Repository of works by Caltech published authors.
Type = Article
Mostrando recursos 1 - 20 de 27.667
PM=EM? Partially massless duality invariance - Deser, S.; Waldron, A.
We show that higher spin, maximal depth, partially massless systems defined in d = 4 de Sitter space enjoy Maxwellian electric-magnetic duality. These photonlike models can also couple to charged matter.
Identification of b-quark jets with the CMS experiment - Chatrchyan, S.; Apresyan, A.; Bornheim, A.; Chen, Y.; Di Marco, E.; Duarte, J.; Gataullin, M.; Ma, Y.; Mott, A.; Newman, H. B.; Rogan, C.; Spiropulu, M.; Timciuc, V.; Veverka, J.; Wilkinson, R.; Xie, S.; Yang, Y.; Zhu, R. Y.; Dias, F. A.; Dubinin, M.
At the Large Hadron Collider, the identification of jets originating from b quarks is important for searches for new physics and for measurements of standard model processes. A variety of algorithms has been developed by CMS to select b-quark jets based on variables such as the impact parameters of charged-particle tracks, the properties of reconstructed decay vertices, and the presence or absence of a lepton, or combinations thereof. The performance of these algorithms has been measured using data from proton-proton collisions at the LHC and compared with expectations based on simulation. The data used in this study were recorded in...
Searching at the right time of day: Evidence for aqueous minerals in Columbus crater with TES and THEMIS data - Baldridge, Alice M.; Lane, Melissa D.; Edwards, Christopher S.
The primary objective of the Thermal Emission Imaging System (THEMIS) experiment, which has been in orbit at Mars since early 2002, is to identify minerals associated with hydrothermal and subaqueous environments. Data from THEMIS have supported the presence of clays, silica-rich deposits, and chlorides but has not before provided definitive evidence for the presence of sulfates. This is an especially puzzling result given that sulfates have been extensively identified with other instruments at Mars. If present, sufficiently exposed, and in high enough abundances, such minerals should be detectable in orbital thermal infrared spectra at the resolution of THEMIS. The extended...
Lower mantle structure from paleogeographically constrained dynamic Earth models - Bower, Dan J.; Gurnis, Michael; Seton, Maria
Seismic tomography reveals two large, low-shear velocity provinces (LLSVPs) beneath Africa and the Pacific Ocean. These structures may have existed for several 100 Myr and are likely compositionally distinct based on observed seismic characteristics interpreted in light of geodynamic models and mineral physics constraints. We investigate the dynamics of the LLSVPs through the use of evolutionary models of thermochemical convection from 250 Ma to present day. We use a spherical convection model in which the anomalous structures have a high bulk modulus, consistent with seismic interpretation. A new progressive assimilation method incorporates constraints from paleogeography using a refined plate history...
Quantum Error Correction via Less Noisy Qubits - Fujiwara, Yuichiro
Known quantum error correction schemes are typically able to take advantage of only a limited class of classical error-correcting codes. Entanglement-assisted quantum error correction is a partial solution which made it possible to exploit any classical linear codes over the binary or quaternary finite field. However, the known entanglement-assisted scheme requires noiseless qubits that help correct quantum errors on noisy qubits, which can be too severe an assumption. We prove that a more relaxed and realistic assumption is sufficient by presenting encoding and decoding operations assisted by qubits on which quantum errors of one particular kind may occur. As in...
Classical Mechanics of Nonconservative Systems - Galley, Chad R.
Hamilton’s principle of stationary action lies at the foundation of theoretical physics and is applied in many other disciplines from pure mathematics to economics. Despite its utility, Hamilton’s principle has a subtle pitfall that often goes unnoticed in physics: it is formulated as a boundary value problem in time but is used to derive equations of motion that are solved with initial data. This subtlety can have undesirable effects. I present a formulation of Hamilton’s principle that is compatible with initial value problems. Remarkably, this leads to a natural formulation for the Lagrangian and Hamiltonian dynamics of generic nonconservative systems,...
Accommodation of transpressional strain in the Arabia-Eurasia collision zone: new constraints from (U-Th)/He thermochronology in the Alborz mountains, north Iran - Ballato, Paolo; Stockli, Daniel F.; Ghassemi, Mohammad R.; Landgraf, Angela; Strecker, Manfred R.; Hassanzadeh, Jamshid; Friedrich, Anke; Tabatabaei, Saeid H.
The Alborz range of N Iran provides key information on the spatiotemporal evolution and characteristics of the Arabia-Eurasia continental collision zone. The southwestern Alborz range constitutes a transpressional duplex, which accommodates oblique shortening between Central Iran and the South Caspian Basin. The duplex comprises NW-striking frontal ramps that are kinematically linked to inherited E-W-striking, right-stepping lateral to obliquely oriented ramps. New zircon and apatite (U-Th)/He data provide a high-resolution framework to unravel the evolution of collisional tectonics in this region. Our data record two pulses of fast cooling associated with SW-directed thrusting across the frontal ramps at ~ 18–14 and 9.5-7.5 Ma, resulting...
Determinacy with Complicated Strategies - Kechris, Alexander S.
For any class of functions F from R into R, AD(F) is the assertion that in every two person game on integers one of the two players has a winning strategy in the class F. It is shown, in ZF + DC + V = L(R), that for any F of cardinality < 2^(N0)(i.e. any F which is a surjective image of R) AD(F) implies AD (the Axiom of Determinacy).
Descriptive Set Theory and Harmonic Analysis - Kechris, A. S.; Louveau, A.
During the 1989 European ASL Summer Meeting in Berlin, the
authors gave a series of eight lectures (short course) on the topic of the title. This
survey article consists basically of the lecture notes for that course distributed to
the participants of that conference. We have purposely tried in this printed version
to preserve the informal style of the original notes.
On the concept of π^1_1-completeness - Kechris, Alexander S.
It is shown that two natural notions of completeness for co-analytic sets in Polish spaces, one in terms of continuous reductions and the other in terms of Borel reductions, coincide. The proof uses methods of effective descriptive set theory.
The classification of hypersmooth Borel equivalence relations - Kechris, Alexander S.; Louveau, Alain
This paper is a contribution to the study of Borel equivalence relations in standard Borel spaces, i.e., Polish spaces equipped with their Borel structure. A class of such equivalence relations which has received particular attention is the class of hyperfinite Borel equivalence relations. These can be defined as the increasing unions of sequences of Borel equivalence relations all of whose equivalence classes are finite or, as it turns out, equivalently those induced by the orbits of a single Borel auto-morphism. Hyperfinite equivalence relations have been classified in [DJK], under two notions of equivalence, Borel bi-reducibility, and Borel isomorphism.
MicroRNA-146a acts as a guardian of the quality and longevity of hematopoietic
stem cells in mice - Zhao, Jimmy L.; Rao, Dinesh S.; O’Connell, Ryan M.; Garcia-Flores, Yvette; Baltimore, David
During inflammation and infection, hematopoietic stem and progenitor cells are
stimulated to proliferate and differentiate into mature immune cells, especially of the myeloid
lineage. MicroRNA-146a (miR-146a) is a critical negative regulator of inflammation. Deletion of
miR-146a produces effects that appear as dysregulated inflammatory hematopoiesis, leading to a
decline in the number and quality of hematopoietic stem cells (HSCs), excessive myeloproliferation,
and, ultimately, to HSC exhaustion and hematopoietic neoplasms. At the cellular level, the defects
are attributable to both an intrinsic problem in the miR-146a–deficient HSCs and extrinsic effects of
lymphocytes and nonhematopoietic cells. At the molecular level, this involves a molecular axis
consisting of miR-146a, signaling protein TRAF6,...
Amenable Versus Hyperfinite Borel Equivalence Relations - Kechris, Alexander S.
Let X be a standard Borel space (i.e., a Polish space with the associated Borel structure), and let E be a countable Borel equivalence relation on X, i.e., a Borel equivalence relation E for which every equivalence class [X]_E is countable. By a result of Feldman-Moore [FM], E is induced by the orbits of a Borel action of a countable group G on X.
A Classification of Baire Class 1 Functions - Kechris, A. S.; Louveau, A.
We study in this paper various ordinal ranks of (bounded) Baire class 1 functions and we show their essential equivalence. This leads to a natural classification of the class of bounded Baire class 1 functions B_1 in a transfinite hierarchy B^ξ_1 ξ < ω_1) of "small" Baire classes, for which (for example) an analysis similar to the Hausdorff-Kuratowski analysis of Δ^0_2 sets via transfinite differences of closed sets can be carried out. The notions of pseudouniform convergence of a sequence of functions and optimal convergence of a sequence of continuous functions to a Baire class 1 function ƒ are introduced...
On a notion of smallness for subsets of the Baire space - Kechris, Alexander S.
Let us call a set A ⊆ ω^ω of functions from ω into ω σ-bounded if there is a countable sequence of functions (α_n: n Є ω)⊆ ω^ω such that every member of A is pointwise dominated by an element of that sequence. We study in this paper definability questions concerning this notion of smallness for subsets of ω^ω. We show that most of the usual definability results about the structure of countable subsets of ω^ω have corresponding versions which hold about σ-bounded subsets of ω^ω. For example, we show that every Σ_(2n+1^1 σ-bounded subset of ω^ω has a Δ_(2n+1)^1...
The Theory of Countable Analytical Sets - Kechris, Alexander S.
The purpose of this paper is the study of the structure of countable sets in the various levels of the analytical hierarchy of sets of reals. It is first shown that, assuming projective determinacy, there is for each odd n a largest countable ∏_n^1 set of reals, C_n (this is also true for n even, replacing ∏_n^1 by Σ_n^1 and has been established earlier by Solovay for n = 2 and by Moschovakis and the author for all even n > 2). The internal structure of the sets C_n is then investigated in detail, the point of departure being the...
Ordinal Rankings on Measures Annihilating Thin Sets - Kechris, Alexander S.; Lyons, Russell
We assign a countable ordinal number to each probability measure which annihilates all H-sets. The descriptive-set theoretic structure of this assignment allows us to show that this class of measures is coanalytic non-Borel. In addition, it allows us to quantify the failure of Rajchman's conjecture. Similar results are obtained for measures annihilating Dirichlet sets.
The Set of Continuous Functions with the Everywhere Convergent Fourier Series - Ajtai, M.; Kechris, A. S.
This paper deals with the descriptive set theoretic properties of the class EC of continuous functions with everywhere convergent Fourier series. It is shown that this set is a complete coanalytic set in C(T). A natural coanalytic rank function on EC is studied that assigns to each ƒ Є EC a countable ordinal number, which measures the "complexity" of the convergence of the Fourier series of ƒ. It is shown that there exist functions in EC (in fact even differentiable ones) which have arbitrarily large countable rank, so that this provides a proper hierarchy on EC with ω_1 distinct levels.
Dynamics of exhaled 13-CO_2 following oral administration of ^(13)C-bicarbonate - Cooper, D.; Barstow, T.; Sobel, E.; Epstein, S.
The ratio of ^(13)CO_2/^(12)CO_2 in the exhaled gas following IV administration of ^(13)C-bicarbonate can be used to estimate VCO_2 at different levels of exercise as well as to gain insight into CO_2 compartmental dynamics. But in children and under field conditions, IV administration is not feasible. To test the efficacy of the oral route, 8 oral and IV studies were performed in 2 subjects at rest and at 2 levels of exercise below the subject's anaerobic threshold. In 2 studies, the oral dose was given 1h and 4h after a meal. while in the remainder,· the subjects were fasted for...
Estimation of CO_2 stores by tracer dilution and VCO_2 kinetics - Barstow, T. J.; Cooper, D. M.; Springer, C.; Epstein, S.
The dynamics of CO_2 content and storage are critically
important in the control of metabolism and ventilation.
We compared two methods of estimating the changes in body
CO_2 stores due to light and moderate exercise: 1) washout
kinetics of exhaled ^(13)CO_2 following IV bolus of labeled
bicarbonate, and 2) analysis of pulmonary gas exchange
kinetics during the transition from rest to the steady state
of exercise. ^(13)CO_2 washout data was fit to a 3
compartment, mammillary model. If it were assumed that
the metabolic production of CO_2 occurred in the same compartment for rest and the 2 exercise conditions, then estimates of the increase in total exchangeable CO_2 ranged