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MIT Open Access Articles

Mostrando recursos 41 - 60 de 20,623

  1. A novel semi-active TMD with folding variable stiffness spring

    Rahimian, M.; Rafieipour, M. H.; Ghorbani-Tanha, A. K.; Mohammadi-Ghazi, Reza
    An innovative variable stiffness device is proposed and investigated based on numerical simulations. The device, called a folding variable stiffness spring (FVSS), can be widely used, especially in tuned mass dampers (TMDs) with adaptive stiffness. An important characteristic of FVSS is its capability to change the stiffness between lower and upper bounds through a small change of distance between its supports. This special feature results in lower time-lag errors and readjustment in shorter time intervals. The governing equations of the device are derived and simplified for a symmetrical FVSS with similar elements. This device is then used to control a...

  2. A multilayered microfluidic blood vessel-like structure

    Hasan, Anwarul; Paul, Arghya; Memic, Adnan; Khademhosseini, Ali
    There is an immense need for tissue engineered blood vessels. However, current tissue engineering approaches still lack the ability to build native blood vessel-like perfusable structures with multi-layered vascular walls. This paper demonstrated a new method to fabricate tri-layer biomimetic blood vessel-like structures on a microfluidic platform using photocrosslinkable gelatin hydrogel. The presented method enables fabrication of physiological blood vessel-like structures with mono-, bi- or tri-layer vascular walls. The diameter of the vessels, the total thickness of the vessel wall and the thickness of each individual layer of the wall were independently controlled. The developed fabrication process is a simple...

  3. Discovering urban activity patterns in cell phone data

    Widhalm, Peter; Yang, Yingxiang; Ulm, Michael; Athavale, Shounak; Gonzalez, Marta C.
    Massive and passive data such as cell phone traces provide samples of the whereabouts and movements of individuals. These are a potential source of information for models of daily activities in a city. The main challenge is that phone traces have low spatial precision and are sparsely sampled in time, which requires a precise set of techniques for mining hidden valuable information they contain. Here we propose a method to reveal activity patterns that emerge from cell phone data by analyzing relational signatures of activity time, duration, and land use. First, we present a method of how to detect stays...

  4. Recent developments in national and international freight transport models within Europe

    de Jong, Gerard; Vierth, Inge; Tavasszy, Lori; Ben-Akiva, Moshe E.
    The past decade has seen many new freight transport models for use in transport planning by public authorities. Some of these models have developed new concepts, such as logistics modules, inclusion of transshipments, storage and sourcing and the determination of shipment size. This paper provides a review of the European literature on freight transport models that operate at the national or international level and have been developed since 2004. The introduction of elements of logistics thinking is identified as a common theme in recently developed models, and further worked out. Furthermore, ideas on what might be the next key developments...

  5. Polygyny in the nest-site limited acacia-ant Crematogaster mimosae

    Kennedy, D.; Rubin, B. E. R.; Anderson, R. M.; Palmer, T. M.; Stanton, M. L.; Lovette, I. J.
    Polygyny is common in social insects despite inevitable decreases in nestmate relatedness and reductions to the inclusive fitness returns for cooperating non-reproductive individuals. We studied the prevalence and mode of polygyny in the African acacia-ant Crematogaster mimosae. These ants compete intensively with neighboring colonies of conspecifics and with three sympatric ant species for resources associated with the whistling-thorn acacias in which they all obligately nest. We used the genotypes of alate males at ten microsatellite loci to reconstruct queen genotypes and found that C. mimosae colonies are frequently secondarily polygynous, in that they include multiple closely related (and sometimes full-sib)...

  6. Combinatorial Aspects of Flashcard Games

    Li, Nan; Lewis, Joel Brewster
    We study a family of discrete dynamical processes introduced by Novikoff, Kleinberg, and Strogatz that we call flashcard games. We prove a number of results on the evolution of these games, and in particular, we settle a conjecture of NKS on the frequency with which a given card appears. We introduce a number of generalizations and variations that we believe are of interest, and we provide a large number of open questions and problems.

  7. Linear growth for semigroups which are disjoint unions of finitely many copies of the free monogenic semigroup

    Abughazalah, Nabilah; Etingof, Pavel I.
    We show that every semigroup which is a finite disjoint union of copies of the free monogenic semigroup (natural numbers under addition) has linear growth. This implies that the corresponding semigroup algebra is a PI algebra.

  8. 2D-Visualisierung des zellulären Sauerstoff verbrauchs in Mikrofluidiksystemen

    Kasuya, Junichi; Pavesi, Andrea; Liebsch, Gregor; Ochs, Christopher J.
    A new imaging system allows visualizing oxygen distributions in 2D. Combining sensor foils with microfluidic devices enables online monitoring of cellular oxygen consumption in whole chip areas. Furthermore, suitable device materials depending on application and cell line can be determined. Numerically simulated oxygen consumption of rat lung microvascular endothelial cells and rat hepatocytes was experimentally validated.

  9. On the practical use of physical unclonable functions in oblivious transfer and bit commitment protocols

    Rührmair, Ulrich; van Dijk, Marten
    In recent years, PUF-based schemes have been suggested not only for the basic tasks of tamper-sensitive key storage or the identification of hardware systems, but also for more complex protocols like oblivious transfer (OT) or bit commitment (BC), both of which possess broad and diverse applications. In this paper, we continue this line of research. We first present an attack on two recent OT and BC protocols which have been introduced by Brzuska et al. (CRYPTO, LNCS 6841, pp 51–70, Springer 2011). The attack quadratically reduces the number of CRPs which malicious players must read out to cheat, and fully...

  10. Optimization of Conical Micro-Diffusers and Micro-Nozzles Considering Entropy Generation

    Ben-Mansour, Rached; Sahin, Ahmet Z.
    Fluid flow characteristics and entropy generation in a circular diffuser/nozzle element are studied numerically. The flow is assumed to be isothermal, laminar and incompressible with constant thermo-physical properties. The velocity field, mass flow rate, and entropy generation are investigated for several half angles in combination with several values of pressure drops. The effect of diffuser half angle on the entropy generation is investigated and discussed. Furthermore, the effect of the half angle of diffuser on the diffuser efficiency and the effect on the rectification efficiency are explained. It is shown that there is an optimum operation half angle for which...

  11. Diurnal Variation of TEC and S 4 Index During the Period of Low Geomagnetic Activity at Ile-Ife, Nigeria

    Doherty, P.; Ariyibi, E. A.; Joshua, E. O.; Coster, Anthea J.
    Ile-Ife lies on the equatorial anomaly region where the ionospheric current is greatly influenced by the existence of the equatorial electrojet. The dual frequency SCINDA NovAtel GSV 4004B GPS receiver recently installed at Ile-Ife [on geographical latitude 7°33′N and longitude 4°33′E and geomagnetic dipole (coordinate) of latitude 9.84°N and longitude 77.25°E] is currently operational and recording data from the available global positioning system satellites. The receiver provides the data on total electron content (TEC) and the scintillation index (S[subscript 4]). This paper presents the first sets of results from this station. Data records for the month of February 2010 were...

  12. Nano-Engineering of Concrete

    Ulm, Franz-Josef
    This paper summarizes recent developments in the field of nanoindentation analysis of highly heterogeneous composites. The fundamental idea of the proposed approach is that it is possible to assess nanostructure from the implementation of micromechanics-based scaling relations for a large array of nanoindentation tests on heterogeneous materials. We illustrate this approach through the application to calcium-silicate-hydrate (C-S-H), the binding phase of all cement-based materials. For this important class of materials, we show that C-S-H exists in at least three structurally distinct but compositionally similar forms: low density, high density and ultra-high density. These three forms differ merely in the packing...

  13. Compression approaches for the regularized solutions of linear systems from large-scale inverse problems

    Voronin, Sergey; Mikesell, Dylan; Nolet, Guust
    We introduce and compare new compression approaches to obtain regularized solutions of large linear systems which are commonly encountered in large scale inverse problems. We first describe how to approximate matrix vector operations with a large matrix through a sparser matrix with fewer nonzero elements, by borrowing from ideas used in wavelet image compression. Next, we describe and compare approaches based on the use of the low rank singular value decomposition (SVD), which can result in further size reductions. We describe how to obtain the approximate low rank SVD of the original matrix using the sparser wavelet compressed matrix. Some...

  14. A game-theoretic approach to optimizing the scale of incorporating renewable sources of energy and electricity storing systems in a regional electrical grid

    Belenky, Alexander S.
    The problem of developing a decision support system for estimating a) the scale of incorporating available renewable sources of energy (such as solar and wind energy) in a part of a country’s electrical grid (called a regional electrical grid further in this paper), and b) the scale of storing electricity in this (regional) electrical grid to make these renewable sources of electric power competitive with traditional power generators (such as fossil-fuel and nuclear ones) and to reduce the cost of acquiring electricity from all the electric power generating facilities in the grid is considered. In the framework of this system,...

  15. Finding an optimal strategy of incorporating renewable sources of energy and electricity storing systems in a regional electrical grid

    Belenky, Alexander S.
    A game with a finite (more than three) number of players on a polyhedron of connected player strategies is studied. This game describes the interaction among (a) the base load power plant (the generator), (b) all the large customers of a regional electrical grid that receive electric energy from the generator, as well as from the available renewable sources of energy, both directly and via electricity storing facilities, and (c) the transmission company. An auxiliary three-person game on polyhedra of disjoint player strategies that is associated with the initial game is also considered. It is shown that an equilibrium point...

  16. A new reverse electrodialysis design strategy which significantly reduces the levelized cost of electricity

    Weiner, Adam Michael; McGovern, Ronan Killian; Lienhard, John H.
    We develop a framework for choosing the optimal load resistance, feed velocity and residence time for a reverse electrodialysis stack based on minimizing the levelized cost of electricity. The optimal load resistance maximizes the gross stack power density and results from a trade-off between stack voltage and stack current. The primary trade-off governing the optimal feed velocity is between stack pumping power losses, which reduce the net power density and concentration polarization losses, which reduce the gross stack power density. Lastly, the primary trade-off governing the optimal residence time is between the capital costs of the stack and pretreatment system....

  17. Resonant tunneling and intrinsic bistability in twisted graphene structures

    Rodriguez Nieva, Joaquin Francisco; Dresselhaus, Mildred; Levitov, Leonid
    We predict that vertical transport in heterostructures formed by twisted graphene layers can exhibit a unique bistability mechanism. Intrinsically bistable I-V characteristics arise from resonant tunneling and interlayer charge coupling, enabling multiple stable states in the sequential tunneling regime. We consider a simple trilayer architecture, with the outer layers acting as the source and drain and the middle layer floating. Under bias, the middle layer can be either resonant or nonresonant with the source and drain layers. The bistability is controlled by geometric device parameters easily tunable in experiments. The nanoscale architecture can enable uniquely fast switching times.

  18. MicroRNA networks regulate development of brown adipocytes

    Trajkovski, Mirko; Lodish, Harvey F.
    Brown adipose tissue (BAT) is specialized for heat generation and energy expenditure as a defense against cold and obesity; in both humans and mice increased amounts of BAT are associated with a lean phenotype and resistance to development of the metabolic syndrome and its complications. Here we summarize recent research showing that several BAT-expressed microRNAs (miRNAs) play important roles in regulating differentiation and metabolism of brown and beige adipocytes; we discuss the key mRNA targets downregulated by these miRNAs and show how these miRNAs affect directly or indirectly transcription factors important for BAT development. We suggest that these miRNAs could...

  19. Catalytic Z-Selective Cross-Metathesis in Complex Molecule Synthesis: A Convergent Stereoselective Route to Disorazole C[subscript 1]

    Speed, Alexander W. H.; Mann, Tyler J.; O’Brien, Robert V.; Schrock, Richard Royce; Hoveyda, Amir H.
    A convergent diastereo- and enantioselective total synthesis of anticancer and antifungal macrocyclic natural product disorazole C1 is reported. The central feature of the successful route is the application of catalytic Z-selective cross-metathesis (CM). Specifically, we illustrate that catalyst-controlled stereoselective CM can be performed to afford structurally complex Z-alkenyl–B(pin) as well as Z-alkenyl iodide compounds reliably, efficiently, and with high selectivity (pin = pinacolato). The resulting intermediates are then joined in a single-step operation through catalytic inter- and intramolecular cross-coupling to furnish the desired 30-membered ring macrocycle containing the critical (Z,Z,E)-triene moieties.

  20. Nucleotide Binding Preference of the Monofunctional Platinum Anticancer-Agent Phenanthriplatin

    Riddell, Imogen Anne; Johnstone, Timothy; Park, Ga Young; Lippard, Stephen J.
    The monofunctional platinum anticancer agent phenanthriplatin generates covalent adducts with the purine bases guanine and adenine. Preferential nucleotide binding was investigated by using a polymerase stop assay and linear DNA amplification with a 163-base pair DNA double helix. Similarly to cisplatin, phenanthriplatin forms the majority of adducts at guanosine residues, but significant differences in both the number and position of platination sites emerge when comparing results for the two complexes. Notably, the monofunctional complex generates a greater number of polymerase-halting lesions at adenosine residues than does cisplatin. Studies with 9-methyladenine reveal that, under abiological conditions, phenanthriplatin binds to the N1...

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