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MIT Open Access Articles

Mostrando recursos 181 - 200 de 26.403

  1. 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,...

  2. 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,...

  3. 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...

  4. 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...

  5. 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...

  6. 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...

  7. 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...

  8. 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...

  9. Cognitive and connectome properties detectable through individual differences in graphomotor organization

    Lamar, Melissa; Ajilore, Olusola; Leow, Alex; Charlton, Rebecca; Cohen, Jamie; GadElkarim, Johnson; Yang, Shaolin; Zhang, Aifeng; Penney, Dana; Libon, David J.; Kumar, Anand; Davis, Randall
    We investigated whether graphomotor organization during a digitized Clock Drawing Test (dCDT) would be associated with cognitive and/or brain structural differences detected with a tractography-derived structural connectome of the brain. 72 non-demented/non-depressed adults were categorized based on whether or not they used 'anchor' digits (i.e., 12, 3, 6, 9) before any other digits while completing dCDT instructions to "draw the face of a clock with all the numbers and set the hands to 10 after 11". 'Anchorers' were compared to 'non-anchorers' across dCDT, additional cognitive measures and connectome-based metrics. In the context of grossly intact clock drawings, anchorers required fewer...

  10. Cognitive and connectome properties detectable through individual differences in graphomotor organization

    Lamar, Melissa; Ajilore, Olusola; Leow, Alex; Charlton, Rebecca; Cohen, Jamie; GadElkarim, Johnson; Yang, Shaolin; Zhang, Aifeng; Penney, Dana; Libon, David J.; Kumar, Anand; Davis, Randall
    We investigated whether graphomotor organization during a digitized Clock Drawing Test (dCDT) would be associated with cognitive and/or brain structural differences detected with a tractography-derived structural connectome of the brain. 72 non-demented/non-depressed adults were categorized based on whether or not they used 'anchor' digits (i.e., 12, 3, 6, 9) before any other digits while completing dCDT instructions to "draw the face of a clock with all the numbers and set the hands to 10 after 11". 'Anchorers' were compared to 'non-anchorers' across dCDT, additional cognitive measures and connectome-based metrics. In the context of grossly intact clock drawings, anchorers required fewer...

  11. Controversy in statistical analysis of functional magnetic resonance imaging data

    Behrmann, Marlene; Brown, Emery Neal
    To test the validity of statistical methods for fMRI data analysis, Eklund et al. (1) used, for the first time, large-scale experimental data rather than simulated data. Using resting-state fMRI measurements to represent a null hypothesis of no task-induced activation, the authors compare familywise error rates for voxel-based and cluster-based inferences for both parametric and nonparametric methods. Eklund et al.’s study used three fMRI statistical analysis packages. They found that, for a target familywise error rate of 5%, the parametric methods gave invalid cluster-based inferences and conservative voxel-based inferences.

  12. Controversy in statistical analysis of functional magnetic resonance imaging data

    Behrmann, Marlene; Brown, Emery Neal
    To test the validity of statistical methods for fMRI data analysis, Eklund et al. (1) used, for the first time, large-scale experimental data rather than simulated data. Using resting-state fMRI measurements to represent a null hypothesis of no task-induced activation, the authors compare familywise error rates for voxel-based and cluster-based inferences for both parametric and nonparametric methods. Eklund et al.’s study used three fMRI statistical analysis packages. They found that, for a target familywise error rate of 5%, the parametric methods gave invalid cluster-based inferences and conservative voxel-based inferences.

  13. Reference-free removal of EEG-fMRI ballistocardiogram artifacts with harmonic regression

    Bonmassar, Giorgio; Poulsen, Catherine; Pierce, Eric T.; Purdon, Patrick L.; Krishnaswamy, Pavitra; Brown, Emery Neal
    Combining electroencephalogram (EEG) recording and functional magnetic resonance imaging (fMRI) offers the potential for imaging brain activity with high spatial and temporal resolution. This potential remains limited by the significant ballistocardiogram (BCG) artifacts induced in the EEG by cardiac pulsation-related head movement within the magnetic field. We model the BCG artifact using a harmonic basis, pose the artifact removal problem as a local harmonic regression analysis, and develop an efficient maximum likelihood algorithm to estimate and remove BCG artifacts. Our analysis paradigm accounts for time-frequency overlap between the BCG artifacts and neurophysiologic EEG signals, and tracks the spatiotemporal variations in...

  14. Reference-free removal of EEG-fMRI ballistocardiogram artifacts with harmonic regression

    Bonmassar, Giorgio; Poulsen, Catherine; Pierce, Eric T.; Purdon, Patrick L.; Krishnaswamy, Pavitra; Brown, Emery Neal
    Combining electroencephalogram (EEG) recording and functional magnetic resonance imaging (fMRI) offers the potential for imaging brain activity with high spatial and temporal resolution. This potential remains limited by the significant ballistocardiogram (BCG) artifacts induced in the EEG by cardiac pulsation-related head movement within the magnetic field. We model the BCG artifact using a harmonic basis, pose the artifact removal problem as a local harmonic regression analysis, and develop an efficient maximum likelihood algorithm to estimate and remove BCG artifacts. Our analysis paradigm accounts for time-frequency overlap between the BCG artifacts and neurophysiologic EEG signals, and tracks the spatiotemporal variations in...

  15. Design and Modeling of Membrane-Based Evaporative Cooling Devices for Thermal Management of High Heat Fluxes

    Salamon, Todd R.; Narayanan, Shankar; Simon, Maria E.; Lu, Zhengmao; Bagnall, Kevin R.; Hanks, Daniel Frank; Antao, Dion Savio; Barabadi, Banafsheh; Sircar, Jay; Wang, Evelyn
    We present a high-heat-flux cooling device for advanced thermal management of electronics. The device incorporates nanoporous membranes supported on microchannels to enable thin-film evaporation. The underlying concept takes advantage of the capillary pressure generated by small pores in the membrane, and minimizes the viscous loss by reducing the membrane thickness. The heat transfer and fluid flow in the device were modeled to determine the effect of different geometric parameters. With the optimization of various parameters, the device can achieve a heat transfer coefficient in excess of 0.05 kW/cm²-K, while dissipating a heat flux of 1 kW/cm². When applied to power...

  16. Design and Modeling of Membrane-Based Evaporative Cooling Devices for Thermal Management of High Heat Fluxes

    Salamon, Todd R.; Narayanan, Shankar; Simon, Maria E.; Lu, Zhengmao; Bagnall, Kevin R.; Hanks, Daniel Frank; Antao, Dion Savio; Barabadi, Banafsheh; Sircar, Jay; Wang, Evelyn
    We present a high-heat-flux cooling device for advanced thermal management of electronics. The device incorporates nanoporous membranes supported on microchannels to enable thin-film evaporation. The underlying concept takes advantage of the capillary pressure generated by small pores in the membrane, and minimizes the viscous loss by reducing the membrane thickness. The heat transfer and fluid flow in the device were modeled to determine the effect of different geometric parameters. With the optimization of various parameters, the device can achieve a heat transfer coefficient in excess of 0.05 kW/cm²-K, while dissipating a heat flux of 1 kW/cm². When applied to power...

  17. CP violation in multibody B decays from QCD factorization

    Klein, Rebecca; Mannel, Thomas; Vos, K. Keri; Virto, Javier
    We test a data-driven approach based on QCD factorization for charmless three-body B-decays by confronting it to measurements of CP violation in B⁻→ π⁻π⁺π⁻. While some of the needed non-perturbative objects can be directly extracted from data, some others can, so far, only be modelled. Although this approach is currently model dependent, we comment on the perspectives to reduce this model dependence. While our model naturally accommodates the gross features of the Dalitz distribution, it cannot quantitatively explain the details seen in the current experimental data on local CP asymmetries. We comment on possible refinements of our simple model and...

  18. CP violation in multibody B decays from QCD factorization

    Klein, Rebecca; Mannel, Thomas; Vos, K. Keri; Virto, Javier
    We test a data-driven approach based on QCD factorization for charmless three-body B-decays by confronting it to measurements of CP violation in B⁻→ π⁻π⁺π⁻. While some of the needed non-perturbative objects can be directly extracted from data, some others can, so far, only be modelled. Although this approach is currently model dependent, we comment on the perspectives to reduce this model dependence. While our model naturally accommodates the gross features of the Dalitz distribution, it cannot quantitatively explain the details seen in the current experimental data on local CP asymmetries. We comment on possible refinements of our simple model and...

  19. The Disciplinary Dislocations of (Architectural) History

    Jarzombek, Mark

  20. The Disciplinary Dislocations of (Architectural) History

    Jarzombek, Mark

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