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Search Results: 1 - 10 of 301 matches for " Ayumu Yamaoka "
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Bilateral Blunt Internal Carotid Artery Occlusions Associated with Multiple Trauma: A Case Report  [PDF]
Ayumu Yamaoka, Kei Miyata, Naofumi Bunya, Eichi Narimatsu
Open Journal of Modern Neurosurgery (OJMN) , 2017, DOI: 10.4236/ojmn.2017.73006
Abstract:

In multiple trauma, blunt carotid artery injuries (BCAIs) have occasionally been reported. However, bilateral blunt carotid artery occlusions (Grade 4 BCAIs) associated with multiple trauma are rare, and delays in diagnosis and treatment result in a lethal outcome. Here, we report our experience with bilateral carotid artery occlusions. A 76-year-old female suffered multiple traumas in a motor vehicle accident. On arrival at our hospital, she presented in a coma, with left mydriasis and unreactive pupils. Computed tomography (CT) showed bifrontal intracranial epidural hematoma and fractures of the facial bone and anterior skull base, and osteoplastic craniotomy was urgently undertaken for the epidural hematoma. However, the comatose state and unreactive pupils persisted during the post-operative course. Serial head CT findings showed progressive bilateral ischemic changes, and radiological examinations revealed bilateral internal carotid artery occlusions. We speculated that bilateral Grade 4 BCAIs had induced progressive cerebral infarctions. The patient partially responded to anticoagulation therapy with heparin infusion, but died of multiple organ failure on day 15. When bilateral progressive ischemic changes are observed in a patient with severe traumatic brain injury, bilateral Grade 4 BCAIs should be considered in the differential diagnosis. CT angiography as part of whole-body CT at admission may be effective for preventing delays in diagnosis and treatment of bilateral Grade 4 BCAIs.

On the Basis of Quantum Statistical Mechanics
Ayumu Sugita
Physics , 2006,
Abstract: We propose a new approach to justify the use of the microcanonical ensemble for isolated macroscopic quantum systems. Since there are huge number of independent observables in a macroscopic system, we cannot see all of them. Actually what we observe can be written in a rather simple combination of local observables. Considering this limitation, we show that almost all states in a energy shell are practically indistinguishable from one another, and hence from the microcanonical ensemble. In particular, the expectation value of a macroscopic observable is very close to its microcanonical ensemble average for almost all states.
Perturbative Analysis of Nonequilibrium Steady States in Quantum Systems
Ayumu Sugita
Physics , 2012,
Abstract: We study the nonequilibrium steady state (NESS) in a quantum system in contact with two heat baths at different temperatures. We use a time-independent perturbative expansion with respect to the coupling with the two heat baths to obtain the density matrix for the NESS. In particular, we show an explicit representation of the density matrix for the reflection symmetric and weakly nonequilibrium case. We also calculate the expectation value of the energy current and show that the Kubo formula holds in this case.
Geometrical properties of Maslov indices in periodic-orbit theory
Ayumu Sugita
Physics , 1999, DOI: 10.1016/S0375-9601(99)00876-2
Abstract: Maslov indices in periodic-orbit theory are investigated using phase space path integral. Based on the observation that the Maslov index is the multi-valued function of the monodromy matrix, we introduce a generalized monodromy matrix in the universal covering space of the symplectic group and show that this index is uniquely determined in this space. The stability of the orbit is shown to determine the parity of the index, and a formula for the index of the n-repetition of the orbit is derived.
Semiclassical trace formulas in terms of phase space path integrals
Ayumu Sugita
Physics , 2000, DOI: 10.1006/aphy.2001.6115
Abstract: Semiclassical trace formulas are examined using phase space path integrals. Our main concern in this paper is the Maslov index of the periodic orbit, which seems not fully understood in previous works. We show that the calculation of the Maslov index is reduced to a classification of connections on a vector bundle over $S^{1}$ with structure group $Sp(2n,R)$. We derive a formula for the index of the n-repetition, and show that a Bohr-Sommerfeld type quantization condition including quadratic fluctuation around the orbit is derived using this formula.
Moments of generalized Husimi distributions and complexity of many-body quantum states
Ayumu Sugita
Physics , 2001, DOI: 10.1088/0305-4470/36/34/310
Abstract: We consider generalized Husimi distributions for many-body systems, and show that their moments are good measures of complexity of many-body quantum states. Our construction of the Husimi distribution is based on the coherent state of the single-particle transformation group. Then the coherent states are independent-particle states, and, at the same time, the most localized states in the Husimi representation. Therefore delocalization of the Husimi distribution, which can be measured by the moments, is a sign of many-body correlation (entanglement). Since the delocalization of the Husimi distribution is also related to chaoticity of the dynamics, it suggests a relation between entanglement and chaos. Our definition of the Husimi distribution can be applied not only to the systems of distinguishable particles, but also to those of identical particles, i.e., fermions and bosons. We derive an algebraic formula to evaluate the moments of the Husimi distribution.
Systematic generation of entanglement measures for pure states
Ayumu Sugita
Physics , 2007, DOI: 10.1103/PhysRevA.77.052304
Abstract: We propose a method to generate entanglement measures systematically by using the irreducible decomposition of some copies of a state under the local unitary (LU) transformations. It is applicable to general multipartite systems. We show that there are entanglement monotones corresponding to singlet representations of the LU group. They can be evaluated efficiently in an algebraic way, and experimentally measurable by local projective measurements of the copies of the state. Non-singlet representations are also shown to be useful to classify entanglement. Our method reproduces many well-known measures in a unified way, and produces also a lot of new ones.
Borromean Entanglement Revisited
Ayumu Sugita
Physics , 2007,
Abstract: An interesting analogy between quantum entangled states and topological links was suggested by Aravind. In particular, he emphasized a connection between the Greenberger-Horne-Zeilinger (GHZ) state and the Borromean rings. However, he made the connection in a way that depends on the choice of measurement basis. We reconsider it in a basis-independent way by using the reduced density matrix.
Quandle and hyperbolic volume
Ayumu Inoue
Mathematics , 2008,
Abstract: We show that the hyperbolic volume of a hyperbolic knot is a quandle cocycle invariant. Further we show that it completely determines invertibility and positive/negative amphicheirality of hyperbolic knots.
Quasi-triviality of quandles for link-homotopy
Ayumu Inoue
Mathematics , 2012,
Abstract: We introduce the notion of quasi-triviality of quandles and define homology of quasi-trivial quandles. Quandle cocycle invariants are invariant under link-homotopy if they are associated with 2-cocycles of quasi-trivial quandles. We thus obtain a lot of numerical link-homotopy invariants.
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