bluuebunny/crossref_metadata_2025 huggingface dataset:
Transplantation of Neuronal and Glial Restricted Precursors into Contused Spinal Cord Improves Bladder and Motor Functions, Decreases Thermal Hypersensitivity, and Modifies Intraspinal Circuitry
Authors: Mitsui Takahiko , Shumsky Jed S. , Lepore Angelo C. , Murray Marion , Fischer Itzhak
Published: October 2005

Transplanting neuronal and glial restricted precursors (NRP/GRP) into a midthoracic injury 9 d after contusion improved bladder and motor function, diminished thermal hypersensitivity, and modified lumbosacral circuitry compared with operated controls (OP-controls). Histological analysis showed that NRP/GRP survived, filled the lesion site, differentiated into neurons and glia, and migrated selectively. Volume of spinal cord spared was increased in NRP/GRP recipients, suggesting local protection. Bladder areflexia developed in both operated groups, but NRP/GRP recipients exhibited an accelerated recovery, with decreased micturition pressure and fewer episodes of detrusor hyperreflexia. Because noradrenergic receptors proliferate after spinal injury and descending noradrenergic pathways contribute to regulation of bladder control, we examined the effects of administering an α-1A-adrenergic antagonist, Tamsulosin, on urodynamics. This improved all cystometric parameters in both operated groups, and micturition pressure in NRP/GRP rats recovered to normal levels. Both operated groups initially showed increased sensitivity to a thermal stimulus applied to the tail; the NRP/GRP rats showed significant improvement over time. NRP/GRP grafts also produced greater recovery of hindlimb function in several tests, although both groups showed persistent and similar deficits in locomotion on a grid.

Because bladder, hindlimb, and tail sensory and motor functions are organized through lumbosacral cord, we examined descending and primary afferent projections at L6-S1. The density of serotonergic, noradrenergic, and corticotrophin releasing factor-positive fibers increased in the NRP/GRP group compared with OP-controls, suggesting some sparing and/or sprouting of these modulatory pathways. Immunocytochemical staining density of dorsal root axons in the dorsal horn increased in the OP-controls but appeared normal in the NRP/GRP group. Synaptophysin immunoreactivity in the lumbosacral dorsal horn was similar among groups, consistent with restoration of synaptic density in both groups of operated animals but by different pathways. We suggest that local protection provided by NRP/GRP resulted in increased sparing/sprouting of descending pathways, which prevented sprouting by dorsal root axons, and that this modification in lumbosacral circuitry contributes to the recovery of function.
Organization of the Human Trichromatic Cone Mosaic
Authors: Hofer Heidi , Carroll Joseph , Neitz Jay , Neitz Maureen , Williams David R.
Published: October 2005

Using high-resolution adaptive-optics imaging combined with retinal densitometry, we characterized the arrangement of short- (S), middle- (M), and long- (L) wavelength-sensitive cones in eight human foveal mosaics. As suggested by previous studies, we found males with normal color vision that varied in the ratio of L to M cones (from 1.1:1 to 16.5:1). We also found a protan carrier with an even more extreme L:M ratio (0.37:1). All subjects had nearly identical S-cone densities, indicating independence of the developmental mechanism that governs the relative numerosity of L/M and S cones. L:M cone ratio estimates were correlated highly with those obtained in the same eyes using the flicker photometric electroretinogram (ERG), although the comparison indicates that the signal from each M cone makes a larger contribution to the ERG than each L cone. Although all subjects had highly disordered arrangements of L and M cones, three subjects showed evidence for departures from a strictly random rule for assigning the L and M cone photopigments. In two retinas, these departures corresponded to local clumping of cones of like type. In a third retina, the L:M cone ratio differed significantly at two retinal locations on opposite sides of the fovea. These results suggest that the assignment of L and M pigment, although highly irregular, is not a completely random process. Surprisingly, in the protan carrier, in which X-chromosome inactivation would favor L- or M-cone clumping, there was no evidence of clumping, perhaps as a result of cone migration during foveal development.
The Translation Repressor 4E-BP2 Is Critical for eIF4F Complex Formation, Synaptic Plasticity, and Memory in the Hippocampus
Authors: Banko Jessica L. , Poulin Francis , Hou Lingfei , DeMaria Christine T. , Sonenberg Nahum , Klann Eric
Published: October 2005

Long-lasting synaptic plasticity and memory requires mRNA translation, yet little is known as to how this process is regulated. To explore the role that the translation repressor 4E-BP2 plays in hippocampal long-term potentiation (LTP) and learning and memory, we examined 4E-BP2 knock-out mice. Interestingly, genetic elimination of 4E-BP2 converted early-phase LTP to late-phase LTP (L-LTP) in the Schaffer collateral pathway, likely as a result of increased eIF4F complex formation and translation initiation. A critical limit for activity-induced translation was revealed in the 4E-BP2 knock-out mice because L-LTP elicited by traditional stimulation paradigms was obstructed. Moreover, the 4E-BP2 knock-out mice also exhibited impaired spatial learning and memory and conditioned fear-associative memory deficits. These results suggest a crucial role for proper regulation of the eIF4F complex by 4E-BP2 during LTP and learning and memory in the mouse hippocampus.
Role ofFabp7, a Downstream Gene of Pax6, in the Maintenance of Neuroepithelial Cells during Early Embryonic Development of the Rat Cortex
Authors: Arai Yoko , Funatsu Nobuo , Numayama-Tsuruta Keiko , Nomura Tadashi , Nakamura Shun , Osumi Noriko
Published: October 2005

Pax6 is a transcription factor with key functional roles in the developing brain. Pax6 promotes neuronal differentiation via transcriptional regulation of theNeurogenin2(Ngn2) gene, although Pax6 expression appears in proliferating neuroepithelial cells before the onset of neurogenesis. Here, we identifiedFabp7(BLBP/B-FABP), a member of the fatty acid-binding protein (FABP) family, as a downregulated gene in the embryonic brain ofPax6mutant rat (rSey2/rSey2) by microarray analysis. Marked reduction ofFabp7expression was confirmed by quantitative PCR. Spatiotemporal expression patterns ofFabp7in the wild-type rat embryos from embryonic day 10.5 (E10.5) to E14.5 were similar to those ofPax6, and expression ofFabp7was undetectable in therSey2/rSey2cortex. The expression pattern ofFabp7in the wild-type mouse embryo at E10.5 (corresponding to E12.5 rat) was different from that in the rat embryo, and no change of expression was observed in theSey/Seymouse embryo. Overexpression of exogenousPax6mainly induced ectopic expression ofFabp7, rather than ofNgn2, in the early cortical primordium. Interestingly, knocking-down FABP7 function by electroporation ofFabp7small interfering RNA severely curtailed cell proliferation but promoted neuronal differentiation. We conclude thatFabp7is a downstream gene of Pax6 transcription factor in the developing rat cortex and essential for maintenance of neuroepithelial cells during early cortical development.
HighwireFunction at theDrosophilaNeuromuscular Junction: Spatial, Structural, and Temporal Requirements
Authors: Wu Chunlai , Wairkar Yogesh P. , Collins Catherine A. , DiAntonio Aaron
Published: October 2005

Highwire is a huge, evolutionarily conserved protein that is required to restrain synaptic growth and promote synaptic transmission at theDrosophilaneuromuscular junction. Current models ofhighwirefunction suggest that it may act as a ubiquitin ligase to regulate synaptic development. However, it is not known in which cellshighwirefunctions, whether its putative ligase domain is required for function, or whetherhighwireregulates the synapse during development or alternatively sets cell fate in the embryo. We performed a series of transgenic rescue experiments to test the spatial, structural, and temporal requirements forhighwirefunction. We find that presynaptic activity ofhighwireis both necessary and sufficient to regulate both synapse morphology and physiology. The Highwire RING domain, which is postulated to function as an E3 ubiquitin ligase, is required forhighwirefunction. In addition,highwireacts throughout larval development to regulate synaptic morphology and function. Finally, we show that the morphological and physiological phenotypes ofhighwiremutants have different dosage and temporal requirements forhighwire, demonstrating thathighwiremay independently regulate the molecular pathways controlling synaptic growth and function.
Hunting Increases Adaptive Auditory Map Plasticity in Adult Barn Owls
Authors: Bergan Joseph F. , Ro Peter , Ro Daniel , Knudsen Eric I.
Published: October 2005

The optic tectum (OT) of barn owls contains topographic maps of auditory and visual space. Barn owls reared with horizontally displacing prismatic spectacles (prisms) acquire a novel auditory space map in the OT that restores alignment with the prismatically displaced visual map. Although juvenile owls readily acquire alternative maps of auditory space as a result of experience, this plasticity is reduced greatly in adults. We tested whether hunting live prey, a natural and critically important behavior for barn owls, increases auditory map plasticity in adult owls. Two groups of naive adult owls were fit with prisms. The first group was fed dead mice during 10 weeks of prism experience, while the second group was required to hunt live prey for an identical period of time. When the owls hunted live prey, auditory maps shifted substantially farther (five times farther, on average) and the consistency of tuning curve shifts within each map increased. Only a short period of time in each day, during which the two groups experienced different conditions, accounts for this effect. In addition, increased map plasticity correlated with behavioral improvements in the owls' ability to strike and capture prey. These results indicate that the experience of hunting dramatically increases adult adaptive plasticity in this pathway.
Blockade of Nociceptin/Orphanin FQ Transmission Attenuates Symptoms and Neurodegeneration Associated with Parkinson's Disease
Authors: Marti Matteo , Mela Flora , Fantin Martina , Zucchini Silvia , Brown Jeffrey M. , Witta Jassir , Di Benedetto Manuela , Buzas Beata , Reinscheid Rainer K. , Salvadori Severo , Guerrini Remo , Romualdi Patrizia , Candeletti Sanzio , Simonato Michele , Cox Brian M. , Morari Michele
Published: October 2005

The opioid-like neuropeptide nociceptin/orphanin FQ (N/OFQ) and its receptor (NOP) are expressed in the substantia nigra (SN), a brain area containing dopamine neurons that degenerate in Parkinson's disease. Endogenous N/OFQ facilitates nigral glutamate release and inhibits nigrostriatal dopamine transmission and motor behavior. Here, we present evidence suggesting that endogenous N/OFQ may contribute to Parkinson's disease. Pharmacological blockade of the SN N/OFQ-NOP receptor system attenuated parkinsonian-like akinesia/hypokinesia in 6-hydroxydopamine hemilesioned or haloperidol-treated rats, whereas deletion of the NOP receptor gene conferred mice partial protection from haloperidol-induced motor depression. The antiparkinsonian action of NOP receptor antagonists was associated with reduction of glutamate release in the SN. In 6-hydroxydopamine hemilesioned rats, enhancement of N/OFQ expression and release was detected in the lesioned compared with the unlesioned SN, indicating that parkinsonism may be associated with overactivation of the N/OFQ-NOP receptor system in the SN. Finally, deletion of the N/OFQ gene conferred mice partial protection against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced loss of SN dopamine neurons. Based on these data, we propose that NOP receptor antagonists may represent a novel approach for combined (symptomatic and neuroprotective) therapy of Parkinson's disease.
Differential Regulation of Synaptic Inputs by Constitutively Released Endocannabinoids and Exogenous Cannabinoids
Authors: Hentges Shane T. , Low Malcolm J. , Williams John T.
Published: October 2005

Endocannabinoid release from a single neuron has been shown to cause presynaptic inhibition of transmitter release at many different sites. Here, we demonstrate that hypothalamic proopiomelanocortin (POMC) neurons release endocannabinoids continuously under basal conditions, unlike other release sites at which endocannabinoid production must be stimulated. The basal endocannabinoid release selectively inhibited GABA release onto POMC neurons, although exogenous administration of cannabinoid agonists also inhibited glutamate release. The CB1 cannabinoid receptor antagonist AM 251 [N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide] blocked endocannabinoid-mediated inhibition of GABA release without affecting excitatory synaptic currents, whereas the CB1 receptor agonist WIN 55,212-2 [R-(+)-(2,3-dihydro-5-methyl-3-[(4-morpholinyl)methyl]pyrol [1,2,3-de]-1,4-benzoxazin-6-yl)(1-naphthalenyl) methanone monomethanesulfonate] inhibited both inhibitory and excitatory synaptic currents in POMC neurons. These data demonstrate that endogenously released cannabinoids and exogenously applied CB1 receptor agonists can have markedly different effects on synaptic inputs. Furthermore, the data suggest a novel form of endocannabinoid-mediated retrograde inhibition, whereby the regulation of a subset of inputs requires either the removal of tonic presynaptic inhibition caused by endocannabinoids or the engagement of a mechanism that actively inhibits endocannabinoid production.
Expression of Rem2, an RGK Family Small GTPase, Reduces N-Type Calcium Current without Affecting Channel Surface Density
Authors: Chen Huanmian , Puhl Henry L. , Niu Shui-Lin , Mitchell Drake C. , Ikeda Stephen R.
Published: October 2005

Rad, Gem/Kir, Rem, and Rem2 are members of the Ras-related RGK (Rad, Gem, and Kir) family of small GTP-binding proteins. Heterologous expression of RGK proteins interferes withde novocalcium channel assembly/trafficking and dramatically decreases the amplitude of currents arising from preexisting high-voltage-activated calcium channels. These effects probably result from the direct interaction of RGK proteins with calcium channel β subunits. Among the RGK family, Rem2 is the only member abundantly expressed in neuronal tissues. Here, we examined the ability of Rem2 to modulate endogenous voltage-activated calcium channels in rat sympathetic and dorsal root ganglion neurons. Heterologous expression of Rem2 nearly abolished calcium currents arising from preexisting high-voltage-activated calcium channels without affecting low-voltage-activated calcium channels. Rem2 inhibition of N-type calcium channels required both the Ras homology (core) domain and the polybasic C terminus. Mutation of a putative GTP/Mg2+binding motif in Rem2 did not affect suppression of calcium currents. Loading neurons with GDP-β-S via the patch pipette did not reverse Rem2-mediated calcium channel inhibition. Finally, [125I]Tyr22-ω-conotoxin GVIA cell surface binding in tsA201 cells stably expressing N-type calcium channels was not altered by Rem2 expression at a time when calcium current was totally abolished. Together, our results support a model in which Rem2 localizes to the plasma membrane via a C-terminal polybasic motif and interacts with calcium channel β subunits in the preassembled N-type channel, thereby forming a nonconducting species.
Full Motor Recovery Despite Striatal Neuron Loss and Formation of Irreversible Amyloid-Like Inclusions in a Conditional Mouse Model of Huntington's Disease
Authors: Díaz-Hernández Miguel , Torres-Peraza Jesús , Salvatori-Abarca Alejandro , Morán María A. , Gómez-Ramos Pilar , Alberch Jordi , Lucas José J.
Published: October 2005

The primary mechanism responsible for Huntington's disease remains unknown. Postulated early pathogenic events include the following: impaired protein folding, altered protein degradation, mitochondrial dysfunction, and transcriptional dysregulation. Although related therapies can delay disease progression in mouse models, they target downstream and probably indirect effects of mutant-huntingtin expression. Accordingly, in case they prove beneficial in humans, they might only palliate some aspects of disease. Our previous studies in the Tet/HD94 conditional model and the recently reported efficacy of RNA interference against mutant huntingtin in another mouse model support silencing mutant-huntingtin expression as a valid therapeutic approach that has the advantage of targeting toxicity at its root. Here, we address whether gene silencing can still be beneficial in the late stages of disease with detectable striatal neuron loss. Stereological analysis was applied to determine an age at which Tet/HD94 mice show a decrease in the number of striatal neurons. Then, progression of neuropathology and motor phenotype were analyzed in mice that were allowed to continue expressing mutant huntingtin and in mice that no longer expressed it. Neuronal loss did not revert in gene-off mice, but the additional loss that takes place in gene-on mice was prevented. The total number of huntingtin-containing inclusions dramatically reverted, but a small fraction of inclusions positive for the amyloid dye thioflavin-S remained. Interestingly, despite a 20% decrease in striatal neurons and the presence of amyloid-like irreversible inclusions, gene-off mice fully recover from their motor deficit, thus ruling out amyloid-like huntingtin inclusions as the main toxic species and suggesting that gene-silencing therapies might work in late stages of disease.
Complementary Roles of Cholecystokinin- and Parvalbumin-Expressing GABAergic Neurons in Hippocampal Network Oscillations
Authors: Klausberger Thomas , Marton Laszlo F. , O'Neill Joseph , Huck Jojanneke H. J. , Dalezios Yannis , Fuentealba Pablo , Suen Wai Yee , Papp Edit , Kaneko Takeshi , Watanabe Masahiko , Csicsvari Jozsef , Somogyi Peter
Published: October 2005

In the hippocampal CA1 area, a relatively homogenous population of pyramidal cells is accompanied by a diversity of GABAergic interneurons. Previously, we found that parvalbumin-expressing basket, axo-axonic, bistratified, and oriens-lacunosum moleculare cells, innervating different domains of pyramidal cells, have distinct firing patterns during network oscillationsin vivo. A second family of interneurons, expressing cholecystokinin but not parvalbumin, is known to target the same domains of pyramidal cells as do the parvalbumin cells. To test the temporal activity of these independent and parallel GABAergic inputs, we recorded the precise spike timing of identified cholecystokinin interneurons during hippocampal network oscillations in anesthetized rats and determined their molecular expression profiles and synaptic targets. The cells were cannabinoid receptor type 1 immunopositive. Contrary to the stereotyped firing of parvalbumin interneurons, cholecystokinin-expressing basket and dendrite-innervating cells discharge, on average, with 1.7 ± 2.0 Hz during high-frequency ripple oscillations in an episode-dependent manner. During theta oscillations, cholecystokinin-expressing interneurons fire with 8.8 ± 3.3 Hz at a characteristic time on the ascending phase of theta waves (155 ± 81°), when place cells start firing in freely moving animals. The firing patterns of some interneurons recorded in drug-free behaving rats were similar to cholecystokinin cells in anesthetized animals. Our results demonstrate that cholecystokinin- and parvalbumin-expressing interneurons make different contributions to network oscillations and play distinct roles in different brain states. We suggest that the specific spike timing of cholecystokinin interneurons and their sensitivity to endocannabinoids might contribute to differentiate subgroups of pyramidal cells forming neuronal assemblies, whereas parvalbumin interneurons contribute to synchronizing the entire network.
Characteristics of tin whiskers formed on sputter-deposited films—an aging study
Authors: Winterstein J.P. , LeBret J.B. , Norton M.G.
Published: October 2005

Tin whiskers formed on sputter-deposited films on Muntz metal substrates have been examined following long-term aging at room temperature. It was found that while the initial annealing conditions determined the original nucleation and growth rates, whisker nucleation and growth was a continuous process and appeared to be occurring throughout the duration of the study. Whisker densities increased for all samples during aging, and samples that initially showed no whiskers during high-temperature annealing had a population density of 2.5 mm−2 after storage for 15 months.
Effect of La and Y on Crystallization Temperatures of Hafnia and Zirconia
Authors: Ushakov Sergey V. , Brown Crystalyn E. , Navrotsky Alexandra
Published: October 2005

Crystallization of amorphous Y- and La-doped HfO2 and ZrO2 nanophase powders was studied using thermal analysis and high-temperature x-ray diffraction. Substantial increase of crystallization temperature of amorphous hafnium and zirconium oxides could be achieved by alloying with La2O3. The crystallization temperature of Hf2La2O7 composition is higher than 900 °C, which makes it a candidate for advanced gate dielectrics. In contrast, Y-doping did not significantly raise the crystallization temperature.
Solution-Based Processing of Sc2O3 Nanopowders Yielding Transparent Ceramics
Authors: Li Ji-Guang , Ikegami Takayasu , Mori Toshiyuki
Published: October 2005

A basic sulfate precursor [Sc(OH)SO4·2H2O] for well-sinterable Sc2O3 powders was precipitated from mixed solutions of scandium nitrate [Sc(NO3)3] and ammonium sulfate [(NH4)2SO4] at room temperature and which was subsequently converted to Sc2O3 via dehydroxylization and desulfurization at temperatures ≥900 °C. With the reactive powders synthesized in this work, polycrystalline Sc2O3 ceramics showing high inline transmittances of approximately 70% in the visible wavelength region (corresponding to ∼90% of the theoretical value of single crystals) have been fabricated via vacuum sintering at a relatively low temperature of 1700 °C.
Luminescence in ZnO Quantum Particles
Authors: Bendre B.S. , Mahamuni Shailaja
Published: October 2005

Wet-chemical and electrochemical routes were used to synthesize zinc oxide nanoparticles showing peculiar luminescent properties. ZnO-I are the nanoparticles that show only band gap ultraviolet (UV) emission, whereas ZnO-II type nanoparticles show the defect green luminescence along with the UV emission. Photoluminescence excitation (PLE) spectra of ZnO-I nanocrystals exhibit a single feature located at about 368 nm whereas ZnO-II nanocrystals show two features in PLE: a prominent feature at about 368 nm which is size dependent and a hump at 325 nm. These results are discussed in detail in view of the luminescence behavior in ZnO quantum particles.
Study on the Interfacial Characterization of the Co5/Cu3/Co5 trilayer and Co3/Cu/Co/Cu3/Co/Cu/Co3 Multilayer
Authors: Yuan Xiaoyu , Bi Xiaofang , Shang Jiaxiang , Xu Huibin
Published: October 2005

Comprehensive results are presented on the influence of interfaces on electronic structure and giant magnetoresistance (GMR). Two structures were calculated for Co5/Cu3/Co5 and Co3/Cu/Co/Cu3/Co/Cu/Co3, where numbers stand for monolayer numbers of atoms, by employing the discrete variational method in the framework of the local spin density approximation. It has been found that the electron spin-dependent scattering is very strong at the interfaces compared to the interiors of the ferromagnetic layers, independent of the moment alignment configuration. The calculation results of total energy for various magnetization configuration revealed that antiferromagnetic exchange coupling was present between any of the ferromagnetic layers separated by Cu layers at zero field in the Co3/Cu/Co/Cu3/Co/Cu/Co3. The evaluated GMR ratio for the Co3/Cu/Co/Cu3/Co/Cu/Co3 (about 35.1%) was much larger than that of the Co5/Cu3/Co5 (about 21.0%), indicating large GMR effect could be expected with more interfaces when the thicknesses were the same. The result also indicated that the negative polarization of 4s electrons could reduce the GMR effect.
A Study of Nanostructures of Thin Films in B–C–N System Produced by Pulsed Laser Deposition and Nitrogen Ion-Beam-Assisted Pulsed Laser Deposition
Authors: Bysakh S. , Chattopadhyay K. , Ling H. , Wu J.D. , Dong C. , Wang Y.Q. , Duan X.F. , Kuo K.H.
Published: October 2005

We report the synthesis of thin films of B–C–N and C–N deposited by N+ ion-beam-assisted pulsed laser deposition (IBPLD) technique on glass substrates at different temperatures. We compare these films with the thin films of boron carbide synthesized by pulsed laser deposition without the assistance of ion-beam. Electron diffraction experiments in the transmission electron microscope shows that the vapor quenched regions of all films deposited at room temperature are amorphous. In addition, shown for the first time is the evidence of laser melting and subsequent rapid solidification of B4C melt in the form of micrometer- and submicrometer-size round particulates on the respective films. It is possible to amorphize B4C melt droplets of submicrometer sizes. Solidification morphologies of micrometer-size droplets show dispersion of nanocrystallites of B4C in amorphous matrix within the droplets. We were unable to synthesize cubic carbon nitride using the current technique. However, the formation of nanocrystalline turbostratic carbo- and boron carbo-nitrides were possible by IBPLD on substrate at elevated temperature and not at room temperature. Turbostraticity relaxes the lattice spacings locally in the nanometric hexagonal graphite in C–N film deposited at 600 °C leading to large broadening of diffraction rings.
Dislocation Mechanics Simulations of the Bilinear Behavior in Micro- and Nanoindentation
Authors: Elmustafa A.A. , Ananda A.A. , Elmahboub W.M.
Published: October 2005

The hardnesses of electropolished, polycrystalline α-brass, and aluminum were measured as functions of load using Vickers microindentation, and Berkovich nanoindentation. Data were compared with literature data for silver, copper, and tungsten. In all cases, the hardness was observed to increase with decreasing size. Theories in the literature based on strain gradient plasticity and the addition of statistically stored and geometrically stored dislocation densities predict that the square of the hardness should increase linearly with inverse size of the indent. Our data and the literature data agree with this prediction over a limited range of indent diameters represented by microhardness and deep nanohardness data, whereas for the shallow nanohardness data, a second linear behavior is observed. The linear behavior of the microhardness and deep nanohardness data together with the second linear behavior generated by the shallow nanohardness data constituted what we designate a bilinear behavior. An algorithm is developed to calculate the induced shear stresses in a circular Volterra dislocation loop from a line integral of the Peach–Koehler equation using dislocation mechanics and isotropic elasticity. The computed induced shear stresses when plotted versus depth of indentation produced curves that exhibited a bilinear behavior identical to the bilinear behavior resulted from experiments, and the curves collapsed to a single curve for the different materials simulated.
Nano-alloys Synthesized by Controlled Crystallization from Supercooled Atomic Clusters of Elements
Authors: Meng X.K. , Ngan A.H.W.
Published: October 2005

Materials in nanocrystalline forms are well known to possess unusual and interesting properties when compared to the bulk conditions, and these open up an exciting range of novel applications. The key step involved in the systematic exploitation of nanocrystals for real applications lies in the development of reliable methods to synthesize nanocrystals of arbitrary chemical compositions in a range of crystal sizes. In particular, metallic alloy nanocrystals pose a special challenge. We demonstrate that nano-to-micro-sized crystals of intermetallic nickel–aluminide (Ni3Al) ranging from approximately 3 nm to over 100 nm in size can be synthesized by co-sputtering from elemental Ni and Al onto unheated, incompatible organic substrates, followed by controlled postdeposition heat treatment at mild temperatures. The crystal size of approximately 3 nm here is the smallest ever reported for monolithic ordered Ni3Al.
Magnetic Properties and Magnetization Reversal of Sm–Co(3x nm)/Co(x nm) Multilayered Films
Authors: You Cai-Yin , Yang ChoongJin , Zhang Z.D. , Han JongSoo , Sun X.K.
Published: October 2005

[Sm–Co (3x nm) /Co (x nm)]10 (x = 10, 7, 4) multilayered films have been prepared by magnetron rf-sputtering. It is found that the thickness of both hard and soft layers has important effects on phase transformation and magnetic interaction of films. With a fixed ratio of hard- to soft-layer thickness, decreasing simultaneously the thickness of these layers results in increasing coercivity. The effects of the external magnetic field during annealing depend on the Co-layer thickness (x value), mainly because of the formation of different main phases for different thickness of Co layer. For the films with x = 10 and 7, the main phase is Sm2Co17 after annealed. Applying a magnetic field during annealing promotes the crystallization of films, and therefore, it increases the coercivity of the films with x = 10 and 7. Magnetic interaction has been investigated by measuring δm and remanence magnetization. All the films show that although the exchange coupling favorable for magnetization is significant, the increase of the coercivity mainly originates from improving the pinning effects. Temperature dependence of the coercivity supports that the pinning of domain-walls constitutes a control mechanism of the coercivity. This behavior can be well understood in terms of the Gaunt’s approach of the coercivity.
Comparison of Magnetostrictive Performance Loss of Particulate Tb0.3 Dy0.7 Fe2 Epoxy Composites Prepared with Different Matrix Polymers M. Shanmugham et al.: Comparison of Magnetostrictive Performance Loss of Particulate Tb0.3 Dy0.7 Fe2 Epoxy Composites
Authors: Shanmugham Manikantan , Bailey Harold , Armstrong William D.
Published: October 2005

Particulate composites of magnetostrictive Terfenol-D were prepared with polyamine and anhydride cured epoxy polymer matrices with the presence or the absence of a strong magnetic field. These composites were studied to investigate (i) the influence of magnetic field that is applied during specimen preparation in strain output levels, (ii) performance loss at high temperatures, and (iii) the influence of matrix material in magnetostrictive strain performance. A six-way comparison is made of materials processed under magnetic field with materials processed under no magnetic field, and magnetostrictive strain performance at glass transition finish temperature with magnetostrictive strain performance at glass transition start temperature, and magnetostrictive strain performance in low modulus matrix systems with magnetostrictive strain performance in high modulus matrix systems. A four-way comparison is also made between the micrographs for strain-cycled and non-strain-cycled samples and relative damage incurred by samples prepared using high and low modulus matrix systems.
Surface Morphology Studies of Sub-Ps Pulsed-Laser-Deposited AlN Thin Films
Authors: György E. , Teodorescu V.S. , Mihailescu I.N. , Klini A. , Zorba V. , Manousaki A. , Fotakis C.
Published: October 2005

Aluminum nitride thin films were deposited by multipulse KrF* (λ = 248 nm, τ∼450 fs) excimer laser ablation of AlN targets in low-pressure nitrogen. We investigated the morphology of the deposited films by scanning as well as transmission electron microscopy, as a function of laser fluence and ambient nitrogen pressure. The AlN films entirely consist of grains (clusters) with average diameters of a few tens of nanometers. In addition, particulates several hundreds of nanometers in diameter (spherical droplets) were observed on the surfaces of the deposited films. Besides these particulates, we noticed the presence of micrometer-size whiskers, or dendritic- and wave-like structures, consisting of agglomerates of nanoparticles. The particulates density decreases with the decrease of the laser fluence, or with the increase of the ambient nitrogen pressure, while their average size increases. This indicates that clustering is the dominant particulates formation mechanism, as a result of the enhanced number of collisions in the fs laser generated ablation plasma.
Float-Zone Growth and Properties of Ferroelectric Lead Titanate
Authors: Maffei N. , Rossetti G.A.
Published: October 2005

Lead titanate (PbTiO3) is a ferroelectric/piezoelectric material widely used in medical ultrasound transducers and infrared detectors. It is also important as an end member of morphotropic solid-solution systems such as Pb(Zn1/3Nb2/3)–PbTiO3 (PZN–PT) and Pb(Mg1/3Nb2/3)–PT (PMN–PT) that exhibit exceptional electromechanical properties as oriented single crystals. The float-zone technique has been used to grow pure crystals of lead titanate. To the best of the authors’ knowledge, this is the first time that the growth of this compound by the float-zone technique has been reported. The principal advantage of the float-zone technique is that no container is required so that a uniform distribution of chemical constituents can be obtained while eliminating problems of heterogeneous nucleation and metal contamination at the container wall. Although large single crystals were not obtained in the current study primarily due to instabilities of the molten liquid zone, the combined results of characterization by electron probe microanalysis, x-ray diffraction, specific heat, and dielectric permittivity measurements show that the float-zone crystal growth technique can produce lead titanate crystals of high chemical and phase purity. However, the results show that to obtain large single crystals, the stability of the molten zone at low cooling rates must be improved.
Tribological Behavior of Polymers Simulated by Molecular Dynamics
Authors: Brostow Witold , Hinze J. Adam , Simões Ricardo
Published: October 2005

Using molecular dynamics to simulate behavior of polymer surfaces during scratch testing, we report the first results of computer simulations of scratch behavior of noncrystals. A previously described procedure for creating realistic polymeric materials on the computer [W. Brostow, A.M. Cunha, and R. Simoes, Mater. Res. Innovat. 7, 19 (2003)] and used until now to simulate mechanical behavior of metals [S. Blonski, W. Brostow, and J. Kubat, Phys. Rev. B 49, 6494 (1994)] and one- and two-phase polymers [W. Brostow, A.M. Cunha, J. Quintanilla, and R. Simoes, Macromol. Theory Simul. 11, 308 (2002); W. Brostow, A.M. Cunha, and R. Simoes, Proc. Ann. Tech. Conf. Soc. Plastics Engrs. 60, 3105 (2002)] was applied. While experiments provide only the macroscopic penetration depth and the recovery (healing) depth, the simulations give the behavior of each macromolecular chain segment at each moment in time. We report results for one-phase polymers and also for systems with varying concentrations of a liquid crystalline (LC) second-phase that acts as a reinforcement. We relate the local structure to scratch resistance and recovery. The orientation of the chemical bonds is a major factor. The presence of a LC phase improves the tribological properties; however, the effect is not as significant as might have been expected.
Anodization Behavior of Al Film on Si Substrate With Different Interlayers for Preparing Si-Based Nanoporous Alumina Template
Authors: Wu M.T. , Leu I.C. , Hon M.H.
Published: October 2005

The fabrication and applications of porous anodic alumina (PAA) have been studied for decades. Recently, preparation of PAA template directly formed on Si has been developed to enhance the performance of the fabricated nanostructures. However, less attention is paid to the anodization mechanism of the Al film on the Si substrate. In the current study, the PAA template was fabricated on Si of which an interlayer was sandwiched between the Al film and the Si substrate. The anodization behavior of the Al film, especially at the alumina–substrate interface, was investigated through the observation of the variation of oxidation current and the structural change of alumina. Different degree of dissolution at the pore base of alumina was revealed when a different interlayer was introduced, leading to the formation of the arched pore bottom. At the same time, difference in the variation of current was also observed as the pore base reached the alumina–Si interface. These features were different from those observed in conventional anodization of Al foils. The findings in this study are of scientific and technological importance for the template-mediated growth of nanostructures, especially for those to be integrated into Si devices.
Hydrothermal Synthesis of Undoped and Mn-Doped ZnGa2O4 Powders and Thin Films
Authors: Loeffler Lars , Lange Fred F.
Published: October 2005

Undoped and manganese-doped zinc gallate powders and thin films have been synthesized via the hydrothermal route from aqueous solutions at a pH between 9.5 and 12.5. The chemical composition and the crystal size of the synthesized powder have been studied as a function of pH, temperature, and the composition of the precursor solution, such as the type of hydroxide used and the zinc, gallium, and lithium content. Specimens have been analyzed by x-ray diffraction, scanning and transmission electron microscopy, energy-dispersive x-ray spectroscopy, thermogravimetry, and inductively coupled plasma atomic emission spectroscopy. It is shown that crystallite size and chemical composition strongly depend on the solubility of the gallium species within the solution, which appears to determine the number of ZnGa2O4 nuclei per unit volume. Crystals of a few micrometers in size can be synthesized from solutions where Ga is very soluble (e.g., pH ≥ 11), whereas when Ga is not very soluble, the synthesis product is nanocrystalline. Thermogravimetric studies indicate that a considerable amount of OH− is incorporated at the oxygen sites (every 5th to 10th site). Hydrothermal growth of heteroepitaxial zinc gallate thin films has been carried out on (111) MgAl2O4 and (00.1) LiNbO3 substrates. Heteroepitaxy is based on a coincident pattern of oxygen sites in the two structures; that is, (111)ZGO ∥ (111)MAO and (111)ZGO ∥ (00.6)LNO for the out-of plane orientation and (1¯10)ZGO ∥ (1¯10)MAO and (1¯10)ZGO ∥ (1¯10)LNO for the in-plane orientation, respectively. The thin films cover the substrate completely and consist of oriented grains of up to several hundred nanometers in size. In general, the films are twinned with two variants (in separate grains) that are related by a 60° rotation around [111]. This twinning can only be suppressed at high pH and high temperature and only on the MgAl2O4 substrates.
Li-Doped NiO Epitaxial Thin Film with Atomically Flat Surface
Authors: Kamiya T. , Ohta H. , Kamiya M. , Nomura K. , Ueda K. , Hirano M. , Hosono H.
Published: October 2005

Li-doped NiO epitaxial films with high electrical conductivity and atomically flat stepped surfaces were fabricated by a combined technique of pulsed laser deposition and subsequent annealing. It was determined that subsequently annealing at temperatures as low as 600 °C significantly decreased electrical conductivity due to Li evaporation when the film surface was not protected from Li evaporation. To suppress Li evaporation, a yttria-stabilized-zironia plate was used to cover the film surface, which raised the annealing temperature up to 1300 °C while maintaining a high Li concentration and electrical conductivity. Thermally annealing at this temperature also improved crystal quality and formed epitaxial films with atomically flat stepped surfaces. The films were single crystalline at least in observation areas, 10 μm × 10 μm. A reasonably large Hall mobility approximately 0.05 cm2/Vs similar to that reported for bulk single-crystal NiO and a visible-light transmission in excess of 75% were obtained on 120-nm-thick films. Although annealing at higher temperatures such as 1400 °C can further improve the structural and optical properties, the Li concentration in the films was decreased to <3% of the as-deposited film.
Synthesis and Characterization of Iron Oxide Nanostructured Particles in Na–Y Zeolite Matrix
Authors: Yee Maxine , Yaacob Iskandar I.
Published: October 2005

Formation of iron oxide nanoparticles within the internal cages of Na–Y zeolites was investigated. Sodium ions within the zeolites were replaced with iron(II) ions. Elemental composition studies showed a significant amount of iron in the exchanged sample. NaOH and dropwise additions of H2O2 at 60 °C triggered formation of zeolite–iron oxide systems. X-ray diffraction (XRD) patterns showed diminishing zeolite peaks along with evolution of peaks corresponding to γ-Fe2O3 and α-Fe2O3 with increasing NaOH concentration. Morphological changes from hexagonal-shaped zeolite to clusters of fine particles were observed under scanning electron microscope. Particles with about 15-nm diameter were detected by transmission electron microscopy. γ-Fe2O3 crystallites of 13.4 nm were determined from the broadening of XRD peaks. The magnetization curves of samples (precipitated using NaOH with concentrations of 2.0 M and above) showed absence of hysteresis and passed through the origin, indicating the particles are superparamagnetic. Gas adsorption–desorption measurement of the system precipitated with 2.0 M NaOH revealed a 26% increase in its specific surface area, indicating the presence of nanometer-sized particles within the zeolites.
Validation of Abundance Estimates from Mark–Recapture and Removal Techniques for Rainbow Trout Captured by Electrofishing in Small Streams
Authors: Rosenberger Amanda E. , Dunham Jason B.
Published: October 2005

Estimation of fish abundance in streams using the removal model or the Lincoln– Peterson mark–recapture model is a common practice in fisheries. These models produce misleading results if their assumptions are violated. We evaluated the assumptions of these two models via electrofishing of rainbow trout Oncorhynchus mykiss in central Idaho streams. For one-, two-, three-, and four-pass sampling effort in closed sites, we evaluated the influences of fish size and habitat characteristics on sampling efficiency and the accuracy of removal abundance estimates. We also examined the use of models to generate unbiased estimates of fish abundance through adjustment of total catch or biased removal estimates. Our results suggested that the assumptions of the mark– recapture model were satisfied and that abundance estimates based on this approach were unbiased. In contrast, the removal model assumptions were not met. Decreasing sampling efficiencies over removal passes resulted in underestimated population sizes and overestimates of sampling efficiency. This bias decreased, but was not eliminated, with increased sampling effort. Biased removal estimates based on different levels of effort were highly correlated with each other but were less correlated with unbiased mark–recapture estimates. Stream size decreased sampling efficiency, and stream size and instream wood increased the negative bias of removal estimates. We found that reliable estimates of population abundance could be obtained from models of sampling efficiency for different levels of effort. Validation of abundance estimates requires extra attention to routine sampling considerations but can help fisheries biologists avoid pitfalls associated with biased data and facilitate standardized comparisons among studies that employ different sampling methods.
Predictive Habitat Models for the Occurrence of Stream Fishes in the Mid-Atlantic Highlands
Authors: Rashleigh Brenda , Parmar Rajbir , Johnston John M. , Barber M. Craig
Published: October 2005

In most wadeable streams of the mid-Atlantic Highlands region of the eastern USA, physical habitat alteration is the primary stressor for fish. Models that predict the occurrence of stream-fish species based on habitat measures can be useful in management, and predicted probability of occurrence can be a measure of habitat suitability with which to compare alternative habitat management scenarios and assess the effectiveness of stream restoration. We developed such models for each of 13 mid-Atlantic Highlands stream-fish species and species groups by using multiple logistic regression and six instream habitat measures: depth, temperature, substrate, percent riffles, cover, and riparian vegetation. The predictive ability of the models ranged from 61% to 79% in cross-validation and from 38% to 85% on an independent data set. The models predicted well for both the original and test data sets for black bass Micropterus spp., brook trout Salvelinus fontinalis, darters Etheostoma and Percina spp., shiners Notropis spp., and suckers Hypentelium and Moxostoma spp. Suitable habitat for most of the fish species groups was characterized by intermediate depth, a high percentage of cobble and riparian vegetation, and a low percentage of instream cover. The relatively high predictive ability and reasonable responses to habitat measures indicated that these models could be useful for management. However, the models were more sensitive to depth and temperature than to measures that are more commonly affected by restoration activities, such as cover and riparian vegetation.
Distribution and Abundance of Nonnative Fishes in Streams of the Western United States
Authors: Schade Charles B. , Bonar Scott A.
Published: October 2005

This report presents data from one of the largest standardized stream surveys conducted in the western United States, which shows that one of every four individual fish in streams of 12 western states are nonnative. The states surveyed included Arizona, California, Colorado, Idaho, Montana, Nevada, North Dakota, Oregon, South Dakota, Utah, Washington, and Wyoming. The most widely distributed and abundant nonnative fishes in the western USA were brook trout Salvelinus fontinalis, brown trout Salmo trutta, rainbow trout Oncorhynchus mykiss, common carp Cyprinus carpio, smallmouth bass Micropterus dolomieu, largemouth bass M. salmoides, green sunfish Lepomis cyanellus, fathead minnow Pimephales promelas, yellow perch Perca flavescens, yellow bullhead Ameiurus natalis, cutthroat trout O. clarkii, western mosquitofish Gambusia affinis, golden shiner Notemigonus crysoleucas, channel catfish Ictalurus punctatus, and red shiner Cyprinella lutrensis. The greatest abundance and distribution of nonnative fishes was in interior states, and the most common nonnatives were introduced for angling. Nonnative fishes were widespread in pristine to highly disturbed streams influenced by all types of land use practices. We present ranges in water temperature, flow, stream order, riparian cover, human disturbance, and other environmental conditions where the 10 most common introduced species were found. Of the total western U.S. stream length bearing fish, 50.1% contained nonnative fishes while 17.9% contained physical environment that was ranked highly or moderately disturbed by humans. Introduced fishes can adversely affect stream communities, and they are much more widespread in western U.S. streams than habitat destruction. The widespread distribution and high relative abundance of nonnative fishes and their documented negative effects suggest their management and control should elicit at least as much attention as habitat preservation in the protection of native western U.S. stream biota.