Characterization of the in vitro propagation of epileptiform electrophysiological activity in organotypic hippocampal slice cultures coupled to 3D microelectrode arrays.

PubMed

Pisciotta, Marzia; Morgavi, Giovanna; Jahnsen, Henrik

2010-10-28

Dynamic aspects of the propagation of epileptiform activity have so far received little attention. With the aim of providing new insights about the spatial features of the propagation of epileptic seizures in the nervous system, we studied in vitro the initiation and propagation of traveling epileptiform waves of electrophysiological activity in the hippocampus by means of substrate three-dimensional microelectrode arrays (MEAs) for extracellular measurements. Pharmacologically disinhibited hippocampal slices spontaneously generate epileptiform bursts mostly originating in CA3 and propagating to CA1. Our study specifically addressed the activity-dependent changes of the propagation of traveling electrophysiological waves in organotypic hippocampal slices during epileptiform discharge and in particular our question is: what happens to the epileptic signals during their propagation through the slice? Multichannel data analysis enabled us to quantify an activity-dependent increase in the propagation velocity of spontaneous bursts. Moreover, through the evaluation of the coherence of the signals, it was possible to point out that only the lower-frequency components (<95Hz) of the electrical activity are completely coherent with respect to the activity originating in the CA3, while components at higher frequencies lose the coherence, possibly suggesting that the cellular mechanism mediating propagation of electrophysiological activity becomes ineffective for those firing rates exceeding an upper bound or that some noise of neuronal origin was added to the signal during propagation. Copyright © 2010 Elsevier B.V. All rights reserved.

An experimental/computational study of sharp fin induced shock wave/turbulent boundary layer interactions at Mach 5 - Experimental results

NASA Technical Reports Server (NTRS)

Rodi, Patrick E.; Dolling, David S.

1992-01-01

A combined experimental/computational study has been performed of sharp fin induced shock wave/turbulent boundary layer interactions at Mach 5. The current paper focuses on the experiments and analysis of the results. The experimental data include mean surface heat transfer, mean surface pressure distributions and surface flow visualization for fin angles of attack of 6, 8, 10, 12, 14 and 16-degrees at Mach 5 under a moderately cooled wall condition. Comparisons between the results and correlations developed earlier show that Scuderi's correlation for the upstream influence angle (recast in a conical form) is superior to other such correlations in predicting the current results, that normal Mach number based correlations for peak pressure heat transfer are adequate and that the initial heat transfer peak can be predicted using pressure-interaction theory.

Wide band cryogenic ultra-high vacuum microwave absorber

DOEpatents

Campisi, Isidoro E.

1992-01-01

An absorber wave guide assembly for absorbing higher order modes of microwave energy under cryogenic ultra-high vacuum conditions, that absorbs wide-band multi-mode energy. The absorber is of a special triangular shape, made from flat tiles of silicon carbide and aluminum nitride. The leading sharp end of the absorber is located in a corner of the wave guide and tapers to a larger cross-sectional area whose center is located approximately in the center of the wave guide. The absorber is relatively short, being of less height than the maximum width of the wave guide.

A role for endocannabinoids in viral-induced dyskinetic and convulsive phenomena.

PubMed

Solbrig, Marylou V; Adrian, Russell; Baratta, Janie; Piomelli, Daniele; Giuffrida, Andrea

2005-08-01

Dyskinesias and seizures are both medically refractory disorders for which cannabinoid-based treatments have shown early promise as primary or adjunctive therapy. Using the Borna disease (BD) virus rat, an animal model of viral encephalopathy with spontaneous hyperkinetic movements and seizure susceptibility, we identified a key role for endocannabinoids in the maintenance of a balanced tone of activity in extrapyramidal and limbic circuits. BD rats showed significant elevations of the endocannabinoid anandamide in subthalamic nucleus, a relay nucleus compromised in hyperkinetic disorders. While direct and indirect cannabinoid agonists had limited motor effects in BD rats, abrupt reductions of endocannabinoid tone by the CB1 antagonist SR141716A (0.3 mg/kg, i.p.) caused seizures characterized by myoclonic jerks time-locked to periodic spike/sharp wave discharges on hippocampal electroencephalography. The general opiate antagonist naloxone (NLX) (1 mg/kg, s.c.), another pharmacologic treatment with potential efficacy in dyskinesias or L-DOPA motor complications, produced similar seizures. No changes in anandamide levels in hippocampus and amygdala were found in convulsing NLX-treated BD rats. In contrast, NLX significantly increased anandamide levels in the same areas of normal uninfected animals, possibly protecting against seizures. Pretreatment with the anandamide transport blocker AM404 (20 mg/kg, i.p.) prevented NLX-induced seizures. These findings are consistent with an anticonvulsant role for endocannabinoids, counteracting aberrant firing produced by convulsive agents, and with a functional or reciprocal relation between opioid and cannabinoid tone with respect to limbic convulsive phenomena.

Rapid classification of hippocampal replay content for real-time applications

PubMed Central

Liu, Daniel F.; Karlsson, Mattias P.; Frank, Loren M.; Eden, Uri T.

2016-01-01

Sharp-wave ripple (SWR) events in the hippocampus replay millisecond-timescale patterns of place cell activity related to the past experience of an animal. Interrupting SWR events leads to learning and memory impairments, but how the specific patterns of place cell spiking seen during SWRs contribute to learning and memory remains unclear. A deeper understanding of this issue will require the ability to manipulate SWR events based on their content. Accurate real-time decoding of SWR replay events requires new algorithms that are able to estimate replay content and the associated uncertainty, along with software and hardware that can execute these algorithms for biological interventions on a millisecond timescale. Here we develop an efficient estimation algorithm to categorize the content of replay from multiunit spiking activity. Specifically, we apply real-time decoding methods to each SWR event and then compute the posterior probability of the replay feature. We illustrate this approach by classifying SWR events from data recorded in the hippocampus of a rat performing a spatial memory task into four categories: whether they represent outbound or inbound trajectories and whether the activity is replayed forward or backward in time. We show that our algorithm can classify the majority of SWR events in a recording epoch within 20 ms of the replay onset with high certainty, which makes the algorithm suitable for a real-time implementation with short latencies to incorporate into content-based feedback experiments. PMID:27535369

Behavior-dependent activity patterns of GABAergic long-range projecting neurons in the rat hippocampus.

PubMed

Katona, Linda; Micklem, Ben; Borhegyi, Zsolt; Swiejkowski, Daniel A; Valenti, Ornella; Viney, Tim J; Kotzadimitriou, Dimitrios; Klausberger, Thomas; Somogyi, Peter

2017-04-01

Long-range glutamatergic and GABAergic projections participate in temporal coordination of neuronal activity in distributed cortical areas. In the hippocampus, GABAergic neurons project to the medial septum and retrohippocampal areas. Many GABAergic projection cells express somatostatin (SOM+) and, together with locally terminating SOM+ bistratified and O-LM cells, contribute to dendritic inhibition of pyramidal cells. We tested the hypothesis that diversity in SOM+ cells reflects temporal specialization during behavior using extracellular single cell recording and juxtacellular neurobiotin-labeling in freely moving rats. We have demonstrated that rare GABAergic projection neurons discharge rhythmically and are remarkably diverse. During sharp wave-ripples, most projection cells, including a novel SOM+ GABAergic back-projecting cell, increased their activity similar to bistratified cells, but unlike O-LM cells. During movement, most projection cells discharged along the descending slope of theta cycles, but some fired at the trough jointly with bistratified and O-LM cells. The specialization of hippocampal SOM+ projection neurons complements the action of local interneurons in differentially phasing inputs from the CA3 area to CA1 pyramidal cell dendrites during sleep and wakefulness. Our observations suggest that GABAergic projection cells mediate the behavior- and network state-dependent binding of neuronal assemblies amongst functionally-related brain regions by transmitting local rhythmic entrainment of neurons in CA1 to neuronal populations in other areas. © 2016 The Authors Hippocampus Published by Wiley Periodicals, Inc. © 2016 The Authors Hippocampus Published by Wiley Periodicals, Inc.

Guiding, bending, and splitting of coupled defect surface modes in a surface-wave photonic crystal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, Zhen; Gao, Fei; Zhang, Baile, E-mail: blzhang@ntu.edu.sg

2016-01-25

We experimentally demonstrate a type of waveguiding mechanism for coupled surface-wave defect modes in a surface-wave photonic crystal. Unlike conventional spoof surface plasmon waveguides, waveguiding of coupled surface-wave defect modes is achieved through weak coupling between tightly localized defect cavities in an otherwise gapped surface-wave photonic crystal, as a classical wave analogue of tight-binding electronic wavefunctions in solid state lattices. Wave patterns associated with the high transmission of coupled defect surface modes are directly mapped with a near-field microwave scanning probe for various structures including a straight waveguide, a sharp corner, and a T-shaped splitter. These results may find usemore » in the design of integrated surface-wave devices with suppressed crosstalk.« less

Hippocampal Sleep Features: Relations to Human Memory Function

PubMed Central

Ferrara, Michele; Moroni, Fabio; De Gennaro, Luigi; Nobili, Lino

2012-01-01

The recent spread of intracranial electroencephalographic (EEG) recording techniques for presurgical evaluation of drug-resistant epileptic patients is providing new information on the activity of different brain structures during both wakefulness and sleep. The interest has been mainly focused on the medial temporal lobe, and in particular the hippocampal formation, whose peculiar local sleep features have been recently described, providing support to the idea that sleep is not a spatially global phenomenon. The study of the hippocampal sleep electrophysiology is particularly interesting because of its central role in the declarative memory formation. Recent data indicate that sleep contributes to memory formation. Therefore, it is relevant to understand whether specific patterns of activity taking place during sleep are related to memory consolidation processes. Fascinating similarities between different states of consciousness (wakefulness, REM sleep, non-REM sleep) in some electrophysiological mechanisms underlying cognitive processes have been reported. For instance, large-scale synchrony in gamma activity is important for waking memory and perception processes, and its changes during sleep may be the neurophysiological substrate of sleep-related deficits of declarative memory. Hippocampal activity seems to specifically support memory consolidation during sleep, through specific coordinated neurophysiological events (slow waves, spindles, ripples) that would facilitate the integration of new information into the pre-existing cortical networks. A few studies indeed provided direct evidence that rhinal ripples as well as slow hippocampal oscillations are correlated with memory consolidation in humans. More detailed electrophysiological investigations assessing the specific relations between different types of memory consolidation and hippocampal EEG features are in order. These studies will add an important piece of knowledge to the elucidation of the ultimate sleep function. PMID:22529835

Regular theta-firing neurons in the nucleus incertus during sustained hippocampal activation.

PubMed

Martínez-Bellver, Sergio; Cervera-Ferri, Ana; Martínez-Ricós, Joana; Ruiz-Torner, Amparo; Luque-Garcia, Aina; Luque-Martinez, Aina; Blasco-Serra, Arantxa; Guerrero-Martínez, Juan; Bataller-Mompeán, Manuel; Teruel-Martí, Vicent

2015-04-01

This paper describes the existence of theta-coupled neuronal activity in the nucleus incertus (NI). Theta rhythm is relevant for cognitive processes such as spatial navigation and memory processing, and can be recorded in a number of structures related to the hippocampal activation including the NI. Strong evidence supports the role of this tegmental nucleus in neural circuits integrating behavioural activation with the hippocampal theta rhythm. Theta oscillations have been recorded in the local field potential of the NI, highly coupled to the hippocampal waves, although no rhythmical activity has been reported in neurons of this nucleus. The present work analyses the neuronal activity in the NI in conditions leading to sustained hippocampal theta in the urethane-anaesthetised rat, in order to test whether such activation elicits a differential firing pattern. Wavelet analysis has been used to better define the neuronal activity already described in the nucleus, i.e., non-rhythmical neurons firing at theta frequency (type I neurons) and fast-firing rhythmical neurons (type II). However, the most remarkable finding was that sustained stimulation activated regular-theta neurons (type III), which were almost silent in baseline conditions and have not previously been reported. Thus, we describe the electrophysiological properties of type III neurons, focusing on their coupling to the hippocampal theta. Their spike rate, regularity and phase locking to the oscillations increased at the beginning of the stimulation, suggesting a role in the activation or reset of the oscillation. Further research is needed to address the specific contribution of these neurons to the entire circuit. © 2015 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.

Prostaglandin E(2) stimulates glutamate receptor-dependent astrocyte neuromodulation in cultured hippocampal cells.

PubMed

Sanzgiri, R P; Araque, A; Haydon, P G

1999-11-05

Recent Ca(2+) imaging studies in cell culture and in situ have shown that Ca(2+) elevations in astrocytes stimulate glutamate release and increase neuronal Ca(2+) levels, and that this astrocyte-neuron signaling can be stimulated by prostaglandin E(2) (PGE(2)). We investigated the electrophysiological consequences of the PGE(2)-mediated astrocyte-neuron signaling using whole-cell recordings on cultured rat hippocampal cells. Focal application of PGE(2) to astrocytes evoked a Ca(2+) elevation in the stimulated cell by mobilizing internal Ca(2+) stores, which further propagated as a Ca(2+) wave to neighboring astrocytes. Whole-cell recordings from neurons revealed that PGE(2) evoked a slow inward current in neurons adjacent to astrocytes. This neuronal response required the presence of an astrocyte Ca(2+) wave and was mediated through both N-methyl-D-aspartate (NMDA) and non-NMDA glutamate receptors. Taken together with previous studies, these data demonstrate that PGE(2)-evoked Ca(2+) elevations in astrocyte cause the release of glutamate which activates neuronal ionotropic receptors. Copyright 1999 John Wiley & Sons, Inc.

[Electroencephalographic effects of chlorphenesin carbamate, a new central muscle relaxant, in rabbits (author's transl)].

PubMed

Watanabe, S; Araki, H; Kawasaki, H; Ueki, S

1977-05-01

Electroencephalographic (EEG) effects of chlorphenesin carbamate were investigated in rabbits with chronic electrode implants, and compared with those of chlormezanone and methocarbamol. Chlorphenesin carbamate (50 mg/kg i.v., 100 mg/kg i.d.) induced a drowsy pattern of spontaneous EEG consisting of high voltage slow waves in the cortex and amygdala, and desynchronization of hippocampal theta waves. Chlormezanone also elicited similar EEG changes but such were much more potent than chlorphenesin carbamate. Methocarbamol showed no effect on spontaneous EEG. Chlorphenesin carbamate caused sedation in this period and muscle relaxation was more potent than that of chlormezanone. The EEG arousal response to auditory stimulation and to electric stimulation of the posterior hypothalamus, centromedian thalamus and mesencephalic reticular formation was slightly depressed by chlorphenesin carbamate. Chlorphenesin carbamate, as with chlormezanone, markedly depressed the limbic afterdischarges elicited by hippocampal stimulation. These EEG effects of chlorphenesin carbamate were qualitatively similar to but much weaker than those of chlormezanone, whereas the muscle relaxant effect of chlorphenesin carbamate was more potent than that of chlormezanone.

Geometrical Determinants of Neuronal Actin Waves.

PubMed

Tomba, Caterina; Braïni, Céline; Bugnicourt, Ghislain; Cohen, Floriane; Friedrich, Benjamin M; Gov, Nir S; Villard, Catherine

2017-01-01

Hippocampal neurons produce in their early stages of growth propagative, actin-rich dynamical structures called actin waves. The directional motion of actin waves from the soma to the tip of neuronal extensions has been associated with net forward growth, and ultimately with the specification of neurites into axon and dendrites. Here, geometrical cues are used to control actin wave dynamics by constraining neurons on adhesive stripes of various widths. A key observable, the average time between the production of consecutive actin waves, or mean inter-wave interval (IWI), was identified. It scales with the neurite width, and more precisely with the width of the proximal segment close to the soma. In addition, the IWI is independent of the total number of neurites. These two results suggest a mechanistic model of actin wave production, by which the material conveyed by actin waves is assembled in the soma until it reaches the threshold leading to the initiation and propagation of a new actin wave. Based on these observations, we formulate a predictive theoretical description of actin wave-driven neuronal growth and polarization, which consistently accounts for different sets of experiments.

Geometrical Determinants of Neuronal Actin Waves

PubMed Central

Tomba, Caterina; Braïni, Céline; Bugnicourt, Ghislain; Cohen, Floriane; Friedrich, Benjamin M.; Gov, Nir S.; Villard, Catherine

2017-01-01

Hippocampal neurons produce in their early stages of growth propagative, actin-rich dynamical structures called actin waves. The directional motion of actin waves from the soma to the tip of neuronal extensions has been associated with net forward growth, and ultimately with the specification of neurites into axon and dendrites. Here, geometrical cues are used to control actin wave dynamics by constraining neurons on adhesive stripes of various widths. A key observable, the average time between the production of consecutive actin waves, or mean inter-wave interval (IWI), was identified. It scales with the neurite width, and more precisely with the width of the proximal segment close to the soma. In addition, the IWI is independent of the total number of neurites. These two results suggest a mechanistic model of actin wave production, by which the material conveyed by actin waves is assembled in the soma until it reaches the threshold leading to the initiation and propagation of a new actin wave. Based on these observations, we formulate a predictive theoretical description of actin wave-driven neuronal growth and polarization, which consistently accounts for different sets of experiments. PMID:28424590

Generic short-time propagation of sharp-boundaries wave packets

NASA Astrophysics Data System (ADS)

Granot, E.; Marchewka, A.

2005-11-01

A general solution to the "shutter" problem is presented. The propagation of an arbitrary initially bounded wave function is investigated, and the general solution for any such function is formulated. It is shown that the exact solution can be written as an expression that depends only on the values of the function (and its derivatives) at the boundaries. In particular, it is shown that at short times (t << 2mx2/hbar, where x is the distance to the boundaries) the wave function propagation depends only on the wave function's values (or its derivatives) at the boundaries of the region. Finally, we generalize these findings to a non-singular wave function (i.e., for wave packets with finite-width boundaries) and suggest an experimental verification.

Spike-like solitary waves in incompressible boundary layers driven by a travelling wave.

PubMed

Feng, Peihua; Zhang, Jiazhong; Wang, Wei

2016-06-01

Nonlinear waves produced in an incompressible boundary layer driven by a travelling wave are investigated, with damping considered as well. As one of the typical nonlinear waves, the spike-like wave is governed by the driven-damped Benjamin-Ono equation. The wave field enters a completely irregular state beyond a critical time, increasing the amplitude of the driving wave continuously. On the other hand, the number of spikes of solitary waves increases through multiplication of the wave pattern. The wave energy grows in a sequence of sharp steps, and hysteresis loops are found in the system. The wave energy jumps to different levels with multiplication of the wave, which is described by winding number bifurcation of phase trajectories. Also, the phenomenon of multiplication and hysteresis steps is found when varying the speed of driving wave as well. Moreover, the nature of the change of wave pattern and its energy is the stability loss of the wave caused by saddle-node bifurcation.

Fast sweeping methods for hyperbolic systems of conservation laws at steady state II

NASA Astrophysics Data System (ADS)

Engquist, Björn; Froese, Brittany D.; Tsai, Yen-Hsi Richard

2015-04-01

The idea of using fast sweeping methods for solving stationary systems of conservation laws has previously been proposed for efficiently computing solutions with sharp shocks. We further develop these methods to allow for a more challenging class of problems including problems with sonic points, shocks originating in the interior of the domain, rarefaction waves, and two-dimensional systems. We show that fast sweeping methods can produce higher-order accuracy. Computational results validate the claims of accuracy, sharp shock curves, and optimal computational efficiency.

An Experimental Study into the Scaling of an Unswept-Sharp-Fin-Generated Shock/Turbulent Boundary Layer Interaction.

DTIC Science & Technology

1983-01-01

Influence Scaling of 2D and 3D Shock/Turbulent ioundary Layer Interactions at Compression Corners." AIM Paper 81-334, January 1981. 5. Kubota, H...generating 3D shock wave/boundary layer interactions 2 Unswept sharp fin interaction and coordinate system 3 Cobra probe measurements of Peake (4) at Mach 4...were made by two Druck 50 PSI transducers, each in- stalled in a computer-controlled 48-port Model 48J4 Scani- valve and referenced to vacuum. A 250

The Development of Drift Wave Turbulence in Magnetic Reconnection

NASA Astrophysics Data System (ADS)

McMurtrie, L.; Drake, J. F.; Swisdak, M. M.

2013-12-01

An important feature in collisionless magnetic reconnection is the development of sharp discontinuities along the separatrices bounding the Alfvenic outflow. The typical scale length of these features is ρs (the Larmor radius based on the sound speed) for guide field reconnection. Temperature gradients in the inflowing plasma (as might be found in the magnetopause) can lead to instabilities at these separatrices, specifically drift wave turbulence. We present standalone 2D and 3D PIC simulations of drift wave turbulence to investigate scaling properties and growth rates. Further investigations of the relative importance of drift wave turbulence in the development of reconnection will also be considered.

Functional optical probing of the hippocampal trisynaptic circuit in vitro: network dynamics, filter properties, and polysynaptic induction of CA1 LTP.

PubMed

Stepan, Jens; Dine, Julien; Eder, Matthias

2015-01-01

Decades of brain research have identified various parallel loops linking the hippocampus with neocortical areas, enabling the acquisition of spatial and episodic memories. Especially the hippocampal trisynaptic circuit [entorhinal cortex layer II → dentate gyrus (DG) → cornu ammonis (CA)-3 → CA1] was studied in great detail because of its seemingly simple connectivity and characteristic structures that are experimentally well accessible. While numerous researchers focused on functional aspects, obtained from a limited number of cells in distinct hippocampal subregions, little is known about the neuronal network dynamics which drive information across multiple synapses for subsequent long-term storage. Fast voltage-sensitive dye imaging in vitro allows real-time recording of activity patterns in large/meso-scale neuronal networks with high spatial resolution. In this way, we recently found that entorhinal theta-frequency input to the DG most effectively passes filter mechanisms of the trisynaptic circuit network, generating activity waves which propagate across the entire DG-CA axis. These "trisynaptic circuit waves" involve high-frequency firing of CA3 pyramidal neurons, leading to a rapid induction of classical NMDA receptor-dependent long-term potentiation (LTP) at CA3-CA1 synapses (CA1 LTP). CA1 LTP has been substantially evidenced to be essential for some forms of explicit learning in mammals. Here, we review data with particular reference to whole network-level approaches, illustrating how activity propagation can take place within the trisynaptic circuit to drive formation of CA1 LTP.

Isolated primary blast alters neuronal function with minimal cell death in organotypic hippocampal slice cultures.

PubMed

Effgen, Gwen B; Vogel, Edward W; Lynch, Kimberly A; Lobel, Ayelet; Hue, Christopher D; Meaney, David F; Bass, Cameron R Dale; Morrison, Barclay

2014-07-01

An increasing number of U.S. soldiers are diagnosed with traumatic brain injury (TBI) subsequent to exposure to blast. In the field, blast injury biomechanics are highly complex and multi-phasic. The pathobiology caused by exposure to some of these phases in isolation, such as penetrating or inertially driven injuries, has been investigated extensively. However, it is unclear whether the primary component of blast, a shock wave, is capable of causing pathology on its own. Previous in vivo studies in the rodent and pig have demonstrated that it is difficult to deliver a primary blast (i.e., shock wave only) without rapid head accelerations and potentially confounding effects of inertially driven TBI. We have previously developed a well-characterized shock tube and custom in vitro receiver for exposing organotypic hippocampal slice cultures to pure primary blast. In this study, isolated primary blast induced minimal hippocampal cell death (on average, below 14% in any region of interest), even for the most severe blasts tested (424 kPa peak pressure, 2.3 ms overpressure duration, and 248 kPa*ms impulse). In contrast, measures of neuronal function were significantly altered at much lower exposures (336 kPa, 0.84 ms, and 86.5 kPa*ms), indicating that functional changes occur at exposures below the threshold for cell death. This is the first study to investigate a tolerance for primary blast-induced brain cell death in response to a range of blast parameters and demonstrate functional deficits at subthreshold exposures for cell death.

Age Is Associated with Reduced Sharp-Wave Ripple Frequency and Altered Patterns of Neuronal Variability.

PubMed

Wiegand, Jean-Paul L; Gray, Daniel T; Schimanski, Lesley A; Lipa, Peter; Barnes, C A; Cowen, Stephen L

2016-05-18

Spatial and episodic memory performance declines with age, and the neural basis for this decline is not well understood. Sharp-wave ripples are brief (∼70 ms) high-frequency oscillatory events generated in the hippocampus and are associated with the consolidation of spatial memories. Given the connection between ripple oscillations and memory consolidation, we investigated whether the structure of ripple oscillations and ripple-triggered patterns of single-unit activity are altered in aged rats. Local field and single-unit activity surrounding sharp-wave ripple events were examined in the CA1 region of the hippocampus of old (n = 5) and young (n = 6) F344 rats during periods of rest preceding and following performance on a place-dependent eyeblink-conditioning task. Neural responses in aged rats differed from responses in young rats in several ways. First, compared with young rats, the rate of ripple occurrence (ripple density) is reduced in aged rats during postbehavior rest. Second, mean ripple frequency during prebehavior and postbehavior rest is lower in aged animals (aged: 132 Hz; young: 146 Hz). Third, single neurons in aged animals responded more consistently from ripple to ripple. Fourth, variability in interspike intervals was greater in aged rats. Finally, neurons were tuned to a narrower range of phases of the ripple oscillation relative to young animals. Together, these results suggest that the CA1 network in aged animals has a reduced "vocabulary" of available representational states. The hippocampus is a structure that is critical for the formation of episodic memories. Sharp-wave ripple events generated in the hippocampus have been implicated in memory consolidation processes critical to memory stabilization. We examine here whether these ripple oscillations are altered over the course of the life span, which could contribute to hippocampus-dependent memory deficits that occur during aging. This experiment used young and aged memory-impaired rats to examine age-related changes in ripple architecture, ripple-triggered spike variance, and spike-phase coherence. We found that there are, indeed, significant changes in characteristics of ripples in older animals that could impact consolidation processes and memory stabilization in the aged brain. Copyright © 2016 the authors 0270-6474/16/365650-11$15.00/0.

Generation of Caustics and Rogue Waves from Nonlinear Instability.

PubMed

Safari, Akbar; Fickler, Robert; Padgett, Miles J; Boyd, Robert W

2017-11-17

Caustics are phenomena in which nature concentrates the energy of waves and may exhibit rogue-type behavior. Although they are known mostly in optics, caustics are intrinsic to all wave phenomena. As we demonstrate in this Letter, the formation of caustics and consequently rogue events in linear systems requires strong phase fluctuations. We show that nonlinear phase shifts can generate sharp caustics from even small fluctuations. Moreover, in that the wave amplitude increases dramatically in caustics, nonlinearity is usually inevitable. We perform an experiment in an optical system with Kerr nonlinearity, simulate the results based on the nonlinear Schrödinger equation, and achieve perfect agreement. As the same theoretical framework is used to describe other wave systems such as large-scale water waves, our results may also aid the understanding of ocean phenomena.

Generation of Caustics and Rogue Waves from Nonlinear Instability

NASA Astrophysics Data System (ADS)

Safari, Akbar; Fickler, Robert; Padgett, Miles J.; Boyd, Robert W.

2017-11-01

Caustics are phenomena in which nature concentrates the energy of waves and may exhibit rogue-type behavior. Although they are known mostly in optics, caustics are intrinsic to all wave phenomena. As we demonstrate in this Letter, the formation of caustics and consequently rogue events in linear systems requires strong phase fluctuations. We show that nonlinear phase shifts can generate sharp caustics from even small fluctuations. Moreover, in that the wave amplitude increases dramatically in caustics, nonlinearity is usually inevitable. We perform an experiment in an optical system with Kerr nonlinearity, simulate the results based on the nonlinear Schrödinger equation, and achieve perfect agreement. As the same theoretical framework is used to describe other wave systems such as large-scale water waves, our results may also aid the understanding of ocean phenomena.

Effects of the Kelvin-Helmholtz surface instability on supersonic jets

NASA Technical Reports Server (NTRS)

Hardee, P. E.

1982-01-01

An exact numerical calculation is provided for of linear growth and phase velocity of Kelvin-Helmholtz unstable wave modes on a supersonic jet of cylindrical cross section. An expression for the maximally unstable wavenumber of each wave mode is found. Provided a sharp velocity discontinuity exists all wave modes are unstable. A combination of rapid jet expansion and velocity shear across a jet can effectively stabilize all wave modes. The more likely case of slow jet expansion and of velocity shear at the jet surface allows wave modes with maximally unstable wavelength longer than or on the order of the jet radius to grow. The relative energy in different wave modes and effect on the jet is investigated. Energy input into a jet resulting from surface instability is discussed.

Broadband high-frequency waves and intermittent energy conversion at dipolarization fronts

NASA Astrophysics Data System (ADS)

Yang, J.; Cao, J.; Fu, H.; Wang, T.; Liu, W.; Yao, Z., Sr.

2017-12-01

Dipolarization front (DF) is a sharp boundary most probably separating the reconnection jet from the background plasma sheet. So far at this boundary, the observed waves are mainly in low-frequency range (e.g., magnetosonic waves and lower hybrid waves). Few high-frequency waves are observed in this region. In this paper, we report the broadband high-frequency wave emissions at the DF. These waves, having frequencies extending from the electron cyclotron frequency fce, up to the electron plasma frequency fpe, could contribute 10% to the in situ measurement of intermittent energy conversion at the DF layer. Their generation may be attributed to electron beams, which are simultaneously observed at the DF as well. Furthermore, we find intermittent energy conversion is primarily to the broadband fluctuations in the lower hybrid frequency range although the net energy conversion is small.

Idealized numerical studies of gravity wave alteration in the tropopause region

NASA Astrophysics Data System (ADS)

Bense, Vera; Spichtinger, Peter

2017-04-01

When travelling through the tropopause region, characterised by strong gradients in static stability, wind shear and trace gases, the properties of gravity waves often change drastically. Within this work, the EULAG model (Prusa et al., 2008) is used to provide an idealized setup for sensitivity studies on these modifications. The characteristics of the tropopause are introduced by specifiying environmental profiles for Brunt-Väisälä frequency and horizontal wind speed, partly extracted from measurement and reanalysis data. Tropospheric and stratospheric wave spectra extracted for flows under varying tropopause sharpness are analysed, respectively. In particular, different regimes for transmission behaviour are classified for a series of Brunt-Väisälä frequency profiles showing a tropopause inversion layer (TIL, see e.g. Birner et al., 2002). Furthermore, this study focusses on the comparison of transmission coefficients deduced from numerical simulations with values derived from asymptotical analysis of the governing equations and investigates where the threshold of linear behaviour are for the respective setups, The wave generation is implemented in the model both through topography at the lower model domain and through the prescription of wave packets at initialization of the simulations. References: Prusa, J. M., P. K. Smolarkiewicz, P. K. and A. A. Wyszogrodzki, 2008: EULAG, a computational model for multiscale flows, Computers & Fluids 37, 1193-1207 Birner, T., A. Doernbrack, and U. Schumann, 2002: How sharp is the tropopause at midlatitudes?, Geophys. Res. Lett., 29, 1700, doi:10.1029/2002GL015142.

Boundary Layer Instabilities Generated by Freestream Laser Perturbations

NASA Technical Reports Server (NTRS)

Chou, Amanda; Schneider, Steven P.

2015-01-01

A controlled, laser-generated, freestream perturbation was created in the freestream of the Boeing/AFOSR Mach-6 Quiet Tunnel (BAM6QT). The freestream perturbation convected downstream in the Mach-6 wind tunnel to interact with a flared cone model. The geometry of the flared cone is a body of revolution bounded by a circular arc with a 3-meter radius. Fourteen PCB 132A31 pressure transducers were used to measure a wave packet generated in the cone boundary layer by the freestream perturbation. This wave packet grew large and became nonlinear before experiencing natural transition in quiet flow. Breakdown of this wave packet occurred when the amplitude of the pressure fluctuations was approximately 10% of the surface pressure for a nominally sharp nosetip. The initial amplitude of the second mode instability on the blunt flared cone is estimated to be on the order of 10 -6 times the freestream static pressure. The freestream laser-generated perturbation was positioned upstream of the model in three different configurations: on the centerline, offset from the centerline by 1.5 mm, and offset from the centerline by 3.0 mm. When the perturbation was offset from the centerline of a blunt flared cone, a larger wave packet was generated on the side toward which the perturbation was offset. The offset perturbation did not show as much of an effect on the wave packet on a sharp flared cone as it did on a blunt flared cone.

Revisiting the Rossby Haurwitz wave test case with contour advection

NASA Astrophysics Data System (ADS)

Smith, Robert K.; Dritschel, David G.

2006-09-01

This paper re-examines a basic test case used for spherical shallow-water numerical models, and underscores the need for accurate, high resolution models of atmospheric and ocean dynamics. The Rossby-Haurwitz test case, first proposed by Williamson et al. [D.L. Williamson, J.B. Drake, J.J. Hack, R. Jakob, P.N. Swarztrauber, A standard test set for numerical approximations to the shallow-water equations on the sphere, J. Comput. Phys. (1992) 221-224], has been examined using a wide variety of shallow-water models in previous papers. Here, two contour-advective semi-Lagrangian (CASL) models are considered, and results are compared with previous test results. We go further by modifying this test case in a simple way to initiate a rapid breakdown of the basic wave state. This breakdown is accompanied by the formation of sharp potential vorticity gradients (fronts), placing far greater demands on the numerics than the original test case does. We also go further by examining other dynamical fields besides the height and potential vorticity, to assess how well the models deal with gravity waves. Such waves are sensitive to the presence or not of sharp potential vorticity gradients, as well as to numerical parameter settings. In particular, large time steps (convenient for semi-Lagrangian schemes) can seriously affect gravity waves but can also have an adverse impact on the primary fields of height and velocity. These problems are exacerbated by a poor resolution of potential vorticity gradients.

Rogue waves in multiple-solitons-inelastic collisions — The complex Sharma-Tasso-Olver equation

NASA Astrophysics Data System (ADS)

Abdel-Gawad, H. I.; Tantawy, M.

2018-03-01

Very recently, a mechanism to the formation of rogue waves (RWs) has been proposed by the authors. In this paper, the formation of RWs in case of the complex Sharma-Tasso-Olver (STO) equation is studied. In the STO equation, one, two and three-soliton solutions are obtained. Due to the inelastic collisions, these soliton waves are fused to one. Under the free parameters constraint this behavior do occurs. The mechanism of formation of RWs is due to the collisions of solitons and multi-periodic waves (like spectral band). These RWs as giant waves, which may be very sharp or chaotic are similar to RWs in laser. The work is done here by using the generalized unified method (GUM).

3-D numerical simulations of earthquake ground motion in sedimentary basins: testing accuracy through stringent models

NASA Astrophysics Data System (ADS)

Chaljub, Emmanuel; Maufroy, Emeline; Moczo, Peter; Kristek, Jozef; Hollender, Fabrice; Bard, Pierre-Yves; Priolo, Enrico; Klin, Peter; de Martin, Florent; Zhang, Zhenguo; Zhang, Wei; Chen, Xiaofei

2015-04-01

Differences between 3-D numerical predictions of earthquake ground motion in the Mygdonian basin near Thessaloniki, Greece, led us to define four canonical stringent models derived from the complex realistic 3-D model of the Mygdonian basin. Sediments atop an elastic bedrock are modelled in the 1D-sharp and 1D-smooth models using three homogeneous layers and smooth velocity distribution, respectively. The 2D-sharp and 2D-smooth models are extensions of the 1-D models to an asymmetric sedimentary valley. In all cases, 3-D wavefields include strongly dispersive surface waves in the sediments. We compared simulations by the Fourier pseudo-spectral method (FPSM), the Legendre spectral-element method (SEM) and two formulations of the finite-difference method (FDM-S and FDM-C) up to 4 Hz. The accuracy of individual solutions and level of agreement between solutions vary with type of seismic waves and depend on the smoothness of the velocity model. The level of accuracy is high for the body waves in all solutions. However, it strongly depends on the discrete representation of the material interfaces (at which material parameters change discontinuously) for the surface waves in the sharp models. An improper discrete representation of the interfaces can cause inaccurate numerical modelling of surface waves. For all the numerical methods considered, except SEM with mesh of elements following the interfaces, a proper implementation of interfaces requires definition of an effective medium consistent with the interface boundary conditions. An orthorhombic effective medium is shown to significantly improve accuracy and preserve the computational efficiency of modelling. The conclusions drawn from the analysis of the results of the canonical cases greatly help to explain differences between numerical predictions of ground motion in realistic models of the Mygdonian basin. We recommend that any numerical method and code that is intended for numerical prediction of earthquake ground motion should be verified through stringent models that would make it possible to test the most important aspects of accuracy.

Electron plasma oscillations in the Venus foreshock

NASA Technical Reports Server (NTRS)

Crawford, G. K.; Strangeway, R. J.; Russell, C. T.

1990-01-01

Plasma waves are observed in the solar wind upstream of the Venus bow shock by the Pioneer Venus Orbiter. These wave signatures occur during periods when the interplanetary magnetic field through the spacecraft position intersects the bow shock, thereby placing the spacecraft in the foreshock region. The electron foreshock boundary is clearly evident in the data as a sharp onset in wave activity and a peak in intensity. Wave intensity is seen to drop rapidly with increasing penetration into the foreshock. The peak wave electric field strength at the electron foreshock boundary is found to be similar to terrestrial observations. A normalized wave spectrum was constructed using measurements of the electron plasma frequency and the spectrum was found to be centered about this value. These results, along with polarization studies showing the wave electric field to be field aligned, are consistent with the interpretation of the waves as electron plasma oscillations.

DNA Methylation Program in Developing Hippocampus and Its Alteration by Alcohol

PubMed Central

Chen, Yuanyuan; Ozturk, Nail Can; Zhou, Feng C.

2013-01-01

During hippocampal development, the Cornus Ammonis (CA) and the dentate gyrus (DG) undergo waves of neurogenesis and neuronal migration and maturation independently. This stage is widely known to be vulnerable to environmental stresses, but its underlying mechanism is unclear. Alcohol exposure has been shown to alter the expression of genes that regulate the fate, survival, migration and differentiation of pyramidal and granule cells. Undermining this process might compromise hippocampal development underlying the learning and memory deficits known in Fetal Alcohol Spectrum Disorders (FASD). We have previously demonstrated that DNA methylation was programmed along with neural tube development. Here, we demonstrated that DNA methylation program (DMP) proceeded along with hippocampal neuronal differentiation and maturation, and how this DMP was affected by fetal alcohol exposure. C57BL/6 mice were treated with 4% v/v ethanol through a liquid diet along with pair-fed and chow-fed controls from gestation day (E) 7 to E16. We found that a characteristic DMP, including 5-methylcytidine (5mC), 5-hydroxylmethylcytidine (5hmC) and their binding proteins, led the hippocampal neuronal differentiation and maturation spatiotemporally as indicated by their phenotypic marks in the CA and DG pre- and post-natally. Alcohol hindered the acquisition and progression of methylation marks, and altered the chromatin translocation of these marks in the nucleus, which was correlated with developmental retardation. PMID:23544149

Spatial Segregation and Interaction of Calcium Signalling Mechanisms in Rat Hippocampal CA1 Pyramidal Neurons

PubMed Central

Nakamura, Takeshi; Lasser-Ross, Nechama; Nakamura, Kyoko; Ross, William N

2002-01-01

Postsynaptic [Ca2+]i increases result from Ca2+ entry through ligand-gated channels, entry through voltage-gated channels, or release from intracellular stores. We found that these sources have distinct spatial distributions in hippocampal CA1 pyramidal neurons. Large amplitude regenerative release of Ca2+ from IP3-sensitive stores in the form of Ca2+ waves were found almost exclusively on the thick apical shaft. Smaller release events did not extend more than 15 μm into the oblique dendrites. These synaptically activated regenerative waves initiated at points where the stimulated oblique dendrites branch from the apical shaft. In contrast, NMDA receptor-mediated increases were observed predominantly in oblique dendrites where spines are found at high density. These [Ca2+]i increases were typically more than eight times larger than [Ca2+]i from this source on the main aspiny apical shaft. Ca2+ entry through voltage-gated channels, activated by backpropagating action potentials, was detected at all dendritic locations. These mechanisms were not independent. Ca2+ entry through NMDA receptor channels or voltage-gated channels (as previously demonstrated) synergistically enhanced Ca2+ release generated by mGluR mobilization of IP3. PMID:12205182

Disrupted hippocampal sharp‐wave ripple‐associated spike dynamics in a transgenic mouse model of dementia

PubMed Central

Witton, Jonathan; Staniaszek, Lydia E.; Bartsch, Ullrich; Randall, Andrew D.; Jones, Matthew W.

2015-01-01

Key points High frequency (100–250 Hz) neuronal oscillations in the hippocampus, known as sharp‐wave ripples (SWRs), synchronise the firing behaviour of groups of neurons and play a key role in memory consolidation.Learning and memory are severely compromised in dementias such as Alzheimer's disease; however, the effects of dementia‐related pathology on SWRs are unknown.The frequency and temporal structure of SWRs was disrupted in a transgenic mouse model of tauopathy (one of the major hallmarks of several dementias).Excitatory pyramidal neurons were more likely to fire action potentials in a phase‐locked manner during SWRs in the mouse model of tauopathy; conversely, inhibitory interneurons were less likely to fire phase‐locked spikes during SWRs.These findings indicate there is reduced inhibitory control of hippocampal network events and point to a novel mechanism which may underlie the cognitive impairments in this model of dementia. Abstract Neurons within the CA1 region of the hippocampus are co‐activated during high frequency (100–250 Hz) sharp‐wave ripple (SWR) activity in a manner that probably drives synaptic plasticity and promotes memory consolidation. In this study we have used a transgenic mouse model of dementia (rTg4510 mice), which overexpresses a mutant form of tau protein, to examine the effects of tauopathy on hippocampal SWRs and associated neuronal firing. Tetrodes were used to record simultaneous extracellular action potentials and local field potentials from the dorsal CA1 pyramidal cell layer of 7‐ to 8‐month‐old wild‐type and rTg4510 mice at rest in their home cage. At this age point these mice exhibit neurofibrillary tangles, neurodegeneration and cognitive deficits. Epochs of sleep or quiet restfulness were characterised by minimal locomotor activity and a low theta/delta ratio in the local field potential power spectrum. SWRs detected off‐line were significantly lower in amplitude and had an altered temporal structure in rTg4510 mice. Nevertheless, the average frequency profile and duration of the SWRs were relatively unaltered. Putative interneurons displayed significantly less temporal and phase locking to SWRs in rTg4510 mice, whilst putative pyramidal neurons showed increased temporal and phase locking to SWRs. These findings indicate there is reduced inhibitory control of hippocampal network events and point to a novel mechanism which may contribute to impairments in memory consolidation in this model of dementia. PMID:25480798

Conformal mapping for the Helmholtz equation: acoustic wave scattering by a two dimensional inclusion with irregular shape in an ideal fluid.

PubMed

Liu, Gang; Jayathilake, Pahala G; Khoo, Boo Cheong; Han, Feng; Liu, Dian Kui

2012-02-01

The complex variables method with mapping function was extended to solve the linear acoustic wave scattering by an inclusion with sharp/smooth corners in an infinite ideal fluid domain. The improved solutions of Helmholtz equation, shown as Bessel function with mapping function as the argument and fractional order Bessel function, were analytically obtained. Based on the mapping function, the initial geometry as well as the original physical vector can be transformed into the corresponding expressions inside the mapping plane. As all the physical vectors are calculated in the mapping plane (η,η), this method can lead to potential vast savings of computational resources and memory. In this work, the results are validated against several published works in the literature. The different geometries of the inclusion with sharp corners based on the proposed mapping functions for irregular polygons are studied and discussed. The findings show that the variation of angles and frequencies of the incident waves have significant influence on the bistatic scattering pattern and the far-field form factor for the pressure in the fluid. © 2012 Acoustical Society of America

Transformation of Waves Across the Surf Zone.

DTIC Science & Technology

1981-03-01

Kuo is more realis- tic but still results in a sharp cut-off of the distribution at the breaking heights. 5. Goda Distribution Goda (1975) derived a...J.I., "Probabilities of Breaking Wave Characteris- tics ," Proc. 12th Coastal Engineering Conf., pp. 399- 412, 1970. Chakrabarty, S.K. and R.P. Cooley...Spring, MD 20910 21. Director 2 Instituto Oceanografico de la Armada Guayaquil, Ecuador 22. Director de Educacion de la Armada Comandancia General de

Azimuthal hotwire measurements in a transitional boundary layer on a flared cone in a Mach 6 quiet wind tunnel

NASA Astrophysics Data System (ADS)

Hofferth, Jerrod; Saric, William

2012-11-01

Hotwire measurements of second-mode instability waves and the early stages of nonlinear interaction are conducted on a sharp-tipped, 5°-half-angle flared cone at zero angle of attack in a low-disturbance Mach 6 wind tunnel at Re = 10 ×106 m-1. Profiles of mean and fluctuating mass flux are acquired at several axial stations along the cone with a bandwidth of over 300 kHz. Frequencies and relative amplitude growth of second-mode instability waves are characterized and compared with nonlinear parabolized stability (NPSE) computations. Additionally, an azimuthal probe-traversing mechanism is used to investigate the character of the nonlinear stages of transition occurring near the base of the cone. Recent Direct Numerical Simulations (DNS) of a sharp cone at Mach 6 have shown that a fundamental resonance (or Klebanoff-type) breakdown mechanism can arise in the late stages of transition, wherein a pair of oblique waves nonlinearly interacts with the dominant two-dimensional wave to create an azimuthal modulation in the form of Λ-vortex structures and streamwise streaks. The azimuthal measurements will identify periodicity qualitatively consistent with these computations and with ``hot streaks'' observed in temperature sensitive paints at Purdue. AFOSR/NASA National Center for Hypersonic Laminar-Turbulent Transition Research, Grant FA9550-09-1-0341.

New Learning of Music after Bilateral Medial Temporal Lobe Damage: Evidence from an Amnesic Patient

PubMed Central

Valtonen, Jussi; Gregory, Emma; Landau, Barbara; McCloskey, Michael

2014-01-01

Damage to the hippocampus impairs the ability to acquire new declarative memories, but not the ability to learn simple motor tasks. An unresolved question is whether hippocampal damage affects learning for music performance, which requires motor processes, but in a cognitively complex context. We studied learning of novel musical pieces by sight-reading in a newly identified amnesic, LSJ, who was a skilled amateur violist prior to contracting herpes simplex encephalitis. LSJ has suffered virtually complete destruction of the hippocampus bilaterally, as well as extensive damage to other medial temporal lobe structures and the left anterior temporal lobe. Because of LSJ’s rare combination of musical training and near-complete hippocampal destruction, her case provides a unique opportunity to investigate the role of the hippocampus for complex motor learning processes specifically related to music performance. Three novel pieces of viola music were composed and closely matched for factors contributing to a piece’s musical complexity. LSJ practiced playing two of the pieces, one in each of the two sessions during the same day. Relative to a third unpracticed control piece, LSJ showed significant pre- to post-training improvement for the two practiced pieces. Learning effects were observed both with detailed analyses of correctly played notes, and with subjective whole-piece performance evaluations by string instrument players. The learning effects were evident immediately after practice and 14 days later. The observed learning stands in sharp contrast to LSJ’s complete lack of awareness that the same pieces were being presented repeatedly, and to the profound impairments she exhibits in other learning tasks. Although learning in simple motor tasks has been previously observed in amnesic patients, our results demonstrate that non-hippocampal structures can support complex learning of novel musical sequences for music performance. PMID:25232312

Gravity Wave Interactions with Fine Structures in the Mesosphere and Lower Thermosphere

NASA Astrophysics Data System (ADS)

Mixa, Tyler; Fritts, David; Bossert, Katrina; Laughman, Brian; Wang, Ling; Lund, Thomas; Kantha, Lakshmi

2017-04-01

An anelastic numerical model is used to probe the influences of fine layering structures on gravity wave propagation in the Mesosphere and Lower Thermosphere (MLT). Recent lidar observations confirm the presence of persistent layered structures in the MLT that have sharp stratification and vertical scales below 1km. Gravity waves propagating through finely layered environments can excite and modulate the evolution of small scale instabilities that redefine the layering structure in these regions. Such layers in turn filter the outgoing wave spectra, promote ducting or reflection, hasten the onset of self-acceleration dynamics, and encourage wave/mean-flow interactions via energy and momentum transport. Using high resolution simulations of a localized gravity wave packet in a deep atmosphere, we identify the relative impacts of various wave and mean flow parameters to improve our understanding of these dynamics and complement recent state-of-the-art observations.

Constraints on seismic anisotropy beneath the Appalachian Mountains from Love-to-Rayleigh wave scattering

NASA Astrophysics Data System (ADS)

Servali, A.; Long, M. D.; Benoit, M.

2017-12-01

The eastern margin of North America has been affected by a series of mountain building and rifting events that have likely shaped the deep structure of the lithosphere. Observations of seismic anisotropy can provide insight into lithospheric deformation associated with these past tectonic events, as well as into present-day patterns of mantle flow beneath the passive margin. Previous work on SKS splitting beneath eastern North America has revealed fast splitting directions parallel to the strike of the Appalachian orogen in the central and southern Appalachians. A major challenge to the interpretation of SKS splitting measurements, however, is the lack of vertical resolution; isolating anisotropic structures at different depths is therefore difficult. Complementary constraints on the depth distribution of anisotropy can be provided by surface waves. In this study, we analyze the scattering of Love wave energy to Rayleigh waves, which is generated via sharp lateral gradients in anisotropic structure along the ray path. The scattered phases, known as quasi-Love (QL) waves, exhibit amplitude behavior that depend on the strength of the anisotropic contrast as well as the angle between the propagation azimuth and the anisotropic symmetry axis. We analyze data collected by the dense MAGIC seismic array across the central Appalachians. We examine teleseismic earthquakes of magnitude 6.7 and greater over a range of backazimuths, and isolate surface waves at periods between 100 and 500 seconds. We compare the data to synthetic seismograms generated by the Princeton Global ShakeMovie initiative to identify anomalous QL arrivals. We find evidence significant QL arrivals at MAGIC stations, with amplitudes depending on propagation azimuth and station location. Preliminary results are consistent with a sharp lateral gradient in seismic anisotropy across the Appalachian Mountains in the depth range between 100-200 km.

The Role of Sleep in Changing Our Minds: A Psychologist's Discussion of Papers on Memory Reactivation and Consolidation in Sleep

ERIC Educational Resources Information Center

Cartwright, Rosalind D.

2004-01-01

The group of papers on memory reactivation and consolidation during sleep included in this volume represents cutting edge work in both animals and humans. They support that the two types of sleep serve different necessary functions. The role of slow wave sleep (SWS) is reactivation of the hippocampal-neocortical circuits activated during a waking…

Wave activity in the neighborhood of the bowshock of Mars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sagdeev, R.Z.; Shapiro, V.D.; Shevchenko, V.I.

Plasma wave activity in the neighborhood of the Martial bow shock were measured for the first time by the Soviet spacecraft Phobos-2 in a wide frequency range from dc to 150 kHz. The wave activity varied in character as the spacecraft moved across different plasma regions: in the neighborhood of the Martian bow shock, inside the magnetosheath and in the tail region. In this paper the authors provide suggestions for the processes responsible for these plasma waves. The most interesting peculiarities of the wave activity around Mars is the sharp increase of wave intensity in the magnetosheath region. This increasemore » is attributed to two different physical mechanisms. High frequency waves are excited at the shock front due to currents flowing along the front; these ion acoustic waves are convected inside by the solar wind. The low frequency waves ({approximately}100 Hz) close to the inside boundary were, they believe, generated by heavy Martian ions diffusing through the planetopause into the magnetosheath.« less

New mechanism of surface polariton resonance at an isolated interface between transparent dielectric media (non-Tamm quasistationary surface polariton states)

NASA Astrophysics Data System (ADS)

Tarasenko, S. V.; Shavrov, V. G.

2017-07-01

A pseudochiral mechanism of the formation of non-Tamm quasistationary surface polariton states, as well as surface polariton waves inside the light cone, has been proposed for an isolated interface between spatially uniform transparent dielectric media. The resonance excitation of these states by a quasimonochromatic plane wave incident from vacuum results in a sharp change in the group delay time of the reflected pulse. The effect is enhanced in the presence of an electromagnetic metasurface.

Animation Sequence of Comet Wild2 Once More Demonstrates Shape Peculiarities of Small Celestial Bodies

NASA Astrophysics Data System (ADS)

Kochemasov, G. G.

The outstanding success of the Stardust mission having acquired in January 2004 images of Comet Wild2 allows us to compare them with images of some other small objects: satellites, asteroids, comets and confirm the earlier conclusion about prevailing shaping forces [1, 2]. The excellent images of the Comet Wild2 core (the best up to date among comets, Internet) show that it is not ``a ball of dirty ice and rock'' but rather a convexo-concave object resembling other small bodies. They all, independently of their nature, sizes, compositions, demonstrate oblong ``banana''-type style. This is a result of pressing in one side and bulging out another antipodean one (the fundamental wave action). Comet Wild2 (5.4 km long core) in this sense can be perfectly compared with asteroid Mathilde (60 km) and satellite Thebe (˜ 116 km). All three have deeply concave hemisphere opposed by clearly convex one. Bulging out friable material often induces deep fracturing of convex hemispheres. This is well visible in comet Borrelli (8 km long core) and especially pronounced in asteroids Eros (33 km) and Annefrank (`˜ 6 km). Deep ``saddle'' at the convex side of both makes their images rather similar. Another characteristic of small oblong bodies is a principal shape difference of two elongated ends: one is blunt, another sharp. Principally, it is the same process which makes the ``banana''-shape (wave1) but of a smaller scale (wave2). The blunt end is made by pressing in, the sharp end by bulging out. Obviously, an impact sculpturing cannot give similar complex forms in so different bodies. The main principal shaping is done by standing inertia-gravity waves arising in celestial bodies in response to their movement in elliptical orbits with periodically changing accelerations. The fundamental wave1 makes convexo-concave shape, the first overtone wave2 sharp-blunt ends. Larger celestial bodies: satellites, planets, stars react to these waves by universal tectonic dichotomy and sectoring [3]. The arctic-antarctic symptom (after Earth) is typical manifestation of sectoring with two antepodean sectors: one pressed in, another bulged out. References: [1] Kochemasov G.G. (1999) On convexo-concave shape of small celestial bodies // ``Asteroids, Comets, Meteors'' conference, Cornell Univ., U.S.A., July 1999, Abstract # 24. 22; [2] Kochemasov G.G. (2002) ``Dirty snowball'' -- now is too primitive for a scientific description of comets // 34th COSPAR Scientific Assembly at the World Space Congress 2002, 10-19 Oct. 2002, Houston, Texas, USA, (CD-ROM); [3] Kochemasov G.G. (1999) Theorems of wave planetary tectonics // Geophys. Res. Abstr., Vol. 1, # 3, 700.

Development of wireless, chipless neural stimulator by using one-port surface acoustic wave delay line and diode-capacitor interface

NASA Astrophysics Data System (ADS)

Kim, Jisung; Kim, Saehan; Lee, Keekeun

2017-06-01

For the first time, a wireless and chipless neuron stimulator was developed by utilizing a surface acoustic wave (SAW) delay line, a diode-capacitor interface, a sharp metal tip, and antennas for the stimulation of neurons in the brain. The SAW delay line supersedes presently existing complex wireless transmission systems composed of a few thousands of transistors, enabling the fabrication of wireless and chipless transceiver systems. The diode-capacitor interface was used to convert AC signals to DC signals and induce stimulus pulses at a sharp metal probe. A 400 MHz RF energy was wirelessly radiated from antennas and then stimulation pulses were observed at a sharp gold probe. A ˜5 m reading distance was obtained using a 1 mW power from a network analyzer. The cycles of electromagnetic (EM) radiation from an antenna were controlled by shielding the antenna with an EM absorber. Stimulation pulses with different amplitudes and durations were successfully observed at the probe. The obtained pulses were ˜0.08 mV in amplitude and 3-10 Hz in frequency. Coupling-of-mode (COM) and SPICE modeling simulations were also used to determine the optimal structural parameters for SAW delay line and the values of passive elements. On the basis of the extracted parameters, the entire system was experimentally implemented and characterized.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rosenau, Philip

A wide variety of propagating disturbances in physical systems are described by equations whose solutions lack a sharp propagating front. We demonstrate that presence of particular nonlinearities may induce such fronts. To exemplify this idea, we study both dissipative u{sub t}+{partial_derivative}{sub x}f(u)=u{sub xx} and dispersive u{sub t}+{partial_derivative}{sub x}f(u)+u{sub xxx}=0 patterns, and show that a weakly singular convection f(u)=-u{sup {alpha}}+u{sup m}, 0<{alpha}<1

Nonlinear waves in subwavelength waveguide arrays: evanescent bands and the "phoenix soliton".

PubMed

Peleg, Or; Segev, Mordechai; Bartal, Guy; Christodoulides, Demetrios N; Moiseyev, Nimrod

2009-04-24

We formulate wave propagation in arrays of subwavelength waveguides with sharp index contrasts and demonstrate the collapse of bands into evanescent modes and lattice solitons with superluminal phase velocity. We find a self-reviving soliton ("phoenix soliton") comprised of coupled forward- and backward-propagating light, originating solely from evanescent bands. In the linear regime, all Bloch waves comprising this beam decay, whereas a proper nonlinearity assembles them into a propagating self-trapped beam. Finally, we simulate the dynamics of such a beam and observe breakup into temporal pulses, indicating a new kind of slow-light gap solitons, trapped in time and in one transverse dimension.

ULF/ELF Waves in Near-Moon Space

NASA Astrophysics Data System (ADS)

Nakagawa, Tomoko

2016-02-01

The reflection of the solar wind protons is equivalent to a beam injection against the solar wind flow. It is expected to produce a ring beam with a 3D distribution function in many cases. The reflected protons are responsible for the generation of ultra-low-frequency (ULF) waves at ˜0.01 Hz and narrowband waves at ˜1 Hz in the extremely low frequency (ELF) range through resonant interaction with magnetohydrodynamic waves and whistler mode waves in the solar wind, respectively. This chapter discusses these commonly observed waves in the near-Moon space. The sinusoidal waveforms and sharp spectra of the monochromatic ELF waves are impressive, but commonly observed are non-monochromatic waves in the ELF range ˜0.03-10 Hz. Some of the solar wind protons reflected by the dayside lunar surface or crustal magnetic field gyrate around the solar wind magnetic field and can access the center of the wake owing to the large Larmour radius.

Terahertz-wave near-field imaging with subwavelength resolution using surface-wave-assisted bow-tie aperture

NASA Astrophysics Data System (ADS)

Ishihara, Kunihiko; Ohashi, Keishi; Ikari, Tomofumi; Minamide, Hiroaki; Yokoyama, Hiroyuki; Shikata, Jun-ichi; Ito, Hiromasa

2006-11-01

We demonstrate the terahertz-wave near-field imaging with subwavelength resolution using a bow-tie shaped aperture surrounded by concentric periodic structures in a metal film. A subwavelength aperture with concentric periodic grooves, which are known as a bull's eye structure, shows extremely large enhanced transmission beyond the diffraction limit caused by the resonant excitation of surface waves. Additionally, a bow-tie aperture exhibits extraordinary field enhancement at the sharp tips of the metal, which enhances the transmission and the subwavelength spatial resolution. We introduced a bow-tie aperture to the bull's eye structure and achieved high spatial resolution (˜λ/17) in the near-field region. The terahertz-wave near-field image of the subwavelength metal pattern (pattern width=20μm) was obtained for the wavelength of 207μm.

Surface wave tomography of Europe from ambient seismic noise

NASA Astrophysics Data System (ADS)

Lu, Yang; Stehly, Laurent; Paul, Anne

2017-04-01

We present a European scale high-resolution 3-D shear wave velocity model derived from ambient seismic noise tomography. In this study, we collect 4 years of continuous seismic recordings from 1293 stations across much of the European region (10˚W-35˚E, 30˚N-75˚N), which yields more than 0.8 million virtual station pairs. This data set compiles records from 67 seismic networks, both permanent and temporary from the EIDA (European Integrated Data Archive). Rayleigh wave group velocity are measured at each station pair using the multiple-filter analysis technique. Group velocity maps are estimated through a linearized tomographic inversion algorithm at period from 5s to 100s. Adaptive parameterization is used to accommodate heterogeneity in data coverage. We then apply a two-step data-driven inversion method to obtain the shear wave velocity model. The two steps refer to a Monte Carlo inversion to build the starting model, followed by a linearized inversion for further improvement. Finally, Moho depth (and its uncertainty) are determined over most of our study region by identifying and analysing sharp velocity discontinuities (and sharpness). The resulting velocity model shows good agreement with main geological features and previous geophyical studies. Moho depth coincides well with that obtained from active seismic experiments. A focus on the Greater Alpine region (covered by the AlpArray seismic network) displays a clear crustal thinning that follows the arcuate shape of the Alps from the southern French Massif Central to southern Germany.

Self-Calibrating Wave-Encoded Variable-Density Single-Shot Fast Spin Echo Imaging.

PubMed

Chen, Feiyu; Taviani, Valentina; Tamir, Jonathan I; Cheng, Joseph Y; Zhang, Tao; Song, Qiong; Hargreaves, Brian A; Pauly, John M; Vasanawala, Shreyas S

2018-04-01

It is highly desirable in clinical abdominal MR scans to accelerate single-shot fast spin echo (SSFSE) imaging and reduce blurring due to T 2 decay and partial-Fourier acquisition. To develop and investigate the clinical feasibility of wave-encoded variable-density SSFSE imaging for improved image quality and scan time reduction. Prospective controlled clinical trial. With Institutional Review Board approval and informed consent, the proposed method was assessed on 20 consecutive adult patients (10 male, 10 female, range, 24-84 years). A wave-encoded variable-density SSFSE sequence was developed for clinical 3.0T abdominal scans to enable high acceleration (3.5×) with full-Fourier acquisitions by: 1) introducing wave encoding with self-refocusing gradient waveforms to improve acquisition efficiency; 2) developing self-calibrated estimation of wave-encoding point-spread function and coil sensitivity to improve motion robustness; and 3) incorporating a parallel imaging and compressed sensing reconstruction to reconstruct highly accelerated datasets. Image quality was compared pairwise with standard Cartesian acquisition independently and blindly by two radiologists on a scale from -2 to 2 for noise, contrast, confidence, sharpness, and artifacts. The average ratio of scan time between these two approaches was also compared. A Wilcoxon signed-rank tests with a P value under 0.05 considered statistically significant. Wave-encoded variable-density SSFSE significantly reduced the perceived noise level and improved the sharpness of the abdominal wall and the kidneys compared with standard acquisition (mean scores 0.8, 1.2, and 0.8, respectively, P < 0.003). No significant difference was observed in relation to other features (P = 0.11). An average of 21% decrease in scan time was achieved using the proposed method. Wave-encoded variable-density sampling SSFSE achieves improved image quality with clinically relevant echo time and reduced scan time, thus providing a fast and robust approach for clinical SSFSE imaging. 1 Technical Efficacy: Stage 6 J. Magn. Reson. Imaging 2018;47:954-966. © 2017 International Society for Magnetic Resonance in Medicine.

Voltage-clamp analysis of the potentiation of the slow Ca2+-activated K+ current in hippocampal pyramidal neurons.

PubMed

Borde, M; Bonansco, C; Fernández de Sevilla, D; Le Ray, D; Buño, W

2000-01-01

Exploring the principles that govern activity-dependent changes in excitability is an essential step to understand the function of the nervous system, because they act as a general postsynaptic control mechanism that modulates the flow of synaptic signals. We show an activity-dependent potentiation of the slow Ca2+-activated K+ current (sl(AHP)) which induces sustained decreases in the excitability in CA1 pyramidal neurons. We analyzed the sl(AHP) using the slice technique and voltage-clamp recordings with sharp or patch-electrodes. Using sharp electrodes-repeated activation with depolarizing pulses evoked a prolonged (8-min) potentiation of the amplitude (171%) and duration (208%) of the sl(AHP). Using patch electrodes, early after entering the whole-cell configuration (<20 min), responses were as those reported above. However, although the sl(AHP) remained unchanged, its potentiation was markedly reduced in later recordings, suggesting that the underlying mechanisms were rapidly eliminated by intracellular dialysis. Inhibition of L-type Ca2+ current by nifedipine (20 microM) markedly reduced the sl(AHP) (79%) and its potentiation (55%). Ryanodine (20 microM) that blocks the release of intracellular Ca2+ also reduced sl(AHP) (29%) and its potentiation (25%). The potentiation of the sl(AHP) induced a marked and prolonged (>50%; approximately equals 8 min) decrease in excitability. The results suggest that sl(AHP) is potentiated as a result of an increased intracellular Ca2+ concentration ([Ca2+]i) following activation of voltage-gated L-type Ca2+ channels, aided by the subsequent release of Ca2+ from intracellular stores. Another possibility is that repeated activation increases the Ca2+-binding capacity of the channels mediating the sl(AHP). This potentiation of the sl(AHP) could be relevant in hippocampal physiology, because the changes in excitability it causes may regulate the induction threshold of the long-term potentiation of synaptic efficacy. Moreover, the potentiation would act as a protective mechanism by reducing excitability and preventing the accumulation of intracellular Ca2+ to toxic levels when intense synaptic activation occurs.

The Properties of Lion Roars and Electron Dynamics in Mirror Mode Waves Observed by the Magnetospheric MultiScale Mission

NASA Astrophysics Data System (ADS)

Breuillard, H.; Le Contel, O.; Chust, T.; Berthomier, M.; Retino, A.; Turner, D. L.; Nakamura, R.; Baumjohann, W.; Cozzani, G.; Catapano, F.; Alexandrova, A.; Mirioni, L.; Graham, D. B.; Argall, M. R.; Fischer, D.; Wilder, F. D.; Gershman, D. J.; Varsani, A.; Lindqvist, P.-A.; Khotyaintsev, Yu. V.; Marklund, G.; Ergun, R. E.; Goodrich, K. A.; Ahmadi, N.; Burch, J. L.; Torbert, R. B.; Needell, G.; Chutter, M.; Rau, D.; Dors, I.; Russell, C. T.; Magnes, W.; Strangeway, R. J.; Bromund, K. R.; Wei, H.; Plaschke, F.; Anderson, B. J.; Le, G.; Moore, T. E.; Giles, B. L.; Paterson, W. R.; Pollock, C. J.; Dorelli, J. C.; Avanov, L. A.; Saito, Y.; Lavraud, B.; Fuselier, S. A.; Mauk, B. H.; Cohen, I. J.; Fennell, J. F.

2018-01-01

Mirror mode waves are ubiquitous in the Earth's magnetosheath, in particular behind the quasi-perpendicular shock. Embedded in these nonlinear structures, intense lion roars are often observed. Lion roars are characterized by whistler wave packets at a frequency ˜100 Hz, which are thought to be generated in the magnetic field minima. In this study, we make use of the high time resolution instruments on board the Magnetospheric MultiScale mission to investigate these waves and the associated electron dynamics in the quasi-perpendicular magnetosheath on 22 January 2016. We show that despite a core electron parallel anisotropy, lion roars can be generated locally in the range 0.05-0.2fce by the perpendicular anisotropy of electrons in a particular energy range. We also show that intense lion roars can be observed up to higher frequencies due to the sharp nonlinear peaks of the signal, which appear as sharp spikes in the dynamic spectra. As a result, a high sampling rate is needed to estimate correctly their amplitude, and the latter might have been underestimated in previous studies using lower time resolution instruments. We also present for the first-time 3-D high time resolution electron velocity distribution functions in mirror modes. We demonstrate that the dynamics of electrons trapped in the mirror mode structures are consistent with the Kivelson and Southwood (1996) model. However, these electrons can also interact with the embedded lion roars: first signatures of electron quasi-linear pitch angle diffusion and possible signatures of nonlinear interaction with high-amplitude wave packets are presented. These processes can lead to electron untrapping from mirror modes.

The P-wave boundary of the Large-Low Shear Velocity Province beneath the Pacific

NASA Astrophysics Data System (ADS)

Frost, Daniel A.; Rost, Sebastian

2014-10-01

The Large Low Shear Velocity Provinces (LLSVPs) in the lower mantle represent volumetrically significant thermal or chemical or thermo-chemical heterogeneities. Their structure and boundaries have been widely studied, mainly using S-waves, but much less is known about their signature in the P-wavefield. We use an extensive dataset recorded at USArray to create, for the first time, a high-resolution map of the location, shape, sharpness, and extent of the boundary of the Pacific LLSVP using P (Pdiff)-waves. We find that the northern edge of the Pacific LLSVP is shallow dipping (26° relative to the horizontal) and diffuse (∼120 km wide transition zone) whereas the eastern edge is steeper dipping (70°) and apparently sharp (∼40 km wide). We trace the LLSVP boundary up to ∼500 km above the CMB in most areas, and 700 km between 120° and 90°W at the eastern extent of the boundary. Apparent P-wave velocity drops are ∼1-3% relative to PREM, indicating a strong influence of LLSVPs on P-wave velocity, at least in the high-frequency wavefield, in contrast to previous studies. A localised patch with a greater velocity drop of ∼15-25% is detected, defined by large magnitude gradients of the travel-time residuals. We identify this as a likely location of an Ultra-Low Velocity Zone (ULVZ), matching the location of a previously detected ULVZ in this area. The boundary of a separate low velocity anomaly, of a similar height to the LLSVP, is detected in the north-west Pacific, matching tomographic images. This outlier appears to be connected to the main LLSVP through a narrow channel close to the CMB and may be in the process of joining or splitting from the main LLSVP. We also see strong velocity increases in the lower mantle to the east of the LLSVP, likely detecting subducted material beneath central America. The LLSVP P-wave boundary is similar to that determined in high-resolution S-wave studies and follows the -0.4% ΔVS iso-velocity contour in the S40RTS tomography model. Additionally, the LLSVP boundary roughly matches the shape of the -0.4% ΔVP iso-velocity contour of the P-wave model GyPSuM but defines an area more similar to that defined by the 0.0% VP iso-velocity contour. High resolution P-wave velocity determination allows for estimation of the ratio of P- and S-wave velocity anomalies (RS,P) which can be used to indicate dominantly thermal or chemical control of seismic velocities. Although the RS,P is found here to be approximately 2.4, which is indicative of a thermo-chemical anomaly. However, this result contains a large amount of uncertainty and the implications for the origin of LLSVPs likely remain inconclusive. Nonetheless, other observations of the Pacific LLSVP are consistent with a thermo-chemical anomaly whose shape and boundary sharpness are controlled by proximity to active and past subduction.

Bradycardia from flash stimulation.

PubMed

Einspenner, Michael; Brunet, Donald G; Boissé Lomax, Lysa; Spiller, Allison E

2015-12-01

This case study documents a patient who experienced bradycardia brought on by flash stimulation during a routine outpatient EEG recording. The patient had known photosensitive seizures in the past. During this routine EEG, the patient's heart rate dropped to about 12 beats per minute with the EEG displaying slow-delta-frequency waves with no epileptiform spikes or sharp waves. During immediate follow-up, in our emergency department, the patient had a brief asystolic event, followed by bradycardia. Cardiology examinations were normal. We propose that this response was a photic-triggered reflex vasovagal reaction.

Skin friction measurements by laser interferometry in swept shock wave/turbulent boundary-layer interactions

NASA Technical Reports Server (NTRS)

Kim, Kwang-Soo; Settles, Gary S.

1988-01-01

The laser interferometric skin friction meter was used to measure wall shear stress distributions in two interactions of fin-generated swept shock waves with turbulent boundary layers. The basic research configuration was an unswept sharp-leading-edge fin of variable angle mounted on a flatplate. The results indicate that such measurements are practical in high-speed interacting flows, and that a repeatability of + or - 6 percent or better is possible. Marked increases in wall shear were observed in both swept interactions tested.

Spontaneous Wave Generation from Submesoscale Fronts and Filaments

NASA Astrophysics Data System (ADS)

Shakespeare, C. J.; Hogg, A.

2016-02-01

Submesoscale features such as eddies, fronts, jets and filaments can be significant sources of spontaneous wave generation at the ocean surface. Unlike near-inertial waves forced by winds, these spontaneous waves are typically of higher frequency and can propagate through the thermocline, whereupon they break and drive mixing in the ocean interior. Here we investigate the spontaneous generation, propagation and subsequent breaking of these waves using a combination of theory and submesoscale resolving numerical models. The mechanism of generation is nearly identical to that of lee waves where flow is deflected over a rigid obstacle on the sea floor. Here, very sharp fronts and filaments of order 100m width moving in the submesoscale surface flow generate "surface lee waves" by presenting an obstacle to the surrounding stratified fluid. Using our numerical model we quantify the net downward wave energy flux from the surface, and where it is dissipated in the water column. Our results suggest an alternative to the classical paradigm where the energy associated with mixing in the ocean interior is sourced from bottom-generated lee waves.

Solar flare induced D-region ionospheric perturbations evaluated from VLF measurements

NASA Astrophysics Data System (ADS)

Singh, Ashutosh K.; Singh, A. K.; Singh, Rajesh; Singh, R. P.

2014-03-01

The results of very low frequency (VLF) wave amplitude measurements carried out at the low latitude station Varanasi (geom. lat. 14∘55'N, long. 154∘E), India during solar flares are presented for the first time. The VLF waves (19.8 kHz) transmitted from the NWC-transmitter, Australia propagated in the Earth-ionosphere waveguide to long distances and were recorded at Varanasi. Data are analyzed and the reflection height H' and the sharpness factor β are evaluated. It is found that the reflection height decreases whereas sharpness factor increases with the increase of solar flare power. The H' is found to be higher and β smaller at low latitudes than the corresponding values at mid and high latitudes. The sunspot numbers were low during the considered period 2011-2012, being the rising phase of solar cycle 24 and as a result cosmic rays may impact the D-region ionosphere. The increased ionization from the flare lowers the effective reflecting height, H', of the D-region roughly in proportion to the logarithm of the X-ray flare intensity from a typical mid-day unperturbed value of about 71-72 km down to about 65 km for an X class flare. The sharpness ( β) of the lower edge of the D-region is also significantly increased by the flare but reaches a clear saturation value of about 0.48 km-1 for flares of magnitude greater than about X1 class.

Subwavelength wave manipulation in a thin surface-wave bandgap crystal.

PubMed

Gao, Zhen; Wang, Zhuoyuan; Zhang, Baile

2018-01-01

It has been recently reported that the unit cell of wire media metamaterials can be tailored locally to shape the flow of electromagnetic waves at deep-subwavelength scales [Nat. Phys.9, 55 (2013)NPAHAX1745-247310.1038/nphys2480]. However, such bulk structures have a thickness of at least the order of wavelength, thus hindering their applications in the on-chip compact plasmonic integrated circuits. Here, based upon a Sievenpiper "mushroom" array [IEEE Trans. Microwave Theory Tech.47, 2059 (1999)IETMAB0018-948010.1109/22.798001], which is compatible with standard printed circuit board technology, we propose and experimentally demonstrate the subwavelength manipulation of surface waves on a thin surface-wave bandgap crystal with a thickness much smaller than the wavelength (1/30th of the operating wavelength). Functional devices including a T-shaped splitter and sharp bend are constructed with good performance.

Probing the ionization wave packet and recollision dynamics with an elliptically polarized strong laser field in the nondipole regime

NASA Astrophysics Data System (ADS)

Maurer, J.; Willenberg, B.; Daněk, J.; Mayer, B. W.; Phillips, C. R.; Gallmann, L.; Klaiber, M.; Hatsagortsyan, K. Z.; Keitel, C. H.; Keller, U.

2018-01-01

We explore ionization and rescattering in strong mid-infrared laser fields in the nondipole regime over the full range of polarization ellipticity. In three-dimensional photoelectron momentum distributions (3D PMDs) measured with velocity map imaging spectroscopy, we observe the appearance of a sharp ridge structure along the major polarization axis. Within a certain range of ellipticity, the electrons in this ridge are clearly separated from the two lobes that commonly appear in the PMD with elliptically polarized laser fields. In contrast to the well-known lobes of direct electrons, the sharp ridge is created by Coulomb focusing of the softly recolliding electrons. These ridge electrons are directly related to a counterintuitive shift of the PMD peak opposite to the laser beam propagation direction when the dipole approximation breaks down. The ellipticity-dependent 3D PMDs give access to different ionization and recollision dynamics with appropriate filters in the momentum space. For example, we can extract information about the spread of the initial wave packet and the Coulomb momentum transfer of the rescattering electrons.

Sharp low-energy feature in single-particle spectra due to forward scattering in d-wave cuprate superconductors.

PubMed

Hong, Seung Hwan; Bok, Jin Mo; Zhang, Wentao; He, Junfeng; Zhou, X J; Varma, C M; Choi, Han-Yong

2014-08-01

There is an enormous interest in the renormalization of the quasiparticle (qp) dispersion relation of cuprate superconductors both below and above the critical temperature T_{c} because it enables the determination of the fluctuation spectrum to which the qp's are coupled. A remarkable discovery by angle-resolved photoemission spectroscopy (ARPES) is a sharp low-energy feature (LEF) in qp spectra well below the superconducting energy gap but with its energy increasing in proportion to T_{c} and its intensity increasing sharply below T_{c}. This unexpected feature needs to be reconciled with d-wave superconductivity. Here, we present a quantitative analysis of ARPES data from Bi_{2}Sr_{2}CaCu_{2}O_{8+δ} (Bi2212) using Eliashberg equations to show that the qp scattering rate due to the forward scattering impurities far from the Cu-O planes is modified by the energy gap below T_{c} and shows up as the LEF. This is also a necessary step to analyze ARPES data to reveal the spectrum of fluctuations promoting superconductivity.

Pretreatment with β-adrenergic receptor agonists facilitates induction of LTP and sharp wave ripple complexes in rodent hippocampus.

PubMed

Ul Haq, Rizwan; Anderson, Marlene; Liotta, Agustin; Shafiq, Maria; Sherkheli, Muhammad Azhar; Heinemann, Uwe

2016-12-01

Norepinephrine, is involved in the enhancement of learning and memory formation by regulating synaptic mechanisms through its ability to activate pre- and post-synaptic adrenergic receptors. Here we show that β-agonists of norepinephrine facilitate the induction of both associational LTP and sharp wave ripples (SPW-Rs) in acute slices of rat hippocampus in area CA3. Surprisingly, this facilitating effect persists when slices are only pretreated with β-receptor agonists followed by wash out and application of the unspecific β-adrenoreceptor (βAR) antagonist propranolol. During application of βAR agonists repeated stimulation resulted in facilitated induction of SPW-Rs. Since SPW-Rs are thought to be involved in memory replay we studied the effects of βAR-agonists on spontaneous SPW-Rs in murine hippocampus and found that amplitude and incidence of SPW-Rs increased. These effects involve cyclic-AMP and the activation of protein kinase A and suggest a supportive role in memory consolidation. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

Doublecortin associates with microtubules preferentially in regions of the axon displaying actin-rich protrusive structures

PubMed Central

Tint, Irina; Jean, Daphney; Baas, Peter W.; Black, Mark M.

2009-01-01

Here we studied doublecortin (DCX) in cultured hippocampal and sympathetic neurons during axonal development. In both types of neurons, DCX is abundant in the growth cone, where it primarily localizes with microtubules. Its abundance is lowest on microtubules in the neck region of the growth cone and highest on microtubules extending into the actin-rich lamellar regions. Interestingly, the microtubule polymer richest in DCX is also deficient in tau. In hippocampal neurons but not sympathetic neurons, discrete focal patches of microtubules rich in DCX and deficient in tau are present along the axonal shaft. Invariably, these patches have actin-rich protrusions resembling those of growth cones. Many of the DCX/actin filament patches exhibit vigorous protrusive activity and also undergo a proximal-to-distal redistribution within the axon at average rates ≈ 2 μm/min, and thus closely resemble the growth-cone-like waves described by previous authors. Depletion of DCX using siRNA had little effect on the appearance of the growth cone or on axonal growth in either type of neuron. However, DCX depletion significantly delayed collateral branching in hippocampal neurons and also significantly lowered the frequency of actin-rich patches along hippocampal axons. Branching by sympathetic neurons, which occurs by growth cone splitting, was not impaired by DCX depletion. These findings reveal a functional relationship between the DCX/actin filament patches and collateral branching. Based on the striking resemblance of these patches to growth cones, we discuss the possibility that they reflect a mechanism for locally boosting morphogenetic activity to facilitate axonal growth and collateral branching. PMID:19726658

Memory consolidation from seconds to weeks: a three-stage neural network model with autonomous reinstatement dynamics

PubMed Central

Fiebig, Florian; Lansner, Anders

2014-01-01

Declarative long-term memories are not created in an instant. Gradual stabilization and temporally shifting dependence of acquired declarative memories in different brain regions—called systems consolidation—can be tracked in time by lesion experiments. The observation of temporally graded retrograde amnesia (RA) following hippocampal lesions points to a gradual transfer of memory from hippocampus to neocortical long-term memory. Spontaneous reactivations of hippocampal memories, as observed in place cell reactivations during slow-wave-sleep, are supposed to drive neocortical reinstatements and facilitate this process. We propose a functional neural network implementation of these ideas and furthermore suggest an extended three-state framework that includes the prefrontal cortex (PFC). It bridges the temporal chasm between working memory percepts on the scale of seconds and consolidated long-term memory on the scale of weeks or months. We show that our three-stage model can autonomously produce the necessary stochastic reactivation dynamics for successful episodic memory consolidation. The resulting learning system is shown to exhibit classical memory effects seen in experimental studies, such as retrograde and anterograde amnesia (AA) after simulated hippocampal lesioning; furthermore the model reproduces peculiar biological findings on memory modulation, such as retrograde facilitation of memory after suppressed acquisition of new long-term memories—similar to the effects of benzodiazepines on memory. PMID:25071536

Determining the relationship between sleep architecture, seizure variables and memory in patients with focal epilepsy.

PubMed

Miller, Laurie A; Ricci, Monica; van Schalkwijk, Frank J; Mohamed, Armin; van der Werf, Ysbrand D

2016-06-01

Sleep has been shown to be important to memory. Both sleep and memory have been found to be abnormal in patients with epilepsy. In this study, we explored the effects that nocturnal epileptiform discharges and the presence of a hippocampal lesion have on sleep patterns and memory. Twenty-five patients with focal epilepsy who underwent a 24-hr ambulatory EEG also completed the Everyday Memory Questionnaire (EMQ). The EEG record was scored for length of time spent in the various sleep stages, time spent awake after sleep onset, and rapid eye movement (REM) latency. Of these sleep variables, only REM latency differed when the epilepsy patients were divided on the bases of either presence/absence of nocturnal discharges or presence/absence of a hippocampal lesion. In both cases, presence of the abnormality was associated with longer latency. Furthermore, longer REM latency was found to be a better predictor of EMQ score than either number of discharges or presence of a hippocampal lesion. Longer REM latency was associated with a smaller percentage of time spent in slow-wave sleep in the early part of the night and may serve as a particularly sensitive marker to disturbances in sleep architecture. (PsycINFO Database Record (c) 2016 APA, all rights reserved).

Quadratic dissipation effect on the moonpool resonance

NASA Astrophysics Data System (ADS)

Liu, Heng-xu; Chen, Hai-long; Zhang, Liang; Zhang, Wan-chao; Liu, Ming

2017-12-01

This paper adopted a semi-analytical method based on eigenfunction matching to solve the problem of sharp resonance of cylindrical structures with a moonpool that has a restricted entrance. To eliminate the sharp resonance and to measure the viscous effect, a quadratic dissipation is introduced by assuming an additional dissipative disk at the moonpool entrance. The fluid domain is divided into five cylindrical subdomains, and the velocity potential in each subdomain is obtained by meeting the Laplace equation as well as the boundary conditions. The free-surface elevation at the center of the moonpool, along with the pressure and velocity at the restricted entrance for first-order wave are evaluated. By choosing appropriate dissipation coefficients, the free-surface elevation calculated at the center of the moonpool is in coincidence with the measurements in model tests both at the peak period and amplitude at resonance. It is shown that the sharp resonance in the potential flow theory can be eliminated and the viscous effect can be estimated with a simple method in some provided hydrodynamic models.

Sharp threshold of blow-up and scattering for the fractional Hartree equation

NASA Astrophysics Data System (ADS)

Guo, Qing; Zhu, Shihui

2018-02-01

We consider the fractional Hartree equation in the L2-supercritical case, and find a sharp threshold of the scattering versus blow-up dichotomy for radial data: If M[u0 ]s -sc/sc E [u0 ] < M[ Q ]s -sc/sc E [ Q ] and M[u0 ]s -sc/sc ‖u0‖ H˙s 2 < M[ Q ]s -sc/sc ‖Q‖ H˙s 2 , then the solution u (t) is globally well-posed and scatters; if M[u0 ]s -sc/sc E [u0 ] < M[ Q ]s -sc/sc E [ Q ] and M[u0 ]s -sc/sc ‖u0‖ H˙s 2 > M[ Q ]s -sc/sc ‖Q‖ H˙s 2 , the solution u (t) blows up in finite time. This condition is sharp in the sense that the solitary wave solution eit Q (x) is global but not scattering, which satisfies the equality in the above conditions. Here, Q is the ground-state solution for the fractional Hartree equation.

Existence and Stability of Traveling Waves for Degenerate Reaction-Diffusion Equation with Time Delay

NASA Astrophysics Data System (ADS)

Huang, Rui; Jin, Chunhua; Mei, Ming; Yin, Jingxue

2018-01-01

This paper deals with the existence and stability of traveling wave solutions for a degenerate reaction-diffusion equation with time delay. The degeneracy of spatial diffusion together with the effect of time delay causes us the essential difficulty for the existence of the traveling waves and their stabilities. In order to treat this case, we first show the existence of smooth- and sharp-type traveling wave solutions in the case of c≥c^* for the degenerate reaction-diffusion equation without delay, where c^*>0 is the critical wave speed of smooth traveling waves. Then, as a small perturbation, we obtain the existence of the smooth non-critical traveling waves for the degenerate diffusion equation with small time delay τ >0 . Furthermore, we prove the global existence and uniqueness of C^{α ,β } -solution to the time-delayed degenerate reaction-diffusion equation via compactness analysis. Finally, by the weighted energy method, we prove that the smooth non-critical traveling wave is globally stable in the weighted L^1 -space. The exponential convergence rate is also derived.

Effects of UGTs on the ionosphere

NASA Astrophysics Data System (ADS)

Argo, P. E.; Fitzgerald, T. J.

The processes that propagate local effects of underground nuclear tests from the ground into the upper atmosphere, and produce a detectable signal in the ionosphere are described. Initially, the blast wave from a underground test (UGT) radially expands, until it reaches the surface of the earth. The wave is both reflected and transmitted at this sharp discontinuity in propagation media. Tne reflected wave combines with the incident wave to form an 'Airy surface,' at which very strong ripping forces tear the earth apart. This broken region is called the 'spat zone,' and is launched into ballistic motion. The resultant ground motion launches an acoustical wave into the atmosphere. This acoustic wave, with overpressures of a few tenths of one percent, propagates upwards at the speed of sound. Assuming purely linear propagation, the path of the acoustic energy can be tracked using raytracing models. Most of the wave energy, which is radiated nearly vertically, tends to propagate into the upper atmosphere, while wave energy radiated at angles greater than about 30 degrees to the vertical will be reflected back to earth and is probably what is seen by most infrasonde measurements.

Existence and Stability of Traveling Waves for Degenerate Reaction-Diffusion Equation with Time Delay

NASA Astrophysics Data System (ADS)

Huang, Rui; Jin, Chunhua; Mei, Ming; Yin, Jingxue

2018-06-01

This paper deals with the existence and stability of traveling wave solutions for a degenerate reaction-diffusion equation with time delay. The degeneracy of spatial diffusion together with the effect of time delay causes us the essential difficulty for the existence of the traveling waves and their stabilities. In order to treat this case, we first show the existence of smooth- and sharp-type traveling wave solutions in the case of c≥c^* for the degenerate reaction-diffusion equation without delay, where c^*>0 is the critical wave speed of smooth traveling waves. Then, as a small perturbation, we obtain the existence of the smooth non-critical traveling waves for the degenerate diffusion equation with small time delay τ >0. Furthermore, we prove the global existence and uniqueness of C^{α ,β }-solution to the time-delayed degenerate reaction-diffusion equation via compactness analysis. Finally, by the weighted energy method, we prove that the smooth non-critical traveling wave is globally stable in the weighted L^1-space. The exponential convergence rate is also derived.

Effect of cooler electrons on a compressive ion acoustic solitary wave in a warm ion plasma — Forbidden regions, double layers, and supersolitons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ghosh, S. S., E-mail: sukti@iigs.iigm.res.in; Sekar Iyengar, A. N.

It is observed that the presence of a minority component of cooler electrons in a three component plasma plays a deterministic role in the evolution of solitary waves, double layers, or the newly discovered structures called supersolitons. The inclusion of the cooler component of electrons in a single electron plasma produces sharp increase in nonlinearity in spite of a decrease in the overall energy of the system. The effect maximizes at certain critical value of the number density of the cooler component (typically 15%–20%) giving rise to a hump in the amplitude variation profile. For larger amplitudes, the hump leadsmore » to a forbidden region in the ambient cooler electron concentration which dissociates the overall existence domain of solitary wave solutions in two distinct parameter regime. It is observed that an inclusion of the cooler component of electrons as low as < 1% affects the plasma system significantly resulting in compressive double layers. The solution is further affected by the cold to hot electron temperature ratio. In an adequately hotter bulk plasma (i.e., moderately low cold to hot electron temperature ratio), the parameter domain of compressive double layers is bounded by a sharp discontinuity in the corresponding amplitude variation profile which may lead to supersolitons.« less

Effects of Nose Bluntness on Stability of Hypersonic Boundary Layers over Blunt Cone

NASA Technical Reports Server (NTRS)

Kara, K.; Balakumar, P.; Kandil, O. A.

2007-01-01

Receptivity and stability of hypersonic boundary layers are numerically investigated for boundary layer flows over a 5-degree straight cone at a free-stream Mach number of 6.0. To compute the shock and the interaction of shock with the instability waves, we solve the Navier-Stokes equations in axisymmetric coordinates. The governing equations are solved using the 5th-order accurate weighted essentially non-oscillatory (WENO) scheme for space discretization and using third-order total-variation-diminishing (TVD) Runge-Kutta scheme for time integration. After the mean flow field is computed, disturbances are introduced at the upstream end of the computational domain. Generation of instability waves from leading edge region and receptivity of boundary layer to slow acoustic waves are investigated. Computations are performed for a cone with nose radii of 0.001, 0.05 and 0.10 inches that give Reynolds numbers based on the nose radii ranging from 650 to 130,000. The linear stability results showed that the bluntness has a strong stabilizing effect on the stability of axisymmetric boundary layers. The transition Reynolds number for a cone with the nose Reynolds number of 65,000 is increased by a factor of 1.82 compared to that for a sharp cone. The receptivity coefficient for a sharp cone is about 4.23 and it is very small, approx.10(exp -3), for large bluntness.

Contribution of Egr1/zif268 to Activity-Dependent Arc/Arg3.1 Transcription in the Dentate Gyrus and Area CA1 of the Hippocampus

PubMed Central

Penke, Zsuzsa; Chagneau, Carine; Laroche, Serge

2011-01-01

Egr1, a member of the Egr family of transcription factors, and Arc are immediate early genes known to play major roles in synaptic plasticity and memory. Despite evidence that Egr family members can control Arc transcriptional regulation, demonstration of a selective role of Egr1 alone is lacking. We investigated the extent to which activity-dependent Arc expression is dependent on Egr1 by analyzing Arc mRNA expression using fluorescence in situ hybridization in the dorsal dentate gyrus and CA1 of wild-type (WT) and Egr1 knockout mice. Following electroconvulsive shock, we found biphasic expression of Arc in area CA1 in mice, consisting in a rapid (30 min) and transient wave followed by a second late-phase of expression (8 h), and a single but prolonged wave of expression in the dentate gyrus. Egr1 deficiency abolished the latest, but not the early wave of Arc expression in CA1, and curtailed that of the dentate gyrus. Since the early wave of Arc expression was not affected in Egr1 mutant mice, we next analyzed behaviorally induced Arc expression patterns as an index of neural ensemble activation in the dentate gyrus and area CA1 of WT and Egr1 mutant mice. Spatial exploration of novel or familiar environments induced in mice a single early and transient wave of Arc expression in the dentate gyrus and area CA1, which were not affected in Egr1 mutant mice. Analyses of Arc-expressing cells revealed that exploration recruits similar size dentate gyrus and CA1 neural ensembles in WT and Egr1 knockout mice. These findings suggest that hippocampal neural ensembles are normally activated immediately following spatial exploration in Egr1 knockout mice, indicating normal hippocampal encoding of information. They also provide evidence that in condition of strong activation Egr1 alone can control late-phases of activity-dependent Arc transcription in the dentate gyrus and area CA1 of the hippocampus. PMID:21887136

Nonlinear structures and anomalous transport in partially magnetized E×B plasmas

DOE PAGES

Janhunen, Salomon; Smolyakov, Andrei; Chapurin, Oleksandr; ...

2017-12-29

Nonlinear dynamics of the electron-cyclotron instability driven by the electron E x B current in a crossed electric and magnetic field is studied. In the nonlinear regime, the instability proceeds by developing a large amplitude coherent wave driven by the energy input from the fundamental cyclotron resonance. Further evolution shows the formation of the long wavelength envelope akin to the modulational instability. Simultaneously, the ion density shows the development of a high-k content responsible for wave focusing and sharp peaks on the periodic cnoidal wave structure. Here, it is shown that the anomalous electron transport (along the direction of themore » applied electric field) is dominated by the long wavelength part of the turbulent spectrum.« less

Effects of cone surface waviness and freestream noise on transition in supersonic flow

NASA Technical Reports Server (NTRS)

Morrisette, E. L.; Creel, T. R., Jr.; Chen, F.-J.

1986-01-01

A comparison of transition on wavy-wall and smooth-wall cones in a Mach 3.5 wind tunnel is made under conditions of either low freestream noise (quiet flow) or high freestream noise (noisy flow). The noisy flow compares to that found in conventional wind tunnels while the quiet flow gives transitional Reynolds numbers on smooth sharp cones comparable to those found in flight. The waves were found to have a much smaller effect on transition than similar sized trip wires. A satisfatory correlating parameter for the effect of waves on transition was simply the wave height-to-length ratio. A given value of this ratio was found to cause the same percentage change in transition location in quiet and noisy flows.

Growth of electron plasma waves above and below f(p) in the electron foreshock

NASA Technical Reports Server (NTRS)

Cairns, Iver H.; Fung, Shing F.

1988-01-01

This paper investigates the conditions required for electron beams to drive wave growth significantly above and below the electron plasma frequency, f(p), by numerically solving the linear dispersion equation. It is shown that kinetic growth well below f(p) may occur over a broad range of frequencies due to the beam instability, when the electron beam is slow, dilute, and relatively cold. Alternatively, a cold or sharp feature at low parallel velocities in the distribution function may drive kinetic growth significantly below f(p). Kinetic broadband growth significantly above f(p) is explained in terms of faster warmer beams. A unified qualitative theory for the narrow-band and broad-band waves is proposed.

An experimental study of a three-dimensional shock wave/turbulent boundary-layer interaction at a hypersonic Mach number

NASA Technical Reports Server (NTRS)

Kussoy, M. I.; Horstman, K. C.; Kim, K.-S.

1991-01-01

Experimental data for a series of three-dimensional shock-wave/turbulent-boundary-layer interaction flows at Mach 8.2 are presented. The test bodies, composed of sharp fins fastened to a flat-plate test surface, were designed to generate flows with varying degrees of pressure gradient, boundary-layer separation, and turning angle. The data include surface-pressure, heat-transfer, and skin-friction distributions, as well as limited mean flowfield surveys both in the undisturbed and interaction regimes. The data were obtained for the purpose of validating computational models of these hypersonic interactions.

On increasing stability in the two dimensional inverse source scattering problem with many frequencies

NASA Astrophysics Data System (ADS)

Entekhabi, Mozhgan Nora; Isakov, Victor

2018-05-01

In this paper, we will study the increasing stability in the inverse source problem for the Helmholtz equation in the plane when the source term is assumed to be compactly supported in a bounded domain Ω with a sufficiently smooth boundary. Using the Fourier transform in the frequency domain, bounds for the Hankel functions and for scattering solutions in the complex plane, improving bounds for the analytic continuation, and the exact observability for the wave equation led us to our goals which are a sharp uniqueness and increasing stability estimate when the wave number interval is growing.

Infrasonic sounds excited by seismic waves of the 2011 Tohoku-oki earthquake as visualized in ionograms

NASA Astrophysics Data System (ADS)

Maruyama, Takashi; Shinagawa, Hiroyuki

2014-05-01

After the M 9.0 Tohoku-oki earthquake in 2011, strong deformation of ionogram echo traces, forming multiple cusp signatures (MCSs), were observed at three stations 790-1880 km from the epicenter. The vertical structure of the ionospheric disturbances was determined by true height analysis and compared with broadband seismograph records at stations close to the ionosondes. These ionospheric disturbances were caused by vertically propagating acoustic waves excited by the up/down ground motion of seismic waves. Numerical simulations have shown that acoustic waves with a period of 15-40 s and amplitude of order 1 mm/s at the ground level were sufficient to create MCSs as sharp as those observed. These acoustic wave parameters are consistent with the seismic records if the motion of the air mass on the ground level is assumed to be the same as the ground motion. The travel time diagram of the seismic records along the line connecting the epicenter and ionosondes showed that the first MCS ionogram detected at each station was caused by P waves, while the others were caused by Rayleigh waves.

Application of the wavenumber jump condition to the normal and oblique interaction of a plane acoustic wave and a plane shock

NASA Technical Reports Server (NTRS)

Kleinstein, G. G.; Gunzburger, M. D.

1977-01-01

The kinematics of normal and oblique interactions between a plane acoustic wave and a plane shock wave are investigated separately using an approach whereby the shock is considered as a sharp discontinuity surface separating two half-spaces, so that the dispersion relation on either side of the shock and the wavenumber jump condition across a discontinuity surface completely specify the kinematics of the problem in the whole space independently of the acoustic-field dynamics. The normal interaction is analyzed for a stationary shock, and the spectral change of the incident wave is investigated. The normal interaction is then examined for the case of a shock wave traveling into an ambient region where an acoustic disturbance is propagating in the opposite direction. Detailed attention is given to the consequences of the existence of a critical shock speed above which the frequency of the transmitted wave becomes negative. Finally, the oblique interaction with a fixed shock is considered, and the existence and nature of the transmitted wave is investigated, particularly as a function of the angle of incidence.

Wavelet analysis of epileptic spikes

NASA Astrophysics Data System (ADS)

Latka, Miroslaw; Was, Ziemowit; Kozik, Andrzej; West, Bruce J.

2003-05-01

Interictal spikes and sharp waves in human EEG are characteristic signatures of epilepsy. These potentials originate as a result of synchronous pathological discharge of many neurons. The reliable detection of such potentials has been the long standing problem in EEG analysis, especially after long-term monitoring became common in investigation of epileptic patients. The traditional definition of a spike is based on its amplitude, duration, sharpness, and emergence from its background. However, spike detection systems built solely around this definition are not reliable due to the presence of numerous transients and artifacts. We use wavelet transform to analyze the properties of EEG manifestations of epilepsy. We demonstrate that the behavior of wavelet transform of epileptic spikes across scales can constitute the foundation of a relatively simple yet effective detection algorithm.

Computational analysis of blunt, thin airfoil sections at supersonic and subsonic speeds

NASA Astrophysics Data System (ADS)

Goodsell, Aga Myung

The past decade has brought renewed interest in commercial supersonic aircraft design. Recent wing designs have included regions of low sweep resulting in supersonic leading edges at cruise. Thin biconvex sections are used in those regions to minimize wave drag and skin-friction drag. However, airfoil sections with sharp leading edges exhibit poor aerodynamic behavior at subsonic flight conditions. Blunt leading edges may improve performance by delaying the onset of separation at subsonic and transonic speeds. Their disadvantage is that they increase both wave drag, due to the formation of a detached bow wave, and skin-friction drag, from a loss of laminar flow. The effect of adding bluntness to a 4%-thick biconvex section was investigated using computational analysis tools. The aerodynamic performance of biconvex sections with circular leading edges was computed at supersonic, transonic, and takeoff conditions. At supersonic cruise, the increase in wave drag due to bluntness is a function of Mach number and leading-edge diameter. Some of the drag penalty is offset by the suction created downstream of the circular leading edge. The possibility of further drag reduction was explored with the development of a semi-analytical method to design blunt airfoil shapes which minimize wave drag. The effect on the transition location was evaluated using linear stability analyses of laminar boundary-layer profiles and the eN method. The analysis showed that laminar boundary layers on blunt airfoil sections are considerably less stable to Tollmien-Schlichting waves than that on a sharp biconvex. At transonic speeds, the results suggest a possible improvement in the lift-to-drag ratio over a limited range of angles of attack. At the takeoff condition, slight blunting of the leading edge does improve the lift-to-drag ratio at low angles of attack, but has little effect on maximum lift. It is concluded that the benefit of a blunt leading edge at off-design conditions is not sufficient to warrant the resulting drag penalty at supersonic cruise. Furthermore, if maintaining laminar flow is critical to the design and some bluntness is necessary for manufacturing purposes, then the leading-edge diameter should be minimized to prevent transition and to reduce wave drag.

Heterogeneous sharpness for cross-spectral face recognition

NASA Astrophysics Data System (ADS)

Cao, Zhicheng; Schmid, Natalia A.

2017-05-01

Matching images acquired in different electromagnetic bands remains a challenging problem. An example of this type of comparison is matching active or passive infrared (IR) against a gallery of visible face images, known as cross-spectral face recognition. Among many unsolved issues is the one of quality disparity of the heterogeneous images. Images acquired in different spectral bands are of unequal image quality due to distinct imaging mechanism, standoff distances, or imaging environment, etc. To reduce the effect of quality disparity on the recognition performance, one can manipulate images to either improve the quality of poor-quality images or to degrade the high-quality images to the level of the quality of their heterogeneous counterparts. To estimate the level of discrepancy in quality of two heterogeneous images a quality metric such as image sharpness is needed. It provides a guidance in how much quality improvement or degradation is appropriate. In this work we consider sharpness as a relative measure of heterogeneous image quality. We propose a generalized definition of sharpness by first achieving image quality parity and then finding and building a relationship between the image quality of two heterogeneous images. Therefore, the new sharpness metric is named heterogeneous sharpness. Image quality parity is achieved by experimentally finding the optimal cross-spectral face recognition performance where quality of the heterogeneous images is varied using a Gaussian smoothing function with different standard deviation. This relationship is established using two models; one of them involves a regression model and the other involves a neural network. To train, test and validate the model, we use composite operators developed in our lab to extract features from heterogeneous face images and use the sharpness metric to evaluate the face image quality within each band. Images from three different spectral bands visible light, near infrared, and short-wave infrared are considered in this work. Both error of a regression model and validation error of a neural network are analyzed.

Effects of Isotropic and Anisotropic Structure in the Lowermost Mantle on High-Frequency Body Waveforms

NASA Astrophysics Data System (ADS)

Parisi, L.; Ferreira, A. M. G.; Ritsema, J.

2015-12-01

It has been observed that vertically (SV) and horizontally (SH) polarised S waves crossing the lowermost mantle sometimes are split by a few seconds The splitting of such waves is often interpreted in terms of seismic anisotropy in the D" region. Here we investigate systematically the effects of elastic, anelastic, isotropic and anisotropic structure on shear-wave splitting, including 3-D variations in some of these physical properties. Taking advantage of accurate waveform modeling techniques such as Gemini and the Spectral Element Method we generate three-component theoretical waveforms in a wide set of 1-D and 3-D, isotropic and radially anisotropic earth models, accurate down to a wave period of T~5.6s. Our numerical simulations in isotropic earth models show that the contamination of S waves by other phases can generate an apparent splitting between SH and SV waves. In particular, in the case of very shallow sources, the sS phase can interfere with the direct S phase, resulting in split SH and SV pulses when the SH and SV (or sSH and sSV) waves have different polarity or a substantial amplitude difference. In the case of deep earthquake sources, a positive shear velocity jump at the top of the D" can cause the triplication of S waves and the ScSH and ScSV phases can have different polarity. Thus, when the triplicated S wave is combined with the ScS phase, the resulting SH-ScSH and SV-ScSV phases may seem split. On the other hand, in the absence of a sharp vertical variation in the shear wave velocity, the difference in polarity between ScSH and ScSV can make the SH pulse larger than SV and thus also lead to apparent splitting between these phases. This effect depends on the thickness of the D" and the Vs gradient within it. S waveforms simulated in radially anisotropic models reveal that a radial anisotropy of ξ=1.07 in the D" seems to be necessary to explain the 2-3s of splitting observed in waveforms recorded in Tanzania from an event in the Banda Sea. However, our analysis also shows that other factors such as sharp vertical variations at the top of D" and gradients of Vs and η within the D'' may also affect the observed waveforms. This study suggests that caution should be taken when interpreting SH-SV splitting of deep mantle body waves exclusively in terms of anisotropy in the lowermost mantle.

A Rossby whistle: A resonant basin mode observed in the Caribbean Sea

NASA Astrophysics Data System (ADS)

Hughes, Chris W.; Williams, Joanne; Hibbert, Angela; Boening, Carmen; Oram, James

2016-07-01

We show that an important source of coastal sea level variability around the Caribbean Sea is a resonant basin mode. The mode consists of a baroclinic Rossby wave which propagates westward across the basin and is rapidly returned to the east along the southern boundary as coastal shelf waves. Almost two wavelengths of the Rossby wave fit across the basin, and it has a period of 120 days. The porous boundary of the Caribbean Sea results in this mode exciting a mass exchange with the wider ocean, leading to a dominant mode of bottom pressure variability which is almost uniform over the Grenada, Venezuela, and Colombia basins and has a sharp spectral peak at 120 day period. As the Rossby waves have been shown to be excited by instability of the Caribbean Current, this resonant mode is dynamically equivalent to the operation of a whistle.

Control of Excitation/Inhibition Balance in a Hippocampal Circuit by Calcium Sensor Protein Regulation of Presynaptic Calcium Channels.

PubMed

Nanou, Evanthia; Lee, Amy; Catterall, William A

2018-05-02

Activity-dependent regulation controls the balance of synaptic excitation to inhibition in neural circuits, and disruption of this regulation impairs learning and memory and causes many neurological disorders. The molecular mechanisms underlying short-term synaptic plasticity are incompletely understood, and their role in inhibitory synapses remains uncertain. Here we show that regulation of voltage-gated calcium (Ca 2+ ) channel type 2.1 (Ca V 2.1) by neuronal Ca 2+ sensor (CaS) proteins controls synaptic plasticity and excitation/inhibition balance in a hippocampal circuit. Prevention of CaS protein regulation by introducing the IM-AA mutation in Ca V 2.1 channels in male and female mice impairs short-term synaptic facilitation at excitatory synapses of CA3 pyramidal neurons onto parvalbumin (PV)-expressing basket cells. In sharp contrast, the IM-AA mutation abolishes rapid synaptic depression in the inhibitory synapses of PV basket cells onto CA1 pyramidal neurons. These results show that CaS protein regulation of facilitation and inactivation of Ca V 2.1 channels controls the direction of short-term plasticity at these two synapses. Deletion of the CaS protein CaBP1/caldendrin also blocks rapid depression at PV-CA1 synapses, implicating its upregulation of inactivation of Ca V 2.1 channels in control of short-term synaptic plasticity at this inhibitory synapse. Studies of local-circuit function revealed reduced inhibition of CA1 pyramidal neurons by the disynaptic pathway from CA3 pyramidal cells via PV basket cells and greatly increased excitation/inhibition ratio of the direct excitatory input versus indirect inhibitory input from CA3 pyramidal neurons to CA1 pyramidal neurons. This striking defect in local-circuit function may contribute to the dramatic impairment of spatial learning and memory in IM-AA mice. SIGNIFICANCE STATEMENT Many forms of short-term synaptic plasticity in neuronal circuits rely on regulation of presynaptic voltage-gated Ca 2+ (Ca V ) channels. Regulation of Ca V 2.1 channels by neuronal calcium sensor (CaS) proteins controls short-term synaptic plasticity. Here we demonstrate a direct link between regulation of Ca V 2.1 channels and short-term synaptic plasticity in native hippocampal excitatory and inhibitory synapses. We also identify CaBP1/caldendrin as the calcium sensor interacting with Ca V 2.1 channels to mediate rapid synaptic depression in the inhibitory hippocampal synapses of parvalbumin-expressing basket cells to CA1 pyramidal cells. Disruption of this regulation causes altered short-term plasticity and impaired balance of hippocampal excitatory to inhibitory circuits. Copyright © 2018 the authors 0270-6474/18/384430-11$15.00/0.

Electromagnetic and electrostatic emissions at the cusp-magnetosphere interface during substorms

NASA Technical Reports Server (NTRS)

Curtis, S. A.; Fairfield, D. H.; Wu, C. S.

1979-01-01

Strongly peaked electrostatic emissions near 10.0 kHz and electromagnetic emissions near 0.56 kHz have been observed by the VLF wave detector on board Imp 6 on crossings from the earth's magnetosphere into the polar cusp during the occurrence of large magnetospheric substorms. The electrostatic emissions were observed to be closely confined to the cusp-magnetosphere interface. The electromagnetic emissions were of somewhat broader spatial extent and were seen on higher-latitude field lines within the cusp. Using these plasma wave observations and additional information provided by plasma, magnetometer and particle measurements made simultaneously on Imp 6, theories are constructed to explain each of the two classes of emission. The electromagnetic waves are modeled as whistlers, and the electrostatic waves as electron-cyclotron harmonics. The resulting growth rates predict power spectra similar to those observed for both emission classes. The electrostatic waves may play a significant role via enhanced diffusion in the relaxation of the sharp substorm time cusp-magnetosphere boundary to a more diffuse quiet time boundary.

Human Hippocampal Structure: A Novel Biomarker Predicting Mnemonic Vulnerability to, and Recovery from, Sleep Deprivation.

PubMed

Saletin, Jared M; Goldstein-Piekarski, Andrea N; Greer, Stephanie M; Stark, Shauna; Stark, Craig E; Walker, Matthew P

2016-02-24

Sleep deprivation impairs the formation of new memories. However, marked interindividual variability exists in the degree to which sleep loss compromises learning, the mechanistic reasons for which are unclear. Furthermore, which physiological sleep processes restore learning ability following sleep deprivation are similarly unknown. Here, we demonstrate that the structural morphology of human hippocampal subfields represents one factor determining vulnerability (and conversely, resilience) to the impact of sleep deprivation on memory formation. Moreover, this same measure of brain morphology was further associated with the quality of nonrapid eye movement slow wave oscillations during recovery sleep, and by way of such activity, determined the success of memory restoration. Such findings provide a novel human biomarker of cognitive susceptibility to, and recovery from, sleep deprivation. Moreover, this metric may be of special predictive utility for professions in which memory function is paramount yet insufficient sleep is pervasive (e.g., aviation, military, and medicine). Copyright © 2016 the authors 0270-6474/16/362355-09$15.00/0.

Hilar Mossy Cell Degeneration Causes Transient Dentate Granule Cell Hyperexcitability and Impaired Pattern Separation

PubMed Central

Jinde, Seiichiro; Zsiros, Veronika; Jiang, Zhihong; Nakao, Kazuhito; Pickel, James; Kohno, Kenji; Belforte, Juan E.; Nakazawa, Kazu

2012-01-01

Summary Although excitatory mossy cells of the hippocampal hilar region are known to project both to dentate granule cells and to interneurons, it is as yet unclear whether mossy cell activity’s net effect on granule cells is excitatory or inhibitory. To explore their influence on dentate excitability and hippocampal function, we generated a conditional transgenic mouse line, using the Cre/loxP system, in which diphtheria toxin receptor was selectively expressed in mossy cells. One week after injecting toxin into this line, mossy cells throughout the longitudinal axis were degenerated extensively, theta wave power of dentate local field potentials increased during exploration, and deficits occurred in contextual discrimination. By contrast, we detected no epileptiform activity, spontaneous behavioral seizures, or mossy-fiber sprouting 5–6 weeks after mossy cell degeneration. These results indicate that the net effect of mossy cell excitation is to inhibit granule cell activity and enable dentate pattern separation. PMID:23259953

Control of a brain-computer interface using stereotactic depth electrodes in and adjacent to the hippocampus

NASA Astrophysics Data System (ADS)

Krusienski, D. J.; Shih, J. J.

2011-04-01

A brain-computer interface (BCI) is a device that enables severely disabled people to communicate and interact with their environments using their brain waves. Most research investigating BCI in humans has used scalp-recorded electroencephalography or intracranial electrocorticography. The use of brain signals obtained directly from stereotactic depth electrodes to control a BCI has not previously been explored. In this study, event-related potentials (ERPs) recorded from bilateral stereotactic depth electrodes implanted in and adjacent to the hippocampus were used to control a P300 Speller paradigm. The ERPs were preprocessed and used to train a linear classifier to subsequently predict the intended target letters. The classifier was able to predict the intended target character at or near 100% accuracy using fewer than 15 stimulation sequences in the two subjects tested. Our results demonstrate that ERPs from hippocampal and hippocampal adjacent depth electrodes can be used to reliably control the P300 Speller BCI paradigm.

Methods for Assessment of Memory Reactivation.

PubMed

Liu, Shizhao; Grosmark, Andres D; Chen, Zhe

2018-04-13

It has been suggested that reactivation of previously acquired experiences or stored information in declarative memories in the hippocampus and neocortex contributes to memory consolidation and learning. Understanding memory consolidation depends crucially on the development of robust statistical methods for assessing memory reactivation. To date, several statistical methods have seen established for assessing memory reactivation based on bursts of ensemble neural spike activity during offline states. Using population-decoding methods, we propose a new statistical metric, the weighted distance correlation, to assess hippocampal memory reactivation (i.e., spatial memory replay) during quiet wakefulness and slow-wave sleep. The new metric can be combined with an unsupervised population decoding analysis, which is invariant to latent state labeling and allows us to detect statistical dependency beyond linearity in memory traces. We validate the new metric using two rat hippocampal recordings in spatial navigation tasks. Our proposed analysis framework may have a broader impact on assessing memory reactivations in other brain regions under different behavioral tasks.

A nonlinear generalization of the Savitzky-Golay filter and the quantitative analysis of saccades

PubMed Central

Dai, Weiwei; Selesnick, Ivan; Rizzo, John-Ross; Rucker, Janet; Hudson, Todd

2017-01-01

The Savitzky-Golay (SG) filter is widely used to smooth and differentiate time series, especially biomedical data. However, time series that exhibit abrupt departures from their typical trends, such as sharp waves or steps, which are of physiological interest, tend to be oversmoothed by the SG filter. Hence, the SG filter tends to systematically underestimate physiological parameters in certain situations. This article proposes a generalization of the SG filter to more accurately track abrupt deviations in time series, leading to more accurate parameter estimates (e.g., peak velocity of saccadic eye movements). The proposed filtering methodology models a time series as the sum of two component time series: a low-frequency time series for which the conventional SG filter is well suited, and a second time series that exhibits instantaneous deviations (e.g., sharp waves, steps, or more generally, discontinuities in a higher order derivative). The generalized SG filter is then applied to the quantitative analysis of saccadic eye movements. It is demonstrated that (a) the conventional SG filter underestimates the peak velocity of saccades, especially those of small amplitude, and (b) the generalized SG filter estimates peak saccadic velocity more accurately than the conventional filter. PMID:28813566

Unsteady separation in sharp fin-induced shock wave/turbulent boundary layer interaction at Mach 5

NASA Technical Reports Server (NTRS)

Schmisseur, J. D.; Dolling, D. S.

1992-01-01

Fluctuating wall-pressure measurements are made in shock-wave/turbulent-boundary-layer interactions generated by sharp/unswept fins at angles of attack of 16, 18, 20, 22, 24, 26, and 28 degrees at Mach 5. The experiment was conducted under approximately adiabatic wall temperature conditions. The mean and rms pressure distributions can be collapsed in conical coordinates. The wall-pressure signal near separation is intermittent for all angles of attack (16-28 deg) and is qualitatively similar to that measured in unswept flows. However, the shock frequencies are higher - about 5 kHz compared to 0.5-1 kHz. Over the range of sweepbacks examined, from 25-55 deg, the spectral content of the fluctuating pressures does not change. Thus, the increase in separation-shock frequency from 1 to 5 kHz occurs at lower interaction sweepback and is not a continuous process with increasing sweepback. Power spectra at the position of maximum rms in the intermittent region for interactions in different incoming boundary layers have the same center frequency. The maximum rms in the intermittent region correlates with interaction sweepback, not with overall inviscid pressure rise.

A nonlinear generalization of the Savitzky-Golay filter and the quantitative analysis of saccades.

PubMed

Dai, Weiwei; Selesnick, Ivan; Rizzo, John-Ross; Rucker, Janet; Hudson, Todd

2017-08-01

The Savitzky-Golay (SG) filter is widely used to smooth and differentiate time series, especially biomedical data. However, time series that exhibit abrupt departures from their typical trends, such as sharp waves or steps, which are of physiological interest, tend to be oversmoothed by the SG filter. Hence, the SG filter tends to systematically underestimate physiological parameters in certain situations. This article proposes a generalization of the SG filter to more accurately track abrupt deviations in time series, leading to more accurate parameter estimates (e.g., peak velocity of saccadic eye movements). The proposed filtering methodology models a time series as the sum of two component time series: a low-frequency time series for which the conventional SG filter is well suited, and a second time series that exhibits instantaneous deviations (e.g., sharp waves, steps, or more generally, discontinuities in a higher order derivative). The generalized SG filter is then applied to the quantitative analysis of saccadic eye movements. It is demonstrated that (a) the conventional SG filter underestimates the peak velocity of saccades, especially those of small amplitude, and (b) the generalized SG filter estimates peak saccadic velocity more accurately than the conventional filter.

A sharp and flat section of the core-mantle boundary

USGS Publications Warehouse

Vidale, J.E.; Benz, H.M.

1992-01-01

THE transition zone between the Earth's core and mantle plays an important role as a boundary layer for mantle and core convection1. This zone conducts a large amount of heat from the core to the mantle, and contains at least one thermal boundary layer2,3; the proximity of reactive silicates and molten iron leads to the possibility of zones of intermediate composition4. Here we investigate one region of the core-mantle boundary using seismic waves that are converted from shear to compressional waves by reflection at the boundary. The use of this phase (known as ScP), the large number of receiving stations, and the large aperture of our array all provide higher resolution than has previously been possible5-7. For the 350-km-long section of the core-mantle boundary under the northeast Pacific sampled by the reflections, the local boundary topography has an amplitude of less than 500 m, no sharp radial gradients exist in the 400 km above the boundary, and the mantle-lo-core transition occurs over less than 1 km. The simplicity of the structure near and above the core-mantle boundary argues against chemical heterogeneity at the base of the mantle in this location.

Hydro morphodynamic modelling in Mediterranean storms: errors and uncertainties under sharp gradients

NASA Astrophysics Data System (ADS)

Sánchez-Arcilla, A.; Gracia, V.; García, M.

2014-02-01

This paper deals with the limits in hydrodynamic and morphodynamic predictions for semi-enclosed coastal domains subject to sharp gradients (in bathymetry, topography, sediment transport and coastal damages). It starts with an overview of wave prediction limits (based on satellite images) in a restricted domain such as is the Mediterranean basin, followed by an in-depth analysis of the Catalan coast, one of the land boundaries of such a domain. The morphodynamic modeling for such gradient regions is next illustrated with the simulation of the largest recorded storm in the Catalan coast, whose morphological impact is a key element of the storm impact. The driving wave and surge conditions produce a morphodynamic response that is validated against the pre and post storm beach state, recovered from two LIDAR images. The quality of the fit is discussed in terms of the physical processes and the suitability of the employed modeling equations. Some remarks about the role of the numerical discretization and boundary conditions are also included in the analysis. From here an assessment of errors and uncertainties is presented, with the aim of establishing the prediction limits for coastal engineering flooding and erosion analyses.

Electrical activity of the cingulate cortex. II. Cholinergic modulation.

PubMed

Borst, J G; Leung, L W; MacFabe, D F

1987-03-24

The role of the cholinergic innervation in the modulation of cingulate electrical activity was studied by means of pharmacological manipulations and brain lesions. In the normal rat, an irregular slow activity (ISA) accompanied with EEG-spikes was recorded in the cingulate cortex during immobility as compared to walking. Atropine sulfate, but not atropine methyl nitrate, increased ISA and the frequency of cingulate EEG-spikes. Pilocarpine suppressed ISA and EEG-spikes during immobility, and induced a slow (4-7 Hz) theta rhythm. Unilateral or bilateral lesions of the substantia innominata and ventral globus pallidus area using kainic acid did not significantly change the cingulate EEG or its relation to behavior. Large electrolytic lesions of the medial septal nuclei and vertical limbs of the diagonal band generally decreased or abolished all theta activity in the cingulate cortex and the hippocampus. However, in 5 rats the cingulate theta rhythm increased while the hippocampal theta disappeared after a medial septal lesion. The large, postlesion cingulate theta, accompanied by sharp EEG-spikes during its negative phase, is an unequivocal demonstration of the existence of a theta rhythm in the cingulate cortex, independent of the hippocampal rhythm. Cholinergic afferents from the medial septum and diagonal band nuclei are inferred to be responsible for the behavioral suppression of cingulate EEG-spikes and ISA, and partially for the generation of a local cingulate theta rhythm. However, an atropine-resistant pathway and a theta-suppressing pathway, possibly coming from the medial septum or the hippocampus, may also be important in cingulate theta generation.

Oscillatory bands, neuronal synchrony and hippocampal function: implications of the effects of prenatal choline supplementation for sleep-dependent memory consolidation.

PubMed

Cheng, Ruey-Kuang; Williams, Christina L; Meck, Warren H

2008-10-27

Choline supplementation of the maternal diet has long-term facilitative effects on spatial and temporal memory processes in the offspring. To further delineate the impact of early nutritional status on brain and behavior, we examined effects of prenatal-choline availability on hippocampal oscillatory frequency bands in 12 month-old male and female rats. Adult offspring of time-pregnant dams that were given a deficient level of choline (DEF=0.0 g/kg), sufficient choline (CON=1.1 g/kg) or supplemental choline (SUP=3.5 g/kg) in their chow during embryonic days (ED) 12-17 were implanted with an electroencephalograph (EEG) electrode in the hippocampal dentate gyrus in combination with an electromyograph (EMG) electrode patch implanted in the nuchal muscle. Five consecutive 8-h recording sessions revealed differential patterns of EEG activity as a function of awake, slow-wave sleep (SWS) and rapid-eye movement (REM) sleep states and prenatal choline status. The main finding was that SUP rats displayed increased power levels of gamma (30-100 Hz) band oscillations during all phases of the sleep/wake cycle. These findings are discussed within the context of a general review of neuronal oscillations (e.g., delta, theta, and gamma bands) and synchronization across multiple brain regions in relation to sleep-dependent memory consolidation in the hippocampus.

Dysbindin-1, WAVE2 and Abi-1 form a complex that regulates dendritic spine formation.

PubMed

Ito, H; Morishita, R; Shinoda, T; Iwamoto, I; Sudo, K; Okamoto, K; Nagata, K

2010-10-01

Genetic variations in dysbindin-1 (dystrobrevin-binding protein-1) are one of the most commonly reported variations associated with schizophrenia. As schizophrenia could be regarded as a neurodevelopmental disorder resulting from abnormalities of synaptic connectivity, we attempted to clarify the function of dysbindin-1 in neuronal development. We examined the developmental change of dysbindin-1 in rat brain by western blotting and found that a 50 kDa isoform is highly expressed during the embryonic stage, whereas a 40 kDa one is detected at postnatal day 11 and increased thereafter. Immunofluorescent analyses revealed that dysbindin-1 is enriched at the spine-like structure of primary cultured rat hippocampal neurons. We identified WAVE2, but not N-WASP, as a binding partner for dysbindin-1. We also found that Abi-1, a binding molecule for WAVE2 involved in spine morphogenesis, interacts with dysbindin-1. Although dysbindin-1, WAVE2 and Abi-1 form a ternary complex, dysbindin-1 promoted the binding of WAVE2 to Abi-1. RNA interference-mediated knockdown of dysbindin-1 led to the generation of abnormally elongated immature dendritic protrusions. The present results indicate possible functions of dysbindin-1 at the postsynapse in the regulation of dendritic spine morphogenesis through the interaction with WAVE2 and Abi-1.

A frequency domain linearized Navier-Stokes equations approach to acoustic propagation in flow ducts with sharp edges.

PubMed

Kierkegaard, Axel; Boij, Susann; Efraimsson, Gunilla

2010-02-01

Acoustic wave propagation in flow ducts is commonly modeled with time-domain non-linear Navier-Stokes equation methodologies. To reduce computational effort, investigations of a linearized approach in frequency domain are carried out. Calculations of sound wave propagation in a straight duct are presented with an orifice plate and a mean flow present. Results of transmission and reflections at the orifice are presented on a two-port scattering matrix form and are compared to measurements with good agreement. The wave propagation is modeled with a frequency domain linearized Navier-Stokes equation methodology. This methodology is found to be efficient for cases where the acoustic field does not alter the mean flow field, i.e., when whistling does not occur.

Computational and experimental investigation of two-dimensional scramjet inlets and hypersonic flow over a sharp flat plate

NASA Astrophysics Data System (ADS)

Messitt, Donald G.

1999-11-01

The WIND code was employed to compute the hypersonic flow in the shock wave boundary layer merged region near the leading edge of a sharp flat plate. Solutions were obtained at Mach numbers from 9.86 to 15.0 and free stream Reynolds numbers of 3,467 to 346,700 in-1 (1.365 · 105 to 1.365 · 107 m-1) for perfect gas conditions. The numerical results indicated a merged shock wave and viscous layer near the leading edge. The merged region grew in size with increasing free stream Mach number, proportional to Minfinity 2/Reinfinity. Profiles of the static pressure in the merged region indicated a strong normal pressure gradient (∂p/∂y). The normal pressure gradient has been neglected in previous analyses which used the boundary layer equations. The shock wave near the leading edge was thick, as has been experimentally observed. Computed shock wave locations and surface pressures agreed well within experimental error for values of the rarefaction parameter, chi/M infinity2 < 0.3. A preliminary analysis using kinetic theory indicated that rarefied flow effects became important above this value. In particular, the WIND solution agreed well in the transition region between the merged flow, which was predicted well by the theory of Li and Nagamatsu, and the downstream region where the strong interaction theory applied. Additional computations with the NPARC code, WIND's predecessor, demonstrated the ability of the code to compute hypersonic inlet flows at free stream Mach numbers up to 20. Good qualitative agreement with measured pressure data indicated that the code captured the important physical features of the shock wave - boundary layer interactions. The computed surface and pitot pressures fell within the combined experimental and numerical error bounds for most points. The calculations demonstrated the need for extremely fine grids when computing hypersonic interaction flows.

Electron Density Dropout Near Enceladus in the Context of Water-Vapor and Water-Ice

NASA Technical Reports Server (NTRS)

Farrell, W. M.; Kurth, W. S.; Gurnett, D. A.; Johnson, R. E.; Kaiser, M. L.; Wahlund, J.-E.; Waite, J. H., Jr.

2009-01-01

On 12 March 2008, the Cassini spacecraft made a close encounter with the Saturnian moon Enceladus, passing within 52 km of the moon. The spacecraft trajectory was intentionally-oriented in a southerly direction to create a close alignment with the intense water-dominated plumes emitted from the south polar region. During the passage, the Cassini Radio and Plasma Wave System (RPWS) detected two distinct radio signatures: 1) Impulses associated with small water-ice dust grain impacts and 2) an upper hybrid (UH) resonance emission that both intensified and displayed a sharp frequency decrease in the near-vicinity of the moon. The frequency decrease of the UH emission is associated with an unexpectedly sharp decrease in electron density from approximately 90 el/cubic cm to below 20 el/cubic cm that occurs on a time scale of a minute near the closest encounter with the moon. In this work, we consider a number of scenarios to explain this sharp electron dropout, but surmise that electron absorption by ice grains is the most likely process.

Biological effects of two successive shock waves focused on liver tissues and melanoma cells.

PubMed

Benes, J; Sunka, P; Králová, J; Kaspar, J; Poucková, P

2007-01-01

A new generator of two successive shock waves focused to a common focal point has been developed. Cylindrical pressure waves created by multichannel electrical discharges on two cylindrical composite anodes are focused by a metallic parabolic reflector - cathode, and near the focus they are transformed to strong shock waves. Schlieren photos of the focal region have demonstrated that mutual interaction of the two waves results in generation of a large number of secondary short-wavelength shocks. Interaction of the focused shockwaves with liver tissues and cancer cell suspensions was investigated. Localized injury of rabbit liver induced by the shock waves was demonstrated by magnetic resonance imaging. Histological analysis of liver samples taken from the injured region revealed that the transition between the injured and the healthy tissues is sharp. Suspension of melanoma B16 cells was exposed and the number of the surviving cells rapidly decreased with increasing number of shocks and only 8 % of cells survived 350 shocks. Photographs of cells demonstrate that even small number of shocks results in perforation of cell membranes.

Marked surface inversions and wind shear: A safety risk for departing aircraft

NASA Technical Reports Server (NTRS)

Korhonen, O.

1983-01-01

Marked surface inversions occur most frequently in dry continental climates, where low atmospheric humidity allows heat transfer by long wave thermal radiation. In the northern latitudes, surface inversions reach their maximum intensity during the winter, when the incoming Sun's radiation is negligible and radiative cooling is dominant during the long nights. During winter, air mass boundaries are sharp, which causes formation of marked surface inversions. The existence of these inversions and sharp boundaries increase the risk of wind shear. The information should refer to marked inversions exceeding a temperature difference of 10 deg C up to 1000 feet. The need to determine the temperature range over which he information is operationally needed and the magnitude of the inversion required before a notification to pilots prior to departure is warranted are outlined.

Super-focusing of center-covered engineered microsphere.

PubMed

Wu, Mengxue; Chen, Rui; Soh, Jiahao; Shen, Yue; Jiao, Lishi; Wu, Jianfeng; Chen, Xudong; Ji, Rong; Hong, Minghui

2016-08-16

Engineered microsphere possesses the advantage of strong light manipulation at sub-wavelength scale and emerges as a promising candidate to shrink the focal spot size. Here we demonstrated a center-covered engineered microsphere which can adjust the transverse component of the incident beam and achieve a sharp photonic nanojet. Modification of the beam width and working distance of the photonic nanojet were achieved by tuning the cover ratio of the engineered microsphere, leading to a sharp spot size which exceeded the optical diffraction limit. At a wavelength of 633 nm, a focal spot of 245 nm (0.387 λ) was achieved experimentally under plane wave illumination. Strong localized field with Bessel-like distribution was demonstrated by employing the linearly polarized beam and a center-covered mask being engineered on the microsphere.

Super-focusing of center-covered engineered microsphere

PubMed Central

Wu, Mengxue; Chen, Rui; Soh, Jiahao; Shen, Yue; Jiao, Lishi; Wu, Jianfeng; Chen, Xudong; Ji, Rong; Hong, Minghui

2016-01-01

Engineered microsphere possesses the advantage of strong light manipulation at sub-wavelength scale and emerges as a promising candidate to shrink the focal spot size. Here we demonstrated a center-covered engineered microsphere which can adjust the transverse component of the incident beam and achieve a sharp photonic nanojet. Modification of the beam width and working distance of the photonic nanojet were achieved by tuning the cover ratio of the engineered microsphere, leading to a sharp spot size which exceeded the optical diffraction limit. At a wavelength of 633 nm, a focal spot of 245 nm (0.387 λ) was achieved experimentally under plane wave illumination. Strong localized field with Bessel-like distribution was demonstrated by employing the linearly polarized beam and a center-covered mask being engineered on the microsphere. PMID:27528093

Proceedings of Hawaiian Winter Workshop (6th) on Dynamics of Oceanic Internal Gravity Waves Held in Manoa, Hawaii on 15-18 January 1991

DTIC Science & Technology

1991-11-01

Gravity Waves 12. PERSONAL AUTHOR(S) MUller, Peter and Henderson, Diane (eds.) 13a. TYPE OF REPORT 13b TIME COVERED 14. DATE OF REPORT (Year, Month, Day) 15...differ by 27r in defining the buoyancy scale.) Because the largest overturns must be several times larger than Dillon’s rms scale, LB is a good upper...0.6 times GM76 at 0.01 cpm. From there, they slope upward as k+ 0.0 7 and k+0 16. The shallow spectrum makes a sharp transition at the rolloff and

Development and Application of PIV in Supersonic flows

NASA Astrophysics Data System (ADS)

Rong, Z.; Liu, H.; Chen, F.

2011-09-01

This paper presents PIV measurements obtained in Mach 4.0 flowfields performed in the SJTU Hypersonic wind tunnel (HWT). In order to certificate this technique, PIV experiments were conducted to the empty test section to provide uniform flow data for comparison with analysis data. Dynamical properties of particle tracers were investigated to measure the particle response across an oblique shock wave. The flow over a sharp cone at Ma = 4.0 were tested in comparasion with the CFD and schlieren visualization. It is shown that shock wave angles measured with PIV are in good agreement with theory and schlieren visualization, in addition the overall flow is consistent with the CFD results.

Novel Experience Induces Persistent Sleep-Dependent Plasticity in the Cortex but not in the Hippocampus

PubMed Central

Ribeiro, Sidarta; Shi, Xinwu; Engelhard, Matthew; Zhou, Yi; Zhang, Hao; Gervasoni, Damien; Lin, Shi-Chieh; Wada, Kazuhiro; Lemos, Nelson A.M.

2007-01-01

Episodic and spatial memories engage the hippocampus during acquisition but migrate to the cerebral cortex over time. We have recently proposed that the interplay between slow-wave (SWS) and rapid eye movement (REM) sleep propagates recent synaptic changes from the hippocampus to the cortex. To test this theory, we jointly assessed extracellular neuronal activity, local field potentials (LFP), and expression levels of plasticity-related immediate-early genes (IEG) arc and zif-268 in rats exposed to novel spatio-tactile experience. Post-experience firing rate increases were strongest in SWS and lasted much longer in the cortex (hours) than in the hippocampus (minutes). During REM sleep, firing rates showed strong temporal dependence across brain areas: cortical activation during experience predicted hippocampal activity in the first post-experience hour, while hippocampal activation during experience predicted cortical activity in the third post-experience hour. Four hours after experience, IEG expression was specifically upregulated during REM sleep in the cortex, but not in the hippocampus. Arc gene expression in the cortex was proportional to LFP amplitude in the spindle-range (10–14 Hz) but not to firing rates, as expected from signals more related to dendritic input than to somatic output. The results indicate that hippocampo-cortical activation during waking is followed by multiple waves of cortical plasticity as full sleep cycles recur. The absence of equivalent changes in the hippocampus may explain its mnemonic disengagement over time. PMID:18982118

Postictal psychosis and its electrophysiological correlates in invasive EEG: a case report study and literature review.

PubMed

Kuba, Robert; Brázdil, Milan; Rektor, Ivan

2012-04-01

We identified two patients with medically refractory temporal lobe epilepsy, from whom intracranial EEG recordings were obtained at the time of postictal psychosis. Both patients had mesial temporal epilepsy associated with hippocampal sclerosis. In both patients, the postictal psychosis was associated with a continual "epileptiform" EEG pattern that differed from their interictal and ictal EEG findings (rhythmical slow wave and "abortive" spike-slow wave complex activity in the right hippocampus and lateral temporal cortex in case 1 and a periodic pattern of triphasic waves in the contacts recording activity from the left anterior cingulate gyrus). Some cases of postictal psychosis might be caused by the transient impairment of several limbic system structures due to the "continual epileptiform discharge" in some brain regions. Case 2 is the first report of a patient with TLE in whom psychotic symptoms were associated with the epileptiform impairment of the anterior cingulate gyrus. Copyright © 2012 Elsevier Inc. All rights reserved.

Midlatitude D region variations measured from broadband radio atmospherics

NASA Astrophysics Data System (ADS)

Han, Feng

The high power, broadband very low frequency (VLF, 3--30 kHz) and extremely low frequency (ELF, 3--3000 Hz) electromagnetic waves generated by lightning discharges and propagating in the Earth-ionosphere waveguide can be used to measure the average electron density profile of the lower ionosphere (D region) across the wave propagation path due to several reflections by the upper boundary (lower ionosphere) of the waveguide. This capability makes it possible to frequently and even continuously monitor the D region electron density profile variations over geographically large regions, which are measurements that are essentially impossible by other means. These guided waves, usually called atmospherics (or sferics for short), are recorded by our sensors located near Duke University. The purpose of this work is to develop and implement algorithms to derive the variations of D region electron density profile which is modeled by two parameters (one is height and another is sharpness), by comparing the recorded sferic spectra to a series of model simulated sferic spectra from using a finite difference time domain (FDTD) code. In order to understand the time scales, magnitudes and sources for the midlatitude nighttime D region variations, we analyzed the sferic data of July and August 2005, and extracted both the height and sharpness of the D region electron density profile. The heights show large temporal variations of several kilometers on some nights and the relatively stable behavior on others. Statistical calculations indicate that the hourly average heights during the two months range between 82.0 km and 87.2 km with a mean value of 84.9 km and a standard deviation of 1.1 km. We also observed spatial variations of height as large as 2.0 km over 5 degrees latitudes on some nights, and no spatial variation on others. In addition, the measured height variations exhibited close correlations with local lightning occurrence rate on some nights but no correlation with local lightning or displaced lightning on others. The nighttime profile sharpness during 2.5 hours in two different nights was calculated, and the results were compared to the equivalent sharpness derived from International Reference Ionosphere (IRI) models. Both the absolute values and variation trends in IRI models are different from those in broadband measurements. Based on sferic data similar to those for nighttime, we also measured the day-time D region electron density profile variations in July and August 2005 near Duke University. As expected, the solar radiation is the dominant but not the only determinant source for the daytime D region profile height temporal variations. The observed quiet time heights showed close correlations with solar zenith angle changes but unexpected spatial variations not linked to the solar zenith angle were also observed on some days, with 15% of days exhibiting regional differences larger than 0.5 km. During the solar flare, the induced height change was approximately proportional to the logarithm of the X-ray fluxes. During the rising and decaying phases of the solar flare, the height changes correlated more consistently with the short (wavelength 0.5--4 A), rather than the long (wavelength 1--8 A) X-ray flux changes. The daytime profile sharpness during morning, noontime and afternoon periods in three different days and for the solar zenith angle range 20 to 75 degrees was calculated. These broadband measured results were compared to narrowband VLF measurements, IRI models and Faraday rotation base IRI models (called FIRI). The estimated sharpness from all these sources was more consistent when the solar zenith angle was small than when it was large. By applying the nighttime and daytime measurement techniques, we also derived the D region variations during sunrise and sunset periods. The measurements showed that both the electron density profile height and sharpness decrease during the sunrise period while increase during the sunset period.

Exploring Moho sharpness in Northeastern North China Craton with frequency-dependence analysis of Ps receiver function

NASA Astrophysics Data System (ADS)

Zhang, P.; Yao, H.; Chen, L.; WANG, X.; Fang, L.

2017-12-01

The North China Craton (NCC), one of the oldest cratons in the world, has attracted wide attention in Earth Science for decades because of the unusual Mesozoic destruction of its cratonic lithosphere. Understanding the deep processes and mechanism of this craton destruction demands detailed knowledge about the deep structure of this region. In this study, we calculate P-wave receiver functions (RFs) with two-year teleseismic records from the North China Seismic Array ( 200 stations) deployed in the northeastern NCC. We observe both diffused and concentered PpPs signals from the Moho in RF waveforms, which indicates heterogeneous Moho sharpness variations in the study region. Synthetic Ps phases generated from broad positive velocity gradients at the depth of the Moho (referred as Pms) show a clear frequency dependence nature, which in turn is required to constrain the sharpness of the velocity gradient. Practically, characterizing such a frequency dependence feature in real data is challenging, because of low signal-to-noise ratio, contaminations by multiples generated from shallow structure, distorted signal stacking especially in double-peak Pms signals, etc. We attempt to address these issues by, firstly, utilizing a high-resolution Moho depth model of this region to predict theoretical delay times of Pms that facilitate more accurate Pms identifications. The Moho depth model is derived by wave-equation based poststack depth migration on both Ps phase and surface-reflected multiples in RFs in our previous study (Zhang et al., submitted to JGR). Second, we select data from a major back azimuth range of 100° - 220° that includes 70% teleseismic events due to the uneven data coverage and to avoid azimuthal influence as well. Finally, we apply an adaptive cross-correlation stacking of Pms signals in RFs for each station within different frequency bands. High-quality Pms signals at different frequencies will be selected after careful visual inspection and adaptive cross-correlation stacking. At last, we will model the stacked Pms signals within different frequency bands to obtain the final sharpness of crust-mantle boundary, which may shed new lights on understanding the mechanism of cratonic reactivation and destruction in the NCC.

Survey of shock-wave structures of smooth-particle granular flows.

PubMed

Padgett, D A; Mazzoleni, A P; Faw, S D

2015-12-01

We show the effects of simulated supersonic granular flow made up of smooth particles passing over two prototypical bodies: a wedge and a disk. We describe a way of computationally identifying shock wave locations in granular flows and tabulate the shock wave locations for flow over wedges and disks. We quantify the shock structure in terms of oblique shock angle for wedge impediments and shock standoff distance for disk impediments. We vary granular flow parameters including upstream volume fraction, average upstream velocity, granular temperature, and the collision coefficient of restitution. Both wedges and disks have been used in the aerospace community as prototypical impediments to flowing air in order to investigate the fundamentally different shock structures emanating from sharp and blunt bodies, and we present these results in order to increase the understanding of the fundamental behavior of supersonic granular flow.

New technique for excitation of bulk and surface spin waves in ferromagnets

NASA Astrophysics Data System (ADS)

Bogacz, S. A.; Ketterson, J. B.

1985-09-01

A meander-line magnetic transducer is discussed in the context of bulk and surface spin-wave generation in ferromagnets. The magnetic field created by the transducer was calculated in closed analytic form for this model. The linear response of the ferromagnet to the inhomogenous surface disturbance of arbitrary ω and k was obtained as a self-consistent solution to the Bloch equation of motion and the Maxwell equations, subject to appropriate boundary condition. In particular, the energy flux through the boundary displays a sharp resonantlike absorption maximum concentrated at the frequency of the magnetostatic Damon-Eshbach (DE) surface mode; furthermore, the energy transfer spectrum is cut off abruptly below the threshold frequency of the bulk spin waves. The application of the meander line to the spin diffusion problem in NMR is also discussed.

Blast waves from detonated military explosive reduce GluR1 and synaptophysin levels in hippocampal slice cultures✩

PubMed Central

Smith, Marquitta; Piehler, Thuvan; Benjamin, Richard; Farizatto, Karen L.; Pait, Morgan C.; Almeida, Michael F.; Ghukasyan, Vladimir V.; Bahr, Ben A.

2017-01-01

Explosives create shockwaves that cause blast-induced neurotrauma, one of the most common types of traumatic brain injury (TBI) linked to military service. Blast-induced TBIs are often associated with reduced cognitive and behavioral functions due to a variety of factors. To study the direct effects of military explosive blasts on brain tissue, we removed systemic factors by utilizing rat hippocampal slice cultures. The long-term slice cultures were briefly sealed air-tight in serum-free medium, lowered into a 37 °C water-filled tank, and small 1.7-gram assemblies of cyclotrimethylene trinitramine (RDX) were detonated 15 cm outside the tank, creating a distinct shockwave recorded at the culture plate position. Compared to control mock-treated groups of slices that received equal submerge time, 1–3 blast impacts caused a dose-dependent reduction in the AMPA receptor subunit GluR1. While only a small reduction was found in hippocampal slices exposed to a single RDX blast and harvested 1–2 days later, slices that received two consecutive RDX blasts 4 min apart exhibited a 26–40% reduction in GluR1, and the receptor subunit was further reduced by 64–72% after three consecutive blasts. Such loss correlated with increased levels of HDAC2, a histone deacetylase implicated in stress-induced reduction of glutamatergic transmission. No evidence of synaptic marker recovery was found at 72 h post-blast. The presynaptic marker synaptophysin was found to have similar susceptibility as GluR1 to the multiple explosive detonations. In contrast to the synaptic protein reductions, actin levels were unchanged, spectrin breakdown was not detected, and Fluoro-Jade B staining found no indication of degenerating neurons in slices exposed to three RDX blasts, suggesting that small, sub-lethal explosives are capable of producing selective alterations to synaptic integrity. Together, these results indicate that blast waves from military explosive cause signs of synaptic compromise without producing severe neurodegeneration, perhaps explaining the cognitive and behavioral changes in those blast-induced TBI sufferers that have no detectable neuropathology. PMID:27720798

Sharp at any Age: Moho boundary thickness estimates along a trans-sect through 2 Ga of tectonic history.

NASA Astrophysics Data System (ADS)

Servali, A.; Levin, V. L.; VanTongeren, J. A.

2015-12-01

In this study we evaluate crustal thickness and Moho sharpness beneath seismic stations in three different tectonic units of the North American continent: the Archean Superior Province, the Proterozoic Grenville Province, and the Paleozoic Appalachian Orogen. Our analysis involves two steps. First, for each site, we produce P-to-S receiver functions (RFs) organized by backazimuth and epicentral distance, and use them to identify the phase most likely representing a conversion from the Moho. Second, we construct averaged RFs for groups of telesismic events located in a similar geographic region, which we employ to examine shapes of Moho P-to-S converted phases in time series with maximum frequencies increasing from 0.25Hz to 2-3 Hz. At some sites we observe a progressive narrowing of a simple Moho converted phase with an increase in frequency, typical of a vertically instantaneous boundary, while at others the converted phase becomes progressively more complex, typical of a diffuse Moho. Thus, we adopt this difference in converted wave shape dependence on increasing frequency as a measure of Moho thickness. Our estimates of Moho thickness range from less than 300 m to over 2 km, with some locations showing evidence for multiple converting boundaries in the 35-50 km depth range. In this study we define "sharp" Moho at those sites where its vertical thickness is less than 1 km. Our results show that sharp Moho is universal in the Archean terranes regardless of surface lithology, likely due to higher Moho temperatures facilitating wide-spread delamination of dense lower crustal rocks. While a sharp Moho is not unique to the Superior Province, all Grenville and Appalachians sites where we find sharp Moho are in regions of granitic plutonism, suggesting a possible general association with reworking and density sorting of the crustal material (e.g. volcanic arc).

Kv7/KCNQ/M and HCN/h, but not KCa2/SK channels, contribute to the somatic medium after-hyperpolarization and excitability control in CA1 hippocampal pyramidal cells

PubMed Central

Gu, Ning; Vervaeke, Koen; Hu, Hua; Storm, Johan F

2005-01-01

In hippocampal pyramidal cells, a single action potential (AP) or a burst of APs is followed by a medium afterhyperpolarization (mAHP, lasting ∼0.1 s). The currents underlying the mAHP are considered to regulate excitability and cause early spike frequency adaptation, thus dampening the response to sustained excitatory input relative to responses to abrupt excitation. The mAHP was originally suggested to be primarily caused by M-channels (at depolarized potentials) and h-channels (at more negative potentials), but not SK channels. In recent reports, however, the mAHP was suggested to be generated mainly by SK channels or only by h-channels. We have now re-examined the mechanisms underlying the mAHP and early spike frequency adaptation in CA1 pyramidal cells by using sharp electrode and whole-cell recording in rat hippocampal slices. The specific M-channel blocker XE991 (10 μm) suppressed the mAHP following 1–5 APs evoked by current injection at −60 mV. XE991 also enhanced the excitability of the cell, i.e. increased the number of APs evoked by a constant depolarizing current pulse, reduced their rate of adaptation, enhanced the afterdepolarization and promoted bursting. Conversely, the M-channel opener retigabine reduced excitability. The h-channel blocker ZD7288 (4-ethylphenylamino-1,2-dimethyl-6-methylaminopyrimidinium chloride; 10 μm) fully suppressed the mAHP at −80 mV, but had little effect at −60 mV, whereas XE991 did not measurably affect the mAHP at −80 mV. Likewise, ZD7288 had little or no effect on excitability or adaptation during current pulses injected from −60 mV, but changed the initial discharge during depolarizing pulses injected from −80 mV. In contrast to previous reports, we found that blockade of Ca2+-activated K+ channels of the SK/KCa type by apamin (100–400 nm) failed to affect the mAHP or adaptation. A computational model of a CA1 pyramidal cell predicted that M- and h-channels will generate mAHPs in a voltage-dependent manner, as indicated by the experiments. We conclude that M- and h-channels generate the somatic mAHP in hippocampal pyramidal cells, with little or no net contribution from SK channels. PMID:15890705

Wave energy trapping and localization in a plate with a delamination

NASA Astrophysics Data System (ADS)

Glushkov, Evgeny; Glushkova, Natalia; Golub, Mikhail V.; Moll, Jochen; Fritzen, Claus-Peter

2012-12-01

The research aims at an experimental approval of the trapping mode effect theoretically predicted for an elastic plate-like structure with a horizontal crack. The effect is featured by a sharp capture of incident wave energy at certain resonance frequencies with its localization between the crack and plate surfaces in the form of energy vortices yielding long-enduring standing waves. The trapping modes are eigensolutions of the related diffraction problem associated with nearly real complex points of its discrete frequency spectrum. To detect such resonance motion, a laser vibrometer based system has been employed for the acquisition and appropriate visualization of piezoelectrically actuated out-of-plane surface motion of a two-layer aluminum plate with an artificial strip-like delamination. The measurements at resonance and off-resonance frequencies have revealed a time-harmonic oscillation of good quality above the delamination in the resonance case. It lasts for a long time after the scattered waves have left that area. The measured frequency of the trapped standing-wave oscillation is in a good agreement with that predicted using the integral equation based mathematical model.

Receptivity of Hypersonic Boundary Layers to Acoustic and Vortical Disturbances

NASA Technical Reports Server (NTRS)

Balakamar, P.; Kegerise, Michael A.

2011-01-01

Boundary layer receptivity to two-dimensional acoustic disturbances at different incidence angles and to vortical disturbances is investigated by solving the Navier-Stokes equations for Mach 6 flow over a 7deg half-angle sharp-tipped wedge and a cone. Higher order spatial and temporal schemes are employed to obtain the solution. The results show that the instability waves are generated in the leading edge region and that the boundary layer is much more receptive to slow acoustic waves as compared to the fast waves. It is found that the receptivity of the boundary layer on the windward side (with respect to the acoustic forcing) decreases when the incidence angle is increased from 0 to 30 degrees. However, the receptivity coefficient for the leeward side is found to vary relatively weakly with the incidence angle. The maximum receptivity is obtained when the wave incident angle is about 20 degrees. Vortical disturbances also generate unstable second modes, however the receptivity coefficients are smaller than that for the acoustic waves. Vortical disturbances first generate the fast acoustic modes and they switch to the slow mode near the continuous spectrum.

Quasi-relativistic electron precipitation due to interactions with coherent VLF waves in the magnetosphere

NASA Technical Reports Server (NTRS)

Chang, H. C.; Inan, U. S.

1983-01-01

The equations of motion for the cyclotron resonance interaction between coherent whistler mode waves and energetic particles are rederived with the inclusion of relativistic effects. The pitch angle scattering of the near-loss-cone quasi-relativistic electrons trapped in the magnetosphere is studied using a test particle method employing these relativistic equations, and the precipitated energy spectrum due to the wave-induced perturbations of a full distribution of particles is computed. Results show that the full width at half maximum peak width of the rms scattering pattern of the near-loss-cone particles would give an upper bound to the peak width of the associated precipitated energy spectrum under the conditions of moderate wave intensities in the low L shell region. In addition, it is found that the peak widths are within the upper limit values measured by recent satellite experiments. It is concluded that interactions of inner radiation belt particles with monochromatic waves could produce precipitated fluxes with relatively sharp spectral widths, and that therefore the L-dependent narrow peaks observed by low altitude satellite particle detectors could be caused by such interactions.

Observations of the directional distribution of the wind energy input function over swell waves

NASA Astrophysics Data System (ADS)

Shabani, Behnam; Babanin, Alex V.; Baldock, Tom E.

2016-02-01

Field measurements of wind stress over shallow water swell traveling in different directions relative to the wind are presented. The directional distribution of the measured stresses is used to confirm the previously proposed but unverified directional distribution of the wind energy input function. The observed wind energy input function is found to follow a much narrower distribution (β∝cos⁡3.6θ) than the Plant (1982) cosine distribution. The observation of negative stress angles at large wind-wave angles, however, indicates that the onset of negative wind shearing occurs at about θ≈ 50°, and supports the use of the Snyder et al. (1981) directional distribution. Taking into account the reverse momentum transfer from swell to the wind, Snyder's proposed parameterization is found to perform exceptionally well in explaining the observed narrow directional distribution of the wind energy input function, and predicting the wind drag coefficients. The empirical coefficient (ɛ) in Snyder's parameterization is hypothesised to be a function of the wave shape parameter, with ɛ value increasing as the wave shape changes between sinusoidal, sawtooth, and sharp-crested shoaling waves.

Time-Frequency Analysis of Boundary-Layer Instabilites Generated by Freestream Laser Perturbations

NASA Technical Reports Server (NTRS)

Chou, Amanda; Schneider, Steven P.

2015-01-01

A controlled disturbance is generated in the freestream of the Boeing/AFOSR Mach-6 Quiet Tunnel (BAM6QT) by focusing a high-powered Nd:YAG laser to create a laser-induced breakdown plasma. The plasma then cools, creating a freestream thermal disturbance that can be used to study receptivity. The freestream disturbance convects down-stream in the Mach-6 wind tunnel to interact with a flared cone model. The adverse pressure gradient created by the flare of the model is capable of generating second-mode instability waves that grow large and become nonlinear before experiencing natural transition in quiet flow. The freestream laser perturbation generates a wave packet in the boundary layer at the same frequency as the natural second mode, complicating time-independent analyses of the effect of the laser perturbation. The data show that the laser perturbation creates an instability wave packet that is larger than the natural waves on the sharp flared cone. The wave packet is still difficult to distinguish from the natural instabilities on the blunt flared cone.

Effects of homogeneous condensation in compressible flows: Ludwieg-tube experiments and simulations

NASA Astrophysics Data System (ADS)

Luo, Xisheng; Lamanna, Grazia; Holten, A. P. C.; van Dongen, M. E. H.

Effects of homogeneous nucleation and subsequent droplet growth in compressible flows in humid nitrogen are investigated numerically and experimentally. A Ludwieg tube is employed to produce expansion flows. Corresponding to different configurations, three types of experiment are carried out in such a tube. First, the phase transition in a strong unsteady expansion wave is investigated to demonstrate the mutual interaction between the unsteady flow and the condensation process and also the formation of condensation-induced shock waves. The role of condensation-induced shocks in the gradual transition from a frozen initial structure to an equilibrium structure is explained. Second, the condensing flow in a slender supersonic nozzle G2 is considered. Particular attention is given to condensation-induced oscillations and to the transition from symmetrical mode-1 oscillations to asymmetrical mode-2 oscillations in a starting nozzle flow, as first observed by Adam & Schnerr. The transition is also found numerically, but the amplitude, frequency and transition time are not yet well predicted. Third, a sharp-edged obstacle is placed in the tube to generate a starting vortex. Condensation in the vortex is found. Owing to the release of latent heat of condensation, an increase in the pressure and temperature in the vortex core is observed. Condensation-induced shock waves are found, for a sufficiently high initial saturation ratio, which interact with the starting vortex, resulting in a very complex flow. As time proceeds, a subsonic or transonic free jet is formed downstream of the sharp-edged obstacle, which becomes oscillatory for a relatively high main-flow velocity and for a sufficiently high humidity.

Frequency dependence of behavioral modulation by hippocampal electrical stimulation

PubMed Central

La Corte, Giorgio; Wei, Yina; Chernyy, Nick; Gluckman, Bruce J.

2013-01-01

Electrical stimulation offers the potential to develop novel strategies for the treatment of refractory medial temporal lobe epilepsy. In particular, direct electrical stimulation of the hippocampus presents the opportunity to modulate pathological dynamics at the ictal focus, although the neuroanatomical substrate of this region renders it susceptible to altering cognition and affective processing as a side effect. We investigated the effects of three electrical stimulation paradigms on separate groups of freely moving rats (sham, 8-Hz and 40-Hz sine-wave stimulation of the ventral/intermediate hippocampus, where 8- and 40-Hz stimulation were chosen to mimic naturally occurring hippocampal oscillations). Animals exhibited attenuated locomotor and exploratory activity upon stimulation at 40 Hz, but not at sham or 8-Hz stimulation. Such behavioral modifications were characterized by a significant reduction in rearing frequency, together with increased freezing behavior. Logistic regression analysis linked the observed changes in animal locomotion to 40-Hz electrical stimulation independently of time-related variables occurring during testing. Spectral analysis, conducted to monitor the electrophysiological profile in the CA1 area of the dorsal hippocampus, showed a significant reduction in peak theta frequency, together with reduced theta power in the 40-Hz vs. the sham stimulation animal group, independent of locomotion speed (theta range: 4–12 Hz). These findings contribute to the development of novel and safe medical protocols by indicating a strategy to constrain or optimize parameters in direct hippocampal electrical stimulation. PMID:24198322

Modeling Mars Cyclogenesis and Frontal Waves: Seasonal Variations and Implications on Dust Activity

NASA Technical Reports Server (NTRS)

Hollingsworth, J. L.; Kahre, M. A.

2014-01-01

Between late autumn through early spring,middle and high latitudes onMars exhibit strong equator-to-polemean temperature contrasts (i.e., "baroclinicity"). Data collected during the Viking era and observations from both the Mars Global Surveyor (MGS) and Mars Reconnaissance Orbiter (MRO) indicate that such strong baroclinicity supports vigorous, large-scale eastward traveling weather systems (i.e., transient synoptic period waves) [1, 2]. For a rapidly rotating, differentially heated, shallow atmosphere such as on Earth and Mars, these large-scale, extratropical weather disturbances are critical components of the global circulation. The wave-like disturbances serve as agents in the transport of heat and momentum between low and high latitudes of the planet. Through cyclonic/anticyclonic winds, intense shear deformations, contractions-dilatations in temperature and density, and sharp perturbations amongst atmospheric tracers (i.e., dust, volatiles (e.g., water vapor) and condensates (e.g., water-ice cloud particles)), Mars' extratropical weather systems have significant sub-synoptic scale ramifications by supporting atmospheric frontal waves (Fig. 1).

High-Resolution Observations of a Meteo-Tsunami

NASA Astrophysics Data System (ADS)

Assink, J. D.; Evers, L. G.; Smink, M.; Apituley, A.

2017-12-01

In the early morning of 29 May 2017, unusually large waves of over 2 m height hit the west coast of the Netherlands, leading to some property damage. The waves were due to a meteo-tsunami, which is a tsunami of meteorological origin, unlike seismogenic tsunamis. This particular event was caused by a rapidly moving cold front which featured a sharp squall line that moved towards the coast. Associated was a large perturbation in air pressure of 5 hPa which, along with Proudman resonance effects and the upsloping seabottom lead to the tidal surge. While the meteorological conditions leading up to such an event are relatively common, the more extreme events appear to happen under specific conditions only. As a result of the meteo-tsunami, gravity waves were observed all over the Netherlands with a variety of meteorlogical instruments, including weather radar, ceilometers and a network of microbarometers that are typically used for the detection of infrasound. In this presentation, these high-resolution observations of gravity waves are compared with mesoscale weather models.

[A case of Creutzfeldt-Jakob in the Mexican north-east and review of current concepts on prion disease].

PubMed

Calderón-Garcidueñas, A L; Sagastegui-Rodríguez, J A; Canales-Ibarra, C; Farías-García, R

2001-01-01

The case reported here is that of a 50-year-old man from Saltillo, Coahuila, Mexico, who during the previous 15 months developed a demential syndrome and myoclonia. The brain biopsy led to establish a diagnosis of spongiform encephalopathy. The EEG showed periodic sharp wave complexes over the right hemisphere. A review on about prion diseases is included.

Cosmic clustering

DOE PAGES

Anninos, Dionysios; Denef, Frederik

2016-06-30

We show that the late time Hartle-Hawking wave function for a free massless scalar in a fixed de Sitter background encodes a sharp ultrametric structure for the standard Euclidean distance on the space of field configurations. This implies a hierarchical, tree-like organization of the state space, reflecting its genesis as a branched diffusion process. In conclusion, an equivalent mathematical structure organizes the state space of the Sherrington-Kirkpatrick model of a spin glass.

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY: Instability and Death of Spiral Wave in a Two-Dimensional Array of Hindmarsh-Rose Neurons

NASA Astrophysics Data System (ADS)

Wang, Chun-Ni; Ma, Jun; Tang, Jun; Li, Yan-Long

2010-02-01

Spiral wave could be observed in the excitable media, the neurons are often excitable within appropriate parameters. The appearance and formation of spiral wave in the cardiac tissue is linked to monomorphic ventricular tachycardia that can denervate into polymorphic tachycardia and ventricular fibrillation. The neuronal system often consists of a large number of neurons with complex connections. In this paper, we theoretically study the transition from spiral wave to spiral turbulence and homogeneous state (death of spiral wave) in two-dimensional array of the Hindmarsh-Rose neuron with completely nearest-neighbor connections. In our numerical studies, a stable rotating spiral wave is developed and selected as the initial state, then the bifurcation parameters are changed to different values to observe the transition from spiral wave to homogeneous state, breakup of spiral wave and weak change of spiral wave, respectively. A statistical factor of synchronization is defined with the mean field theory to analyze the transition from spiral wave to other spatial states, and the snapshots of the membrane potentials of all neurons and time series of mean membrane potentials of all neurons are also plotted to discuss the change of spiral wave. It is found that the sharp changing points in the curve for factor of synchronization vs. bifurcation parameter indicate sudden transition from spiral wave to other states. And the results are independent of the number of neurons we used.

Frequent sleep-related bitemporal focal seizures in transient epileptic amnesia syndrome: Evidence from ictal video-EEG.

PubMed

Burkholder, David B; Jones, Amy L; Jones, David T; Fabris, Rachel R; Britton, Jeffrey W; Lagerlund, Terrence D; So, Elson L; Cascino, Gregory D; Worrell, Gregory A; Shin, Cheolsu; St Louis, Erik K

2017-06-01

Two patients who shared similar presenting clinical features of anterograde and retrograde autobiographical amnesia typical of transient epileptic amnesia (TEA) underwent prolonged video electroencephalogram (VEEG) monitoring and were found to have sleep-activated epileptiform activity and frequent subclinical bitemporal seizures predominantly during sleep. Case 1 is a 59-year-old woman whose presenting complaint was memory impairment. Over 18 months, she had three distinct 8-h-long episodes of confusion and disorientation with persistent anterograde and retrograde autobiographical amnesia. VEEG recorded frequent interictal bitemporal sharp waves confined to sleep, and 14 subclinical seizures, also mostly during sleep. Case 2 is a 50-year-old woman with known focal epilepsy also presented with memory complaints. Over the course of 1 year, she had two discrete 2-h-long episodes of amnesia, with ongoing anterograde and retrograde autobiographical amnesia. VEEG recorded independent bitemporal sharp waves, and 14 subclinical seizures during sleep and drowsiness. Memory impairment improved in both patients with successful treatment of their seizures. Although the etiology of accelerated long-term forgetting (ALF) and remote memory impairment (RMI) in transient epileptic amnesia (TEA) is unknown, these cases suggest frequent sleep-related seizures may contribute, and they highlight the importance of video-EEG monitoring.

Positive temporal sharp waves in preterm infants with and without brain ultrasound lesions.

PubMed

Castro Conde, José Ramón; Martínez, Eduardo Doménech; Campo, Candelaria González; Pérez, Arturo Méndez; McLean, Michael Lee

2004-11-01

Clinical significance of neonatal positive temporal sharp waves (PTS) is controversial. The aim of this work is to study (1) PTS incidence in preterm infants with or without major ultrasound lesion (MUL) per gestational age (GA), and (2) the relationship between PTS in both sleep states and other electroencephalographic (EEG) findings with poor prognoses. 97 preterm infants of <27-36 weeks GA, and 12 full-term healthy infants were presented. Prospective study included (1) neurodevelopmental assessment at 40-42 weeks conceptional age (CA), (2) serial neurosonography, and (3) EEG recording at postnatal week 1, 2, 4 and at 40-42 weeks CA. In 50 neonates without MUL, peak PTS was at 31-32 weeks GA. In 47 neonates with MUL, PTS increased significantly from week 2 after birth, descending at the 4th. Neonates of <33 weeks GA with MUL showed significantly increased PTS at term. A significant relationship was found between PTS and other EEG abnormalities with poor neurologic prognoses. PTS incidence varied with sleep states, being predominant in indeterminate sleep in neonates with MUL. PTS increased significantly in infants with MUL, mainly at week 2 of postnatal life, persisting high until term CA, and correlated with other abnormal EEG findings. PTS are highly sensitive to MUL.

Upstream electron oscillations and ion overshoot at an interplanetary shock wave

NASA Technical Reports Server (NTRS)

Potter, D. W.; Parks, G. K.

1983-01-01

During the passage of a large interplanetary shock on Oct. 13, 1981, the ISEE-1 and -2 spacecraft were in the solar wind outside of the upstream region of the bow shock. The high time resolution data of the University of California particle instruments allow pinpointing the expected electron spike as occurring just before the magnetic ramp. In addition, two features that occur at this shock have not been observed before: electron oscillations associated with low frequency waves upstream of the shock and sharp 'overshoot' (about 1 sec) in the ion fluxes that occur right after the magnetic ramp. This interplanetary shock exhibits many of the same characteristics that are observed at the earth's bow shock.

Making High-Pass Filters For Submillimeter Waves

NASA Technical Reports Server (NTRS)

Siegel, Peter H.; Lichtenberger, John A.

1991-01-01

Micromachining-and-electroforming process makes rigid metal meshes with cells ranging in size from 0.002 in. to 0.05 in. square. Series of steps involving cutting, grinding, vapor deposition, and electroforming creates self-supporting, electrically thick mesh. Width of holes typically 1.2 times cutoff wavelength of dominant waveguide mode in hole. To obtain sharp frequency-cutoff characteristic, thickness of mesh made greater than one-half of guide wavelength of mode in hole. Meshes used as high-pass filters (dichroic plates) for submillimeter electromagnetic waves. Process not limited to square silicon wafers. Round wafers also used, with slightly more complication in grinding periphery. Grid in any pattern produced in electroforming mandrel. Any platable metal or alloy used for mesh.

Ultrasound shock wave generator with one-bit time reversal in a dispersive medium, application to lithotripsy

NASA Astrophysics Data System (ADS)

Montaldo, Gabriel; Roux, Philippe; Derode, Arnaud; Negreira, Carlos; Fink, Mathias

2002-02-01

The building of high-power ultrasonic sources from piezoelectric ceramics is limited by the maximum voltage that the ceramics can endure. We have conceived a device that uses a small number of piezoelectric transducers fastened to a cylindrical metallic waveguide. A one-bit time- reversal operation transforms the long-lasting low-level dispersed wave forms into a sharp pulse, thus taking advantage of dispersion to generate high-power ultrasound. The pressure amplitude that is generated at the focus is found to be 15 times greater than that achieved with comparable standard techniques. Applications to lithotripsy are discussed and the destructive efficiency of the system is demonstrated on pieces of chalk.

Investigation of standing wave formation in a human skull for a clinical prototype of a large-aperture, transcranial MR-guided Focused Ultrasound (MRgFUS) phased array: An experimental and simulation study

PubMed Central

Song, Junho; Pulkkinen, Aki; Huang, Yuexi; Hynynen, Kullervo

2014-01-01

Standing wave formation in an ex vivo human skull was investigated using a clinical prototype of a 30 cm diameter with 15 cm radius of curvature, low frequency (230 kHz), hemispherical transcranial Magnetic Resonance guided Focused Ultrasound (MRgFUS) phased-array. Experimental and simulation studies were conducted with changing aperture size and f-number configurations of the phased array, and qualitatively and quantitatively examined the acoustic pressure variation at the focus due to standing waves. The results demonstrated that the nodes and anti-nodes of standing wave produced by the small aperture array were clearly seen at approximately every 3 mm. The effect of the standing wave became more pronounced as the focus was moved closer to skull base. However, a sharp focus was seen for the full array, and there was no such standing wave pattern in the acoustic plane or near the skull base. This study showed that the fluctuation pressure amplitude would be greatly reduced by using a large-scale, hemispherical phased array with a low f-number. PMID:22049360

Selenomethionine promoted hippocampal neurogenesis via the PI3K-Akt-GSK3β-Wnt pathway in a mouse model of Alzheimer's disease.

PubMed

Zheng, Rui; Zhang, Zhong-Hao; Chen, Chen; Chen, Yao; Jia, Shi-Zheng; Liu, Qiong; Ni, Jia-Zuan; Song, Guo-Li

2017-03-25

The maintenance of neural system integrity and function is the ultimate goal for the treatment of neurodegenerative disease such as Alzheimer's disease (AD). Neurogenesis plays an integral role in the maintenance of neural and cognitive functions, and its dysfunction is regarded as a major cause of cognitive impairment in AD. Moreover, the induction of neurogenesis by targeting endogenous neural stem cells (NSCs) is considered as one of the most promising treatment strategies. Our previous studies demonstrated that selenomethionine (Se-Met) was able to reduce β-amyloid peptide (Aβ) deposition, decrease Tau protein hyperphosphorylation and markedly improve cognitive functions in triple transgenic (3xTg) AD mice. In this study, we reported that the therapeutic effect of Se-Met on AD could also be due to neurogenesis modulation. By using the cultured hippocampal NSCs from 3xTg AD mice, we discovered that Se-Met (1-10 μM) with low concentration could promote NSC proliferation, while the one with a high concentration (50,100 μM) inhibiting proliferation. In subsequent studies, we also found that Se-Met activated the signaling pathway of PI3K/Akt, and thereby inhibited the GSK3β activity, which would further activated the β-catenin/Cyclin-D signaling pathway and promote NSC proliferation. Besides, after the induction of Se-Met, the number of neurons differentiated from NSCs significantly increased, and the number of astrocytes decreased. After a 90-day treatment with Se-Met (6 μg/mL), the number of hippocampal neurons in 4-month-old AD mice increased significantly, while the one of astrocyte saw a sharp drop. Thus, Se-Met treatment promoted NSCs differentiation into neurons, and subsequently repaired damaged neural systems in AD mice. Being consistent with our in vitro studies, Se-Met acts through the PI3K-Akt- GSK3β-Wnt signaling pathway in vivo. This study provides an unparalleled evidence that selenium (Se) compounds are, to some extent, effective in promoting neurogenesis, and therefore we propose a novel mechanism for Se-Met treatment in AD. Copyright © 2017 Elsevier Inc. All rights reserved.

WOOLLY CUSPS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nauenberg, M.; Pais, A.

1962-04-01

A study is made of the elastic scattering 1 + 2 yields 1 + 2 in the energy region where the inelastic process 1 + 2 yields 3 + 4 sets in, for the case that particle 3 is unstable. By woolly cusp'' is meant the phenomenon that corresponds to the sharp cusp in the stable case. The procedure followed is to consider the inelastic channel to be of the three-body type, where the three- body states are parametrized by a Breit-Wigner formula around a mean mass m of particle 3. The connection between a woolly and a sharp cuspmore » is made evident. The problem is studied in terms of a twochannel S-wave K matrix. In the two- channel approximation the woolly cusp necessarily shows a decrease in the elastic cross section sigma above a characteristic energy. As a function of energy, sigma must either show a maximum or an inflection point. In either case, the energy at which this happens may lie above or below the inelastic threshold for the fictitious case that particle 3 has a sharp mass m. The sign and magnitude of the elastic scattering phase shift at this m point'' approximately determines which case is actually realized. (auth)« less

Low Frequency Turbulence as the Source of High Frequency Waves in Multi-Component Space Plasmas

NASA Technical Reports Server (NTRS)

Khazanov, George V.; Krivorutsky, Emmanuel N.; Uritsky, Vadim M.

2011-01-01

Space plasmas support a wide variety of waves, and wave-particle interactions as well as wavewave interactions are of crucial importance to magnetospheric and ionospheric plasma behavior. High frequency wave turbulence generation by the low frequency (LF) turbulence is restricted by two interconnected requirements: the turbulence should be strong enough and/or the coherent wave trains should have the appropriate length. These requirements are strongly relaxed in the multi-component plasmas, due to the heavy ions large drift velocity in the field of LF wave. The excitation of lower hybrid waves (LHWs), in particular, is a widely discussed mechanism of interaction between plasma species in space and is one of the unresolved questions of magnetospheric multi-ion plasmas. It is demonstrated that large-amplitude Alfven waves, in particular those associated with LF turbulence, may generate LHW s in the auroral zone and ring current region and in some cases (particularly in the inner magnetosphere) this serves as the Alfven wave saturation mechanism. We also argue that the described scenario can playa vital role in various parts of the outer magnetosphere featuring strong LF turbulence accompanied by LHW activity. Using the data from THEMIS spacecraft, we validate the conditions for such cross-scale coupling in the near-Earth "flow-braking" magnetotail region during the passage of sharp injection/dipolarization fronts, as well as in the turbulent outflow region of the midtail reconnection site.

Genesis of the characteristic pulmonary venous pressure waveform as described by the reservoir-wave model

PubMed Central

Bouwmeester, J Christopher; Belenkie, Israel; Shrive, Nigel G; Tyberg, John V

2014-01-01

Conventional haemodynamic analysis of pulmonary venous and left atrial (LA) pressure waveforms yields substantial forward and backward waves throughout the cardiac cycle; the reservoir wave model provides an alternative analysis with minimal waves during diastole. Pressure and flow in a single pulmonary vein (PV) and the main pulmonary artery (PA) were measured in anaesthetized dogs and the effects of hypoxia and nitric oxide, volume loading, and positive-end expiratory pressure (PEEP) were observed. The reservoir wave model was used to determine the reservoir contribution to PV pressure and flow. Subtracting reservoir pressure and flow resulted in ‘excess’ quantities which were treated as wave-related. Wave intensity analysis of excess pressure and flow quantified the contributions of waves originating upstream (from the PA) and downstream (from the LA and/or left ventricle (LV)). Major features of the characteristic PV waveform are caused by sequential LA and LV contraction and relaxation creating backward compression (i.e. pressure-increasing) waves followed by decompression (i.e. pressure-decreasing) waves. Mitral valve opening is linked to a backwards decompression wave (i.e. diastolic suction). During late systole and early diastole, forward waves originating in the PA are significant. These waves were attenuated less with volume loading and delayed with PEEP. The reservoir wave model shows that the forward and backward waves are negligible during LV diastasis and that the changes in pressure and flow can be accounted for by the discharge of upstream reservoirs. In sharp contrast, conventional analysis posits forward and backward waves such that much of the energy of the forward wave is opposed by the backward wave. PMID:25015922

Damping of Quasi-stationary Waves Between Two Miscible Liquids

NASA Technical Reports Server (NTRS)

Duval, Walter M. B.

2002-01-01

Two viscous miscible liquids with an initially sharp interface oriented vertically inside a cavity become unstable against oscillatory external forcing due to Kelvin-Helmholtz instability. The instability causes growth of quasi-stationary (q-s) waves at the interface between the two liquids. We examine computationally the dynamics of a four-mode q-s wave, for a fixed energy input, when one of the components of the external forcing is suddenly ceased. The external forcing consists of a steady and oscillatory component as realizable in a microgravity environment. Results show that when there is a jump discontinuity in the oscillatory excitation that produced the four-mode q-s wave, the interface does not return to its equilibrium position, the structure of the q-s wave remains imbedded between the two fluids over a long time scale. The damping characteristics of the q-s wave from the time history of the velocity field show overdamped and critically damped response; there is no underdamped oscillation as the flow field approaches steady state. Viscous effects serve as a dissipative mechanism to effectively damp the system. The stability of the four-mode q-s wave is dependent on both a geometric length scale as well as the level of background steady acceleration.

Study of Proximity Effect at D-Wave Superconductors in Quasiclassical Methods

NASA Astrophysics Data System (ADS)

Tanuma, Y.; Tanaka, Y.; Kashiwaya, S.

2005-08-01

Tunneling spectra via Andreev bound states between a normal metal (N) / dx2-y2-wave superconductor (S) (in the presence of a subdominant s-wave pair potential) junction are investigated. In the present work, in order to study the role of proximity effect, we employ quasiclassical Green's function methods. This merit is that we can determine the spatial variation of the pair potentials self-consistently, where the leaking of pair potentials into the N side is involved. In the N/S junction with orientational angle θ = π/4, we can regard as the isolated d-wave superconductor, where attractive interaction in the N side is negligible. On the other hand, in the case of a high transparent contact to the d-wave superconductor (θ = 0), the pair potential penetrates into the inside of the N due to the proximity effect, where the is-wave is not indued at all. Then, the tunneling spectra has a very sharp zero-energy peak (ZEP). This ZEP originates from the fact that quasiparticles feel different sign of the pair potentials between normal metals and d-wave superconductors through Andreev reflections. We show that the spatial dependence of pair potentials is significantly sensitive to the transparency of the junction.

Unexpected Occurrence of Mesospheric Frontal Gravity Wave Events Over South Pole (90°S)

NASA Astrophysics Data System (ADS)

Pautet, P.-D.; Taylor, M. J.; Snively, J. B.; Solorio, C.

2018-01-01

Since 2010, Utah State University has operated an infrared Advanced Mesospheric Temperature Mapper at the Amundsen-Scott South Pole station to investigate the upper atmosphere dynamics and temperature deep within the vortex. A surprising number of "frontal" gravity wave events (86) were recorded in the mesospheric OH(3,1) band intensity and rotational temperature images (typical altitude of 87 km) during four austral winters (2012-2015). These events are gravity waves (GWs) characterized by a sharp leading wave front followed by a quasi-monochromatic wave train that grows with time. A particular subset of frontal gravity wave events has been identified in the past (Dewan & Picard, 1998) as "bores." These are usually associated with wave ducting within stable mesospheric inversion layers, which allow them to propagate over very large distances. They have been observed on numerous occasions from low-latitude and midlatitude sites, but to date, very few have been reported at high latitudes. This study provides new analyses of the characteristics of frontal events at high latitudes and shows that most of them are likely ducted. The occurrence of these frontal GW events over this isolated region strongly supports the existence of horizontally extensive mesospheric thermal inversion layers over Antarctica, leading to regions of enhanced stability necessary for GW trapping and ducting.

Targeting Neural Synchrony Deficits is Sufficient to Improve Cognition in a Schizophrenia-Related Neurodevelopmental Model

PubMed Central

Lee, Heekyung; Dvorak, Dino; Fenton, André A.

2014-01-01

Cognitive symptoms are core features of mental disorders but procognitive treatments are limited. We have proposed a “discoordination” hypothesis that cognitive impairment results from aberrant coordination of neural activity. We reported that neonatal ventral hippocampus lesion (NVHL) rats, an established neurodevelopmental model of schizophrenia, have abnormal neural synchrony and cognitive deficits in the active place avoidance task. During stillness, we observed that cortical local field potentials sometimes resembled epileptiform spike-wave discharges with higher prevalence in NVHL rats, indicating abnormal neural synchrony due perhaps to imbalanced excitation–inhibition coupling. Here, within the context of the hypothesis, we investigated whether attenuating abnormal neural synchrony will improve cognition in NVHL rats. We report that: (1) inter-hippocampal synchrony in the theta and beta bands is correlated with active place avoidance performance; (2) the anticonvulsant ethosuximide attenuated the abnormal spike-wave activity, improved cognitive control, and reduced hyperlocomotion; (3) ethosuximide not only normalized the task-associated theta and beta synchrony between the two hippocampi but also increased synchrony between the medial prefrontal cortex and hippocampus above control levels; (4) the antipsychotic olanzapine was less effective at improving cognitive control and normalizing place avoidance-related inter-hippocampal neural synchrony, although it reduced hyperactivity; and (5) olanzapine caused an abnormal pattern of frequency-independent increases in neural synchrony, in both NVHL and control rats. These data suggest that normalizing aberrant neural synchrony can be beneficial and that drugs targeting the pathophysiology of abnormally coordinated neural activities may be a promising theoretical framework and strategy for developing treatments that improve cognition in neurodevelopmental disorders such as schizophrenia. PMID:24592242

Adiabatic description of superfocusing of femtosecond plasmon polaritons

NASA Astrophysics Data System (ADS)

Golovinski, P. A.; Manuylovich, E. S.; Astapenko, V. A.

2018-05-01

A surface plasmon polariton is a collective oscillation of free electrons at a metal-dielectric interface. As wave phenomena, surface plasmon polaritons can be focused with the use of an appropriate excitation geometry of metal structures. In the adiabatic approximation, we demonstrate a possibility to control nanoscale short pulse superfocusing based on generation of a radially polarized surface plasmon polariton mode of a conical metal needle in view of wave reflection. The results of numerical simulations of femtosecond pulse propagation along a nanoneedle are discussed. The space-time evolution of a pulse for the near field strongly depends on a linear chirp of an initial laser pulse, which can partially compensate wave dispersion. The field distribution is calculated for different metals, chirp parameters, cone opening angles and propagation distances. The electric field near a sharp tip is described as a field of a fictitious time-dependent electric dipole located at the tip apex.

Shock wave refraction enhancing conditions on an extended interface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Markhotok, A.; Popovic, S.

2013-04-15

We determined the law of shock wave refraction for a class of extended interfaces with continuously variable gradients. When the interface is extended or when the gas parameters vary fast enough, the interface cannot be considered as sharp or smooth and the existing calculation methods cannot be applied. The expressions we derived are general enough to cover all three types of the interface and are valid for any law of continuously varying parameters. We apply the equations to the case of exponentially increasing temperature on the boundary and compare the results for all three types of interfaces. We have demonstratedmore » that the type of interface can increase or inhibit the shock wave refraction. Our findings can be helpful in understanding the results obtained in energy deposition experiments as well as for controlling the shock-plasma interaction in other settings.« less

The Data Analysis in Gravitational Wave Detection

NASA Astrophysics Data System (ADS)

Wang, Xiao-ge; Lebigot, Eric; Du, Zhi-hui; Cao, Jun-wei; Wang, Yun-yong; Zhang, Fan; Cai, Yong-zhi; Li, Mu-zi; Zhu, Zong-hong; Qian, Jin; Yin, Cong; Wang, Jian-bo; Zhao, Wen; Zhang, Yang; Blair, David; Ju, Li; Zhao, Chun-nong; Wen, Lin-qing

2017-01-01

Gravitational wave (GW) astronomy based on the GW detection is a rising interdisciplinary field, and a new window for humanity to observe the universe, followed after the traditional astronomy with the electromagnetic waves as the detection means, it has a quite important significance for studying the origin and evolution of the universe, and for extending the astronomical research field. The appearance of laser interferometer GW detector has opened a new era of GW detection, and the data processing and analysis of GWs have already been developed quickly around the world, to provide a sharp weapon for the GW astronomy. This paper introduces systematically the tool software that commonly used for the data analysis of GWs, and discusses in detail the basic methods used in the data analysis of GWs, such as the time-frequency analysis, composite analysis, pulsar timing analysis, matched filter, template, χ2 test, and Monte-Carlo simulation, etc.

Investigations on flexural wave propagation and attenuation in a modified one-dimensional acoustic black hole using a laser excitation technique

NASA Astrophysics Data System (ADS)

Ji, Hongli; Luo, Jing; Qiu, Jinhao; Cheng, Li

2018-05-01

Acoustic Black Holes (ABHs), as a new type of passive structure for vibration damping enhancement and noise attenuation, have been drawing increasing attentions of many researchers. Due to the difficulty in manufacturing the sharp edges required by the ABH structures, it is important to understand the wave propagation and attenuation process in the presence of damping layers in non-ideal ABHs with a truncated edge. In this paper, an analytical expression of the wave reflection coefficient in a modified one-dimensional ABH is derived and a time-domain experimental method based on a laser excitation technique is used to visualize the wave propagation. In the experimental studies, the flexural waves in the ABH were excited by a scanning pulse laser and measured by a Laser Doppler Vibrometer (LDV). The incident wave and reflected wave were separated from the measured original wave field and the decrease of the wave velocity in the ABH was exhibited. The reflection coefficient was calculated from the ratio of the amplitude of the reflected wave to that of the incident wave for different ABH parameters and different thicknesses of the damping layer. The measured reflection coefficients were used to identify the unknown coefficients in the theoretical formula. The results confirm that there exists an optimal thickness for the damping layer, which leads to the minimum wave reflection. Based on the laser-induced visualization technique and various signal processing and feature extraction methods, the entire process of the wave propagation in a non-ideal one-dimensional ABH structure can be visualized and scrutinized.

On the initial value problem for the wave equation in Friedmann-Robertson-Walker space-times.

PubMed

Abbasi, Bilal; Craig, Walter

2014-09-08

The propagator W ( t 0 , t 1 )( g , h ) for the wave equation in a given space-time takes initial data ( g ( x ), h ( x )) on a Cauchy surface {( t , x ) :  t = t 0 } and evaluates the solution ( u ( t 1 , x ),∂ t u ( t 1 , x )) at other times t 1 . The Friedmann-Robertson-Walker space-times are defined for t 0 , t 1 >0, whereas for t 0 →0, there is a metric singularity. There is a spherical means representation for the general solution of the wave equation with the Friedmann-Robertson-Walker background metric in the three spatial dimensional cases of curvature K =0 and K =-1 given by S. Klainerman and P. Sarnak. We derive from the expression of their representation three results about the wave propagator for the Cauchy problem in these space-times. First, we give an elementary proof of the sharp rate of time decay of solutions with compactly supported data. Second, we observe that the sharp Huygens principle is not satisfied by solutions, unlike in the case of three-dimensional Minkowski space-time (the usual Huygens principle of finite propagation speed is satisfied, of course). Third, we show that for 0< t 0 < t the limit, [Formula: see text] exists, it is independent of h ( x ), and for all reasonable initial data g ( x ), it gives rise to a well-defined solution for all t >0 emanating from the space-time singularity at t =0. Under reflection t →- t , the Friedmann-Robertson-Walker metric gives a space-time metric for t <0 with a singular future at t =0, and the same solution formulae hold. We thus have constructed solutions u ( t , x ) of the wave equation in Friedmann-Robertson-Walker space-times which exist for all [Formula: see text] and [Formula: see text], where in conformally regularized coordinates, these solutions are continuous through the singularity t =0 of space-time, taking on specified data u (0,⋅)= g (⋅) at the singular time.

Electronic Transport and Possible Superconductivity at Van Hove Singularities in Carbon Nanotubes.

PubMed

Yang, Y; Fedorov, G; Shafranjuk, S E; Klapwijk, T M; Cooper, B K; Lewis, R M; Lobb, C J; Barbara, P

2015-12-09

Van Hove singularities (VHSs) are a hallmark of reduced dimensionality, leading to a divergent density of states in one and two dimensions and predictions of new electronic properties when the Fermi energy is close to these divergences. In carbon nanotubes, VHSs mark the onset of new subbands. They are elusive in standard electronic transport characterization measurements because they do not typically appear as notable features and therefore their effect on the nanotube conductance is largely unexplored. Here we report conductance measurements of carbon nanotubes where VHSs are clearly revealed by interference patterns of the electronic wave functions, showing both a sharp increase of quantum capacitance, and a sharp reduction of energy level spacing, consistent with an upsurge of density of states. At VHSs, we also measure an anomalous increase of conductance below a temperature of about 30 K. We argue that this transport feature is consistent with the formation of Cooper pairs in the nanotube.

Simulation of Acoustic Scattering from a Trailing Edge

NASA Technical Reports Server (NTRS)

Singer, Bart A.; Brentner, Kenneth S.; Lockard, David P.; Lilley, Geoffrey M.

1999-01-01

Three model problems were examined to assess the difficulties involved in using a hybrid scheme coupling flow computation with the the Ffowcs Williams and Hawkings equation to predict noise generated by vortices passing over a sharp edge. The results indicate that the Ffowcs Williams and Hawkings equation correctly propagates the acoustic signals when provided with accurate flow information on the integration surface. The most difficult of the model problems investigated inviscid flow over a two-dimensional thin NACA airfoil with a blunt-body vortex generator positioned at 98 percent chord. Vortices rolled up downstream of the blunt body. The shed vortices possessed similarities to large coherent eddies in boundary layers. They interacted and occasionally paired as they convected past the sharp trailing edge of the airfoil. The calculations showed acoustic waves emanating from the airfoil trailing edge. Acoustic directivity and Mach number scaling are shown.

Schottky's conjecture on multiplication of field enhancement factors

NASA Astrophysics Data System (ADS)

Miller, Ryan; Lau, Y. Y.; Booske, John H.

2009-11-01

Of great interest to high power microwave, millimeter wave to terahertz sources, x-ray tubes, electrons guns, etc., is the electric field enhancement obtained from sharp emitting structures fabricated by various microfabrication methods. In this paper, we use conformal mapping to investigate the field enhancement of several rectilinear geometries, including a single rectangular ridge, a trapezoidal ridge, and their superposition, i.e., one ridge on top of another. We show that the composite field enhancement factor of the double ridge with a microprotrusion on top of a macroprotrusion is dominated by the product of the individual protrusions' field enhancement factors over a very wide range of geometric aspect ratios, as conjectured by Schottky. Simplified scaling laws are proposed. Significant deviation from Schottky's product rule occurs almost exclusively when the half-width of the macroprotrusion is less than the height of the microprotrusion. Accurate expressions of the divergent electric field near the sharp edges are derived.

The right hippocampus leads the bilateral integration of gamma-parsed lateralized information

PubMed Central

Benito, Nuria; Martín-Vázquez, Gonzalo; Makarova, Julia; Makarov, Valeri A; Herreras, Oscar

2016-01-01

It is unclear whether the two hippocampal lobes convey similar or different activities and how they cooperate. Spatial discrimination of electric fields in anesthetized rats allowed us to compare the pathway-specific field potentials corresponding to the gamma-paced CA3 output (CA1 Schaffer potentials) and CA3 somatic inhibition within and between sides. Bilateral excitatory Schaffer gamma waves are generally larger and lead from the right hemisphere with only moderate covariation of amplitude, and drive CA1 pyramidal units more strongly than unilateral waves. CA3 waves lock to the ipsilateral Schaffer potentials, although bilateral coherence was weak. Notably, Schaffer activity may run laterally, as seen after the disruption of the connecting pathways. Thus, asymmetric operations promote the entrainment of CA3-autonomous gamma oscillators bilaterally, synchronizing lateralized gamma strings to converge optimally on CA1 targets. The findings support the view that interhippocampal connections integrate different aspects of information that flow through the left and right lobes. DOI: http://dx.doi.org/10.7554/eLife.16658.001 PMID:27599221

Inhibition of local estrogen synthesis in the hippocampus impairs hippocampal memory consolidation in ovariectomized female mice

PubMed Central

Tuscher, Jennifer J.; Szinte, Julia S.; Starrett, Joseph R.; Krentzel, Amanda A.; Fortress, Ashley M.; Remage-Healey, Luke; Frick, Karyn M.

2016-01-01

The potent estrogen 17β-Estradiol (E2) plays a critical role in mediating hippocampal function, yet the precise mechanisms through which E2 enhances hippocampal memory remain unclear. In young adult female rodents, the beneficial effects of E2 on memory are generally attributed to ovarian-synthesized E2. However, E2 is also synthesized in the adult brain in numerous species, where it regulates synaptic plasticity and is synthesized in response to experiences such as exposure to females or conspecific song. Although de novo E2 synthesis has been demonstrated in rodent hippocampal cultures, little is known about the functional role of local E2 synthesis in mediating hippocampal memory function. Therefore, the present study examined the role of hippocampal E2 synthesis in hippocampal memory consolidation. Using bilateral dorsal hippocampal infusions of the aromatase inhibitor letrozole, we first found that blockade of dorsal hippocampal E2 synthesis impaired hippocampal memory consolidation. We next found that elevated levels of E2 in dorsal hippocampus observed 30 min after object training were blocked by dorsal hippocampal infusion of letrozole, suggesting that behavioral experience increases acute and local E2 synthesis. Finally, aromatase inhibition did not prevent exogenous E2 from enhancing hippocampal memory consolidation, indicating that hippocampal E2 synthesis is not necessary for exogenous E2 to enhance hippocampal memory. Combined, these data are consistent with the hypothesis that hippocampally-synthesized E2 is necessary for hippocampus-dependent memory consolidation in rodents. PMID:27178577

Upper ocean fine-scale features in synthetic aperture radar imagery. Part I: Simultaneous satellite and in-situ measurements

NASA Astrophysics Data System (ADS)

Soloviev, A.; Maingot, C.; Matt, S.; Fenton, J.; Lehner, S.; Brusch, S.; Perrie, W. A.; Zhang, B.

2011-12-01

The new generation of synthetic aperture radar (SAR) satellites provides high resolution images that open new opportunities for identifying and studying fine features in the upper ocean. The problem is, however, that SAR images of the sea surface can be affected by atmospheric phenomena (rain cells, fronts, internal waves, etc.). Implementation of in-situ techniques in conjunction with SAR is instrumental for discerning the origin of features on the image. This work is aimed at the interpretation of natural and artificial features in SAR images. These features can include fresh water lenses, sharp frontal interfaces, internal wave signatures, as well as slicks of artificial and natural origin. We have conducted field experiments in the summer of 2008 and 2010 and in the spring of 2011 to collect in-situ measurements coordinated with overpasses of the TerraSAR-X, RADARSAT-2, ALOS PALSAR, and COSMO SkyMed satellites. The in-situ sensors deployed in the Straits of Florida included a vessel-mounted sonar and CTD system to record near-surface data on stratification and frontal boundaries, a bottom-mounted Nortek AWAC system to gather information on currents and directional wave spectra, an ADCP mooring at a 240 m isobath, and a meteorological station. A nearby NOAA NEXRAD Doppler radar station provided a record of rainfall in the area. Controlled releases of menhaden fish oil were performed from our vessel before several satellite overpasses in order to evaluate the effect of surface active materials on visibility of sea surface features in SAR imagery under different wind-wave conditions. We found evidence in the satellite images of rain cells, squall lines, internal waves of atmospheric and possibly oceanic origin, oceanic frontal interfaces and submesoscale eddies, as well as anthropogenic signatures of ships and their wakes, and near-shore surface slicks. The combination of satellite imagery and coordinated in-situ measurements was helpful in interpreting fine-scale features on the sea surface observed in the SAR images and, in some cases, linking them to thermohaline features in the upper ocean. Finally, we have been able to reproduce SAR signatures of freshwater plumes and sharp frontal interfaces interacting with wind stress, as well as internal waves by combining hydrodynamic simulations with a radar imaging algorithm. The modeling results are presented in a companion paper (Matt et al., 2011).

CDKL5 gene-related epileptic encephalopathy: electroclinical findings in the first year of life.

PubMed

Melani, Federico; Mei, Davide; Pisano, Tiziana; Savasta, Salvatore; Franzoni, Emilio; Ferrari, Anna Rita; Marini, Carla; Guerrini, Renzo

2011-04-01

Cyclin-dependent kinase-like 5 (CDKL5) gene abnormalities cause an early-onset epileptic encephalopathy. We performed video-electroencephalography (video-EEG) monitoring early in the course of CDKL5-related epileptic encephalopathy in order to examine the early electroclinical characteristics of the condition. We used video-EEG to monitor six infants (five females, one male) with CDKL5-related epileptic encephalopathy (five mutations; one deletion), at ages 45 days to 12 months and followed them up to the ages of 14 months to 5 years (mean age 23 mo). We focused our analysis on the first year of life. The results were evaluated against those of a comparison group of nine infants (aged below 1y) with epileptic encephalography who had tested negative for CDKL5 mutations and deletions. One infant exhibited normal background activity, three exhibited moderate slowing, and two exhibited a suppression burst pattern. Two participants had epileptic spasms and four had a stereotyped complex seizure pattern, which we defined as a 'prolonged' generalized tonic-clonic event consisting of a tonic-tonic/vibratory contraction, followed by a clonic phase with series of spasms, gradually translating into repetitive distal myoclonic jerks. Seizure duration ranged from 2 to 4 minutes. The EEG correlate of each clinical phase included an initial electrodecremental event (tonic vibratory phase), irregular series of sharp waves and spike slow waves (clonic phase with series of spasms), and bilateral rhythmic sharp waves (time locked with myoclonus). Infants with CDKL5-related early epileptic encephalopathy can present in the first year of life with an unusual electroclinical pattern of 'prolonged' generalized tonic-clonic seizures. © The Authors. Journal compilation © Mac Keith Press 2011.

Local strong slow S-wave anomalies at western edge of Pacific LLSVP

NASA Astrophysics Data System (ADS)

Obayashi, M.; Niu, F.; Yoshimitsu, J.

2017-12-01

Seismic tomography studies have revealed two broad slow shear-wave speed anomalies regions beneath the Pacific and Africa called as LLSVPs (Large Low Seismic Velocity Provinces). There are geographic correlations between the LLSVPs and hotspots, and the LLSVPs could probably play an important role for convection throughout the mantle and thermal structure and evolution of the earth. The LLSVPs have been considered to be heterogeneous in composition since the boundaries between the normal mantle are sharp. To investigate the details of the sharp LLSVP edge we measure ScS-S and SKS-S differential traveltimes in the hypocentral distance of about 60°-90° using Japanese and Chinese seismic networks. We used 25events for the Chinese network and 16 events for Japanese network that occurred in Tonga-Kermadec region and obtained 3750 event-station pairs of ScS-S and 1500 pairs of SKS-S differential travel times. We found anomalously large (more than 5 sec) ScS-S travel times accompanying normal SKS-S travel times, suggesting local strong slow region in the vicinity of the ScS bounce points (red circles in Figure 1). Such ScS bounce points locate to the northeast of New Guinea Island extending over 20 degrees in NE-SW direction. However below New Guinea Island, both ScS-S and SKS-S travel times are normal (green circles in Figure 1), indicating abrupt end of the local strong slow anomalies. We inverted the ScS-S and SKS-S differential traveltimes for lowermost mantle S-wave speed structure, assuming isotropic mantle. The result shows very strong slow anomalies of more than 5% at western edge of Pacific LLSVP that extend vertically not more than 200 km from the core mantle boundary.

Nonlinear dynamics of a two-dimensional Wigner solid on superfluid helium

NASA Astrophysics Data System (ADS)

Monarkha, Yu. P.

2018-04-01

Nonlinear dynamics and transport properties of a 2D Wigner solid (WS) on the free surface of superfluid helium are theoretically studied. The analysis is nonperturbative in the amplitude of the WS velocity. An anomalous nonlinear response of the liquid helium surface to the oscillating motion of the WS is shown to appear when the driving frequency is close to subharmonics of the frequency of a capillary wave (ripplon) whose wave vector coincides with a reciprocal-lattice vector. As a result, the effective mass of surface dimples formed under electrons and the kinetic friction acquire sharp anomalies in the low-frequency range, which affects the mobility and magnetoconductivity of the WS. The results obtained here explain a variety of experimental observations reported previously.

Heating of ions to superthermal energies in the topside ionosphere by electrostatic ion cyclotron waves

NASA Technical Reports Server (NTRS)

Ungstrup, E.; Klumpar, D. M.; Heikkila, W. J.

1979-01-01

The soft particle spectrometer on the Isis 2 spacecraft occasionally observes fluxes of ions moving upward out of the ionosphere in the vicinity of the auroral oval. These ion fluxes are characterized by a sharp pitch angle distribution usually peaked at an angle somewhat greater than 90 deg, indicative of particles heated to a large transverse temperature in a narrow range below the spacecraft. The observations are interpreted in terms of electrostatic ion cyclotron waves, which heat the ions to superthermal energies transverse to the earth's magnetic field. When the transverse energy increases, the repulsive force of the earth's magnetic field, proportional to the particle magnetic moment, repels the particles away from the earth.

Repeated sharp flux dropouts observed at 6.6 earth radii during a geomagnetic storm

NASA Technical Reports Server (NTRS)

Su, S.-Y.; Fritz, T. A.; Konradi, A.

1976-01-01

A number of repeated rapid flux dropouts have been observed at 6.6 earth radii by the low-energy proton detectors on board the ATS 6 satellite during the July 4-6, 1974, geomagnetic storm period. These rapid flux changes are caused by the fact that the outer boundary of the trapped radiation region moves back and forth past the satellite. Although a tilting field line configuration can cause the boundary to pass the satellite, as has frequently been reported in the literature, the boundary is shown to be distorted by a large surface wave traveling eastward around the earth. The maximum velocity of the wave was observed to be about 40 km/s.

Inhibition of local estrogen synthesis in the hippocampus impairs hippocampal memory consolidation in ovariectomized female mice.

PubMed

Tuscher, Jennifer J; Szinte, Julia S; Starrett, Joseph R; Krentzel, Amanda A; Fortress, Ashley M; Remage-Healey, Luke; Frick, Karyn M

2016-07-01

The potent estrogen 17β-Estradiol (E2) plays a critical role in mediating hippocampal function, yet the precise mechanisms through which E2 enhances hippocampal memory remain unclear. In young adult female rodents, the beneficial effects of E2 on memory are generally attributed to ovarian-synthesized E2. However, E2 is also synthesized in the adult brain in numerous species, where it regulates synaptic plasticity and is synthesized in response to experiences such as exposure to females or conspecific song. Although de novo E2 synthesis has been demonstrated in rodent hippocampal cultures, little is known about the functional role of local E2 synthesis in mediating hippocampal memory function. Therefore, the present study examined the role of hippocampal E2 synthesis in hippocampal memory consolidation. Using bilateral dorsal hippocampal infusions of the aromatase inhibitor letrozole, we first found that blockade of dorsal hippocampal E2 synthesis impaired hippocampal memory consolidation. We next found that elevated levels of E2 in the dorsal hippocampus observed 30min after object training were blocked by dorsal hippocampal infusion of letrozole, suggesting that behavioral experience increases acute and local E2 synthesis. Finally, aromatase inhibition did not prevent exogenous E2 from enhancing hippocampal memory consolidation, indicating that hippocampal E2 synthesis is not necessary for exogenous E2 to enhance hippocampal memory. Combined, these data are consistent with the hypothesis that hippocampally-synthesized E2 is necessary for hippocampus-dependent memory consolidation in rodents. Copyright © 2016 Elsevier Inc. All rights reserved.

Interferometric imaging of nonlocal electromechanical power transduction in ferroelectric domains.

PubMed

Zheng, Lu; Dong, Hui; Wu, Xiaoyu; Huang, Yen-Lin; Wang, Wenbo; Wu, Weida; Wang, Zheng; Lai, Keji

2018-05-22

The electrical generation and detection of elastic waves are the foundation for acoustoelectronic and acoustooptic systems. For surface acoustic wave devices, microelectromechanical/nanoelectromechanical systems, and phononic crystals, tailoring the spatial variation of material properties such as piezoelectric and elastic tensors may bring significant improvements to the system performance. Due to the much slower speed of sound than speed of light in solids, it is desirable to study various electroacoustic behaviors at the mesoscopic length scale. In this work, we demonstrate the interferometric imaging of electromechanical power transduction in ferroelectric lithium niobate domain structures by microwave impedance microscopy. In sharp contrast to the traditional standing-wave patterns caused by the superposition of counterpropagating waves, the constructive and destructive fringes in microwave dissipation images exhibit an intriguing one-wavelength periodicity. We show that such unusual interference patterns, which are fundamentally different from the acoustic displacement fields, stem from the nonlocal interaction between electric fields and elastic waves. The results are corroborated by numerical simulations taking into account the sign reversal of piezoelectric tensor in oppositely polarized domains. Our work paves ways to probe nanoscale electroacoustic phenomena in complex structures by near-field electromagnetic imaging.

Autocrine signal transmission with extracellular ligand degradation

NASA Astrophysics Data System (ADS)

Muratov, C B; Posta, F; Shvartsman, S Y

2009-03-01

Traveling waves of cell signaling in epithelial layers orchestrate a number of important processes in developing and adult tissues. These waves can be mediated by positive feedback autocrine loops, a mode of cell signaling where binding of a diffusible extracellular ligand to a cell surface receptor can lead to further ligand release. We formulate and analyze a biophysical model that accounts for ligand-induced ligand release, extracellular ligand diffusion and ligand-receptor interaction. We focus on the case when the main mode for ligand degradation is extracellular and analyze the problem with the sharp threshold positive feedback nonlinearity. We derive expressions that link the speed of propagation and other characteristics of traveling waves to the parameters of the biophysical processes, such as diffusion rates, receptor expression level, etc. Analyzing the derived expressions we found that traveling waves in such systems can exhibit a number of unusual properties, e.g. non-monotonic dependence of the speed of propagation on ligand diffusivity. Our results for the fully developed traveling fronts can be used to analyze wave initiation from localized perturbations, a scenario that frequently arises in the in vitro models of epithelial wound healing, and guide future modeling studies of cell communication in epithelial layers.

Localized water reverberation phases and its impact on back-projection images

NASA Astrophysics Data System (ADS)

Yue, H.; Castillo, J.; Yu, C.; Meng, L.; Zhan, Z.

2017-12-01

Coherent radiators imaged by back-projections (BP) are commonly interpreted as part of the rupture process. Nevertheless, artifacts introduced by structure related phases are rarely discriminated from the rupture process. In this study, we adopt the logic of empirical Greens' function analysis (EGF) to discriminate between rupture and structure effect. We re-examine the waveforms and BP images of the 2012 Mw 7.2 Indian Ocean earthquake and an EGF event (Mw 6.2). The P wave codas of both events present similar shape with characteristic period of approximately 10 s, which are back-projected as coherent radiators near the trench. S wave BP doesn't image energy radiation near the trench. We interpret those coda waves as localized water reverberation phases excited near the trench. We perform a 2D waveform modeling using realistic bathymetry model, and find that the sharp near-trench bathymetry traps the acoustic water waves forming localized reverberation phases. These waves can be imaged as coherent near-trench radiators with similar features as that in the observations. We present a set of methodology to discriminate between the rupture and propagation effects in BP images, which can serve as a criterion of subevent identification.

Dynamic groundwater flows and geochemistry in a sandy nearshore aquifer over a wave event

NASA Astrophysics Data System (ADS)

Malott, Spencer; O'Carroll, Denis M.; Robinson, Clare E.

2016-07-01

Dynamic coastal forcing influences the transport of pollutants in nearshore aquifers and their ultimate flux to coastal waters. In this study, field data are presented that show, for the first time, the influence of a period of intensified wave conditions (wave event) on nearshore groundwater flows and geochemistry in a sandy beach. Field measurements at a freshwater beach allow wave effects to be quantified without other complex forcing that are present along marine shorelines (e.g., tides). Pressure transducer data obtained over an isolated wave event reveal the development of transient groundwater flow recirculations. The groundwater flows were simulated in FEFLOW using a phase-averaged wave setup approach to represent waves acting on the sediment-water interface. Comparison of measured and simulated data indicates that consideration of wave setup alone is able to adequately capture wave-induced perturbations in groundwater flows. While prior studies have shown sharp pH and redox spatial zonations in nearshore aquifers, this study reveals rapid temporal variations in conductivity, pH, and redox (ORP) in shallow sediments (up to 0.5 m depth) in response to varying wave conditions. Comparison of head gradients with calculated conductivity and pH mixing ratios indicates the controlling effect of the wave-induced water exchange and flows in driving the observed geochemical dynamics. While we are not able to conclusively determine the extent to which temporal variations are caused by conservative mixing versus reactive processes, the pH and ORP variations observed will have significant implications for the fate of reactive pollutants discharging through sandy nearshore aquifers.

Finite-surface method for the Maxwell equations with corner singularities

NASA Technical Reports Server (NTRS)

Vinokur, Marcel; Yarrow, Maurice

1994-01-01

The finite-surface method for the two-dimensional Maxwell equations in generalized coordinates is extended to treat perfect conductor boundaries with sharp corners. Known singular forms of the grid and the electromagnetic fields in the neighborhood of each corner are used to obtain accurate approximations to the surface and line integrals appearing in the method. Numerical results are presented for a harmonic plane wave incident on a finite flat plate. Comparisons with exact solutions show good agreement.

Theoretical Investigation of 3-D Shock Wave-Turbulent Boundary Layer Interactions. Part 7

DTIC Science & Technology

1988-11-15

Particle traces - y/= 1.0 (80 SFC) 1 18II I I l U0 Flow .>4 .16. on Ange 8deg -5.0 9.81 24.6 39.4 54,2 69.0 0.1 N....,..X (b) CaseFG n Angle =8 dog . (a...generated by a sharp fin geometry. Both porn - zyada tries chosmn are ’d-mensouess’ and the interactions in the rij is the stress tensor (laminar + turbulent

Simulation of pattern and defect detection in periodic amplitude and phase structures using photorefractive four-wave mixing

NASA Astrophysics Data System (ADS)

Nehmetallah, Georges; Banerjee, Partha; Khoury, Jed

2015-03-01

The nonlinearity inherent in four-wave mixing in photorefractive (PR) materials is used for adaptive filtering. Examples include script enhancement on a periodic pattern, scratch and defect cluster enhancement, periodic pattern dislocation enhancement, etc. through intensity filtering image manipulation. Organic PR materials have large space-bandwidth product, which makes them useful in adaptive filtering techniques in quality control systems. For instance, in the case of edge enhancement, phase conjugation via four-wave mixing suppresses the low spatial frequencies of the Fourier spectrum of an aperiodic image and consequently leads to image edge enhancement. In this work, we model, numerically verify, and simulate the performance of a four wave mixing setup used for edge, defect and pattern detection in periodic amplitude and phase structures. The results show that this technique successfully detects the slightest defects clearly even with no enhancement. This technique should facilitate improvements in applications such as image display sharpness utilizing edge enhancement, production line defect inspection of fabrics, textiles, e-beam lithography masks, surface inspection, and materials characterization.

First electric field measurements from the plasma environment of comet 67P/Churyumov-Gerasimenko

NASA Astrophysics Data System (ADS)

Karlsson, Tomas; Eriksson, Anders; Odelstad, Elias; André, Mats; Dickeli, Guillaume; Kullen, Anita; Lindqvist, Per-Arne

2017-04-01

We present the first electric field measurements from the plasma environment of comet 67P/Churyumov-Gerasimenko, performed by the Rosetta dual Langmuir probe instrument LAP. For two time intervals, measurements of the electric field from cometocentric distances of 149 and 348 km are presented together with estimates of the spacecraft potential, which can be used as an indicator of plasma density changes. Persistent wave activity around the local water ion lower hybrid frequency (determined from the magnetic field measurements from the fluxgate magnetometer MAG) is observed. The largest amplitudes are observed at sharp plasma gradients. We discuss the probability that these waves are excited by the lower hybrid drift instability (LHDI), and conclude that the necessary requirements for the LHDI to be operating are fulfilled. We also present first statistical results of the electric field measurements, showing that the wave activity is concentrated to certain regions of the comet, and varies with heliocentric distance. We also discuss the possible effects the waves have on the ambient plasma, and suggest that they may explain hot plasma populations.

Standing waves, clustering, and phase waves in 1D simulations of kinetic relaxation oscillations in NO+NH 3 on Pt(1 0 0) coupled by diffusion

NASA Astrophysics Data System (ADS)

Uecker, Hannes

2004-04-01

The Lombardo-Imbihl-Fink (LFI) ODE model of the NO+NH 3 reaction on a Pt(1 0 0) surface shows stable relaxation oscillations with very sharp transitions for temperatures T between 404 and 433 K. Here we study numerically the effect of linear diffusive coupling of these oscillators in one spatial dimension. Depending on the parameters and initial conditions we find a rich variety of spatio-temporal patterns which we group into four main regimes: bulk oscillations (BOs), standing waves (SW), phase clusters (PC), and phase waves (PW). Two key ingredients for SW and PC are identified, namely the relaxation type of the ODE oscillations and a nonlocal (and nonglobal) coupling due to relatively fast diffusion of the kinetically slaved variables NH 3 and H. In particular, the latter replaces the global coupling through the gas phase used to obtain SW and PC in models of related surface reactions. The PW exist only under the assumption of (relatively) slow diffusion of NH 3 and H.

The quasi 2 day wave response in TIME-GCM nudged with NOGAPS-ALPHA

NASA Astrophysics Data System (ADS)

Wang, Jack C.; Chang, Loren C.; Yue, Jia; Wang, Wenbin; Siskind, D. E.

2017-05-01

The quasi 2 day wave (QTDW) is a traveling planetary wave that can be enhanced rapidly to large amplitudes in the mesosphere and lower thermosphere (MLT) region during the northern winter postsolstice period. In this study, we present five case studies of QTDW events during January and February 2005, 2006 and 2008-2010 by using the Thermosphere-Ionosphere-Mesosphere Electrodynamics-General Circulation Model (TIME-GCM) nudged with the Navy Operational Global Atmospheric Prediction System-Advanced Level Physics High Altitude (NOGAPS-ALPHA) Weather Forecast Model. With NOGAPS-ALPHA introducing more realistic lower atmospheric forcing in TIME-GCM, the QTDW events have successfully been reproduced in the TIME-GCM. The nudged TIME-GCM simulations show good agreement in zonal mean state with the NOGAPS-ALPHA 6 h reanalysis data and the horizontal wind model below the mesopause; however, it has large discrepancies in the tropics above the mesopause. The zonal mean zonal wind in the mesosphere has sharp vertical gradients in the nudged TIME-GCM. The results suggest that the parameterized gravity wave forcing may need to be retuned in the assimilative TIME-GCM.

Concentrated energy addition for active drag reduction in hypersonic flow regime

NASA Astrophysics Data System (ADS)

Ashwin Ganesh, M.; John, Bibin

2018-01-01

Numerical optimization of hypersonic drag reduction technique based on concentrated energy addition is presented in this study. A reduction in wave drag is realized through concentrated energy addition in the hypersonic flowfield upstream of the blunt body. For the exhaustive optimization presented in this study, an in-house high precision inviscid flow solver has been developed. Studies focused on the identification of "optimum energy addition location" have revealed the existence of multiple minimum drag points. The wave drag coefficient is observed to drop from 0.85 to 0.45 when 50 Watts of energy is added to an energy bubble of 1 mm radius located at 74.7 mm upstream of the stagnation point. A direct proportionality has been identified between energy bubble size and wave drag coefficient. Dependence of drag coefficient on the upstream added energy magnitude is also revealed. Of the observed multiple minimum drag points, the energy deposition point (EDP) that offers minimum wave drag just after a sharp drop in drag is proposed as the most optimum energy addition location.

Kelvin-Helmholtz waves in extratropical cyclones passing over mountain ranges: KH Waves in Extratropical Cyclones over Mountain Ranges

DOE Office of Scientific and Technical Information (OSTI.GOV)

Medina, Socorro; Houze, Robert A.

2016-02-19

Kelvin–Helmholtz billows with horizontal scales of 3–4 km have been observed in midlatitude cyclones moving over the Italian Alps and the Oregon Cascades when the atmosphere was mostly statically stable with high amounts of shear and Ri < 0.25. In one case, data from a mobile radar located within a windward facing valley documented a layer in which the shear between down-valley flow below 1.2 km and strong upslope cross-barrier flow above was large. Several episodes of Kelvin–Helmholtz waves were observed within the shear layer. The occurrence of the waves appears to be related to the strength of the shear:more » when the shear attained large values, an episode of billows occurred, followed by a sharp decrease in the shear. The occurrence of large values of shear and Kelvin–Helmholtz billows over two different mountain ranges suggests that they may be important features occurring when extratropical cyclones with statically stable flow pass over mountain ranges.« less

Receptivity of Hypersonic Boundary Layers to Distributed Roughness and Acoustic Disturbances

NASA Technical Reports Server (NTRS)

Balakumar, P.

2013-01-01

Boundary-layer receptivity and stability of Mach 6 flows over smooth and rough seven-degree half-angle sharp-tipped cones are numerically investigated. The receptivity of the boundary layer to slow acoustic disturbances, fast acoustic disturbances, and vortical disturbances is considered. The effects of three-dimensional isolated roughness on the receptivity and stability are also simulated. The results for the smooth cone show that the instability waves are generated in the leading edge region and that the boundary layer is much more receptive to slow acoustic waves than to the fast acoustic waves. Vortical disturbances also generate unstable second modes, however the receptivity coefficients are smaller than that of the slow acoustic wave. Distributed roughness elements located near the nose region decreased the receptivity of the second mode generated by the slow acoustic wave by a small amount. Roughness elements distributed across the continuous spectrum increased the receptivity of the second mode generated by the slow and fast acoustic waves and the vorticity wave. The largest increase occurred for the vorticity wave. Roughness elements distributed across the synchronization point did not change the receptivity of the second modes generated by the acoustic waves. The receptivity of the second mode generated by the vorticity wave increased in this case, but the increase is lower than that occurred with the roughness elements located across the continuous spectrum. The simulations with an isolated roughness element showed that the second mode waves generated by the acoustic disturbances are not influenced by the small roughness element. Due to the interaction, a three-dimensional wave is generated. However, the amplitude is orders of magnitude smaller than the two-dimensional wave.

The effects of hormones and physical exercise on hippocampal structural plasticity.

PubMed

Triviño-Paredes, Juan; Patten, Anna R; Gil-Mohapel, Joana; Christie, Brian R

2016-04-01

The hippocampus plays an integral role in certain aspects of cognition. Hippocampal structural plasticity and in particular adult hippocampal neurogenesis can be influenced by several intrinsic and extrinsic factors. Here we review how hormones (i.e., intrinsic modulators) and physical exercise (i.e., an extrinsic modulator) can differentially modulate hippocampal plasticity in general and adult hippocampal neurogenesis in particular. Specifically, we provide an overview of the effects of sex hormones, stress hormones, and metabolic hormones on hippocampal structural plasticity and adult hippocampal neurogenesis. In addition, we also discuss how physical exercise modulates these forms of hippocampal plasticity, giving particular emphasis on how this modulation can be affected by variables such as exercise regime, duration, and intensity. Understanding the neurobiological mechanisms underlying the modulation of hippocampal structural plasticity by intrinsic and extrinsic factors will impact the design of new therapeutic approaches aimed at restoring hippocampal plasticity following brain injury or neurodegeneration. Copyright © 2016 Elsevier Inc. All rights reserved.

On the non-existence of a sharp cooling break in gamma-ray burst afterglow spectra

DOE Office of Scientific and Technical Information (OSTI.GOV)

Uhm, Z. Lucas; Zhang, Bing, E-mail: uhm@physics.unlv.edu, E-mail: zhang@physics.unlv.edu

Although the widely used analytical afterglow model of gamma-ray bursts (GRBs) predicts a sharp cooling break ν {sub c} in its afterglow spectrum, the GRB observations so far rarely show clear evidence for a cooling break in their spectra or a corresponding temporal break in their light curves. Employing a Lagrangian description of the blast wave, we conduct a sophisticated calculation of the afterglow emission. We precisely follow the cooling history of non-thermal electrons accelerated into each Lagrangian shell. We show that a detailed calculation of afterglow spectra does not in fact give rise to a sharp cooling break atmore » ν {sub c}. Instead, it displays a very mild and smooth transition, which occurs gradually over a few orders of magnitude in energy or frequency. The main source of this slow transition is that different mini shells have different evolutionary histories of the comoving magnetic field strength B, so that deriving the current value of ν {sub c} of each mini shell requires an integration of its cooling rate over the time elapsed since its creation. We present the time evolution of optical and X-ray spectral indices to demonstrate the slow transition of spectral regimes and discuss the implications of our result in interpreting GRB afterglow data.« less

Surface wave inversion of central Texas quarry blasts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bonner, J.L.; Goforth, T.T.

1993-02-01

Compressional and shear wave models of the upper crust in central Texas were obtained by inverting Rayleigh and Love waves recorded at the new W.M. Keck Foundation Seismological Observatory at Baylor University. The Keck Observatory, which became operational in April 1992, consists of a three-component, broadband Geotech seismometer located at a depth of 130 feet in a borehole 17 miles from the Baylor campus. The field station is solar powered, and the 140-dB dynamic range digital data are transmitted to the Baylor analysis lab via radio, where they are analyzed and archived. Limestone quarries located in all directions from themore » Keck Observatory detonate two to four tons of explosives per blast several times a week. Recordings of these blasts show sharp onsets of P and S waves, as well as dispersed Rayleigh and Love waves in the period band 1 to 3 seconds. Multiple filter analysis and phase matched filtering techniques were used to obtain high quality dispersion curves for the surface waves, and inversion techniques were applied to produce shear velocity models of the upper crust. A rapid increase in shear velocity at a depth of about 1.5 km is associated with the Ouachita Overthrust Belt. Portable seismic recording systems were placed at the quarries to monitor start times and initial wave forms. These data were combined with the Keck recordings to produce attenuation and compressional velocity models.« less

Impact damage imaging in a curved composite panel with wavenumber index via Riesz transform

NASA Astrophysics Data System (ADS)

Chang, Huan-Yu; Yuan, Fuh-Gwo

2018-03-01

The barely visible impact damages reduce the strength of composite structures significantly; however, they are difficult to be detected during regular visual inspection. A guided wave based damage imaging condition method is developed and applied on a curved composite panel, which is a part of an aileron from a retired Boeing C-17 Globemaster III. Ultrasonic guided waves are excited by a piezoelectric transducer (PZT) and then captured by a laser Doppler vibrometer (LDV). The wavefield images are constructed by measuring the out-of-plane velocity point by point within interrogation region, and the anomalies at the damage area can be observed with naked eye. The discontinuities of material properties leads to the change of wavenumber while the wave propagating through the damaged area. These differences in wavenumber can be observed by deriving instantaneous wave vector via Riesz transform (RT), and then be shown and highlighted with the proposed imaging condition named wavenumber index (WI). RT can be introduced as a two-dimensional (2-D) generalization of Hilbert transform (HT) to derive instantaneous phases, amplitudes, orientations of a guided-wave field. WI employs the instantaneous wave vector and weighted instantaneous wave energy computed from the instantaneous amplitudes, yielding high sensitivity and sharp damage image with computational efficiency. The BVID of the composite structure becomes therefore "visible" with the developed technique.

Deficits in morphofunctional maturation of hippocampal mossy fiber synapses in a mouse model of intellectual disability.

PubMed

Lanore, Frederic; Labrousse, Virginie F; Szabo, Zsolt; Normand, Elisabeth; Blanchet, Christophe; Mulle, Christophe

2012-12-05

The grik2 gene, coding for the kainate receptor subunit GluK2 (formerly GluR6), is associated with autism spectrum disorders and intellectual disability. Here, we tested the hypothesis that GluK2 could play a role in the appropriate maturation of synaptic circuits involved in learning and memory. We show that both the functional and morphological maturation of hippocampal mossy fiber to CA3 pyramidal cell (mf-CA3) synapses is delayed in mice deficient for the GluK2 subunit (GluK2⁻/⁻). In GluK2⁻/⁻ mice this deficit is manifested by a transient reduction in the amplitude of AMPA-EPSCs at a critical time point of postnatal development, whereas the NMDA component is spared. By combining multiple probability peak fluctuation analysis and immunohistochemistry, we have provided evidence that the decreased amplitude reflects a decrease in the quantal size per mf-CA3 synapse and in the number of active synaptic sites. Furthermore, we analyzed the time course of structural maturation of CA3 synapses by confocal imaging of YFP-expressing cells followed by tridimensional (3D) anatomical reconstruction of thorny excrescences and presynaptic boutons. We show that major changes in synaptic structures occur subsequently to the sharp increase in synaptic transmission, and more importantly that the course of structural maturation of synaptic elements is impaired in GluK2⁻/⁻ mice. This study highlights how a mutation in a gene linked to intellectual disability in the human may lead to a transient reduction of synaptic strength during postnatal development, impacting on the proper formation of neural circuits linked to memory.

Electron Microscopic Analysis of Hippocampal Axo‐Somatic Synapses in a Chronic Stress Model for Depression

PubMed Central

Csabai, Dávid; Seress, László; Varga, Zsófia; Ábrahám, Hajnalka; Miseta, Attila; Wiborg, Ove

2016-01-01

ABSTRACT Stress can alter the number and morphology of excitatory synapses in the hippocampus, but nothing is known about the effect of stress on inhibitory synapses. Here, we used an animal model for depression, the chronic mild stress model, and quantified the number of perisomatic inhibitory neurons and their synapses. We found reduced density of parvalbumin‐positive (PV+) neurons in response to stress, while the density of cholecystokinin‐immunoreactive (CCK+) neurons was unaffected. We did a detailed electron microscopic analysis to quantify the frequency and morphology of perisomatic inhibitory synapses in the hippocampal CA1 area. We analyzed 1100 CA1 pyramidal neurons and 4800 perisomatic terminals in five control and four chronically stressed rats. In the control animals we observed the following parameters: Number of terminals/soma = 57; Number of terminals/100 µm cell perimeter = 10; Synapse/terminal ratio = 32%; Synapse number/100 terminal = 120; Average terminal length = 920nm. None of these parameters were affected by the stress exposure. Overall, these data indicate that despite the depressive‐like behavior and the decrease in the number of perisomatic PV+ neurons in the light microscopic preparations, the number of perisomatic inhibitory synapses on CA1 pyramidal cells was not affected by stress. In the electron microscope, PV+ neurons and the axon terminals appeared to be normal and we did not find any apoptotic or necrotic cells. This data is in sharp contrast to the remarkable remodeling of the excitatory synapses on spines that has been reported in response to stress and depressive‐like behavior. © 2016 The Authors Hippocampus Published by Wiley Periodicals, Inc. PMID:27571571

The role of BK-type Ca2+-dependent K+ channels in spike broadening during repetitive firing in rat hippocampal pyramidal cells

PubMed Central

Shao, Li-Rong; Halvorsrud, Ragnhild; Borg-Graham, Lyle; Storm, Johan F

1999-01-01

The role of large-conductance Ca2+-dependent K+ channels (BK-channels; also known as maxi-K- or slo-channels) in spike broadening during repetitive firing was studied in CA1 pyramidal cells, using sharp electrode intracellular recordings in rat hippocampal slices, and computer modelling. Trains of action potentials elicited by depolarizing current pulses showed a progressive, frequency-dependent spike broadening, reflecting a reduced rate of repolarization. During a 50 ms long 5 spike train, the spike duration increased by 63·6 ± 3·4% from the 1st to the 3rd spike. The amplitude of the fast after-hyperpolarization (fAHP) also rapidly declined during each train. Suppression of BK-channel activity with (a) the selective BK-channel blocker iberiotoxin (IbTX, 60 nM), (b) the non-peptidergic BK-channel blocker paxilline (2–10 μM), or (c) calcium-free medium, broadened the 1st spike to a similar degree (≈60%). BK-channel suppression also caused a similar change in spike waveform as observed during repetitive firing, and eliminated (occluded) most of the spike broadening during repetitive firing. Computer simulations using a reduced compartmental model with transient BK-channel current and 10 other active ionic currents, produced an activity-dependent spike broadening that was strongly reduced when the BK-channel inactivation mechanism was removed. These results, which are supported by recent voltage-clamp data, strongly suggest that in CA1 pyramidal cells, fast inactivation of a transient BK-channel current (ICT), substantially contributes to frequency-dependent spike broadening during repetitive firing. PMID:10562340

Heterogeneity in Kv2 Channel Expression Shapes Action Potential Characteristics and Firing Patterns in CA1 versus CA2 Hippocampal Pyramidal Neurons

PubMed Central

Chevaleyre, Vivien; Murray, Karl D.; Piskorowski, Rebecca A.

2017-01-01

Abstract The CA1 region of the hippocampus plays a critical role in spatial and contextual memory, and has well-established circuitry, function and plasticity. In contrast, the properties of the flanking CA2 pyramidal neurons (PNs), important for social memory, and lacking CA1-like plasticity, remain relatively understudied. In particular, little is known regarding the expression of voltage-gated K+ (Kv) channels and the contribution of these channels to the distinct properties of intrinsic excitability, action potential (AP) waveform, firing patterns and neurotransmission between CA1 and CA2 PNs. In the present study, we used multiplex fluorescence immunolabeling of mouse brain sections, and whole-cell recordings in acute mouse brain slices, to define the role of heterogeneous expression of Kv2 family Kv channels in CA1 versus CA2 pyramidal cell excitability. Our results show that the somatodendritic delayed rectifier Kv channel subunits Kv2.1, Kv2.2, and their auxiliary subunit AMIGO-1 have region-specific differences in expression in PNs, with the highest expression levels in CA1, a sharp decrease at the CA1-CA2 boundary, and significantly reduced levels in CA2 neurons. PNs in CA1 exhibit a robust contribution of Guangxitoxin-1E-sensitive Kv2-based delayed rectifier current to AP shape and after-hyperpolarization potential (AHP) relative to that seen in CA2 PNs. Our results indicate that robust Kv2 channel expression confers a distinct pattern of intrinsic excitability to CA1 PNs, potentially contributing to their different roles in hippocampal network function. PMID:28856240

Effect of serum on intracellular calcium homeostasis and survival of primary cortical and hippocampal CA1 neurons following brief glutamate treatment.

PubMed

Uto, A; Dux, E; Hossmann, K A

1994-12-01

Glutamate neurotoxicity was studied in primary neuronal cultures prepared from rat cerebral cortex and hippocampal CA1 sector. Neurons were cultivated with 5% native horse serum and then exposed to 0.1 or 1.0 mM glutamate for 5 min. Subsequently, neurons were allowed to recover for 24 hours either in the presence or in the absence of 5% native horse serum. In the absence of serum, neurons showed morphological signs of degeneration and exhibited marked loss of vitality as tested by vital staining and release of lactate dehydrogenase (LDH). In contrast, when neurons were cultivated in the presence of serum, no degenerative changes were seen and the neurons survived. Heat inactivated serum did not prevent neuronal death but addition of basic fibroblast growth factor (bFGF) or transforming growth factor-beta 1 (TGF-beta 1) had the same protective effect as native serum. Measurements of intracellular calcium activity ([Ca2+]i) with the indicator dye fura-2 revealed a sharp increase during glutamate exposure. In the absence of serum, [Ca2+]i returned to near control within 5 min but it secondarily increased after 1 hour to almost the same level as during glutamate exposure. This delayed increase was more pronounced in CA1 than in cortical neurons, it correlated linearly with the initial rise during glutamate exposure, and it was greatly reduced in the presence of serum. These observations suggest that glutamate neurotoxicity in vitro is a function of the delayed and not of the primary rise of intracellular calcium activity, and that trophic factors prevent neurotoxicity by attenuating this delayed response.

Characteristics of seismic waves composing Hawaiian volcanic tremor and gas-piston events observed by a near-source array

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ferrazzini, V.; Aki, K.; Chouet, B.

1991-04-10

A correlation method, specifically designed for describing the characteristics of a complex wave field, is applied to volcanic tremor and gas-piston events recorded by a semicircular array of GEOS instruments set at the foot of the Puu Oo crater on the east rift of Kilauea volcano, Hawaii. The spatial patterns of correlation coefficients obtained as functions of frequency for the three components of motion over the entire array are similar for gas-piston events and tremor, and clearly depict dispersive waves propagating across the array from the direction of Puu Oo. The wave fields are composed of comparable amounts of Rayleighmore » and Love waves propagating with similar and extremely slow phase velocities ranging from 700 m/s at 2 Hz to 300 m/s at 8 Hz. The results from Puu Oo stand in sharp contrast to those obtained in an experiment conducted in 1976 on the partially solidified lava lake of Kilauea Iki. Rayleigh waves were not observed in Kilauea Iki, but well-developed trains of Love waves were seen to propagate there with velocities twice as high as those observed near Puu Oo. These differences in the propagation characteristics of surface waves at the two sites may be attributed to the presence of a soft horizontal layer of molten rock in Kilauea Iki, which may have lowered the phase velocity of Rayleigh waves more drastically than that of Love waves, resulting in severe scattering of the Rayleigh wave mode. On the other hand, the thin superficial pahoehoe flow under the array at Puu Oo may have favored the development of vertical columnar joints more extensively at this location than at Kilauea Iki, which may have reduced the shear moduli controlling Love wave mode.« less

Cholinergic modulation of the CAN current may adjust neural dynamics for active memory maintenance, spatial navigation and time-compressed replay

PubMed Central

Yoshida, Motoharu; Knauer, Beate; Jochems, Arthur

2012-01-01

Suppression of cholinergic receptors and inactivation of the septum impair short-term memory, and disrupt place cell and grid cell activity in the medial temporal lobe (MTL). Location-dependent hippocampal place cell firing during active waking, when the acetylcholine level is high, switches to time-compressed replay activity during quiet waking and slow-wave-sleep (SWS), when the acetylcholine level is low. However, it remains largely unknown how acetylcholine supports short-term memory, spatial navigation, and the functional switch to replay mode in the MTL. In this paper, we focus on the role of the calcium-activated non-specific cationic (CAN) current which is activated by acetylcholine. The CAN current is known to underlie persistent firing, which could serve as a memory trace in many neurons in the MTL. Here, we review the CAN current and discuss possible roles of the CAN current in short-term memory and spatial navigation. We further propose a novel theoretical model where the CAN current switches the hippocampal place cell activity between real-time and time-compressed sequential activity during encoding and consolidation, respectively. PMID:22435051

Hippocampal sclerosis in advanced age: clinical and pathological features.

PubMed

Nelson, Peter T; Schmitt, Frederick A; Lin, Yushun; Abner, Erin L; Jicha, Gregory A; Patel, Ela; Thomason, Paula C; Neltner, Janna H; Smith, Charles D; Santacruz, Karen S; Sonnen, Joshua A; Poon, Leonard W; Gearing, Marla; Green, Robert C; Woodard, John L; Van Eldik, Linda J; Kryscio, Richard J

2011-05-01

Hippocampal sclerosis is a relatively common neuropathological finding (∼10% of individuals over the age of 85 years) characterized by cell loss and gliosis in the hippocampus that is not explained by Alzheimer's disease. Hippocampal sclerosis pathology can be associated with different underlying causes, and we refer to hippocampal sclerosis in the aged brain as hippocampal sclerosis associated with ageing. Much remains unknown about hippocampal sclerosis associated with ageing. We combined three different large autopsy cohorts: University of Kentucky Alzheimer's Disease Centre, the Nun Study and the Georgia Centenarian Study to obtain a pool of 1110 patients, all of whom were evaluated neuropathologically at the University of Kentucky. We focused on the subset of cases with neuropathology-confirmed hippocampal sclerosis (n=106). For individuals aged≥95 years at death (n=179 in our sample), each year of life beyond the age of 95 years correlated with increased prevalence of hippocampal sclerosis pathology and decreased prevalence of 'definite' Alzheimer's disease pathology. Aberrant TAR DNA protein 43 immunohistochemistry was seen in 89.9% of hippocampal sclerosis positive patients compared with 9.7% of hippocampal sclerosis negative patients. TAR DNA protein 43 immunohistochemistry can be used to demonstrate that the disease is usually bilateral even when hippocampal sclerosis pathology is not obvious by haematoxylin and eosin stains. TAR DNA protein 43 immunohistochemistry was negative on brain sections from younger individuals (n=10) after hippocampectomy due to seizures, who had pathologically confirmed hippocampal sclerosis. There was no association between cases with hippocampal sclerosis associated with ageing and apolipoprotein E genotype. Age of death and clinical features of hippocampal sclerosis associated with ageing (with or without aberrant TAR DNA protein 43) were distinct from previously published cases of frontotemporal lobar degeneration TAR DNA protein 43. To help sharpen our ability to discriminate patients with hippocampal sclerosis associated with ageing clinically, the longitudinal cognitive profile of 43 patients with hippocampal sclerosis associated with ageing was compared with the profiles of 75 controls matched for age, gender, education level and apolipoprotein E genotype. These individuals were followed from intake assessment, with 8.2 (average) longitudinal cognitive assessments. A neuropsychological profile with relatively high-verbal fluency but low word list recall distinguished the hippocampal sclerosis associated with ageing group at intake (P<0.015) and also 5.5-6.5 years before death (P<0.005). This may provide a first step in clinical differentiation of hippocampal sclerosis associated with ageing versus pure Alzheimer's disease in their earliest stages. In summary, in the largest series of autopsy-verified patients with hippocampal sclerosis to date, we characterized the clinical and pathological features associated with hippocampal sclerosis associated with ageing.

Hippocampal sclerosis in advanced age: clinical and pathological features

PubMed Central

Schmitt, Frederick A.; Lin, Yushun; Abner, Erin L.; Jicha, Gregory A.; Patel, Ela; Thomason, Paula C.; Neltner, Janna H.; Smith, Charles D.; Santacruz, Karen S.; Sonnen, Joshua A.; Poon, Leonard W.; Gearing, Marla; Green, Robert C.; Woodard, John L.; Van Eldik, Linda J.; Kryscio, Richard J.

2011-01-01

Hippocampal sclerosis is a relatively common neuropathological finding (∼10% of individuals over the age of 85 years) characterized by cell loss and gliosis in the hippocampus that is not explained by Alzheimer’s disease. Hippocampal sclerosis pathology can be associated with different underlying causes, and we refer to hippocampal sclerosis in the aged brain as hippocampal sclerosis associated with ageing. Much remains unknown about hippocampal sclerosis associated with ageing. We combined three different large autopsy cohorts: University of Kentucky Alzheimer’s Disease Centre, the Nun Study and the Georgia Centenarian Study to obtain a pool of 1110 patients, all of whom were evaluated neuropathologically at the University of Kentucky. We focused on the subset of cases with neuropathology-confirmed hippocampal sclerosis (n = 106). For individuals aged ≥95 years at death (n = 179 in our sample), each year of life beyond the age of 95 years correlated with increased prevalence of hippocampal sclerosis pathology and decreased prevalence of ‘definite’ Alzheimer’s disease pathology. Aberrant TAR DNA protein 43 immunohistochemistry was seen in 89.9% of hippocampal sclerosis positive patients compared with 9.7% of hippocampal sclerosis negative patients. TAR DNA protein 43 immunohistochemistry can be used to demonstrate that the disease is usually bilateral even when hippocampal sclerosis pathology is not obvious by haematoxylin and eosin stains. TAR DNA protein 43 immunohistochemistry was negative on brain sections from younger individuals (n = 10) after hippocampectomy due to seizures, who had pathologically confirmed hippocampal sclerosis. There was no association between cases with hippocampal sclerosis associated with ageing and apolipoprotein E genotype. Age of death and clinical features of hippocampal sclerosis associated with ageing (with or without aberrant TAR DNA protein 43) were distinct from previously published cases of frontotemporal lobar degeneration TAR DNA protein 43. To help sharpen our ability to discriminate patients with hippocampal sclerosis associated with ageing clinically, the longitudinal cognitive profile of 43 patients with hippocampal sclerosis associated with ageing was compared with the profiles of 75 controls matched for age, gender, education level and apolipoprotein E genotype. These individuals were followed from intake assessment, with 8.2 (average) longitudinal cognitive assessments. A neuropsychological profile with relatively high-verbal fluency but low word list recall distinguished the hippocampal sclerosis associated with ageing group at intake (P < 0.015) and also 5.5–6.5 years before death (P < 0.005). This may provide a first step in clinical differentiation of hippocampal sclerosis associated with ageing versus pure Alzheimer’s disease in their earliest stages. In summary, in the largest series of autopsy-verified patients with hippocampal sclerosis to date, we characterized the clinical and pathological features associated with hippocampal sclerosis associated with ageing. PMID:21596774

Hippocampal subfield volume changes in subtypes of attention deficit hyperactivity disorder.

PubMed

Al-Amin, Mamun; Zinchenko, Artyom; Geyer, Thomas

2018-04-15

Attention-deficit hyperactivity disorder (ADHD) is accompanied by reduction of total hippocampal volume. However, disorder-related fine-grained structural alterations of hippocampal subfields remain unclear. Here we compared hippocampal subfield volumes in a large sample of patients with ADHD and healthy controls. We used T1-weighted structural 3-Tesla MRI images of 880 individuals (7-21 years old) from the ADHD-200 database. The images were acquired from 553 healthy individuals and 327 children and adolescents with combined (N = 196) and inattentive (N = 131) ADHD subtypes. Hippocampal subfields were segmented into the cornu amonis regions (CA1, CA2/3, CA4), fimbria, hippocampal fissure, presubiculum, subiculum, hippocampal tail, parasubiculum, granule cell layers of the dentate gyrus, molecular layer within the subiculum and the CA fields, and the hippocampal-amygdala transition area using an automatic algorithm available in Freesurfer 6.0. We found a significant reduction of total hippocampal volume in the combined ADHD group compared to healthy controls. This reduction was due to the atrophy of CA1, CA4, molecular layer, granule cell layers of the dentate gyrus, presubiculum, subiculum, and hippocampal tail. These differences were exclusively driven by the corresponding brain volume reduction in the combined ADHD-subtype, while hippocampal volumes in inattentive ADHD showed no reliable differences relative to controls. Finally, there were negative correlations between the reduced hippocampal subfields and behavioral ADHD indices. The present results point to a clear dissociation between inattentive and combined subtypes of ADHD. Therefore, hippocampal subfields may contribute towards understanding the pathophysiology of ADHD. Copyright © 2018 Elsevier B.V. All rights reserved.

Hippocampal subfield segmentation in temporal lobe epilepsy: Relation to outcomes.

PubMed

Kreilkamp, B A K; Weber, B; Elkommos, S B; Richardson, M P; Keller, S S

2018-06-01

To investigate the clinical and surgical outcome correlates of preoperative hippocampal subfield volumes in patients with refractory temporal lobe epilepsy (TLE) using a new magnetic resonance imaging (MRI) multisequence segmentation technique. We recruited 106 patients with TLE and hippocampal sclerosis (HS) who underwent conventional T1-weighted and T2 short TI inversion recovery MRI. An automated hippocampal segmentation algorithm was used to identify twelve subfields in each hippocampus. A total of 76 patients underwent amygdalohippocampectomy and postoperative seizure outcome assessment using the standardized ILAE classification. Semiquantitative hippocampal internal architecture (HIA) ratings were correlated with hippocampal subfield volumes. Patients with left TLE had smaller volumes of the contralateral presubiculum and hippocampus-amygdala transition area compared to those with right TLE. Patients with right TLE had reduced contralateral hippocampal tail volumes and improved outcomes. In all patients, there were no significant relationships between hippocampal subfield volumes and clinical variables such as duration and age at onset of epilepsy. There were no significant differences in any hippocampal subfield volumes between patients who were rendered seizure free and those with persistent postoperative seizure symptoms. Ipsilateral but not contralateral HIA ratings were significantly correlated with gross hippocampal and subfield volumes. Our results suggest that ipsilateral hippocampal subfield volumes are not related to the chronicity/severity of TLE. We did not find any hippocampal subfield volume or HIA rating differences in patients with optimal and unfavorable outcomes. In patients with TLE and HS, sophisticated analysis of hippocampal architecture on MRI may have limited value for prediction of postoperative outcome. © 2018 The Authors. Acta Neurologica Scandinavica Published by John Wiley & Sons Ltd.

Laser skin friction measurements and CFD comparison of weak-to-strong swept shock/boundary-layer interactions

NASA Technical Reports Server (NTRS)

Kim, K.-S.; Lee, Y.; Alvi, F. S.; Settles, G. S.; Horstman, C. C.

1990-01-01

A joint experimental and computational study of skin friction in weak-to-strong swept shock wave/turbulent boundary-layer interactions has been carried out. A planar shock wave is generated by a sharp fin at angles of attack alpha = 10 deg and 16 deg at M(infinity) = 3 and 16 and 20 deg at M(infinity) = 4. Measurements are made using the Laser Interferometer Skin Friction meter, which optically detects the rate of thinning of an oil film applied to the test surface. The results show a systematic rise in the peak c(f) at the rear part of the interaction, where the separated flow atttaches. For the stronget case studied, this peak is an order of magnitude higher than the incoming freestream c(f)level.

Tunneling dynamics in relativistic and nonrelativistic wave equations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Delgado, F.; Muga, J. G.; Ruschhaupt, A.

2003-09-01

We obtain the solution of a relativistic wave equation and compare it with the solution of the Schroedinger equation for a source with a sharp onset and excitation frequencies below cutoff. A scaling of position and time reduces to a single case all the (below cutoff) nonrelativistic solutions, but no such simplification holds for the relativistic equation, so that qualitatively different ''shallow'' and ''deep'' tunneling regimes may be identified relativistically. The nonrelativistic forerunner at a position beyond the penetration length of the asymptotic stationary wave does not tunnel; nevertheless, it arrives at the traversal (semiclassical or Buettiker-Landauer) time {tau}. Themore » corresponding relativistic forerunner is more complex: it oscillates due to the interference between two saddle-point contributions and may be characterized by two times for the arrival of the maxima of lower and upper envelopes. There is in addition an earlier relativistic forerunner, right after the causal front, which does tunnel. Within the penetration length, tunneling is more robust for the precursors of the relativistic equation.« less

Bound states and propagating modes in quantum wires with sharp bends and/or constrictions

NASA Astrophysics Data System (ADS)

Razavy, M.

1997-06-01

A number of interesting problems of quantum wires with different geometries can be studied with the help of conformal mapping. These include crossed wires, twisting wires, conductors with constrictions, and wires with a bend. Here the Helmholz equation with Dirichlet boundary condition on the surface of the wire is transformed to a Schröautdinger-like equation with an energy-dependent nonseparable potential but with boundary conditions given on two straight lines. By expanding the wave function in terms of the Fourier series of one of the variables one obtains an infinite set of coupled ordinary differential equations. Only the propagating modes plus a few of the localized modes contribute significantly to the total wave function. Once the problem is solved, one can express the results in terms of the original variables using the inverse conformal mapping. As an example, the total wave function, the components of the current density, and the bound-state energy for a Γ-shaped quantum wire is calculated in detail.

A mechanism for plasma waves at the harmonics of the plasma frequency foreshock boundary

NASA Technical Reports Server (NTRS)

Klimas, A. J.

1982-01-01

A bump-on-tail unstable reduced velocity distribution, constructed from data obtained at the upstream boundary of the electron foreshock by the GSFC electron spectrometer experiment on the ISEE-1 satellite, is used as the initial plasma state for a numerical integration of the 1D-Vlasov-Maxwell system of equations. The integration is carried through the growth of the instability, beyond its saturation, and well into the stabilized plasma regime. A power spectrum computed for the electric field of the stabilized plasma is dominated by a narrow peak at the Bohm-Gross frequency of the unstable field mode but also contains significant power at the harmonics of the Bohm-Gross frequency. The harmonic power is in sharp peaks which are split into closely spaced doublets. The fundamental peak at the Bohm-Gross frequency is split into a closely spaced triplet. The mechanism for excitation of the second harmonic is shown to be second order wave-wave coupling.

Thermal Transport in Nd-doped CeCoIn5

NASA Astrophysics Data System (ADS)

Kim, Duk Y.; Lin, Shi-Zeng; Weickert, Franziska; Rosa, P. F. S.; Bauer, Eric D.; Ronning, Filip; Thompson, J. D.; Movshovich, Roman

Heavy-fermion superconductor CeCoIn5 shows spin-density-wave (SDW) magnetic order in its superconducting state when a high magnetic field is applied. In this Q-phase, the antiferromagnetic order has a single ordering wave vector, and switches its orientation very sharply as magnetic field is rotated within the ab -plane around the [100] (anti-nodal) direction. This hypersensitivity induces a sharp jump of the thermal conductivity. Recently, the SDW with the same ordering wave vector was observed in Nd-doped CeCoIn5 in zero magnetic field. We have measured the thermal conductivity of 5% Nd-doped CeCoIn5 in the magnetic field rotating within the ab -plane. The anisotropy is significantly smaller in the doped material, and the switching transition is much broader. The superconducting transition near Hc 2 is first order, as for the pure CeCoIn5, which indicates the Pauli limited superconductivity. We gratefully acknowledge the support of the U.S. Department of Energy through the LANL/LDRD Program.

Synaptically activated Ca2+ waves and NMDA spikes locally suppress voltage-dependent Ca2+ signalling in rat pyramidal cell dendrites

PubMed Central

Manita, Satoshi; Miyazaki, Kenichi; Ross, William N

2011-01-01

Abstract Postsynaptic [Ca2+]i changes contribute to several kinds of plasticity in pyramidal neurons. We examined the effects of synaptically activated Ca2+ waves and NMDA spikes on subsequent Ca2+ signalling in CA1 pyramidal cell dendrites in hippocampal slices. Tetanic synaptic stimulation evoked a localized Ca2+ wave in the primary apical dendrites. The [Ca2+]i increase from a backpropagating action potential (bAP) or subthreshold depolarization was reduced if it was generated immediately after the wave. The suppression had a recovery time of 30–60 s. The suppression only occurred where the wave was generated and was not due to a change in bAP amplitude or shape. The suppression also could be generated by Ca2+ waves evoked by uncaging IP3, showing that other signalling pathways activated by the synaptic tetanus were not required. The suppression was proportional to the amplitude of the [Ca2+]i change of the Ca2+ wave and was not blocked by a spectrum of kinase or phosphatase inhibitors, consistent with suppression due to Ca2+-dependent inactivation of Ca2+ channels. The waves also reduced the frequency and amplitude of spontaneous, localized Ca2+ release events in the dendrites by a different mechanism, probably by depleting the stores at the site of wave generation. The same synaptic tetanus often evoked NMDA spike-mediated [Ca2+]i increases in the oblique dendrites where Ca2+ waves do not propagate. These NMDA spikes suppressed the [Ca2+]i increase caused by bAPs in those regions. [Ca2+]i increases by Ca2+ entry through voltage-gated Ca2+ channels also suppressed the [Ca2+]i increases from subsequent bAPs in regions where the voltage-gated [Ca2+]i increases were largest, showing that all ways of raising [Ca2+]i could cause suppression. PMID:21844002

The effect of adult-acquired hippocampal damage on memory retrieval: an fMRI study.

PubMed

Maguire, Eleanor A; Frith, Christopher D; Rudge, Peter; Cipolotti, Lisa

2005-08-01

Bilateral hippocampal pathology typically results in significant memory problems. Despite apparently similar structural damage, patients with such lesions can differ in the pattern of impairment and preservation of memory functions. Previously, an fMRI study of a developmental amnesic patient whose anoxic hippocampal damage was incurred perinatally revealed his residual hippocampal tissue to be active during memory retrieval. This hippocampal activity was apparent during the retrieval of personal and general facts relative to a control task. In this study, we used a similar fMRI paradigm to investigate whether residual hippocampal activation was present also in patient VC with adult-acquired anoxic hippocampal pathology. VC's performance and reaction times on the experimental personal and general fact tasks were comparable to age-matched control subjects. However, in contrast to the elderly control sample and the previous developmental amnesic patient, his residual hippocampal tissue did not show activation changes during the experimental tasks. This finding indicates that patient VC's successful retrieval of personal and general facts was achieved without a significant hippocampal contribution. It further suggests that the hippocampal activation observed in the elderly controls and previous developmental amnesic patient was not necessary for successful task performance. The reason for this difference in hippocampal responsivity between VC and the developmental amnesic patient remains to be determined. We speculate that it may relate to the age at which hippocampal damage occurred reflecting plasticity within the developing brain, or to cognitive differences between VC, the developmental amnesic patient, and the control subjects.

Associations Between Left Ventricular Dysfunction and Brain Structure and Function: Findings From the SABRE (Southall and Brent Revisited) Study.

PubMed

Park, Chloe M; Williams, Emily D; Chaturvedi, Nish; Tillin, Therese; Stewart, Robert J; Richards, Marcus; Shibata, Dean; Mayet, Jamil; Hughes, Alun D

2017-04-18

Subclinical left ventricular (LV) dysfunction has been inconsistently associated with early cognitive impairment, and mechanistic pathways have been poorly considered. We investigated the cross-sectional relationship between LV dysfunction and structural/functional measures of the brain and explored the role of potential mechanisms. A total of 1338 individuals (69±6 years) from the Southall and Brent Revisited study underwent echocardiography for systolic (tissue Doppler imaging peak systolic wave) and diastolic (left atrial diameter) assessment. Cognitive function was assessed and total and hippocampal brain volumes were measured by magnetic resonance imaging. Global LV function was assessed by circulating N-terminal pro-brain natriuretic peptide. The role of potential mechanistic pathways of arterial stiffness, atherosclerosis, microvascular disease, and inflammation were explored. After adjusting for age, sex, and ethnicity, lower systolic function was associated with lower total brain (beta±standard error, 14.9±3.2 cm 3 ; P <0.0001) and hippocampal volumes (0.05±0.02 cm 3 , P =0.01). Reduced diastolic function was associated with poorer working memory (-0.21±0.07, P =0.004) and fluency scores (-0.18±0.08, P =0.02). Reduced global LV function was associated with smaller hippocampal volume (-0.10±0.03 cm 3 , P =0.004) and adverse visual memory (-0.076±0.03, P =0.02) and processing speed (0.063±0.02, P =0.006) scores. Separate adjustment for concomitant cardiovascular risk factors attenuated associations with hippocampal volume and fluency only. Further adjustment for the alternative pathways of microvascular disease or arterial stiffness attenuated the relationship between global LV function and visual memory. In a community-based sample of older people, measures of LV function were associated with structural/functional measures of the brain. These associations were not wholly explained by concomitant risk factors or potential mechanistic pathways. © 2017 The Authors. Published on behalf of the American Heart Association, Inc., by Wiley.

Alterations in hippocampal and cortical densities of functionally different interneurons in rat models of absence epilepsy.

PubMed

Papp, Péter; Kovács, Zsolt; Szocsics, Péter; Juhász, Gábor; Maglóczky, Zsófia

2018-05-31

Recent data from absence epileptic patients and animal models provide evidence for significant impairments of attention, memory, and psychosocial functioning. Here, we outline aspects of the electrophysiological and structural background of these dysfunctions by investigating changes in hippocampal and cortical GABAergic inhibitory interneurons in two genetically absence epileptic rat strains: the Genetic Absence Epilepsy Rats from Strasbourg (GAERS) and the Wistar Albino Glaxo/Rijswijk (WAG/Rij) rats. Using simultaneously recorded field potentials from the primary somatosensory cortex (S1 cortex, seizure focus) and the hippocampal hilus, we demonstrated that typical frequencies of spike-wave discharges (SWDs; 7-8 Hz, GAERS; 7-9 Hz, WAG/Rij) and their harmonics appeared and their EEG spectral power markedly increased on recordings not only from the S1 cortex, but also from the hilus in both GAERS and WAG/Rij rats during SWDs. Moreover, we observed an increased synchronization between S1 cortex and hilus at 7-8 Hz (GAERS) and 7-9 Hz (WAG/Rij) and at their harmonics when SWDs occurred in the S1 cortex in both rat strains. In addition, using immunohistochemistry we demonstrated changes in the densities of perisomatic (parvalbumin-immunopositive, PV+) and interneuron-selective (calretinin-immunopositive, CR+) GABAergic inhibitory interneuron somata. Specifically, GAERS and WAG/Rij rats displayed lower densities of PV-immunopositivity in the hippocampal hilus compared to non-epileptic control (NEC) and normal Wistar rats. GAERS and WAG/Rij rats also show a marked reduction in the density of CR + interneurons in the same region in comparison with NEC rats. Data from the S1 cortex reveals bidirectional differences in PV + density, with GAERS displaying a significant increase, whereas WAG/Rij a reduction compared to control rat strains. Our results suggest an enhanced synchronization and functional connections between the hippocampus and S1 cortex as well as thalamocortical activities during SWDs and a functional alteration of inhibitory mechanisms in the hippocampus and S1 cortex of two genetic models of absence epilepsy, presumably in relation with increased neuronal activity and seizure-induced neuronal injury. Copyright © 2018 Elsevier B.V. All rights reserved.

Acute Hippocampal Slice Preparation and Hippocampal Slice Cultures

PubMed Central

Lein, Pamela J.; Barnhart, Christopher D.; Pessah, Isaac N.

2012-01-01

A major advantage of hippocampal slice preparations is that the cytoarchitecture and synaptic circuits of the hippocampus are largely retained. In neurotoxicology research, organotypic hippocampal slices have mostly been used as acute ex vivo preparations for investigating the effects of neurotoxic chemicals on synaptic function. More recently, hippocampal slice cultures, which can be maintained for several weeks to several months in vitro, have been employed to study how neurotoxic chemicals influence the structural and functional plasticity in hippocampal neurons. This chapter provides protocols for preparing hippocampal slices to be used acutely for electrophysiological measurements using glass microelectrodes or microelectrode arrays or to be cultured for morphometric assessments of individual neurons labeled using biolistics. PMID:21815062

Neuronal excitability level transition induced by electrical stimulation

NASA Astrophysics Data System (ADS)

Florence, G.; Kurths, J.; Machado, B. S.; Fonoff, E. T.; Cerdeira, H. A.; Teixeira, M. J.; Sameshima, K.

2014-12-01

In experimental studies, electrical stimulation (ES) has been applied to induce neuronal activity or to disrupt pathological patterns. Nevertheless, the underlying mechanisms of these activity pattern transitions are not clear. To study these phenomena, we simulated a model of the hippocampal region CA1. The computational simulations using different amplitude levels and duration of ES revealed three states of neuronal excitability: burst-firing mode, depolarization block and spreading depression wave. We used the bifurcation theory to analyse the interference of ES in the cellular excitability and the neuronal dynamics. Understanding this process would help to improve the ES techniques to control some neurological disorders.

Temporal lobe epilepsy patients with severe hippocampal neuron loss but normal hippocampal volume: Extracellular matrix molecules are important for the maintenance of hippocampal volume.

PubMed

Peixoto-Santos, Jose Eduardo; Velasco, Tonicarlo Rodrigues; Galvis-Alonso, Orfa Yineth; Araujo, David; Kandratavicius, Ludmyla; Assirati, Joao Alberto; Carlotti, Carlos Gilberto; Scandiuzzi, Renata Caldo; Santos, Antonio Carlos dos; Leite, Joao Pereira

2015-10-01

Hippocampal sclerosis is a common finding in patients with temporal lobe epilepsy (TLE), and magnetic resonance imaging (MRI) studies associate the reduction of hippocampal volume with the neuron loss seen on histologic evaluation. Astrogliosis and increased levels of chondroitin sulfate, a major component of brain extracellular matrix, are also seen in hippocampal sclerosis. Our aim was to evaluate the association between hippocampal volume and chondroitin sulfate, as well as neuronal and astroglial populations in the hippocampus of patients with TLE. Patients with drug-resistant TLE were subdivided, according to hippocampal volume measured by MRI, into two groups: hippocampal atrophy (HA) or normal volume (NV) cases. Hippocampi from TLE patients and age-matched controls were submitted to immunohistochemistry to evaluate neuronal population, astroglial population, and chondroitin sulfate expression with antibodies against neuron nuclei protein (NeuN), glial fibrillary acidic protein (GFAP), and chondroitin sulfate (CS-56) antigens, respectively. Both TLE groups were clinically similar. NV cases had higher hippocampal volume, both ipsilateral and contralateral, when compared to HA. Compared to controls, NV and HA patients had reduced neuron density, and increased GFAP and CS-56 immunopositive area. There was no statistical difference between NV and HA groups in neuron density or immunopositive areas for GFAP and CS-56. Hippocampal volume correlated positively with neuron density in CA1 and prosubiculum, and with immunopositive areas for CS-56 in CA1, and negatively with immunopositive area for GFAP in CA1. Multiple linear regression analysis indicated that both neuron density and CS-56 immunopositive area in CA1 were statistically significant predictors of hippocampal volume. Our findings indicate that neuron density and chondroitin sulfate immunopositive area in the CA1 subfield are crucial for the hippocampal volume, and that chondroitin sulfate is important for the maintenance of a normal hippocampal volume in some cases with severe neuron loss. Wiley Periodicals, Inc. © 2015 International League Against Epilepsy.

Hippocampal shape variations at term equivalent age in very preterm infants compared with term controls: perinatal predictors and functional significance at age 7

PubMed Central

Thompson, Deanne K.; Adamson, Christopher; Roberts, Gehan; Faggian, Nathan; Wood, Stephen J.; Warfield, Simon K.; Doyle, Lex W.; Anderson, Peter J.; Egan, Gary F.; Inder, Terrie E.

2013-01-01

The hippocampus undergoes rapid growth and development in the perinatal months. Infants born very preterm (VPT) are vulnerable to hippocampal alterations, and can provide a model of disturbed early hippocampal development. Hippocampal shape alterations have previously been associated with memory impairment, but have never been investigated in infants. The aims of this study were to determine hippocampal shape differences between 184 VPT infants (<30 weeks’ gestation or <1250 g at birth) and 32 full-term infants, effects of perinatal factors, and associations between infant hippocampal shape and volume, and 7 year verbal and visual memory (California Verbal Learning Test- Children’s Version and Dot Locations). Infants underwent 1.5T magnetic resonance imaging at term equivalent age. Hippocampi were segmented, and spherical harmonics-point distribution model shape analysis was undertaken. VPT infants’ hippocampi were less infolded than full-term infants, being less curved toward the midline and less arched superior-inferiorly. Straighter hippocampi were associated with white matter injury and postnatal corticosteroid exposure. There were no significant associations between infant hippocampal shape and 7 year memory measures. However, larger infant hippocampal volumes were associated with better verbal memory scores. Altered hippocampal shape in VPT infants at term equivalent age may reflect delayed or disrupted development. This study provides further insight into early hippocampal development and the nature of hippocampal abnormalities in prematurity. PMID:23296179

Abnormalities of hippocampal-cortical connectivity in temporal lobe epilepsy patients with hippocampal sclerosis

NASA Astrophysics Data System (ADS)

Li, Wenjing; He, Huiguang; Lu, Jingjing; Wang, Chunheng; Li, Meng; Lv, Bin; Jin, Zhengyu

2011-03-01

Hippocampal sclerosis (HS) is the most common damage seen in the patients with temporal lobe epilepsy (TLE). In the present study, the hippocampal-cortical connectivity was defined as the correlation between the hippocampal volume and cortical thickness at each vertex throughout the whole brain. We aimed to investigate the differences of ipsilateral hippocampal-cortical connectivity between the unilateral TLE-HS patients and the normal controls. In our study, the bilateral hippocampal volumes were first measured in each subject, and we found that the ipsilateral hippocampal volume significantly decreased in the left TLE-HS patients. Then, group analysis showed significant thinner average cortical thickness of the whole brain in the left TLE-HS patients compared with the normal controls. We found significantly increased ipsilateral hippocampal-cortical connectivity in the bilateral superior temporal gyrus, the right cingulate gyrus and the left parahippocampal gyrus of the left TLE-HS patients, which indicated structural vulnerability related to the hippocampus atrophy in the patient group. However, for the right TLE-HS patients, no significant differences were found between the patients and the normal controls, regardless of the ipsilateral hippocampal volume, the average cortical thickness or the patterns of hippocampal-cortical connectivity, which might be related to less atrophies observed in the MRI scans. Our study provided more evidence for the structural abnormalities in the unilateral TLE-HS patients.

Inducing amnesia through systemic suppression

PubMed Central

Hulbert, Justin C.; Henson, Richard N.; Anderson, Michael C.

2016-01-01

Hippocampal damage profoundly disrupts the ability to store new memories of life events. Amnesic windows might also occur in healthy people due to disturbed hippocampal function arising during mental processes that systemically reduce hippocampal activity. Intentionally suppressing memory retrieval (retrieval stopping) reduces hippocampal activity via control mechanisms mediated by the lateral prefrontal cortex. Here we show that when people suppress retrieval given a reminder of an unwanted memory, they are considerably more likely to forget unrelated experiences from periods surrounding suppression. This amnesic shadow follows a dose-response function, becomes more pronounced after practice suppressing retrieval, exhibits characteristics indicating disturbed hippocampal function, and is predicted by reduced hippocampal activity. These findings indicate that stopping retrieval engages a suppression mechanism that broadly compromises hippocampal processes and that hippocampal stabilization processes can be interrupted strategically. Cognitively triggered amnesia constitutes an unrecognized forgetting process that may account for otherwise unexplained memory lapses following trauma. PMID:26977589

Radiation Dose–Dependent Hippocampal Atrophy Detected With Longitudinal Volumetric Magnetic Resonance Imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seibert, Tyler M.; Karunamuni, Roshan; Bartsch, Hauke

Purpose: After radiation therapy (RT) to the brain, patients often experience memory impairment, which may be partially mediated by damage to the hippocampus. Hippocampal sparing in RT planning is the subject of recent and ongoing clinical trials. Calculating appropriate hippocampal dose constraints would be improved by efficient in vivo measurements of hippocampal damage. In this study we sought to determine whether brain RT was associated with dose-dependent hippocampal atrophy. Methods and Materials: Hippocampal volume was measured with magnetic resonance imaging (MRI) in 52 patients who underwent fractionated, partial brain RT for primary brain tumors. Study patients had high-resolution, 3-dimensional volumetric MRI beforemore » and 1 year after RT. Images were processed using software with clearance from the US Food and Drug Administration and Conformité Européene marking for automated measurement of hippocampal volume. Automated results were inspected visually for accuracy. Tumor and surgical changes were censored. Mean hippocampal dose was tested for correlation with hippocampal atrophy 1 year after RT. Average hippocampal volume change was also calculated for hippocampi receiving high (>40 Gy) or low (<10 Gy) mean RT dose. A multivariate analysis was conducted with linear mixed-effects modeling to evaluate other potential predictors of hippocampal volume change, including patient (random effect), age, hemisphere, sex, seizure history, and baseline volume. Statistical significance was evaluated at α = 0.05. Results: Mean hippocampal dose was significantly correlated with hippocampal volume loss (r=−0.24, P=.03). Mean hippocampal volume was significantly reduced 1 year after high-dose RT (mean −6%, P=.009) but not after low-dose RT. In multivariate analysis, both RT dose and patient age were significant predictors of hippocampal atrophy (P<.01). Conclusions: The hippocampus demonstrates radiation dose–dependent atrophy after treatment for brain tumors. Quantitative MRI is a noninvasive imaging technique capable of measuring radiation effects on intracranial structures. This technique could be investigated as a potential biomarker for development of reliable dose constraints for improved cognitive outcomes.« less

Collective transport for active matter run-and-tumble disk systems on a traveling-wave substrate

DOE PAGES

Sándor, Csand; Libál, Andras; Reichhardt, Charles; ...

2017-01-17

Here, we examine numerically the transport of an assembly of active run-and-tumble disks interacting with a traveling-wave substrate. We show that as a function of substrate strength, wave speed, disk activity, and disk density, a variety of dynamical phases arise that are correlated with the structure and net flux of disks. We find that there is a sharp transition into a state in which the disks are only partially coupled to the substrate and form a phase-separated cluster state. This transition is associated with a drop in the net disk flux, and it can occur as a function of themore » substrate speed, maximum substrate force, disk run time, and disk density. Since variation of the disk activity parameters produces different disk drift rates for a fixed traveling-wave speed on the substrate, the system we consider could be used as an efficient method for active matter species separation. Within the cluster phase, we find that in some regimes the motion of the cluster center of mass is in the opposite direction to that of the traveling wave, while when the maximum substrate force is increased, the cluster drifts in the direction of the traveling wave. This suggests that swarming or clustering motion can serve as a method by which an active system can collectively move against an external drift.« less

Synoptic-scale Rossby waves and the geographic distribution of lateral transport routes between the tropics and the extratropics in the lower stratosphere

NASA Astrophysics Data System (ADS)

Horinouchi, Takeshi; Sassi, Fabrizio; Boville, Byron A.

2000-11-01

Atmospheric transport between the tropics and the extratropics, in the lowest part of the stratosphere during Northern Hemisphere winter, is investigated. The role of synoptic-scale disturbances that propagate laterally into the tropics is examined using the middle atmosphere version of the National Center for Atmospheric Research Community Climate Model Version 3 general circulation model. In the lower stratosphere, synoptic-scale Rossby waves propagate vigorously from the northern (i.e., winter) extratropics through two ``westerly ducts,'' where the westerly zonal mean winds near the equator are favorable to Rossby wave propagation. The waves break in the westerly ducts and modify the mean potential vorticity (PV) structure to connect subtropical and equatorial regions of sharp PV gradients. Frequent wave breaking and the wave -induced PV structure create distinct routes where transport occurs vigorously between the tropics and the northern extratropics. Interhemispheric transport also occurs through regions associated with the westerly ducts. In the Southern (summer) Hemisphere lower stratosphere, synoptic-scale disturbances propagate mainly as ``tongues'' of PV elongated from extratropical disturbances. The transport between the tropics and the southern extratropics has a strong geographic preference but is dominated by the monsoon circulation, as was shown for the upper troposphere by Chen [1995]. PV tongues and other transient anomalies are of secondary importance.

Collective transport for active matter run-and-tumble disk systems on a traveling-wave substrate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sándor, Csand; Libál, Andras; Reichhardt, Charles

Here, we examine numerically the transport of an assembly of active run-and-tumble disks interacting with a traveling-wave substrate. We show that as a function of substrate strength, wave speed, disk activity, and disk density, a variety of dynamical phases arise that are correlated with the structure and net flux of disks. We find that there is a sharp transition into a state in which the disks are only partially coupled to the substrate and form a phase-separated cluster state. This transition is associated with a drop in the net disk flux, and it can occur as a function of themore » substrate speed, maximum substrate force, disk run time, and disk density. Since variation of the disk activity parameters produces different disk drift rates for a fixed traveling-wave speed on the substrate, the system we consider could be used as an efficient method for active matter species separation. Within the cluster phase, we find that in some regimes the motion of the cluster center of mass is in the opposite direction to that of the traveling wave, while when the maximum substrate force is increased, the cluster drifts in the direction of the traveling wave. This suggests that swarming or clustering motion can serve as a method by which an active system can collectively move against an external drift.« less

Absence of splash singularities for surface quasi-geostrophic sharp fronts and the Muskat problem.

PubMed

Gancedo, Francisco; Strain, Robert M

2014-01-14

In this paper, for both the sharp front surface quasi-geostrophic equation and the Muskat problem, we rule out the "splash singularity" blow-up scenario; in other words, we prove that the contours evolving from either of these systems cannot intersect at a single point while the free boundary remains smooth. Splash singularities have been shown to hold for the free boundary incompressible Euler equation in the form of the water waves contour evolution problem. Our result confirms the numerical simulations in earlier work, in which it was shown that the curvature blows up because the contours collapse at a point. Here, we prove that maintaining control of the curvature will remove the possibility of pointwise interphase collapse. Another conclusion that we provide is a better understanding of earlier work in which squirt singularities are ruled out; in this case, a positive volume of fluid between the contours cannot be ejected in finite time.

Absence of splash singularities for surface quasi-geostrophic sharp fronts and the Muskat problem

PubMed Central

Gancedo, Francisco; Strain, Robert M.

2014-01-01

In this paper, for both the sharp front surface quasi-geostrophic equation and the Muskat problem, we rule out the “splash singularity” blow-up scenario; in other words, we prove that the contours evolving from either of these systems cannot intersect at a single point while the free boundary remains smooth. Splash singularities have been shown to hold for the free boundary incompressible Euler equation in the form of the water waves contour evolution problem. Our result confirms the numerical simulations in earlier work, in which it was shown that the curvature blows up because the contours collapse at a point. Here, we prove that maintaining control of the curvature will remove the possibility of pointwise interphase collapse. Another conclusion that we provide is a better understanding of earlier work in which squirt singularities are ruled out; in this case, a positive volume of fluid between the contours cannot be ejected in finite time. PMID:24347645

Laser beat wave excitation of terahertz radiation in a plasma slab

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chauhan, Santosh; Parashar, Jetendra, E-mail: j.p.parashar@gmail.com

2014-10-15

Terahertz (THz) radiation generation by nonlinear mixing of lasers, obliquely incident on a plasma slab is investigated. Two cases are considered: (i) electron density profile is parabolic but density peak is below the critical density corresponding to the beat frequency, (ii) plasma boundaries are sharp and density is uniform. In both cases, nonlinearity arises through the ponderomotive force that gives rise to electron drift at the beat frequency. In the case of inhomogeneous plasma, non zero curl of the nonlinear current density gives rise to electromagnetic THz generation. In case of uniform plasma, the sharp density variation at the plasmamore » boundaries leads to radiation generation. In a slab width of less than a terahertz wavelength, plasma density one fourth of terahertz critical density, laser intensities ∼10{sup 17 }W/cm{sup 2} at 1 μm, one obtains the THz intensity ∼1 GW/cm{sup 2} at 3 THz radiation frequency.« less

Intense deformation field at oceanic front inferred from directional sea surface roughness observations

NASA Astrophysics Data System (ADS)

Rascle, Nicolas; Molemaker, Jeroen; Marié, Louis; Nouguier, Frédéric; Chapron, Bertrand; Lund, Björn; Mouche, Alexis

2017-06-01

Fine-scale current gradients at the ocean surface can be observed by sea surface roughness. More specifically, directional surface roughness anomalies are related to the different horizontal current gradient components. This paper reports results from a dedicated experiment during the Lagrangian Submesoscale Experiment (LASER) drifter deployment. A very sharp front, 50 m wide, is detected simultaneously in drifter trajectories, sea surface temperature, and sea surface roughness. A new observational method is applied, using Sun glitter reflections during multiple airplane passes to reconstruct the multiangle roughness anomaly. This multiangle anomaly is consistent with wave-current interactions over a front, including both cross-front convergence and along-front shear with cyclonic vorticity. Qualitatively, results agree with drifters and X-band radar observations. Quantitatively, the sharpness of roughness anomaly suggests intense current gradients, 0.3 m s-1 over the 50 m wide front. This work opens new perspectives for monitoring intense oceanic fronts using drones or satellite constellations.

Questa Baseline and Pre-Mining Ground-Water Quality Investigation. 1. Depth to Bedrock Determinations Using Shallow Seismic Data Acquired in the Straight Creek Drainage Near Red River, New Mexico

USGS Publications Warehouse

Powers, Michael H.; Burton, Bethany L.

2004-01-01

In late May and early June of 2002, the U.S. Geological Survey (USGS) acquired four P-wave seismic profiles across the Straight Creek drainage near Red River, New Mexico. The data were acquired to support a larger effort to investigate baseline and pre-mining ground-water quality in the Red River basin (Nordstrom and others, 2002). For ground-water flow modeling, knowledge of the thickness of the valley fill material above the bedrock is required. When curved-ray refraction tomography was used with the seismic first arrival times, the resulting images of interval velocity versus depth clearly show a sharp velocity contrast where the bedrock interface is expected. The images show that the interpreted buried bedrock surface is neither smooth nor sharp, but it is clearly defined across the valley along the seismic line profiles. The bedrock models defined by the seismic refraction images are consistent with the well data.

Gain and frequency tuning within the mouse cochlear apex

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oghalai, John S.; Raphael, Patrick D.; Gao, Simon

Normal mammalian hearing requires cochlear outer hair cell active processes that amplify the traveling wave with high gain and sharp tuning, termed cochlear amplification. We have used optical coherence tomography to study cochlear amplification within the apical turn of the mouse cochlea. We measured not only classical basilar membrane vibratory tuning curves but also vibratory responses from the rest of the tissues that compose the organ of Corti. Basilar membrane tuning was sharp in live mice and broad in dead mice, whereas other regions of the organ of Corti demonstrated phase shifts consistent with additional filtering beyond that provided bymore » basilar membrane mechanics. We use these experimental data to support a conceptual framework of how cochlear amplification is tuned within the mouse cochlear apex. We will also study transgenic mice with targeted mutations that affect different biomechanical aspects of the organ of Corti in an effort to localize the underlying processes that produce this additional filtering.« less

Dynamics of electron injection in a laser-wakefield accelerator

NASA Astrophysics Data System (ADS)

Xu, J.; Buck, A.; Chou, S.-W.; Schmid, K.; Shen, B.; Tajima, T.; Kaluza, M. C.; Veisz, L.

2017-08-01

The detailed temporal evolution of the laser-wakefield acceleration process with controlled injection, producing reproducible high-quality electron bunches, has been investigated. The localized injection of electrons into the wakefield has been realized in a simple way—called shock-front injection—utilizing a sharp drop in plasma density. Both experimental and numerical results reveal the electron injection and acceleration process as well as the electron bunch's temporal properties. The possibility to visualize the plasma wave gives invaluable spatially resolved information about the local background electron density, which in turn allows for an efficient suppression of electron self-injection before the controlled process of injection at the sharp density jump. Upper limits for the electron bunch duration of 6.6 fs FWHM, or 2.8 fs (r.m.s.) were found. These results indicate that shock-front injection not only provides stable and tunable, but also few-femtosecond short electron pulses for applications such as ultrashort radiation sources, time-resolved electron diffraction or for the seeding of further acceleration stages.

Coupling to Tamm-plasmon-polaritons: dependence on structural parameters

NASA Astrophysics Data System (ADS)

Kumari, Anupa; Kumar, Samir; Shukla, Mukesh Kumar; Kumar, Govind; Sona Maji, Partha; Vijaya, R.; Das, Ritwick

2018-06-01

Tamm plasmon-polaritons (TPPs), formed at the interface of a plasmon-active metal and a distributed Bragg reflector (DBR), are characterized by sharp resonances in the reflection spectrum. The features of these sharp TPP resonances are primarily dictated by the structural parameters as well as by the nature of materials of the constituent DBR and metal. In the present investigation, we experimentally and theoretically analyze the role played by the DBR parameters and the metal layer thickness in determining the efficiency of TPP-mode excitation using plane waves. The findings reveal that the minimum in the reflection spectrum depicting the TPP resonance is strongly influenced by the thickness of plasmon-active metal film as well as the number of DBR unit cells. In fact, there exists an optimum combination of the geometrical parameters for achieving a maximum coupling to TPP modes. A brief theoretical analysis elucidating the underlying mechanism behind such observations is also presented so as to optimally design TPP-based architectures for different applications.

Complex Modeling of the Seismic Structure of the Trans-European Suture Zone's Margin from Receiver Function Analysis

NASA Astrophysics Data System (ADS)

Wilde-Piorko, M.; Chrapkiewicz, K.; Lepore, S.; Polkowski, M.; Grad, M.

2016-12-01

The Trans-European Suture Zone (TESZ) is one of the most prominent suture zones in Europe separating the young Paleozoic Platform from the much older Precambrian East European Craton. The data recorded by "13 BB Star" broadband seismic stations (Grad et al., 2015) are analyzed to investigate the crustal and upper mantle structure of the margin of the Trans-European Suture Zone (TESZ) in northern Poland. Receiver function (RF) locally provides the signature of sharp seismic discontinuities and information about the shear wave (S-wave) velocity distribution beneath the seismic station. Recorded seismograms are rotated from ZNE to LQT system with method using the properties of RF (Wilde-Piórko, 2015). Different techniques of receiver function interpretation are applied, including 1-D inversion of RF, 1-D forward modeling of RF, 2.5D forward modeling of RF, 1-D join inversion of RF and dispersion curves of surface wave, to find the best S-wave velocity model of the TESZ margin. A high-resolution 3D P-wave velocity model in the area of Poland (Grad et al. 2016) are used as a starting model. National Science Centre Poland provided financial support for this work by NCN grant DEC-2011/02/A/ST10/00284.

Utilizing upper hybrid resonance for high density plasma production and negative ion generation in a downstream region

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sahu, Debaprasad; Bhattacharjee, Sudeep

2012-09-15

Localized wave-induced resonances are created by microwaves launched directly into a multicusp (MC) plasma device in the k Up-Tack B mode, where k is the wave vector and B is the static magnetic field. The resonance zone is identified as upper hybrid resonance (UHR), and lies r = {approx}22 mm away from the MC boundary. Measurement of radial wave electric field intensity confirms the right hand cutoff of the wave (r = 22.5-32.1 mm) located near the UHR zone. A sharp rise in the corresponding electron temperature in the resonance region by {approx}13 eV from its value away from resonancemore » at r = 0, is favorable for the generation of vibrationally excited molecules of hydrogen. A transverse magnetic filter allows cold electrons ({approx}1-2 eV) to pass into the downstream region where they generate negative ions by dissociative attachment. Measurements of electron energy distribution function (EEDF) support the viewpoint. H{sup -} current density of {approx}0.26 mA/cm{sup 2} is obtained at a wave power density of {approx}3 W/cm{sup 2} at 2.0 mTorr pressure, which agrees reasonably well with results obtained from a steady state model using particle balance equations.« less

Higgs-mode radiance and charge-density-wave order in 2 H -NbSe2

NASA Astrophysics Data System (ADS)

Grasset, Romain; Cea, Tommaso; Gallais, Yann; Cazayous, Maximilien; Sacuto, Alain; Cario, Laurent; Benfatto, Lara; Méasson, Marie-Aude

2018-03-01

Despite being usually considered two competing phenomena, charge-density wave and superconductivity coexist in few systems, the most emblematic one being the transition-metal dichalcogenide 2 H -NbSe2 . This unusual condition is responsible for specific Raman signatures across the two phase transitions in this compound. While the appearance of a soft phonon mode is a well-established fingerprint of the charge-density-wave order, the nature of the sharp subgap mode emerging below the superconducting temperature is still under debate. In this work we use external pressure as a knob to unveil the delicate interplay between the two orders, and consequently the nature of the superconducting mode. Thanks to an advanced extreme-conditions Raman technique, we are able to follow the pressure evolution and the simultaneous collapse of the two intertwined charge-density-wave and superconducting modes. The comparison with microscopic calculations in a model system supports the Higgs-type nature of the superconducting mode and suggests that charge-density wave and superconductivity in 2 H -NbSe2 involve mutual electronic degrees of freedom. These findings fill the knowledge gap on the electronic mechanisms at play in transition-metal dichalcogenides, a crucial step to fully exploit their properties in few-layer systems optimized for device applications.

Photonic-magnonic crystals: Multifunctional periodic structures for magnonic and photonic applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kłos, J. W., E-mail: klos@amu.edu.pl; Krawczyk, M.; Dadoenkova, Yu. S.

2014-05-07

We investigate the properties of a photonic-magnonic crystal, a complex multifunctional one-dimensional structure with magnonic and photonic band gaps in the GHz and PHz frequency ranges for spin waves and light, respectively. The system consists of periodically distributed dielectric magnetic slabs of yttrium iron garnet and nonmagnetic spacers with an internal structure of alternating TiO{sub 2} and SiO{sub 2} layers which form finite-size dielectric photonic crystals. We show that the spin-wave coupling between the magnetic layers, and thus the formation of the magnonic band structure, necessitates a nonzero in-plane component of the spin-wave wave vector. A more complex structure perceivedmore » by light is evidenced by the photonic miniband structure and the transmission spectra in which we have observed transmission peaks related to the repetition of the magnetic slabs in the frequency ranges corresponding to the photonic band gaps of the TiO{sub 2}/SiO{sub 2} stack. Moreover, we show that these modes split to very high sharp (a few THz wide) subpeaks in the transmittance spectra. The proposed novel multifunctional artificial crystals can have interesting applications and be used for creating common resonant cavities for spin waves and light to enhance the mutual influence between them.« less

Hippocampal-targeted Theta-burst Stimulation Enhances Associative Memory Formation.

PubMed

Tambini, Arielle; Nee, Derek Evan; D'Esposito, Mark

2018-06-19

The hippocampus plays a critical role in episodic memory, among other cognitive functions. However, few tools exist to causally manipulate hippocampal function in healthy human participants. Recent work has targeted hippocampal-cortical networks by performing TMS to a region interconnected with the hippocampus, posterior inferior parietal cortex (pIPC). Such hippocampal-targeted TMS enhances associative memory and influences hippocampal functional connectivity. However, it is currently unknown which stages of mnemonic processing (encoding or retrieval) are affected by hippocampal-targeted TMS. Here, we examined whether hippocampal-targeted TMS influences the initial encoding of associations (vs. items) into memory. To selectively influence encoding and not retrieval, we performed continuous theta-burst TMS before participants encoded object-location associations and assessed memory after the direct effect of stimulation dissipated. Relative to control TMS and baseline memory, pIPC TMS enhanced associative memory success and confidence. Item memory was unaffected, demonstrating a selective influence on associative versus item memory. The strength of hippocampal-pIPC functional connectivity predicted TMS-related memory benefits, which was mediated by parahippocampal and retrosplenial cortices. Our findings indicate that hippocampal-targeted TMS can specifically modulate the encoding of new associations into memory without directly influencing retrieval processes and suggest that the ability to influence associative memory may be related to the fidelity of hippocampal TMS targeting. Our results support the notion that pIPC TMS may serve as a potential tool for manipulating hippocampal function in healthy participants. Nonetheless, future work combining hippocampal-targeted continuous theta-burst TMS with neuroimaging is needed to better understand the neural basis of TMS-induced memory changes.

Moderate exercise ameliorates dysregulated hippocampal glycometabolism and memory function in a rat model of type 2 diabetes.

PubMed

Shima, Takeru; Matsui, Takashi; Jesmin, Subrina; Okamoto, Masahiro; Soya, Mariko; Inoue, Koshiro; Liu, Yu-Fan; Torres-Aleman, Ignacio; McEwen, Bruce S; Soya, Hideaki

2017-03-01

Type 2 diabetes is likely to be an independent risk factor for hippocampal-based memory dysfunction, although this complication has yet to be investigated in detail. As dysregulated glycometabolism in peripheral tissues is a key symptom of type 2 diabetes, it is hypothesised that diabetes-mediated memory dysfunction is also caused by hippocampal glycometabolic dysfunction. If so, such dysfunction should also be ameliorated with moderate exercise by normalising hippocampal glycometabolism, since 4 weeks of moderate exercise enhances memory function and local hippocampal glycogen levels in normal animals. The hippocampal glycometabolism in OLETF rats (model of human type 2 diabetes) was assessed and, subsequently, the effects of exercise on memory function and hippocampal glycometabolism were investigated. OLETF rats, which have memory dysfunction, exhibited higher levels of glycogen in the hippocampus than did control rats, and breakdown of hippocampal glycogen with a single bout of exercise remained unimpaired. However, OLETF rats expressed lower levels of hippocampal monocarboxylate transporter 2 (MCT2, a transporter for lactate to neurons). Four weeks of moderate exercise improved spatial memory accompanied by further increase in hippocampal glycogen levels and restoration of MCT2 expression independent of neurotrophic factor and clinical symptoms in OLETF rats. Our findings are the first to describe detailed profiles of glycometabolism in the type 2 diabetic hippocampus and to show that 4 weeks of moderate exercise improves memory dysfunction in type 2 diabetes via amelioration of dysregulated hippocampal glycometabolism. Dysregulated hippocampal lactate-transport-related glycometabolism is a possible aetiology of type-2-diabetes-mediated memory dysfunction.

Shock-wave propagation and reflection in semicrystalline polyethylene: A molecular-level investigation

NASA Astrophysics Data System (ADS)

Elder, Robert M.; O'Connor, Thomas C.; Chantawansri, Tanya L.; Sliozberg, Yelena R.; Sirk, Timothy W.; Yeh, In-Chul; Robbins, Mark O.; Andzelm, Jan W.

2017-09-01

Semicrystalline polyethylene (PE) is attractive for a variety of mechanically demanding applications, where shock compression can occur. Although often highly crystalline, PE invariably contains nanoscale amorphous domains that influence shock propagation. Our objective in this work is to study the effects of such domains. To this end, we adopt a novel approach wherein we parametrize a simple continuum-level theory based on the shock impedance from molecular dynamics (MD) simulations. Using this theory, we predict how crystalline/amorphous interfaces attenuate shocks via energy reflection due to the impedance mismatch between the phases. The theory predicts that these interfaces attenuate weak shocks more effectively than strong shocks. We compare the theory to explicit nonequilibrium MD simulations of compressive shocks in semicrystalline PE containing nanometer-scale amorphous regions of varying size, where we analyze the pressure response and reflection of energy. The theory and simulations show good agreement for strong shocks (≥1.0 km /s ), but for weak shocks (<1.0 km /s ) the simulations show enhanced energy reflection relative to the continuum predictions. Furthermore, the simulations show an effect not captured by the continuum theory: the size of amorphous regions is important. The theory assumes a sharp (discontinuous) interface between two bulk phases and a sharp change in thermodynamic and hydrodynamic quantities at the shock front. However, the simulations show that when amorphous domains are narrow—with widths comparable to the shock front—reflection is reduced compared to the predictions. We identify several nanoscale mechanisms that reduce the impedance mismatch, and thus reduce reflection, at thin amorphous domains. First, the two-wave elastic-plastic structure of shocks in crystalline PE allows the faster-moving elastic precursor wave to compress small amorphous domains before the plastic wave arrives. Second, confinement between stiff, ordered crystalline domains increases the stiffness and chain ordering in small amorphous regions. Moreover, in terms of stiffness the interfaces are similar in width to the shock front, which may contribute to the underprediction of the theory for weak shocks, where the shock front is widest. We conclude by discussing the significance of these results, namely, how they can be applied to tune shock attenuation for particular applications.

Venlafaxine inhibits apoptosis of hippocampal neurons by up-regulating brain-derived neurotrophic factor in a rat depression model

PubMed Central

Huang, Xiao; Mao, Yue-Shi; Li, Chao; Wang, Hao; Ji, Jian-Lin

2014-01-01

Objective: To study the effect of venlafaxine on the expression of brain-derived neurotrophic factor (BDNF) in rat hippocampal neurons, as well as its inhibitory effect on apoptosis of hippocampal neurons. Methods: Differences in behavioral ability between the depression model group and the Venlafaxine treatment group were observed using behavioral, sucrose-water and open field tests. The rat hippocampal tissue was sliced, stained and observed for BDNF distribution by immunohistochemistry. Apoptosis of hippocampal neurons was detected by TUNEL. BDNF expression in the hippocampal tissue was detected by Western blot. Injury and apoptosis of the hippocampal tissue were observed by electron microscopy. Results: Behavioral test showed that venlafaxine effectively improved the behavioral abilities of depressed rats. Immunohistochemistry showed that venlafaxine markedly increased the BDNF expression in the rat hippocampus. TUNEL showed that venlafaxine markedly inhibited apoptosis of hippocampal neurons, which was also confirmed by electron microscopic observation of the pathologic sections. Conclusion: Venlafaxine improved the expression of BDNF through working on PI3k/PKB/eNOS pathway and repressed the apoptosis of hippocampal neurons. PMID:25197330

Global Intracellular Slow-Wave Dynamics of the Thalamocortical System

PubMed Central

Sheroziya, Maxim

2014-01-01

It is widely accepted that corticothalamic neurons recruit the thalamus in slow oscillation, but global slow-wave thalamocortical dynamics have never been experimentally shown. We analyzed intracellular activities of neurons either from different cortical areas or from a variety of specific and nonspecific thalamic nuclei in relation to the phase of global EEG signal in ketamine-xylazine anesthetized mice. We found that, on average, slow-wave active states started off within frontal cortical areas as well as higher-order and intralaminar thalamus (posterior and parafascicular nuclei) simultaneously. Then, the leading edge of active states propagated in the anteroposterior/lateral direction over the cortex at ∼40 mm/s. The latest structure we recorded within the slow-wave cycle was the anterior thalamus, which followed active states of the retrosplenial cortex. Active states from different cortical areas tended to terminate simultaneously. Sensory thalamic ventral posterior medial and lateral geniculate nuclei followed cortical active states with major inhibitory and weak tonic-like “modulator” EPSPs. In these nuclei, sharp-rising, large-amplitude EPSPs (“drivers”) were not modulated by cortical slow waves, suggesting their origin in ascending pathways. The thalamic active states in other investigated nuclei were composed of depolarization: some revealing “driver”- and “modulator”-like EPSPs, others showing “modulator”-like EPSPs only. We conclude that sensory thalamic nuclei follow the propagating cortical waves, whereas neurons from higher-order thalamic nuclei display “hub dynamics” and thus may contribute to the generation of cortical slow waves. PMID:24966387

Diffraction of waves past two vertical thin plates on the free surface: A comparison of theory and experiment

NASA Astrophysics Data System (ADS)

Shin, Dong Min; Cho, Yeunwoo

2017-11-01

Diffraction of waves past two vertical thin plates on the free surface is studied theoretically and experimentally. A particular attention is paid to the wave motions depending on the relationship between the wavelength (λ) and the width (b) between the two plates for a given draft (d) and water depth (h). For d/h =0.19, at resonance modes when b/ λ = 0.245 (first), 0.695 (second), 1.11 (third), 1.55 (fourth), etc., the overall transmission features the maximum with no reflection. In the first mode, the water column between the plates moves up and down with no wave motions. In the second mode, it shows the fundamental standing wave motion. In the remaining modes, it shows another standing wave motions with relatively higher frequencies. As d/h increases (0.1-0.4), the resonance points move to values b/ λ = 0, 0.5, 1, 1.5, etc., and, at those resonance points, the peaks of reflection and transmission coefficients become more sharp and narrow. The loss of energy of incoming waves is also observed at every transmission in the two plate system, and, in particular, more energy loss near a resonant frequency. In addition, it is found that energy is lost mainly due to the transmission process not the reflection process. This work was supported by the National Research Foundation of Korea (NRF). (NRF-2017R1D1A1B03028299).

Nonmonotonous electron mobility due to structurally induced resonant coupling of subband states in an asymmetric double quantum well

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nayak, R. K.; Das, S.; Panda, A. K.

We show that sharp nonmonotic variation of low temperature electron mobility μ can be achieved in GaAs/Al{sub x}Ga{sub 1-x}As barrier delta-doped double quantum well structure due to quantum mechanical transfer of subband electron wave functions within the wells. We vary the potential profile of the coupled structure as a function of the doping concentration in order to bring the subbands into resonance such that the subband energy levels anticross and the eigen states of the coupled structure equally share both the wells thereby giving rise to a dip in mobility. When the wells are of equal widths, the dip inmore » mobility occurs under symmetric doping of the side barriers. In case of unequal well widths, the resonance can be obtained by suitable asymmetric variation of the doping concentrations. The dip in mobility becomes sharp and also the wavy nature of mobility takes a rectangular shape by increasing the barrier width. We show that the dip in mobility at resonance is governed by the interface roughness scattering through step like changes in the subband mobilities. It is also gratifying to show that the drop in mobility at the onset of occupation of second subband is substantially supressed through the quantum mechanical transfer of subband wave functions between the wells. Our results can be utilized for performance enhancement of coupled quantum well devices.« less

β-amyloid disrupts human NREM slow waves and related hippocampus-dependent memory consolidation

PubMed Central

Mander, Bryce A.; Marks, Shawn M.; Vogel, Jacob W.; Rao, Vikram; Lu, Brandon; Saletin, Jared M.; Ancoli-Israel, Sonia; Jagust, William J.; Walker, Matthew P.

2015-01-01

Independent evidence associates β-amyloid pathology with both NREM sleep disruption and memory impairment in older adults. However, whether the influence of β-amyloid pathology on hippocampus-dependent memory is, in part, driven by impairments of NREM slow wave activity (SWA) and associated overnight memory consolidation is unknown. Here, we show that β-amyloid burden within medial prefrontal cortex (mPFC) is significantly correlated with the severity of impairment in NREM SWA generation. Moreover, reduced NREM SWA generation was further associated with impaired overnight memory consolidation and impoverished hippocampal-neocortical memory transformation. Furthermore, structural equation models revealed that the association between mPFC β-amyloid pathology and impaired hippocampus-dependent memory consolidation is not direct, but instead, statistically depends on the intermediary factor of diminished NREM SWA. By linking β-amyloid pathology with impaired NREM SWA, these data implicate sleep disruption as a novel mechanistic pathway through which β-amyloid pathology may contribute to hippocampus-dependent cognitive decline in the elderly. PMID:26030850

A coordinated sequence of distinct flagellar waveforms enables a sharp flagellar turn mediated by squid sperm pH-taxis.

PubMed

Iida, Tomohiro; Iwata, Yoko; Mohri, Tatsuma; Baba, Shoji A; Hirohashi, Noritaka

2017-10-11

Animal spermatozoa navigate by sensing ambient chemicals to reach the site of fertilization. Generally, such chemicals derive from the female reproductive organs or cells. Exceptionally, squid spermatozoa mutually release and perceive carbon dioxide to form clusters after ejaculation. We previously identified the pH-taxis by which each spermatozoon can execute a sharp turn, but how flagellar dynamics enable this movement remains unknown. Here, we show that initiation of the turn motion requires a swim down a steep proton gradient (a theoretical estimation of ≥0.025 pH/s), crossing a threshold pH value of ~5.5. Time-resolved kinematic analysis revealed that the turn sequence results from the rhythmic exercise of two flagellar motions: a stereotypical flagellar 'bent-cane' shape followed by asymmetric wave propagation, which enables a sharp turn in the realm of low Reynolds numbers. This turning episode is terminated by an 'overshoot' trajectory that differs from either straight-line motility or turning. As with bidirectional pH-taxes in some bacteria, squid spermatozoa also showed repulsion from strong acid conditions with similar flagellar kinematics as in positive pH-taxis. These findings indicate that squid spermatozoa might have a unique reorientation mechanism, which could be dissimilar to that of classical egg-guided sperm chemotaxis in other marine invertebrates.

Classic hippocampal sclerosis and hippocampal-onset epilepsy produced by a single “cryptic” episode of focal hippocampal excitation in awake rats

PubMed Central

Norwood, Braxton A.; Bumanglag, Argyle V.; Osculati, Francesco; Sbarbati, Andrea; Marzola, Pasquina; Nicolato, Elena; Fabene, Paolo F.; Sloviter, Robert S.

2010-01-01

In refractory temporal lobe epilepsy, seizures often arise from a shrunken hippocampus exhibiting a pattern of selective neuron loss called “classic hippocampal sclerosis.” No single experimental injury has reproduced this specific pathology, suggesting that hippocampal atrophy might be a progressive “endstage” pathology resulting from years of spontaneous seizures. We posed the alternate hypothesis that classic hippocampal sclerosis results from a single excitatory event that has never been successfully modeled experimentally because convulsive status epilepticus, the insult most commonly used to produce epileptogenic brain injury, is too severe and necessarily terminated before the hippocampus receives the needed duration of excitation. We tested this hypothesis by producing prolonged hippocampal excitation in awake rats without causing convulsive status epilepticus. Two daily 30-minute episodes of perforant pathway stimulation in Sprague-Dawley rats increased granule cell paired-pulse inhibition, decreased epileptiform afterdischarge durations during 8 hours of subsequent stimulation, and prevented convulsive status epilepticus. Similarly, one 8-hour episode of reduced-intensity stimulation in Long-Evans rats, which are relatively resistant to developing status epilepticus, produced hippocampal discharges without causing status epilepticus. Both paradigms immediately produced the extensive neuronal injury that defines classic hippocampal sclerosis, without giving any clinical indication during the insult that an injury was being inflicted. Spontaneous hippocampal-onset seizures began 16–25 days post-injury, before hippocampal atrophy developed, as demonstrated by sequential magnetic resonance imaging. These results indicate that classic hippocampal sclerosis is uniquely produced by a single episode of clinically “cryptic” excitation. Epileptogenic insults may often involve prolonged excitation that goes undetected at the time of injury. PMID:20575073

Failure of replicating the association between hippocampal volume and 3 single-nucleotide polymorphisms identified from the European genome-wide association study in Asian populations.

PubMed

Li, Ming; Ohi, Kazutaka; Chen, Chunhui; He, Qinghua; Liu, Jie-Wei; Chen, Chuansheng; Luo, Xiong-Jian; Dong, Qi; Hashimoto, Ryota; Su, Bing

2014-12-01

Hippocampal volume is a key brain structure for learning ability and memory process, and hippocampal atrophy is a recognized biological marker of Alzheimer's disease. However, the genetic bases of hippocampal volume are still unclear although it is a heritable trait. Genome-wide association studies (GWASs) on hippocampal volume have implicated several significantly associated genetic variants in Europeans. Here, to test the contributions of these GWASs identified genetic variants to hippocampal volume in different ethnic populations, we screened the GWAS-identified candidate single-nucleotide polymorphisms in 3 independent healthy Asian brain imaging samples (a total of 990 subjects). The results showed that none of these single-nucleotide polymorphisms were associated with hippocampal volume in either individual or combined Asian samples. The replication results suggested a complexity of genetic architecture for hippocampal volume and potential genetic heterogeneity between different ethnic populations. Copyright © 2014 Elsevier Inc. All rights reserved.

Novel genetic loci associated with hippocampal volume.

PubMed

Hibar, Derrek P; Adams, Hieab H H; Jahanshad, Neda; Chauhan, Ganesh; Stein, Jason L; Hofer, Edith; Renteria, Miguel E; Bis, Joshua C; Arias-Vasquez, Alejandro; Ikram, M Kamran; Desrivières, Sylvane; Vernooij, Meike W; Abramovic, Lucija; Alhusaini, Saud; Amin, Najaf; Andersson, Micael; Arfanakis, Konstantinos; Aribisala, Benjamin S; Armstrong, Nicola J; Athanasiu, Lavinia; Axelsson, Tomas; Beecham, Ashley H; Beiser, Alexa; Bernard, Manon; Blanton, Susan H; Bohlken, Marc M; Boks, Marco P; Bralten, Janita; Brickman, Adam M; Carmichael, Owen; Chakravarty, M Mallar; Chen, Qiang; Ching, Christopher R K; Chouraki, Vincent; Cuellar-Partida, Gabriel; Crivello, Fabrice; Den Braber, Anouk; Doan, Nhat Trung; Ehrlich, Stefan; Giddaluru, Sudheer; Goldman, Aaron L; Gottesman, Rebecca F; Grimm, Oliver; Griswold, Michael E; Guadalupe, Tulio; Gutman, Boris A; Hass, Johanna; Haukvik, Unn K; Hoehn, David; Holmes, Avram J; Hoogman, Martine; Janowitz, Deborah; Jia, Tianye; Jørgensen, Kjetil N; Karbalai, Nazanin; Kasperaviciute, Dalia; Kim, Sungeun; Klein, Marieke; Kraemer, Bernd; Lee, Phil H; Liewald, David C M; Lopez, Lorna M; Luciano, Michelle; Macare, Christine; Marquand, Andre F; Matarin, Mar; Mather, Karen A; Mattheisen, Manuel; McKay, David R; Milaneschi, Yuri; Muñoz Maniega, Susana; Nho, Kwangsik; Nugent, Allison C; Nyquist, Paul; Loohuis, Loes M Olde; Oosterlaan, Jaap; Papmeyer, Martina; Pirpamer, Lukas; Pütz, Benno; Ramasamy, Adaikalavan; Richards, Jennifer S; Risacher, Shannon L; Roiz-Santiañez, Roberto; Rommelse, Nanda; Ropele, Stefan; Rose, Emma J; Royle, Natalie A; Rundek, Tatjana; Sämann, Philipp G; Saremi, Arvin; Satizabal, Claudia L; Schmaal, Lianne; Schork, Andrew J; Shen, Li; Shin, Jean; Shumskaya, Elena; Smith, Albert V; Sprooten, Emma; Strike, Lachlan T; Teumer, Alexander; Tordesillas-Gutierrez, Diana; Toro, Roberto; Trabzuni, Daniah; Trompet, Stella; Vaidya, Dhananjay; Van der Grond, Jeroen; Van der Lee, Sven J; Van der Meer, Dennis; Van Donkelaar, Marjolein M J; Van Eijk, Kristel R; Van Erp, Theo G M; Van Rooij, Daan; Walton, Esther; Westlye, Lars T; Whelan, Christopher D; Windham, Beverly G; Winkler, Anderson M; Wittfeld, Katharina; Woldehawariat, Girma; Wolf, Christiane; Wolfers, Thomas; Yanek, Lisa R; Yang, Jingyun; Zijdenbos, Alex; Zwiers, Marcel P; Agartz, Ingrid; Almasy, Laura; Ames, David; Amouyel, Philippe; Andreassen, Ole A; Arepalli, Sampath; Assareh, Amelia A; Barral, Sandra; Bastin, Mark E; Becker, Diane M; Becker, James T; Bennett, David A; Blangero, John; van Bokhoven, Hans; Boomsma, Dorret I; Brodaty, Henry; Brouwer, Rachel M; Brunner, Han G; Buckner, Randy L; Buitelaar, Jan K; Bulayeva, Kazima B; Cahn, Wiepke; Calhoun, Vince D; Cannon, Dara M; Cavalleri, Gianpiero L; Cheng, Ching-Yu; Cichon, Sven; Cookson, Mark R; Corvin, Aiden; Crespo-Facorro, Benedicto; Curran, Joanne E; Czisch, Michael; Dale, Anders M; Davies, Gareth E; De Craen, Anton J M; De Geus, Eco J C; De Jager, Philip L; De Zubicaray, Greig I; Deary, Ian J; Debette, Stéphanie; DeCarli, Charles; Delanty, Norman; Depondt, Chantal; DeStefano, Anita; Dillman, Allissa; Djurovic, Srdjan; Donohoe, Gary; Drevets, Wayne C; Duggirala, Ravi; Dyer, Thomas D; Enzinger, Christian; Erk, Susanne; Espeseth, Thomas; Fedko, Iryna O; Fernández, Guillén; Ferrucci, Luigi; Fisher, Simon E; Fleischman, Debra A; Ford, Ian; Fornage, Myriam; Foroud, Tatiana M; Fox, Peter T; Francks, Clyde; Fukunaga, Masaki; Gibbs, J Raphael; Glahn, David C; Gollub, Randy L; Göring, Harald H H; Green, Robert C; Gruber, Oliver; Gudnason, Vilmundur; Guelfi, Sebastian; Håberg, Asta K; Hansell, Narelle K; Hardy, John; Hartman, Catharina A; Hashimoto, Ryota; Hegenscheid, Katrin; Heinz, Andreas; Le Hellard, Stephanie; Hernandez, Dena G; Heslenfeld, Dirk J; Ho, Beng-Choon; Hoekstra, Pieter J; Hoffmann, Wolfgang; Hofman, Albert; Holsboer, Florian; Homuth, Georg; Hosten, Norbert; Hottenga, Jouke-Jan; Huentelman, Matthew; Hulshoff Pol, Hilleke E; Ikeda, Masashi; Jack, Clifford R; Jenkinson, Mark; Johnson, Robert; Jönsson, Erik G; Jukema, J Wouter; Kahn, René S; Kanai, Ryota; Kloszewska, Iwona; Knopman, David S; Kochunov, Peter; Kwok, John B; Lawrie, Stephen M; Lemaître, Hervé; Liu, Xinmin; Longo, Dan L; Lopez, Oscar L; Lovestone, Simon; Martinez, Oliver; Martinot, Jean-Luc; Mattay, Venkata S; McDonald, Colm; McIntosh, Andrew M; McMahon, Francis J; McMahon, Katie L; Mecocci, Patrizia; Melle, Ingrid; Meyer-Lindenberg, Andreas; Mohnke, Sebastian; Montgomery, Grant W; Morris, Derek W; Mosley, Thomas H; Mühleisen, Thomas W; Müller-Myhsok, Bertram; Nalls, Michael A; Nauck, Matthias; Nichols, Thomas E; Niessen, Wiro J; Nöthen, Markus M; Nyberg, Lars; Ohi, Kazutaka; Olvera, Rene L; Ophoff, Roel A; Pandolfo, Massimo; Paus, Tomas; Pausova, Zdenka; Penninx, Brenda W J H; Pike, G Bruce; Potkin, Steven G; Psaty, Bruce M; Reppermund, Simone; Rietschel, Marcella; Roffman, Joshua L; Romanczuk-Seiferth, Nina; Rotter, Jerome I; Ryten, Mina; Sacco, Ralph L; Sachdev, Perminder S; Saykin, Andrew J; Schmidt, Reinhold; Schmidt, Helena; Schofield, Peter R; Sigursson, Sigurdur; Simmons, Andrew; Singleton, Andrew; Sisodiya, Sanjay M; Smith, Colin; Smoller, Jordan W; Soininen, Hilkka; Steen, Vidar M; Stott, David J; Sussmann, Jessika E; Thalamuthu, Anbupalam; Toga, Arthur W; Traynor, Bryan J; Troncoso, Juan; Tsolaki, Magda; Tzourio, Christophe; Uitterlinden, Andre G; Hernández, Maria C Valdés; Van der Brug, Marcel; van der Lugt, Aad; van der Wee, Nic J A; Van Haren, Neeltje E M; van 't Ent, Dennis; Van Tol, Marie-Jose; Vardarajan, Badri N; Vellas, Bruno; Veltman, Dick J; Völzke, Henry; Walter, Henrik; Wardlaw, Joanna M; Wassink, Thomas H; Weale, Michael E; Weinberger, Daniel R; Weiner, Michael W; Wen, Wei; Westman, Eric; White, Tonya; Wong, Tien Y; Wright, Clinton B; Zielke, Ronald H; Zonderman, Alan B; Martin, Nicholas G; Van Duijn, Cornelia M; Wright, Margaret J; Longstreth, W T; Schumann, Gunter; Grabe, Hans J; Franke, Barbara; Launer, Lenore J; Medland, Sarah E; Seshadri, Sudha; Thompson, Paul M; Ikram, M Arfan

2017-01-18

The hippocampal formation is a brain structure integrally involved in episodic memory, spatial navigation, cognition and stress responsiveness. Structural abnormalities in hippocampal volume and shape are found in several common neuropsychiatric disorders. To identify the genetic underpinnings of hippocampal structure here we perform a genome-wide association study (GWAS) of 33,536 individuals and discover six independent loci significantly associated with hippocampal volume, four of them novel. Of the novel loci, three lie within genes (ASTN2, DPP4 and MAST4) and one is found 200 kb upstream of SHH. A hippocampal subfield analysis shows that a locus within the MSRB3 gene shows evidence of a localized effect along the dentate gyrus, subiculum, CA1 and fissure. Further, we show that genetic variants associated with decreased hippocampal volume are also associated with increased risk for Alzheimer's disease (r g =-0.155). Our findings suggest novel biological pathways through which human genetic variation influences hippocampal volume and risk for neuropsychiatric illness.

Novel genetic loci associated with hippocampal volume

PubMed Central

Hibar, Derrek P.; Adams, Hieab H. H.; Jahanshad, Neda; Chauhan, Ganesh; Stein, Jason L.; Hofer, Edith; Renteria, Miguel E.; Bis, Joshua C.; Arias-Vasquez, Alejandro; Ikram, M. Kamran; Desrivières, Sylvane; Vernooij, Meike W.; Abramovic, Lucija; Alhusaini, Saud; Amin, Najaf; Andersson, Micael; Arfanakis, Konstantinos; Aribisala, Benjamin S.; Armstrong, Nicola J.; Athanasiu, Lavinia; Axelsson, Tomas; Beecham, Ashley H.; Beiser, Alexa; Bernard, Manon; Blanton, Susan H.; Bohlken, Marc M.; Boks, Marco P.; Bralten, Janita; Brickman, Adam M.; Carmichael, Owen; Chakravarty, M. Mallar; Chen, Qiang; Ching, Christopher R. K.; Chouraki, Vincent; Cuellar-Partida, Gabriel; Crivello, Fabrice; Den Braber, Anouk; Doan, Nhat Trung; Ehrlich, Stefan; Giddaluru, Sudheer; Goldman, Aaron L.; Gottesman, Rebecca F.; Grimm, Oliver; Griswold, Michael E.; Guadalupe, Tulio; Gutman, Boris A.; Hass, Johanna; Haukvik, Unn K.; Hoehn, David; Holmes, Avram J.; Hoogman, Martine; Janowitz, Deborah; Jia, Tianye; Jørgensen, Kjetil N.; Karbalai, Nazanin; Kasperaviciute, Dalia; Kim, Sungeun; Klein, Marieke; Kraemer, Bernd; Lee, Phil H.; Liewald, David C. M.; Lopez, Lorna M.; Luciano, Michelle; Macare, Christine; Marquand, Andre F.; Matarin, Mar; Mather, Karen A.; Mattheisen, Manuel; McKay, David R.; Milaneschi, Yuri; Muñoz Maniega, Susana; Nho, Kwangsik; Nugent, Allison C.; Nyquist, Paul; Loohuis, Loes M. Olde; Oosterlaan, Jaap; Papmeyer, Martina; Pirpamer, Lukas; Pütz, Benno; Ramasamy, Adaikalavan; Richards, Jennifer S.; Risacher, Shannon L.; Roiz-Santiañez, Roberto; Rommelse, Nanda; Ropele, Stefan; Rose, Emma J.; Royle, Natalie A.; Rundek, Tatjana; Sämann, Philipp G.; Saremi, Arvin; Satizabal, Claudia L.; Schmaal, Lianne; Schork, Andrew J.; Shen, Li; Shin, Jean; Shumskaya, Elena; Smith, Albert V.; Sprooten, Emma; Strike, Lachlan T.; Teumer, Alexander; Tordesillas-Gutierrez, Diana; Toro, Roberto; Trabzuni, Daniah; Trompet, Stella; Vaidya, Dhananjay; Van der Grond, Jeroen; Van der Lee, Sven J.; Van der Meer, Dennis; Van Donkelaar, Marjolein M. J.; Van Eijk, Kristel R.; Van Erp, Theo G. M.; Van Rooij, Daan; Walton, Esther; Westlye, Lars T.; Whelan, Christopher D.; Windham, Beverly G.; Winkler, Anderson M.; Wittfeld, Katharina; Woldehawariat, Girma; Wolf, Christiane; Wolfers, Thomas; Yanek, Lisa R.; Yang, Jingyun; Zijdenbos, Alex; Zwiers, Marcel P.; Agartz, Ingrid; Almasy, Laura; Ames, David; Amouyel, Philippe; Andreassen, Ole A.; Arepalli, Sampath; Assareh, Amelia A.; Barral, Sandra; Bastin, Mark E.; Becker, Diane M.; Becker, James T.; Bennett, David A.; Blangero, John; van Bokhoven, Hans; Boomsma, Dorret I.; Brodaty, Henry; Brouwer, Rachel M.; Brunner, Han G.; Buckner, Randy L.; Buitelaar, Jan K.; Bulayeva, Kazima B.; Cahn, Wiepke; Calhoun, Vince D.; Cannon, Dara M.; Cavalleri, Gianpiero L.; Cheng, Ching-Yu; Cichon, Sven; Cookson, Mark R.; Corvin, Aiden; Crespo-Facorro, Benedicto; Curran, Joanne E.; Czisch, Michael; Dale, Anders M.; Davies, Gareth E.; De Craen, Anton J. M.; De Geus, Eco J. C.; De Jager, Philip L.; De Zubicaray, Greig I.; Deary, Ian J.; Debette, Stéphanie; DeCarli, Charles; Delanty, Norman; Depondt, Chantal; DeStefano, Anita; Dillman, Allissa; Djurovic, Srdjan; Donohoe, Gary; Drevets, Wayne C.; Duggirala, Ravi; Dyer, Thomas D.; Enzinger, Christian; Erk, Susanne; Espeseth, Thomas; Fedko, Iryna O.; Fernández, Guillén; Ferrucci, Luigi; Fisher, Simon E.; Fleischman, Debra A.; Ford, Ian; Fornage, Myriam; Foroud, Tatiana M.; Fox, Peter T.; Francks, Clyde; Fukunaga, Masaki; Gibbs, J. Raphael; Glahn, David C.; Gollub, Randy L.; Göring, Harald H. H.; Green, Robert C.; Gruber, Oliver; Gudnason, Vilmundur; Guelfi, Sebastian; Håberg, Asta K.; Hansell, Narelle K.; Hardy, John; Hartman, Catharina A.; Hashimoto, Ryota; Hegenscheid, Katrin; Heinz, Andreas; Le Hellard, Stephanie; Hernandez, Dena G.; Heslenfeld, Dirk J.; Ho, Beng-Choon; Hoekstra, Pieter J.; Hoffmann, Wolfgang; Hofman, Albert; Holsboer, Florian; Homuth, Georg; Hosten, Norbert; Hottenga, Jouke-Jan; Huentelman, Matthew; Pol, Hilleke E. Hulshoff; Ikeda, Masashi; Jack Jr, Clifford R.; Jenkinson, Mark; Johnson, Robert; Jönsson, Erik G.; Jukema, J. Wouter; Kahn, René S.; Kanai, Ryota; Kloszewska, Iwona; Knopman, David S.; Kochunov, Peter; Kwok, John B.; Lawrie, Stephen M.; Lemaître, Hervé; Liu, Xinmin; Longo, Dan L.; Lopez, Oscar L.; Lovestone, Simon; Martinez, Oliver; Martinot, Jean-Luc; Mattay, Venkata S.; McDonald, Colm; McIntosh, Andrew M.; McMahon, Francis J.; McMahon, Katie L.; Mecocci, Patrizia; Melle, Ingrid; Meyer-Lindenberg, Andreas; Mohnke, Sebastian; Montgomery, Grant W.; Morris, Derek W.; Mosley, Thomas H.; Mühleisen, Thomas W.; Müller-Myhsok, Bertram; Nalls, Michael A.; Nauck, Matthias; Nichols, Thomas E.; Niessen, Wiro J.; Nöthen, Markus M.; Nyberg, Lars; Ohi, Kazutaka; Olvera, Rene L.; Ophoff, Roel A.; Pandolfo, Massimo; Paus, Tomas; Pausova, Zdenka; Penninx, Brenda W. J. H.; Pike, G. Bruce; Potkin, Steven G.; Psaty, Bruce M.; Reppermund, Simone; Rietschel, Marcella; Roffman, Joshua L.; Romanczuk-Seiferth, Nina; Rotter, Jerome I.; Ryten, Mina; Sacco, Ralph L.; Sachdev, Perminder S.; Saykin, Andrew J.; Schmidt, Reinhold; Schmidt, Helena; Schofield, Peter R.; Sigursson, Sigurdur; Simmons, Andrew; Singleton, Andrew; Sisodiya, Sanjay M.; Smith, Colin; Smoller, Jordan W.; Soininen, Hilkka; Steen, Vidar M.; Stott, David J.; Sussmann, Jessika E.; Thalamuthu, Anbupalam; Toga, Arthur W.; Traynor, Bryan J.; Troncoso, Juan; Tsolaki, Magda; Tzourio, Christophe; Uitterlinden, Andre G.; Hernández, Maria C. Valdés; Van der Brug, Marcel; van der Lugt, Aad; van der Wee, Nic J. A.; Van Haren, Neeltje E. M.; van 't Ent, Dennis; Van Tol, Marie-Jose; Vardarajan, Badri N.; Vellas, Bruno; Veltman, Dick J.; Völzke, Henry; Walter, Henrik; Wardlaw, Joanna M.; Wassink, Thomas H.; Weale, Michael E.; Weinberger, Daniel R.; Weiner, Michael W.; Wen, Wei; Westman, Eric; White, Tonya; Wong, Tien Y.; Wright, Clinton B.; Zielke, Ronald H.; Zonderman, Alan B.; Martin, Nicholas G.; Van Duijn, Cornelia M.; Wright, Margaret J.; Longstreth, W. T.; Schumann, Gunter; Grabe, Hans J.; Franke, Barbara; Launer, Lenore J.; Medland, Sarah E.; Seshadri, Sudha; Thompson, Paul M.; Ikram, M. Arfan

2017-01-01

The hippocampal formation is a brain structure integrally involved in episodic memory, spatial navigation, cognition and stress responsiveness. Structural abnormalities in hippocampal volume and shape are found in several common neuropsychiatric disorders. To identify the genetic underpinnings of hippocampal structure here we perform a genome-wide association study (GWAS) of 33,536 individuals and discover six independent loci significantly associated with hippocampal volume, four of them novel. Of the novel loci, three lie within genes (ASTN2, DPP4 and MAST4) and one is found 200 kb upstream of SHH. A hippocampal subfield analysis shows that a locus within the MSRB3 gene shows evidence of a localized effect along the dentate gyrus, subiculum, CA1 and fissure. Further, we show that genetic variants associated with decreased hippocampal volume are also associated with increased risk for Alzheimer's disease (rg=−0.155). Our findings suggest novel biological pathways through which human genetic variation influences hippocampal volume and risk for neuropsychiatric illness. PMID:28098162

The hippocampal formation: morphological changes induced by thyroid, gonadal and adrenal hormones.

PubMed

Gould, E; Woolley, C S; McEwen, B S

1991-01-01

The hippocampal formation is of considerable interest due to its proposed role in a number of important functions, including learning and memory processes. Manipulations of thyroid, gonadal and adrenal hormones have been shown to influence hippocampal physiology as well as learning and memory. The cellular events which underlie these hormone-induced functional changes are largely unexplored. However, studies suggest that hormonal manipulations during development and in adulthood result in dramatic morphological changes within the hippocampal formation. Because neuronal physiology has been suggested to depend upon neuronal morphology, we have been determining the morphologic sensitivity of hippocampal neurons to thyroid and steroid hormones in an effort to elucidate possible structural mechanisms to account for differences in hippocampal function. In this review, hormone-induced structural changes in the developing and adult hippocampal formation are discussed, with particular emphasis on their functional relevance. Sex differences, as well as the developmental effects of thyroid hormone and glucocorticoids, are described. Moreover, the effects of ovarian steroids, thyroid hormone and glucocorticoids on neuronal morphology in the hippocampal formation of the adult rat are reviewed. These hormone-induced structural changes may account, at least in part, for previously reported hormone-induced changes in hippocampal function.

Carbon Dioxide Snow Storms During the Polar Night on Mars

NASA Technical Reports Server (NTRS)

Toon, Owen B.; Colaprete, Anthony

2001-01-01

The Mars Orbiter Laser Altimeter (MOLA) detected clouds associated with topographic features during the polar night on Mars. While uplift generated from flow over mountains initiates clouds on both Earth and Mars, we suggest that the Martian clouds differ greatly from terrestrial mountain wave clouds. Terrestrial wave clouds are generally compact features with sharp edges due to the relatively small particles in them. However, we find that the large mass of condensible carbon dioxide on Mars leads to clouds with snow tails that may extend many kilometers down wind from the mountain and even reach the surface. Both the observations and the simulations suggest substantial carbon dioxide snow precipitation in association with the underlying topography. This precipitation deposits CO2, dust and water ice to the polar caps, and may lead to propagating geologic features in the Martian polar regions.

New results on the generation of broadband electrostatic waves in the magnetotail

NASA Technical Reports Server (NTRS)

Grabbe, C. L.

1985-01-01

The theory of the generation of broadband electrostatic noise (BEN) in the magnetotail is extended through numerical solution of the dispersion relation under conditions that exist in the plasma sheet boundary layer. It is found that the low-frequency portion of the spectrum has a broad angular spectrum but a fairly sharp peak near 75 deg with respect to the magnetic field, while the high-frequency portion has a narrower angular spectrum that is strongly concentrated along the magnetic field line. These results are in excellent agreement with observations of the broadband wave spectrum and a recent measurement of the propagation direction. The effect of a second cold component of electrons is analyzed, and it is found that it can increase the upper cutoff frequency of BEN to the observed value at about the plasma frequency.

Experimental Study of Second-Mode Instabilities on a 7-Degree Cone at Mach 6

NASA Technical Reports Server (NTRS)

Rufer, Shann J.; Berridge, Dennis C.

2011-01-01

Experiments have been carried out in the NASA Langley Research Center 20-Inch Mach 6 Air Tunnel to measure the second-mode boundary-layer instability on a 7deg half-angle cone using high-frequency pressure sensors. Data were obtained with both blunt and sharp nosetips installed on the cone. The second-mode wave amplitudes were observed to saturate and then begin to decrease in the Langley tunnels, indicating wave breakdown. Pressure fluctuation measurements and thermocouple data indicated the location of transition along the cone at the different conditions tested. Comparisons between the power density spectra obtained during the current test and previous data from the Langley 15-Inch Mach 6 High Temperature Tunnel and the Boeing/AFOSR Mach 6 Quiet tunnel illustrate the effect of tunnel noise on instability growth and transition.

Ultrafast propagation of Schroedinger waves in absorbing media

DOE Office of Scientific and Technical Information (OSTI.GOV)

Delgado, F.; Muga, J.G.; Ruschhaupt, A.

2004-02-01

We show that the temporal peak of a quantum wave may arrive at different locations simultaneously in an absorbing medium. The arrival occurs at the lifetime of the particle in the medium from the instant when a point source with a sharp onset is turned on. We also identify other characteristic times. In particular, the 'traversal' or 'Buettiker-Landauer' time (which grows linearly with the distance to the source) for the Hermitian, non-absorbing case is substituted by several characteristic quantities in the absorbing case. The simultaneous arrival due to absorption, unlike the Hartman effect, occurs for carrier frequencies under or abovemore » the cutoff, and for arbitrarily large distances. It holds also in a relativistic generalization but limited by causality. A possible physical realization is proposed by illuminating a two-level atom with a detuned laser.« less

Catastrophe theory—one of the basic components in the analysis of the seismic response of rock mass to explosions

NASA Astrophysics Data System (ADS)

Khachay, OA; Khachay, OYu

2018-03-01

It is shown that the dynamic process of mining can be controlled using the catastrophe theory. The control parameters can be values of blasting energy and locations of explosions relative to an area under study or operation. The kinematic and dynamic parameters of the deformation waves, as well as the structural features of rock mass through which these waves pass act as internal parameters. The use of the analysis methods for short-term and medium-term forecast of rock mass condition with the control parameters only is insufficient in the presence of sharp heterogeneity. However, the joint use of qualitative recommendations of the catastrophe theory and spatial–temporal data of changes in the internal parameters of rock mass will allow accident prevention in the course of mining.

RCS of resonant scatterers with attached wires

NASA Astrophysics Data System (ADS)

Trueman, C. W.; Mishra, S. R.; Kubina, S. J.; Larose, C. L.

1993-03-01

Some aircraft carry wire antennas for HF communication. This paper investigates the effect of such wires on the radar cross section (RCS) at HF frequencies by comparing the RCS of a strip, a cylinder, and a rod with and without an attached wire. The RCS is found for broadside incidence and for end-on incidence of the plane wave for scatterer lengths from 0.4 to 3.8 wavelengths, typical of aircraft size at HF frequencies. It is shown that the RCS of such fuselage-like targets with a wire 'antenna' is quite different from that of the targets without the wire. For broadside incidence, the wire contributes a sharp peak-and-trough to the RCS at the wire's fundamental resonant frequency. For end-on incidence the wire considerably enhances the RCS at frequencies making its length odd multiples of the quarter-wave.

An experimental study of fluctuating pressure loads beneath swept shock/boundary-layer interactions

NASA Technical Reports Server (NTRS)

Settles, Gary S.

1991-01-01

A database is established on the fluctuating pressure loads produced on aerodynamic surfaces beneath 3-D shock wave/boundary layer interactions. Such loads constitute a fundamental problem of critical concern to future supersonic and hypersonic flight vehicles. A turbulent boundary layer on a flat plate is subjected to interactions with swept planar shock waves generated by sharp fins. Fin angles from 5 to 25 deg at freestream Mach numbers between 2.5 and 4 produce a variety of interaction strengths from weak to very strong. Miniature Kulite pressure transducers mounted in the flat plate were used to measure interaction-induced wall pressure fluctuations. These data will be correlated with proposed new optical data on the fluctuations of the interaction structure, especially that of the lambda-shock system and its associated high-speed jet impingement.

Modelling of radio frequency sheath and fast wave coupling on the realistic ion cyclotron resonant antenna surroundings and the outer wall

NASA Astrophysics Data System (ADS)

Lu, L.; Colas, L.; Jacquot, J.; Després, B.; Heuraux, S.; Faudot, E.; Van Eester, D.; Crombé, K.; Křivská, A.; Noterdaeme, J.-M.; Helou, W.; Hillairet, J.

2018-03-01

In order to model the sheath rectification in a realistic geometry over the size of ion cyclotron resonant heating (ICRH) antennas, the self-consistent sheaths and waves for ICH (SSWICH) code couples self-consistently the RF wave propagation and the DC SOL biasing via nonlinear RF and DC sheath boundary conditions applied at plasma/wall interfaces. A first version of SSWICH had 2D (toroidal and radial) geometry, rectangular walls either normal or parallel to the confinement magnetic field B 0 and only included the evanescent slow wave (SW) excited parasitically by the ICRH antenna. The main wave for plasma heating, the fast wave (FW) plays no role on the sheath excitation in this version. A new version of the code, 2D SSWICH-full wave, was developed based on the COMSOL software, to accommodate full RF field polarization and shaped walls tilted with respect to B 0 . SSWICH-full wave simulations have shown the mode conversion of FW into SW occurring at the sharp corners where the boundary shape varies rapidly. It has also evidenced ‘far-field’ sheath oscillations appearing at the shaped walls with a relatively long magnetic connection length to the antenna, that are only accessible to the propagating FW. Joint simulation, conducted by SSWICH-full wave within a multi-2D approach excited using the 3D wave coupling code (RAPLICASOL), has recovered the double-hump poloidal structure measured in the experimental temperature and potential maps when only the SW is modelled. The FW contribution on the potential poloidal structure seems to be affected by the 3D effects, which was ignored in the current stage. Finally, SSWICH-full wave simulation revealed the left-right asymmetry that has been observed extensively in the unbalanced strap feeding experiments, suggesting that the spatial proximity effects in RF sheath excitation, studied for SW only previously, is still important in the vicinity of the wave launcher under full wave polarizations.

Geometric Effects on the Amplification of First Mode Instability Waves

NASA Technical Reports Server (NTRS)

Kirk, Lindsay C.; Candler, Graham V.

2013-01-01

The effects of geometric changes on the amplification of first mode instability waves in an external supersonic boundary layer were investigated using numerical techniques. Boundary layer stability was analyzed at Mach 6 conditions similar to freestream conditions obtained in quiet ground test facilities so that results obtained in this study may be applied to future test article design to measure first mode instability waves. The DAKOTA optimization software package was used to optimize an axisymmetric geometry to maximize the amplification of the waves at first mode frequencies as computed by the 2D STABL hypersonic boundary layer stability analysis tool. First, geometric parameters such as nose radius, cone half angle, vehicle length, and surface curvature were examined separately to determine the individual effects on the first mode amplification. Finally, all geometric parameters were allowed to vary to produce a shape optimized to maximize the amplification of first mode instability waves while minimizing the amplification of second mode instability waves. Since first mode waves are known to be most unstable in the form of oblique wave, the geometries were optimized using a broad range of wave frequencies as well as a wide range of oblique wave angles to determine the geometry that most amplifies the first mode waves. Since first mode waves are seen most often in flows with low Mach numbers at the edge of the boundary layer, the edge Mach number for each geometry was recorded to determine any relationship between edge Mach number and the stability of first mode waves. Results indicate that an axisymmetric cone with a sharp nose and a slight flare at the aft end under the Mach 6 freestream conditions used here will lower the Mach number at the edge of the boundary layer to less than 4, and the corresponding stability analysis showed maximum first mode N factors of 3.

Aerobic fitness, hippocampal viscoelasticity, and relational memory performance

PubMed Central

Schwarb, Hillary; Johnson, Curtis L.; Daugherty, Ana M.; Hillman, Charles H.; Kramer, Arthur F.; Cohen, Neal J.; Barbey, Aron K.

2017-01-01

The positive relationship between hippocampal structure, aerobic fitness, and memory performance is often observed among children and older adults; but evidence of this relationship among young adults, for whom the hippocampus is neither developing nor atrophying, is less consistent. Studies have typically relied on hippocampal volumetry (a gross proxy of tissue composition) to assess individual differences in hippocampal structure. While volume is not specific to microstructural tissue characteristics, microstructural differences in hippocampal integrity may exist even among healthy young adults when volumetric differences are not diagnostic of tissue health or cognitive function. Magnetic resonance elastography (MRE) is an emerging noninvasive imaging technique for measuring viscoelastic tissue properties and provides quantitative measures of tissue integrity. We have previously demonstrated that individual differences in hippocampal viscoelasticity are related to performance on a relational memory task; however, little is known about health correlates to this novel measure. In the current study, we investigated the relationship between hippocampal viscoelasticity and cardiovascular health, and their mutual effect on relational memory in a group of healthy young adults (N=51). We replicated our previous finding that hippocampal viscoelasticity correlates with relational memory performance. We extend this work by demonstrating that better aerobic fitness, as measured by VO2max, was associated with hippocampal viscoelasticity that mediated the benefits of fitness on memory function. Hippocampal volume, however, did not account for individual differences in memory. Therefore, these data suggest that hippocampal viscoelasticity may provide a more sensitive measure to microstructural tissue organization and its consequences to cognition among healthy young adults. PMID:28366763

The Laughlin liquid in an external potential

NASA Astrophysics Data System (ADS)

Rougerie, Nicolas; Yngvason, Jakob

2018-04-01

We study natural perturbations of the Laughlin state arising from the effects of trapping and disorder. These are N-particle wave functions that have the form of a product of Laughlin states and analytic functions of the N variables. We derive an upper bound to the ground state energy in a confining external potential, matching exactly a recently derived lower bound in the large N limit. Irrespective of the shape of the confining potential, this sharp upper bound can be achieved through a modification of the Laughlin function by suitably arranged quasi-holes.

Synaptically activated Ca2+ waves in layer 2/3 and layer 5 rat neocortical pyramidal neurons

PubMed Central

Larkum, Matthew E; Watanabe, Shigeo; Nakamura, Takeshi; Lasser-Ross, Nechama; Ross, William N

2003-01-01

Calcium waves in layer 2/3 and layer 5 neocortical somatosensory pyramidal neurons were examined in slices from 2- to 8-week-old rats. Repetitive synaptic stimulation evoked a delayed, all-or-none [Ca2+]i increase primarily on the main dendritic shaft. This component was blocked by 1 mm (R,S)-α-methyl-4-carboxyphenylglycine (MCPG), 10 μm ryanodine, 1 mg ml−1 internal heparin, and was not blocked by 400 μm internal Ruthenium Red, indicating that it was due to Ca2+ release from internal stores by inositol 1,4,5-trisphosphate (IP3) mobilized via activation of metabotropic glutamate receptors. Calcium waves were initiated on the apical shaft at sites between the soma to around the main branch point, mostly at insertion points of oblique dendrites, and spread in both directions along the shaft. In the proximal dendrites the peak amplitude of the resulting [Ca2+]i change was much larger than that evoked by a train of Na+ spikes. In distal dendrites the peak amplitude was comparable to the [Ca2+]i change due to a Ca2+ spike. IP3-mediated Ca2+ release also was observed in the presence of the metabotropic agonists t-ACPD and carbachol when backpropagating spikes were generated. Ca2+ entry through NMDA receptors was observed primarily on the oblique dendrites. The main differences between waves in neocortical neurons and in previously described hippocampal pyramidal neurons were, (a) Ca2+ waves in L5 neurons could be evoked further out along the main shaft, (b) Ca2+ waves extended slightly further out into the oblique dendrites and (c) higher concentrations of bath-applied t-ACPD and carbachol were required to generate Ca2+ release events by backpropagating action potentials. PMID:12692172

Mild neurotrauma indicates a range-specific pressure response to low level shock wave exposure.

PubMed

Vandevord, Pamela J; Bolander, Richard; Sajja, Venkata Siva Sai Sujith; Hay, Kathryn; Bir, Cynthia A

2012-01-01

Identifying the level of overpressure required to create physiological deficits is vital to advance prevention, diagnostic, and treatment strategies for individuals exposed to blasts. In this study, a rodent model of primary blast neurotrauma was employed to determine the pressure at which acute neurological alterations occurred. Rats were exposed to a single low intensity shock wave at a pressure of 0, 97, 117, or 153 kPa. Following exposure, rats were assessed for acute cognitive alterations using the Morris water maze and motor dysfunction using the horizontal ladder test. Subsequently, histological analyses of three brain regions (primary motor cortex, the hippocampal dentate gyrus region, and the posteromedial cortical amygdala) were conducted. Histological parameters included measuring the levels of glial fibrillary acidic protein (GFAP) to identify astrocyte activation, cleaved caspase-3 for early apoptosis identification and Fluoro-Jade B (FJB) which labels degenerating neurons within the brain tissue. The results demonstrated that an exposure to a single 117 kPa shock wave revealed a significant change in overall neurological deficits when compared to controls and the other pressures. The animals showed significant alterations in water maze parameters and a histological increase in the number of GFAP, caspase-3, and FJB-positive cells. It is suggested that when exposed to a low level shock wave, there may be a biomechanical response elicited by a specific pressure range which can cause low level neurological deficits within the rat. These data indicate that neurotrauma induced from a shock wave may lead to cognitive deficits in short-term learning and memory of rats. Additional histological evidence supports significant and diffuse glial activation and cellular damage. Further investigation into the biomechanical aspects of shock wave exposure is required to elucidate this pressure range-specific phenomenon.

Prospective and Episodic Memory in Relation to Hippocampal Volume in Adults with Spina Bifida Myelomeningocele

PubMed Central

Treble-Barna, Amery; Juranek, Jenifer; Stuebing, Karla K.; Cirino, Paul T.; Dennis, Maureen; Fletcher, Jack M.

2014-01-01

The present study examined prospective and episodic memory in relation to age, functional independence, and hippocampal volume in younger to middle-aged adults with spina bifida myelomeningocele (SBM) and typically developing (TD) adults. Prospective and episodic memory, as well as hippocampal volume, were reduced in adults with SBM relative to TD adults. Neither memory performance nor hippocampal volume showed greater decrements in older adults. Lower hippocampal volume was associated with reduced prospective memory in adults with SBM, and this relation was specific to the hippocampus and not to a contrast structure, the amygdala. Prospective memory mediated the relation between hippocampal volume and functional independence in adults with SBM. The results add to emerging evidence for reduced memory function in adults with SBM, and provide quantitative evidence for compromised hippocampal macrostructure as a neural correlate of reduced memory in this population. PMID:25068670

Non-invasive Investigation of Human Hippocampal Rhythms Using Magnetoencephalography: A Review.

PubMed

Pu, Yi; Cheyne, Douglas O; Cornwell, Brian R; Johnson, Blake W

2018-01-01

Hippocampal rhythms are believed to support crucial cognitive processes including memory, navigation, and language. Due to the location of the hippocampus deep in the brain, studying hippocampal rhythms using non-invasive magnetoencephalography (MEG) recordings has generally been assumed to be methodologically challenging. However, with the advent of whole-head MEG systems in the 1990s and development of advanced source localization techniques, simulation and empirical studies have provided evidence that human hippocampal signals can be sensed by MEG and reliably reconstructed by source localization algorithms. This paper systematically reviews simulation studies and empirical evidence of the current capacities and limitations of MEG "deep source imaging" of the human hippocampus. Overall, these studies confirm that MEG provides a unique avenue to investigate human hippocampal rhythms in cognition, and can bridge the gap between animal studies and human hippocampal research, as well as elucidate the functional role and the behavioral correlates of human hippocampal oscillations.

Non-invasive Investigation of Human Hippocampal Rhythms Using Magnetoencephalography: A Review

PubMed Central

Pu, Yi; Cheyne, Douglas O.; Cornwell, Brian R.; Johnson, Blake W.

2018-01-01

Hippocampal rhythms are believed to support crucial cognitive processes including memory, navigation, and language. Due to the location of the hippocampus deep in the brain, studying hippocampal rhythms using non-invasive magnetoencephalography (MEG) recordings has generally been assumed to be methodologically challenging. However, with the advent of whole-head MEG systems in the 1990s and development of advanced source localization techniques, simulation and empirical studies have provided evidence that human hippocampal signals can be sensed by MEG and reliably reconstructed by source localization algorithms. This paper systematically reviews simulation studies and empirical evidence of the current capacities and limitations of MEG “deep source imaging” of the human hippocampus. Overall, these studies confirm that MEG provides a unique avenue to investigate human hippocampal rhythms in cognition, and can bridge the gap between animal studies and human hippocampal research, as well as elucidate the functional role and the behavioral correlates of human hippocampal oscillations. PMID:29755314

Lessons from the Short GRB 170817A: The First Gravitational-wave Detection of a Binary Neutron Star Merger

NASA Astrophysics Data System (ADS)

Granot, Jonathan; Guetta, Dafne; Gill, Ramandeep

2017-12-01

The first, long-awaited, detection of a gravitational-wave (GW) signal from the merger of a binary neutron star (NS-NS) system was finally achieved (GW170817) and was also accompanied by an electromagnetic counterpart—the short-duration gamma-ray burst (GRB) 170817A. It occurred in the nearby (D≈ 40 Mpc) elliptical galaxy NGC 4993 and showed optical, IR, and UV emission from half a day up to weeks after the event, as well as late-time X-ray (at ≥slant 8.9 days) and radio (at ≥slant 16.4 days) emission. There was a delay of {{Δ }}t≈ 1.74 {{s}} between the GW merger chirp signal and the prompt GRB emission onset, and an upper limit of {θ }{obs}< 28^\\circ was set on the viewing angle w.r.t the jet’s symmetry axis from the GW signal. In this letter we examine some of the implications of these groundbreaking observations. The delay {{Δ }}t sets an upper limit on the prompt GRB emission radius, {R}γ ≲ 2c{{Δ }}t/{({θ }{obs}-{θ }0)}2, for a jet with sharp edges at an angle {θ }0< {θ }{obs}. GRB 170817A’s relatively low isotropic equivalent γ-ray energy output may suggest a viewing angle slightly outside the jet’s sharp edge, {θ }{obs}-{θ }0˜ {(0.05-0.1)({{Γ }}/100)}-1, but its peak ν {F}ν photon energy and afterglow emission suggest instead that the jet does not have sharp edges and the prompt emission was dominated by less energetic material along our line of sight, at {θ }{obs}≳ 2{θ }0. Finally, we consider the type of remnant that is produced by the NS-NS merger and find that a relatively long-lived (> 2 s) massive NS is strongly disfavored, while a hyper-massive NS of lifetime ˜ 1 {{s}} appears to be somewhat favored over the direct formation of a black hole.

CFD-based aero-optical analysis of flow fields over two-dimensional cavities with active flow control

NASA Astrophysics Data System (ADS)

Tan, Yan

Prediction and control of optical wave front distortions and aberrations in a high energy laser beam due to interaction with an unsteady highly non-uniform flow field is of great importance in the development of directed energy weapon systems for Unmanned Air Vehicles (UAV). The unsteady shear layer over the weapons bay cavity is the primary cause of this distortion of the optical wave front. The large scale vortical structure of the shear layer over the cavity can be significantly reduced by employing an active flow control technique combined with passive flow control. This dissertation explores various active and passive control methods to suppress the cavity oscillations and thereby improve the aero-optics of cavity flow. In active flow control technique, a steady or a pulsed jet is applied at the sharp leading edge of cavities of different aspect ratios L/D (=2, 4, 15), where L and D are the width and the depth of a cavity respectively. In the passive flow control approach, the sharp leading or trailing edge of the cavity is modified into a round edge of different radii. Both of these active and passive flow control approaches are studied independently and in combination. Numerical simulations are performed, with and without active flow control for subsonic free stream flow past two-dimensional sharp and round leading or trailing edge cavities using Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations with a two-equation Shear Stress Transport (SST) turbulence model or a hybrid SST/Large Eddy Simulation (LES) model. Aero-optical analysis is developed and applied to all the simulation cases. Index of refraction and Optical Path Difference (OPD) are compared for flow fields without and with active flow control. Root-Mean-Square (RMS) value of OPD is calculated and compared with the experimental data, where available. The effect of steady and pulsed blowing on buffet loading on the downstream face of the cavity is also computed. Using the numerical simulations, the most effective approach for controlling the cavity oscillations and aero-optical signatures is determined.

Additive gene-environment effects on hippocampal structure in healthy humans.

PubMed

Rabl, Ulrich; Meyer, Bernhard M; Diers, Kersten; Bartova, Lucie; Berger, Andreas; Mandorfer, Dominik; Popovic, Ana; Scharinger, Christian; Huemer, Julia; Kalcher, Klaudius; Pail, Gerald; Haslacher, Helmuth; Perkmann, Thomas; Windischberger, Christian; Brocke, Burkhard; Sitte, Harald H; Pollak, Daniela D; Dreher, Jean-Claude; Kasper, Siegfried; Praschak-Rieder, Nicole; Moser, Ewald; Esterbauer, Harald; Pezawas, Lukas

2014-07-23

Hippocampal volume loss has been related to chronic stress as well as genetic factors. Although genetic and environmental variables affecting hippocampal volume have extensively been studied and related to mental illness, limited evidence is available with respect to G × E interactions on hippocampal volume. The present MRI study investigated interaction effects on hippocampal volume between three well-studied functional genetic variants (COMT Val158Met, BDNF Val66Met, 5-HTTLPR) associated with hippocampal volume and a measure of environmental adversity (life events questionnaire) in a large sample of healthy humans (n = 153). All three variants showed significant interactions with environmental adversity with respect to hippocampal volume. Observed effects were additive by nature and driven by both recent as well as early life events. A consecutive analysis of hippocampal subfields revealed a spatially distinct profile for each genetic variant suggesting a specific role of 5-HTTLPR for the subiculum, BDNF Val66Met for CA4/dentate gyrus, and COMT Val158Met for CA2/3 volume changes. The present study underscores the importance of G × E interactions as determinants of hippocampal volume, which is crucial for the neurobiological understanding of stress-related conditions, such as mood disorders or post-traumatic stress disorder (PTSD). Copyright © 2014 the authors 0270-6474/14/349917-10$15.00/0.

Long-Term Treatment with Paroxetine Increases Verbal Declarative Memory and Hippocampal Volume in Posttraumatic Stress Disorder

PubMed Central

Vermetten, Eric; Vythilingam, Meena; Southwick, Steven M.; Charney, Dennis S.; Bremner, J. Douglas

2011-01-01

Background Animal studies have shown that stress is associated with damage to the hippocampus, inhibition of neurogenesis, and deficits in hippocampal-based memory dysfunction. Studies in patients with posttraumatic stress disorder (PTSD) found deficits in hippocampal-based declarative verbal memory and smaller hippocampal volume, as measured with magnetic resonance imaging (MRI). Recent preclinical evidence has shown that selective serotonin reuptake inhibitors promote neurogenesis and reverse the effects of stress on hippocampal atrophy. This study assessed the effects of long-term treatment with paroxetine on hippocampal volume and declarative memory performance in PTSD. Methods Declarative memory was assessed with the Wechsler Memory Scale–Revised and Selective Reminding Test before and after 9–12 months of treatment with paroxetine in PTSD. Hippocampal volume was measured with MRI. Of the 28 patients who started the protocol, 23 completed the full course of treatment and neuropsychological testing. Twenty patients were able to complete MRI imaging. Results Patients with PTSD showed a significant improvement in PTSD symptoms with treatment. Treatment resulted in significant improvements in verbal declarative memory and a 4.6% increase in mean hippocampal volume. Conclusions These findings suggest that long-term treatment with paroxetine is associated with improvement of verbal declarative memory deficits and an increase in hippocampal volume in PTSD. PMID:14512209

Structural development of the hippocampus and episodic memory: developmental differences along the anterior/posterior axis.

PubMed

DeMaster, Dana; Pathman, Thanujeni; Lee, Joshua K; Ghetti, Simona

2014-11-01

The hippocampus is critically involved in episodic memory, yet relatively little is known about how the development of this structure contributes to the development of episodic memory during middle to late childhood. Previous research has inconsistently reported associations between hippocampal volume and episodic memory performance during this period. We argue that this inconsistency may be due to assessing the hippocampus as a whole, and propose to examine associations separately for subregions along the longitudinal axis of the hippocampus. In the present study, we examined age-related differences in volumes of the hippocampal head, body, and tail, and collected episodic memory measures in children ages 8-11 years and young adults (N = 62). We found that adults had a smaller right hippocampal head, larger hippocampal body bilaterally, and smaller right hippocampal tail compared with children. In adults, but not in children, better episodic memory performance was associated with smaller right hippocampal head and larger hippocampal body. In children, but not in adults, better episodic memory was associated with larger left hippocampal tail. Overall, the results suggest that protracted development of hippocampal subregions contribute to age-related differences in episodic memory. © The Author 2013. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.

Hippocampal atrophy on MRI is predictive of histopathological patterns and surgical prognosis in mesial temporal lobe epilepsy with hippocampal sclerosis.

PubMed

Jardim, Anaclara Prada; Corso, Jeana Torres; Garcia, Maria Teresa Fernandes Castilho; Gaça, Larissa Botelho; Comper, Sandra Mara; Lancellotti, Carmen Lúcia Penteado; Centeno, Ricardo Silva; Carrete, Henrique; Cavalheiro, Esper Abrão; Scorza, Carla Alessandra; Yacubian, Elza Márcia Targas

2016-12-01

To correlate hippocampal volumes obtained from brain structural imaging with histopathological patterns of hippocampal sclerosis (HS), in order to predict surgical outcome. Patients with mesial temporal lobe epilepsy (MTLE) with HS were selected. Clinical data were assessed pre-operatively and surgical outcome in the first year post surgery. One block of mid hippocampal body was selected for HS classification according to ILAE criteria. NeuN-immunoreactive cell bodies were counted within hippocampal subfields, in four randomly visual fields, and cell densities were transformed into z-score values. FreeSurfer processing of 1.5T brain structural images was used for subcortical and cortical volumetric estimation of the ipsilateral hippocampus. Univariate analysis of variance and Pearson's correlation test were applied for statistical analyses. Sixty-two cases (31 female, 32 right HS) were included. ILAE type 1 HS was identified in 48 patients, type 2 in eight, type 3 in two, and four had no-HS. Better results regarding seizure control, i.e. ILAE 1, were achieved by patients with type 1 HS (58.3%). Patients with types 1 and 2 had smaller hippocampal volumes compared to those with no-HS (p<0.001 and p=0.004, respectively). Positive correlation was encountered between hippocampal volumes and CA1, CA3, CA4, and total estimated neuronal densities. CA2 was the only sector which did not correlate its neuronal density with hippocampal volume (p=0.390). This is the first study correlating hippocampal volume on MRI submitted to FreeSurfer processing with ILAE patterns of HS and neuronal loss within each hippocampal subfield, a fundamental finding to anticipate surgical prognosis for patients with drug-resistant MTLE and HS. Copyright © 2016 Elsevier B.V. All rights reserved.

Posterior cingulate glucose metabolism, hippocampal glucose metabolism, and hippocampal volume in cognitively normal, late-middle-aged persons at 3 levels of genetic risk for Alzheimer disease.

PubMed

Protas, Hillary D; Chen, Kewei; Langbaum, Jessica B S; Fleisher, Adam S; Alexander, Gene E; Lee, Wendy; Bandy, Daniel; de Leon, Mony J; Mosconi, Lisa; Buckley, Shannon; Truran-Sacrey, Diana; Schuff, Norbert; Weiner, Michael W; Caselli, Richard J; Reiman, Eric M

2013-03-01

To characterize and compare measurements of the posterior cingulate glucose metabolism, the hippocampal glucose metabolism, and hippocampal volume so as to distinguish cognitively normal, late-middle-aged persons with 2, 1, or 0 copies of the apolipoprotein E (APOE) ε4 allele, reflecting 3 levels of risk for late-onset Alzheimer disease. Cross-sectional comparison of measurements of cerebral glucose metabolism using 18F-fluorodeoxyglucose positron emission tomography and measurements of brain volume using magnetic resonance imaging in cognitively normal ε4 homozygotes, ε4 heterozygotes, and noncarriers. Academic medical center. A total of 31 ε4 homozygotes, 42 ε4 heterozygotes, and 76 noncarriers, 49 to 67 years old, matched for sex, age, and educational level. The measurements of posterior cingulate and hippocampal glucose metabolism were characterized using automated region-of-interest algorithms and normalized for whole-brain measurements. The hippocampal volume measurements were characterized using a semiautomated algorithm and normalized for total intracranial volume. Although there were no significant differences among the 3 groups of participants in their clinical ratings, neuropsychological test scores, hippocampal volumes (P = .60), or hippocampal glucose metabolism measurements (P = .12), there were significant group differences in their posterior cingulate glucose metabolism measurements (P = .001). The APOE ε4 gene dose was significantly associated with posterior cingulate glucose metabolism (r = 0.29, P = .0003), and this association was significantly greater than those with hippocampal volume or hippocampal glucose metabolism (P < .05, determined by use of pairwise Fisher z tests). Although our findings may depend in part on the analysis algorithms used, they suggest that a reduction in posterior cingulate glucose metabolism precedes a reduction in hippocampal volume or metabolism in cognitively normal persons at increased genetic risk for Alzheimer disease.

Hippocampal Atrophy Is Associated with Altered Hippocampus-Posterior Cingulate Cortex Connectivity in Mesial Temporal Lobe Epilepsy with Hippocampal Sclerosis.

PubMed

Shih, Y C; Tseng, C E; Lin, F-H; Liou, H H; Tseng, W Y I

2017-03-01

Unilateral mesial temporal lobe epilepsy and hippocampal sclerosis have structural and functional abnormalities in the mesial temporal regions. To gain insight into the pathophysiology of the epileptic network in mesial temporal lobe epilepsy with hippocampal sclerosis, we aimed to clarify the relationships between hippocampal atrophy and the altered connection between the hippocampus and the posterior cingulate cortex in patients with mesial temporal lobe epilepsy with hippocampal sclerosis. Fifteen patients with left mesial temporal lobe epilepsy with hippocampal sclerosis and 15 healthy controls were included in the study. Multicontrast MR imaging, including high-resolution T1WI, diffusion spectrum imaging, and resting-state fMRI, was performed to measure the hippocampal volume, structural connectivity of the inferior cingulum bundle, and intrinsic functional connectivity between the hippocampus and the posterior cingulate cortex, respectively. Compared with controls, patients had decreased left hippocampal volume (volume ratio of the hippocampus and controls, 0.366% ± 0.029%; patients, 0.277% ± 0.063%, corrected P = .002), structural connectivity of the bilateral inferior cingulum bundle (generalized fractional anisotropy, left: controls, 0.234 ± 0.020; patients, 0.193 ± 0.022, corrected P = .0001, right: controls, 0.226 ± 0.022; patients, 0.208 ± 0.017, corrected P = .047), and intrinsic functional connectivity between the left hippocampus and the left posterior cingulate cortex (averaged z-value: controls, 0.314 ± 0.152; patients, 0.166 ± 0.062). The left hippocampal volume correlated with structural connectivity positively (standardized β = 0.864, P = .001), but it had little correlation with intrinsic functional connectivity (standardized β = -0.329, P = .113). On the contralesional side, the hippocampal volume did not show any significant correlation with structural connectivity or intrinsic functional connectivity ( F 2,12 = 0.284, P = .757, R 2 = 0.045). In left mesial temporal lobe epilepsy with hippocampal sclerosis, the left inferior cingulum bundle undergoes degeneration in tandem with the left hippocampal volume, whereas intrinsic functional connectivity seems to react by compensating the loss of connectivity. Such insight might be helpful in understanding the development of the epileptic network in left mesial temporal lobe epilepsy with hippocampal sclerosis. © 2017 by American Journal of Neuroradiology.

A method for the computational modeling of the physics of heart murmurs

NASA Astrophysics Data System (ADS)

Seo, Jung Hee; Bakhshaee, Hani; Garreau, Guillaume; Zhu, Chi; Andreou, Andreas; Thompson, William R.; Mittal, Rajat

2017-05-01

A computational method for direct simulation of the generation and propagation of blood flow induced sounds is proposed. This computational hemoacoustic method is based on the immersed boundary approach and employs high-order finite difference methods to resolve wave propagation and scattering accurately. The current method employs a two-step, one-way coupled approach for the sound generation and its propagation through the tissue. The blood flow is simulated by solving the incompressible Navier-Stokes equations using the sharp-interface immersed boundary method, and the equations corresponding to the generation and propagation of the three-dimensional elastic wave corresponding to the murmur are resolved with a high-order, immersed boundary based, finite-difference methods in the time-domain. The proposed method is applied to a model problem of aortic stenosis murmur and the simulation results are verified and validated by comparing with known solutions as well as experimental measurements. The murmur propagation in a realistic model of a human thorax is also simulated by using the computational method. The roles of hemodynamics and elastic wave propagation on the murmur are discussed based on the simulation results.

Reply to “Comment on ‘Magnetotransport signatures of a single nodal electron pocket constructed from Fermi arcs' ”

DOE PAGES

Harrison, N.; Sebastian, S. E.

2017-10-12

In this paper, we provide arguments relating to those recently made in a comment by Chakravarty and Wang, who question the validity of our proposed charge-density wave Fermi surface reconstruction model and its relation to sign changes in the Hall effect. First, we show that the form of rounding of the vertices (i.e. sharp corners) of the reconstructed electron pocket, as used in our model calculations of the Hall coefficient, is consistent with Bragg reflection from the periodic potential of a charge-density wave, rather than being arbitrarily chosen. Second, we provide further justifications for why an oscillatory transport scattering timemore » provides a useful means for modeling Shubnikov–de Haas oscillations in the Hall effect, in the situation where a Fermi surface pocket departs from the ideal circular form. Third and finally, we discuss recent experimental evidence gathered from two different families of underdoped cuprates supporting the existence of a single electron pocket produced by biaxial charge-density wave order as a universal phenomena.« less

Stable lattice Boltzmann model for Maxwell equations in media

NASA Astrophysics Data System (ADS)

Hauser, A.; Verhey, J. L.

2017-12-01

The present work shows a method for stable simulations via the lattice Boltzmann (LB) model for electromagnetic waves (EM) transiting homogeneous media. LB models for such media were already presented in the literature, but they suffer from numerical instability when the media transitions are sharp. We use one of these models in the limit of pure vacuum derived from Liu and Yan [Appl. Math. Model. 38, 1710 (2014), 10.1016/j.apm.2013.09.009] and apply an extension that treats the effects of polarization and magnetization separately. We show simulations of simple examples in which EM waves travel into media to quantify error scaling, stability, accuracy, and time scaling. For conductive media, we use the Strang splitting and check the simulations accuracy at the example of the skin effect. Like pure EM propagation, the error for the static limits, which are constructed with a current density added in a first-order scheme, can be less than 1 % . The presented method is an easily implemented alternative for the stabilization of simulation for EM waves propagating in spatially complex structured media properties and arbitrary transitions.

Resonant absorption of electromagnetic waves in transition anisotropic media.

PubMed

Kim, Kihong

2017-11-27

We study the mode conversion and resonant absorption phenomena occurring in a slab of a stratified anisotropic medium, optical axes of which are tilted with respect to the direction of inhomogeneity, using the invariant imbedding theory of wave propagation. When the tilt angle is zero, mode conversion occurs if the longitudinal component of the permittivity tensor, which is the one in the direction of inhomogeneity in the non-tilted case, varies from positive to negative values within the medium, while the transverse component plays no role. When the tilt angle is nonzero, the wave transmission and absorption show an asymmetry under the sign change of the incident angle in a range of the tilt angle, while the reflection is always symmetric. We calculate the reflectance, the transmittance and the absorptance for several configurations of the permittivity tensor and find that resonant absorption is greatly enhanced when the medium from the incident surface to the resonance region is hyperbolic than when it is elliptic. For certain configurations, the transmittance and absorptance curves display sharp peaks at some incident angles determined by the tilt angle.

Constraints on the anisotropic contributions to velocity discontinuities at ∼60 km depth beneath the Pacific

PubMed Central

Harmon, Nicholas

2017-01-01

Abstract Strong, sharp, negative seismic discontinuities, velocity decreases with depth, are observed beneath the Pacific seafloor at ∼60 km depth. It has been suggested that these are caused by an increase in radial anisotropy with depth, which occurs in global surface wave models. Here we test this hypothesis in two ways. We evaluate whether an increase in surface wave radial anisotropy with depth is robust with synthetic resolution tests. We do this by fitting an example surface wave data set near the East Pacific Rise. We also estimate the apparent isotropic seismic velocity discontinuities that could be caused by changes in radial anisotropy in S‐to‐P and P‐to‐S receiver functions and SS precursors using synthetic seismograms. We test one model where radial anisotropy is caused by olivine alignment and one model where it is caused by compositional layering. The result of our surface wave inversion suggests strong shallow azimuthal anisotropy beneath 0–10 Ma seafloor, which would also have a radial anisotropy signature. An increase in radial anisotropy with depth at 60 km depth is not well‐resolved in surface wave models, and could be artificially observed. Shallow isotropy underlain by strong radial anisotropy could explain moderate apparent velocity drops (<6%) in SS precursor imaging, but not receiver functions. The effect is diminished if strong anisotropy also exists at 0–60 km depth as suggested by surface waves. Overall, an increase in radial anisotropy with depth may not exist at 60 km beneath the oceans and does not explain the scattered wave observations. PMID:29097907

Constraints on the anisotropic contributions to velocity discontinuities at ∼60 km depth beneath the Pacific.

PubMed

Rychert, Catherine A; Harmon, Nicholas

2017-08-01

Strong, sharp, negative seismic discontinuities, velocity decreases with depth, are observed beneath the Pacific seafloor at ∼60 km depth. It has been suggested that these are caused by an increase in radial anisotropy with depth, which occurs in global surface wave models. Here we test this hypothesis in two ways. We evaluate whether an increase in surface wave radial anisotropy with depth is robust with synthetic resolution tests. We do this by fitting an example surface wave data set near the East Pacific Rise. We also estimate the apparent isotropic seismic velocity discontinuities that could be caused by changes in radial anisotropy in S-to-P and P-to-S receiver functions and SS precursors using synthetic seismograms. We test one model where radial anisotropy is caused by olivine alignment and one model where it is caused by compositional layering. The result of our surface wave inversion suggests strong shallow azimuthal anisotropy beneath 0-10 Ma seafloor, which would also have a radial anisotropy signature. An increase in radial anisotropy with depth at 60 km depth is not well-resolved in surface wave models, and could be artificially observed. Shallow isotropy underlain by strong radial anisotropy could explain moderate apparent velocity drops (<6%) in SS precursor imaging, but not receiver functions. The effect is diminished if strong anisotropy also exists at 0-60 km depth as suggested by surface waves. Overall, an increase in radial anisotropy with depth may not exist at 60 km beneath the oceans and does not explain the scattered wave observations.

Studies on the influence of axial bends on ultrasonic guided waves in hollow cylinders (pipes)

NASA Astrophysics Data System (ADS)

Verma, Bhupesh; Balasubramaniam, Krishnan; Rajagopal, Prabhu

2013-01-01

Ultrasonic guided waves in hollow cylinders (pipes) are today widely applied as rapid screening tools in the inspection of straight pipe segments in oil, power generation and petrochemical processing industries. However, the characteristics of guided wave propagation across features such as bends in the pipe network are complicated, hampering a wider application of the developed techniques. Although a growing number of studies in recent years have considered guided wave propagation across elbows and U-type bends, the topic is still not very well understood for a general bend angle φ, mean bend radius R and pipe thickness b. Here we use 3D Finite Element (FE) simulation to illumine the propagation of fundamental guided pipe modes across bends of several different angles φ. Two different bend radius regimes, R/λ ≈ 1 and 10 (where λ denotes the wavelength of the mode studied) are considered, exemplifying 'sharp' and gradual or 'slow' bends. Different typical pipe thicknesses b within these regimes are also studied. The results confirm the expectation that different bend radius regimes affect the waves differently. Further, while as observed in earlier studies, at moderate bend radii, fundamental modes travel almost unaffected by an elbow (bend angle φ = 90 degrees), we find that as the bend angle is reduced, there is a progressively larger extent of mode-conversion. These trends and results are validated using experiments.

Deficits in memory and visuospatial learning correlate with regional hippocampal atrophy in MS.

PubMed

Longoni, Giulia; Rocca, Maria A; Pagani, Elisabetta; Riccitelli, Gianna C; Colombo, Bruno; Rodegher, Mariaemma; Falini, Andrea; Comi, Giancarlo; Filippi, Massimo

2015-01-01

The hippocampus has a critical role in episodic memory and visuospatial learning and consolidation. We assessed the patterns of whole and regional hippocampal atrophy in a large group of multiple sclerosis (MS) patients, and their correlations with neuropsychological impairment. From 103 MS patients and 28 healthy controls (HC), brain dual-echo and high-resolution 3D T1-weighted images were acquired using a 3.0-Tesla scanner. All patients underwent a neuropsychological assessment of hippocampal-related cognitive functions, including Paired Associate Word Learning, Short Story, delayed recall of Rey-Osterrieth Complex Figure and Paced Auditory Serial Attention tests. The hippocampi were manually segmented and volumes derived. Regional atrophy distribution was assessed using a radial mapping analysis. Correlations between hippocampal atrophy and clinical, neuropsychological and MRI metrics were also evaluated. Hippocampal volume was reduced in MS patients vs HC (p < 0.001 for both right and hippocampus). In MS patients, radial atrophy affected CA1 subfield and subiculum of posterior hippocampus, bilaterally. The dentate hilus (DG:H) of the right hippocampal head was also affected. Regional hippocampal atrophy correlated with brain T2 and T1 lesion volumes, while no correlation was found with disability. Damage to the CA1 and subiculum was significantly correlated to the performances at hippocampal-targeted neuropsychological tests. These results show that hippocampal subregions have a different vulnerability to MS-related damage, with a relative sparing of the head of the left hippocampus. The assessment of regional hippocampal atrophy may help explain deficits of specific cognitive functions in MS patients, including memory and visuospatial abilities.

Global and regional alterations of hippocampal anatomy in long-term meditation practitioners.

PubMed

Luders, Eileen; Thompson, Paul M; Kurth, Florian; Hong, Jui-Yang; Phillips, Owen R; Wang, Yalin; Gutman, Boris A; Chou, Yi-Yu; Narr, Katherine L; Toga, Arthur W

2013-12-01

Studies linking meditation and brain structure are still relatively sparse, but the hippocampus is consistently implicated as one of the structures altered in meditation practitioners. To explore hippocampal features in the framework of meditation, we analyzed high-resolution structural magnetic resonance imaging data from 30 long-term meditators and 30 controls, closely matched for sex, age, and handedness. Hippocampal formations were manually traced following established protocols. In addition to calculating left and right hippocampal volumes (global measures), regional variations in surface morphology were determined by measuring radial distances from the hippocampal core to spatially matched surface points (local measures). Left and right hippocampal volumes were larger in meditators than in controls, significantly so for the left hippocampus. The presence and direction of this global effect was confirmed locally by mapping the exact spatial locations of the group differences. Altogether, radial distances were larger in meditators compared to controls, with up to 15% difference. These local effects were observed in several hippocampal regions in the left and right hemisphere though achieved significance primarily in the left hippocampal head. Larger hippocampal dimensions in long-term meditators may constitute part of the underlying neurological substrate for cognitive skills, mental capacities, and/or personal traits associated with the practice of meditation. Alternatively, given that meditation positively affects autonomic regulation and immune activity, altered hippocampal dimensions may be one result of meditation-induced stress reduction. However, given the cross-sectional design, the lack of individual stress measures, and the limited resolution of brain data, the exact underlying neuronal mechanisms remain to be established. Copyright © 2012 Wiley Periodicals, Inc.

Global and Regional Alterations of Hippocampal Anatomy in Long-Term Meditation Practitioners

PubMed Central

Luders, Eileen; Thompson, Paul M.; Kurth, Florian; Hong, Jui-Yang; Phillips, Owen R.; Wang, Yalin; Gutman, Boris A.; Chou, Yi-Yu; Narr, Katherine L.; Toga, Arthur W.

2014-01-01

Studies linking meditation and brain structure are still relatively sparse, but the hippocampus is consistently implicated as one of the structures altered in meditation practitioners. To explore hippocampal features in the framework of meditation, we analyzed high-resolution structural magnetic resonance imaging data from 30 long-term meditators and 30 controls, closely matched for sex, age, and handedness. Hippocampal formations were manually traced following established protocols. In addition to calculating left and right hippocampal volumes (global measures), regional variations in surface morphology were determined by measuring radial distances from the hippocampal core to spatially matched surface points (local measures). Left and right hippocampal volumes were larger in meditators than in controls, significantly so for the left hippocampus. The presence and direction of this global effect was confirmed locally by mapping the exact spatial locations of the group differences. Altogether, radial distances were larger in meditators compared to controls, with up to 15% difference. These local effects were observed in several hippocampal regions in the left and right hemisphere though achieved significance primarily in the left hippocampal head. Larger hippocampal dimensions in long-term meditators may constitute part of the underlying neurological substrate for cognitive skills, mental capacities, and/or personal traits associated with the practice of meditation. Alternatively, given that meditation positively affects autonomic regulation and immune activity, altered hippocampal dimensions may be one result of meditation-induced stress reduction. However, given the cross-sectional design, the lack of individual stress measures, and the limited resolution of brain data, the exact underlying neuronal mechanisms remain to be established. PMID:22815233

Hippocampal volume changes following electroconvulsive therapy: a systematic review and meta-analysis.

PubMed

Wilkinson, Samuel T; Sanacora, Gerard; Bloch, Michael H

2017-05-01

Reduced hippocampal volume is one of the most consistent morphological findings in Major Depressive Disorder (MDD). Electroconvulsive therapy (ECT) is the most effective therapy for MDD, yet its mechanism of action remains poorly understood. Animal models show that ECT induces several neuroplastic processes, which lead to hippocampal volume increases. We conducted a meta-analysis of ECT studies in humans to investigate its effects on hippocampal volume. PubMed was searched for studies examining hippocampal volume before and after ECT. A random-effects model was used for meta-analysis with standardized mean difference (SMD) of the change in hippocampal volume before and after ECT as the primary outcome. Nine studies involving 174 participants were included. Total hippocampal volumes increased significantly following ECT compared to pre-treatment values (SMD=1.10; 95% CI 0.80-1.39; z=7.34; p<0.001; k=9). Both right (SMD=1.01; 95% CI 0.72-1.30; z=6.76; p<0.001; k=7) and left (SMD=0.87; 95% CI 0.51-1.23; z=4.69; p<0.001; k=7) hippocampal volumes were also similarly increased significantly following ECT. We demonstrated no correlation between improvement in depression symptoms with ECT and change in total hippocampal volume (beta=-1.28, 95% CI -4.51-1.95, z=-0.78, p=0.44). We demonstrate fairly consistent increases in hippocampal volume bilaterally following ECT treatment. The relationship among these volumetric changes and clinical improvement and cognitive side effects of ECT should be explored by larger, multisite studies with harmonized imaging methods.

Diagnosis and body mass index effects on hippocampal volumes and neurochemistry in bipolar disorder.

PubMed

Bond, D J; Silveira, L E; MacMillan, E L; Torres, I J; Lang, D J; Su, W; Honer, W G; Lam, R W; Yatham, L N

2017-03-28

We previously reported that higher body mass index (BMI) was associated with greater hippocampal glutamate+glutamine in people with bipolar disorder (BD), but not in non-BD healthy comparator subjects (HSs). In the current report, we extend these findings by examining the impact of BD diagnosis and BMI on hippocampal volumes and the concentrations of several additional neurochemicals in 57 early-stage BD patients and 31 HSs. Using 3-T magnetic resonance imaging and magnetic resonance spectroscopy, we measured bilateral hippocampal volumes and the hippocampal concentrations of four neurochemicals relevant to BD: N-acetylaspartate+N-acteylaspartylglutamate (tNAA), creatine+phosphocreatine (Cre), myoinositol (Ins) and glycerophosphocholine+phosphatidylcholine (Cho). We used multivariate factorial analysis of covariance to investigate the impact of diagnosis (patient vs HS) and BMI category (normal weight vs overweight/obese) on these variables. We found a main effect of diagnosis on hippocampal volumes, with patients having smaller hippocampi than HSs. There was no association between BMI and hippocampal volumes. We found diagnosis and BMI effects on hippocampal neurochemistry, with patients having lower Cre, Ins and Cho, and overweight/obese subjects having higher levels of these chemicals. In patient-only models that controlled for clinical and treatment variables, we detected an additional association between higher BMI and lower tNAA that was absent in HSs. To our knowledge, this was the first study to investigate the relative contributions of BD diagnosis and BMI to hippocampal volumes, and only the second to investigate their contributions to hippocampal chemistry. It provides further evidence that diagnosis and elevated BMI both impact limbic brain areas relevant to BD.

Study of the surface wave off-great-circle propagation based on dense seismic array: a case study in Northeast China

NASA Astrophysics Data System (ADS)

Chen, H.; Chong, J.

2016-12-01

The traditional surface wave tomography is based on the ray theory, which assumes that surface wave propagates along the great-circle. The great-circle assumption is valid only when the size of the anomaly is larger than the width of the Fresnel zone and the lateral variation is relatively smooth. However, off-great-circle propagation may occur when the surface wave travels across tectonic boundaries with strong heterogeneity and sharp velocity change, e.g., continental margin, mid-ridge and sea trench, resulting in arrival angle anomaly and multi-pathing effect. The off-great-circle propagation may deviate the result of surface wave tomography based on great-circle approximation, so it is of great importance to study the off-great-circle propagation. In this study, we used the teleseismic waveforms from September 2009 to August 2011, recorded by the NECESSArray in Northeast China, to study the off-great-circle propagation of Rayleigh wave by the Beamforming method. Our results show that the off-great-circle effect increases with decreasing period. At the period of 60 s, the off-great-circle effect is relatively weak and the Rayleigh wave propagates approximately along the great-circle. While at the period of 20 s, the off-great-circle effect becomes strong, the arrival angle anomaly measured from some events can be as large as 20º, and obvious multi-pathing effect is also observed. Lateral variations of the arrival angle anomaly and phase velocity have also been found in the study region, which may be correlated with the lithosphere heterogeneity in Northeast China. Our results demonstrate the necessity to study the surface wave off-great-circle propagation. Acknowledgement: This study is financially supported by National Natural Science Foundation of China under Grant No. 41590854.

Space-borne observation of mesospheric bore by Visible and near Infrared Spectral Imager onboard the International Space Station

NASA Astrophysics Data System (ADS)

Hozumi, Y.; Saito, A.; Sakanoi, T.; Yamazaki, A.; Hosokawa, K.

2017-12-01

Mesospheric bores were observed by Visible and near Infrared Spectral Imager (VISI) of the ISS-IMAP mission (Ionosphere, Mesosphere, upper Atmosphere and Plasmasphere mapping mission from the International Space Station) in O2 airglow at 762 nm wavelength. The mesospheric bore is moving front of sharp jump followed by undulations or turbulence in the mesopause region. Since previous studies of mesospheric bore were mainly based on ground-based airglow imaging that is limited in field-of-view and observing site, little is known about its horizontal extent and global behavior. Space-borne imaging by ISS-IMAP/VISI provides an opportunity to study the mesospheric bore with a wide field-of-view and global coverage. A mesospheric bore was captured by VISI in two consecutive paths on 9 July 2015 over the south of African continent (48ºS - 54ºS and 15ºE). The wave front aligned with south-north direction and propagated to west. The phase velocity and wave length of the following undulation were estimated to 100 m/s and 30 km, respectively. Those parameters are similar to those reported by previous studies. 30º anti-clockwise rotation of the wave front was recognized in 100 min. Another mesospheric bore was captured on 9 May 2013 over the south Atlantic ocean (35ºS - 43ºS and 24ºW - 1ºE) with more than 2,200 km horizontal extent of wave front. The wave front aligned with southeast-northwest direction. Because the following undulation is recognized in the southwest side of the wave front, it is estimated to propagate to northeast direction. The wave front was modulated with 1,000 km wave length. This modulation implies inhomogeneity of the phase velocity.

Neuropsychology, autobiographical memory, and hippocampal volume in "younger" and "older" patients with chronic schizophrenia.

PubMed

Herold, Christina Josefa; Lässer, Marc Montgomery; Schmid, Lena Anna; Seidl, Ulrich; Kong, Li; Fellhauer, Iven; Thomann, Philipp Arthur; Essig, Marco; Schröder, Johannes

2015-01-01

Despite a wide range of studies on neuropsychology in schizophrenia, autobiographical memory (AM) has been scarcely investigated in these patients. Hence, less is known about AM in older patients and hippocampal contribution to autobiographical memories of varying remoteness. Therefore, we investigated hippocampal volume and AM along with important neuropsychological domains in patients with chronic schizophrenia and the respective relationships between these parameters. We compared 25 older patients with chronic schizophrenia to 23 younger patients and an older healthy control group (N = 21) with respect to AM, additional neuropsychological parameters, and hippocampal volume. Personal episodic and semantic memory was investigated using a semi-structured interview. Additional neuropsychological parameters were assessed by using a battery of standard neuropsychological tests. Structural magnetic resonance imaging data were analyzed with an automated region-of-interest procedure. While hippocampal volume reduction and neuropsychological impairment were more pronounced in the older than in the younger patients, both groups showed equivalent reduced AM performance for recent personal episodes. In the patient group, significant correlations between left hippocampal volume and recent autobiographical episodes as well as personal semantic memories arose. Verbal memory and working memory were significantly correlated with right hippocampal volume; executive functions, however, were associated with bilateral hippocampal volumes. These findings underline the complexity of AM and its impairments in the course of schizophrenia in comparison to rather progressive neuropsychological deficits and address the importance of hippocampal contribution.

Phase matters: responding to and learning about peripheral stimuli depends on hippocampal θ phase at stimulus onset

PubMed Central

Waselius, Tomi; Mikkonen, Jarno E.; Wikgren, Jan; Penttonen, Markku

2015-01-01

Hippocampal θ (3–12 Hz) oscillations are implicated in learning and memory, but their functional role remains unclear. We studied the effect of the phase of local θ oscillation on hippocampal responses to a neutral conditioned stimulus (CS) and subsequent learning of classical trace eyeblink conditioning in adult rabbits. High-amplitude, regular hippocampal θ-band responses (that predict good learning) were elicited by the CS when it was timed to commence at the fissure θ trough (Trough group). Regardless, learning in this group was not enhanced compared with a yoked control group, possibly due to a ceiling effect. However, when the CS was consistently presented to the peak of θ (Peak group), hippocampal θ-band responding was less organized and learning was retarded. In well-trained animals, the hippocampal θ phase at CS onset no longer affected performance of the learned response, suggesting a time-limited role for hippocampal processing in learning. To our knowledge, this is the first study to demonstrate that timing a peripheral stimulus to a specific phase of the hippocampal θ cycle produces robust effects on the synchronization of neural responses and affects learning at the behavioral level. Our results support the notion that the phase of spontaneous hippocampal θ oscillation is a means of regulating the processing of information in the brain to a behaviorally relevant degree. PMID:25979993

Peripheral telomere length and hippocampal volume in adolescents with major depressive disorder.

PubMed

Henje Blom, E; Han, L K M; Connolly, C G; Ho, T C; Lin, J; LeWinn, K Z; Simmons, A N; Sacchet, M D; Mobayed, N; Luna, M E; Paulus, M; Epel, E S; Blackburn, E H; Wolkowitz, O M; Yang, T T

2015-11-10

Several studies have reported that adults with major depressive disorder have shorter telomere length and reduced hippocampal volumes. Moreover, studies of adult populations without major depressive disorder suggest a relationship between peripheral telomere length and hippocampal volume. However, the relationship of these findings in adolescents with major depressive disorder has yet to be explored. We examined whether adolescent major depressive disorder is associated with altered peripheral telomere length and hippocampal volume, and whether these measures relate to one another. In 54 unmedicated adolescents (13-18 years) with major depressive disorder and 63 well-matched healthy controls, telomere length was assessed from saliva using quantitative polymerase chain reaction methods, and bilateral hippocampal volumes were measured with magnetic resonance imaging. After adjusting for age and sex (and total brain volume in the hippocampal analysis), adolescents with major depressive disorder exhibited significantly shorter telomere length and significantly smaller right, but not left hippocampal volume. When corrected for age, sex, diagnostic group and total brain volume, telomere length was not significantly associated with left or right hippocampal volume, suggesting that these cellular and neural processes may be mechanistically distinct during adolescence. Our findings suggest that shortening of telomere length and reduction of hippocampal volume are already present in early-onset major depressive disorder and thus unlikely to be only a result of accumulated years of exposure to major depressive disorder.

Delayed recall, hippocampal volume and Alzheimer neuropathology: findings from the Nun Study.

PubMed

Mortimer, J A; Gosche, K M; Riley, K P; Markesbery, W R; Snowdon, D A

2004-02-10

To examine the associations of hippocampal volume and the severity of neurofibrillary lesions determined at autopsy with delayed verbal recall performance evaluated an average of 1 year prior to death. Hippocampal volumes were computed using postmortem brain MRI from the first 56 scanned participants of the Nun Study. Quantitative neuropathologic studies included lesion counts, Braak staging, and determination of whether neuropathologic criteria for Alzheimer disease (AD) were met. Multiple regression was used to assess the association of hippocampal volume and neuropathologic lesions with the number of words (out of 10) recalled on the Consortium to Establish a Registry for Alzheimer's Disease Delayed Word Recall Test administered an average of 1 year prior to death. When entered separately, hippocampal volume, Braak stage, and the mean neurofibrillary tangle counts in the CA-1 region of the hippocampus and the subiculum were strongly associated with the number of words recalled after a delay, adjusting for age and education. When hippocampal volume was entered together with each neuropathologic index, only hippocampal volume retained a significant association with the delayed recall measure. The association between hippocampal volume and the number of words recalled was present in both demented and nondemented individuals as well as in those with and without substantial AD neurofibrillary pathology. The association of neurofibrillary tangles with delayed verbal recall may reflect associated hippocampal atrophy.

Detection of changes of high-frequency activity by statistical time-frequency analysis in epileptic spikes

PubMed Central

Kobayashi, Katsuhiro; Jacobs, Julia; Gotman, Jean

2013-01-01

Objective A novel type of statistical time-frequency analysis was developed to elucidate changes of high-frequency EEG activity associated with epileptic spikes. Methods The method uses the Gabor Transform and detects changes of power in comparison to background activity using t-statistics that are controlled by the false discovery rate (FDR) to correct type I error of multiple testing. The analysis was applied to EEGs recorded at 2000 Hz from three patients with mesial temporal lobe epilepsy. Results Spike-related increase of high-frequency oscillations (HFOs) was clearly shown in the FDR-controlled t-spectra: it was most dramatic in spikes recorded from the hippocampus when the hippocampus was the seizure onset zone (SOZ). Depression of fast activity was observed immediately after the spikes, especially consistently in the discharges from the hippocampal SOZ. It corresponded to the slow wave part in case of spike-and-slow-wave complexes, but it was noted even in spikes without apparent slow waves. In one patient, a gradual increase of power above 200 Hz preceded spikes. Conclusions FDR-controlled t-spectra clearly detected the spike-related changes of HFOs that were unclear in standard power spectra. Significance We developed a promising tool to study the HFOs that may be closely linked to the pathophysiology of epileptogenesis. PMID:19394892

Encoding, Consolidation, and Retrieval of Contextual Memory: Differential Involvement of Dorsal CA3 and CA1 Hippocampal Subregions

ERIC Educational Resources Information Center

Daumas, Stephanie; Halley, Helene; Frances, Bernard; Lassalle, Jean-Michel

2005-01-01

Studies on human and animals shed light on the unique hippocampus contributions to relational memory. However, the particular role of each hippocampal subregion in memory processing is still not clear. Hippocampal computational models and theories have emphasized a unique function in memory for each hippocampal subregion, with the CA3 area acting…

Effects of estradiol on learned helplessness and associated remodeling of hippocampal spine synapses in female rats.

PubMed

Hajszan, Tibor; Szigeti-Buck, Klara; Sallam, Nermin L; Bober, Jeremy; Parducz, Arpad; Maclusky, Neil J; Leranth, Csaba; Duman, Ronald S

2010-01-15

Despite the fact that women are twice as likely to develop depression as men, our understanding of depression neurobiology in female subjects is limited. We have recently reported in male rats that development of helpless behavior is associated with a severe loss of hippocampal spine synapses, which is reversed by treatment with the antidepressant desipramine. Considering that estradiol has a hippocampal synaptogenic effect similar to those of antidepressants, the presence of estradiol during the female reproductive life might influence behavioral and synaptic responses to stress and depression. With electron microscopic stereology, we analyzed hippocampal spine synapses in association with helpless behavior in ovariectomized female rats (n = 70), under different conditions of estradiol exposure. Stress induced an acute and persistent loss of hippocampal spine synapses, whereas subchronic treatment with desipramine reversed the stress-induced synaptic loss. Estradiol supplementation given either before stress or before escape testing of nonstressed animals increased the number of hippocampal spine synapses. Correlation analysis demonstrated a statistically significant negative correlation between the severity of helpless behavior and hippocampal spine synapse numbers. These findings suggest that hippocampal spine synapse remodeling might be a critical factor underlying learned helplessness and, possibly, the neurobiology of depression.

Episodic autobiographical memory is associated with variation in the size of hippocampal subregions.

PubMed

Palombo, Daniela J; Bacopulos, Agnes; Amaral, Robert S C; Olsen, Rosanna K; Todd, Rebecca M; Anderson, Adam K; Levine, Brian

2018-02-01

Striking individual differences exist in the human capacity to recollect past events, yet, little is known about the neural correlates of such individual differences. Studies investigating hippocampal volume in relation to individual differences in laboratory measures of episodic memory in young adults suggest that whole hippocampal volume is unrelated (or even negatively associated) with episodic memory. However, anatomical and functional specialization across hippocampal subregions suggests that individual differences in episodic memory may be linked to particular hippocampal subregions, as opposed to whole hippocampal volume. Given that the DG/CA 2/3 circuitry is thought to be especially critical for supporting episodic memory in humans, we predicted that the volume of this region would be associated with individual variability in episodic memory. This prediction was supported using high-resolution MRI of the hippocampal subfields and measures of real-world (autobiographical) episodic memory. In addition to the association with DG/CA 2/3 , we further observed a relationship between episodic autobiographical memory and subiculum volume, whereas no association was observed with CA 1 or with whole hippocampal volume. These findings provide insight into the possible neural substrates that mediate individual differences in real-world episodic remembering in humans. © 2017 Wiley Periodicals, Inc.

EEG power as a biomarker to predict the outcome after cardiac arrest and cardiopulmonary resuscitation induced global ischemia.

PubMed

Weitzel, Lindsay-Rae; Sampath, Dayalan; Shimizu, Kaori; White, Andrew M; Herson, Paco S; Raol, Yogendra H

2016-11-15

Cardiac arrest (CA) is a major cause of mortality and survivors often develop neurologic deficits. The objective of this study was to determine the effect of CA and cardiopulmonary resuscitation (CPR) in mice on the EEG and neurologic outcomes, and identify biomarkers that can prognosticate poor outcomes. Video-EEG records were obtained at various periods following CA-CPR and examined manually to determine the presence of spikes and sharp-waves, and seizures. EEG power was calculated using a fast Fourier transform (FFT) algorithm. Fifty percent mice died within 72h following CA and successful CPR. Universal suppression of the background EEG was observed in all mice following CA-CPR, however, a more severe and sustained reduction in EEG power occurred in the mice that did not survive beyond 72h than those that survived until sacrificed. Spikes and sharp wave activity appeared in the cortex and hippocampus of all mice, but only one out of eight mice developed a purely electrographic seizure in the acute period after CA-CPR. Interestingly, none of the mice that died experienced any acute seizures. At 10days after the CA-CPR, 25% of the mice developed spontaneous convulsive and nonconvulsive seizures that remained restricted to the hippocampus. The frequency of nonconvulsive seizures was higher than that of convulsive seizures. A strong association between changes in EEG power and mortality following CA-CPR were observed in our study. Therefore, we suggest that the EEG power can be used to prognosticate mortality following CA-CPR induced global ischemia. Copyright © 2016 Elsevier Inc. All rights reserved.

Influence of parental care on offspring hippocampal volume in young adults varies as a function of overprotection

PubMed Central

Wang, Yinan; Song, Yiying; Li, Xueting; Zhang, Lin; Liu, Jia

2017-01-01

Parental care results in increased hippocampal volumes through adaptive stress responses in developing animals. However, human studies have not yet provided consistent findings analogous to the animal literature, possibly because parental care in humans is likely intermingled with parental overprotection, as suggested by the optimal parenting theory. Here, we tested the hypothesis that the effect of parental care on offspring hippocampal volume varies as a function of parental overprotection with a large cohort of young adult participants (N = 257). Consistent with some previous human studies, we found that parental care in childhood alone had little association with the hippocampal volume in adulthood. However, when parental overprotection was low, parental care was positively correlated with offspring hippocampal volume, whereas there was no association between parental care and offspring hippocampal volume when parental overprotection was high. Thus, an interaction exists between parental care and overprotection in human’s hippocampal development, which contributes to the elucidation of the complex relationship between brain structure and environmental factors. PMID:28401913

Influence of parental care on offspring hippocampal volume in young adults varies as a function of overprotection.

PubMed

Wang, Yinan; Song, Yiying; Li, Xueting; Zhang, Lin; Liu, Jia

2017-04-12

Parental care results in increased hippocampal volumes through adaptive stress responses in developing animals. However, human studies have not yet provided consistent findings analogous to the animal literature, possibly because parental care in humans is likely intermingled with parental overprotection, as suggested by the optimal parenting theory. Here, we tested the hypothesis that the effect of parental care on offspring hippocampal volume varies as a function of parental overprotection with a large cohort of young adult participants (N = 257). Consistent with some previous human studies, we found that parental care in childhood alone had little association with the hippocampal volume in adulthood. However, when parental overprotection was low, parental care was positively correlated with offspring hippocampal volume, whereas there was no association between parental care and offspring hippocampal volume when parental overprotection was high. Thus, an interaction exists between parental care and overprotection in human's hippocampal development, which contributes to the elucidation of the complex relationship between brain structure and environmental factors.

MR-based in vivo hippocampal volumetrics: 2. Findings in neuropsychiatric disorders.

PubMed

Geuze, E; Vermetten, E; Bremner, J D

2005-02-01

Magnetic resonance imaging (MRI) has opened a new window to the brain. Measuring hippocampal volume with MRI has provided important information about several neuropsychiatric disorders. We reviewed the literature and selected all English-language, human subject, data-driven papers on hippocampal volumetry, yielding a database of 423 records. Smaller hippocampal volumes have been reported in epilepsy, Alzheimer's disease, dementia, mild cognitive impairment, the aged, traumatic brain injury, cardiac arrest, Parkinson's disease, Huntington's disease, Cushing's disease, herpes simplex encephalitis, Turner's syndrome, Down's syndrome, survivors of low birth weight, schizophrenia, major depression, posttraumatic stress disorder, chronic alcoholism, borderline personality disorder, obsessive-compulsive disorder, and antisocial personality disorder. Significantly larger hippocampal volumes have been correlated with autism and children with fragile X syndrome. Preservation of hippocampal volume has been reported in congenital hyperplasia, children with fetal alcohol syndrome, anorexia nervosa, attention-deficit and hyperactivity disorder, bipolar disorder, and panic disorder. Possible mechanisms of hippocampal volume loss in neuropsychiatric disorders are discussed.

Increased hippocampal blood volume and normal blood flow in schizophrenia

PubMed Central

Talati, Pratik; Rane, Swati; Skinner, Jack; Gore, John; Heckers, Stephan

2015-01-01

Neuroimaging studies have provided compelling evidence for abnormal hippocampal activity in schizophrenia. Most studies made inferences about baseline hippocampal activity using a single hemodynamic parameter (e.g., blood volume or blood flow). Here we studied several hemodynamic measures in the same cohort to test the hypothesis of increased hippocampal activity in schizophrenia. We used dynamic susceptibility contrast- (DSC-) magnetic resonance imaging to assess blood volume, blood flow, and mean transit time in the hippocampus of 15 patients with chronic schizophrenia and 15 healthy controls. Left and right hippocampal measurements were combined for absolute measures of cerebral blood volume (CBV), blood flow (CBF), and mean transit time (MTT). We found significantly increased hippocampal CBV, but normal CBF and MTT, in schizophrenia. The uncoupling of CBV and CBF could be due to several factors, including antipsychotic medication, loss of cerebral perfusion pressure, or angiogenesis. Further studies need to incorporate several complementary imaging modalities to better characterize hippocampal dysfunction in schizophrenia. PMID:25896442

Momentum-Space Entanglement and Loschmidt Echo in Luttinger Liquids after a Quantum Quench.

PubMed

Dóra, Balázs; Lundgren, Rex; Selover, Mark; Pollmann, Frank

2016-07-01

Luttinger liquids (LLs) arise by coupling left- and right-moving particles through interactions in one dimension. This most natural partitioning of LLs is investigated by the momentum-space entanglement after a quantum quench using analytical and numerical methods. We show that the momentum-space entanglement spectrum of a LL possesses many universal features both in equilibrium and after a quantum quench. The largest entanglement eigenvalue is identical to the Loschmidt echo, i.e., the overlap of the disentangled and final wave functions of the system. The second largest eigenvalue is the overlap of the first excited state of the disentangled system with zero total momentum and the final wave function. The entanglement gap is universal both in equilibrium and after a quantum quench. The momentum-space entanglement entropy is always extensive and saturates fast to a time independent value after the quench, in sharp contrast to a spatial bipartitioning.

Blast waves from violent explosive activity at Yasur Volcano, Vanuatu

NASA Astrophysics Data System (ADS)

Marchetti, E.; Ripepe, M.; Delle Donne, D.; Genco, R.; Finizola, A.; Garaebiti, E.

2013-11-01

and seismic waveforms were collected during violent strombolian activity at Yasur Volcano (Vanuatu). Averaging ~3000 seismic events showed stable waveforms, evidencing a low-frequency (0.1-0.3 Hz) signal preceding ~5-6 s the explosion. Infrasonic waveforms were mostly asymmetric with a sharp compressive (5-106 Pa) onset, followed by a small long-lasting rarefaction phase. Regardless of the pressure amplitude, the ratio between the positive and negative phases was constant. These waveform characteristics closely resembled blast waves. Infrared imagery showed an apparent cold spherical front ~20 m thick, which moved between 342 and 405 m/s before the explosive hot gas/fragments cloud. We interpret this cold front as that produced by the vapor condensation induced by the passage of the shock front. We suggest that violent strombolian activity at Yasur was driven by supersonic dynamics with gas expanding at 1.1 Mach number inside the conduit.

Imaging the dynamics of free-electron Landau states

PubMed Central

Schattschneider, P.; Schachinger, Th.; Stöger-Pollach, M.; Löffler, S.; Steiger-Thirsfeld, A.; Bliokh, K. Y.; Nori, Franco

2014-01-01

Landau levels and states of electrons in a magnetic field are fundamental quantum entities underlying the quantum Hall and related effects in condensed matter physics. However, the real-space properties and observation of Landau wave functions remain elusive. Here we report the real-space observation of Landau states and the internal rotational dynamics of free electrons. States with different quantum numbers are produced using nanometre-sized electron vortex beams, with a radius chosen to match the waist of the Landau states, in a quasi-uniform magnetic field. Scanning the beams along the propagation direction, we reconstruct the rotational dynamics of the Landau wave functions with angular frequency ~100 GHz. We observe that Landau modes with different azimuthal quantum numbers belong to three classes, which are characterized by rotations with zero, Larmor and cyclotron frequencies, respectively. This is in sharp contrast to the uniform cyclotron rotation of classical electrons, and in perfect agreement with recent theoretical predictions. PMID:25105563

Nonlinear self-sustained structures and fronts in spatially developing wake flows

NASA Astrophysics Data System (ADS)

Pier, Benoît; Huerre, Patrick

2001-05-01

A family of slowly spatially developing wakes with variable pressure gradient is numerically demonstrated to sustain a synchronized finite-amplitude vortex street tuned at a well-defined frequency. This oscillating state is shown to be described by a steep global mode exhibiting a sharp Dee Langer-type front at the streamwise station of marginal absolute instability. The front acts as a wavemaker which sends out nonlinear travelling waves in the downstream direction, the global frequency being imposed by the real absolute frequency prevailing at the front station. The nonlinear travelling waves are determined to be governed by the local nonlinear dispersion relation resulting from a temporal evolution problem on a local wake profile considered as parallel. Although the vortex street is fully nonlinear, its frequency is dictated by a purely linear marginal absolute instability criterion applied to the local linear dispersion relation.

Identifying the effects of microsaccades in tripolar EEG signals.

PubMed

Bellisle, Rachel; Steele, Preston; Bartels, Rachel; Lei Ding; Sunderam, Sridhar; Besio, Walter

2017-07-01

Microsaccades are tiny, involuntary eye movements that occur during fixation, and they are necessary to human sight to maintain a sharp image and correct the effects of other fixational movements. Researchers have theorized and studied the effects of microsaccades on electroencephalography (EEG) signals to understand and eliminate the unwanted artifacts from EEG. The tripolar concentric ring electrode (TCRE) sensors are used to acquire TCRE EEG (tEEG). The tEEG detects extremely focal signals from directly below the TCRE sensor. We have noticed a slow wave frequency found in some tEEG recordings. Therefore, we conducted the current work to determine if there was a correlation between the slow wave in the tEEG and the microsaccades. This was done by analyzing the coherence of the frequency spectrums of both tEEG and eye movement in recordings where microsaccades are present. Our preliminary findings show that there is a correlation between the two.

Planar resonator and integrated oscillator using magnetostatic waves.

PubMed

Kinoshita, Y; Kubota, S; Takeda, S; Nakagoshi, A

1990-01-01

A simple planar resonator using a magnetostatic wave (MSW) excited by aluminum finger electrodes with two bonding pads was realized on YIG/GGG (yttrium-iron-garnet film on a gadolinium-gallium-garnet crystal) substrate with two reflection edges. The tunable MSW resonator chip (2 mmx5 mm) exhibited a sharp notch filter response, as deep as 20-35 dB, and a high loaded Q up to 2000, which was tunable over the microwave frequency range from 2 to 4 GHz. A small tunable oscillator (8 cm(3)) was experimentally demonstrated using the MSW planar resonator and a silicon bipolar transistor integrated on a ceramic microwave circuit substrate. Microwave oscillation with spectral purity, at the same level as that of YIG sphere technology, was observed at 3 GHz. The experimental results indicate the technical areas where improvement must be made to realize a practical oscillator configuration.

Observation of giant Goos-Hänchen and angular shifts at designed metasurfaces

PubMed Central

Yallapragada, Venkata Jayasurya; Ravishankar, Ajith P.; Mulay, Gajendra L.; Agarwal, Girish S.; Achanta, Venu Gopal

2016-01-01

Metasurfaces with sub-wavelength features are useful in modulating the phase, amplitude or polarization of electromagnetic fields. While several applications are reported for light manipulation and control, the sharp phase changes would be useful in enhancing the beam shifts at reflection from a metasurface. In designed periodic patterns on metal film, at surface plasmon resonance, we demonstrate Goos-Hanchen shift of the order of 70 times the incident wavelength and the angular shifts of several hundred microradians. We have designed the patterns using rigorous coupled wave analysis (RCWA) together with S-matrices and have used a complete vector theory to calculate the shifts as well as demonstrate a versatile experimental setup to directly measure the shifts. The giant shifts demonstrated could prove to be useful in enhancing the sensitivity of experiments ranging from atomic force microscopy to gravitational wave detection. PMID:26758471

Q^2 Dependence of the S_{11}(1535) Photocoupling and Evidence for a P-wave resonance in eta electroproduction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haluk Denizli; James Mueller; Steven Dytman

2007-07-01

New cross sections for the reactionmore » $$ep \\to e'\\eta p$$ are reported for total center of mass energy $W$=1.5--2.3 GeV and invariant squared momentum transfer $Q^2$=0.13--3.3 GeV$^2$. This large kinematic range allows extraction of new information about response functions, photocouplings, and $$\\eta N$$ coupling strengths of baryon resonances. A sharp structure is seen at $$W\\sim$$ 1.7 GeV. The shape of the differential cross section is indicative of the presence of a $P$-wave resonance that persists to high $Q^2$. Improved values are derived for the photon coupling amplitude for the $$S_{11}$$(1535) resonance. The new data greatly expands the $Q^2$ range covered and an interpretation of all data with a consistent parameterization is provided.« less

The Recent Atlantic Cold Anomaly: Causes, Consequences, and Related Phenomena

NASA Astrophysics Data System (ADS)

Josey, Simon A.; Hirschi, Joel J.-M.; Sinha, Bablu; Duchez, Aurélie; Grist, Jeremy P.; Marsh, Robert

2018-01-01

Cold ocean temperature anomalies have been observed in the mid- to high-latitude North Atlantic on interannual to centennial timescales. Most notably, a large region of persistently low surface temperatures accompanied by a sharp reduction in ocean heat content was evident in the subpolar gyre from the winter of 2013-2014 to 2016, and the presence of this feature at a time of pervasive warming elsewhere has stimulated considerable debate. Here, we review the role of air-sea interaction and ocean processes in generating this cold anomaly and place it in a longer-term context. We also discuss the potential impacts of surface temperature anomalies for the atmosphere, including the North Atlantic Oscillation and European heat waves; contrast the behavior of the Atlantic with the extreme warm surface event that occurred in the North Pacific over a similar timescale; and consider the possibility that these events represent a response to a change in atmospheric planetary wave forcing.

Canine hippocampal formation composited into three-dimensional structure using MPRAGE.

PubMed

Jung, Mi-Ae; Nahm, Sang-Soep; Lee, Min-Su; Lee, In-Hye; Lee, Ah-Ra; Jang, Dong-Pyo; Kim, Young-Bo; Cho, Zang-Hee; Eom, Ki-Dong

2010-07-01

This study was performed to anatomically illustrate the living canine hippocampal formation in three-dimensions (3D), and to evaluate its relationship to surrounding brain structures. Three normal beagle dogs were scanned on a MR scanner with inversion recovery segmented 3D gradient echo sequence (known as MP-RAGE: Magnetization Prepared Rapid Gradient Echo). The MRI data was manually segmented and reconstructed into a 3D model using the 3D slicer software tool. From the 3D model, the spatial relationships between hippocampal formation and surrounding structures were evaluated. With the increased spatial resolution and contrast of the MPRAGE, the canine hippocampal formation was easily depicted. The reconstructed 3D image allows easy understanding of the hippocampal contour and demonstrates the structural relationship of the hippocampal formation to surrounding structures in vivo.

A sharp interface method for compressible liquid–vapor flow with phase transition and surface tension

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fechter, Stefan, E-mail: stefan.fechter@iag.uni-stuttgart.de; Munz, Claus-Dieter, E-mail: munz@iag.uni-stuttgart.de; Rohde, Christian, E-mail: Christian.Rohde@mathematik.uni-stuttgart.de

The numerical approximation of non-isothermal liquid–vapor flow within the compressible regime is a difficult task because complex physical effects at the phase interfaces can govern the global flow behavior. We present a sharp interface approach which treats the interface as a shock-wave like discontinuity. Any mixing of fluid phases is avoided by using the flow solver in the bulk regions only, and a ghost-fluid approach close to the interface. The coupling states for the numerical solution in the bulk regions are determined by the solution of local two-phase Riemann problems across the interface. The Riemann solution accounts for the relevantmore » physics by enforcing appropriate jump conditions at the phase boundary. A wide variety of interface effects can be handled in a thermodynamically consistent way. This includes surface tension or mass/energy transfer by phase transition. Moreover, the local normal speed of the interface, which is needed to calculate the time evolution of the interface, is given by the Riemann solution. The interface tracking itself is based on a level-set method. The focus in this paper is the description of the two-phase Riemann solver and its usage within the sharp interface approach. One-dimensional problems are selected to validate the approach. Finally, the three-dimensional simulation of a wobbling droplet and a shock droplet interaction in two dimensions are shown. In both problems phase transition and surface tension determine the global bulk behavior.« less

Pre-Monsoon Drought and Heat Waves in India

NASA Image and Video Library

2015-09-12

In June 2015, news organizations around the world reported on a deadly heat wave in India that killed more than 2,300 people. Prior to the arrival of the summer monsoon in India, weather conditions had been extremely hot and dry. Such conditions can lead to economic and agricultural disaster, human suffering and loss of life. NASA satellite sensors are allowing scientists to characterize pre-monsoon droughts and heat waves and postulate their scientific cause. This figure shows the longitude-time variations, averaged between 21 and 22 degrees North, across the middle of the India subcontinent from mid-April to mid-June. Longitude from the Arabian Sea to the Bay of Bengal is represented on the horizontal axis; while the vertical axis shows the timeframe. Rainfall is shown on the left, soil moisture is in the center, and surface air temperature is on the right. For both years (2012 and 2015), the summer monsoon begins in June, with sharp rises in rainfall and soil moisture, and a sharp drop in air temperature. The hottest and driest weeks occurred just before the summer monsoon onsets. Similar dry and hot periods, varying from one to a few weeks, were observed in 2013 and 2014. Soil moisture as an indication of drought as measured by NASA's Aquarius mission was first available in 2012. Rainfall data are from NASA's Tropical Rainfall Measuring Mission (TRMM), and surface air temperature is from NASA's Atmospheric Infrared Sounder (AIRS) instrument on NASA's Aqua satellite. The TRMM and Aquarius missions ended in April 2015, before the drought and heat waves. Their data were replaced by those presently available from NASA's Soil Moisture Active Passive Mission (SMAP) and Global Precipitation Mission (GPM) to show the drought and heatwave in 2015. Scientists from NASA's Jet Propulsion Laboratory, Pasadena, California, have shown that during the summer monsoon season, moisture is transported into the India Subcontinent from the Arabian Sea and out to the Bay of Bengal. The difference between moisture input from the west and output to the east is deposited as rain over land. The pre-monsoon drought and heat waves coincide with the short period when moisture is advected out to the Bay of Bengal ahead of input from the Arabian Sea. The onset of southwest monsoon winds begins in the Bay of Bengal and sucks moisture out from the subcontinent earlier than the onset in the Arabian Sea. http://photojournal.jpl.nasa.gov/catalog/PIA19939

Elevation of Hippocampal Neurogenesis Induces a Temporally Graded Pattern of Forgetting of Contextual Fear Memories.

PubMed

Gao, Aijing; Xia, Frances; Guskjolen, Axel J; Ramsaran, Adam I; Santoro, Adam; Josselyn, Sheena A; Frankland, Paul W

2018-03-28

Throughout life neurons are continuously generated in the subgranular zone of the hippocampus. The subsequent integration of newly generated neurons alters patterns of dentate gyrus input and output connectivity, potentially rendering memories already stored in those circuits harder to access. Consistent with this prediction, we previously showed that increasing hippocampal neurogenesis after training induces forgetting of hippocampus-dependent memories, including contextual fear memory. However, the brain regions supporting contextual fear memories change with time, and this time-dependent memory reorganization might regulate the sensitivity of contextual fear memories to fluctuations in hippocampal neurogenesis. By virally expressing the inhibitory designer receptor exclusively activated by designer drugs, hM4Di, we first confirmed that chemogenetic inhibition of dorsal hippocampal neurons impairs retrieval of recent (day-old) but not remote (month-old) contextual fear memories in male mice. We then contrasted the effects of increasing hippocampal neurogenesis at recent versus remote time points after contextual fear conditioning in male and female mice. Increasing hippocampal neurogenesis immediately following training reduced conditioned freezing when mice were replaced in the context 1 month later. In contrast, when hippocampal neurogenesis was increased time points remote to training, conditioned freezing levels were unaltered when mice were subsequently tested. These temporally graded forgetting effects were observed using both environmental and genetic interventions to increase hippocampal neurogenesis. Our experiments identify memory age as a boundary condition for neurogenesis-mediated forgetting and suggest that, as contextual fear memories mature, they become less sensitive to changes in hippocampal neurogenesis levels because they no longer depend on the hippocampus for their expression. SIGNIFICANCE STATEMENT New neurons are generated in the hippocampus throughout life. As they integrate into the hippocampus, they remodel neural circuitry, potentially making information stored in those circuits harder to access. Consistent with this, increasing hippocampal neurogenesis after learning induces forgetting of the learnt information. The current study in mice asks whether these forgetting effects depend on the age of the memory. We found that post-training increases in hippocampal neurogenesis only impacted recently acquired, and not remotely acquired, hippocampal memories. These experiments identify memory age as a boundary condition for neurogenesis-mediated forgetting, and suggest remote memories are less sensitive to changes in hippocampal neurogenesis levels because they no longer depend critically on the hippocampus for their expression. Copyright © 2018 the authors 0270-6474/18/383190-09$15.00/0.

Thalamic stimulation to improve level of consciousness after seizures: evaluation of electrophysiology and behavior.

PubMed

Gummadavelli, Abhijeet; Motelow, Joshua E; Smith, Nicholas; Zhan, Qiong; Schiff, Nicholas D; Blumenfeld, Hal

2015-01-01

Understanding the neural mechanisms that support human consciousness is an important frontier in neuroscience and medicine. We previously developed a rodent model of temporal lobe seizures that recapitulates the human electroencephalography (EEG) signature of ictal and postictal neocortical slow waves associated with behavioral impairments in level of consciousness. The mechanism of slow-wave production in epilepsy may involve suppression of the subcortical arousal systems including the brainstem and intralaminar thalamic nuclei. We hypothesized that intralaminar thalamic stimulation may lead to electrophysiologic and functional rescue from postictal slow waves and behavioral arrest. We electrically stimulated the central lateral thalamic nucleus (a member of the intralaminar nuclei) under anesthesia and after electrically induced hippocampal seizures in anesthetized and in awake-behaving animal model preparations. We demonstrated a proof-of-principle restoration of electrophysiologic and behavioral measures of consciousness by stimulating the intralaminar thalamic nuclei after seizures. We measured decreased cortical slow waves and increased desynchronization and multiunit activity in the cortex with thalamic stimulation following seizures. Functionally, thalamic stimulation produced resumption of exploratory behaviors in the postictal state. Targeting of nodes in the neural circuitry of consciousness has important medical implications. Impaired consciousness with epilepsy has dangerous consequences including decreased school/work performance, social stigmatization, and impaired airway protection. These data suggest a novel therapeutic approach for restoring consciousness after seizures. If paired with responsive neurostimulation, this may allow rapid implementation to improve level of consciousness in patients with epilepsy. Wiley Periodicals, Inc. © 2014 International League Against Epilepsy.

Effects of voluntary running on plasma levels of neurotrophins, hippocampal cell proliferation and learning and memory in stressed rats.

PubMed

Yau, S-Y; Lau, B W-M; Zhang, E-D; Lee, J C-D; Li, A; Lee, T M C; Ching, Y-P; Xu, A-M; So, K-F

2012-10-11

Previous studies have shown that a 2-week treatment with 40 mg/kg corticosterone (CORT) in rats suppresses hippocampal neurogenesis and decreases hippocampal brain-derived neurotrophic factor (BDNF) levels and impairs spatial learning, all of which could be counteracted by voluntary wheel running. BDNF and insulin-like growth factor (IGF-1) have been suggested to mediate physical exercise-enhanced hippocampal neurogenesis and cognition. Here we examined whether such running-elicited benefits were accompanied by corresponding changes of peripheral BDNF and IGF-1 levels in a rat model of stress. We examined the effects of acute (5 days) and chronic (4 weeks) treatment with CORT and/or wheel running on (1) hippocampal cell proliferation, (2) spatial learning and memory and (3) plasma levels of BDNF and IGF-1. Acute CORT treatment improved spatial learning without altered cell proliferation compared to vehicle treatment. Acute CORT-treated non-runners showed an increased trend in plasma BDNF levels together with a significant increase in hippocampal BDNF levels. Acute running showed no effect on cognition, cell proliferation and peripheral BDNF and IGF-1 levels. Conversely, chronic CORT treatment in non-runners significantly impaired spatial learning and suppressed cell proliferation in association with a decreased trend in plasma BDNF level and a significant increase in hippocampal BDNF levels. Running counteracted cognitive deficit and restored hippocampal cell proliferation following chronic CORT treatment; but without corresponding changes in plasma BDNF and IGF-1 levels. The results suggest that the beneficial effects of acute stress on cognitive improvement may be mediated by BDNF-enhanced synaptic plasticity that is hippocampal cell proliferation-independent, whereas chronic stress may impair cognition by decreasing hippocampal cell proliferation and BDNF levels. Furthermore, the results indicate a trend in changes of plasma BDNF levels associated with a significant alteration in hippocampal levels, suggesting that treatment with running/CORT for 4 weeks may induce a change in central levels of hippocampal BDNF level, which may not lead to a significant change in peripheral levels. Copyright © 2012 IBRO. Published by Elsevier Ltd. All rights reserved.

Automated T2 relaxometry of the hippocampus for temporal lobe epilepsy.

PubMed

Winston, Gavin P; Vos, Sjoerd B; Burdett, Jane L; Cardoso, M Jorge; Ourselin, Sebastien; Duncan, John S

2017-09-01

Hippocampal sclerosis (HS), the most common cause of refractory temporal lobe epilepsy, is associated with hippocampal volume loss and increased T2 signal. These can be identified on quantitative imaging with hippocampal volumetry and T2 relaxometry. Although hippocampal segmentation for volumetry has been automated, T2 relaxometry currently involves subjective and time-consuming manual delineation of regions of interest. In this work, we develop and validate an automated technique for hippocampal T2 relaxometry. Fifty patients with unilateral or bilateral HS and 50 healthy controls underwent T 1 -weighted and dual-echo fast recovery fast spin echo scans. Hippocampi were automatically segmented using a multi-atlas-based segmentation algorithm (STEPS) and a template database. Voxelwise T2 maps were determined using a monoexponential fit. The hippocampal segmentations were registered to the T2 maps and eroded to reduce partial volume effect. Voxels with T2 >170 msec excluded to minimize cerebrospinal fluid (CSF) contamination. Manual determination of T2 values was performed twice in each subject. Twenty controls underwent repeat scans to assess interscan reproducibility. Hippocampal T2 values were reliably determined using the automated method. There was a significant ipsilateral increase in T2 values in HS (p < 0.001), and a smaller but significant contralateral increase. The combination of hippocampal volumes and T2 values separated the groups well. There was a strong correlation between automated and manual methods for hippocampal T2 measurement (0.917 left, 0.896 right, both p < 0.001). Interscan reproducibility was superior for automated compared to manual measurements. Automated hippocampal segmentation can be reliably extended to the determination of hippocampal T2 values, and a combination of hippocampal volumes and T2 values can separate subjects with HS from healthy controls. There is good agreement with manual measurements, and the technique is more reproducible on repeat scans than manual measurement. This protocol can be readily introduced into a clinical workflow for the assessment of patients with focal epilepsy. © 2017 The Authors. Epilepsia published by Wiley Periodicals, Inc. on behalf of International League Against Epilepsy.

Data-Informed Large-Eddy Simulation of Coastal Land-Air-Sea Interactions

NASA Astrophysics Data System (ADS)

Calderer, A.; Hao, X.; Fernando, H. J.; Sotiropoulos, F.; Shen, L.

2016-12-01

The study of atmospheric flows in coastal areas has not been fully addressed due to the complex processes emerging from the land-air-sea interactions, e.g., abrupt change in land topography, strong current shear, wave shoaling, and depth-limited wave breaking. The available computational tools that have been applied to study such littoral regions are mostly based on open-ocean assumptions, which most times do not lead to reliable solutions. The goal of the present study is to better understand some of these near-shore processes, employing the advanced computational tools, developed in our research group. Our computational framework combines a large-eddy simulation (LES) flow solver for atmospheric flows, a sharp-interface immersed boundary method that can deal with real complex topographies (Calderer et al., J. Comp. Physics 2014), and a phase-resolved, depth-dependent, wave model (Yang and Shen, J. Comp. Physics 2011). Using real measured data taken in the FRF station in Duck, North Carolina, we validate and demonstrate the predictive capabilities of the present computational framework, which are shown to be in overall good agreement with the measured data under different wind-wave scenarios. We also analyse the effects of some of the complex processes captured by our simulation tools.

Nonuniform Expansion of the Youngest Galactic Supernova Remnant G1.9+0.3

NASA Technical Reports Server (NTRS)

Borkowski, Kazimierz J.; Reynolds, Stephen P.; Green, David A.; Hwang, Una; Petre, Robert; Krishnamurthy, Kalyani; Willett, Rebecca

2014-01-01

We report measurements of the X-ray expansion of the youngest Galactic supernova remnant, G1.9+0.3, using Chandra observations in 2007, 2009, and 2011. The measured rates strongly deviate from uniform expansion, decreasing radially by about 60 along the X-ray bright SE-NW axis from 0.84 plus or minus 0.06% yr(exp -1) to 0.52% plus or minus 0.03 yr(exp -1). This corresponds to undecelerated ages of 120-190 yr, confirming the young age of G1.9+0.3 and implying a significant deceleration of the blast wave. The synchrotron-dominated X-ray emission brightens at a rate of 1.9% plus or minus 0.4% yr(exp -1). We identify bright outer and inner rims with the blast wave and reverse shock, respectively. Sharp density gradients in either the ejecta or ambient medium are required to produce the sudden deceleration of the reverse shock or the blast wave implied by the large spread in expansion ages. The blast wave could have been decelerated recently by an encounter with a modest density discontinuity in the ambient medium, such as may be found at a wind termination shock, requiring strong mass loss in the progenitor.

Broad ion energy distributions in helicon wave-coupled helium plasma

NASA Astrophysics Data System (ADS)

Woller, K. B.; Whyte, D. G.; Wright, G. M.

2017-05-01

Helium ion energy distributions were measured in helicon wave-coupled plasmas of the dynamics of ion implantation and sputtering of surface experiment using a retarding field energy analyzer. The shape of the energy distribution is a double-peak, characteristic of radiofrequency plasma potential modulation. The broad distribution is located within a radius of 0.8 cm, while the quartz tube of the plasma source has an inner radius of 2.2 cm. The ion energy distribution rapidly changes from a double-peak to a single peak in the radius range of 0.7-0.9 cm. The average ion energy is approximately uniform across the plasma column including the double-peak and single peak regions. The widths of the broad distribution, ΔE , in the wave-coupled mode are large compared to the time-averaged ion energy, ⟨E ⟩. On the axis (r = 0), ΔE / ⟨E ⟩ ≲ 3.4, and at a radius near the edge of the plasma column (r = 2.2 cm), ΔE / ⟨E ⟩ ˜ 1.2. The discharge parameter space is scanned to investigate the effects of the magnetic field, input power, and chamber fill pressure on the wave-coupled mode that exhibits the sharp radial variation in the ion energy distribution.

Simulations of viscous and compressible gas-gas flows using high-order finite difference schemes

NASA Astrophysics Data System (ADS)

Capuano, M.; Bogey, C.; Spelt, P. D. M.

2018-05-01

A computational method for the simulation of viscous and compressible gas-gas flows is presented. It consists in solving the Navier-Stokes equations associated with a convection equation governing the motion of the interface between two gases using high-order finite-difference schemes. A discontinuity-capturing methodology based on sensors and a spatial filter enables capturing shock waves and deformable interfaces. One-dimensional test cases are performed as validation and to justify choices in the numerical method. The results compare well with analytical solutions. Shock waves and interfaces are accurately propagated, and remain sharp. Subsequently, two-dimensional flows are considered including viscosity and thermal conductivity. In Richtmyer-Meshkov instability, generated on an air-SF6 interface, the influence of the mesh refinement on the instability shape is studied, and the temporal variations of the instability amplitude is compared with experimental data. Finally, for a plane shock wave propagating in air and impacting a cylindrical bubble filled with helium or R22, numerical Schlieren pictures obtained using different grid refinements are found to compare well with experimental shadow-photographs. The mass conservation is verified from the temporal variations of the mass of the bubble. The mean velocities of pressure waves and bubble interface are similar to those obtained experimentally.

Hippocampal sclerosis: volumetric evaluation of the substructures of the hippocampus by magnetic resonance imaging.

PubMed

Granados Sánchez, A M; Orejuela Zapata, J F

2018-05-25

The pathological classification of hippocampal sclerosis is based on the loss of neurons in the substructures of the hippocampus. This study aimed to evaluate these substructures in patients with hippocampal sclerosis by magnetic resonance imaging and to compare the usefulness of this morphological analysis compared to that of volumetric analysis of the entire hippocampus. We included 25 controls and 25 patients with hippocampal sclerosis whose diagnosis was extracted from the institutional epilepsy board. We used FreeSurfer to process the studies and obtain the volumetric data. We evaluated overall volume and volume by substructure: fimbria, subiculum, presubiculum, hippocampal sulcus, CA1, CA2-CA3, CA4, and dentate gyrus (DG). We considered p < 0.05 statistically significant. We observed statistically significant decreases in the volume of the hippocampus ipsilateral to the epileptogenic focus in 19 (76.0%) of the 25 cases. With the exception of the hippocampal sulcus, we observed a decrease in all ipsilateral hippocampal substructures in patients with right hippocampal sclerosis (CA1, p=0.0223; CA2-CA3, p=0.0066; CA4-GD, p=0.0066; fimbria, p=0.0046; presubiculum, p=0.0087; subiculum, p=0.0017) and in those with left hippocampal sclerosis (CA1, p<0.0001; CA2-CA3, p<0. 0001; CA4-GD, p<0. 0001; fimbria, p=0.0183; presubiculum, p<0. 0001; subiculum, p<0. 0001). In four patients with left hippocampal sclerosis, none of the substructures had statistically significant alterations, although a trend toward atrophy was observed, mainly in CA2-CA3 and CA4-GD. The findings suggest that it can be useful to assess the substructures of the hippocampus to improve the performance of diagnostic imaging in patients with hippocampal sclerosis. Copyright © 2018 SERAM. Publicado por Elsevier España, S.L.U. All rights reserved.

Effects of gintonin-enriched fraction on hippocampal cell proliferation in wild-type mice and an APPswe/PSEN-1 double Tg mouse model of Alzheimer's disease.

PubMed

Kim, Hyeon-Joong; Kim, Dae-Joong; Shin, Eun-Ju; Lee, Byung-Hwan; Choi, Sun-Hye; Hwang, Sung-Hee; Rhim, Hyewhon; Cho, Ik-Hyun; Kim, Hyoung-Chun; Nah, Seung-Yeol

2016-12-01

We previously showed that gintonin, an exogenous lysophosphatidic acid (LPA) receptor ligand, attenuated β-amyloid plaque formation in the cortex and hippocampus, and restored β-amyloid-induced memory dysfunction. Both endogenous LPA and LPA receptors play a key role in embryonic brain development. However, little is known about whether gintonin can induce hippocampal cell proliferation in adult wild-type mice and an APPswe/PSEN-1 double Tg mouse model of Alzheimer's disease (AD). In the present study, we examined the effects of gintonin on the proliferation of hippocampal neural progenitor cells (NPCs) in vitro and its effects on the hippocampal cell proliferation in wild-type mice and a transgenic AD mouse model. Gintonin treatment increased 5-bromo-2'-deoxyuridine (BrdU) incorporation in hippocampal NPCs in a dose- and time-dependent manner. Gintonin (0.3 μg/ml) increased the immunostaining of glial fibrillary acidic protein, NeuN, and LPA1 receptor in hippocampal NPCs. However, the gintonin-induced increase in BrdU incorporation and immunostaining of biomarkers was blocked by an LPA1/3 receptor antagonist and Ca 2+ chelator. Oral administration of the gintonin-enriched fraction (50 and 100 mg/kg) increased hippocampal BrdU incorporation and LPA1/3 receptor expression in adult wild-type and transgenic AD mice. The present study showed that gintonin could increase the number of hippocampal neurons in adult wild-type mice and a transgenic AD mouse model. Our results indicate that gintonin-mediated hippocampal cell proliferation contributes to the gintonin-mediated restorative effect against β-amyloid-induced hippocampal dysfunction. These results support the use of gintonin for the prevention or treatment of neurodegenerative diseases such as AD via promotion of hippocampal neurogenesis. Copyright © 2016 Elsevier Ltd. All rights reserved.

Posterior Cingulate Glucose Metabolism, Hippocampal Glucose Metabolism, and Hippocampal Volume in Cognitively Normal, Late-Middle-Aged Persons at 3 Levels of Genetic Risk for Alzheimer Disease

PubMed Central

Protas, Hillary D.; Chen, Kewei; Langbaum, Jessica B. S.; Fleisher, Adam S.; Alexander, Gene E.; Lee, Wendy; Bandy, Daniel; de Leon, Mony J.; Mosconi, Lisa; Buckley, Shannon; Truran-Sacrey, Diana; Schuff, Norbert; Weiner, Michael W.; Caselli, Richard J.; Reiman, Eric M.

2013-01-01

Objective To characterize and compare measurements of the posterior cingulate glucose metabolism, the hippocampal glucose metabolism, and hippocampal volume so as to distinguish cognitively normal, late-middle-aged persons with 2, 1, or 0 copies of the apolipoprotein E (APOE) ε4 allele, reflecting 3 levels of risk for late-onset Alzheimer disease. Design Cross-sectional comparison of measurements of cerebral glucose metabolism using 18F-fluorodeoxy-glucose positron emission tomography and measurements of brain volume using magnetic resonance imaging in cognitively normal ε4 homozygotes, ε4 heterozygotes, and noncarriers. Setting Academic medical center. Participants A total of 31 ε4 homozygotes, 42 ε4 heterozygotes, and 76 noncarriers, 49 to 67 years old, matched for sex, age, and educational level. Main Outcome Measures The measurements of posterior cingulate and hippocampal glucose metabolism were characterized using automated region-of-interest algorithms and normalized for whole-brain measurements. The hippocampal volume measurements were characterized using a semiautomated algorithm and normalized for total intracranial volume. Results Although there were no significant differences among the 3 groups of participants in their clinical ratings, neuropsychological test scores, hippocampal volumes (P=.60), or hippocampal glucose metabolism measurements (P = .12), there were significant group differences in their posterior cingulate glucose metabolism measurements (P=.001). The APOE ε4 gene dose was significantly associated with posterior cingulate glucose metabolism (r=0.29, P=.0003), and this association was significantly greater than those with hippocampal volume or hippocampal glucose metabolism (P<.05, determined by use of pairwise Fisher z tests). Conclusions Although our findings may depend in part on the analysis algorithms used, they suggest that a reduction in posterior cingulate glucose metabolism precedes a reduction in hippocampal volume or metabolism in cognitively normal persons at increased genetic risk for Alzheimer disease. PMID:23599929

Hippocampal volume in healthy controls given 3-day stress doses of hydrocortisone.

PubMed

Brown, E Sherwood; Jeon-Slaughter, Haekyung; Lu, Hanzhang; Jamadar, Rhoda; Issac, Sruthy; Shad, Mujeeb; Denniston, Daren; Tamminga, Carol; Nakamura, Alyson; Thomas, Binu P

2015-03-13

In animal models, corticosterone elevations are associated with hippocampal changes that can be prevented with phenytoin. In humans, Cushing's syndrome and long-term prescription corticosteroid use are associated with a reduction in the hippocampal volume. However, little is known about the effects of short-term corticosteroid administration on the hippocampus. The current report examines changes in the hippocampal volume during a brief hydrocortisone exposure and whether volumetric changes can be blocked by phenytoin. A randomized, double-blind, placebo-controlled, within-subject crossover study was conducted in healthy adults (n=17). Participants received hydrocortisone (160 mg/day)/placebo, phenytoin/placebo, both medications together, or placebo/placebo, with 21-day washouts between the conditions. Structural MRI scans and cortisol levels were obtained following each medication condition. No significant difference in the total brain volume was observed with hydrocortisone. However, hydrocortisone was associated with a significant 1.69% reduction in the total hippocampal volume compared with placebo. Phenytoin blocked the volume reduction associated with hydrocortisone. Reduction in hippocampal volume correlated with the change in cortisol levels (r=-0.58, P=0.03). To our knowledge, this is the first report of structural hippocampal changes with brief corticosteroid exposure. The correlation between the change in hippocampal volume and cortisol level suggests that the volume changes are related to cortisol elevation. Although the findings from this pilot study need replication, they suggest that the reductions in hippocampal volume occur even during brief exposure to corticosteroids, and that hippocampal changes can, as in animal models, be blocked by phenytoin. The results may have implications both for understanding the response of the hippocampus to stress as well as for patients receiving prescription corticosteroids.

Hippocampal Volume in Healthy Controls Given 3-Day Stress Doses of Hydrocortisone

PubMed Central

Brown, E Sherwood; Jeon-Slaughter, Haekyung; Lu, Hanzhang; Jamadar, Rhoda; Issac, Sruthy; Shad, Mujeeb; Denniston, Daren; Tamminga, Carol; Nakamura, Alyson; Thomas, Binu P

2015-01-01

In animal models, corticosterone elevations are associated with hippocampal changes that can be prevented with phenytoin. In humans, Cushing's syndrome and long-term prescription corticosteroid use are associated with a reduction in the hippocampal volume. However, little is known about the effects of short-term corticosteroid administration on the hippocampus. The current report examines changes in the hippocampal volume during a brief hydrocortisone exposure and whether volumetric changes can be blocked by phenytoin. A randomized, double-blind, placebo-controlled, within-subject crossover study was conducted in healthy adults (n=17). Participants received hydrocortisone (160 mg/day)/placebo, phenytoin/placebo, both medications together, or placebo/placebo, with 21-day washouts between the conditions. Structural MRI scans and cortisol levels were obtained following each medication condition. No significant difference in the total brain volume was observed with hydrocortisone. However, hydrocortisone was associated with a significant 1.69% reduction in the total hippocampal volume compared with placebo. Phenytoin blocked the volume reduction associated with hydrocortisone. Reduction in hippocampal volume correlated with the change in cortisol levels (r=−0.58, P=0.03). To our knowledge, this is the first report of structural hippocampal changes with brief corticosteroid exposure. The correlation between the change in hippocampal volume and cortisol level suggests that the volume changes are related to cortisol elevation. Although the findings from this pilot study need replication, they suggest that the reductions in hippocampal volume occur even during brief exposure to corticosteroids, and that hippocampal changes can, as in animal models, be blocked by phenytoin. The results may have implications both for understanding the response of the hippocampus to stress as well as for patients receiving prescription corticosteroids. PMID:25409592

Regulation of Hippocampal α1d Adrenergic Receptor mRNA by Corticosterone in Adrenalectomized Rats

PubMed Central

Day, Heidi E.W.; Kryskow, Elisa M.; Watson, Stanley J.; Akil, Huda; Campeau, Serge

2008-01-01

The hippocampal formation receives extensive noradrenergic projections and expresses high levels of mineralocorticoid (MR) and glucocorticoid (GR) receptors. Considerable evidence suggests that the noradrenergic system influences hippocampal corticosteroid receptors. However, there is relatively little data describing the influence of glucocorticoids on noradrenergic receptors in the hippocampal formation. α1d adrenergic receptor (ADR) mRNA is expressed at high levels in the hippocampal formation, within cells that express MR or GR. In order to determine whether expression of α1d ADR mRNA is influenced by circulating glucocorticoids, male rats underwent bilateral adrenalectomy (ADX) or sham surgery, and were killed after 1, 3, 7 or 14 days. Levels of α1d ADR mRNA were profoundly decreased in hippocampal subfields CA1, CA2 and CA3 and the medial and lateral blades of the dentate gyrus, as early as 1 day after ADX, as determined by in situ hybridization. The effect was specific for the hippocampal formation, with levels of α1d mRNA unaltered by ADX in the lateral amygdala, reticular thalamic nucleus, retrosplenial cortex or primary somatosensory cortex. Additional rats underwent ADX or sham surgery and received a corticosterone pellet (10 or 50 mg) or placebo for 7 days. Corticosterone replacement prevented the ADX-induced decrease in hippocampal α1d ADR mRNA, with the magnitude of effect depending on corticosterone dose and hippocampal subregion. These data indicate that α1d ADR mRNA expression in the hippocampal formation is highly sensitive to circulating levels of corticosterone, and provides further evidence for a close interaction between glucocorticoids and the noradrenergic system in the hippocampus. PMID:18534559

Trim9 Deletion Alters the Morphogenesis of Developing and Adult-Born Hippocampal Neurons and Impairs Spatial Learning and Memory

PubMed Central

Winkle, Cortney C.; Olsen, Reid H. J.; Kim, Hyojin; Moy, Sheryl S.

2016-01-01

During hippocampal development, newly born neurons migrate to appropriate destinations, extend axons, and ramify dendritic arbors to establish functional circuitry. These developmental stages are recapitulated in the dentate gyrus of the adult hippocampus, where neurons are continuously generated and subsequently incorporate into existing, local circuitry. Here we demonstrate that the E3 ubiquitin ligase TRIM9 regulates these developmental stages in embryonic and adult-born mouse hippocampal neurons in vitro and in vivo. Embryonic hippocampal and adult-born dentate granule neurons lacking Trim9 exhibit several morphological defects, including excessive dendritic arborization. Although gross anatomy of the hippocampus was not detectably altered by Trim9 deletion, a significant number of Trim9−/− adult-born dentate neurons localized inappropriately. These morphological and localization defects of hippocampal neurons in Trim9−/− mice were associated with extreme deficits in spatial learning and memory, suggesting that TRIM9-directed neuronal morphogenesis may be involved in hippocampal-dependent behaviors. SIGNIFICANCE STATEMENT Appropriate generation and incorporation of adult-born neurons in the dentate gyrus are critical for spatial learning and memory and other hippocampal functions. Here we identify the brain-enriched E3 ubiquitin ligase TRIM9 as a novel regulator of embryonic and adult hippocampal neuron shape acquisition and hippocampal-dependent behaviors. Genetic deletion of Trim9 elevated dendritic arborization of hippocampal neurons in vitro and in vivo. Adult-born dentate granule cells lacking Trim9 similarly exhibited excessive dendritic arborization and mislocalization of cell bodies in vivo. These cellular defects were associated with severe deficits in spatial learning and memory. PMID:27147649

Trim9 Deletion Alters the Morphogenesis of Developing and Adult-Born Hippocampal Neurons and Impairs Spatial Learning and Memory.

PubMed

Winkle, Cortney C; Olsen, Reid H J; Kim, Hyojin; Moy, Sheryl S; Song, Juan; Gupton, Stephanie L

2016-05-04

During hippocampal development, newly born neurons migrate to appropriate destinations, extend axons, and ramify dendritic arbors to establish functional circuitry. These developmental stages are recapitulated in the dentate gyrus of the adult hippocampus, where neurons are continuously generated and subsequently incorporate into existing, local circuitry. Here we demonstrate that the E3 ubiquitin ligase TRIM9 regulates these developmental stages in embryonic and adult-born mouse hippocampal neurons in vitro and in vivo Embryonic hippocampal and adult-born dentate granule neurons lacking Trim9 exhibit several morphological defects, including excessive dendritic arborization. Although gross anatomy of the hippocampus was not detectably altered by Trim9 deletion, a significant number of Trim9(-/-) adult-born dentate neurons localized inappropriately. These morphological and localization defects of hippocampal neurons in Trim9(-/-) mice were associated with extreme deficits in spatial learning and memory, suggesting that TRIM9-directed neuronal morphogenesis may be involved in hippocampal-dependent behaviors. Appropriate generation and incorporation of adult-born neurons in the dentate gyrus are critical for spatial learning and memory and other hippocampal functions. Here we identify the brain-enriched E3 ubiquitin ligase TRIM9 as a novel regulator of embryonic and adult hippocampal neuron shape acquisition and hippocampal-dependent behaviors. Genetic deletion of Trim9 elevated dendritic arborization of hippocampal neurons in vitro and in vivo Adult-born dentate granule cells lacking Trim9 similarly exhibited excessive dendritic arborization and mislocalization of cell bodies in vivo These cellular defects were associated with severe deficits in spatial learning and memory. Copyright © 2016 the authors 0270-6474/16/364940-19$15.00/0.

Differential regulation of the Rac1 GTPase-activating protein (GAP) BCR during oxygen/glucose deprivation in hippocampal and cortical neurons.

PubMed

Smith, Katharine R; Rajgor, Dipen; Hanley, Jonathan G

2017-12-08

Brain ischemia causes oxygen and glucose deprivation (OGD) in neurons, triggering a cascade of events leading to synaptic accumulation of glutamate. Excessive activation of glutamate receptors causes excitotoxicity and delayed cell death in vulnerable neurons. Following global cerebral ischemia, hippocampal CA1 pyramidal neurons are more vulnerable to injury than their cortical counterparts, but the mechanisms that underlie this difference are unclear. Signaling via Rho-family small GTPases, their upstream guanine nucleotide exchange factors, and GTPase-activating proteins (GAPs) is differentially dysregulated in response to OGD/ischemia in hippocampal and cortical neurons. Increased Rac1 activity caused by OGD/ischemia contributes to neuronal death in hippocampal neurons via diverse effects on NADPH oxidase activity and dendritic spine morphology. The Rac1 guanine nucleotide exchange factor Tiam1 mediates an OGD-induced increase in Rac1 activity in hippocampal neurons; however, the identity of an antagonistic GAP remains elusive. Here we show that the Rac1 GAP breakpoint cluster region (BCR) associates with NMDA receptors (NMDARs) along with Tiam1 and that this protein complex is more abundant in hippocampal compared with cortical neurons. Although total BCR is similar in the two neuronal types, BCR is more active in hippocampal compared with cortical neurons. OGD causes an NMDAR- and Ca 2+ -permeable AMPAR-dependent deactivation of BCR in hippocampal but not cortical neurons. BCR knockdown occludes OGD-induced Rac1 activation in hippocampal neurons. Furthermore, disrupting the Tiam1-NMDAR interaction with a fragment of Tiam1 blocks OGD-induced Tiam1 activation but has no effect on the deactivation of BCR. This work identifies BCR as a critical player in Rac1 regulation during OGD in hippocampal neurons. © 2017 by The American Society for Biochemistry and Molecular Biology, Inc.

Differential gene expression in dentate granule cells in mesial temporal lobe epilepsy with and without hippocampal sclerosis.

PubMed

Griffin, Nicole G; Wang, Yu; Hulette, Christine M; Halvorsen, Matt; Cronin, Kenneth D; Walley, Nicole M; Haglund, Michael M; Radtke, Rodney A; Skene, J H Pate; Sinha, Saurabh R; Heinzen, Erin L

2016-03-01

Hippocampal sclerosis is the most common neuropathologic finding in cases of medically intractable mesial temporal lobe epilepsy. In this study, we analyzed the gene expression profiles of dentate granule cells of patients with mesial temporal lobe epilepsy with and without hippocampal sclerosis to show that next-generation sequencing methods can produce interpretable genomic data from RNA collected from small homogenous cell populations, and to shed light on the transcriptional changes associated with hippocampal sclerosis. RNA was extracted, and complementary DNA (cDNA) was prepared and amplified from dentate granule cells that had been harvested by laser capture microdissection from surgically resected hippocampi from patients with mesial temporal lobe epilepsy with and without hippocampal sclerosis. Sequencing libraries were sequenced, and the resulting sequencing reads were aligned to the reference genome. Differential expression analysis was used to ascertain expression differences between patients with and without hippocampal sclerosis. Greater than 90% of the RNA-Seq reads aligned to the reference. There was high concordance between transcriptional profiles obtained for duplicate samples. Principal component analysis revealed that the presence or absence of hippocampal sclerosis was the main determinant of the variance within the data. Among the genes up-regulated in the hippocampal sclerosis samples, there was significant enrichment for genes involved in oxidative phosphorylation. By analyzing the gene expression profiles of dentate granule cells from surgically resected hippocampal specimens from patients with mesial temporal lobe epilepsy with and without hippocampal sclerosis, we have demonstrated the utility of next-generation sequencing methods for producing biologically relevant results from small populations of homogeneous cells, and have provided insight on the transcriptional changes associated with this pathology. Wiley Periodicals, Inc. © 2016 International League Against Epilepsy.

Hippocampal Morphology and Distinguishing Late-Onset From Early-Onset Elderly Depression

PubMed Central

Ballmaier, Martina; Narr, Katherine L.; Toga, Arthur W.; Elderkin-Thompson, Virginia; Thompson, Paul M.; Hamilton, Liberty; Haroon, Ebrahim; Pham, Daniel; Heinz, Andreas; Kumar, Anand

2010-01-01

Objective Despite evidence for hippocampal abnormalities in elderly depression, it is unknown whether these changes are regionally specific. This study used three-dimensional mapping techniques to identify regional hippocampal abnormalities in early- and late-onset depression. Neuropsychological correlates of hippocampal morphology were also investigated. Method With high-resolution magnetic resonance imaging, hippocampal morphology was compared among elderly patients with early- (N=24) and late-onset (N=22) depression and comparison subjects (N=34). Regional structural abnormalities were identified by comparing distances, measured from homologous hippocampal surface points to the central core of each individual’s hippocampal surface model, between groups. Results Hippocampal volumes differed between depressed patients and comparison subjects but not between patients with early- and late-onset depression. However, statistical mapping results showed that regional surface contractions were significantly pronounced in late-compared to early-onset depression in the anterior of the subiculum and lateral posterior of the CA1 subfield in the left hemisphere. Significant shape differences were observed bilaterally in anterior CA1–CA3 subfields and the subiculum in patients in relation to comparison subjects. These results were similar when each disease group was separately compared to comparison subjects. Hippocampal surface contractions significantly correlated with memory measures among late- but not early-onset depressed patients or comparison subjects. Conclusions More pronounced regional volume deficits and their associations with memory in late-onset depression may suggest that these patients are more likely to develop cognitive impairment over time than individuals with early-onset depression. Mapping regional hippocampal abnormalities and their cognitive correlates may help guide research in defining risk profiles and treatment strategies. PMID:17986679

Late-Onset Alzheimer's Disease Polygenic Risk Profile Score Predicts Hippocampal Function.

PubMed

Xiao, Ena; Chen, Qiang; Goldman, Aaron L; Tan, Hao Yang; Healy, Kaitlin; Zoltick, Brad; Das, Saumitra; Kolachana, Bhaskar; Callicott, Joseph H; Dickinson, Dwight; Berman, Karen F; Weinberger, Daniel R; Mattay, Venkata S

2017-11-01

We explored the cumulative effect of several late-onset Alzheimer's disease (LOAD) risk loci using a polygenic risk profile score (RPS) approach on measures of hippocampal function, cognition, and brain morphometry. In a sample of 231 healthy control subjects (19-55 years of age), we used an RPS to study the effect of several LOAD risk loci reported in a recent meta-analysis on hippocampal function (determined by its engagement with blood oxygen level-dependent functional magnetic resonance imaging during episodic memory) and several cognitive metrics. We also studied effects on brain morphometry in an overlapping sample of 280 subjects. There was almost no significant association of LOAD-RPS with cognitive or morphometric measures. However, there was a significant negative relationship between LOAD-RPS and hippocampal function (familywise error [small volume correction-hippocampal region of interest] p < .05). There were also similar associations for risk score based on APOE haplotype, and for a combined LOAD-RPS + APOE haplotype risk profile score (p < .05 familywise error [small volume correction-hippocampal region of interest]). Of the 29 individual single nucleotide polymorphisms used in calculating LOAD-RPS, variants in CLU, PICALM, BCL3, PVRL2, and RELB showed strong effects (p < .05 familywise error [small volume correction-hippocampal region of interest]) on hippocampal function, though none survived further correction for the number of single nucleotide polymorphisms tested. There is a cumulative deleterious effect of LOAD risk genes on hippocampal function even in healthy volunteers. The effect of LOAD-RPS on hippocampal function in the relative absence of any effect on cognitive and morphometric measures is consistent with the reported temporal characteristics of LOAD biomarkers with the earlier manifestation of synaptic dysfunction before morphometric and cognitive changes. Copyright © 2017 Society of Biological Psychiatry. All rights reserved.

Imbalance of incidental encoding across tasks: an explanation for non-memory-related hippocampal activations?

PubMed

Reas, Emilie T; Brewer, James B

2013-11-01

Functional neuroimaging studies have increasingly noted hippocampal activation associated with a variety of cognitive functions--such as decision making, attention, perception, incidental learning, prediction, and working memory--that have little apparent relation to declarative memory. Such findings might be difficult to reconcile with classical hippocampal lesion studies that show remarkable sparing of cognitive functions outside the realm of declarative memory. Even the oft-reported hippocampal activations during confident episodic retrieval are not entirely congruent with evidence that hippocampal lesions reliably impair encoding but inconsistently affect retrieval. Here we explore the conditions under which the hippocampus responds during episodic recall and recognition. Our findings suggest that anterior hippocampal activity may be related to the imbalance of incidental encoding across tasks and conditions rather than due to retrieval per se. Incidental encoding and hippocampal activity may be reduced during conditions where retrieval requires greater attentional engagement. During retrieval, anterior hippocampal activity decreases with increasing search duration and retrieval effort, and this deactivation corresponds with a coincident impaired encoding of the external environment (Israel, Seibert, Black, & Brewer, 2010; Reas & Brewer, 2013; Reas, Gimbel, Hales, & Brewer, 2011). In light of this emerging evidence, we discuss the proposal that some hippocampal activity observed during memory retrieval, or other non-memory conditions, may in fact be attributable to concomitant encoding activity that is regulated by the attentional demands of the principal task. PsycINFO Database Record (c) 2013 APA, all rights reserved.

Agmatine inhibits chronic morphine exposure-induced impairment of hippocampal neural progenitor proliferation in adult rats.

PubMed

Liu, Ying; Lu, Guan-Yi; Chen, Wen-Qiang; Li, Yun-Feng; Wu, Ning; Li, Jin

2018-01-05

Our previous studies have shown that agmatine inhibited opioid dependence, yet the neural mechanism remains unclear. Growing evidence showed that opioids decrease neurogenesis in the adult hippocampal subgranular zone by inhibiting neural progenitor proliferation. However, whether agmatine affects chronic opioid exposure-induced impairment to hippocampal neural progenitor cell proliferation remains unknown. In the present study, we investigated the role of agmatine in hippocampal neural progenitors in morphine dependence rats. We found that chronic administration of morphine for 12 days induced morphine dependence in rats. This treatment not only decreased the proliferation of hippocampal neural progenitors in the granule cell layer, but also decreased the levels of hippocampal cAMP, pCREB and BDNF. However, these alterations can be restored to normal levels by co-treatment of agmatine (10mg/kg, s.c.). In vitro treatment with agmatine (10µM) for two days significantly increased proliferation of the cultured hippocampal neural progenitors. Concurrent treatment of agmatine (10µM) with morphine (10 or 50µM) reversed the supression of morphine-induced neural progenitor proliferation. In conclusion, we found that agmatine abolished chronic morphine-induced decrease in proliferation of hippocampal progenitors in vivo and in vitro, which may be due to the increase in cAMP-CREB-BDNF signaling. The enhancement of agmatine to proliferation of hippocampal progenitors may be one of the important mechanisms involved in the inhibition of morphine dependence by agmatine. Copyright © 2017. Published by Elsevier B.V.

Neuropsychology, Autobiographical Memory, and Hippocampal Volume in “Younger” and “Older” Patients with Chronic Schizophrenia

PubMed Central

Herold, Christina Josefa; Lässer, Marc Montgomery; Schmid, Lena Anna; Seidl, Ulrich; Kong, Li; Fellhauer, Iven; Thomann, Philipp Arthur; Essig, Marco; Schröder, Johannes

2015-01-01

Despite a wide range of studies on neuropsychology in schizophrenia, autobiographical memory (AM) has been scarcely investigated in these patients. Hence, less is known about AM in older patients and hippocampal contribution to autobiographical memories of varying remoteness. Therefore, we investigated hippocampal volume and AM along with important neuropsychological domains in patients with chronic schizophrenia and the respective relationships between these parameters. We compared 25 older patients with chronic schizophrenia to 23 younger patients and an older healthy control group (N = 21) with respect to AM, additional neuropsychological parameters, and hippocampal volume. Personal episodic and semantic memory was investigated using a semi-structured interview. Additional neuropsychological parameters were assessed by using a battery of standard neuropsychological tests. Structural magnetic resonance imaging data were analyzed with an automated region-of-interest procedure. While hippocampal volume reduction and neuropsychological impairment were more pronounced in the older than in the younger patients, both groups showed equivalent reduced AM performance for recent personal episodes. In the patient group, significant correlations between left hippocampal volume and recent autobiographical episodes as well as personal semantic memories arose. Verbal memory and working memory were significantly correlated with right hippocampal volume; executive functions, however, were associated with bilateral hippocampal volumes. These findings underline the complexity of AM and its impairments in the course of schizophrenia in comparison to rather progressive neuropsychological deficits and address the importance of hippocampal contribution. PMID:25954208

Microinjection of procaine and electrolytic lesion in the ventral tegmental area suppresses hippocampal theta rhythm in urethane-anesthetized rats.

PubMed

Orzeł-Gryglewska, Jolanta; Jurkowlaniec, Edyta; Trojniar, Weronika

2006-01-30

The midbrain ventral tegmental area (VTA), a key structure of the mesocorticolimbic system is anatomically connected with the hippocampal formation. In addition mesocortical dopamine was found to influence hippocampus-related memory and hippocampal synaptic plasticity, both being linked to the theta rhythm. Therefore, the aim of the present study was to evaluate the possible role of the VTA in the regulation of the hippocampal theta activity. The study was performed on urethane-anesthetized male Wistar rats in which theta rhythm was evoked by tail pinch. It was found that unilateral, temporal inactivation of the VTA by means of direct procaine injection resulted in bilateral suppression of the hippocampal theta which manifested as a loss of synchronization of hippocampal EEG and respective reduction of the power and also the frequency of the 3-6 Hz theta band. Depression of the power of the 3-6 Hz component of the EEG signal was also seen in spontaneous hippocampal EEG after procaine. The permanent destruction of the VTA by means of unilateral electrocoagulation evoked a long-lasting, mainly ipsilateral depression of the power of the theta with some influence on its frequency. Simultaneously, there was a substantial increase of the power in higher frequency bands indicating decrease of a synchrony of the hippocampal EEG activity. On the basis of these results indicating impairment of synchronization of the hippocampal activity the VTA may be considered as another part of the brainstem theta synchroning system.

Simultaneous Changes in Sleep, qEEG, Physiology, Behaviour and Neurochemistry in Rats Exposed to Repeated Social Defeat Stress.

PubMed

Ahnaou, A; Drinkenburg, W H I M

2016-01-01

Depression is a heterogeneous disorder characterized by alterations at psychological, behavioural, physiological, neurophysiological, and neurochemical levels. Social stress is a prevalent stress in man, and the repeated social defeat stress model in rats has been proposed as being the rodent equivalent to loss of control, which in subordinate animals produces alterations that resemble several of the cardinal symptoms found in depressed patients. Here, rats followed a resident-intruder protocol for 4 consecutive days during which behavioural, physiological, and electroencephalographic (EEG) parameters were simultaneously monitored in subordinate rats. On day 5, prefrontal dopamine (DA) and hippocampal serotonin (5-HT) as well as corticosterone were measured in submissive rats that had visual, acoustic, and olfactory (but no physical) contact with a dominant, resident conspecific rat. Socially defeated rats demonstrated increases in ultrasonic vocalizations (20-25 KHz), freezing, submissive defensive behaviour, inactivity, and haemodynamic response, while decreases were found in repetitive grooming behaviour and body weight. Additionally, alterations in the sleep-wake architecture were associated with reduced active waking, enhanced light sleep, and increased frequency of transitions from light sleep to quiet wakefulness, indicating sleep instability. Moreover, the attenuation of EEG power over the frequency range of 4.2-30 Hz, associated with a sharp transient increase in delta oscillations, appeared to reflect increased brain activity and metabolism in subordinate animals. These EEG changes were synchronous with a marked increase in body temperature and a decrease in locomotor activity. Furthermore, psychosocial stress consistently increased 5-HT, DA, and corticosterone levels. The increased levels of cortical DA and hippocampal 5-HT during social threat may reflect a coping mechanism to promote alertness and psychological adaptation to provocative and threatening stimuli. These neurophysiological changes are hypothesized to be the consequence of dynamics in monoamine systems, which could be useful markers for disease progression in the aetiology of depression. © 2016 S. Karger AG, Basel.

Aging is accompanied by a subfield-specific reduction of serotonergic fibers in the tree shrew hippocampal formation.

PubMed

Keuker, Jeanine I H; Keijser, Jan N; Nyakas, Csaba; Luiten, Paul G M; Fuchs, Eberhard

2005-12-01

The hippocampal formation is a crucial structure for learning and memory, and serotonin together with other neurotransmitters is essential in these processes. Although the effects of aging on various neurotransmitter systems in the hippocampus have been extensively investigated, it is not entirely clear whether or how the hippocampal serotonergic innervation changes during aging. Rat studies, which have mostly focused on aging-related changes in the dentate gyrus, have implied a loss of hippocampal serotonergic fibers. We used the tree shrew (Tupaia belangeri), an intermediate between insectivores and primates, as a model of aging. We applied immunocytochemistry with an antibody against serotonin to assess serotonergic fiber densities in the various hippocampal subfields of adult (0.9-1.3 years) and old (5-7 years) tree shrews. Our results have revealed a reduction of serotonergic fiber densities in the stratum radiatum of CA1 and CA3, and in the stratum oriens of CA3. A partial depletion of serotonin in the hippocampal formation, as can be expected from our current observations, will probably have an impact on the functioning of hippocampal principal neurons. Our findings also indicate that the rat and the tree shrew hippocampal serotonergic innervation show some variations that seem to be differentially affected during aging.

Changes in fitness are associated with changes in hippocampal microstructure and hippocampal volume among older adults.

PubMed

Kleemeyer, Maike Margarethe; Kühn, Simone; Prindle, John; Bodammer, Nils Christian; Brechtel, Lars; Garthe, Alexander; Kempermann, Gerd; Schaefer, Sabine; Lindenberger, Ulman

2016-05-01

This study investigates the effects of fitness changes on hippocampal microstructure and hippocampal volume. Fifty-two healthy participants aged 59-74years with a sedentary lifestyle were randomly assigned to either of two levels of exercise intensity. Training lasted for six months. Physical fitness, hippocampal volumes, and hippocampal microstructure were measured before and after training. Hippocampal microstructure was assessed by mean diffusivity, which inversely reflects tissue density; hence, mean diffusivity is lower for more densely packed tissue. Mean changes in fitness did not differ reliably across intensity levels of training, so data were collapsed across groups. Multivariate modeling of pretest-posttest differences using structural equation modeling (SEM) revealed that individual differences in latent change were reliable for all three constructs. More positive changes in fitness were associated with more positive changes in tissue density (i.e., more negative changes in mean diffusivity), and more positive changes in tissue density were associated with more positive changes in volume. We conclude that fitness-related changes in hippocampal volume may be brought about by changes in tissue density. The relative contributions of angiogenesis, gliogenesis, and/or neurogenesis to changes in tissue density remain to be identified. Copyright © 2015 Elsevier Inc. All rights reserved.

A Subset of Dogs with Presumptive Idiopathic Epilepsy Show Hippocampal Asymmetry: A Volumetric Comparison with Non-Epileptic Dogs Using MRI

PubMed Central

Estey, Chelsie M.; Dewey, Curtis W.; Rishniw, Mark; Lin, David M.; Bouma, Jennifer; Sackman, Joseph; Burkland, Erica

2017-01-01

MRI-acquired volumetric measurements from 100 dogs with presumptive idiopathic epilepsy (IE) and 41 non-epileptic (non-IE) dogs were used to determine if hippocampal asymmetry exists in the IE as compared to the non-IE dogs. MRI databases from three institutions were searched for dogs that underwent MRI of the brain and were determined to have IE and those that were considered non-IE dogs. Volumes of the right and left hippocampi were measured using Mimics® software. Median hippocampal volumes of IE and non-IE dogs were 0.47 and 0.53 cm3, respectively. There was no significant difference in overall hippocampal volume between IE and non-IE dogs; however, IE dogs had greater hippocampal asymmetry than non-IE dogs (P < 0.012). A threshold value of 1.16 from the hippocampal ratio had an 85% specificity for identifying IE-associated asymmetry. Thirty five percent of IE dogs had a hippocampal ratio >1.16. Asymmetry was not associated with any particular hemisphere (P = 0.67). Our study indicates that hippocampal asymmetry occurs in a subset of dogs with presumptive idiopathic/genetic epilepsy, suggesting a structural etiology to some cases of IE. PMID:29167797

Cortisol, learning, memory, and attention in relation to smaller hippocampal volume in police officers with posttraumatic stress disorder.

PubMed

Lindauer, Ramón J L; Olff, Miranda; van Meijel, Els P M; Carlier, Ingrid V E; Gersons, Berthold P R

2006-01-15

A proposed explanation for memory impairments in posttraumatic stress disorder (PTSD) is stress-induced hippocampal damage due to elevated cortisol levels. We have previously reported smaller hippocampi in police officers with PTSD. In this study, we examined changes in and associations between cortisol, learning, memory, attention, and hippocampal volume in PTSD. In a case-matched control study, 12 police officers with PTSD and 12 traumatized police officers without lifetime PTSD were examined with magnetic resonance imaging (for hippocampal volume), salivary cortisol tests, and neurocognitive assessments. Significantly smaller hippocampi and higher early morning salivary cortisol levels were found in PTSD. Subjects with PTSD performed worse on a delayed visual memory recall task at trend level, and made more perseverations and intrusions on a verbal memory task. Negative correlations were found between PTSD symptom severity and immediate recall function, and between re-experiencing symptoms and left hippocampal volume. A positive correlation was found between salivary cortisol level in early morning and right hippocampal volume; however, hippocampal volume did not correlate with memory. Smaller hippocampi, higher cortisol levels, and memory impairments were associated with PTSD but were not directly correlated to one another. Memory impairments in PTSD do not seem to be a direct consequence of hippocampal size.

Effects of Estradiol on Learned Helplessness and Associated Remodeling of Hippocampal Spine Synapses in Female Rats

PubMed Central

Hajszan, Tibor; Szigeti-Buck, Klara; Sallam, Nermin L; Bober, Jeremy; Parducz, Arpad; MacLusky, Neil J; Leranth, Csaba; Duman, Ronald S

2009-01-01

Background Despite the fact that women are twice as likely to develop depression as men, our understanding of depression neurobiology in females is limited. We have recently reported in male rats that development of helpless behavior is associated with a severe loss of hippocampal spine synapses, which is reversed by treatment with the antidepressant, desipramine. Considering the fact that estradiol has a hippocampal synaptogenic effect similar to those of antidepressants, the presence of estradiol during the female reproductive life may influence behavioral and synaptic responses to stress and depression. Methods Using electron microscopic stereology, we analyzed hippocampal spine synapses in association with helpless behavior in ovariectomized female rats (n=70), under different conditions of estradiol exposure. Results Stress induced an acute and persistent loss of hippocampal spine synapses, while subchronic treatment with desipramine reversed the stress-induced synaptic loss. Estradiol supplementation given either prior to stress or prior to escape testing of nonstressed animals both increased the number of hippocampal spine synapses. Correlation analysis demonstrated a statistically significant negative correlation between the severity of helpless behavior and hippocampal spine synapse numbers. Conclusions These findings suggest that hippocampal spine synapse remodeling may be a critical factor underlying learned helplessness and, possibly, the neurobiology of depression. PMID:19811775

Verbal and non-verbal memory and hippocampal volumes in a memory clinic population.

PubMed

Bonner-Jackson, Aaron; Mahmoud, Shamseldeen; Miller, Justin; Banks, Sarah J

2015-10-15

Better characterization of the relationship between episodic memory and hippocampal volumes is crucial in early detection of neurodegenerative disease. We examined these relationships in a memory clinic population. Participants (n = 226) underwent structural magnetic resonance imaging and tests of verbal (Hopkins Verbal Learning Test-Revised, HVLT-R) and non-verbal (Brief Visuospatial Memory Test-Revised, BVMT-R) memory. Correlational analyses were performed, and analyses on clinical subgroups (i.e., amnestic Mild Cognitive Impairment, non-amnestic Mild Cognitive Impairment, probable Alzheimer's disease, intact memory) were conducted. Positive associations were identified between bilateral hippocampal volumes and both memory measures, and BVMT-R learning slope was more strongly positively associated with hippocampal volumes than HVLT-R learning slope. Amnestic Mild Cognitive Impairment (aMCI) participants showed specific positive associations between BVMT-R performance and hippocampal volumes bilaterally. Additionally, analyses of the aMCI group showed trend-level evidence of material-specific lateralization, such that retention of verbal information was positively associated with left hippocampal volume, whereas learning curve and retention of non-verbal information was positively associated with right hippocampal volume. Findings support the link between episodic memory and hippocampal volumes in a memory clinic population. Non-verbal memory measures also may have higher diagnostic value, particularly in individuals at elevated risk for Alzheimer's disease.

2015 Volcanic Tsunami Earthquake near Torishima Island: Array analysis of ocean bottom pressure gauge records

NASA Astrophysics Data System (ADS)

Fukao, Y.; Sugioka, H.; Ito, A.; Shiobara, H.; Sandanbata, O.; Watada, S.; Satake, K.

2016-12-01

An array of ocean bottom pressure gauges was deployed off east of Aogashima island of the Izu-Bonin arc from May 2014 to May 2015. The array consists of 10 ocean bottom pressure gauges using ParoScientific quartz resonators which can measure absolute water pressure at 7000m depth with nano-resolution. The array configures equilateral triangles with minimum and maximum lengths of 10 and 30km. This array recorded seismic and tsunami waves from the CLVD-type earthquake (M5.7) of May 02, 2015, that occurred near Torishima Island 100 km distant from the array. Comparison with records of ordinary thrust earthquakes with similar magnitudes at similar distances indicates that this event generated anomalously large tsunamis relative to seismic waves. We made an array analysis for the phase speed, propagating azimuth and travel time of tsunami wave in a frequency range 1-10 mHz, where the dispersion effect is significant. The results show excellent agreements with the frequency-dependent ray-tracing calculations. The tsunami trace apparently starts with positive onset (pressure increase) and reaches a maximum amplitude of about 200Pa (≈2cm in tsunami height). A closer inspection, however, shows a preceding negative small pulse (Fig. 1), suggesting that the seafloor deformation at the tsunami source consists of a central large uplift and a peripheral small depression. This mode of deformation is qualitatively consistent with a finite CLVD source uniformly shortened laterally and uniformly stretched vertically without volume change. The detection of weak initial motions is indebted to the array deployment of sensitive pressure gauges far away from coastal regions. The bandpass-filtered waveform is drastically different between the lower and higher frequency ranges. The waveform is single-peaked in the lower frequency range (<5 mHz) but is ringing in the higher frequency range (>5 mHz), corresponding to the tsunami spectrum that consists of the broad primary peak around 3.5 mHz and the sharp double peaks at around 6.5 and 9 mHz. We interpret the broad primary peak as due to the tsunami source associated with seafloor deformation and the sharp double peaks as due to wave resonance (seiche) inside the Smith Caldera.

Time trend in the impact of heat waves on daily mortality in Spain for a period of over thirty years (1983-2013).

PubMed

Díaz, J; Carmona, R; Mirón, I J; Luna, M Y; Linares, C

2018-07-01

Many of the studies that analyze the future impact of climate change on mortality assume that the temperature that constitutes a heat wave will not change over time. This is unlikely, however, given the process of adapting to heat changes, prevention plans, and improvements in social and health infrastructure. The objective of this study is to analyze whether, during the 1983-2013 period, there has been a temporal change in the maximum daily temperatures that constitute a heat wave (T threshold ) in Spain, and to investigate whether there has been variation in the attributable risk (AR) associated with mortality due to high temperatures in this period. This study uses daily mortality data for natural causes except accidents CIEX: A00-R99 in municipalities of over 10,000 inhabitants in 10 Spanish provinces and maximum temperature data from observatories located in province capitals. The time series is divided into three periods: 1983-1992, 1993-2003 and 2004-2013. For each period and each province, the value of T threshold was calculated using scatter-plot diagram of the daily mortality pre-whitened series. For each period and each province capitals, it has been calculated the number of heat waves and quantifying the impact on mortality through generalized linear model (GLM) methodology with the Poisson regression link. These models permits obtained the relative risks (RR) and attributable risks (AR). Via a meta-analysis, using the Global RR and AR were calculated the heat impact for the total of the 10 provinces. The results show that in the first two periods RR remained constant RR: 1.14 (CI95%: 1.09 1.19) and RR: 1.14 (CI95%: 1.10 1.18), while the third period shows a sharp decrease with respect to the prior two periods RR: 1.01 (CI95%: 1.00 1.01); the difference is statistically significant. In Spain there has been a sharp decrease in mortality attributable to heat over the past 10 years. The observed variation in RR puts into question the results of numerous studies that analyze the future impact of heat on mortality in different temporal scenarios and show it to be constant over time. Copyright © 2018 Elsevier Ltd. All rights reserved.

Selenomethionine promoted hippocampal neurogenesis via the PI3K-Akt-GSK3β-Wnt pathway in a mouse model of Alzheimer's disease

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zheng, Rui; Zhang, Zhong-Hao; Chen, Chen

The maintenance of neural system integrity and function is the ultimate goal for the treatment of neurodegenerative disease such as Alzheimer's disease (AD). Neurogenesis plays an integral role in the maintenance of neural and cognitive functions, and its dysfunction is regarded as a major cause of cognitive impairment in AD. Moreover, the induction of neurogenesis by targeting endogenous neural stem cells (NSCs) is considered as one of the most promising treatment strategies. Our previous studies demonstrated that selenomethionine (Se-Met) was able to reduce β-amyloid peptide (Aβ) deposition, decrease Tau protein hyperphosphorylation and markedly improve cognitive functions in triple transgenic (3xTg)more » AD mice. In this study, we reported that the therapeutic effect of Se-Met on AD could also be due to neurogenesis modulation. By using the cultured hippocampal NSCs from 3xTg AD mice, we discovered that Se-Met (1–10 μM) with low concentration could promote NSC proliferation, while the one with a high concentration (50,100 μM) inhibiting proliferation. In subsequent studies, we also found that Se-Met activated the signaling pathway of PI3K/Akt, and thereby inhibited the GSK3β activity, which would further activated the β-catenin/Cyclin-D signaling pathway and promote NSC proliferation. Besides, after the induction of Se-Met, the number of neurons differentiated from NSCs significantly increased, and the number of astrocytes decreased. After a 90-day treatment with Se-Met (6 μg/mL), the number of hippocampal neurons in 4-month-old AD mice increased significantly, while the one of astrocyte saw a sharp drop. Thus, Se-Met treatment promoted NSCs differentiation into neurons, and subsequently repaired damaged neural systems in AD mice. Being consistent with our in vitro studies, Se-Met acts through the PI3K-Akt- GSK3β-Wnt signaling pathway in vivo. This study provides an unparalleled evidence that selenium (Se) compounds are, to some extent, effective in promoting neurogenesis, and therefore we propose a novel mechanism for Se-Met treatment in AD. - Highlights: • It's the first time to evidence that a selenium (Se) compounds is effective in promoting neurogenesis. • Selenomethionine promotes neural stem cell proliferation and differentiation into neurons. • Selenomethionine activates the PI3K-Akt-GSK3β signaling pathway. • Selenomethionine activates the Wnt signaling pathway.« less

Age-dependent axonal expression of potassium channel proteins during development in mouse hippocampus.

PubMed

Prüss, Harald; Grosse, Gisela; Brunk, Irene; Veh, Rüdiger W; Ahnert-Hilger, Gudrun

2010-03-01

The development of the hippocampal network requires neuronal activity, which is shaped by the differential expression and sorting of a variety of potassium channels. Parallel to their maturation, hippocampal neurons undergo a distinct development of their ion channel profile. The age-dependent dimension of ion channel occurrence is of utmost importance as it is interdependently linked to network formation. However, data regarding the exact temporal expression of potassium channels during postnatal hippocampal development are scarce. We therefore studied the expression of several voltage-gated potassium channel proteins during hippocampal development in vivo and in primary cultures, focusing on channels that were sorted to the axonal compartment. The Kv1.1, Kv1.2, Kv1.4, and Kv3.4 proteins showed a considerable temporal variation of axonal localization among neuronal subpopulations. It is possible, therefore, that hippocampal neurons possess cell type-specific mechanisms for channel compartmentalization. Thus, age-dependent axonal sorting of the potassium channel proteins offers a new approach to functionally distinguish classes of hippocampal neurons and may extend our understanding of hippocampal circuitry and memory processing.

Hippocampal Structure Predicts Statistical Learning and Associative Inference Abilities during Development.

PubMed

Schlichting, Margaret L; Guarino, Katharine F; Schapiro, Anna C; Turk-Browne, Nicholas B; Preston, Alison R

2017-01-01

Despite the importance of learning and remembering across the lifespan, little is known about how the episodic memory system develops to support the extraction of associative structure from the environment. Here, we relate individual differences in volumes along the hippocampal long axis to performance on statistical learning and associative inference tasks-both of which require encoding associations that span multiple episodes-in a developmental sample ranging from ages 6 to 30 years. Relating age to volume, we found dissociable patterns across the hippocampal long axis, with opposite nonlinear volume changes in the head and body. These structural differences were paralleled by performance gains across the age range on both tasks, suggesting improvements in the cross-episode binding ability from childhood to adulthood. Controlling for age, we also found that smaller hippocampal heads were associated with superior behavioral performance on both tasks, consistent with this region's hypothesized role in forming generalized codes spanning events. Collectively, these results highlight the importance of examining hippocampal development as a function of position along the hippocampal axis and suggest that the hippocampal head is particularly important in encoding associative structure across development.

Comprehensive numerical methodology for direct numerical simulations of compressible Rayleigh-Taylor instability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reckinger, Scott James; Livescu, Daniel; Vasilyev, Oleg V.

A comprehensive numerical methodology has been developed that handles the challenges introduced by considering the compressive nature of Rayleigh-Taylor instability (RTI) systems, which include sharp interfacial density gradients on strongly stratified background states, acoustic wave generation and removal at computational boundaries, and stratification-dependent vorticity production. The computational framework is used to simulate two-dimensional single-mode RTI to extreme late-times for a wide range of flow compressibility and variable density effects. The results show that flow compressibility acts to reduce the growth of RTI for low Atwood numbers, as predicted from linear stability analysis.

Optical calculation of correlation filters for a robotic vision system

NASA Technical Reports Server (NTRS)

Knopp, Jerome

1989-01-01

A method is presented for designing optical correlation filters based on measuring three intensity patterns: the Fourier transform of a filter object, a reference wave and the interference pattern produced by the sum of the object transform and the reference. The method can produce a filter that is well matched to both the object, its transforming optical system and the spatial light modulator used in the correlator input plane. A computer simulation was presented to demonstrate the approach for the special case of a conventional binary phase-only filter. The simulation produced a workable filter with a sharp correlation peak.

Wide band cryogenic ultra-high vacuum microwave absorber

DOEpatents

Campisi, I.E.

1992-05-12

An absorber waveguide assembly for absorbing higher order modes of microwave energy under cryogenic ultra-high vacuum conditions, that absorbs wide-band multi-mode energy. The absorber is of a special triangular shape, made from flat tiles of silicon carbide and aluminum nitride. The leading sharp end of the absorber is located in a corner of the waveguide and tapers to a larger cross-sectional area whose center is located approximately in the center of the wave guide. The absorber is relatively short, being of less height than the maximum width of the waveguide. 11 figs.

Coexistence of collapse and stable spatiotemporal solitons in multimode fibers

NASA Astrophysics Data System (ADS)

Shtyrina, Olga V.; Fedoruk, Mikhail P.; Kivshar, Yuri S.; Turitsyn, Sergei K.

2018-01-01

We analyze spatiotemporal solitons in multimode optical fibers and demonstrate the existence of stable solitons, in a sharp contrast to earlier predictions of collapse of multidimensional solitons in three-dimensional media. We discuss the coexistence of blow-up solutions and collapse stabilization by a low-dimensional external potential in graded-index media, and also predict the existence of stable higher-order nonlinear waves such as dipole-mode spatiotemporal solitons. To support the main conclusions of our numerical studies we employ a variational approach and derive analytically the stability criterion for input powers for the collapse stabilization.

Beam-plasma instability in inhomogeneous magnetic field and second order cyclotron resonance effects

NASA Astrophysics Data System (ADS)

Trakhtengerts, V. Y.; Hobara, Y.; Demekhov, A. G.; Hayakawa, M.

1999-03-01

A new analytical approach to cyclotron instability of electron beams with sharp gradients in velocity space (step-like distribution function) is developed taking into account magnetic field inhomogeneity and nonstationary behavior of the electron beam velocity. Under these conditions, the conventional hydrodynamic instability of such beams is drastically modified and second order resonance effects become important. It is shown that the optimal conditions for the instability occur for nonstationary quasimonochromatic wavelets whose frequency changes in time. The theory developed permits one to estimate the wave amplification and spatio-temporal characteristics of these wavelets.

Borman effect in resonant diffraction of X-rays

NASA Astrophysics Data System (ADS)

Oreshko, A. P.

2013-08-01

A dynamic theory of resonant diffraction (occurring when the energy of incident radiation is close to the energy of the absorption edge of an element in the composition of a given substance) of synchronous X-rays is developed in the two-wave approximation in the coplanar Laue geometry for large grazing angles in perfect crystals. A sharp decrease in the absorption coefficient in the substance with simultaneously satisfied diffraction conditions (Borman effect) is demonstrated, and the theoretical and first experimental results are compared. The calculations reveal the possibility of applying this approach in analyzing the quadrupole-quadrupole contribution to the absorption coefficient.

Smart Gold Nanobowls (Nano-Crescent Moon) with Sub-10 nm Circular Edge for Local Electromagnetic Field Enhancement Effect, Spatial, and NIR Temporal/Thermal Modulations for Molecular and Cellular Dynamic Imaging

DTIC Science & Technology

2006-01-31

nanoring [10], the Au nanocrescent has a higher local field enhancement factor in the near infrared wavelength region due to the simultaneous...incorporation of SERS hot spots including sharp nanotip and nanoring geometries and thus the strong hybrid resonance modes from nanocavity resonance mode and tip...Raman, "A change of wave-length in light scattering," Nature 121, 619-619 (1928). 22. Y. Lu, G. L. Liu, and L. P. Lee, "High-density silver nanoparticle

Traces of warping subsided tectonic blocks on Miranda, Enceladus, Titan

NASA Astrophysics Data System (ADS)

Kochemasov, G.

2007-08-01

Icy satellites of the outer Solar system have very large range of sizes - from kilometers to thousands of kilometers. Bodies less than 400-500 km across have normally irregular shapes , often presenting simple Plato's polyhedrons woven by standing inertiagravity waves (see an accompanying abstract of Kochemasov). Larger bodies with enhanced gravity normally are rounded off and have globular shapes but far from ideal spheres. This is due to warping action of inertia-gravity waves of various wavelengths origin of which is related to body movements in elliptical keplerian orbits with periodically changing accelerations (alternating accelerations cause periodically changing forces acting upon a body what means oscillations of its spheres in form of standing warping waves). The fundamental wave 1 and its first overtone wave 2 produce ubiquitous tectonic dichotomy - two segmental structure and tectonic sectoring superimposed on this dichotomy. Two kinds of tectonic blocks (segments and sectors) are formed: uplifted (+) and subsided (-). Uplifting means increasing planetary radius of blocks, subsiding - decreasing radius (as a sequence subsiding blocks diminishing their surfaces must be warped, folded, wrinkled; uplifting blocks increasing their surfaces tend to be deeply cracked, fallen apart). To level changing angular momenta of blocks subsided areas are filled with denser material than uplifted ones (one of the best examples is Earth with its oceanic basins filled with dense basalts and uplifted continents built of less dense on average andesitic material). Icy satellites follow the same rule. Their warped surfaces show differing chemistries or structures of constructive materials. Uplifted blocks are normally built with light (by color and density) water ice. Subsided blocks - depressions, "seas', "lakes", coronas - by somewhat denser material differing in color from water ice (very sharply - Iapetus, moderately - Europa, slightly - many saturnian satellites). A very sharp difference between uplifted and subsided blocks presents Miranda having very sharp relief range. Subsided areas (coronas) are strongly folded, uplifted areas strongly degassed what was witnessed by numerous craters of various sizes (not all craters are of impact origin!). Coronas on Miranda present subsided segment and sectors. Typical is a very sharp boundary between risen (+) and fallen (-) blocks. On Enceladus the subsided (squeezed) southern pole area is characterized by "tiger stripes" - traces of contraction, young ice deposits and famous ejections of water vapor and ice. The squeezed area expels 'molten" material from interior - compare with periodically active Hawaiian volcano expelling basalts from constantly under contraction Pacific basin interior. As to the subsided Pacific basin, it is antepodean to uplifted deeply cracked and degassing Africa. On Enceladus to contracted south is opposed expanded north where past degassing is witnessed by numerous craters (not all of them are impacts!). Contraction traces are very impressive on subsided Titan's surfaces - methane filled thinly folded huge areas mainly in near equatorial regions (some scientists think that these folds are eolian dunes but they are parallel, not perpendicular to presumed winds and, besides, winds below ˜60 km in Titan's atmosphere are not detected by "Huygens") [1, 2]. This methane rich area of intensive folding is antepodean to the uplifted and mainly composed of water ice region Xanadu cut by numerous tectonically controlled dry "valleys". So, in spite of many varieties of surface features on icy satellites of the outer Solar system a common main tectonic tendency exists: opposition of subsided contracted and uplifted expanded blocks. References: [1] Kochemasov G.G. (2006)Titan's radar images: crosscutting ripples are dunes or warping surface waves?// Berlin, 22-26 Sept. 2006, EUROPLANET Sci. Conf. 1, EPSC2006-A-00045. [2] Kochemasov G.G. (2006)Planetary plains: subsidence and warping // Ibid., EPSC2006-A-00018.