Broadband Performance Assessment of an RF Power Transistor Employing the Real Frequency Technique

selected active device is essential to design an RF power amplifier for optimum gain and power added efficiency. As they are obtained, these impedances may not be realizable network functions over the desired frequency band to yield the input and the output matching networks for the amplifier. Therefore, in this paper, first, we introduce a new method to test if a given impedance is realizable. Then, a novel “Real Frequency Line Segment Technique” based numerical procedure is introduced to assess the gain-bandwidth limitations of the given source and load impedances, which in turn results in the ultimate RF-power intake/ delivering performance of the amplifier. During the numerical performance assessments process, a robust tool called “Virtual Gain Optimization” is presented. Finally, a new definition called “Power-Performance-Product” is introduced to measure the quality of an active device. Examples are presented to test the realizability of the given source/load pull data and to assess the gain-bandwidth limitations of the given source/load pull impedances for a 45W-GaN power transistor, namely “Cree CG2H40045”, over 0.8 -3.8 GHz bandwidth.

Broadband Performance Assessment of an RF Power Transistor Employing the Real Frequency Technique

selected active device is essential to design an RF power amplifier for optimum gain and power added efficiency. As they are obtained, these impedances may not be realizable network functions over the desired frequency band to yield the input and the output matching networks for the amplifier. Therefore, in this paper, first, we introduce a new method to test if a given impedance is realizable. Then, a novel “Real Frequency Line Segment Technique” based numerical procedure is introduced to assess the gain-bandwidth limitations of the given source and load impedances, which in turn results in the ultimate RF-power intake/ delivering performance of the amplifier. During the numerical performance assessments process, a robust tool called “Virtual Gain Optimization” is presented. Finally, a new definition called “Power-Performance-Product” is introduced to measure the quality of an active device. Examples are presented to test the realizability of the given source/load pull data and to assess the gain-bandwidth limitations of the given source/load pull impedances for a 45W-GaN power transistor, namely “Cree CG2H40045”, over 0.8 -3.8 GHz bandwidth.

Current inconsistencies in the reporting of cases of intraabdominal retained textile foreign bodies

Background: It is assumed that the incidence of textile foreign bodies (TFB) unintentionally left in abdominal cavity is underreported, mostly due to the legal implications of their detection. Material and methods: One hundred thirty-five responses were received to a specially developed anonymous questionnaire on the TFB problem, including medico-legal aspects. Of the total number of respondents, 81 were surgeons and 54 – gynecologists. Results: Over 80% of respondents consider that if TFB was removed from abdominal cavity during the surgical intervention, it should be indicated in the final diagnosis. At the same time, the fact of detecting and removing TFB retained in abdomen in the real cases known by respondents was reflected in the surgical report and in diagnosis in only 49.1%. False description in case of detection and removal of intra-abdominal TFB admits 29.6% from total number of respondents, but only 24.5% with a shorter length of work (<15 years), and 40.7% – with a work experience over 15 years. Conclusions: Surprisingly, about 20% of respondents consider it justified not to indicate retained TFB in the final diagnosis. Moreover, the real frequency of TFB diagnosis concealment is 1.6 times higher and sharply contradicts the declared intentions about the need to report the true cause of pathology. Almost half of surgeons with a long lasting work experience allow a false description of intraoperative findings and, as a result, the official diagnosis.

Stellar dynamics in the periodic cube

ABSTRACT We use the problem of dynamical friction within the periodic cube to illustrate the application of perturbation theory in stellar dynamics, testing its predictions against measurements from N-body simulations. Our development is based on the explicitly time-dependent Volterra integral equation for the cube’s linear response, which avoids the subtleties encountered in analyses based on complex frequency. We obtain an expression for the self-consistent response of the cube to steady stirring by an external perturber. From this, we show how to obtain the familiar Chandrasekhar dynamical friction formula and construct an elementary derivation of the Lenard–Balescu equation for the secular quasi-linear evolution of an isolated cube composed of N equal-mass stars. We present an alternative expression for the (real-frequency) van Kampen modes of the cube and show explicitly how to decompose any linear perturbation of the cube into a superposition of such modes.

Physics of Absorption and generation of Electromagnetic Radiation

The chapter is divided into two parts. In the first part, the chapter discusses the theory of propagation of electromagnetic waves in different media with the help of Maxwell’s equations of electromagnetic fields. The electromagnetic waves with low frequency are suitable for the communication in sea water and are illustrated with numerical examples. The underwater communication have been used for the oil (gas) field monitoring, underwater vehicles, coastline protection, oceanographic data collection, etc. The mathematical expression of penetration depth of electromagnetic waves is derived. The significance of penetration depth (skin depth) and loss angle are clarified with numerical examples. The interaction of electromagnetic waves with human tissue is also discussed. When an electric field is applied to a dielectric, the material takes a finite amount of time to polarize. The imaginary part of the permittivity is corresponds to the absorption length of radiation inside biological tissue. In the second part of the chapter, it has been shown that a high frequency wave can be generated through plasma under the presence of electron beam. The electron beam affects the oscillations of plasma and triggers the instability called as electron beam instability. In this section, we use magnetohydrodynamics theory to obtain the modified dispersion relation under the presence of electron beam with the help of the Poisson’s equation. The high frequency instability in plasma grow with the magnetic field, wave length, collision frequency and the beam density. The growth rate linearly increases with collision frequency of electrons but it is decreases with the drift velocity of electrons. The real frequency of the instability increases with magnetic field, azimuthal wave number and beam density. The real frequency is almost independent with the collision frequency of the electrons.

Love Waves in a Viscoelastic Stratum: Explicit Expression for Complex Velocity as a Function of Frequency

ABSTRACT Propagation of Love wave is considered in a two-layered stratum of isotropic viscoelastic solids. The complex dispersion equation for this wave is solved through a complex analysis technique. This gets an analytical expression for complex velocity, as a function of real frequency rather than the complex wavenumber. This complex (phase) velocity is used further to calculate the (complex) group velocity. Numerical example is solved to analyze the dispersion in speed and attenuation of the viscoelastic Love waves.

Quasi-particle functional Renormalisation Group calculations in the two-dimensional half-filled Hubbard model at finite temperatures

We present a highly parallelisable scheme for treating functional Renormalisation Group equations which incorporates a quasi-particle-based feedback on the flow and provides direct access to real-frequency self-energy data. This allows to map out the boundaries of Fermi-liquid regimes and to study the effect of quasi-particle degradation near Fermi liquid instabilities. As a first application, selected results for the two-dimensional half-filled perfectly nested Hubbard model are shown.

Improvement of Jain’s algorithm for frequency estimation

In this paper we propose a procedure to correct Jain's algorithm, which in certain situations fails in correctly estimating the frequency by indicating frequency values that are very far from the real frequency. It happens because the two points considered for the method proposed by Jain are not on the same lobe. Thus, a method is proposed according to which these points are chosen so that the results are improved.