323 research outputs found
Optimal prediction and the Klein-Gordon equation
The method of optimal prediction is applied to calculate the future means of
solutions to the Klein-Gordon equation. It is shown that in an appropriate
probability space, the difference between the average of all solutions that
satisfy certain constraints at time t=0, and the average computed by an
approximate method, is small with high probability.Comment: 18 page
Inverse spectral problems for Sturm-Liouville operators with singular potentials
The inverse spectral problem is solved for the class of Sturm-Liouville
operators with singular real-valued potentials from the space .
The potential is recovered via the eigenvalues and the corresponding norming
constants. The reconstruction algorithm is presented and its stability proved.
Also, the set of all possible spectral data is explicitly described and the
isospectral sets are characterized.Comment: Submitted to Inverse Problem
Time-Local Quantum-State-Diffusion Equation for Multilevel Quantum Dynamics
An open quantum system with multiple levels coupled to a bosonic environment
at zero temperature is investigated systematically using the non-Markovian
quantum-state-diffusion (QSD) method [W. T. Strunz, L. Di\'osi, and N. Gisin,
Phys. Rev. Lett. 82, 1801 (1999)]. We have established exact time-local QSD
equations for a set of interesting multilevel open systems, including high-spin
systems, multiple-transition atomic models, and multilevel atomic models driven
by time-dependent external fields. These exact QSD equations have paved the way
to evaluate the dynamics of open multilevel atomic systems in the general
non-Markovian regimes without any approximation.Comment: 7 pages, 3 figures, 1 tabl
Review of biorthogonal coupled cluster representations for electronic excitation
Single reference coupled-cluster (CC) methods for electronic excitation are
based on a biorthogonal representation (bCC) of the (shifted) Hamiltonian in
terms of excited CC states, also referred to as correlated excited (CE) states,
and an associated set of states biorthogonal to the CE states, the latter being
essentially configuration interaction (CI) configurations. The bCC
representation generates a non-hermitian secular matrix, the eigenvalues
representing excitation energies, while the corresponding spectral intensities
are to be derived from both the left and right eigenvectors. Using the
perspective of the bCC representation, a systematic and comprehensive analysis
of the excited-state CC methods is given, extending and generalizing previous
such studies. Here, the essential topics are the truncation error
characteristics and the separability properties, the latter being crucial for
designing size-consistent approximation schemes. Based on the general order
relations for the bCC secular matrix and the (left and right) eigenvector
matrices, formulas for the perturbation-theoretical (PT) order of the
truncation errors (TEO) are derived for energies, transition moments, and
property matrix elements of arbitrary excitation classes and truncation levels.
In the analysis of the separability properties of the transition moments, the
decisive role of the so-called dual ground state is revealed. Due to the use of
CE states the bCC approach can be compared to so-called intermediate state
representation (ISR) methods based exclusively on suitably orthonormalized CE
states. As the present analysis shows, the bCC approach has decisive advantages
over the conventional CI treatment, but also distinctly weaker TEO and
separability properties in comparison with a full (and hermitian) ISR method
A stationary source of non-classical or entangled atoms
A scheme for generating continuous beams of atoms in non-classical or
entangled quantum states is proposed and analyzed. For this the recently
suggested transfer technique of quantum states from light fields to collective
atomic excitation by Stimulated Raman adiabatic passage [M.Fleischhauer and
M.D. Lukin, Phys.Rev.Lett. 84, 5094 (2000)] is employed and extended to matter
waves
Phase Coherence and Control of Stored Photonic Information
We report the demonstration of phase coherence and control for the recently
developed "light storage" technique. Specifically, we use a pulsed magnetic
field to vary the phase of atomic spin excitations which result from the
deceleration and storing of a light pulse in warm Rb vapor. We then convert the
spin excitations back into light and detect the resultant phase shift in an
optical interferometric measurement. The coherent storage of photon states in
matter is essential for the practical realization of many basic concepts in
quantum information processing.Comment: 5 pages, 3 figures. Submitted to Phys. Rev. Let
Storage of light in atomic vapor
We report an experiment in which a light pulse is decelerated and trapped in
a vapor of Rb atoms, stored for a controlled period of time, and then released
on demand. We accomplish this storage of light by dynamically reducing the
group velocity of the light pulse to zero, so that the coherent excitation of
the light is reversibly mapped into a collective Zeeman (spin) coherence of the
Rb vapor
Deep Learning Analysis of Cardiac MRI in Legacy Datasets:Multi-Ethnic Study of Atherosclerosis
The shape and motion of the heart provide essential clues to understanding
the mechanisms of cardiovascular disease. With the advent of large-scale
cardiac imaging data, statistical atlases become a powerful tool to provide
automated and precise quantification of the status of patient-specific heart
geometry with respect to reference populations. The Multi-Ethnic Study of
Atherosclerosis (MESA), begun in 2000, was the first large cohort study to
incorporate cardiovascular MRI in over 5000 participants, and there is now a
wealth of follow-up data over 20 years. Building a machine learning based
automated analysis is necessary to extract the additional imaging information
necessary for expanding original manual analyses. However, machine learning
tools trained on MRI datasets with different pulse sequences fail on such
legacy datasets. Here, we describe an automated atlas construction pipeline
using deep learning methods applied to the legacy cardiac MRI data in MESA. For
detection of anatomical cardiac landmark points, a modified VGGNet
convolutional neural network architecture was used in conjunction with a
transfer learning sequence between two-chamber, four-chamber, and short-axis
MRI views. A U-Net architecture was used for detection of the endocardial and
epicardial boundaries in short axis images. Both network architectures resulted
in good segmentation and landmark detection accuracies compared with
inter-observer variations. Statistical relationships with common risk factors
were similar between atlases derived from automated vs manual annotations. The
automated atlas can be employed in future studies to examine the relationships
between cardiac morphology and future events
Quantum memory for photons: I. Dark state polaritons
An ideal and reversible transfer technique for the quantum state between
light and metastable collective states of matter is presented and analyzed in
detail. The method is based on the control of photon propagation in coherently
driven 3-level atomic media, in which the group velocity is adiabatically
reduced to zero. Form-stable coupled excitations of light and matter
(``dark-state polaritons'') associated with the propagation of quantum fields
in Electromagnetically Induced Transparency are identified, their basic
properties discussed and their application for quantum memories for light
analyzed.Comment: 13 pages, 6 figures, paragraph on photon echo adde
Social prescribing in cardiology : rediscovering the nature of and within us
Personalised care is integral to the delivery of the NHSE Long Term Plan. Enabling choice and supporting patients to make decisions predicated on what matters to them, rather than what is the matter with them, is a fundamental part of the NHS vision. Social prescribing uses nonmedical, asset based, salutogenic approaches to promote this personalised paradigm, and places the patient central to decision making. We discuss how Personalised care can be used to help people with Cardiovascular Disease (CVD) using socially prescribed ânature-basedâ interventions to support the prehabilitation and rehabilitation of patients with CVD. The concept of Personalised care outlined and the significance of salutogenic principles as complementary approach to the pathogenic model is discussed. We argue that this seemingly novel approach to using nature-based interventions can help promote wellbeing for people with CVD as part of the wider personalised agenda
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