408 research outputs found
Cohomologically hyperbolic endomorphisms of complex manifolds
We show that if a compact Kahler manifold X admits a cohomologically
hyperbolic surjective endomorphism then its Kodaira dimension is non-positive.
This gives an affirmative answer to a conjecture of Guedj in the holomorphic
case. The main part of the paper is to determine the geometric structure and
the fundamental groups (up to finite index) for those X of dimension 3.Comment: International Journal of Mathematics (to appear
On the canonical degrees of curves in varieties of general type
A widely believed conjecture predicts that curves of bounded geometric genus
lying on a variety of general type form a bounded family. One may even ask
whether the canonical degree of a curve in a variety of general type is
bounded from above by some expression , where and are
positive constants, with the possible exceptions corresponding to curves lying
in a strict closed subset (depending on and ). A theorem of Miyaoka
proves this for smooth curves in minimal surfaces, with . A conjecture
of Vojta claims in essence that any constant is possible provided one
restricts oneself to curves of bounded gonality.
We show by explicit examples coming from the theory of Shimura varieties that
in general, the constant has to be at least equal to the dimension of the
ambient variety.
We also prove the desired inequality in the case of compact Shimura
varieties.Comment: 10 pages, to appear in Geometric and Functional Analysi
Noise Characteristics of the FORE+OSEM(DB) Reconstruction Method for the MiCES PET Scanner
The FORE+OSEM(DB) image reconstruction method has been proposed for the fully-3D MiCES PET scanner under construction at the University of Washington. It is based on Fourier rebinning followed by 2D OSEM and an incorporated model of detector blurring (DB). As an extension, this paper presents the noise/resolution characteristics of this method. Multiple realizations were simulated to estimate the noise properties of the algorithm. The results are compared with OSEM followed by post reconstruction 3D Gaussian smoothing. The results show that the incorporation of detector blurring (OSEM(DB)) into the system matrix improves resolution compared to OSEM, while also inducing an increased variance at all radial locations. In addition, radially-varying noise characteristics are more apparent with OSEM(DB) than with OSEM.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85836/1/Fessler204.pd
Cohomological aspects on complex and symplectic manifolds
We discuss how quantitative cohomological informations could provide
qualitative properties on complex and symplectic manifolds. In particular we
focus on the Bott-Chern and the Aeppli cohomology groups in both cases, since
they represent useful tools in studying non K\"ahler geometry. We give an
overview on the comparisons among the dimensions of the cohomology groups that
can be defined and we show how we reach the -lemma
in complex geometry and the Hard-Lefschetz condition in symplectic geometry.
For more details we refer to [6] and [29].Comment: The present paper is a proceeding written on the occasion of the
"INdAM Meeting Complex and Symplectic Geometry" held in Cortona. It is going
to be published on the "Springer INdAM Series
Molecular dynamics simulations of oxide memristors: thermal effects
We have extended our recent molecular-dynamic simulations of memristors to
include the effect of thermal inhomogeneities on mobile ionic species appearing
during operation of the device. Simulations show a competition between an
attractive short-ranged interaction between oxygen vacancies and an enhanced
local temperature in creating/destroying the conducting oxygen channels. Such a
competition would strongly affect the performance of the memristive devices.Comment: submit/0169777; 6 pages, 4 figure
Pragmatic fully 3D image reconstruction for the MiCES mouse imaging PET scanner
We present a pragmatic approach to image reconstruction for data from the micro crystal elements system (MiCES) fully 3D mouse imaging positron emission tomography (PET) scanner under construction at the University of Washington. Our approach is modelled on fully 3D image reconstruction used in clinical PET scanners, which is based on Fourier rebinning (FORE) followed by 2D iterative image reconstruction using ordered-subsets expectation-maximization (OSEM). The use of iterative methods allows modelling of physical effects (e.g., statistical noise, detector blurring, attenuation, etc), while FORE accelerates the reconstruction process by reducing the fully 3D data to a stacked set of independent 2D sinograms. Previous investigations have indicated that non-stationary detector point-spread response effects, which are typically ignored for clinical imaging, significantly impact image quality for the MiCES scanner geometry. To model the effect of non-stationary detector blurring (DB) in the FORE+OSEM(DB) algorithm, we have added a factorized system matrix to the ASPIRE reconstruction library. Initial results indicate that the proposed approach produces an improvement in resolution without an undue increase in noise and without a significant increase in the computational burden. The impact on task performance, however, remains to be evaluated.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/48978/2/pmb4_19_008.pd
Stand-alone tsunami alarm equipment
One of the quickest means of tsunami evacuation is transfer to
higher ground soon after strong and long ground shaking. Ground shaking
itself is a good initiator of the evacuation from disastrous tsunami. Longer period seismic waves are considered to be more correlated with the
earthquake magnitude. We investigated the possible application of this to
tsunami hazard alarm using single-site ground motion observation. Information
from the mass media is sometimes unavailable due to power failure soon after
a large earthquake. Even when an official alarm is available, multiple
information sources of tsunami alert would help people become aware of the coming
risk of a tsunami. Thus, a device that indicates risk of a tsunami without requiring other data would be helpful to those who should evacuate. Since
the sensitivity of a low-cost MEMS (microelectromechanical systems)
accelerometer is sufficient for this purpose, tsunami alarm equipment for
home use may be easily realized. Amplitude of long-period (20 s cutoff)
displacement was proposed as the threshold for the alarm based on empirical
relationships among magnitude, tsunami height, hypocentral distance, and peak
ground displacement of seismic waves. Application of this method to recent
major earthquakes indicated that such equipment could effectively alert
people to the possibility of tsunami
A randomized controlled multicenter trial of post-suicide attempt case management for the prevention of further attempts in Japan (ACTION-J)
<p>Abstract</p> <p>Background</p> <p>A previous suicide attempt is a potent risk factor for suicide later on. Crisis intervention, psychiatric and psychosocial evaluation at emergency medical facilities, and follow-up care for suicide attempters are considered important components for suicide prevention. The Japanese Multimodal Intervention Trials for Suicide Prevention (J-MISP) includes a randomized, controlled, multicenter trial of post-suicide attempt case management for the prevention of further attempts (ACTION-J) to address the continuing increase in suicides in Japan. The primary aim of ACTION-J is to examine the effectiveness of an extensive intervention for suicide attempters in prevention of recurrent suicidal behavior, as compared with standard intervention. This paper describes the rationale and protocol of the ACTION-J trial.</p> <p>Methods/Design</p> <p>In this clinical trial, case management intervention will be provided at 19 emergency medical facilities in Japan. After crisis intervention including psychiatric evaluation, psychosocial assessment, and psychological education, subjects will be randomly assigned to either a group receiving continuous case management or a control group receiving standard care. Suicidal ideation, depressive symptoms, and general health condition will be evaluated as secondary measures. The intervention was initiated in July 2006. By December, 2009, 842 subjects will be randomized. Subject follow-up will continue for 1.5 to 5 years.</p> <p>Discussion</p> <p>Suicide is a complex phenomenon that encompasses multiple factors. Case management by multi-sector collaboration is needed. ACTION-J may provide valuable information on suicide attempters and may develop effective case management to reduce future risk for suicide attempters.</p> <p>Trial registration</p> <p>UMIN Clinical Trials Registry number, UMIN000000444. ClinicalTrials.gov number, NCT00736918.</p
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