Molar and local effects of the fixed-ratio changeover requirement on choice, changeovers, and visits: A parametric examination of the fixed-ratio changeover requirement

The distribution of behavior by organisms in choice situations is of long-standing interest to psychologists. The generalized matching relation accurately predicts choice between concurrent variable-interval schedules of reinforcement. Researchers have assumed, on weak grounds, that the effect of the changeover requirement on sensitivity to reinforcement--the exponent in the generalized matching equation--was consistent. This experiment considered the effects of the changeover requirement by parametrically manipulating the fixed-ratio schedule required to switch alternatives. Pigeons pecked either of two side-response keys in a standard three-key operant chamber for food, delivered according to independent variable-interval schedules. No changeover delay was used, instead completion of five fixed-ratio schedules (FR 0, 2, 6, 12, or 20) on the center-response key alternated the active side key. Five reinforcer ratio (1:1, 1:2, 2:1, 1:4, and 4:1) were paired with most FR schedules. A matching relation analysis indicated that for two pigeons response-allocation sensitivity generally overmatched for all but the FR 0 condition, which undermatched. The other two pigeons\u27 sensitivity increased to overmatching when FR 12 was in force. Excepting FR 0 conditions, time-allocation sensitivity, on the other hand, decreased from extreme overmatching toward matching as the changeover requirement increased. Reliable changes in response rates to the two alternatives account for the results. A positive relation between the conditional probability of switching and run length is reported. That is, the greater the number of consecutive pecks to an alternative, the greater the likelihood of switching. This result suggests that behavior is controlled in part by local reinforcement contingencies. I speculate that factors that increase visit duration may increase local control of switching. The procedure encourages a foraging interpretation. The FR changeover requirement can be considered functionally equivalent to travel between patches. An analysis of visit measures supported earlier evidence that residence measures increase as travel between patches increases. These results together with the matching results suggest that behavior ecologists and operant psychologists are working on similar problems and the traditional tools of operant psychology can be used to simulate travel, an important component of foraging in the wild

Lif, the lysostaphin immunity factor, complements FemB in staphylococcal peptidoglycan interpeptide bridge formation

The formation of the Staphylococcus aureus peptidoglycan pentaglycine interpeptide chain needs FemA and FemB for the incorporation of glycines Gly2-Gly3, and Gly4-Gly5, respectively. The lysostaphin immunity factor Lif was able to complement FemB, as could be shown by serine incorporation and by an increase in lysostaphin resistance in the wild-type as well as in a femB mutant. However, Lif could not substitute for FemA in femA or in femAB-null mutants. Methicillin resistance, which is dependent on functional FemA and FemB, was not complemented by Lif, suggesting that serine-substituted side chains are a lesser substrate for penicillin-binding protein PBP2′ in methicillin resistanc

X-ray Bright Active Galactic Nuclei in Massive Galaxy Clusters II: The Fraction of Galaxies Hosting Active Nuclei

We present a measurement of the fraction of cluster galaxies hosting X-ray bright Active Galactic Nuclei (AGN) as a function of clustercentric distance scaled in units of $r_{500}$. Our analysis employs high quality Chandra X-ray and Subaru optical imaging for 42 massive X-ray selected galaxy cluster fields spanning the redshift range of $0.2 < z < 0.7$. In total, our study involves 176 AGN with bright ($R <23$) optical counterparts above a $0.5-8.0$ keV flux limit of $10^{-14} \rm{erg} \ \rm{cm}^{-2} \ \rm{s}^{-1}$. When excluding central dominant galaxies from the calculation, we measure a cluster-galaxy AGN fraction in the central regions of the clusters that is $\sim 3$ times lower that the field value. This fraction increases with clustercentric distance before becoming consistent with the field at $\sim 2.5 r_{500}$. Our data exhibit similar radial trends to those observed for star formation and optically selected AGN in cluster member galaxies, both of which are also suppressed near cluster centers to a comparable extent. These results strongly support the idea that X-ray AGN activity and strong star formation are linked through their common dependence on available reservoirs of cold gas.Comment: 9 Pages, 4 Figures, accepted for publication in MNRAS, please contact Steven Ehlert ([email protected]) with any querie

X-ray bright active galactic nuclei in massive galaxy clusters III: New insights into the triggering mechanisms of cluster AGN

We present the results of a new analysis of the X-ray selected Active Galactic Nuclei (AGN) population in the vicinity of 135 of the most massive galaxy clusters in the redshift range of 0.2 < z < 0.9 observed with Chandra. With a sample of more than 11,000 X-ray point sources, we are able to measure, for the first time, evidence for evolution in the cluster AGN population beyond the expected evolution of field AGN. Our analysis shows that overall number density of cluster AGN scales with the cluster mass as $\sim M_{500}^{-1.2}$. There is no evidence for the overall number density of cluster member X-ray AGN depending on the cluster redshift in a manner different than field AGN, nor there is any evidence that the spatial distribution of cluster AGN (given in units of the cluster overdensity radius r_500) strongly depends on the cluster mass or redshift. The $M^{-1.2 \pm 0.7}$ scaling relation we measure is consistent with theoretical predictions of the galaxy merger rate in clusters, which is expected to scale with the cluster velocity dispersion, $\sigma$, as $\sim \sigma^{-3}$ or $\sim M^{-1}$. This consistency suggests that AGN in clusters may be predominantly triggered by galaxy mergers, a result that is further corroborated by visual inspection of Hubble images for 23 spectroscopically confirmed cluster member AGN in our sample. A merger-driven scenario for the triggering of X-ray AGN is not strongly favored by studies of field galaxies, however, suggesting that different mechanisms may be primarily responsible for the triggering of cluster and field X-ray AGN.Comment: 21 Pages, 8 figures, 5 tables. Submitted to MNRAS. Comments are welcome, and please request Steven Ehlert for higher resolution figure

Fuller Library Bulletin - April-June, 1950, No. 6

Originally published in print for the library of Fuller Theological Seminary from 1949 through 1958.https://digitalcommons.fuller.edu/fts-lib-bulletin/1004/thumbnail.jp

Fuller Library Bulletin - January-March, 1955, No. 25

Originally published in print for the library of Fuller Theological Seminary from 1949 through 1958.https://digitalcommons.fuller.edu/fts-lib-bulletin/1015/thumbnail.jp

Fuller Library Bulletin -January-March, 1950, No.5

Originally published in print for the library of Fuller Theological Seminary from 1949 through 1958.https://digitalcommons.fuller.edu/fts-lib-bulletin/1003/thumbnail.jp

Fuller Library Bulletin -July-December, 1950, No. 7, 8

Originally published in print for the library of Fuller Theological Seminary from 1949 through 1958.https://digitalcommons.fuller.edu/fts-lib-bulletin/1005/thumbnail.jp