Finite temperature properties of the triangular lattice t-J model, applications to Nax_xCoO2_2

We present a finite temperature ($T$) study of the t-J model on the two-dimensional triangular lattice for the negative hopping $t$, as relevant for the electron-doped Na$_x$CoO$_2$ (NCO). To understand several aspects of this system, we study the $T$-dependent chemical potential, specific heat, magnetic susceptibility, and the dynamic Hall-coefficient across the entire doping range. We show systematically, how this simplest model for strongly correlated electrons describes a crossover as function of doping ($x$) from a Pauli-like weakly spin-correlated metal close to the band-limit (density $n=2$) to the Curie-Weiss metallic phase ($1.5<n<1.75$) with pronounced anti-ferromagnetic (AFM) correlations at low temperatures and Curie-Weiss type behavior in the high-temperature regime. Upon further reduction of the doping, a new energy scale, dominated by spin-interactions ($J$) emerges (apparent both in specific heat and susceptibility) and we identify an effective interaction $J_{eff}(x)$, valid across the entire doping range. This is distinct from Anderson's formula, as we choose here $t<0$, hence the opposite sign of the usual Nagaoka-ferromagnetic situation. This expression includes the subtle effect of weak kinetic AFM - as encountered in the infinitely correlated situation ($U=\infty$). By explicit computation of the Kubo-formulae, we address the question of practical relevance of the high-frequency expression for the Hall coefficient $R_H^*$. We hope to clarify some open questions concerning the applicability of the t-J model to real experimental situations through this study

William (Bill) Peterson's contributions to ocean science, management, and policy

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Schwing, F. B., Sissenwine, M. J., Batchelder, H., Dam, H. G., Gomez-Gutierrez, J., Keister, J. E., Liu, H., & Peterson, J. O. William (Bill) Peterson's contributions to ocean science, management, and policy. Progress in Oceanography, 182, (2020): 102241, doi:10.1016/j.pocean.2019.102241.In addition to being an esteemed marine ecologist and oceanographer, William T. (Bill) Peterson was a dedicated public servant, a leader in the ocean science community, and a mentor to a generation of scientists. Bill recognized the importance of applied science and the need for integrated “big science” programs to advance our understanding of ecosystems and to guide their management. As the first US GLOBEC program manager, he was pivotal in transitioning the concept of understanding how climate change impacts marine ecosystems to an operational national research program. The scientific insight and knowledge generated by US GLOBEC informed and advanced the ecosystem-based management approaches now being implemented for fishery management in the US. Bill held significant leadership roles in numerous international efforts to understand global and regional ecological processes, and organized and chaired a number of influential scientific conferences and their proceedings. He was passionate about working with and training young researchers. Bill’s academic affiliations, notably at Stony Brook and Oregon State Universities, enabled him to advise, train, and mentor a host of students, post-doctoral researchers, and laboratory technicians. Under his collegial guidance they became critical independent thinkers and diligent investigators. His former students and colleagues carry on Bill Peterson’s legacy of research that helps us understand marine ecosystems and informs more effective resource stewardship and conservation

Phenomenological study of charm photoproduction at HERA

We present predictions for single inclusive distributions of charmed mesons, relevant to the HERA experiments. Our results are based upon a computation that correctly incorporates mass effects up to the next-to-leading order level, and the resummation of transverse momentum logarithms up to next-to-leading-logarithmic level. We apply the same acceptance cuts as the H1 and Zeus experiments, and compare our results to their data. We perform a study of the sensitivity of our predictions on the charm mass, \LambdaQCD, factorization scale, renormalization scale, and fragmentation parameters.Comment: 15 pages Latex; 25 figures include

Swimming Wolves, Canis lupus, Attack a Swimming Moose, Alces alces

In August 2008 at a small pond on Isle Royale, Michigan, we saw three Wolves (Canis lupus) run towards and leap at or onto a cow Moose (Alces alces) standing at the shore's edge in water ca. 1.7 m deep. The Moose swam out into the pond with the Wolves swimming in pursuit while attempting, with occasional success, to climb on the back of the Moose. The chase eventually moved out of our view, but a week later we found a Wolf-eaten cow on the pond's shoreline where we estimated it might have been killed. The animal was ca. 14-yr old with arthritic lesions in the pelvic region. This is apparently the first published report of swimming Wolves attacking and killing a swimming Moose, the kill likely having been made as the Moose emerged from the pond. Remains of a second kill in that pond were found shortly thereafter

Tempo and mode of performance evolution across multiple independent origins of adhesive toe pads in lizards

Understanding macroevolutionary dynamics of trait evolution is an important endeavor in evolutionary biology. Ecological opportunity can liberate a trait as it diversifies through trait space, while genetic and selective constraints can limit diversification. While many studies have examined the dynamics of morphological traits, diverse morphological traits may yield the same or similar performance and as performance is often more proximately the target of selection, examining only morphology may give an incomplete understanding of evolutionary dynamics. Here, we ask whether convergent evolution of pad‐bearing lizards has followed similar evolutionary dynamics, or whether independent origins are accompanied by unique constraints and selective pressures over macroevolutionary time. We hypothesized that geckos and anoles each have unique evolutionary tempos and modes. Using performance data from 59 species, we modified Brownian motion (BM) and Ornstein–Uhlenbeck (OU) models to account for repeated origins estimated using Bayesian ancestral state reconstructions. We discovered that adhesive performance in geckos evolved in a fashion consistent with Brownian motion with a trend, whereas anoles evolved in bounded performance space consistent with more constrained evolution (an Ornstein–Uhlenbeck model). Our results suggest that convergent phenotypes can have quite distinctive evolutionary patterns, likely as a result of idiosyncratic constraints or ecological opportunities

Thermoelectric effects in a strongly correlated model for Nax_xCoO2_2

Thermal response functions of strongly correlated electron systems are of appreciable interest to the larger scientific community both theoretically and technologically. Here we focus on the infinitely correlated t-J model on a geometrically frustrated two-dimensional triangular lattice. Using exact diagonalization on a finite sized system we calculate the dynamical thermal response functions in order to determine the thermopower, Lorenz number, and dimensionless figure of merit. The dynamical thermal response functions is compared to the infinite frequency limit and shown to be very weak functions of frequency, hence, establishing the validity of the high frequency formalism recently proposed by Shastry for the thermopower, Lorenz number, and the dimensionless figure of merit. Further, the thermopower is demonstrated to have a low to mid temperature enhancement when the sign of the hopping parameter $t$ is switched from positive to negative for the geometrically frustrated lattice considered.Comment: 16 pages, 10 figures, color version available at http://physics.ucsc.edu/~peterson/mrpeterson-condmat-NCO.pdf. V.2 has fixed minor typos in Eq. 11, 19, 25, and 26. V.3 is a color versio

Relationship of national institutes of health stroke scale to 30-day mortality in medicare beneficiaries with acute ischemic stroke.

BackgroundThe National Institutes of Health Stroke Scale (NIHSS), a well-validated tool for assessing initial stroke severity, has previously been shown to be associated with mortality in acute ischemic stroke. However, the relationship, optimal categorization, and risk discrimination with the NIHSS for predicting 30-day mortality among Medicare beneficiaries with acute ischemic stroke has not been well studied.Methods and resultsWe analyzed data from 33102 fee-for-service Medicare beneficiaries treated at 404 Get With The Guidelines-Stroke hospitals between April 2003 and December 2006 with NIHSS documented. The 30-day mortality rate by NIHSS as a continuous variable and by risk-tree determined or prespecified categories were analyzed, with discrimination of risk quantified by the c-statistic. In this cohort, mean age was 79.0 years and 58% were female. The median NIHSS score was 5 (25th to 75th percentile 2 to 12). There were 4496 deaths in the first 30 days (13.6%). There was a strong graded relation between increasing NIHSS score and higher 30-day mortality. The 30-day mortality rates for acute ischemic stroke by NIHSS categories were as follows: 0 to 7, 4.2%; 8 to 13, 13.9%; 14 to 21, 31.6%; 22 to 42, 53.5%. A model with NIHSS alone provided excellent discrimination whether included as a continuous variable (c-statistic 0.82 [0.81 to 0.83]), 4 categories (c-statistic 0.80 [0.79 to 0.80]), or 3 categories (c-statistic 0.79 [0.78 to 0.79]).ConclusionsThe NIHSS provides substantial prognostic information regarding 30-day mortality risk in Medicare beneficiaries with acute ischemic stroke. This index of stroke severity is a very strong discriminator of mortality risk, even in the absence of other clinical information, whether used as a continuous or categorical risk determinant. (J Am Heart Assoc. 2012;1:42-50.)

Intermittent permeation of cylindrical nanopores by water

Molecular Dynamics simulations of water molecules in nanometre sized cylindrical channels connecting two reservoirs show that the permeation of water is very sensitive to the channel radius and to electric polarization of the embedding material. At threshold, the permeation is {\emph{intermittent}} on a nanosecond timescale, and strongly enhanced by the presence of an ion inside the channel, providing a possible mechanism for gating. Confined water remains surprisingly fluid and bulk-like. Its behaviour differs strikingly from that of a reference Lennard-Jones fluid, which tends to contract into a highly layered structure inside the channel.Comment: 4 pages, 4 figure

Intermediate resolution H-beta spectroscopy and photometric monitoring of 3C 390.3 I. Further evidence of a nuclear accretion disk

We have monitored the AGN 3C390.3 between 1995 and 2000.Two large amplitude outbursts, of different duration, in continuum and H beta light were observed ie.: in October 1994 a brighter flare that lasted about 1000 days and in July 1997 another one that lasted about 700 days were detected. The flux in the H beta wings and line core vary simultaneously, a behavior indicative of predominantly circular motions in the BLR.Important changes of the Hbeta emission profiles were detected: at times, we found profiles with prominent asymmetric wings, as those normaly seen in Sy1s, while at other times, we observe profiles with weak almost symmetrical wings, similar to those seen in Sy1.8s. We found that the radial velocity difference between the red and blue bumps is anticorrelated with the light curves of H beta and continuum radiation.e found that the radial velocity difference between the red and blue bumps is anticorrelated with the light curves of H-beta and continuum radiation. Theoretical H-beta profiles were computed for an accretion disk, the observed profiles are best reproduced by an inclined disk (25 deg) whose region of maximum emission is located roughly at 200 Rg. The mass of the black hole in 3C 390.3, estimated from the reverberation analysis is Mrev = 2.1 x 10^9 Msun, ie. 5 times larger than previous estimatesComment: 18 pages, 13 figures, 4 tables. to appear in Astronomy and Astrophysic