http://ilp-www.mit.edu/ List of 40 most recently entered publications, as compiled by the Industrial Liaison Office. en-us Copyright 2009 MIT ILP Tue, 24 Nov 2009 09:00:36 GMT http://ilp-www.mit.edu/favicon.ico http://ilp-www.mit.edu/display_page.a4d?key=P5d http://ilp-www.mit.edu/display_paper.a4d?paperId=84270 We study the effects of a superconducting condensate on holographic Fermi surfaces. With a suitable coupling between the fermion and the condensate, there are stable quasiparticles with a gap. We find some similarities with the phenomenology of the cuprates: in systems whose normal state is a non-Fermi liquid with no stable quasiparticles, a stable quasiparticle peak appears in the condensed phase. 11/23/09 John McGreevy http://ilp-www.mit.edu/display_paper.a4d?paperId=84269 We develop a systematic framework for realizing general anomaly-free chiral 6D supergravity theories in F-theory. We focus on 6D (1, 0) models with one tensor multiplet whose gauge group is a product of simple factors (modulo a finite abelian group) with matter in arbitrary representations. Such theories can be decomposed into blocks associated with the simple factors in the gauge group; each block depends only on the group factor and the matter charged under it. All 6D chiral supergravity models can be constructed by gluing such blocks together in accordance with constraints from anomalies. Associating a geometric structure to each block gives a dictionary for translating a supergravity model into a set of topological data for an F-theory construction. We construct the dictionary of F-theory divisors explicitly for some simple gauge group factors and associated matter representations. Using these building blocks we analyze a variety of models. We identify some 6D supergravity models which do not map to integral F-theory divisors, possibly indicating quantum inconsistency of these 6D theories. 11/23/09 Washington Taylor http://ilp-www.mit.edu/display_paper.a4d?paperId=84268 Supersymmetry and R-symmetry Ward identities relate on-shell amplitudes in a supersymmetric field theory. We solve these Ward identities for NKMHV amplitudes of the maximally supersymmetric N = 4 and N = 8 theories. The resulting superamplitude is written in a new, manifestly supersymmetric and R-invariant form: it is expressed as a sum of very simple SUSY and SU(N)R-invariant Grassmann polynomials, each multiplied by a “basis amplitude”. For NKMHV n-point superamplitudes the number of basis amplitudes is equal to the dimension of the irreducible representation of SU(nĹ|4) corresponding to the rectangular Young diagram with N columns and K rows. The linearly independent amplitudes in this algebraic basis may still be functionally related by permutation of momenta. We show how cyclic and reflection symmetries can be used to obtain a smaller functional basis of color-ordered single-trace amplitudes in N = 4 gauge theory. We also analyze the more significant reduction that occurs in N = 8 supergravity because gravity amplitudes are not ordered. All results are valid at both tree and loop level. 11/23/09 Daniel Freedman http://ilp-www.mit.edu/display_paper.a4d?paperId=84267 The general second-order massive field equations for arbitrary positive integer spin in three spacetime dimensions, and their “self-dual” limit to first-order equations, are shown to be equivalent to gauge-invariant higher-derivative field equations. We recover most known equivalences for spins 1 and 2, and find some new ones. In particular, we find a non-unitary massive 3D gravity theory with a 5th order term obtained by contraction of the Ricci and Cotton tensors; this term is part of an N = 2 super-invariant that includes the “extended Chern-Simons” term of 3D electrodynamics. We also find a new unitary 6th order gauge theory for “self-dual” spin 3. 11/23/09 Edward Farhi http://ilp-www.mit.edu/display_paper.a4d?paperId=84266 We present a new open superstring field theory, whose string fields carry an arbitrary picture number and reside in the large Hilbert space. Picture changing amounts to a gauge transformation in this formalism. This new theory solves the problems with the Ramond sector shared by other RNS superstring field theories, while naturally unifying the NS and Ramond string fields. When partially gauge fixed, it reduces in the NS sector to the modified cubic superstring field theory. Hence, it shares all the good properties of this theory, e.g., it has analytical vacuum and marginal deformation solutions. Treating the redundant gauge symmetry using the BV formalism is straightforward and results in a simple cubic action with a single string field, whose quantum numbers are unconstrained. We also discuss the supersymmetry structure of the theory. 11/23/09 Michael Kroyter http://ilp-www.mit.edu/display_paper.a4d?paperId=84265 We consider linear least squares problems of very large dimension, such as those arising for example in inverse problems. We introduce an associated approximate problem, within a subspace spanned by a relatively small number of basis functions, and solution methods that use simulation, importance sampling, and low-dimensional calculations. The main components of this methodology are a regression/ regularization approach that can deal with nearly singular problems, and an importance sampling design approach that exploits existing continuity structures in the underlying models, and allows the solution of very large problems. 11/23/09 Mengdi Wang http://ilp-www.mit.edu/display_paper.a4d?paperId=84263 We propose a unifying framework for polyhedral approximation in convex optimization. It subsumes classical methods, such as cutting plane and simplicial decomposition, but also includes new methods, and new versions/extensions of old methods, such as a simplicial decomposition method for non-differentiable optimization, and a new piecewise linear approximation method for convex single commodity network flow problems. Our framework is based on an extended form of monotropic programming, a broadly applicable model, which includes as special cases Fenchel duality and Rockafellar's monotropic programming, and is characterized by an elegant and symmetric duality theory. Our algorithm combines flexibly outer and inner linearization of the cost function. The linearization is progressively refined by using primal and dual differentiation, and the roles of outer and inner linearization are reversed i a mathematically equivalent dual algorithm. We provide convergence results and error bounds for the general case where outer and inner linearization are combined in the same algorithm. 11/23/09 Dimitri Bertsekas http://ilp-www.mit.edu/display_paper.a4d?paperId=84262 We consider the approximate solution of linear ill-posed inverse problems of high dimension with a simulation-based algorithm that approximates the solution within a low-dimensional subspace. The algorithm uses Tikhonov regularization, regression, and low-dimensional linear algebra calculations and storage. For sampling efficiency, we use variance reduction/importance sampling schemes, specially tailored to the structure of inverse problems. We demonstrate the implementation of our algorithm in a series of practical large-scale examples arising from Fredholm integral equations of the first kind. 11/23/09 Dimitri Bertsekas http://ilp-www.mit.edu/display_paper.a4d?paperId=84260 Conducting polymers can act as actuators when an electrochemical stimulus causes the materials to undergo volumetric changes. Ion flux into the polymer causes volumetric expansion and ion outflow causes contraction. Polypyrrole is an attractive actuator material due to its ability to generate up to 30 MPa active stress and 10% to 26% maximum strain with voltage supply lower than 2 V. The polymer’s mechanical performance depends upon the solvent used and the dominating ion species. In this study, we used 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6) to characterize the effect of temperature increase on ion flow and how it contributes to strain and maximum strain rate of polypyrrole. In this solvent, the cation BMIM+ diffuses in and out of the polymer under applied voltage to cause strain changes. For approximately each increment of 10oC from 27oC to 83oC, isotonic tests were done with +/-0.8 V square pulses, using a custom built device that is capable of performing temperature controlled dynamic mechanical analyses and electrochemistry simultaneously. Results showed that, independent of voltage polarity, from 27 to 83oC the strain increased from 0.4% to 2.0%. Both the maximum charge and strain rate rates increased with temperature, and were higher at positive voltage than at negative voltage throughout the same temperature range. Positive voltage caused the maximum strain rate to increase exponentially from 0.1 %/s to 0.67 %/s, while negative voltage caused it to increase more linearly from 0.06 %/s to 0.23 %/s. The results suggest that the increase in strain resulted from the charge delivered to the polymer in higher quantities at higher temperature. Furthermore, BMIM+ ions are expelled faster than those being attracted in to the polymer, perhaps due to the ions preferentially remaining in the bulk solution. As the temperature increased, the ionic mobility increased and as a result, BMIM+ ions are expelled back into the solvent even faster. 11/23/09 Ian Hunter http://ilp-www.mit.edu/display_paper.a4d?paperId=84258 The wettability of electrochemically deposited conducting polymer films is highly dependent on several parameters including the deposition conditions, the dopant, and the roughness of the working electrode. To produce superhydrophobic surfaces, one must be able to control the micro and nanostructure of the film. In this study, a template-free method of producing superhydrophobic (water contact angle of 154°) polypyrrole films was demonstrated. The polypyrrole was doped with the low surface-energy heptadecafluorooctanesulfonic acid and had microstructures with nanometer-scale roughness. The microstructures served to increase the roughness of the film and amplify the hydrophobicity of the surface. It is also of interest to be able to dynamically adjust the wettability of a polypyrrole surface after deposition. Applications of this functionality include microfluidics, self-cleaning surfaces, liquid lenses, and smart textiles. By oxidizing or reducing a polypyrrole film, one can change the surface morphology as well as the chemical composition, and control the wettability of the surface. This study characterizes the electrochemically-induced changes in surface energy of polypyrrole. The relationship between applied voltage, charge transferred, surface roughness, and water contact angle was investigated. Upon reduction, the polypyrrole film was switched to a superhydrophilic state and the maximum change in contact angle was observed to be 154°. Surface wettability was found to be not fully reversible, with some hysteresis occurring after the first electrochemical cycle. 11/23/09 Ian Hunter http://ilp-www.mit.edu/display_paper.a4d?paperId=84257 Electroactive conducting polymers are currently studied for use in smart textiles that incorporate sensing, actuation, control, and data transmission. The development of intelligent garments that integrate these various functionalities over wide areas (i.e. the human body) requires the production of long, highly conductive, and mechanically robust fibers. This study focuses on the electrical, mechanical and electrochemical characterization of high aspect ratio polypyrrole fibers produced using a novel, custom-built fiber slicing instrument. In order to ensure high conductivity and mechanical robustness, the fibers are sliced from tetraethylammonium hexafluorophosphate-doped polypyrrole thin films electrodeposited onto a glassy carbon crucible. The computer-controlled, four-axis slicing instrument precisely cuts the film into thin, long fibers by running a sharp blade over the crucible in a continuous helical pattern. This versatile fabrication process has been used to produce free-standing fibers with square cross-sections of 2 µm °— 3 µm, 20 µm °— 20 µm, and 100 µm °— 20 µm with lengths of 15 mm, 460 mm, and 1,200 mm, respectively. An electrochemical dynamic mechanical analyzer built in-house for nano- and microfiber testing was used to perform stress-strain and conductivity measurements in air. The fibers were found to, on average, have an elastic modulus of 1.7 GPa, yield strength of 37 MPa, ultimate tensile strength of 80 MPa, elongation at break of 49%, and an electrical conductivity of 12,700 S/m. SEM micrographs show that the fibers are free of defects and have cleanly cut edges. Preliminary measurements of the fibers’ strain-resistance relationship have resulted in gage factors suitable for strain sensing applications. Initial tests of the actuation performance of fibers in neat 1-butyl-3-methylimidazolium hexaflourophosphate have shown promising results. These monofilament fibers may be spun into yarns or braided into 2- and 3-dimensional structures for use as actuators, sensors, antennae, and electrical interconnects in smart fabrics. 11/23/09 Ian Hunter http://ilp-www.mit.edu/display_paper.a4d?paperId=84256 Conducting polymer materials can be developed as muscle-like actuators for applications in robotics, micro-electro mechanical systems, drug delivery systems etc. These materials are available in a large number of different varieties that can be synthesized and processed in different ways. However, their applications as actuators are limited due to the inability to create conducting polymer materials with robust mechanical properties. Currently most of the dynamic mechanical analysis technologies require the polymer created to be free standing and able to withstand large stresses. This severely limits the development of new materials with potential actuator applications. In this study, a technique to measure the actuation of polymers in the electrochemical deposition environment is described. This allows testing of an electrochemically grown conducting polymer sample on the surface of the deposition electrode itself. Thin polypyrrole films (2to 20 microns thick) doped with tetraethylammonium hexaflourophosphate were grown on the surface of a glassy carbon electrode. These films were then tested on the surface of the glassy carbon using a custom built electrochemical dynamic mechanical analyzer. A square wave potential (+/- 0.8 V) is applied to the films that results in the actuation of the films. The films are able to generate a changing force of 3 mN of force against a 0.1 N sensor preloaded at 5 mN. The resulting magnitude of the measured force is a function of the film thickness while the change in force due to actuation is approximately constant. 11/23/09 Ian Hunter http://ilp-www.mit.edu/display_paper.a4d?paperId=84255 Relfections on a 30-year friendship with Mike Cornwall. 11/23/09 Roman Jackiw http://ilp-www.mit.edu/display_paper.a4d?paperId=84254 Trafficking and regulation of mobile zinc pools influence cellular functions and pathological conditions in multiple organs, including brain, pancreas, and prostate. The quest for a dynamic description of zinc distribution and mobilization in live cells fuels the development of increasingly sophisticated probes. Detection systems that respond to zinc binding with changes of their fluorescence emission properties have provided sensitive tools for mobile zinc imaging, and fluorescence microscopy experiments have afforded depictions of zinc distribution within live cells and tissues. Both small-molecule and protein-based fluorescent probes can address complex imaging challenges, such as analyte quantification, site-specific sensor localization, and real-time detection. 11/19/09 Stephen Lippard http://ilp-www.mit.edu/display_paper.a4d?paperId=84253 These are some rambling thoughts of an occasional rambling adult from some lectures in Kyoto and a conference in Tokyo in 2003. They continue travel reflections that began with a summer scout trip around the U.S. in 1950, trips to Europe in 1960, Mexico and Guatemala in 1961, a year spent traveling around the world in 1964, and travel and teaching reflections based on living in France and England in 1970-71, Belgium 1991, Vienna in 1993 and China 1995 (http://web.mit.edu/gtmarx/www/china.html). At some point Professor Max hopes to combine these and all the photos along with travel and teaching experiences in the U.S. in Morgantown, Evanston, Urbana , Gainesville, Richmond, Claremont and San Juan. 11/18/09 Gary Marx http://ilp-www.mit.edu/display_paper.a4d?paperId=84252 In this paper we offer some observations to guide a research project we are beginning. The project is concerned with understanding new surveillance and communication technologies as they are applied to permitted (in a double sense as wIll be clear below) political protests and other behavior in “public” gatherings within democratic societies.1 Public order maintenance, and the specific policing of political protests within large scale mega-events such as the Olympics, offer a distinctive arena for contrasts with more conventional, single shot collective behavior gatherings and with routinely occurring events. It also permits contrasting the use of new surveillance technologies across contexts and substantive areas. 11/18/09 Gary Marx http://ilp-www.mit.edu/display_paper.a4d?paperId=84251 The seemingly omniscient, omnipresent, colonizing power of 21st century new surveillance softly spreads ever outward and inward in society. The future gallops in on diffuse, almost invisible sensors embedded everywhere. Nowhere is this clearer than in the case of the hierarchal family with responsibility for the care of children. A focus on children and the home offers an ideal setting to see broader social forms and processes and to make comparative statements across tools, applications, life cycle stages, institutions and geographical places, and can highlight some enduring tensions. Kids are literally the poster children for surveillance. Relative to other contexts such as work or government, children illustrate a broader (and perhaps clearer) array of central surveillance concepts and dynamics. Attention to childhood offers a unique transom into how we learn what it means to be watched and to watch and to how surveillance changes as roles and related rights and responsibilities shift over time. It also illustrates the unclear meaning of values or goals in conflict and the absence of ways for resolving tensions between them. There is a growing literature on children and surveillance. Most of it focuses on particular applications or needs (as do the articles in this volume). In contrast, we treat the broader topic of surveillance of and by children. We look at the universe of tools available and ask how can these be categorized and contrasted? What cultural messages do they send? How are they justified? How do children as subjects respond? What is distinctive about the surveillance of children and why does it seem to be a particularly contentious issue? What broader social and policy questions does the topic raise? This article is part of broader projects that look at other settings such as work and government (Marx forthcoming) and at legal and policy questions involving children and the internet (Steeves 2006, 2007, 2009; Steeves & Webster 2008). The methods used are interviews with agents and subjects of surveillance, document analysis, observation, case studies and participant observation as kids, parents and a grandparent, and our involvement in policy groups. The article has three sections. It begins with a satirical statement from an imaginary social movement dedicated to protecting children through the use of technology. This reflects surveillphiliac themes within our culture taken to an extreme. Yet it hopefully has enough authenticity to provoke thought. Its more controversial assertions highlight the complexity and conflicts associated with the topic, and set the stage for our analysis in the concluding section. It also contains some moral and empirical truths that even the most libertarian of parents would likely agree to. 11/18/09 Gary Marx http://ilp-www.mit.edu/display_paper.a4d?paperId=84250 In this paper we investigate distributed computation in dynamic networks in which the network topology changes from round to round. We consider a worst-case model in which the communication links for each round are chosen by an adversary, and nodes do not know who their neighbors for the current round are before they broadcast their messages. The model allows the study of the fundamental computation power of dynamic networks. In particular, it captures mobile networks and wireless networks, in which mobility and interference render communication unpredictable. In contrast to much of the existing work on dynamic networks, we do not assume that the network eventually stops changing; we require correctness and termination even in networks that change continually. We introduce a stability property called T -interval connectivity, which stipulates that for every T consecutive rounds there exists a stable connected spanning subgraph. For T = 1 this means that the graph is connected in every round, but changes arbitrarily between rounds. Algorithms for the dynamic graph model must cope with these unceasing changes. We show that in 1-interval connected graphs it is possible for nodes to determine the size of the network and compute any computable function of their initial inputs in O(n2) rounds using messages of size O(log n + d), where d is the size of the input to a single node. Further, if the graph is T -interval connected for T > 1, the computation can be sped up by a factor of T , and any function can be computed in O(n+n2/T ) rounds using messages of size O(log n+d). We also give two lower bounds on the gossip problem, which requires the nodes to disseminate k pieces of information to all the nodes in the network. We show an Ł[(n log k) bound on gossip in 1-interval connected graphs against centralized algorithms, and an Ł[(n + nk/T ) bound on exchanging k pieces of information in T -interval connected graphs for a restricted class of randomized distributed algorithms. The T-interval connected dynamic graph model is a novel model, which we believe opens new avenues for research in the theory of distributed computing in wireless, mobile and dynamic networks. 11/17/09 Nancy Lynch http://ilp-www.mit.edu/display_paper.a4d?paperId=84249 The currently prevailing equilibrium-based approach to mechanism design suffers from a plurality of fundamental problems, and new conceptual frameworks are needed to solve or sufficiently alleviate them. In this paper, we put forward rational robustness, a new solution concept/implementation notion that is not equilibrium-based; prove its fundamental structural theorems; and compare it with prior notions. The notion of implementation is specifically built so as to be robust against the problem of equilibrium selection. We prove it robust against other fundamental problems as well in different papers. 11/17/09 Silvio Micali http://ilp-www.mit.edu/display_paper.a4d?paperId=84248 This paper introduces the open-source Graphite distributed parallel multicore simulator infrastructure. Graphite is designed from the ground up for exploration of future multicore processors containing dozens, hundreds, or even thousands of cores. It provides high performance for fast design space exploration and software development for future processors. Several techniques are used to achieve this performance including: direct execution, multi-machine distribution, analytical modeling, and lax synchronization. Graphite is capable of accelerating simulations by leveraging several machines. It can distribute simulation of an off-the-shelf threaded application across a cluster of commodity Linux machines with no modification to the source code. It does this by providing a single, shared address space and consistent single-process image across machines. Graphite is designed to be a simulation framework, allowing different component models to be easily replaced to either model different architectures or tradeoff accuracy for performance. We evaluate Graphite from a number of perspectives and demonstrate that it can simulate target architectures containing over 1000 cores on ten 8-core servers. Performance scales well as more machines are added with near linear speedup in many cases. Simulation slowdown is as low as 41°— versus native execution for some applications. The Graphite infrastructure and existing models will be released as open-source software to allow the community to simulate their own architectures and extend and improve the framework. 11/17/09 Jason Miller http://ilp-www.mit.edu/display_paper.a4d?paperId=84247 As multicore processors become increasingly prevalent, system complexity is skyrocketing. The advent of the asymmetric multicore compounds this – it is no longer practical for an average programmer to balance the system constraints associated with today’s multicores and worry about new problems like asymmetric partitioning and thread interference. Adaptive, or self-aware, computing has been proposed as one method to help application and system programmers confront this complexity. These systems take some of the burden off of programmers by monitoring themselves and optimizing or adapting to meet their goals. This paper introduces an open-source self-aware synchronization library for multicores and asymmetric multicores called Smartlocks. Smartlocks is a spin-lock library that adapts its internal implementation during execution using heuristics and machine learning to optimize toward a user-defined goal, which may relate to performance, power, or other problem-specific criteria. Smartlocks builds upon adaptation techniques from prior work like reactive locks [1], but introduces a novel form of adaptation designed for asymmetric multicores that we term lock acquisition scheduling. Lock acquisition scheduling is optimizing which waiter will get the lock next for the best long-term effect when multiple threads (or processes) are spinning for a lock. Results demonstrate empirically that lock scheduling is important for asymmetric multicores and that Smartlocks significantly outperform conventional and reactive locks for asymmetries like dynamic variations in processor clock frequencies caused by thermal throttling events. 11/17/09 Anant Agarwal http://ilp-www.mit.edu/display_paper.a4d?paperId=84246 In this paper, we present a generative model for co-clustering and develop algorithms based on the mean field approximation for the corresponding modeling problem. These algorithms can be viewed as generalizations of the traditional model-based clustering; they extend hard co-clustering algorithms such as Bregman co-clustering to include soft assignments. We show empirically that these model-based algorithms offer better performance than their hard-assignment counterparts, especially with increasing problem complexity. 11/17/09 Polina Golland http://ilp-www.mit.edu/display_paper.a4d?paperId=84243 Glossy surfaces are everywhere. If you stand in a typical bathroom and look around, you’ll see that most of the surfaces surrounding you are lustrous or glossy. Glazed tiles, gleaming faucets, polished basins and plastic shampoo bottles are all peppered with specular highlights. Given that highlights are so common it seems plausible that the visual system might somehow be able to make use of them in the estimation of three-dimensional shape. Indeed, it is now well established that specular reflections aid shape perception in the presence of other cues, and in fact are sufficient on their own to confer a vivid sense of shape. This is demonstrated in Figure 1, which shows a computer-generated image of a perfectly specular (i.e. mirrored) surface. Despite the fact that the image contains no shading, texture or other cues to 3D shape, we nevertheless have a vivid impression of its 3D shape. 11/17/09 Antonio Torralba http://ilp-www.mit.edu/display_paper.a4d?paperId=84242 Engineering projects that support government enterprises face substantial challenges due to demands from diverse stakeholders and rapidly-changing technologies. In this paper, we present findings from analysis of five case studies of systems engineering projects for large government enterprises. We focus on what can be learned from systems engineers, their essential role, and their engineering practices. As they work to establish interoperability across pre-existing and new technologies -- thereby evolving infrastructure -- the engineers commonly face “agonistic” tensions between groups of stakeholders. Temporal pacing conflicts are especially prevalent, such as those between stakeholder groups concerned with fast-paced streams of innovation and stakeholder groups concerned with current operations. In response, many engineers are following an evolutionary approach, developing new capabilities for managing projects and individual professional skill sets. The engineers’ adaptive response can be understood as incremental modularization and re/integration of technologies and associated practices across organizational (stakeholder) boundaries. Additionally, engineers are developing new skills of influence to support these capabilities for addressing stakeholder tensions. We close by discussing implications of our findings for the management of infrastructure technology projects, emergent design and engineering of organizational infrastructure, and the changing role of systems engineers. 11/17/09 Jo Ann Brooks http://ilp-www.mit.edu/display_paper.a4d?paperId=84241 Recent research identifies stochastic dominance as critical for understanding the relationship be- tween network structure and diffusion. This paper introduces the concept of stochastic dominance, explains the theory linking stochastic dominance and diffusion, and applies this theory to a number of diffusion studies in the literature. The paper illustrates how the theory connects observations from different disciplines, and details when and how those observations can be generalized to broader classes of networks. 11/17/09 PJ Lamberson http://ilp-www.mit.edu/display_paper.a4d?paperId=84240 While organizations strive to manage the time and attention of workers effectively, the practice of asking workers to contribute to multiple teams simultaneously can result in the opposite. We present a model of the effects of multiple team membership (MTM) on learning and productivity via the mediating processes of individual context switching, team temporal misalignment, and intra-organizational connectivity. These effects are curvilinear, with learning and productivity peaking at moderate levels of these mediating processes 11/17/09 Mark Mortensen http://ilp-www.mit.edu/display_paper.a4d?paperId=84239 We investigate momentum transport in the Hamiltonian electrostatic gyrokinetic formulation in Dubin D H E et al. We prove that the long wavelength electric field obtained from the gyrokinetic quasineutrality introduces a non-physical momentum source in the low flow ordering. 11/17/09 Peter Catto http://ilp-www.mit.edu/display_paper.a4d?paperId=84238 We derive a self-consistent equation for the turbulent transport of toroidal angular momentum in tokamaks in the low flow ordering that only requires solving gyrokinetic Fokker-Planck and quasineutrality equations correct to second order in an expansion on the gyroradius over scale length. We also show that according to our orderings the long wavelength toroidal rotation and the long wavelength radial electric field satisfy the neoclassical relation that gives the toroidal rotation as a function of the radial electric field and the radial gradients of pressure and temperature. Thus, the radial electric field can be solved for once the toroidal rotation is calculated from the transport of toroidal angular momentum. Unfortunately, even though this methodology only requires a gyrokinetic model correct to second order in gyroradius over scale length, current gyrokinetic simulations are only valid to first order. To overcome this difficulty, we exploit the smallish ratio Bp/B, where B is the total magnetic field and Bp is its poloidal component. When Bp/B is small, the usual first order gyrokinetic equation provides solutions that are accurate enough to employ for our expression for the transport of toroidal angular momentum. We show that current f and full f simulations only need small corrections to achieve this accuracy. Full f simulations, however, are still unable to determine the long wavelength, radial electric field from the quasineutrality equation. 11/17/09 Felix Parra http://ilp-www.mit.edu/display_paper.a4d?paperId=84237 A recent publication [F. I. Parra et al., Plasma Phys. Control. Fusion 50, 065014 (2008)] warned against the use of the lower order gyrokinetic Poisson equation at long wavelengths because the long wavelength, radial electric must remain undetermined to the order the equation is obtained. Another reference [W. W. Lee et al., Phys. Plasmas 16, 044506 (2009)] criticizes these results by arguing that the higher order terms neglected in the most common gyrokinetic Poisson equation are formally smaller than the terms that are left. This argument is naive and ignores that the lower order terms, although formally larger, vanish without determining the long wavelength, radial electric Żeld. The reason for this cancellation is discussed. In addition, the origin of a nonlinear term present in the gyrokinetic Poisson equation of Ref. [F. I. Parra et al., Plasma Phys. Control. Fusion 50, 065014 (2008)] is explained. 11/17/09 Peter Catto http://ilp-www.mit.edu/display_paper.a4d?paperId=84236 We are pursuing a dual strategy for investigating the chemistry of nitric oxide as a biological signaling agent. In one approach, metal-based fluorescent sensors for the detection of NO in living cells are evaluated, and a sensor based on a copper fluorescein complex has proved to be a valuable lead compound. Sensors of this class permit identification of NO from both inducible and constitutive forms of nitric oxide synthase and facilitate investigation of different NO functions in response to external stimuli. In the other approach, we employ synthetic model complexes of iron-sulfur clusters to probe their reactivity toward nitric oxide as biomimics of the active sites of iron-sulfur proteins. Our studies reveal that NO disassembles the Fe-S clusters to form dinitrosyl iron complexes (DNICs). 11/17/09 Stephen Lippard http://ilp-www.mit.edu/display_paper.a4d?paperId=84235 Dioxygen activation by carboxylate-bridged diiron enzymes is involved in essential biological processes ranging from DNA synthesis and hydrocarbon metabolism to cell proliferation. The carboxylate-bridged diiron superfamily of proteins includes ribonucleotide reductase (RNR),4 delta-9 desaturase, bacterial multicomponent monooxygenases (BMMs),6,7 and most recently human deoxyhypusine hydroxylase (hDOHH). In all of these systems, the O2 reduction step proceeds through a (peroxo)diiron(III) intermediate,3,8-10 in which the resulting peroxo ligand is proposed to bridge two iron atoms in a µ-1,2 or µ-n2n2 coordination mode. Extensive studies of soluble methane monooxygenase (sMMO), a BMM family member that oxidizes methane to methanol, reveal that the generation and activation of Fe2O2 units requires protons. Given the complexity of protein environments, identifying the sites involved in such proton transfer events and their effect on O2 activation is not a trivial undertaking. 11/17/09 Takahiro Hayashi http://ilp-www.mit.edu/display_paper.a4d?paperId=84234 Gas release in photic-zone microbialites can lead to preservable morphological biosignatures. Here we investigate the formation and stability of oxygen-rich bubbles enmeshed by filamentous cyanobacteria. Sub-millimetric and millimetric bubbles can be stable for weeks and even months. During this time, the lithification of organic laminae surrounding the bubbles can preserve their shape. Cm-scale unstable bubbles support the growth of centimetric tubular towers with distinctly laminated mineralized walls. In environments that enable high photosynthetic rates, only small stable bubbles will be enclosed by a dense microbial mesh, while in deep waters extensive microbial mesh will cover even larger photosynthetic bubbles, increasing their preservation potential. Stable photosynthetic bubbles may be preserved as sub-millimeter and millimeter-diameter features with nearly-circular cross-sections in the crests of some Proterozoic conical stromatolites, while centrimetric tubes formed around unstable bubbles provide a model for the formation of carbonate microbialites that are not markedly depleted in 13C. 11/13/09 Tanja Bosak http://ilp-www.mit.edu/display_paper.a4d?paperId=84233 We discuss possible inhomogeneous phases in two regions of the QCD phase diagram: We begin with color superconducting quark matter at moderately high densities, which is an imbalanced Fermi system due to the finite strange quark mass and neutrality constraints. Within an NJL-type toy model we find that this situation could lead to the formation of a soliton lattice. Similar solutions also exist in the context of the chiral phase transition. As an interesting result, the first-order transition line in the phase diagram of homogeneous phases gets replaced by an inhomogeneous phase which is bordered by two second-order transition lines. 11/13/09 Michael Buballa http://ilp-www.mit.edu/display_paper.a4d?paperId=84232 Organizational design in the context of new venture development is particularly challenging due to initially severe resource constraints. Deepening our understanding of differential productivity in the startup resource assembly process is therefore important. We address the twin questions of what assets are important to venture performance, and under what conditions are those assets especially important? We do so by considering initial venture idea assets and founder contracting experience. The resource-based view of the firm stresses developing the right assets, which accords with idea assets. Firm boundary theories of the firm emphasize structuring relationships in the right way given a set of organizational assets, which accords with founder contracting experience. Using unique survey data, we find that neither view by itself is as important as both theories taken together. We therefore advance an integrated perspective by showing that new ventures perform better when they both identify valuable resources and also assemble human assets with expertise in structuring organizational arrangements to commercialize those ideas. An important implication is that organizational resources have a range of potential values, and that realizing the upper range of value capture involves the additional ability to structure organizational relationships. 11/12/09 Charles Eesley http://ilp-www.mit.edu/display_paper.a4d?paperId=84231 Dual-micropatterned all-polymer surfaces with sub-10 µm resolution are demonstrated from pairs of conformally grown initiated chemical vapor deposition (iCVD) polymeric layers. A commercial TEM grid serves dual purposes, acting simultaneously as 1) an etch mask for the first polymer and as 2)a lift-off mask for the second polymer, resulting in self-alignment of the patterns in a single lithographic step. The thickness of each of the two layers is independently controlled during iCVD, so that the resultant surface displays both chemical and topographical contrast. The patterning scheme is independent of the polymers used and the deposition of the pair can proceed in either order. Chemical patterning is used to create surfaces with differential water condensation properties. Topographical patterning is used to create microwells. A combination of chemical and topographical patterning is used to make microwells whose depth responds to a water stimulus. 11/12/09 Salvador Borros http://ilp-www.mit.edu/display_paper.a4d?paperId=84230 Poly(4-aminostyrene) (PAS) thin films were synthesized via initiated chemical vapor deposition (iCVD) with tert-butyl peroxide as the initiator, representing the first time that the library of iCVD functional groups has been extended to amine moieties. The retention of the pendent amine chemical functionality was confirmed by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Scanning electron microscope (SEM) reveals that the iCVD PAS coatings are conformal over nonplanar structures. Fluorescence microscopy and photoluminescence of quantum dot functionalized surfaces confirm that the reactive amine functional group density at the surface of iCVD PAS is ~ one order of magnitude greater than for films grown by plasma enhanced chemical vapor deposition (PECVD). The higher amine density of the iCVD films enables the formation of a robust nanoadhesive with complementary epoxy functional groups. Prototype microfluidic structures were fabricated using the low-temperature (50 °C) and zero-outgassing reaction between the amine groups in iCVD PAS and the epoxy groups in iCVD poly(glycidal methacrylate) (PGMA). Bonded devices able to withstand >150 psia were achieved between polydimethylsiloxane (PDMS) and a variety of other materials including Si wafers, polycarbonate (PC), glass, polyethylene terephthalate (PET), polyethylene (PE), polyacrylate (PA), and cyclo-olefin-copolymer (COC). Additionally, the alliCVD nanoadhesion bonding process displays superior resistance against hydrolytic degradation (>2 weeks). Within the channels of the bonded devices, the epoxy and amine groups remain available for subsequent functionalization. 11/12/09 Karen Gleason http://ilp-www.mit.edu/display_paper.a4d?paperId=84229 A novel technique, combining the plasma assisted deposition of SiOx-like coatings with the initiated Chemical Vapor Deposition (iCVD) of organosilicon films in a single-chamber process, was investigated for the production of multistack barriers against the water vapor permeation. Hexavinyldisiloxane (HVDSO) was used as the film precursor for both kinds of polymerization. iCVD of HVDSO resulted in highly crosslinked and adherent carbon–rich polymer which reduced the substrate roughness of the substrate, thus acting as a primer for the deposition of the denser C-depleted uplayer. The plasma ion bombardment of the C-rich underlayer produced a graded interphase which enhanced the adhesion between the layers and of the multilayer stack to the polymer substrate. The C-rich interlayers effectively decoupled the defects of the C-depleted layers, indeed a barrier improvement factor of 100 over the single C-depleted barrier layer was obtained with a hexalayer structure. 11/12/09 Antonella Milella http://ilp-www.mit.edu/display_paper.a4d?paperId=84226 Transition metal-catalyzed couplings of organic electrophiles with Grignard reagents (“Kumada reactions”) were among the first cross-coupling processes that were discovered. Like other families of cross-couplings, this versatile method for the synthesis of carbon–carbon bonds has been applied primarily to reactions of aryl and vinyl electrophiles.3 It is nevertheless noteworthy that the earliest successes in cross-coupling alkyl electrophiles were Kumada-type reactions with Grignard reagents. Despite that initial progress, to date there have been no examples of enantioselective Kumada couplings of alkyl electrophiles. In this report, we begin to address this challenge, establishing that a Ni/bis(oxazoline) catalyst achieves asymmetric cross-couplings of alpha-bromoketones with aryl Grignard reagents (eq 1). 11/12/09 Gregory Fu http://ilp-www.mit.edu/display_paper.a4d?paperId=84225 We study random linear network coding for timedivision duplexing channels for sharing information between nodes. We assume a packet erasure channel with nodes that cannot transmit and receive information simultaneously. Each node will act as both a sender of its own information and a receiver for the information of the other nodes. When a node acts as the sender, it transmits coded data packets back-toback before stopping to wait for the receivers to acknowledge the number of degrees of freedom, if any, that are required to decode correctly the information. This acknowledgment comes in the header of the coded packets that are sent by the other nodes. We study the mean time to complete the sharing process between the nodes. We provide a simple algorithm to compute the number of coded packets to be sent back-to-back depending on the state of the system. We present numerical results for the case of two nodes sharing data and show that the mean completion time of our scheme is close to the performance of a full duplex network coding scheme and can outperform full duplex schemes with no coding. 11/12/09 Milica Stojanovic http://ilp-www.mit.edu/display_paper.a4d?paperId=84227 Silk, a protein material that has been utilized extensively since its development in China thousands of years ago, features exceptional mechanical properties such as high tensile strength, great extensibility, and is one of the toughest materials known. The exceptional strength of silks, exceeding that of steel and other engineered materials, arises from beta-sheet nanocrystals, formed by a dense H-bond network consisting of highly conserved poly-(Gly-Ala) and poly-Ala domains. The great strength and toughness of silk is particularly puzzling since the key molecular interactions in the beta-sheet nanocrystals are H-bonds, one of the weakest chemical bonds known. The process of utilizing H-bonds to achieve this feat has remained undiscovered and has thus far limited our ability to transfer material strategies from silks towards biomimetic materials. Here we report a series of large-scale atomistic simulations of silk beta-sheet nanocrystals, revealing that nanocrystals confined to a few nanometers achieve a greatly enhanced stiffness, strength and mechanical toughness compared with larger crystals. The key to explain these properties is a combination of uniform shear deformation that makes most efficient use of weak H-bonds, and the existence of dissipative molecular stick-slip motions, phenomena that emerge only when the dimensions of the nanocrystals are confined to a few nanometers. Conversely, larger nanocrystals display a loss of uniform deformation, which results in brittle structures that lose their ability to dissipate mechanical energy. Our results elucidate fundamental size-effects in beta-sheet nanocrystals that explain how mechanically inferior H-bonds can provide the structural basis for superior stiffness, resilience and toughness. These results may enable the development of new generation synthetic fibers by utilizing similar size effects. 11/06/09 Markus Buehler