Evidence for nonlinear binding of PAHs to dissolved humic acids

Binding of pyrene, fluoranthene, and phenanthrene to dissolved humic acids (HA) was determined by the fluorescence quenching (FQ) and complexation-flocculation (CF) methods. Determinations by the CF method, using varying contaminant concentrations and a constant HA concentration, yielded nonlinear Freundlich-type isotherms (n = 0.65-0.84). Experiments using both the CF and the FQ methods with varying HA concentrations and a constant contaminant concentration yielded curved "Stern-Volmer"-type plots that also indicate nonlinear binding. These findings suggest that linear partitioning or site complexation in the presence of excess available sites cannot fully describe the interactions of hydrophobic compounds with dissolved humic material. Site-specific hydrophobic interactions at limited interior or external molecular surfaces may be considered.     

Activity of units in the hippocampal circuit of the rat during differential classical conditioning.

Recorded unit activity from electrodes chronically implanted in various hippocampal areas of 17 male Holtzman albino rats during differential classical conditioning. 1 auditory frequency signaled food, another signaled electric shock. Unit activity was recorded during 1 sec. prior to applications of the tones and during the 1-sec CS-UCS intervals. Response latencies and changes in frequency of unit activity throughout the recording period were determined. Units in the dentate had longer latencies than units in the hippocampus, some of which responded within 16 msec. of the application of the CS. The dentate was the only area to show excitation in response to a positive signal and inhibition in response to a negative signal. (18 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Organic groups and molecular weight distribution in tertiary effluents and renovated waters

Group composition and MW distribution of soluble organics in effluents from successive biological and chemical treatment stages were investigated.In secondary effluents, most of the organics fell within the high MW range. Lime treatment caused marked reduction of the latter group, combined with removal of proteins, humics, and carbohydrates. (The overall removal amounted to approx. 65–75%). Simultaneously, there was an increase in the lowest MW range group—strongly hydrophilic, unidentifiable compounds outside the classification scheme used.     

Convergence of sensory input on units in the hippocampal system of the rat.

Recorded unit responses to auditory and visual stimuli from chronically implanted electrodes in the limbic system of 22 albino male Holtzman rats. The stimuli were presented first in a random order and later in a classical sensory conditioning paradigm in which a flash of light followed a tone. Short latency unit responses to both light and tone were found in the medial septum and the cingulate cortex. The conditioning paradigm did not cause significant changes in the firing rates of nonresponding units and did not significantly change existing responses. Only small transient changes were noticed in CA1 hippocampal units. It is concluded that sensory responses could be detected in the hippocampus and its afferents, but a classical sensory paradigm is not an efficient way to enhance hippocampal responsiveness to neutral stimuli. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dynamic Regulation of Mitochondrial [Ca2+] in Hippocampal Neurons

While neuronal mitochondria have been studied extensively in their role in health and disease, the rules that govern calcium regulation in mitochondria remain somewhat vague. In the present study using cultured rat hippocampal neurons transfected with the mtRCaMP mitochondrial calcium sensor, we investigated the effects of cytosolic calcium surges on the dynamics of mitochondrial calcium ([Ca²⁺]m). Cytosolic calcium ([Ca²⁺]c) was measured using the high affinity sensor Fluo-2. We recorded two types of calcium events: local and global ones. Local events were limited to a small, 2–5 µm section of the dendrite, presumably caused by local synaptic activity, while global events were associated with network bursts and extended throughout the imaged dendrite. In both cases, cytosolic surges were followed by a delayed rise in [Ca²⁺]m. In global events, the rise lasted longer and was observed in all mitochondrial clusters. At the end of the descending part of the global event, [Ca²⁺]m was still high. Global events were accompanied by short and rather high [Ca²⁺]m surges which we called spikelets, and were present until the complete decay of the cytosolic event. In the case of local events, selective short-term responses were limited to the part of the mitochondrial cluster that was located directly in the center of [Ca²⁺]c activity, and faded quickly, while responses in the neighboring regions were rarely observed. Caffeine (which recruits ryanodine receptors to supply calcium to the mitochondria), and carbonyl cyanide m-chlorophenyl hydrazine (CCCP, a mitochondrial uncoupler) could affect [Ca²⁺]m in both global and local events. We constructed a computational model to simulate the fundamental role of mitochondria in restricting calcium signals within a narrow range under synapses, preventing diffusion into adjacent regions of the dendrite. Our results indicate that local cytoplasmic and mitochondrial calcium concentrations are highly correlated. This reflects a key role of signaling pathways that connect the postsynaptic membrane to local mitochondrial clusters.     

Is object-based attention mandatory? Strategic control over mode of attention.

Is object-based attention mandatory or under strategic control? In an adapted spatial cuing paradigm, participants focused initially on a central arrow cue that was part of a perceptual group (Experiment 1) or a uniformly connected object (Experiment 2), encompassing one of the potential target locations. The cue always pointed to an opposite, different-object location. By varying cue validity, the strategic incentive to prevent the spread of attention to the entire cue object, and consequently to the same-object location, was manipulated: With invalid cuing and (consequently) equal probability of targets at same-object and different-object locations, a same-object target identification advantage was observed. With highly valid cuing and targets much more probable at the different-object location than at the same-object location, the same-object advantage disappeared. Object-based attention appears to be a default mode that may be ecologically adaptive but can be overridden by strategic control when there is a strong immediate benefit in doing so. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Volatile organic acids in raw wastewater and in physico-chemical treatment

The purpose of the present study was to identify soluble organics, which comprise the high BOD remaining in the effluent from direct physico-chemical treatment of strong raw sewage. Salts of volatile organic acids were found to be the main constituents of the organic fraction remaining after chemical treatment and activated carbon adsorption. The fate of the volatile acids such as acetic, propionic, butyric, valeric, isovaleric and hexanoic acids was followed in each stage of the physicochemical treatment.     

Modulation of object-based attention by spatial focus under endogenous and exogenous orienting.

In R. Egly, J. Driver, and R. D. Rafal's (1994) influential double-rectangle spatial-cuing paradigm, exogenous cues consistently induce object-based attention, whereas endogenous cues generally induce space-based attention. This difference suggests an interdependency between mode of orienting (endogenous vs exogenous) and mode of selection (object based vs space based). However, mode of orienting is generally confounded with initial focus of attention: Endogenous orienting begins with attention focused on a central cue, whereas exogenous orienting begins with attention widely spread. In this study, an attentional-focusing hypothesis is examined and supported by experiments showing that for both endogenous and exogenous cuing, object-based effects are obtained under conditions that encourage spread attention, but they are attenuated under conditions that encourage focused attention. General implications for object-based attention are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Estimation of Regional Myocardial Blood Flow Using Computed Tomography: A Stochastic Formulation

Previously, we have presented a deterministic formulation for estimation of regional myocardial blood flow (RMBF) using X-ray computed tomography (CT) [1]. Quantitation of RMBF with the deterministic theory requires computing the zeroth and first moments of extrapolated myocardial contrast enhancement (CT numbers versus time) curves. This extrapolation is a potential source of error in the presence of recirculation, especially in myocardial regions with reduced flows. In the present paper, a stochastic approach for parameter estimation is undertaken, which renders an optimal RMBF estimate based upon the least squares error criteria. Random measurement errors are minimized, curve extrapolation is avoided, and the accuracy of RMBF estimates is predicted. The advantages of the stochastic versus the deterministic approach are demonstrated in the results obtained from the in vivo estimation of RMBF in normal and acutely ischemic myocardium of dogs.     

On the numerical solution of a nonlinear partial differential equation related to the optimal control of a noisy oscillator

This paper deals with the optimal control of a linear oscillator with parametric excitation. It is shown that, in order to implement the optimal feedback control law, a nonlinear partial differential equation has to be solved. A finite difference algorithm for the solution of this equation is proposed, and its efficiency and applicability are demonstrated with examples.