy emission from off-axis relativistic jets

We analyze how the spectrum of synchrotron and inverse Compton radiation from a narrow relativistic jet changes with the observation angle. It is shown that diversity of acceleration mechanisms (in particular, taking the converter mechanism (Derishev et al. 2003) into account) allows for numerous modifications of the observed spectrum. In general, the off-axis emission in GeV-TeV energy range appears to be brighter, has a much harder spectrum and a much higher cut-off frequency compared to the values derived from Doppler boosting considerations alone. The magnitude of these effects depends on the details of particle acceleration mechanisms, what can be used to discriminate between different models. One of the implications is the possibility to explain high-latitude unidentified EGRET sources as off-axis but otherwise typical relativistic-jet sources, such as blazars. We also discuss the broadening of beam pattern in application to bright transient jet sources, such as Gamma-Ray Bursts.Comment: 6 pages, Proceedings of the International Symposium "High Energy Gamma-Ray Astronomy", 26-30 July 2004, Heidelberg, German

Nucleosynthesis in gamma-ray bursts outflows

It is shown that fusion of neutrons and protons to He-4 nuclei occurs in gamma-ray burst outflows in a process similar to big-bang nucleosynthesis in the early Universe. Only the surviving free neutrons can then decouple kinematically from the charged fluid so that the multi-GeV neutrino signal predicted from inelastic nuclear n-p collisions is significantly reduced. It is also argued that a sizeable fraction of ultra-high energy cosmic rays accelerated in gamma-ray bursts should be He-4 nuclei.Comment: 4 pages, v2: minor modifications, to appear in A&A Letter