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MIT Open Access Articles
Mostrando recursos 41 - 60 de 9,054
41.
A measurement distribution framework for cooperative navigation using multiple AUVs - Fallon, Maurice Francis; Papadopoulos, Georgios; Leonard, John Joseph
In recent years underwater survey and surveillance missions with more than a single Autonomous Underwater Vehicle (AUV) have become more common thanks to more reliable and cheaper platforms, as well as the addition of remote command and control communications using, for example, the WHOI acoustic modem. However cooperative navigation of AUVs has thus far been limited to a single AUV supported by a dedicated surface vehicle with access to GPS. In this paper a scalable and modular framework is presented in which any number of vehicles can broadcast, forward and acknowledge range, dead-reckoning, feature and GPS measurements so that the...
42.
Cooperative AUV Navigation using a Single Maneuvering Surface Craft - Fallon, Maurice Francis; Papadopoulos, Georgios; Leonard, John Joseph; Patrikalakis, Nicholas M.
In this paper we describe the experimental implementation of an online algorithm for cooperative localization of submerged autonomous underwater vehicles (AUVs) supported by an autonomous surface craft. Maintaining accurate localization of an AUV is difficult because electronic signals, such as GPS, are highly attenuated by water. The usual solution to the problem is to utilize expensive navigation sensors to slow the rate of dead-reckoning divergence. We investigate an alternative approach that utilizes the position information of a surface vehicle to bound the error and uncertainty of the on-board position estimates of a low-cost AUV. This approach uses the Woods Hole...
43.
Hybrid chromophore/template nanostructures: A customizable platform material for solar energy storage and conversion - Kolpak, Alexie M.; Grossman, Jeffrey C.
Challenges with cost, cyclability, and/or low energy density have largely prevented the development of solar thermal fuels, a potentially attractive alternative energy technology based on molecules that can capture and store solar energy as latent heat in a closed cycle. In this paper, we present a set of novel hybrid photoisomer/template solar thermal fuels that can potentially circumvent these challenges. Using first-principles computations, we demonstrate that these fuels, composed of organic photoisomers bound to inexpensive carbon-based templates, can reversibly store solar energy at densities comparable to Li-ion batteries. Furthermore, we show that variation of the template material in combination with...
44.
Bioinspired Multivalent DNA Network for Capture and Release of Cells - Zhao, Weian; Cui, Cheryl; Bose, Suman; Guo, Dagang; Shen, Chong; Wong, Wesley P.; Halvorsen, Ken; Farokhzad, Omid C.; Teo, Grace Sock Leng; Phillips, Joseph A.; Dorfman, David M.; Karnik, Rohit N.; Karp, Jeffrey Michael
Capture and isolation of flowing cells and particulates from body fluids has enormous implications in diagnosis, monitoring, and drug testing, yet monovalent adhesion molecules used for this purpose result in inefficient cell capture and difficulty in retrieving the captured cells. Inspired by marine creatures that present long tentacles containing multiple adhesive domains to effectively capture flowing food particulates, we developed a platform approach to capture and isolate cells using a 3D DNA network comprising repeating adhesive aptamer domains that extend over tens of micrometers into the solution. The DNA network was synthesized from a microfluidic surface by rolling circle amplification...
45.
Cell sorting by deterministic cell rolling - Choi, Sungyoung; Karp, Jeffrey Michael; Karnik, Rohit N.
This communication presents the concept of “deterministic cell rolling”, which leverages transient cell-surface molecular interactions that mediate cell rolling to sort cells with high purity and efficiency in a single step.
46.
Enhanced discrimination of DNA molecules in nanofluidic channels through multiple measurements - Sen, Yi-Heng; Jain, Tarun Kumar; Aguilar, Carlos A.; Karnik, Rohit N.
Nanofluidic sensing elements have been the focus of recent experiments for numerous applications ranging from nucleic acid fragment sizing to single-molecule DNA sequencing. These applications critically rely on high measurement fidelity, and methods to increase resolution are required. Herein, we describe fabrication and testing of a nanochannel device that enhances measurement resolution by performing multiple measurements (>100) on single DNA molecules. The enhanced measurement resolution enabled length discrimination between a mixture of λ-DNA (48.5 kbp) and T7 DNA (39.9 kbp) molecules, which were detected as transient current changes during translocation of the molecules through the nanochannel. As long DNA molecules...
47.
Studying cell rolling trajectories on asymmetric receptor patterns - Lee, Chia-Hua; Bose, Suman; Van Vliet, Krystyn J.; Karp, Jeffrey M.; Karnik, Rohit N.
Lateral displacement of cells orthogonal to a flow stream by rolling on asymmetric receptor patterns presents an opportunity for development of new devices for label-free separation and analysis of cells[1]. Such devices may use lateral displacement for continuous-flow separation, or receptor patterns that modulate adhesion to distinguish between different cell phenotypes or levels of receptor expression. Understanding the nature of cell rolling trajectories on receptor-patterned substrates is necessary for engineering of the substrates and design of such devices.
Here, we demonstrate a protocol for studying cell rolling trajectories on asymmetric receptor patterns that support cell rolling adhesion[2]. Well-defined, μm-scale patterns of...
48.
Neutral pion lifetime measurements and the QCD chiral anomaly - Bernstein, Aron M.; Holstein, Barry R.
A fundamental property of QCD is the presence of the chiral anomaly, which is the dominant component of the π[superscript 0]→γγ decay rate. Based on this anomaly and its small (≃4.5%) chiral correction, a prediction of the π[superscript 0] lifetime can be used as a test of QCD at confinement scale energies. The interesting experimental and theoretical histories of the π[superscript 0] meson are reviewed, from discovery to the present era. Experimental results are in agreement with the theoretical prediction, within the current (≃3%) experimental error; however, they are not yet sufficiently precise to test the chiral corrected result, which...
49.
Examining the Lateral Displacement of HL60 Cells Rolling on Asymmetric P-Selectin Patterns - Lee, Chia-Hua; Bose, Suman; Van Vliet, Krystyn J.; Karp, Jeffrey M.; Karnik, Rohit N.
The lateral displacement of cells orthogonal to a flow stream by rolling on asymmetrical receptor patterns presents a new opportunity for the label-free separation and analysis of cells. Understanding the nature of cell rolling trajectories on such substrates is necessary to the engineering of substrates and the design of devices for cell separation and analysis. Here, we investigate the statistical nature of cell rolling and the effect of pattern geometry and flow shear stress on cell rolling trajectories using micrometer-scale patterns of biomolecular receptors with well-defined edges. Leukemic myeloid HL60 cells expressing the PSGL-1 ligand were allowed to flow across...
50.
Engineering of self-assembled nanoparticle platform for precisely controlled combination drug therapy - Kolishetti, Nagesh; Dhar, Shanta; Valencia, Pedro Miguel; Lin, Lucy Q.; Karnik, Rohit N.; Lippard, Stephen J.; Langer, Robert; Farokhzad, Omid C.
The genomic revolution has identified therapeutic targets for a plethora of diseases, creating a need to develop robust technologies for combination drug therapy. In the present work, we describe a self-assembled polymeric nanoparticle (NP) platform to target and control precisely the codelivery of drugs with varying physicochemical properties to cancer cells. As proof of concept, we codelivered cisplatin and docetaxel (Dtxl) to prostate cancer cells with synergistic cytotoxicity. A polylactide (PLA) derivative with pendant hydroxyl groups was prepared and conjugated to a platinum(IV) [Pt(IV)] prodrug, c,t,c-[Pt(NH[subscript 3])[subscript 2](O[subscript 2]CCH[subscript 2]CH[subscript 2]COOH)(OH)Cl[subscript 2]] [PLA-Pt(IV)]. A blend of PLA-Pt(IV) functionalized polymer and...
51.
Superconducting Spin Switch with Infinite Magnetoresistance Induced by an Internal Exchange Field - Li, Bin; Roschewsky, Niklas; Assaf, Badih A.; Eich, Marius; Epstein-Martin, Marguerite; Heiman, Don; Mu¨nzenberg, Markus; Moodera, Jagadeesh
A theoretical prediction by de Gennes suggests that the resistance in a FI/S/FI (where FI is a ferromagnetic insulator, and S is a superconductor) structure will depend on the magnetization direction of the two FI layers. We report a magnetotransport measurement in a EuS/Al/EuS structure, showing that an infinite magnetoresistance can be produced by tuning the internal exchange field at the FI/S interface. This proximity effect at the interface can be suppressed by an Al[subscript 2]O[subscript 3] barrier as thin as 0.3 nm, showing the extreme confinement of the interaction to the interface giving rise to the demonstrated phenomena.
52.
Quantitative analysis of cell composition and purity of human pancreatic islet preparations - Pisania, Anna; Weir, Gordon C.; O’Neil, John J.; Omer, Abdulkadir; Tchipashvili, Vaja; Lei, Ji; Colton, Clark K.
Despite improvements in outcomes for human islet transplantation, characterization of islet preparations remains poorly defined. This study used both light microscopy (LM) and electron microscopy (EM) to characterize 33 islet preparations used for clinical transplants. EM allowed an accurate identification and quantification of cell types with measured cell number fractions (mean±s.e.m.) of 35.6±2.1% β-cells, 12.6±1.0% non-β-islet cells (48.3±2.6% total islet cells), 22.7±1.5% duct cells, and 25.3±1.8% acinar cells. Of the islet cells, 73.6±1.7% were β-cells. For comparison with the literature, estimates of cell number fraction, cell volume, and extracellular volume were combined to convert number fraction data to volume fractions...
53.
Enumeration of islets by nuclei counting and light microscopic analysis - Pisania, Anna; Papas, Klearchos K.; Powers, Daryl E.; Rappel, Michael J.; Omer, Abdulkadir; Bonner-Weir, Susan; Weir, Gordon C.; Colton, Clark K.
Islet enumeration in impure preparations by conventional dithizone staining and visual counting is inaccurate and operator dependent. We examined nuclei counting for measuring the total number of cells in islet preparations, and we combined it with morphological analysis by light microscopy (LM) for estimating the volume fraction of islets in impure preparations. Cells and islets were disrupted with lysis solution and shear, and accuracy of counting successively diluted nuclei suspensions was verified with (1) visual counting in a hemocytometer after staining with crystal violet, and automatic counting by (2) aperture electrical resistance measurement and (3) flow cytometer measurement after staining...
54.
Some exact properties of the effective slip over surfaces with hydrophobic patternings - Six, Pierre; Kamrin, Kenneth N.
Shear flows of viscous fluid layers over nonuniformly hydrophobic surfaces are characterized in the far-field by an effective slip velocity, which relates to the applied stress through some mobility tensor characterizing the surface. Here, we identify two methods to determine the mobility tensor for flat surfaces with arbitrary slip-length variations. A family of “Cross Flow Identities” is then analyzed, which equate mobility components of different unidirectional patternings. We also calculate an analytical mobility solution for a family of continuously varying patterns. We validate the results numerically and discuss implications in various limits.
55.
Forecast-Based Decision Support for San Francisco International Airport: A NextGen Prototype System That Improves Operations during Summer Stratus Season - Reynolds, David W.; Clark, David A.; Wilson, Charles F.; Cook, Lara
During summer, marine stratus encroaches into the approach to San Francisco International Airport (SFO) bringing low ceilings. Low ceilings restrict landings and result in a high number of arrival delays, thus impacting the National Air Space (NAS). These delays are managed by implementation of ground delay programs (GDPs), which hold traffic on the ground at origination airports in anticipation of insufficient arrival capacity at SFO. In an effort to reduce delays and improve both airport and NAS efficiency, the Federal Aviation Administration (FAA) funded a research effort begun in 1995 to develop an objective decision support system to aid forecasters...
56.
Sulfur isotopes of organic matter preserved in 3.45-billion-year-old stromatolites reveal microbial metabolism - Bontognali, Tomaso R. R.; Sessions, Alex L.; Allwood, Abigail C.; Fischer, Woodward W.; Grotzinger, John P.; Summons, Roger Everett; Eiler, John M.
The 3.45-billion-year-old Strelley Pool Formation of Western Australia preserves stromatolites that are considered among the oldest evidence for life on Earth. In places of exceptional preservation, these stromatolites contain laminae rich in organic carbon, interpreted as the fossil remains of ancient microbial mats. To better understand the biogeochemistry of these rocks, we performed microscale in situ sulfur isotope measurements of the preserved organic sulfur, including both Δ33S and [superscript 34]S[subscript CDT]. This approach allows us to tie physiological inference from isotope ratios directly to fossil biomass, providing a means to understand sulfur metabolism that is complimentary to, and independent from,...
57.
Effects of dopamine depletion on LFP oscillations in striatum are task- and learning-dependent and selectively reversed by l-DOPA - Lemaire, Nune; Ledia, F. Hernandez; Hu, Dan; Kubota, Yasuo; Howe, Mark William; Graybiel, Ann M.
A major physiologic sign in Parkinson disease is the occurrence of abnormal oscillations in cortico-basal ganglia circuits, which can be normalized by l-DOPA therapy. Under normal circumstances, oscillatory activity in these circuits is modulated as behaviors are learned and performed, but how dopamine depletion affects such modulation is not yet known. We here induced unilateral dopamine depletion in the sensorimotor striatum of rats and then recorded local field potential (LFP) activity in the dopamine-depleted region and its contralateral correspondent as we trained the rats on a conditional T-maze task. Unexpectedly, the dopamine depletion had little effect on oscillations recorded in...
58.
Genetic Programs Constructed from Layered Logic Gates in Single Cells - Moon, Tae Seok; Lou, Chunbo; Tamsir, Alvin; Stanton, Brynne Christine; Voigt, Christopher A.
Genetic programs function to integrate environmental sensors, implement signal processing algorithms and control expression dynamics[1]. These programs consist of integrated genetic circuits that individually implement operations ranging from digital logic to dynamic circuits[2, 3, 4, 5, 6], and they have been used in various cellular engineering applications, including the implementation of process control in metabolic networks and the coordination of spatial differentiation in artificial tissues. A key limitation is that the circuits are based on biochemical interactions occurring in the confined volume of the cell, so the size of programs has been limited to a few circuits[1, 7]. Here we...
59.
α[subscript v]β[subscript 3] Integrin-Targeted PLGA-PEG Nanoparticles for Enhanced Anti-tumor Efficacy of a Pt(IV) Prodrug - Graf, Nora; Bielenberg, Diane R.; Kolishetti, Nagesh; Muus, Christoph; Banyard, Jacqueline; Farokhzad, Omid C.; Lippard, Stephen J.
Targeted delivery of therapeutics to tumor neovasculature is potentially a powerful approach for selective cancer treatment. Integrins are heterodimeric transmembrane proteins involved in cell adhesion and cell signaling, and their expression is commonly upregulated in cancers and inflammatory diseases. The α[subscript v]β[subscript 3] integrin is differentially upregulated on angiogenic endothelial cells as well as on many cancer cells. Here we demonstrate the differential targeting of cisplatin prodrug-encapsulated poly(d,l-lactic-co-glycolic acid)-block-polyethylene glycol (PLGA-PEG) nanoparticles (NPs) to the α[subscript v]β[subscript 3] integrin on cancer cells using the cyclic pentapeptide c(RGDfK). Cisplatin is one of the most widely used anticancer drugs, and approaches that...
60.
Cell-surface sensors for real-time probing of cellular environments - Zhao, Weian; Schafer, Sebastian; Choi, Jonghoon; Yamanaka, Yvonne Joy; Lombardi, Maria L.; Bose, Suman; Carlson, Alicia L.; Phillips, Joseph A.; Teo, Weisuong; Droujinine, Ilia A.; Cui, Cheryl H.; Jain, Rakesh K.; Lammerding, Jan; Love, J. Christopher; Lin, Charles P.; Sarkar, Debanjan; Karnik, Rohit; Karp, Jeffrey M.
The ability to explore cell signalling and cell-to-cell communication is essential for understanding cell biology and developing effective therapeutics. However, it is not yet possible to monitor the interaction of cells with their environments in real time. Here, we show that a fluorescent sensor attached to a cell membrane can detect signalling molecules in the cellular environment. The sensor is an aptamer (a short length of single-stranded DNA) that binds to platelet-derived growth factor (PDGF) and contains a pair of fluorescent dyes. When bound to PDGF, the aptamer changes conformation and the dyes come closer to each other, producing a...
41.
