987 research outputs found
Assessment of white matter microstructure in stroke patients using NODDI
pre-printDiffusion weighted imaging (DWI) is widely used to study changes in white matter following stroke. In various studies employing diffusion tensor imaging (DTI) and high angular resolution diffusion imaging (HARDI) modalities, it has been shown that fractional anisotropy (FA), mean diffusivity (MD), and generalized FA (GFA) can be used as measures of white matter tract integrity in stroke patients. However, these measures may be non-specific, as they do not directly delineate changes in tissue microstructure. Multi-compartment models overcome this limitation by modeling DWI data using a set of indices that are directly related to white matter microstructure. One of these models which is gaining popularity, is neurite orientation dispersion and density imaging (NODDI). his model uses conventional single or multi-shell HARDI data to describe fiber orientation dispersion as well as densities of different tissue types in the imaging voxel. In this paper, we apply for the first time the NODDI model to 4-shell HARDI stroke data. By computing NODDI indices over the entire brain in two stroke patients, and comparing tissue regions in ipsilesional and contralesional hemispheres, we demonstrate that NODDI modeling provides specific information on tissue microstructural changes. We also introduce an information theoretic analysis framework to investigate the non-local effects of stroke in the white matter. Our initial results suggest that the NODDI indices might be more specific markers of white matter reorganization following stroke than other measures previously used in studies of stroke recovery
On Prediction Using Variable Order Markov Models
This paper is concerned with algorithms for prediction of discrete sequences
over a finite alphabet, using variable order Markov models. The class of such
algorithms is large and in principle includes any lossless compression
algorithm. We focus on six prominent prediction algorithms, including Context
Tree Weighting (CTW), Prediction by Partial Match (PPM) and Probabilistic
Suffix Trees (PSTs). We discuss the properties of these algorithms and compare
their performance using real life sequences from three domains: proteins,
English text and music pieces. The comparison is made with respect to
prediction quality as measured by the average log-loss. We also compare
classification algorithms based on these predictors with respect to a number of
large protein classification tasks. Our results indicate that a "decomposed"
CTW (a variant of the CTW algorithm) and PPM outperform all other algorithms in
sequence prediction tasks. Somewhat surprisingly, a different algorithm, which
is a modification of the Lempel-Ziv compression algorithm, significantly
outperforms all algorithms on the protein classification problems
Modulated Floquet Topological Insulators
Floquet topological insulators are topological phases of matter generated by
the application of time-periodic perturbations on otherwise conventional
insulators. We demonstrate that spatial variations in the time-periodic
potential lead to localized quasi-stationary states in two-dimensional systems.
These states include one-dimensional interface modes at the nodes of the
external potential, and fractionalized excitations at vortices of the external
potential. We also propose a setup by which light can induce currents in these
systems. We explain these results by showing a close analogy to px+ipy
superconductors
Temperature effects on high strain rate properties of graphite/epoxy composites
A unidirectional graphite epoxy material (AS4/3501-6) was characterized at strain rates ranging from 5 x 10(exp 6) s(exp -1) to 5(exp -1), at room temperature and at 128 C. Results are presented in the form of stress-strain curves to failure. The longitudinal properties remain nearly unchanged with strain rate and temperature. The transverse modulus increases with strain rate but decreases with temperature. The transverse strength and transverse ultimate tensile strain have a positive rate sensitivity at low rates, which changes to negative at intermediate rates and returns to positive rate sensitivity at the highest rates tested. A temperature-time equivalence principle was applied and master curves were obtained for the transverse mechanical properties. The in-plane shear modulus and in-plane shear strength have a positive rate sensitivity. The ultimate intralaminar shear strain has a positive rate sensitivity at low rates, which changes to negative at high rates. At the elevated temperature of 128 C, the ultimate shear strain is 25 to 30 percent higher than the room temperature value, but its strain rate dependence is moderate
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Cosmic ray measurements in the atmosphere at several latitudes in October, 2014
Cosmic ray fluxes in the atmosphere were recorded during balloon flights in October 2014 in northern Murmansk region, Apatity (Russia; 67o33’N, 33o24’E), in Antarctica (observatory Mirny; 66o33’S, 93o00’E), in Moscow (Russia; 55o45’N, 37o37’E), in Reading (United King-dom; 51o27’N, 0o 58’W), in Mitzpe-Ramon (Israel; 30o36’N, 34o48’E) and in Zaragoza (Spain; 41o9’N, 0o54’W). Two type of cosmic ray detectors were used, namely, (1) the standard ra-diosonde and its modification constructed at the Lebedev Physical Institute (Moscow, Russia) and (2) the device manufactured at the Reading University (Reading, United Kingdom). We compare and analyze obtained data and focus on the estimation of the cosmic ray latitudinal effect in the atmosphere
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A global atmospheric electricity monitoring network for climate and geophysical research
The Global atmospheric Electric Circuit (GEC) is a fundamental coupling network of the climate system connecting electrically disturbed weather regions with fair weather regions across the planet. The GEC sustains the fair weather electric field (or potential gradient, PG) which is present globally and can be measured routinely at the surface using durable instrumentation such as modern electric field mills, which are now widely deployed internationally. In contrast to lightning or magnetic fields, fair weather PG cannot be measured remotely. Despite the existence of many PG datasets (both contemporary and historical), few attempts have been made to coordinate and integrate these fragmented surface measurements within a global framework. Such a synthesis is important elvinin order to fully study major influences on the GEC such as climate variations and space weather effects, as well as more local atmospheric electrical processes such as cloud electrification, lightning initiation, and dust and aerosol charging.
The GloCAEM (Global Coordination of Atmospheric Electricity Measurements) project has brought together experts in atmospheric electricity to make the first steps towards an effective global network for atmospheric electricity monitoring, which will provide data in near real time. Data from all sites are available in identically-formatted files, at both one second and one minute temporal resolution, along with meteorological data (wherever available) for ease of interpretation of electrical measurements. This work describes the details of the GloCAEM database and presents what is likely to be the largest single analysis of PG data performed from multiple datasets at geographically distinct locations. Analysis of the diurnal variation in PG from all 17 GloCAEM sites demonstrates that the majority of sites show two daily maxima, characteristic of local influences on the PG, such as the sunrise effect. Data analysis methods to minimise such effects are presented and recommendations provided on the most suitable GloCAEM sites for the study of various scientific phenomena. The use of the dataset for a further understanding of the GEC is also demonstrated, in particular for more detailed characterization of day-to-day global circuit variability. Such coordinated effort enables deeper insight into PG phenomenology which goes beyond single-location PG measurements, providing a simple measurement of global thunderstorm variability on a day-to-day timescale. The creation of the GloCAEM database is likely to enable much more effective study of atmospheric electricity variables than has ever been possible before, which will improve our understanding of the role of atmospheric electricity in the complex processes underlying weather and climate
Intellectual Property and Public Health – A White Paper
On October 26, 2012, the University of Akron School of Law’s Center for Intellectual Property and Technology hosted its Sixth Annual IP Scholars Forum. In attendance were thirteen legal scholars with expertise and an interest in IP and public health who met to discuss problems and potential solutions at the intersection of these fields. This report summarizes this discussion by describing the problems raised, areas of agreement and disagreement between the participants, suggestions and solutions made by participants and the subsequent evaluations of these suggestions and solutions. Led by the moderator, participants at the Forum focused generally on three broad questions. First, are there alternatives to either the patent system or specific patent doctrines that can provide or help provide sufficient incentives for health-related innovation? Second, is health information being used proprietarily and if so, is this type of protection appropriate? Third, does IP conflict with other non-IP values that are important in health and how does or can IP law help resolve these conflicts? This report addresses each of these questions in turn
Simulating noise on a quantum processor: interactions between a qubit and resonant two-level system bath
Material defects fundamentally limit the coherence times of superconducting
qubits, and manufacturing completely defect-free devices is not yet possible.
Therefore, understanding the interactions between defects and a qubit in a real
quantum processor design is essential. We build a model that incorporates the
standard tunneling model, the electric field distributions in the qubit, and
open quantum system dynamics, and draws from the current understanding of
two-level system (TLS) theory. Specifically, we start with one million TLSs
distributed on the surface of a qubit and pick the 200 systems that are most
strongly coupled to the qubit. We then perform a full Lindbladian simulation
that explicitly includes the coherent coupling between the qubit and the TLS
bath to model the time dependent density matrix of resonant TLS defects and the
qubit. We find that the 200 most strongly coupled TLSs can accurately describe
the qubit energy relaxation time. This work confirms that resonant TLSs located
in areas where the electric field is strong can significantly affect the qubit
relaxation time, even if they are located far from the Josephson junction.
Similarly, a strongly-coupled resonant TLS located in the Josephson junction
does not guarantee a reduced qubit relaxation time if a more strongly coupled
TLS is far from the Josephson junction. In addition to the coupling strengths
between TLSs and the qubit, the model predicts that the geometry of the device
and the TLS relaxation time play a significant role in qubit dynamics. Our work
can provide guidance for future quantum processor designs with improved qubit
coherence times.Comment: 8 pages, 5 figure
Properties of Classical and Quantum Jensen-Shannon Divergence
Jensen-Shannon divergence (JD) is a symmetrized and smoothed version of the
most important divergence measure of information theory, Kullback divergence.
As opposed to Kullback divergence it determines in a very direct way a metric;
indeed, it is the square of a metric. We consider a family of divergence
measures (JD_alpha for alpha>0), the Jensen divergences of order alpha, which
generalize JD as JD_1=JD. Using a result of Schoenberg, we prove that JD_alpha
is the square of a metric for alpha lies in the interval (0,2], and that the
resulting metric space of probability distributions can be isometrically
embedded in a real Hilbert space. Quantum Jensen-Shannon divergence (QJD) is a
symmetrized and smoothed version of quantum relative entropy and can be
extended to a family of quantum Jensen divergences of order alpha (QJD_alpha).
We strengthen results by Lamberti et al. by proving that for qubits and pure
states, QJD_alpha^1/2 is a metric space which can be isometrically embedded in
a real Hilbert space when alpha lies in the interval (0,2]. In analogy with
Burbea and Rao's generalization of JD, we also define general QJD by
associating a Jensen-type quantity to any weighted family of states.
Appropriate interpretations of quantities introduced are discussed and bounds
are derived in terms of the total variation and trace distance.Comment: 13 pages, LaTeX, expanded contents, added references and corrected
typo
Navigated interventions in the head and neck area: standardized assessment of a new handy field generator
Electromagnetic (EM) tracking enables localization of surgical instruments
within the magnetic field emitted by an EM field generator (FG). Usually, the
larger a FG is, the larger its tracking volume is. However, the company NDI
(Northern Digital Inc., Waterloo, ON, Canada) recently introduced the Planar
10-11 FG, which combines a compact construction (97mm x 112mm x 31mm) with a
relatively large, cylindrical tracking volume (diameter: 340mm, height: 340mm).
Using the standardized assessment protocol of Hummel et al., the FG was tested
with regard to its tracking accuracy and to its robustness with respect to
external sources of disturbance. The mean positional error (5cm distance metric
according to Hummel protocol) was 0.59mm, with a mean jitter of 0.26mm in the
standard setup. The mean orientational error was found to be 0.10{\deg}. The
highest positional error (4.82mm) due to metallic sources of disturbance was
caused by the steel SST 303. In contrast, steel SST 416 caused the lowest
positional error (0.10mm). Overall, the Planar 10-11 FG tends to achieve better
tracking accuracy results compared to other NDI FGs. Due to its compact
construction and portability, the FG could contribute to increased clinical use
of EM tracking systems.Comment: This is the preprint version of the BVM paper already published in
the conference proceedings of "Bildverarbeitung in der Medizin 2019". Paper
written in Germa
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