University of Arizona

About: University of Arizona is a education organization based out in Tucson, Arizona, United States. It is known for research contribution in the topics: Population & Galaxy. The organization has 63805 authors who have published 155998 publications receiving 6854915 citations. The organization is also known as: UA & U of A.

Comparison of spatial firing characteristics of units in dorsal and ventral hippocampus of the rat

Abstract: The septal and temporal poles of the hippocampus differ markedly in their anatomical and neurochemical organization. Although it is well established that the internal representation of space is a fundamental function of hippocampal neurons, most of what is known about spatial coding in the hippocampus of freely moving animals has come from recordings from the dorsal one-third (largely for technical convenience). The present study therefore compared the spatial selectivity of CA1 neurons in the dorsal and ventral hippocampi of rats during performance of a food reinforced, random search task in a square chamber containing simple visual landmarks. Neural activity was recorded in the dorsal and ventral hippocampi of opposite hemispheres in the same rats, in many cases simultaneously. As in dorsal hippocampus, ventral CA1 units could be classified as "complex spike" (pyramidal) cells or "theta" interneurons. Both dorsal and ventral theta cells fired at relatively high rates and with low spatial selectivity in the apparatus. Of the population of complex spike cells in the ventral hippocampus, a significantly smaller number had "place fields" than in the dorsal hippocampus, and the average spatial selectivity was of significantly lower resolution than that found among dorsal hippocampal complex spike cells. Thus, a septotemporal difference of spatial selectivity was found in the CA1 field of the rat hippocampus, complementing many other anatomical and neuropharmacological studies. A number of possible functional interpretations can be suggested from these results, including a computational advantage of representing space at different scales or a preeminence of essentially nonspatial information processing in the ventral hippocampus.

Cross-Sectional Versus Longitudinal Survey Research: Concepts, Findings and Guidelines

Abstract: Marketing academics and practitioners frequently employ cross-sectional surveys. In recent years, editors, reviewers, and authors have expressed increasing concern about the validity of this approach. These validity concerns center on reducing common method variance bias and enhancing causal inferences. Longitudinal data collection is commonly offered as a solution to these problems. In this article, the authors conceptually examine the role of longitudinal surveys in addressing these validity concerns. Then, they provide an illustrative comparison of the validity of cross-sectional versus longitudinal surveys using two data sets and a Monte Carlo simulation. The conceptualization and findings suggest that under certain conditions, the results from cross-sectional data exhibit validity comparable to the results obtained from longitudinal data. This article concludes by offering a set of guidelines to assist researchers in deciding whether to employ a longitudinal survey approach.

The Arabidopsis thaliana SOS2 gene encodes a protein kinase that is required for salt tolerance

Abstract: In Arabidopsis thaliana, the Salt Overly Sensitive 2 (SOS2) gene is required for intracellular Na+ and K+ homeostasis. Mutations in SOS2 cause Na+ and K+ imbalance and render plants more sensitive toward growth inhibition by high Na+ and low K+ environments. We isolated the SOS2 gene through positional cloning. SOS2 is predicted to encode a serine/threonine type protein kinase with an N-terminal catalytic domain similar to that of the yeast SNF1 kinase. Sequence analyses of sos2 mutant alleles reveal that both the N-terminal catalytic domain and the C-terminal regulatory domain of SOS2 are functionally essential. The steady-state level of SOS2 transcript is up-regulated by salt stress in the root. Autophosphorylation assays show that SOS2 is an active protein kinase. In the recessive sos2-5 allele, a conserved glycine residue in the kinase catalytic domain is changed to glutamate. This mutation abolishes SOS2 autophosphorylation, indicating that SOS2 protein kinase activity is required for salt tolerance.

Thermonuclear (Type I) X-Ray Bursts Observed by the Rossi X-Ray Timing Explorer

Abstract: We have assembled a sample of 1187 thermonuclear (type I) X-ray bursts from observations of 48 accreting neutron stars by the Rossi X-ray Timing Explorer, spanning more than 10 years. The sample contains examples of two of the three theoretical ignition regimes (confirmed via comparisons with numerical models) and likely examples of the third. We present a detailed analysis of the variation of the burst profiles, energetics, recurrence times, presence of photospheric radius expansion, and presence of burst oscillations, as a function of accretion rate. We estimated the distance for 35 sources exhibiting radius-expansion bursts, and found that the peak flux of such bursts varies typically by 13%. We classified sources into two main groups based on the burst properties: (1) both long and short bursts (indicating mixed H/He accretion), and (2) consistently short bursts (primarily He accretion), and we calculated the mean burst rate as a function of accretion rate for the two groups. The decrease in burst rate observed at > 0.06dot MEdd (~2 × 10^37 ergs s^−1) is associated with a transition in the persistent spectral state and (as has been suggested previously) may be related to the increasing role of steady He burning. We found many examples of bursts with recurrence times <30 minutes, including burst triplets and even quadruplets. We describe the oscillation amplitudes for 13 of the 16 burst oscillation sources, as well as the stages and properties of the bursts in which the oscillations are detected. The burst properties are correlated with the burst oscillation frequency; sources spinning at <400 Hz generally have consistently short bursts, while the more rapidly spinning systems have both long and short bursts. This correlation suggests either that shear-mediated mixing dominates the burst properties, or alternatively that the nature of the mass donor (and hence the evolutionary history) has an influence on the long-term spin evolution.