Ab initio quantum Monte Carlo calculations of spin superexchange in cuprates: the benchmarking case of Ca2_2CuO3_3

In view of the continuous theoretical efforts aimed at an accurate microscopic description of the strongly correlated transition metal oxides and related materials, we show that with continuum quantum Monte Carlo (QMC) calculations it is possible to obtain the value of the spin superexchange coupling constant of a copper oxide in a quantitatively excellent agreement with experiment. The variational nature of the QMC total energy allows us to identify the best trial wave function out of the available pool of wave functions, which makes the approach essentially free from adjustable parameters and thus truly ab initio. The present results on magnetic interactions suggest that QMC is capable of accurately describing ground state properties of strongly correlated materials.Comment: Published in Physical Review

Measuring The Equations Of State In A Relaxed Magnetohydrodynamic Plasma

We report measurements of the equations of state of a fully relaxed magnetohydrodynamic (MHD) laboratory plasma. Parcels of magnetized plasma, called Taylor states, are formed in a coaxial magnetized plasma gun, and are allowed to relax and drift into a closed flux conserving volume. Density, ion temperature, and magnetic field are measured as a function of time as the Taylor states compress and heat. The theoretically predicted MHD and double adiabatic equations of state are compared to experimental measurements. We find that the MHD equation of state is inconsistent with our data

Targeting multiple rescatterings through VUV-controlled high-order-harmonic generation

We theoretically investigate the use of an isolated attosecond vacuum ultraviolet (VUV) pulse to control the emergence of multiple wave-packet rescatterings in the process of high-harmonic generation (HHG). Through numerical solution of the time-dependent Schrödinger equation for a He atom driven by 0.8 – 2.0 − μm light, we establish the relationship between evidence of multiple rescatterings in HHG and the time delay between the VUV and infrared pulses. We find features of multiple rescatterings present in both the time and frequency domains of emitted HHG, and demonstrate the use of VUV-induced multiple rescatterings for generating trains of ultrashort light pulses.M.M. acknowledges support by the National Science Foundation Graduate Research Fellowship under Grant No. DGE 1144083 and was also supported via a grant awarded by the U.S. Department of Energy Office of Basic Energy Science, Chemical Sciences, Geosciences and Biosciences Division, Atomic, Molecular, and Optical Sciences Program (Grant No. DE-FG02-09ER16103). C.H.G. acknowledges support by a Marie Curie International Outgoing Fellowship within the EU Seventh Framework Programme for Research and Technological Development (2007-2013), under REA Grant No. 328334. A.J.B. was supported by the U.S. National Science Foundation under Grants No. PHY-1125844 and No. PHY-1068706. A.B. acknowledges support by the U.S. Department of Energy Office of Basic Energy Science, Chemical Sciences, Geosciences and Biosciences Division, Atomic, Molecular, and Optical Sciences Program (Grant No. DE-FG02-09ER16103). This work utilized the Janus supercomputer, which is supported by the U.S. National Science Foundation (Award No. CNS- 0821794) and the University of Colorado Boulde

An Introduction to Causal Inference Methods for Observational Human-Robot Interaction Research

Quantitative methods in Human-Robot Interaction (HRI) research have primarily relied upon randomized, controlled experiments in laboratory settings. However, such experiments are not always feasible when external validity, ethical constraints, and ease of data collection are of concern. Furthermore, as consumer robots become increasingly available, increasing amounts of real-world data will be available to HRI researchers, which prompts the need for quantative approaches tailored to the analysis of observational data. In this article, we present an alternate approach towards quantitative research for HRI researchers using methods from causal inference that can enable researchers to identify causal relationships in observational settings where randomized, controlled experiments cannot be run. We highlight different scenarios that HRI research with consumer household robots may involve to contextualize how methods from causal inference can be applied to observational HRI research. We then provide a tutorial summarizing key concepts from causal inference using a graphical model perspective and link to code examples throughout the article, which are available at https://gitlab.com/causal/causal_hri. Our work paves the way for further discussion on new approaches towards observational HRI research while providing a starting point for HRI researchers to add causal inference techniques to their analytical toolbox.Comment: 28 page

Monomorphic trypanozoon:Towards reconciling phylogeny and pathologies

Trypanosoma brucei evansi and T. brucei equiperdum are animal infective trypanosomes conventionally classified by their clinical disease presentation, mode of transmission, host range, kinetoplast DNA (kDNA) composition and geographical distribution. Unlike other members of the subgenus Trypanozoon, they are non-tsetse transmitted and predominantly morphologically uniform (monomorphic) in their mammalian host. Their classification as independent species or subspecies has been long debated and genomic studies have found that isolates within T. brucei evansi and T. brucei equiperdum have polyphyletic origins. Since current taxonomy does not fully acknowledge these polyphyletic relationships, we re-analysed publicly available genomic data to carefully define each clade of monomorphic trypanosome. This allowed us to identify, and account for, lineage-specific variation. We included a recently published isolate, IVM-t1, which was originally isolated from the genital mucosa of a horse with dourine and typed as T. equiperdum. Our analyses corroborate previous studies in identifying at least four distinct monomorphic T. brucei clades. We also found clear lineage-specific variation in the selection efficacy and heterozygosity of the monomorphic lineages, supporting their distinct evolutionary histories. The inferred evolutionary position of IVM-t1 suggests its reassignment to the T. brucei evansi type B clade, challenging the relationship between the Trypanozoon species, the infected host, mode of transmission and the associated pathological phenotype. The analysis of IVM-t1 also provides, to our knowledge, the first evidence of the expansion of T. brucei evansi type B, or a fifth monomorphic lineage represented by IVM-t1, outside of Africa, with important possible implications for disease diagnosis