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2013 MRS Fall Meeting

作者： Lai, Changquan Thompson, Carl V. Choi, W.K. Singapore MIT Alliance National University of Singapore Singapore 117576 Singapore Department of Materials Science and Engineering Massachusetts Institute of Technology Cambridge MA 02139 United States Department of Electrical and Computer Engineering National University of Singapore Singapore 117576 Singapore

Ordered arrays of polymeric nanostructures with different shapes were generated using laser interference lithography and plasma etching. Surface energy anisotropy was produced in each nanostructure in the array through oblique angle deposition of a hydrophilic metal. When a water droplet was placed on such a surface, it was found to wet preferentially in the direction of the hydrophilic face. Depending on the shape of the nanostructure and the deposition direction, wetting can be made uni-, bi- or tri-directional. Insights obtained in this study contribute to the understanding of wetting on rough, chemically heterogeneous surfaces and provide new methods to engineer functional surfaces for the control of wetting directions. Copyright © Materials Research Society 2014.

关键词： Nanostructures

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Limitations and Trade-offs in Gene Expression due to Competition for Shared Cellular Resources

Limitations and Trade-offs in Gene Expression due to Competi...

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IEEE Annual Conference on Decision and Control

作者： Andras Gyorgy Domitilla Del Vecchio Department of Electrical Engineering and Computer Science MIT Cambridge MA 02139 USA Department of Mechanical Engineering MIT Cambridge MA 02139 USA

ISBN: (纸本)9781467360890

Gene circuits share transcriptional and translational resources in the cell. The fact that these common resources are available only in limited amounts leads to unexpected couplings in protein expressions. As a result, our predictive ability of describing the behavior of gene circuits is limited. In this paper, we consider the simultaneous expression of proteins and describe the coupling among protein concentrations due to competition for RNA polymerase and ribosomes. In particular, we identify the limitations and trade-offs in gene expression by characterizing the attainable combinations of protein concentrations. We further present two application examples of our results: we show that even in the absence of regulatory linkages, genes can seemingly behave as repressors, and surprisingly, as activators to each other, purely due to the limited availability of shared cellular resources.

关键词： Gene Regulatory Networks Gene Circuits Competition Protein Expression RNA polymerase Cells Ribosomes protein concentration Activators Genes Couplings

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Algebraic methods of classifying directed graphical models

Algebraic methods of classifying directed graphical models

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IEEE International Symposium on Information Theory

作者： Hajir Roozbehani Yury Polyanskiy Department of Aeronautics and Astronautics MIT Cambridge MA USA Department of Electrical Engineering and Computer Science MIT Cambridge MA USA

In information theory, structural system constraints are frequently described in the form of a directed acyclic graphical model (DAG). This paper addresses the question of classifying DAGs up to an isomorphism. By considering Gaussian densities, the question reduces to verifying equality of certain algebraic varieties. A question of computing equations for these varieties has been previously raised in the literature. Here it is shown that the most natural method adds spurious components with singular principal minors, proving a conjecture of Sullivant. This characterization is used to establish an algebraic criterion for isomorphism, and to provide a randomized algorithm for checking that criterion. Results are applied to produce a list of the isomorphism classes of tree models on 4 and 5 nodes.

关键词： Graphical models Random variables Covariance matrices Markov processes Information theory Polynomials

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DSOS and SDSOS optimization: LP and SOCP-based alternatives to sum of squares optimization

DSOS and SDSOS optimization: LP and SOCP-based alternatives ...

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Annual Conference on Information sciences and Systems (CISS)

作者： Amir Ali Ahmadi Anirudha Majumdar Mathematical Programming Group IBM Watson Research Center Department of Electrical Engineering and Computer Science MIT

Sum of squares (SOS) optimization has been a powerful and influential addition to the theory of optimization in the past decade. Its reliance on relatively large-scale semidefinite programming, however, has seriously challenged its ability to scale in many practical applications. In this paper, we introduce DSOS and SDSOS optimization as more tractable alternatives to sum of squares optimization that rely instead on linear programming and second order cone programming. These are optimization problems over certain subsets of sum of squares polynomials and positive semidefinite matrices and can be of potential interest in general applications of semidefinite programming where scalability is a limitation.

关键词： Optimization Robustness Collision avoidance Pricing Geometry

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Stochastic Throughput Optimization for Two-hop Systems with Finite Relay Buffers

Stochastic Throughput Optimization for Two-hop Systems with ...

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IEEE Global Communications Conference

作者： Bo Zhou Ying Cui Meixia Tao Dept. of Electronic Engineering Shanghai Jiao Tong University Dept. of Electrical Engineering and Computer Science MIT

ISBN: (纸本)9781479935130

Optimal queueing control of multi-hop networks remains a challenging problem even in the simplest scenarios. In this paper, we consider a two-hop half-duplex relaying system with random channel connectivity. The relay is equipped with a finite buffer. We focus on stochastic link selection and transmission rate control to maximize the average system throughput subject to a half-duplex constraint. We formulate this stochastic optimization problem as an infinite horizon average cost Markov decision process (MDP), which is well-known to be a difficult problem. By using sample-path analysis and exploiting the specific problem structure, we first obtain an equivalent Bellman equation with reduced state and action spaces. By using relative value iteration algorithm, we analyze the properties of the value function of the MDP. Then, we show that the optimal policy has a threshold-based structure by characterizing the supermodularity in the optimal control. Based the threshold-based structure and Markov chain theory, we further simplify the original complex stochastic optimization problem to a static optimization problem over a small discrete feasible set and propose a simple algorithm to solve the static optimization problem. Furthermore, we obtain the closed-form optimal threshold for the symmetric case. The analytical results obtained in this paper also provide design insights for two-hop relaying systems with multiple relays equipped with finite relay buffers.

关键词： Markov processes iterative methods optimisation relay networks (telecommunication) Bellman equation MDP Markov decision process finite relay buffers original complex stochastic optimization problem random channel connectivity relative value iteration algorithm static optimization problem stochastic link selection stochastic throughput optimization problem threshold-based structure transmission rate control two-hop half-duplex relaying system Aerospace electronics Equations Optimization Relays Throughput

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Theoretical Efficiency Limits of a 2 Terminal Dual Junction Step Cell

Theoretical Efficiency Limits of a 2 Terminal Dual Junction ...

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IEEE Photovoltaic Specialist Conference

作者： Sabina Abdul Hadi Tim Milakovich Mayank Bulsara Evelina Polyzoeva Eugene A. Fitzgerald Judy L. Hoyt Ammar Nayfeh Institute Center for Future Energy Systems (iFES) Department of Electrical Engineering and Computer Science (EECS) Masdar Institute of Science and Technology P.O. Box 54224 Abu Dhabi UAE MIT Microsystems Technology Laboratories Cambridge MA 02139 USA

ISBN: (纸本)9781479979455

In this paper we present theoretical analysis for upper efficiency limit of a novel 2 terminal dual junction step-cell. Results show that step cell design relaxes bandgap requirements for efficient tandem cell. While conventional tandem cell with optimized bandgap combination (1.64/ 0.96 eV) has the highest efficiency (45.78 %), the step-cell design provides significant efficiency improvement for cells with non-optimized bandgap values. Efficiency upper limit for Si based step-cell with top cell bandgap equal to 1.41 eV (~GaAs), efficiency upper limit increases from~21% in conventional tandem cell to 38.7% for optimized step-cell design. Step-cell design provides opportunity for wider selection of materials used in tandem solar cell applications.

关键词： Multijunction solar cells theoretical efficiency limit detailed balance method step-cell silicon

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Multi-Robot Active Sensing of Non-Stationary Gaussian Process-Based Environmental Phenomena 14

Multi-Robot Active Sensing of Non-Stationary Gaussian Proces...

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International Conference on Autonomous Agents and Multiagent Systems

作者： Ruofei Ouyang Kian Hsiang Low Jie Chen Patrick Jaillet Department of Computer Science National University of Singapore Singapore-MIT Alliance for Research and Technology Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology

ISBN: (纸本)9781634391313

A key challenge of environmental sensing and monitoring is that of sensing, modeling, and predicting large-scale, spatially correlated environmental phenomena, especially when they are unknown and non-stationary. This paper presents a decentralized multi-robot active sensing (DEC-MAS) algorithm that can efficiently coordinate the exploration of multiple robots to gather the most informative observations for predicting an unknown, non-stationary phenomenon. By modeling the phenomenon using a Dirichlet process mixture of Gaussian processes (DPM-GPs), our work here is novel in demonstrating how DPM-GPs and its structural properties can be exploited to (a) formalize an active sensing criterion that trades off between gathering the most informative observations for estimating the unknown, non-stationary spatial correlation structure vs. that for predicting the phenomenon given the current, imprecise estimate of the correlation structure, and (b) support efficient decentralized coordination. We also provide a theoretical performance guarantee for DEC-MAS and analyze its time complexity. We empirically demonstrate using two real-world datasets that DEC-MAS outperforms state-of-the-art MAS algorithms.

关键词： Algorithms Performance Experimentation Theory Dirichlet process mixture of Gaussian processes Multi-robot exploration and mapping Adaptive sampling Active learning Resampling Experiential Learning Environmental phenomena experimentation algorithms Gaussian processes Cooperating robots theories complexity classes

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On determination of LFSR structures to assure more reliable and secure designs of cryptographic systems

On determination of LFSR structures to assure more reliable ...

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International Conference on Reliability, Infocom Technologies and Optimization (ICRITO) (Trends and Future Directions)

作者： Afaq Ahmad Samarth Arora Ahmed Al Maashri Sayyid Samir Al-Busaidi Ali Al Shidhani Electrical and Computer Engineering Sultan Qaboos University Department of Computer Science and Engineering MIT India Under IAESTE program at Sultan Qaboos University Oman

This paper presents an algorithmic procedure for determining the cryptographic key properties and hence matching with the required complexity and strength to assure a more reliable and secure designs of cryptographic systems. The designed algorithm is capable to provide the cryptographic key structure based on optimum solution approach. Using the Hardware Description Language (HDL), Verilog, the key can be realized on Field Programmable Gate Array (FPGA) platform and then translated into Printed Circuit Board (PCB).

关键词： computers Ciphers Generators Educational institutions Shift registers Polynomials

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Dynamic Estimation of the Price-Response of Deadline-Constrained Electric Loads under Threshold Policies

Dynamic Estimation of the Price-Response of Deadline-Constra...

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American Control Conference

作者： Mesrob I. Ohannessian Mardavij Roozbehani Donatello Materassi Munther A. Dahleh Departement de Mathematiques of the Universite Paris-Sud Laboratory for Information and Decision Systems (LIDS) Massachusetts Institute of Technology (MIT) LIDS MIT Electrical Engineering and Computer Science (EECS) at MIT

ISBN: (纸本)9781479932757

The paper presents a consistent and unbiased estimator for dynamic, one-step-ahead prediction of the aggregate response of a large number of individual loads to a common price signal, using only aggregate past response data. The price per unit of consumption is an exogenous signal which is updated at discrete time intervals. It is assumed that individual loads arrive in the system at random times with random demands and random consumption deadlines, and may defer their consumption up to the deadline in order to minimize their total cost. It is further assumed that the individual loads adopt a threshold policy in the sense that they only consume when the price is below a certain threshold. A dynamic aggregate model is constructed from models of independent individual loads. A consistent and unbiased estimator which only uses aggregate data, i.e., the price and aggregate consumption time-series is presented for estimating the aggregate consumption as a function of price.

关键词： Load Scheduling Estimation

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34.4:Invited Paper: Combinatorial Design of OLED-Emitting Materials

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SID Symposium Digest of Technical Papers 2015年第1期46卷

作者： Alán Aspuru-Guzik Ryan Adams Marc Baldo Jorge Aguilera-Iparraguirre Rafael Gómez-Bombarelli Department of Chemistry and Chemical Biology Harvard University Cambridge MA. School of Engineering and Applied Sciences Harvard University Cambridge MA. Department of Electrical Engineering and Computer Science MIT Cambridge MA.

We report the first results from a combinatorial design effort focused on new OLED emitters that exploit thermally-activated delayed fluorescence. Using quantum chemistry and machine learning techniques to prune a pool of over 400,000 combinations of donor and acceptor subgroups, we demonstrate new dyes that are state-of-the-art, yet entirely computationally-derived.

关键词： DFT TD-DFT computational theoretical theory-driven high-throughputscreening HTVS TADF

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