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DSpace at MIT (78,135 recursos)
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MIT Open Access Articles

Mostrando recursos 1 - 20 de 14,251

1. Quantum Spin Hall Effect and Topological Field Effect Transistor in Two-Dimensional Transition Metal Dichalcogenides - Qian, Xiaofeng; Liu, Junwei; Fu, Liang; Li, Ju
Quantum spin Hall (QSH) effect materials feature edge states that are topologically protected from backscattering. However, the small band gap in materials that have been identified as QSH insulators limits applications. We use first-principles calculations to predict a class of large-gap QSH insulators in two-dimensional transition metal dichalcogenides with 1T′ structure, namely, 1T′-MX[subscript 2] with M = (W, Mo) and X = (Te, Se, S). A structural distortion causes an intrinsic band inversion between chalcogenide-p and metal-d bands. Additionally, spin-orbit coupling opens a gap that is tunable by vertical electric field and strain. We propose a topological field effect transistor...

2. A Nanoparticle-Based Combination Chemotherapy Delivery System for Enhanced Tumor Killing by Dynamic Rewiring of Signaling Pathways - Morton, Stephen Winford; Lee, Michael J.; Deng, Zhou J.; Dreaden, Erik Christopher; Siouve, Elise; Shopsowitz, Kevin; Shah, Nisarg J.; Yaffe, Michael B.; Hammond, Paula T.
Exposure to the EGFR (epidermal growth factor receptor) inhibitor erlotinib promotes the dynamic rewiring of apoptotic pathways, which sensitizes cells within a specific period to subsequent exposure to the DNA-damaging agent doxorubicin. A critical challenge for translating this therapeutic network rewiring into clinical practice is the design of optimal drug delivery systems. We report the generation of a nanoparticle delivery vehicle that contained more than one therapeutic agent and produced a controlled sequence of drug release. Liposomes, representing the first clinically approved nanomedicine systems, are well-characterized, simple, and versatile platforms for the manufacture of functional and tunable drug carriers. Using...

3. A Latent Source Model for Online Collaborative Filtering - Bresler, Guy; Chen, George; Shah, Devavrat
Despite the prevalence of collaborative filtering in recommendation systems, there has been little theoretical development on why and how well it works, especially in the “online” setting, where items are recommended to users over time. We address this theoretical gap by introducing a model for online recommendation systems, cast item recommendation under the model as a learning problem, and analyze the performance of a cosine-similarity collaborative filtering method. In our model, each of n users either likes or dislikes each of m items. We assume there to be k types of users, and all the users of a given type...

4. Studies of jet quenching using isolated-photon+jet correlations in PbPb and pp collisions at √ sNN=2.76 TeV - Bauer, Gerry P.; Bendavid, Joshua L.; Busza, Wit; Butz, Erik M.; Cali, Ivan Amos; Chan, M.; Dutta, Valentina; Gomez-Ceballos, Guillelmo; Goncharov, Maxim; Hahn, Kristian Allan; Kim, Yongsun; Klute, Markus; Li, Wei; Luckey, P. David; Ma, Teng; Nahn, Steven; Paus, Christoph M. E.; Ralph, Duncan Kelley; Roland, Christof E.; Roland, Gunther M.; Rudolph, Matthew Scott; Stephans, George S. F.; Stoeckli, Fabian; Sumorok, Konstanty C.; Sung, Kevin Kai Hong; Velicanu, Dragos Alexandru; Wenger, Edward Allen; Wolf, R.; Wyslouch, Boleslaw; Xie, Si; Yang, Mingming; Yilmaz, Yetkin; Yoon, Andre S.; Zanetti, Marco; CMS Collaboration
Results from the first study of isolated-photon + jet correlations in relativistic heavy ion collisions are reported. The analysis uses data from PbPb collisions at a centre-of-mass energy of 2.76 TeV per nucleon pair corresponding to an integrated luminosity of 150 μb−1 recorded by the CMS experiment at the LHC. For events containing an isolated photon with transverse momentum pγ[over]T >60 GeV/c and an associated jet with pJet[over]T>30 GeV/c, the photon + jet pT imbalance is studied as a function of collision centrality and compared to pp data and pythia calculations at the same collision energy. Using the pγ[over]T of...

5. Virus-templated Au and Au–Pt core–shell nanowires and their electrocatalytic activities for fuel cell applications - Lee, Youjin; Kim, Junhyung; Yun, Dong Soo; Nam, Yoon Sung; Shao-Horn, Yang; Belcher, Angela M.
A facile synthetic route was developed to make Au nanowires (NWs) from surfactant-mediated bio-mineralization of a genetically engineered M13 phage with specific Au binding peptides. From the selective interaction between Au binding M13 phage and Au ions in aqueous solution, Au NWs with uniform diameter were synthesized at room temperature with yields greater than 98% without the need for size selection. The diameters of Au NWs were controlled from 10 nm to 50 nm. The Au NWs were found to be active for electrocatalytic oxidation of CO molecules for all sizes, where the activity was highly dependent on the surface...

6. Magnetic interactions in 3d metal chains on Cu[subscript 2]X/Cu(001) (X = N, O): Comparison with corresponding unsupported chains - Urdaniz, M. C.; Barral, M. A.; Llois, A. M.; Saul, Alberto Andres
In this work we present a systematic study of the magnetic interactions within 3d transition-metal chains adsorbed on Cu[subscript 2]N and Cu[subscript 2]O monolayers grown on Cu(001). We are interested in the particular geometric adsorption configuration which gives rise, after relaxation, to the development of diatomic TM - X(X = N, O) chains. By using density functional theory (DFT), we calculate the energy difference between the ferromagnetic and antiferromagnetic intrachain configurations for Ti, V, Cr, Mn, Fe, and Co. Both substrates give rise, with minor differences, to the same magnetic trends, the only chains which are ferromagnetic after adsorption are...

7. Fixed-Point Quantum Search with an Optimal Number of Queries - Low, Guang Hao; Yoder, Theodore James; Chuang, Isaac
Grover’s quantum search and its generalization, quantum amplitude amplification, provide a quadratic advantage over classical algorithms for a diverse set of tasks but are tricky to use without knowing beforehand what fraction λ of the initial state is comprised of the target states. In contrast, fixed-point search algorithms need only a reliable lower bound on this fraction but, as a consequence, lose the very quadratic advantage that makes Grover’s algorithm so appealing. Here we provide the first version of amplitude amplification that achieves fixed-point behavior without sacrificing the quantum speedup. Our result incorporates an adjustable bound on the failure probability...

8. Deterministic coupling of a single atom to a nanoscale optical cavity - Thompson, J. D.; Tiecke, T. G.; de Leon, N. P.; Feist, J.; Akimov, A. V.; Gullans, M.; Zibrov, A. S.; Lukin, M. D.; Vuletic, Vladan
Hybrid quantum devices, in which dissimilar quantum systems are combined in order to attain qualities not available with either system alone, may enable far-reaching control in quantum measurement, sensing, and information processing. A paradigmatic example is trapped ultracold atoms, which offer excellent quantum coherent properties, coupled to nanoscale solid-state systems, which allow for strong interactions. We demonstrate a deterministic interface between a single trapped rubidium atom and a nanoscale photonic crystal cavity. Precise control over the atom's position allows us to probe the cavity near-field with a resolution below the diffraction limit and to observe large atom-photon coupling. This approach...

9. All-Optical Switch and Transistor Gated by One Stored Photon - Chen, Wenlan; Beck, Kristin Marie; Bucker, Robert; Gullans, Michael; Lukin, Mikhail D.; Tanji-Suzuki, Haruka; Vuletic, Vladan
The realization of an all-optical transistor, in which one “gate” photon controls a “source” light beam, is a long-standing goal in optics. By stopping a light pulse in an atomic ensemble contained inside an optical resonator, we realized a device in which one stored gate photon controls the resonator transmission of subsequently applied source photons. A weak gate pulse induces bimodal transmission distribution, corresponding to zero and one gate photons. One stored gate photon produces fivefold source attenuation and can be retrieved from the atomic ensemble after switching more than one source photon. Without retrieval, one stored gate photon can...

10. Resonant bonding leads to low lattice thermal conductivity - Lee, Sangyeop; Esfarjani, Keivan; Luo, Tengfei; Zhou, Jiawei; Tian, Zhiting; Chen, Gang
Understanding the lattice dynamics and low thermal conductivities of IV–VI, V[subscript 2]–VI[subscript 3] and V materials is critical to the development of better thermoelectric and phase-change materials. Here we provide a link between chemical bonding and low thermal conductivity. Our first-principles calculations reveal that long-ranged interaction along the 〈100〉 direction of the rocksalt structure exist in lead chalcogenides, SnTe, Bi[subscript 2]Te[subscript 3], Bi and Sb due to the resonant bonding that is common to all of them. This long-ranged interaction in lead chalcogenides and SnTe cause optical phonon softening, strong anharmonic scattering and large phase space for three-phonon scattering processes,...

11. Solar nebula magnetic fields recorded in the Semarkona meteorite - Fu, Roger Rennan; Weiss, Benjamin P.; Andrade Lima, Eduardo; Harrison, Richard J.; Bai, Xue-Ning; Desch, Steven J.; Ebel, Denton S.; Suavet, Clement Romain; Wang, Huapei; Glenn, David; Le Sage, David; Kasama, Takeshi; Walsworth, Ronald L.; Kuan, Aaron T.
Magnetic fields are proposed to have played a critical role in some of the most enigmatic processes of planetary formation by mediating the rapid accretion of disk material onto the central star and the formation of the first solids. However, there have been no experimental constraints on the intensity of these fields. Here we show that dusty olivine-bearing chondrules from the Semarkona meteorite were magnetized in a nebular field of 54 ± 21 μT. This intensity supports chondrule formation by nebular shocks or planetesimal collisions rather than by electric currents, the x-wind, or other mechanisms near the sun. This implies...

12. Continuum Modeling of Secondary Rheology in Dense Granular Materials - Henann, David L.; Kamrin, Kenneth N.
Recent dense granular flow experiments have shown that shear deformation in one region of a granular medium fluidizes its entirety, including regions far from the sheared zone, effectively erasing the yield condition everywhere. This enables slow creep deformation to occur when an external force is applied to a probe in the nominally static regions of the material. The apparent change in rheology induced by far-away motion is termed the “secondary rheology,” and a theoretical rationalization of this phenomenon is needed. Recently, a new nonlocal granular rheology was successfully used to predict steady granular flow fields, including grain-size-dependent shear-band widths in...

13. Band structure engineering through orbital interaction for enhanced thermoelectric power factor - Zhu, Hong; Sun, Wenhao; Armiento, Rickard; Lazic, Predrag; Ceder, Gerbrand
Band structure engineering for specific electronic or optical properties is essential for the further development of many important technologies including thermoelectrics, optoelectronics, and microelectronics. In this work, we report orbital interaction as a powerful tool to finetune the band structure and the transport properties of charge carriers in bulk crystalline semiconductors. The proposed mechanism of orbital interaction on band structure is demonstrated for IV-VI thermoelectric semiconductors. For IV-VI materials, we find that the convergence of multiple carrier pockets not only displays a strong correlation with the s-p and spin-orbit coupling but also coincides with the enhancement of power factor. Our...

14. Synthesis and Lithiation Mechanisms of Dirutile and Rutile LiMnF4: Two New Conversion Cathode Materials - Twu, Nancy H.; Li, Xin; Moore, Charles J.; Ceder, Gerbrand
Driven by the need for new cathode battery materials with high energy density, fluorides have emerged as promising candidates due to their high voltages. From high throughput computations, dirutile LiMnF4 was identified as a promising cathode with a high conversion voltage and a theoretical specific capacity of 584 mAh/g. In this work, we study the formation of dirutile LiMnF4 through a new, low-temperature synthesis route and report its electrochemical properties. We also report the discovery of a new rutile polymorph of LiMnF4 which has Li-Mn disorder on the cation site. Electron diffraction confirmed both dirutile and rutile LiMnF4 to convert...

15. Electrochemical Properties of Li3Fe0.2Mn0.8CO3PO4 as a Li-Ion Battery Cathode - Matts, Ian L.; Chen, Hailong; Ceder, Gerbrand
Previously conducted high-throughput ab initio calculations have identified carbonophosphates as a new class of polyanion cathode materials. Li3MnCO3PO4 is the most promising candidate due to its high theoretical capacity and ideal voltage range. However, a major limitation of this material is its poor cyclability and experimentally observed capacity. In this work we synthesize Li3Fe0.2Mn0.8CO3PO4 to combine the high theoretical capacity of Li3MnCO3PO4 with the high cyclability of Li3FeCO3PO4. Li3Fe0.2Mn0.8CO3PO4 outperforms Li3MnCO3PO4 in cyclability, and shows little capacity fade over 25 cycles. The observed reversible capacity of 105 mAh/g is slightly greater than in Li3FeCO3PO4, and occurs at a higher average...

16. A Critical Review of the Li Insertion Mechanisms in LiFePO[subscript 4] Electrodes - Malik, Rahul; Abdellahi, Aziz; Ceder, Gerbrand
With the ever-growing public and now commercial sentiment supporting the widespread adoption of low and zero-emission vehicles, it is unsurprising that Li-ion batteries which currently assume the bulk of the cost of electrified vehicles (a significant proportion coming from cost of battery materials) have become prolific not only in the primary research literature but have also entered the general public consciousness. Since the initial work in 1997, over 2000 research publications have been authored on lithium iron phosphate (LiFePO[subscript 4]), one of only a handful of commercially viable Li-ion battery cathode materials currently used in electrified vehicles. Despite the sheer...

17. First-principles insights on the magnetism of cubic SrTi1−xCoxO3−δ - Florez Uribe, Juan Manuel; Ong, S. P.; Onbasli, Mehmet Cengiz; Dionne, Gerald F.; Vargas, P.; Ceder, Gerbrand; Ross, Caroline A.
We present hybrid density functional calculations suggesting that magnetism in cubic SrTi1 − x Co x O3 − δ (STCO) with x = 0.25 is sensitive to the nearest neighbor arrangement of the Co and the presence of oxygen vacancies. Spin polarized calculations for x = 0.25 in which the nearest neighbor (nn) Co spacing is a, 2√a or 3√a with a the lattice parameter predict lowest energies for the 2√a nn separation and favor the ferromagnetic state. Oxygen deficiency (δ=0.125) lowers the average Co valence state and favors mixed valence and spin states (high spin for the Co adjacent to the vacancy and...

18. Charmed bottom baryon spectroscopy from lattice QCD - Brown, Zachary S.; Detmold, William; Meinel, Stefan; Orginos, Kostas
We calculate the masses of baryons containing one, two, or three heavy quarks using lattice QCD. We consider all possible combinations of charm and bottom quarks, and compute a total of 36 different states with J[superscript P] = [1+ over 2] and J[superscript P] = [3+ over 2]. We use domain-wall fermions for the up, down, and strange quarks, a relativistic heavy-quark action for the charm quarks, and nonrelativistic QCD for the bottom quarks. Our analysis includes results from two different lattice spacings and seven different pion masses. We perform extrapolations of the baryon masses to the continuum limit and...

19. Anisotropic Complementary Acoustic Metamaterial for Canceling out Aberrating Layers - Shen, Chen; Xu, Jun; Jing, Yun; Fang, Nicholas Xuanlai
In this paper, we investigate a type of anisotropic, acoustic complementary metamaterial (CMM) and its application in restoring acoustic fields distorted by aberrating layers. The proposed quasi two-dimensional (2D), nonresonant CMM consists of unit cells formed by membranes and side branches with open ends. Simultaneously, anisotropic and negative density is achieved by assigning membranes facing each direction (x and y directions) different thicknesses, while the compressibility is tuned by the side branches. Numerical examples demonstrate that the CMM, when placed adjacent to a strongly aberrating layer, could acoustically cancel out that aberrating layer. This leads to dramatically reduced acoustic field...

20. M13 Virus based detection of bacterial infections in living hosts - Ghosh, Debadyuti; Belcher, Angela M.; Bardhan, Neelkanth Manoj
We report a first method for using M13 bacteriophage as a multifunctional scaffold for optically imaging bacterial infections in vivo. We demonstrate that M13 virus conjugated with hundreds of dye molecules (M13-Dye) can target and distinguish pathogenic infections of F- pili expressing and F -negative strains of E. coli. Further, in order to tune this M13-Dye complex suitable for targeting other strains of bacteria, we have used a 1-step reaction for creating an anti-bacterial antibody -M13-Dye probe. As an example, we show anti-S. aureus -M13-Dye able to target and image infections of S. aureus in living hosts, with a 3.7×...

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