555 research outputs found
Exploiting quantum parallelism of entanglement for a complete experimental quantum characterization of a single qubit device
We present the first full experimental quantum tomographic characterization
of a single-qubit device achieved with a single entangled input state. The
entangled input state plays the role of all possible input states in quantum
parallel on the tested device. The method can be trivially extended to any
n-qubits device by just replicating the whole experimental setup n times.Comment: 4 pages in revtex4 with 4 eps figure
Lie-Algebraic Characterization of 2D (Super-)Integrable Models
It is pointed out that affine Lie algebras appear to be the natural
mathematical structure underlying the notion of integrability for
two-dimensional systems. Their role in the construction and classification of
2D integrable systems is discussed. The super- symmetric case will be
particularly enphasized. The fundamental examples will be outlined.Comment: 6 pages, LaTex, Talk given at the conference in memory of D.V.
Volkov, Kharkhov, January 1997. To appear in the proceeding
On the Nonperturbative Consistency of String Theory
An infinite number of distinct matrix models reproduce the perturbation
theory of string theory. Due to constraints of causality, however, we
argue that none of the existing constructions gives a consistent
nonperturbative definition of the string.Comment: 10 pages, 2 figures, LaTeX (author's name added
Periastron shift in Weyl class spacetimes
The periastron position advance for geodesic motion in axially symmetric
solutions of the Einstein field equations belonging to the Weyl class of vacuum
solutions is investigated. Explicit examples corresponding to either static
solutions (single Chazy-Curzon, Schwarzschild and a pair of them), or
stationary solution (single rotating Chazy-Curzon and Kerr black hole) are
discussed. The results are then applied to the case of S2-SgrA binary
system of which the periastron position advance will be soon measured with a
great accuracy.Comment: To appear on General Relativity and Gravitation, vol. 37, 200
On Proper Polynomial Maps of
Two proper polynomial maps are said to be \emph{equivalent} if there exist such that .
We investigate proper polynomial maps of arbitrary topological degree up to equivalence. Under the further assumption that the maps are Galois
coverings we also provide the complete description of equivalence classes. This
widely extends previous results obtained by Lamy in the case .Comment: 15 pages. Final version, to appear in Journal of Geometric Analysi
SENSE EPI reconstruction with 2D phase error correction and channel-wise noise removal
Nyquist ghost; Denoising; DiffusionFantasma de Nyquist; Eliminación de ruido; DifusiónFantasma de Nyquist; Eliminació de soroll; DifusióPurpose
To develop a robust reconstruction pipeline for EPI data that enables 2D Nyquist phase error correction using sensitivity encoding without incurring major noise artifacts in low SNR data.
Methods
SENSE with 2D phase error correction (PEC-SENSE) was combined with channel-wise noise removal using Marcenko–Pastur principal component analysis (MPPCA) to simultaneously eliminate Nyquist ghost artifacts in EPI data and mitigate the noise amplification associated with phase correction using parallel imaging. The proposed pipeline (coined SPECTRE) was validated in phantom DW-EPI data using the accuracy and precision of diffusion metrics; ground truth values were obtained from data acquired with a spin echo readout. Results from the SPECTRE pipeline were compared against PEC-SENSE reconstructions with three alternate denoising strategies: (i) no denoising; (ii) denoising of magnitude data after image formation; (iii) denoising of complex data after image formation. SPECTRE was then tested using high -value (i.e., low SNR) diffusion data (up to s/mm
) in four healthy subjects.
Results
Noise amplification associated with phase error correction incurred a 23% bias in phantom mean diffusivity (MD) measurements. Phantom MD estimates using the SPECTRE pipeline were within 8% of the ground truth value. In healthy volunteers, the SPECTRE pipeline visibly corrected Nyquist ghost artifacts and reduced associated noise amplification in high -value data.
Conclusion
The proposed reconstruction pipeline is effective in correcting low SNR data, and improves the accuracy and precision of derived diffusion metrics.EPSRC-funded UCL Centre for Doctoral Training in Medical Imaging, Grant/Award Number: EP/L016478/
Solving Virasoro Constraints on Integrable Hierarchies via the Kontsevich-Miwa Transform
We solve Virasoro constraints on the KP hierarchy in terms of minimal
conformal models. The constraints we start with are implemented by the Virasoro
generators depending on a background charge . Then the solutions to the
constraints are given by the theory which has the same field content as the
David-Distler-Kawai theory: it consists of a minimal matter scalar with
background charge , dressed with an extra `Liouville' scalar. The
construction is based on a generalization of the Kontsevich parametrization of
the KP times achieved by introducing into it Miwa parameters which depend on
the value of . Under the thus defined Kontsevich-Miwa transformation, the
Virasoro constraints are proven to be equivalent to a master equation depending
on the parameter . The master equation is further identified with a
null-vector decoupling equation. We conjecture that constraints on
the KP hierarchy are similarly related to a level- decoupling equation. We
also consider the master equation for the -reduced KP hierarchies. Several
comments are made on a possible relation of the generalized master equation to
{\it scaled} Kontsevich-type matrix integrals and on the form the equation
takes in higher genera.Comment: 23pp (REVISED VERSION, 10 April 1992
Late and early onset dementia: what is the role of vascular factors? A retrospective study.
Neuropathology of Alzheimer's disease (AD) demonstrates that the common occurrence of vascular lesions and vascular factors is suggested to contribute significantly to the clinical progression of the disease. This study has assessed the presence of vascular brain lesions and risk factors in subjects with diagnosis of AD and their influence on the disease course both in Late Onset Dementia (LOD) and in Early Onset Dementia (EOD).
METHODS:
MRI scans of 374 LOD and of 67 EOD patients were evaluated for the presence of vascular associated lesions and rated according to the age-related white matter changes (ARWMC) scale as "pure degenerative", "mixed" and "vascular" cases of dementia. Vascular risk factors burden (hypertension, diabetes, dyslipidemia, myocardial infarction) and disease progression were also assessed.
RESULTS:
44% of LOD cases and 46% of EOD were classified as "mixed dementia cases". The vascular risk factors burden showed an increase from the pure degenerative to the pure vascular forms. Disease progression, calculated in two years using the Mini Mental State Evaluation (MMSE), Activities of Daily Living (ADL) and Instrumental Activities of Daily Living (IADL) scores, did not reveal differences among the three different classes of dementias.
CONCLUSIONS:
Vascular lesions are found in the majority of LOD cases and in about one half of EOD. This observation is consistent with the hypothesis of a synergistic effect of the degenerative and vascular factors on the development of cognitive dysfunction. The linear increase of the vascular burden supports the idea of a continuum spectrum between the pure degenerative and the pure vascular forms of adult-onset dementia disorder
Coupling Of Ribosome And tRNA Dynamics During Translation
Interstellar matter and star formatio
- …