Metal profiles used as environmental markers of green turtle (Chelonia mydas) foraging resources

The Baja California Peninsula, Mexico serves an important role for feeding and developing sea turtles. High concentrations of metals detected in green turtles (Chelonia mydas) from Magdalena Bay prompted an investigation into the sources of metals in the region. We compared metal concentrations in sea turtle tissues with plant species found in their stomach contents, and with the same species of plants collected inside a sea turtle refuge area known as Estero Banderitas. Differences in the metal concentrations between marine plant species were minimal. Principal components analysis of the percent contribution of individual metals to the overall metal signature of each plant or tissue sample generated three principal components that explained 80.7% of the total variance in the data. The plant samples collected within Estero Banderitas formed a separate grouping from the green turtle tissue samples and the plants from the stomach contents. The plants in the stomach contents contained greater percent contributions of Cd and Zn than the plants collected inside the bay, while Pb and Mn contributed more to the metal profiles in the bay samples. The metal profiles in the sea turtle tissues more closely resembled the stomach contents than the same species of plants collected within Estero Banderitas, and suggest that sea turtles collected inside Magdalena Bay use foraging resources outside of the Estero Banderitas region. This work supports the suggestion that metal profiles can be used as "environmentally acquired markers" to improve our understanding of the extent of sea turtle foraging areas.     

Effect of admicellar properties on adsolubilization: column studies and solute transport

Mixtures of anionic and cationic surfactants exhibit synergistic behavior as evidenced by low critical micelle concentrations (CMC) of the mixed system, increased surface activity, and improved detergency performance. The adsorption of a single-head anionic surfactant, sodium dodecyl sulfate (SDS), in mixture with a twin-head cationic surfactant, pentamethyl-octadecyl-1,3-propane diammonium dichloride (PODD), showed synergism of adsorption onto silica when present at a mixing ratio of 1:3 (cationic-rich), and also demonstrated lower surfactant desorption with water flushing of columns packed with the surfactant-modified media. In addition, the proportion of the mixed surfactants in the admicelles moved from the initial ratio of 1:3 towards equimolar after rinsing the surfactant-modified silica absorbent. The retardation of organic solutes passing through columns packed with modified-silica adsorbent increased nominally three fold for silica modified with mixed surfactants versus single surfactants (retardation factors increase from 4.0 to 12.8 for styrene and from 32.1 to 90.2 for ethylcyclohexane for single and mixed surfactants, respectively). Thus, this study demonstrates that mixed surfactant systems more effectively modified the silica surface than single surfactant systems both in terms of enhanced retardation of organic solutes and in terms of reduced surfactant desorption.     

The characteristic curvature (Cc) definition and its use in assessing Cc for single ionic surfactants

The hydrophilic–lipophilic-difference (HLD) is a set of empirical equations that correlate the formulation conditions at phase inversion (HLD = 0). Based on partition studies for nonionic surfactants, the HLD can be interpreted as a normalized chemical potential difference between the surfactant dissolved in water and oil. The net-average curvature (NAC) model extrapolates this interpretation into a curvature form that has been used to fit and predict the phase behavior of surfactant-oil–water (SOW) systems. The curvature interpretation led to renaming the HLD surfactant parameter, sigma (σ), as the characteristic curvature (Cc). This work tests the validity of the curvature interpretation of the HLD, and the Cc concept, for single ionic surfactants and the use of this concept as a method to assess the Cc without the use of reference surfactants or alcohols. To this end, the net curvature of six anionic and two cationic surfactants was evaluated from solubilization data at the characteristic condition of 25°C, no added cosolvent, in the presence of an oil mixture with equivalent alkane carbon number (EACN) of zero, and as a function of salinity. These studies showed that the original HLD equation for ionic surfactant could not be interpreted as chemical potential or curvature because a salinity prefactor (coefficient) “bi” was missing. The revised equation, HLD_bi = bi∙ln(S)-k_bi∙EACN+Cc_bi -a_Tbi∙(T-25°C), could now be interpreted as a curvature expression, and it was demonstrated that Cc could be obtained from curvature using the expression Cc = Cc_bi/bi. This single surfactant method produces uncertainties that, for most surfactants, ranged from 0.2 to 1 Cc units, similar to the uncertainty obtained with the conventional method of Cc determination using mixtures of test and reference surfactants.     

Influence of composition on the unipolar electric fatigue of Ba(Zr0.2Ti0.8)O3‐(Ba0.7Ca0.3)TiO3 lead‐free piezoceramics

The lead‐free (1?x)Ba(Zr_0.2Ti_0.8)O₃‐x(Ba_0.7Ca_0.3)TiO₃ system is considered as promising candidate for the replacement of lead‐based piezoceramics in actuation applications, during which electric fatigue is a major concern. This issue was addressed in this work, where the unipolar fatigue resistance of three (1?x)Ba(Zr_0.2Ti_0.8)O₃‐x(Ba_0.7Ca_0.3)TiO₃ compositions with different crystallographic structures (rhombohedral, orthorhombic, and tetragonal) was evaluated. Strain asymmetry and development of an internal bias field were observed in all compositions. The decrease in the remanent polarization and the large signal piezoelectric coefficient after 10⁷ unipolar cycles was found to lie between 6%‐12% and 2%‐13%, respectively. The most pronounced fatigue was observed for the orthorhombic composition, which has the largest extrinsic contribution to strain. On the other hand, the best fatigue resistance was observed for the tetragonal composition, which has a predominantly intrinsic strain response. The correlation of fatigue resistance with strain mechanism was corroborated with determination of the Rayleigh parameters and changes in the domain morphology after cycling as confirmed by piezoresponse force microscopy.     

Differential Action of Connexin Hemichannel and Pannexin Channel Therapeutics for Potential Treatment of Retinal Diseases

Dysregulation of retinal function in the early stages of light-induced retinal degeneration involves pannexins and connexins. These two types of proteins may contribute to channels that release ATP, leading to activation of the inflammasome pathway, spread of inflammation and retinal dysfunction. However, the effect of pannexin channel block alone or block of both pannexin channels and connexin hemichannels in parallel on retinal activity in vivo is unknown. In this study, the pannexin channel blocker probenecid and the connexin hemichannel blocker tonabersat were used in the light-damaged rat retina. Retinal function was evaluated using electroretinography (ERG), retinal structure was analyzed using optical coherence tomography (OCT) imaging and the tissue response to light-induced injury was assessed immunohistochemically with antibodies against glial fibrillary acidic protein (GFAP), Ionized calcium binding adaptor molecule 1 (Iba-1) and Connexin43 (Cx43). Probenecid did not further enhance the therapeutic effect of connexin hemichannel block in this model, but on its own improved activity of certain inner retina neurons. The therapeutic benefit of blocking connexin hemichannels was further evaluated by comparing these data against results from our previously published studies that also used the light-damaged rat retina model. The analysis showed that treatment with tonabersat alone was better than probenecid alone at restoring retinal function in the light-damaged retina model. The results assist in the interpretation of the differential action of connexin hemichannel and pannexin channel therapeutics for potential treatment of retinal diseases.     

Power‐efficient analog design based on the class AB super source follower

A class AB version of the conventional super source follower (SSF) is described. The circuit greatly increases slew rate (SR) and current efficiency, maintaining the low distortion and low output resistance of the SSF. Class AB operation is achieved without extra power dissipation or supply requirements, and without bandwidth or noise degradation. The circuit can advantageously replace the SSF in a wide variety of analog systems, opening a new research line in analog design. To illustrate the widespread application of this cell, a class AB differential unity‐gain buffer, a class AB differential current mirror and two class AB differential transconductors are designed, fabricated in a 0.5µm CMOS technology and tested. Measurement results using a dual supply of ±1.65V show that the proposed class AB version of the SSF improves SR by a factor 21.5 and increases bandwidth by 10%, keeping noise level, input range, power consumption, and supply requirements unaltered. The fabricated class AB current mirror features a THD at 100 kHz of ? 62dB for signal currents 20 times larger than the bias current. The fabricated transconductors feature an IM3 at 1 MHz of ? 56.6dB for output currents more than 13 times larger than the bias currents. Copyright © 2011 John Wiley & Sons, Ltd.     

Usability perception of different video game devices in elderly users

The purpose of this study was to evaluate the usability perception of seniors on video game use with different control devices. Twenty-four seniors participated in the study (12 women, 12 men, 69 years old in average) and eight children (8 years old in average). The setting included the use of two Kinect motion sensors, three computers, three projectors, three video cameras, two audio devices, the Angry Birds and Happy Sky videogames, one Xbox 360 console, a Nintendo Wii device and a Touchscreen configured so that participants could play the games in senior–child pairs. Data were collected according to user friendliness, experience and social interaction. This study suggests that video game control devices for seniors should be adapted to compensate for their function, sensor and cognitive limitations.     

电化传感器设计

本文介绍了电化传感器的工作方式及原理,并据此探讨电化传感设计中应注意的一些关键问题。