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MIT Open Access Articles

Mostrando recursos 41 - 60 de 11,663

41. Impact of Sr segregation on the electronic structure and oxygen reduction activity of SrTi[subscript 1−x]Fe[subscript x]O[subscript 3] surfaces - Chen, Yan; Cai, Zhuhua; Kim, Jae Jin; Tuller, Harry L.; Yildiz, Bilge; Jung, Woo Chul
The correlation between the surface chemistry and electronic structure is studied for SrTi[subscript 1−x]Fe[subscript x]O[subscript 3] (STF), as a model perovskite system, to explain the impact of Sr segregation on the oxygen reduction activity of cathodes in solid oxide fuel cells. Dense thin films of SrTi[subscript 0.95]Fe[subscript 0.05]O[subscript 3] (STF5), SrTi[subscript 0.65]Fe[subscript 0.35]O[subscript 3] (STF35) and SrFeO[subscript 3] (STF100) were investigated using a coordinated combination of surface probes. Composition, chemical binding, and valence band structure analysis using angle-resolved X-ray photoelectron spectroscopy showed that Sr enrichment increases on the STF film surfaces with increasing Fe content. In situ scanning tunnelling microscopy/spectroscopy...

42. STM Study of Gold(I) Pyrazolates: Distinct Morphologies, Layer Evolution, and Cooperative Dynamics - den Boer, Duncan; Krikorian, Markrete; Esser, Birgit; Swager, Timothy Manning
We describe the first study of trinuclear gold(I) pyrazolates on the molecular level by time-dependent scanning tunneling microscopy (STM). On the graphite/1-octanoic acid interface dodecyl-functionalized gold pyrazolates formed concentration-controlled morphologies. We found two types of monomeric packing and one dimeric type with two trinuclear gold pyrazolates next to each other on the surface. For an octadecyl-functionalized derivative all studied concentrations resulted in a dimeric morphology. However, different concentrations led to different transient states during the layer evolution. At low concentrations, a transient monomeric state was present with the alkyl chains in a gauche-conformation that subsequently converted to a more optimized...

43. Hunt for new phenomena using large jet multiplicities and missing transverse momentum with ATLAS in 4.7 fb[superscript −1] of √s = 7 TeV proton-proton collisions - Taylor, Frank E.
Results are presented of a search for new particles decaying to large numbers of jets in association with missing transverse momentum, using 4.7 fb[superscript −1] of pp collision data at √s = 7 TeV collected by the ATLAS experiment at the Large Hadron Collider in 2011. The event selection requires missing transverse momentum, no isolated electrons or muons, and from ≥6 to ≥9 jets. No evidence is found for physics beyond the Standard Model. The results are interpreted in the context of a MSUGRA/CMSSM supersymmetric model, where, for large universal scalar mass m [subscript 0], gluino masses smaller than 840...

44. Worst-Case Optimal Tree Layout in External Memory - Demaine, Erik D.; Iacono, John; Langerman, Stefan
Consider laying out a fixed-topology binary tree of N nodes into external memory with block size B so as to minimize the worst-case number of block memory transfers required to traverse a path from the root to a node of depth D. We prove that the optimal number of memory transfers is Θ([D over lg(1+B))] when D = O(lgN), Θ([lgN over lg(1+[BlgN over D])]) when D=Ω(lgN) and D=O(BlgN), Θ([D over B]) ,when D=Ω(BlgN).

45. A search for flavour changing neutral currents in top-quark decays in pp collision data collected with the ATLAS detector at √s = 7 TeV - Taylor, Frank E.
A search for flavour changing neutral current (FCNC) processes in top-quark decays by the ATLAS Collaboration is presented. Data collected from pp collisions at the LHC at a centre-of-mass energy of √s = 7 TeV during 2011, corresponding to an integrated luminosity of 2.1 fb[superscript −1], were used. A search was performed for top-quark pair-production events, with one top quark decaying through the t → Zq FCNC (q = u, c) channel, and the other through the Standard Model dominant mode t → W b. Only the decays of the Z boson to charged leptons and leptonic W -boson decays...

46. Search for scalar top quark production in p[bar over p] collisions at √s = 1.96 TeV - Gomez-Ceballos, Guillelmo; Goncharov, Maxim; Paus, Christoph M. E.
We report on a search for the supersymmetric partner of the top quark (scalar top) decaying into a charm quark and a neutralino in p[¯ over p] collisions at √s = 1.96 TeV. The data sample, collected by the CDF II detector at the Fermilab Tevatron, corresponds to an integrated luminosity of 2.6 fb[superscript −1]. Candidate events are selected by requiring two or more jets and a large imbalance in the transverse momentum. To enhance the analysis sensitivity, at least one of the jets is required to be identified as originating from a charm quark using an algorithm specifically designed...

47. Search for resonances decaying into top-quark pairs using fully hadronic decays in pp collisions with ATLAS at √s = 7 TeV - Taylor, Frank E.
A search for resonances produced in 7 TeV proton-proton collisions and decaying into top-quark pairs is described. In this Letter events where the top-quark decay produces two massive jets with large transverse momenta recorded with the ATLAS detector at the Large Hadron Collider are considered. Two techniques that rely on jet substructure are used to separate top-quark jets from those arising from light quarks and gluons. In addition, each massive jet is required to have evidence of an associated bottom-quark decay. The data are consistent with the Standard Model, and limits can be set on the production cross section times...

48. Measurement of isolated-photon pair production in pp collisions at √s =7 TeV with the ATLAS detector - Taylor, Frank E.
The ATLAS experiment at the LHC has measured the production cross section of events with two isolated photons in the final state, in proton-proton collisions at √s = 7 TeV . The full data set collected in 2011, corresponding to an integrated luminosity of 4.9 fb[superscript −1], is used. The amount of background, from hadronic jets and isolated electrons, is estimated with data-driven techniques and subtracted. The total cross section, for two isolated photons with transverse energies above 25 GeV and 22 GeV respectively, in the acceptance of the electromagnetic calorimeter (|η| < 1.37 and 1.52 < |η| < 2.37) and with an angular separation ΔR > 0.4,...

49. Issues Faced in a Remote Instrumentation Laboratory - Malani, Shreya; Prasanna, G.N. Srinivasa; del Alamo, Jesus A.; Hardison, James L.; Moudgalya, Kannan; Chopella, Venkatesh
An Online Lab is a multi-university shared laboratory environment, where students can exercise their knowledge as they would do in a physical lab. The idea is to have maximum resource utilization and collaboration between universities by sharing of ideas. This kind of remote laboratory negates the economic issues to set up a laboratory and allows every student to have an experience of real laboratory. As part of Ministry of Human Resource Development (MHRD) Robotics Lab project a study on state of art of remote labs was conducted. This paper discusses some key issues in the design and operation of such...

50. Spatial distribution of structural degradation under high-power stress in AlGaN/GaN high electron mobility transistors - Li, Libing; Joh, Jungwoo; Thompson, Carl V.; del Alamo, Jesus A.
The two-dimensional spatial distribution of structural degradation of AlGaN/GaN high electron mobility transistors was investigated under high-power electrical stressing using atomic force and scanning electron microscopy. It was found that pits form on the surface of the GaN cap layer at the edges of the gate fingers in the middle of the device. The average pit area and density increase gradually from the edge to the center of the fingers and are more common along inner fingers than fingers. It was also found that pit formation and growth are thermally activated.

51. Multiscale Metrology and Optimization of Ultra-Scaled InAs Quantum Well FETs - Kharche, Neerav; Klimeck, Gerhard; Kim, Dae-Hyun; Luisier, Mathieu; del Alamo, Jesus A.
A simulation methodology for ultra-scaled InAs quantum well field-effect transistors (QWFETs) is presented and used to provide design guidelines and a path to improve device performance. A multiscale modeling approach is adopted, where strain is computed in an atomistic valence-force-field method, an atomistic sp[superscript 3]d[superscript 5]s* tight-binding model is used to compute channel effective masses, and a 2-D real-space effective mass-based ballistic quantum transport model is employed to simulate three-terminal current-voltage characteristics including gate leakage. The simulation methodology is first benchmarked against experimental I-V data obtained from devices with gate lengths ranging from 30 to 50 nm. A good quantitative...

52. Gesture spotting and recognition using salience detection and concatenated hidden markov models - Yin, Ying; Davis, Randall
We developed a gesture salience based hand tracking method, and a gesture spotting and recognition method based on concatenated hidden Markov models. A 3-fold cross validation using the ChAirGest development data set with 10 users gives an F1 score of 0.907 and an accurate temporal segmentation rate (ATSR) of 0.923. The average final score is 0.9116. Compared with using the hand joint position from the Kinect SDK, using our hand tracking method gives a 3.7% absolute increase in the recognition F1 score.

53. Learning a sparse codebook of facial and body microexpressions for emotion recognition - Song, Yale; Morency, Louis-Philippe; Davis, Randall
Obtaining a compact and discriminative representation of facial and body expressions is a difficult problem in emotion recognition. Part of the difficulty is capturing microexpressions, i.e., short, involuntary expressions that last for only a fraction of a second: at a micro-temporal scale, there are so many other subtle face and body movements that do not convey semantically meaningful information. We present a novel approach to this problem by exploiting the sparsity of the frequent micro-temporal motion patterns. Local space-time features are extracted over the face and body region for a very short time period, e.g., few milliseconds. A codebook of...

54. Action Recognition by Hierarchical Sequence Summarization - Song, Yale; Morency, Louis-Philippe; Davis, Randall
Recent progress has shown that learning from hierarchical feature representations leads to improvements in various computer vision tasks. Motivated by the observation that human activity data contains information at various temporal resolutions, we present a hierarchical sequence summarization approach for action recognition that learns multiple layers of discriminative feature representations at different temporal granularities. We build up a hierarchy dynamically and recursively by alternating sequence learning and sequence summarization. For sequence learning we use CRFs with latent variables to learn hidden spatio-temporal dynamics, for sequence summarization we group observations that have similar semantic meaning in the latent space. For each...

55. Physink: sketching physical behavior - Davis, Randall; Scott, Jeremy Kenneth
Describing device behavior is a common task that is currently not well supported by general animation or CAD software. We present PhysInk, a system that enables users to demonstrate 2D behavior by sketching and directly manipulating objects on a physics-enabled stage. Unlike previous tools that simply capture the user's animation, PhysInk captures an understanding of the behavior in a timeline. This enables useful capabilities such as causality-aware editing and finding physically-correct equivalent behavior. We envision PhysInk being used as a physics teacher's sketchpad or a WYSIWYG tool for game designers.

56. Distribution-sensitive learning for imbalanced datasets - Song, Yale; Morency, Louis-Philippe; Davis, Randall
Many real-world face and gesture datasets are by nature imbalanced across classes. Conventional statistical learning models (e.g., SVM, HMM, CRY), however, are sensitive to imbalanced datasets. In this paper we show how an imbalanced dataset affects the performance of a standard learning algorithm, and propose a distribution-sensitive prior to deal with the imbalanced data problem. This prior analyzes the training dataset before learning a model, and puts more weight on the samples from underrepresented classes, allowing all samples in the dataset to have a balanced impact in the learning process. We report on two empirical studies regarding learning with imbalanced...

57. Multimodal human behavior analysis: Learning correlation and interaction across modalities - Song, Yale; Morency, Louis-Philippe; Davis, Randall
Multimodal human behavior analysis is a challenging task due to the presence of complex nonlinear correlations and interactions across modalities. We present a novel approach to this problem based on Kernel Canonical Correlation Analysis (KCCA) and Multi-view Hidden Conditional Random Fields (MV-HCRF). Our approach uses a nonlinear kernel to map multimodal data to a high-dimensional feature space and finds a new projection of the data that maximizes the correlation across modalities. We use a multi-chain structured graphical model with disjoint sets of latent variables, one set per modality, to jointly learn both view-shared and view-specific sub-structures of the projected data,...

58. Candidate genes and functional noncoding variants identified in a canine model of obsessive-compulsive disorder - Tang, Ruqi; Noh, Hyun J; Wang, Dongqing; Sigurdsson, Snaevar; Swofford, Ross; Perloski, Michele; Duxbury, Margaret; Patterson, Edward E; Albright, Julie; Castelhano, Marta; Auton, Adam; Boyko, Adam R; Feng, Guoping; Lindblad-Toh, Kerstin; Karlsson, Elinor K; Noh, Hyun
Background: Obsessive-compulsive disorder (OCD), a severe mental disease manifested in time-consuming repetition of behaviors, affects 1 to 3% of the human population. While highly heritable, complex genetics has hampered attempts to elucidate OCD etiology. Dogs suffer from naturally occurring compulsive disorders that closely model human OCD, manifested as an excessive repetition of normal canine behaviors that only partially responds to drug therapy. The limited diversity within dog breeds makes identifying underlying genetic factors easier. Results: We use genome-wide association of 87 Doberman Pinscher cases and 63 controls to identify genomic loci associated with OCD and sequence these regions in 8 affected dogs from...

59. Movement-generated afference paired with transcranial magnetic stimulation: an associative stimulation paradigm - Edwards, Dylan J; Dipietro, Laura; Demirtas-Tatlidede, Asli; Medeiros, Ana H; Thickbroom, Gary W; Mastaglia, Francis L; Pascual-Leone, Alvaro; Krebs, Hermano Igo
Background: A peripheral nerve stimulus can enhance or suppress the evoked response to transcranial magnetic stimulation (TMS) depending on the latency of the preceding peripheral nerve stimulation (PNS) pulse. Similarly, somatosensory afference from the passively moving limb can transiently alter corticomotor excitability, in a phase-dependent manner. The repeated association of PNS with TMS is known to modulate corticomotor excitability; however, it is unknown whether repeated passive-movement associative stimulation (MAS) has similar effects. Methods: In a proof-of-principle study, using a cross-over design, seven healthy subjects received in separate sessions: (1) TMS (120% of the resting motor threshold-RMT, optimal site for Flexor Carpi Radialis) with...

60. Measurement of the cross-section for W boson production in association with b-jets in pp collisions at √s = 7 TeV with the ATLAS detector - Taylor, Frank E.
This paper reports a measurement of the W +b-jets (W +b+ X and W + b[¯ over b] +X) production cross-section in proton-proton collisions at a centre-of-mass energy of 7 TeV at the LHC. These results are based on data corresponding to an integrated luminosity of 4.6 fb[superscript −1], collected with the ATLAS detector. Cross-sections are presented as a function of jet multiplicity and of the transverse momentum of the leading b-jet for both the muon and electron decay modes of the W boson. The W +b-jets cross-section, corrected for all known detector effects, is quoted in a limited kinematic...

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