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DSpace at MIT (72,757 recursos)
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MIT Open Access Articles

Mostrando recursos 41 - 60 de 11,708

41. Correlation chemical shift imaging with low-power adiabatic pulses and constant-density spiral trajectories - Andronesi, Ovidiu C.; Gagoski, Borjan Aleksandar; Adalsteinsson, Elfar; Sorensen, A. Gregory
In this work we introduce the concept of correlation chemical shift imaging (CCSI). Novel CCSI pulse sequences are demonstrated on clinical scanners for two-dimensional Correlation Spectroscopy (COSY) and Total Correlation Spectroscopy (TOCSY) imaging experiments. To date there has been limited progress reported towards a feasible and robust multivoxel 2D COSY. Localized 2D TOCSY imaging is shown for the first time in this work. Excitation with adiabatic GOIA-W(16,4) pulses (Gradient Offset Independent Adiabaticity Wurst modulation) provides minimal chemical shift displacement error, reduced lipid contamination from subcutaneous fat, uniform optimal flip angles, and efficient mixing for coupled spins, while enabling short repetition...

42. Probabilistic projections of 21st century climate change over Northern Eurasia - Monier, Erwan; Sokolov, Andrei P.; Schlosser, Adam; Scott, Jeffery R.; Gao, Xiang
We present probabilistic projections of 21st century climate change over Northern Eurasia using the Massachusetts Institute of Technology (MIT) Integrated Global System Model (IGSM), an integrated assessment model that couples an Earth system model of intermediate complexity with a two-dimensional zonal-mean atmosphere to a human activity model. Regional climate change is obtained by two downscaling methods: a dynamical downscaling, where the IGSM is linked to a three-dimensional atmospheric model, and a statistical downscaling, where a pattern scaling algorithm uses climate change patterns from 17 climate models. This framework allows for four major sources of uncertainty in future projections of regional...

43. The value of high-frequency, high-precision methane isotopologue measurements for source and sink estimation - Rigby, Matthew; Manning, A. J.; Prinn, Ronald G.
We present an observing system simulation experiment examining the potential benefits of new methane isotopologues measurements for global- and national-scale source and sink inversions. New measurements are expected in the coming years, using quantum cascade laser spectroscopy with sample preconcentration, that will allow observations ofδ13C - CH4 and δD - CH4at approximately hourly intervals and higher precision than previously possible. Using model-generated ‘pseudo-data’, we predict the variability that these new systems should encounter in the atmosphere, and estimate the additional uncertainty reduction that should result from their use in source and sink inversions. We find that much of theδ-value variability...

44. Reducing Physical Hazards: Encouraging Inherently Safer Production (Chapter 17) - Ashford, Nicholas A.
Physical hazards differ from hazards related to the toxicity of chemicals and materials in a number of ways. Their origin is the sudden and accidental release of chemicals and/ or energy - that is, chemical accidents, explosions, and spills - as distinct from the expected products, by-products, or gradual pollution associated with chemical production and use. The chemicals or materials are not always inherently toxic. For example, flour or olive oil can be explosive in an industrial operation if the particles or mist, respectively, are fine enough such that a spark leads to an ignition. Therefore, not only are the...

45. Caged Mono- and Divalent Ligands for Light-Assisted Disruption of PDZ Domain-Mediated Interactions - Sainlos, Matthieu; Iskenderian-Epps, Wendy S.; Olivier, Nelson B.; Choquet, Daniel; Imperiali, Barbara
We report a general method for light-assisted control of interactions of PDZ domain binding motifs with their cognate domains by the incorporation of a photolabile caging group onto the essential C-terminal carboxylate binding determinant of the motif. The strategy was implemented and validated for both simple monovalent and biomimetic divalent ligands, which have recently been established as powerful tools for acute perturbation of native PDZ domain-dependent interactions in live cells.

46. Cyanophycin Mediates the Accumulation and Storage of Fixed Carbon in Non-Heterocystous Filamentous Cyanobacteria from Coniform Mats - Liang, Biqing; Wu, Ting-Di; Sun, Hao-Jhe; Vali, Hojatollah; Guerquin-Kern, Jean-Luc; Wang, Chung-Ho; Bosak, Tanja
Thin, filamentous, non-heterocystous, benthic cyanobacteria (Subsection III) from some marine, lacustrine and thermal environments aggregate into macroscopic cones and conical stromatolites. We investigate the uptake and storage of inorganic carbon by cone-forming cyanobacteria from Yellowstone National Park using high-resolution stable isotope mapping of labeled carbon (H13CO3−) and immunoassays. Observations and incubation experiments in actively photosynthesizing enrichment cultures and field samples reveal the presence of abundant cyanophycin granules in the active growth layer of cones. These ultrastructurally heterogeneous granules rapidly accumulate newly fixed carbon and store 18% of the total particulate labeled carbon after 120 mins of incubation. The intracellular distribution...

47. Regulatory T Cells Expanded from Hiv-1-Infected Individuals Maintain Phenotype, Tcr Repertoire and Suppressive Capacity - Angin, Mathieu; Klarenbeek, Paul L.; King, Melanie; Sharma, Siddhartha M.; Moodley, Eshia S.; Rezai, Ashley; Piechocka-Trocha, Alicja; Toth, Ildiko; Chan, Andrew T.; Goulder, Philip J.; Ndung'u, Thumbi; Kwon, Douglas; Addo, Marylyn M.
While modulation of regulatory T cell (Treg) function and adoptive Treg transfer are being explored as therapeutic modalities in the context of autoimmune diseases, transplantation and cancer, their role in HIV-1 pathogenesis remains less well defined. Controversy persists regarding their beneficial or detrimental effects in HIV-1 disease, which warrants further detailed exploration. Our objectives were to investigate if functional CD4+ Tregs can be isolated and expanded from HIV-1-infected individuals for experimental or potential future therapeutic use and to determine phenotype and suppressive capacity of expanded Tregs from HIV-1 positive blood and tissue. Tregs and conventional T cell controls were isolated...

48. Deriving emissions time series from sparse atmospheric mole fractions - Rigby, Matthew; Ganesan, Anita Lakshmi; Prinn, Ronald G.
A growth-based Bayesian inverse method is presented for deriving emissions of atmospheric trace species from temporally sparse measurements of their mole fractions. This work is motivated by many recent studies that have deduced emissions using archived air samples with measurement intervals of the order of a year or longer in the early part of the record. Several techniques have been used to make this underdetermined problem invertible. These include the incorporation of prior emissions estimates, the smoothing of observations or derived emissions, the approximation of emissions time series by polynomials, or the application of regularization schemes. However, these methods often...

49. A linguistic approach to assess the dynamics of design team preference in concept selection - Dong, Andy; Sarkar, Somwrita; Honda, Tomonori; Yang, Maria
This paper addresses the problem of describing the decision-making process of a committee of engineers based upon their verbalized linguistic appraisals of alternatives. First, we show a way to model an individual’s evaluation of an alternative through natural language based on the Systemic-Functional Linguistics system of APPRAISAL. The linguistic model accounts for both the degree of intensity and the uncertainty of expressed evaluations. Second, this multi-dimensional linguistic model is converted into a scalar to represent the degree of intensity and a probability distribution function for the stated evaluation. Finally, we present a Markovian model to calculate the time-varying change in...

50. Approaches for Identifying Consumer Preferences for the Design of Technology Products: A Case Study of Residential Solar Panels - Chen, Heidi Q.; Honda, Tomonori; Yang, Maria
This paper investigates ways to obtain consumer preferences for technology products to help designers identify the key attributes that contribute to a product's market success. A case study of residential photovoltaic panels is performed in the context of the California, USA, market within the 2007–2011 time span. First, interviews are conducted with solar panel installers to gain a better understanding of the solar industry. Second, a revealed preference method is implemented using actual market data and technical specifications to extract preferences. The approach is explored with three machine learning methods: Artificial neural networks (ANN), Random Forest decision trees, and Gradient...

51. A Study of Student Design Team Behaviors in Complex System Design - Honda, Tomonori; Austin-Breneman, Jesse Lauren; Yang, Maria
Large-scale engineering systems require design teams to balance complex sets of considerations using a wide range of design and decision-making skills. Formal, computational approaches for optimizing complex systems offer strategies for arriving at optimal solutions in situations where system integration and design optimization are well-formulated. However, observation of design practice suggests engineers may be poorly prepared for this type of design. Four graduate student teams completed a distributed, complex system design task. Analysis of the teams' design histories suggests three categories of suboptimal approaches: global rather than local searches, optimizing individual design parameters separately, and sequential rather than concurrent optimization...

52. Understanding the role of phase function in translucent appearance - Gkioulekas, Ioannis; Xiao, Bei; Zhao, Shuang; Adelson, Edward H.; Zickler, Todd; Bala, Kavita
Multiple scattering contributes critically to the characteristic translucent appearance of food, liquids, skin, and crystals; but little is known about how it is perceived by human observers. This article explores the perception of translucency by studying the image effects of variations in one factor of multiple scattering: the phase function. We consider an expanded space of phase functions created by linear combinations of Henyey-Greenstein and von Mises-Fisher lobes, and we study this physical parameter space using computational data analysis and psychophysics. Our study identifies a two-dimensional embedding of the physical scattering parameters in a perceptually meaningful appearance space. Through our analysis...

53. Sensing and Recognizing Surface Textures Using a GelSight Sensor - Li, Rui; Adelson, Edward H.
Sensing surface textures by touch is a valuable capability for robots. Until recently it was difficult to build a compliant sensor with high sensitivity and high resolution. The GelSight sensor is compliant and offers sensitivity and resolution exceeding that of the human fingertips. This opens the possibility of measuring and recognizing highly detailed surface textures. The GelSight sensor, when pressed against a surface, delivers a height map. This can be treated as an image, and processed using the tools of visual texture analysis. We have devised a simple yet effective texture recognition system based on local binary patterns, and enhanced...

54. Microgeometry capture using an elastomeric sensor - Johnson, Micah K.; Cole, Forrester; Raj, Alvin; Adelson, Edward H.
We describe a system for capturing microscopic surface geometry. The system extends the retrographic sensor [Johnson and Adelson 2009] to the microscopic domain, demonstrating spatial resolution as small as 2 microns. In contrast to existing microgeometry capture techniques, the system is not affected by the optical characteristics of the surface being measured---it captures the same geometry whether the object is matte, glossy, or transparent. In addition, the hardware design allows for a variety of form factors, including a hand-held device that can be used to capture high-resolution surface geometry in the field. We achieve these results with a combination of...

55. Lump detection with a gelsight sensor - Jia, Xiaodan; Li, Rui; Srinivasan, Mandayam A.; Adelson, Edward H.
A GelSight sensor is a tactile sensing device comprising a clear elastomeric pad covered with a reflective membrane, coupled with optics to measure the membrane's deformations. When the pad is pressed against an object's surface, the membrane changes shape in accord with mechanical and geometrical properties of the object. Since soft tissue is more compliant than hard tissue, one can detect an embedded lump by pressing the GelSight pad against the tissue surface and observing the hump that forms over the lump. We tested this system's sensitivity by constructing phantoms of soft rubber with hard embedded lumps. The system is...

56. Low-cost, single-mode diode-pumped Cr:Colquiriite lasers - Demirbas, Umit; Li, Duo; Birge, Jonathan R.; Sennaroglu, Alphan; Petrich, Gale S.; Kolodziejski, Leslie A.; Kaertner, Franz X.; Fujimoto, James G.
We present three Cr[superscript 3+]:Colquiriite lasers as low-cost alternatives to Ti:Sapphire laser technology. Single-mode laser diodes, which cost only $150 each, were used as pump sources. In cw operation, with ~520 mW of absorbed pump power, up to 257, 269 and 266 mW of output power and slope efficiencies of 53%, 62% and 54% were demonstrated for Cr:LiSAF, Cr:LiSGaF and Cr:LiCAF, respectively. Record cw tuning ranges from 782 to 1042 nm for Cr:LiSAF, 777 to 977 nm for Cr:LiSGaF, and 754 to 871 nm for Cr:LiCAF were demonstrated. In cw mode-locking experiments using semiconductor saturable absorber mirrors at 800 and...

57. Accidental Pinhole and Pinspeck Cameras - Torralba, Antonio; Freeman, William T.
We identify and study two types of “accidental” images that can be formed in scenes. The first is an accidental pinhole camera image. The second class of accidental images are “inverse” pinhole camera images, formed by subtracting an image with a small occluder present from a reference image without the occluder. Both types of accidental cameras happen in a variety of different situations. For example, an indoor scene illuminated by natural light, a street with a person walking under the shadow of a building, etc. The images produced by accidental cameras are often mistaken for shadows or interreflections. However, accidental...

58. Phase-based video motion processing - Wadhwa, Neal; Rubinstein, Michael; Freeman, William T.; Durand, Fredo
We introduce a technique to manipulate small movements in videos based on an analysis of motion in complex-valued image pyramids. Phase variations of the coefficients of a complex-valued steerable pyramid over time correspond to motion, and can be temporally processed and amplified to reveal imperceptible motions, or attenuated to remove distracting changes. This processing does not involve the computation of optical flow, and in comparison to the previous Eulerian Video Magnification method it supports larger amplification factors and is significantly less sensitive to noise. These improved capabilities broaden the set of applications for motion processing in videos. We demonstrate the...

59. Fabricating BRDFs at high spatial resolution using wave optics - Levin, Anat; Glasner, Daniel; Xiong, Ying; Matusik, Wojciech; Zickler, Todd; Durand, Fredo; Freeman, William T.
Recent attempts to fabricate surfaces with custom reflectance functions boast impressive angular resolution, yet their spatial resolution is limited. In this paper we present a method to construct spatially varying reflectance at a high resolution of up to 220dpi, orders of magnitude greater than previous attempts, albeit with a lower angular resolution. The resolution of previous approaches is limited by the machining, but more fundamentally, by the geometric optics model on which they are built. Beyond a certain scale geometric optics models break down and wave effects must be taken into account. We present an analysis of incoherent reflectance based...

60. Porosity Controls Spread of Excitation in Tectorial Membrane Traveling Waves - Ghaffari, Roozbeh; Farrahi, Shirin; Richardson, Guy P.; Freeman, Dennis M.; Sellon, Jonathan Blake; Freeman, Dennis M.
Cochlear frequency selectivity plays a key role in our ability to understand speech, and is widely believed to be associated with cochlear amplification. However, genetic studies targeting the tectorial membrane (TM) have demonstrated both sharper and broader tuning with no obvious changes in hair bundle or somatic motility mechanisms. For example, cochlear tuning of Tectb[superscript –/–] mice is significantly sharper than that of Tecta[superscript Y1870C/+] mice, even though TM stiffnesses are similarly reduced relative to wild-type TMs. Here we show that differences in TM viscosity can account for these differences in tuning. In the basal cochlear turn, nanoscale pores of...

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