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MIT Open Access Articles

Mostrando recursos 1 - 20 de 23.960

  1. Concentrating solar thermoelectric generators with a peak efficiency of 7.4%

    Jie, Qing; Cao, Feng; Liu, Weishu; Ren, Zhifeng; Kraemer, Daniel; McEnaney, Kenneth; Weinstein, Lee Adragon; Loomis III, Robert James; Chen, Gang
    Concentrating solar power normally employs mechanical heat engines and is thus only used in large-scale power plants; however, it is compatible with inexpensive thermal storage, enabling electricity dispatchability. Concentrating solar thermoelectric generators (STEGs) have the advantage of replacing the mechanical power block with a solid-state heat engine based on the Seebeck effect, simplifying the system. The highest reported efficiency of STEGs so far is 5.2%. Here, we report experimental measurements of STEGs with a peak efficiency of 9.6% at an optically concentrated normal solar irradiance of 211 kW m⁻², and a system efficiency of 7.4% after considering optical concentration losses. The performance...

  2. Nearly maximally predictive features and their dimensions

    Crutchfield, James P.; Marzen, Sarah E.
    Scientific explanation often requires inferring maximally predictive features from a given data set. Unfortunately, the collection of minimal maximally predictive features for most stochastic processes is uncountably infinite. In such cases, one compromises and instead seeks nearly maximally predictive features. Here, we derive upper bounds on the rates at which the number and the coding cost of nearly maximally predictive features scale with desired predictive power. The rates are determined by the fractal dimensions of a process' mixed-state distribution. These results, in turn, show how widely used finite-order Markov models can fail as predictors and that mixed-state predictive features can...

  3. First-principles calculations of thermal, electrical, and thermoelectric transport properties of semiconductors

    Zhou, Jiawei; Liao, Bolin; Chen, Gang
    The transport properties of semiconductors are key to the performance of many solid-state devices (transistors, data storage, thermoelectric cooling and power generation devices, etc). An understanding of the transport details can lead to material designs with better performances. In recent years simulation tools based on first-principles calculations have been greatly improved, being able to obtain the fundamental ground-state properties of materials (such as band structure and phonon dispersion) accurately. Accordingly, methods have been developed to calculate the transport properties based on an ab initio approach. In this review we focus on the thermal, electrical, and thermoelectric transport properties of semiconductors,...

  4. Epitaxial CrN Thin Films with High Thermoelectric Figure of Merit

    Quintela, Camilo X.; Podkaminer, Jacob P.; Paudel, Tula R.; Thies, Eric L.; Hillsberry, Daniel A.; Tenne, Dmitri A.; Tsymbal, Evgeny Y.; Eom, Chang-Beom; Rivadulla, Francisco; Luckyanova, Maria N; Chen, Gang
    A large enhancement of the thermoelectric figure of merit is reported in single-crystalline films of CrN. The mechanism of the reduction of the lattice thermal conductivity in cubic CrN is similar to the resonant bonding in IV–VI compounds. Therefore, useful ideas from classic thermo­electrics can be applied to tune functionalities in transition metal nitrides and oxides.

  5. Ignition Delay Correlation for Engine Operating with Lean and with Rich Fuel-Air Mixtures

    McKenzie, Jacob Elijah; Cheng, Wai K
    An ignition delay correlation encompassing the effects of temperature, pressure, residual gas, EGR, and lambda (on both the rich and lean sides) has been developed. The procedure uses the individual knocking cycle data from a boosted direct injection SI engine (GM LNF) operating at 1250 to 2000 rpm, 8-14 bar GIMEP, EGR of 0 to 12.5%, and lambda of 0.8 to 1.3 with a certification fuel (Haltermann 437, with RON=96.6 and MON=88.5). An algorithm has been devised to identify the knock point on individual pressure traces so that the large data set (of some thirty three thousand cycles) could be...

  6. Network motifs emerge from interconnections that favour stability

    Angulo, Marco Tulio; Liu, Yang-Yu; Slotine, Jean-Jacques E
    The microscopic principles organizing dynamic units in complex networks—from proteins to power generators—can be understood in terms of network ‘motifs’: small interconnection patterns that appear much more frequently in real networks than expected in random networks. When considered as small subgraphs isolated from a large network, these motifs are more robust to parameter variations, easier to synchronize than other possible subgraphs, and can provide specific functionalities. But one can isolate these subgraphs only by assuming, for example, a significant separation of timescales, and the origin of network motifs and their functionalities when embedded in larger networks remain unclear. Here we...

  7. The Calibration and Performance of a Non-homothetic CDE Demand System for CGE Models

    Chen, Yen-Heng
    In computable general equilibrium modeling, whether the simulation results are consistent with a set of valid own-price and income demand elasticities that are observed empirically remains a key challenge in many modeling exercises, since functional forms that are not fully flexible can only allow a limited subset of elasticities. While not fully flexible, the Constant Difference of Elasticities (CDE) demand system has enough free parameters to match own-price and income elasticities in some cases, leading to its adoption by some models since the 1990s. However, perhaps due to complexities of the system, the applications of CDE demand in other models...

  8. A Matched Filter Technique for Slow Radio Transient Detection and First Demonstration with the Murchison Widefield Array

    Feng, Lu; Vaulin, Ruslan; Remillard, Ronald A; Cappallo, Roger J; Lonsdale, Colin John; McWhirter, Stephen R.; Morgan, Edward H; Williams, Christopher Leigh
    Many astronomical sources produce transient phenomena at radio frequencies, but the transient sky at low frequencies (<300 MHz) remains relatively unexplored. Blind surveys with new wide-field radio instruments are setting increasingly stringent limits on the transient surface density on various timescales. Although many of these instruments are limited by classical confusion noise from an ensemble of faint, unresolved sources, one can in principle detect transients below the classical confusion limit to the extent that the classical confusion noise is independent of time. We develop a technique for detecting radio transients that is based on temporal matched filters applied directly to...


    Segal, Ilya; Whinston, Michael Dennis
    We show that efficient bargaining is impossible for a wide class of economic settings and property rights. These settings are characterized by (i) the existence of “adverse efficient opt-out types”, whose participation does not change the efficient allocation and who, when they opt out, are the worst type other agents can face, and (ii) non-existence of the “marginal core”, and its multivaluedness with a positive probability. We also examine the optimal allocation of property rights within a given class that satisfies (i), such as simple property rights, liability rules, and dual-chooser rules. We characterize property rights that minimize the expected...

  10. Funding Translational Medicine via Public Markets: The Business Development Company

    Forman, Sandra M.; Shilling, Monica; Sweeney, Grace K.; Lo, Andrew W
    A business development company (BDC) is a type of closed-end investment fund with certain relaxed requirements that allow it to raise money in the public equity and debt markets, and can be used to fund multiple early-stage biomedical ventures, using financial diversification to de-risk translational medicine. By electing to be a “Regulated Investment Company” for tax purposes, a BDC can avoid double taxation on income and net capital gains distributed to its shareholders. BDCs are ideally suited for long-term investors in biomedical innovation, including: (i) investors with biomedical expertise who understand the risks of the FDA approval process, (ii) “banking...

  11. Précis of Context

    Stalnaker, Robert
    The book is a general discussion of the notion of a speech context, and the development and defense of a particular way of representing context in a theory of the dynamics of discourse. A context, on the account I develop, is a body of information, represented by a set of possibilities—the common ground, or the information that is presumed to be shared by the participants in the conversation. This evolving body of information plays two roles: first, it represents the information that is available to the participants to use in order to interpret what is said; second, it is a...

  12. Subleading power corrections for N-jettiness subtractions

    Rothen, Lorena; Tackmann, Frank J.; Moult, Ian James; Stewart, Iain W; Zhu, HuaXing
    The N-jettiness observable T[subscript N] provides a way of describing the leading singular behavior of the N-jet cross section in the τ=T[subscript N]/Q→0 limit, where Q is a hard interaction scale. We consider subleading-power corrections in the τ≪1 expansion, and employ soft-collinear effective theory to obtain analytic results for the dominant α[subscript s]τlnτ and α[superscript 2][subscript s]τln[superscript 3]τ subleading terms for thrust in e[superscript +]e[superscript -] collisions and 0-jettiness for q[bar over q]-initiated Drell-Yan–like processes at hadron colliders. These results can be used to significantly improve the numerical accuracy and stability of the N-jettiness subtraction technique for performing fixed-order calculations...

  13. Design of a 100 kW Concentrated Solar Power on Demand Volumetric Receiver With Integral Thermal Energy Storage Prototype

    Codd, Daniel S.; Zhou, Lei; Grange, Benjamin; Calvet, Nicolas; Armstrong, Peter; Gil Pujol, Antoni; Trumper, David L; Campbell, Ronald B; Slocum, Alexander H
    A new concept of Thermal Energy Storage (TES) system based on current available technologies is being developed under the framework of the Masdar Institute (MI) and Massachusetts Institute of Technology (MIT) collaborative Flagship Program. The key feature of this concept lies on concentrating sun light directly on the molten salt storage tank, avoiding the necessity of pumping the salts to the top of a tower thereby avoiding thermal losses and pumping and electric tracing needs inherent in most conventional CSP plants. This Concentrated Solar Power on Demand (CSPonD) volumetric receiver/TES unit prototype will be tested in the existing MI heliostat field...

  14. A Rapid and Efficient Luminescence-based Method for Assaying Phosphoglycosyltransferase Enzymes

    Das, Debasis; Walvoort, Maria Theresia Cornelia; Lukose, Vinita; Imperiali, Barbara
    Phosphoglycosyltransferases (PGTs) are families of integral membrane proteins with intriguingly diverse architectures. These enzymes function to initiate many important biosynthetic pathways including those leading to peptidoglycan, N-linked glycoproteins and lipopolysaccharide O-antigen. In spite of tremendous efforts, characterization of these enzymes remains a challenge not only due to the inherent difficulties associated with the purification of integral membrane proteins but also due to the limited availability of convenient assays. Current PGT assays include radioactivity-based methods, which rely on liquid-liquid or solid-liquid extractions, multienzyme systems linked to lactate dehydrogenase and NAD+ generation, and HPLC-based approaches, all of which may suffer from low...

  15. The thermodynamic scale of inorganic crystalline metastability

    Ong, S. P.; Hautier, G.; Jain, A.; Gamst, A. C.; Persson, K. A.; Sun, Wenhao; Dacek, Stephen Thomas; Richards, William D; Ceder, Gerbrand
    The space of metastable materials offers promising new design opportunities for next-generation technological materials, such as complex oxides, semiconductors, pharmaceuticals, steels, and beyond. Although metastable phases are ubiquitous in both nature and technology, only a heuristic understanding of their underlying thermodynamics exists. We report a large-scale data-mining study of the Materials Project, a high-throughput database of density functional theory–calculated energetics of Inorganic Crystal Structure Database structures, to explicitly quantify the thermodynamic scale of metastability for 29,902 observed inorganic crystalline phases. We reveal the influence of chemistry and composition on the accessible thermodynamic range of crystalline metastability for polymorphic and phase-separating...

  16. Model reduction for a class of singularly perturbed stochastic differential equations: Fast variable approximation

    Vecchio, Domitilla Del; Herath, Narmada K
    We consider a class of stochastic differential equations in singular perturbation form, where the drift terms are linear and diffusion terms are nonlinear functions of the state variables. In our previous work, we approximated the slow variable dynamics of the original system by a reduced-order model when the singular perturbation parameter ϵ is small. In this work, we obtain an approximation for the fast variable dynamics. We prove that the first and second moments of the approximation are within an O(ϵ)-neighborhood of the first and second moments of the fast variable of the original system. The result holds for a...

  17. GPS for QSP: A Summary of the ACoP6 Symposium on Quantitative Systems Pharmacology and a Stage for Near-Term Efforts in the Field

    Musante, CJ; Abernethy, DR; Allerheiligen, SR; Zager, MG; Lauffenburger, Douglas A
    Quantitative Systems Pharmacology (QSP) is experiencing increased application in the drug discovery and development process. Like its older sibling, systems biology, the QSP field is comprised of a mix of established disciplines and methods, from molecular biology to engineering to pharmacometrics.[1] As a result, there exist critical segments of the discipline that differ dramatically in approach and a need to bring these groups together toward a common goal.

  18. Helicobacter pylori Eradication in Patients with Immune Thrombocytopenic Purpura: A Review and the Role of Biogeography

    Beck, Paul L.; Frydman, Galit; Davis, Nicholas K.; Fox, James G
    Idiopathic thrombocytopenic purpura (ITP) is typically a diagnosis of exclusion, assigned by clinicians after ruling out other identifiable etiologies. Since a report by Gasbarrini et al. in 1998, an accumulating body of evidence has proposed a pathophysiological link between ITP and chronic Helicobacter pylori (H. pylori) infection. Clinical reports have described a spontaneous resolution of ITP symptoms in about 50% of chronic ITP patients following empirical treatment of H. pylori infection, but response appears to be geography dependent. Studies have also documented that ITP patients in East Asian countries are more likely to express positive antibody titers against H. pylori-specific...

  19. Pancreas-enriched miRNAs are altered in the circulation of subjects with diabetes: a pilot cross-sectional study

    Nunez Lopez, Yury O.; Xie, Hui; Yi, Fanchao; Mathews, Clayton; Pasarica, Magdalena; Pratley, Richard E.; Seyhan, Attila A
    The clinical presentation of diabetes sometimes overlaps, contributing to ambiguity in the diagnosis. Thus, circulating pancreatic islet-enriched microRNAs (miRNAs) might be useful biomarkers of β-cell injury/dysfunction that would allow more accurate subtyping of diabetes. We measured plasma levels of selected miRNAs in subjects with prediabetes (n = 12), type 2 diabetes (T2D, n = 31), latent autoimmune diabetes of adults (LADA, n = 6) and type 1 diabetes (T1D, n = 16) and compared them to levels in healthy control subjects (n = 27). The study was conducted at the Translational Research Institute for Metabolism and Diabetes (TRI-MD), Florida Hospital. MiRNAs including miR-375 (linked to β-cell injury), miR-21 (associated with...

  20. Site-specific protein modification using immobilized sortase in batch and continuous-flow systems

    Witte, Martin D; Wu, Tongfei; Guimaraes, Carla P; Theile, Christopher S; Blom, Annet E M; Ingram, Jessica R; Li, Zeyang; Kundrat, Lenka; Goldberg, Shalom D; Ploegh, Hidde
    Transpeptidation catalyzed by ​sortase A allows the preparation of proteins that are site-specifically and homogeneously modified with a wide variety of functional groups, such as fluorophores, PEG moieties, lipids, glycans, bio-orthogonal reactive groups and affinity handles. This protocol describes immobilization of ​sortase A on a solid support (Sepharose beads). Immobilization of ​sortase A simplifies downstream purification of a protein of interest after labeling of its N or C terminus. Smaller batch and larger-scale continuous-flow reactions require only a limited amount of enzyme. The immobilized enzyme can be reused for multiple cycles of protein modification reactions. The described protocol also works...

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