Working physicists, and especially astrophysicists, value a good `back-of-the-envelope' calculation, meaning a short, elegant computation or argument that starts from general principles and leads to an interesting result. This book guides students on how to understand astrophysics using general principles and concise calculations - endeavouring to be elegant where possible and using short computer programs where necessary. The material proceeds in approximate historical order. The book begins with the Enlightenment-era insight that the orbits of the planets is easy, but the orbit of the Moon is a real headache, and continues to deterministic chaos. This is followed by a chapter on spacetime and black holes. Four chapters reveal how microphysics, especially quantum mechanics, allow us to understand how stars work. The last two chapters are about cosmology, bringing us to 21st-century developments on the microwave background and gravitational waves.

So far a detailed study on Heterojunction Bipolar Transistor made of Inp/InGaAs with nearly Gaussian Base doping profile, has not been done .Because of that a detailed study on Inp-InGaAs HBT is presented in this work. Two important factors for determining the performance of a transistor are base transit time and current gain ( ). Variations of base transit time and gain with temperature and other device parameters for both uniform and non-uniform base doping profiles are studied here. The non-uniform base doping profile studied here is nearly Gaussian in nature. Dependence of diffusion coefficient (Dn) on temperature (T) and base doping concentration (Na) are taken into account in this study. Dependence on composition variation in the base is also taken into consideration. Also studied Gummel No in relation with base doping concentration (Na(x)). I think this work may be helpful for the final year students of Bachelor Degree and Master Degree, if they work on HBTs and their different device parameters and all those who have interest in latest works and developments in the field of Electronic Devices."

Working physicists, and especially astrophysicists, value a good `back-of-the-envelope' calculation, meaning a short, elegant computation or argument that starts from general principles and leads to an interesting result. This book guides students on how to understand astrophysics using general principles and concise calculations - endeavouring to be elegant where possible and using short computer programs where necessary. The material proceeds in approximate historical order. The book begins with the Enlightenment-era insight that the orbits of the planets is easy, but the orbit of the Moon is a real headache, and continues to deterministic chaos. This is followed by a chapter on spacetime and black holes. Four chapters reveal how microphysics, especially quantum mechanics, allow us to understand how stars work. The last two chapters are about cosmology, bringing us to 21st-century developments on the microwave background and gravitational waves.