bluuebunny/crossref_metadata_2025 huggingface dataset:
Turning Visitors into Customers: A Usability-Centric Perspective on Purchase Behavior in Electronic Channels
Authors: Venkatesh Viswanath , Agarwal Ritu
Published: March 2006

We develop a theoretical model for predicting purchase behavior in electronic channels. The model suggests that website use (i.e., technology use), a key indicator of the degree to which a site is “sticky,” is a significant antecedent of purchase behavior. Furthermore, we relate the usability of a website to use behavior and purchase behavior. Specifically, individual characteristics and product type are argued to differentially influence the weights that customers place on five different categories of usability. The weighted ratings of the five categories together determine use behavior and purchase behavior, after controlling for purchase need, experience with similar sites, and previous purchase on the specific sites. The model was tested in a longitudinal field study among 757 customers who provided usability assessments for multiple websites from four different industries—i.e., airlines, online bookstores, automobile manufacturers, and car rental agencies. Six months later, 370 of these individuals provided responses to help understand the transition from visitor to customer, i.e., whether they actually transacted with a specific website. Results provided strong support for the model and yield important theoretical and practical implications.
Behavioral Estimation of Mathematical Programming Objective Function Coefficients
Authors: Troutt Marvin D. , Pang Wan-Kai , Hou Shui-Hung
Published: March 2006

We propose a parameter estimation method based on what we call the minimum decisional regret principle. We focus on mathematical programming models with objective functions that depend linearly on costs or other parameters. The approach is illustrated for cost estimation in production planning using linear programming models. The method uses past planning data to estimate costs that are otherwise difficult to estimate. We define a monetary measure of distance between observed plans and optimal ones, called decisional regret. The proposed estimation algorithm finds parameter values for which the associated optimal plans are as near as possible to the observed ones on average. Such techniques may be called behavioral estimation because they are based on the observed planning or decision-making behavior of managers or firms. Two numerical illustrations are given. A supporting hyperplane algorithm is used to solve the estimation model. A method is proposed for obtaining range estimates of the parameters when multiple alternative estimates exist. We also propose a new validation approach for this estimation principle, which we call the target-mode agreement criterion.
The Optimizer’s Curse: Skepticism and Postdecision Surprise in Decision Analysis
Authors: Smith James E. , Winkler Robert L.
Published: March 2006

Decision analysis produces measures of value such as expected net present values or expected utilities and ranks alternatives by these value estimates. Other optimization-based processes operate in a similar manner. With uncertainty and limited resources, an analysis is never perfect, so these value estimates are subject to error. We show that if we take these value estimates at face value and select accordingly, we should expect the value of the chosen alternative to be less than its estimate, even if the value estimates are unbiased. Thus, when comparing actual outcomes to value estimates, we should expect to be disappointed on average, not because of any inherent bias in the estimates themselves, but because of the optimization-based selection process. We call this phenomenon the optimizer’s curse and argue that it is not well understood or appreciated in the decision analysis and management science communities. This curse may be a factor in creating skepticism in decision makers who review the results of an analysis. In this paper, we study the optimizer’s curse and show that the resulting expected disappointment may be substantial. We then propose the use of Bayesian methods to adjust value estimates. These Bayesian methods can be viewed as disciplined skepticism and provide a method for avoiding this postdecision disappointment.
Conjoint Optimization: An Exact Branch-and-Bound Algorithm for the Share-of-Choice Problem
Authors: Camm Jeffrey D. , Cochran James J. , Curry David J. , Kannan Sriram
Published: March 2006

Conjoint analysis is a statistical technique used to elicit partworth utilities for product attributes from consumers to aid in the evaluation of market potential for new products. The objective of the share-of-choice problem (a common approach to new product design) is to find the design that maximizes the number of respondents for whom the new product’s utility exceeds a specific hurdle (reservation utility). We present an exact branch-and-bound algorithm to solve the share-of-choice problem. Our empirical results, based on several large commercial data sets and simulated data from a controlled experiment, suggest that the approach is useful for finding provably optimal solutions to realistically sized problems, including cases where partworths contain estimation error.
Organizational Learning Curves for Customer Dissatisfaction: Heterogeneity Across Airlines
Authors: Lapré Michael A. , Tsikriktsis Nikos
Published: March 2006

In the extensive literature on learning curves, scholars have ignored outcome measures of organizational performance evaluated by customers. We explore whether customer dissatisfaction follows a learning-curve pattern. Do organizations learn to reduce customer dissatisfaction? Customer dissatisfaction occurs when customers’ ex ante expectations about a product or service exceed ex post perceptions about the product or service. Because customers can increase expectations over time, customer dissatisfaction may not decline even when the product or service improves. Consequently, it is an open question whether customer dissatisfaction follows a learning-curve pattern. Drawing from the literatures on learning curves and organizational learning, we hypothesize that customer dissatisfaction follows a U-shaped function of operating experience (Hypothesis 1), that focused airlines learn faster to reduce customer dissatisfaction than full-service airlines (Hypothesis 2), and that organizational learning curves for customer dissatisfaction are heterogeneous across airlines (Hypothesis 3). We test these hypotheses with quarterly data covering 1987 to 1998 on consumer complaints against the 10 largest U.S. airlines. We find strong support for Hypothesis 1 and Hypothesis 3. Hypothesis 2 is not supported in the sense that the average focused airline did not learn faster than the average full-service airline. However, we do find that the best focused airline learns faster than the best full-service airline. We explore this result by extending a knowledge-based view of managing productivity learning curves in factories to complaint learning curves in airlines.
Environmental Volatility, Development Decisions, and Software Volatility: A Longitudinal Analysis
Authors: Barry Evelyn J. , Kemerer Chris F. , Slaughter Sandra A.
Published: March 2006

Although product development research often focuses on activities prior to product launch, for long-lived, adaptable products like software, development can continue over the entire product life cycle. For managers of these products the challenges are to predict when and how much the products will change and to understand how their development decisions influence the timing and magnitude of future change activities. We develop a two-stage model that relates environmental volatility to product development decisions and product development decisions to software volatility. The model is evaluated using a data archive that captures changes over 20 years to a firm’s environment, its managers’ development choices, and its software products. In Stage 1 we find that higher environmental volatility leads to greater use of process technology and standard component designs but less team member rotation. Earlier development decisions strongly influence current development choices, especially for product design and process technology. In Stage 2 we find that increased use of standard component designs dampens future software volatility by decreasing the average rate and magnitude of change. Adding new team members increases product enhancements at a faster pace than more intense use of process technology but adds repairs at almost the same rate as enhancements.
The Effectiveness of Simple Decision Heuristics: Forecasting Commercial Success for Early-Stage Ventures
Authors: Åstebro Thomas , Elhedhli Samir
Published: March 2006

We investigate the decision heuristics used by experts to forecast that early-stage ventures are subsequently commercialized. Experts evaluate 37 project characteristics and subjectively combine data on all cues by examining both critical flaws and positive factors to arrive at a forecast. A conjunctive model is used to describe their process, which sums “good” and “bad” cue counts separately. This model achieves a 91.8% forecasting accuracy of the experts’ correct forecasts. The model correctly predicts 86.0% of outcomes in out-of-sample, out-of-time tests. Results indicate that reasonably simple decision heuristics can perform well in a natural and very difficult decision-making context.
Alternative Splicing of the Voltage-Gated Ca2+Channel β4Subunit Creates a Uniquely Folded N-Terminal Protein Binding Domain with Cell-Specific Expression in the Cerebellar Cortex
Authors: Vendel Andrew C. , Terry Mark D. , Striegel Amelia R. , Iverson Nicole M. , Leuranguer Valerie , Rithner Christopher D. , Lyons Barbara A. , Pickard Gary E. , Tobet Stuart A. , Horne William A.
Published: March 2006

Ca2+channel β subunits regulate cell-surface expression and gating of voltage-dependent Ca2+channel α1 subunits. Based on primary sequence comparisons, β subunits are predicted to be modular structures composed of five domains (A–E) that are related to the large family of membrane-associated guanylate kinase proteins. The crystal structure of the β subunit core B–D domains has been reported recently; however, little is known about the structures of the A and E domains. The N-terminal A domain differs among the four subtypes of Ca2+channel β subunits (β1–β4) primarily as the result of two duplications of an ancestral gene containing multiple alternatively spliced exons. At least nine A domain sequences can be generated by alternative splicing. In this report, we focus on one A domain sequence, the highly conserved β4aA domain. We solved its three-dimensional structure and show that it is expressed in punctate structures throughout the molecular layer of the cerebellar cortex. We also demonstrate that it does not participate directly in Cav2.1 Ca2+channel gating but serves as a binding site in protein–protein interactions with synaptotagmin I and the LC2 domain of microtubule-associated protein 1A. With respect to β4subunits, the interactions are specific for the β4asplice variant, because they do not occur with the β4bA domain. These results have strong bearing on our current understanding of the structure of alternatively spliced Ca2+channel β subunits and the cell-specific roles they play in the CNS.
An Epilepsy Mutation in the Sodium ChannelSCN1AThat Decreases Channel Excitability
Authors: Barela Arthur J. , Waddy Salina P. , Lickfett Jay G. , Hunter Jessica , Anido Aimee , Helmers Sandra L. , Goldin Alan L. , Escayg Andrew
Published: March 2006

Mutations in three voltage-gated sodium channel genes,SCN1A,SCN2A, andSCN1B, and two GABAAreceptor subunit genes,GABRG2andGABRD, have been identified in families with generalized epilepsy with febrile seizures plus (GEFS+). A novel mutation, R859C, in the Nav1.1 sodium channel was identified in a four-generation, 33-member Caucasian family with a clinical presentation consistent with GEFS+. The mutation neutralizes a positively charged arginine in the domain 2 S4 voltage sensor of the Nav1.1 channel α subunit. This residue is conserved in mammalian sodium channels as well as in sodium channels from lower organisms. When the mutation was placed in the rat Nav1.1 channel and expressed inXenopusoocytes, the mutant channel displayed a positive shift in the voltage dependence of sodium channel activation, slower recovery from slow inactivation, and lower levels of current compared with the wild-type channel. Computational analysis suggests that neurons expressing the mutant channel have higher thresholds for firing a single action potential and for firing multiple action potentials, along with decreased repetitive firing. Therefore, this mutation should lead to decreased neuronal excitability, in contrast to most previous GEFS+ sodium channel mutations, which have changes predicted to increase neuronal firing.
Dissociating Arbitrary Stimulus-Response Mapping from Movement Planning during Preparatory Period: Evidence from Event-Related Functional Magnetic Resonance Imaging
Authors: Cavina-Pratesi Cristiana , Valyear Kenneth F. , Culham Jody C. , Köhler Stefan , Obhi Sukhvinder S. , Marzi Carlo Alberto , Goodale Melvyn A.
Published: March 2006

In the present study, we aimed to dissociate the neural correlates of two subprocesses involved in the preparatory period in the context of arbitrary, prelearned stimulus-response (S-R) associations, namely, S-R mapping and movement planning (MP). We teased apart these two subprocesses by comparing three tasks in which the complexity of both S-R mapping and MP were independently manipulated: simple reaction time (SRT) task, go/no-go reaction time (GNGRT) task, and choice reaction time (CRT) task. We found that a more complex S-R mapping, which is the common element differentiating CRT and GNGRT from SRT, was associated with higher brain activation in the left superior parietal lobe (SPL). Conversely, a greater number of planned finger movements, which is the common difference between CRT and both SRT and GNGRT, was associated with higher brain activation in a number of frontal areas, including the left supplementary motor area (SMA), left dorsal premotor cortex (dPM), and left anterior cingulate cortex (ACC). The left-hemisphere dominance for S-R mapping could be related to the fact that arbitrary S-R mapping is often verbally mediated in humans. Overall, these results suggest a clear dissociation in the preparatory-set period between the more abstract role of left SPL in activating the appropriate S-R associations and the more concrete role played by the SMA, dPM, and ACC in preparing the required motor programs.
Role of Efficient Neurotransmitter Release in Barrel Map Development
Authors: Lu Hui-Chen , Butts Daniel A. , Kaeser Pascal S. , She Wei-Chi , Janz Roger , Crair Michael C.
Published: March 2006

Cortical maps are remarkably precise, with organized arrays of thalamocortical afferents (TCAs) that project into distinct neuronal modules. Here, we present evidence for the involvement of efficient neurotransmitter release in mouse cortical barrel map development usingbarrellessmice, a loss-of-function mutant of calcium/calmodulin-activated adenylyl cyclase I (AC1), and mice with a mutation in Rab3-interacting molecule 1α (RIM1α), an active zone protein that regulates neurotransmitter release. We demonstrate that release efficacy is substantially decreased inbarrellessTCAs. We identify RIMs as important phosphorylation targets for AC1 in the presynaptic terminal. We further show that RIM1α mutant mice have reduced TCA neurotransmitter release efficacy and barrel map deficits, although not as severe as those found inbarrellessmice. This supports the role of RIM proteins in mediating, in part, AC1 signaling in barrel map development. Finally, we present a model to show how inadequacies in presynaptic function can interfere with activity-dependent processes in neuronal circuit formation. These results demonstrate how efficient synaptic transmission mediated by AC1 function contributes to the development of cortical barrel maps.
A Common Ankyrin-G-Based Mechanism Retains KCNQ and NaVChannels at Electrically Active Domains of the Axon
Authors: Pan Zongming , Kao Tingching , Horvath Zsolt , Lemos Julia , Sul Jai-Yoon , Cranstoun Stephen D. , Bennett Vann , Scherer Steven S. , Cooper Edward C.
Published: March 2006

KCNQ (KV7) potassium channels underlie subthreshold M-currents that stabilize the neuronal resting potential and prevent repetitive firing of action potentials. Here, antibodies against four different KCNQ2 and KCNQ3 polypeptide epitopes show these subunits concentrated at the axonal initial segment (AIS) and node of Ranvier. AIS concentration of KCNQ2 and KCNQ3, like that of voltage-gated sodium (NaV) channels, is abolished in ankyrin-G knock-out mice. A short motif, common to KCNQ2 and KCNQ3, mediates bothin vivoankyrin-G interaction and retention of the subunits at the AIS. This KCNQ2/KCNQ3 motif is nearly identical to the sequence on NaVα subunits that serves these functions. All identified NaVand KCNQ genes of worms, insects, and molluscs lack the ankyrin-G binding motif. In contrast, vertebrate orthologs of NaVα subunits, KCNQ2, and KCNQ3 (including from bony fish, birds, and mammals) all possess the motif. Thus, concerted ankyrin-G interaction with KCNQ and NaVchannels appears to have arisen through convergent molecular evolution, after the division between invertebrate and vertebrate lineages, but before the appearance of the last common jawed vertebrate ancestor. This includes the historical period when myelin also evolved.
Properties and Opioid Inhibition of Mesolimbic Dopamine Neurons Vary according to Target Location
Authors: Ford Christopher P. , Mark Gregory P. , Williams John T.
Published: March 2006

The mesolimbic dopamine system, which mediates the rewarding properties of nearly all drugs of abuse, originates in the ventral tegmental area (VTA) and sends major projections to both the nucleus accumbens (NAc) and the basolateral amygdala (BLA). To address whether differences occur between neurons that project to these separate areas, retrograde microspheres were injected to either the BLA or the NAc of DBA/2J mice. Whole-cell recordings were made from labeled VTA dopamine neurons. We found that identified neurons that projected to the BLA and NAc originated within different quadrants of the VTA with neither group exhibiting large-amplitude h-currents. Neurons that projected to the NAc exhibited a greater outward current in response to the κ-opioid agonist (5α,7α,8α)-(+)-N-methyl-N-[7-(pyrrolidinyl)-1-oxaspiro [4,5]dec-8-yl]-benzeneacetamide (U69593; 200 nm), whereas neurons that projected to the BLA exhibited greater inhibition to the μ/δ opioid agonist [Met5] enkephalin (ME; 3 μm). In addition, we found that the presynaptic inhibition of GABAergic transmission at both GABAAand GABABreceptors was differentially regulated by U69593 between the two groups. When dopamine IPSCs were examined, U69593 caused a greater inhibition in NAc- than BLA-projecting neurons. ME had no effect on either. Finally, the regulation of extracellular dopamine by dopamine uptake transporters was equal across the VTA. These results suggest that opioids differentially inhibit mesolimbic neurons depending on their target projections. Identifying the properties of projecting mesolimbic VTA dopamine neurons is crucial to understanding the action of drugs of abuse.
Calcium Signaling Pathways Mediating Synaptic Potentiation Triggered by Amyotrophic Lateral Sclerosis IgG in Motor Nerve Terminals
Authors: Pagani Mario R. , Reisin Ricardo C. , Uchitel Osvaldo D.
Published: March 2006

Sporadic amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease that affects particularly motoneurons. Several pieces of evidence suggested the involvement of autoimmune mechanisms mediated by antibodies in ALS. However, the significance of those antibodies in the disease and the underlying mechanisms are unknown. Here we showed that IgG purified from a group of sporadic ALS patients, but not familial ALS patients, specifically interact with the presynaptic membrane of motoneurons through an antigen–antibody interaction and modulated synaptic transmission. Immunoreactivity against nerve terminals showed strong correlation with synaptic modulation ability. In addition, several controls have ruled out the possibility for this synaptic modulation to be mediated through proteases or nonspecific effects. Effective IgG potentiated both spontaneous and asynchronous transmitter release. Application of pharmacological inhibitors suggested that activation of this increased release required a nonconstitutive Ca2+influx through N-type (Cav2.2) channels and phospholipase C activity and that activation of IP3and ryanodine receptors were necessary to both activate and sustain the increased release. Consistent with the notion that ALS is heterogeneous disorder, our results reveal that, in ∼50% of ALS patients, motor nerve terminals constitutes a target for autoimmune response.
NMDA Receptors Mediate Neuron-to-Glia Signaling in Mouse Cortical Astrocytes
Authors: Lalo Ulyana , Pankratov Yuri , Kirchhoff Frank , North R. Alan , Verkhratsky Alexei
Published: March 2006

Chemical transmission between neurons and glial cells is an important element of integration in the CNS. Here, we describe currents activated by NMDA in cortical astrocytes, identified in transgenic mice that express enhanced green fluorescent protein under control of the human glial fibrillary acidic protein promoter. Astrocytes were studied by whole-cell voltage clamp either in slices or after gentle nonenzymatic mechanical dissociation. Acutely isolated astrocytes showed a three-component response to glutamate. The initial rapid component was blocked by 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo[f]quinoxaline-7-sulfonamide (NBQX), which is an antagonist of AMPA receptors (IC50, 2 μm), and the NMDA receptor antagonistd-AP-5 blocked the later sustained component (IC50, 0.6 μm). The third component of glutamate application response was sensitive tod,l-threo-β-benzyloxyaspartate, a glutamate transporter blocker. Fast application of NMDA evoked concentration-dependent inward currents (EC50, 0.3 μm); these showed use-dependent block by (+)-5-methyl-10,11-dihydro-5H-dibenzo [a,d] cyclohepten-5,10-imine maleate (MK-801). These NMDA-evoked currents were linearly dependent on membrane potential and were not affected by extracellular magnesium at concentrations up to 10 mm. Electrical stimulation of axons in layer IV–VI induced a complex inward current in astrocytes situated in the cortical layer II, part of which was sensitive to MK-801 at holding potential −80 mV and was not affected by the AMPA glutamate receptor antagonist NBQX. The fast miniature spontaneous currents were observed in cortical astrocytes in slices as well. These currents exhibited both AMPA and NMDA receptor-mediated components. We conclude that cortical astrocytes express functional NMDA receptors that are devoid of Mg2+block, and these receptors are involved in neuronal–glial signal transmission.
Physiological Modulation of Intestinal Motility by Enteric Dopaminergic Neurons and the D2Receptor: Analysis of Dopamine Receptor Expression, Location, Development, and Function in Wild-Type and Knock-Out Mice
Authors: Li Zhi Shan , Schmauss Claudia , Cuenca Abigail , Ratcliffe Elyanne , Gershon Michael D.
Published: March 2006

Dopaminergic neurons are present in both plexuses of the murine bowel and are upregulated after extrinsic denervation but play unknown roles in enteric nervous system (ENS) physiology. Transcripts encoding dopamine (DA) receptors D1–D5were analyzed by reverse transcription-PCR in stomach ≈ duodenum ≈ ileum ≈ proximal ≫ distal colon. Dissected muscle and myenteric plexus contained transcripts encoding D1–D3and D5, whereas mucosa contained D1and D3–D5. D1–D5expression began in fetal gut [embryonic day 10 (E10)], before the appearance of neurons (E12), and was sustained without developmental regulation through postnatal day 1.In situhybridization revealed that subsets of submucosal and myenteric neurons contained mRNA encoding D2or D3. Immunoblots confirmed that D1, D2, and D5receptor proteins were present from stomach through distal colon. Subsets of submucosal and myenteric neurons were also D1, D2, or D3immunoreactive. When double labeled byin situhybridization, these neurons contained mRNA encoding the respective receptors. Total gastrointestinal transit time (TGTT) and colonic transit time (CTT) were measured in mice lacking D2, D3, or D2plus D3. Both TGTT and CTT were decreased significantly (motility increased) in D2and D2plus D3, but not D3, knock-out animals. Mice lacking D2and D2plus D3but not D3were smaller than wild-type littermates, yet ate significantly more and had greater stool frequency, water content, and mass. Because motility is abnormal when D2is absent, the net inhibitory DA effect on motility is physiologically significant. The early expression of DA receptors is also consistent with the possibility that DA affects ENS development.
p35/p25 Is Not Essential for Tau and Cytoskeletal Pathology or Neuronal Loss in Niemann–Pick Type C Disease
Authors: Hallows Janice L. , Iosif Robert E. , Biasell Rebecca D. , Vincent Inez
Published: March 2006

Hyperactivation of the cyclin-dependent kinase 5 (cdk5), triggered by proteolytic conversion of its neuronal activator, p35, to a more potent byproduct, p25, has been implicated in Alzheimer's disease (AD), amyotrophic lateral sclerosis, and Niemann–Pick type C disease (NPC). This mechanism is thought to lead to the development of neuropathological hallmarks, i.e., hyperphosphorylated cytoskeletal proteins, neuronal inclusions, and neurodegeneration, that are common to all three diseases. This pathological ensemble is recapitulated in a single model, the npc-1 (npc−/−) mutant mouse. Previously, we showed that pharmacological cdk inhibitors dramatically reduced hyperphosphorylation, lesion formation, and locomotor defects innpc−/−mice, suggesting that cdk activity is required for NPC pathogenesis. Here, we used genetic ablation of thep35gene to examine the specific involvement of p35, p25, and hence cdk5 activation in NPC neuropathogenesis. We found that lack of p35/p25 does not slow the onset or progression or improve the neuropathology of NPC. Our results provide direct evidence that p35/p25-mediated cdk5 deregulation is not essential for NPC pathology and suggest that similar pathology in AD may also be cdk5 independent.
RE-1 Silencer of Transcription/Neural Restrictive Silencer Factor Modulates Ectodermal Patterning duringXenopusDevelopment
Authors: Olguín Patricio , Oteíza Pablo , Gamboa Eduardo , Gómez-Skármeta José Luis , Kukuljan Manuel
Published: March 2006

RE-1 silencer of transcription/neural restrictive silencer factor (REST/NRSF), a transcriptional repressor, binds to the RE-1 element present in many vertebrate genes.In vitrostudies indicate that REST/NRSF plays important roles in several stages of neural development. However, a full understanding of its physiological function requiresin vivoapproaches. We find that impairment of REST/NRSF function inXenopusembryos leads to the perturbation of neural tube, cranial ganglia, and eye development. The origin of these defects is the abnormal patterning of the ectoderm during gastrulation. Interference of REST/NRSF function during the late blastula stage leads to an expansion of the neural plate, concomitant with a decrease of the expression of epidermal keratin and neural crest markers. Furthermore, neurogenesis proceeds abnormally, with loss of the expression of proneural, neurogenic, and neuronal genes. The interference of REST/NRSF mimics several features associated with a decreased bone morphogenetic protein (BMP) function and counteracts some effects of BMP4 misexpression. Our results indicate that REST/NRSF function is requiredin vivofor the acquisition of specific ectodermal cell fates.
Novel Subcellular Distribution Pattern of A-Type K+Channels on Neuronal Surface
Authors: Kollo Mihaly , Holderith Noémi B. , Nusser Zoltan
Published: March 2006

Potassium channels comprise the most diverse family of ion channels. In nerve cells, their critical roles in synaptic integration and output generation have been demonstrated. Here, we provide evidence for a distribution that predicts a novel role of K+channels in the CNS. Our experiments revealed a highly selective clustering of the Kv4.3 A-type K+channel subunits at specialized junctions between climbing fibers and cerebellar GABAergic interneurons. High-resolution ultrastructural and immunohistochemical experiments demonstrated that these junctions are distinct from known chemical and electrical (gap junctions) synapses and also from puncta adherentia. Each cerebellar interneuron contains many such K+channel-rich specializations, which seem to be distributed throughout the somatodendritic surface. We also show that such K+channel-rich specializations are not only present in the cerebellum but are widespread in the rat CNS. For example, mitral cells of the main olfactory bulb establish Kv4.2 subunit-positive specializations with each other. At these specializations, both apposing membranes have a high density of K+channels, indicating bidirectional signaling. Similar specializations with pronounced coclustering of the Kv4.2 and 4.3 subunits were observed between nerve cells in the medial nucleus of the habenula. Based on our results and on the known properties of A-type K+channels, we propose that strategically clustered K+channels at unique membrane specializations could mediate a novel type of communication between nerve cells.
Local piezoelectric and ferroelectric responses in nanotube-patterned thin films of BaTiO3synthesized hydrothermally at 200 °C
Authors: Poyato Rosalía , Huey Bryan D. , Padture Nitin P.
Published: March 2006

Piezoresponse atomic-force microscopy (PFM) has been used to characterize the local piezoelectric properties of a novel, nanotube-patterned (“honeycomb”) thin film of BaTiO3on Ti substrate synthesized hydrothermally at 200 °C. PFM amplitude and phase images, prior to the application of any direct current (dc) field, show ring-shaped piezoelectric regions that correspond to the nanostructure of this film. These results show clearly that the as-synthesized nanotube-patterned BaTiO3thin film is piezoelectric, with a net spontaneous polarization perpendicular to the film–substrate interface. In addition, polarization switching and hysteresis were observed as a function of applied dc field, confirming that this novel fabrication procedure results in unique configurations of BaTiO3film that are also ferroelectric.
Precursor and processing effects on BaPbO3 formation kinetics
Authors: Tani Jun-ichi , Popov Guerman , Mort Paul R. , Riman Richard E.
Published: March 2006

The synthesis of BaPbO3 from a wide range of mixtures containing metalorganic precursors, nitrate precursors, lead oxides, barium oxide and peroxide was investigated, and the kinetics was analyzed using the Johnson–Mehl–Avrami (JMA) equation. It was found that Ba and Pb stearate soaps and Pb oxalate that were used as metalorganic precursors formed BaCO3 and PbO or Pb3O4 after firing at 440 °C. The formation rate of BaPbO3 from a metalorganic precursor system is not higher than that from the conventional BaCO3–PbO system and does not depend on mixing methods or the kinds of metalorganic precursors but instead on the synthesis atmosphere. In the case of the BaCO3–PbO system, the Avrami exponent (n) is ∼1, indicating that the reaction is controlled by the phase-boundary-contraction interface reaction. For the BaO2–PbO2 system, n has two values ∼1 and ∼0.3, depending on the reaction temperature and time, indicating that the reaction is either controlled by the phase-boundary-contraction interface reaction or diffusion-controlled reaction. In the Ba nitrate–Pb nitrate system, phase-pure BaPbO3 is obtained at 550 °C, which is 250 °C lower than in the case of the BaCO3–PbO system. The value of n for the nitrate system is ∼1.5, indicating that the reaction is controlled by a three-dimensional (3D) diffusion-controlled nucleation mechanism. In the BaO–PbO system, the formation of BaPbO3 started at 350 °C by an exothermic reaction and the content of BaPbO3 in the product was ∼40 wt%, which is independent of reaction temperature as well as time in the temperature range of 350–500 °C.
Nanocrystallization of gas atomized Cu47Ti33Zr11Ni8Si1 metallic glass
Authors: Venkataraman S. , Scudino S. , Eckert J. , Gemming T. , Mickel C. , Schultz L. , Sordelet D.J.
Published: March 2006

Cu47Ti33Zr11Ni8Si1 metallic glass powder was prepared by gas atomization. Decomposition in the amorphous alloy and primary crystallization has been studied by differential scanning calorimetry (DSC), x-ray diffraction (XRD), and transmission electron microscopy (TEM). The glassy powder exhibits a broad DSC exotherm prior to bulk crystallization. Controlled annealing experiments reveal that this exotherm corresponds to a combination of structural relaxation and nanocrystallization. A uniform featureless amorphous contrast is observed in the TEM prior to the detection of nanocrystals of 4–6 nm in size. High-resolution TEM studies indicate that this nanocrystalline phase has a close crystallographic relationship with the γ–CuTi phase having a tetragonal structure. The product of the main crystallization event is also nanocrystalline, hexagonal Cu51Zr14, having dimensions of 20 nm. However, there is no evidence for possible amorphous phase separation prior to the nanocrystallization events.
Microstructure and compressive properties of chill-cast Mg–Al–Ca alloys
Authors: Shi Ling-Ling , Ma Han , Liu Teng , Xu Jian , Ma En
Published: March 2006

Mg82Al8Ca10 was determined to be a pseudo-binary eutectic composition [liquid solidifying into α–Mg and (Mg,Al)2Ca in the Mg–Al–Ca ternary system with a eutectic melting temperature of 789 K]. A series of Mgx(Al0.44Ca0.56)100−x alloys, where 75 ≤ x ≤ 95, were cast into Φ4 mm rods using copper mold casting. The eutectic alloy exhibits the highest fracture strength, σf = 609 MPa. For 75 ≤ x ≥ 79, the alloys have hypereutectic microstructures with Mg2Ca as the primary phase, and σf is reduced together with diminishing plasticity. For hypoeutectic alloys with 86 ≤ x ≥ 95, the volume fraction of the primary α–Mg dendrites dispersed in the eutectic matrix increases with increasing x, resulting in a gradual decrease of the yield and fracture strengths but improved plastic strain to as large as 9%. The refined microstructures created in bulk samples via chill casting can lead to a good combination of strength and plasticity, with specific strength superior to commercial Mg alloys.
Facile route to tin oxide containing mesoporous silica composites with room-temperature photoluminescence
Authors: Liu Zhicheng , Chen Hangrong , Huang Weiming , Gu Jinlou , Bu Wenbo , Hua Zile , Shi Jianlin
Published: March 2006

In this paper, we report a facile route, the tin vapor treatment method, to prepare tin oxide containing mesoporous silica composites (TOMS), which display room-temperature photoluminescence (RT-PL). Among them, TOMS-1 and TOMS-2 were synthesized from mesoporous silica SBA-15 and KIT-6, respectively. They are composed of amorphous SiO2 and tin oxide species and they display strong emission near ultraviolet (UV) when excited by UV light. By increasing the preparation temperature, their Sn content can be increased and subsequently their photoluminescence (PL) intensities can be greatly enhanced. Besides, their PL properties are revealed to be closely related to 2-fold-coordinated tin oxygen-deficient centers.
Identification of viscoplastic material parameters from spherical indentation data: Part II. Experimental validation of the method
Authors: Klötzer D. , Ullner Ch. , Tyulyukovskiy E. , Huber N.
Published: March 2006

A neural network-based analysis method for the identification of a viscoplasticity model from spherical indentation data, developed in the first part of this work [J. Mater. Res.21, 664 (2006)], was applied for different metallic materials. Besides the comparison of typical parameters like Young’s modulus and yield stress with values from tensile experiments, the uncertainties in the identified material parameters representing modulus, hardening behavior, and viscosity were investigated in relation to different sources. Variations in the indentation position, tip radius, force application rate, and surface preparation were considered. The extensive experimental validation showed that the applied neural networks are very robust and show small variation coefficients, especially regarding the important parameters of Young’s modulus and yield stress. On the other hand, important requirements were quantified, which included a very good spherical indenter geometry and good surface preparation to obtain reliable results.
Lead titanate nano- and microtubes
Authors: Zhao Lili , Steinhart Martin , Yu Jian , Gösele Ulrich
Published: March 2006

Lead titanate (PbTiO3) nano- and microtubes were fabricated by wetting ordered porous alumina and macroporous silicon with precursor oligomers coupled with templated thermolysis. The diameters of the PbTiO3 tubes range from a few tens of nanometers up to one micron. The proper selection of the template allowed for a precise adjustment of their size over two orders of magnitude. Electron microscopy and x-ray diffraction revealed that the tube walls were polycrystalline. The generic approach presented here can be adapted for the fabrication of tubes and rods from a multitude of functional inorganic oxides.
Nanoindentation and contact-mode imaging at high temperatures
Authors: Schuh Christopher A. , Packard Corinne E. , Lund Alan C.
Published: March 2006

Technical issues surrounding the use of nanoindentation at elevated temperatures are discussed, including heat management, thermal equilibration, instrumental drift, and temperature-induced changes to the shape and properties of the indenter tip. After characterizing and managing these complexities, quantitative mechanical property measurements are performed on a specimen of standard fused silica at temperatures up to 405 °C. The extracted values of hardness and Young's modulus are validated against independent experimental data from conventional mechanical tests, and accuracy comparable to that obtained in standard room-temperature nanoindentation is demonstrated. In situ contact-mode images of the surface at temperature are also presented.
Piezoelectric nanoindentation
Authors: Rar Andrei , Pharr G.M. , Oliver W.C. , Karapetian E. , Kalinin Sergei V.
Published: March 2006

Piezoelectric nanoindentation (PNI) has been developed to quantitatively address electromechanical coupling and pressure-induced dynamic phenomena in ferroelectric materials on the nanoscale. In PNI, an oscillating voltage is applied between the back side of the sample and the indenter tip, and the first harmonic of bias-induced surface displacement at the area of indenter contact is detected. PNI is implemented using a standard nanoindentation system equipped with a continuous stiffness measurement system. The piezoresponse of polycrystalline lead zirconate titanate (PZT) and BaTiO3 piezoceramics was studied during a standard nanoindentation experiment. For PZT, the response was found to be load independent, in agreement with theoretical predictions. In polycrystalline barium titanate, a load dependence of the piezoresponse was observed. The potential of piezoelectric nanoindentation for studies of phase transitions and local structure-property relations in piezoelectric materials is discussed.
Micromechanical modeling of ferroelectric films
Authors: Huber J.E.
Published: March 2006

Ferroelectric films are growing in significance as non-volatile memory devices, sensors, and microactuators. The stress state of the film, induced by processing or constraints such as the substrate, strongly affects device behavior. Thus, it is important to be able to model the coupled and constrained behavior of film material. This work presents a preliminary study of the application of micromechanical modeling to ferroelectric films. A self-consistent micromechanics model developed for bulk ferroelectrics is adapted for thin film behavior by incorporating several features of the microstructure, mechanical clamping by the substrate, residual stresses, and the crystallographic orientation of the film.
Erbium doped silicon single- and multilayer structures for light-emitting device and laser applications
Authors: Krasilnik Zakhary F. , Andreev Boris A. , Kryzhkov Denis I. , Krasilnikova Ludmila V. , Kuznetsov Viktor P. , Remizov Dmitry Yu. , Shmagin Viacheslav B. , Stepikhova Margarita V. , Yablonskiy Artem N. , Gregorkievicz Tom , Vinh Nguyen Q. , Jantsch Wolfgang , Przybylinska Hanka , Timoshenko Victor Yu. , Zhigunov Denis M.
Published: March 2006

The paper is a brief retrospective review of our contribution to the Si:Er problem in the last decade. It contains a description of the experimental facilities, results of the light-emitting media (Si:Er and Si1−xGex:Er) research, and device applications.
New configuration of a [001] superdislocation formed during high-temperature creep in the γ′ phase of a single-crystal superalloy TMS-138
Authors: Zhang J.X. , Harada H. , Koizumi Y.
Published: March 2006

A new configuration of a superdislocation in the γ′ phase of a fourth-generation single-crystal TMS-138 superalloy was found after creep rupture in a [001] tensile test at 1150 °C and 137 MPa. The segments of the superdislocation lie in four directions, i.e., [110], [110], [100], and [010], strictly on a (001) plane with a Burgers vectorb= [001]. This superdislocation is pure edge in character and does not dissociate into superpartials. Microstructural evidence shows that this kind of superdislocation is formed by combination of two interfacial dislocations with different Burgers vectors, i.e., 1/2[011] + 1/2[011] → [001].
Effect of unloading strain rate on the elastic modulus of a viscoelastic solid determined by nanoindentation
Authors: Fujisawa Naoki , Swain Michael V.
Published: March 2006

The elastic modulus of an amorphous polymer was investigated by nanoindentation using combinations of ten total penetration depths and three constant unload rates. This experimental design provided a range of unloading strain rates coexisting with a range of depths. The elastic modulus of the material was found to correlate strongly with the unloading strain rate, whereas its correlation with the indentation depth was statistically nonsignificant. Thus, the increase of elastic modulus that occurred with decreasing depth at each constant unload rate was merely due to the increasing unloading strain rate associated with the decreasing depth. The true depth dependence of a rate-dependent material can therefore be studied only by maintaining a constant unloading strain rate across the entire depth range. The implications of these results to the continuous stiffness measurement technique are considered.
Novel technique for measuring the mechanical properties of porous materials by nanoindentation
Authors: Chen Xi , Xiang Yong , Vlassak Joost J.
Published: March 2006

A new technique for measuring the elastic-plastic properties of porous thin films by means of nanoindentation is proposed. The effects of porosity on indentation hardness and modulus are investigated through finite element analyses based on the Gurson model for plastic deformation of ductile porous materials. Intrinsic mechanical properties of the thin film are obtained by eliminating both substrate and densification effects. The technique is applied to the special case of a porous, low-permittivity dielectric thin film. The results are in good agreement with those obtained independently using the plane-strain bulge test.
High-temperature oxidation behavior of arc ion plated NiCoCrAlYSiB coatings on cobalt-based superalloy
Authors: Tang Y.J. , Wang Q.M. , Yuan F.H. , Gong J. , Sun C.
Published: March 2006

NiCoCrAlYSiB coatings were deposited on the Co-based superalloy K40 by arc ion plating (AIP). The oxidation behavior of the bare alloy and of the coated specimens was tested in static air for 200 h at 1000 °C and 100 h at 1050 °C. The results showed that the oxidation rate of the system was greatly reduced by the addition of the NiCoCrAlYSiB coatings. Thin and adherent α–Al2O3 scales that formed on the coated specimens protected the substrates from further oxidation attack while non-protective oxide scales, mainly of Cr2O3 and CoCr2O4, appeared on bare K40 alloy. Element profiles on metallographic cross sections indicated that apparent interdiffusion occurred between the coatings and the substrates. The interdiffusion behavior and the resulting microstructure were investigated. As compared to aluminide coatings, NiCoCrAlYSiB coatings have less influence on the substrate microstructure.
Extended solubility of CoO in ZnO and effects on magnetic properties
Authors: Schaedler Tobias A. , Gandhi Ashutosh S. , Saito Mitsuhiro , Rühle Manfred , Gambino Richard , Levi Carlos G.
Published: March 2006

The metastable solid solubility extension of CoO in ZnO (wurtzite) was investigated in precursor-derived powders as well as in thin films grown on sapphire substrates by pulsed laser deposition. A maximum solubility of 30% Co2+ in ZnO was achieved in the powders. Transmission electron microscopy (TEM) of the films revealed them to have grown epitaxially and retained up to nearly 40% CoO in solid solution, but some Co2+ precipitated as rock-salt. The temperature dependence of the metastable solubility limit in the ZnO–CoO system was assessed and is discussed in terms of the relevant thermodynamic factors. The magnetic properties of n-type conductive Zn0.79Co0.2Al0.01Ofilms were studied, yielding evidence of a ferromagnetic phase with a TC of 25 K and a second, magnetically ordered, phase with positive exchange and arguably a TC of ∼250 K. Connections between the properties and microstructural observations in high resolution TEM are proposed.
Deformation and failure of a film/substrate system subjected to spherical indentation: Part I. Experimental validation of stresses and strains derived using Hankel transform technique in an elastic film/substrate system
Authors: Math Souvik , Jayaram V. , Biswas S.K.
Published: March 2006

Our concern here is to rationalize experimental observations of failure modes brought about by indentation of hard thin ceramic films deposited on metallic substrates. By undertaking this exercise, we would like to evolve an analytical framework that can be used for designs of coatings. In Part I of the paper we develop an algorithm and test it for a model system. Using this analytical framework we address the issue of failure of columnar TiN films in Part II [J. Mater. Res.21, 783 (2006)] of the paper. In this part, we used a previously derived Hankel transform procedure to derive stress and strain in a birefringent polymer film glued to a strong substrate and subjected to spherical indentation. We measure surface radial strains using strain gauges and bulk film stresses using photo elastic technique (stress freezing). For a boundary condition based on Hertzian traction with no film interface constraint and assuming the substrate constraint to be a function of the imposed strain, the theory describes the stress distributions well. The variation in peak stresses also demonstrates the usefulness of depositing even a soft film to protect an underlying substrate.