University of Arkansas

About: University of Arkansas is a education organization based out in Fayetteville, Arkansas, United States. It is known for research contribution in the topics: Population & Poison control. The organization has 17225 authors who have published 33329 publications receiving 941102 citations. The organization is also known as: Arkansas & UA.

Ligand Bonding and Dynamics on Colloidal Nanocrystals at Room Temperature: The Case of Alkylamines on CdSe Nanocrystals

Abstract: With CdSe nanocrystals stabilized with very weak ligands (pyridine) as the starting materials, NMR techniques were applied to distinguish the bonded and free alkylamine ligands in an equilibrated adsorption/desorption system for the CdSe−amine nanocrystal−ligand pair. NMR and photoluminescence (PL) measurements were further correlated to identify the linear relationship between PL intensity and the surface ligand coverage of the amine-coated CdSe nanocrystals. For 3.5 nm CdSe nanocrystals and octylamine ligands, the chemical equilibrium constant (K) of the CdSe−amine nanocrystal−ligand adsorption/desorption process was found to be around 50−100, and the corresponding ΔrGo was calculated as 9.8−11.5 kJ/mol. With a proposed mathematic method, the corresponding chemical kinetic constants for the desorption (kd) and adsorption (ka) processes were measured to be 0.01 s-1 and 0.5 L mol-1 s-1, respectively. K, kd, and ka obtained here are generally 2−4 magnitudes different from those estimated in literature. Ana...

Supporting Listening Comprehension and Vocabulary Acquisition in French with Multimedia Annotations

Abstract: English-speaking college students enrolled in a French course listened to a 2-minute, 20-second historical account in French presented by a computer program. The participants were randomly assigned to one of four listening treatments: the listening text (a) with no annotations available, (b) with only written annotations available, (c) with only pictorial annotations available, and (d) with both written and pictorial annotations available. The students remembered word translations and recalled the passage better when they had selected both written and pictorial annotations while listening rather than one of these types or no annotations. In addition, effect sizes were much larger for pictorial annotations than for written annotations, especially for delayed tests. The results were consistent with Mayer's (1997, 2001) Generative Theory of Multimedia Learning and extend this theory to listening comprehension.

Electromagnetically induced grating: Homogeneously broadened medium

Abstract: A strong coupling standing wave, interacting with three-level \ensuremath{\Lambda}-type (or ladder-type) atoms, can diffract a weak probe field (propagating along a direction normal to the standing wave) into high-order diffractions, a phenomenon which we name electromagnetically induced grating (EIG). We develop in this work a theory for studying EIG in a homogeneously broadened medium consisting of three-level \ensuremath{\Lambda}-type atoms. We show that by taking advantage of the absorption and dispersion properties of electromagnetically induced transparency one can create an atomic grating that can effectively diffract light into the first-order direction.

Reconstruction and Analysis of Spring Rainfall over the Southeastern U.S. for the Past 1000 Years

Abstract: Tree-ring chronologies can provide surprisingly accurate estimates of the natural variability of important climate parameters such as precipitation and temperature during the centuries prior to the industrial Revolution. Bald cypress tree-ring chronologies have been used to reconstruct spring rainfall for the past 1000 years in North Carolina, South Carolina, and Georgia. These rainfall reconstructions explain from 54% to 68% of the spring rainfall variance in each state, and are well verified against independent rainfall measurements. In fact, these tree-ring data explain only 6% to 13% less statewide rainfall variance than is explained by the same number of instrumental raingage records. The reconstructions indicate that the spring rainfall extremes and decade-long regimes witnessed during the past century of instrumental observation have been a prominent feature of southeastern United States climate over the past millennium. These spring rainfall regimes are linked in part to anomalies in the seasonal expansion and migration of the subtropical anticyclone over the North Atlantic. The western sector of the Bermuda high often ridges strongly westward into the southeastern United States during dry springs, but during wet springs it is usually located east of its mean position and well offshore. Similar anomalies in the western sector of themore » Bermuda high occurred during multidecadal regimes of spring rainfall over the Southeast. During the relatively dry springs from 1901 to 1939, the high often ridged into the Southeast, but the western periphery of the high was more frequently located offshore during the relatively wet period from 1940 to 1980. Spring and summer rainfall extremes and decade-long regimes over the Southeast are frequently out of phase, and the tendency for wet (dry) springs to be followed by dry (wet) summers also appears to reflect anomalies in the zonal position of the Bermuda high during spring and summer.« less