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MIT Open Access Articles

Mostrando recursos 41 - 60 de 22.484

  1. Disorder-Induced Quantum Spin Liquid in Spin Ice Pyrochlores

    Balents, Leon; Savary, Lucile
    We propose that in a certain class of magnetic materials, known as non-Kramers “spin ice,” disorder induces quantum entanglement. Instead of driving glassy behavior, disorder provokes quantum superpositions of spins throughout the system and engenders an associated emergent gauge structure and set of fractional excitations. More precisely, disorder transforms a classical phase governed by a large entropy, classical spin ice, into a quantum spin liquid governed by entanglement. As the degree of disorder is increased, the system transitions between (i) a “regular” Coulombic spin liquid, (ii) a phase known as “Mott glass,” which contains rare gapless regions in real space, but whose...

  2. Brief Report: Just-in-Time Visual Supports to Children with Autism via the Apple Watch:® A Pilot Feasibility Study

    O’Brien, Amanda; Abramson, Jennifer; Yu, Christina; Dimery, Katherine; Schlosser, Ralf W.; Shane, Howard C.; Allen, Anna A.; Flynn, Suzanne
    Using augmented input might be an effective means for supplementing spoken language for children with autism who have difficulties following spoken directives. This study aimed to (a) explore whether JIT-delivered scene cues (photos, video clips) via the Apple Watch® enable children with autism to carry out directives they were unable to implement with speech alone, and (b) test the feasibility of the Apple Watch® (with a focus on display size). Results indicated that the hierarchical JIT supports enabled five children with autism to carry out the majority of directives. Hence, the relatively small display size of the Apple Watch does...

  3. Special Issue on Survivable and Resilient Communication Networks and Services

    Dutta, Rudra; Qian, Yi; Modiano, Eytan H
    Communication networks and services play a vital role in our modern lives. This importance is expected to continue to grow in future decades. More and more business, healthcare or government organizations will become increasingly dependent on the communication between their offices and people. Not only does modern society depend on these services in terms of availability but also in terms of proper functioning in all circumstances. These services having stringent requirements with respect to protection of privacy and security. Anonymity (such as e-health) cannot accept, for example, temporary leakage of confidential information by accident whether a result of human error...

  4. The Staggers Act at 35: Railroad Economics and Regulation

    Wilson, Wesley W.; Schmalensee, Richard
    This collection of papers includes authors who served on the National Academy of Science-Transportation Research Board (TRB) Committee for a Study of Freight Rail Transportation and Regulation (2014–15) and other authors who participated in the Economics and Regulation of the Freight Railroad Industry Research Colloquium at Georgetown University (June 2015). It covers topics from the TRB report and a wide range of other topics related to the freight railroad industry. These include: a synopsis of the research and findings of the TRB committee, the financial performance of railroads since deregulation, examination of price regulation, costing theory and methods, measuring revenue...

  5. Optimal L[subscript 2]-norm empirical importance weights for the change of probability measure

    Allaire, Douglas; Willcox, Karen E; Amaral, Sergio Daniel Marques
    This work proposes an optimization formulation to determine a set of empirical importance weights to achieve a change of probability measure. The objective is to estimate statistics from a target distribution using random samples generated from a (different) proposal distribution. This work considers the specific case in which the proposal distribution from which the random samples are generated is unknown; that is, we have available the samples but no explicit description of their underlying distribution. In this setting, the Radon–Nikodym theorem provides a valid but indeterminable solution to the task, since the distribution from which the random samples are generated...

  6. Revisiting compressed sensing: exploiting the efficiency of simplex and sparsification methods

    Vanderbei, Robert; Lin, Kevin; Liu, Han; Wang, Lie
    We propose two approaches to solve large-scale compressed sensing problems. The first approach uses the parametric simplex method to recover very sparse signals by taking a small number of simplex pivots, while the second approach reformulates the problem using Kronecker products to achieve faster computation via a sparser problem formulation. In particular, we focus on the computational aspects of these methods in compressed sensing. For the first approach, if the true signal is very sparse and we initialize our solution to be the zero vector, then a customized parametric simplex method usually takes a small number of iterations to converge....

  7. Optimum Mixed-State Discrimination for Noisy Entanglement-Enhanced Sensing

    Zhuang, Quntao; Zhang, Zheshen; Shapiro, Jeffrey H
    Quantum metrology utilizes nonclassical resources, such as entanglement or squeezed light, to realize sensors whose performance exceeds that afforded by classical-state systems. Environmental loss and noise, however, easily destroy nonclassical resources and, thus, nullify the performance advantages of most quantum-enhanced sensors. Quantum illumination (QI) is different. It is a robust entanglement-enhanced sensing scheme whose 6 dB performance advantage over a coherent-state sensor of the same average transmitted photon number survives the initial entanglement’s eradication by loss and noise. Unfortunately, an implementation of the optimum quantum receiver that would reap QI’s full performance advantage has remained elusive, owing to its having to...

  8. Rotational Symmetry Breaking in a Trigonal Superconductor Nb-doped Bi[subscript 2]Se[subscript 3]

    Asaba, Tomoya; Lawson, B. J.; Tinsman, Colin; Chen, Lu; Corbae, Paul; Li, Gang; Qiu, Y.; Hor, Y. S.; Li, Lu; Fu, Liang
    The search for unconventional superconductivity has been focused on materials with strong spin-orbit coupling and unique crystal lattices. Doped bismuth selenide (Bi[subscript 2]Se[subscript 3]) is a strong candidate, given the topological insulator nature of the parent compound and its triangular lattice. The coupling between the physical properties in the superconducting state and its underlying crystal symmetry is a crucial test for unconventional superconductivity. In this paper, we report direct evidence that the superconducting magnetic response couples strongly to the underlying trigonal crystal symmetry in the recently discovered superconductor with trigonal crystal structure, niobium (Nb)-doped Bi[subscript 2]Se[subscript 3]. As a result,...

  9. Cell freezing protocol suitable for ATAC-Seq on motor neurons derived from human induced pluripotent stem cells

    Shelley, Brandon C.; Mandefro, Berhan; Sareen, Dhruv; Svendsen, Clive N.; Milani, Pamela; Escalante, Renan A.; Patel-Murray, Natasha Leanna; Xin, Xiaofeng; Adam, Miriam; Fraenkel, Ernest
    In recent years, the assay for transposase-accessible chromatin using sequencing (ATAC-Seq) has become a fundamental tool of epigenomic research. However, it is difficult to perform this technique on frozen samples because freezing cells before extracting nuclei can impair nuclear integrity and alter chromatin structure, especially in fragile cells such as neurons. Our aim was to develop a protocol for freezing neuronal cells that is compatible with ATAC-Seq; we focused on a disease-relevant cell type, namely motor neurons differentiated from induced pluripotent stem cells (iMNs) from a patient affected by spinal muscular atrophy. We found that while flash-frozen iMNs are not...

  10. Methodology of Resonant Equiangular Composite Quantum Gates

    Low, Guang Hao; Yoder, Theodore James; Chuang, Isaac
    The creation of composite quantum gates that implement quantum response functions [^ over U](θ) dependent on some parameter of interest θ is often more of an art than a science. Through inspired design, a sequence of L primitive gates also depending on θ can engineer a highly nontrivial [^ over U](θ) that enables myriad precision metrology, spectroscopy, and control techniques. However, discovering new, useful examples of [^ over U](θ) requires great intuition to perceive the possibilities, and often brute force to find optimal implementations. We present a systematic and efficient methodology for composite gate design of arbitrary length, where phase-controlled...

  11. Self-Targeting: Evidence from a Field Experiment in Indonesia

    Alatas, Vivi; Hanna, Rema; Purnamasari, Ririn; Wai-Poi, Matthew; Banerjee, Abhijit; Olken, Benjamin
    This paper shows that adding a small application cost to a transfer program can substantially improve targeting through self-selection. Our village-level experiment in Indonesia finds that requiring beneficiaries to apply for benefits results in substantially poorer beneficiaries than automatic enrollment using the same asset test. Marginally increasing application costs on an experimental basis does not further improve targeting. Estimating a model of the application decision implies that the results are largely driven by the nonpoor, who make up the bulk of the population, forecasting that they are unlikely to pass the asset test and therefore not bothering to apply.

  12. The Scientific Measurement System of the Gravity Recovery and Interior Laboratory (GRAIL) Mission

    Kruizinga, Gerhard; Paik, Meegyeong; Yuan, Dah-Ning; Fahnestock, Eugene; Strekalov, Dmitry; Harvey, Nate; Lu, Wenwen; Kahan, Daniel; Oudrhiri, Kamal; Smith, David E; Zuber, Maria T; Asmar, Sami W.; Konopliv, Alexander S.; Watkins, Michael M.; Williams, James G.; Park, Ryan S.; Zuber, Maria; Smith, David E.
    The Gravity Recovery and Interior Laboratory (GRAIL) mission to the Moon utilized an integrated scientific measurement system comprised of flight, ground, mission, and data system elements in order to meet the end-to-end performance required to achieve its scientific objectives. Modeling and simulation efforts were carried out early in the mission that influenced and optimized the design, implementation, and testing of these elements. Because the two prime scientific observables, range between the two spacecraft and range rates between each spacecraft and ground stations, can be affected by the performance of any element of the mission, we treated every element as part...

  13. Solar Wind Electrons Alphas and Protons (SWEAP) Investigation: Design of the Solar Wind and Coronal Plasma Instrument Suite for Solar Probe Plus

    Kasper, Justin C; Abiad, Robert; Austin, Gerry; Balat-Pichelin, Marianne; Bale, Stuart D; Berg, Peter; Bergner, Henry; Berthomier, Matthieu; Bookbinder, Jay; Brodu, Etienne; Caldwell, David; Case, Anthony W; Chandran, Benjamin D G; Cheimets, Peter; Cirtain, Jonathan W; Cranmer, Steven R; Curtis, David W; Daigneau, Peter; Dalton, Greg; Dasgupta, Brahmananda; DeTomaso, David; Diaz-Aguado, Millan; Djordjevic, Blagoje; Donaskowski, Bill; Effinger, Michael; Florinski, Vladimir; Fox, Nichola; Freeman, Mark; Gallagher, Dennis; Gary, S. P; Gauron, Tom; Gates, Richard; Goldstein, Melvin; Golub, Leon; Gordon, Dorothy A; Gurnee, Reid; Guth, Giora; Halekas, Jasper; Hatch, Ken; Heerikuisen, Jacob; Ho, George; Hu, Qiang; Johnson, Greg; Jordan, Steven P; Korreck, Kelly E; Larson, Davin; Li, Gang; Livi, Roberto; Ludlam, Michael; Maksimovic, Milan; McFadden, James P; Marchant, William; Maruca, Bennet A; McComas, David J; Messina, Luciana; Mercer, Tony; Park, Sang; Peddie, Andrew M; Pogorelov, Nikolai; Reinhart, Matthew J; Robinson, Miles; Rosen, Irene; Skoug, Ruth M; Slagle, Amanda; Steinberg, John T; Stevens, Michael L; Szabo, Adam; Taylor, Ellen R; Tiu, Chris; Turin, Paul; Velli, Marco; Webb, Gary; Whittlesey, Phyllis; Wright, Ken; Wu, S. T; Zank, Gary; Belcher, John Winston; Lazarus, Alan J; Richardson, John D
    The Solar Wind Electrons Alphas and Protons (SWEAP) Investigation on Solar Probe Plus is a four sensor instrument suite that provides complete measurements of the electrons and ionized helium and hydrogen that constitute the bulk of solar wind and coronal plasma. SWEAP consists of the Solar Probe Cup (SPC) and the Solar Probe Analyzers (SPAN). SPC is a Faraday Cup that looks directly at the Sun and measures ion and electron fluxes and flow angles as a function of energy. SPAN consists of an ion and electron electrostatic analyzer (ESA) on the ram side of SPP (SPAN-A) and an electron...

  14. Biotemplated Silica and Silicon Materials as Building Blocks for Micro- to Nanostructures

    Dorval Courchesne, Noemie-Manuelle; Steiner III, Stephen Alan; Cantu, Victor Javier; Hammond, Paula T; Belcher, Angela M
    Materials designed to undergo a phase transition at a prescribed temperature have been advanced as elements for controlling thermal flux. Such phase change materials can be used as components of reversible thermal diodes, or materials that favor heat flux in a preferred direction; however, a thorough mathematical analysis of such diodes is thus far absent from the literature. Herein, it is shown mathematically that the interface of a phase change material with a phase invariant one can function as a simple thermal diode. Design equations are derived for such phase change diodes, solving for the limits where the transition temperature...

  15. Online and official price indexes: Measuring Argentina's inflation

    Cavallo, Alberto F.
    Prices collected from online retailers can be used to construct daily price indexes that complement official statistics. This paper studies their ability to match official inflation estimates in five Latin American countries, with a focus on Argentina, where official statistics have been heavily criticized in recent years. The data were collected between October 2007 and March 2011 from the largest supermarket in each country. In Brazil, Chile, Colombia, and Venezuela, online price indexes approximate both the level and main dynamics of official inflation. By contrast, Argentina's online inflation rate is nearly three times higher than the official estimate.

  16. Decline in oceanic sulfate levels during the early Mesoproterozoic

    Huang, Junhua; Algeo, Thomas J.; Li, Chao; Zhou, Lian; Robinson, Andrew; Lyons, Timothy W.; Xie, Shucheng; Luo, Genming; Ono, Shuhei
    Multiple-sulfur isotope compositions ([superscript 32]S, [superscript 33]S, [superscript 34]S and [superscript 36]S) were analyzed for paired carbonate-associated sulfate (CAS) and disseminated pyrite (PY) from the ∼1.6-Ga Gaoyuzhuang Formation of the North China Craton to reconstruct the history of sulfate levels in Proterozoic oceans. The 200-m-thick study interval yielded relatively constant values for δ[superscript 34]S[subscript CAS] (13.0 ± 1.8‰), δ[superscript 34]S[subscript PY] (8.0 ± 2.3‰), and Δ[superscript 34]S[subscript CAS-PY] (∼5‰), as well as relatively constant Δ[superscript 33]S (0 ± 0.05‰) and Δ[superscript 36]S (0.35 ± 0.15‰) for both CAS and pyrite. Limited variation in δ[superscript 34]S[subscript PY] and slightly lower Δ[superscript...

  17. Loop Optimization for Tensor Network Renormalization

    Yang, Shuo; Gu, Zheng-Cheng; Wen, Xiao-Gang
    We introduce a tensor renormalization group scheme for coarse graining a two-dimensional tensor network that can be successfully applied to both classical and quantum systems on and off criticality. The key innovation in our scheme is to deform a 2D tensor network into small loops and then optimize the tensors on each loop. In this way, we remove short-range entanglement at each iteration step and significantly improve the accuracy and stability of the renormalization flow. We demonstrate our algorithm in the classical Ising model and a frustrated 2D quantum model.

  18. PF4 Promotes Platelet Production and Lung Cancer Growth

    Pucci, Ferdinando; Newton, Andita P.; Garris, Christopher; Nunes, Ernesto; Evavold, Charles; Pfirschke, Christina; Mino-Kenudson, Mari; Pittet, Mikael J.; Engblom, Camilla; Rickelt, Steffen; Hynes, Richard O; Weissleder, Ralph
    Co-option of host components by solid tumors facilitates cancer progression and can occur in both local tumor microenvironments and remote locations. At present, the signals involved in long-distance communication remain insufficiently understood. Here, we identify platelet factor 4 (PF4, CXCL4) as an endocrine factor whose overexpression in tumors correlates with decreased overall patient survival. Furthermore, engineered PF4 over-production in a Kras-driven lung adenocarcinoma genetic mouse model expanded megakaryopoiesis in bone marrow, augmented platelet accumulation in lungs, and accelerated de novo adenocarcinogenesis. Additionally, anti-platelet treatment controlled mouse lung cancer progression, further suggesting that platelets can modulate the tumor microenvironment to accelerate...

  19. Design of a Compact Biaxial Tensile Stage for Fabrication and Tuning of Complex Micro- and Nano-scale Wrinkle Patterns

    Saha, Sourabh Kumar; Culpepper, Martin
    Wrinkling of thin films is a strain-driven process that enables scalable and low-cost fabrication of periodic micro- and nano-scale patterns. In the past, single-period sinusoidal wrinkles have been applied for thin-film metrology and microfluidics applications. However, real-world adoption of this process beyond these specific applications is limited by the inability to predictively fabricate a variety of complex functional patterns. This is primarily due to the inability of current tools and techniques to provide the means for applying large, accurate, and nonequal biaxial strains. For example, the existing biaxial tensile stages are inappropriate because they are too large to fit within...

  20. Automated probabilistic reconstruction of white-matter pathways in health and disease using an atlas of the underlying anatomy

    Yendiki, Anastasia; Panneck, Patricia; Srinivasan, Priti; Stevens, Allison; Zollei, Lilla; Augustinack, Jean; Wang, Ruopeng; Salat, David; Ehrlich, Stefan; Behrens, Tim; Jbabdi, Saad; Gollub, Randy; Fischl, Bruce
    We have developed a method for automated probabilistic reconstruction of a set of major white-matter pathways from diffusion-weighted MR images. Our method is called TRACULA (TRActs Constrained by UnderLying Anatomy) and utilizes prior information on the anatomy of the pathways from a set of training subjects. By incorporating this prior knowledge in the reconstruction procedure, our method obviates the need for manual interaction with the tract solutions at a later stage and thus facilitates the application of tractography to large studies. In this paper we illustrate the application of the method on data from a schizophrenia study and investigate whether...

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