Background[ edit ] The first published description of S-parameters was in the thesis of Vitold Belevitch in
The normal flow is balanced by a flow of the superfluid component from the cold to the hot end. At the end sections a normal to superfluid conversion takes place and vice versa. So heat is transported, not by heat conduction, but by convection.
This kind of heat transport is very effective, so the thermal conductivity of He-II is very much better than the best materials.
The situation is comparable with heat pipes where heat is transported via gas—liquid conversion. Theory[ edit ] Landau two-fluid approach[ edit ] L. Landau's phenomenological and semi-microscopic theory of superfluidity of helium-4 earned him the Nobel Prize in physics, in Logarithmic amplifier thesis Assuming that sound waves are the most important excitations in helium-4 at low temperatures, he showed that helium-4 flowing past a wall would not spontaneously create excitations if the flow velocity was less than the sound velocity.
In this model, the sound velocity is the "critical velocity" above which superfluidity is destroyed. Helium-4 actually has a lower flow velocity than the sound velocity, but this model is useful to illustrate the concept. Landau also showed that the sound wave and other excitations could equilibrate with one another and flow separately from the rest of the helium-4, which is known as the "condensate".
From the momentum and flow velocity of the excitations he could then define a "normal fluid" density, which is zero at zero temperature and increases with temperature. At the so-called Lambda temperature, where the normal fluid density equals the total density, the helium-4 is no longer superfluid.
To explain the early specific heat data on superfluid helium-4, Landau posited the existence of a type of excitation he called a " roton ", but as better data became available he considered that the "roton" was the same as a high momentum version of sound.
The Landau theory does not elaborate on the microscopic structure of the superfluid component of liquid helium. Their main objective is to derive the form of the inter-particle potential between helium atoms in superfluid state from first principles of quantum mechanics.
To date, a number of models of this kind have been proposed, including: Vortex ring model[ edit ] Landau thought that vorticity entered superfluid helium-4 by vortex sheets, but such sheets have since been shown to be unstable. Lars Onsager and, later independently, Feynman showed that vorticity enters by quantized vortex lines.
They also developed the idea of quantum vortex rings. Arie Bijl in the s,  and Richard Feynman around developed microscopic theories for the roton, which was shortly observed with inelastic neutron experiments by Palevsky.
Later on, Feynman admitted that his model gives only qualitative agreement with experiment.* NUES. The student will submit a synopsis at the beginning of the semester for approval from the departmental committee in a specified format.
The student will have to present the progress of the work through seminars and progress reports. E02 - DEVELOPMENTS IN ENGINEERING. Note: Subject matter will vary from term to term and from year to alphabetnyc.comts may re-register for these courses, providing that the course content has changed.
Changes in content will be indicated by the letter following . ANTheory and Applications of Logarithmic Amplifiers..
ABSTRACT A number of instrumentation applications can benefit from the use of logarithmic or exponential signal processing techniques.
Screening of plant extracts and plant constituents for calcium-channel blocking activity. - welcome to the wonderful world of soviet books.
- this site attempts to catalogue the amazing books in english, hindi and other indian languages, published the soviet union (ussr). Scattering parameters or S-parameters (the elements of a scattering matrix or S-matrix) describe the electrical behavior of linear electrical networks when undergoing various steady state stimuli by electrical signals..
The parameters are useful for several branches of electrical engineering, including electronics, communication systems design, and especially for microwave engineering.