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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

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Application of X-ray Synchrotron microscopy instrumentation in Biology

Application of X-ray Synchrotron microscopy instrumentation ...

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International Conference on Advancements in nuclear Instrumentation Measurement Methods and their Applications (ANIMMA)

作者： F. M. Gasperini G. R. Pereira J. M. Granjeiro M. D. Calasans-Maia A. M. Rossi C. A. Perez R. T. Lopes I. Lima Medical Science Program of Fluminense Federal University Niteroi Brazil Department of Metallurgical and Materials Engineering Federal University Rio de Janeiro Brazil Molecular and Cell Biology Department Fluminense Federal University Niteroi Rio de Janeiro Brazil Oral Surgery Department Fluminense Federal University Niteroi Rio de Janeiro Brazil Brazilian Center of Physics Research Biomaterials Laboratory Rio de Janeiro Brazil Brazilian Synchrotron Light Laboratory Campinas Sao Paulo Brazil Nuclear Engineering Laboratory Federal University of Rio de Janeiro Brazil

X-ray microfluorescence imaging technique has been used as a significant tool in order to investigate minerals contents in some kinds of materials. The aim of this study was to evaluate the elemental distribution of calcium and zinc in bone substitute materials (nanohydroxyapatite spheres) and cortical bones through X-Ray Microfluorescence analysis with the increment of Synchrotron Radiation in order to evaluate the characteristics of the newly formed bone and its interface, the preexisting bone and biomaterials by the arrangement of collagen fibers and its birefringence. The elemental mapping was carried out at Brazilian Synchrotron Light Laboratory, Campinas - Sao Paulo, Brazil working at D09-XRF beam line. Based on this study, the results suggest that hydroxyapatite-based biomaterials are biocompatible, promote osteoconduction and favored bone repair.

关键词： Bones Materials Zinc Calcium Nanobioscience Laboratories X-ray imaging

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Operation and testing of the PULSTAR reactor intense slow positron beam and PALS spectrometers

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Journal of physics: Conference Series 2011年第1期262卷

作者： Ayman I Hawari David W Gidley Jeremy Moxom Alfred G Hathaway Saurabh Mukherjee Nuclear Reactor Program Department of Nuclear Engineering North Carolina State University PO Box 7909 Raleigh NC 27695 USA Physics Department University of Michigan 450 Church Street Ann Arbor MI 48109 USA

An intense slow positron beam has been established at the 1-MW PULSTAR nuclear reactor. The beam is operational generating mono-energetic positrons with an energy of 1-keV. The maximum measured intensity slightly exceeds 109 e+/s. The beam is operated routinely with an intensity of approximately 5×108 e+/s. The positrons are generated through gamma-ray pair production interactions in two back-to-back banks of tungsten converter/moderators. The gamma-rays are produced in the PULSTAR core and by thermal neutron capture in a cadmium shroud that surrounds the tungsten. The primary utilization of the PULSTAR positron beam is the characterization of nanoscale structure in materials. Consequently, the beam has been equipped with two state-of-the-art PALS spectrometers. The first spectrometer is dedicated to measurements in materials such as metals and semiconductors. This spectrometer is based on pulsing and bunching of the primary beam and is currently operating with a timing resolution of approximately 390 picoseconds. The second spectrometer is dedicated to measurements in materials where positronium formation is promoted. The timing resolution of this spectrometer is designed to be ~ 0.5 nanosecond with an on-sample spot size of 1–2 mm. For both spectrometers, the energy of the positrons can be varied to allow depth profiling with on-sample intensity exceeding 106 e+/s.

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10.5: Development of THz gyrotrons with pulse solenoids for detecting concealed radioactive materials

10.5: Development of THz gyrotrons with pulse solenoids for ...

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2010 IEEE International Vacuum Electronics Conference, IVEC 2010

作者： Nusinovich, Gregory S. Granatstein, Victor L. Antonsen Jr., Thomas M. Pu, Ruifeng Sinitsyn, Oleksandr V. Rodgers, John Mohamed, Ali B. Silverman, Joseph Al-Sheikhly, Mohamad Dimant, Yakov S. Institute for Research in Electronics and Applied Physics University of Maryland College Park MD 20742-3511 United States Graduate Program in Nuclear Engineering A. James Clark School of Engineering University of Maryland College Park MD 20742-3511 United States Center for Space Physics Boston University Boston MA 02215 United States

ISBN: (纸本)9781424470976

This paper describes the first steps in the development of high-power THz-range gyrotrons with pulsed solenoids for remote detection of concealed radioactive materials. We first discuss the detection concept based on focusing high-power THz wave beams in small spots where the wave electric field amplitude exceeds the threshold required for initiating the breakdown. The specific feature of this concept in the case of using the THz radiation is a small volume in which the electromagnetic energy is localized. As a rule, in the absence of gamma rays causing additional ionization there should be initially no free electrons in this volume to initiate the discharge. Thus, the fact that the breakdown takes place in this volume immediately after the THz source is turned on will indicate that there is an additional source of ionization (such as radioactive materials). In the paper, we report first results on the study of air ionization by concealed radioactive materials and the first results of the design of a 670 GHz gyrotron. First estimates show that the gyrotron efficiency can be in the range of 20-25% and the gyrotron power can exceed 100 kW. © 2010 IEEE.

关键词： Gyrotrons

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

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

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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

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Resolution recoverable statistical listmode reconstruction using depth dependent point spread function for Compton camera

Resolution recoverable statistical listmode reconstruction u...

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IEEE Symposium on nuclear Science (NSS/MIC)

作者： Soo Mee Kim Jae Sung Lee Hee Seo Jin-Hyung Park Chan Hyeong Kim Chun Sik Lee Myung Chul Lee Dong Soo Lee Soo-Jin Lee Department of Nuclear Medicine and Interdisciplinary Program in Radiation Applied Life Science Major Seoul National University Seoul South Korea Department of Nuclear Engineering Hanyang University Seoul South Korea Department of Physics Chung-Ang University Seoul South Korea Department of Electronic Engineering Pai Chai University Daejeon South Korea

A Compton camera is an imaging system for three-dimensional (3D) distribution of gamma emitting sources based on Compton scattering interaction. The measurement error on energies and positions directly leads to uncertainties on the formation of cones and degrades the spatial resolution of the reconstructed images. Mostly the limited energy resolution, Doppler broadening and position segmentation of detectors cause angular and positional uncertainties on measurements. Since the conical surfaces are delocalized by angular and positional uncertainties into image space, degradation of spatial resolution may be severe depending on the distance (or depth) from the Compton camera. In order to enhance the deteriorated spatial resolution due to angular and positional uncertainties, this study investigates 3D Gaussian point spread function (PSF) incorporable into listmode ordered subset expectation maximization (LMOSEM) as a part of system matrix. Especially the depth-dependent PSF is applied as resolution recovery (RR) technique by image-space convolution operation. We investigated two different RR approaches: one (denoted by LMOSEM-RR-F) is when the convolution is performed in forward projection step only, and the other (denoted by LMOSEM-RR-FB) is when it is performed in both forward and backward projection steps. Using Monte Carlo data for 7 point sources at different depth from the Compton camera, the fitted axial and radial FWHM functions were obtained as FWHM axial (i)=0.2442i+1.054 and FWHM radial (i)=0.2369i-1.005, respectively. The simulation results showed that both RR approaches with depth dependent PSF gave an improvement on spatial resolution comparing to LMOSEM without RR techniques. Although LMOSEM-RR-F provided better resolution than LMOSEM-RR-FB, LMOSEM-RR-FB could still be useful for low counting statistics in measurement.

关键词： Cameras Spatial resolution Image reconstruction Three dimensional displays Uncertainty

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Simulation of left ventricular dyssynchrony using the XCAT phantom

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

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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

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

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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

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Historically Black Colleges and Universities educational and research outreach program in nuclear science and engineering from the university of Texas at Austin

Historically Black Colleges and Universities educational and...

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2009 ASEE Annual Conference and Exposition

作者： Landsberger, Sheldon Ezekoye, Ofodike Hearnsberger, David Stiffin, Rose Tamalis, Dimitri Elliott, Michael Handy, Carlos Stefanova, Elena Russ, Muchere Nuclear and Radiation Engineering Program University of Texas Austin United States Mechanical Engineering Department National Society of Black Engineers University of Texas Austin United States Kaizen Innovations Radioactive Waste Management Health Physics and Health Physics Instrumentation Nuclear and Radiation Engineering Program University of Texas Austin United States School of Health and Natural Sciences Florida Memorial University United States Department of Physics Texas Southern University United States Texas Southern University United States Health Physics Undergradaute Program Department of Chemistry College of Arts and Sciences

With the passing of the Energy Policy Act of 2005, the United States is experiencing for the first time in over two decades, what some refer to as the "nuclear Renaissance." Twenty-year operating license extension applications have been filed to extend the already approved 40-year operating period out to 60 years and some are already being approved. In addition, many utilities are filing a combined Construction and Operating License (COL) application to allow building new power plants within the existing restricted areas, while others are opting to build new power plants in different areas. The nuclear Regulatory Commission (NRC) recognizes this surge in application submissions and is committed to reviewing these applications in a timely manner to support the country's growing energy demands. Notwithstanding these facts, it is understood that the nuclear industry requires appropriately trained and educated personnel to support the growing needs of the nuclear industry and the US nuclear Regulatory Commission. Equally important is the need to educate the next generation of students in nuclear non-proliferation, nuclear forensics and various aspects of homeland security for the national laboratories and the Department of Defense. From mechanical engineers educated and experienced in materials, thermal/fluid dynamics, and component failure analysis, to physicists using advanced computing techniques to design the next generation of nuclear reactor fuel elements, the need for new engineers, scientists, and health physicist has never been greater. To help existing and burgeoning academic programs succeed, we propose to work with Historically Black Colleges and Universities and other Minority Institutions (HBCU/MI) to increase enrollment at the graduate level to provide a higher better educated engineers and health physicists. © American Society for engineering Education, 2009.

关键词： nuclear industry

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Multidetector CT (MDCT) modeling for organ dose assessments of various patient phantoms

Multidetector CT (MDCT) modeling for organ dose assessments ...

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

作者： Gu, Jianwei Caracappa, Peter F. George, X.X. Nuclear Engineering and Engineering Physics Program Rensselaer Polytechnic Institute Troy NY 12180 United States

ISBN: (纸本)9781615673490

Multiple-detector computed tomography (MDCT), a diagnostic imaging modality that is rapidly evolving, has caused an increased concern about the potential radiation risk to the patient. The need for assessing radiation dose associated with the associated MDCT protocols can be met by the use of Monte Carlo-based CT source models that are integrated with patient computational phantoms for organ dose calculations. This paper summarizes our work on the development and application of an MDCT scanner model using the Monte Carlo methods. The MCNPX code was used to simulate the x-ray source including the energy spectrum, filter, and scan trajectory. Detailed GE LightSpeed CT scanner components were specified using an iterative trial-and-error procedure. The scanner model was validated by comparing simulated results against measured CTDI values. The validated scanner model was then integrated with various phantoms, including RPI Adult Male phantom, RPI Adult Female phantom, RPI-P regnant Female phantoms in three different gestational periods to calculate organ doses. Organ doses are compared for different phantoms. Also, it was found that the dose to the fetus of the 3-, 6-and 9-month was 0.13 mGy/100mAs, 0,21mGy/100mAs, and 0.26mGy/100mAs, respectively. This work demonstrates the feasibility of modeling and validating MDCT scanner by Monte Carlo methods, as well as assessing organ dose by combining the MDCT scanner model and patient phantoms.

关键词： Phantoms

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