bluuebunny/crossref_metadata_2025 huggingface dataset:
Feature-Dependent Sensitive Periods in the Development of Complex Sound Representation
Authors: Insanally Michele N. , Köver Hania , Kim Heesoo , Bao Shaowen
Published: April 2009

Simple tonal stimuli can shape spectral tuning of cortical neurons during an early epoch of brain development. The effects of complex sound experience on cortical development remain to be determined. We exposed rat pups to a frequency-modulated (FM) sweep in different time windows during early development, and examined the effects of such sensory experience on sound representations in the primary auditory cortex (AI). We found that early exposure to a FM sound resulted in altered characteristic frequency representations and broadened spectral tuning in AI neurons, whereas later exposure to the same sound only led to greater selectivity for the sweep rate and direction of the experienced FM sound. These results indicate that cortical representations of different acoustic features are shaped by complex sounds in a series of distinct sensitive periods.
Activity Pattern-Dependent Long-Term Potentiation in Neocortex and Hippocampus of GluA1 (GluR-A) Subunit-Deficient Mice
Authors: Frey Marco C. , Sprengel Rolf , Nevian Thomas
Published: April 2009

The AMPA receptor subunit GluA1 (GluR-A) has been implicated to be critically involved in the expression of long-term potentiation (LTP) and memory formation. Mice lacking this subunit possess a profound spatial working memory deficit. We investigated the influence of the GluA1 subunit on the expression of LTP in pyramidal neurons of the hippocampus CA1 region and somatosensory cortex layer 2/3 for different cellular LTP protocols in adult mice. We found that the GluA1 subunit was not required for LTP in cortical pyramidal neurons. In contrast, GluA1-dependent LTP expression in CA1 pyramidal neurons was differentially dependent on the LTP induction parameters. Depolarization pairing was exclusively, theta-burst pairing was partially, and spike-timing-dependent plasticity (STDP) was independent of the GluA1 subunit. Spike-timing-dependent LTP required postsynaptic membrane fusion in CA1 pyramidal neurons. We conclude that during LTP induction at the hippocampal CA3-to-CA1 synapse the recruitment of the GluA1 subunit is controlled by particular electrical activity patterns that might reflect specific behavioral states. Furthermore, other LTP expression mechanisms exist that do not require the presence of GluA1. The previously reported spatial working memory deficits in GluA1-lacking mice (Gria1−/−mice) together with these results suggest that STDP might be a likely basis for the formation of spatial reference memory whereas it is not required for the rapid formation of spatial working memory where a fast but transient increase of synaptic efficacy might be needed.
Persistent Transcription- and Translation-Dependent Long-Term Potentiation Induced by mGluR1 in Hippocampal Interneurons
Authors: Ran Israeli , Laplante Isabel , Bourgeois Catherine , Pépin Julie , Lacaille Philippe , Costa-Mattioli Mauro , Pelletier Jerry , Sonenberg Nahum , Lacaille Jean-Claude
Published: April 2009

Hippocampal interneurons synchronize the activity of large neuronal ensembles during memory consolidation. Although the latter process is manifested as increases in synaptic efficacy which require new protein synthesis in pyramidal neurons, it is unknown whether such enduring plasticity occurs in interneurons. Here, we uncover a long-term potentiation (LTP) of transmission at individual interneuron excitatory synapses which persists for at least 24 h, after repetitive activation of type-1 metabotropic glutamate receptors [mGluR1-mediated chemical late LTP (cL-LTPmGluR1)]. cL-LTPmGluR1involves presynaptic and postsynaptic expression mechanisms and requires both transcription and translation via phosphoinositide 3-kinase/mammalian target of rapamycin and MAP kinase kinase-extracellular signal-regulated protein kinase signaling pathways. Moreover, cL-LTPmGluR1involves translational control at the level of initiation as it is prevented by hippuristanol, an inhibitor of eIF4A, and facilitated in mice lacking the cap-dependent translational repressor, 4E-BP. Our results reveal novel mechanisms of long-term synaptic plasticity that are transcription and translation-dependent in inhibitory interneurons, indicating that persistent synaptic modifications in interneuron circuits may contribute to hippocampal-dependent cognitive processes.
DrosophilaMiro Is Required for Both Anterograde and Retrograde Axonal Mitochondrial Transport
Authors: Russo Gary J. , Louie Kathryn , Wellington Andrea , Macleod Greg T. , Hu Fangle , Panchumarthi Sarvari , Zinsmaier Konrad E.
Published: April 2009

Microtubule-based transport of mitochondria into dendrites and axons is vital for sustaining neuronal function. Transport along microtubule tracks proceeds in a series of plus and minus end-directed movements that are facilitated by kinesin and dynein motors. How the opposing movements are controlled to achieve effective transport over large distances remains unclear. Previous studies showed that the conserved mitochondrial GTPase Miro is required for mitochondrial transport into axons and dendrites and serves as a Ca2+sensor that controls mitochondrial mobility. To directly examine Miro's significance for kinesin- and/or dynein-mediated mitochondrial motility, we live-imaged movements of GFP-tagged mitochondria in larvalDrosophilamotor axons upon genetic manipulations of Miro. Loss ofDrosophilaMiro (dMiro) reduced the effectiveness ofbothanterograde and retrograde mitochondrial transport by selectively impairing kinesin- or dynein-mediated movements, depending on the direction of net transport. Net anterogradely transported mitochondria exhibited reduced kinesin- but normal dynein-mediated movements. Net retrogradely transported mitochondria exhibited much shorter dynein-mediated movements, whereas kinesin-mediated movements were minimally affected. In both cases, the duration of short stationary phases increased proportionally. Overexpression (OE) of dMiro also impaired the effectiveness of mitochondrial transport. Finally, loss and OE of dMiro altered the length of mitochondria in axons through a mechanistically separate pathway. We suggest that dMiro promotes effective antero- and retrograde mitochondrial transport by extending the processivity of kinesin and dynein motors according to a mitochondrion's programmed direction of transport.
Nicotinamide Mononucleotide Adenylyl Transferase-Mediated Axonal Protection Requires Enzymatic Activity But Not Increased Levels of Neuronal Nicotinamide Adenine Dinucleotide
Authors: Sasaki Yo , Vohra Bhupinder P. S. , Lund Frances E. , Milbrandt Jeffrey
Published: April 2009

Axonal degeneration is a hallmark of many neurological disorders. Studies in animal models of neurodegenerative diseases indicate that axonal degeneration is an early event in the disease process, and delaying this process can lead to decreased progression of the disease and survival extension. Overexpression of the Wallerian degeneration slow (Wlds) protein can delay axonal degeneration initiated via axotomy, chemotherapeutic agents, or genetic mutations. The Wldsprotein consists of the N-terminal portion of the ubiquitination factor Ube4b fused to the nicotinamide adenine dinucleotide (NAD+) biosynthetic enzyme nicotinamide mononucleotide adenylyl transferase 1 (Nmnat1). We previously showed that the Nmnat1 portion of this fusion protein was the critical moiety for Wlds-mediated axonal protection. Here, we describe the development of an automated quantitative assay for assessing axonal degeneration. This method successfully showed that Nmnat1 enzymatic activity is important for axonal protection as mutants with reduced enzymatic activity lacked axon protective activity. We also found that Nmnat enzymes with diverse sequences and structures from various species, includingDrosophila melanogaster,Saccharomyces cerevisiae, and archaebacteriumMethanocaldococcus jannaschii, which encodes a protein with no homology to eukaryotic Nmnat enzymes, all mediate robust axonal protection after axotomy. Besides the importance of Nmnat enzymatic activity, we did not observe changes in the steady-state NAD+level, and we found that inhibition of nicotinamide phosphoribosyltransferase (Nampt), which synthesizes substrate for Nmnat in mammalian cells, did not affect the protective activity of Nmnat1. These results provide the possibility of a role for new Nmnat enzymatic activity in axonal protection in addition to NAD+synthesis.
Neural Dynamics in Inferior Temporal Cortex during a Visual Working Memory Task
Authors: Woloszyn Luke , Sheinberg David L.
Published: April 2009

Intelligent organisms are capable of tracking objects even when they temporarily disappear from sight, a cognitive capacity commonly referred to as visual working memory (VWM). The neural basis of VWM has been the subject of significant scientific debate, with recent work focusing on the relative roles of posterior visual areas, such as the inferior temporal cortex (ITC), and the prefrontal cortex. Here we reexamined the contribution of ITC to VWM by recording from highly selective individual ITC neurons as monkeys engaged in multiple versions of an occlusion-based memory task. As expected, we found strong evidence for a role of ITC in stimulus encoding. We also found that almost half of these selective cells showed stimulus-selective delay period modulation, with a small but significant fraction exhibiting differential responses even in the presence of simultaneously visible interfering information. When we combined the informational content of multiple neurons, we found that the accuracy with which we could decode memory content increased drastically. The memory epoch analyses suggest that behaviorally relevant visual memories were reinstated in ITC. Furthermore, we observed a population-wide enhancement of neuronal response to a match stimulus compared with the same stimulus presented as a nonmatch. The single-cell enhancement preceded any match effects identified in the local field potential, leading us to speculate that enhancement is the result of neural processing local to ITC. Moreover, match enhancement was only later followed by the more commonly observed match suppression. Altogether, the data support the hypothesis that, when a stimulus is held in memory, ITC neurons are actively biased in favor of task-relevant visual representations and that this bias can immediately impact subsequent recognition events.
The N-Terminal Domain of Slack Determines the Formation and Trafficking of Slick/Slack Heteromeric Sodium-Activated Potassium Channels
Authors: Chen Haijun , Kronengold Jack , Yan Yangyang , Gazula Valeswara-Rao , Brown Maile R. , Ma Liqun , Ferreira Gonzalo , Yang Youshan , Bhattacharjee Arin , Sigworth Fred J. , Salkoff Larry , Kaczmarek Leonard K.
Published: April 2009

Potassium channels activated by intracellular Na+ions (KNa) play several distinct roles in regulating the firing patterns of neurons, and, at the single channel level, their properties are quite diverse. Two known genes,SlickandSlack, encodeKNachannels. We have now found that Slick and Slack subunits coassemble to form heteromeric channels that differ from the homomers in their unitary conductance, kinetic behavior, subcellular localization, and response to activation of protein kinase C. Heteromer formation requires the N-terminal domain of Slack-B, one of the alternative splice variants of the Slack channel. This cytoplasmic N-terminal domain of Slack-B also facilitates the localization of heteromericKNachannels to the plasma membrane. Immunocytochemical studies indicate that Slick and Slack-B subunits are coexpressed in many central neurons. Our findings provide a molecular explanation for some of the diversity in reported properties of neuronalKNachannels.
Propriospinal Bypass of the Serotonergic System That Can Facilitate Stepping
Authors: Gerasimenko Yury , Musienko Pavel , Bogacheva Irina , Moshonkina Tatiana , Savochin Alexandr , Lavrov Igor , Roy Roland R. , Edgerton V. Reggie
Published: April 2009

The neurotransmitter systems mediating spinal locomotion in response to epidural spinal cord stimulation (ES) have not been identified. Here, we examine the role of the serotonergic system in regulating locomotor behavior of decerebrated cats during ES at L4–L5. ES elicited coordinated, weight-bearing, hindlimb stepping with plantar foot placement on a moving treadmill belt. Ketanserin [a 5-hydroxytryptamine (serotonin) (5-HT)2/7receptor antagonist] depressed this locomotor activity: only weak rhythmic movements without plantar foot placement and depressed EMG activity were observed. Cyproheptadine, a nonselective 5-HT blocker, prevented facilitation of stepping by epidural stimulation. These data demonstrate an important role of the serotonergic system in facilitating locomotion in the presence of epidural stimulation. In the presence of ketanserin, passive movements of one forelimb in a step-like manner immediately induced stepping of both hindlimbs with EMG patterns similar to those observed with ES without ketanserin. Thus, a non-5-HT-dependent spinal circuitry projecting from the cervical to the lumbar region of the spinal cord can facilitate stepping. The specific neurotransmitters responsible for this forelimb-facilitated stepping of the hindlimbs are unknown. These data suggest that a 5-HT2/7receptor-dependent pathway that processes hindlimb locomotor-like proprioception to facilitate hindlimb stepping can be complemented with proprioceptive afferents from the forelimbs via a non-5-HT2/7receptor neurotransmitter system. Thus, different neurotransmitter receptor systems can be used to mediate the same type of sensory event, i.e., locomotor-like proprioception to facilitate the same motor task, i.e., hindlimb stepping.
The Szilard Hypothesis on the Nature of Aging Revisited
Authors: Zetterberg Henrik , Båth Magnus , Zetterberg Madeleine , Bernhardt Peter , Hammarsten Ola
Published: April 2009

This year marks the 50th anniversary of a nearly forgotten hypothesis on aging by Leo Szilard, best known for his pioneering work in nuclear physics, his participation in the Manhattan Project during World War II, his opposition to the nuclear arms race in the postwar era, and his pioneering ideas in biology. Given a specific set of assumptions, Szilard hypothesized that the major reason for the phenomenon of aging was aging hits, e.g., by ionizing radiation, to the gene-bearing chromosomes and presented a mathematical target-hit model enabling the calculation of the average and maximum life span of a species, as well as the influence of increased exposure to DNA-damaging factors on life expectancy. While many new findings have cast doubt on the specific features of the model, this was the first serious effort to posit accumulated genetic damage as a cause of senescence. Here, we review Szilard's assumptions in the light of current knowledge on aging and reassess his mathematical model in an attempt to reach a conclusion on the relevance of Szilard's aging hypothesis today.
P-type conduction in room-temperature high-energy electron-irradiated ZnO thin films
Authors: Yun Eui-Jung , Jung Jin Woo , Cheon Chae Il , Kim Jeong Seog , Han Young Hwan , Kim Min-Wan , Lee Byung Cheol
Published: April 2009

We report the realization of the p-type conductivity and the enhancement of the photoluminescence (PL) intensity in undoped ZnO films treated with high-energy (1 MeV) electron-beam irradiation (HEEBI), suggesting that the HEEBI process is compatible with a low-temperature requirement for the fabrication of transparent thin film transistors with good efficiency on a plastic substrate. The p-type conductivity of the films was revealed by the Hall, x-ray photoelectron spectroscopy, and PL measurements after being electron-irradiated in air at room temperature. The major acceptor-like defects were determined to be oxygen interstitial and zinc vacancy. A model was proposed in terms of O as well as Zn diffusion to explain the observed results. It was also observed that HEEBI treatment has little influence on the optical transmittance of ZnO films, whereas HEEBI treatment shifts the optical band gap toward the lower energy region from 3.29 to 3.28 eV.
Room temperature creep of fine-grained pure Mg: A direct comparison between nanoindentation and uniaxial tension
Authors: Wang C.L. , Mukai T. , Nieh T.G.
Published: April 2009

Nanoindentation creep and uniaxial tension were conducted on pure Mg with a grain size of about 2 μm at room temperature and the data were directly compared. Despite the differences in stress state, the two sets of data were found to match remarkably well with each other. An apparent stress exponent value of 4 was obtained and the deformation mechanism was discussed in light of dislocation slips and twinning in anisotropic Mg.
Alloying effects of iridium on glass formation and glass-forming ability of the Zr–Cu–Al system
Authors: Liu Z.Y. , Wu Y. , Li H.X. , Bei H. , Lu Z.P.
Published: April 2009

Alloying effects of iridium on the glass formability (GFA) of the Zr–Ir–Cu–Al system have been investigated, and several new bulk metallic glasses (BMGs) with high GFA have been successfully developed. Additions of Ir in the Zr–Cu–Al system can yield a beneficial distribution in atomic sizes, but the strong chemical interaction of the Zr–Ir atomic pair limits the maximum addable Ir contents and the resultant GFA. Our analyses indicate that the optimum composition for alloying elements is determined by not only topological but also chemical factors. Phase competition upon solidification, rather than effects from individual affecting factors, dictates the GFA of BMG systems.
Tunable luminescence from Sm3+, Ce3+codoped Al2O3–La2O3–SiO2glasses for white light emission
Authors: Yang Hucheng , Lakshminarayana G. , Teng Yu , Zhou Shifeng , Qiu Jianrong
Published: April 2009

Sm3+, Ce3+codoped Al2O3–La2O3–SiO2glasses were prepared and their luminescence properties were characterized. Blue-cyan to orange-red tunable luminescence was observed from these glasses with different excitation wavelengths ranging from 385 to 410 nm. White light emission with internal luminescence efficiency 42% has been observed using commercially available purple light-emitting-diode excitation. The energy transfer between Ce3+and Sm3+has also been investigated from fluorescence decay curves and spectral properties.
SrAl12O19:Pr3+nanodisks and nanoplates: New processing technique and photon cascade emission
Authors: Nie Zhaogang , Zhang Jiahua , Zhang Xia , Lim Ki-Soo
Published: April 2009

High-quality SrAl12O19:Pr3+nanodisks and nanoplates were fabricated via a new processing technique based on a modified polymer steric entrapment method. Serious agglomeration and large particle size distribution of final products, which usually occurred in the conventional method, were eliminated completely. The effects of new synthetic processes on the morphology, crystallization, and yield of products and the relevant mechanisms were discussed. As far as we know, SrAl12O19:Pr3+nanodisks with mean diameter ∼60 nm and thickness between 5 and 10 nm were successfully synthesized for the first time by this low-cost technique. The new synthetic method may provide a general route to synthesize other refractory mixed-oxide nanocrystals. Photon cascade emission involving transitions1S0–1I6followed by3P0–3H4in SrAl12O19:1% Pr3+nanodisks was investigated. Size-effect-induced blue shift of the 4f5dstates of Pr3+was observed in SrAl12O19:1% Pr3+nanodisks, in which the quantum efficiency was preserved, as in the bulk counterparts.
Modified method developed for contact-induced adhesion in indentation
Authors: Shen Yan Xing , Wei Pal Jen , Lin Jen Fin
Published: April 2009

A modified method for contact-induced adhesion on the elastic deformation contact between a rigid spherical indenter and a polydimethylsiloxane (PDMS) specimen is proposed in the present study. Adhesion due to van der Waals interactions was found to be minimal during loading processes. During the unloading process, the experimental load-displacement data revealed two-stage phenomena. The successive advancing contacts between the specimen and the indenter were considered to induce interfacial adhesion and resulted in elastic tension outside the Hertzian contact radius. A real-coded genetic algorithm (RGA) was applied to evaluate how adhesion energy varied with penetration depth.
Application of novel ionic liquids for reverse atom transfer radical polymerization of methacrylonitrile without any additional ligand
Authors: Chen Hou , Meng Yanfeng , Liang Ying , Lu Zixuan , Lv Pingli
Published: April 2009

Reverse atom transfer radical polymerization of methacrylonitrile (MAN) initiated by azobisisobutyronitrile (AIBN) was approached for the first time in the absence of any ligand in four novel ionic liquids, 1-methylimidazolium acetate ([mim][AT]), 1-methylimidazolium butyrate ([mim][BT]), 1-methylimidazolium caproate ([mim][CT]), and 1-methylimidazolium heptylate ([mim][HT]). The polymerization in [mim][AT] not only showed the best control of molecular weight and its distribution but also provided a more rapid reaction rate with the ratio of [MAN]:[FeCl3]:[AIBN] at 300:2:1. The block copolymer PMAN-b-PSt was obtained via a conventional ATRP process in [mim][AT] by using the resulting PMAN as a macroinitiator. After simple purification, [mim][AT] and FeCl3 could be easily recycled and reused and had no effect on the living nature of reverse atom transfer radical polymerization of MAN.
Soft lithography-mediated microscale patterning of silica on diverse substrates
Authors: Butler Randall , Ferrell Nicholas , Hansford Derek , Naik Rajesh
Published: April 2009

We have developed a soft lithography-based process to create microscale patterns of silica on a diverse array of substrates. A sacrificial polymer layer was first patterned using a micromolding technique. A peptide was adsorbed on the substrate and the sacrificial layer was removed. The patterned peptide template then catalyzed the deposition of silica from a silicic acid solution. With this procedure, we have created both continuous and discontinuous silica patterns on metallic, ceramic, and polymer substrates.
Effect of Nb doping on microstructure and electric properties of lead zirconate stannum titanate antiferroelectric ceramics
Authors: Tang H. , Feng Y.J. , Xu Z. , Zhang C.H. , Gao J.Q.
Published: April 2009

The aim of this work is to study the effect of Nb element doping on the microstructure and electrical properties of lead zirconate stannum titanate (PZST) ceramic and to improve phase transition properties of PZST. Nb-doped Pb(Zr,Sn,Ti)O3 ceramic samples were prepared by the conventional mixed oxide method. Phase transitions induced by temperature, pressure, and electric field were measured with electric dielectric permittivity, hydrostatic pressure, and hysteresis. The microstructure of the samples was observed by electron scanning microscope to discuss the effect of Nb doping on PZST ceramics. The experiment results indicated that the remnant polarization (Pr), dielectric constant, phase transition, and microstructure were strongly dependent on Nb doping content.
Extracting yield strength and strain-hardening exponent of metals with a double-angle indenter
Authors: Hou Genliang , Wang Fei , Xu Kewei
Published: April 2009

A double-angle indenter model is proposed to determine the representative strain in the indentation process, and a new method is then developed aiming at the extraction of the yield strength and strain-hardening exponent from the surface layer of metals, because surface properties, especially in a small region, may differ from bulk ones and are sometimes closer to service properties such as fatigue strength, wear, and corrosion resistance. First, the isotropic metal was analyzed, the elastic modulus of which was fixed at 128 GPa, the yield strength was 50 to 200 MPa, and the strain-hardening exponent was 0.1 to 0.5. By introducing the yield strain to substitute the yield strength in the calculation, it was proved that the model can cover the majority of metals because the introduced weight parameter λ is independent of the yield strength and the elastic modulus, although it depends on the strain-hardening exponent to some extent. For the determination of yield strain εY (or yield strength Y), the precision is better for low C/E and low n, whereas for the determination of strain-hardening exponent n, the precision is better for high C/E and low εY. By using the double-angle indenter, the material constitutive relationship at the surface can be evaluated from just one indentation without any other measurements.
Effects of zinc, lithium, and indium on the grain size of magnesium
Authors: Becerra A. , Pekguleryuz M.
Published: April 2009

The grain size of magnesium solid-solution alloys with lithium, indium, and/or zinc has been determined. Lithium, indium, and zinc additions decreased the grain size, D, of magnesium solid-solution alloys cast in a copper mold. The most effective grain refinement was obtained by zinc. In binary Mg–Zn alloys, grain size is related to the growth restriction factor, Q as D = 94 + 312/Q. In Mg–Li and Mg–In binary alloys, grain size versus growth relationships described as D = a + b/Q indicated that these alloys have lower numbers of nucleants but with higher potency than the Mg–Zn binary system. For Mg–Li and especially Mg–In, grain size could be related to growth restriction as D = 383Q−n with higher R2. Ternary and quaternary alloys based on Mg–Zn with Li and/or In additions also follow the D = a + b/Q relationship with the parameters indicating a larger number of lower potency nucleants than the Mg–Zn binary alloys. Electron probe microanalysis showed that Mg–Zn alloys exhibit pronounced and persistent grain-boundary enrichment of Zn, pointing toward Scheil solidification.
Upconversion luminescence properties of monodisperse spherical Y2O2S:Yb,Ho nanocrystals
Authors: Luo Xixian , Cao Wanghe , Xing Mingming
Published: April 2009

Monodisperse spherical Y2O2S:Yb,Ho nanocrystals with particle size about 50 nm were prepared by a modified homogeneous precipitation method combined with low-temperature sulfurization process. The Y2O2S:Yb,Ho nanocrystals exhibit an intense green emission assigned to the Ho3+ ions 5F4, 5S2 → 4I15/2 transition under 980 nm infrared pump. The upconversion luminescence brightness of Y2O2S:Yb,Ho is 526 Cd/m2 under 4.63 W/cm2 pump density, indicating that the as-prepared Y2O2S:Yb,Ho nanocrystals can meet the requirement of in vivo imaging. The formation mechanism of monodisperse spherical oxysulfide nanoparticles is also discussed.
Impedance spectroscopy analysis of zirconia:8 mol% yttria solid electrolytes with graphite pore former
Authors: Muccillo R.
Published: April 2009

Porous ZrO2:8 mol% Y2O3 sintered ceramics were prepared by adding graphite powder as pore former before sintering. The thermal elimination of graphite was evaluated by thermogravimetric analysis. Impedance spectroscopy analysis was carried out in the 5 Hz to 13 MHz frequency range in specimens sintered with and without pore former. The deconvolution of the impedance diagrams, [Z″(ω) × Z′(ω)] and [Z″(ω) × log f], and the numerical residuals resulting from the subtraction of normalized impedance spectroscopy diagrams measured in specimens with and without pore formers were evaluated. A comparison of the impedance diagrams of samples sintered with and without pore former shows evidence of a modification of the electrical response caused by pores. The results show the unequivocal ability of the impedance spectroscopy technique to gauge microstructural modification caused by the presence of pores in ionic conducting solids.
A multifunctional poly(acrylic acid)/gelatin hydrogel
Authors: Tang Qunwei , Wu Jihuai , Lin Jianming , Fan Shijun , Hu De
Published: April 2009

A poly(acrylic acid)/gelatin interpenetrating network hydrogel was synthesized by aqueous solution polymerization. The influences of preparation conditions including cross-linker, initiator, gelatin content, and neutralization degree on the swelling ratios of the hydrogels are investigated. The swelling, mechanical strength, biodegradability, and drug-release properties of poly(acrylic acid)/gelatin hydrogel are evaluated. The hydrogel has excellent mechanical properties; tensile strength is 1500 kPa, and elongation at break is 887%, respectively. The in vitro biodegradation shows that an interpenetrating network structure exists in the poly(acrylic acid)/gelatin hybrid hydrogel. A release study indicates that the theophylline release from the hydrogel depends on the cross-linking density of the hydrogel and pH of the medium, and the drug diffusion obeys an anomalous transport model.
First-principles study of deformation-induced phase transformations in Ti–Al intermetallics
Authors: Chen C.L. , Lu W. , He L.L. , Ye H.Q.
Published: April 2009

The structural phase stability and electronic properties of the Ti–Al intermetallic compounds were investigated by means of density-functional theory (DFT) calculations in a generalized gradient approximation. Through comparison of the calculated formation energies of the parent and product phases, an in-depth theoretical understanding of the deformation-induced γ ↔ α2 phase transitions observed previously in TiAl alloys was achieved. The formation energy plays an important role in evaluating the feasibility of these phase transformations during plastic deformation of TiAl alloys. In addition, the density of states (DOS) was also calculated and used to analyze the stability of Ti–Al intermetallic compounds. The reasons for the absence of the deformation-induced (DI)-α2 and DI-γ (L12) phases in underformed TiAl alloys were analyzed.
Sol-gel-derived titanium oxide–cerium oxide biocompatible nanocomposite film for urea sensor
Authors: Ansari Anees A. , Sumana G. , Pandey M.K. , Malhotra B.D.
Published: April 2009

Sol-gel-derived biocompatible titanium oxide–cerium oxide (TiO2–CeO2) nanocomposite film was deposited onto indium tin oxide (ITO)-coated glass substrate by the dip-coating method. This nanobiocomposite film has been characterized using x-ray diffraction, Fourier transform infrared, atomic force microscope, and electrochemical techniques, respectively. The particle size of the TiO2–CeO2 nanobiocomposite film was found to be 23 nm. The urea biosensor fabricated by immobilizing mixed enzyme [urease (Urs) and glutamate dehydrogenase (GLDH)] on this nanobiocomposite showed a response time of 10 s, sensitivity as 0.9165 μAcm−2mM−1, detection limit of 0.166 μM, and negligible effect due to interferants uric acid, cholesterol, glucose, and ascorbic acid. The value of Michaelis–Menten constant (Km) estimated using Lineweaver–Burke plot as 4.8 mM indicated enhancement in the affinity and/or activity of enzyme attached to their nanobiocomposite. This bioelectrode retained 95% of enzyme activity after 6 months at 4 °C.
Augmented instrumented indentation using nonlinear electrical contact current-voltage curves
Authors: Fang Lei , Muhlstein Christopher L. , Romasco Amber L. , Collins James G. , Friedman Lawrence H.
Published: April 2009

An electrical technique was recently developed to measure the in situ contact area continuously during instrumented indentation by simultaneously monitoring electrical contact response between a conductive indenter tip and a conductive sample. This technique has the potential to overcome limitations of the Oliver-Pharr method caused by the lack of a direct contact area measurement. However, the electrical contact current-voltage (I-V) curves measured from the technique were nonlinear, posing a significant challenge to inferring accurate in situ contact areas. To overcome this challenge and extend the electrical technique to more applications, various I-V curve analysis methods were investigated for their abilities to infer in situ contact area and hardness. Annealed Cu was indented using both linear and exponential loading tests. When analyzing the resulting data, the feasibility of each method was evaluated and the optimal methods to calculate the in situ contact area and hardness were determined. It was found that a simple summation of the absolute values of area under I-V curves or the area under I-V curves at positive voltages yielded the most robust area measure, whereas error in the inferred contact area was systematic and primarily from velocity dependence of the I-V response.
Formation of 14H-type long period stacking ordered structure in the as-cast and solid solution treated Mg–Gd–Zn–Zr alloys
Authors: Ding W.J. , Wu Y.J. , Peng L.M. , Zeng X.Q. , Yuan G.Y. , Lin D.L.
Published: April 2009

The coherent fine lamellae consisting of the 2H-Mg and the 14H-type long period stacking ordered (LPSO) structure within α′-Mg matrix have been first observed in an as-cast Mg96.32Gd2.5Zn1Zr0.18 alloy. During subsequent solid solution heat treatment at 698–813 K, in addition to the lamellae within matrix, a novel lamellar X phase (Mg–8.37±1.0Zn–11.32±1.0Gd, at.%) with the 14H-type LPSO structure was transformed from the dendritical β phase, and a corresponding time–temperature–transformation (TTT) diagram was established. The 14H-type LPSO structure existing in Mg–Gd–Zn–Zr alloys derives from two variant means: the formation of LPSO structure within α′-Mg matrix and the transformation of the dendritical β phase to a lamellar X phase with the LPSO structure. The alloy solid solution treated at 773 K for 35 h exhibits higher tensile strength and better elongation than the nonheated alloy because of the lamellar X phase with the 14H-type LPSO structure and the 14H-type LPSO structure within matrix.
Processing and microstructure characterization of a novel porous hierarchical TiO2structure
Authors: Crawford G.A. , Chawla N. , Ringnalda J.
Published: April 2009

We report on a novel biocompatible hierarchical TiO2porous coating on the surface of Ti, processed via anodic oxidation. The coating consists of large (∼1–20 μm) pores on the microscale and nanotubes (∼50 nm diameter) on the nanoscale. This structure is exciting because of its potential application as a bioactive coating for Ti bone implants. Surface characterization of the coating showed nanotubes of relatively uniform diameter. The interface between TiO2nanotubes and Ti, studied by transmission electron microscopy, was incoherent. The tubes were also somewhat interconnected.
Deformation behavior and indentation size effect in amorphous and crystallized Pd40Cu30Ni10P20 alloy
Authors: Li N. , Liu L. , Chan K.C.
Published: April 2009

The deformation behavior and indentation size effect (ISE) in amorphous and crystallized Pd40Cu30Ni10P20 alloy were comparatively studied through instrumented nanoindentation. It was found that the two alloys showed different deformation behaviors, the amorphous alloy exhibited conspicuous pop-in events in the load-depth (P-h) curve, while the crystallized alloy showed a relatively smooth P-h curve. In addition, the indentation hardness was observed to decrease with increasing penetration depth in the two alloys, exhibiting a significant ISE. However, the crystallized alloy displayed a sharper reduction of hardness with indentation depth as compared to the amorphous alloy, indicating a more significant indentation size effect in the crystalline alloy. The structure difference and friction factor associated with the surface residual stress are taken into account to interpret the difference in the deformation behavior and indentation size effect of the two alloys.
Imidazole catalyzed silica synthesis: Progress toward understanding the role of histidine in (bio)silicification
Authors: Liang Mei-Keat , Patwardhan Siddharth V. , Danilovtseva Elena N. , Annenkov Vadim V. , Perry Carole C.
Published: April 2009

Histidine is an amino acid present in proteins involved in biosilica formation and often found in peptides identified during phage display studies but its role(s) and the extent of its involvement in the silica precipitation process is not fully understood. In this contribution we describe results from an in vitro silicification study conducted using poly-histidine (P-His) and a series of different molecular weight synthetic polymers containing the imidazole functionality (polyvinylimidazole, PVI) for comparison. We show that the presence of imidazole from PVI or P-His is able to catalyze silicic acid condensation; the effect being greater for P-His. The catalytic mechanism is proposed to involve the dual features of the imidazole group—its ability to form hydrogen bonds with silicic acid and electrostatic attraction toward oligomeric silicic acid species.
Luminescent silica nanotubes and nanowires: Preparation from cellulose whisker templates and investigation of irradiation-induced luminescence
Authors: Scheel Hanne , Zollfrank Cordt , Greil Peter
Published: April 2009

Luminescent silica nanotubes and nanowires were fabricated from cellulose whisker templates by sol-gel processing. The cellulose templates were removed by calcination at 650 °C to generate silica nanotubes with diameters of 15 nm and lengths up to 500 nm. At temperatures of 900 °C the core region previously occupied by the cellulose template was closed yielding silica nanowires. Cathodoluminescence spectra of the silica nanotubes and nanowires were measured in the transmission electron microscope during irradiation with 150 keV electrons. A blue emission at 450 nm was observed for the silica nanowires calcined at 900 °C. This luminescence was found to be related to defects induced by electron irradiation and was investigated in situ as a function of irradiation dose. The as-synthesized and 650 °C calcined nanowires and nanotubes showed a fast decay of the signal. The observed irradiation dose dependent changes in the luminescence spectra will be discussed in terms of defect formation and transformation mechanisms.
Allometric Growth in Hatchery-Reared Gilthead Seabream
Authors: Çoban Deniz , Kamaci H Okan , Suzer Cüneyt , Saka Şahin , Firat Kürşat
Published: April 2009

Morphological development and allometric growth were investigated in the gilthead seabream Sparus aurata during larval development until the end of the weaning period on day 41. Fertilized eggs had a diameter of 1.01 ± 0.02 mm (mean ± SE) and a lipid vesicle diameter of 0.227 ± 0.021 mm. Mean total length (TL) was 2.68 ± 0.04 mm for newly hatched larvae and 3.57 ± 0.09 mm at the onset of feeding (4 d after hatching [DAH]). At 10 DAH, initial swim bladder inflation occurred, mean TL was 4.19 ± 0.08 mm, and notochord length (NL) was 4.00 ± 0.07 mm. At 16 DAH, the swim bladder became more elongated, TL was 5.13 ± 0.09 mm, and NL was 4.94 ± 0.07 mm. Notochord flexion occurred at 6.46 ± 0.11 mm TL on 23 DAH, and the complement of the flexion occurred at 8.67 ± 0.109 mm TL on 35 DAH. At the end of the weaning period (at 41 DAH), larvae were 10.85 ± 0.116 mm TL. The majority of all allometric changes from the inflection point were expressed during the larval stage and integrated with the metamorphosis stage. Inflections in body proportion changes occurred mainly at 4.19 and 7.04 mm TL, corresponding to initial swim bladder inflation and the notochord flexion period, respectively.
Ser criança e ser aluno: concepções das professoras do 1° ciclo do ensino básico
Authors: Fátima Pereira , Lopes Amélia
Published: April 2009

Apresentam-se dados parciais do projeto "As crianças são importantes: a reorganização curricular no 1º CEB e as concepções de infância dos professores"¹, que pretendeu conhecer as concepções de infância que emergem dos discursos dos professores sobre as suas práticas. Os resultados parciais revelam-nos concepções sobre a infância ambíguas e contraditórias, fazendo corresponder as possibilidades de expressão das subjetividades das crianças a seres que não parecem partilhar a mesma categoria social, quando se encontram fora e dentro do contexto escolar. A idealização sobre a infância e a sua relação com os princípios estruturantes da escolarização situam-se num domínio mais simbólico do que real e a sua distanciação relativamente às subjetividades das crianças e às práticas sociais escolares tem constituído um fator de sofrimento para as professoras e para os alunos.
Grupo e trabalho coletivo na escola: trocando olhares, mudando práticas
Authors: Chaluh Laura Noemi
Published: April 2009

O presente artigo trata do trabalho desenvolvido por um grupo de formação instituído em uma escola de ensino fundamental da Rede Municipal de Campinas-SP, no período de 2004 a 2005, cujo objetivo foi a redefinição do trabalho com as classes de alfabetização. Uma das inquietações do grupo foi a não-aprendizagem de alguns dos alunos das primeiras séries no tempo que a escola seriada estipula. Em função disso, as professoras promoveram uma mudança significativa ao assumir a responsabilidade pela aprendizagem de todos os alunos dessas séries que precisavam de "outros tempos". Enfatizo, neste texto, a potencialidade do trabalho conjunto dessas professoras quando decidiram mudar a prática do reforço já instituída na escola, prática solitária professora-aluno. A prática coletiva do reforço estabeleceu novas formas de organização que possibilitaram aos alunos vivenciar o trabalho com outras professoras, bem como proporcionar-lhes a possibilidade de trocar olhares sobre um mesmo aluno.
O movimento da produção acadêmica sobre a Rede Municipal de Educação de Belo Horizonte
Authors: Zaidan Samira , Caldeira Anna Maria Salgueiro , Sousa Eustáquia Salvadora de , Azevedo Ana Lúcia de Faria , Soares Cláudia Caldeira
Published: April 2009

Este artigo apresenta uma análise da produção acadêmica sobre a Rede Municipal de Educação de Belo Horizonte, de 1986/2005, considerando o contexto histórico social e educacional referente ao período. As 162 dissertações e teses que integram o estudo foram organizadas em 12 "focos temáticos". Os trabalhos desenvolvidos ao longo desses vinte anos revelam uma riqueza de temas e problemas e expressam um deslocamento do "olhar" dos pesquisadores das questões mais gerais para as mais específicas, em que a escola e seus sujeitos são colocados no centro do sistema educacional. São analisadas práticas escolares, programas da escola e de governo, projetos e os docentes e discentes em seus saberes, memórias, histórias de vida, relativas aos níveis de ensino da educação básica. A instituição escolar é entendida como um tempo/espaço de formação de sujeitos e de vivência de conflitos e possibilidades. O estudo revela uma rede de escolas que chama a atenção pelo número de trabalhos nela referenciados, pela diversificação de teorias e temas abordados, pela contribuição que deixa para a elaboração de projetos e políticas públicas.
A opção pelo magistério representada por professoras de Ensino Fundamental em memoriais
Authors: Maurício Lúcia Velloso
Published: April 2009

Este trabalho procurou elucidar a constituição de representações sociais por meio da memória social. Foram analisados 31 memoriais de professoras de 1ª a 4ª série como trabalho final em curso de atualização. Memórias pessoais têm como objeto a história de vida de cada um, mas são sociais pelo seu conteúdo. As professoras se distribuíram equitativamente entre efetivas e contratadas, com largo leque etário. As categorias emergiram dos memoriais por meio da análise de conteúdo. Os resultados apontaram maior coesão nos relatos das professoras concursadas e perceptível preocupação com a renovação de contrato pelas não-efetivas. Em vez de representação social sobre o fazer docente, os depoimentos estavam ancorados na representação de aluno, responsável pelos obstáculos que se impõem à prática docente. Predominou a valorização do aprendizado prático: aprende-se trabalhando. Os memoriais indicaram que a opção pelo magistério se dá pela vocação, pela instituição formadora e pelas experiências iniciais de trabalho.
Ofício "impossível"? Uma piada inesgotável
Authors: Cifali Mireille
Published: April 2009

A autora analisa a expressão "ofício impossível" tal como aparece em dois textos de Sigmund Freud: seu "Prefácio à 'Juventude desorientada' de Aichhorn" (1925) e "Análise terminável e interminável" (1937). Em seguida, elabora uma interpretação atual à expressão freudiana, entendendo-a como piada, na associação aos três ofícios: governar, curar e educar. Aborda ainda três aspectos talvez cruciais para o futuro: o poder, a clínica e a ética.
Criança: objeto a liberado?
Authors: Lima Glaucineia Gomes de
Published: April 2009

Lacan (1968-69) abordou a criança como objeto a liberado. Assim, ela é capturada no gozo, drama em torno do qual a família se estrutura. Tais formulações são questionadas no texto que discute o lugar da criança como objeto de gozo nos tempos atuais. Parte-se da discussão sobre a sociedade da globalização, cuja lógica se orienta para a produção incessante de objetos de consumo, marcada pelo declínio dos ideais e o impulso ao hedonismo mortífero. O imperativo do consumo na sociedade globalizada não é sem conseqüências para a educação, que se guia pela lógica de educar para o mercado, empreitada que tem como efeito o fracasso escolar, um dos nomes do 'mal-estar' na educação. Desponta, entre educadores e educandos, apatia, tédio e indiferença no vazio em que parece ter se tornado o espaço escolar. Os efeitos de retorno do gozo incidem sobre o corpo das crianças, que é objeto de maus-tratos, violência, pedofilia e todo tipo de abusos. Assim, conclui-se questionando qual é o lugar para a escuta do sintoma, face ao imperativo de consumo e a ascensão do objeto, e as suas conseqüências para o apagamento da subjetividade da criança.
Desejo de encadear letras
Authors: Burgarelli Cristóvão Giovani
Published: April 2009

Este texto se propõe pensar algumas questões sobre a entrada da criança em processo de alfabetização na leitura e na produção textual. Partindo da discussão sobre a relação entre a criança, o professor e o texto, busca-se uma articulação entre essas três instâncias e o conceito de inconsciente, cuja estrutura é a da linguagem. Situando-se, por fim, que se trata da constituição de um sujeito desejante, serão privilegiados os conceitos psicanalíticos de pulsão, escrita e letra.
A roda de conversa e a assembléia de crianças: a palavra líquida e a escola de educação infantil
Authors: Mrech Leny Magalhães , Rahme Monica
Published: April 2009

Este artigo discute, inicialmente, alguns dos impasses da Educação Infantil contemporânea no Brasil, enfocando, em seguida, questões que emergiram em um projeto de Psicanálise e Educação Inclusiva desenvolvido em uma escola de Educação Infantil do município de São Paulo, envolvendo professores, alunos, pais, funcionários e equipe técnica. A metodologia utilizada foi a da Conversação, estabelecida por Jacques-Alain Miller (2005). O texto analisa algumas questões específicas que emergiram durante este trabalho, a partir de teorizações referentes à "palavra líquida" (MILLER, 2008) e de sua interface com a noção de "modernidade líquida" (BAUMAN, 2001). Por fim, problematizamos aspectos referentes à escolarização das pessoas com necessidades educacionais especiais, na atualidade, e sua relação com os processos de segregação e normalização.
Joaquim Nabuco e os abolicionistas britânicos: correspondência, 1880-1905
Authors: Bethell Leslie , Carvalho José Murilo de
Published: April 2009

Aspecto pouco estudado da luta contra a escravidão no Brasil é a relação estabelecida entre Joaquim Nabuco e a Sociedade Britânica e Estrangeira Antiescravidão, sediada em Londres. A correspondência entre Nabuco e Charles Harris Allen, secretário da Sociedade, e outros abolicionistas britânicos, ao longo da década de 1880 e posteriormente, revela uma parceria conscientemente buscada por Nabuco para levar a luta ao plano internacional. As cartas fornecem uma nítida visão das dificuldades encontradas por Nabuco no Brasil e da poderosa ajuda que encontrou em Londres. Uma de suas principais dificuldades foi a acusação a ele feita de falta de patriotismo a que ele respondeu afirmando a estreita relação que via entre pátria e civilização.