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MIT Open Access Articles

Mostrando recursos 101 - 120 de 26.336

  1. Search for Gravitational Waves Associated with Gamma-Ray Bursts during the First Advanced LIGO Observing Run and Implications for the Origin of GRB 150906B

    Aggarwal, Nancy; Barsotti, Lisa; Biscans, Sebastien; Brown, N. M.; Buikema, Aaron; Donovan, Frederick J; Eisenstein, Robert Alan; Essick, Reed Clasey; Evans, Matthew J; Fernandez Galiana, Alvaro-Miguel; Fritschel, Peter K; Gras, Slawomir; Isogai, Tomoki; Katsavounidis, Erotokritos; Kontos, Antonios; Lanza Jr, Robert K; Libson, Adam A.; Lynch, Ryan Christopher; MacInnis, Myron E; Martynov, Denis; Mason, Kenneth R; Matichard, Fabrice; Mavalvala, Nergis; Miller, John; Mittleman, Richard K; Ray Pitambar Mohapatra, Satyanarayan; Oelker, Eric Glenn; Shoemaker, David H; Tse, Maggie; Vitale, Salvatore; Weiss, Rainer; Yam, William; Yu, Hang; Yu, Haocun; Zucker, Michael E
    We present the results of the search for gravitational waves (GWs) associated with γ-ray bursts detected during the first observing run of the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO). We find no evidence of a GW signal for any of the 41 γ-ray bursts for which LIGO data are available with sufficient duration. For all γ-ray bursts, we place lower bounds on the distance to the source using the optimistic assumption that GWs with an energy of were emitted within the-Hz band, and we find a median 90% confidence limit of 71 Mpc at 150 Hz. For the subset of...

  2. A Search for Additional Bodies in the GJ 1132 Planetary System from 21 Ground-based Transits and a 100-hr

    Dittmann, Jason A.; Irwin, Jonathan M.; Charbonneau, David; Berta-Thompson, Zachory K.; Newton, Elisabeth R
    We present the results of a search for additional bodies in the GJ 1132 system through two methods: photometric transits and transit timing variations of GJ 1132b. We collected 21 transit observations of GJ 1132b with the MEarth-South array. We obtained 100 near-continuous hours of observations with the Spitzer Space Telescope, including two transits of GJ 1132b and spanning 60% of the orbital phase of the maximum (6.9-day) period at which bodies coplanar with GJ 1132b would transit. We exclude transits of additional Mars-sized bodies, such as a second planet or a moon, with a confidence of 99.7%. We find...

  3. A Search for Additional Bodies in the GJ 1132 Planetary System from 21 Ground-based Transits and a 100-hr

    Dittmann, Jason A.; Irwin, Jonathan M.; Charbonneau, David; Berta-Thompson, Zachory K.; Newton, Elisabeth R
    We present the results of a search for additional bodies in the GJ 1132 system through two methods: photometric transits and transit timing variations of GJ 1132b. We collected 21 transit observations of GJ 1132b with the MEarth-South array. We obtained 100 near-continuous hours of observations with the Spitzer Space Telescope, including two transits of GJ 1132b and spanning 60% of the orbital phase of the maximum (6.9-day) period at which bodies coplanar with GJ 1132b would transit. We exclude transits of additional Mars-sized bodies, such as a second planet or a moon, with a confidence of 99.7%. We find...

  4. Size and Shape of Chariklo from Multi-epoch Stellar Occultations

    Sickafoose, Amanda A
    We use data from five stellar occultations observed between 2013 and 2016 to constrain Chariklo's size and shape, and the ring reflectivity. We consider four possible models for Chariklo (sphere, Maclaurin spheroid, triaxial ellipsoid, and Jacobi ellipsoid), and we use a Bayesian approach to estimate the corresponding parameters. The spherical model has a radius R = 129 ±3 km. The Maclaurin model has equatorial and polar radii a = b 143 [subscript -6][superscript +3] km and c = 96 [subscript -4][superscript +14] km, respectively, with density 970 [subscript -180][superscript +300] kg m [superscript -3]. The ellipsoidal model has semiaxes a...

  5. Size and Shape of Chariklo from Multi-epoch Stellar Occultations

    Sickafoose, Amanda A
    We use data from five stellar occultations observed between 2013 and 2016 to constrain Chariklo's size and shape, and the ring reflectivity. We consider four possible models for Chariklo (sphere, Maclaurin spheroid, triaxial ellipsoid, and Jacobi ellipsoid), and we use a Bayesian approach to estimate the corresponding parameters. The spherical model has a radius R = 129 ±3 km. The Maclaurin model has equatorial and polar radii a = b 143 [subscript -6][superscript +3] km and c = 96 [subscript -4][superscript +14] km, respectively, with density 970 [subscript -180][superscript +300] kg m [superscript -3]. The ellipsoidal model has semiaxes a...

  6. The Structure of Chariklo’s Rings from Stellar Occultations

    Sickafoose, Amanda A
    Two narrow and dense rings (called C1R and C2R) were discovered around the Centaur object (10199) Chariklod uring a stellar occultation observed on 2013 June 3. Following this discovery, we planned observations of several occultations by Chariklos system in order to better characterize the physical properties of the ring and main body. Here, we use 12 successful occulations by Chariklo observed between 2014 and 2016. They provide ring profiles (physical width, opacity, edge structure) and constraints on the radii and pole position. Our new observations are currently consistent with the circular ring solution and pole position, to within the ±3.3...

  7. The Structure of Chariklo’s Rings from Stellar Occultations

    Sickafoose, Amanda A
    Two narrow and dense rings (called C1R and C2R) were discovered around the Centaur object (10199) Chariklod uring a stellar occultation observed on 2013 June 3. Following this discovery, we planned observations of several occultations by Chariklos system in order to better characterize the physical properties of the ring and main body. Here, we use 12 successful occulations by Chariklo observed between 2014 and 2016. They provide ring profiles (physical width, opacity, edge structure) and constraints on the radii and pole position. Our new observations are currently consistent with the circular ring solution and pole position, to within the ±3.3...

  8. Distributed Sequential Consensus in Networks: Analysis of Partially Connected Blockchains with Uncertainty

    Kushch, Sergii; Corchado, Juan Manuel; Prieto Castrillo, Francisco
    This work presents a theoretical and numerical analysis of the conditions under which distributed sequential consensus is possible when the state of a portion of nodes in a network is perturbed. Specifically, it examines the consensus level of partially connected blockchains under failure/attack events. To this end, we developed stochastic models for both verification probability once an error is detected and network breakdown when consensus is not possible. Through a mean field approximation for network degree we derive analytical solutions for the average network consensus in the large graph size thermodynamic limit. The resulting expressions allow us to derive connectivity...

  9. Distributed Sequential Consensus in Networks: Analysis of Partially Connected Blockchains with Uncertainty

    Kushch, Sergii; Corchado, Juan Manuel; Prieto Castrillo, Francisco
    This work presents a theoretical and numerical analysis of the conditions under which distributed sequential consensus is possible when the state of a portion of nodes in a network is perturbed. Specifically, it examines the consensus level of partially connected blockchains under failure/attack events. To this end, we developed stochastic models for both verification probability once an error is detected and network breakdown when consensus is not possible. Through a mean field approximation for network degree we derive analytical solutions for the average network consensus in the large graph size thermodynamic limit. The resulting expressions allow us to derive connectivity...

  10. Flow-based fabrication: An integrated computational workflow for design and digital additive manufacturing of multifunctional heterogeneously structured objects

    Duro-Royo, Jorge; Mogas-Soldevila, Laia; Oxman, Neri
    Structural hierarchy and material organization in design are traditionally achieved by combining discrete homogeneous parts into functional assemblies where the shape or surface is the determining factor in achieving function. In contrast, biological structures express higher levels of functionality on a finer scale through volumetric cellular constructs that are heterogeneous and complex. Despite recent advancements in additive manufacturing of functionally graded materials, the limitations associated with computational design and digital fabrication of heterogeneous materials and structures frame and limit further progress. Conventional computer-aided design tools typically contain geometric and topologic data of virtual constructs, but lack robust means to integrate...

  11. Flow-based fabrication: An integrated computational workflow for design and digital additive manufacturing of multifunctional heterogeneously structured objects

    Duro-Royo, Jorge; Mogas-Soldevila, Laia; Oxman, Neri
    Structural hierarchy and material organization in design are traditionally achieved by combining discrete homogeneous parts into functional assemblies where the shape or surface is the determining factor in achieving function. In contrast, biological structures express higher levels of functionality on a finer scale through volumetric cellular constructs that are heterogeneous and complex. Despite recent advancements in additive manufacturing of functionally graded materials, the limitations associated with computational design and digital fabrication of heterogeneous materials and structures frame and limit further progress. Conventional computer-aided design tools typically contain geometric and topologic data of virtual constructs, but lack robust means to integrate...

  12. Why Don’t Households Smooth Consumption? Evidence from a $25 Million Experiment

    Parker, Jonathan A.
    This paper evaluates theoretical explanations for the propensity of households to increase spending in response to the arrival of predictable, lump-sum payments, using households in the Nielsen Consumer Panel who received $25 million in randomly distributed stimulus payments. The pattern of spending is inconsistent with models in which identical households cycle rapidly through high and low- response states as they manage liquidity, but is instead highly predictable by income years before the payment. Spending responses are unrelated to expectation errors, almost unrelated to crude measures of procrastination and self-control, significantly related to sophistication and planning, and highly related to impatience.

  13. Why Don’t Households Smooth Consumption? Evidence from a $25 Million Experiment

    Parker, Jonathan A.
    This paper evaluates theoretical explanations for the propensity of households to increase spending in response to the arrival of predictable, lump-sum payments, using households in the Nielsen Consumer Panel who received $25 million in randomly distributed stimulus payments. The pattern of spending is inconsistent with models in which identical households cycle rapidly through high and low- response states as they manage liquidity, but is instead highly predictable by income years before the payment. Spending responses are unrelated to expectation errors, almost unrelated to crude measures of procrastination and self-control, significantly related to sophistication and planning, and highly related to impatience.

  14. Modeling growth paths of interacting crack pairs in elastic media

    Ghelichi, Ramin; Kamrin, Kenneth N
    The problem of predicting the growth of a system of cracks, each crack influencing the growth of the others, arises in multiple fields. We develop an analytical framework toward this aim, which we apply to the 'En-Passant' family of crack growth problems, in which a pair of initially parallel, offset cracks propagate nontrivially toward each other under far-field opening stress. We utilize boundary integral and perturbation methods of linear elasticity, linear elastic fracture mechanics, and common crack opening criteria to calculate the first analytical model for curved En-Passant crack paths. The integral system is reduced under a hierarchy of approximations,...

  15. Modeling growth paths of interacting crack pairs in elastic media

    Ghelichi, Ramin; Kamrin, Kenneth N
    The problem of predicting the growth of a system of cracks, each crack influencing the growth of the others, arises in multiple fields. We develop an analytical framework toward this aim, which we apply to the 'En-Passant' family of crack growth problems, in which a pair of initially parallel, offset cracks propagate nontrivially toward each other under far-field opening stress. We utilize boundary integral and perturbation methods of linear elasticity, linear elastic fracture mechanics, and common crack opening criteria to calculate the first analytical model for curved En-Passant crack paths. The integral system is reduced under a hierarchy of approximations,...

  16. DNA nanotechnology: new adventures for an old warhorse

    Zakeri, Bijan; Lu, Timothy K
    As the blueprint of life, the natural exploits of DNA are admirable. However, DNA should not only be viewed within a biological context. It is an elegantly simple yet functionally complex chemical polymer with properties that make it an ideal platform for engineering new nanotechnologies. Rapidly advancing synthesis and sequencing technologies are enabling novel unnatural applications for DNA beyond the realm of genetics. Here we explore the chemical biology of DNA nanotechnology for emerging applications in communication and digital data storage. Early studies of DNA as an alternative to magnetic and optical storage mediums have not only been promising, but...

  17. DNA nanotechnology: new adventures for an old warhorse

    Zakeri, Bijan; Lu, Timothy K
    As the blueprint of life, the natural exploits of DNA are admirable. However, DNA should not only be viewed within a biological context. It is an elegantly simple yet functionally complex chemical polymer with properties that make it an ideal platform for engineering new nanotechnologies. Rapidly advancing synthesis and sequencing technologies are enabling novel unnatural applications for DNA beyond the realm of genetics. Here we explore the chemical biology of DNA nanotechnology for emerging applications in communication and digital data storage. Early studies of DNA as an alternative to magnetic and optical storage mediums have not only been promising, but...

  18. Biodegradable nano-films for capture and non-invasive release of circulating tumor cells

    Reátegui, Eduardo; Hsu, Bryan; Jensen, Anne E.; Sequist, Lecia V.; Maheswaran, Shyamala; Haber, Daniel A.; Toner, Mehmet; Stott, Shannon L.; Li, Wei; Park, Myoung Hwan; Castleberry, Steven A; Deng, Zhou; Hsu, Bryan Boen; Mayner, Sarah E.; Hammond, Paula T
    Selective isolation and purification of circulating tumor cells (CTCs) from whole blood is an important capability for both clinical medicine and biological research. Current techniques to perform this task place the isolated cells under excessive stresses that reduce cell viability, and potentially induce phenotype change, therefore losing valuable information about the isolated cells. We present a biodegradable nano-film coating on the surface of a microfluidic chip, which can be used to effectively capture as well as non-invasively release cancer cell lines such as PC-3, LNCaP, DU 145, H1650 and H1975. We have applied layer-by-layer (LbL) assembly to create a library...

  19. Biodegradable nano-films for capture and non-invasive release of circulating tumor cells

    Reátegui, Eduardo; Hsu, Bryan; Jensen, Anne E.; Sequist, Lecia V.; Maheswaran, Shyamala; Haber, Daniel A.; Toner, Mehmet; Stott, Shannon L.; Li, Wei; Park, Myoung Hwan; Castleberry, Steven A; Deng, Zhou; Hsu, Bryan Boen; Mayner, Sarah E.; Hammond, Paula T
    Selective isolation and purification of circulating tumor cells (CTCs) from whole blood is an important capability for both clinical medicine and biological research. Current techniques to perform this task place the isolated cells under excessive stresses that reduce cell viability, and potentially induce phenotype change, therefore losing valuable information about the isolated cells. We present a biodegradable nano-film coating on the surface of a microfluidic chip, which can be used to effectively capture as well as non-invasively release cancer cell lines such as PC-3, LNCaP, DU 145, H1650 and H1975. We have applied layer-by-layer (LbL) assembly to create a library...

  20. Optimizations of the energy grid search algorithm in continuous-energy Monte Carlo particle transport codes

    Romano, Paul K.; Walsh, Jonathan Alan; Forget, Benoit Robert Yves; Smith, Kord S.
    In this work we propose, implement, and test various optimizations of the typical energy grid-cross section pair lookup algorithm in Monte Carlo particle transport codes. The key feature common to all of the optimizations is a reduction in the length of the vector of energies that must be searched when locating the index of a particle's current energy. Other factors held constant, a reduction in energy vector length yields a reduction in CPU time. The computational methods we present here are physics-informed. That is, they are designed to utilize the physical information embedded in a simulation in order to reduce...

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