5,552 research outputs found
Unsolved problems in the lowermost mantle
Many characteristics of D '' layer may be attributed to the recently discovered MgSiO3 post-perovskite phase without chemical heterogeneities. They include a sharp discontinuity at the top of D '', regional variation in seismic anisotropy, and a steep Clapeyron slope. However, some features remain unexplained. The seismically inferred velocity jump is too large in comparison to first principles calculations, and the sharpness of the discontinuity may require a chemical boundary. Chemical heterogeneity may play an important role in addition to the phase transformation from perovskite to post-perovskite. Phase transformation and chemical heterogeneity and the attendant changes in physical properties, such as rheology and thermal conductivity, are likely to play competing roles in defining the dynamical stability of the D '' layer. Revealing the relative roles between phase transition and chemical anomalies is an outstanding challenge in the study of the role of D '' in thermal-chemical evolution of the Earth
Bayesian Updating of Nonlinear Model Predictions using Markov Chain Monte Carlo Simulation
The usual practice in system identification is to use system
data to identify one model from a set of possible models and
then to use this model for predicting system behavior. In contrast,
the present robust predictive approach rigorously combines
the predictions of all the possible models, appropriately weighted
by their updated probabilities based on the data. This Bayesian
system identification approach is applied to update the robust reliability
of a dynamical system based on its measured response
time histories. A Markov chain simulation method based on the
Metropolis-Hastings algorithm and an adaptive scheme is proposed
to evaluate the robust reliability integrals. An example for
updating the reliability of a Duffing oscillator is given to illustrate
the proposed method
Phase measurements with weak reference pulses
Quantum state discrimination for two coherent states with opposite phases as
measured relative to a reference pulse is analyzed as functions of the
intensities of both the signal states and of the reference pulse. This problem
is relevant for Quantum Key Distribution with phase encoding. We consider both
the optimum measurements and simple measurements that require only
beamsplitters and photodetectors.Comment: 5 pages, 5 figures. I apologize for this boring pape
Liver esterase polymorphisms in sepat Siam (Trichogaster pectoralis)
Esterase D and general esterases (which use a- or J3-naphthyl acetate as substrates) were investigated electrophoretically in the paddy field fish, Trichogaster pectoralis. Variants were observed for these enzymes.
It is hypothesized that esterase D phenotypes are due to two codominant alleles at an autosomal locus, and that
four loci are involved in the control of the general esterases
Measuring the quantum statistics of an atom laser beam
We propose and analyse a scheme for measuring the quadrature statistics of an
atom laser beam using extant optical homodyning and Raman atom laser
techniques. Reversal of the normal Raman atom laser outcoupling scheme is used
to map the quantum statistics of an incoupled beam to an optical probe beam. A
multimode model of the spatial propagation dynamics shows that the Raman
incoupler gives a clear signal of de Broglie wave quadrature squeezing for both
pulsed and continuous inputs. Finally, we show that experimental realisations
of the scheme may be tested with existing methods via measurements of Glauber's
intensity correlation function.Comment: 4 pages, 3 figure
Is there a gap between recommended and ‘real world’ practice in the management of depression in young people? A medical file audit of practice
BACKGROUND: Literature has shown that dissemination of guidelines alone is insufficient to ensure that guideline recommendations are incorporated into every day clinical practice. METHODS: We aimed to investigate the gaps between guideline recommendations and clinical practice in the management of young people with depression by undertaking an audit of medical files in a catchment area public mental health service for 15 to 25 year olds in Melbourne, Australia. RESULTS: The results showed that the assessment and recording of depression severity to ensure appropriate treatment planning was not systematic nor consistent; that the majority of young people (74.5%) were prescribed an antidepressant before an adequate trial of psychotherapy was undertaken and that less than 50% were monitored for depression symptom improvement and antidepressant treatment emergent suicide related behaviours (35% and 30% respectively). Encouragingly 92% of first line prescriptions for those aged 18 years or under who were previously antidepressant-naïve was for fluoxetine as recommended. CONCLUSIONS: This research has highlighted the need for targeted strategies to ensure effective implementation. These strategies might include practice system tools that allow for systematic monitoring of depression symptoms and adverse side effects, particularly suicide related behaviours. Additionally, youth specific psychotherapy that incorporates the most effective components for this age group, delivered in a youth friendly way would likely aid effective implementation of guideline recommendations for engagement in an adequate trial of psychotherapy before medication is initiated
Pulsed squeezed light: simultaneous squeezing of multiple modes
We analyze the spectral properties of squeezed light produced by means of
pulsed, single-pass degenerate parametric down-conversion. The multimode output
of this process can be decomposed into characteristic modes undergoing
independent squeezing evolution akin to the Schmidt decomposition of the
biphoton spectrum. The main features of this decomposition can be understood
using a simple analytical model developed in the perturbative regime. In the
strong pumping regime, for which the perturbative approach is not valid, we
present a numerical analysis, specializing to the case of one-dimensional
propagation in a beta-barium borate waveguide. Characterization of the
squeezing modes provides us with an insight necessary for optimizing homodyne
detection of squeezing. For a weak parametric process, efficient squeezing is
found in a broad range of local oscillator modes, whereas the intense
generation regime places much more stringent conditions on the local
oscillator. We point out that without meeting these conditions, the detected
squeezing can actually diminish with the increasing pumping strength, and we
expose physical reasons behind this inefficiency
Operational Theory of Homodyne Detection
We discuss a balanced homodyne detection scheme with imperfect detectors in
the framework of the operational approach to quantum measurement. We show that
a realistic homodyne measurement is described by a family of operational
observables that depends on the experimental setup, rather than a single field
quadrature operator. We find an explicit form of this family, which fully
characterizes the experimental device and is independent of a specific state of
the measured system. We also derive operational homodyne observables for the
setup with a random phase, which has been recently applied in an ultrafast
measurement of the photon statistics of a pulsed diode laser. The operational
formulation directly gives the relation between the detected noise and the
intrinsic quantum fluctuations of the measured field. We demonstrate this on
two examples: the operational uncertainty relation for the field quadratures,
and the homodyne detection of suppressed fluctuations in photon statistics.Comment: 7 pages, REVTe
Capacities of Quantum Channels for Massive Bosons and Fermions
We consider the capacity of classical information transfer for noiseless
quantum channels carrying a finite average number of massive bosons and
fermions. The maximum capacity is attained by transferring the Fock states
generated from the grand-canonical ensemble. Interestingly, the channel
capacity for a Bose gas indicates the onset of a Bose-Einstein condensation, by
changing its qualitative behavior at the criticality, while for a channel
carrying weakly attractive fermions, it exhibits the signatures of
Bardeen-Cooper-Schrieffer transition. We also show that for noninteracting
particles, fermions are better carriers of information than bosons.Comment: 4 pages, 3 eps figures, RevTeX4; v2: discussions added, small
changes, published versio
Distinguishing between optical coherent states with imperfect detection
Several proposed techniques for distinguishing between optical coherent
states are analyzed under a physically realistic model of photodetection.
Quantum error probabilities are derived for the Kennedy receiver, the Dolinar
receiver and the unitary rotation scheme proposed by Sasaki and Hirota for
sub-unity detector efficiency. Monte carlo simulations are performed to assess
the effects of detector dark counts, dead time, signal processing bandwidth and
phase noise in the communication channel. The feedback strategy employed by the
Dolinar receiver is found to achieve the Helstrom bound for sub-unity detection
efficiency and to provide robustness to these other detector imperfections
making it more attractive for laboratory implementation than previously
believed
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