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Edge-Stress-Induced Warping of Graphene Sheets and Nanoribbons

Physical Review Letters 2008年第24期101卷 245501-245501页

作者： V. B. Shenoy C. D. Reddy A. Ramasubramaniam Y. W. Zhang Division of Engineering Brown University Providence Rhode Island 02912 USA Institute of High Performance Computing Singapore 138632 Program in Applied and Computational Mathematics Princeton University Princeton New Jersey 08544 USA Department of Materials Science and Engineering National University of Singapore Singapore 119260

We show that edge stresses introduce intrinsic ripples in freestanding graphene sheets even in the absence of any thermal effects. Compressive edge stresses along zigzag and armchair edges of the sheet cause out-of-plane warping to attain several degenerate mode shapes. Based on elastic plate theory, we identify scaling laws for the amplitude and penetration depth of edge ripples as a function of wavelength. We also demonstrate that edge stresses can lead to twisting and scrolling of nanoribbons as seen in experiments. Our results underscore the importance of accounting for edge stresses in thermal theories and electronic structure calculations for freestanding graphene sheets.

关键词： Nanoribbons

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On the relationship between forecast accuracy and detection performance: An application to biosurveillance

On the relationship between forecast accuracy and detection ...

引用

IEEE Conference on Technologies for Homeland Security

作者： Thomas Lotze Galit Shmueli Applied Mathematics and Scientific Computation Program University of Maryland College Park MD USA Department of Decision Operations & Information Technologies and Center for Health and Information Decision Systems University of Maryland College Park MD USA

While many methods have been proposed for detecting disease outbreaks from pre-diagnostic data, their performance is usually not well understood. In this paper, we describe the relationship between forecast accuracy and the detection accuracy of a method. We argue that most existing temporal detection methods for biosurveillance can be characterized as a forecasting component coupled with a monitoring/detection component. We show that improved forecasting results in improved detection and we quantify the relationship between forecast accuracy and detection metrics under different scenarios. The forecast accuracy can then be used to rate an algorithm's expected performance in detecting outbreaks. Simulation is used to compare empirical performance with theoretical results; we also show examples with authentic biosurveillance data.

关键词： Control charts Yttrium Educational institutions Diseases Signal generators Bioinformatics Probability Condition monitoring Error correction Statistics

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The Elastic Continuum Limit of the Tight Binding Model

引用

Chinese Annals of mathematics,Series B 2007年第6期28卷 665-676页

作者： Weinan E Jianfeng LU Department of Mathematics and Program in Applied and Computational Mathematics Princeton University Princeton NJ 08544 USA Program in Applied and Computational Mathematics Princeton University Princeton NJ 08544 USA

The authors consider the simplest quantum mechanics model of solids, the tight binding model, and prove that in the continuum limit, the energy of tight binding model converges to that of the continuum elasticity model obtained using Cauchy-Born rule. The technique in this paper is based mainly on spectral perturbation theory for large matrices.

关键词： Continuum limit Elasticity theory Cauchy-Born rule Tight binding model

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Minute ventilation recovery time measured using a new, simplified methodology predicts extubation outcome

引用

Journal of Intensive Care Medicine 2008年第1期23卷 52-60页

作者： Seymour, Christopher W. Halpern, Scott Christie, Jason D. Gallop, Robert Fuchs, Barry D. Department of Medicine Hospital of the University of Pennsylvania Philadelphia PA United States Division of Pulmonary Allergy and Critical Care Medicine Hospital of the University of Pennsylvania Philadelphia PA United States Medical Intensive Care Unit Respiratory Care Services Hospital of the University of Pennsylvania Philadelphia PA United States Department of Mathematics Applied Statistics Program West Chester University of Pennsylvania West Chester PA United States Medical Intensive Care Unit Division of Pulmonary Allergy and Critical Care Medicine Hospital of the University of Pennsylvania Philadelphia PA 19104 3400 Spruce St United States

Extubation failure is associated with poor intensive care unit and hospital outcomes. Minute ventilation recovery time, an integrative measure of a patient's respiratory reserve, has been shown in a pilot study to predict extubation outcome;however, the methodology is subjective and impractical for routine use. The authors hypothesize that minute ventilation recovery time, measured using an objective and simpler method, would predict extubation outcome. A prospective cohort study was performed in adult medical and surgical intensive care unit patients intubated for >24 hours who were weaning from mechanical ventilation. Minute ventilation recovery time was measured using a new, simplified, and objective method following the final spontaneous breathing trial prior to extubation. The primary outcome was extubation failure, defined as reintubation within 7 days. The study cohort comprised 88 patients, of whom 22 (25%) failed extubation after a median of 3 days. Demographic data, weaning parameters, and the proportion of patients who passed an extubation screen were similar between groups (P >.05). Minute ventilation recovery time was significantly longer in patients who failed extubation (15 [5-15] vs 2 [1-5] minutes, P <.001), consistent in both medical and surgical subgroups. Operating characteristics for a preliminary threshold (minute ventilation recovery time ≥5 minutes) for prediction of extubation failure were sensitivity = 0.78, specificity = 0.71, positive predictive value = 0.47, negative predictive value = 0.90, correctly classified = 0.72. Adjustment for significant covariates did not alter the relationship between minute ventilation recovery time ≥5 minutes and extubation failure (odds ratio = 4.9, 95% confidence interval 1.45-16.2, P <.02). C statistic was 0.79 ± 0.17. It was concluded that minute ventilation recovery time, measured using a feasible methodology, can predict extubation outcome in medical and surgical intensive care unit patients. © 2008 Sa

关键词： Extubation failure Mechanical Ventilation Weaning

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Rate-achievability strategies for two-hop interference flows

Rate-achievability strategies for two-hop interference flows

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Annual Allerton Conference on Communication, Control, and Computing

作者： P.S. Chandrashekhar Thejaswi Amir Bennatan Junshan Zhang Robert Calderbank Douglas Cochran Department of Electrical Engineering Arizona Stare University Tempe 85287 USA Program in Applied and Computational Mathematics (PACM) at Princeton University Princeton NJ USA Department of Electrical Engineering Arizona State University Tempe AZ USA Department of Electrical Engineering Arizona Stare University Tempe AZ USA

We consider a basic model for two-hop transmissions of two information flows which interfere with each other. In this model, two sources simultaneously transmit to two relays (in the first hop), which then simultaneously transmit to two destinations (in the second hop). While the transmission during the first hop is essentially the transmission over a classical interference channel, the transmission in the second hop enjoys an interesting advantage. Specifically, as a byproduct of the Han-Kobayashi transmission scheme applied to the first hop, each of the relays (in the second hop) has access to some of the data that is intended to the other destination, in addition to its own data. As recently observed by Simeone et al., this opens the door to cooperation between the relays. In this paper, we observe that the cooperation can take the form of distributed MIMO broadcast, thus greatly enhancing its effectiveness at high SNR. However, since each relay is only aware of part of the data beyond its own, full cooperation is not possible. We propose several approaches that combine MIMO broadcast strategies (including ldquodirty paperrdquo) with standard non-cooperative strategies for the interference channel. Numerical results are provided, which indicate that our approaches provide substantial benefits at high SNR.

关键词： Relays Interference channels Decoding MIMO Broadcasting Context Wireless networks mathematics Electronic mail

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Negative Poisson’s Ratio Materials via Isotropic Interactions

引用

Physical Review Letters 2008年第8期101卷 085501-085501页

作者： Mikael C. Rechtsman Frank H. Stillinger Salvatore Torquato Department of Physics Princeton University Princeton New Jersey 08544 USA Department of Chemistry Princeton University Princeton New Jersey 08544 USA Program in Applied and Computational Mathematics and PRISM Princeton New Jersey 08544 USA Princeton Center for Theoretical Science Princeton New Jersey 08544 USA School of Natural Sciences Institute for Advanced Study Princeton New Jersey 08544 USA

We show that under tension a classical many-body system with only isotropic pair interactions in a crystalline state can, counterintuitively, have a negative Poisson’s ratio, or auxetic behavior. We derive the conditions under which the triangular lattice in two dimensions and lattices with cubic symmetry in three dimensions exhibit a negative Poisson’s ratio. In the former case, the simple Lennard-Jones potential can give rise to auxetic behavior. In the latter case, a negative Poisson’s ratio can be exhibited even when the material is constrained to be elastically isotropic.

关键词： Lennard-Jones potential

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Non-Markovian noise mediated through anomalous diffusion within ion channels

引用

Physical Review E 2008年第4期78卷 041920-041920页

作者： Sisir Roy Indranil Mitra Rodolfo Llinas Physics and Applied Mathematics Unit Indian Statistical Institute 203 Barrackpore Trunk Road Kolkata 700108 India Brain & Behavior Program Department of Physics Georgia State University 29 Peachtree Center Avenue Atlanta Georgia 30303 USA New York University School of Medicine 530 First Avenue New York New York 10016 USA

It is evident from a wide range of experimental findings that ion channel gating is inherently stochastic. The issue of “memory effects” (diffusional retardation due to local changes in water viscosity) in ionic flow has been recently addressed using Brownian dynamics simulations. The results presented indicate such memory effects are negligible, unless the diffusional barrier is much higher than that of free solute. In this paper using differential stochastic methods we conclude that the Markovian property of exponential dwell times gives rise to a high barrier, resulting in diffusional memory effects that cannot be ignored in determining ionic flow through channels. We have addressed this question using a generalized Langevin equation that contains a combination of Markovian and non-Markovian processes with different time scales. This approach afforded the development of an algorithm that describes an oscillatory ionic diffusional sequence. The resulting oscillatory function behavior, with exponential decay, was obtained at the weak non-Markovian limit with two distinct time scales corresponding to the processes of ionic diffusion and drift. This will be analyzed further in future studies using molecular dynamics simulations. We propose that the rise of time scales and memory effects is related to differences of shear viscosity in the cytoplasm and extracellular matrix.

关键词： Molecular dynamics

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Optimal Packings of Superdisks and the Role of Symmetry

引用

Physical Review Letters 2008年第24期100卷 245504-245504页

作者： Y. Jiao F. H. Stillinger S. Torquato Department of Mechanical and Aerospace Engineering Princeton University Princeton New Jersey 08544 USA Department of Chemistry Princeton University Princeton New Jersey 08544 USA Program in Applied and Computational Mathematics Princeton University Princeton New Jersey 08544 USA School of Natural Sciences Institute for Advanced Study Princeton New Jersey 08540 USA Princeton Center for Theoretical Science Princeton University Princeton New Jersey 08544 USA

Almost all studies of the densest particle packings consider convex particles. Here, we provide exact constructions for the densest known two-dimensional packings of superdisks whose shapes are defined by |x1|2p+|x2|2... 详细信息

关键词： Condensed matter physics

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Erratum: Toward the jamming threshold of sphere packings: Tunneled crystals (Journal of applied Physics (2007) 102 (093511))

引用

Journal of applied Physics 2008年第12期103卷

作者： Torquato, S. Stillinger, F.H. Department of Chemistry Princeton University Princeton NJ 08544 United States Program in Applied and Computational Mathematics Princeton University Princeton NJ 08544 United States Princeton Institute for the Science and Technology of Materials Princeton University Princeton NJ 08544 United States Princeton Center for Theoretical Physics Princeton University Princeton NJ 08544 United States

No abstract available

关键词：

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Simulation of Impurity Diffusion in a Strained Nanowire Using Off-Lattice KMC

引用

Communications in Computational Physics 2007年第1期2卷 164-176页

作者： Weidong Guo Tim P.Schulze Weinan E Department of Mathematics University of TennesseeKnoxvilleTN 37996-1300USA Department of Mathematics and Program in Applied and Computational Mathematics Princeton UniversityPrincetonNJ 08544-1000USA.

Kinetic Monte Carlo(KMC)is a stochastic model used to simulate crystal ***,most KMC models rely on a pre-defined lattice that neglects dislocations,lattice mismatch and strain *** this paper,we investigate the use of a 3D off-lattice KMC *** test this method by investigating impurity diffusion in a strained FCC *** faster than a molecular dynamics simulation,the most general implementation of off-lattice KMC is much slower than a lattice-based *** improved procedure is achieved for weakly strained systems by precomputing approximate saddle point locations based on unstrained lattice *** this way,one gives up some of the flexibility of the general method to restore some of the computational speed of lattice-based *** addition to providing an alternative approach to nano-materials simulation,this type of simulation will be useful for testing and calibrating methods that seek to parameterize the variation in the transition rates for lattice-based KMC using continuum modeling.

关键词： Off-lattice KMC nanowire strain rate impurity diffusion.

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