67,445 research outputs found
Decay process of quantum open system at finite-temperature
Starting from the formal solution to the Heisenberg equation, we revisit an
universal model for a quantum open system with a harmonic oscillator linearly
coupled to a boson bath. The analysis of the decay process for a Fock state and
a coherent state demonstrate that this method is very useful in dealing with
the problems in decay process of the open system. For finite temperature, the
calculations of the reduced density matrix and the mean excitation number for
the open system show that an initial coherent state will evolve into a
temperature-dependant coherent state after tracing over the bath variables.
Also in short-time limit, a temperature-dependant effective Hamiltonian for the
open system characterizes the decay process of the open system
The effect of piston bowl temperature on diesel exhaust emissions
In modern, high-speed, direct injection diesel engines for passenger vehicles, there is extensive impingement of the fuel sprays on to the piston bowl walls. Recent trends towards smaller engine sizes, equipped with high-pressure common-rail fuel injection systems, have tended to increase the spray/piston wall interaction. This paper describes tests carried out in a high-speed direct injection automotive diesel engine, during which the temperature of the piston was increased in a controlled manner between 189 and 227 degrees C while being continuously monitored. The aim of the work was to quantify the effects of piston temperature on pollutant exhaust emissions. The results show a significant reduction in unburned hydrocarbon emission, a significant increase in smoke emission, and no significant change in the emission of oxides of nitrogen. The increase in smoke emission cannot be ascribed to changes in the engine volumetric efficiency or air-fuel ratio. The paper demonstrates that fuel spray deposition on the piston surface was in the form of a thin film that did not experience bulk boiling. A number of suggestions are put forward to help explain the observed changes in exhaust emissions with increasing piston temperature
Hunting for New Physics with Unitarity Boomerangs
Although the unitarity triangles () carry information about the
Kobayashi-Maskawa (KM) quark mixing matrix, it explicitly contains just three
parameters which is one short to completely fix the KM matrix. It has been
shown recently, by us, that the unitarity boomerangs () formed using two
, with a common inner angle, can completely determine the KM matrix and,
therefore, better represents, quark mixing. Here, we study detailed properties
of the , of which there are a total 18 possible. Among them, there is only
one which does not involve very small angles and is the ideal one for practical
uses. Although the have different areas, there is an invariant quantity,
for all , which is equal to a quarter of the Jarlskog parameter
squared. Hunting new physics, with a unitarity boomerang, can reveal more
information, than just using a unitarity triangle.Comment: Latex 9 pages with two figures. References updated
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