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MIT Open Access Articles

Mostrando recursos 1 - 20 de 21.210

  1. Knowledge, Belief, and Science Education: A Contribution from the Epistemology of Testimony

    Ferreira, Tiago Alfredo S.; El-Hani, Charbel N.; Da Silva Filho, Waldomiro Jose
    This article intends to show that the defense of “understanding” as one of the major goals of science education can be grounded on an anti-reductionist perspective on testimony as a source of knowledge. To do so, we critically revisit the discussion between Harvey Siegel and Alvin Goldman about the goals of science education, especially where it involves arguments based on the epistemology of testimony. Subsequently, we come back to a discussion between Charbel N. El-Hani and Eduardo Mortimer, on the one hand, and Michael Hoffmann, on the other, striving to strengthen the claim that rather than students’ belief change, understanding...

  2. Characterization of axonal transport defects in Drosophila Huntingtin mutants

    Weiss, Kurt Richard; Littleton, J. Troy
    Polyglutamine (polyQ) expansion within Huntingtin (Htt) causes the fatal neurodegenerative disorder Huntington’s Disease (HD). Although Htt is ubiquitously expressed and conserved from Drosophila to humans, its normal biological function is still being elucidated. Here we characterize a role for the Drosophila Htt homolog (dHtt) in fast axonal transport (FAT). Generation and expression of transgenic dHtt-mRFP and human Htt-mRFP fusion proteins in Drosophila revealed co-localization with mitochondria and synaptic vesicles undergoing FAT. However, Htt was not ubiquitously associated with the transport machinery, as it was excluded from dense-core vesicles and APLIP1 containing vesicles. Quantification of cargo movement in dHtt deficient axons...

  3. Thought, thoughts, and deflationism

    McGee, Vann
    Deflationists about truth embrace the positive thesis that the notion of truth is useful as a logical device, for such purposes as blanket endorsement, and the negative thesis that the notion doesn’t have any legitimate applications beyond its logical uses, so it cannot play a significant theoretical role in scientific inquiry or causal explanation. Focusing on Christopher Hill as exemplary deflationist, the present paper takes issue with the negative thesis, arguing that, without making use of the notion of truth conditions, we have little hope for a scientific understanding of human speech, thought, and action. For the reference relation, the...

  4. Acyl-CoA Dehydrogenase Drives Heat Adaptation by Sequestering Fatty Acids

    Li, Zhijie; Sun, Fang; Chen, Sidi; Rothe, Michael; Menzel, Ralph; Sun, Fei; Ma, Dengke; Lu, Alice Y.; Horvitz, Howard Robert
    Cells adapt to temperature shifts by adjusting levels of lipid desaturation and membrane fluidity. This fundamental process occurs in nearly all forms of life, but its mechanism in eukaryotes is unknown. We discovered that the evolutionarily conserved C. elegans gene acdh-11 (acyl CoAdehydrogenase, ACDH) facilitates heat adaptation by regulating the lipid desaturase FAT-7. Human ACDH deficiency causes the most common inherited disorders of fatty acid oxidation, with syndromes that are exacerbated by hyperthermia. Heat up-regulates acdh-11 expression to decrease fat-7 expression. We solved the high-resolution crystal structure of ACDH-11 and established the molecular basis of its selective and high-affinity binding to...

  5. Selectivity in subunit composition of Ena/VASP tetramers

    Riquelme, Daisy Noelia; Meyer, Aaron Samuel; Barzik, Melanie; Keating, Amy E; Gertler, Frank
    The members of the actin regulatory family of Ena/VASP proteins form stable tetramers. The vertebrate members of the Ena/VASP family, VASP, Mena and EVL, have many overlapping properties and expression patterns, but functional and regulatory differences between paralogues have been observed. The formation of mixed oligomers may serve a regulatory role to refine Ena/VASP activity. While it has been assumed that family members can form mixed oligomers, this possibility has not been investigated systematically. Using cells expressing controlled combinations of VASP, Mena and EVL, we evaluated the composition of Ena/VASP oligomers and found that VASP forms oligomers without apparent bias...

  6. Challenges in Developing a Collaborative Robotic Assistant for Automotive Assembly Lines

    Unhelkar, Vaibhav Vasant; Shah, Julie A
    Industrial robots are on the verge of emerging from their cages, and entering the final assembly to work along side humans. Towards this we are developing a collaborative robot capable of assisting humans in the final automotive assembly. Several algorithmic as well as design challenges exist when the robots enter the unpredictable, human-centric and time-critical environment of final assembly. In this work, we briefly discuss a few of these challenges along with developed solutions and proposed methodologies, and their implications for improving human-robot collaboration.

  7. Inherited Disease Genetics Improves the Identification of Cancer-Associated Genes

    Pritchard, Justin R.; Zhao, Boyang
    The identification of biologically significant variants in cancer genomes is critical to therapeutic discovery, but it is limited by the statistical power needed to discern driver from passenger. Independent biological data can be used to filter cancer exomes and increase statistical power. Large genetic databases for inherited diseases are uniquely suited to this task because they contain specific amino acid alterations with known pathogenicity and molecular mechanisms. However, no rigorous method to overlay this information onto the cancer exome exists. Here, we present a computational methodology that overlays any variant database onto the somatic mutations in all cancer exomes. We...

  8. Time independent universal computing with spin chains: quantum plinko machine

    Thompson, K F; Gokler, C; Lloyd, Seth; Shor, Peter Williston
    We present a scheme for universal quantum computing using XY Heisenberg spin chains. Information is encoded into packets propagating down these chains, and they interact with each other to perform universal quantum computation. A circuit using g gate blocks on m qubits can be encoded into chains of length O(g[superscript 3+ δ]m[superscript 3 + δ]) for all δ > 0 with vanishingly small error.

  9. Finding and proving the exact ground state of a generalized Ising model by convex optimization and MAX-SAT

    Urban, Alexander; Luo, Chuan; Huang, Wenxuan; Kitchaev, Daniil Andreevich; Dacek, Stephen Thomas; Cao, Shan; Ceder, Gerbrand; Rong, Ziqin
    Lattice models, also known as generalized Ising models or cluster expansions, are widely used in many areas of science and are routinely applied to the study of alloy thermodynamics, solid-solid phase transitions, magnetic and thermal properties of solids, fluid mechanics, and others. However, the problem of finding and proving the global ground state of a lattice model, which is essential for all of the aforementioned applications, has remained unresolved for relatively complex practical systems, with only a limited number of results for highly simplified systems known. In this paper, we present a practical and general algorithm that provides a provable...

  10. Engineering holographic phase diagrams

    Dai, Shou-Huang; Maity, Debaprasad; Zhang, Yun-Long; Chen, Jiunn-Wei
    By introducing interacting scalar fields, we tried to engineer physically motivated holographic phase diagrams which may be interesting in the context of various known condensed matter systems. We introduce an additional scalar field in the bulk which provides a tunable parameter in the boundary theory. By exploiting the way the tuning parameter changes the effective masses of the bulk interacting scalar fields, desired phase diagrams can be engineered for the boundary order parameters dual to those scalar fields. We give a few examples of generating phase diagrams with phase boundaries which are strikingly similar to the known quantum phases at...

  11. Convective Heat Transfer in a High Aspect Ratio Minichannel Heated on One Side

    Forrest, Eric C.; Buongiorno, Jacopo; Hu, Lin-Wen; McKrell, Thomas J
    Experimental results are presented for single-phase heat transfer in a narrow rectangular minichannel heated on one side. The aspect ratio and gap thickness of the test channel were 29:1 and 1.96 mm, respectively. Friction pressure drop and Nusselt numbers are reported for the transition and fully turbulent flow regimes, with Prandtl numbers ranging from 2.2 to 5.4. Turbulent friction pressure drop for the high aspect ratio channel is well-correlated by the Blasius solution when a modified Reynolds number, based upon a laminar equivalent diameter, is utilized. The critical Reynolds number for the channel falls between 3500 and 4000, with Nusselt numbers...

  12. Generalized Derivatives of Differential–Algebraic Equations

    Stechlinski, Peter G; Barton, Paul I
    Nonsmooth equation-solving and optimization algorithms which require local sensitivity information are extended to systems with nonsmooth parametric differential–algebraic equations embedded. Nonsmooth differential–algebraic equations refers here to semi-explicit differential–algebraic equations with algebraic equations satisfying local Lipschitz continuity and differential right-hand side functions satisfying Carathéodory-like conditions. Using lexicographic differentiation, an auxiliary nonsmooth differential–algebraic equation system is obtained whose unique solution furnishes the desired parametric sensitivities. More specifically, lexicographic derivatives of solutions of nonsmooth parametric differential–algebraic equations are obtained. Lexicographic derivatives have been shown to be elements of the plenary hull of the Clarke (generalized) Jacobian and thus computationally relevant in the aforementioned...

  13. Dynamical indicators for the prediction of bursting phenomena in high-dimensional systems

    Farazmand, Mohammad M; Sapsis, Themistoklis P.
    Drawing upon the bursting mechanism in slow-fast systems, we propose indicators for the prediction of such rare extreme events which do not require a priori known slow and fast coordinates. The indicators are associated with functionals defined in terms of optimally time-dependent (OTD) modes. One such functional has the form of the largest eigenvalue of the symmetric part of the linearized dynamics reduced to these modes. In contrast to other choices of subspaces, the proposed modes are flow invariant and therefore a projection onto them is dynamically meaningful. We illustrate the application of these indicators on three examples: a prototype...

  14. Degradable Polyhydroxyalkanoates as Herbicide Carriers

    Prudnikova, S. V.; Boyandin, A. N.; Kalacheva, G. S.; Sinskey, Anthony J
    The biodegradable polymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) has been used to design experimental sustained-release formulations of the herbicide Zellek Super in the form of films and microgranules. The kinetics of polymer degradation and the dynamics of herbicide release show that the rate and extent of herbicide release from the polymer matrix into the soil depends on the geometry of the carrier and the proportion of the pesticide loaded into it (polymer/pesticide mass ratio). Experiments with the creeping bentgrass (Agrostis stolonifera L.) show that the formulations of the herbicide Zellek Super constructed as microgranules and films can be successfully used to suppress the growth...

  15. Landmark-Matching Transformation with Large Deformation Via n-dimensional Quasi-conformal Maps

    Lam, Ka Chun; Lui, Lok Ming; Lee, Yin Tat
    We propose a new method to obtain landmark-matching transformations between n-dimensional Euclidean spaces with large deformations. Given a set of feature correspondences, our algorithm searches for an optimal folding-free mapping that satisfies the prescribed landmark constraints. The standard conformality distortion defined for mappings between 2-dimensional spaces is first generalized to the n-dimensional conformality distortion K(f) for a mapping f between n-dimensional Euclidean spaces (n ≥ 3). We then propose a variational model involving K(f) to tackle the landmark-matching problem in higher dimensional spaces. The generalized conformality term K(f) enforces the bijectivity of the optimized mapping and minimizes its local geometric...

  16. A review of wetting versus adsorption, complexions, and related phenomena: the rosetta stone of wetting

    Chatain, Dominique; Wynblatt, Paul; Kaplan, Wayne D.; Carter, W Craig
    This paper reviews the fundamental concepts and the terminology of wetting. In particular, it focuses on high temperature wetting phenomena of primary interest to materials scientists. We have chosen to split this review into two sections: one related to macroscopic (continuum) definitions and the other to a microscopic (or atomistic) approach, where the role of chemistry and structure of interfaces and free surfaces on wetting phenomena are addressed. A great deal of attention has been placed on thermodynamics. This allows clarification of many important features, including the state of equilibrium between phases, the kinetics of equilibration, triple lines, hysteresis, adsorption...

  17. Growth and interfacial properties of epitaxial oxides on semiconductors: ab initio insights

    Ismail-Beigi, Sohrab; Garrity, Kevin F.; Kolpak, Alexie M.
    Crystalline metal oxides display a large number of physical functionalities such as ferroelectricity, magnetism, superconductivity, and Mott transitions. High quality heterostructures involving metal oxides and workhorse semiconductors such as silicon have the potential to open new directions in electronic device design that harness these degrees of freedom for computation or information storage. This review describes how first-principles theoretical modeling has informed current understanding of the growth mechanisms and resulting interfacial structures of crystalline, coherent, and epitaxial metal oxide thin films on semiconductors. Two overarching themes in this general area are addressed. First, the initial steps of oxide growth involve careful...

  18. Block characters of the symmetric groups

    Gnedin, Alexander; Kerov, Sergei; Gorin, Vadim
    A block character of a finite symmetric group is a positive definite function which depends only on the number of cycles in a permutation. We describe the cone of block characters by identifying its extreme rays, and find relations of the characters to descent representations and the coinvariant algebra of S[subscript n]. The decomposition of extreme block characters into the sum of characters of irreducible representations gives rise to certain limit shape theorems for random Young diagrams. We also study counterparts of the block characters for the infinite symmetric group S[subscript n], along with their connection to the Thoma characters...

  19. Effects of Interfacial Bonding on Friction and Wear at Silica/Silica Interfaces

    Li, Ao; Szlufarska, Izabela; Liu, Yun
    Static friction between amorphous silica surfaces with a varying number of interfacial siloxane (Si–O–Si) bridges was studied using molecular dynamic simulations. Static friction was found to increase linearly with the applied normal pressure, which can be explained in the framework of Prandlt–Tomlinson’s model. Friction force was found to increase with concentration of siloxane bridges, but with a decreasing gradient, with the latter being due to interactions between neighboring siloxane bridges. In addition, we identified atomic-level wear mechanisms of silica. These mechanisms include both transfer of individual atoms accompanied by breaking interfacial siloxane bridges and transfer of atomic cluster initialized by...

  20. Epigenetic stability in the adult mouse cortex under conditions of pharmacologically induced histone acetylation

    Ayoub, Albert; Rakic, Pasko; Benoit, Jamie Dale
    Histone acetylation is considered a major epigenetic process that affects brain development and synaptic plasticity, as well as learning and memory. The transcriptional effectors and morphological changes responsible for plasticity as a result of long-term modifications to histone acetylation are not fully understood. To this end, we pharmacologically inhibited histone deacetylation using Trichostatin A in adult (6-month-old) mice and found significant increases in the levels of the acetylated histone marks H3Lys9, H3Lys14 and H4Lys12. High-resolution transcriptome analysis of diverse brain regions uncovered few differences in gene expression between treated and control animals, none of which were plasticity related. Instead, after...

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