1,361 research outputs found
Orographic cirrus in a future climate
A cloud resolving model (CRM) is used to investigate the formation of orographic cirrus clouds in the current and future climate. The formation of cirrus clouds depends on a variety of dynamical and thermodynamical processes, which act on different scales. First, the capability of the CRM in realistically simulating orographic cirrus clouds has been tested by comparing the simulated results to aircraft measurements of an orographic cirrus cloud. The influence of a warmer climate on the microphysical and optical properties of cirrus clouds has been investigated by initializing the CRM with vertical profiles of horizontal wind, potential temperature and equivalent potential temperature, respectively. The vertical profiles are extracted from IPCC A1B simulations for the current climate and for the period 2090â2099 for two regions representative for North and South America. The influence of additional moisture in a future climate on the propagation of gravity waves and the formation of orographic cirrus could be estimated. In a future climate, the increase in moisture dampens the vertical propagation of gravity waves and the occurring vertical velocities in the moist simulations. Together with higher temperatures fewer ice crystals nucleate homogeneously. Assuming that the relative humidity does not change in a warmer climate the specific humidity in the model is increased. This increase in specific humidity in a warmer climate results in a higher ice water content. The net effect of a reduced ice crystal number concentration and a higher ice water content is an increased optical depth. However, in some moist simulations dynamical changes contribute to changes in the ice water content, ice crystal number concentration and optical depth. For the corresponding dry simulations dynamical changes are more pronounced leading to a decreased optical depth in a future climate in some cases
Universality of Uhrig dynamical decoupling for suppressing qubit pure dephasing and relaxation
The optimal -pulse dynamical decoupling discovered by Uhrig for a
spin-boson mmodel [Phys. Rev. Lett, {\bf 98}, 100504 (2007)] is proved to be
universal in suppressing to the pure dephasing or the longitudinal
relaxation of a qubit (or spin-1/2) coupled to a generic bath in a short-time
evolution of duration . It is also found that for the purpose of suppressing
the longitudinal relaxation, an ideal Uhrig -pulse sequence can be
generalized to a sequence consisting of the ideal one superimposed with
finite-duration pulses satisfying certain symmetry requirements.Comment: 4 pages, 1 figure
The University MĂŒnster model surgery system for Orthognathic surgery. Part I â The idea behind
Background: We describe a procedure for diagnosis and planning for orthognatic surgery based on international standards. A special 2D planning based on lateral cephalograms (Axis Orbital Marker Lines System) realize a transmission to the SAM 2P articulator (3D) by means of the Axis Orbital Plane.
Methods: Former intraoperative measurement of the average height of the LeFort I osteotomy plane relative to the molar occlusal plane allow to construct a virtual osteotomy plane in the lateral cephalogram. This is the basis for the development of the Axis Orbital Marker Lines System (AO-MLS).
Results: The AO-MLS is presented graphically, and in detail, with construction guidelines. The system could be integrated into various lateral cephalometric analysis- and surgical prediction schemes. It forms the basis for a standardized transfer of the 2D planning to the 3D planning in the articulator, and vice versa. This procedure makes it possible to generate surgical planning protocols based on the model surgery, which represent the dislocations in the proximity of the real osteotomy planes.
Conclusions: The Axis Orbital Marker Lines System (software component) in conjunction with the University MĂŒnster Model Surgery System (hardware system) increases the predictability of model operations in orthognathic surgery
Decoherence and the Nature of System-Environment Correlations
We investigate system-environment correlations based on the exact dynamics of
a qubit and its environment in the framework of pure decoherence (phase
damping). We focus on the relation of decoherence and the build-up of
system-reservoir entanglement for an arbitrary (possibly mixed) initial qubit
state. In the commonly employed regime where the qubit dynamics can be
described by a Markov master equation of Lindblad type, we find that for almost
all qubit initial states inside the Bloch sphere, decoherence is complete while
the total state is still separable - no entanglement is involved. In general,
both "separable" and "entangling" decoherence occurs, depending on temperature
and initial qubit state. Moreover, we find situations where classical and
quantum correlations periodically alternate as a function of time in the regime
of low temperatures
Music Perception of Cochlear Implant recipients using a Genetic Algorithm MAP
Cochlear implant (CI) users have traditionally reported less enjoyment and have performed more poorly on tasks of music perception (timbre, melody and pitch) than their normal hearing (NH) counterparts. The enjoyment and perception of music can be affected by the MAP programmed into a userâs speech processor, the parameters of which can be altered to change the way that a CI recipient hears sound. However, finding the optimal MAP can prove challenging to clinicians because altering one parameter will affect others.
Until recently the only way to find the optimal MAP has theoretically been to present each
potential combination of parameters systematically, however this is impractical in a clinical setting
due to the thousands of different potential combinations. Thus, in general, clinicians can find a good
MAP, but not necessarily the best one. The goal of this study was to assess whether a Genetic
Algorithm would assist clinicians to create a better MAP for music listening than current methods.
Seven adult Nucleus Freedom CI users were assessed on tasks of timbre identification, melody identification and pitch-ranking using their original MAP. The participants then used the GA software to create an individualised MAP for music listening (referred to as their âGA MAPâ). They then spent four weeks comparing their GA and original MAPs in their everyday life, and recording their listening experiences in a listening diary. At the end of this period participants were assessed on the same timbre, melody, and pitch tasks using their GA MAP.
The results of the study showed that the GA process took an average of 35 minutes (range: 13-72 minutes) to create a MAP for music listening. As a group, participants reported the GA MAP to be slightly better than their original MAP for music listening, and preferred the GA MAP when at the cinema. Participants, on average, also performed significantly better on the melody identification task with their GA MAP; however they were significantly better on the half-octave interval pitch ranking task with their original MAP. The results also showed that participants were significantly more accurate on the single-instrument identification task than the ensemble instrument identification task regardless of which MAP they used. Overall, the results show that a GA can be used to successfully create a MAP for music listening, with two participants creating a MAP that they decided to keep at the conclusion of the study
Quantum Decoherence of Two Qubits
It is commonly stated that decoherence in open quantum systems is due to
growing entanglement with an environment. In practice, however, surprisingly
often decoherence may equally well be described by random unitary dynamics
without invoking a quantum environment at all. For a single qubit, for
instance, pure decoherence (or phase damping) is always of random unitary type.
Here, we construct a simple example of true quantum decoherence of two qubits:
we present a feasible phase damping channel of which we show that it cannot be
understood in terms of random unitary dynamics. We give a very intuitive
geometrical measure for the positive distance of our channel to the convex set
of random unitary channels and find remarkable agreement with the so-called
Birkhoff defect based on the norm of complete boundedness.Comment: 5 pages, 4 figure
The Pondicherry interpretation of quantum mechanics: An overview
An overview of the Pondicherry interpretation of quantum mechanics is
presented. This interpretation proceeds from the recognition that the
fundamental theoretical framework of physics is a probability algorithm, which
serves to describe an objective fuzziness (the literal meaning of Heisenberg's
term "Unschaerfe," usually mistranslated as "uncertainty") by assigning
objective probabilities to the possible outcomes of unperformed measurements.
Although it rejects attempts to construe quantum states as evolving ontological
states, it arrives at an objective description of the quantum world that owes
nothing to observers or the goings-on in physics laboratories. In fact, unless
such attempts are rejected, quantum theory's true ontological implications
cannot be seen. Among these are the radically relational nature of space, the
numerical identity of the corresponding relata, the incomplete spatiotemporal
differentiation of the physical world, and the consequent top-down structure of
reality, which defies attempts to model it from the bottom up, whether on the
basis of an intrinsically differentiated spacetime manifold or out of a
multitude of individual building blocks.Comment: 18 pages, 1 eps figure, v3: with corrections made in proo
Influence of lip closure on alveolar cleft width in patients with cleft lip and palate
<p>Abstract</p> <p>Background</p> <p>The influence of surgery on growth and stability after treatment in patients with cleft lip and palate are topics still under discussion. The aim of the present study was to investigate the influence of early lip closure on the width of the alveolar cleft using dental casts.</p> <p>Methods</p> <p>A total of 44 clefts were investigated using plaster casts, 30 unilateral and 7 bilateral clefts. All infants received a passive molding plate a few days after birth. The age at the time of closure of the lip was 2.1 month in average (range 1-6 months). Plaster casts were obtained at the following stages: shortly after birth, prior to lip closure, prior to soft palate closure. We determined the width of the alveolar cleft before lip closure and prior to soft palate closure measuring the alveolar cleft width from the most lateral point of the premaxilla/anterior segment to the most medial point of the smaller segment.</p> <p>Results</p> <p>After lip closure 15 clefts presented with a width of 0 mm, meaning that the mucosa of the segments was almost touching one another. 19 clefts showed a width of up to 2 mm and 10 clefts were still over 2 mm wide. This means a reduction of 0% in 5 clefts, of 1-50% in 6 clefts, of 51-99% in 19 clefts, and of 100% in 14 clefts.</p> <p>Conclusions</p> <p>Early lip closure reduces alveolar cleft width. In most cases our aim of a remaining cleft width of 2 mm or less can be achieved. These are promising conditions for primary alveolar bone grafting to restore the dental bony arch.</p
Exact stochastic simulation of dissipation and non-Markovian effects in open quantum systems
The exact dynamics of a system coupled to an environment can be described by
an integro-differential stochastic equation of its reduced density. The
influence of the environment is incorporated through a mean-field which is both
stochastic and non-local in time and where the standard two-times correlation
functions of the environment appear naturally. Since no approximation is made,
the presented theory incorporates exactly dissipative and non-Markovian
effects. Applications to the spin-boson model coupled to a heat-bath with
various coupling regimes and temperature show that the presented stochastic
theory can be a valuable tool to simulate exactly the dynamics of open quantum
systems. Links with stochastic Schroedinger equation method and possible
extensions to "imaginary time" propagation are discussed.Comment: accepted for publication in Physical Review
System-environment correlations and Non-Markovian dynamics
We determine the total state dynamics of a dephasing open quantum system
using the standard environment of harmonic oscillators. Of particular interest
are random unitary approaches to the same reduced dynamics and
system-environment correlations in the full model. Concentrating on a model
with an at times negative dephasing rate, the issue of "non-Markovianity" will
also be addressed. Crucially, given the quantum environment, the appearance of
non-Markovian dynamics turns out to be accompanied by a loss of
system-environment correlations. Depending on the initial purity of the qubit
state, these system-environment correlations may be purely classical over the
whole relevant time scale, or there may be intervals of genuine
system-environment entanglement. In the latter case, we see no obvious relation
between the build-up or decay of these quantum correlations and
"Non-Markovianity"
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