129 research outputs found
A Path Intergal Approach to Current
Discontinuous initial wave functions or wave functions with discontintuous
derivative and with bounded support arise in a natural way in various
situations in physics, in particular in measurement theory. The propagation of
such initial wave functions is not well described by the Schr\"odinger current
which vanishes on the boundary of the support of the wave function. This
propagation gives rise to a uni-directional current at the boundary of the
support. We use path integrals to define current and uni-directional current
and give a direct derivation of the expression for current from the path
integral formulation for both diffusion and quantum mechanics. Furthermore, we
give an explicit asymptotic expression for the short time propagation of
initial wave function with compact support for both the cases of discontinuous
derivative and discontinuous wave function. We show that in the former case the
probability propagated across the boundary of the support in time is
and the initial uni-directional current is . This recovers the Zeno effect for continuous detection of a particle
in a given domain. For the latter case the probability propagated across the
boundary of the support in time is and the
initial uni-directional current is . This is an anti-Zeno
effect. However, the probability propagated across a point located at a finite
distance from the boundary of the support is . This gives a decay
law.Comment: 17 pages, Late
Developing a novel welfare assessment tool for loose-housed laying hens â the Aviary Transect method
publishedVersio
A quantum decay model with exact explicit analytical solution
A simple decay model is introduced. The model comprises of a point potential
well, which experiences an abrupt change. Due to the temporal variation the
initial quantum state can either escape from the well or stay localized as a
new bound state. The model allows for an exact analytical solution while having
the necessary features of a decay process. The results show that the decay is
never exponential, as classical dynamics predicts. Moreover, at short times the
decay has a \textit{fractional} power law, which differs from perturbation
quantum methods predictions.Comment: 4 pages, 3 figure
Magnetospectroscopy of symmetric and anti-symmetric states in double quantum wells
The experimental results obtained for the magneto-transport in the
InGaAs/InAlAs double quantum wells (DQW) structures of two different shapes of
wells are reported. The beating-effect occurred in the Shubnikov-de Haas (SdH)
oscillations was observed for both types of the structures at low temperatures
in the parallel transport when magnetic field was perpendicular to the layers.
An approach to the calculation of the Landau levels energies for DQW structures
was developed and then applied to the analysis and interpretation of the
experimental data related to the beating-effect. We also argue that in order to
account for the observed magneto-transport phenomena (SdH and Integer Quantum
Hall effect), one should introduce two different quasi-Fermi levels
characterizing two electron sub-systems regarding symmetry properties of their
states, symmetric and anti-symmetric ones which are not mixed by
electron-electron interaction.Comment: 20 pages, 20 figure
Trapping of quantum particles and light beams by switchable potential wells
We consider basic dynamical effects in settings based on a pair of local
potential traps that may be effectively switched on and off, or suddenly
displaced, by means of appropriate control mechanisms, such as the scanning
tunneling microscopy (STM) or photo-switchable quantum dots. The same models,
based on the linear Schrodinger equation with time-dependent trapping
potentials, apply to the description of optical planar systems designed for the
switching of trapped light beams. The analysis is carried out in the analytical
form, using exact solutions of the Schrodinger equation. The first dynamical
problem considered in this work is the retention of a particle released from a
trap which was suddenly turned off, while another local trap was switched on at
a distance - immediately or with a delay. In this case, we demonstrate that the
maximum of the retention rate is achieved at a specific finite value of the
strength of the new trap, and at a finite value of the temporal delay,
depending on the distance between the two traps. Another ptoblem is retrapping
of the bound particle when the addition of the second trap transforms the
single-well setting into a double-well potential (DWP). In that case, we find
probabilities for the retrapping into the ground or first excited state of the
DWP. We also analyze effects entailed by the application of a kick to a bound
particle, the most interesting one being a kick-induced transition between the
DWP's ground and excited states. In the latter case, the largest transition
probability is achieved at particular strength of the kick.Comment: 20 pages, 10 figure
Experimental results for a 1.5 MW, 110 GHz gyrotron oscillator with reduced mode competition
A new result from a 110 GHz gyrotron at MIT is reported with an output power of 1.67 MW and an efficiency of 42% when operated at 97 kV and 41 A for 3 mu s pulses in the TE22,6 mode. These results are a major improvement over results obtained with an earlier cavity design, which produced 1.43 MW of power at 37% efficiency. These new results were obtained using a cavity with a reduced output taper angle and a lower ohmic loss when compared with the earlier cavity. The improved operation is shown experimentally to be the result of reduced mode competition from the nearby TE19,7 mode. The reduced mode competition agrees well with an analysis of the startup scenario based on starting current simulations. The present results should prove useful in planning long pulse and CW versions of the 110 GHz gyrotron.open141
Exact propagators for atom-laser interactions
A class of exact propagators describing the interaction of an -level atom
with a set of on-resonance -lasers is obtained by means of the Laplace
transform method. State-selective mirrors are described in the limit of strong
lasers. The ladder, V and configurations for a three-level atom are
discussed. For the two level case, the transient effects arising as result of
the interaction between both a semi-infinite beam and a wavepacket with the
on-resonance laser are examined.Comment: 13 pages, 6 figure
Cluster analysis of the organic peaks in bulk mass spectra obtained during the 2002 New England Air Quality Study with an Aerodyne aerosol mass spectrometer
International audienceWe applied hierarchical cluster analysis to an Aerodyne aerosol mass spectrometer (AMS) bulk mass spectral dataset collected aboard the NOAA research vessel Ronald H. Brown during the 2002 New England Air Quality Study off the east coast of the United States. Emphasizing the organic peaks, the cluster analysis yielded a series of categories that are distinguishable with respect to their mass spectra and their occurrence as a function of time. The differences between the categories mainly arise from relative intensity changes rather than from the presence or absence of specific peaks. The most frequent category exhibits a strong signal at m/z 44 and represents oxidized organic matter most probably originating from both, anthropogenic as well as biogenic sources. On the basis of spectral and trace gas correlations, the second most common category with strong signals at m/z 29, 43, and 44 contains contributions from isoprene oxidation products. The third through the fifth most common categories have peak patterns characteristic of monoterpene oxidation products and were most frequently observed when air masses from monoterpene rich regions were sampled. Taken together, the second through the fifth most common categories represent as much as 5 ”g/m3 organic aerosol mass ? 17% of the total organic mass ? that can be attributed to biogenic sources. These numbers have to be viewed as lower limits since the most common category was attributed to anthropogenic sources for this calculation. The cluster analysis was also very effective in identifying a few contaminated mass spectra that were not removed during pre-processing. This study demonstrates that hierarchical clustering is a useful tool to analyze the complex patterns of the organic peaks in bulk aerosol mass spectra from a field study
Matter wave pulses characteristics
We study the properties of quantum single-particle wave pulses created by
sharp-edged or apodized shutters with single or periodic openings. In
particular, we examine the visibility of diffraction fringes depending on
evolution time and temperature; the purity of the state depending on the
opening-time window; the accuracy of a simplified description which uses
``source'' boundary conditions instead of solving an initial value problem; and
the effects of apodization on the energy width.Comment: 11 pages, 11 figure
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