检索结果-内蒙古大学图书馆

Ferroelectricity and ferromagnetism in EuTiO3 nanowires

Physical Review B 2011年第20期84卷 205403-205403页

作者： Anna N. Morozovska Maya D. Glinchuk Rakesh K. Behera Basil Zaulychny Chaitanya S. Deo Eugene A. Eliseev Institute for Problems of Materials Science NAS of Ukraine Krjijanovskogo 3 03142 Kiev Ukraine V. Lashkaryov Institute of Semiconductor Physics NAS of Ukraine pr. Nauki 41 03028 Kiev Ukraine Nuclear and Radiological Engineering Program George W. Woodruff School of Mechanical Engineering Georgia Institute of Technology Atlanta Georgia 30332 USA

We predicted the ferroelectric–ferromagnetic multiferroic properties of EuTiO3 nanowires and generated the phase diagrams in coordinates of temperature and wire radii. The calculations were performed within the Landau-Ginzburg-Devonshire theory with phenomenological parameters extracted from tabulated experimental data and first-principles calculations. Since bulk EuTiO3 is antiferromagnetic at temperatures lower than 5.5 K and paraelectric at all temperatures, our goal was to investigate the possibility of inducing the ferroelectric and ferromagnetic properties of EuTiO3 by reducing the bulk to nanosystems. Our results indicate that ferroelectric spontaneous polarization of ∼0.1–0.5 C/m2 is induced in EuTiO3 nanowires due to the intrinsic surface stress, which is inversely proportional to the nanowire radius. Spontaneous polarization exists at temperatures lower than 300 K for wire diameter of ∼4 lattice constants with 10 N/m surface stress coefficient. Due to the strong biquadratic magnetoelectric coupling, the spontaneous polarization in turn induces the ferromagnetic phase at temperatures lower than 30 K for 2-nm nanowire and at temperatures lower than 10 K for 4-nm nanowire in EuTiO3. Thus, we predicted that the EuTiO3 nanowires can be the new ferroelectric–ferromagnetic multiferroic.

关键词： FERROELECTRICITY LANDAU levels NANOWIRES MAGNETIC couplings LATTICE theory FERROMAGNETISM

来源：评论

学校读者我要写书评

暂无评论

引用

2010 ANS Annual Meeting and Embedded Topical Meetings

作者： Su, Bingjing He, Tao University of Cincinnati Nuclear and Radiological Engineering Program Cincinnati OH 45221-0072 United States

来源：评论

学校读者我要写书评

暂无评论

Atomistic calculations of fundamental physical properties of uranium

Atomistic calculations of fundamental physical properties of...

引用

6th International Conference on Plutonium Futures - The Science 2010

作者： Good, Benjamin Deo, Chaitanya Baskes, Michael Nuclear and Radiological Engineering Program G. W. Woodruff School of Mechanical Engineering Georgia Institute of Technology United States Department of Mechanical and Aerospace Engineering University of California San Diego CA United States

来源：评论

学校读者我要写书评

暂无评论

Noise reduction for Multi-Harmonic Phase Analysis of gated SPECT myocardial perfusion imaging

Noise reduction for Multi-Harmonic Phase Analysis of gated S...

引用

IEEE Symposium on nuclear Science (NSS/MIC)

作者： Alice A. Cheung Tianye Niu Ji Chen Lei Zhu Nuclear and Radiological Engineering and Medical Physics Program Georgia Institute of Technology Atlanta GA USA Department of Radiology Emory University Atlanta GA USA

Multi-Harmonic Phase Analysis (MHPA) has been developed for heart failure prognosis by reliably measuring left-ventricular (LV) dyssynchrony from conventional gated single photon emission tomography (GSPECT) myocardial perfusion imaging (MPI). Although MHPA has been evaluated in multiple clinical studies, its accuracy can be limited under highly noisy conditions. The purpose of this study is to develop a 4D postreconstruction method for suppressing noise in GSPECT MPI data. SPECT images acquired at different temporal points were first registered to the same point. By summing the registered images, the uncorrelated noise was greatly reduced and the myocardial signals were strengthened. The same process then repeated for different temporal points. A deformable registration with a simulated annealing optimization scheme was implemented in this work. The proposed method was evaluated using a simulation study on an extended cardiac torso phantom (XCAT). The projection data were first calculated analytically and Poisson noise was added with a level matching that in clinical data. An ordered subsets expectation maximization (OSEM) algorithm was used in the reconstruction. The comparison of SPECT images without versus with the noise reduction showed that the proposed noise reduction method increased the signal-to-noise ratio (SNR) by an average factor of ~2.3. Our approach was able to substantially reduce image noise without losing faithful information of myocardial activities. The next step is to use this method to reduce noise in clinical GSPECT MPI data to improve the accuracy of MHPA, especially in a region with severe myocardial scar.

关键词： Noise reduction Myocardium Heart Pixel Signal to noise ratio Imaging

来源：评论

学校读者我要写书评

暂无评论

Summary Report of Working Group 1: Laser‐Plasma Acceleration

引用

AIP Conference Proceedings 2010年第1期1299卷 79-87页

作者： C. G. R. Geddes C. Clayton W. Lu A. G. R. Thomas aLOASIS program Lawrence Berkeley National Laboratory 1 Cyclotron Rd Berkeley CA 94720 USA bDepartment of Electrical Engineering University of California Los Angeles Westwood CA 90024 USA cDepartment of Nuclear Engineering and Radiological Sciences University of Michigan Ann Arbor MI 48109 USA

Advances in and physics of the acceleration of particles using underdense plasma structures driven by lasers were the topics of presentations and discussions in Working Group 1 of the 2010 Advanced Accelerator Concepts Workshop. Such accelerators have demonstrated gradients several orders beyond conventional machines, with quasi‐monoenergetic beams at MeV‐GeV energies, making them attractive candidates for next generation accelerators. Workshop discussions included advances in control over injection and laser propagation to further improve beam quality and stability, detailed diagnostics and physics models of the acceleration process, radiation generation as a source and diagnostic, and technological tools and upcoming facilities to extend the reach of laser‐plasma accelerators.

关键词：

来源：评论

学校读者我要写书评

暂无评论

Simulation of left ventricular dyssynchrony using the XCAT phantom

Simulation of left ventricular dyssynchrony using the XCAT p...

引用

IEEE Symposium on nuclear Science (NSS/MIC)

作者： Alice A. Cheung Tianye Niu Tracy L. Faber W. Paul Segars Lei Zhu Ji Chen Nuclear and Radiological Engineering and Medical Physics Program Georgia Institute of Technology Atlanta GA USA Department of Radiology Emory University Atlanta GA USA Department of Radiology Duke University Durham NC USA

Multi-Harmonic Phase Analysis (MHPA) has been developed to quantify left-ventricular (LV) mechanical dyssynchrony with gated single photon emission tomography (SPECT) myocardial perfusion imaging (MPI). Although MHPA has shown promising clinical results, it needs to be optimized technically. The purpose of this study is to develop a tool to simulate LV mechanical dyssynchrony in gated SPECT MPI using an extended cardiac torso phantom (XCAT). A special version of the XCAT phantom was developed to control regional myocardial wall thickening using more than 300 B-splines points over the LV myocardium and 26 temporal frames over a cardiac cycle. By shifting the regional myocardial wall thickness values in the temporal domain, regional phase delays can be simulated to represent LV mechanical dyssynchrony. Gated SPECT data were created with phase delays of 0°, ±20°, ±40°, and ±60° in the anterior wall for a LV with normal perfusion. The activity maps given by XCAT were submitted to a SPECT simulator to generate gated SPECT projections. The gated SPECT projections were reconstructed and reoriented into gated short-axis images, which were then submitted to MHPA. A correlation of R 2 = 0.9941 between MHPA measured and simulated regional phase delays was obtained, indicating that MHPA can accurately measure the simulated phase delays. Thus, a simulation tool based on the XCAT phantom has been developed to simulate regional phase delays, which can be accurately measured by MHPA. This tool can offer the opportunities to investigate the relationship between phase delay and myocardial defect, and to optimize MHPA for various factors such as noise and cardiac torsion in future studies.

关键词： Delay Myocardium Logic gates Phantoms Phase measurement Heart

来源：评论

学校读者我要写书评

暂无评论

TH-D-201C-04: Quantification of Cellular Response in Myocardial Infarction Using Iron Oxide Particles-Enhanced MRI

引用

Medical Physics 2010年第6PART8期37卷 3469-3470页

作者： Y Yang J Liu X Shi W Hill T Hu Department of Radiology Medical College of Georgia Augusta GA Department of Pathology Medical College of Georgia Augusta GA Department of Cellular Biology and Anatomy Veterans Affairs Medical Center Medical College of Georgia Augusta GA Nuclear & Radiological Engineering and Medical Physics Program Georgia Institute of Technology Atlanta GA

Purpose: To quantify the cellular response in myocardial infarction by using iron oxide particles cell labeling and MR imaging techniques. Method and Materials: Iron oxide particles can produce signal attenuation in MRI and were used to label either macrophages or mesenchymal stem cells. Macrophages were labeled via an intravenous administration of iron oxide particles whereas mesenchymal stem cells were labeled in vitro and then transplanted into the animal bone marrow. In the macrophage study varied doses (1.1–14.5 μg Fe/g body weight) were applied. After surgically inducing a myocardial infarction in the C57 mouse the labeled cells would mobilize to the infarction site attempting to repair the damaged tissue. To monitor the cellular response T 2 *-weighted MRI was used to acquire short-axis cardiac images at 3 7 14 and 21 days post-infarction. Signal intensity normalized to the maximum signal from the ventricular blood was used to quantify labeled cells at infarction sites. Results: Cellular response during myocardial infarction was temporally and noninvasively monitored. In the macrophage study linear regression of normalized signal intensity at each time point revealed a linear relationship between the normalized signal intensity and iron oxide dose at 7 days (r 2 =0.92) and 14 days (r 2 =0.98) post-infarction. An optimum dose as well as imaging time window for monitoring inflammatory cell response was also obtained. Either labeled macrophages or mesenchymal stem cells were evidenced at the infarction site in histology. Conclusions: A linear signal-dose relationship at 7 and 14 days post-infarction suggests that the number of labeled cells at the infarction site can be interpreted from the MR signal within this time window. This linear relationship may further apply to quantify labeled mesenchymal stem cells. Therefore the cell labeling and MR imaging technique have a potential to quantify cellular response in pathological processes as well as during cell thera

关键词： Heart disease Iron Medical imaging Magnetic resonance imaging Intracellular signaling Medical magnetic resonance imaging Linear regression Tissue engineering Tissues

来源：评论

学校读者我要写书评

暂无评论

SU-GG-T-428: Photon Beam Spectrum Characterization Using Scatter Radiation Analysis

引用

Medical Physics 2010年第6PART22期37卷 3285-3285页

作者： M Hawwari M Lamba H Elson H Spitz A Miron S Glover Nuclear and Radiological Engineering Program University of Cincinnati Cincinnati OH Department of Radiation Oncology University of Cincinnati Cincinnati OH

Purpose : A method is described to characterize a linac bremsstrahlung spectrum. The method employs a combination of monoenergetic scatter simulations, polyenergetic scatter measurements, and matrix solutions. Method and Materials : Monte Carlo simulations were used to predict the ratio of primary to scattered photons for narrow mono-energetic photon beams at 9 different locations, with 10 degree increments and 15 cm from a scattering material. Measurements were performed in the same geometry using the photon beams produced by linear accelerators. A linear matrix system, A×F=T, was developed to describe the scattering interactions and their relationship to the primary spectrum. Matrix “A” is the monoenergetic scatter kernel determined from the Monte Carlo simulations, “F” is the incident photon spectrum, and “T” represents the scatter distribution characterized by empirical measurement. Direct matrix inversion methods produce results that are not physically consistent due to errors inherent in the system. Tikhonov regularization methods were applied to address the effects of these errors and solve the system for physically consistent bremsstrahlung spectra. The technique was applied to two photon energy spectra -a helical tomotherapy accelerator operating at therapeutic energy and at imaging energy. Results : The resulting spectra were qualitatively and quantitatively similar to other published data and consistent with expected behavior such as maximum photon energy. Conclusion : The results of this research provide a method to empirically characterize the primary radiation energy spectrum produced by a linear accelerator. Key words : photon energy, spectrum, scatter analysis, regularization, Tikhonov

关键词： Photons Photon scattering Linear accelerators Spectrum analysis Monte Carlo methods Matrix inversion Therapeutics

来源：评论

学校读者我要写书评

暂无评论

Simulating small changes in system response by MCNP

Simulating small changes in system response by MCNP

引用

International Conference on Mathematics, Computational Methods and Reactor Physics 2009, M and C 2009

作者： He, Tao Su, Bingjing Nuclear and Radiological Engineering Program Department of Mechanical Engineering University of Cincinnati Cincinnati OH 45221-0072 United States

ISBN: (纸本)9781615673490

Correlated sampling and perturbation are two developed techniques that enable MCNP to simulate small changes in system response with an acceptable uncertainty at reasonable number of particle histories. In this work the performance of correlated sampling is investigated. It is found that under certain conditions using the default output format of MCNP5 and the original practice of batch statistics developed for correlated sampling may overestimate the uncertainty of the change in system response. The cause of the overestimation is analyzed;correspondingly two improved procedures are proposed for correlated sampling to ensure correct estimation of the uncertainty. In addition, the performance of improved correlated sampling method is also compared with that of the perturbation technique of MCNP5. In terms of precision of the change in system response, the perturbation technique is found to be capable of producing smaller uncertainty than correlated sampling when response change is small;as response change becomes larger, the uncertainty predicted by correlated sampling is comparable with or even better than that predicted by the perturbation technique. In terms of accuracy of the change in system response, however, it is found that the perturbation technique may produce less accurate results than correlated sampling for certain problems that involve intermediate or even small changes in system response. Overall, correlated sampling seems to be a more robust technique than the current perturbation technique of MCNP5 for simulating small changes in system response.

关键词： Perturbation techniques

来源：评论

学校读者我要写书评

暂无评论

Detectability of pin diversion in PWR spent fuel assemblies

Detectability of pin diversion in PWR spent fuel assemblies

引用

2009 ANS Annual Meeting and Embedded Topical Meetings: Risk Management and 2009 Young Professionals Congress

作者： Burdo, J.S. Maldonado, G.I. Christenson, J.M. Ham, Y.S. Nuclear and Radiological Engineering Program University of Cincinnati United States Department of Nuclear Engineering University of Tennessee United States Lawrence Livermore National Laboratory United States

来源：评论

学校读者我要写书评

暂无评论

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案：

请选择收藏分类：

通借通还

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：