Recursos de colección

Caltech Authors (166.781 recursos)

Repository of works by Caltech published authors.

Type = Report or Paper

Mostrando recursos 1 - 20 de 3.272

  1. Performance of Viscous Damping in Inelastic Seismic Analysis of Moment-Frame Buildings

    Hall, John
    This report investigates the performance of several viscous damping formulations in the inelastic seismic response of moment-frame buildings. The evaluation employs a detailed model of a 20-story steel building. Damping schemes included in the study are Rayleigh, condensed Rayleigh, Wilson-Penzien, two versions of tangent Rayleigh and one implementation of capped damping. Caughey damping is found not to be computationally viable. Differences among the damping schemes, as quantified by amounts of plastic hinge rotations and story drifts, become noticeable once these quantities reach the 3% level. In order of least to greatest hinge rotations and drifts that occur under lateral response...

  2. Star Formation Histories of the LEGUS dwarf galaxies. II. Spatially resolved star formation history of the Magellanic irregular NGC 4449

    Sacchi, E.; Cignoni, M.; Aloisi, A.; Tosi, M.; Calzetti, D.; Lee, J. C.; Adamo, A.; Annibali, F.; Dale, D. A.; Elmegreen, B. G.; Gouliermis, D. A.; Grasha, K.; Grebel, E. K.; Hunter, D. A.; Sabbi, E.; Smith, L. J.; Thilker, D. A.; Ubeda, L.; Whitmore, B C.
    We present a detailed study of the Magellanic irregular galaxy NGC 4449 based on both archival and new photometric data from the Legacy Extragalactic UV Survey, obtained with the Hubble Space Telescope Advanced Camera for Surveys and Wide Field Camera 3. Thanks to its proximity ($D=3.82\pm 0.27$ Mpc) we reach stars 3 magnitudes fainter than the tip of the red giant branch in the F814W filter. The recovered star formation history spans the whole Hubble time, but due to the age-metallicity degeneracy of the red giant branch stars, it is robust only over the lookback time reached by our photometry, i.e. $\sim 3$ Gyr. The most recent peak...

  3. Actions of trees on semigroups, and an infinitary Gowers-Hales-Jewett Ramsey theorem

    Lupini, Martino
    We introduce the notion of (Ramsey) action of a tree on a (filtered) semigroup. We then prove in this setting a general result providing a common generalization of the infinitary Gowers Ramsey theorem for multiple tetris operations, the infinitary Hales--Jewett theorems (for both located and nonlocated words), and the Farah--Hindman--McLeod Ramsey theorem for layered actions on partial semigroups. We also establish a polynomial version of our main result, recovering the polynomial Milliken--Taylor theorem of Bergelson--Hindman--Williams as a particular case. We present applications of our Ramsey-theoretic results to the structure of delta sets in amenable groups.

  4. Boundary representations of operator spaces, and compact rectangular matrix convex sets

    Fuller, Adam H.; Hartz, Michael; Lupini, Martino
    We initiate the study of matrix convexity for operator spaces. We define the notion of compact rectangular matrix convex set, and prove the natural analogs of the Krein-Milman and the bipolar theorems in this context. We deduce a canonical correspondence between compact rectangular matrix convex sets and operator spaces. We also introduce the notion of boundary representation for an operator space, and prove the natural analog of Arveson's conjecture: every operator space is completely normed by its boundary representations. This yields a canonical construction of the triple envelope of an operator space.

  5. Games orbits play and obstructions to Borel reducibility

    Lupini, Martino; Panagiotopoulos, Aristotelis
    We introduce a new game-theoretic approach to anti-classification results for orbit equivalence relations. Within this framework, we give a short conceptual proof of Hjorth's turbulence theorem. We also introduce a new dynamical criterion providing an obstruction to classification by orbits of CLI groups. We apply this criterion to the relation of equality of countable sets of reals, and the relations of unitary conjugacy of unitary and selfadjoint operators on the separable infinite-dimensional Hilbert space.

  6. Rokhlin dimension for compact quantum group actions

    Gardella, Eusebio; Kalantar, Mehrdad; Lupini, Martino
    We show that, for a given compact or discrete quantum group G, the class of actions of G on C*-algebras is first-order axiomatizable in the logic for metric structures. As an application, we extend the notion of Rokhlin property for G-C*-algebra, introduced by Barlak, Szabó, and Voigt in the case when G is second countable and coexact, to an arbitrary compact quantum group G. All the the preservations and rigidity results for Rokhlin actions of second countable coexact compact quantum groups obtained by Barlak, Szabó, and Voigt are shown to hold in this general context. As a further application, we...

  7. The Ramsey property for Banach spaces, Choquet simplices, and their noncommutative analogs

    Bartošová, Dana; López-Abad, Jordi; Lupini, Martino; Mbombo, Brice
    We show that the Gurarij space G and its noncommutative analog NG both have extremely amenable automorphism group. We also compute the universal minimal flows of the automorphism groups of the Poulsen simplex P and its noncommutative analogue NP. The former is P itself, and the latter is the state space of the operator system associated with NP. This answers a question of Conley and Törnquist. We also show that the pointwise stabilizer of any closed proper face of P is extremely amenable. Similarly, the pointwise stabilizer of any closed proper biface of the unit ball of the dual of...

  8. The complexity of conjugacy, orbit equivalence, and von Neumann equivalence of actions of nonamenable groups

    Gardella, Eusebio; Lupini, Martino
    Building on work of Popa, Ioana, and Epstein--Törnquist, we show that, for every nonamenable countable discrete group Γ, the relations of conjugacy, orbit equivalence, and von Neumann equivalence of free ergodic (or weak mixing) measure preserving actions of Γ on the standard atomless probability space are not Borel, thus answering questions of Kechris. This is an optimal and definitive result, which establishes a neat dichotomy with the amenable case, since any two free ergodic actions of an amenable group on the standard atomless probability space are orbit equivalent by classical results of Dye and Ornstein--Weiss. The statement about conjugacy solves...

  9. An invitation to model theory and C*-algebras

    Lupini, Martino
    We present an introductory survey to first order logic for metric structures and its applications to C*-algebras.

  10. Giant earthquakes on quiet faults governed by rheological transitions

    van den Ende, Martijn P. A.; Chen, Jianye; Ampuero, Jean-Paul; Niemeijer, André R.
    The apparent stochastic nature of earthquakes poses major challenges for earthquake forecasting attempts. Physical constraints on the seismogenic potential of major fault zones may greatly aid in improving seismic hazard assessments, but the mechanics of earthquake nucleation and rupture are obscured by the enormous complexity that natural faults display. In this study, we investigate the mechanisms behind giant earthquakes by employing a microphysically based seismic cycle simulator. This microphysical approach is directly based on the mechanics of friction as inferred from laboratory tests, and can explain a broad spectrum of fault slip behaviour. We show that exceptionally large, fault-spanning earthquakes...

  11. An intrinsic order-theoretic characterization of the weak expectation property

    Lupini, Martino
    We prove the following characterization of the weak expectation property for operator systems in terms of Wittstock's matricial Riesz separation property: an operator system S satisfies the weak expectation property if and only if M_q(S) satisfies the matricial Riesz separation property for every q∈N. This can be seen as the noncommutative analog of the characterization of simplex spaces among function systems in terms of the classical Riesz separation property.

  12. The Fraïssé limit of matrix algebras with the rank metric

    Anderson, Aaron; Lupini, Martino
    We realize the F_q-algebra M(F_q) studied by von Neumann and Halperin as the Fraïssé limit of the class of finite-dimensional matrix algebras over a finite field F_q equipped with the rank metric. We then provide a new Fraïssé-theoretic proof of uniqueness of such an object. Using the results of Carderi and Thom, we show that the automorphism group of Aut(F_q) is extremely amenable. We deduce a Ramsey-theoretic property for the class of algebras M(F_q), and provide an explicit bound for the quantities involved.

  13. Actions of nonamenable groups on Z-stable C*-algebras

    Gardella, Eusebio; Lupini, Martino
    We study strongly outer actions of discrete groups on C*-algebras in relation to (non)amenability. In contrast to related results for amenable groups, where uniqueness of strongly outer actions on the Jiang-Su algebra is expected, we show that uniqueness fails for all nonamenable groups, and that the failure is drastic. Our main result implies that if G contains a copy of the free group, then there exist uncountable many, non-cocycle conjugate strongly outer actions of G on any Jiang-Su stable tracial C*-algebra. Similar conclusions apply for outer actions on McDuff tracial von Neumann algebras. We moreover show that G is amenable...

  14. Nonlocal Games and Quantum Permutation Groups

    Lupini, Martino; Mančinska, Laura; Roberson, David E.
    We present a strong connection between quantum information and quantum permutation groups. Specifically, we define a notion of quantum isomorphisms of graphs based on quantum automorphisms from the theory of quantum groups, and then show that this is equivalent to the previously defined notion of quantum isomorphism corresponding to perfect quantum strategies to the isomorphism game. Moreover, we show that two connected graphs X and Y are quantum isomorphic if and only if there exists x∈V(X) and y∈V(Y) that are in the same orbit of the quantum automorphism group of the disjoint union of X and Y. This connection links...

  15. A von Neumann algebra characterization of property (T) for groupoids

    Lupini, Martino
    For an arbitrary discrete probability-measure-preserving groupoid G, we provide a characterization of property (T) for G in terms of the groupoid von Neumann algebra L(G). More generally, we obtain a characterization of relative property (T) for a subgroupoid H⊂G in terms of the inclusion L(H)⊂L(G).

  16. Transport property analysis method for thermoelectric materials: material quality factor and the effective mass model

    Kang, Stephen Dongmin; Snyder, G. Jeffrey
    Thermoelectric semiconducting materials are often evaluated by their figure-of-merit, zT. However, by using zT as the metric for showing improvements, it is not immediately clear whether the improvement is from an enhancement of the inherent material property or from optimization of the carrier concentration. Here, we review the quality factor approach which allows one to separate these two contributions even without Hall measurements. We introduce practical methods that can be used without numerical integration. We discuss the underlying effective mass model behind this method and show how it can be further advanced to study complex band structures using the Seebeck...

  17. Nonstandard Methods in Ramsey Theory and Combinatorial Number Theory

    Di Nasso, Mauro; Goldbring, Isaac; Lupini, Martino
    The goal of this present manuscript is to introduce the reader to the nonstandard method and to provide an overview of its most prominent applications in Ramsey theory and combinatorial number theory.

  18. Behavior of homing endonuclease gene drives targeting genes required for viability or female fertility with multiplexed guide RNAs

    Oberhofer, Georg; Ivy, Tobin; Hay, Bruce A.
    A gene drive method of particular interest for population suppression utilizes homing endonuclease genes (HEGs), wherein a site-specific nuclease-encoding cassette is copied, in the germline, into a target gene whose loss of function results in loss of viability or fertility in homozygous, but not heterozygous progeny. Earlier work in Drosophila and mosquitoes utilized HEGs consisting of Cas9 and a single gRNA that together target a specific gene for cleavage. Homing was observed, but resistant alleles, immune to cleavage, while retaining wildtype gene function, were also created through non-homologous end joining. Such alleles prevent drive and population suppression. Targeting a gene...

  19. Single day construction of multi-gene circuits with 3G assembly

    Halleran, Andrew D.; Swaminathan, Anandh; Murray, Richard M.
    The ability to rapidly design, build, and test prototypes is of key importance to every engineering discipline. DNA assembly often serves as a rate limiting step of the prototyping cycle for synthetic biology. Recently developed DNA assembly methods such as isothermal assembly and type IIS restriction enzyme systems take different approaches to accelerate DNA construction. We introduce a hybrid method, Golden Gate-Gibson (3G), that takes advantage of modular part libraries introduced by type IIS restriction enzyme systems and isothermal assembly's ability to build large DNA constructs in single pot reactions. Our method is highly efficient and rapid, facilitating construction of...

  20. Wilsonian effective field theory of 2D van Hove singularities

    Kapustin, Anton; McKinney, Tristan; Rothstein, Ira Z.
    We study 2D fermions with a short-range interaction in the presence of a van Hove singularity. It is shown that this system can be consistently described by an effective field theory whose Fermi surface is subdivided into regions as defined by a factorization scale, and that the theory is renormalizable in the sense that all of the counterterms are well defined in the IR limit. The theory has the unusual feature that the renormalization group equation for the coupling has an explicit dependence on the renormalization scale, much as in theories of Wilson lines. In contrast to the case of a round Fermi surface, there are multiple marginal...

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