We use the influence functional path-integral method to derive an exact master equation for the quantum Brownian motion of a particle linearly coupled to a general environment (ohmic, subohmic, or supraohmic) at arbitrary temperature and apply it to study certain aspects of the loss of quantum coherence.PACS nurnber(s1: 05.40.+j, 03.65.Bz, 03.65.Db I. INTRODUCTION AND SUMMARYRecent revival of interest in quantum Brownian motion (QBM) as a paradigm of quantum open systems was motivated by possible observation of macroscopic effects in quantum systems (such as dissipation in tunneling [I-41) and problems of quantum measurement theory (such as the loss of quantum coherence due to a system's interaction with its environment [5-81). We are led to this very old problem because of our interest in the issue of quantum-to-classical transition in quantum cosmology [9,10], which involves quantum decoherence [11,12], dissipation [13], and correlation problems [14]. This issue also enters in the foundations of semiclassical gravity [15] which involves back reaction, particle creation, and dissipation problems as well [16,17]. How noise and fluctuations can act as germs of galaxies in inflationary and other evolutionary cosmologies [18,19] is also an important issue which statistical-mechanics studies can help to clarify.These problems all point to the necessity of a better understanding of the nature and structure of quantum open systems, especially for quantum fields. The interplay of statistical and quantum effects in processes involving noise and fluctuation such as dissipation, decoherence, correlation, particle creation, and back reaction could have left indelible marks on the state of the early Universe, which in its evolution could have strongly influenced the outcome of our present observable classical Universe [20]. The complexity of these problems requires the extension of previous analysis of the QBM problem to nonlinear couplings and more general environments giving rise to nonlocal dissipations, and colored noise, and eventually for stochastic quantum fields. This 'Electronic address: hu@umdhep.bitnet.

Bringing together the key ideas from nonequilibrium statistical mechanics and powerful methodology from quantum field theory, this book captures the essence of nonequilibrium quantum field theory. Beginning with the foundational aspects of the theory, the book presents important concepts and useful techniques, discusses issues of basic interest, and shows how thermal field, linear response, kinetic theories and hydrodynamics emerge. It also illustrates how these concepts and methodology are applied to current research topics including nonequilibrium phase transitions, thermalization in relativistic heavy ion collisions, the nonequilibrium dynamics of Bose-Einstein condensation, and the generation of structures from quantum fluctuations in the early Universe. Divided into five parts, with each part addressing a particular stage in the conceptual and technical development of the subject, this self-contained book is a valuable reference for graduate students and researchers in particle physics, gravitation, cosmology, atomic-optical and condensed matter physics.

No abstract

A flow-independent method for imaging the coronary arteries within a breath-hold on a standard whole-body MR imager was developed. The technique is based on interleaved spiral k-space scanning and forms a cardiac-gated image in 20 heartbeats. The spiral readouts have good flow properties and generate minimal flow artifacts. The oblique slices are positioned so that the arteries are in the plane and so that the chamber blood does not obscure the arteries. Fat suppression by a spectral-spatial pulse improves the visualization of the arteries.

No abstract