4,981 research outputs found
A "Garden of Forking Paths" - the Quantum Mechanics of Histories of Events
We present a short survey of a novel approach, called "ETH approach", to the
quantum theory of events happening in isolated physical systems and to the
effective time evolution of states of systems featuring events. In particular,
we attempt to present a clear explanation of what is meant by an "event" in
quantum mechanics and of the significance of this notion. We then outline a
theory of direct (projective) and indirect observations or recordings of
physical quantities and events. Some key ideas underlying our general theory
are illustrated by studying a simple quantum-mechanical model of a mesoscopic
system.Comment: 26 pages, 3 figure
A rigorous proof of the Landau-Peierls formula and much more
We present a rigorous mathematical treatment of the zero-field orbital
magnetic susceptibility of a non-interacting Bloch electron gas, at fixed
temperature and density, for both metals and semiconductors/insulators. In
particular, we obtain the Landau-Peierls formula in the low temperature and
density limit as conjectured by T. Kjeldaas and W. Kohn in 1957.Comment: 30 pages - Accepted for publication in A.H.
Experimental study of parametric subharmonic instability for internal waves
Internal waves are believed to be of primary importance as they affect ocean
mixing and energy transport. Several processes can lead to the breaking of
internal waves and they usually involve non linear interactions between waves.
In this work, we study experimentally the parametric subharmonic instability
(PSI), which provides an efficient mechanism to transfer energy from large to
smaller scales. It corresponds to the destabilization of a primary plane wave
and the spontaneous emission of two secondary waves, of lower frequencies and
different wave vectors. Using a time-frequency analysis, we observe the time
evolution of the secondary waves, thus measuring the growth rate of the
instability. In addition, a Hilbert transform method allows the measurement of
the different wave vectors. We compare these measurements with theoretical
predictions, and study the dependence of the instability with primary wave
frequency and amplitude, revealing a possible effect of the confinement due to
the finite size of the beam, on the selection of the unstable mode
Wicking through a confined micropillar array
This study considers the spreading of a Newtonian and perfectly wetting
liquid in a square array of cylindric micropillars confined between two plates.
We show experimentally that the dynamics of the contact line follows a
Washburn-like law which depends on the characteristics of the micropillar array
(height, diameter and pitch). The presence of pillars can either enhanced or
slow down the motion of the contact line. A theoretical model based on
capillary and viscous forces has been developed in order to rationalize our
observations. Finally, the impact of pillars on the volumic flow rate of liquid
which is pumped in the microchannel is inspected
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