Distribution by Scientific Domains
Distribution within Life Sciences

Selected Abstracts

Prenatal predictors of infant temperament

Elizabeth A. Werner
Abstract Emerging data suggest that prenatal factors influence children's temperament. In 50 dyads, we examined fetal heart rate (FHR) activity and women's antenatal psychiatric illness as predictors of infant temperament at 4 months (response to novelty and the Infant Behavior Checklist). FHR change during maternal challenge was positively associated with observed infant motor reactivity to novelty (p,=,.02). The odds of being classified as high versus low motor among fetuses who had an increase in FHR during maternal stress was 11 times those who had a decrease in FHR (p,=,.0006). Antenatal psychiatric diagnosis was associated with an almost fourfold greater odds of having a high cry reactivity classification (p,=,.03). There also were modest associations between baseline FHR and maternal reports of infant temperament and between observed temperament and that based on mothers' reports. All of the infant results were found independent of the influence of women's postnatal anxiety. These data indicate that physiological markers of individual differences in infant temperament are identifiable in the fetal period, and possibly shaped by the prenatal environment. 2007 Wiley Periodicals, Inc. Dev Psychobiol 49: 474-484, 2007. [source]

Cross-species investigations of prenatal experience, hatching behavior, and postnatal behavioral laterality

Michael Bernard Casey
Abstract Turning biases have been reported in some mammalian species, but less is known about such biases in nonmammalians. This study investigated turning biases in domestic chicks, bobwhite and Japanese quail, leopard geckos, and snapping turtles. Domestic chicks (white leghorn and bantam) and bobwhite quail demonstrate strong group laterality. Japanese quail chicks, snapping turtles, and leopard geckos demonstrate no significant group bias. Results are discussed with regard to differences in embryonic experience, hatching behavior, and postnatal environment. 2001 John Wiley & Sons, Inc. Dev Psychobiol 39: 84,91, 2001 [source]

Size-related differences in diel activity of two species of juvenile eel (Anguilla) in a laboratory stream

G. J. Glova
Abstract , The diel activity of three size groups (small=<100 mm; medium=100,199 mm; large=200,299 mm total length) of juvenile shortfinned ("shortfin") eels (Anguilla australis) and longfinned ("longfin") eels (A. dieffenbachii) was tested in a laboratory flow tank over a 48-h period during summer. All size groups of both species were nocturnally active, with the eels hiding in the substratum during the day and coming out on top of the cobbles from dusk to dawn, to feed. During the foraging period, the numbers and activity of all sizes of longfins visible were greater than those seen of shortfins, with the differences being more pronounced for small and medium eels. The activity of all eels consisted mostly of foraging by crawling, searching and probing for prey among the cobbles. Rate of activity increased with size of eel for both species. Small eels of either species did more swimming than eels of the larger sizes, whereas large eels were observed more frequently with only their head out of the substrate than were the smaller individuals. Feeding of small eels within the interstitial spaces of the streambed may explain their significantly lower activity on top of the substrate at night. The significantly lower rate of activity recorded for shortfins than longfins of all sizes may be due partly to their ability to feed within the interstices of the stream bed, and (or) longer time to recover from handling and habituate to the test environment., [source]

R-learning with multiple state-action value tables

Koichiro Ishikawa
Abstract We propose a method to improve the performance of R-learning, a reinforcement learning algorithm, by using multiple state-action value tables. Unlike Q- or Sarsa learning, R-learning learns a policy to maximize undiscounted rewards. Multiple state-action value tables cause substantial explorations as needed and make R-learning work well. Efficiency of the proposed method is verified through experiments in a simulated environment. 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(3): 34, 47, 2007; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/eej.20473 [source]

A cooperative distance learning method based on narrow-band Internet and its evaluation

Dilmurat Tilwaldi
Abstract This paper describes the experimental evaluation of a cooperative distance learning method, which can be utilized on narrow-band Internet. In this method, students in a group learning environment perform a series of study tasks several times, then create an online report, communicating through a chat facility about a given topic. They try to gain a benefit from their study through a more cooperative attitude. The teacher gives a short lecture at the first stage, and then gives supplementary explanations after ascertaining the degree of understanding by the students at the middle stage of the study. Teaching materials are distributed to the students' PCs beforehand and the lecture can be carried out in a narrow-band environment by transmitting commands. The teacher analyzes the students' communication logs and gives advice for the next study session. This paper describes the result of an evaluation of the proposed method involving a simulated installation of the environment within the campus, which simulated a trial of cooperative distance learning in the periphery of an overseas desert environment. 2010 Wiley Periodicals, Inc. Electron Comm Jpn, 93(4): 36,49, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10139 [source]

Toxicity of arsenic species to Lemna gibba L. and the influence of phosphate on arsenic bioavailability

Martin Mkandawire
Abstract The toxicity of arsenic (As) species to Lemna gibba L. and the influence of PO on As bioavailability and uptake were tested in batch culture. L. gibba were exposed to six test concentrations of NaHAsO4 7H2O and NaAsO3, with 0, 0.0136, 13.6, and 40 mg L,1 KH2PO4. In batch culture As toxicity to L. gibba did not relate linearly to As concentration. The growth rate, related to frond number as recommended by OECD and ISO/DIN, was significantly inhibited in fronds exposed to 20,50 ,g L,1 As(III) compared with fronds exposed to As(V). The growth rate was stimulated when plants were exposed to 50,250 ,g L,1 of both As(III) and As(V). After exposure to 300,800 ,g L,1 growth inhibition was significantly higher for As(III) than for As(V), whereas above 800 ,g L,1 As(V) was inhibited the most. The bioaccumulation of As(III) and As(V) was significantly higher for P-deficient cultures (0.98 0.08 and 1.02 0.19 g kg,1, respectively for 0.0136 mg L,1 PO) than for P-sufficient cultures (243 and 343 mg kg,1 for 40 mg L,1, respectively). Plants exposed to As(V) had uptake and accumulation values slightly higher than did plants exposed to As(III). No significant differences in bioaccumulation were found between plants exposed to a concentration of As(III) >1 mg L,1 and those exposed to As(V) at the same concentration. This indicates a direct relationship to P content in the culture. Toxicity may result from the uptake of As(V) instead of PO as a result of ion competition during uptake because of close thermodynamic properties, which may change the interaction among components in the media. The toxicity pattern is interpreted as a manifestation of changing speciation in the batch culture and of the oxidation of As(III) to As(V) in an oxygen-rich environment. 2004 Wiley Periodicals, Inc. Environ Toxicol 19: 26,34, 2004. [source]

Alterations in behaviour and glutamate transmission following presentation of stimuli previously associated with cocaine exposure

Gregory Hotsenpiller
Abstract To study the role of glutamate in cocaine-conditioned responses, we developed a rat model in which conditioned locomotion is produced by repeated pairing of cocaine with discrete stimuli (flashing light and metronome). ,Paired' subjects received cocaine (15 mg/kg) prior to six exposures to stimuli for 30 min in the test environment. ,Unpaired' subjects received equivalent presentations of the stimuli yet received cocaine in home cages. Tests with the stimuli alone demonstrated that the conditioned locomotion displayed by Paired subjects was evident at 3 or 10 days post-training and resistant to two sessions of testing. The degree of conditioned locomotion was not correlated with the subjects' response to novelty or cocaine. Administration of the noncompetitive AMPA receptor antagonist GYKI 52466 (2.5 mg/kg, a dose without effect on spontaneous activity) attenuated the expression of conditioned activity. In vivo microdialysis revealed that Paired subjects had significantly lower basal glutamate levels in the nucleus accumbens (NAc) than did Unpaired subjects when no stimuli were presented. Presentation of the conditioned stimuli resulted in significant increases in glutamate levels in the NAc in the Paired group whilst glutamate levels in the Unpaired group remained unchanged. The associative control of glutamate levels in the NAc by stimuli formerly paired with a drug of abuse is an unprecedented finding. It is likely to reflect the convergence of excitatory inputs that the NAc receives from limbic structures. [source]

Rearrangement of upstream sequences of the hTERT gene during cellular immortalization

Yuanjun Zhao
Telomerase expression, resulting from transcriptional activation of the hTERT gene, allows cells to acquire indefinite proliferative potential during cellular immortalization and tumorigenesis. However, mechanisms of hTERT gene activation in many immortal cell lines and cancer cells are poorly understood. Here, we report our studies on hTERT activation using genetically related pairs of telomerase-negative (Tel,) and -positive (Tel+) fibroblast lines. First, whereas transiently transfected plasmid reporters did not recapitulate the endogenous hTERT promoter, the promoter in chromosomally integrated bacterial artificial chromosome (BAC) reporters was activated in a subset of Tel+ cells, indicating that activation of the hTERT promoter required native chromatin context and/or distal regulatory elements. Second, the hTERT gene, located near the telomere of chromosome 5p, was translocated in all three Tel+ cell lines but not in their parental precrisis cells and Tel, immortal siblings. The breakage points were mapped to regions upstream of the hTERT promoter, indicating that the hTERT gene was the target of these chromosomal rearrangements. In two Tel+ cell lines, translocation of the endogenous hTERT gene appeared to be the major mechanism of its activation as the activity of hTERT promoter in many chromosomally integrated BAC reporters, with intact upstream and downstream neighboring loci, remained relatively low. Therefore, our results suggest that rearrangement of upstream sequences is an important new mechanism of hTERT promoter activation during cellular immortalization. The chromosomal rearrangements likely occurred during cellular crisis and facilitated by telomere dysfunction. Such translocations allowed the hTERT promoter to escape from the native condensed chromatin environment. 2009 Wiley-Liss, Inc. [source]

Speleothem preservation and diagenesis in South African hominin sites implications for paleoenvironments and geochronology

Philip J. Hopley
Plio-Pleistocene speleothems from australopithecine-bearing caves of South Africa have the potential to yield paleoenvironmental and geochronological information using isotope geochemistry. Prior to such studies it is important to assess the preservation of geochemical signals within the calcitic and aragonitic speleothems, given the tendency of aragonitic speleothems to recrystallize to calcite. This study documents the geochemical suitability of speleothems from the principal hominin-bearing deposits of South Africa. We use petrography, together with stable isotope and trace element analysis, to identify the occurrence of primary aragonite, primary calcite, and secondary calcite. This study highlights the presence of diagenetic alteration at many of the sites, often observed as interbedded primary and secondary fabrics. Trace element and stable isotopic values distinguish primary calcite from secondary calcite and offer insights into geochemical aspects of the past cave environment. ,13C values of the primary and secondary calcites range from +6 to ,9, and ,18O values range from ,4 to ,6,. The data are thus typical of meteoric calcites with highly variable ,13C and relatively invariant ,18O. High carbon isotope values in these deposits are associated with the effects of recrystallization and rapid outgassing of CO2 during precipitation. Mg/Ca and Sr/Ca ratios differ between primary and secondary calcite speleothems, aiding their identification. Carbon and oxygen isotope values in primary calcite reflect the proportion of C3 and C4 vegetation in the local environment and the oxygen isotope composition of rainfall. Primary calcite speleothems preserve the pristine geochemical signals vital for ongoing paleoenvironmental and geochronological research. 2009 Wiley Periodicals, Inc. [source]

A micromorphological and mineralogical study of site formation processes at the late Pleistocene site of Obi-Rakhmat, Uzbekistan

Carolina Mallol
Site formation processes at the Late Pleistocene rockshelter deposit of Obi-Rakhmat were reconstructed through soil micromorphology and Fourier transform infrared spectroscopy (FTIR). The entire sequence has undergone limited diagenesis and is well preserved. The base of the stratified sequence represents a karstic setting with intermittent, low-energy deposition of autochthonous gravitational debris and anthropogenic material in a wet, muddy environment. These sediments were post-depositionally affected by episodic waterlogging. The bulk of the sequence overlying the karstic layers comprises a continuous series of primary freshwater spring deposits containing reworked anthropogenic material that was buried penecontemporaneously with calcium carbonate deposition. The top of the sequence is weakly cryoturbated, indicating a periodically cold, wet environment. No alluvial elements that could suggest sediment inputs from the nearby river terraces were documented. A single exogenous layer was identified, representing an episode of colluviation from directly above the rockshelter preceding a major roofspall event. The basal part of the sequence contains slightly reworked anthropogenic remnants of intense activities, including combustion. The anthropogenic elements present in the spring deposits show higher degrees of reworking, suggesting within-layer translocation. The development of spring activity at the site did not cause humans to abandon the rockshelter; they continued to carry out their activities throughout a changing local environment. 2009 Wiley Periodicals, Inc. [source]

Examining the performance of Google and AltaVista through the lens of the Cube One framework

Richard E. Kopelman
This article examines the management, marketing, and human resource practices of two Internet search companies through the lens of the Cube One framework, a three-dimensional model of the determinants of organizational performance that posits that successful organizations must simultaneously meet the needs of customers, employees, and the providers of capital. A detailed examination of enacted practices reveals that Google, which has been extraordinarily successful, has succeeded in all three regards. In contrast, AltaVista, which went out of business, did not. The Cube One framework, then, is useful for explaining differences in organizational performance and can serve as a guide for managing organizations in a globally competitive environment. 2010 Wiley Periodicals, Inc. [source]

Learning in a geometric model of place cell firing

HIPPOCAMPUS, Issue 9 2007
Caswell Barry
Abstract Following Hartley et al. (Hartley et al. (2000) Hippocampus 10:369,379), we present a simple feed-forward model of place cell (PC) firing predicated on neocortical information regarding the environmental geometry surrounding the animal. Incorporating the idea of boundaries with distinct sensory qualities, we show that synaptic plasticity mediated by a BCM-like rule (Bienenstock et al. (1982) J Neurosci 2:32,48) produces PCs that encode position relative to specific extended landmarks. In an unchanging environment the model is shown to undergo an initial phase of learning, resulting in the formation of stable place fields. In familiar environments, perturbation of environmental cues produces graded changes in the firing rate and position of place fields. Model simulations are compared favorably with three sets of experimental data: (1) Results published by Barry et al. (Barry et al. (2006) Rev Neurosci 17:71,97) showing the slow disappearance of duplicate place fields produced when a barrier is placed into a familiar environment. (2) Rivard et al.'s (Rivard et al. (2004) J Gen Physiol 124:9,25) study showing a graded response in PC firing such that fields near to a centrally placed object encode space relative to the object, whereas more distant fields respond to the surrounding environment. (3) Fenton et al.'s (Fenton et al. (2000a) J Gen Physiol 116:191,209) observation that inconsistent rotation of cue cards produces parametric changes in place field positions. The merits of the model are discussed in terms of its extensibility and biological plausibility. 2007 Wiley-Liss, Inc. [source]

An oscillatory interference model of grid cell firing

HIPPOCAMPUS, Issue 9 2007
Neil Burgess
Abstract We expand upon our proposal that the oscillatory interference mechanism proposed for the phase precession effect in place cells underlies the grid-like firing pattern of dorsomedial entorhinal grid cells (O'Keefe and Burgess (2005) Hippocampus 15:853,866). The original one-dimensional interference model is generalized to an appropriate two-dimensional mechanism. Specifically, dendritic subunits of layer II medial entorhinal stellate cells provide multiple linear interference patterns along different directions, with their product determining the firing of the cell. Connection of appropriate speed- and direction- dependent inputs onto dendritic subunits could result from an unsupervised learning rule which maximizes postsynaptic firing (e.g. competitive learning). These inputs cause the intrinsic oscillation of subunit membrane potential to increase above theta frequency by an amount proportional to the animal's speed of running in the "preferred" direction. The phase difference between this oscillation and a somatic input at theta-frequency essentially integrates velocity so that the interference of the two oscillations reflects distance traveled in the preferred direction. The overall grid pattern is maintained in environmental location by phase reset of the grid cell by place cells receiving sensory input from the environment, and environmental boundaries in particular. We also outline possible variations on the basic model, including the generation of grid-like firing via the interaction of multiple cells rather than via multiple dendritic subunits. Predictions of the interference model are given for the frequency composition of EEG power spectra and temporal autocorrelograms of grid cell firing as functions of the speed and direction of running and the novelty of the environment. 2007 Wiley-Liss, Inc. [source]

Role of active movement in place-specific firing of hippocampal neurons

HIPPOCAMPUS, Issue 1 2005
Eun Young Song
Abstract The extent of external and internal factors contributing to location-specific firing of hippocampal place cells is currently unclear. We investigated the role of active movement in location-specific firing by comparing spatial firing patterns of hippocampal neurons, while rats either ran freely or rode a motorized cart on the same circular track. Most neurons changed their spatial firing patterns across the two navigation conditions ("remapping"), and they were stably maintained across repeated active or passive navigation sessions. These results show that active movement is a critical factor in determining place-specific firing of hippocampal neurons. This could explain why passive displacement is not an effective way of acquiring spatial knowledge for subsequent active navigation in an unfamiliar environment. 2004 Wiley-Liss, Inc. [source]

Detection of novelty, but not memory of spatial habituation, is associated with an increase in phosphorylated cAMP response element-binding protein levels in the hippocampus

HIPPOCAMPUS, Issue 1 2004
Milena Winograd
Abstract There is a growing body of evidence showing that the formation of associative memories is associated with an increase in phosphorylated cAMP response element-binding protein (pCREB) levels. We recently reported increased pCREB levels in the rat hippocampus after an exploration to a novel environment. In the present work, we studied whether this increment in CREB activation is associated with the formation of memory of habituation to a novel environment or with the detection of novelty. Rats were submitted to consecutive open field sessions at 3-h intervals. Measurement of the hippocampal pCREB level, carried out 1 h after each training session, showed that (1) it did not increase when rats explored a familiar environment; (2) it did not increase after a reexposure that improves the memory of habituation; (3) it increased after a brief novel exploration unable to form memory of habituation; and (4) it increased in amnesic rats for spatial habituation. Taken as a whole, our results suggest that the elevated pCREB level after a single open field exploration is not associated with the memory formation of habituation. It is indeed associated with the detection of a novel environment. 2003 Wiley-Liss, Inc. [source]

Effects of hippocampal cholinergic deafferentation on learning strategy selection in a visible platform version of the water maze

HIPPOCAMPUS, Issue 6 2003
J.L. Bizon
Abstract Recent evidence has suggested that the relative levels of acetylcholine (ACh) between brain structures may be an important factor in the choice of behavioral strategy in settings in which either hippocampal or dorsal striatal brain systems can be employed both effectively and independently (McIntyre and Gold. 1999. Soc Neurosci Abs 25:1388). The current investigation used the neurotoxin 192 IgG-saporin to deplete the hippocampus of ACh selectively, while leaving ACh in other brain regions, including dorsal striatum, intact. Rats were then trained on a version of the Morris water maze, in which behavioral strategies attributed to the hippocampus and dorsal striatum are placed in direct competition. It was predicted that rats with hippocampal ACh depletion would display a cue bias. Contrary to this prediction, depleting hippocampal ACh did not bias against and, in fact, promoted use of a hippocampal place strategy in this task, as indicated by choice in competition tests and performance on hidden platform training trials. These data add to a growing literature demonstrating that the septohippocampal cholinergic system is not required for accurate spatial learning and suggest a complex role for basal forebrain projections in processing information about the spatial environment. 2003 Wiley-Liss, Inc. [source]

Perception of safe robot speed in virtual and real industrial environments

Vincent G. Duffy
The purpose of this project was to study the influences of dynamic virtual objects in an Internet-based virtual industrial environment. The main objectives of this study were to investigate perception of safe robot speed and perception of acceptability. Virtual industrial environments were designed and developed to conduct the experiment. The hypotheses specifying the relationships between perceptions of the robot size, type, different robot starting speed conditions, and gender were tested through data collected from 32 participants. The results indicated that the perception of safe speed was significantly different depending on robot sizes and the initial robot speed conditions. This was consistent with results shown in previous literature for tests in a real industrial environment. 2006 Wiley Periodicals, Inc. Hum Factors Man 16: 369,383, 2006. [source]

Advanced and intelligent technologies for reliable operation of power systems and electricity markets

Ryuichi Yokoyama Senior Member
Abstract Deregulation of power industries is still progressing in many countries, aiming at reduction of the electricity price, diversity of customer diverse choices, services and promotion of new business and keeping supply reliability. Many countries are testing this notion in anticipation of lower power prices through open competition. In such a competitive situation, it is necessary for suppliers to take on the responsibility of keeping supply reliability at the load end in order to prevent outages, for instance, independent power producers (IPP) placing distributed generations (DGs) close to the load or conventional utilities utilizing advanced and intelligent system operation/control technologies that are costly. Usually, customers pay one price for power that is good enough for ordinary use, therefore not necessarily highly consistent in quality of voltage, current, frequency or reliability. However, if customers desire better quality power, additional fees are added according to the particular characteristics desired, thus customers are supplied with this type of better power that they choose. Under such a worldwide new trend in power systems and markets, this article is edited for the purpose of introducing the most advanced technologies and the newest issues related to reliable and stable operations of power markets and systems in the competitive environment. 2008 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source]

A Fast Stereo Matching Algorithm for Sewer Inspection Robots

Alireza Ahrary Non-member
Abstract In this paper, we present a fast stereo matching algorithm for sewer inspection robots. Conventional algorithms such as the sum of squared difference (SSD) and cross-correlation based on segmentation, graph cuts and so on have been proposed. However, most of them are computationally expensive. In order to solve the problem, we propose a fast stereo matching algorithm using interpolation in this paper. In our algorithm, an image is initially divided into many blocks. Then, a matching measure combining SSD and the cross-correlation is calculated only at the corner points of each block. A down sampled sewer disparity image is composed of only the corner points. Because the disparities change continuously in the sewer environment, we use the cubic interpolation for extending the down sampled sewer disparity image into a regular-sized disparity image. The experimental results show that our algorithm outperforms the conventional algorithms in both accuracy and speed in the sewer environment. 2008 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source]

Modeling naturalistic argumentation in research literatures: Representation and interaction design issues

Simon J. Buckingham Shum
This article characterizes key weaknesses in the ability of current digital libraries to support scholarly inquiry, and as a way to address these, proposes computational services grounded in semiformal models of the naturalistic argumentation commonly found in research literatures. It is argued that a design priority is to balance formal expressiveness with usability, making it critical to coevolve the modeling scheme with appropriate user interfaces for argument construction and analysis. We specify the requirements for an argument modeling scheme for use by untrained researchers and describe the resulting ontology, contrasting it with other domain modeling and semantic web approaches, before discussing passive and intelligent user interfaces designed to support analysts in the construction, navigation, and analysis of scholarly argument structures in a Web-based environment. 2007 Wiley Periodicals, Inc. Int J Int Syst 22: 17,47, 2007. [source]

Relaxation of quantum hydrodynamic modes

Eric R. Bittner
Abstract In this article, we develop a series of hierarchical mode-coupling equations for the momentum cumulants and moments of the density matrix for a mixed quantum system. Working in the Lagrange representation, we show how these can be used to compute quantum trajectories for dissipative and nondissipative systems. This approach is complementary to the de Broglie,Bohm approach in that the moments evolve along hydrodynamic/Lagrangian paths. In the limit of no dissipation, the paths are the Bohmian paths. However, the "quantum force" in our case is represented in terms of momentum fluctuations and an osmotic pressure. Representative calculations for the relaxation of a harmonic system are presented to illustrate the rapid convergence of the cumulant expansion in the presence of a dissipative environment. 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002 [source]

Composites of rigid polyurethane foam and cellulose fiber residue

M. C. Silva
Abstract Rigid polyurethane composite foams were prepared with cellulose fibers as a filler. The cellulose fibers were an industrial residue of blanched cellulose pulp production. The influence of the cellulose fiber concentration on the structural, thermal, mechanical, and morphological properties of the foams was investigated. We also studied the influence of the cellulose fibers on the foam's resistance to fungal attack by placing a suspension of known fungus in contact with the surface of the foam and following the morphological evolution as a function of time (for 60 days). The increase in the cellulose filler concentration in the foams, up to 16% w/w with respect to the polyol, changed their properties as follows: (1) the cell size decreased, (2) the thermooxidative stability and mechanical properties remained approximately constant, (3) the thermal conductivity decreased slightly, and (4) fungal growth was observed. Therefore, a cellulosic fibrous industrial residue was rationally valorized as a filler in classical rigid polyurethane foams; this yielded materials with mechanical resistance and a susceptibility to fungi in a wet environment. 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]

Bio-hybrid nanocomposite coatings from sonicated chitosan and nanoclay

Jari Vartiainen
Abstract Nanocomposite films and coatings with improved properties were produced from ultrasonic dispersed chitosan and hydrophilic bentonite nanoclay. Bio-hybrid coatings were applied onto argon,plasma-activated LDPE coated paper. The intercalation of chitosan in the silicate layers was confirmed by the decrease of diffraction angles as the chitosan/nanoclay ratio increased. Nanocomposite films and multilayer coatings had improved barrier properties against oxygen, water vapor, grease, and UV-light transmission. Oxygen transmission was significantly reduced under all humidity conditions. In dry conditions, over 99% reduction and at 80% relative humidity almost 75% reduction in oxygen transmission rates was obtained. Hydrophilic chitosan was lacking the capability of preventing water vapor transmission, thus total barrier effect of nanoclay containing films was not more than 15% as compared with pure chitosan. Because to very thin coatings (,1 ,m), nanoclay containing chitosan did not have antimicrobial activity against test strains. All coating raw materials were "generally recognized as safe" (GRAS) and the calculated total migration was in all cases ,6 mg/dm2, thus the coatings met the requirements set by the packaging legislation. Processing of the developed bio-hybrid nanocomposite coated materials was safe as the amounts of released particles under rubbing conditions were comparable with the particle concentrations in a normal office environment. 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]

Influence of the copolymer architecture and composition on the response and mechanical properties of pH-sensitive fibers

Anasuya Sahoo
Abstract A series of copolymers based on acrylonitrile (AN) and acrylic acid (AA) with varying architecture and composition were synthesized using free radical polymerization. The distribution of monomers in the copolymer chains could be successfully controlled by regulating the addition of more reactive monomer (AA). Copolymers having nearly random distribution of comonomer moieties to block type distribution with different composition (10,50 mol % AA) were synthesized to investigate the effect of polymer architecture and composition on pH response and mechanical properties of resultant structures. These copolymers were solution spun from dimethylformamide-water system, drawn in coagulation bath, and annealed at 120C for 2 h to make pH-sensitive fibers which were structurally stable without the need of chemical crosslinking. The fibers from block copolymers showed significantly better tensile strength (34.3 MPa), higher retractive forces (0.26 MPa), and enhanced pH response (swelling 3890%) in comparison with fibers from random copolymer (13.55 MPa, 0.058 MPa, and 1723%, respectively). The tensile strength and retractive forces could be further improved to a value of 72 MPa and 0.36 MPa, respectively, by changing the composition of the block copolymer while retaining the swelling percentage similar to the random copolymer mentioned above. It is proposed that on processing to fibers, the block copolymers could form a segregated domain structure with separate domains of AA and AN, where AN domains were responsible for high structural integrity by providing connectivity among polymer chains, while AA domains showed improved response to changing pH of the environment. 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source]

Acinetobacter bioreporter assessing heavy metals toxicity

Desouky Abd-El-Haleem Dr.
This work was conducted to employ a whole cell-based biosensor to monitor toxicity of heavy metals in water and wastewater. An isolate of industrial wastewater bacterium, Acinetobacter sp. DF4, was genetically modified with lux reporter gene to create a novel bioluminescent bacterial strain, designated as DF4/PUTK2. This bioreporter can investigate the toxicity through light inhibition due to cell death or metabolic burden and the specific stress effects of the tested soluble materials simultaneously. The use of Acinetobacter DF4/PUTK2 as a bioluminescent reporter for heavy metal toxicity testing and for the application of wastewater treatment influent toxicity screening is presented in this study. Among eight heavy metals tested, the bioluminescence of DF4/PUTK2 was most sensitive to Zn, Cd, Fe, Co, Cr followed by Cu in order of decreasing sensitivity. The same pattern of sensitivity was observed when several contaminated water and wastewater effluents were assayed. This work suggested that luxCDABE -marked Acinetobacter bacterium DF4/PUTK2 can be used to bioassay the ecotoxicity of wastewater and effluent samples contaminated with heavy metals. Using this assay, it is possible to pre-select the more toxic samples for further chemical analysis and to discard wastewater samples with low or no inhibition because they are not toxic to the environment. ( 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

A Mu-class glutathione S -transferase from gills of the marine shrimp Litopenaeus vannamei: Purification and characterization

Carmen A. Contreras-Vergara
Abstract Glutathione S -transferases (GSTs) are a family of detoxifying enzymes that catalyze the conjugation of glutathione (GSH) to electrophiles, thereby increasing the solubility of GSH and aiding its excretion from the cell. In this study, a glutatione S -transferase from the gills of the marine shrimp Litopenaeus vannamei was purified by affinity chromatography using a glutathione,agarose affinity column. GST was purified to homogeneity as judged by reducing SDS-PAGE and zymograms. This enzyme is a homodimer composed of ,25-kDa subunits and identified as a Mu-class GST based on its activity against 1-chloro-2,4-dinitrobenzene (CDNB) and internal peptide sequence. The specific activity of purified GST was 440.12 ,mol/(min mg), and the Km values for CDNB and GSH are very similar (390 and 335 ,M, respectively). The intersecting pattern of the initial velocities of this enzyme in the Lineweaver,Burke plot is consistent with a sequential steady-state kinetic mechanism. The high specific activity of shrimp GST may be related to a highly effective detoxification mechanism necessary in gills since they are exposed to the external and frequently contaminated environment. 2007 Wiley Periodicals, Inc. J Biochem Mol Toxicol 21:62,67, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.20162 [source]

Fluoropassivation and gelatin sealing of polyester arterial prostheses to skip preclotting and constrain the chronic inflammatory response

Xingyi Xie
Abstract Fluoropassivation and gelatin coating have been applied to polyethylene terephthalate (PET) vascular prosthesis to combine the advantages of both polytetrafluoroethylene (PTFE) and PET materials, and to eliminate the preclotting procedure. The morphological, chemical, physical, and mechanical properties of such prostheses were investigated and compared with its original model. Fluoropassivation introduced OCF3, CF3, and CFCF2 structures onto the surface of the polyester fibers. However, the surface fluorine content was only 28,32% compared to the 66% in expanded PTFE (ePTFE) grafts. The fluoropassivation decreased the hydrophilicity, slightly increased the water permeability, and marginally lowered the melting point and the crystallinity of the PET fibers. After gelatin coating, the fluoropassivated and nonfluoropassivated prostheses showed similar surface morphology and chemistry. While gelatin coating eliminated preclotting, it also renders the prostheses slightly stiffer. The original prosthesis had the highest bursting strength (275 N), with the fluoropassivated and gelatin-sealed devices showing similar bursting strength between 210 and 230 N. Fluoropassivation and gelatin coating lowered the retention strength by 23 and 30% on average, respectively. In vitro enzymatic incubation had only marginal effect on the surface fluorine content of the nongelatin-sealed prostheses. However, the gelatin-sealed ones significantly lost their surface fluorine after in vitro enzymatic incubation (by 69,85%) or in vivo 6-month implantation (by 51,60%), showing the lability of the fluoropolymer layer under the hostile biological environment. 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2010 [source]

Perceived criticism only matters when it comes from those you live with

Keith D. RenshawArticle first published online: 30 OCT 200
Perceived criticism (PC) is the amount of criticism that a respondent perceives from another individual, typically a relative with whom the respondent lives. Measured in this way, PC has been shown to predict symptom fluctuation, treatment outcome, and relapse rates across many disorders. Three recent studies failed to replicate these results, but in all three studies, investigators did not require patients to rate people with whom they lived on the measure of PC, which may have changed the overall meaning of the construct. To address this possibility, the current study examined change in depressive symptoms in relation to ratings of PC from multiple individuals who did and did not live with respondents. Only PC from family members or romantic partners who lived with participants predicted change in depressive symptoms. Perceived criticism from friends and PC from individuals ranked as most influential did not. These findings suggest that PC is most meaningful and informative when viewed in its original conceptual form, as a reflection of the family home environment. 2007 Wiley Periodicals, Inc. J Clin Psychol 63: 1171,1179, 2007. [source]

Temperature dependence of structure and dynamics of the hydrated Ca2+ ion according to ab initio quantum mechanical charge field and classical molecular dynamics

Len Herald V. Lim
Abstract Simulations using ab initio quantum mechanical charge field molecular dynamics (QMCF MD) and classical molecular dynamics using two-body and three-body potentials were performed to investigate the hydration of the Ca2+ ion at different temperatures. Results from the simulations demonstrate significant effects of temperature on solution dynamics and the corresponding composition and structure of hydrated Ca2+. Substantial increase in ligand exchange events was observed in going from 273.15 K to 368.15 K, resulting in a redistribution of coordination numbers to lower values. The effect of temperature is also visible in a red-shift of the ion-oxygen stretching frequencies, reflecting weakened ligand binding. Even the moderate increase from ambient to body temperature leads to significant changes in the properties of Ca2+ in aqueous environment. 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 [source]

Metal,thiolate bonds in bioinorganic chemistry

Edward I. Solomon
Abstract Metal,thiolate active sites play major roles in bioinorganic chemistry. The MSthiolate bonds can be very covalent, and involve different orbital interactions. Spectroscopic features of these active sites (intense, low-energy charge transfer transitions) reflect the high covalency of the MSthiolate bonds. The energy of the metal,thiolate bond is fairly insensitive to its ionic/covalent and ,/, nature as increasing MS covalency reduces the charge distribution, hence the ionic term, and these contributions can compensate. Thus, trends observed in stability constants (i.e., the Irving,Williams series) mostly reflect the dominantly ionic contribution to bonding of the innocent ligand being replaced by the thiolate. Due to high effective nuclear charges of the CuII and FeIII ions, the cupric, and ferric,thiolate bonds are very covalent, with the former having strong , and the latter having more , character. For the blue copper site, the high , covalency couples the metal ion into the protein for rapid directional long range electron transfer. For rubredoxins, because the redox active molecular orbital is , in nature, electron transfer tends to be more localized in the vicinity of the active site. Although the energy of hydrogen bonding of the protein environment to the thiolate ligands tends to be fairly small, H-bonding can significantly affect the covalency of the metal,thiolate bond and contribute to redox tuning by the protein environment. 2006 Wiley Periodicals, Inc. J Comput Chem 27: 1415,1428, 2006 [source]