bluuebunny/crossref_metadata_2025 huggingface dataset:
Hyperstriatum ventrale in pigeons: Effects of lesions on color-discrimination and color-reversal learning
Authors: Chaves Lin M. , Hodos William
Published: June 2009

Previous lesion studies of color-reversal learning in pigeons show that an impairment results when (1) the tectofugal visual pathway is damaged at either the thalamic level (nucleus rotundus) or the telencephalic level (ectostriatum), or (2) the thalamofugal visual pathway is damaged at the telencephalic level (the visual Wulst). An impairment does not result, however, when the thalamic source of thalamofugal input (n. opticus principalis thalami or OPT) to the visual Wulst is damaged. These results suggest that the visual Wulst plays a role in color-reversal learning as a consequence of visual information routed from the tectofugal pathway via other visual areas in the telencephalon. One such area is the hyperstriatum ventrale (HV). In the present study, after ablation of the medial and lateral regions of HV, pigeons were trained postoperatively to discriminate between two colors presented simultaneously. After reaching criterion, the pigeons were required to perform a series of discrimination reversals in which the positive and negative stimuli were interchanged. Lesions of medial HV resulted in impaired performance of a color-discrimination task (i.e. original learning), but did not affect discrimination reversal. An impairment in color-reversal learning resulted from combined damage to lateral HV and the fronto-thalamic tract (FT), which carries ascending visual input from OPT to the visual Wulst. No deficits were observed when either lateral HV or FT were damaged alone. These findings suggest that both the thalamofugal and tectofugal pathways provide the visual Wulst with visual input relevant to color-reversal learning.
Differential timing for the appearance of neuronal and astrocytic β-adrenergic receptors in the developing rat visual cortex as revealed by light and electron-microscopic immunocytochemistry
Authors: Aoki Chiye
Published: June 2009

The developing cerebral cortex is likely to exhibit synaptic circuitries differing from those in adulthood, due to the asynchronous maturation of the various neurotransmitter systems. Two antisera directed against mammalian β-adrenergic receptors (βAR), βAR248 and βAR404, were used to characterize the laminar, cellular, and subcellular distributions of βAR in postnatally developing visual cortex of rats. The antigenic sites were the receptor's third intracellular loop for βAR248 and the C-terminus for βAR404. During week 1, most of the βAR404- and βAR248-immunoreactive sites were dendritic. Morphologically identifiable synapses were rare, even in layer 1: yet, semiquantitative analysis revealed that βAR404-immunoreactive synapses comprise half of those in layer 1. During week 2, the two antisera began to diverge in their immunoreactivity patterns. With βAR248, there was an overall decline in immunoreactivity, while with βAR404, there was an increase in immunoreactive sites, primarily due to labeled astrocytic processes that increased 200-fold in areal density by week 3. In contrast, the areal density of synaptic labeling by βAR404 barely doubled, in spite of the 30-fold increase in areal density of synapses. These results suggest that βAR undergo conformational changes during early postnatal periods, causing alterations in their relative antigenicity to the two antisera. Furthermore, the first 2 weeks appear to be characterized by modulation of earliest-formed synapses, and the subsequent phase is marked by addition of astrocytic responses that would be more diffuse temporally and spatially. Activation of βAR is recognized to increase visually evoked activity relative to spontaneous activity. Moreover, astrocytic βAR are documented to regulate extracellular concentrations of glutamate, ATP, and neurotrophic factors important for the formation of binocular connections. Thus, neuronal and astrocytic responses may, together and in tandem, facilitate strengthening of intracortical synaptic circuitry during early life.
Conservation of receptive-field properties of superior colliculus cells after developmental rearrangements of retinal input
Authors: Pallas S. L. , Finlay B. L.
Published: June 2009

The formation of topographic maps requires not only that afferents synapse with the appropriate targets, but that the spatial relationships between the afferents be maintained. During development, in addition to the formation of the topographic map, the connectivity patterns responsible for the receptive-field properties of the target cells are being formed. The extent of interaction between these two processes is unknown. The present study addresses this question by manipulating afferent/target ratios during development, thus altering the topography of the map, and studying the effects of this alteration on the receptive-field properties of single target cells in the adult.

Partial unilateral lesions of the superior colliculus (SC) were made in neonatal hamsters. These lesions result in a compression of the retinotopic map onto the remaining collicular fragment. Single cells were recorded from the superficial gray layer of the SC in the adult in response to visual stimuli. Receptive-field properties observed in lesioned animals were compared to those in normal animals and in sham operates.

Receptive-field properties were largely unaffected by the change in the topographic map. There was no difference in the receptive-field size of single tectal cells of lesioned and unlesioned animals. Stimulus velocity and stimulus size tuning functions remained the same. This raises the possibility that, rather than the expected increase in convergence of retinal ganglion cells (RGC) onto single collicular cells, single SC cells receive input from ganglion cells representing the same amount of retinal area as in unlesioned animals. The excess ganglion cells created by the partial target removal would then project elsewhere and/or reduce their arbor within the SC. Regardless of the mechanism, it is clear from our results that circuitry in the retinotectal system of the hamster can compensate for conditions of increased afferent availability and thus maintain receptive-field properties.
The human fetal retinal nerve fiber layer and optic nerve head: A DiI and DiA tracing study
Authors: Fitzgibbon T.
Published: June 2009

The organization of the primate nerve fiber layer and optic nerve head with respect to the positioning of central and peripheral axons remains controversial. Data were obtained from 32 human fetal retinae aged between 15 and 21 weeks of gestation. Crystals of the carbocyanine dyes, DiI or DiA, and fluorescence microscopy were used to identify axonal populations from peripheral retinal ganglion cells. Peripheral ganglion cell axons were scattered throughout the vitreal-scleral depth of the nerve fiber layer. Such a scattered distribution was maintained as the fibers passed through the optic nerve head and along the optic nerve. There was a rough topographic representation within the optic nerve head according to retinal quadrant such that both peripheral and central fibers were mixed within a wedge extending from the periphery to the center of the nerve. There was no indication that the fibers were reorganized in any way as they passed through the optic disc and into the nerve. The present results suggest that any degree of order present within the fiber layer and optic nerve is not an active process but a passive consequence of combining the fascicles of the retinal nerve fiber layer. Optic axons are not instructed to establish a retinotopic order and the effect of guidance cues in reordering fibers, particularly evident prechiasmatically and postchiasmatically, does not appear to be present within the nerve fiber layer or optic nerve head in humans.
Physiology of the A1 amacrine: A spiking, axon-bearing interneuron of the macaque monkey retina
Authors: Stafford Donna K. , Dacey Dennis M.
Published: June 2009

We characterized the light response, morphology, and receptive-field structure of a distinctive amacrine cell type (Dacey, 1989), termed here the Al amacrine, by applying intracellular recording and staining methods to the macaque monkey retina in vitro. A1 cells show two morphologically distinct components: a highly branched and spiny dendritic tree, and a more sparsely branched axon-like tree that arises from one or more hillock-like structures near the soma and extends for several millimeters beyond the dendritic tree. Intracellular injection of Neurobiotin reveals an extensive and complex pattern of tracer coupling to neighboring A1 amacrine cells, to two other amacrine cell types, and to a single ganglion cell type. The A1 amacrine is an ON-OFF cell, showing a large (10–20 mV) transient depolarization at both onset and offset of a photopic, luminance modulated stimulus. A burst of fast, large-amplitude (Σ60 mV) action potentials is associated with the depolarizations at both the ON and OFF phase of the response. No evidence was found for an inhibitory receptive-field surround. The spatial extent of the ON-OFF response was mapped by measuring the strength of the spike discharge and/or the amplitude of the depolarizing slow potential as a function of the position of a bar or spot of light within the receptive field. Receptive fields derived from the slow potential and associated spike discharge corresponded in size and shape. Thus, the amplitude of the slow potential above spike threshold was well encoded as spike frequency. The diameter of the receptive field determined from the spike discharge was Σ10% larger than the spiny dendritic field. The correspondence in size between the spiking receptive field and the spiny dendritic tree suggests that light driven signals are conducted to the soma from the dendritic tree but not from the axon-like arbor. The function of the axon-like component is unknown but we speculate that it serves a classical output function, transmitting spikes distally from initiation sites near the soma.
Regional specialization in the eye of the sphingid mothManduca sexta: Blue sensitivity of the ventral retina
Authors: Bennett Ruth R. , White Richard H. , Meadows Jeffery
Published: June 2009

The compound eye of the tobacco hornworm mothManduca sextacontains green-, blue-, and ultraviolet-sensitive photoreceptors. Electroretinogram spectral-sensitivity measurements were recorded from different regions of the retina in order to broadly map the distribution of the three receptor types. The relative contribution of the three receptors to spectral-sensitivity curves was estimated by fitting theoretical curves based on the absorption spectra of the three rhodopsins. This analysis indicated that the dorsal retina is green and ultraviolet dichromatic, with green-sensitive cells greatly predominating. The ventral retina is trichromatic with a substantial population of blue- and ultraviolet-sensitive receptors. We previously showed that flower visitation for nectar feeding is mediated mainly by blue-sensitive cells. Their localization in the ventral retina seems an appropriate adaptation of the receptor mosaic, since the moths hover above flowers as they feed.
A comparison of the components of the multifocal and full-field ERGs
Authors: Hood Donald C. , Seiple William , Holopigian Karen , Greenstein Vivienne
Published: June 2009

The multi-input technique of Sutter and Tran (1992) yields multiple focal ERGs. The purpose here was to compare the components of this multifocal ERG to the components of the standard, full-field ERG. To record multifocal ERGs, an array of 103 hexagons was displayed on a monitor. Full-field (Ganzfeld) ERGs were elicited by flashes presented upon steady background fields. The latencies of two prominent subcomponents of the full-field ERG were altered by varying the intensity of the incremental flash or the intensity of the background field. By showing that similar manipulations of the multi-input parameters produce similar changes in latency, we were able to relate the components of the multifocal ERG to the components of the full-field ERG. The biphasic responses of the multifocal ERG appear to be generated by the same cells generating the a-wave and positive peaks of the full-field cone ERG.
Distribution of GABA immunoreactivity in the cat retina: A light- and electron-microscopic study
Authors: Pourcho Roberta G. , Owczarzak Michael T.
Published: June 2009

The distribution of GABA-like immunoreactivity in the cat retina was studied through the use of preembedding immunocytochemistry for light microscopy and by postembedding immunogold techniques for electron microscopy. Staining was observed in both inner and outer plexiform layers. Approximately 30% of the somata in the amacrine portion of the inner nuclear layer were immunoreactive and included amacrine and interplexiform cells. Horizontal cells and a subpopulation of cone bipolar cells were also stained. In the ganglion cell layer, staining was observed in both small- and medium-sized neurons. GABA-labeled amacrine cells were presynaptic to somata of amacrine cells and to dendrites of amacrine, bipolar, and ganglion cells. Bipolar cells were a major target, receiving more than 60% of all labeled synapses in the inner plexiform layer. Many of these contacts were reciprocal synapses. These findings support a major role for GABA-labeled amacrines in providing feedback inhibition to bipolar cells in the inner retina.
Characterization of a goldfish antigen during development and regeneration of the visual system
Authors: Braverman S. B. , Rappaport I. , Sharma S. C.
Published: June 2009

Normal, regenerating, and developing optic nerves of the goldfish were studied utilizing a monoclonal antibody (mAb) 1E1T which has specificity for Müller cells in the retina, radial ghal cells in the tectum, and non-neuronal cells in the optic nerve.

Sections of the normal optic nerve revealed longitudinally oriented chains of non-neuronal cells, that were 4–8 cells long The number of chains in the normal nerve was very few. In addition, short acellular septa, probably the connective tissue septa, were also labeled with mAb 1E1T. Sections of crushed optic nerves showed an increase in the antigen recognized by mAb 1E1T within the septa and new septa were now visualized. Furthermore, the existing septa were longer and extended the length of the optic nerve. The formation and elongation of the septa occurred as early as 3 day postcrush. Between 3 and 11 d postcrush, there was heavy labeling of the septa and a large accumulation of non-neuronal cells at the crush site. At 3 months postcrush, the accumulation of non-neuronal cells labeled by mAb 1E1T were no longer visible but heavy labeling of the septa was still apparent.
Responses in ventral intraparietal area of awake macaque monkey to optic flow patterns corresponding to rotation of planes in depth can be explained by translation and expansion effects
Authors: Schaafsma S.J. , Duysens J. , Gielen C.C.A.M.
Published: June 2009

There is evidence that neurons in medial superior temporal area (MST) respond to rotation in depth of textured planes. MST neurons project to the ventral intraparietal area (VIP) and the question arises whether VIP neurons are responsive to rotation in depth as well. In the present study on awake monkeys, we have simulated movement of a flat board, covered with dots, by a computer. The two-dimensional images corresponded to the projection of structured planes rotating around a fronto-parallel axis. In the literature this stimulus is called fanning. Fanning effectively induced responses in VIP neurons. Most often the responses were nearly as strong as for translation, expansion/contraction, or rotation, indicating that there was no special sensitivity for rotation in depth. For neurons, sensitive to expansion, the response to fanning could often be explained by the positioning of the expanding part of the fanning stimulus over the area which was most responsive to expansion. For neurons which were direction selective to translation, the optimal direction of fanning was usually the same as the preferred direction for translation. It is concluded that VIP neurons may be sensitive to movement of structured planes but they are not specialized for the detection of such movement.
Immunocytochemical and histochemical localization of nitric oxide synthase in the turtle retina
Authors: Blute Todd A. , Mayer Bernd , Eldred William D.
Published: June 2009

Recent interest in nitric oxide and its relationship to cGMP has produced many attempts to anatomically localize the enzyme synthesizing nitric oxide, nitric oxide synthase. In the retina, numerous previous studies have used the NADPH-diaphorase enzyme activity of nitric oxide synthase as a histochemical method to localize nitric oxide synthase. However, all NADPH-diaphorase activity is not necessarily nitric oxide synthase, because several enzymes have similar biochemical activity. Additionally, various histochemical methods have been used to demonstrate NADPH-diaphorase activity, which makes comparisons between studies difficult. The purpose of this study was twofold. First, we wanted to examine the histochemical labeling of NADPH-diaphorase in the turtle retina to allow comparisons to previous studies. Second, we wanted to compare the histochemical localization of NADPH-diaphorase activity to the immunocytochemical localization of nitric oxide synthase in the turtle retina. Our histochemical localization of NADPH-diaphorase activity and our localization of nitric oxide synthase-like immunoreactivity in the turtle retina both produced similar results. Both the histochemistry and immunocytochemistry consistently labeled photoreceptor inner segments, at least three amacrine cell types, and processes in the inner plexiform layer. In optimized double-labeled preparations, all cells with NADPH-diaphorase activity were also positive for nitric oxide synthase-like immunoreactivity, although some somata in the ganglion cell layer only had nitric oxide synthase-like immunoreactivity. The immunocytochemical localization of nitric oxide synthase in photoreceptors, amacrine cells, and putative ganglion cells indicates that nitric oxide may function at several levels of visual processing in the turtle retina.
Le rôle de l'adverbenotammentdans la mise en oeuvre des relations de discours
Authors: VERGEZ-COURET MARIANNE
Published: June 2009

Dans cet article, nous proposons une description du rôle de l'adverbenotammentdans la mise en œuvre des relations de discours, et plus particulièrement de la relation d’Elaboration. Cette dernière est, de façon informelle, la relation qui s'établit entre un segment de discours apportant une information générale et un segment de discours apportant une ou des informations venant spécifier cette information générale.

Notammentest un adverbe qui permet d'attirer l'attention sur un ou plusieurs éléments parmi un ensemble d'éléments explicitement cité ou sous-entendu. Lorsquenotammentporte sur un syntagme verbal, nous allons montrer quenotammentpermet d'attirer l'attention sur une éventualité parmi un ensemble d'éventualités explicitement cité ou sous-entendu. Nous verrons alors que son rôle dans la mise en œuvre des relations de discours diffère selon que l'ensemble est précédemment explicitement cité ou sous-entendu.
ON THE INTERSECTION OF RATIONAL TRANSVERSAL SUBTORI
Authors: NAZIR SHAHEEN
Published: June 2009

We show that under a suitable transversality condition, the intersection of two rational subtori in an algebraic torus (ℂ*)n is a finite group which can be determined using the torsion part of some associated lattice. We also give applications to the study of characteristic varieties of smooth complex algebraic varieties. As an example we discuss A. Suciu’s line arrangement, the so-called deleted B3-arrangement.
CONTINUOUS AND DISCRETE FLOWS ON OPERATOR ALGEBRAS
Authors: ITZÁ-ORTIZ BENJAMÍN A.
Published: June 2009

Let (N,ℝ,θ) be a centrally ergodic W* dynamical system. When N is not a factor, we show that for each nonzero real number t, the crossed product induced by the time t automorphism θt is not a factor if and only if there exist a rational number r and an eigenvalue s of the restriction of θ to the center of N, such that rst=2π. In the C* setting, minimality seems to be the notion corresponding to central ergodicity. We show that if (A,ℝ,α) is a minimal unital C* dynamical system and A is not simple, then, for each nonzero real number t, the crossed product induced by the time t automorphism αt is not simple if there exist a rational number r and an eigenvalue s of the restriction of α to the center of A, such that rst=2π. The converse is true if, in addition, A is commutative or prime.
INVERSE IMAGES OF SECTORS BY FUNCTIONS IN WEIGHTED BERGMAN–ORLICZ SPACES
Authors: PÉREZ-GONZÁLEZ FERNANDO , RAMOS FERNÁNDEZ JULIO C.
Published: June 2009

For ε>0, let Σε={z∈ℂ:∣arg z∣<ε}. It has been proved (D. E. Marshall and W. Smith,Rev. Mat. Iberoamericana15(1999), 93–116) that ∫f−1(Σε)∣f(z)∣ dA(z)≃∫𝔻∣f(z)∣ dA(z) for every ε>0, uniformly for every univalent functionfin the classical Bergman spaceA1that fixes the origin. In this paper, we extend this result to those conformal maps on 𝔻 belonging to weighted Bergman–Orlicz classes such thatf(0)=∣f′(0)∣−1=0.
Statistics of multispacecraft observations of chorus dispersion and source location
Authors: Breneman Aaron W. , Kletzing Craig A. , Pickett Jolene , Chum Jaroslav , Santolik Ondrej
Published: June 2009

We report emission characteristics of 52 chorus events on 23 August 2003 and 10 events on three other days, modeled with a ray tracing technique. Chorus waves have a characteristic frequency/time variation that is a combination of frequency separation by propagation dispersion and a time‐dependent source frequency emission drift. A cross‐correlation technique comparing data from multiple Cluster spacecraft quantifies the frequency variation owing to propagation dispersion. The comparison of the data cross correlations with the simulated cross correlations allows the identification of a correlation region which has at least one common point with the chorus source region. Any remaining frequency/time variation in the single‐spacecraft spectrograms not accounted for by the cross correlations is then used to determine the time‐dependent source frequency emission drift. The final modeled correlation region and source frequency emission drift for each chorus event is consistent with both the cross‐correlation and single‐spacecraft data. The modeled correlation regions are located near the magnetic equator and are, in general, more extended parallel to the Earth's magnetic field than perpendicular to it. It is found that waves with frequencies above and below 1/2 the equatorial electron cyclotron frequency on the magnetic field line of the spacecraft (lower and upper band, respectively) are emitted in a broad spectrum of wave normal angles. There is also some preference for lower band waves observed at the spacecraft to have been emitted near the Gendrin angle and at earthward‐pointing wave normal angles of between −20° and −30°. The latter result is close to the range of wave normal angles shown recently to be connected with chorus that propagates into the plasmasphere and evolves into the incoherent plasmaspheric hiss spectrum, known to be connected to pitch angle scattering and loss of electrons in the electron slot region. Finally, the time‐dependent source frequency emission drift for these events ranges from 1 to 20 kHz/s. For most events these rates account for at least 2/3 of the chorus frequency/time variation with the rest being due to propagation dispersion.
New insights into the basement structure of the West Siberian Basin from forward and inverse modeling of GRACE satellite gravity data
Authors: Braitenberg C. , Ebbing J.
Published: June 2009

The oil‐ and gas‐rich West Siberian Basin is underlain by a layer of flood basalts of late Permian‐Triassic age that are coeval with the Siberian traps. The extent and thickness of the basalts are unknown, but knowing their thickness is important for discussions on the end‐Permian mass extinction because basalt volume constrains estimates of emitted volatiles. We have used GRACE satellite and terrestrial gravity data to study the structure of the crust and basalt distribution. Published seismic sections are used to constrain the sediment isopachs and to estimate a depth‐density function. We use published models of crustal thickness and basement depth to reduce the observed gravity field to the basement level. The resulting three‐dimensional density model gives information on density anomalies in the lower crust and upper mantle and on the basalt thickness. We identify several rift‐graben structures that are presumably filled with basalt. The lower crust below the West Siberian Basin shows considerable density variations, and these variations allow the region to be divided into four major blocks. The eastern part of the basin, toward the Siberian platform, shows an arch‐shaped density increase in the lower crust that is accompanied by a linear high‐density anomaly at shallower depths. Our work demonstrates the way in which the GRACE‐gravity field can be applied to map geological structures like buried rifts and large basins. The same techniques can be used for other large, remote basins such as those in cratonic South America.
Microwave motion induced synthetic aperture radiometer using sparse array
Authors: Park Hyuk , Kim Yong‐Hoon
Published: June 2009

Several studies have been performed on microwave aperture synthesis carried out from a moving platform, in order to achieve high spatial resolution with a small number of antennas. In this paper, the limitations of previous developed Motion Induced Synthetic Aperture Radiometer systems are discussed, and an improved observation model, imaging method, and antenna array configuration are presented. An observation model and an imaging method suitable for imaging extended sources are developed, which is a more practical consideration than a point source. It is found that the antenna array configuration used in previous studies causes significant degradation of imaging performance. To improve this, the use of a sparse array is proposed. The sparse T‐shaped array is designed and discussed based on the analysis of spatial frequency coverage. The proposed sparse T‐shaped array can cover a spatial frequency plane efficiently, resulting in a better imaging performance than that of previously developed aperture synthesis systems that used moving platform. The improvement in performance is demonstrated by simulating the point source response, which shows the reduced sidelobes.
Geodesy in the 21st Century
Authors: Wdowinski Shimon , Eriksson Susan
Published: June 2009

From flat Earth, to round Earth, to a rough and oblate Earth, people's understanding of the shape of our planet and its landscapes has changed dramatically over the course of history. These advances in geodesy—the study of Earth's size, shape, orientation, and gravitational field, and the variations of these quantities over time—developed because of humans' curiosity about the Earth and because of geodesy's application to navigation, surveying, and mapping, all of which were very practical areas that benefited society.
3‐D Seismic Interpretation
Authors: Moore Gregory F.
Published: June 2009

This volume is a brief introduction aimed at those who wish to gain a basic and relatively quick understanding of the interpretation of three‐dimensional (3‐D) seismic reflection data. The book is well written, clearly illustrated, and easy to follow. Enough elementary mathematics are presented for a basic understanding of seismic methods, but more complex mathematical derivations are avoided. References are listed for readers interested in more advanced explanations. After a brief introduction, the book logically begins with a succinct chapter on modern 3‐D seismic data acquisition and processing. Standard 3‐D acquisition methods are presented, and an appendix expands on more recent acquisition techniques, such as multiple‐azimuth and wide‐azimuth acquisition. Although this chapter covers the basics of standard time processing quite well, there is only a single sentence about prestack depth imaging, and anisotropic processing is not mentioned at all, even though both techniques are now becoming standard.
Thermochemical remanence acquisition in single‐domain particle ensembles: A case for possible overestimation of the geomagnetic paleointensity
Authors: Fabian Karl
Published: June 2009

Single‐domain (SD) particle ensembles are the best studied systems in rock magnetism. Yet even for this simple system, a complete theoretical treatment of the acquisition of thermochemical remanent magnetization (TCRM) is missing. On the basis of the SD theory of chemical remanent magnetization, it is generally taken for granted that TCRM acquisition must be less efficient than acquisition of a thermoremanent magnetization (TRM) and that consequently, the paleofield intensity is inevitably underestimated when a TCRM is interpreted as a TRM. Here it is shown that this conclusion holds only when a continuous chemical change (e.g., grain growth) takes place during remanence blocking. In cases where an initial TRM, at a later time and at lower temperature, is modified by chemical processes, the final TCRM can result in considerable paleofield overestimation when interpreted as a TRM. This is demonstrated for two different scenarios. First, partial grain dissolution after TRM acquisition and second, low‐temperature oxidation. These mechanisms are not unlikely to occur in nature, and numerical experiments indicate that both would lead to perfectly straight Arai plots, which makes such SD TCRMs indistinguishable from true TRMs in the Thellier experiment.
Broad‐scale applicability of correlation detectors to China seismicity
Authors: Schaff David P.
Published: June 2009

It is demonstrated that cross‐correlation methods can successfully be applied on a large scale to the detection of seismic events arising in a variety of tectonic settings. The locations of about thousand earthquakes a year occurring in and near China are reported using phase picks from a large national network. We performed more than 100 million cross correlations on the waveforms of more than 18,800 events over 20 years, as recorded by a relatively sparse network; and detected about two thirds of the nationally reported events. Additional events (70% increase), beyond what standard processing detects for China on the sparse network, were also found. A corresponding reduction in detection threshold approaches 0.9 magnitude units for increasing station distance. As networks densify and archives grow, cross‐correlation is likely to become more and more useful for purposes of maximizing the number of detected events and hence to improve knowledge of seismicity.
Energy dissipation and the spectral distribution of whitecaps
Authors: Thomson Jim , Gemmrich Johannes R. , Jessup Andrew T.
Published: June 2009

Energy dissipation by breaking water waves is quantified indirectly using remote observations (digital video recordings) and directly using in situ observations (acoustic Doppler velocity profiles). The analysis is the first validation using field data to test the Duncan‐Phillips formulation relating energy dissipation to the spectral distribution of whitecap speeds and lengths. Energy dissipation estimates are in agreement over two orders of magnitude, and demonstrate a promising method for routine observation of wave breaking dynamics. Breaking statistics are partitioned into contributions from waves at the peak of the wave‐height spectrum and waves at higher frequencies in the spectrum. Peak waves are found to be only 10% of the total breaking rate, however peak waves contribute up to 75% of the total dissipation rate. In addition, breaking statistics are found to depend on the peak wave steepness and the energy input by the wind.
Building Language Competence With Students Using AAC Devices: Six Challenges
Authors: Van Tatenhove Gail M.
Published: June 2009

There is an adage used by teachers in the American education system that says, “You learn to communicate before you communicate to learn.” This saying reminds us that communication skills are the foundation for learning and that naturally developing children are generally competent communicators before they enter school. They use their foundational language skills to be successful in the classroom. This adage is not typically true for students using AAC systems. These students often enter school without competent communication skills and must work on these skills, while also trying to master school subjects. The reader is challenged to assess his or her role in the language development process of children using AAC systems. Speech-language pathologists will be encouraged to go beyond the role of programming AAC devices and return to the role of “language therapist.” Educators, who spend the majority of the school day with the student, are reminded that they hold the keys to augmentative communication success in schools. Their role is critical in supporting and applying language skills in the classroom.
Data Collection and Monitoring AAC Intervention in the Schools
Authors: Hill Katya
Published: June 2009

Speech-language pathologists working in the schools with students who rely on AAC are expected to measure progress to document gains in language competence. This article provides an overview of some of the basic considerations SLPs make in collecting clinical data to monitor building language competence. Three hypothetical students are used as examples to illustrate data collection through the three transitional stages in language development SLPs frequently encounter on a school caseload: (a) pragmatics to semantics, (b) semantics to syntax, (c) phonology to metaphonology. Examples of performance and outcomes data including language activity monitoring are provided for each transition. SLPs addressing the what, when, how, who, where, and why of data collection find AAC intervention manageable. Strong evidence from clinical practice is needed to optimize the language competence of students who rely on AAC.
Competitive effects of an axial magnetic field and of neutral gas depletion in a positive column
Authors: Liard L. , Raimbault J.-L. , Chabert P.
Published: May 2009

Neutral gas dynamics has been incorporated in plasma transport equations in recent studies of nonmagnetized plasma discharge equilibrium. It was found that when the plasma density increases, the neutral gas density becomes depleted in the discharge center, leading to plasma deconfinement. Consequently, larger electron temperature, flatter plasma density profiles, and larger edge-to-center plasma density ratios were observed. In this paper, we investigate the effect of adding a static axial magnetic field to the discharge. We find that at fixed plasma density at the center, the magnetic field reduces the calculated neutral depletion and all the associated effects. Nevertheless, the action of the magnetic field is less pronounced if one keeps the power deposited into the discharge fixed instead. This is because at fixed power, the plasma density increases with the magnetic field.
Blowing bubbles in Lennard-Jonesium along the saturation curve
Authors: Ashbaugh Henry S.
Published: May 2009

Extensive molecular simulations of the Lennard-Jones fluid have been performed to determine its liquid-vapor coexistence properties and solvent contact densities with cavities up to ten times the diameter of the solvent from the triple point to the critical point. These simulations are analyzed using a revised scaled-particle theory [H. S. Ashbaugh and L. R. Pratt, Rev. Mod. Phys. 78, 159 (2006)] to evaluate the thermodynamics of cavity solvation and curvature dependent interfacial properties along the saturation curve. While the thermodynamic signatures of cavity solvation are distinct from those in water, exhibiting a chemical potential dominated by a large temperature independent enthalpy, the solvent dewets cavities of increasing size similar with water near coexistence. The interfacial tension for forming a liquid-wall interface is found to be consistently greater than the liquid-vapor surface tension of the Lennard-Jones fluid by up to 10% and potentially reflects the suppression of high amplitude fluctuations at the cavity surface. The first-order curvature correction for the surface tension is negative and appears to diverge to negative infinity at temperatures approaching the critical point. Our results point to the success of the revised scaled-particle theory at bridging molecular and macroscopic descriptions of cavity solvation.
Solid-state electric generator based on chemically induced internal electron emission in metal-semiconductor heterojunction nanostructures
Authors: Karpov E. G. , Nedrygailov I. I.
Published: May 2009

Internal electron emission induced by hydrogen oxidation to water on surface of Pd/n-SiC heterojunction nanostructures is observed and the possibility for a new type of chemoelectrical power generator is discussed. The noble metal nanolayer serves both as reaction catalyst and emitter of hot electrons traveling over Schottky barrier and toward semiconductor anode. In situ chemical process provides significantly higher output of hot electrons compared to devices with externally heated cathodes. Large fraction of the hot electrons is generated nonadiabatically to complement the usual thermal excitation, leading to very high total internal quantum efficiency of the device, reaching 0.20 for the nanostructure studied here.
Capacitance-voltage and retention characteristics of Pt/SrBi2Ta2O9/HfO2/Si structures with various buffer layer thickness
Authors: Tang M. H. , Sun Z. H. , Zhou Y. C. , Sugiyama Y. , Ishiwara H.
Published: May 2009

The metal-ferroelectric-insulator-semiconductor (MFIS) structure diodes with SrBi2Ta2O9 (SBT) as ferroelectric thin film and HfO2 as insulating buffer layer were fabricated. The electrical properties of MFIS structure were investigated for different HfO2 buffer layer thickness. The experimental results show that the memory window extended significantly as the HfO2 layer thickness increased from 6 to 10 nm. It is also observed that the leakage current was reduced to about 10−10 A at applied voltage of 4 V, and the high and low capacitances remained distinguishable for over 8 h even if we extrapolate the measured data to 10 years.
Functional evolution of photochemical energy transformations in oxygen-producing organisms
Authors: Raven John A.
Published: June 2009

Chlorophyll a is the photochemical agent accounting for most oxygenic photosynthesis, that is, over 99.9% of photosynthetic primary activity on Earth. The spectral and energetic properties of chlorophyll a can, at least in part, be rationalised in terms of the solar spectral output and the energetics of oxygen production and carbon dioxide reduction with two photochemical reactions. The long wavelength limit on in vivo chlorophyll a absorption is probably close to the energetic limit: longer wavelengths could not support a high rate and efficiency of oxygenic photosynthesis. Retinal, a β-carotene derivative that is the chromophore of rhodopsin, acts not only as a sensory pigment, but also as an ion-pumping photochemical transducer. Both sensory and energy-transforming rhodopsins occur in oxygenic phototrophs, although the extent of expression and the function of the latter are not well understood.
ERK activation in axonal varicosities modulates presynaptic plasticity in the CA3 region of the hippocampus through synapsin I
Authors: Vara Hugo , Onofri Franco , Benfenati Fabio , Sassoè-Pognetto Marco , Giustetto Maurizio
Published: June 2009

Activity-dependent changes in the strength of synaptic connections in the hippocampus are central for cognitive processes such as learning and memory storage. In this study, we reveal an activity-dependent presynaptic mechanism that is related to the modulation of synaptic plasticity. In acute mouse hippocampal slices, high-frequency stimulation (HFS) of the mossy fiber (MF)-CA3 pathway induced a strong and transient activation of extracellular-regulated kinase (ERK) in MF giant presynaptic terminals. Remarkably, pharmacological blockade of ERK disclosed a negative role of this kinase in the regulation of a presynaptic form of plasticity at MF-CA3 contacts. This ERK-mediated inhibition of post-tetanic enhancement (PTE) of MF-CA3 synapses was both frequency- and pathway-specific and was observed only with HFS at 50 Hz. Importantly, blockade of ERK was virtually ineffective on PTE of MF-CA3 synapses in mice lacking synapsin I, 1 of the major presynaptic ERK substrates, and triple knockout mice lacking all synapsin isoforms displayed PTE kinetics resembling that of wild-type mice under ERK inhibition. These findings reveal a form of short-term synaptic plasticity that depends on ERK and is finely tuned by the firing frequency of presynaptic neurons. Our results also demonstrate that presynaptic activation of the ERK signaling pathway plays part in the activity-dependent modulation of synaptic vesicle mobilization and transmitter release.
Measurement of internal body time by blood metabolomics
Authors: Minami Yoichi , Kasukawa Takeya , Kakazu Yuji , Iigo Masayuki , Sugimoto Masahiro , Ikeda Satsuki , Yasui Akira , van der Horst Gijsbertus T. J. , Soga Tomoyoshi , Ueda Hiroki R.
Published: June 2009

Detection of internal body time (BT) via a few-time-point assay has been a longstanding challenge in medicine, because BT information can be exploited to maximize potency and minimize toxicity during drug administration and thus will enable highly optimized medication. To address this challenge, we previously developed the concept, “molecular-timetable method,” which was originally inspired by Linné's flower clock. In Linné's flower clock, one can estimate the time of the day by watching the opening and closing pattern of various flowers. Similarly, in the molecular-timetable method, one can measure the BT of the day by profiling the up and down patterns of substances in the molecular timetable. To make this method clinically feasible, we now performed blood metabolome analysis and here report the successful quantification of hundreds of clock-controlled metabolites in mouse plasma. Based on circadian blood metabolomics, we can detect individual BT under various conditions, demonstrating its robustness against genetic background, sex, age, and feeding differences. The power of this method is also demonstrated by the sensitive and accurate detection of circadian rhythm disorder in jet-lagged mice. These results suggest the potential for metabolomics-based detection of BT (“metabolite-timetable method”), which will lead to the realization of chronotherapy and personalized medicine.
Yeast Rev1 protein promotes complex formation of DNA polymerase ζ with Pol32 subunit of DNA polymerase δ
Authors: Acharya Narottam , Johnson Robert E. , Pagès Vincent , Prakash Louise , Prakash Satya
Published: June 2009

Yeast DNA polymerase (Pol) δ, essential for DNA replication, is comprised of 3 subunits, Pol3, Pol31, and Pol32. Of these, the catalytic subunit Pol3 and the second subunit Pol31 are essential, whereas the Pol32 subunit is not essential for DNA replication. Although Pol32 is an integral component of Polδ, it is also required for translesion synthesis (TLS) by Polζ. To begin to decipher the bases of Pol32 involvement in Polζ-mediated TLS, here we examine whether Pol32 physically interacts with Polζ or its associated proteins and provide evidence for the physical interaction of Pol32 with Rev1. Rev1 plays an indispensable structural role in Polζ-mediated TLS and it binds the Rev3 catalytic subunit of Polζ. Here, we show that although Pol32 does not directly bind Polζ, Pol32 can bind the Rev1–Polζ complex through its interaction with Rev1. We find that Pol32 binding has no stimulatory effect on DNA synthesis either by Rev1 in the Rev1–Pol32 complex or by Polζ in the Polζ–Rev1–Pol32 complex, irrespective of whether proliferating cell nuclear antigen has been loaded onto DNA or not. We discuss evidence for the biological significance of Rev1 binding to Pol32 for Polζ function in TLS and suggest a structural role for Rev1 in modulating the binding of Polζ with Pol32 in Polδ stalled at a lesion site.
Engineering botulinum neurotoxin to extend therapeutic intervention
Authors: Chen Sheng , Barbieri Joseph T.
Published: June 2009

Clostridium botulinum
neurotoxins (BoNTs) are effective therapeutics for a variety of neurological disorders, such as strabismus, blepharospam, hemificial spasm, and cervical dystonia, because of the toxin's tropism for neurons and specific cleavage of neuronal soluble N-ethylmaleimide-sensitive fusion protein-attachment protein receptors (SNARE) proteins. Modifying BoNT to bind nonneuronal cells has been attempted to extend therapeutic applications. However, prerequisite to develop nonneuronal therapies requires the retargeting the catalytic activity of BoNTs to nonneuronal SNARE isoforms. Here, we reported the engineering of a BoNT derivative that cleaves SNAP23, a nonneuronal SNARE protein. SNAP23 mediates vesicle-plasma membrane fusion processes, including secretion of airway mucus, antibody, insulin, gastric acids, and ions. This mutated BoNT/E light chain LC/E(K
224
D) showed extended substrate specificity to cleave SNAP23, and the natural substrate, SNAP25, but not SNAP29 or SNAP47. Upon direct protein delivery into cultured human epithelial cells, LC/E(K
224
D) cleaved endogenous SNAP23, which inhibited secretion of mucin and IL-8. These studies show the feasibility of genetically modifying LCs to target a nonneuronal SNARE protein that extends therapeutic potential for treatment of human hypersecretion diseases.
Toolbox model of evolution of prokaryotic metabolic networks and their regulation
Authors: Maslov Sergei , Krishna Sandeep , Pang Tin Yau , Sneppen Kim
Published: May 2009

It has been reported that the number of transcription factors encoded in prokaryotic genomes scales approximately quadratically with their total number of genes. We propose a conceptual explanation of this finding and illustrate it using a simple model in which metabolic and regulatory networks of prokaryotes are shaped by horizontal gene transfer of coregulated metabolic pathways. Adapting to a new environmental condition monitored by a new transcription factor (e.g., learning to use another nutrient) involves both acquiring new enzymes and reusing some of the enzymes already encoded in the genome. As the repertoire of enzymes of an organism (its toolbox) grows larger, it can reuse its enzyme tools more often and thus needs to get fewer new ones to master each new task. From this observation, it logically follows that the number of functional tasks and their regulators increases faster than linearly with the total number of genes encoding enzymes. Genomes can also shrink, e.g., because of a loss of a nutrient from the environment, followed by deletion of its regulator and all enzymes that become redundant. We propose several simple models of network evolution elaborating on this toolbox argument and reproducing the empirically observed quadratic scaling. The distribution of lengths of pathway branches in our model agrees with that of the real-life metabolic network of
Escherichia coli
. Thus, our model provides a qualitative explanation for broad distributions of regulon sizes in prokaryotes.