A pointwise cubic average for two commuting transformations

Huang, Shao and Ye recently studied pointwise multiple averages by using suitable topological models. Using a notion of dynamical cubes introduced by the authors, the Huang-Shao-Ye technique and the Host machinery of magic systems, we prove that for a system $(X,\mu,S,T)$ with commuting transformations $S$ and $T$, the average $$\frac{1}{N^2} \sum_{i,j=0}^{N-1} f_0(S^i x)f_1(T^j x)f_2(S^i T^j x)$$ converges a.e. as $N$ goes to infinity for any $f_1,f_2,f_3\in L^{\infty}(\mu)$

Robust Stylized Facts on Comovement for the Spanish Economy

In this article we further develop the suggestion of obtaining stylized facts on comovement on the basis of prewhitened time series proposed in André, Pérez and Martín (2002). Firstly, we show some examples on the robustness of the method. Secondly, we test the relevance of such a proposal by revisiting some of the existing stylized facts on comovement for the Spanish economy in Dolado, Sebastián and Vallés (1993).Stylized Facts, Comovement, Cross Correlation Function, HP-Filter, Prewhitening

Endogenous differential information in financial markets

We develop a two period general equilibrium model with incomplete financial markets and differential information. Making endogenous the traditional informational restriction on consumption, we allow agents to obtain information from physical and financial markets. Thus, the investment in financial promises and the trade of commodities in spot markets appear as natural channels to improve the information that an agent has about the realization of future states of nature.Incomplete Markets, Differential information, Enlightening equilibrium.

Does Stock Return Predictability Affect ESO Fair Value?

Executive Stock Options (ESOs) are modified American options that cannot be valued using standard methods. With a few exceptions, the literature has discussed the ESO fair value by assuming unpredictable stock returns which are not supported by the available empirical evidence. In this paper we obtain the fair value of American ESOs when stock returns are predictable and, specifically, driven by the trending Ornstein-Uhlenbeck process of Lo and Wang (1995). We solve the executive’s portfolio allocation problem for a simple buy-and-hold strategy when his wealth can be distributed between a risk-free asset and a market portfolio. This problem is jointly solved with the executive’s optimal exercise policy. We find that executives tend to wait longer the higher the predictability, independently of the composition of executive’s asset menu. We have also analyzed the implications under the FAS123R proposals for the ESO fair value and found that, even for low autocorrelations, there is a meaningful mispricing when unpredictable returns are erroneously assumed.Executive Stock Options; Risk Aversion; Undiversification; Predictability; FAS123R

Electron refraction at lateral atomic interfaces

We present theoretical simulations of electron refraction at the lateral atomic interface between a “homogeneous” Cu(111) surface and the “nanostructured” one-monolayer (ML) Ag/Cu(111) dislocation lattice. Calculations are performed for electron binding energies barely below the 1 ML Ag/ Cu(111) M-point gap (binding energy EB ¼53 meV, below the Fermi level) and slightly above its C -point energy (EB ¼160 meV), both characterized by isotropic/circular constant energy surfaces. Using plane-wave-expansion and boundary-element methods, we show that electron refraction occurs at the interface, the Snell law is obeyed, and a total internal reflection occurs beyond the critical angle. Additionally, a weak negative refraction is observed for EB ¼53 meV electron energy at beam incidence higher than the critical angle. Such an interesting observation stems from the interface phase-matching and momentum conservation with the umklapp bands at the second Brillouin zone of the dislocation lattice. The present analysis is not restricted to our Cu-Ag/Cu model system but can be readily extended to technologically relevant interfaces with spinpolarized, highly featured, and anisotropic constant energy contours, such as those characteristic for Rashba systems and topological insulators. Published by AIP Publishing.Peer ReviewedPostprint (published version

String Department Recital, April 21, 1993

This is the concert program of the String Department Recital on Wednesday, April 21, 1993 at 8:00 p.m., at the Marshall Room, 855 Commonwealth Avenue. Works performed were Lachrymae by Benjamin Britten, Andantino cantabile and Vivace giocoso from Concerto for Violin in C major, Op. 48 by Dmitry Kabalevsky, Breit (attacca) and Sehr frisch und straff from Sonata for Solo Viola, Op. 25, No. 1 by Paul Hindemith, and Andante and Allegrissimo from Sonata No. 1 in F minor, Op. 80 by Sergey Prokofiev. Digitization for Boston University Concert Programs was supported by the Boston University Humanities Library Endowed Fund

Lecture Notes on Topological Crystalline Insulators

We give an introduction to topological crystalline insulators, that is, gapped ground states of quantum matter that are not adiabatically connected to an atomic limit without breaking symmetries that include spatial transformations, like mirror or rotational symmetries. To deduce the topological properties, we use non-Abelian Wilson loops. We also discuss in detail higher-order topological insulators with hinge and corner states, and in particular present interacting bosonic models for the latter class of systems.Comment: Lectures given at the San Sebasti\'an Topological Matter School 2017, published in "Topological Matter. Springer Series in Solid-State Sciences, vol 190. Springer, Cham

Functional traits driving species role in the structure of terrestrial vertebrate scavenger networks

Species assemblages often have a non-random nested organization, which in vertebrate scavenger (carrion-consuming) assemblages is thought to be driven by facilitation in competitive environments. However, not all scavenger species play the same role in maintaining assemblage structure, as some species are obligate scavengers (i.e., vultures) and others are facultative, scavenging opportunistically. We used a database with 177 vertebrate scavenger species from 53 assemblages in 22 countries across five continents to identify which functional traits of scavenger species are key to maintaining the scavenging network structure. We used network analyses to relate ten traits hypothesized to affect assemblage structure with the “role” of each species in the scavenging assemblage in which it appeared. We characterized the role of a species in terms of both the proportion of monitored carcasses on which that species scavenged, or scavenging breadth (i.e., the species “normalized degree”), and the role of that species in the nested structure of the assemblage (i.e., the species “paired nested degree”), therefore identifying possible facilitative interactions among species. We found that species with high olfactory acuity, social foragers, and obligate scavengers had the widest scavenging breadth. We also found that social foragers had a large paired nested degree in scavenger assemblages, probably because their presence is easier to detect by other species to signal carcass occurrence. Our study highlights differences in the functional roles of scavenger species and can be used to identify key species for targeted conservation to maintain the ecological function of scavenger assemblages.Generalitat Valenciana SEJI/2018/024, APOSTD/2019/016, CIDEGENT/ 2020/030, ACIF/2019/056Ministerio de Educación y Cultura CI-2017-32149, FJCI-2015-25632, IJC2018-036642-I, YC-2019-027216-I, RYC-2015-19231, RYC-2017-2273, GL2012-40013-C02-01/02, CGL2015- 66966-C2-1-R, CGL2015-66966-C2-1-R2, CGL2017-89905-R, RTI2018-099609-B-C21, RTI2018-099609-B-C22Govern de les Illes Balears PD/039/201National Science Centre in Poland 2013/08/M/ NZ9/00469, 2016/22/Z/NZ8/00Slovenian Research Agency P4-0059US Department of Energy DE- EM000439USA National Science Foundation #1255913California Department of Fish & Wildlife P0880013Junta de Andalucía RNM-192