83 research outputs found
Full control by locally induced relaxation
We demonstrate a scheme for controlling a large quantum system by acting on a
small subsystem only. The local control is mediated to the larger system by
some fixed coupling Hamiltonian. The scheme allows to transfer arbitrary and
unknown quantum states from a memory on the large system (``upload access'') as
well as the inverse (``download access''). We study sufficient conditions of
the coupling Hamiltonian and give lower bounds on the fidelities for
downloading and uploading.Comment: 4 pages, 2 figure
The Generalized Lyapunov Theorem and its Application to Quantum Channels
We give a simple and physically intuitive necessary and sufficient condition
for a map acting on a compact metric space to be mixing (i.e. infinitely many
applications of the map transfer any input into a fixed convergency point).
This is a generalization of the "Lyapunov direct method". First we prove this
theorem in topological spaces and for arbitrary continuous maps. Finally we
apply our theorem to maps which are relevant in Open Quantum Systems and
Quantum Information, namely Quantum Channels. In this context we also discuss
the relations between mixing and ergodicity (i.e. the property that there exist
only a single input state which is left invariant by a single application of
the map) showing that the two are equivalent when the invariant point of the
ergodic map is pure.Comment: 13 pages, 3 figure
Pollutant dispersion in a developing valley cold-air pool
Pollutants are trapped and accumulate within cold-air pools, thereby affecting air quality. A numerical model is used to quantify the role of cold-air-pooling processes in the dispersion of air pollution in a developing cold-air pool within an alpine valley under decoupled stable conditions. Results indicate that the negatively buoyant downslope flows transport and mix pollutants into the valley to depths that depend on the temperature deficit of the flow and the ambient temperature structure inside the valley. Along the slopes, pollutants are generally entrained above the cold-air pool and detrained within the cold-air pool, largely above the ground-based inversion layer. The ability of the cold-air pool to dilute pollutants is quantified. The analysis shows that the downslope flows fill the valley with air from above, which is then largely trapped within the cold-air pool, and that dilution depends on where the pollutants are emitted with respect to the positions of the top of the ground-based inversion layer and cold-air pool, and on the slope wind speeds. Over the lower part of the slopes, the cold-air-pool-averaged concentrations are proportional to the slope wind speeds where the pollutants are emitted, and diminish as the cold-air pool deepens. Pollutants emitted within the ground-based inversion layer are largely trapped there. Pollutants emitted farther up the slopes detrain within the cold-air pool above the ground-based inversion layer, although some fraction, increasing with distance from the top of the slopes, penetrates into the ground-based inversion layer.Peer reviewe
Spatial distribution of aerosols in the Inn Valley atmosphere during wintertime
This study analyzes the structure of the wintertime
boundary layer in an Alpine valley (Inn Valley, Austria)
for a case of high air pollution. We present airborne aerosol
observations collected with particle counters and a backscatter
lidar. The effect of upslope winds on the spatial
distribution of pollutants is investigated. An asymmetry in
the aerosol distribution is observed in the cross-valley
direction which presumably is related to differences in
orientation and albedo of the two valley slopes. A one-sided
thermal circulation, which develops above the sun-exposed
slope, is most likely responsible for the observed redistribution
of aerosols during daytime. Elevated aerosol
layers form at the height of shallow inversion layers.
Despite this vertical transport of pollutants by slope winds,
no effective vertical venting of the polluted air mass into the
free atmosphere can be achieved
Quantifying horizontal and vertical tracer mass fluxes in an idealized valley during daytime
The transport and mixing of pollution during the daytime evolution of a
valley boundary layer is studied in an idealized way. The goal is to quantify
horizontal and vertical tracer mass fluxes between four different valley
volumes: the convective boundary layer, the slope wind layer, the stable
core,
and the atmosphere above the valley. For this purpose, large eddy simulations
(LES)
are conducted with the Weather Research and Forecasting (WRF) model for a
quasi-two-dimensional valley. The valley geometry consists of two slopes with
constant slope angle and is homogeneous in the along-valley direction. The
surface sensible heat flux is horizontally homogeneous and prescribed by a
sine function. The initial sounding is characterized by an atmosphere at rest
and a constant Brunt–Väisälä frequency. Various experiments are conducted
for different combinations of surface heating amplitudes and initial
stability conditions. A passive tracer is released with an arbitrary but
constant rate at the valley floor and resulting tracer mass fluxes are
evaluated between the aforementioned volumes.As a result of the surface heating, a convective boundary layer is
established in the lower part of the valley with a stable layer on top –
the so-called stable core. The height of the slope wind layer, as well as the wind
speed within, decreases with height due to the vertically increasing stability.
Hence, the mass flux within the slope wind layer decreases with height as
well. Due to mass continuity, this along-slope mass flux convergence leads to
a partial redirection of the flow from the slope wind layer towards the
valley centre and the formation of a horizontal intrusion above the
convective boundary layer. This intrusion is associated with a transport of
tracer mass from the slope wind layer towards the valley centre. A strong
static stability and/or weak forcing lead to large tracer mass fluxes
associated with this phenomenon. The total export of tracer mass out of the
valley atmosphere increases with decreasing stability and increasing forcing.
The effects of initial stability and forcing can be combined to a single
parameter, the breakup parameter B. An analytical function is presented
that describes the exponential decrease of the percentage of exported tracer
mass with increasing B. This study is limited by the idealization of the
terrain shape, stratification, and forcing, but quantifies transport
processes for a large range of forcing amplitudes and atmospheric stability
A multimethodological approach to study the spatial distribution of air pollution in an Alpine valley during wintertime
In order to investigate the spatial distribution of air pollutants in the Inn valley (Tyrol, Austria) during wintertime, a joint field campaign of the three research projects ALPNAP (Monitoring and Minimisation of Traffic-Induced Noise and Air Pollution Along Major Alpine Transport Routes), INNAP (Boundary Layer Structure in the Inn Valley during high Air Pollution) and INNOX (NOx-structure in the Inn Valley during High Air Pollution) was carried out in January/February 2006. In addition to continuous ground based measurements, vertical profiles of various air pollutants and meteorological parameters were obtained on six selected days. For in-situ investigations, a tethered balloon was used to analyse the lowest atmospheric layers, 0�500 m above the valley bottom (a.v.b.), and a research aircraft sampled at 150�2200 m a.v.b. An aircraft equipped with an aerosol backscatter lidar performed nadir measurements at 3000 m a.v.b. Combined results from a typical day show a strongly polluted layer up to about 125 m a.v.b. in the morning. Around midday concentrations on the valley floor decrease indicating some vertical air exchange despite thermally stable conditions. Strong vertical and horizontal gradients with enhanced pollution levels along the sunny side of the valley up to 1300 m a.v.b. were observed in the afternoon. This vertical mixing due to thermally or dynamically driven slope winds reduces the concentration of air pollutants at the bottom of the valley and causes the formation of elevated pollution layers
The impact of embedded valleys on daytime pollution transport over a mountain range
Idealized large-eddy simulations were performed to investigate the impact of
different mountain geometries on daytime pollution transport by thermally
driven winds. The main objective was to determine interactions between
plain-to-mountain and slope wind systems, and their influence on the
pollution distribution over complex terrain. For this purpose, tracer
analyses were conducted over a quasi-two-dimensional mountain range with
embedded valleys bordered by ridges with different crest heights and a flat
foreland in cross-mountain direction. The valley depth was varied
systematically. It was found that different flow regimes develop dependent on
the valley floor height. In the case of elevated valley floors, the
plain-to-mountain wind descends into the potentially warmer valley and
replaces the opposing upslope wind. This superimposed plain-to-mountain wind
increases the pollution transport towards the main ridge by an additional
20 % compared to the regime with a deep valley. Due to mountain and
advective venting, the vertical exchange is 3.6 times higher over complex
terrain than over a flat plain. However, the calculated vertical exchange is
strongly sensitive to the definition of the convective boundary layer height.
In summary, the impact of the terrain geometry on the mechanisms of pollution
transport confirms the necessity to account for topographic effects in future
boundary layer parameterization schemes
Air Pollution Transport in an Alpine Valley: Results From Airborne and Ground-Based Observations
An observational dataset from a wintertime field campaign in the Inn Valley, Austria, is analysed in order to study mechanisms of air pollution transport in an Alpine valley. The results illustrate three types of mechanisms: transport by a density current, back-and-forth transport by valley winds, and transport by slope winds. The first type is associated with an air mass difference along the valley. Cooler air located in the lower part of the valley behaves like a density current and produces the advection of pollutants by upvalley winds. In the second type, strong horizontal gradients in pollution concentrations exist close to ground. Multiple wind reversals result in a back-and-forth transport of pollutants by weak valley winds. In the third type, upslope winds during daytime decrease low-level pollution concentrations and cause the formation of elevated pollution layers
Spatial distribution of aerosols in the Inn Valley atmosphere during wintertime - a detailed view
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