bluuebunny/crossref_metadata_2025 huggingface dataset:
Gas turbine engine configurations for power generation cycles having CO2 sequestration
Authors: Jackson A. J B. , Audus H , Singh R
Published: April 2004

Atmospheric CO2 is believed to cause over 60 per cent of the present ‘greenhouse gas’ global warming effect; its concentration is increasing, due partly to the growth in power production plants that burn hydrocarbon fuels. Gas turbines burning natural gas are used increasingly in new power producing plant. Sequestering the CO2 from the entire exhaust of a gas turbine requires large, expensive plant. Some alternative options for eliminating CO2 emissions are explored herein. Only the engine implications are examined in detail. One option is to burn hydrogen-rich fuel that is carbon-free; manufacture of such fuels must include sequestration of any CO2. Another option is to use closed-cycle plants fuelled by hydrocarbons, having CO2 as the working fluid, with exhaust sequestration of CO2. Sequestration in this case needs much smaller plant because only a small fraction of the exhaust is processed. Both options have already been explored for single-shaft, synchronous engines. This paper presents a study of possible free power turbine engines. The engine hardware changes needed when switching from natural gas to hydrogen-rich fuel are mainly the combustor and the control system, for both configurations. The hardware and performance changes from switching from air to a CO2-rich working fluid are, for both configurations. considerable.
Stand-alone and grid-connected performance analysis of a regenerative micro gas turbine cogeneration plant
Authors: Bruno J. C. , Massagués L. I. , Coronas A
Published: April 2004

Distributed generation is an attractive way of producing energy, minimizing transport losses and enhancing energy efficiency. Micro gas turbines in distributed generation systems add other advantages such as low emissions and fuel flexibility. The objective of this paper is to summarize the experimental data from a small-capacity cogeneration plant that consists of a natural gas fired 28 kWe microturbine and a hot-water waste-heat boiler installed at CREVER's testing facilities in Tarragona. The results include the electrical efficiency, natural gas consumption, electrical power quality, thermal power production and air emissions at different loads and ambient temperatures. The electrical efficiency is in the range of the specifications provided by the manufacturer and decreases considerably when the power output drops. Thermal production at full load is around 57 kW. Air emissions are very low at full load and do not increase appreciably until the load is below 60–70 per cent of the full load capacity. The results confirm that the power quality and air emissions in microturbines comply with the existing legal limits, and that they are very competitive in comparison with other technologies in these aspects. Thus, considerable market development is expected in the coming years, although further research and development will be needed.
Exergy analysis of carryover leakage irreversibilities of a power plant regenerative air heater
Authors: Jassim R. K. , Habeebullah B. A. , Habeebullah A. S.
Published: April 2004

Energy recovery devices can have substantial impact on process efficiency and their relevance to the problem of conservation of energy resources is generally recognized to be beyond dispute. One type of such a device, which is commonly used in fossil-fired and air conditioning systems, is the rotary regenerator, in which a stream of hot waste gas exchanges heat with fresh atmospheric air through the intermediate agency of a rotating matrix. As there are gas streams involved in the heat transfer and mixing processes, then there are irreversibilities, or exergy destruction, due to mixing, pressure losses IΔP and due to temperature gradients IΔP. These principle components of total process irreversibility are not independent and there is a trade-off between them. Therefore the purpose of this case study is to demonstrate the importance of the use of exergy analysis in the minimization of carryover leakage irreversibilities of a symmetric balanced rotary regenerator. The chemical exergy Ėo and physical exergy Ėph are calculated and the ratio of chemical and physical irreversibilities has been evaluated for a rotary regenerator used for air preheating in a coal-fired power plant. A numerical finite difference technique has been used to calculate the fluid and matrix temperature distributions effect on the regenerator performance. The effects of variation of the principal design parameters on the irreversibilities and on the regenerator effectiveness are examined and recommendations are made for the selection of the most appropriate parameters.
Cross-flow fan design guidelines for multi-objective performance optimization
Authors: Toffolo A , Lazzaretto A , Martegani A. D.
Published: April 2004

More than one century has passed since Mortier's first cross-flow fan patent in 1891, but the design is still based on empirical considerations and on the re-adaptation of previously developed configurations. The complexity of the flow field inside the machine is the main reason for the lack of an established design procedure, because the characteristics of the eccentric vortex that forms within the impeller are deeply influenced by the geometry of the impeller and also of the casing. In this paper, the objectives that should be pursued in the design procedure are discussed and defined, and guidelines for cross-flow fan design are determined through the analysis of an experimental database of fan performance and efficiencies, which is obtained by the systematic variation of the most important geometric parameters of the casing in combination with different impellers.
Interference of laminar flow on displacement thickness in a streamwise corner
Authors: Wattananusorn S
Published: April 2004

This paper features a mathematical model of the wave function of fully developed nonperturbed laminar flow in the viscous region along an arbitrary-angle corner formed by the intersection of two semi-infinite flat plates. This model is then applied to determine the displacement thickness in the presence of a corner in the flow field.
Detection of shaft-seal rubbing in large-scale power generation turbines with acoustic emissions. Case study
Authors: Mba D , Cooke A , Roby D , Hewitt G
Published: April 2004

Rubbing between the central rotor and the surrounding stationary components of machinery such as large-scale turbine units can escalate into severe vibration, resulting in costly damage. Although conventional vibration analysis remains an important condition monitoring technique for diagnosing such rubbing phenomena, the non-destructive measurement of acoustic emission (AE) activity at the bearings on such plant is evolving into a viable complementary detection approach, especially adept at indicating the early stages of shaft-seal rubbing. This paper presents a case study on the application of high-frequency acoustic emissions as a means of detecting and verifying shaft-seal rubbing on a 217 MVA operational steam turbine unit. The generation of AE activity is attributed to the contact, deformation, adhesion and ploughing of surface asperities on the rubbing surfaces of the rotor and stator.
Heat transfer in neuron composite laminated phase-change drywall
Authors: Darkwa K , Kim J. S.
Published: April 2004

Inadequate heat transfer and overall reduction in thermal conductivities during energy recovery are identified as the main barriers affecting the performance of a phase-change material (PCM) wallboard system. Two integrated PCM drywall systems have been evaluated numerically, and the results showed a great advantage of the laminated PCM wallboard system over the randomly mixed PCM type in terms of enhanced thermal performance and rapid heat transfer rates under a narrow temperature swing. For instance, the maximum instantaneous enhancement in heat flux obtained was between 20 and 50 per cent higher during the phase change process, with up to about 18 per cent more heat storage and release capacity. However, experimental evaluation is required for validation and development.
Performance of NOX reduction catalysts with simulated dimethyl ether diesel engine exhaust gas
Authors: Alam M , Fujita O , Ito K
Published: April 2004

Characteristics of dimethyl ether oxidation and formaldehyde formation with NOX reduction catalysts were investigated in comparison with noble metal catalysts. The catalysts used in this research were Co and Sn as NOX catalysts and Pt, Pd, Rh as noble metal catalysts. Moreover, all the catalysts were loaded with gamma alumina (γ-Al2O3). In addition, a pure γ-Al2O3 catalyst was also used. Laboratory experiments were conducted by using the above catalysts in the presence of oxygen-rich simulated dimethyl ether engine exhaust gas. The catalyst temperature and the concentration of NO in the simulated exhaust gas were selected as experimental parameters. The experimental results showed that low-temperature dimethyl ether oxidation was possible with Pt, Pd and Rh catalysts, whereas higher-temperature dimethyl ether oxidation was observed with Co, Sn and pure γ-Al2O3 catalysts. A large amount of formaldehyde was formed during the use of NOX reduction catalysts over a certain temperature range. However, the noble metal catalysts did not show any formation of formaldehyde. The effect of NO on dimethyl ether oxidation and formaldehyde formation with NOX reduction catalysts was significant. The dimethyl ether oxidation ratio became lower and the amount of formaldehyde formation increased with increase in NO in the simulated exhaust gas.
Modelling and numerical optimization of dual- and triple-pressure combined cycles
Authors: Bassily A. M.
Published: April 2004

Optimization of the combined-cycle efficiency by optimizing the gas or steam cycle efficiencies does not guarantee an optimum combined cycle. In this paper, triple-pressure and dual-pressure non-reheat combined cycles are modelled and optimized for 50 and 300 cases respectively. The layout for the triple-pressure cycle was chosen to reduce NOX emission. Constraints are set on the pressure of the feed water heater, the minimum temperature difference for pinch points, the superheat approach temperature difference, the steam turbine inlet temperature and the dryness fraction at the steam turbine outlet. The combined-cycle efficiency is optimized using two different methods: the direct search method and the variable metric method. The effects of the inlet temperature of both the gas turbine and the steam turbine and of the minimum pinch point temperature difference on the performance of the optimum cycles are presented and discussed. The optimization results indicate that the layout for the triple-pressure cycle redefines the temperature differences for pinch points and adds a constraint on the intermediate pressure of the steam generator, which reduces the optimum efficiency by 2–3 percent when compared with the dual-pressure cycle under the same conditions. For the dual-pressure cycle, the optima of the most efficient cases were found to be 0.5-2 percent higher in efficiency than the optima of the regular design case, which is the usual design case for a commercial combined cycle. The optimum dual-pressure combined cycle was found to be almost as efficient as the most efficient commercially available triple-pressure reheat combined cycle, when compared at the same firing temperature.
Ejector-assisted liquid metal topping cycles
Authors: Angelino G , Invernizzi C
Published: April 2004

Direct fired coal power stations exhibit a comparatively poor performance since they cannot be operated in a combined cycle. A liquid metal topping cycle could dramatically improve their overall conversion efficiency. The high temperature required poses demanding technical problems both in the primary heat exchanger and in the turbine. The present paper discusses the possibility of alleviating the turbine-related problems through the use of an ejector which transfers the energy produced in a metal vapour topping cycle to a helium-vapour mixture at much lower temperature and pressure. Ejector performance is analysed both from a mechanical and from a thermodynamic point of view. Three typical alkali metal fluids are examined: sodium, potassium and cesium. The efficiency of the energy transfer from vapour to helium significantly increases with the metal molecular weight and attains optimum values of around 90 per cent. Turbine inlet temperature reduction due to the ejector action is about 500 K. Important gains are also the reduction in turbine inlet pressure and expansion ratio. After the energy transfer to helium and the turbine expansion, metal vapour and inert gas are separated by vapour condensation at a decreasing temperature. Such cooling represents the main thermodynamic loss in the process. At a maximum temperature of 1500 K and a condensation temperature for the reference vapour cycle of 950 K, computed efficiencies of the ejector-assisted topping cycle are in the range 17–19 per cent, as against pure vapour cycle efficiencies in the range 24–26 per cent. The strong cooling of the mixture needed to separate the liquid metal implies a significant increase in heat consumption which can be mitigated by means of an internal heat regeneration, which improves cycle efficiency to 19–22 per cent. With reference to a standard steam bottoming cycle, and including electrical, mechanical and boiler losses, plant efficiencies of around 50 per cent seem achievable.
Alcohol Enhances GABAergic Transmission to Cerebellar Granule Cells via an Increase in Golgi Cell Excitability
Authors: Carta Mario , Mameli Manuel , Valenzuela C. Fernando
Published: April 2004

Alcohol intoxication alters coordination and motor skills, and this is responsible for a significant number of traffic accident-related deaths around the world. Although the precise mechanism of action of ethanol (EtOH) is presently unknown, studies suggest that it acts, in part, by interfering with normal cerebellar functioning. An important component of cerebellar circuits is the granule cell. The excitability of these abundantly expressed neurons is controlled by the Golgi cell, a subtype of GABAergic interneuron. Granule cells receive GABAergic input in the form of phasic and tonic currents that are mediated by synaptic and extrasynaptic receptors, respectively. Using the acute cerebellar slice preparation and patch-clamp electrophysiological techniques, we found that ethanol induces a parallel increase in both the frequency of spontaneous IPSCs and the magnitude of the tonic current. EtOH (50 mm) did not produce this effect when spontaneous action potentials were blocked with tetrodotoxin. Recordings in the loose-patch cell-attached configuration demonstrated that ethanol increases the frequency of spontaneous action potentials in Golgi cells. Taken together, these findings indicate that ethanol enhances GABAergic inhibition of granule cells via a presynaptic mechanism that involves an increase in action potential-dependent GABA release from Golgi cells. This effect is likely to have an impact on the flow of information through the cerebellar cortex and may contribute to the mechanism by which acute ingestion of alcoholic beverages induces motor impairment.
Convergence of Depth from Texture and Depth from Disparity in Macaque Inferior Temporal Cortex
Authors: Liu Yan , Vogels Rufin , Orban Guy A.
Published: April 2004

The visual system must reconstruct the three-dimensional structure of an object from two-dimensional retinal images. Previous research has shown that macaque inferior temporal (IT) neurons, although belonging to the ventral visual stream, code for depth defined by binocular disparity gradients. Here, we demonstrate that macaque IT neurons also code for depth defined by texture gradients, a monocular depth cue. Single IT neurons were selective for the tilt of texture-defined surfaces, and the tilt preferences of individual neurons remained the same, whether surfaces were defined by texture or disparity cues. Furthermore, the tilt preference was invariant over different types of textures and slants, suggesting an abstract representation of surface tilt in ventral visual cortex.
Passive or Active Immunization with Myelin Basic Protein Impairs Neurological Function and Exacerbates Neuropathology after Spinal Cord Injury in Rats
Authors: Jones T. Bucky , Ankeny Daniel P. , Guan Zhen , McGaughy Violeta , Fisher Lesley C. , Basso D. Michele , Popovich Phillip G.
Published: April 2004

Myelin-reactive T-cells are activated by traumatic spinal cord injury (SCI) in rodents and humans. Despite the historical association of these cells with experimental and clinical neuropathology, recent data suggest a neuroprotective role for myelin-reactive T-cells. Because of the biological and therapeutic implications of these findings, we attempted to reproduce the original neuroprotective vaccine protocols in a model of rat SCI. Specifically, MBP-reactive T-cell function was enhanced in SCI rats via passive or active immunization. Locomotor function was assessed using a standardized locomotor rating scale (Basso–Beattie–Bresnahan scale) and was correlated with myelin and axon sparing. The functional and anatomical integrity of the rubrospinal pathway also was analyzed using the inclined plane test and anatomical tract tracing. MBP-immunized rats exhibited varying degrees of functional impairment, exacerbated lesion pathology, greater rubrospinal neuron loss, increased intraspinal T-cell accumulation, and enhanced macrophage activation relative to SCI control groups. These data are consistent with the conventional view of myelin-reactive T-cells as pathological effector cells.
Corticohippocampal Contributions to Spatial and Contextual Learning
Authors: Burwell Rebecca D. , Saddoris Michael P. , Bucci David J. , Wiig Kjesten A.
Published: April 2004

Spatial and contextual learning are considered to be dependent on the hippocampus, but the extent to which other structures in the medial temporal lobe memory system support these functions is not well understood. This study examined the effects of individual and combined lesions of the perirhinal, postrhinal, and entorhinal cortices on spatial and contextual learning. Lesioned subjects were consistently impaired on measures of contextual fear learning and consistently unimpaired on spatial learning in the Morris water maze. Neurotoxic lesions of perirhinal or postrhinal cortex that were previously shown to impair contextual fear conditioning (Bucci et al., 2000) or contextual discrimination (Bucci et al., 2002) caused little or no impairment in place learning and incidental learning in the water maze. Combined lesions of perirhinal plus lateral entorhinal or postrhinal plus medial entorhinal cortices resulted in deficits in acquisition of contextual discrimination but had no effect on place learning in the water maze. Finally, a parahippocampal lesion comprising combined neurotoxic damage to perirhinal, postrhinal, and entorhinal cortices resulted in profound impairment in acquisition of a standard passive avoidance task but failed to impair place learning. In the same experiment, rats with hippocampal lesions were impaired in spatial navigation. These results indicate that tasks requiring the association between context and an aversive stimulus depend on corticohippocampal circuitry, whereas place learning in the water maze can be accomplished without the full complement of highly processed information from the cortical regions surrounding the hippocampus. The evidence that different brain systems underlie spatial navigation and contextual learning has implications for research on memory when parahippocampal regions are involved.
Regulation of Axonal Extension and Growth Cone Motility by Calmodulin-Dependent Protein Kinase I
Authors: Wayman Gary A. , Kaech Stefanie , Grant Wilmon F. , Davare Monika , Impey Soren , Tokumitsu Hiroshi , Nozaki Naohito , Banker Gary , Soderling Thomas R.
Published: April 2004

Calcium and calmodulin (CaM) are important signaling molecules that regulate axonal or dendritic extension and branching. The Ca2+-dependent stimulation of neurite elongation has generally been assumed to be mediated by CaM-kinase II (CaMKII), although other members of the CaMK family are highly expressed in developing neurons. We have examined this assumption using a combination of dominant–negative CaMKs (dnCaMKs) and other specific CaMK inhibitors. Here we report that inhibition of cytosolic CaMKI, but not CaMKII or nuclear CaMKIV, dramatically decreases axonal outgrowth and branching in cultured neonatal hippocampal and postnatal cerebellar granule neurons. CaMKI is found throughout the cell cytosol, including the growth cone. Growth cones of neurons expressing dnCaMI or dnCaMKK, the upstream activator of CaMKI, exhibit collapsed morphology with a prominent reduction in lamellipodia. Live-cell imaging confirms that these morphological changes are associated with a dramatic decrease in growth cone motility. Treatment of neurons with 1,8-naphthoylene benzimidazole-3-carboxylic acid (STO-609), an inhibitor of CaMKK, causes a similar change in morphology and reduction in growth cone motility, and this inhibition can be rescued by transfection with an STO-609-insensitive mutant of CaMKK or by transfection with constitutively active CaMKI. These results identify CaMKI as a positive transducer of growth cone motility and axon outgrowth and provide a new physiological role for the CaMKK–CaMKI pathway.
The Role of the Theta Isoform of Protein Kinase C (PKC) in Activity-Dependent Synapse Elimination: Evidence from the PKC Theta Knock-Out MouseIn VivoandIn Vitro
Authors: Li Min-Xu , Jia Min , Yang Li-Xia , Jiang Hao , Lanuza Maria A. , Gonzalez Carmen M. , Nelson Phillip G.
Published: April 2004

PKC plays a critical role in competitive activity-dependent synapse modification at the neuromuscular synapsein vitroandin vivo. This action involves a reduction of the strength of inactive inputs to muscle cells that are activated by other inputs. A decrease of postsynaptic responsiveness and a loss of postsynaptic acetyl choline receptors account for the heterosynaptic lossin vitro. The loss is not seen in preparations in which PKC has been blocked pharmacologically. Here, we show that the loss does not occur inin vitropreparations made from animals genetically modified to lack the theta isoform of PKC. Synapse elimination in the newborn periodin vivois delayed but is eventually expressed in knock-out animals. PKC-dependent synapse reduction is suppressed in heterologous cultures combining normal nerve and PKC theta-deficient muscle, as might be expected from the postsynaptic locus of the changes that underlie the activity-dependent plasticity. Preparations in which PKC theta-deficient neurons innervated normal muscle also exhibited a marked deficit in PKC-deficient synapse reduction. The presynaptic action of PKC theta implied by this observation is blocked by TTX, and we propose that activity-related synapse strengthening is decreased by presynaptic PKC theta. Thus, PKC theta in both presynaptic and postsynaptic elements plays a critical role in activity-dependent synapse modulation and loss. We provide a model for activity-dependent synapse loss incorporating these findings.
Role of the Basolateral Amygdala in the Storage of Fear Memories across the Adult Lifetime of Rats
Authors: Gale Greg D. , Anagnostaras Stephan G. , Godsil Bill P. , Mitchell Shawn , Nozawa Takashi , Sage Jennifer R. , Wiltgen Brian , Fanselow Michael S.
Published: April 2004

The basolateral amygdala (BLA) is intimately involved in the development of conditional fear. Converging lines of evidence support a role for this region in the storage of fear memory but do not rule out a time-limited role in the memory consolidation. To examine this issue, we assessed the stability of BLA contribution to fear memories acquired across the adult lifetime of rats. Fear conditioning consisted of 10 tone–shock pairings in one context (remote memory), followed 16 months later by 10 additional tone–shock pairings with a novel tone in a novel context (recent memory). Twenty-four hours after recent training, rats were given NMDA or sham lesions of the BLA. Contextual and tone freezing were independently assessed in individual test sessions. Sham-lesioned rats showed high and comparable levels of freezing across all context and tone tests. In contrast, BLA-lesioned rats displayed robust freezing deficits across both recent and remote tests. Subsequent open-field testing revealed no effects of BLA lesions on activity patterns in a dark open field or during bright light exposure. Lesioned rats were able to reacquire normal levels of context-specific freezing after an overtraining procedure (76 unsignaled shocks). Together, these findings indicate that BLA lesions do not disrupt freezing behavior by producing hyperactivity, an inability to suppress behavior, or an inability to freeze. Rather, the consistent pattern of freezing deficits at both training-to-lesion intervals supports a role for the BLA in the permanent storage of fear memory.
Information Tuning of Populations of Neurons in Primary Visual Cortex
Authors: Kang Kukjin , Shapley Robert M. , Sompolinsky Haim
Published: April 2004

Neurons in macaque primary visual cortex (V1) show a diversity of orientation tuning properties, exhibiting a broad distribution of tuning width, baseline activity, peak response, and circular variance (CV). Here, we studied how the different tuning features affect the performance of these cells in discriminating between stimuli with different orientations. Previous studies of the orientation discrimination power of neurons in V1 focused on resolving two nearby orientations close to the psychophysical threshold of orientation discrimination. Here, we developed a theoretical framework, the information tuning curve, that measures the discrimination power of cells as a function of the orientation difference, δθ, of the two stimuli. This tuning curve also represents the mutual information between the neuronal responses and the stimulus orientation. We studied theoretically the dependence of the information tuning curve on the orientation tuning width, baseline, and peak responses. Of main interest is the finding that narrow orientation tuning is not necessarily optimal for all angular discrimination tasks. Instead, the optimal tuning width depends linearly onδθ. We applied our theory to study the discrimination performance of a population of 490 neurons in macaque V1. We found that a significant fraction of the neuronal population exhibits favorable tuning properties for large δθ. We also studied how the discrimination capability of neurons is distributed and compared several other measures of the orientation tuning such as CV with Chernoff distances for normalized tuning curves.
Defining a Molecular Atlas of the Hippocampus Using DNA Microarrays and High-ThroughputIn SituHybridization
Authors: Lein Ed S. , Zhao Xinyu , Gage Fred H.
Published: April 2004

The hippocampus consists of a series of cytoarchitecturally discrete subregions that can be distinguished from one another on the basis of morphology, connectivity, and electrophysiological properties. To understand the molecular underpinnings for these differences, DNA microarrays were used to find genes predicted to be enriched in subregions CA1, CA3, and the dentate gyrus, and >100 of these genes were subsequently analyzed usingin situhybridization to obtain cellular-level localization of their transcripts. The most striking commonality among the resulting patterns of gene expression is the extent to which cytoarchitectural boundaries within the hippocampus are respected, although the complexity of these patterns could not have been predicted on the basis of the microarray data alone. Among those genes with expression that can be characterized as “restricted” to neurons in one or more subregions of the hippocampus are a number of signal transduction molecules, transcription factors, calcium-binding proteins, and carbohydrate-modifying enzymes. These results suggest that important determinants of the unique identities of adult hippocampal neurons are differential signal transduction, regulation of gene expression, calcium homeostasis, and the maintenance of a unique extracellular milieu. Furthermore, the extremely high correlation between microarray data andin situexpression demonstrates the great utility of using DNA microarrays to genetically profile discrete brain regions.
Endoplasmic Reticulum Export Site Formation and Function in Dendrites
Authors: Aridor Meir , Guzik Amy K. , Bielli Anna , Fish Kenneth N.
Published: April 2004

The elongated and polarized characteristics of neurons render targeting of receptors to the plasma membrane of distal axonal projections and dendritic branches a major sorting task. Although the majority of biosynthetic cargo synthesis, transport, and sorting are believed to occur in the soma, local membrane protein translation and sorting has been reported recently to take place in dendrites and axons. We investigated where endoplasmic reticulum (ER) export occurs in dendrites using anin vitropermeabilized neuron system that enables us to specifically control the assembly of ER export sites. We show that ER export sites are assembled regularly throughout the entire dendritic tree by the regulated sequential recruitment of Sar1 and COPII (coat protein complex II). Moreover, activation of metabotropic glutamate receptors leads to the recruitment of the NMDA receptor subunit NR1 to remodeled ER export sites. We propose that regulation of receptor assembly and export from the ER in dendrites plays an important role in modulating receptor surface expression and neuronal function.
Functional Signal- and Paradigm-Dependent Linear Relationships between Synaptic Activity and Hemodynamic Responses in Rat Somatosensory Cortex
Authors: Nemoto Masahito , Sheth Sameer , Guiou Michael , Pouratian Nader , Chen James W. Y. , Toga Arthur W.
Published: April 2004

Linear relationships between synaptic activity and hemodynamic responses are critically dependent on functional signal etiology and paradigm. To investigate these relationships, we simultaneously measured local field potentials (FPs) and optical intrinsic signals in rat somatosensory cortex while delivering a small number of electrical pulses to the hindpaw with varied stimulus intensity, number, and interstimulus interval. We used 570 and 610 nm optical signals to estimate cerebral blood volume (CBV) and oxygenation, respectively.

The spatiotemporal evolution patterns and trial-by-trial correlation analyses revealed that CBV-related optical signals have higher fidelity to summed evoked FPs (ΣFPs) than oxygenation-derived signals. CBV-related signals even correlated with minute ΣFP fluctuations within trials of the same stimulus condition. Furthermore, hemodynamic signals (CBV and late oxygenation signals) increased linearly with ΣFP while varying stimulus number, but they exhibited a threshold and steeper gradient while varying stimulus intensity, suggesting insufficiency of the homogeneity property of linear systems and the importance of spatiotemporal coherence of neuronal population activity in hemodynamic response formation. These stimulus paradigm-dependent linear and nonlinear relationships demonstrate that simple subtraction-based analyses of hemodynamic signals produced by complex stimulus paradigms may not reflect a difference in ΣFPs between paradigms. Functional signal- and paradigm-dependent linearity have potentially profound implications for the interpretation of perfusion-based functional signals.
Critical Role for DP5/Harakiri, a Bcl-2 Homology Domain 3-Only Bcl-2 Family Member, in Axotomy-Induced Neuronal Cell Death
Authors: Imaizumi Kazunori , Benito Adalberto , Kiryu-Seo Sumiko , Gonzalez Victor , Inohara Naohiro , Leiberman Andrew P. , Kiyama Hiroshi , Nuñez Gabriel
Published: April 2004

The survival of neurons is maintained primarily by neurotrophic factors that suppress the apoptotic program. Axotomy or removal of peripheral targets causes neuronal cell death, but the mechanisms involved in the induction of this type of cell death remain poorly understood. Here, we show that DP5/Harakiri, a Bcl-2 homology domain 3-only member of the Bcl-2 family, is induced in motoneurons after transection of the hypoglossal nerve in mice and in sympathetic neurons after nerve growth factor (NGF) withdrawal. To assess the role of DP5 in neuronal cell death, mutant mice deficient in DP5 were generated by gene targeting. DP5–/–mice were viable and exhibited normal postnatal development. Notably, motoneurons from DP5–/–mice were highly protected from cell death induced by resection of the hypoglossal nerve compared with motoneurons from DP5+/+littermate mice. In addition, deficiency of DP5 in superior cervical ganglia (SCG) neurons resulted in delayed neuronal cell death triggered by NGF withdrawal. Analysis of SCG neurons from DP5–/–mice revealed increased preservation of mitochondrial membrane potential and reduced activation of caspase-3 compared with neurons from wild-type mice. These results indicate that DP5 plays an important role in neuronal cell death induced by axotomy and NGF deprivation through the regulation of mitochondrial function and caspase-3 activation.
Cognitive Aging and the Hippocampus: How Old Rats Represent New Environments
Authors: Wilson Iain A. , Ikonen Sami , Gureviciene Irina , McMahan Robert W. , Gallagher Michela , Eichenbaum Howard , Tanila Heikki
Published: April 2004

Spatial learning impairment in aged rats is associated with changes in hippocampal connectivity and plasticity. Several studies have explored the age-related deficit in spatial information processing by recording the location-specific activity of hippocampal neurons (place cells). However, these studies have generated disparate characterizations of place cells in aged rats as unstable (Barnes et al., 1997), resistant to change (Tanila et al., 1997b; Oler and Markus, 2000; Wilson et al., 2003), or delayed in using external cues (Rosenzweig et al., 2003). To reconcile these findings, we recorded place cells from aged and young rats as they repeatedly explored both a highly familiar environment and an initially novel environment, and we repeatedly tested whether the place fields formed in the novel environment were anchored by external cues. Initially, spatial representations in aged rats were abnormally maintained between the familiar and novel environments. Then, new representations were formed but were also delayed in becoming anchored to the external landmarks. Finally, even when the new spatial representations became bound to the landmarks, they were multi-stable across repetitive exposures to the formerly novel environment. These observations help to reconcile previously divergent characterizations of spatial representation in aged rats and suggest a model of cognitive aging and hippocampal function.
The Classical Receptive Field Surround of Primate Parasol Ganglion Cells Is Mediated Primarily by a Non-GABAergic Pathway
Authors: McMahon Matthew J. , Packer Orin S. , Dacey Dennis M.
Published: April 2004

Although the center-surround receptive field is a fundamental property of retinal ganglion cells, the circuitry that mediates surround inhibition remains controversial. We examined the contribution of horizontal cells and amacrine cells to the surround of parasol ganglion cells of macaque and baboon retina by measuring receptive field structure before and during the application of drugs that have been shown previously to affect surrounds in a range of mammalian and nonmammalian species. Carbenoxolone and cobalt, thought to attenuate feedback from horizontal cells to cones, severely reduced the surround. Tetrodotoxin, which blocks sodium spiking in amacrine cells, and picrotoxin, which blocks the inhibitory action of GABA, only slightly reduced the surround. These data are consistent with the hypothesis that the surrounds of light-adapted parasol ganglion cells are generated primarily by non-GABAergic horizontal cell feedback in the outer retina, with a small contribution from GABAergic amacrine cells of the inner retina.
Sequential Release of GABA by Exocytosis and Reversed Uptake Leads to Neuronal Swelling in Simulated Ischemia of Hippocampal Slices
Authors: Allen Nicola J. , Rossi David J. , Attwell David
Published: April 2004

GABA release during cerebral energy deprivation (produced by anoxia or ischemia) has been suggested either to be neuroprotective, because GABA will hyperpolarize neurons and reduce release of excitotoxic glutamate, or to be neurotoxic, because activation of GABAAreceptors facilitates Cl–entry into neurons and consequent cell swelling. We have used the GABAAreceptors of hippocampal area CA1 pyramidal cells to sense the rise of [GABA]ooccurring in simulated ischemia. Ischemia evoked, after several minutes, a large depolarization to ∼–20 mV. Before this “anoxic depolarization,” there was an increase in GABA release by exocytosis (spontaneous IPSCs). After the anoxic depolarization, there was a much larger, sustained release of GABA that was not affected by blocking action potentials, vesicular release, or the glial GABA transporter GAT-3 but was inhibited by blocking the neuronal GABA transporter GAT-1. Blocking GABAAreceptors resulted in a more positive anoxic depolarization but decreased cell swelling at the time of the anoxic depolarization. The influence of GABAAreceptors diminished in prolonged ischemia because glutamate release evoked by the anoxic depolarization inhibited GABAAreceptor function by causing calcium entry through NMDA receptors. These data show that ischemia releases GABA initially by exocytosis and then by reversal of GAT-1 transporters and that the resulting Cl–influx through GABAAreceptor channels causes potentially neurotoxic cell swelling.
Dimeric Amyloid β Protein Rapidly Accumulates in Lipid Rafts followed by Apolipoprotein E and Phosphorylated Tau Accumulation in the Tg2576 Mouse Model of Alzheimer's Disease
Authors: Kawarabayashi Takeshi , Shoji Mikio , Younkin Linda H. , Wen-Lang Lin , Dickson Dennis W. , Murakami Tetsuro , Matsubara Etsuro , Abe Koji , Ashe Karen Hsiao , Younkin Steven G.
Published: April 2004

To investigate lipid rafts as a site where amyloid β protein (Aβ) oligomers might accumulate and cause toxicity in Alzheimer's disease (AD), we analyzed Aβ in the Tg2576 transgenic mouse model of AD. Aβ was highly concentrated in lipid rafts, which comprise a small fraction of brain volume but contain 27% of brain Aβ42 and 24% of Aβ40 in young mice. In the Tg2576 model, memory impairment begins at 6 months before amyloid plaques are visible. Here we show that Aβ dimers appear in lipid rafts at 6 months and that raft Aβ, which is primarily dimeric, rapidly accumulates reaching levels >500× those in young mice by 24–28 months. A similar large accumulation of dimeric Aβ was observed in lipid rafts from AD brain. In contrast to extracellular amyloid fibrils, which are SDS-insoluble, virtually all Aβ in lipid rafts is SDS soluble. Coupled with recent studies showing that synthetic and naturally occurring Aβ oligomers can inhibit hippocampal long-term potentiation, thein vivoage-dependent accumulation of SDS-soluble Aβ dimers in lipid rafts at the time when memory impairment begins in Tg2576 mice provides strong evidence linking Aβ oligomers to memory impairment. After dimeric Aβ began to accumulate in lipid rafts of the Tg2576 brain, apolipoprotein E (ApoE) and then phosphorylated tau accumulated. A similar increase in ApoE and a large increase in phosphorylated tau was observed in lipid rafts from AD brain. These findings suggest that lipid rafts may be an important site for interaction between dimeric Aβ, ApoE, and tau.
Lipid Rafts and Integrin Activation Regulate Oligodendrocyte Survival
Authors: Decker Laurence , ffrench-Constant Charles
Published: April 2004

Newly formed oligodendrocytes in the CNS derive survival cues from their target axons. These cues are provided in part by laminins expressed on the axon, which are recognized by α6β1 integrin on the oligdendrocyte and amplify platelet-derived growth factor (PDGF) signaling through the phosphatidylinositol 3′-kinase (PI3K) pathway. The α6β1 integrin is localized in oligodendrocyte lipid rafts. We show here using the sphingolipid synthesis inhibitor fumonisin-B1 to deplete rafts that this localization is important for normal survival signaling, because depletion increases oligodendrocyte apoptosis and inhibits PI3K signaling. We have shown previously that PDGF-mediated integrin activation is an important component of oligodendrocyte proliferation signaling, and here we present evidence that a similar mechanism operates in survival signaling. Integrin activation using manganese increases raft localization and rescues the effects of both raft depletion and PDGF removal on survival and PI3K signaling. Together, these results point to an essential role for rafts in oligodendrocyte survival signaling on the basis of the provision of a favorable environment for growth factor-mediated integrin activation.
Two‐bond
NMR
Spin–Spin Coupling Constants across Hydrogen Bonds
Authors: Del Bene Janet E
Published: April 2004

This article presents a summary of the results of
ab initio
equation‐of‐motion coupled‐cluster singles and doubles (EOM‐CCSD) calculations performed on series of complexes stabilized by N–H–N, C–H–N, and F–H–N hydrogen bonds. For these complexes, the total X–Y spin–spin coupling constant across an X–H–Y hydrogen bond (
2h
J
X–Y
) is determined solely by the Fermi‐contact term, which is distance dependent. Curves are presented that relate the X–Y distance to
2h
J
X–Y
for each series. The dependence of coupling constants on the hybridization and bonding of X and Y are discussed. Relationships are noted between hydrogen bond type, X–Y distances, NMR spin–spin coupling constants, and infrared proton‐stretching frequencies. The effects of zero‐point motion, thermal vibrational averaging, and isotopic substitution on coupling constants are also discussed. Comparisons are made with available experimental data.
Cautious hierarchical switching control of stochastic linear systems
Authors: Campi M.C. , Hespanha João P. , Prandini Maria
Published: April 2004

Standard switching control methods are based on the certainty equivalence philosophy in that, at each switching time, the supervisor selects the candidate controller that is better tuned to the currently estimated process model. In this paper, we propose a new supervisory switching logic that takes into account the uncertainty on the process description when performing the controller selection. Specifically, a probability measure describing the likelihood of the different models is computed on‐line based on the collected data and, at each switching time, the supervisor selects the candidate controller that, according to this probability measure, performs the best on the average. If the candidate controller class is hierarchically structured so that for each model one has available several controllers with distinct levels of robustness, the supervisor automatically selects the controller that suitably compromises robustness versus performance, given the current level of model uncertainty. The use of randomized algorithms makes the supervisor implementation computationally tractable. Copyright © 2004 John Wiley & Sons, Ltd.
Nonequilibrium thermodynamics of membrane transport
Authors: Hwang Sun‐Tak
Published: April 2004

All membrane processes are nonequilibrium processes. The transport equation describing a particular membrane process must satisfy the principles of nonequilibrium thermodynamics. However, many expressions for the flux through a membrane as functions of the driving forces can be found in the literature without resorting to nonequilibrium thermodynamics. In fact, the choice of fluxes and driving forces for a particular membrane process frequently seems to be arbitrary and accidental; this is attributed to historical developments. Some exceptions are the cases of reverse osmosis and ultrafiltration processes. Katchalsky and coworkers successfully applied the principles of nonequilibrium thermodynamics by Onsager to analyze reverse osmosis and ultrafiltration processes. A generalized treatise of nonequilibrium thermodynamic analysis is given for all different membrane processes including gas permeation, pervaporation, dialysis, reverse osmosis, ultrafiltration, microfiltration, and electrodialysis. Starting from the entropy production term, fluxes and driving forces are ascertained for each membrane process and the linear expressions between fluxes and driving forces are presented with corresponding coefficients. These are identified with the conventional entities whenever possible. As a consequence of this treatment, flux equations are more generalized to contain additional terms with additional driving forces representing the coupling phenomena. 2004 American Institute of Chemical Engineers AIChE J, 50:862–870, 2004
Exposure to maternal diabetes is associated with altered fetal growth patterns: A hypothesis regarding metabolic allocation to growth under hyperglycemic‐hypoxemic conditions
Authors: Lampl Michelle , Jeanty Philippe
Published: April 2004

The prevalence of diabetes is rising worldwide, including women who grew poorly in early life, presenting intergenerational health problems for their offspring. It is well documented that fetuses exposed to maternal diabetes during pregnancy experience both macrosomia and poor growth outcomes in birth size. Less is known about the in utero growth patterns that precede these risk factor expressions. Fetal growth patterns and the effects of clinical class and glycemic control were investigated in 37 diabetic pregnant women and their fetuses and compared to 29 nondiabetic, nonsmoking maternal/fetal pairs who were participants in a biweekly longitudinal ultrasound study with measurements of the head, limb, and trunk dimensions. White clinical class of the diabetic women was recorded (A2‐FR) and glycosylated hemoglobin levels taken at the time of measurement assessed glycemic control (median 6.9%, interquartile range 5.6–9.2%). No significant difference in fetal weight was found by exposure. The exposed sample had greater abdominal circumferences from 21 weeks (P ≤ 0.05) and shorter legs, but greater upper arm and thigh circumferences accompanied increasing glycemia in the second trimester. In the third trimester, exposed fetuses had a smaller slope for the occipital frontal diameter (P = 0.00) and were brachycephalic. They experienced a proximal/distal growth gradient in limb proportionality with higher humerus / femur ratios (P = 0.04) and arms relatively long by comparison with legs (P = 0.02). HbA1c levels above 7.5% accompanied shorter femur length for thigh circumference after 30 gestational weeks of age. Significant effects of diabetic clinical class and glycemic control were identified in growth rate timing. These growth patterns suggest that hypoxemic and hyperglycemic signals cross‐talk with their target receptors in a developmentally regulated, hierarchical sequence. The increase in fetal fat often documented with diabetic pregnancy may reflect altered growth at the level of cell differentiation and proximate mechanisms controlling body composition. These data suggest that the maternal–fetal interchange circuit, designed to share and capture resources on the fetal side, may not have had a long evolutionary history of overabundance as a selective force, and modern health problems drive postnatal sequelae that become exacerbated by increasing longevity. Am. J. Hum. Biol. 16:237–263, 2004. © 2004 Wiley‐Liss, Inc.