bluuebunny/crossref_metadata_2025 huggingface dataset:
Cerebral Changes during Performance of Overlearned Arbitrary Visuomotor Associations
Authors: Grol Meike J. , de Lange Floris P. , Verstraten Frans A. J. , Passingham Richard E. , Toni Ivan
Published: January 2006

The posterior parietal cortex (PPC) is known to be involved in the control of automatic movements that are spatially guided, such as grasping an apple. We considered whether the PPC might also contribute to the performance of visuomotor associations in which stimuli and responses are linked arbitrarily, such as producing a certain sound for a typographical character when reading aloud or pressing pedals according to the color of a traffic light when driving a motor vehicle. The PPC does not appear to be necessary for learning new arbitrary visuomotor associations, but with extensive training, the PPC can encode nonspatial sensory features of task-relevant cues. Accordingly, we have tested whether the contributions of the PPC might become apparent once arbitrary sensorimotor mappings are overlearned.

We have used functional magnetic resonance imaging to measure cerebral activity while subjects were learning novel arbitrary visuomotor associations, overlearning known mappings, or attempting to learn frequently changing novel mappings. To capture the dynamic features of cerebral activity related to the learning process, we have compared time-varying modulations of activity between conditions rather than average (steady-state) responses.

Frontal, striatal, and intraparietal regions showed decreasing or stable activity when subjects learned or attempted to learn novel associations, respectively. Importantly, the same frontal, striatal, and intraparietal regions showed time-dependent increases in activity over time as the mappings become overlearned, i.e., despite time-invariant behavioral responses. The automaticity of these mappings predicted the degree of intraparietal changes, indicating that the contribution of the PPC might be related to a particular stage of the overlearning process. We suggest that, as the visuomotor mappings become robust to interference, the PPC may convey relevant sensory information toward the motor cortex. More generally, our findings illustrate how rich cerebral dynamics can underlie stable behavior.
Activation of Protein Kinase C in Sensory Neurons Accelerates Ca2+Uptake into the Endoplasmic Reticulum
Authors: Usachev Yuriy M. , Marsh Anthony J. , Johanns Tanner M. , Lemke Michelle M. , Thayer Stanley A.
Published: January 2006

The rate of Ca2+clearance from the neuronal cytoplasm affects the amplitude, duration, and localization of Ca2+signals and influences a variety of Ca2+-dependent functions. We reported previously that activation of protein kinase C (PKC) accelerates Ca2+efflux in rat sensory neurons mediated by the plasma membrane Ca2+-ATPase isoform 4 (PMCA4). Here we show that sarco-endoplasmic reticulum Ca2+-ATPase (SERCA)-mediated Ca2+uptake into intracellular stores is also accelerated by PKC activation. The rate of intracellular Ca2+concentration ([Ca2+]i) clearance was studied after small (<350 nm) action potential-induced Ca2+loads in rat dorsal root ganglion neurons. Under these conditions, mitochondrial Ca2+uptake and Na+/Ca2+exchange do not significantly influence [Ca2+]irecovery. Phorbol dibutyrate (PDBu) increased the rate of [Ca2+]iclearance by 71% in a manner sensitive to the selective PKC inhibitors GF109203x (2-[1-(3-dimethylaminopropyl)-1H-indol-3-yl]-3-(1H-indol-3-yl)maleimide) and calphostin. PKC-dependent acceleration was still observed (∼39%) when the PKC-sensitive PMCA isoform was knocked down by expression of an antisense PMCA4 cDNA (AS4). Direct measurement of Ca2+in the endoplasmic reticulum (ER) lumen revealed that PKC increased the rate of store refilling more than twofold after depletion by treatment with cyclopiazonic acid. ER refilling was less complete in PDBu-treated cells, although, in AS4-expressing cells, PDBu accelerated the rate without reducing the ER capacity, suggesting that PMCA and SERCA compete for Ca2+. Thus, activation of PKC accelerates the clearance of Ca2+from the cytoplasm by the concerted stimulation of Ca2+sequestration and Ca2+efflux.
Hypothalamic Tumor Necrosis Factor-α Converting Enzyme Mediates Excitatory Amino Acid-Dependent Neuron-to-Glia Signaling in the Neuroendocrine Brain
Authors: Lomniczi Alejandro , Cornea Anda , Costa Maria E. , Ojeda Sergio R.
Published: January 2006

Glial erbB1 receptors play a significant role in the hypothalamic control of female puberty. Activation of these receptors by transforming growth factor α (TGFα) results in production of prostaglandin E2, which then stimulates luteinizing hormone releasing hormone (LHRH) neurons to secrete LHRH, the neuropeptide controlling sexual development. Glutamatergic neurons set in motion this glia-to-neuron signaling pathway by transactivating erbB1 receptors via coactivation of AMPA receptors (AMPARs) and metabotropic glutamate receptors (mGluRs). Because the metalloproteinase tumor necrosis factor α converting enzyme (TACE) releases TGFα from its transmembrane precursor before TGFα can bind to erbB1 receptors, we sought to determine whether TACE is required for excitatory amino acids to activate the TGFα–erbB1 signaling module in hypothalamic astrocytes, and thus facilitate the advent of puberty. Coactivation of astrocytic AMPARs and mGluRs caused extracellular Ca2+influx, a Ca2+/protein kinase C-dependent increase in TACE-like activity, and enhanced release of TGFα. Within the hypothalamus, TACE is most abundantly expressed in astrocytes of the median eminence (ME), and its enzymatic activity increases selectively in this region at the time of the first preovulatory surge of gonadotropins. ME explants respond to stimulation of AMPARs and mGluRs with LHRH release, and this response is prevented by blocking TACE activity.In vivoinhibition of TACE activity targeted to the ME delayed the age at first ovulation, indicating that ME-specific changes in TACE activity are required for the normal timing of puberty. These results suggest that TACE is a component of the neuron-to-glia signaling process used by glutamatergic neurons to control female sexual development.
Listening in Silence Activates Auditory Areas: A Functional Magnetic Resonance Imaging Study
Authors: Voisin Julien , Bidet-Caulet Aurélie , Bertrand Olivier , Fonlupt Pierre
Published: January 2006

Directing attention to some acoustic features of a sound has been shown repeatedly to modulate the stimulus-induced neural responses. On the contrary, little is known about the neurophysiological impact of auditory attention when the auditory scene remains empty. We performed an experiment in which subjects had to detect a sound emerging from silence (the sound was detectable after different durations of silence). Two frontal activations (right dorsolateral prefrontal and inferior frontal) were found, regardless of the side where sound was searched for, consistent with the well established role of these regions in attentional control. The main result was that the superior temporal cortex showed activations contralateral to the side where sound was expected to be present. The area extended from the vicinity of Heschl's gyrus to the surrounding areas (planum temporale/anterior lateral areas). The effect consisted of both an increase in the response to a sound delivered after attention was directed to detect its emergence and a baseline shift during the silent period. Thus, in absence of any acoustic stimulus, the search for an auditory input was found to activate the auditory cortex.
Capture of the Late Phase of Long-Term Potentiation within and across the Apical and Basilar Dendritic Compartments of CA1 Pyramidal Neurons: Synaptic Tagging Is Compartment Restricted
Authors: Alarcon Juan M. , Barco Angel , Kandel Eric R.
Published: January 2006

Studies in the rodent hippocampus have demonstrated that when the late phase of long-term potentiation (L-LTP) is induced in a set of synapses by suprathreshold stimulation, L-LTP can also be expressed by other synapses receiving subthreshold stimulation, a phenomenon usually referred as “capture of L-LTP.” Because the pyramidal neurons in the mammalian hippocampus have both apical and basal dendrites, we have now investigated whether capture of L-LTP, previously described only within the apical dendritic compartment, can also take place within the basilar dendritic compartment and, if so, whether capture can be accomplished from one dendritic compartment to the other. We found that capture of L-LTP can also occur within the basilar dendritic compartment and that the tagging signal that enables capture appears to be the same in both dendritic compartments. However, capture across compartments, between the apical and basilar dendrites, follows different rules and requires a stronger triggering stimulation than capture within a compartment. These results suggest that the tag appears specific to a compartment either apical or basilar and that an additional mechanism may be required to capture across compartments.
Inhibitions of Nucleus Accumbens Neurons Encode a Gating Signal for Reward-Directed Behavior
Authors: Taha Sharif A. , Fields Howard L.
Published: January 2006

The nucleus accumbens (NAcc) is critical in the control of goal-directed behavior. Pharmacological studies suggest that the NAcc may act in both instructive and permissive modes; however, previous electrophysiological studies in behaving rats have reported firing patterns consistent with an instructive, but not permissive, role for NAcc neurons. We now report that a subset of NAcc neurons shows a long-lasting inhibition in firing rate whose onset precedes initiation of goal-directed sequences of behavior and terminates at the conclusion of the sequence. Together with data from previous behavioral studies, this firing pattern suggests that, when active, these neurons tonically inhibit appetitive and consummatory behaviors and that, when inhibited, these neurons permissively gate those behaviors.
Donut-Like Topology of Synaptic Vesicles with a Central Cluster of Mitochondria Wrapped into Membrane Protrusions: A Novel Structure–Function Module of the Adult Calyx of Held
Authors: Wimmer Verena C. , Horstmann Heinz , Groh Alexander , Kuner Thomas
Published: January 2006

Structural and functional properties of synapses are intricately and reciprocally coupled. To cope with the functional requirements in auditory processing, the calyx of Held developed distinct structural specializations such as a large number of active zones, large size, elaborate morphology, and defined distribution of ion channels. These specializations typically appear during postnatal maturation within the first 3 weeks of life and are accompanied by marked changes in the properties of synaptic transmission. We examined the arrangement of synaptic vesicles at different postnatal stages of maturation by genetically labeling vesicles with the fluorescent fusion protein synaptophysin–enhanced green fluorescent protein. Fluorescence and electron microscopy-based analyses revealed a new anatomical specialization in the mature calyx of Held. Within small, membrane-delimited compartments (swellings), synaptic vesicles formed donut-like assemblies around a central cluster of interconnected mitochondria. Adult calyces contained ∼100 such structural units, each of them consisting of ∼800 synaptic vesicles, six to nine mitochondria, and five to nine active zones. A donut of synaptic vesicles measured ∼1 μm in diameter and was placed in a swelling with a volume of ∼5 fl. Conspicuously, this structural specialization appears with the onset of hearing and may contribute to maturational changes in presynaptic function.
Distinct Morphological Stages of Dentate Granule Neuron Maturation in the Adult Mouse Hippocampus
Authors: Zhao Chunmei , Teng E. Matthew , Summers Robert G. , Ming Guo-li , Gage Fred H.
Published: January 2006

Adult neurogenesis in the dentate gyrus may contribute to hippocampus-dependent functions, yet little is known about when and how newborn neurons are functional because of limited information about the time course of their connectivity. By using retrovirus-mediated gene transduction, we followed the dendritic and axonal growth of adult-born neurons in the mouse dentate gyrus and identified distinct morphological stages that may indicate different levels of connectivity. Axonal projections of newborn neurons reach the CA3 area 10–11 d after viral infection, 5–6 d before the first spines are formed. Quantitative analyses show that the peak of spine growth occurs during the first 3–4 weeks, but further structural modifications of newborn neurons take place for months. Moreover, the morphological maturation is differentially affected by age and experience, as shown by comparisons between adult and postnatal brains and between housing conditions. Our study reveals the key morphological transitions of newborn granule neurons during their course of maturation.
The Full Expression of Fasting-Induced Torpor Requires β3-Adrenergic Receptor Signaling
Authors: Swoap Steven J. , Gutilla Margaret J. , Liles L. Cameron , Smith Ross O. , Weinshenker David
Published: January 2006

Torpor, a controlled rapid drop in metabolic rate and body temperature (Tb), is a hypometabolic adaptation to stressful environmental conditions, which occurs in many small mammals, marsupials, and birds. To date, signaling pathways required for torpor have not been identified. We examined the role of the sympathetic nervous system (SNS) in mediating the torpor adaptation to fasting by telemetrically monitoring theTbof dopamine β-hydroxylase knock-out (Dbh–/–) mice, which lack the ability to produce the SNS transmitters, norepinephrine (NE), and epinephrine. Control (Dbh+/–) mice readily reduced serum leptin levels and entered torpor after a fast in a cool environment. In contrast,Dbh–/– mice failed to reduce serum leptin and enter torpor under fasting conditions, whereas restoration of peripheral but not central NE lowered serum leptin levels and rescued the torpor response. Torpor was expressed in fastedDbh–/– mice immediately after administration of either the nonselective β-adrenergic receptor agonist isoproterenol or the β3-adrenergic receptor (AR)-specific agonist CL 316243 [disodium (RR)-5-[2-[[2-(3-chlorophenyl)-2-hydroxyethyl]-amino]propyl]-1,3-benzodioxazole-2,2-dicarboxylate], but not after administration of β1, β2, or α1 agonists. Importantly, the β3-specific antagonist SR 59230A [3-(2-ethylphenoxy)-1-[(1,S)-1,2,3,4-tetrahydronapth-1-ylamino]-2S-2-propanol oxalate] severely blunted fasting-induced torpor in control mice, whereas other AR antagonists were ineffective. These results define a critical role of peripheral SNS activity at β3-AR-containing tissues in the torpor adaptation to limited energy availability and cool ambient temperature.
Mislocalized Rhodopsin Does Not Require Activation to Cause Retinal Degeneration and Neurite Outgrowth inXenopus laevis
Authors: Tam Beatrice M. , Xie Guifu , Oprian Daniel D. , Moritz Orson L.
Published: January 2006

Mutations in the C terminus of rhodopsin disrupt a rod outer segment localization signal, causing rhodopsin mislocalization and aggressive forms of retinitis pigmentosa (RP). Studies of cultured photoreceptors suggest that activated mislocalized rhodopsin can cause cell death via inappropriate G-protein-coupled signaling. To determine whether this pathway occursin vivo, we developed a transgenicXenopus laevismodel of RP based on the class I rhodopsin mutation Q344Ter (Q350Ter inX. laevis). We used a second mutation, K296R, to block the ability of rhodopsin to bind chromophore and activate transducin. We compared the effects of expression of both mutants onX. laevisretinas alone and in combination. K296R did not significantly alter the cellular distribution of rhodopsin and did not induce retinal degeneration. Q350Ter caused rhodopsin mislocalization and induced an RP-like degeneration, including loss of rods and development of sprouts or neurites in some remaining rods, but did not affect the distribution of endogenous rhodopsin. The double mutant K296R/Q350Ter caused a similar degeneration and neurite outgrowth. In addition, we found no protective effects of dark rearing in these animals. Our results demonstrate that the degenerative effects of mislocalized rhodopsin are not mediated by the activated form of rhodopsin and therefore do not proceed via conventional G-protein-coupled signaling.
A Resilient, Low-Frequency, Small-World Human Brain Functional Network with Highly Connected Association Cortical Hubs
Authors: Achard Sophie , Salvador Raymond , Whitcher Brandon , Suckling John , Bullmore Ed
Published: January 2006

Small-world properties have been demonstrated for many complex networks. Here, we applied the discrete wavelet transform to functional magnetic resonance imaging (fMRI) time series, acquired from healthy volunteers in the resting state, to estimate frequency-dependent correlation matrices characterizing functional connectivity between 90 cortical and subcortical regions. After thresholding the wavelet correlation matrices to create undirected graphs of brain functional networks, we found a small-world topology of sparse connections most salient in the low-frequency interval 0.03–0.06 Hz. Global mean path length (2.49) was approximately equivalent to a comparable random network, whereas clustering (0.53) was two times greater; similar parameters have been reported for the network of anatomical connections in the macaque cortex. The human functional network was dominated by a neocortical core of highly connected hubs and had an exponentially truncated power law degree distribution. Hubs included recently evolved regions of the heteromodal association cortex, with long-distance connections to other regions, and more cliquishly connected regions of the unimodal association and primary cortices; paralimbic and limbic regions were topologically more peripheral. The network was more resilient to targeted attack on its hubs than a comparable scale-free network, but about equally resilient to random error. We conclude that correlated, low-frequency oscillations in human fMRI data have a small-world architecture that probably reflects underlying anatomical connectivity of the cortex. Because the major hubs of this network are critical for cognition, its slow dynamics could provide a physiological substrate for segregated and distributed information processing.
Local Synthesis of Actin-Binding Protein β-Thymosin Regulates Neurite Outgrowth
Authors: van Kesteren Ronald E. , Carter Christopher , Dissel Helga M. G. , van Minnen Jan , Gouwenberg Yvonne , Syed Naweed I. , Spencer Gaynor E. , Smit August B.
Published: January 2006

Local protein synthesis plays an essential role in the regulation of various aspects of axonal and dendritic function in adult neurons. At present, however, there is no direct evidence that local protein translation is functionally contributing to neuronal outgrowth. Here, we identified the mRNA encoding the actin-binding protein β-thymosin as one of the most abundant transcripts in neurites of outgrowing neurons in culture. β-Thymosin mRNA is not evenly distributed in neurites, but appears to accumulate at distinct sites such as turning points and growth cones. Using double-stranded RNA knockdown, we show that reducing β-thymosin mRNA levels results in a significant increase in neurite outgrowth, both in neurites of intact cells and in isolated neurites. Together, our data demonstrate that local synthesis of β-thymosin is functionally involved in regulating neuronal outgrowth.
Differential Control of Central Cardiorespiratory Interactions by Hypercapnia and the Effect of Prenatal Nicotine
Authors: Huang Zheng-Gui , Griffioen Kathleen J. S. , Wang Xin , Dergacheva Olga , Kamendi Harriet , Gorini Christopher , Bouairi Euguenia , Mendelowitz David
Published: January 2006

Hypercapnia evokes a strong cardiorespiratory response including gasping and a pronounced bradycardia; however, the mechanism responsible for these survival responses initiated in the brainstem is unknown. To examine the effects of hypercapnia on the central cardiorespiratory network, we used anin vitromedullary slice that allows simultaneous examination of rhythmic respiratory-related activity and inhibitory synaptic neurotransmission to cardioinhibitory vagal neurons (CVNs). Hypercapnia differentially modulated inhibitory neurotransmission to CVNs; whereas hypercapnia selectively depressed spontaneous glycinergic IPSCs in CVNs without altering respiratory-related increases in glycinergic neurotransmission, it decreased both spontaneous and inspiratory-associated GABAergic IPSCs. Because maternal smoking is the highest risk factor for sudden infant death syndrome (SIDS) and prenatal nicotine exposure is proposed to be the link between maternal smoking and SIDS, we examined the cardiorespiratory responses to hypercapnia in animals exposed to nicotine in the prenatal and perinatal period. In animals exposed to prenatal nicotine, hypercapnia evoked an exaggerated depression of GABAergic IPSCs in CVNs with no significant change in glycinergic neurotransmission. Hypercapnia altered inhibitory neurotransmission to CVNs at both presynaptic and postsynaptic sites. Although the results obtained in this studyin vitrocannot be extrapolated with certainty toin vivoresponses, the results of this study provide a likely neurochemical mechanism for hypercapnia-evoked bradycardia and the dysregulation of this response with exposure to prenatal nicotine, creating a higher risk for SIDS.
Multivesicular Release at Schaffer Collateral–CA1 Hippocampal Synapses
Authors: Christie Jason M. , Jahr Craig E.
Published: January 2006

Whether an individual synapse releases single or multiple vesicles of transmitter per action potential is contentious and probably depends on the type of synapse. One possibility is that multivesicular release (MVR) is determined by the instantaneous release probability (Pr) and therefore can be controlled by activity-dependent changes inPr. We investigated transmitter release across a range ofPrat synapses between Schaffer collaterals (SCs) and CA1 pyramidal cells in acute hippocampal slices using patch-clamp recordings. The size of the synaptic glutamate transient was estimated by the degree of inhibition of AMPA receptor EPSCs with the rapidly equilibrating antagonist γ-d-glutamylglycine. The glutamate transient sensed by AMPA receptors depended onPrbut not spillover, indicating that multiple vesicles are essentially simultaneously released from the same presynaptic active zone. Consistent with an enhanced glutamate transient, increasingPrprolonged NMDA receptor EPSCs when glutamate transporters were inhibited. We suggest that MVR occurs at SC–CA1 synapses whenPris elevated by facilitation and that MVR may be a phenomenon common to many synapses throughout the CNS.
Images of Bach in the Perspective of Basic Research and Interpretative Scholarship
Authors: WOLFF CHRISTOPH
Published: January 2006

Beginning with remarks on the complementary functions of basic research and interpretive scholarship, the first part of the essay focuses on varying concepts of Bach images, discusses authentic and unauthentic Bach portraits as well as images of the composer's personality, and criticizes the often insufficient regard for basic research. The second part of the article deals with the development of Bach's self-image on the basis of documentary evidence and its interpretation. It suggests that the composer himself contributed significantly during his lifetime to the shape of the emerging “genius” image that emerges during the second half of the 18th century and that constitutes the foundation of the icon of “the man from whom all musical wisdom proceeded” (Haydn).
Symptomatic Myocardial Bridging in a Child Without Hypertrophic Cardiomyopathy
Authors: Daana Muhannad , Wexler Isaiah , Milgalter Eli , Rein Azaria J.J.T. , Perles Zeev
Published: January 2006

Myocardial bridging (MB) is a rare coronary anomaly in children that is typically associated with hypertrophic cardiomyopathy or left ventricular hypertrophy. Several reports, mainly in adults, have suggested an association between MB and sudden death or ischemia without other cardiac abnormalities. In this report, we describe an 11-year-old girl with syncope and manifestations of cardiac ischemia associated with MB of the middle segment of the left anterior descending artery. The coronary anomaly was not associated with left ventricular hypertrophy. Surgical unroofing of the affected coronary artery segment resulted in complete recovery. MB should be included in the differential diagnosis of children presenting with syncope and signs of ischemia even in the absence of ventricular hypertrophy.
Association of H2-Blocker Therapy and Higher Incidence of Necrotizing Enterocolitis in Very Low Birth Weight Infants
Authors: Guillet Ronnie , Stoll Barbara J. , Cotten C. Michael , Gantz Marie , McDonald Scott , Poole W. Kenneth , Phelps Dale L. ,   for members of the National Institute of Child Health and Human Development Neonatal Research Network
Published: January 2006

OBJECTIVE. We sought to determine if an association exists between the use of histamine-2 receptor (H2) blockers and the incidence of necrotizing enterocolitis (NEC) in infants of 401 to 1500 g in birth weight.

STUDY DESIGN. Data from the National Institute of Child Health and Human Development Neonatal Research Network very low birth weight (401–1500 g) registry from September 1998 to December 2001 were analyzed. The relation between the diagnosis of NEC (Bell stage II or greater) and antecedent H2-blocker treatment was determined by using case-control methodology. Conditional logistic regression was implemented, controlling for gender, site of birth (outborn versus inborn), Apgar score of <7 at 5 minutes, and postnatal steroids.

RESULTS. Of 11072 infants who survived for at least 12 hours, 787 (7.1%) developed NEC (11.5% of infants 401–750 g, 9.1% of infants 751–1000 g, 6.0% of infants 1001–1250 g, and 3.9% of infants 1251–1500 g). Antecedent H2-blocker use was associated with an increased incidence of NEC (P < .0001).

CONCLUSIONS. H2-blocker therapy was associated with higher rates of NEC, which is in agreement with a previous randomized trial of acidification of infant feeds that resulted in a decreased incidence of NEC. In combination, these data support the hypothesis that gastric pH level may be a factor in the pathogenesis of NEC.
Domain switch toughening in polycrystalline ferroelectrics
Authors: Wang Jianxin , Landis Chad M.
Published: January 2006

Mode I steady crack growth was analyzed to determine the toughening due to domain switching in ferroelectric ceramics. A multi-axial, electromechanically coupled, incremental constitutive theory is applied to model the material behavior of the ferroelectric ceramic. The constitutive law is then implemented within the finite element method to study steady crack growth. The effects of mechanical and electrical poling on the fracture toughness are investigated. Results for the predicted fracture toughness, remanent strain distributions, and domain switching zone shapes and sizes are presented. Finally, the model predictions are discussed in comparison discrete switching models and to experimental observations.
Electrical transport properties of size-tuned ZnO nanorods
Authors: Yun Young Su , Park Jae Young , Oh Hwangyou , Kim Ju-Jin , Kim Sang Sub
Published: January 2006

Size-tuned ZnO nanorod arrays (NRAs), aligned well vertically and laterally, were synthesized by catalyst-free, metalorganic chemical vapor deposition on GaN-buffered Al2O3 (0001) substrates by adjusting the O/Zn precursor ratio in the reactor. Their electrical transport properties were investigated using field effect transistors based on individual ZnO nanorods. We find that the carrier concentrations and mobilities in the nanorods are not very sensitive to the change of the precursor ratio. This suggests that altering the precursor ratio is a way of fabricating size-tuned ZnO NRAs with quite consistent electrical properties.
Relieving the current crowding effect in flip-chip solder joints during current stressing
Authors: Liang S.W. , Shao T.L. , Chen Chih , Yeh Everett C.C. , Tu K.N.
Published: January 2006

Three-dimensional simulations for relieving the current crowding effect in solder joints under current stressing were carried out using the finite element method. Three possible approaches were examined in this study, including varying the size of the passivation opening, increasing the thickness of Cu underbump metallization (UBM), and adopting or inserting a thin highly resistive UBM layer. It was found that the current crowding effect in the solder bump could be successfully relieved with the thick Cu UBM or with the highly resistive UBM. Compared to the solder joint with Al/Ni(V)/Cu UBM, for instance, the maximum current density in a solder bump decreased dramatically by a factor of fifteen, say from 1.11 × 105 A/cm2 to 7.54 × 103 A/cm2 when a 20-μm-thick Cu UBM was used. It could be lowered by a factor of seven, say to 1.55 × 104 A/cm2, when a 0.7-μm UBM of 14770 μΩ cm was adopted. It is worth noting that although a resistive UBM layer was used, the penalty on overall resistance increase was negligible because the total resistance was dominated by the Al trace instead of the solder bump. Thermal simulation showed that the average temperature increase due to Joule heating effect was only 2.8 °C when the solder joints with UBM of 14770 μΩ cm were applied by 0.2 A.
Preferable orientation of turbostratic BN basal planes from an x-ray absorption study
Authors: Zhou X.T. , Sham T.K. , Chan C.Y. , Zhang W.J. , Bello I. , Lee S.T. , Heigl F. , Jürgenen A. , Hofsäss H.
Published: January 2006

Two cubic boron nitride (c-BN) thin films (thickness, 80 nm), which were grown on silicon by mass-selected ion beam deposition and thin diamond film-coated silicon by magnetron sputtering technique respectively, were investigated by x-ray absorption near-edge spectroscopy (XANES) at the B K-edge. The angular dependences of the XANES recorded in fluorescence yield (FY) were used to show that the preferable orientation of the sp2-bonded turbostratic BN (t-BN) basal planes at the interfacial layers between the top c-BN film and Si substrate is normal or nearly normal to the substrate, which is consistent with previous transmission electron microscope analysis. The angular dependence was also used to show that the film deposited on diamond-coated Si has a higher relative amount of ordered t-BN at its film-substrate interface than the film on Si substrate. This work that shows a technique to determine the thin film structure, especially the interfacial structure between the thin films and their substrates x-ray absorption fine structure is a powerful mode.
Characterization of rate-dependent shear behavior of Zr-based bulk metallic glass using shear-punch testing
Authors: Liu L.F. , Dai L.H. , Bai Y.L. , Wei B.C. , Eckert J.
Published: January 2006

In this study, the rate-dependent mechanical behavior of a Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk metallic glass was studied using quasi-static and dynamic shear-punch testing at room temperature. The results demonstrate that the shear strength of this alloy is insensitive to the applied strain rate. However, the formation of shear bands and the serrated flow exhibits a significant strain rate effect. The shear banding-induced fracture patterns and the fracture-melting phenomenon were analyzed based on the free volume theory and the energy transfer model.
Modified embedded-atom method interatomic potential for the Fe–Pt alloy system
Authors: Kim Jaesong , Koo Yangmo , Lee Byeong-Joo
Published: January 2006

A semi-empirical interatomic potential formalism, the modified embedded atom method (MEAM), has been applied to obtain an interatomic potential for the Fe–Pt alloy system, based on the previously developed potentials for pure Fe and Pt. The potential can describe basic physical properties of the alloys (lattice parameter, bulk modulus, stability of individual phases, and order/disorder transformations), in good agreement with experimental information. The procedure for the determination of potential parameter values and comparisons between the present calculation and experimental data or high level calculation are presented. The applicability of the potential to atomistic studies to investigate structural evolution of Fe50Pt50 alloy thin films during post-annealing is also discussed.
Silicon-germanium films deposited by low-frequency plasma-enhanced chemical vapor deposition: Effect of H2 and Ar dilution
Authors: Kosarev A. , Torres A. , Hernandez Y. , Ambrosio R. , Zuniga C. , Felter T.E. , Asomoza R. , Kudriavtsev Y. , Silva-Gonzalez R. , Gomez-Barojas E. , Ilinski A. , Abramov A.S.
Published: January 2006

We have studied structure and electrical properties of Si1−YGeY:H films deposited by low-frequency plasma-enhanced chemical vapor deposition over the entire composition range from Y = 0 to Y = 1. The deposition rate of the films and their structural and electrical properties were measured for various ratios of the germane/silane feed gases and with and without dilution by Ar and by H2. Structure and composition was studied by Auger electron spectroscopy (AES), secondary ion mass spectroscopy (SIMS), and Fourier transform infrared (FTIR) spectroscopy. Surface morphology was characterized by atomic force microscopy (AFM). We found that the deposition rate increased with Y, maximizing at Y = 1 without dilution. The relative rate of Ge and Si incorporation is affected by dilution. Hydrogen preferentially bonds to silicon. Hydrogen content decreases for increasing Y. In addition, optical measurements showed that as Y goes for 0 to 1, the Fermi level moves from mid gap to the conduction band edge; i.e., the films become more n-type. No correlation was found between the pre-exponential and the activation energy of conductivity. The behavior of the conductivity γ-factor suggests a local minimum in the density of states at E ≈ 0.33 eV for the films grown with or without H-dilution and E ≈ 0.25 eV for the films with Ar dilution.
Synthesis of silver-gold alloy nanoparticles by a phase-transfer system
Authors: Chimentão R.J. , Cota I. , Dafinov A. , Medina F. , Sueiras J.E. , de la Fuente J.L. Gómez , Fierro J.L.G. , Cesteros Y. , Salagre P.
Published: January 2006

We have studied the preparation of silver-gold alloy nanoparticles based on the phase transfer of metal precursors from aqueous phase to organic solution by a fatty amine at room temperature. Silver-gold nanoparticles were synthesized with different molar ratios (2:1, 1:1, 1:2). Ultraviolet-visible absorption spectra suggested the formation of alloy phases. The elemental Ag:Au ratios in the bimetallic nanoparticles determined by energy dispersive x-ray analysis (EDX) were consistent with the Ag:Au molar ratios used in the feeding solution. Transmission electron microscopy (TEM) revealed the formation of a uniform size distribution of Ag:Au nanoparticles (around 5 nm). X-ray photoelectron spectroscopy (XPS) showed that the composition in the outer part of the Ag:Au nanoparticles was similar to that obtained by EDX analysis, which indicates the formation of homogeneous silver-gold nanoparticles. Silver-gold alloy nanoparticles on a gram scale can be obtained with this method.
Growth stresses and viscosity of thermal oxides on silicon and polysilicon
Authors: Kahn H. , Jing N. , Huh M. , Heuer A.H.
Published: January 2006

Stresses in thermally grown SiO2films on silicon have traditionally been determined by substrate curvature measurements. This technique is useful for studying stresses in thin films, but it cannot be used to investigate stresses generated in the substrate during film growth. In the present work, we used microelectromechanical systems-based microstrain gauge devices fabricated from single-crystal and polycrystalline silicon (henceforth silicon and polysilicon, respectively) to measure oxidation-induced stresses in both dry and wet oxidizing ambients. Our microstrain gauges had thicknesses on the micrometer scale, and were themselves used as the substrates to be oxidized. Stresses could be detected in both the SiO2scales and the silicon and polysilicon substrates. In the SiO2scales, the stresses were compressive and exhibited viscoelastic relaxation. The as-grown compressive stresses were greater for wet oxidation than they were for dry oxidation, and greater in scales grown on polysilicon than they were in scales grown on silicon. The viscosity of thermally grown SiO2was the same whether scales formed by wet or dry oxidation, and the same for oxide scales on silicon and polysilicon. Significant compressive stresses were also generated in polysilicon during oxidation, but not in silicon.
Evaluation of the effectiveness of representative methods for determining Young's modulus and hardness from instrumented indentation data
Authors: Ma Dejun , Zhang Taihua , Ong Chung Wo
Published: January 2006

The effectiveness of Oliver & Pharr's (O&P's) method, Cheng & Cheng's (C&C’s) method, and a new method developed by our group for estimating Young's modulus and hardness based on instrumented indentation was evaluated for the case of yield stress to reduced Young's modulus ratio (σy/Er) ≥ 4.55 × 10−4 and hardening coefficient (n) ≤ 0.45. Dimensional theorem and finite element simulations were applied to produce reference results for this purpose. Both O&P's and C&C's methods overestimated the Young's modulus under some conditions, whereas the error can be controlled within ±16% if the formulation was modified with appropriate correction functions. Similar modification was not introduced to our method for determining Young's modulus, while the maximum error of results was around ±13%. The errors of hardness values obtained from all the three methods could be even larger and were irreducible with any correction scheme. It is therefore suggested that when hardness values of different materials are concerned, relative comparison of the data obtained from a single standard measurement technique would be more practically useful. It is noted that the ranges of error derived from the analysis could be different if different ranges of material parameters σy/Er and n are considered.
High glass-forming ability and good mechanical properties of new bulk glassy alloys in Cu–Zr–Ag ternary system
Authors: Zhang W. , Inoue A.
Published: January 2006

The addition of Ag to Cu–Zr alloys is very effective for the increase in the stability of supercooled liquid as well as the glass-forming ability (GFA). The large supercooled liquid region (ΔTx) exceeding 60 K in Cu–Zr–Ag ternary system was obtained in a wide range of 25–55 at.% Cu, 40–65 at.% Zr, and 5–25 at.% Ag. The best GFA was obtained around Cu45Zr45Ag10, and glassy alloy rods with diameters up to 6.0 mm were formed by copper mold casting. The bulk glassy alloys exhibit good mechanical properties, i.e., compressive fracture strength of 1780–1940 MPa, Young's modulus of 106–112 GPa, compressive plastic elongation of 0.2–2.9%, and Vickers hardness of 534–599. The finding of the new Cu–Zr–Ag ternary glassy alloy system with high GFA and good mechanical properties is important for development and scientific studies of bulk glassy alloys.
Nitrate-based metalorganic deposition of CeO2 on yttria-stabilized zirconia
Authors: Wesolowski D.E. , Cima M.J.
Published: January 2006

An aqueous nitrate metalorganic deposition (MOD) process was used to form a 30-nm-thick c-axis-textured ceria (CeO2) layer on a yttria-stabilized zirconia (YSZ) single-crystal substrate. X-ray diffraction showed the CeO2 layer was an (001) oriented film with a ω-scan full width at half-maximum of 1.47°. The average roughness of the ceria films, measured by atomic force microscopy, was about 5 nm. Critical current densities of up to 3.6 × 106 A/cm2 were measured on a 0.35-μm Ba2YCu3O7−x (YBCO) layer deposited over this cap layer using a trifluoroacetate (TFA)-based MOD ex situ process. The physical vapor deposition-derived ceria cap layer used in the most common coated conductor buffer layer stacks may be replaced by such a MOD processed film.
Microstructural evolution in laser-ablation-deposited Fe–25 at.% Ge thin film
Authors: Biswas Krishanu , Das Puspendu Kumar , Chattopadhyay Kamanio
Published: January 2006

Films with Fe–25 at.% Ge composition are deposited by the process of laser ablation on single crystal NaCl and Cu substrates at room temperature. Both the vapor and liquid droplets generated in this process are quenched on the substrate. The microstructures of the embedded droplets show size as well as composition dependence. The hierarchy of phase evolution from amorphous to body-centered cubic (bcc) to DO3 has been observed as a function of size. Some of the medium-sized droplets also show direct formation of ordered DO19 phase from the starting liquid. The evolution of disordered bcc structure in some of the droplets indicates disorder trapping during liquid to solid transformation. The microstructural evolution is analyzed on the basis of heat transfer mechanisms and continuous growth model in the solidifying droplets.
Bioactive comparison of a borate, phosphate and silicate glass
Authors: Liang Wen , Rüssel Christian , Day Delbert E. , Völksch Günter
Published: January 2006

A borate glass, phosphate glass, and silicate glass were converted to hydroxyapatite (HA) by soaking the substrates in a solution of K2HPO4with a pH value of 9.0 at 37 °C. The weight loss of the substrates was studied as a function of time. Unlike the silicate glasses, the reaction processes of the borate glasses and phosphate glasses were bulk dissolution. X-ray diffraction and scanning electron microscopy revealed an initially amorphous product that subsequently crystallized to HA. The data suggest good bioactive characteristics for the borate and phosphate glass and the potential use of them as a favorable template for bone-tissue formation.
CeO2 insulating films for application to high-temperature superconducting digital devices
Authors: Kamitani Ai , Wakana H. , Ogawa A. , Adachi S. , Higuchi K. , Yamamoto H. , Tanabe K.
Published: January 2006

CeO2 thin films as insulating layers for high-temperature superconducting digital devices were studied. The dependence on substrate temperature and oxygen pressure of the surface morphology and crystallinity of CeO2 thin films prepared by pulsed laser deposition were investigated. CeO2 thin films with a flat and closely grained surface were obtained at a relatively low oxygen pressure of 3.6 Pa, whereas higher oxygen pressure led to CeO2 thin films with a rough surface and columnar grains. The recovery of oxygen content in superconducting layers was examined for multilayer structures with CeO2 thin films. Enough oxygen was supplied to the upper and lower superconducting layers when the multilayer was cooled slowly in 3 × 10−4 Pa oxygen pressure after deposition. Resistively shunted junction type I-V characteristics were confirmed for interface-engineered ramp-edge junctions in a multilayer structure including four superconducting layers with CeO2 thin films.
Formation of discontinuous Al2O3layers during high-temperature oxidation of RuAl alloys
Authors: Bellina P.J. , Catanoiu A. , Morales F.M. , Rühle M.
Published: January 2006

Bond coats play a crucial role in the performance of thermal barrier coating systems. Ru alloys have been identified as promising candidates; therefore, systematic studies were performed on the oxidation behavior of bulk RuAl (50–50 at.%). Isothermal oxidation and thermogravimetric analyses were performed at 1100 °C for different times ranging from 0.1 h to 500 h. Microstructural characterization was performed by scanning and transmission electron microscopy. The results showed the formation of an α–Al2O3layer on top of a δ–Ru layer. Interface instability between these layers and evaporation of gaseous Ru-oxides lead to the formation of large elongated cavities and alternating α–Al2O3/δ–Ru layers.
Electrochemical deposition and characterization of Fe3O4 films produced by the reduction of Fe(III)-triethanolamine
Authors: Kothari Hiten M. , Kulp Elizabeth A. , Limmer Steven J. , Poizot Philippe , Bohannan Eric W. , Switzer Jay A.
Published: January 2006

In this paper, we demonstrate that films of magnetite, Fe3O4, can be deposited by the electrochemical reduction of a Fe(III)-triethanolamine complex in aqueous alkaline solution. The films were deposited with a columnar microstructure and a [100] preferred orientation on stainless steel substrates. In-plane electrical transport and magnetoresistance measurements were performed on the films after they were stripped off onto glass substrates. The resistance of the films was dependent on the oxygen partial pressure. We attribute the increase in resistance in O2 and the decrease in resistance in Ar to the oxidation and reduction of grain boundaries. The decrease in resistance in an Ar atmosphere exhibited first-order kinetics, with an activation energy of 0.2 eV. The temperature dependence of the resistance showed a linear dependence of log(R) versus T−1/2, consistent with tunneling across resistive grain boundaries. A room-temperature magnetoresistance of −6.5% was observed at a magnetic field of 9 T.
Structural characterization of electrodeposited nanophase Ni–Cu alloys
Authors: Ghosh S.K. , Grover A.K. , Dey G.K. , Kulkarni U.D. , Dusane R.O. , Suri A.K. , Banerjee S.
Published: January 2006

An investigation of Ni–Cu alloys electrodeposited from aqueous bath, using bothdirect current (dc) and pulsed current (pc) deposition techniques, has revealed many interesting features: A modulated structure with typical layer thickness of 90 and75 nm of copper-rich and nickel-rich layers, respectively, is formed in dc plating. A surprising observation was that the modulation direction was parallel to the substrate, unlike in the case of artificial multilayers wherein it is along the growth direction. No such compositional modulations were observed in pc-plating in the present work. Spinodal phase separation, accompanied by L10 ordering, was found to have occurred in the as deposited samples in both the cases. The size of the deposited crystals in both the cases has been found to be in the range of 2.5–30 nm. Detailed high-resolution transmission electron microscopy has shown that the atomic arrangements are nearly perfect right upto the boundaries of the nanosized grains.
Instrumented indentation study of plastic deformation in bulk metallic glasses
Authors: Li W.H. , Zhang T.H. , Xing D.M. , Wei B.C. , Wang Y.R. , Dong Y.D.
Published: January 2006

Mechanical properties and micro-plastic deformation behavior of five bulk metallic glasses (BMGs) were studied by instrumented indentation. These materials included La60Al10Ni10Cu20, Mg65Cu25Gd10, Zr52.5Al10Ni10Cu15Be12.5, Cu60Zr20Hf10Ti10, and Ni60Nb37Sn3alloys. Remarkable difference in deformation behavior was found in the load–displacement curves of nanoindentation and pileup morphologies around the indents. Serrated plastic deformation depended on the loading rate was found in Mg-, Zr-, and Cu-based BMGs. The subsurface plastic deformation zone of typical alloys was investigated through bonded interface technique using depth-sensing microindentation. Large and widely spaced shear bands were observed in Mg-based BMG. The effect of loading rate on the indentation deformation behaviors in different BMGs was elucidated by the change of shear band pattern.