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Multiphoton absorption in germanium using pulsed infrared free-electron laser radiation

Physical Review B 2011年第19期83卷 195203-195203页

作者： D. Seo J. M. Gregory L. C. Feldman N. H. Tolk P. I. Cohen Department of Electrical and Computer Engineering University of Minnesota Minneapolis Minnesota 55455 USA Department of Physics and Astronomy Vanderbilt University Nashville Tennessee 37235 USA Institute of Advanced Materials Devices and Nanotechnology Rutgers The State University of New Jersey Piscataway New Jersey 08854 USA

We report wavelength- and intensity-dependent transmission measurements of intense mid-infrared radiation from the Vanderbilt free-electron laser in single-crystal Ge(100) in the wavelength range of 2.8–5.2 μm. This range accesses both the direct and indirect energy gaps in Ge, requiring in each case either two or three photons (2PA or 3PA) for absorption. Large changes in the multiphoton absorption rate are seen at the direct-to-indirect and 2PA-to-3PA transitions. Photon interactions are dominated by free-carrier absorption (FCA), primarily due to holes. The entire absorption process is modeled with the two- and three-photon absorption coefficients (β and γ) as fitting parameters. Using newly measured values of the low-intensity FCA cross sections, we find a best fit to the data at 2.8 μm that is in agreement with theory and previous measurements. We report a ratio of 175 for β across the direct-to-indirect transition, and a ratio of 5 across the same transition for γ. These ratios are independent of systematic variations in free-carrier cross sections and beam diameter.

关键词： PHONON spectra GERMANIUM spectra MULTIPHOTON processes ABSORPTION spectra LASER beams FREE electron lasers

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Magnetic Nanostructures Produced By Electron Beam Direct Writing

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MRS Online Proceedings Library (OPL) 2011年第1期777卷 T4.13-T4.13页

作者： J.P. Wang Y. Zhao T.J. Zhou J.T.L. Thong T.C. Chong Dept. of Electrical and Computer Engineering The Center for Micromagnetics and Information Technologies (MINT) University of Minnesota MN 55455-0154 Data Storage Institute DSI building 5 Engineering Drive 1 Singapore 117608 Center for IC Failure Analysis and Reliability (CICFAR) Faculty of Engineering NationalUniversity of Singapore Singapore

We present a method of direct magnetic patterning of nonmagnetic CoC and CoTaC films by electron irradiation-induced nano-scale phase transition. CoxC1-x (0.4<X<0.8) films were prepared by co-sputtering. The as-...

We present a method of direct magnetic patterning of nonmagnetic CoC and CoTaC films by electron irradiation-induced nano-scale phase transition. CoxC1-x (0.4

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Relations between structure and estimators in networks of dynamical systems

Relations between structure and estimators in networks of dy...

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IEEE Conference on Decision and Control

作者： Donatello Materassi Murti V. Salapaka Laura Giarrè Laboratory for Informations and Decision Systems Massachusetts Institute of Technology USA Department of Electrical and Computer Engineering University of Minnesota USA Dipartimento di Ingegneria Elettrica Elettronica e delle Telecomunicazioni Università di Palermo Italy

ISBN: (纸本)9781612848006;9781612848013

The article main focus is on the identification of a graphical model from time series data associated with different interconnected entities. The time series are modeled as realizations of stochastic processes (representing nodes of a graph) linked together via transfer functions (representing the edges of the graph). Both the cases of non-causal and causal links are considered. By using only the measurements of the node outputs and without assuming any prior knowledge of the network topology, a method is provided to estimate the graph connectivity. In particular, it is proven that the method determines links to be present only between a node and its “kins”, where kins of a node consist of parents, children and co-parents (other parents of all of its children) in the graph. With the additional hypothesis of strictly casual links, a similar method is provided that allows one to exactly reconstruct the original graph. Main tools for determining the network topology are based on Wiener, Wiener-Hopf and Granger filtering. Analogies with the problem of Compressing Sensing are drawn and two greedy algorithms to address the problem of reducing the complexity of the network structure are also suggested.

关键词： Vectors Transfer functions Network topology Least squares approximation Random variables Topology Stochastic processes

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A generic framework for scalable and convergent multi-robot active simultaneous localization, mapping and target tracking

A generic framework for scalable and convergent multi-robot ...

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Mediterranean Conference on Control and Automation (MED)

作者： E.B. Kosmatopoulos D.V. Rovas L. Doitsidis K. Aboudolas S.I. Roumeliotis Informatics & Telematics Institute Center of Research and Technology-Hellas (ITI-CERTH) Thessaloniki Greece Department of Electrical and Computer Engineering Democritus University of Thrace Xanthi Greece Department of Production & Management Engineering Technical University of Crete Chania Greece Department of Electronics Technological Educational Institute of Crete Chania Greece Department of Computer Science and Engineering University of Minnesota Minneapolis MN USA

In this paper, a new approach is proposed and analyzed for developing efficient and scalable methodologies for multi-robot active Cooperative Simultaneous Localization And Mapping and Target Tracking (C-SLAMTT). The proposed approach employs an active estimation scheme that switches among linear elements and, as a result, its computational requirements scale linearly with the number of estimated quantities (number of number of robots, landmarks and targets). The parameters of the proposed scheme are calculated off-line using a convex optimization algorithm which is based on Semi Definite Programming (SDP) and approximation using Sum-of-Squares (SoS) polynomials. As shown by rigorous arguments, the estimation accuracy of the proposed scheme is equal to the optimal estimation accuracy plus a term that is inversely proportional to the number of estimator's switching elements (or, equivalently, to the memory storage capacity of the robots' equipment). The proposed approach can handle various types of constraints such as "stay-within-an-area", obstacle avoidance and maximum speed constraints. The efficiency of the approach is demonstrated on a 3D active cooperative simultaneous mapping and target tracking application employing flying robots.

关键词： Robot sensing systems Optimization Estimation Target tracking Robot kinematics

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Preface

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Mathematical Programming 2011年第2期129卷 159-162页

作者： Dimitri P. Bertsekas Zhi-Quan Luo Laboratory for Information and Decision Systems Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology Cambridge USA Department of Electrical and Computer Engineering University of Minnesota Minneapolis USA

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Sex differences in the human connectome: 4-Tesla high angular resolution diffusion imaging (HARDI) tractography in 234 young adult twins

Sex differences in the human connectome: 4-Tesla high angula...

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IEEE International Symposium on Biomedical Imaging

作者： Neda Jahanshad Iman Aganj Christophe Lenglet Anand Joshi Yan Jin Marina Barysheva Katie L. McMahon Greig I. de Zubicaray Nicholas G. Martin Margaret J. Wright Arthur W. Toga Guillermo Sapiro Paul M. Thompson Laboratory of Neuro Imaging Department of NeurologySchool of Medicine University of California Los Angeles Los Angeles CA USA Department of Electrical and Computer Engineering University of Minnesota Minneapolis MN USA Center for Magnetic Resonance Research University of Minnesota Medical School Minneapolis MN USA Centre for Advanced Imaging University of Queensland Brisbane Australia School of Psychology University of Queensland Brisbane Australia Queensland Institute of Medical Research Brisbane Australia

ISBN: (纸本)9781424441273

Cortical connectivity is associated with cognitive and behavioral traits that are thought to vary between sexes. Using high-angular resolution diffusion imaging at 4 Tesla, we scanned 234 young adult twins and siblings (mean age: 23.4 ± 2.0 SD years) with 94 diffusion-encoding directions. We applied a novel Hough transform method to extract fiber tracts throughout the entire brain, based on fields of constant solid angle orientation distribution functions (ODFs). Cortical surfaces were generated from each subject's 3D T1-weighted structural MRI scan, and tracts were aligned to the anatomy. Network analysis revealed the proportions of fibers interconnecting 5 key subregions of the frontal cortex, including connections between hemispheres. We found significant sex differences (147 women/87 men) in the proportions of fibers connecting contralateral superior frontal cortices. Interhemispheric connectivity was greater in women, in line with long-standing theories of hemispheric specialization. These findings may be relevant for ongoing studies of the human connectome.

关键词： Optical fiber theory Imaging Optical fiber networks Humans Brain modeling Joining processes Image resolution

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Boole and Bell inequality

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AIP Conference Proceedings 2011年第1期1327卷

作者： K. Michielsen H. De Raedt K. Hess Institute for Advanced Simulation Jülich Supercomputing Centre Research Centre Jülich D‐52425 Jülich Germany Department of Applied Physics Zernike Institute for Advanced Materials University of Groningen Nijenborgh 4 NL‐9747 AG Groningen The Netherlands Beckman Institute Department of Electrical and Computer Engineering and Department of Physics University of Illinois Urbana Il 61801

We discuss the relation between Bell’s and Boole’s inequality. We apply both to the analysis of measurement results in idealized Einstein‐Podolsky‐Rosen‐Bohm experiments. We present a local realist model that violates Bell’s and Boole’s inequality due to the absence of Boole’s one‐to‐one correspondence between the two‐valued variables of the mathematical description and the two‐valued measurement results.

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Efficiently Generalizing Ultra-Cold Atomic Simulations via Inhomogeneous Dynamical Mean-Field Theory from Two- to Three-Dimensions

Efficiently Generalizing Ultra-Cold Atomic Simulations via I...

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DoD High Performance Computing Modernization Program Users Group

作者： J. K. Freericks H. R. Krishnamurthy P. Carrier Y. Saad Department of Physics Georgetown University Washington DC Department of Physics Indian Institute of Science Bangalore India Department of Computer Science & Engineering and Minnesota Supercomputing Institute University of Minnesota Minneapolis MN

We describe techniques that we are implementing to move inhomogeneous dynamical mean-field theory simulations from two-to three-dimensions. Two-dimensional simulations typically run on 2,000 - 10,000 lattice sites, while three-dimensional simulations typically need to run on 1,000,000 or more lattice sites. The inhomogeneous dynamical mean-field theory requires the diagonal of the inverse of many sparse matrices with the same sparsity pattern, and a dimension equal to the number of lattice-sites. For two-dimensional systems, we have employed general dense LAPACK routines since the matrices are small enough. For three-dimensional systems, we need to employ sparse matrix techniques. Here, we present one possible strategy for the sparse matrix routine, based on the well-known Lanczos technique, with a long run of the algorithm and (partial) reorthogonalization. This approach is about two-times faster than the LAPACK routines with identical accuracy, and hence will become the standard we use on the two-dimensional problems. We illustrate this approach on the problem of increasing the efficiency for pre-forming dipolar molecules in K-Rb mixtures on a lattice. We compare the local density approximation to inhomogeneous dynamical mean-field theory to illustrate how the local density approximation fails at low-temperature, and to illustrate the benefits of the new algorithms. For a three-dimensional problem, a speed-up of 1,000 or more times is needed. We end by discussing some options that are promising toward reaching this goal.

关键词： Lattices Nonhomogeneous media Sparse matrices Approximation methods Algorithm design and analysis Symmetric matrices Mathematical model

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Separation of system dynamics and line spectra via sparse representation

Separation of system dynamics and line spectra via sparse re...

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IEEE Conference on Decision and Control

作者： Lipeng Ning Tryphon T. Georgiou Allen Tannenbaum Department of Electrical and Computer Engineering University of Minnesota Minneapolis MN USA Department of Electrical Engineering Technion-Israel Institute of Technology Haifa Israel Schools of Electrical & Computer and Biomedical Engineering Georgia Technology Research Institute Atlanta GA USA

The purpose of this work is to explore the use of sparse representation in the context of system identification and, in particular, to address the important problem of identifying spectral lines in the presence of colored noise. To this end we formulate an ℓ 1 optimization problem, similar to Lasso, to incorporate an AR-model that accounts for the noise-color dynamics with contribution of sinusoids drawn out of an over-complete basis (dictionary). A suitable generalization for correlated time series sharing common components is also considered.

关键词： Colored noise Time series analysis Optimization Mathematical model Context Signal to noise ratio

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Novel in situ collection of tumor interstitial fluid from a head and neck squamous carcinoma reveals a unique proteome with diagnostic potential

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Clinical Proteomics 2010年第3期6卷 75-82页

作者： Stone, Matthew D. Odland, Rick M. McGowan, Thomas Onsongo, Getiria Tang, Chaunning Rhodus, Nelson L. Jagtap, Pratik Bandhakavi, Sricharan Griffin, Timothy J. Department of Biochemistry Molecular Biology and Biophysics University of Minnesota Minneapolis MN 55455 United States Department of Otolaryngology Hennepin County Medical Center Minneapolis MN 55415 United States Department of Otolaryngology University of Minnesota Medical School Minneapolis MN 55455 United States Department of Computer Science and Engineering University of Minnesota Minneapolis MN 55455 United States Key Laboratory for Cell Proliferation and Regulation Biology Ministry of Education Beijing Normal University Beijing 100875 China Department of Oral Medicine Diagnosis and Radiology School of Dentistry University of Minnesota Minneapolis MN 55455 United States Minnesota Supercomputing Institute University of Minnesota Minneapolis MN 55455 United States

Introduction: Tumors lack normal drainage of secreted fluids and consequently build up tumor interstitial fluid (TIF). Unlike other bodily fluids, TIF likely contains a high proportion of tumor-specific proteins with potential as biomarkers. Methods: Here, we evaluated a novel technique using a unique ultrafiltration catheter for in situ collection of TIF and used it to generate the first catalog of TIF proteins from a head and neck squamous cell carcinoma (HNSCC). To maximize proteomic coverage, TIF was immunodepleted for high abundance proteins and digested with trypsin, and peptides were fractionated in three dimensions prior to mass spectrometry. Results: We identified 525 proteins with high confidence. The HNSCC TIF proteome was distinct compared to proteomes of other bodily fluids. It contained a relatively high proportion of proteins annotated by Gene Ontology as " extracellular" compared to other secreted fluid and cellular proteomes, indicating minimal cell lysis from our in situ collection technique. Several proteins identified are putative biomarkers of HNSCC, supporting our catalog's value as a source of potential biomarkers. Conclusions: In all, we demonstrate a reliable new technique for in situ TIF collection and provide the first HNSCC TIF protein catalog with value as a guide for others seeking to develop tumor biomarkers. © 2010 The Author(s).

关键词： Biomarker discovery Head and neck squamous cell carcinoma In situ collection Tumor interstitial fluid

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