The response of Musa cultivar root systems to a tree shade gradient

Poster presented at Tropentag 2011 - Development on the Margin. Bonn (Germany), 3-7 Oct 2011

Universal magnetic and structural behaviors in the iron arsenides

Commonalities among the order parameters of the ubiquitous antiferromagnetism present in the parent compounds of the iron arsenide high temperature superconductors are explored. Additionally, comparison is made between the well established two-dimensional Heisenberg-Ising magnet, K$_2$NiF$_4$ and iron arsenide systems residing at a critical point whose structural and magnetic phase transitions coincide. In particular, analysis is presented regarding two distinct classes of phase transition behavior reflected in the development of antiferromagnetic and structural order in the three main classes of iron arsenide superconductors. Two distinct universality classes are mirrored in their magnetic phase transitions which empirically are determined by the proximity of the coupled structural and magnetic phase transitions in these materials.Comment: 6 pages, 4 figure

A preliminary demonstration of transformation of functions through hierarchical relations

The current study focuses on the experimental analysis of hierarchical responding, and aims at analyzing some of the transformation of functions that take place at different levels of hierarchical categories. Ten university students participated. During Phase 1, four arbitrary stimuli were established as INCLUDES, BELONGS TO, SAME, and DIFFERENT relational cues, respectively. During Phase 2, three four-member equivalence classes were trained and tested (A1-B1-C1-D1; A2-B2-C2-D2; A3-B3-C3-D3). These equivalence classes constituted the bottom level of two hierarchical categories. The middle and top levels of the hierarchical categories were formed during Phase 3. The middle level was established by training hierarchical relations (INCLUDES and BELONGS TO) between novel stimuli X.1 and A1/B1; X. 2 and A2/B2; and Y and A3/B3. The top level was established by training hierarchical relations between X and X.1/X.2, and between Y and Y.1. During Phase 4, X.1 was established as always cold, D2 as always heavy and C3 as always sweet. During Phase 5 (Critical Test), six stimuli from both hierarchical categories (Y, X, C1, X.2, D3, C2) and a non-related stimulus (M) were tested for the transformation of functions. Nine of the ten participants responded correctly to the test. The implications and limitations of these findings, as well as lines for future research, are discussed

A further experimental step in the analysis of hierarchical responding

This study is a step forward in the difficult task of analyzing the transformation of functions via hierarchical relations. Eight participants underwent a computer task with five phases. During Phase 1, four stimuli were trained to become the following relational cues: INCLUDES, BELONGS TO, SAME, and DIFFERENT. In Phase 2, three equivalence classes were trained and tested (A1-B1-C1-D1; A2-B2-C2-D2; A3-B3-C3-D3). During Phase 3, inclusion relations were first established, by using the INCLUDES and BELONGS TO relational cues, between the to-be lower levels of the hierarchy, namely A1/B1, A2/B2, and A3/B3; and stimuli X.1, X.2, and Y.1, respectively. Then, the INCLUDES relational cue was used to establish inclusion relations between X.1/X.2 and X, and between Y.1 and Y, so that X and Y would become the most inclusive levels of two separate hierarchical networks. In Phase 4, X.1 was established as cold, D2 as heavy, and C3 as sweet. Lastly, in Phase 5 (Critical Test), seven stimuli from both hierarchical networks were tested for the transformation of functions. Five of the six participants who made it to this test responded correctly. Implications, limitations, and further research are discussed

Antiferromagnetic Critical Fluctuations in BaFe2_2As2_2

Magnetic correlations near the magneto-structural phase transition in the bilayer iron pnictide parent compound, BaFe$_2$As$_2$, are measured. In close proximity to the antiferromagnetic phase transition in BaFe$_2$As$_2$, a crossover to three dimensional critical behavior is anticipated and has been preliminarily observed. Here we report complementary measurements of two-dimensional magnetic fluctuations over a broad temperature range about T$_N$. The potential role of two-dimensional critical fluctuations in the magnetic phase behavior of BaFe$_2$As$_2$ and their evolution near the anticipated crossover to three dimensional critical behavior and long-range order are discussed.Comment: 6 pages, 4 figures; Accepted for publication in Physical Review

Heat capacity study of BaFe2_{2}As2_{2}: effects of annealing

Heat-capacity, X-ray diffraction, and resistivity measurements on a high-quality BaFe$_{2}$As$_{2}$ sample show an evolution of the magneto-structural transition with successive annealing periods. After a 30-day anneal the resistivity in the (ab) plane decreases by more than an order of magnitude, to 12 $\mu\Omega$cm, with a residual resistance ratio $\sim$36; the heat-capacity anomaly at the transition sharpens, to an overall width of less than K, and shifts from 135.4 to 140.2 K. The heat-capacity anomaly in both the as-grown sample and after the 30-day anneal shows a hysteresis of $\sim$0.15 K, and is unchanged in a magnetic field $\mu_{0}$H = 14 T. The X-ray and heat-capacity data combined suggest that there is a first order jump in the structural order parameter. The entropy of the transition is reported

Functional and Morphological Studies of Mitochondria Exposed to Undecagold Clusters: Biologic Surfaces Labeling with Gold Clusters

This study reports morphological and functional alterations observed in respiring isolated mitochondria when they are exposed to nonpenetrating, positive electrostatically charged synthetic undecagold clusters. Modification of the undecagold clusters positive charges change or prevent the functional effects and the binding to the outside surface of the mitochondria. The mitochondrial functional alterations are dependent on the oxidative phosphorylation capacity of the isolated organelles. The results of these experiments indicate that artificial undecagold may be useful to explore the molecular mechanisms of biological energy transducers which require electric charges separation, ionic fluxes, and electric surface properties

Blockade of nucleus accumbens 5-HT2A and 5-HT2C receptors prevents the expression of cocaine-induced behavioral and neurochemical sensitization in rats

The serotonin 5-HT2A and 5-HT2C receptors regulate the capacity of acute cocaine to augment behavior and monoamine levels within the nucleus accumbens (NAC), a brain region involved in cocaine’s addictive and psychotogenic properties. In the present study, we tested the hypothesis that NAC 5-HT2A and 5-HT2C receptor activation is involved in the expression of cocaine-induced neuroplasticity following protracted withdrawal from a sensitizing repeated cocaine regimen (days 1 and 7, 15 mg/kg; days 2–6, 30 mg/kg, i.p.). The effects of intra-NAC infusions of the 5-HT2A antagonist R-(+)-α-(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenylethyl)]-4-piperidine methanol (MDL 100907; 0, 50, 100, 500 nM) or the 5-HT2C antagonist [6-chloro-5-methyl-1-(6-(2-methylpiridin-3-yloxy)pyridine-3-yl carbamoyl] inodoline dihydrochloride (SB 242084; 0, 50, 100, 500 nM) were first assessed upon the expression of locomotor activity elicited by a 15-mg/kg cocaine challenge injection administered at 3-week withdrawal. A follow-up in vivo microdialysis experiment then compared the effects of the local perfusion of 0, 50, or 100 nM of each antagonist upon cocaine-induced dopamine and glutamate sensitization in the NAC. Although neither MDL 100907 nor SB 242084 altered acute cocaine-induced locomotion, SB 242084 reduced acute cocaine-elevated NAC dopamine and glutamate levels. Intra-NAC perfusion with either compound blocked the expression of cocaine-induced locomotor and glutamate sensitization, but only MDL 100907 pretreatment prevented the expression of cocaine-induced dopamine sensitization. These data provide the first evidence that NAC 5-HT2A and 5-HT2C receptors are critical for the expression of cocaine-induced neuroplasticity following protracted withdrawal, which has relevance for their therapeutic utility in the treatment of addiction

Relevance of mytilid shell microtopographies for fouling defence - a global comparison

Prevention of epibiosis is of vital importance for most aquatic organisms, which can have consequences for their ability to invade new areas. Surface microtopography of the shell periostracum has been shown to have antifouling properties for mytilid mussels, and the topography shows regional differences. This article examines whether an optimal shell design exists and evaluates the degree to which shell microstructure is matched with the properties of the local fouling community. Biomimics of four mytilid species from different regional provenances were exposed at eight different sites in both northern and southern hemispheres. Tendencies of the microtopography to both inhibit and facilitate fouling were detected after 3 and 6 weeks of immersion. However, on a global scale, all microtopographies failed to prevent fouling in a consistent manner when exposed to various fouling communities and when decoupled from other shell properties. It is therefore suggested that the recently discovered chemical anti-microfouling properties of the periostracum complement the anti-macrofouling defence offered by shell microtopography