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MIT Open Access Articles

Mostrando recursos 41 - 60 de 26.052

  1. Optimization of the Thermoelectric Figure of Merit in Crystalline C₆₀ with Intercalation Chemistry

    Kim, Jeong Yun; Grossman, Jeffrey C.
    Crystalline C₆₀ is an appealing candidate material for thermoelectric (TE) applications due to its extremely low thermal conductivity and potentially high electrical conductivity with metal atom intercalation. We investigate the TE properties of crystalline C₆₀ intercalated with alkali and alkaline earth metals using both classical and quantum mechanical calculations. For the electronic structure, our results show that variation of intercalated metal atoms has a large impact on energy dispersions, which leads to broad tunability of the power factor. For the thermal transport, we show that dopants introduce strong phonon scattering into crystalline C₆₀, leading to considerably lower thermal conductivity. Taking...

  2. Prolonged energy harvesting for ingestible devices

    Nadeau, Phillip; El-Damak, Dina Reda; Glettig, Dean; Kong, Yong Lin; Mo, Stacy H.; Cleveland, Cody; Booth, Lucas; Roxhed, Niclas; Langer, Robert S; Chandrakasan, Anantha P; Traverso, Carlo Giovanni
    Ingestible electronics have revolutionized the standard of care for a variety of health conditions. Extending the capacity and safety of these devices, and reducing the costs of powering them, could enable broad deployment of prolonged-monitoring systems for patients. Although previous biocompatible power-harvesting systems for in vivo use have demonstrated short (minute-long) bursts of power from the stomach, little is known about the potential for powering electronics in the longer term and throughout the gastrointestinal tract. Here, we report the design and operation of an energy-harvesting galvanic cell for continuous in vivo temperature sensing and wireless communication. The device delivered an...

  3. Prolonged energy harvesting for ingestible devices

    Nadeau, Phillip; El-Damak, Dina Reda; Glettig, Dean; Kong, Yong Lin; Mo, Stacy H.; Cleveland, Cody; Booth, Lucas; Roxhed, Niclas; Langer, Robert S; Chandrakasan, Anantha P; Traverso, Carlo Giovanni
    Ingestible electronics have revolutionized the standard of care for a variety of health conditions. Extending the capacity and safety of these devices, and reducing the costs of powering them, could enable broad deployment of prolonged-monitoring systems for patients. Although previous biocompatible power-harvesting systems for in vivo use have demonstrated short (minute-long) bursts of power from the stomach, little is known about the potential for powering electronics in the longer term and throughout the gastrointestinal tract. Here, we report the design and operation of an energy-harvesting galvanic cell for continuous in vivo temperature sensing and wireless communication. The device delivered an...

  4. Red InGaP light-emitting diodes epitaxially grown on engineered Ge-on-Si substrates

    Wang, Bing; Wang, Cong; Lee, Kwang Hong; Bao, Shuyu; Lee, Kenneth Eng Kian; Tan, Chuan Seng; Yoon, Soon Fatt; Michel, Jurgen; Fitzgerald, Eugene A
    The integration of light emitting devices on silicon substrates has attracted intensive research for many years. In contrast to the InGaN light emitting diodes (LEDs) whose epitaxy technology on Si substrates is robust and mature, the epitaxy of other compound semiconductor light emitting materials covering the visible wavelength range on Si is still challenging. We have studied epitaxial growth of red InGaP light emitting materials on engineered Ge-on-Si substrates. Ge-on-Si was grown on 8'' Si substrates in a metal organic chemical vapour deposition (MOCVD) reactor using two- step growth and cycling annealing. Threading dislocation densities (TDDs) were controlled to as...

  5. Red InGaP light-emitting diodes epitaxially grown on engineered Ge-on-Si substrates

    Wang, Bing; Wang, Cong; Lee, Kwang Hong; Bao, Shuyu; Lee, Kenneth Eng Kian; Tan, Chuan Seng; Yoon, Soon Fatt; Michel, Jurgen; Fitzgerald, Eugene A
    The integration of light emitting devices on silicon substrates has attracted intensive research for many years. In contrast to the InGaN light emitting diodes (LEDs) whose epitaxy technology on Si substrates is robust and mature, the epitaxy of other compound semiconductor light emitting materials covering the visible wavelength range on Si is still challenging. We have studied epitaxial growth of red InGaP light emitting materials on engineered Ge-on-Si substrates. Ge-on-Si was grown on 8'' Si substrates in a metal organic chemical vapour deposition (MOCVD) reactor using two- step growth and cycling annealing. Threading dislocation densities (TDDs) were controlled to as...

  6. Reduction of threading dislocation density in Ge/Si using a heavily As-doped Ge seed layer

    Lee, Kwang Hong; Bao, Shuyu; Wang, Bing; Wang, Cong; Yoon, Soon Fatt; Tan, Chuan Seng; Michel, Jurgen; Fitzgerald, Eugene A
    High quality germanium (Ge) epitaxial film is grown directly on silicon (001) substrate with 6° off-cut using a heavily arsenic (As) doped Ge seed layer. The growth steps consists of (i) growth of a heavily As-doped Ge seed layer at low temperature (LT, at 400°C), (ii) Ge growth with As gradually reduced to zero at high temperature (HT, at 650°C), (iii) pure Ge growth at HT. This is followed by thermal cyclic annealing in hydrogen at temperature ranging from 600 to 850°C. Analytical characterization have shown that the Ge epitaxial film with a thickness of ∼1.5 μm experiences thermally induced...

  7. Reduction of threading dislocation density in Ge/Si using a heavily As-doped Ge seed layer

    Lee, Kwang Hong; Bao, Shuyu; Wang, Bing; Wang, Cong; Yoon, Soon Fatt; Tan, Chuan Seng; Michel, Jurgen; Fitzgerald, Eugene A
    High quality germanium (Ge) epitaxial film is grown directly on silicon (001) substrate with 6° off-cut using a heavily arsenic (As) doped Ge seed layer. The growth steps consists of (i) growth of a heavily As-doped Ge seed layer at low temperature (LT, at 400°C), (ii) Ge growth with As gradually reduced to zero at high temperature (HT, at 650°C), (iii) pure Ge growth at HT. This is followed by thermal cyclic annealing in hydrogen at temperature ranging from 600 to 850°C. Analytical characterization have shown that the Ge epitaxial film with a thickness of ∼1.5 μm experiences thermally induced...

  8. Thermal conductivity of GaAs/Ge nanostructures

    Jia, Roger Qingfeng; Zeng, Lingping; Chen, Gang; Fitzgerald, Eugene A
    Superlattices are of great interest as platform materials for thermoelectric technology that are capable of directly converting low-grade heat energy into useful electrical power. In this work, the thermal conductivities of GaAs/Ge superlattice nanostructures were investigated systematically in relation to their morphologies and interfaces. Thermal conductivities were measured using ultrafast time-domain thermoreflectance and were found to decrease with increasing interface densities, consistent with past understanding of microscopic phonon transport in the particle regime. The lowest thermal conductivities were observed in (GaAs)[subscript 0.77](Ge₂)[subscript 0.23] alloys, and transmission electron microscopy study reveals phase separation in the alloys. These alloys can be interpreted...

  9. Thermal conductivity of GaAs/Ge nanostructures

    Jia, Roger Qingfeng; Zeng, Lingping; Chen, Gang; Fitzgerald, Eugene A
    Superlattices are of great interest as platform materials for thermoelectric technology that are capable of directly converting low-grade heat energy into useful electrical power. In this work, the thermal conductivities of GaAs/Ge superlattice nanostructures were investigated systematically in relation to their morphologies and interfaces. Thermal conductivities were measured using ultrafast time-domain thermoreflectance and were found to decrease with increasing interface densities, consistent with past understanding of microscopic phonon transport in the particle regime. The lowest thermal conductivities were observed in (GaAs)[subscript 0.77](Ge₂)[subscript 0.23] alloys, and transmission electron microscopy study reveals phase separation in the alloys. These alloys can be interpreted...

  10. Digital design of multimaterial photonic particles

    Tao, Guangming; Kaufman, Joshua J.; Shabahang, Soroush; Rezvani Naraghi, Roxana; Sukhov, Sergey V.; Dogariu, Aristide; Abouraddy, Ayman F.; Joannopoulos, John; Fink, Yoel
    Scattering of light from dielectric particles whose size is on the order of an optical wavelength underlies a plethora of visual phenomena in nature and is a foundation for optical coatings and paints. Tailoring the internal nanoscale geometry of such "photonic particles" allows tuning their optical scattering characteristics beyond those afforded by their constitutive materials - however, flexible yet scalable processing approaches to produce such particles are lacking. Here, we show that a thermally induced in-fiber fluid instability permits the "digital design" of multimaterial photonic particles: the precise allocation of high refractive-index contrast materials at independently addressable radial and azimuthal...

  11. Enriched Protein Screening of Human Bone Marrow Mesenchymal Stromal Cell Secretions Reveals MFAP5 and PENK as Novel IL-10 Modulators

    Elman, Jessica S; Shen, Keyue; Gabow, Aaron; Yarmush, Joshua; Jiao, Yunxin; Fletcher, Anne; Lee, Jungwoo; Yarmush, Martin L; Parekkadan, Biju; Milwid, Jack Miles; Li, Matthew; Manrai, Arjun Kumar; Cima, Michael J
    The secreted proteins from a cell constitute a natural biologic library that can offer significant insight into human health and disease. Discovering new secreted proteins from cells is bounded by the limitations of traditional separation and detection tools to physically fractionate and analyze samples. Here, we present a new method to systematically identify bioactive cell-secreted proteins that circumvent traditional proteomic methods by first enriching for protein candidates by differential gene expression profiling. The bone marrow stromal cell secretome was analyzed using enriched gene expression datasets in combination with potency assay testing. Four proteins expressed by stromal cells with previously unknown...

  12. First

    Calligaris, David; Methuku, Kashi Reddy; Poe, MichaelM.; Francois, Jessica Pierre; Tranghese, Frank; Changelian, Armen; Sieghart, Werner; Ernst, Margot; Pomeranz Krummel, Daniel A.; Cook, M. James; Pomeroy, Scott L.; Agar, Nathalie Y. R.; Sengupta, Soma; Poe, Michael M.; Jonas, Oliver H.; Cima, Michael J; Langer, Robert S
    Medulloblastoma is the most common childhood malignant brain tumor. The most lethal medulloblastoma subtype exhibits a high expression of the GABA A receptor α5 subunit gene and MYC amplification. New benzodiazepines have been synthesized to function asα5-GABA A receptor ligands. To compare their efficacy with that of standard-of-care treatments, we have employed a newly developed microscale implantable device that allows for high-throughput localized intratumor drug delivery and efficacy testing. Microdoses of each drug were delivered into small distinct regions of tumors, as confirmed by tissue mass spectrometry, and the local drug effect was determined by immunohistochemistry. We have identified a...

  13. Correction for Upadhyay et al., Intracranial microcapsule chemotherapy delivery for the localized treatment of rodent metastatic breast adenocarcinoma in the brain

    Upadhyay, Urvashi M.; Tyler, Betty; Wicks, Robert; Upadhyay, Urvashi M.; Tyler, Betty; Patta, Yoda; Wicks, Robert; Hwang, Lee; Grossman, Rachel; Brem, Henry; Patta, Yoda Rante; Spencer, Kevin C; Scott, Alexander Wesley; Masi, Byron Colley; Cima, Michael J; Langer, Robert S
    Correction for “Intracranial microcapsule chemotherapy delivery for the localized treatment of rodent metastatic breast adenocarcinoma in the brain,” by Urvashi M. Upadhyay, Betty Tyler, Yoda Patta, Robert Wicks, Kevin Spencer, Alexander Scott, Byron Masi, Lee Hwang, Rachel Grossman, Michael Cima, Henry Brem, and Robert Langer, which appeared in issue 45, November 11, 2014, of Proc Natl Acad Sci USA (111:16071–16076; first published October 27, 2014, 10.1073/pnas.1313420110).

  14. Enforcement of developmental lineage specificity by transcription factor Oct1

    Shen, Zuolian; Kang, Jinsuk; Shakya, Arvind; Tabaka, Marcin; Jarboe, Elke A; Tantin, Dean; Regev, Aviv
    Embryonic stem cells co-express Oct4 and Oct1, a related protein with similar DNA-binding specificity. To study the role of Oct1 in ESC pluripotency and transcriptional control, we constructed germline and inducible-conditional Oct1-deficient ESC lines. ESCs lacking Oct1 show normal appearance, self-renewal and growth but manifest defects upon differentiation. They fail to form beating cardiomyocytes, generate neurons poorly, form small, poorly differentiated teratomas, and cannot generate chimeric mice. Upon RA-mediated differentiation, Oct1-deficient cells induce lineage-appropriate developmentally poised genes poorly while lineage-inappropriate genes, including extra-embryonic genes, are aberrantly expressed. In ESCs, Oct1 co-occupies a specific set of targets with Oct4, but does...

  15. Characterization of Mechanically Matched Hydrogel Coatings to Improve the Biocompatibility of Neural Implants

    Spencer, Kevin C; Sy, Jay C.; Ramadi, Khalil; Graybiel, Ann M; Langer, Robert S; Cima, Michael J
    Glial scar is a significant barrier to neural implant function. Micromotion between the implant and tissue is suspected to be a key driver of glial scar formation around neural implants. This study explores the ability of soft hydrogel coatings to modulate glial scar formation by reducing local strain. PEG hydrogels with controllable thickness and elastic moduli were formed on the surface of neural probes. These coatings significantly reduced the local strain resulting from micromotion around the implants. Coated implants were found to significantly reduce scarring in vivo, compared to hard implants of identical diameter. Increasing implant diameter was found to...

  16. Characterization of Mechanically Matched Hydrogel Coatings to Improve the Biocompatibility of Neural Implants

    Spencer, Kevin C; Sy, Jay C.; Ramadi, Khalil; Graybiel, Ann M; Langer, Robert S; Cima, Michael J
    Glial scar is a significant barrier to neural implant function. Micromotion between the implant and tissue is suspected to be a key driver of glial scar formation around neural implants. This study explores the ability of soft hydrogel coatings to modulate glial scar formation by reducing local strain. PEG hydrogels with controllable thickness and elastic moduli were formed on the surface of neural probes. These coatings significantly reduced the local strain resulting from micromotion around the implants. Coated implants were found to significantly reduce scarring in vivo, compared to hard implants of identical diameter. Increasing implant diameter was found to...

  17. Synergistic interactions with PI3K inhibition that induce apoptosis

    Zwang, Yaara; Chen, Casandra; Rinne, Mikael L; Doench, John G; Piccioni, Federica; Tan, Li; Huang, Hai-Tsang; Wang, Jinhua; Ham, Young Jin; O'Connell, Joyce; Bhola, Patrick; Doshi, Mihir; Whitman, Matthew; Letai, Anthony; Root, David E; Gray, Nathanael; Hahn, William C; Jonas, Oliver H.; Cima, Michael J; Langer, Robert S
    Activating mutations involving the PI3K pathway occur frequently in human cancers. However, PI3K inhibitors primarily induce cell cycle arrest, leaving a significant reservoir of tumor cells that may acquire or exhibit resistance. We searched for genes that are required for the survival of PI3K mutant cancer cells in the presence of PI3K inhibition by conducting a genome scale shRNA-based apoptosis screen in a PIK3CA mutant human breast cancer cell. We identified 5 genes (PIM2, ZAK, TACC1, ZFR, ZNF565) whose suppression induced cell death upon PI3K inhibition. We showed that small molecule inhibitors of the PIM2 and ZAK kinases synergize with...

  18. Synergistic interactions with PI3K inhibition that induce apoptosis

    Zwang, Yaara; Chen, Casandra; Rinne, Mikael L; Doench, John G; Piccioni, Federica; Tan, Li; Huang, Hai-Tsang; Wang, Jinhua; Ham, Young Jin; O'Connell, Joyce; Bhola, Patrick; Doshi, Mihir; Whitman, Matthew; Letai, Anthony; Root, David E; Gray, Nathanael; Hahn, William C; Jonas, Oliver H.; Cima, Michael J; Langer, Robert S
    Activating mutations involving the PI3K pathway occur frequently in human cancers. However, PI3K inhibitors primarily induce cell cycle arrest, leaving a significant reservoir of tumor cells that may acquire or exhibit resistance. We searched for genes that are required for the survival of PI3K mutant cancer cells in the presence of PI3K inhibition by conducting a genome scale shRNA-based apoptosis screen in a PIK3CA mutant human breast cancer cell. We identified 5 genes (PIM2, ZAK, TACC1, ZFR, ZNF565) whose suppression induced cell death upon PI3K inhibition. We showed that small molecule inhibitors of the PIM2 and ZAK kinases synergize with...

  19. Electrochemical Charge Transfer Reaction Kinetics at the Silicon-Liquid Electrolyte Interface

    Swamy, Tushar; Chiang, Yet-Ming
    Since the gravimetric lithiation capacity of silicon is roughly ten times that of graphite, while their mass densities are comparable, for the same particle size the current density required to cycle a silicon electrode at a given C-rate is about ten times greater than that of graphite. Depending on the magnitude of the corresponding Butler-Volmer exchange current density, jo, such high current densities may cause the charge transfer kinetics at the silicon-electrolyte interface to become rate limiting. Previously reported values of jo for Si differ by about 10 orders of magnitude. Here we report jo measurements using electrochemical impedance spectroscopy...

  20. Electrochemical Charge Transfer Reaction Kinetics at the Silicon-Liquid Electrolyte Interface

    Swamy, Tushar; Chiang, Yet-Ming
    Since the gravimetric lithiation capacity of silicon is roughly ten times that of graphite, while their mass densities are comparable, for the same particle size the current density required to cycle a silicon electrode at a given C-rate is about ten times greater than that of graphite. Depending on the magnitude of the corresponding Butler-Volmer exchange current density, jo, such high current densities may cause the charge transfer kinetics at the silicon-electrolyte interface to become rate limiting. Previously reported values of jo for Si differ by about 10 orders of magnitude. Here we report jo measurements using electrochemical impedance spectroscopy...

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