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47
نتائج ل
"Steane, Andrew M"
صنف حسب:
On determining absolute entropy without quantum theory or the third law of thermodynamics
We employ classical thermodynamics to gain information about absolute entropy, without recourse to statistical methods, quantum mechanics or the third law of thermodynamics. The Gibbs-Duhem equation yields various simple methods to determine the absolute entropy of a fluid. We also study the entropy of an ideal gas and the ionization of a plasma in thermal equilibrium. A single measurement of the degree of ionization can be used to determine an unknown constant in the entropy equation, and thus determine the absolute entropy of a gas. It follows from all these examples that the value of entropy at absolute zero temperature does not need to be assigned by postulate, but can be deduced empirically.
Journal Article
The fields and self-force of a constantly accelerating spherical shell
We present a partial differential equation describing the electromagnetic potentials around a charge distribution undergoing rigid motion at constant proper acceleration, and obtain a set of solutions to this equation. These solutions are used to find the self-force exactly in a chosen case. The electromagnetic self-force for a spherical shell of charge of proper radius R undergoing rigid motion at constant proper acceleration a0 is, to high-order approximation, , and this is conjectured to be exact.
Journal Article
The Wonderful World of Relativity
This book provides a lively and visual introduction to Einstein's theory of relativity. It brings to life the excitement of this fascinating subject, for an audience including young people at school (post-16) and the general public with an interest in modern physics.
eBook
Relativity made relatively easy
This book unfolds the subject of Relativity for undergraduate students of physics. It fills a gap between introductory descriptions and texts for researchers. Assuming almost no prior knowledge, it allows the student to handle all the Relativity needed for a university course, with explanations as simple, thorough, and engaging as possible.
eBook
Efficient fault-tolerant quantum computing
Quantum computing-the processing of information according
to the fundamental laws of physics-offers a means to solve efficiently
a small but significant set of classically intractable problems. Quantum computers
are based on the controlled manipulation of entangled quantum states, which
are extremely sensitive to noise and imprecision; active correction of errors
must therefore be implemented without causing loss of coherence. Quantum error-correction
theory has made great progress in this
regard, by predicting error-correcting 'codeword' quantum states.
But the coding is inefficient and requires many quantum bits,
which results in physically unwieldy fault-tolerant quantum circuits. Here I report a general technique
for circumventing the trade-off between the achieved noise tolerance and the
scale-up in computer size that is required to realize the error correction.
I adapt the recovery operation (the process by which noise is suppressed through
error detection and correction) to simultaneously correct errors and perform
a useful measurement that drives the computation. The result is that a quantum
computer need be only an order of magnitude larger than the logic device contained
within it. For example, the physical scale-up factor, required to factorize a thousand-digit number is reduced from 1,500
to 22, while preserving the original tolerated gate error rate (10
−5) and memory noise per bit (10−7). The
difficulty of realizing a useful quantum computer is therefore significantly
reduced.
Journal Article
Relativity Made Relatively Easy Volume 2
Aimed at advanced undergraduate or graduate physics students, the book aims to give a working understanding of astronomy and gravitational waves, as well as introducing the reader to the key concepts in cosmology and classical field theory.
eBook
The fields and self-force of a constantly accelerating spherical shell
We present a partial differential equation describing the electromagnetic potentials around a charge distribution undergoing rigid motion at constant proper acceleration, and obtain a set of solutions to this equation. These solutions are used to find the self-force exactly in a chosen case. The electromagnetic self-force for a spherical shell of charge of proper radius R undergoing rigid motion at constant proper acceleration a0 is, to high-order approximation, $(2{\\mathrm{e}}^{2}{\\mathrm{a}}_{0}/\\mathrm{R})\\sum _{\\mathrm{n}=0}^{\\mathrm{\\infty }}\\left({\\mathrm{a}}_{0}\\mathrm{R}{)}^{2\\mathrm{n}}\\right((2\\mathrm{n}-1)(2\\mathrm{n}+1{)}^{2}(2\\mathrm{n}+3){)}^{-1}$, and this is conjectured to be exact.
Journal Article
Irreversible behaviour of a gas owing to Unruh radiation
When gas molecules collide, they accelerate, and therefore encounter the Fulling-Davies-Unruh and Moore-DeWitt effects. The size of these effects is sufficient to randomize the motion of the gas molecules after about 1 nanosecond at standard temperature and pressure. Such observations show that quantum field theory modifies what is required to isolate a physical system sufficiently for its behaviour to be unitary. In practice the requirements are never satisfied exactly. Therefore the evolution of the observable universe is non-unitary and thermodynamically irreversible.
Paper
Gregarious atoms
Bose-Einstein condensation, a quantum effect that occurs at low energies when the wavefunctions of atoms overlap so that the individual particles become indistinguishable, has been observed in a gas of rubidium-87 atoms. This progress in quantum physics is discussed.
Journal Article