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Lipid Microdomains: Structural Correlations, Fluctuations, and Formation Mechanisms

Physical Review Letters 2010年第11期104卷 118101-118101页

作者： Jun Fan Maria Sammalkorpi Mikko Haataja Department of Mechanical and Aerospace Engineering Princeton Institute for the Science and Technology of Materials (PRISM) Program in Applied and Computational Mathematics (PACM) Princeton University Princeton New Jersey 08544 USA

Compositional lipid microdomains (“lipid rafts”) in mammalian plasma membranes are believed to facilitate many important cellular processes. While several physically distinct scenarios predicting the presence of finite-sized microdomains in vivo have been proposed in the past, direct experimental verification or falsification of model predictions has remained elusive. Herein, we demonstrate that the combination of the spatial correlation and temporal fluctuation spectra of the lipid domains can be employed to unambiguously differentiate between the existing theoretical scenarios. Furthermore, the differentiation of the raft formation mechanisms using this methodology can be achieved by collecting data at physiologically relevant conditions without the need to tune control parameters.

关键词： Cell membranes

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Influence of nonequilibrium lipid transport, membrane compartmentalization, and membrane proteins on the lateral organization of the plasma membrane

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Physical Review E 2010年第1期81卷 011908-011908页

作者： Jun Fan Maria Sammalkorpi Mikko Haataja Department of Mechanical and Aerospace Engineering Princeton Institute for the Science and Technology of Materials (PRISM) and Program in Applied and Computational Mathematics (PACM) Princeton University Princeton New Jersey 08544 USA

Compositional lipid domains (lipid rafts) in plasma membranes are believed to be important components of many cellular processes. The mechanisms by which cells regulate the sizes, lifetimes, and spatial localization of these domains are rather poorly understood at the moment. We propose a robust mechanism for the formation of finite-sized lipid raft domains in plasma membranes, the competition between phase separation in an immiscible lipid system and active cellular lipid transport processes naturally leads to the formation of such domains. Simulations of a continuum model reveal that the raft size distribution is broad and the average raft size is strongly dependent on the rates of cellular and interlayer lipid transport processes. We demonstrate that spatiotemporal variations in the recycling may enable the cell to localize larger raft aggregates at specific parts along the membrane. Moreover, we show that membrane compartmentalization may further facilitate spatial localization of the raft domains. Finally, we demonstrate that local interactions with immobile membrane proteins can spatially localize the rafts and lead to further clustering.

关键词： Cell membranes

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Maximal Potential Energy Transport: A Variational Principle for Solidification Problems

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Physical Review Letters 2010年第25期105卷 254502-254502页

作者： A. J. Wells J. S. Wettlaufer S. A. Orszag Department of Geology and Geophysics Yale University New Haven Connecticut 06520 USA Program in Applied Mathematics Yale University New Haven Connecticut 06520 USA Department of Physics Yale University New Haven Connecticut 06520-8109 USA Department of Mathematics Yale University New Haven Connecticut 06520-8283 USA

We analyze numerically the mechanisms controlling the spacing of chimneys—channels devoid of solid—in two-dimensional mushy layers formed by solidifying a binary alloy. Chimneys are the principal conduits through which buoyancy effects material transport out of the mushy layer and into the liquid from which it formed. Experiments show a coarsening of chimney spacing; we pursue the hypothesis that the spacing adjusts to optimize material transport and hence maximize the rate of removal of potential energy stored in the mushy layer. The optimal solute flux increases approximately linearly with the mush Rayleigh number. However, for spacings below a critical value, the chimneys collapse and solute fluxes cease, revealing a hysteresis between chimney convection and no flow. The results are consistent with a variational principle controlling the dynamics of this dissipative system.

关键词： Potential energy

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Quantifying behavioral data sets of criminal activity

Quantifying behavioral data sets of criminal activity

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2010 AAAI Spring Symposium

作者： Toole, Jameson Eagle, Nathan Plotkin, Joshua Department of Physics University of Michigan Ann Arbor MI 48109 United States Santa Fe Institute 1399 Hyde Park Rd Santa Fe NM 87501 United States Department of Biology and Program in Applied Mathematics and Computational Science University of Pennsylvania Philadelphia PA 19104 United States

ISBN: (纸本)9781577354550

With the increased availability of rich behavioral data sets, we present a novel combination of tools to analyze to analyze this information. Using criminal offense records as an example, we employ cross-correlation measures, eigenvalue spectrum analysis, and results from random matrix theory to identify spatiotemporal patterns. Finally, with multivariate autoregressive models, we demonstrate a possible source of structure within the data. instructions. © 2010, Association for the Advancement of Artificial Intelligence.

关键词： Spectrum analysis

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An end-to-end simulator for the all-electric ship MVDC integrated power system

An end-to-end simulator for the all-electric ship MVDC integ...

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Grand Challenges in Modeling and Simulation Symposium, GCMS 2010, Part of the 2010 Summer Simulation Multiconference, SummerSim 2010

作者： Milošević Marden, M. Prempraneerach, P. Kirtley, J.L. Karniadakis, G. Chryssostomidis, C. Design Laboratory MIT Sea Grant College Program United States Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology Cambridge MA United States Department of Mechanical Engineering Rajamangala University of Technology Thunyaburi Pathumthani Thailand Division of Applied Mathematics Brown University Providence RI United States

ISBN: (纸本)9781617387043

In this paper, a large scale Medium Voltage DC all-electric ship integrated power system is modeled from the prime mover (gas turbine) to the propulsion load. This system has a three-phase 21MW synchronous machine as a main generator and a three-phase 19MW induction motor as a main propulsion drive. The influence of propeller emergence on both electrical and mechanical components of the system is investigated.

关键词： Ship propulsion

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State estimation in hybrid systems with a bounded number of mode transitions

State estimation in hybrid systems with a bounded number of ...

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International Conference on Information Fusion

作者： Daniel Sigalov Yaakov Oshman Program of Applied Mathematics Technion-Israel Institute of Technology Haifa Israel Department of Aerospace Engineering Technion-Israel Institute of Technology Haifa Israel

We consider the problem of tracking the state of a hybrid system capable of performing a bounded number of mode switches. The system is assumed to follow either a nominal or an anomalous model, where the nominal model may stand for, e.g., the non-maneuvering motion regime of a target or the fault-free operation mode of a sensor, and the anomalous model may stand for, e.g., the abrupt evasive maneuvers of a target or the faulty operation of a sensor. As is well known, the optimal algorithm requires implementation of an exponentially growing number of primitive Kalman filters. On the other hand, the system's switching dynamics is not Markov because of the a priori bounded number of model switches, thus ruling out the use of popular estimation schemes such as the interacting multiple model (IMM) and generalized pseudo-Bayesian (GPB) filters. We derive an efficient scheme that uses a number of primitive Kalman filters that is linear in the number of possible maneuvers. The scheme resembles the IMM algorithm in that it uses interaction between some of the primitive filters before every estimation cycle, thus reducing the number of such filters. The algorithm's performance is evaluated via a simulation study, and shown to outperform the state-of-the-art IMM filter in a typical example.

关键词： Markov processes Estimation Target tracking Switches Heuristic algorithms Computational modeling

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TEXAS HOLD'EM ALGORITHMS FOR DISTRIBUTED COMPRESSIVE SENSING

TEXAS HOLD'EM ALGORITHMS FOR DISTRIBUTED COMPRESSIVE SENSING

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IEEE International Conference on Acoustics, Speech, and Signal Processing

作者： Stephen R. Schnelle Jason N. Laska Chinmay Hegde Marco F. Duarte Mark A. Davenport Richard G. Baraniuk Department of Electrical and Computer Engineering Rice University Houston TX 77005 Program in Applied and Computational Mathematics Princeton University Princeton NJ 08544

ISBN: (纸本)9781424442959

This paper develops a new class of algorithms for signal recovery in the distributed compressive sensing (DCS) framework. DCS exploits both intra-signal and inter-signal correlations through the concept of joint sparsity to further reduce the number of measurements required for recovery. DCS is well-suited for sensor network applications due to its universality, computational asymmetry, tolerance to quantization and noise, and robustness to measurement loss. In this paper we propose recovery algorithms for the sparse common and innovation joint sparsity model. Our approach leads to a class of efficient algorithms, the Texas Hold 'Em algorithms, which are scalable both in terms of communication bandwidth and computational complexity.

关键词： Signal reconstruction multisensor systems data compression Multisensor systems Signal reconstruction Data compression New classes algorithms Texas Signal restoration Quantization Scalability

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KRONECKER PRODUCT MATRICES FOR COMPRESSIVE SENSING

KRONECKER PRODUCT MATRICES FOR COMPRESSIVE SENSING

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IEEE International Conference on Acoustics, Speech, and Signal Processing

作者： Marco F. Duarte Richard G. Baraniuk Program in Applied and Computational Mathematics Princeton University Princeton NJ 08544 Department of Electrical and Computer Engineering Rice University Houston TX 77005

ISBN: (纸本)9781424442959

Compressive sensing (CS) is an emerging approach for acquisition of signals having a sparse or compressible representation in some basis. While CS literature has mostly focused on problems involving 1-D and 2-D signals, many important applications involve signals that are multidimensional. We propose the use of Kronecker product matrices in CS for two purposes. First, we can use such matrices as sparsifying bases that jointly model the different types of structure present in the signal. Second, the measurement matrices used in distributed measurement settings can be easily expressed as Kronecker products. This new formulation enables the derivation of analytical bounds for sparse approximation and CS recovery of multidimensional signals.

关键词： Data compression multidimensional signal processing signal reconstruction

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EarthSpace educational system and the scientific but people-oriented education

EarthSpace educational system and the scientific but people-...

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2010 Third International Conference on Education Technology and Training (ETT 2010)

作者： Ayodele A.Faiyetole Yuki Takahashi Serena Eley Serina Diniega EarthSpace Innovations to Society Department of Physics University of California Berkeley Department of Physics University of Illinois Urbanna Champaign Program in Applied Mathematics University of Arizona Tucson

Two significant indices that measure a country's development are related to science and education. To address the people’s peculiar needs as developing nations, which include the aspiration to develop and the desire to compete in a competitive global village, a scientific education that addresses the specific needs of the people has to be in place. Every nation must create and maintain a scientifically educated culture to become developed or sustain its development. In the light of developing economies, they need to establish a program that addresses literacy efficiency in the technical labor force and world aware citizenry. This paper examines how the scientific but people-oriented education, EarthSpace educational system, and EarthSpace, climate change and the renewable energy education initiative may impact sustainable development in the states of its deployment.

关键词： Science,technology,engineering and mathematics Scientific but people-oriented education EarthSpace educational system EarthSpace research laboratory the Young EarthSpace scientists

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Theory of ice premelting in porous media

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Physical Review E 2010年第3期81卷 031604-031604页

作者： Hendrik Hansen-Goos J. S. Wettlaufer Department of Geology and Geophysics Yale University New Haven Connecticut 06520 USA Department of Physics Yale University New Haven Connecticut 06520 USA Program in Applied Mathematics Yale University New Haven Connecticut 06520 USA

Premelting describes the confluence of phenomena that are responsible for the stable existence of the liquid phase of matter in the solid region of its bulk phase diagram. Here we develop a theoretical description of the premelting of water ice contained in a porous matrix, made of a material with a melting temperature substantially larger than ice itself, to predict the amount of liquid water in the matrix at temperatures below its bulk freezing point. Our theory combines the interfacial premelting of ice in contact with the matrix, grain-boundary melting in the ice, and impurity and curvature induced premelting, with the latter occurring in regions which force the ice-liquid interface into a high curvature configuration. These regions are typically found at points where the matrix surface is concave, along contact lines of a grain boundary with the matrix, and in liquid veins. Both interfacial premelting and curvature induced premelting depend on the concentration of impurities in the liquid, which, due to the small segregation coefficient of impurities in ice are treated as homogeneously distributed in the premelted liquid. Our principal result is an equation for the fraction of liquid in the porous medium as a function of the undercooling, which embodies the combined effects of interfacial premelting, curvature induced premelting, and impurities. The result is analyzed in detail and applied to a range of experimentally relevant settings.

关键词： Ice

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