Time Scales Of Physical Processes Research Articles

Quantum speed limits on operator flows and correlation functions

Quantum speed limits (QSLs) identify fundamental time scales of physical processes by providing lower bounds on the rate of change of a quantum state or the expectation value of an observable. We introduce a generalization of QSL for unitary operator flows, which are ubiquitous in physics and relevant for applications in both the quantum and classical domains. We derive two types of QSLs and assess the existence of a crossover between them, that we illustrate with a qubit and a random matrix Hamiltonian, as canonical examples. We further apply our results to the time evolution of autocorrelation functions, obtaining computable constraints on the linear dynamical response of quantum systems out of equilibrium and the quantum Fisher information governing the precision in quantum parameter estimation.

Cycle-resolved measurements of in-cylinder constituents during diesel engine transients and insight into their impact on emissions

Diesel engine transients, in particular the rapid increase of load from idle, lead to significant excursions of operating parameters from normal, steady-state operation. A typical transient event is initiated by a sudden increase of fuelling followed by a turbo lag period. The trajectories of key parameters, such as boost pressure, air/fuel ratio, and amount of residual in the cylinder, depend on the complex interplay between the control system behaviour, actuator response, and time scales of physical processes. The end result is a significant deviation of the combustion event and emission formation. For example, it has been shown that transient spikes of soot may be responsible for up to half of total particulate emissions during a city driving cycle. The present paper introduces an experimental technique to quantify cycle-resolved pre-combustion in-cylinder constituents during transient engine operation and uses measurements to generate insight into mechanisms that cause increased emissions during a diesel engine transient event. A 6.0-litre V-8 diesel engine is instrumented for fuel injector needle lift and injection pressure measurements, cylinder pressure, simultaneous fast measurements of CO2 concentrations in the exhaust and in the cylinder, and fast measurements of NO and particulate spectrum. Analytical techniques are introduced to process measurements and determine cycle-resolved mass of fuel, air, and stoichiometric combustion products, thus providing insight into reasons for significant variations of emission during the transient. The technique is utilized to study engine behaviour over an FTP-72 driving cycle.